HomeMy WebLinkAboutres1997-060WHATCOM COUNTY COUNCIL AGENDA BILL NO. 97 -308A
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Initial
Date
Date Received in Council Office:
Agenda date
Assigned to:
_.ginator: Jeff Monsen
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9123197
Public Works / Council
Division Head:
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Dept. Head:
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Executive: Pete Kremen
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SUBJECT.
A resolution in the matter of the Nooksack River Community Rating System Flood Management Plan
ATTACHMENTS.
Cover memorandum
Letter from FEMA regarding National Flood Insurance Program
Resolution adopting Community Rating System Flood Management Plan
'UMMARYSTATEMENT. Please complete sections of box as appropriate & explain, the item belt
Related County contract #: N/A Should Clerk schedule a hearing? NO /_ / YES / / Requested date:
-count budgeted for this item/project: Is it (or will it be) within budget? YES /_ / NO / / (Please explain below)
. dget line item number(s):
V.
This Community Rating System Flood Management Plan is required by the Federal Emergency Management Agency and has
been recommended for approval by the Flood Control Zone District Advisorty Committee.
ORIGINATOR'S RECOMMENDED ACTION.
Council approval
COMMITTEE ACTION TAKEN:
COUNCIL ACTION TAKEN.
1997 - 308 A 9123197: Amended & approved 7 - 0. Res. #97 -060
?elated File Numbers: Ordinance or Resolution Number (this item only):
SPONSORED BY: Public Works
PROPOSED BY Consent
INTRODUCTION DATE: 9/23/97
1 RESOLUTION NO. 97 -060
2 A RESOLUTION IN THE MATTER OF THE
3 NOOKSACK RIVER COMMUNITY RATING SYSTEM
4 FLOOD MANAGEMENT PLAN
5 WHEREAS, the Federal Emergency Management Agency requires that Whatcom County
6 adopt a repetitive loss plan in order to maintain the current reduction in flood insurance rates
7 within Whatcom County, and
8 WHEREAS, Whatcom County is nearing completion of the Lower Nooksack
9 Comprehensive Flood Hazard Management Plan (CFHMP) which contains the required elements
10 for a repetitive loss plan, and
11 WHEREAS, a repetitive loss plan, hereafter referred to as a Community Rating System
12 Flood Management Plan ( CRSFMP), has been created by extracting all the necessary language
13 from Chapters 1, 2, 8 and 9 of the January 1997 Draft CFHMP.
14 NOW, THEREFORE, BE IT RESOLVED by the Whatcom County Council that the
15 CRSFMP attached as Exhibit A is hereby adopted.
16 APPROVED this 23 day ofSf2 embet997.
17
18 ATTEST:
19
20 and rown-TPsVils, County Clerk
21 APPROVED AS TO FORM:
22 "k 1W
23 Civil Deputy Prosec i Attorney
WHATCOM COUNTY COUNCIL
WHATCOM COUNTY, WASHINGTON
L. Ward Nelson, Co ncil Cha'
EXHIBIT
NOOKSACK RIVER COMMUNITY RATING SYSTEM
FLOODPLAIN MANAGEMENT PLAN
SEPTEMBER 1997
Prepared by:
Whatcom County
Department of Public Works
2
TABLE OF CONTENTS
Page
Flooding on the Lower Nooksack
Introduction
4
Flood Magnitude
7
The Causes Of Nooksack River Flooding
8
How The River Changes Along Its Length
9
The Lower Nooksack's Main Reaches
10
Whatcom County's Role
10
Whatcom County Flood Control Zone District
11
The Advisory Committee
11
Mission Statement And Goals
12
Public Involvement In Plan Preparation
12
Management Techniques - What Are Our Options?
FEMA Floodplain Mapping
13
New Maps To Show Where Flooding Can Be Expected
13
Problems With The Current FEMA Mapping
14
Buyouts And Relocation Of Sites In Harm's Way
15
Floodproofing - Helping Structures Withstand The Waters
15
The Details - Zoning And Other Ordinances
17
Connecting the River And The Floodplain
18
Designated Overtopping Locations
18
Agricultural Levees
19
Levee Maintenance
19
Setback Levees
19
A Dam And A Reservoir
20
The Issue Of Sediment
20
Dealing With Flood Preparedness
21
Monitoring
22
Forecasting
22
Flood Warning
23
Flood Response
23
2
TABLE OF CONTENTS - CONTINUED
Page
Implementation Plan - Moving Forward From Planning To Action
One Approach To Partnering - Setting Up FCZD Subzones 25
The Procedures For Revising The Floodplain Maps
26
A Plan For Properties At Risk
27
Property Buyouts
27
Floodproofing Structures
28
Systems For Buyout / Floodproofing Designations
29
Recommendations For Flood Forecasting And Response
29
Engineering Design Of Overflows And Of Levees In Between
30
A Levee Inventory Program
32
Land Use Recommendations
32
Public Education To Enhance Flood Preparedness
32
FLOODING ON THE LOWER NOOKSACK
INTRODUCTION
The Nooksack River in Whatcom County has long been subject to severe flooding. While
the frequency and severity of the river's flooding have posed a perennial problem for
County residents, the debate over appropriate solutions came to a head after devastating
back -to -back floods in 1989 and 1990. Each of those floods was more damaging than any
other in the preceding 15 years.
In 1991 the County made a commitment to address flooding problems through the
creation of a county-wide Flood Control Zone District (FCZD). Soon after its formation,
it was soon agreed on the need for a long range local strategy in the form of a
comprehensive flood hazard management plan (CFHIvIP). The January 1997 draft
CFHIVIP explains the history of Nooksack River flooding and outlines ways to address the
problems that flooding causes.
The Nooksack River Community Rating System Floodplain Management Plan focuses on
a flood hazard assessment, management alternatives, and an implementation plan for
Whatcom County's flood hazard areas. It was prepared according to the guidelines
produced by the Federal Emergency Management Agency, in support of the National
Flood Insurance Program, Community hating System. The text for this document was
extracted from Whatcom County's January 1997 draft Lower Nooksack River
Comprehensive Flood Hazard Management Plan.
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The mountainous upper regions of the Nooksack River watershed make up by far the largest portion of its
area.
