Living with the RiveR 

A Guide to understAndinG 
Western WAshinGton rivers And 
ProtectinG Yourself from floods 


JUNE, 2007 
PUBLICATION 07-06-016 


Living 
with 
the 
RiveR 

A Guide to understAndinG 
Western WAshinGton 
rivers And ProtectinG 
Yourself from floods 


Sponsored by: 

SHORELINES & ENVIRONMENTAL 
ASSISTANCE PROGRAM 

Washington Department of Ecology 
Olympia 

JUNE, 2007 


PUBLICATION 07-06-016 


Acknowledgments 

The preparation of this booklet was made possible through funding and staff time 
from the Washington State Department of Ecology, Shorelines and Environmental 
Assistance Program and the Federal Emergency Management Agency. 

The authors would like to acknowledge three people whose shared concept and 
technical review helped bring this publication to life: Dan Sokol (Washington 
State Department of Ecology, State Floodplain Manager), Patricia Olson 
(Washington State Department of Ecology, Hydrogeologist) and Lois Lopez 
(Federal Emergency Management Program Lead). 

If you need this publication in an alternate format, please call Ecology’s Shorelands 
and Environmental Assistance Program at 360-407-7000. Persons with hearing 
loss can call 711 for Washington Relay Service. Persons with a speech disability 
can call 877-833-6341. 

Important Notice 

The contents of this publication are for general information and applications only 

and should not be construed as a substitute for site specific design and installation 

recommendations from professionals who are expert in geomorphology, 
hydrology or civil engineering practices. Accordingly, Washington Department 
of Ecology and the preparers of this booklet make no representation or 
warranty of any kind, whether expressed or implied, concerning the accuracy, 
completeness, suitability, or utility of any information, apparatus, product, 
material, or technique presented in this publication and assume no liability. 

Booklet Author: Nancy Deschu 
Graphic Design: Anne Walker 

The recommended bibliographic citation for this publication is: Deschu, Nancy and Anne Walker. 
2007. Living With the River: A Guide to Understanding Western Washington Rivers and Protecting 
Yourself from Floods. Shorelines and Environmental Assistance Program, Washington Department of 
Ecology, Olympia. Publication 07- 06-016 


Contents • 


Contents 

Introduction................................................................................... 7 
The Basics of River Behavior..........................................................8 
What Happens When a River Floods? ............................................ 13 
Stories of Western Washington Flood Hazards .............................. 18 
Learning About Your Watershed and River.................................... 22 
Sources of Information on Floods and Floodplains........................26 
How to Reduce Your Flood Hazard Risk........................................34 
Summary ....................................................................................... 39 
Glossary ......................................................................................... 41 
Recommended Reading ................................................................. 44 


 


Introduction • 


Introduction 
Rivers carve through Western Washington from their headwaters 
in the Cascade and Olympic mountain ranges to Puget Sound, 
the Columbia River and the Pacific Ocean. Along the way these 
rivers are constantly shifting as they pick up rock, sediment and 
wood and then deposit it elsewhere. This is the inherent nature 
of a river, to balance its load of rock and sediment with its steepness 
and the volume of water it carries. This river balancing act 
is a fascinating process but that process is often hidden from our 
view in a world filled with buildings and roads. 
In Western Washington we all live in a watershed. Maybe we 
do not live directly on a river, but we live in unique watersheds 
where the water in the area flows into rivers, lakes, groundwater 
and the sea. Those of us who live or work along a river may be 
more aware of seasonal pulses - the change in shape of the river 
over years and the dangers inherent when the river floods. But 
most of us don’t think much about the workings of a river until a 
flood is upon us or has passed, leaving its wreckage behind. 
Washington is one of the states most prone to flooding. Between 
1956 and 2006, there were 32 floods in Washington that 
were declared Federal disasters by the President. Because of the 
extreme flood hazard in Washington, this booklet, “Living With 
the River”, has been prepared for the public. The purpose of this 
booklet is to: 
Describe the behavior of rivers in Western Washington • 
Describe land cover and land use in watersheds in Western • 
Washington 
Assist you in conducting a flood hazard survey where you • 
live or work A glossary of 
Provide guidance on how to reduce your greatest flood haz• 
technical terms 
ards used in “Living With 
the River” can be 
It is our hope that this booklet will help you better protect your found at the end of 
life and property from flooding in Western Washington. this booklet. 

