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pdfNational Flood Insurance Program
Community Rating System
Special Hazards Supplement to the
CRS Coordinator’s Manual
2006
A community interested in more information on obtaining flood insurance premium
credits through the Community Rating System (CRS) should have the CRS
Application. This and other publications on the CRS are available at no cost from
Flood Publications
NFIP/CRS
P.O. Box 501016
Indianapolis, IN 46250-1016
(317) 848-2898
Fax: (317) 848-3578
[email protected]
They can also be viewed and downloaded from FEMA’s CRS website,
http://training.fema.gov/emiweb/CRS/index.htm
Contents
Section
Page
Introduction ..................................................................................... 1
Background on the Special Hazards ................................................. 3
Ice Jam Flooding ........................................................................ 3
Hazards Related to Closed Basin Lakes ...................................... 5
Hazards Related to Mudflows ..................................................... 6
Hazards Related to Land Subsidence........................................... 7
Hazards Related to Uncertain Flow Path Flooding .................... 12
CRS Credit..................................................................................... 14
300 Public Information Activities ............................................ 22
310 Elevation Certificates .................................................. 22
320 Map Information.......................................................... 22
330 Outreach Projects ........................................................ 22
340 Flood Hazard Disclosure.............................................. 23
350 Flood Protection Information ....................................... 23
360 Flood Protection Assistance ......................................... 24
400 Mapping and Regulatory Activities ................................... 25
410SH Additional Flood Data for Special Hazard Areas ..... 25
420 SH Open Space Preservation in Special Hazard Areas.. 33
430SH Higher Regulatory Standards for Special Hazards ... 36
430LZSH Low Density Zoning in Special Hazard Areas..... 48
440 Flood Data Maintenance ............................................... 51
500 Flood Damage Reduction Activities .................................. 52
510 Floodplain Management Planning ................................ 52
520 Acquisition and Relocation .......................................... 53
530 Flood Protection .......................................................... 53
540 Drainage System Maintenance ..................................... 54
600 Flood Preparedness Activities ............................................ 55
610 Flood Warning.............................................................. 55
620 Levee Safety ................................................................. 56
630 Dam Safety ................................................................... 56
References ..................................................................................... 57
Activity Worksheets
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Introduction
The Community Rating System (CRS) rewards communities that are doing more than
meeting the minimum requirements of the National Flood Insurance Program (NFIP) to
help their citizens prevent or reduce flood losses. The CRS also provides an incentive
for communities to initiate new flood protection activities. The goal of the CRS is to
encourage, by the use of flood insurance premium adjustments, community and state
activities beyond those required by the NFIP to:
•
Reduce flood losses, i.e.,
o protect public health and safety,
o reduce damage to buildings and contents,
o prevent increases in flood damage from new construction,
o reduce the risk of erosion damage, and
o protect natural and beneficial floodplain functions;
•
Facilitate accurate insurance rating; and
•
Promote the awareness of flood insurance.
The CRS includes 18 creditable activities, organized under four categories or series:
300—Public Information
400—Mapping and Regulations
500—Flood Damage Reduction
600—Flood Preparedness.
Credit points are based on the extent to which an activity advances the three goals of
the CRS. Communities are invited to propose alternative approaches to these activities
in their applications.
The Federal Emergency Management Agency (FEMA) and many communities in the
United States have long recognized that the mapping and minimum regulatory
standards of the NFIP do not adequately address all of the flood problems in the
country. In particular, a number of “special” flood hazards deserve attention. They
include
•
Ice jam flooding,
•
Flooding adjacent to closed basin lakes,
•
Mudflow hazards,
•
Flooding affected by land subsidence,
•
Uncertain flow path flood hazards,
•
Coastal erosion, and
•
Tsunamis.
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This publication discusses the credits provided by the CRS for mapping and
management of the first five of these hazards. Coastal flood hazards are addressed in
the publication CRS Credit for Management of Coastal Erosion Hazards, and tsunami
hazards are addressed in the publication CRS Credit for Management of Tsunami
Hazards. Both are supplements to the CRS Coordinator’s Manual, and include
additional Schedule sections and Commentary.
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BACKGROUND ON THE SPECIAL HAZARDS
Ice Jam Flooding
An ice jam may be defined as an
accumulation of ice in a river,
stream, or other flooding source that
reduces the cross-sectional area
available to carry the flow and
increases the water-surface elevation.
Ice usually accumulates at a natural
or human-made obstruction or a
relatively sudden change in channel
slope, alignment, or cross-section
shape or depth. Ice jams are common
in locations where the channel slope
changes from relatively steep to
mild, and where a tributary stream
enters a large river. Ice jams often
cause considerable increases in
upstream water surface elevation,
and the flooding often occurs quite
rapidly after the jam forms (FEMA,
2002).
Typical ice jam locations (from Association of
State Floodplain Managers).
In many northern regions, ice covers the rivers and lakes annually. The yearly freezeup
and breakup usually take place without major flooding. However, some communities
face serious ice jam threats every year, while others experience ice-jam-induced
flooding at random intervals. The former often have developed emergency plans to deal
with ice jam problems,
but the latter are often illprepared to cope with a
jam.
In a 1992 survey, the U.S.
Army Corps of Engineers
District and Division
offices reported ice jam
problems in 36 states,
primarily in the northern
tier of the United State.
However, even
mountainous regions as
far south as New Mexico
and Arizona experience
river ice. Ice jams affect
the major navigable
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Distribution of ice jam events in the continental United
States as of September 1999 (from U.S. Army Corps of
Engineers, 2006a).
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inland waterways of the United States, including the Great Lakes. A study conducted in
Maine, New Hampshire, and Vermont identified over 200 small towns and cities that
reported ice jam flooding over a 10-year period. In March 1992 alone, 62 towns in New
Hampshire and Vermont
reported ice jam flooding
problems after two rainfall
episodes.
Ice jams in the United
States cause approximately
$125 million in damage
annually, including an
estimated $50 million in
personal property damage
and $25 million in
operation and maintenance
costs to navigation, flood
control, and channel
stabilization structures.
Because ice jam floods are
Ice jam flood on the Iroquois River, Illinois, March 1979
less common and more
(photo from Kankakee County Planning Department).
poorly documented than
open-water floods, it is
more difficult to
characterize these events compared to open-water flooding. In addition, because of the
complex processes involved in the formation and progression of ice jams and the highly
site-specific nature of these jams, these events are more difficult to predict than openwater flooding. The rates of water level rise can vary from feet per minute to feet per
hour during ice jam flooding.
There are generally two types of ice jams:
• Frazil ice freezes the river and forms a dam.
• When warm weather and rain break up frozen rivers or any time there is a rapid
cycle of freezing and thawing, broken ice floats downriver until it is blocked by an
obstruction such as a bridge or shallow area.
In both cases, an ice dam forms, blocking the channel and causing flooding upstream. Ice jams
present three hazards:
• Sudden flooding of areas upstream from the jam, often on clear days with little or
no warning,
• Sudden flooding of areas downstream when an ice jam breaks. The impact is
similar to a dam break, and damages or destroys buildings and structures.
• Movement of ice chunks that can push over trees and crush buildings (see photo,
next page).
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Ice jams tend to recur at the same locations on streams, and ice jam flood elevations
have a recurrence interval just like clear water floods. Because freezeup jams rely
heavily on periods of intense cold that produce large quantities of frazil ice, they can
be somewhat easier to predict than breakup jams, which are caused by a site-specific
combination of complex physical processes. Evaluation of historical ice,
meteorological, and hydrological records is necessary for developing a prediction
method for either type of jam.
Kankakee River ice jam damage, 1982
(photo from French & Associates, Ltd.).
Hazards Related to Closed Basin Lakes
Two types of lakes pose special hazards to adjacent development: lakes with no outlets,
like the Great Salt Lake and the Salton Sea; and lakes with inadequate, regulated, or
elevated outlets, such as the Great Lakes and many glacial lakes. All of these are
referred to as “closed basin lakes.” Closed basin lakes are subject to very large
fluctuations in elevation that can persist for weeks, months, or years.
Closed basin lakes occur in almost every part of the United States for a variety of
reasons. Lakes in the northern tier of states and Alaska were scoured out by glaciers.
Lakes with no outlets (playas) formed in the West as a result of tectonic action. Oxbow
lakes along the Mississippi and other large rivers are a consequence of channel
migration. Sinkhole lakes formed where there are large limestone deposits at or near
the surface and adequate surface water and rainfall to dissolve the limestone (karst
topography).
The Great Salt Lake in Utah is perhaps the best known closed basin lake in the United
States. There is little permanent development adjacent to the Great Salt Lake, but there
is a thriving tourism industry, and roads and railroads near the lake are affected by high
lake levels. The graph on the next page shows how the persistence of high (or low) lake
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Level of the Great Salt Lake, Utah, 1847–2001. The Great Salt Lake is located on a
shallow playa, so small changes in the water surface elevation result in large changes in
the surface area of the lake. This is particularly evident when the lake spills into the west
desert at an elevation of about 4215 feet, greatly increasing its area. … At the historic
average (1847-1986) surface elevation of 4,200 feet …, the lake covers an area of about
1,700 square miles. At the historic low elevation of 4,191.35 in 1963, the lake covered only
950 square miles. The drop of about 8.5 feet in elevation resulted in a loss of about 44
percent in surface area. During 1986 and again in 1987, the lake reached an elevation of
4,211.6 feet and had a surface area of about 3,300 square miles (USGS, 2006).
levels mean everything to management of development adjacent to closed basin lakes.
Imagine that a flood protection level for the great Salt Lake were set at 4,212 feet msl.
No buildings would have flooded during the 185 years of lake level records.
Hazards Related to Mudflows
Mudflows (or debris flows) are rivers of rock, earth, and other debris saturated with
water. They occur when water rapidly accumulates in the ground, such as during heavy
rainfall or rapid snowmelt, changing the earth into a flowing river of mud or “slurry.”
A slurry can flow rapidly down slopes or through channels, and can strike with little or
no warning at avalanche speeds. A slurry can travel several miles from its source,
growing in size as it picks up trees, cars, and other materials along the way.
Although floods and mudflows are covered under the NFIP, landslides are not covered.
Typically, a combination of flooding, mudflow and landslide conditions can occur in
the same general area. Under a flood insurance policy a property is covered for the
portion of the damage to the insured building or contents caused by the flooding and
mudflow, but not the portion of the damage caused by the landslide.
Mudflows are common types of fast-moving landslides. These flows generally occur
during periods of intense rainfall or rapid snow melt. They usually start on steep
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hillsides as shallow landslides that
liquefy and accelerate to speeds that
are typically about 10 miles per hour,
but can exceed 35 miles per hour. The
consistency of debris flows ranges
from watery mud to thick, rocky mud
that can carry large items such as
boulders, trees, and cars.
Mudflows from different sources can
combine in channels, and their
destructive power may be greatly
increased. They continue flowing
down hills and through channels,
growing in volume with the addition
of water, sand, mud, boulders, trees,
and other materials. When the flows
reach flatter ground, the debris spreads
over a broad area, sometimes
accumulating in thick deposits that can
wreak havoc on developed areas.
March 1999 ice jam on the First Branch White
River, Tunbridge, Vermont (photo from U.S.
Army Corps of Engineers 2006b).
Hazards Related to Land Subsidence
The U.S. Geological Survey (USGS) and others have been studying the phenomenon of
land subsidence, its causes, and its impacts for at least 100 years. USGS Circular 1182
provides background information on land subsidence and case studies, quoted below.
Land subsidence is a gradual settling or sudden sinking of the Earth’s surface
owing to subsurface movement of earth materials. Subsidence is a global
problem and, in the United States, more than 17,000 square miles in 45 States,
an area roughly the size of New Hampshire and Vermont combined, have been
directly affected by subsidence. . . . More than 80 percent of the identified
subsidence in the Nation is a consequence of our exploitation of underground
water, and the increasing development of land and water resources threatens to
exacerbate existing land subsidence problems and initiate new ones. In many
areas of the arid Southwest, and in more humid areas underlain by soluble
rocks such as limestone, gypsum, or salt, land subsidence is an oftenoverlooked environmental consequence of our land- and water-use practices
(Galloway et al., 1999, p. 1).
In 1991, the National Research Council estimated that annual costs in the
United States from flooding and structural damage caused by land subsidence
exceeded $125 million. The assessment of other costs related to land
subsidence, especially those due to groundwater withdrawal, is complicated by
difficulties in identifying and mapping the affected areas, establishing causeand-effect relations,
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Subsidence problems in the United States (from Leake, 1997).
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assigning economic value
to environmental
resources, and by inherent
conflicts in the legal
system regarding the
recovery of damages
caused by resource
removal under established
land and water rights. Due
to these “hidden” costs, the
total cost of subsidence is
probably significantly
larger than our current best
estimate (Galloway et al.,
1999, p. 1).
Evidence of a subsidence fault on Highway 11 bridge. (photo
from Lake Pontchartrain Basin Foundation).
Several other types of subsidence involve processes more or less similar to the
three mechanisms just cited, but are not covered in detail in this Circular.
These include the consolidation of sedimentary deposits on geologic time
scales; subsidence associated with tectonism; the compaction of sediments due
to the removal of oil and gas reserves; subsidence of thawing permafrost; and
the collapse of underground mines. Underground mining for coal accounts for
most of the mining-related subsidence in the United States and has been
thoroughly addressed through Federal and State programs prompted by the
1977 Surface Mining Control and Reclamation Act. No such nationally
integrated approach has been implemented to deal with the remaining 80
percent of land subsidence associated with ground-water processes (Galloway
et al., 1999, p. 3).
An earlier study noted that
“Ideally, the development of
sinkholes can be eliminated or
minimized by ceasing the
pumpage that causes the decline
of the water table. The cessation
of or drastic decrease in
sinkhole activity following a
recovery of the water table has
been recognized previously.
Most efforts . . . have been
directed toward measures
minimizing sinkhole
development and eliminating
potential hazards and damage to
structures rather than dealing
with the cause” (Newton, 1984,
p. 250).
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A recent sinkhole in Huntsville, Alabama
(photo from Dr. Warren Campbell).
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Subsidence increases the Frequency and Intensity of Flooding
Located along a low-lying coast that is subject to tropical storms, the Houston area is naturally
vulnerable to flooding. In coastal areas, subsidence has increased the amount of land subject to
the threat of tidal inundation. Flooding by tidal surges and heavy rains accompanying hurricanes
may block evacuation routes many hours before the storms move inland, endangering
inhabitants of islands and other coastal communities. The increased incidence of flooding in
coastal areas eventually led to the growing public awareness of subsidence and its costs.
The fate of the Brownwood subdivision of Baytown affords a particularly dramatic example of the
dangers of coastal subsidence. Brownwood was constructed, beginning in 1938, as an upperincome subdivision on wooded lots along Galveston Bay (Holzschuh, 1991). At that time the
area was generally 10 feet or less above sea level. By 1978 more than 8 feet of subsidence had
occurred.
The subdivision is on a small peninsula bordered by three bays. [It] is a community of
about 500 single-unit family houses. Because of subsidence, a perimeter road was
elevated in 1974 to allow ingress and egress during periods of normal high tide [about
16 inches], and to provide some protection during unusual high tide. Pumps were
installed to remove excess rainfall from inside the leveed area. Because of subsidence
after the roadway was elevated, tides of about [4 feet] will cause flow over the road.
The United States Army Corps of Engineers studied methods to protect the
subdivision from flooding. The cost of a levee system was estimated to be about $70
million. In 1974, the Army Corps estimated that it would cost about $16 million to
purchase 442 homes, relocate 1,550 people, and convert [750 acres] of the peninsula
into a park.