The Nooksack River floods of 1989 and 1990 wrought havoc on towns, farms, and
transportation routes along the river. Fields were inundated, roads were closed or washed
out, levees broke, and the banks of the river were subject to extreme erosion.
The severity of these floods boosted public awareness of the river's flood threat and
revitalized the drive for a comprehensive search for solutions.
The damage from the 1990 floods was estimated to be $21 million. The U.S. Army Corps
of Engineers estimates that flood damage from the Nooksack averages $2.5 million per
year for all recorded floods. Clearly, the continued flooding of the river represents a
significant expense for Whatcom County and its residents. Every County resident has a
stake in the flooding problem —from residents whose homes lie in the floodplain, to
private and commercial users of roads threatened by floodwaters, to the taxpayers who
must help cover the cost of river control and flood damage repair
WHO IS AFFECTED BY FLOODING?
When.a river floods, some immediate impacts are readily apparent, especially damage that takes
place in the flooded areas. While the costs of such damage often are incurred by the affected
property owners, flooding also has broad effects that can mean short -term and long -term costs to a
much larger group. Below are some common results of flooding, along with a summary of who is
affected by them.
Residents,
Business and Agriculture
Agriculture Residents and Business
in outside outside Local
Problem Caused by Flooding Flood lain Flood lain Flood lain Government
Damage to homes and buildings X X
MAN
Erosion and loss of property X X
Damage to bridges, roads, and public facilities X X X X
e -
Loss of sales and wages X X X
Loss of public utilities such as gas, power, and telephone X X X y X
Health hazards from contaminated water supply and/or X X X
damaged sewage treatment plants
Crop damage from inundation of farmlands X X
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D o IM, t . v � l _.... Y �-
Isolation and/or drowning of livestock X
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FLOOD MAGNITUDE
Large floods on the Nooksack River have occurred throughout history. As a rule —and as
one would expect—floods with greater flow rates, or magnitudes, cause greater levels of
damage. Today, however, large floods cause more damage than in past decades; not
necessarily because the floods themselves have grown, but because development that is
susceptible to flood damage has spread.
The most serious flood on the Lower Nooksack since recording began in 1935 was the
Veterans Day flood of November 10 -11, 1990. The four most recent large floods —in
1989, 1990 (twice), and 1995 —are four of the five largest floods monitored at Ferndale in
the last 44 years.
The U.S. Geological Survey (USGS) maintains gauges to record Nooksack River flows at
Ferndale and Deming and on the North, Middle, and South Forks of the Nooksack. The
gauges measure the flow in cubic feet per second (cfs), telling us how much water, in
cubic feet, passes through that section of the river each second.
The records from the USGS gauges over the years are used to determine the likelihood:,of
floods of a certain magnitude on the Nooksack (measured as a "recurrence interval'). In
the U.S., government agencies such as the Federal Emergency Management Agency
(FEMA) use the 100 -year flood as a "base flood" to rate the effectiveness of flood hazard
management measures. In Canada, for comparison, the 200 -year flood is used for the base
flood.
River Flow (in cfs)
Ferndale Everson Overflow
10 -Year Flood
42,000
40,000
0
50 -Year Flood
67,000
55,800
15,300
100 -Year Flood
79,000
63,000
22,600
November 10, 1990
64,000
57,000
13,500
The November 10, 1990 flood flow rate of 57,000 cfs at Ferndale was a
large flood with a return period of about 50- years. The November 10, 1990
flood was about twice the average annual flood at Ferndale. The 100 -year
flood flow rate of 63,000 cfs at Ferndale is about 11 percent larger than
that of the November 10, 1990 flood.
As the table below shows, the magnitude of the November 1990 flood, the biggest
Nooksack River flood since recording began in 1932, was less than what can be expected
in the 100 -year base flood. Essentially, this means that it's only a matter of time before a
flood bigger than the November 1990 flood will strike. That's why it's so important to
prepare for future flooding.
THE CAUSES OF NOOKSACK RIVER FLOODING
Wedged between Puget Sound and the Cascade Mountains, the Nooksack River draws its
flow from a watershed that lies largely on the western slopes of the mountains. This area is
subject to intense rainfall during warm fall and winter storms.
The heavy rain results from an effect called orographic uplift, which raises precipitation
levels on the windward side of mountain ranges.
All told, some 826 square miles of mostly mountainous terrain drain to the Nooksack
River. Within that area, the ground rises from sea level at the river mouth to more than
10,000 feet atop Mt. Baker.
The heavy rainfall, the large area steepness of the land add up to the potential for large
amounts of runoff that can quickly reach the flat lands along the river's lower reaches.
The worst flooding happens during the so- called "pineapple express" weather pattern of
the fall and winter. When these fronts bring warm, wet air sweeping into the watershed,
the rainfall can be very heavy.
8
LARGESTRECORDED
NOOKSACK RIVER
FLOODS
River
Flow at
Ferndale
Date
(cfs)
November 10, 1990
57,000
November 24, 1990
56,600
February 10, 1951
55,000
November 11, 1989
47,800
November 30, 1995
47,200
December 3, 1975
46,700
October 25, 1945
41,600
January 4, 1984
41,500
January 30, 1971
38,100
December 15, 1979
36,400
THE CAUSES OF NOOKSACK RIVER FLOODING
Wedged between Puget Sound and the Cascade Mountains, the Nooksack River draws its
flow from a watershed that lies largely on the western slopes of the mountains. This area is
subject to intense rainfall during warm fall and winter storms.
The heavy rain results from an effect called orographic uplift, which raises precipitation
levels on the windward side of mountain ranges.
All told, some 826 square miles of mostly mountainous terrain drain to the Nooksack
River. Within that area, the ground rises from sea level at the river mouth to more than
10,000 feet atop Mt. Baker.
The heavy rainfall, the large area steepness of the land add up to the potential for large
amounts of runoff that can quickly reach the flat lands along the river's lower reaches.
The worst flooding happens during the so- called "pineapple express" weather pattern of
the fall and winter. When these fronts bring warm, wet air sweeping into the watershed,
the rainfall can be very heavy.
8
If such rainfall takes place after snow already has accumulated in the mountains, the
resulting snowmelt significantly increases the flow of water to the river.
The results of the heavy rain on snow are even more severe if preceded by a period of
steady rain that leaves the ground in the area too saturated to absorb any more runoff.