 


.Living With the River 
The Basics of River Behavior 


NANCy dEsChU 
A headwaters tributary to Nisqually River, Mount 
Rainier National Park. 


“It has been said that streams are the gutters 
down which flow the ruins of the continents.” 

Leopold, Wolman and Miller, 199 . 

Rivers are not isolated 
bands of water 
running through the 
landscape. They are 
complex systems that 
sit within a watershed. 
A watershed is 
the region that drains 
water from the 
surface of the land 
and from beneath 
the ground into a 
river system. There 
are vast and intricate 
connections between 

the river and its watershed. 

What factors define a 
watershed? 

Watersheds vary in size, underlying 
geology, steepness, 
elevation, rainfall, snowfall, 
soil type, vegetation type 
and aspect (the direction the 
watershed slope faces). All 
of these watershed factors 
contribute to the behavior of 
a river. 

Watershed Size: The highest 
streams in a watershed are 

commonly referred to as 1st 
order streams. When a 1st 
order stream meets another 
stream, that is a 2nd order 
stream and now carries the 
combined water of both 
watersheds. This process of 
increasing order goes on until 
the river reaches the sea. 
By that time the watershed 
can be very large and carry 
a great volume of water. In 
Washington, for example, 
the Snohomish River is a 5th 
order river that encompasses 
1,856 square miles. 

Geology: There are 3 
geologic factors that greatly 

influence a river: the type 

of rock the river must cut 
through as it moves downstream; 
the type of rock and 
sediment available to a river 
to transport downstream; 
and the degree to which 
water can percolate into the 
ground (permeability). For 
example, granite rock is 
impermeable whereas gravel, 
because of the many spaces 

 


The Basics of River Behavior • 


around each stone, is a very 
porous geological formation. 

Steepness and Aspect: The 
steepness (or gradient) of a 
watershed affects the path 
and the shape a river takes as 

it flows downstream, always 

adjusting to the changing 
gradient of the landscape. 
The aspect of a watershed determines 
the angle at which 
sunlight hits the watershed. 

Aspect influences things like 

the intensity of sunlight, humidity 
near the ground, the 
development of soil, and the 
type of vegetation. 

Elevation and Precipitation: 

The aspect of a watershed 
combined with its elevation 
affect whether precipitation 
falls as rain or snow. 
At colder, higher elevations 
precipitation usually falls 
as snow. Aspect and eleva


tion also influence whether 

snow accumulates or melts 
and runs off quickly. In 
general, more precipitation 
falls on the windward side of 
a mountain range than the 
leeward side. In the Cascade 
Range, the west side of the 
mountains receive substantially 
more precipitation than 
the east side. 

Glaciers: Glaciers 
form where snow 
continues to accumulate, 
compact, 
and eventually 
turn into glacial 
ice. As a glacier 
moves downslope 
it erodes the terrain, 
picking up 
rocks and grinding 
bedrock into 

fine sediment called glacial 

silt. Water from melting ice 
and water within the glacier 
carry the rocks and glacial 

flour and then release it into 

streams, rivers or the ocean. 
This load of rock and glacial 

flour makes glacial-fed rivers 

behave much differently than 
non-glacial rivers in the same 
region. Non-glacial rivers 
carry less sediment, run clear 
most of the year and have 
less sediment available to 
carry and deposit. 

Land Cover Type: 

If you look at 
a map of your 
entire watershed, 
from headwaters 
to the sea, you 

may find glaciers, 

scree slopes, 
alpine meadows, 
conifer forests, Snohomish River near its mouth on North Puget 



Sound. 

The effect of wind direction and mountains on 
precipitation. 