This proposed solution was approved by the Congress of the United States and
provided necessary funding. However, the project required that a local sponsor (the
City of Baytown) should approve the project, provide 20 per cent of the funds ($3
million) and agree to maintain the park. By the time the first election to fund the project
was held on 23 July 1979, the cost estimate had increased to $37.6 million, of which
the local share was $7.6 million. The proposal was defeated, and two days later 12
inches of rain fell on Brownwood causing the flooding of 187 homes. Another bond
election was held on 9 January 1980 and again the proposal was defeated. Accepting
the residents’ decision, Baytown officials began planning the sale of $3.5 million worth
of bonds to finance the first stage of a fifteen-year, $6.5-million programme to upgrade
utilities in the subdivision. Meanwhile, those who own the houses generally also owe
mortgages and cannot afford to purchase other homes. Although they continue to live
in the subdivision many have to evacuate their homes about three times each year
(Gabrysch, 1983, p. 42).
The year that article was published, Hurricane Alicia struck a final blow to Brownwood. All homes
in the subdivision were abandoned. Today, most of the subdivision is a swampy area well-suited
for waterfowl; egrets and scarlet ibis are often seen (Galloway et al., 1999, p. 42 ).
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Hazards Related to Uncertain Flow Path Flooding
Uncertain flow path flooding includes alluvial fan flooding and hazards associated with
moveable bed streams. These hazards differ from other flood hazards in that they
usually include the added hazard of large quantities of moving debris and sediment,
and the location and nature of the flood hazard changes over time.
One of the uncertainties about moveable bed streams is the change in the stability of
the channel over time. Throughout much of the arid and semi-arid regions of the United
States, there is evidence that human activities over as short a time as a decade have
drastically changed the nature of some streams. It is important to understand the causes
of aggradation, degradation, and channel migration in order to project the future
configuration of the channel.
Alluvial Fan Hazards
As defined in 44 CFR 59.1, “alluvial fan flooding” means flooding that occurs on the
surface of an alluvial fan or similar landform, originates at the apex, and is
characterized by high-velocity flows; active processes of erosion, sediment transport,
and deposition; and unpredictable flowpaths.
FEMA’s Guidelines for Determining Flood Hazards on Alluvial Fans (FEMA, 2000)
generally addresses many of the issues raised in Alluvial Fan Flooding (National
Research Council, 1996). “This document provides guidance for the identification and
mapping of flood hazards occurring on alluvial fans, irrespective of the level of fan
forming activity. The term alluvial fan flooding encompasses what will be described as
active alluvial fan flooding and inactive alluvial fan flooding” (FEMA, 2000, p. 1).
Alluvial fans do not exhibit the more predictable behavior and well-defined
boundaries normally found in most riverine floods. The behavior and path of
floodwater in any individual event as it proceeds from the apex to the toe is a
direct result of the flood processes previously illustrated. These processes vary
as a function of the flow’s sediment content and velocity, the fan’s slope, soil
and vegetative cover, and types and amount of fan development.
Alluvial fan flows are subject to lateral migration and sudden relocation during
the course of a flood, and may not even follow the same path in subsequent
floods; in any flood event, however, a part of the fan will always be subject to
flood hazards. Thus, it is generally not appropriate to utilize the location of
past flow-paths in the prediction of future floods. The full range of hazards
that occur on fan include:
• High velocity flow (as high as 15 – 30 feet per second), producing significant
hydrodynamic forces (pressure against buildings caused by the movement of
flowing water)
• Erosion/scour (to depths of several feet)
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Alluvial fan extending from the Panamint Mountains in the background to the floor of
Death Valley in the foreground (Miller, 1995, p. 18).
• Deposition of sediment and debris (depths of 15–20 feet have been observed)
• Debris flows/impact forces
• Mudflows
• Inundation, producing hydrostatic/buoyant forces (pressure against buildings
caused by standing water)
• Flash flooding (little, if any, warning time) (FEMA, 1989).
Streams with Aggrading, Degrading, and Migrating Channels
For the purposes of this discussion, areas subject to uncertain flow paths will include
streams where erosion (degradation of the streambed), sedimentation (aggradation of
the streambed), channel migration, or combinations of these processes cause sufficient
changes in the topography of the stream and/or its floodplain to affect the flood
elevation or the delineation of the floodplain or floodway. In some locations, these
processes may occur simultaneously, or one process may occur in one event while
another process occurs in a subsequent event.
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All of the floodplains in the world are formed by the eroding of mountain and the
deposition of the eroded material on the floodplains. There is an equilibrium among the
rainfall, the sediment source, the slope of the watershed, and the slope of the
floodplain. The equilibrium is different for each stream, but there are regional
similarities and differences. These differences may require different approaches to
mapping and management of their floodplains.
Sedimentation and erosion make traditional methods of mapping and management of
flood hazards more difficult. Some stream reaches aggrade, some degrade, and in some
reaches, the channels change their course within the floodplain, even from one flood to
the next.
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CRS CREDIT
The hazards associated with ice jam flooding, flooding adjacent to closed basin lakes,
mudflow hazards, flooding affected by land subsidence, and uncertain flow path
flooding must be dealt with at the community level using all of the tools used in
conventional floodplain management. Under the CRS, these tools are organized under
four series of credited activities:
• Informing the public and specific populations, such as developers and engineers,
about the hazards (300 series)
• Mapping and regulation of the hazard areas with recognition of the unique
problems associated with the hazards (400 series)
• Special structural and nonstructural efforts to solve existing problems (500 series)
and
• Special emergency preparedness efforts that recognize the particular problems
associated with these hazards (600 series).
This section reviews the proven mitigation measures for the five special hazards
addressed in this publication. In some cases, CRS credit is provided for an activity in
the CRS Coordinator’s Manual. In other cases, particularly in the 400 series, special
credit is provided in this publication. For those credits, this document is a supplement
to the Schedule and Commentary in the Coordinator’s Manual and the same formatting
is used. The special hazard credit points calculated under this publication are
transferred to the regular credit points in the Coordinator’s Manual.
Just as riverine and coastal flood hazards require different mapping and management
techniques, these special hazards require different techniques as well. This does not
require a different or separate department in local government, just an additional set of
standards that recognize the features of these flood hazards and the appropriate use of
the public information, engineering, planning, and other staff.
A number of CRS activities have credit for the special hazards discussed in this
publication. However, a community’s special hazard management program should
include other activities that do not receive CRS credit. For example, post-disaster
recovery and mitigation policies might require damaged areas to be redeveloped with
new street patterns to accommodate the clustering of structures away from high hazard
areas.
On the next few pages are some fictitious examples of communities with areas subject
to these special hazards. Note that in each case, special techniques are used to map the
hazards, and special regulatory requirements have been adopted to mitigate them.
The first fictitious example shows why and how a local government might develop a
program to deal with ice jam hazards and how the CRS would recognize its efforts.
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Example 100IJ. North County is generally hilly, with the North River
running generally south to north through the center of the county. North City,
the main population center in the county, lies on both sides of the North River
near the center of the county.
The North River has a history of ice jams both near the northern edge of the
county, where there is virtually no development, and within North City. Ice
jams in North City have caused flood damage in the adjacent county.
The 1987 Flood Insurance Study for North County and North City used river
gage data for the North River to determine the base flood peak flow and the
base flood elevation (BFE). Since 1987, three ice jam floods have caused
higher flood elevations than the BFE in North City, and two caused higher
flood elevations in the county. After the 1993 floods in the upper Midwest,
North County requested a restudy of the North River. FEMA agreed to do a
county-wide restudy.
The restudy developed new hydrology for the North River based on river gage
data that included the 1993 flood. The study contractor was also instructed to
do a separate analysis for flood elevations under ice jam conditions. The
resulting base flood based on river gage data has a peak flow about 15%
larger than that in the 1987 study, and the resulting BFE was the same as the
50-year elevation from ice jam flooding in and upstream from North City. An
ice jam analysis was also done for the undeveloped area near the northern
edge of the county. Again, the new BFE based on clear water flooding was the
same as the elevation of the 50-year ice jam flood.
For the reaches of North River that have experienced ice jam flooding, North
County established a regulatory requirement that every new building in the
Special Flood Hazard Area (SFHA) must have an engineering analysis of its
foundation to ensure that it is safe from moving ice at the ice jam flood
elevation, which is three feet higher than the BFE. They also prohibited
development in the floodway of the North River in those reaches. The county
also established zoning with a minimum lot size of 3 acres for the area near
the northern edge of the county.
North County had joined the CRS after the 1993 flood as a Class 9
community. In 1996, when its revised FIRM was adopted along with its higher
regulatory standards for areas subject to ice jam hazards, it improved to Class
8. The county received considerable credit for preservation of open space
(Activity 420) because of its prohibition on development in floodways where
there is an ice jam hazard. In Activity 430, the county received CRS credit for
its foundation requirements in areas subject to ice jam hazards, and for low
density zoning.
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Lake City is a fictitious county in the upper Midwest. The following example shows
why and how a community might develop a program to deal with closed basin lake
hazards.
Example 100CB. Lake City is a growing city of about 60,000 people
located on the east end of Glacial Lake. Glacial lake is about 10 miles long
from east to west and about 3 miles across at its widest point. There are small
resorts and residences around the lake. Almost all of the land around the lake
is owned by a paper company, and these resorts and residences are on land
leased from the company.
Glacial Lake is a closed basin lake. Sporadic records have been kept of lake
levels for a long time. A trading post built in 1810 atop a rock outcrop was
flooded and abandoned in 1825. Farms were established in the area in the
1840s, and several farmers kept records of high and low lake levels until the
farms failed because of a drought in the late 1870s. At that time, a lumber
company began acquiring the homesteads at tax sales. In 1898, Lake City
was established as a mill town. Since World War II, the area has attracted
summer vacationers, and the lumber mill has been replaced by a paper mill.
The paper mill and tourism are now of about equal importance to Lake City,
and tourism and retirement appear to be the economic future of the area.
The water level in Glacial Lake began rising in 1985, and by 1990, buildings all
around the lake had been flooded. Lake City asked the U.S. Army Corps of
Engineers to study the problem and develop a project to deal with it. The
Corps determined that
o Lake levels have varied from about 976 feet to 1,010 feet above mean
sea level (msl) since 1810.
o The natural outlet from the lake is at 1,015 feet msl
o The buildings flooded in 1990 were built between 1,000 feet and 1,005
feet msl.
o Lake levels never reached 1,000 feet msl between the drought in the
1870s and 1989.
o The City’s FIRM was based on a lake level of 1,001 feet msl.
o The lake has probably not had an elevation above 1,005 feet msl
since 1825, when the trading post was flooded.
o Winds from the west during the spring, when lake levels are highest,
raise the lake level at Lake City about 6 inches (windset), and cause
18-inch waves.
o No structural project would provide protection from the highest
potential lake elevations.
Lake City and the paper company discussed this situation and decided to work
together to solve the flood problem. In 1990, Lake City had two miles of
lakefront. There were 510 buildings in the City at an elevation less below
1,012’ feet msl. The area of the City that was below 1,012 feet msl was about
200 feet wide and included 50.8 acres. The paper mill, the downtown area,
and the mall on the highway were all above 1,012 feet msl.
The paper company had a 160-acre lakefront parcel that had been used as a
dump by the lumber mill and the paper mill from 1898 until 1975. This parcel
abutted the City on its south side. Although the site was not especially
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hazardous, it was a U.S. Environmental Protection Agency superfund site
because runoff from the site degraded the water quality of the lake. The
company ceded this land to the City.
In 1992, the City adopted a master plan to relocate all buildings below 1,010
feet mean sea level to the superfund site, which was named Glacial Lake
Park. Ninety-eight acres of Glacial Lake Park is above 1,012 feet msl. The City
prohibited new buildings on land lower than 1,010 feet and required new
buildings on land between 1,010 feet and 1,012 feet to be placed on fill with
floodproofed utilities. They stated that 1,010 feet msl was the BFE for Glacial
Lake, and that they added 2 feet of freeboard to account for windset and wave
action.
From 1992 through 1994, the City secured funds from EPA, the Corps, and
FEMA to clean up the site. The citizens voted bonds to install streets and
utilities as the area developed. The City offered free lots to lakefront residents
who would relocate from their floodprone houses to Glacial Lake Park and
deed their property to the City. By 1995, 102 buildings had either been moved
to the Park or demolished. When the lake rose to 1,007 feet msl in 1999, 396
buildings were moved or demolished. The remaining 12 buildings were on
land above 1,010 feet. Six of these buildings were already above 1,012 feet
and the others were raised to that elevation. The 1999 relocations were
facilitated by NFIP funds, including payments under Increased Cost of
Construction coverage, a grant from the Corps, and funds from the state.
By 2000, the City had converted 48 acres of the abandoned area to a City
park.
Lake City had been too busy solving its flood problems to join the CRS until
2000. When it joined the CRS in 2000, it was rated a Class 6 community.
Steep County is a fictitious county in the West. The following example is intended to
show why and how a community might develop a program to deal with mudflow
hazards.
Example 100MF. The western half of Steep County is a broad, relatively
level river valley. The eastern half is foothills and mountains. Historically, more
than 90% of Steep County’s population lived in the valley, but in recent
decades, more people are moving into the canyons in the foothills, and the
year-round recreational amenities in the higher mountains have led to the
development of large resorts and condominium complexes almost all the way
to the tops of the mountains.
In the valley, floodplain management had been dealing with the problems
associated with uncertain flow path flood hazards. During the 1990s, sediment
transport modeling was used to delineate the floodplains for streams flowing
from the mountains to the large river to the west.
In 1998, a different hazard became important to Steep County. Unusually
heavy snows during the late winter, combined with a warm rainstorm in the
early spring caused near-record flooding in the valley, but it also caused
numerous landslides and mudflows in the foothills and mountains. The
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mudflows destroyed a considerable amount of new development and killed 12
people.
Steep County immediately contacted the State Department of Mining and
Geology (DMG). DMG did a reconnaissance study that showed that there
were numerous areas in both the foothills and farther up in the mountains that
showed historic signs of landslide activity, and that recent development and
road building had increased the probability of future landslides.
Steep County contracted with DMG to map the geologic hazards in western
Steep County. The maps were completed in 2000. After three months of public
hearings, Steep County adopted the DMG maps and a geologic hazards
regulation. In some areas, the regulation prohibits development, and in other
areas, it requires engineering and geologic studies before development, road
building, or clearing or disturbing the surface.
In 2001, Steep County updated its comprehensive plan. The CRS planning
process was used to receive CRS credit in Activity 510, and the geologic
hazards maps and regulations were included in the plan.
Throughout the process of developing the geologic hazards maps and
regulations and the development of the comprehensive plan, Steep County
had mounted a public information campaign on landslide and mudflow
hazards in the foothills and in the mountains.
As a result of the comprehensive plan, the County adopted regulations
requiring two feet of freeboard above the BFE for all watercourses with slopes
greater than 5%. This provision allows for the sudden accumulation of
sediment in channels downstream from landslides and mudflows. When a
landslide occurs, it typically flows down a steep slope into a channel with a
much shallower slope. The soil and rocks stop, raising the flood elevation.
Subsequent flows erode the material away and carry it downstream. The
freeboard was intended to provide protection during this process.
Because of these actions and other efforts of the Steep County staff, the
County received CRS credit for Activities 330—Outreach Projects, 340—
Hazard Disclosure, 350—Flood Hazard Information, 360—Flood Protection
Assistance, 410—Additional Map Data, 420—Open Space Preservation,
420LDC—Land Development Criteria, 430—Higher Regulatory Standards,
440—Flood Data Maintenance, and 510—Floodplain Management Planning.