Together, these three conditions —heavy rain, accumulated snow, and saturated soil —
create the potential for severe flooding along the Lower Nooksack River.
HOW THE RIVER CHANGES ALONG ITS LENGTH
The upper Nooksack River consists of three major forks, each having very steep gradients.
Downstream from the upper forks, the lower Nooksack River undergoes drastic changes
in steepness and the width of its floodplain.
The uppermost reach (Reach 4 - Deming to Everson) is steep and constantly meandering.
The floodplain in this reach is narrow, and spotted with overflow or abandoned side
channels.
Between Everson and Lynden (Reach 3), the river is much flatter and the floodplain much
wider. To accommodate agricultural use of some of the surrounding floodplain in this
reach, side channels have been filled and levees constructed along the banks of the river.
The result is a gently meandering river.
As the river flows from Lynden to Ferndale (Reach 2), its gradient continues to flatten,
although the floodplain narrows slightly.
In its final, lowermost reach, below Ferndale (Reach 1), the river continues at its flattest
gradient and ultimately forms a river delta in Bellingham Bay.
Historically, flooding has varied significantly on different stretches of the river. These
differences in flooding along the length of the river are caused by such factors as the
distribution of rainfall during the flood, the amount of melting snow, the duration of the
flood, and the timing of flood waves from the three river forks in the upper basin.
One of the most distinctive, and troubling, features of the Nooksack River is the flooding
pattern near Everson. There, during the most serious floods, the river overtops the right
bank and a portion of its flow heads northward along what is known as the Johnson Creek
corridor.
These Everson overflows never return to the Nooksack River. Instead, they continue
north through Sumas to Canada, causing considerable damage in Canada and the U.S.
The overflows at Everson are a natural occurrence where flood waters retrace what is
believed to be a historic route from the Nooksack River to the Fraser River. They have
occurred 14 times in the past 65 years, an average of about once every five years. Finding
ways to address the Everson overflow is one of the top priorities.
THE LOWER NOOKSACK'S MAIN REACHES
* * From Deming to Nugents Corner, the river covers 5.6 miles at a gradient of 12.1
feet per mile. Its 100 -year floodplain is an average of 0.4 miles wide and covers a total'of
2.2 square miles.
** From Nugents Corner to Everson, the river covers 7.4 miles at a gradient of 9.2
feet per mile. Its 100 -year floodplain is an average of 0.9 miles wide and covers a total of
5.3 square miles.
** From Everson to Lynden, the river covers 8.3 miles at a gradient of 4.9 feet per
mile. Its 100 -year floodplain is an average of 1.9 miles wide and covers a total of 12.0
square miles.
** From Lynden to Ferndale, the river covers 9.3 miles at a gradient of 2.3 feet per
mile. Its 100 -year floodplain is an average of 1.1 miles wide and covers a total of 8.3
square miles.
* * From Ferndale to Puget Sound, the river covers 6.0 miles at a gradient of 1.8 feet
per mile. Its 100 -Year floodplain is an average of 2.8 miles wide and covers a total of 13.8
square miles.
WHATCOM COUNTY'S ROLE
Until recently, Whatcom County's role in flood control generally was limited to assisting
local flood fight efforts, maintenance and stream bank erosion control projects, small
projects to control flooding for local areas, and the regulatory responsibilities associated
with zoning and the floodplain ordinance administration.
The County is now the most active player on the river, in part because of its renewed
dedication to this effort supported by the funding available through the Flood Control
Zone District. The fund's resources are provided by a special assessment on all County
property.
10
WHATCOM COUNTY FLOOD CONTROL ZONE DISTRICT
With the emphasis in recent years on a comprehensive approach to flood hazard
management, the County Council created a new governmental entity —the Whatcom
County Flood Control Zone District (FCZD). The district is overseeing preparation of the
comprehensive flood hazard management plan.
The FCZD faces the challenge of developing comprehensive flood hazard management
measures that address flood problems effectively and are acceptable to a wide range of
public, private, and tribal interests.
The FCZD differs from other special districts in that it was created by and is under direct
control of the County government. The district has funding authority as well as all County
authority for flood control. The Whatcom County Council operates as the District's board
of supervisors.
The district has the authority to implement flood control actions without public vote, but..% - .
relies upon advisory committee review and recommendations for major proposals.
Funding
With its independent authority, the District draws funding from Whatcom County
residents and businesses. Grant money from both state and federal sources supplements
County funding.
THE ADVISORY COMMITTEE
The FCZD's advisory committee aims to achieve a consensus on flood - related issues
through the participation of diverse public and private interests.
The 15- member panel, appointed by the District's Board of Supervisors, carries out
review of flood hazard management programs and discussion of budget appropriations.
The group has no direct authority, however. Its decisions serve as recommendations to the
Board of Supervisors.
Meetings
The advisory committee's monthly meetings are open to the public. In addition, minutes
and videotapes of the meetings are kept on file. The group's subcommittees also hold
occasional meetings, the results of which are reported at the monthly meetings of the full
committee.
MISSION STATEMENT AND GOALS
The following mission statement has been adopted by the FCZD Advisory Committee:
Have a comprehensive program in place to minimize flood hazards to lives and
property while providing a net positive impact on natural and human resources,
and have an ongoing effort to continue into the future, consistent with proper
stewardship of economic resources.
The following goals have been adopted by the FCZD Advisory Committee:
* Protect lives.
* Minimize damage to public and private property and public resources.
* Provide a comprehensive understanding of the river.
* Propose projects with a positive environmental benefit.
* Maintain ongoing jurisdictional involvement/cooperation.
* Emphasize long -term solutions.
* Minimize public expenditures related to flooding.
PUBLIC INVOLVEMENT IN PLAN PREPARATION
To ensure that planning represents the broadest possible cross - section of local needs and
interest, public involvement will be stressed. Oversight of the process by the FCZD
advisory committee, with its well- balanced membership, provides the first element of
diversifying involvement. In addition to that group's ongoing meetings, special meetings
must continue for participation of the general public.
12
MANAGEMENT TECHNIQUES - WHAT ARE OUR OPTIONS?
FEMA FLOODPLAIN MAPPING
Since 1968, FEMA has offered flood insurance for personal property and structures
through the National Flood Insurance Program (NFIP). The flood hazard areas are
identified on maps prepared as part of the NFIP.