.Living With the River 
Aerial view of a braided channel. 

hardwood forests, lowland 

meadows, coastal mudflats, 

forest clear-cuts, farmlands 
and urban development. All 
of these types of land cover 
and land uses affect how a 
watershed functions and how 

floods behave. For example, 

up to 50% of a year’s precipitation 
in a forested area 
may be intercepted by and 
evaporate from the forest 
vegetation. Similarly, the 

forest floor with its spongy 

layer can absorb and hold 
rainfall. In contrast, parking 
lots and highways (known 
as impermeable surfaces) 
prevent water from naturally 
soaking into the ground. 

What determines a river’s 
behavior? 

A river is always changing. As 
a river flows down its watershed 
it cuts through and dissolves 
the landscape. Along 
its course the river constantly 
picks up, carries and deposits 
rocks and sediments. These 
processes cause the shape and 
path of the channel to be in a 
constant state of change. 

A floodplain is the relatively 
flat land that borders a river 

channel and is occasionally 
inundated. Floodplains 

are formed when the river 
deposits rock and sediment 
along its channel during high 

flow. So most of the year the 
river flows in its channel and 
the adjacent floodplain is dry. 

There might be thick vegetation 
on a floodplain, sometimes 
even large trees. Even 

so, the floodplain is there 

for the river to escape to, to 
release its powerful water 

when its flow is high. A river 
and its floodplain are forever 

inter-dependent. 

If a river carries a heavy load 
of sediment and rock, as do 
glacial rivers for a good part 
of the year, the width of the 

floodplain can be very large. 

As a river moves down from 
the mountains to a wider and 
wider valley, the water slows 
down and drops its sediment 
and rock. On this shifting 

sediment floodplain, a river 

may cut and follow new 
channels as 

Braided Channel 

is the case 
in the lowlands 
west of 
the Cascade 
Range. A 
river is 
referred to 

as “braided” 

when there 



The Basics of River Behavior • 


are many shifting channels 

in one broad floodplain. 

In areas where there is 
unforgiving bedrock, the 

river may be forced to flow 

fast and deep in a narrow 
canyon. At these constricted 
points along a river, a traditional 
floodplain may not exist 
– instead the river’s water 
rises in its canyon because it 
cannot spread out horizontally. 


The degree to which a river 
meanders along its course is 
called its sinuosity. Sinuosity 
can become so great that the 
river makes extreme loops 
(oxbows). Eventually these 
loops may be cut off from 
the river, forming oxbow 

lakes in the broad floodplain. 

When a swift flooding 

stream leaves a mountain 
canyon and opens into a 
wider area, the water will 
suddenly slow down and 
drop its heavy load of rock 
and sediment. A formation 
called an alluvial fan develops 
at the base of these types 
of canyons. (See “What Happens 
When a River Floods?”) 


Two Simple Hydrology 
Lessons 

How much water does the 
river channel carry? 

There are four interacting 
variables that are useful 
to learn if you want to 

Nisqually River 
near its mouth 
on South Puget 
Sound. 

The evolution of a meandering channel. 

understand the basics of 
river behavior: channel 
width, channel depth, 
water velocity (or speed) 

and volume of flow. 

Once you understand 
the relationship of these 
four components, you 


can observe a river with 
a new perspective. It’s 
actually quite simple. At any 
point on a river: 

Channel Width (feet) x Channel Depth (feet) x Water 
Velocity (feet per second) = River Flow (cubic feet per second) 


.Living With the River 
PhOTO COUrTEsy Of UsGs 
A hydrologist measures stream flow. 


Measuring a 
river’s width, 
depth and 
velocity is 
not always 
straight forward 
or easy 
to do. Depth 
may vary 
greatly across 
a river, width 
is sometimes 
hard to 
pinpoint if it 
is a shallow 
meandering 
river, and 

velocity is often a logistical 
challenge to measure. 
Field scientists follow 

specific methods and 

use specialized instruments 
to measure these 
variables. But for the 
person who just wants 
to observe a river over 
time, estimating these 
variables can help unravel 
some of the questions 
behind a river’s 
behavior, especially 

during floods. 