These activities improved Steep County’s CRS class to 6, meaning that
buildings in the floodplains shown on the FIRM receive a 20% discount on
their NFIP premiums, and buildings outside the SFHA receive a 10% discount.
Flat County is a fictitious county in the West. Its experience shows why and how a
community might develop a program to deal with land subsidence hazards.
Example 100SU. The central portion of Flat County is a broad, relatively
level river valley. The north and south portions of the County are arid
mountains with rocky terrain and virtually no reliable water supply. Flat County
was settled by the descendants of Europeans who moved into the area from
the eastern United States in the mid to late 1800s. They ranched and
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developed limited agriculture with the available surface water from the Flat
River. Agriculture increased dramatically with the introduction of the windmill,
and by the mid 1900s the entire central portion of the County had been
irrigated by groundwater pumped from ever-increasing depths.
By the 1990s, three things were becoming apparent. First, traditional kinds of
agriculture were becoming uneconomical because of the energy costs for
raising water 600 to 700 feet with pumps. Second, the cost of maintaining
infrastructure was increasing due to land subsidence. Farms had to be releveled to irrigate properly. Ditches had to be replaced with pipes because
they no longer had a slope appropriate to carry water. Roads, gas pipelines,
and other infrastructure were also requiring more repairs. Finally, floods on the
Flat River in the 1990s flooded areas three or four times as wide as the
SFHAs shown on FIRMs produced in the late 1970s.
The state geological survey studied Flat County and determined that there had
been up to 20 feet of subsidence near the center of the county, immediately
adjacent to the Flat River. The average slope of the Flat River through Flat
County is 7 feet per mile, but land subsidence had increased the slope to
about 9 feet per mile upstream from the center of the subsidence area and
decreased the slope to about 5 feet per mile for a 10-mile reach downstream
from the center of subsidence. This change in slope caused the channel to
downcut in the steeper reach and caused sedimentation in the flatter reach. In
the flatter reach, the combination of the lessened slope and the sedimentation
resulted in a much wider floodplain.
In 1996, Flat County had a reconnaissance study done to find alternative
solutions to the problems of subsidence and flooding. This study concluded
that there was no feasible way to reverse the subsidence. It was estimated
that if all groundwater pumping ceased immediately, subsidence would
continue for another five years, and the maximum amount of subsidence
would be about 25 feet. If groundwater pumping continued at the current rate,
water would become uneconomical for agriculture in about 10 years, and the
ultimate subsidence would be about 30 feet. There were no alternatives for the
flood problem except to map and regulate a wider, and widening, floodplain.
After working with the local agriculture interests for two years, in 1998 Flat
County secured state and federal funds to acquire the water rights for about
90% of the farm land. The landowners would be allowed to use the land for
urban development, which requires only about 7% of the water used for
irrigated agriculture.
In 1999, Flat County finalized a long-range comprehensive plan. This plan
assumed that the remaining 10% of the farmland would become uneconomical
to irrigate by 2010. It also assumed 10% annual population growth through
2010 and 5% annual growth from 2010 through 2020. A hydrogeologic study
estimated that subsidence would end in 2030, with a maximum subsidence of
about 27 feet. The comprehensive plan included a surface water model that
estimated the runoff from development through 2030 as well as the maximum
subsidence. Floodplain maps were made based on these conditions. Within
the entire area subject to subsidence, the county adopted a special building
code provision to require foundations that will resist damage due to
subsidence.
Beginning with the results of the reconnaissance study in 1996, Flat County
had mounted a public information campaign explaining the nature and the
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cause of the subsidence problem and the related flood problems. In 1998, it
placed a temporary moratorium on development of any land that had been
flooded in the big flood of 1995. By 1999, when its comprehensive plan was
adopted, it was able to combine local, state, and federal funds to buy
conservation easements and offer density trades to preserve about 75% of the
floodplain based on 2030 hydrology and subsidence.
Flat County joined the CRS after the 1995 flood. By 2001, it was a Class 8
community. When it adopted the comprehensive plan in 2001, it became a
Class 4 community. It receives near maximum credit for all of the public
information activities (the 300 series). It received credit for the mapping of the
Flat River floodplain and additional credit because it is a special hazard area
(Activity 410). It received credit for preservation of open space (Activity 420),
and additional credit because it is in a special hazard area. It received credit
for 3 feet of freeboard in most of the remaining floodplain because its futureconditions mapping produced flood elevations almost 5 feet higher than
existing conditions, the basis for the sale of flood insurance (Activity 430). It
also received credit under Activity 430 for foundation protection and land
development criteria. Its entire floodplain was entered into a geographic
information system (GIS), and it set up a program to obtain new topographic
maps every three years using LiDAR. It established a program to resurvey its
benchmarks every year (Activity 440).
The comprehensive plan received almost the maximum credit for both
stormwater master planning (Activity 450) and floodplain management
planning (Activity 510). Because the County had been almost entirely
agricultural in 1996, there were only 37 residences in the entire floodplain. By
1999, it had obtained grants from FEMA and the Nature Conservancy to
purchase and demolish 20 of these homes (Activity 520).
Arid County is a fictitious county in the arid West. The following example shows why
and how a community might develop a program to deal with uncertain flow path flood
hazards and how the CRS would recognize that effort.
Example 100UF. The northeast part of Arid County, the Oriental Fan, is
subject to alluvial fan flooding where flood water from the desert mountains
flows onto the desert floor.
In the western part of the County, two rivers are subject to uncertain flow path
flooding.
West River is a perennial stream that carries a heavy sediment load during
floods. It flows in a broad sandy-bottomed gorge. The 100-year floodplain just
covers the half-mile-wide bottom of the gorge, and the floodway shown on Arid
County’s Flood Insurance Rate Map (FIRM) averages 300 feet in width.
Dry Creek is a degrading stream for most of its reach in Arid County. Intense
development in the upper parts of the Dry Creek watershed since 1950 has
caused an estimated 400% increase in the runoff from a 100-year storm. The
channel has become incised, increasing the velocity and causing ongoing
scour in most reaches within the County
In 1985, the Arid County Flood Control District did a study of the Oriental Fan
area. Although the report indicated that the floodplains shown on the County’s
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FIRM did not accurately reflect the flood hazard in the area, the Board of
Supervisors declined to adopt stricter regulations.
In 1987, the Flood Control District completed studies on West River and Dry
Creek. They were able to use the County’s existing regulations to control
development to avoid the worst of the hazards in those areas.
In 1997, a 50- to 100-year storm hit the mountains above the Oriental Fan and
the fan itself. More than 100 residences were destroyed by erosion and
sediment and debris hitting the structures, 27 more suffered substantial
damage, and 300 more were damaged to a lesser degree. Flood depths were
less than 3 feet in the affected areas, and the flood was gone 6 hours after it
began. Most of the damage occurred outside the SFHA shown on the FIRM.
Damage to County and private infrastructure nearly equaled the damage to
structures.
Within a week of the Oriental Fan flood, the County Board of Supervisors
instructed the Flood Control District to contract for a comprehensive hazard
mitigation plan. The District is responsible for the County’s floodplain
management, stormwater management, and flood warning system, and it is
the coordinating agency for the community’s participation in the CRS.
The comprehensive plan was produced in a way that would get maximum
CRS credit for Activity 510—Floodplain Management Planning. The contractor
reviewed the County’s Flood Insurance Study, the studies of Oriental Fan,
West River, Dry Creek, and numerous other studies conducted by the Flood
Control District, the Corps of Engineers, the U.S. Geological Survey, and
others. Among other things, they reviewed all flood hazards, alluvial fan
hazards, and all moveable bed hazards in the County.
As a result of the hazard mitigation plan, the County adopted development
regulations for the Oriental fan area, West River, and Dry Creek, and adopted
the maps produced by the Flood Control District in the 1980s. The regulations
included a county-wide requirement for retention of stormwater runoff. The
Flood Control District also implemented a public information strategy to inform
its residents about the County’s special hazard areas.
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300 Public Information Activities
Because the flood hazards associated with the special hazards are different from
“normal” flood hazards, there are special needs for public education. Property owners
and developers must be made aware of the hazards and the methods needed to mitigate
them.
When a state or local government has mapped special hazard areas, information identifying these
areas and how to protect oneself from them should be automatically included in the community’s
public information program. Likewise, when higher regulatory standards for development in
these areas have been adopted, these standards should be included in local public information and
education programs.
There are several ways to provide this information, including
•
Newsletter and newspaper articles;
•
Signs posted in the hazardous areas;
•
Brochures and booklets on the hazards and what can be done;
•
Outreach projects, such as booths at shopping malls;
•
Presentations to civic associations or neighborhood groups;
•
Providing information on the location and severity of the hazard areas to inquirers;
•
Putting references on the hazard and protection measures in the public library; and
•
Providing technical assistance to property owners.
310 Elevation Certificates
Although there is no special or additional CRS credit for elevation certificates in areas
of special flood hazard, FEMA elevation certificates, which are required for the
purchase of NFIP flood insurance, and which must be maintained by CRS communities,
MUST be based upon the current FIRM for the community, and they must be completed
using the flood information from the FIRM and the corresponding Flood Insurance
Study. There is no requirement to maintain elevation certificates outside the SFHA.
That means that if a community has mapped an area of alluvial fan flooding or an
aggrading or migrating channel, and it is regulating areas outside the SFHA, and/or the
regulatory flood elevation is higher than that shown on the FIRM, everyone must still
use the data from the FIRM for the purpose of filling out the elevation certificate.
320 Map Information
Many communities provide inquirers with flood information from the Flood Insurance
Study and FIRM. Some use this opportunity to explain local regulations, including the
coastal erosion setback standards. This provides the inquirers with a more complete
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picture of the local coastal hazard and the importance of regulations as property
protection measures.
Providing information from the community’s FIRM yields many benefits to residents,
businesses, real estate and insurance agents, lenders, and those interested in
purchasing, developing, or repairing property. CRS credit is provided for advertising
this service and for providing information as described in the Coordinator’s Manual.
If the community is receiving CRS credit for mapping and regulating its special
hazards, the map information service must include telling inquirers if the property in
question is mapped as a special hazard area. The community must also disclose any
special hazard regulatory requirements for developing the property. This can help
property owners and potential buyers better understand the natural hazards risks of a
particular location. Understanding these risks can help property owners and builders
identify and evaluate potential property protection measures.
330 Outreach Projects
This activity provides credit for newsletters, mailings, presentations, booths, brochures,
and a host of other means of getting the word out to the public or target audiences, such
as builders or school children. Credit for some of the elements is based on covering
topics such as “flood hazard,” “flood hazard map,” “flood safety” and “property
protection.” These topics should include information on the special hazards, in addition
to the flood hazard mapped on the Flood Insurance Rate Map.
One of the elements in Activity 330 provides 100 points for developing and
implementing a public information program strategy. The community identifies its most
important public information needs and identifies the best way to meet those needs.
The strategy could focus on special hazards, if the strategy team determines that that is
as important or even more important than “normal” flooding. The full credit of 100
points would still be provided.
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340 Flood Hazard Disclosure
The CRS provides credit when real estate agents disclose information about a
property’s flood hazard to prospective buyers. More credit is provided if the disclosure
includes other hazards, such as special hazards. State or local mandates for sellers,
landlords, or developers to disclose these hazards can receive credit. If real estate
agents don’t actually disclose a property’s hazards, but provide a handout advising
house hunters about what to look for and what questions to ask, additional points are
provided.
350 Flood Protection Information
Under Activity 350, communities receive credit for putting flood protection
information in their public libraries and on their websites. These materials should cover
all known flood-related hazards, including special hazards. Additional credit points are
specifically provided if the library has references on uncertain flow path hazards,
provided they are present in the community. This publication can be cataloged in the
library to receive that credit.
The community or the librarian should also review the references at the end of this
supplement to identify additional documents that would be helpful locally. Some of the
websites mentioned in this publication could also be good links for the community’s
website coverage of its special hazards and ways people can protect themselves and
their property.
Example. Arid County has several publications on alluvial fans in its library,
including Alluvial Fan Flooding, by the National Research Council. Its website
includes several pages on alluvial fan flooding and channel migration, along
with an explanation of how the floodplain management ordinance protects new
development from damage while enhancing the County’s system of linear
parks and trails.
360 Flood Protection Assistance
Floodplain residents are more likely to undertake activities to reduce the risks from
special hazards to their property if reliable information is available locally. The CRS
provides credit if a local government provides technical advice to interested property
owners and publicizes that this service is available.
A community that is offering assistance and receiving credit for Activity 360 should
have its staff trained about the hazards associated with uncertain flow paths.
Example. Upon requests from property owners, an Arid County staff
member will make visits to properties to explain the requirements of its
floodplain management ordinance and to help the property owners locate their
structures on their property if it is in a delineated alluvial fan, or if it is within a
setback area.
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400 Mapping and Regulatory Activities
FEMA and many communities have long recognized that the mapping and/or minimum
regulatory standards of the NFIP do not adequately address the problems of special
hazards. Since these special hazards have the potential for extraordinary flood damage,
it is important that communities deal with the hazards in ways that go beyond the
minimum NFIP standards.
To protect new development in areas subject to special hazards, a community must
have maps that adequately define the hazards and ordinance language that deals with
the specific hazards in those areas.
410SH Additional Flood Data for Special Hazard Areas
Mapping criteria for areas with special hazards are discussed in this section. For areas
that meet the mapping criteria, credit is provided in Activity 410. All special hazards
credits are provided only if those areas are mapped by methods described in this
section.
411SH Credit Points
a. Prerequisites for mapping credit:
1. Credit for mapping areas subject to special hazards is only given if the
community has special-hazard-related development regulations that receive
at least 20 points under Section 420SH and/or Section 430SH.
2. To receive credit for mapping, open space preservation, and/or management
of special hazards, either the community or FEMA must either map the
hazard areas in detail, or the community must require developers to do so as
a condition of any development permit. The mapping technique must be
accepted by the FEMA Regional office.
b. Mapping credit for special hazards:
1. Mapping credit for ice jam hazards (MIJ):
There is no 410SH credit for mapping ice jam hazards because Flood
Insurance Study Guidelines and Specifications for Study Contractors
specifies mapping criteria for this hazard. However, this hazard must be
mapped in order for the community to receive credit for management of ice
jam hazards in Section 431SH and/or for credit for preservation of open
space in these hazard areas under Section 420SH.
If the community prepares a new map that includes the ice jam technique, it
is eligible for regular Activity 410 credit.
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Mapping areas subject to ice jam hazards requires a hydrologic analysis of the stream
reach that includes ice jam flooding. Although the FEMA Flood Insurance Study
Guidelines and Specifications for Study Contractors specifies methods for analyzing ice jam
floods, the hydrology typically done for flood insurance studies and most other types of
studies is based on clear water flow.
For CRS credit, ice jam hazards must be mapped using either the direct or indirect
method of determining ice jam flood elevations as specified in Appendix 3 of the
current version of Flood Insurance Study Guidelines and Specifications for Study
Contractors. This manual can be found at the website
http://www.fema.gov/plan/prevent/fhm/dl_scg.shtm .
Example 411IJ-1. In 1996, FEMA mapped North County’s floodplains
based on new hydrology. The 100-year ice jam flood elevations based on
historic ice jam flooding also were determined. This makes North County
eligible for special hazards credit under Sections 420SH and 430SH.
2. Mapping credit for closed basin lakes (MCB):
There is no 410SH credit for mapping closed basin lake flooding hazards
because the Flood Insurance Study Guidelines and Specifications for Study
Contractors specifies mapping criteria for this hazard. However, this hazard
must be mapped in order for the community to receive credit for management
of closed basin lake hazards in Section 431SH and/or for credit for
preservation of open space in these hazard areas under Section 420SH.