Flood -prone communities must take steps to reduce the risks of future flooding before
their residents are eligible for NFIP flood insurance. FEMA offers guidelines for the
communities to follow to reduce flood hazards. The focus of the guidelines is on limiting
development in designated flood -prone areas. Participating communities are required to
adopt and administer ordinances which control development and building according to the
flood hazard shown on the NFIP maps.
The NFIP relies on maps that show the boundaries of the expected 100 -year flood. In
most cases, the maps also show the boundaries of the floodway —the portion of the
floodplain along the river that must be left undeveloped to leave an open corridor for the
flood to pass through. The 100 -year floodplain are a outside the floodway is called the
flood fringe.
The floodplain, floodway, and flood fringe designations are key tools in flood hazard
management, as they establish boundaries within which development restrictions are
imposed for the sake of reducing flood hazards.
FEMA's current mapping for the Nooksack River was released in 1990 and is based on
hydraulic modeling completed in 1977. The FEMA floodway and 100 -year floodplain
limits currently in effect are shown on page 2.
NEW MAPS TO SHOW WHERE FLOODING CAN BE EXPECTED
One of the most proactive steps that can be taken for managing flood hazards is to limit
the amount of new development going up in the expected path of future flooding. This
approach requires mapping of predicted flood areas that is as accurate as possible.
The Federal Emergency Management Agency prepares maps of 100 -year flood boundaries
and floodways along water bodies in the U.S. The floodway is an area FEMA defines in
which no development is allowed that causes any increase in flood elevations. Exceptions
are allowed only after a rigorous process to certify that the increase will not affect any
existing structure.
The area between the floodway and the 100 -year flood boundary is called the flood fringe.
Development is generally allowed within the flood fringe only if it is constructed above the
100 -year flood elevation.
13
FEMA's current mapping of the Lower Nooksack River fails to address the path and
depth of floodwaters after they leave the river. Updating the FEMA maps to provide
accurate flood predictions is an important management technique for the Lower Nooksack
River.
PROBLEMS WITH THE CURRENT FEMA MAPPING
Although the FEMA flood maps for the Nooksack River were generated following
FEMA's standard approach, special conditions of the Nooksack make the resulting maps
flawed in some areas for use as flood hazard management tools.
To determine floodway limits, FEMA calculates how far in from the outer limits of the
100 -year floodplain the flow can be blocked without raising flood levels more than a foot.
This approach usually results in a floodway that is adjacent to the river channel, with the
flood fringe extending outward to the limits of the floodplain. Usually, this approach
makes sense because the river channel is where most of the floodwaters are conveyed.
As we've seen in our study of the Lower Nooksack's reaches, however, typical flooding
patterns along the river do not always carry the floodwater in and directly alongside the
river channel.
In Reach 3, as a notable example, overflows travel along Scott Ditch, over a half mile
from the river's left bank, and areas between the river and the overflow may actually
escape inundation because they have higher ground. Yet the FEMA mapping for that area
has most of Scott Ditch outside the floodway, while high ground between the river and the
overflow corridor is classified as the floodway.
This sort of discrepancy creates problems because of the development it allows. It means
that development restrictions that apply to floodways do not apply to Scott Ditch, which
often experiences extreme inundation from overflows.
When a river floods, the area along both banks becomes part of the flow corridor, conveying the floodwaters
downstream. This makes the use of the overflow corridors an important element of flood hazard management.
14
BUYOUTS AND RELOCATION OF SITES IN HARM'S WAY
For some properties, where the dangers of flooding to people, structures, or livestock are
very high, or where repeated flood damage can be expected over the years, the best
management technique may be to buy the property from its private owner or relocate
structures on the property to sites outside the floodplain risk.
A policy to acquire at -risk property or relocate at -risk structures can, over time, reduce
the amount of property value and population exposed to the dangers of flooding.
Such a policy is never mandatory for the private property owners. Rather, an agency
designates floodplain properties as eligible for buyout or relocation following a severe
flood, and it's up to the owner to decide whether to take advantage of the offer.
After the buyout or relocation, future development is limited on the at -risk property.
Purchased land can be leased for uses that are suitable for property within a floodplain,
such as compatible farming practices.
One of the most proactive steps that can be taken for managing flood hazards is to limit
the amount and kind of new development going up in the expected path of future flooding.
This approach takes two steps: mapping predicted flood areas as accurately as possible;
and establishing policies to allow only land uses that can withstand the flooding in those
areas.
FLOODPROOFING - HELPING STRUCTURES WITHSTAND THE WATERS
Given the approach of letting floodwaters follow their natural overflow corridors, it is
critical to address the risks to structures and activities within those corridors.
The management technique that best. addresses this concern is floodproofing, which
includes a variety of forms.
Structural floodproofing consists of modifying structures, their sites, or their contents to
keep water out or to reduce the effects of water getting in. The modifications can be
permanent or they can be made with each impending flood.
15
FLOODPROOFING TECHNIQUES
ELEVATION
Lightweight or
mobile items
can be stored
under the
house and /
moved
the flood
warning
BARRIERS
Berm is compacted
till with 2:1 or 3:1
slope (for stability)
Sump and ppump
handle underseepage
and intemaf drainage
DRY FLOODPROOFING
Maximum protection
level is three feet
WET FLOODPROOFING
Openings provided I F"
to let water in
Mechanical and
electrical equipment
moved above
flood level
Openings on each wall ensure entry
of water to prevent hydrostatic bad
Not for buildings
with basements
Closures for openings
Furnace and utilities
are relocated
Large appliances are moved
or wrapped in waterproof bags
16
Flood proofed walls
100 -Year Flood
50 -Year Flood
I 0 -Year Flood
Floodwall is reinforced
and anchored to withstand
hydrostatic load \
100 -Year Flood
50 -Year Flood
10 -Year Flood
The four basic types of floodproofing are:
* Elevation— Physically raising the portions of structures that would be damaged by
flooding.
* Barriers — Constructing a berm or levee between the expected floodwaters and the
structure to be protected.
* Dry Floodproofing— Designing structure walls and floors to be watertight so that
floodwaters cannot penetrate.
* Wet Floodproofing— Modifying the structure to direct how floodwaters flow in and out
and by removing items that could be damaged from the areas that will be flooded.