How much rock can 
the river carry? 

The river’s velocity 
and volume of water 
determines how large a 

particle or rock it can move. 
Other factors also affect 
movement including the 
incline of the riverbed and 
forces of friction. But for this 
general discussion, put simply, 
the faster the water, the 
larger the submerged rocks 
that can be moved. The 
inverse is also important to 
think about: the slower the 
water moves, the less it can 
carry and will therefore drop 
its load of rock and sediment, 
in some cases, very suddenly. 
Both swift moving rocks and 
suddenly dropped rocks can 
pose serious threats to life 
and property. 

NANCy dEsChU 
Headwaters of Nisqually River in Mount Rainier 
National Park. 



What happens when a river floods?• 


What Happens When a River Floods? 


Rivers flood for many 

reasons – extreme rainfall, 
rapid snowmelt, rain falling 
on snow, glacier or lake 
outbursts and tidal surge 

moving upriver. Most floods 

in Washington occur due to 
persistent heavy rainfalls, 
heavy rainfall on a snowpack 
and rapid snowmelt during 
very hot weather. In addition 
to these climatic factors, 
floods happen or are exacerbated 
by manmade alterations 
of a river’s channel or 

floodplain. 

Flooding can occur in the 
Western Cascades and the 
Olympic Range year round. 
In watersheds lower than 
1,000 feet, precipitation is 
primarily rain and most 
of that falls in the winter 

months. Therefore floods 

caused by rain are more 
likely to occur in these lower 
elevations in winter. At elevations 
higher than 3,500 feet, 
the predominant precipitation 
in the winter is snow, so 
larger floods occur more often 
in the spring when snow 
melts during a period of hot 
weather or when spring rains 
hit the snowpack. 

Flooding from rain is determined 
by more than just 
how much rain falls. The 
intensity of the rainfall is 
important. For example, a 
long drizzle may drop the 
same volume of rain as a 
short-lived severe storm but 
over a much longer period 
of time. When the ground 
and the river have more time 
to slowly receive and adjust, 
as they do during a long 
drizzle, the less likely there 

will be severe flooding. 

A large amount of precipitation 
that falls does not 
directly run off to rivers. 
Instead it falls on vegetation 
and evaporates. Also rain and 
snowmelt is wicked up by 
plants and transpired to the 
atmosphere, absorbed and 
held by the soil, or passed 
through the soil where it 
moves slowly underground. 

The condition of the ground 
affects how water reaches a 
river. If the ground is already 
saturated and cannot absorb 
more water, water quickly 
runs off to the river. Likewise, 
if the ground is frozen, 
water is less able to soak in 


.Living With the River 
Aerial view of an alluvial fan, near Packwood. 


and so more water 
runs off quickly to 
the river. 

Rivers can carry 
a certain volume 
of water. Before 

a flood becomes 

widely apparent 
to the public, the 
river has already 
used its capacity 
to store additional 

flood waters. This 
floodwater storage 

can be in gravel, 

sand or other 
loosely consolidated material 
surrounding the channel. 
The water may also move 
into river banks and wetlands 
and ponds along the 
river where it is temporarily 
stored. 

When the volume of water 
becomes so great that the river 
and its storage is full, the 
water must leave its channel, 

frequently used historic 

floodplain. 

The lateral 
movement 
of a channel 
across its 

floodplain is called channel 

migration. 

At extreme flows a river 

can also widen and deepen 
its channel, jump to old 
channels and even cut new 
channels. While the river is 
carving new channel shapes, 
it is also picking up and 
dropping its heavy load of 
rock and sediment. During 

these high flows, channels 
can become filled with rock 

which can lead to damming 
and redirection of the river. 
The river is always working, 

even in extreme floods, to 
find its equilibrium between 

erosion and deposition of its 
load of rock and sediment. 