If the community prepares a new map that includes the closed basin lake
mapping technique, it is eligible for regular Activity 410 credit.
3. Mapping credit for mudflow hazards (MMF) (Maximum credit: 50 points)
(a) Prerequisite: To receive credit for mapping mudflow hazards, the
community must either map the hazard areas in detail, or it must require
developers to do so as a condition of any development permit. The
methods used must be accepted by the FEMA Regional Office.
(b) MMF credit:
(1) 50 points, for mapping mudflow or landslide hazards in areas outside
the SFHA as shown on the community’s FIRM if the scale of the
mapping is 1:10,000 or smaller.
(2) 50 points, for mapping mudflow or landslide hazards in areas inside
the SFHA as shown on the community’s FIRM if the scale of the
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mapping is 1:10,000 or smaller and the regulatory flood elevation is
higher than the base flood elevation shown on the FIRM..
(3) 20 points, for mapping mudflow or landslide hazards in areas outside
the SFHA as shown on the community’s FIRM if the scale of the
mapping is larger than 1:10,000.
Mapping areas subject to mudflow hazards requires examination of previous landslides,
topography, and soils. No specific method is recommended for CRS credit. Maps from
any source that are used by the community for regulatory purposes, as long as they are
at an appropriate scale, are acceptable for CRS credit with approval from the FEMA
Regional Office.
Example 411MF-1. The state Department of Mining and Geology (DMG)
mapped Steep County’s mudflow hazards at a scale of 1” = 200’ (1:2,400).
MMF = 50.
4. Mapping credit for areas subject to land subsidence (MSU) (Maximum credit:
50 points)
(a) Prerequisites:
(1) To receive CRS credit for mapping areas of land subsidence where
subsidence is due to the withdrawal of fluids or gasses, or is
associated with organic soils, maps of future subsidence must be
provided. The entire floodprone area subject to subsidence must be
mapped by methods accepted by the FEMA Regional Office. Credit is
provided for mapped floodprone areas where the combination of
historic and projected subsidence is greater than 1.0 foot.
(2) If the community is requesting credit for reducing future land
subsidence, but not for regulation of development in areas subject to
flooding as a result of future land subsidence, mapping of the area
subject to future subsidence by methods accepted by the FEMA
Regional Office is necessary.
(3) To receive CRS credit for mapping, areas of land subsidence where
subsidence is due to the formation of sinkholes, the maps must at
least show all existing sinkholes in the community. To receive CRS
credit for open space preservation and/or management of land
subsidence where subsidence is due to the formation of sinkholes,
the maps must include areas where there is a potential for new
sinkholes using methods accepted by the FEMA Regional Office.
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(b) MSU credit:
(1) MSU credit of 50 points is provided for the area outside the SFHA
shown on the community’s FIRM that is mapped as subject to
subsidence.
(2) MSU credit of 20 points is provided for areas inside the SFHA as
shown on the community’s FIRM that are mapped as subject to
subsidence.
Understanding and mapping land subsidence itself is usually only the first step.
Gradual land subsidence subtly changes the land surface so that the flood hazard
changes. This is easy to imagine in a coastal situation: if the land is ten feet above sea
level, and it subsides eleven feet, it will be below sea level.
It may be more difficult to envision the results of land subsidence at an inland location.
Imagine a tabletop model of a river flowing through a broad valley. Now deform the
land surface by placing a large bowl or sphere in the middle of the model and pushing
it down just an inch or so. When the bowl is removed, the slope at the upper side of the
depression is slightly greater, so water flows a little faster. Since the quantity of water
is the same, if it is flowing faster, it will not be quite as deep.
However, at the lower side of the depression, the slope is slightly less, so the water will
flow more slowly. The water level will be somewhat higher, and the area it covers will
be somewhat larger. The deeper the depression, the larger the flooded area. This is
what happens to relatively large areas where there is land subsidence. The floodplain
gradually increases over time, and the flood elevation relative to the land surface
gradually increases.
Therefore, to really understand the flood hazards associated with land subsidence, it is
necessary first to map historic land subsidence, then to project future land subsidence,
and finally, to map the projected floodplain and future flood elevations.
Example 411SU. In 1999, Flat County mapped the floodplain based on
ultimate subsidence and development through the year 2030. At the same
time, FEMA hired the County’s consultant to map the floodplain under existing
conditions. Flat County receives MSU1 = 50 for areas that were outside the
SFHA on its 1978 FIRM. It receives MSU2 = 20 for areas that were within the
SFHA on its 1978 FIRM.
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Managing Subsidence in the Houston Area
The Harris-Galveston Coastal Subsidence District (District) was created in 1975 to regulate the
withdrawal of groundwater within Harris and Galveston Counties. The District was created “…for the
purpose of ending subsidence, which contributes to or precipitates flooding, inundation, or overflow of
the district, including without limitation rising waters resulting from storms or hurricanes.”
Since 1976, the District has adopted three regulatory plans. The initial plan focused on having an
immediate impact in the area where the most subsidence had taken place and where surface water was
available as an alternative to groundwater. The 1976 plan regulated pumpage in all of Galveston
County and much of eastern Harris County in an area referred to as the “area of concentrated
emphasis.”
The 1985 plan divided the District into eight regulatory areas so that subsidence could be addressed
throughout the entire District. This plan had an overall goal of changing primary water usage from
groundwater to surface water through a series of steps.
The 1992 plan modified the 1985 plan based on a detailed re-analysis of regional population and water
demand data. The 1992 plan divided the District into seven regulatory areas with goals for each area to
reduce groundwater withdrawal by certain dates. The areas were based on surface water availability,
geophysical characteristics, and groundwater demand.
The 1999 regulatory plan divides the District into three regulatory areas. The regulatory areas of this
plan have been reconfigured from the 1992 plan to generally reflect converted versus unconverted
areas. The requirements contained within the regulatory plan are based on the most current data and
studies on water demand, aquifer levels, and projected subsidence, and provide permittees with
organizational flexibility in meeting these regulations.
In the most critical areas (closest to the Gulf Coast), water users must limit groundwater use
to 10% of their total water use. In the next most critical area, groundwater use is limited to
20% of total water use (Harris-Galveston Coastal Subsidence District, 2001).
Even with these regulatory measures in effect, water levels declined as much as 100 feet
during 2002, and land subsidence of up to one foot was measured. Rainfall was above
average at most locations in the District (Harris-Galveston Coastal Subsidence District,
2003).
5. Mapping credit for uncertain flow path hazards (MUF) (Maximum credit: 50
points)
(a) Alluvial fan hazards: There is no credit for mapping alluvial fan hazards.
Because the Flood Insurance Study Guidelines and Specifications for
Study Contractors specifies mapping criteria for this hazard, such
mapping is a minimum requirement of the NFIP. However, this hazard
must be mapped in order for the community to receive credit for
management of alluvial fan hazards in Section 431SH and/or for credit for
preservation of open space in these hazard areas under Section 420SH.
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If the community prepares a new map that includes alluvial fan hazards, it
is eligible for regular 410 credit.
(b) Moveable bed stream hazards:
(1) MUF1: Credit of 50 points is provided for moveable bed streams:
((a))
In the case of aggrading or degrading streams, a sediment
transport model is required that includes the availability of
sediment to the stream, and that accounts for its movement
through the floodplain. Modeling of these streams for CRS
credit must look at present conditions and projections of future
conditions based upon changes in the source of sediment and
the floodplain. Mapping must be based upon the worst case of
aggradation or degradation.
((b))
In the case of channel migration, the local history of migration
must be reflected in the mapping process. For full credit,
mapping must be based upon floodplain soils and historic
channel migration that indicate the probable extent of future
migration.
(2) MUF2 credit of 25 points is provided for the following requirements
when there are no studies that meet the criteria of (a) above.
((a))
In the case of aggrading or degrading streams, for permits for
single structures the community may require only a statement
from a registered professional engineer that the proposed
structure is reasonably safe from the erosion- or
sedimentation-related flood hazard.
((b))
In the case of channel migration, credit is provided if a
community uses a locally developed standard building setback
for unstudied streams in lieu of a detailed study by a
developer. Such a setback standard must be based upon data
from the general area regulated.
Example 411UF-1.
Arid County mapped the West River as a stream with a migrating channel and
Dry Creek as a stream with a degrading channel. These studies were also
adopted by the County Commission in 1997.
Arid County requests CRS credit for MUF2a and MUF2b.
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Mapping Alluvial Fans: Since the Guidelines for Determining Flood Hazards on
Alluvial Fans (FEMA, 2000) prescribes methods for mapping alluvial fan hazards,
mapping alluvial fan floodplains is a minimum requirement of the NFIP. Therefore,
there is no CRS credit for such mapping. Although there is no CRS credit for mapping
alluvial fan hazards, these hazards must be mapped before other CRS credit can be verified for
management of these hazards.
Although the Guidelines prescribe mapping methods for alluvial fans, active support is
generally needed by the community to get such mapping included on the community’s
Flood Insurance Rate Map. This is because alluvial fan mapping must generally be
accompanied by specific ordinance language.
If a community has alluvial fan hazards, it should seriously consider appropriate
mapping and management of these hazards.
Mapping Degrading Stream Reaches: Mapping degrading stream reaches for
management purposes is relatively simple. As the channel degrades, the inundated area
shrinks until it is contained within the degraded channel. Unless the stream banks
become unstable and the channel migrates, errors will generally be on the safe side,
since the areal extent of the flood hazard is either stable or becoming smaller. There are
no known maps used for floodplain management purposes that account for channel
degradation, although local studies of degradation and scour have been performed in
many communities.
The objective when mapping degrading stream reaches is to identify the location and
progress of the degradation process so that facilities in and immediately adjacent to the
channel can be designed to be safe from the ongoing degradation.
Mapping Aggrading Stream Reaches: In areas where aggradation is suspected or has
occurred during historic flooding, it is expected that the channel is losing capacity, the
floodplain is getting wider and flood elevations are getting higher. These are the
problems to be addressed by mapping. The result may be similar to mapping
floodplains based on future-condition hydrology for developing watersheds.
Mapping Reaches Subject to Channel Migration: In stream reaches where the channel
may migrate outside the 100-year floodplain as defined by fixed-bed modeling, the
establishment of setbacks from the channel banks based on historic channel migration
may take the place of more rigorous mapping techniques. This approach requires a
developer to perform a detailed study of the channel morphology before developing
inside the setback.
Example. In King County, Washington, a mapping process similar to that in
Arizona was used to map a migrating channel. In a study of the Green River,
the effect of sediment transport throughout most of the reach was related to
locations of channel migration, rather than ongoing aggradation or
degradation. Delineation of “probable unconstrained limits of channel
migration” was based primarily on historic data. The “mitigated hard area” was
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then delineated assuming that ongoing protection would be provided for major
roads, subdivisions and levees in the floodplain.
Example. Pima County, Arizona applies a construction setback of 500 feet
from the channel bank of specified major streams, 250 feet for streams where
the 100-year flow is more than 10,000 cfs, 100 feet for streams with 100-year
discharges greater than 2,000 cfs, and 50 feet for streams with 100-year
discharges greater than 100 cfs (Cella Barr Associates, 1987). These
setbacks are based on the experience of the Pima County Flood Control
District. Pima County also used recent and historic aerial photos and old land
survey notes to more precisely determine setback limits for the Rillito River in
and near Tucson, Arizona. Exceptions are made where there is bedrock or
other impediment to channel migration, where there is bank protection
provided, or where an engineering study indicates that the channel will not
migrate.
Example. The State of Arizona developed a similar standardized approach
that is applied statewide. It establishes a setback for all streams based on the
100-year flow, the curvature of the channel and other parameters. This
approach has been implemented by Arizona communities as a minimum
standard.
412SH Credit Calculation
cAFDSH = cMMF + cMSU + cMUF
413SH Credit Documentation
The documentation required for special hazards mapping credit must show how the
mapping addresses the special hazard mapping criteria described in this section.
The community must provide the following:
a. A map that shows the areas subject to the special hazards and the other
floodplains (including the SFHA) in the community. If only a small area of the
community is mapped for special hazards, only the SFHA in that area need be
shown on the map.
b. A description of the method used for the mapping that shows that it reasonably
delineates areas subject to the special hazards, along with documentation that
the method is acceptable to the FEMA Regional Office.
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c. Credit for 410SH is only provided if the mapping is used for land use regulation to
prevent damage from the special hazard. The documentation required for Activity
430SH will suffice for this prerequisite.
414SH For More Information
The following publications may be obtained from
FEMA Distribution Center
P.O. Box 2010
Jessup, MD 20794-2012
1-800-480-2520
Fax: (301) 362-5335
Guidelines and Specifications for Flood Hazard Mapping Partners, FEMA-37,
February 2002. http://www.fema.gov/plan/prevent/fhm/gs_main.shtm
Alluvial Fan Guidelines, FEMA, February 2000.
http://www.fema.gov/pdf/fhm/ft_afgd.pdf
Arizona State Standard for Watercourse System Sediment Balance, Arizona
Department of Water Resources, Phoenix, AZ, 1996.
http://www.azwater.gov/dwr/Content/Find_by_Program/Dam_Safety_and_Flood_Mitigati
on/Floodplain_Managment_Docs/SS5-96_System_Sediment_Balance.pdf
Maricopa County, Arizona, floodplain management regulations.
http://www.fcd.maricopa.gov/Services/FloodplainRegulations.asp
420SH Open Space Preservation in Special Hazard Areas
NOTE : This section is a supplement to Activity 420 (Open Space Preservation) in the
Coordinator’s Manual. Much of the discussion in this section relies on Activity 420.
Please read that section before proceeding.
One of the best ways to prevent flood damage is to keep floodprone areas free from
development. In addition to the flood protection benefits, preserving open space can
greatly enhance the natural and beneficial functions that floodplains serve. For CRS
credit, “open space,” means that the land must be free from buildings, pavement, fill, or
other encroachments to flood flows.
In areas subject to special flood hazards, preservation of open space may be the single
most important tool for protection of future development.
For example, there are two hazards associated with ice jam flooding: higher flood
elevations when ice plugs the channel and/or floodplain; and the movement of ice floes.
The elevation hazard can be mitigated by elevating or floodproofing buildings. The
movement of ice floes may be difficult or impossible to mitigate with construction
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methods (see photo on page 5), and preservation of areas subject to this hazard as open
space may be the only sure way to mitigate the hazard.
In areas adjacent to closed basin lakes, the primary cause of flood damage is the
duration of flooding. There may be areas at the edge of this hazard that can be
developed with special attention to access and utilities, but inside this area,
preservation of open space may be the only viable means of mitigating the hazard.
This activity provides credit for having floodprone property within a designated special
hazard area preserved as publicly owned or controlled open space. This credit is in
addition to the credit provided for open space (OS) in Activity 420.
All of the requirements of Activity 420 apply to 420SH credit. In addition, areas for
which this credit is provided must be mapped as areas subject to special hazards as
discussed in Section 410SH.
421SH Credit Points
Special hazard area preserved as open space (SHOS) (Maximum credit: 50 points)
a. Prerequisites: Up to 50 points are provided if at least five acres of the regulatory
floodplain meets two prerequisites:
1. The area must be eligible for credit for open space preservation as discussed
in Activity 420; and
2. The area must be designated as an area subject to special hazards in a
study that is credited under Activity 410SH.
This requirement may be met in one of three ways:
1. Public land such as state and local parks and easements: However, as noted in
Section 403 of the Coordinator’s Manual, there is no open space credit for
federal lands. All portions of city and county parks, forest preserves, state parks
and state forests, publicly owned beaches, or natural areas that are within the
regulatory floodplain may be counted for open space credit. Separate parcels
owned by a school district or other public agency can be counted, provided there
are no buildings on them within the regulatory floodplain.