Floodproofing targets individual properties and is usually paid for by the property owner,
however, a public program providing cost sharing, technical assistance and guidance can
enhance the effectiveness of floodproofing as a management technique.
THE DETAILS - ZONING AND OTHER ORDINANCES
The specifics as to what kinds of development and uses are and aren't allowed within the
floodplain are laid out in a number of Whatcom county codes and ordinances: the zoning,
subdivision, health and building codes, land- clearing and critical area ordinances,
development standards, the shoreline management program, and the flood damage
prevention ordinance. Coordination of these regulatory programs is critical to ensure
consistent policies are enforced.
Open spaces are the ideal use for flood -prone areas because they involve little or no
development of structures that would be at risk from floodwaters. Perhaps the most
important fact about zoning in the Lower Nooksack River floodplain is this: About 75
percent of the 20,000 -acre floodplain is zoned for agricultural use, and about an additional
10 percent is zoned for other open space uses, such as forestry. That makes a total of 85
percent of the floodplain zoned for flood - compatible uses.
In addition to the zoning designations, nearly 80 percent of the Lower Nooksack River
floodplain is classified as open space through the county's tax incentive program, which
gives tax breaks to property owners who register and maintain their eligible land as open
space. Changing the use of property registered in this program can carry severe tax
penalties, which helps ensure that the property remains in use as open space.
17
All in all, the existing designations in the floodplain represent the best uses for these flood -
prone areas.
CONNECTING THE RIVER AND THE FLOODPLAIN
As rivers repeatedly flood with the passing of years, they create natural corridors to carry
the overflowing floodwaters.
In many cases, it is a good flood management strategy to work with these natural
corridors rather than against them. They often include areas of depression that can store
some of the floodwaters for a time, helping to ease the severity of flooding downstream.
To accomplish this, many flood management techniques are designed to establish a
connection between the river and its floodplain, maintaining the natural flow paths the
river has developed over time.
A level of minimum protection needs to be established. In agricultural. areas along the
Nooksack, a five to ten year protection level has been found to be adequate.
DESIGNATED OVERTOPPING LOCATIONS
It is often desirable to designate where floodwaters will overtop river banks or adjoining
levees.
The selected locations are generally where overtopping has occurred historically. In most
cases, this means maintaining the current level of protection of existing levees or
prohibiting construction of new ones.
When the historical site of an overflow is blocked off by a new or higher levee, the
floodwaters are likely to find the next weak levee section downstream and break through
it, often resulting in very expensive damage. In such cases, one area's solution to flooding
turns out to be another area's problem.
Designating sites for overtopping helps reduce the likelihood of a sudden levee failure, or
breach, at random locations. The volume and rate of flows through a levee breach, .
particularly when the breach is in a developed area, can cause severe damage and even be
life - threatening.
After recent Nooksack River floods, hundreds of thousands of dollars have been spent at
individual breach locations to repair the stream bank and levee as well as the scour
damage outside the levee.
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One of the goals of levee design and placement should be to allow floodwaters to reach
their historically defined overflow corridors.
AGRICULTURAL LEVEES
Agricultural levees are so called because they typically prevent nuisance flooding of
farmlands. They eliminate standing water and flows across agricultural lands during the
relatively low floods that occur almost every year. Flooding in areas protected by
agricultural levees is close to the natural condition during extreme floods.
The FCZD Advisory Committee decided existing agriculture levees on the lower
Nooksack serve a very important purpose and that wholesale removal of these levees
should not occur. The committee determined that agriculture levees should be maintained
and even enhanced as long as they provide a flood management benefit and do not
adversely affect other flood management activities.
LEVEE MAINTENANCE
It's important to identify and provide routine maintenance of levees designated for
overtopping or located where a breach would be especially dangerous.
Levee maintenance includes removing undesirable brush and trees, caring for desirable
vegetation, such as sod on the back side of the levee to prevent scour, and inspecting the
levee for erosion, seepage or saturation. It also calls for maintaining access to the levee
and repairing identified problems.
SETBACK LEVEES
Sometimes levees are constructed some distance from the banks of the river, leaving room
in between to convey and store some or all of the natural overflow during a flood.
Such levees are called setback levees Like levees along the river bank, they protect the
property behind them. In addition, however, they put to use the storage and conveyance
capacity of a part of the river's floodplain that would otherwise be lost if more restrictive
measures are implemented.
The area between the river and a setback levee can remain agriculturally productive with
selected, flood compatible farming practices, as well as provide an area of riparian habitat.
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I:� u : ►I 1 : i 0 L� Is
In the 1960s, the U.S. Army Corps of Engineers investigated the idea of building a dam to
create a flood - control reservoir on one of the three forks of the Nooksack. Of 16 sites
considered, the Corps found only one to be feasible —a site on the South Fork near Edfro
Creek.
A dam and reservoir offer the advantages of reducing peak flood flows, trapping sediment
that would otherwise travel downstream, and stabilizing river flows during the dry season.
However, they also block fish migration, destroy habitat, are very expensive to build and
operate, and are virtually impossible to get permits for these days.
The dam required at the Edfro Creek site would be 150 feet high and 1,400 feet wide. It
would cost $159 million (in 1992 dollars) to build. The Corps estimated that the reservoir
could reduce annual flood damage along the Nooksack by $900,000 to $1.4 million, but
annual debt payments and operation costs would be $16.3 million.
Given the extreme cost of a single purpose dam compared to its flood- control benefit, the
FCZD Advisory Committee voted to omit this option from consideration.
THE ISSUE OF SEDMMNT
Removing accumulated sediment from the river channel and from gravel bars that build up
in the channel can increase the river's capacity to carry floodwaters, thus reducing flood
levels. Strategic removal bf channel sediments may assist in lowering bank stress and
thereby reduce stream bank erosion, land loss and the need for costly stream bank repair
and maintenance.
Before addressing specific locations, further general understanding is necessary. Sediment
removal includes two kinds of activities: "in channel dredging" and "gravel bar scalping."
In Channel Dredging
Dredging is the removal of sediment from the sides and bottom of the river channel.