Debris flows are extreme 
cases of floodwater carrying 
and depositing rock and 
sediment. When a hillslope 
becomes water-saturated 
and unstable, a mixture of 
water, earth and rock can 
move downslope, often very 

fast. A specific type of debris 
flow is an alluvial fan flood. 
This happens when a flooded 

stream carrying a heavy load 
of rock and sediment leaves 
a mountainous canyon and 
suddenly drops its huge load. 

To the casual observer, an 

seeking to spread out over 
its floodplain. In extreme 
flood events, the river can 
swell to its much wider, less 
Debris flow 

What happens when a river floods?• 


alluvial fan might simply 

appear as a stream flowing 

out of the mountains on to 
a fan-shaped, gently sloping 
hill. Often there is vegetation, 
including large trees, 

making it difficult to identify 

an alluvial fan. But the landscape 
speaks the history of a 
stream that has raced down 
the canyon carrying tons and 
tons of mud and rock. Both 

debris flows and alluvial fan 
flows are not uncommon in 

Western Washington. Both 

are more difficult to predict 
than normal river flooding 

and both are extremely dangerous 
to people and structures 
in their paths. 

Trees can become part of a 

flood when riverbanks erode, 

new channels are cut, or 
when landslides or avalanches 
carry trees into the 
river channel. Although these 
downed trees can be hazard


ous during a flood, they are 

a natural and important part 
of a river system. The large 
root wads, when embedded 
into the river bed and bank, 
help stabilize the channel 
and work to capture rock and 
sediment. Embedded root 
wads and downed trees, in 
turn, provide nutrients to the 


Alluvial Fan 

river and help the river estab


lish healthy fish habitat. 

What are the Likely 
Effects of Climate Change 
on River Flooding in 
Western Washington? 

It is predicted that climate 
warming in Western Washington 
will cause 
more autumn and 
winter precipitation 
to fall as rain 
rather than snow. 
This increased 
autumn and winter 
rainfall would produce 
higher river 

flows and result in 
increased flooding 

between October 
and March. In a 

Nisqually River, downed trees, November 2006 flood. 


NATIONAL ACAdEmIEs PrEss 

sTEvE sUTTON 

1 


.Living With the River 
normal temperature pattern, 
this winter snow would be 
stored in the mountains in 
snowpacks or glaciers, which 
would melt more slowly in 
springtime. 

Another result of warming 
temperatures is that any existing 
mountain snow would 
melt earlier in the springtime 
and more of it would 
melt. This increased snow-
melt would also contribute 
water to late winter and early 

springtime flooding. Faster 

melting combined with less 
snowfall would cause snow


fields and glaciers to become 

noticeably smaller. 

Warming temperatures could 
also cause glacier meltwa-

Stillaguamish River, sea dike emergency repair. 

ter to pool at the foot of a 
glacier, forming a lake. As 
meltwater continues to accumulate 
in the lake, the lake 
could break through its wall 

causing an outburst flood, an 

often devastating event for 
people or structures downstream. 


What are the Effects 
of Development in the 
Watershed? 

In an ideal world, a river 
would have its broad natural 

floodplain where it could 

travel unimpeded, dropping 
its load of rock and sediment, 
constantly reshaping itself. 
But a naturally functioning 

river and floodplain are rare 
to find these days. 

We have altered rivers and 

floodplains in many ways, 

sometimes unknowingly and 
sometimes knowingly with 
the intent to control flooding. 
Across the country, 
we have built all types of 
buildings and infrastructure 

in floodplains, even schools 

and hospitals. Parking lots, 
highways and roofs have 

prevented floodwater from 

slowly soaking into the 
ground. When there is less 
ground area to absorb water, 

NANCy dEsChU 

rain and snowmelt are forced 

to find alternative ways to 

run to a river. This leads 
to tremendous amounts of 

rain and snowmelt flowing 

swiftly across the landscape, 
seeking a body of water. 