2. Preserve land: private wildlife or nature preserves that are maintained for open
space purposes. Examples would be church retreats, hunting club lands,
Audubon Society preserves, and similar privately owned areas that are set aside
and not intended to be developed. A parcel set aside by a developer as a
temporary “preserve” until the area develops is not considered permanent open
space.
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3. Restrictive development regulations: privately owned lands subject to state or
local regulations that prevent construction of buildings or the placement of fill
or other obstructions. Credit is only given for such regulated lands that are
vacant at the time of application for CRS credit. Some examples are setback
regulations, natural areas regulations, or any state or local law that prohibits
new buildings from a defined area. The regulations must also prohibit fill,
grading, or other obstructions to flood flows.
Example 421UF-1.
Arid County mapped 212 acres of the Oriental Fan as “Active Alluvial Fan
Area” and prohibits structures and fill within those areas. These areas were
not developed when the mapping was done. There is also a 565-acre County
park preserve in the AO zone.
Since the prohibition of structures and fill in undeveloped areas of the Oriental
Fan and West River qualify for credit for preservation of open space (OS) in
Activity 420, both of these areas are eligible for UFOS credit.
This gives a total of 777 acres of open space in uncertain flow path hazard
areas.
422SH Impact Adjustment
a. Option 1: If the entire area of the special hazard is preserved as open space, the
impact adjustment, rSHOS, is 1.0.
b. Option 2: If five or more acres of the special hazard area is preserved as open
space, the impact adjustment, rSHOS, is 0.2.
c. Option 3: Where more than 20% of the special hazard area is preserved as
open space, the community may calculate an impact adjustment by dividing the
special open space area (aSHOS) by the area of the mapped special hazard
(aSH).
rSHOS = aSHOS
aSH
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423SH Credit Calculation
Maximum credit for special hazard open space is 50 points.
cSHOS = SHOS x rSHOS
424SH Credit Documentation
The community must provide the following:
a. The community must receive credit under 410SH.
b. Documentation that the area where open space credit is requested is in the
special hazard area and meets the open space requirements of Activity 420
(Open Space Preservation) in the Coordinator’s Manual.
430SH Higher Regulatory Standards for Special Hazards
431SH Credit Points
NOTE: This section is a supplement to Activity 430 (Higher Regulatory Standards) in
the Coordinator’s Manual. Much of the discussion in this section relies on Activity
430. Please read that section before proceeding.
In areas where it is not feasible to restrict land to open space uses, other land use
planning measures can be used to minimize flood damage. These include strategically
controlling the type of development and uses allowed in hazard areas, and avoiding
high-value and high-occupancy uses as much as possible. For example, plan
designations and zoning districts can use density restrictions or large-lot zoning to
ensure that only very low density residential uses are allowed in hazard areas.
Credit is provided for regulating special hazard areas in a manner that recognizes those
elements of the hazard not addressed by the NFIP minimum standards for floodplain
management. This credit is in addition to credit provided for other regulatory standards
under Activity 430 in the Coordinator’s Manual.
Maximum credit for Activity 430SH: 100 points.
a. Prerequisites for credit for 430SH:
1. The community must have received credit for mapping areas subject to
special hazards under Section 410SH, except for ice jam hazards, closed
basin lakes, and alluvial fan hazards, which must have been mapped
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according to the Guidelines and Specifications for Flood Hazard Mapping
Partners.
2. The community must adopt and enforce regulatory standards that address
the special risks associated with these hazards.
b. Regulation of special hazard areas (SHR)
1. Ice jam regulations (IJR) (Maximum credit: 100 points) Credit for IJR is the
sum of the following:
(a) 50 points, for requiring new structures to be constructed on engineered fill
or engineered pilings at or above the ice jam regulatory flood elevation;
(b) 12 points x freeboard above the ice jam regulatory flood elevation (in feet)
(maximum credit = 36 points for 3 feet of freeboard); and
(c) 14 points for prohibiting new structures in areas subject to ice floe
damage (this is in addition to credit for open space preservation).
Regulation of areas subject to ice jam flood hazards should include protecting buildings
from both the hazard from higher flood elevations and the hazard associated with
moving ice floes. These regulations may include higher minimum floor elevations and
structural requirements for buildings so that they are not damaged or destroyed by
moving ice. There may also be special requirements for infrastructure in areas subject
to ice jam hazards.
Land development criteria, such as clustering the buildings in a development to keep
them out of the area subject to ice jam hazards, and low density zoning, which reduces
the development potential in the ice jam hazard area, also reduce the damage potential.
Example 431IJ.1. North County prohibits development in the reach of the
floodway affected by ice jam flooding. IJR1 = 50 + 14 = 64. In the reaches
regulated for ice jam hazards outside the floodway, IJR2 = 50.
2. Closed basin lake hazards regulations (CBR) (Maximum credit: 100 points)
Credit for CBR is the sum of the following:
(a) 60 points, if new structures are required to be built on fill at or above the
regulatory flood elevation for closed basin lakes credited in 410SH;
(b) 10 points, if access is required at the regulatory flood elevation;
(c) 10 points, if all utilities are required to be protected to the regulatory flood
elevation and functional during the regulatory event;
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(d) 15 points, if all utilities and basements within 1,000 feet of the shoreline
established by the regulatory flood elevation are required to be
floodproofed to the regulatory flood elevation unless it can be demonstrated that the water table under the proposed development will not be
affected by lake elevations; and
(e) 5 points, if new wells constructed within the hazard area are required to
be floodproofed to the regulatory flood elevation, and all existing wells
that are to be abandoned are required to be sealed to eliminate the
mixing of groundwater and lake water.
CRS credit for regulation of areas subject to closed basin lake flood hazards should
anticipate both the flood elevation and the long duration of high water surface
elevations. It is important to protect utilities and infrastructure from long periods of
inundation and to ensure access to buildings at the highest anticipated lake level. There
is credit for land development criteria that reduce development adjacent to closed basin
lakes, such as density trades, and for low density zoning in these areas.
Example 431CB. Lake City requires buildings on land between 1,010 feet
and 1,012 feet msl to be elevated on fill to 1,012 feet. No septic tanks or wells
are allowed in areas where the land elevation is below 1,012. CBR = 85.
3. Mudflow
hazard regulations (MFR) (Maximum credit: 35 points): Credit for
MFR is the sum of the following:
(a) 25 points, if a study by a soils engineer and/or an engineering geologist is
required for any hillside grading where stability will be lessened by the
grading, and at historic or prehistoric landslide sites;
(b) 5 points, if where buildings are to be supported on stilts over a fill slope
with a slope greater than two horizontal to one vertical, footings must
extend at least 3 feet into the underlying bedrock, but not less than the
depth required to resist the lateral load; and
(c) 5 points, if drainage from impervious surfaces must be collected and
conducted to the street in a non-erosive manner.
There is no safe way to develop an area that is subject to mudflow hazards. However,
maps of mudflow hazard areas are usually based on relatively large-scale map analysis,
so most regulations require an engineering study, a geologic study, or both. The idea is
that some of the area mapped as mudflow hazard may actually not have such a hazard,
but it is the developer’s responsibility to determine the true hazard.
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4. Land subsidence hazards:
(a) Land subsidence regulations (SUR1) (Maximum credit: 100 points):
Credit is provided for regulating development in the floodprone areas
subject to land subsidence based upon the regulatory flood elevation
considering projected subsidence as determined in accordance with the
criteria of Section 411SH. Credit for SUR is the sum of (1) and (2):
(1) 80 points, if all new buildings must be built on engineered foundations
with pilings that will prevent the building from sinking as subsidence
continues.
(2) 20 points, if all new public facilities and utilities are required to be
designed for the subsidence hazard.
(b) If the community does not apply for regulation of development (SUR1)
under the above section, credit is provided for activities intended to
reduce future land subsidence. If the community has mapped current
subsidence, and if that subsidence is greater than 1.0 foot, and if the
community has a scientific plan to reduce future subsidence, SUR2 = 50.
Regulation of the activities that cause subsidence is the most direct approach to
subsidence mitigation. Approaches to prevent or control subsidence vary according to
the type of subsidence. In the case of resource extraction, they range from banning
extraction to controlling how materials are removed. In the case of land development
practices that cause subsidence, they range from banning development to regulating
construction practices.
Different causes of subsidence require different regulatory approaches for controlling
the subsidence. For example,
• If land subsidence is a result of aquifer compaction, then changes in the amount of
groundwater extracted and/or perhaps the locations at which it is extracted, may be
required to reduce or eliminate subsidence. This is a difficult choice to make when
groundwater is needed to support existing and projected land uses. State or federal
funding may be required to provide alternate sources of municipal, industrial, and
agricultural water, and multiple jurisdictions may have to work together to control
land subsidence.
• If land subsidence is due to the dewatering of organic soils, controlling the water table
by extensive pumping may have to be combined with extensive levee systems if the
land is to be used and the subsidence controlled.
• If land subsidence is caused by the dissolution of soluble subsurface materials, any
subsurface movement of water makes the problem worse. Extraction or recharge of
groundwater may accelerate the natural processes that cause sinkholes or more gradual
land subsidence.
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The local causes of land subsidence must be understood before regulatory standards
can be applied. Where subsidence is gradual and ongoing, land use regulations may be
effective in reducing flood damage. If the relatively constant rate of subsidence in an
area is known, new development can be prohibited or elevated to compensate for
predicted future subsidence. If the probability of subsidence (like sinkholes) is not
uniform over an area, low density zoning may reduce the damage in the areas with
highest risk. Again, the cause of land subsidence, combined with some ability to
predict future subsidence, is required.
5. Uncertain flow path regulations (UFR) (Maximum credit: 100 points): A
community may receive credit for regulation of areas subject to four types of
uncertain flow path hazards: alluvial fans, aggrading stream channels,
degrading stream channels, and migrating stream channels. Credit for only
one type of uncertain flow path hazard is allowed in a particular area. For
each stream reach or area, the community should seek credit for the one that
gives the highest credit for UFR.
(a) Credit is provided for regulating development in areas subject to alluvial
fan hazards that account for the flood, sediment, erosion, debris, velocity,
and avulsion hazards in the area. For alluvial fans, credit for UFR1 is the
sum of the following:
(1) 80 points, if all new structures are required to be protected from
alluvial fan hazards;
(2) 10 points, if all utilities are required to be designed to function and
minimize damage during the 100-year event; and
(3) 10 points, if access is required during the 100-year event.
(b). Credit is provided for regulating development in areas subject to
moveable bed stream hazards that have been mapped in accordance
with the criteria of Section 411UF.a.
(1) In the case of aggrading streams, UFR2 credit is provided for
management of future development to the UFR2 flood elevation. The
minimum area to be regulated must be the area inundated by that
flood. UFR2 credit is the total of the following:
((a))
50 points, if new residential structures are required to be
elevated to the regulatory flood elevation;
((b))
20 points, if new non-residential structures are required to be
elevated or floodproofed to the UFR2 flood elevation;
((c))
20 points, if public improvements and utilities are required to
be protected from the UFR2 flood elevation; and
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((d))
10 points, if protection is required to at least 1 foot above the
UFR2 flood elevation. This credit is in addition to appropriate
FRB credit in Activity 430.
(2) In the case of degrading streams, UFR3 credit is given for
management of future development within the floodplain inundated by
the worst case of the base flood (probably the present channel
condition) and to the regulatory flood elevation. Channel
developments would be regulated based upon the channel condition
during that worst-case flood. UFR3 credit is the total of the following:
((a))
50 points, if new structures within 200 feet of the banks are
required to have engineered foundations; and
((b))
50 points, if public improvements and utilities within the
floodplain are required to be designed to withstand the worstcase base flood and channel conditions.
(3) In the case of streams subject to channel migration, UFR4 credit is
provided for appropriate management of future development in the
stream reaches subject to channel migration. UFR4 credit is:
((a))
100 points, if a detailed study of the migration potential has
been mapped, and if all public and private developments are
required to be located and designed to be safe from channel
migration; or
((b))
50 points, if a standard setback is mapped, and all public and
private development is permitted only after a detailed study of
the channel migration hazard.
Credit for the three types of moveable bed streams is mutually exclusive, and exclusive
of alluvial fan areas. If the mapping process indicates that the nature of the stream
changes over time (for example, the channel degrades for a period and then aggrades
over another period), the community must demonstrate that its regulation addresses the
“worst case” of flood hazard over the entire period.
“Worst case” for purposes of this element means the worst hazard over the period of
the mapping study. If, for example, a stream is shown to be aggrading, the worst case
might be a combination of unstable vertical banks today, requiring a setback, and a
higher flood elevation in the future, requiring higher floor elevations. In the case of a
degrading channel, the worst case is the present flood elevation and future unstable
banks or channel migration.
Management of flood hazards on alluvial fans requires more than a knowledge of the
existence and extent of the fans. The management techniques used at a particular
location on a particular fan should be appropriate for the hazards (depth, velocity, and
sediment and debris load) at that location. Within a small area, such as a county, fans
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may be similar enough to manage under a single set of standards, but these standards
must be carefully developed.
Neither Alluvial Fan Flooding (National Research Council, 1996) nor Guidelines for
Determining Flood Hazards on Alluvial Fans (FEMA, 2000) suggest much in the way
of regulatory standards. In a discussion of several specific alluvial fans, the former has
recommendations such as “avoidance of the hazard” and “only major structural controls
will be effective because development is along the entire lower portion of the active
fan.” For the Carefree Fan in Maricopa County, Arizona, the suggested mitigation is
“low-density development with restriction of structures to the stable ridges . . . and
elevation of structure floors.”
Mitigation of flood hazards on alluvial fans must respond to three components of the
hazard: velocity of the water, sediment, and debris; the volume and movement of
sediment and debris during floods; and the potential for channel migration across the
fan during flood episodes (avulsions). All of these components are present where there
are no confined channels. Where there are confined channels, only the first two
components of the flood hazards exist.
Example. Maricopa County, Arizona, has two separate management
schemes for “active” and “inactive” fan areas. Inactive fan areas are
designated as unnumbered A Zones, and development is required to be
elevated two feet above grade. Active fan areas are designated as
“Administrative Floodways,” with management similar to that required by the
NFIP for floodways
From the “Floodplain Regulations for Maricopa County” as amended
November 2000:
Section 1301. Development in Alluvial Fan Zone A.
1. Where alluvial fans have been designated using the District’s
Piedmont Assessment Manual, the following shall apply:
a. Development within an Alluvial Fan High Hazard Area, Alluvial
Fan Uncertain Flow Distribution Area and Alluvial Fan Floodway
shall be regulated in a manner similar to a floodway. Only major
engineering measures as outlined in 44 CFR 65.13 can be used
to mitigate the alluvial fan flood hazard in these areas
b. Development within an Alluvial Fan Zone A (AFZA) shall be
regulated in a manner similar to a Zone A riverine floodplain.
Development may require an engineered plan.
Example. Pima County, Arizona, has identified a 154-square-mile area as
the Tortolita Watershed, consisting of the mountainous headwaters and
sediment source and the associated alluvial fans. The following standards
were recommended for application throughout the watershed (Cella Barr
Associates, 1987):
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o Washes with a 100-year peak flow in excess of 1,000 cfs should be maintained
as natural undisturbed riverine environments, and detention facilities should not
intercept them;
o The basin is designated as a “critical” basin, so development must decrease
existing runoff;
o Drainage maintenance plans are required for developments that exceed 40 acres
in the upper watershed or 120 acres in the lower watershed, or if they contain or
abut a major wash or propose major channel modification;
o Rezoning densities should be maintained at or below those specified in a Countydeveloped area plan (1.21 to about 2.70 residences per acre);
o Sedimentation should be considered in drainage studies; and
o Floodway surcharges and post-development velocities are limited.