In 1991, the Corps of Engineers investigated the idea of dredging about 2 miles of the
Nooksack River channel downstream of Ferndale. The Corps study found that deepening
the river by a foot along this reach —at a cost of $1.4 million —would increase the level of
flood protection there only to 5 -year protection. The study compared this to protection
against the 2- to 3 -year flood, which it said was already provided by existing levees.
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In other studies, the Corps has given different estimates for the protection the existing
levees provide, but regardless of their actual protection level, this study showed how slight
an improvement dredging would offer in this reach.
In addition to providing only limited additional flood protection, the dredging would have
to be repeated about every 10 years.
The limited increase in flood protection at a relatively high cost, coupled with the
environmental impacts of dredging, led the Advisory Committee to rule out in- channel
dredging on any large scale as a flood management technique.
Gravel Bar Scalping
The removal of gravel accumulated in the river channel above the normal low water level
from exposed gravel bars is referred to as scalping. Scalping does not deepen the river,
but it increases the cross - sectional area available to carry floodwaters.
The FCZD Advisory Committee did not investigate in detail the practice of gravel bar
scalping, but the group has indicated a strong support for developing a comprehensive
sediment management program.
DEALING WITH FLOOD PREPAREDNESS
There is no way to keep the Nooksack River from flooding. Floods will come, and some
will be larger than any yet recorded.
Most of the management strategies outlined so far are steps to be taken before the floods.
It's also essential, however, that we have a plan for recognizing when a flood is likely so
that we are prepared to respond to it.
Predicting an oncoming flood requires a system for monitoring regional conditions in
order to determine how much rain has fallen, the amount of snowmelt that can increase the
river's flow, and the river's height upstream. It also requires a system for using the data
collected Together with records of how floods have behaved in the past, a prediction of
what kind of flooding to expect can be made.
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MONITORING
In 1995 and 1996, the county, with FEMA and state financial assistance, and together
with other agencies, such as the National Weather Service, the Natural Resources
Conservation Service, and the U.S. Geological Survey, enhanced existing resources and
added new ones to improve the supply of flood monitoring information.
Two new weather stations were established in the Nooksack watershed to complement the
existing one at Glacier on the North Fork. These stations measure rainfall and
temperature and transmit the information automatically to a central, computerized system
operated by the NWS.
Volunteer rain spotters" were recruited to monitor rainfall at their homes or workplaces
throughout the watershed. These volunteers, trained to measure rainfall and told how to
report it to a centralized system, ensure a steady input of information even if more high -
tech systems should fail for any reason.
* Two snow pillow stations — automated devices for measuring the amount of water held
in the mountain snowpack —were established in the upper basin.
* Three new or retrofitted stations were established to measure the river stage at Lynden
on the middle and south fork channels, complementing the gauging stations already in
place at Ferndale, Deming, and Glacier.
The NWS installed a Doppler radar system on Camano Island. This system allows a
better look at weather conditions in the mountainous upper portions of the Nooksack
watershed.
FORECASTING
The NWS is the primary weather forecaster in the U.S., and many communities rely
heavily on the agency for weather - related predictions.
The worst floods on the Nooksack River happen during the weather system called the
Pineapple Express —warm, heavy rain falling on an unstable snowpack so that runoff from
snowmelt joins with precipitation runoff to swell the river and its tributaries.
Data from rain and temperature gauges, snow pillows, and river gauging stations help us
see when these conditions are forming, giving us advance notice of the potential for severe
flooding.
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As records from the improved monitoring systems throughout the region accumulate over
time, we will be better able to see from past trends what kind of flooding to expect from a
given set of weather conditions.
FLOOD WARNING
Whatcom County's Emergency Operations Center (EOC), a unit of the Division of
Emergency Management in the county Sheriff's Office, takes the lead in putting out the
word when a flood is on the way.
The EOC has a many - pronged approach to flood warning:
* The unit phones or faxes public officials in the U.S. and Canada to let them know about
impending floods.
* Press releases are sent to local radio stations with flood warning messages to be
broadcast.
* The county participates in the Emergency Broadcast System, which broadcasts
emergency messages on radio, television and cable.
* The EOC operates a telephone "Hot Line" that the public can call for the newest
information about flood conditions.
FLOOD RESPONSE
The next steps in dealing with a flood come when the floodwaters actually arrive.
The flood response effort involves many people, from individuals protecting their own
property to municipal, county, federal, and other agency crews mobilized to prevent
serious harm to the community:
* The EOC begins 24 hour operations and serves as the communication center and
coordinates response and evacuation shelter openings and supply efforts.
Private individuals and groups launch grass -roots efforts to protect property from
floodwaters, primarily through sandbagging, evacuation, and relocation of animals or
farm equipment to higher ground.
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* Police and other emergency agencies conduct evacuations as needed and respond to
crisis situations.
* Municipal governments lead the floodfighting effort in their own communities.
* Whatcom County sector observers cover portions of the county observing and
reporting where the dangers are the greatest.
* The County's Maintenance and Operations Division clears debris from bridge openings
and roadway culverts to help keep the waters from backing up and over roadways.
* Diking districts patrol their levees and perform small repairs where possible.
* The U.S. Army Corps of Engineers patrols Corps - approved levees to inspect them for
damage and carry out repairs when they're needed.
* The county's maintenance and operations division maintains a supply of sand and
sandbags, and plays a key role in the delivery of these supplies to critical floodfight
areas.
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IMPLEMENTATION PLAN
- MOVING FORWARD FROM PLANNING TO ACTION
ONE APPROACH TO PARTNERING - SETTING UP FCZD SUBZONES
The implementation plan we've outlined in this section is extensive and will be costly and
time - consuming. Whatcom County cannot carry it out on its own but must work together
with many public and private groups and individuals to make the plan a reality. The
County can play a leadership role in bringing all these parties together. Partnering makes
sense for many reasons:
* Because Nooksack River flooding inundates and damages roads and bridges, ties up
traffic, knocks out. such public utilities as gas, power and telephone; and diverts County
staff from everyday duties to flood fighting, everyone in the County is affected when
the river overflows.
Landowners and residents along the Nooksack River are affected directly. Even though
development in the floodplain is sparse, these landowners will benefit directly from
recommendations to make flooding more predictable.
* Flooding affects state and federal agencies involved in regulating floodplain activities
and providing financial assistance after floods.
Many people and groups with local knowledge have already contributed to the
recommendations. Their contributions include identifying locations of historical overflows
and helping select the best areas for designating future overflows.