Floodplains and rivers have 
also been altered by mining, 
agriculture and forest practices 
through the removal of 
native vegetation, changes 
to channel width and depth, 
changes to ground permeability 
and alterations to the 
storage capacity of floodplains. 


Although many structures 
such as dikes, dams and 
levees have been built in 
watersheds to help prevent 

flood damage, often these 

structures fail. This can occur 
because the structures were 
originally under-designed 
or poorly designed; are old 
and not maintained; or do 
not function as expected. 

Another reason why flood 

control structures fail is that 
land use conditions upstream 
have changed, so now the 
river behaves very differently 
than when the structure was 
designed and built. 

Rivers are powerful and 
tend to have their own way 

during a flood. There is little 

we can do beforehand to 
control the river’s powerful 

path during an extreme flood 

event. Yet, we live and work 
in these watersheds throughout 
Western Washington. 
Though we can not reliably 

control a river’s flood, we can 

plan ahead for our safety and 
protect the economic and 
ecological values of our rivers. 
Perhaps the most impor


tant rule, first and foremost: 
Avoid building in a flood 

hazard area. 

What happens when a river floods?• 


1 


.Living With the River 
Stories of Western Washington Flood Hazards 


The Muddy Fork 

The Muddy Fork begins 

in snowfields and glaciers 
on the southern flank of 

Mount Rainier. Along its 
12-mile course, the Muddy 
Fork steeply descends 5,000 
vertical feet to meet the 
Cowlitz River at a point 4 
miles upstream of the town 
of Packwood. Because of its 
mountainous headwaters 
and glaciers, the Muddy Fork 
often carries tremendous 
loads of sediment and rock. 
Erosion, glacier-melting and 
sediment movement work to 
form the ever-shifting braided 
channels in the lower 
reach. In these braided areas 
the channel migration zone 

is very wide. The land cover 
in the Muddy Fork watershed 
is mostly dense forest. 

In November, 2006 a severe 

storm caused flooding on the 
Muddy Fork. Near its confluence 
with the Cowlitz River, 
the Muddy Fork jumped west 
to an old channel where it 

last flowed in the 1930’s. 

The new channel was cut 
3 to 5 feet deeper than the 
old channel. When the rapid 
channel change occurred, the 
water sheared a wide corridor 
through the riparian 
forest. Downed trees washed 
into the new channel and became 
embedded in the newly 
deposited sediment. 

Aerial views of the Muddy Fork-Cowlitz River confluence. 
1 


Stories of Western Washington Flood Hazards • 


During the 2006 flood, 

riverfront land was eroded 
and houses were damaged 
at two small communities at 

the confluence of the Muddy 

and Cowlitz. As of December, 
2006, the new Muddy 
Fork channel appeared to be 
relatively stable for now. 

The braided channels at the 

confluence of the Muddy 

Fork and the Cowlitz River 
will always be shifting to 
some degree within the 
channel migration zone 

– this is the natural behavior 
of these types of rivers. The 
challenge to these communities 
is to find innovative and 

safe ways to live alongside 
such dynamic rivers. 

Jones Creek Alluvial Fan 

The South Fork of the Nook-
sack River begins in the 
mountains on the south side 
of Mount Baker in Whatcom 

County. The river flows over 

70 miles east to Belling-
ham Bay. About 40 miles 
upstream from Bellingham 
Bay a small tributary, Jones 
Creek, steeply descends 2000 
vertical feet. Jones Creek 
watershed is only 2.6 square 
miles but it is dynamic and 
dangerous. 

The underlying 
rock in the Jones 
Creek watershed 
is brittle. 
It breaks easily 
and weathers 
quickly, making 
conditions in 
the watershed 
unstable. During 
severe storms, 

floodwater races 

down the steep 
canyon carrying 
rock, sediment 
and trees. When 
the creek exits 
the canyon, it 
opens on to a 
wider, more 
level area. At 
this point the raging floodwater 
suddenly slows down 
and drops its load. This area 
is the Jones Creek alluvial 
fan. 