Example. Whatcom County, Washington, has mapped alluvial fans as one
of several geologic hazards. The ordinance states, “No critical facilities shall
be constructed or located in geologically hazard areas without fully mitigating
the hazard.” Also, “All projects on an alluvial fan must be engineered and
constructed to withstand alluvial fan hazards and/or flooding equivalent to the
largest known event evident on the fan as determined by professional
assessment” (Whatcom County, 1997).
Regulation of Areas Subject to Moveable Bed Streams
The management needs are somewhat different for the three types of moveable bed
streams, so they are discussed separately.
Example. In the State of Washington, the State Department of Ecology has
developed the Stormwater Management Manual for Western Washington
(Washington Department of the Environment, 2001) to maintain current levels
of peak flow and sediment for all floods up to the 100-year event as a means
of protecting its fisheries. This manual will ultimately apply to all Washington
communities between the Cascade Mountains, the Puget Sound, the Pacific
Ocean, and the Columbia River. Regulation of sediment transport throughout
the watershed should allow the watercourses to come into equilibrium,
minimizing future erosion, sedimentation, and channel migration.
Areas Subject to Degradation—In stream reaches that are subject to channel
degradation, the greatest potential threats are to development in the channel (including
sand and gravel operations and public recreation facilities) and infrastructure in and
adjacent to the channel (including flood control projects, roads, bridges, and buried
utilities). If the channel degradation does not cause instability in the banks, protection
of these facilities may be managed by construction standards and special use permits
that recognize the hazards. If the banks are unstable, setbacks may also be needed. No
regulations have been found that specifically address the increased future hazards
associated with degrading streams.
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Regulation of sand and gravel operations may be extremely important in some locations
to control channel degradation but, to be effective, such regulation would have to be
based on the kind of comprehensive modeling approach described by the State of
Arizona. If a sand and gravel pit is located where floodwater can enter it, it may act as
a sediment trap, allowing sediment to settle out. When the water leaves the pit, it is free
of sediment, and immediately scours the bed downstream to restore its sediment load.
Water entering the pit may also cause headcutting upstream from the pit. Detailed
sediment transport studies are usually required to determine the effects of sand and
gravel pits in floodplains, particularly in floodways.
Example. Maricopa County, Arizona, has adopted a regulation specifically
for sand and gravel operations. It states:
A Floodplain Use Permit for the extraction of sand and gravel or other
materials within the Floodway shall be granted if the applicant shows
that excavations will not have cumulative adverse impact nor be of
such depth, width, length, or location as to present a hazard to life or
property or to the watercourse in which they are located and that they
will comply with any applicable Watercourse Master Plan adopted by
the Board of Directors… Excavations shall not be permitted so close
to any floodway crossings, utility structures or facilities as to cause or
have the potential to cause an adverse effect on such crossings,
utilities or similar facilities... A plan of development shall be submitted
with an application for a Floodplain Use Permit to the Floodplain
Administrator. The Floodplain Administrator will determine whether an
engineered plan will be required and whether a sediment transport
analysis is necessary… The plan of development shall be required to
include a plan of reclamation to leave the land when the approved use
is terminated in such a condition as to maintain stability of the
floodway by backfilling, contouring, leveling, removal of equipment
and materials or other appropriate means… The plan of development
is subject to post-flood review and possible modification if necessary
due to flood related changes in river morphology.”
Areas Subject to Aggradation—Aggrading stream reaches cause more flood damage
in both the channel area and the overbank area than those expected if the reach is
delineated using a fixed-bed model. In Maricopa County, Arizona, aggradation in the
channel of the Gila River caused a 100-year flood to inundate the 500-year floodplain
in 1980. The old primary river channel, choked with vegetation watered by sewage
effluent, was filled with silt and a new channel was cut up to 1,500 feet away.
Management of aggrading stream reaches should account for the ongoing loss of
channel and/or floodplain conveyance capacity and the resulting increase in future
flood elevations and larger areal extent of flooding in future events.
No regulations have been found that specifically address the increased future hazards
associated with aggrading streams. Setback lines and freeboard requirements provide
some mitigation for these hazards, but if they are to provide true mitigation, they need
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to be based on a detailed study that forecasts future flood elevations and floodplain
limits. Such studies may be included in mapping projects that are based on futureconditions hydrology.
Areas Subject to Channel Migration—In stream reaches where there is a history or
geologic evidence of channel migration, floodplain management to reduce future flood
damage must consider the possibility of future channel migration.
Example. King, County, Washington, has established setback lines along
at least one river based on a study of historic and potential channel migration.
Example. Pima County and Tucson, Arizona, have established setback
lines along all watercourses based on recent experience and an examination
of selected floodplains. In Pima County, a developer must provide a detailed
study, including a sediment transport analysis, in order to develop inside the
setbacks. Setbacks range from 50 feet on minor washes to as much as 500
feet. The setback is from the channel bank or the 100-year floodplain,
whichever is wider (Pima County, 1999).
Example. In San Diego County, California, a Resource Protection
Ordinance requires a setback of 100 feet or 15% of the floodway width,
whichever is less, from the floodway boundary. Where erosion/sedimentation
hazards are identified, no development is allowed. Also, the floodway is
established using a maximum increase in flood elevation of 0.2 feet, and
floodways are limited to velocities of 6 feet per second flood, which increases
the floodway width in many steep floodplains. Although it is not quantifiable,
these floodway restrictions should provide more protection than floodways
delineated using the standard FEMA criteria of an allowable 1.0 foot rise with
no consideration of velocity.
Example 431UF-1.
In the Oriental Fan area, the mapping study upon which Arid County’s
regulations are based produced elevations based on water, sediment, and
debris. Flood velocities are estimated throughout the area. New development
must be designed to protect against these hazards. UFR1a = 80.
In the West River floodplain, the County adopted a setback line and prohibits
new buildings and fill within this area. This regulatory standard is credited in
Activity 420UF.
Adjacent to Dry Creek, which is a degrading channel, the County requires all
new buildings to have engineered foundations. UFR3a = 50. Public
improvements and utilities within the floodplain are required to be designed to
withstand the worst-case base flood and channel conditions. UFR3b = 50.
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432SH Impact Adjustment
The area affected by the special regulations must exclude areas designated as
open space that are receiving Open Space (OS) credit under Activity 420 (Open
Space Preservation).
a. Option 1:
1. If new development within the entire area of the special hazard is subject to
the regulations, and no credit was requested for SHOS in Section 420SH, the
impact adjustment rSHR is 1.0
2. If new development within the entire area of the special hazard is subject to
the regulations, and credit was requested for SHOS in Section 420SH, the
impact adjustment rSHR = 1.0 – rOS.
As with other regulatory elements, areas for which open space credit (Activity 420) is
requested must be excluded from the area credited for the special regulations.
b. Option 2:
If the special regulations cover only a portion of the special hazard area, rSHR =
0.25.
c. Option 3:
If the special regulations cover more than 25% of the special hazard area, the
impact adjustment ratio may be computed by dividing the area affected (aSHR)
by the area of the mapped special hazard (aSH). Any area for which SHOS
credit is requested must be excluded from the element’s area measurements.
rSHR = aSHR
aSH
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432SH Credit Calculation
a. cIJR = IJR x rIJR
b. cCBR = CBR x rCBR
c. cMFR = MFR x rMFR
e. cSUR = SUR x rSUR
e. cUFR = UFR x rUFR
f. cSHR = cIJR + cCBR + cMFR + cSUR + cUFR + cLZSH
The value for cLZSH is found in Section 433LZSH.
The value of cSHR is added to SHR in Activity 430.
The maximum credit for cSHR is 150 points, so if cSHR is greater than 150 points,
cSHR = 150.
433SH Credit Documentation
The community must provide the following documentation:
a. The state or local law or ordinance language that adopts the regulatory standard.
The acronym SH must be marked in the margin of the sections of the ordinance
that apply to this activity.
A photocopy of the appropriate pages of the ordinance is sufficient and should be
attached to the activity worksheet. The Chief Executive Officer’s application
certification is considered to include a certification that the ordinance or statute has
been enacted into law and is being enforced (see Section 212.a in the Coordinator’s
Manual).
The community must have the following documentation available to verify
implementation of this activity:
b. An explanation of the procedures followed for enforcement.
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The ISO/CRS Specialist will ask to see permit records for development in the special
hazard area to verify that the regulations are enforced.
430LZSH Low Density Zoning in Special Hazard Areas
Credit is provided for zoning areas to keep them substantially open. This credit is
available for undeveloped land within low density zoning districts, as well as for areas
developed in accordance with the density requirements.
431LZSH Credit Points
Areas subject to special hazards with low density zoning (LZSH) (Maximum credit:
50 points):
Within the areas subject to special hazards, credit is provided for low density
zoning.
Credit is given for those portions of the mapped special hazard area that are subject
to zoning rules that require a minimum of 1 acre per building or unit. Maximum
credit is provided for a 10-acre or larger lot size.
s = the minimum lot size in acres.
LZSHs = 5 x s, for areas with special hazards and with minimum lot sizes of at least
1 acre.
The credit for low density zoning is based upon the traditional zoning approach of
setting minimum lot sizes for different zoning districts. The bigger the lot size, the less
dense the development will be in the special hazard area.
432LZSH Impact Adjustment
The area affected by the low density zoning regulation must exclude areas
designated as open space that are receiving Open Space (OS) credit under Activity
420 (Open Space Preservation).
a. Option 1:
1. If new development within the entire area of the special hazard is subject to
low density zoning regulations, and no credit was requested for SHOS in
Section 420SH, the impact adjustment rLZSH = 1.0
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2. If new development within the entire area of the special hazard is subject to
low density zoning regulations, and credit was requested for SHOS in Section
420SH, the impact adjustment rLZSH = 1.0 – rOS.
As with other regulatory elements, areas for which open space credit (Activity 420) is
requested must be excluded from the area credited for low density zoning.
b. Option 2: The community may use the default value if its low density zone
covers at least 5 acres of the special hazard area. rLZSH = 0.2.
The use of Option 2 is limited to one zoning density for at least 5 acres. Communities
with more than 20% low density zoning within their special hazard area may find
Option 3 provides more credit.
c. Option 3:
The impact adjustment ratio for each low density zoning district is computed by
dividing the area affected (aLZSHs) by the area of the mapped special hazard
(aSH). Any area for which SHOS credit is requested must be excluded from the
element’s area measurements.
rLZSHs = aLZSHs
aSH
If there is more than one low density zoning district within the special hazard area,
each must be appropriately designated on the Impact Adjustment Map (see Section
403) and the area of each must be determined in order to calculate the impact
adjustments.
433LZSH Credit Calculation
Maximum credit for special hazard low density zoning is 50 points.
LZSH = ∑(LZSHs x rLZSHs)
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434LZSH Credit Documentation
The community must submit the following:
a. The ordinance language that adopts the low density zoning standard. The
appropriate acronym(s) (LZSH1, LZSH5, etc.) must be marked in the margin of
the sections that pertain to the element.
A photocopy of the appropriate pages of the ordinance is sufficient. The CEO’s
certification of the application or modification is considered to include a certification
that the ordinance or statute has been enacted and is being enforced (see Section
212.a).
The community must have the following documentation available to verify
implementation of this activity:
b. The Impact Adjustment Map prepared in accordance with Section 403 must be
provided. Each area listed in Section 431LZSH for which credit is being
requested must be designated on the Impact Adjustment Map and in the map’s
key.
Areas subject to low density zoning are designated as “LZSHs” on the Impact
Adjustment Map (see Section 403), where the “s” designates the minimum lot size (in
acres). An area of 5-acre zoning would be designated “LZSH5”; an area in which one
structure is allowed on a 100,000-square-foot lot would be designated “LZSH2.3”
(100,000 square feet is 2.30 acres).
c. An explanation of the procedures followed for enforcement of the regulatory
standard.
d. Examples of developments constructed in accordance with the ordinance
language.
During the verification visit, the ISO/CRS Specialist will need to see site plans and
final plats that will document how the land development criteria or zoning density is
applied. The ISO/CRS Specialist will also visit a sample of new developments to verify
that they have been constructed in accordance with the approved plans.
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440 Flood Data Maintenance
Any special hazard areas should be included in the community’s flood data. If the
community has a GIS system used for floodplain management, all special hazards
should be included in this system.
CRS credit (8 points) is provided for including special flood-related hazard areas in a
geographic information system (GIS), in a digitized parcel system, or on an overlay
map. This is found in Section 441.a.2(g) of the Coordinator’s Manual.
450 Stormwater Management
Although no specific credit is provided in this activity for special hazards, some items
credited in the stormwater master plan (SMP) may relate directly to these hazards. For
example, in Activity 420, Example 421UF.1, Arid County receives open space credit
because it prohibits development or fill in areas that are designated “active alluvial
channels.” In Section 451.b of the 2002 CRS Coordinator’s Manual, SMP credit is
provided:
(d) 15, if the plan identifies existing wetlands or other natural open space
areas to be preserved from development to provide natural
attenuation, retention, or detention of runoff.
(e) 10, if the plan prohibits development, alteration, or modification of
existing natural channels.
(f) 10, if the plan requires that channel improvement projects use natural or
“soft” approaches rather than gabions, rip rap, concrete, or other
“hard” techniques.
Arid County’s regulatory requirements for the Oriental Fan area should qualify for all
of these credit points because the regulations were adopted as a result of the hydrologic
study performed by the Flood Control District for the floodplain management master
plan.
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500 Flood Damage Reduction Activities
510 Planning
Reducing the risk of damage from natural hazards has always been part of local
planning and policymaking. By incorporating hazard information in a comprehensive
plan, the local government can provide a sound basis and justification for those
approaches that it decides to pursue in managing development and post-disaster
reconstruction. Local governments have traditionally responded to natural hazards by
delineating hazardous areas and by establishing land use controls, construction
standards, and public investment policies governing development within those areas.
Planning tools are designed to guide land use and development patterns while assuring
public safety and infrastructure services. Some states have established a planning
framework for local governments that sets guidelines for local plans. Some encourage
or require local governments to develop their own land use and development plans
either for the entire community or for specifically defined resource management areas.
The causes of these special hazards, their locations, and the nature of the hazards make
master planning an almost essential element of mitigation of the hazard. Consider that
• Ice jams tend to recur in the same locations;
• The hazards associated with closed basin lakes are due to their long duration of
flooding;
• The locations of mudflow hazards can be mapped. If hazard maps are available for
a community at a usable scale, they should be incorporated into the community’s
land use plan, hazard mitigation plan, etc.;
• Relatively large areas are affected by land subsidence, and the hazard develops
over a long time period. Even in the case of sinkholes, which may appear
suddenly, the causes of subsidence have been present for decades; and
• In areas subject to alluvial fan flooding, better floodplain maps may result from the
use of watershed master planning, since seemingly minor obstructions or
diversions at critical locations on alluvial fans may cause significant changes in
the locations and quantities of downstream flows.
A combination of floodplain management and watershed management under a unified
plan may be implemented to mitigate each of these special hazards.
510 Floodplain Management Planning
Communities are encouraged to prepare and adopt floodplain management plans that
guide land use development, redevelopment, post-disaster recovery, and mitigation
decisions. Credit for preparing, adopting, implementing, evaluating, and updating such
a plan could be credited under Activity 510 (Floodplain Management Planning).
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Section 511.a.4(b) of the Coordinator’s Manual provides extra points for a discussion
of all special hazards that affect the community.
520 Acquisition and Relocation
As in riverine areas, acquisition and relocation of some structures may be the only
viable way to reduce flood damage associated with these special hazards.