Landowners along the floodplain must continue to be involved in working out the details
through the implementation plan. For example, their input is needed in discussions on how
best to keep overflow corridors open to convey floods, with minimal impact on present
agriculture activities.
Although it's the job of the County to coordinate recommendations for individual river
reaches into a comprehensive approach for the Lower Nooksack, landowners along the
river are most interested in flooding as it affects them directly. The best partnering
approach for implementing recommendations is a grouping that accommodates the
County's broader role as well as the local interests of floodplain landowners.
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One way to do this is to divide the river into "sub" flood control zones within the County-
wide FCZD. This keeps the County in a leadership role, but breaks out local areas so the
County can deal with local landowners.
The river can be divided into sections in which landowners have common concerns, which
we can call sections of "hydraulic consistency." For example, just downstream from
Everson, floodwaters overtop the left bank, follow a corridor along Scott Ditch, and
return to the river upstream or just downstream of Guide Meridian. This path can be
considered to be connected and affected by a single hydraulic phenomenon, and hence a
section of hydraulic consistency.
THE PROCEDURES FOR REVISING THE FLOODPLAIN MAPS
Our most important tool for revising the Lower Nooksack floodplain maps will be
computer modeling of the river. The results of that modeling, together with input from
citizens and county staff, will be used to establish consistent criteria for designating high
flood hazard areas in the floodplain. Potential sites for designation will be rated based on
criteria such as:
* Predicted depth of inundation.
* Predicted floodwater flow velocity.
* Proximity to proposed overflow corridors.
* Proximity to the river channel (to account for hazards from meander and levee
breaches, as well as jurisdiction of various regulatory programs).
Here's a quick look at the work we'll have to do to revise the floodplain maps and put
them to use:
Refine the analysis we've already begun in the CFHMP on overflow corridors and the
meander corridor along the Lower Nooksack River to represent designated overflow
locations on individual reaches. Develop a clearer picture of where we expect the most
severe flooding.
* Involve property owners in the floodplain, to get their ideas on appropriate lines for the
regulatory and overflow floodways and floodplain. Their input is especially important
given the consequences of changing some areas from flood fringe to floodway. The
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more restrictive floodway designation will affect not only future construction, but
possibly existing structures as well.
* Develop a set of criteria to be used in drawing new map boundaries.
Review policies and ordinances for what will be allowed in the newly designated high
hazard areas.
Some existing structures will be compatible with the new map designations— buildings in
the hydraulic shadow of other buildings, for example, or flow - through pole barns. Other
buildings now in place, however, are not compatible with the level of flooding they
experience, and we will need policies for what to do about those structures.
Policies will also establish requirements for professional engineering certification of
development proposals in the floodplain.
* Coordinate with state and federal agencies to ensure that the new maps and associated
ordinances will comply with their regulations.
* Formally adopt the new floodplain maps and associated ordinances.
A PLAN FOR PROPERTIES AT RISK
Our program to improve the Lower Nooksack's floodplain mapping and associated land
use ordinances will help us to ensure that future development does not increase the risks
the river's flooding poses to people and property.
Unfortunately, development that already has occurred presents a different challenge. What
are we to do about structures now in place inside the existing floodway, structures in areas
that will be designated high hazard areas once the floodplain maps are revised, and
structures throughout the flood fringe?
PROPERTY BUYOUTS
Some existing homes and other structures in the Nooksack floodplain are in areas of very
high risk and are damaged, or at least are susceptible to damage, every time the river
floods.
The best way to address this flood hazard is to identify these structures and designate
them as candidates for buyout by a public agency.
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The designation by the county of all floodplain properties would make these buildings
automatically eligible for purchase when local, state or federal buyout programs are put in
place following damaging floods. When funding is limited, a priority system could be used,
with buyout funds being used in the following order:
* Buyout of properties that are damaged and repetitive loss properties.
* Buyout of properties in the regulatory floodway.
* Buyout of properties in the overflow floodway.
* Buyout of properties in the flood fringe.
In recent years, FEMA has grown increasingly supportive of buyout programs to reduce
flood hazards, and the amount of funds available for such programs has increased steadily.
The advantage to an agency such as FEMA is that buying and vacating at -risk properties
eliminates recurring damage in the future, thus eliminating ongoing costs for repair.
It is important to note, however, that the designation only makes properties candidates for
buyout. It is always up to the property owner whether to take advantage of the program.
Many landowners have lived in the floodplain for many years, even generations, and they
accept the flood hazards and potential damage. Extreme floods in recent years, however,
may have created a new awareness of flood hazards, and some landowners may be
interested in the buyout program.
Whatcom County's role in a buyout program would be to provide technical assistance and
to act as a facilitator for grant programs.
FLOODPROOFING STRUCTURES
As we described in the section on flood hazard management techniques, floodproofing is
an important tool for protecting structures in the path of floodwaters. The four basic kinds
of floodproofing are:
Elevation - Physically raising the portions of structures that would be damaged by
flooding.
* Barriers --- Constructing a berm or levee between the expected floodwaters and the
structure to be protected.
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* Dry Floodproofing — Designing structure walls and floors to be watertight so that
floodwaters cannot penetrate.
* Wet Floodproofing — Modifying the structure to direct how floodwaters get in and
removing items that could be damaged from the areas that will be flooded.
The Whatcom county flood damage prevention ordinance includes requirements for
elevating and floodproofing structures.
Buildings throughout the floodplain— whether in the floodway or the flood fringe —are
appropriate candidates for floodproofing. This is especially so for structures in high hazard
areas whose owners choose to remain.
The cost of floodproofing varies with the likely level of flooding and the type of
floodproofing. Like buyouts, floodproofing is the property owner's choice.
The county can offer technical assistance and manuals, and provide landowners with
information on likely flooding on their property and on available funding sources.
SYSTEMS FOR BUYOUT / FLOODPROOFING DESIGNATIONS
For buyout and floodproofing designation programs, the county could take one of two
approaches to identifying eligible properties: Designate all properties in the floodplain as
eligible; or, Designate only selected properties.
The second alternative — making only some floodplain properties eligible— presents
several difficulties. It would require that detailed criteria be developed to ensure the
fairness of recommendations for eligibility. The criteria would have to include flood
frequency, potential for damage, and hazard level, and these would have to be determined
for every floodplain property.