On occasion, landslides from 
unstable slopes along Jones 
Creek dam the creek. In this 
situation, water can back up 
and then break through as an 

outburst flood. Earthquakes 

can also cause rockfall and 
subsequent outburst flooding. 
Whether flooding is 

caused by severe rain storms, 
landslides or earthquakes, 

Jones Creek alluvial fan zone (within triangle area) at 
South Fork Nooksack River. 



.Living With the River 
the result can be the same – a 
violent and destructive event. 
Where there is weak rock, a 
canyon and a sudden opening 
like the conditions in the 
Jones Creek watershed, there 
is potential danger. 

Unfortunately alluvial fan 
flooding is difficult to predict. 
When it happens, it 
occurs suddenly, often with 
no time for warning. The 

last significant debris flow 

on Jones Creek occurred in 
1983. There are also accounts 
of smaller events in 
1953 and 1990. 

The natural conditions in 
the Jones Creek watershed 
make it a dangerous place. 
Climate change predictions- 
increased rainfall at lower 

elevations in 
Western Washington 
– will 
only make this 
already dangerous 
situation 
worse. Wetter 
conditions 
would increase 
the likelihood 
of landslides, 
rockfalls and 

flooding in 

watersheds like 
Jones Creek. 

Ross Lake Dam, Upper Skagit River 


The difficulty of predicting 
alluvial fan floods combined 
with the likelihood of 
increased landslides in the 
future make alluvial fans 
a great hazard in Western 
Washington. 

There are currently 99 
houses on the Jones Creek 
alluvial fan. The community 
lives with this hazard and 
is considering options of 
how to reduce their risk to a 
highly destructive alluvial fan 

flood that could occur in the 

future. 

Skagit River 

The Skagit River is one of the 
longest and most flood-dangerous 
rivers in the Pacific 

Northwest. The river begins 
in British Columbia and 

flows southwest from the 

Cascades Range for 163 miles 
to its fertile outwash plain at 
Skagit Bay. Except for its steep 
headwaters, the Skagit River 
has a low gradient, dropping 
only 1,600 feet over its 
long journey to the sea. The 
large watershed covers 3,140 
square miles. In places, the 

lower Skagit River floodplain 

is over 20 miles wide. 


Stories of Western Washington Flood Hazards • 


The Lower Skagit River 
valley is a checkerboard of 
many land uses. The fertile 
lowlands provide some of the 
best farmland in the State. 
Urban towns, rural communities, 
major highways, 
a railroad line, wastewater 

plants, petroleum refineries 

and natural- gas pipelines 
can all be found in the Lower 
Skagit River valley. In the Upper 
Skagit watershed natural 
meadows, dense forests and 
glacier-fed tributary streams 
are predominant. 

Since the mid-1800s, when 
settlers reached the Skagit 
River valley, people have 
worked to tame and direct 

the river and its flooding. 

Dams, sea dikes and levees 
were built over time and are 
now common throughout the 
watershed. 

More than 110,000 people 
were living in Skagit County 
in 2006. Over 30% of the 
people live in the river’s 

floodplain and the wide 

Skagit delta. 

The Skagit has flooded more 

than 60 times in the past 
century. In October 2003, 

a flood crested at record 

levels in three communities, 

surging 14 
feet above 

flood stage. 

Nearly 4,000 
people had 
to evacuate 
their homes. 
Bridges, 
roads, and 
houses were 
damaged or 
destroyed. In 
November 
2006, major 
flooding returned 
to the 
Skagit River 
and similarly caused severe 
damage and loss of life. 

A 100-year flood event on the 

Skagit River would be dangerous 
and highly destructive. 
Interstate-5, railroads, 
water and power supplies 

and petroleum refineries 

could be damaged, leading 
to a shutdown of services. 
The economic impacts to the 
region would be severe. With 
this specter looming, Skagit 
County and local govern


ment officials are working to 

protect public facilities from 

future flood damage and 

educating the public about 
how to protect their homes 
and increase their personal 
safety. 