The technical feasibility of moving both small and large structures has been
demonstrated on several occasions. Moving one- and two-story residential buildings
has proven particularly cost-effective for readily movable structures.
Under current policy, if an insured building is damaged by a flood and the state or
community declares the building to be substantially damaged, the NFIP may provide
assistance to help pay to relocate the structure, up to a maximum benefit of $30,000.
This is in addition to coverage for repair of physical damage from flooding.
If there are structures in areas of uncertain flow path flooding that pose a danger to the
occupants, or are repetitively flooded, acquisition and relocation may be the most costeffective way of solving the problem. Although there is no extra credit for acquisition
and relocation of properties in areas of special flooding, the credit offered in Activity
520 is substantial.
Credit is only provided for buildings within the regulatory floodplain (aRF) that is
managed by the community, so the mapping of special hazard areas in Activity 410SH
may be important for this credit.
Acquisition and relocation of these properties may also significantly reduce the costs of
maintaining and repairing infrastructure in these areas.
530 Flood Protection
There are various structural measures that may be effective in mitigating ice jam
hazards. These measures differ according to the type of ice and the type of ice jam
hazard expected. Due to the nature and/or the expense of structural measure that are
effective in reducing ice jam hazards, it may be necessary to develop multijurisdictional or even multi-state projects. For more information, see the U.S. Army
Corps of Engineers’ Ice Engineering manual (U.S. Army Corps of Engineers, 2002),
which can be found on the website at http://www.usace.army.mil/inet/usace-docs/engmanuals/em1110-2-1612/toc.htm.
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In areas adjacent to closed basin lakes,
structural measures should be
considered a last-ditch effort to protect
buildings and infrastructure from rising
lake levels. Because lake levels tend to
remain high for long periods of time, the
water table will rise on the landward
side of levees and flood walls.
Structural measures may be effective if
the lake level is approaching its outflow
point. Structural measures
(channelization) may be effective for
lowering the maximum potential level
of a lake, and this would be eligible for
CRS credit for structural protection of
buildings.
An ice control structure and ice storage area
(from U.S. Army Corps of Engineers, 2002, p.
12-11).
There are some structural measures that
may be effective in mitigating mudflow and landslide hazards. These measures differ
according to the type of hazard and its location relative to the community. Due to the
nature and/or the expense of structural measure that are effective in mudflow or
landslide hazards, it may be necessary to develop multi-jurisdictional or even multistate projects.
If the rate of land subsidence is low, levees may provide protection, but they may be
damaged as a result of differential land subsidence, making them subject to failure.
A variety of structural approaches to mitigate uncertain flow path hazards are in use to
some extent in many communities. Sediment dams are expensive and require removal
of the sediment by mechanical means after every major flood. Grade control structures
and bank protection in reaches where channels tend to migrate are expensive and
subject to failure. In general, the very nature of uncertain flow path flooding causes
structural measures to be expensive and difficult to design.
540 Drainage System Maintenance
Drainage system maintenance may be extremely important in areas with special
hazards. The nature of some of these hazards indicates that there will be changes
during every flooding episode and, in some cases, the hazard and the hazard area will
change from time to time. The only way to even begin to deal with these problems is to
inspect all channels and critical areas annually and after every significant event. These
inspections will ensure that the system is not damaged and that debris is removed so
that the system is fully operational. There is also credit in this activity for capital
improvement plans that fund projects to reduce maintenance problems.
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600 Flood Preparedness Activities
Areas subject to special hazards are inherently more dangerous than most riverine
floodplains because of the high velocities and the sediment and debris in the water.
Although there is no specific credit in CRS Activities 610, 620, and 630, they deserve
special attention by communities that face these hazards.
610 Flood Warning
NOTE: A separate publication, CRS Credit for Flood Warning Programs, includes
examples of community programs and application documentation. Communities are
encouraged to read this document before applying for flood warning credit. It will
improve the quality of the application and reduce the need for additional
documentation later. For a free copy, see Appendix E of the Coordinator’s Manual.
In communities with a history of ice jam flood damage, the community’s emergency
plan should include warning dissemination and evacuation planning for the area subject
to ice jam damage. In most cases, ice jam flooding can be predicted, and advance
warning can allow property owners to move building contents, vehicles, and animals
away from areas that are to be flooded. If the area is only subject to higher flood levels
as a result of an ice jam, some temporary floodproofing measures may also be effective
where there is a warning.
Because closed basin lake flooding generally occurs over a long period of time (weeks,
months, or years), flood warning is generally not needed as a mitigation tool.
Flood hazards due to land subsidence, on the other hand, may be mitigated by flood
warning. Even though the hazard generally develops slowly, the increased flood hazard
that results may include rapid-onset flooding.
In some communities, the U.S. Geological Survey and/or state agencies are actively
working on systems to monitor potential mudflows in real time. Any community that
would benefit from such a system should make sure that this system will serve as a
warning mechamism by informing the public of the system, integrating the monitoring
system into its emergency response plan, and taking the other actions needed to use the
real-time information effectively to save lives and reduce damage.
In many areas in the arid West, large tracts of land are owned by state and federal
agencies and are virtually unpopulated. Flood warning may be needed for populated
areas downstream. Due to the steep slopes in many of these areas, floods develop
quickly in response to rainfall. They travel downstream rapidly and the flood levels rise
quickly when the flows arrive. The watershed response time for a watershed of several
thousand square miles may be less than 24 hours.
Traditional flood warning for these areas usually does not exist. There is little
population in the watershed, so there are few rain gages. The streams are usually dry,
so there are few stream gages.
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A number of large communities, counties and even states have developed “ALERT”
(automated local evaluation in real time) warning systems in the watersheds that affect
them. See Activity 610 in the Coordinator’s Manual for a discussion of these flood
warning systems.
620 Levee Safety
Levees in arid regions may require more frequent and more extensive maintenance due
to erosion, sedimentation, and channel migration. Levees may also require special
construction standards and/or maintenance if they are in areas subject to subsidence, or
if they are in long-term contact with water adjacent to a closed basin lake.
630 Dam Safety
Dams in arid regions are no more or less unsafe than other dams. However, they serve
as sediment traps, and their effective lifetime is limited unless the sediment is removed.
In some areas, dams have been built for the specific purpose of removing sediment
from streams upstream from developed areas so that the channels below remain more
stable. The reservoir areas behind these dams must be cleaned frequently or they will
become ineffective.
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References
Cella Barr Associates. 1987. Tortolita Fan Area Basin Management Plan, Phase I and
Phase IA. Prepared for the Pima County Flood Control District. Tucson, AZ.
County of San Diego. 1987. Flood Control on Alluvial Fans (draft). San Diego, CA:
County of San Diego Department of Public Works.
FEMA, 1989. Alluvial Fans: Hazards and Management. FEMA 165. Washington, D.C.:
FEMA. http://www.fema.gov/hazard/flood/pubs/lib165.shtm.
FEMA. 1995. Engineering Principles and Practices of Retrofitting Flood-Prone
Residential Structures. Washington, D.C.: FEMA.
FEMA, 2000. Guidelines for Determining Flood Hazards on Alluvial Fans, Federal
Emergency Management Agency, Washington, DC, February 23, 2000.
http://www.fema.gov/pdf/fhm/ft_afgd.pdf.
FEMA, 2001. Flood Insurance Rate Map: Maricopa County, Arizona and Incorporated
Areas (revised to reflect LOMR dated Nov 30, 2001). Washington, D.C.: FEMA.
FEMA. 2002. Flood Insurance Study Guidelines and Specifications for Study
Contractors. Washington, D.C.: FEMA. http://www.fema.gov/plan/prevent/fhm/dl_scg.shtm .
FEMA. 2003. Guidelines and Specifications for Flood Hazard Mapping Partners.
FEMA-37. http://www.floodmaps.net/mit/tsd/dl_cgs.htm .
Florsheim, Joan. 1994. “Management Issues related to Wildfire and Flooding in SemiArid Stream Channels,” in Proceedings of the Conference on Arid West Floodplain
Management Issues. Madison, WI: Association of State Floodplain Managers.
Fuller, Jonathon E., Stephen D. Waters, Richard H. French, and Steven R. Walker.
1994. “Alluvial Fan Data Collection and Monitoring Study, Maricopa County,
Arizona,” in Proceedings of the Conference on Arid West Floodplain Management
Issues. Madison, WI: Association of State Flood Plain Managers.
Gabrysch, R.K.. 1983. “The Impact of Land-surface Subsidence.” Pp. 117–123 in
Impact of Science on Society, Managing our Fresh-water Resources. Paris: United
Nations Educational, Scientific and Cultural Organization.
Galloway, Devin, David R. Jones, and S.E. Ingebritsen, eds. 1999. Land Subsidence in
the United States. Circular 1182. Reston, VA: U.S. Geological Survey.
Grindeland, Thomas R., J.S. O’Brien and Rhu-Ming Li. 1990. “Flood Hazard
Delineation on Alluvial Fans,” in Richard French, ed., Hydraulics and Hydrology of
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Leake S.A. 1997. “Land Subsidence from Ground-Water Pumping.” Paper presented at
the Workshop of the U.S. Global Change Research Program Workshop. University of
Arizona, September 1997. Reston: U.S. Geological Survey.
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Lutes, Gordon K. and Joseph C. Hill. 1989. “Case Study: Borrego Valley Flood Control
General Plan, in Proceedings of the Conference on Arid West Floodplain Management
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Maricopa County, Arizona. 1998. Piedmont Flood Hazard Assessment for Floodplain
Management User’s Manual for Maricopa County, Arizona. Draft.
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Newton, J.G. 1984. “Case History No. 9.11. Alabama, U.S.A.” Pp. 245-251 in Joseph
F. Poland, ed., Guidebook to Studies of Land Subsidence due to Ground-water
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Sisk, T.D., editor. 1998. Perspectives on the Land-Use History of North America: A
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Tettemer, John M., 1986. “Alluvial Fan Management—The Community Perspective,”
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WI: Association of State Floodplain Managers.
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Washington, D.C.: Corps of Engineers. http://www.usace.army.mil/inet/usace-docs/engmanuals/em1110-2-1612/toc.htm
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http://www.crrel.usace.army.mil/ierd/icejam/ijdatabase.html .
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Research and Engineering Laboratory.”
http://www.crrel.usace.army.mil/ierd/icejam/icejam.htm
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Ward, Robert L. 1988. Present Status of Management and Technical Practices on
Alluvial Fan Areas in Arizona. Report No. FHWA-AZ88-278. Phoenix, AZ.: Arizona
Department of Transportation.
Washington Department of the Environment. 2001. Stormwater Management Manual
for Western Washington. Publications 99-11 through 99-15. Olympia, WA: Washington
Department of the Environment.
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Special Hazards Supplement to the
CRS Coordinator’s Manual
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2006
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Emergency Management Agency, 500 C St., S.W., Washington, D.C. 20472, Paperwork Reduction Project
(OMB Control Number 1660-0022). You are not required to respond to this collection of information unless a
valid OMB control number is displayed in the upper right corner of this form. Note: do not send your completed
questionnaire to this address.
Activity Worksheet No.
Title
AW-210
AW-214
AW-230
CRS Application Cover Page
Recertification Worksheet
Modification/Cycle Cover Page
AW-310
AW-320
AW-330
AW-340
AW-350
AW-360
Elevation Certificates
Map Information Service
Outreach Projects
Hazard Disclosure
Flood Protection Information
Flood Protection Assistance
AW-410
AW-420
AW-430
AW-430LD
AW-440
AW-450
Additional Flood Data
Open Space Preservation
Higher Regulatory Standards
Land Development Criteria
Flood Data Maintenance
Stormwater Management
AW-501
AW-502
AW-510
AW-520
AW-530
AW-540
Repetitive Loss List
Repetitive Loss Requirements
Floodplain Management Planning
Acquisition and Relocation
Flood Protection
Drainage System Maintenance
AW-610
AW-620
AW-630
Flood Warning Program
Levee Safety
Dam Safety
AW-710
AW-720
AW-720m
Community Growth Adjustment
Community Credit Calculations
Community Credit Calculations (Modification)
AW-CB
AW-CE
AW-DB
AW-IJ
AW-MF
AW-SU
AW-TS
AW-UF
Closed Basin Lake Hazards
Coastal Erosion Hazards
Dunes and Beaches
Ice Jam Hazards
Mudflow Hazards
Land Subsidence Hazards
Tsunami Hazards
Uncertain Flow Path Hazards
INSTRUCTIONS
The following activity worksheets are to facilitate calculations of Community Rating
System (CRS) credit points. They are not used for a community’s initial application to
the CRS. I NITIAL APPLICATIONS FOR THE CRS ARE SUBMITTED USING THE WORKSHEET
PAGES IN THE CRS A PPLICATION .
These activity worksheets are for internal use by the community, for submittal of
modifications, and for use by the ISO/CRS Specialist during verification and cycle
verification of a community’s program.
These worksheets are designed to be used in conjunction with the Special Hazards
Supplement to the CRS Coordinator’s Manual. Each section of the worksheets corresponds to a section in that supplement. If a section is missing from the worksheets, it is
because the Special Hazards Supplement shows that no data or calculations are
required for that section.
It is recommended that these worksheets be photocopied before they are used.
When used for submitting a modification, the Credit Points, Credit Calculation, and
Credit Documentation parts of the worksheets should be completed for each activity for
which credit is requested. Fill in the blanks with the value for each variable.
Each worksheet has a Credit Documentation section. Check the blanks to denote that
all of the required documentation is available. In some cases, the documentation must
be provided with the modification. In others, checking the appropriate spaces confirms
that you will provide the documentation when needed. Please consult the Special
Hazards Supplement to the CRS Coordinator’s Manual if you have questions about
which documentation is to be provided with the request for a modification.
ATTACH THE REQUIRED DOCUMENTATION FOR AN ACTIVITY TO THE WORKSHEET FOR
THAT ACTIVITY . If the documentation is ordinance language, attach only the necessary
page(s) from the ordinance.
M ARK THE MARGINS OF THE DOCUMENTATION WITH THE ACRONYM for the element so the
ISO/CRS Specialist can identify the basis for the credit.
Special Hazards Supplement
AW-SH-iii
Edition: 2006
[This page intentionally blank.]
Special Hazards Supplement
AW-SH-iv
Edition: 2006
OMB No.1660-0022
Expires June 30, 2007
Community : ____________________________
410SH Additional Flood Data for Special Hazard Areas
411SH Credit Points
a. Prerequisites
___
___
1. The community receives at least 20 points for its special hazard area
regulations.
2. The community has a regulatory map showing the special hazard areas or
it requires developers to provide the needed map information.
b. Mapping Credit:
1. Ice jams: no credit because mapping ice jams is an
NFIP mapping requirement
2. Closed basin lakes: no credit because mapping closed
basin lakes is an NFIP mapping requirement
3. Mudflow hazards:
4. Areas subject to land subsidence:
5. Uncertain flow paths:
(a) Alluvial fans: no credit because mapping alluvial
fans is an NFIP mapping requirement.
(b) Moveable bed streams:
MMF = _____
MSU = _____
MUF = _____
412SH Credit Calculation
cAFDSH = MMF + MSU + MUF
cAFDSH = _____
Note that the total of cAFDSH + cSHOS + cSHR cannot exceed 200 points.
413SH Credit Documentation
____
a. A map that shows the areas subject to the special hazards and the other
floodplains (including the SFHA) in the community.
____
b. A description of the method used for the mapping that shows that it reasonably
delineates areas subject to the special hazards and documentation that the
method is acceptable to the FEMA Region.
____
c. Credit for 410SH is only provided if the mapping is used for land use regulation to
prevent damage from the special hazard. The documentation required for Activity
430SH will suffice for this prerequisite.