The selected - properties approach also would require the county to make a formal funding
commitment for the buyout/floodproofing program. Such an approach also would have to
deal with property owners' wishes, which could be in conflict with the designations.
RECOMMENDATIONS FOR FLOOD FORECASTING AND RESPONSE
Several steps are recommended to ensure that the county's monitoring, forecasting,
warning, and response systems remain effective in the future:
* Encourage the National Weather Service's use of Doppler radar for forecasting in the
Whatcom county area.
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* Encourage the incorporation of new stream gauge data by the NWS for use in its
overall forecasting efforts and in updating its flood modeling and forecasting.
* Encourage broader distribution of NWS data over such resources as the Internet.
* Maintain the county's financial commitment to support the operation of monitoring
systems for the snow pillows in the upper watershed and for stream - gauging stations.
* Encourage the continuation and enhancement of cooperation between agencies —
integrating flood response programs; coordinating an annual public information
program; holding annual meetings to update operational plans; and conducting annual
response practice drills.
* Get certification of the county's emergency operations plan from the state Division of
Emergency Management
* Maintain a reserve fund for emergency flood response and recovery.
ENGINEERING DESIGN OF OVERFLOWS AND OF LEVEES IN BETWEEN
The detailed hydraulic analysis will tell us the desired channel capacity and river bank or
levee elevation at every point along both banks of the Lower Nooksack. The next step in
the implementation plan will be to draw up designs for the levees and, where necessary,
bank stabilization projects.
Owing to the critical nature and the environmental sensitivity of the bank riparian area,
future bank and levee standards should be structurally sound, resistant to erosion,
environmentally acceptable, and easy to maintain.
The Overflows
The designated overflow locations must meet two requirements: They must have the
capacity to let out floodwaters expected for up to the design -year flood; and they must
have the stability to withstand the forces of escaping floodwater without failing.
Some of the overflow locations that have been identified do not have levees; they are
natural river banks where floods historically overflowed to the floodplain. Although bank
protection projects may be appropriate at some of these sites, they do not otherwise need
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engineered designs. What these sites do need is a policy that will ensure that they are
preserved at their current elevations and flood resistant condition.
Other overflow locations are levee segments that must be designed to be overtopped.
These levees must have lower crests than adjoining levees to make sure the overflow
occurs at the targeted area.
A standard design should be used for overflow levees to guarantee their ability to
withstand flow forces. This concept should be formally adopted and utilized for all levees
at overflow locations.
An important element of the concept design is the use of trees, shrubs, and other
vegetation on top of the levee. These are intended to filter debris from the overtopping
floodwaters to keep the debris out of the floodplain. These debris fences must be
maintained to ensure the function and structural integrity of the levee.
The vegetation requirements add another benefit —they restore and enhance the
environmental quality of the riparian areas along the Lower Nooksack, providing wildlife
and fisheries habitat as well as aesthetic enhancement.
Between The Overflows
Our strategy of designating overflow locations will not succeed if levees at other locations
fail.
To minimize such failures, all levees should use a standard design with provisions to
withstand expected hydraulic forces. The design must recognize that a very large flood
could overtop the levees, so they must be stable enough to withstand overtopping without
failure.
Like the overflow levee design, the design for overtoppable levees must be adopted as a
standard and used for all future levee construction and reconstruction between the
overflow locations.
It will take time for all levees between the overflow locations to be converted to the
design standard. It isn't feasible to launch a program to immediately replace all existing
levees with the new standard, but they could be modified under a systematic program
when they require repair or when some project makes fill economically available.
US Army Corps of Engineers Levee Program
An important consideration should be the potential levee compliance with the USACOE
PL99 program. Requirements for inclusion of existing or retrofitted levees into this
program are rigid. However, the associated benefit is USACOE assistance in cases of
flood damage. All levees should be analyzed for their possible inclusion in this program.
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A LEVEE INVENTORY PROGRAM
At the overflow locations and in between, levees ultimately must be stabilized and
modified to the proper elevation. The detailed hydraulic modeling that is the first part of
the implementation plan will determine the design elevations.
Unfortunately, no accurate, comprehensive information is now available on the elevation
and condition of existing levees. Whatcom County's 1993 topographic maps do not
include detailed levee crest data, and the Corps of Engineers' inventory from the 1980s is
out of date.
To determine how much work is required to achieve the design levee cross- section, a
levee surveying and inventory project is recommended.
In addition to a survey of crest elevations, this program should include an inspection of the
levees to determine their structural integrity, the condition of vegetation on them, and
environmental issues that need to be addressed such as the presence of critical habitat
features, nesting areas, and fisheries. This information should be updated as projects are,
implemented and as changes occur because of floods.
LAND USE RECOMMENDATIONS
Now that we have outlined concepts for moving floodwaters through each reach and for
revising the floodplain maps, we can also recommend specific flood hazard management
actions that apply to land use. To provide compatible land use with flood hazard
reduction, we should retain the current county floodplain zoning, which provides for
flood - compatible land uses such as agriculture, forestry, open space, and parks.
PUBLIC EDUCATION TO ENHANCE FLOOD PREPAREDNESS
The planning process has made clear a number of important points about flood hazard
management planning for the river:
Many groups and individuals along the river, with a wide range of interests, hold a
stake in planning for flood hazard management. All these people must understand the
interests and concerns of one another to ensure that planning decisions address
everybody's needs.
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* Flooding along the Lower Nooksack cannot be prevented, but we can reduce flood
risks as long as we have reliable information on how much water we can expect, how
high the water will rise, and what areas are subject to the greatest hazards.
* Although severe floods have affected many people in recent years, everyone must
understand that even bigger floods will come someday.
* Property owners are very familiar with flood issues in their immediate area, but much
less informed about issues elsewhere along the river. It's essential to understand how
taking steps in one part of the river can affect flooding somewhere else.
* Because the recommendations will affect so many property owners, they can never be
implemented unless the public buys into them. This will require the public to be
knowledgeable about what is being proposed and why.
Since many of these points involve the public, a program to educate Whatcom County
citizens about flooding and flood hazard management is essential. The education program .
must get out the word, not only about flooding and flood hazards, but.also about the
measures proposed to address them.
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