_____________________________________________
Comments: _________________________________________________________
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
Activity Worksheet
AW-410SH-1
Edition: 2006
OMB No. 1660-0022
Expires: June 30, 2007
Public reporting burden for this information collection is estimated at 35 hours for the application and certification
process. Burden means the time, effort, and financial resources expended by persons to generate, maintain,
retain, disclose, or to provide information to us. You may send comments regarding the burden estimate or any
aspect of the collection, including suggestions for reducing the burden to: Information Collections Management,
U.S. Department of Homeland Security, Emergency Preparedness and Response Directorate, Federal
Emergency Management Agency, 500 C St., S.W., Washington, D.C. 20472, Paperwork Reduction Project
(OMB Control Number 1660-0022). You are not required to respond to this collection of information unless a
valid OMB control number is displayed in the upper right corner of this form. Note: do not send your completed
questionnaire to this address.
Activity Worksheet No.
Title
AW-210
AW-214
AW-230
CRS Application Cover Page
Recertification Worksheet
Modification/Cycle Cover Page
AW-310
AW-320
AW-330
AW-340
AW-350
AW-360
Elevation Certificates
Map Information Service
Outreach Projects
Hazard Disclosure
Flood Protection Information
Flood Protection Assistance
AW-410
AW-420
AW-430
AW-430LD
AW-440
AW-450
Additional Flood Data
Open Space Preservation
Higher Regulatory Standards
Land Development Criteria
Flood Data Maintenance
Stormwater Management
AW-501
AW-502
AW-510
AW-520
AW-530
AW-540
Repetitive Loss List
Repetitive Loss Requirements
Floodplain Management Planning
Acquisition and Relocation
Flood Protection
Drainage System Maintenance
AW-610
AW-620
AW-630
Flood Warning Program
Levee Safety
Dam Safety
AW-710
AW-720
AW-720m
Community Growth Adjustment
Community Credit Calculations
Community Credit Calculations (Modification)
AW-CB
AW-CE
AW-DB
AW-IJ
AW-MF
AW-SU
AW-TS
AW-UF
Closed Basin Lake Hazards
Coastal Erosion Hazards
Dunes and Beaches
Ice Jam Hazards
Mudflow Hazards
Land Subsidence Hazards
Tsunami Hazards
Uncertain Flow Path Hazards
OMB No.1660-0022
Expires June 30, 2007
Community : ____________________________
420SH Open Space Preservation in Special Hazard Areas
421SH Credit Points
a. Prerequisites
_____1. The area is eligible for credit for open space preservation under
Activity 420
_____2. The area is mapped as subject to the special hazard as credited under
Activity 410SH.
422SH Impact Adjustment
a. Option 1: rSHOS = 1.0
b. Option 2: rSHOS = 0.2
c. Option 3: rSHOS = aSHOS
= ________
aSH_____
423SH Credit Calculation
cSHOS = 50 x rSHOS _______
cSHOS = _____
Enter this value in line 423.d on AW-420-1
Note that the total of cAFDSH + cSHOS + cSHR cannot exceed 200 points.
424SH Credit Documentation
____
a. Documentation showing the community qualifies for credit under 410SH.
____
b. Documentation showing the area where open space credit is requested is in the
special hazard area and meets the open space requirements of Activity 420.
_____________________________________________
Comments: _________________________________________________________
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
Activity Worksheet
AW-420SH-1
Edition: 2006
OMB No. 1660-0022
Expires: June 30, 2007
Public reporting burden for this information collection is estimated at 35 hours for the application and certification
process. Burden means the time, effort, and financial resources expended by persons to generate, maintain,
retain, disclose, or to provide information to us. You may send comments regarding the burden estimate or any
aspect of the collection, including suggestions for reducing the burden to: Information Collections Management,
U.S. Department of Homeland Security, Emergency Preparedness and Response Directorate, Federal
Emergency Management Agency, 500 C St., S.W., Washington, D.C. 20472, Paperwork Reduction Project
(OMB Control Number 1660-0022). You are not required to respond to this collection of information unless a
valid OMB control number is displayed in the upper right corner of this form. Note: do not send your completed
questionnaire to this address.
Activity Worksheet No.
Title
AW-210
AW-214
AW-230
CRS Application Cover Page
Recertification Worksheet
Modification/Cycle Cover Page
AW-310
AW-320
AW-330
AW-340
AW-350
AW-360
Elevation Certificates
Map Information Service
Outreach Projects
Hazard Disclosure
Flood Protection Information
Flood Protection Assistance
AW-410
AW-420
AW-430
AW-430LD
AW-440
AW-450
Additional Flood Data
Open Space Preservation
Higher Regulatory Standards
Land Development Criteria
Flood Data Maintenance
Stormwater Management
AW-501
AW-502
AW-510
AW-520
AW-530
AW-540
Repetitive Loss List
Repetitive Loss Requirements
Floodplain Management Planning
Acquisition and Relocation
Flood Protection
Drainage System Maintenance
AW-610
AW-620
AW-630
Flood Warning Program
Levee Safety
Dam Safety
AW-710
AW-720
AW-720m
Community Growth Adjustment
Community Credit Calculations
Community Credit Calculations (Modification)
AW-CB
AW-CE
AW-DB
AW-IJ
AW-MF
AW-SU
AW-TS
AW-UF
Closed Basin Lake Hazards
Coastal Erosion Hazards
Dunes and Beaches
Ice Jam Hazards
Mudflow Hazards
Land Subsidence Hazards
Tsunami Hazards
Uncertain Flow Path Hazards
OMB No.1660-0022
Expires June 30, 2007
Community : ____________________________
430SH Higher Regulatory Standards For Special Hazards
431SH Credit Points
a. Prerequisites
_____ 1. The area regulated is mapped as subject to the special hazard as credited
under Activity 410SH.
_____ 2. The community has adopted and is enforcing the higher regulatory
standards.
b. Credit points
1. Ice jam regulations:
IJR = _____
2. Closed basin lake regulations:
CBR = _____
3. Mudflow hazard regulations:
MFR = _____
4. Land subsidence regulations:
SUR = _____
5. Uncertain flow path regulations:
UFR = _____
432SH Impact Adjustment
a. Option 1: If the community does not receive credit for SHOS in 420SH,
then rSHOS = 0.
rIJR = 1.0 – rSHOS = _____
rCBR = 1.0 – rSHOS = _____
rMFR = 1.0 – rSHOS = _____
rSUR = 1.0 – rSHOS = _____
rUFR = 1.0 – rSHOS = _____
b. Option 2: rSHOS = 0.25
c. Option 3:
rIJR = aIJR
= ________
aIJ_____
rCBR = aCBR
= ________
aCB_____
rMFR = aMFR
= ________
aMF_____
rSUR = aSUR
= ________
aSU_____
rUFR = aUFR
= ________
aUF_____
Activity Worksheet
AW-430SH-1
Edition: 2006
OMB No. 1660-0022
Expires: June 30, 2007
Public reporting burden for this information collection is estimated at 35 hours for the application and certification
process. Burden means the time, effort, and financial resources expended by persons to generate, maintain,
retain, disclose, or to provide information to us. You may send comments regarding the burden estimate or any
aspect of the collection, including suggestions for reducing the burden to: Information Collections Management,
U.S. Department of Homeland Security, Emergency Preparedness and Response Directorate, Federal
Emergency Management Agency, 500 C St., S.W., Washington, D.C. 20472, Paperwork Reduction Project
(OMB Control Number 1660-0022). You are not required to respond to this collection of information unless a
valid OMB control number is displayed in the upper right corner of this form. Note: do not send your completed
questionnaire to this address.
Activity Worksheet No.
Title
AW-210
AW-214
AW-230
CRS Application Cover Page
Recertification Worksheet
Modification/Cycle Cover Page
AW-310
AW-320
AW-330
AW-340
AW-350
AW-360
Elevation Certificates
Map Information Service
Outreach Projects
Hazard Disclosure
Flood Protection Information
Flood Protection Assistance
AW-410
AW-420
AW-430
AW-430LD
AW-440
AW-450
Additional Flood Data
Open Space Preservation
Higher Regulatory Standards
Land Development Criteria
Flood Data Maintenance
Stormwater Management
AW-501
AW-502
AW-510
AW-520
AW-530
AW-540
Repetitive Loss List
Repetitive Loss Requirements
Floodplain Management Planning
Acquisition and Relocation
Flood Protection
Drainage System Maintenance
AW-610
AW-620
AW-630
Flood Warning Program
Levee Safety
Dam Safety
AW-710
AW-720
AW-720m
Community Growth Adjustment
Community Credit Calculations
Community Credit Calculations (Modification)
AW-CB
AW-CE
AW-DB
AW-IJ
AW-MF
AW-SU
AW-TS
AW-UF
Closed Basin Lake Hazards
Coastal Erosion Hazards
Dunes and Beaches
Ice Jam Hazards
Mudflow Hazards
Land Subsidence Hazards
Tsunami Hazards
Uncertain Flow Path Hazards
OMB No.1660-0022
Expires June 30, 2007
Community : ____________________________
433SH Credit Calculation
a. cIJR = IJR x rIJR _______
cIJR = _____
b. cCBR = CBR x rCBR _______
cCBR = _____
c. cMFR = MFR x rMFR _______
cMFR = _____
d. cSUR = SUR x rSUR _______
cSUR = _____
e. cUFR = UFR x rUFR _______
cUFR = _____
f.
cLZSH (from AW-430LZSH)
cLZSH = _____
Add the lines above
cSHR = _____
Enter this value in line 433.k on AW-430-2
NOTE: the total of cAFDSH + cSHOS + cSHR cannot exceed 200 points.
434SH Credit Documentation
____
a. The state or local law or ordinance language that adopts the regulatory standard.
____
b. An explanation of the procedures followed for enforcement.
_____________________________________________
Comments: _________________________________________________________
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
Activity Worksheet
AW-430SH-2
Edition: 2006
OMB No. 1660-0022
Expires: June 30, 2007
Public reporting burden for this information collection is estimated at 35 hours for the application and certification
process. Burden means the time, effort, and financial resources expended by persons to generate, maintain,
retain, disclose, or to provide information to us. You may send comments regarding the burden estimate or any
aspect of the collection, including suggestions for reducing the burden to: Information Collections Management,
U.S. Department of Homeland Security, Emergency Preparedness and Response Directorate, Federal
Emergency Management Agency, 500 C St., S.W., Washington, D.C. 20472, Paperwork Reduction Project
(OMB Control Number 1660-0022). You are not required to respond to this collection of information unless a
valid OMB control number is displayed in the upper right corner of this form. Note: do not send your completed
questionnaire to this address.
Activity Worksheet No.
Title
AW-210
AW-214
AW-230
CRS Application Cover Page
Recertification Worksheet
Modification/Cycle Cover Page
AW-310
AW-320
AW-330
AW-340
AW-350
AW-360
Elevation Certificates
Map Information Service
Outreach Projects
Hazard Disclosure
Flood Protection Information
Flood Protection Assistance
AW-410
AW-420
AW-430
AW-430LD
AW-440
AW-450
Additional Flood Data
Open Space Preservation
Higher Regulatory Standards
Land Development Criteria
Flood Data Maintenance
Stormwater Management
AW-501
AW-502
AW-510
AW-520
AW-530
AW-540
Repetitive Loss List
Repetitive Loss Requirements
Floodplain Management Planning
Acquisition and Relocation
Flood Protection
Drainage System Maintenance
AW-610
AW-620
AW-630
Flood Warning Program
Levee Safety
Dam Safety
AW-710
AW-720
AW-720m
Community Growth Adjustment
Community Credit Calculations
Community Credit Calculations (Modification)
AW-CB
AW-CE
AW-DB
AW-IJ
AW-MF
AW-SU
AW-TS
AW-UF
Closed Basin Lake Hazards
Coastal Erosion Hazards
Dunes and Beaches
Ice Jam Hazards
Mudflow Hazards
Land Subsidence Hazards
Tsunami Hazards
Uncertain Flow Path Hazards
OMB No.1660-0022
Expires June 30, 2007
Community : ____________________________
430LZSH Low Density Zoning in Special Hazard Areas
432LZSH Impact Adjustment
a. Option 1: Enter rSHOS from AW-420SH-1. If the community does not receive credit
for SHOS in 420SH, then rSHOS = 0.
rLZSH__ = 1.0 - rSHOS ______ = ______
b. Option 2: rLZSH__ = 0.2
c. Option 3:
1. rLZSH___ = aLZSH
aSH
= ______
2. rLZSH___ = aLZSH
aSH
= ______
3. rLZSH___ = aLZSH
aSH
= ______
433LZSH Credit Calculation
cLZSH____ = LZSH____ _____ x rLZSH____ ______
cLZSH___ = ______
cLZSH____ = LZSH____ _____ x rLZSH____ ______
cLZSH___ = ______
cLZSH____ = LZSH____ _____ x rLZSH____ ______
cLZSH___ = ______
Add the lines above
cLZSH = ______
Enter this value in line 433SH.f on AW-430SH-2
434LZSH Credit Documentation
____
a. The ordinance language that adopts the low density zoning standard.
____
b. The Impact Adjustment Map
____
c. An explanation of how the regulations are enforced.
____
d. Examples of developments constructed in accordance with the zoning density.
_____________________________________________
Comments: _________________________________________________________
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
Activity Worksheet
AW-430LZSH-1
Edition: 2006
OMB No. 1660-0022
Expires: June 30, 2007
Public reporting burden for this information collection is estimated at 35 hours for the application and certification
process. Burden means the time, effort, and financial resources expended by persons to generate, maintain,
retain, disclose, or to provide information to us. You may send comments regarding the burden estimate or any
aspect of the collection, including suggestions for reducing the burden to: Information Collections Management,
U.S. Department of Homeland Security, Emergency Preparedness and Response Directorate, Federal
Emergency Management Agency, 500 C St., S.W., Washington, D.C. 20472, Paperwork Reduction Project
(OMB Control Number 1660-0022). You are not required to respond to this collection of information unless a
valid OMB control number is displayed in the upper right corner of this form. Note: do not send your completed
questionnaire to this address.
Activity Worksheet No.
Title
AW-210
AW-214
AW-230
CRS Application Cover Page
Recertification Worksheet
Modification/Cycle Cover Page
AW-310
AW-320
AW-330
AW-340
AW-350
AW-360
Elevation Certificates
Map Information Service
Outreach Projects
Hazard Disclosure
Flood Protection Information
Flood Protection Assistance
AW-410
AW-420
AW-430
AW-430LD
AW-440
AW-450
Additional Flood Data
Open Space Preservation
Higher Regulatory Standards
Land Development Criteria
Flood Data Maintenance
Stormwater Management
AW-501
AW-502
AW-510
AW-520
AW-530
AW-540
Repetitive Loss List
Repetitive Loss Requirements
Floodplain Management Planning
Acquisition and Relocation
Flood Protection
Drainage System Maintenance
AW-610
AW-620
AW-630
Flood Warning Program
Levee Safety
Dam Safety
AW-710
AW-720
AW-720m
Community Growth Adjustment
Community Credit Calculations
Community Credit Calculations (Modification)
AW-CB
AW-CE
AW-DB
AW-IJ
AW-MF
AW-SU
AW-TS
AW-UF
Closed Basin Lake Hazards
Coastal Erosion Hazards
Dunes and Beaches
Ice Jam Hazards
Mudflow Hazards
Land Subsidence Hazards
Tsunami Hazards
Uncertain Flow Path Hazards
| File Type | application/pdf |
| File Title | Microsoft Word - Special Hazards Supplement final 2006.doc |
| Author | Owner |
| File Modified | 2009-01-09 |
| File Created | 2009-01-09 |