COUrTEsy Of skAGIT COUNTy PUBLIC WOrks dEPArTmENT 
Log Jam on the Skagit River near Sedrow Wooley, October 
2003 flood 



.Living With the River 
Historic imagery of Western Washington: 
http://riverhistory.ess.washington.edu 
Go to link: Data 


Learning About Your Watershed and River 

. Checklist 
To understand flooding 

in your watershed and to 

identify flood hazards at 

your location, it is helpful to 
know: the type of land cover 
and land uses in your watershed; 
your location in relation 
to the river channel and 

floodplain; and the specific 

geologic and hydrologic features 
at your location. When 
you review your watershed 
information along with your 

site specific information, you 

will be able to make better 
decisions on how to reduce 

your risk from flood hazards. 

There are four sources of 
information that may be very 
helpful before you begin 
your watershed and site investigation: 


Local Government Maps: 

Your local government may 
have zoning maps outlining 
flood hazard zones and critical 
hazard areas (For more 

information on flood maps, 
see “Sources of Information 

on Floods and Floodplains”). 
Talk to your county engineer 
to learn about maps and data 
that may be available on 

Shoreline Aerial Photos 
http://apps.ecy.wa.gov/shorephotos/ 


flood hazards in your county. 

Aerial photographs and 
satellite imagery: A series 
of images taken over decades 
can provide great information 
about your watershed 
and the changes that have 
taken place over time. You 
may observe features such as 
the historic natural meanders 

of the river; rock flow onto 

an alluvial fan; the effects of 
reservoir construction; new 
areas of pavement or build


ings in the floodplain; and 

changes in channel patterns 

after construction of flood 

control structures. Some 
historic imagery of Western 
Washington watersheds is 
available at University of 
Washington’s Puget Sound 
River History Project: 

http://riverhistory.ess.washington.edu 

Technical Studies: Local, 
State or Federal governments 

may have conducted flood or 
debris flow studies in your 

area. Although you may not 

find a hazard zone drawn 

on a government map, you 
may be able to gather useful 

flood hazard information 


Learning About Your Watershed and River • 


about your location from a Explore your neighborhood: 
flood or debris flow techni-Take a walk and get a sense 
cal study. (See “Sources of of the local topography and 
Information on Floods and vegetation. Take notes on the 
Floodplains”.) location of streams, wetlands 

and ponds; where mountains 

Locals’ Knowledge: Long-

and rolling hills are in rela


time residents whose fami


tion to your neighborhood; if 

lies have been in an area for 

there are rocky cliffs nearby; 

generations can often provide 

and the names of topograph


good local information on 

ic features that may tell you 

historic flood height, river 

something about the natural 

behavior during flood events, 

history and topographic fea


riverbank stability, and debris 

tures of your surroundings 

flow hazards. 

(for example, Canyon Creek). 

You can visit websites to learn about your watershed. Aerial 
photographs, topographic maps and watershed information 
are available at: 

EPA, “Surf Your Watershed” 

http://www.epa.gov/surf 

USGS, “Science in Your Watershed” 

http://water.usgs.gov/wsc/map_index.html 

Coastal Atlas: 

http://www.ecy.wa.gov/programs/sea/sma/atlas_home.html 

TerraServer: 

http://terraserver.microsoft.com 

Microsoft Live (oblique aerial photographs): 

http://maps.live.com 

USGS Geospatial data Layers: 

http://seamless.usgs.gov 


.Living With the River 
Learning About Your Watershed and River • 


. Investigate Your Watershed 

. 
Determine the boundary of your watershed. 
You may find a map of your watershed 
on a local, State or Federal government 
website that covers your area. An 
alternative is to use a USGS topographic 
map and outline your watershed. 
. 
Determine what types of land cover and 
land use are in your watershed. (For 
example: glacier, rocky mountain slope, 
forest, meadow, clear-cut, gravel mining, 
farmland, urban development.) A 
Washington land cover and land use map 
can be found online at: 
http://wdfw.wa.gov/wlm/gap/landcov.htm 

. 
Determine how much of your watershed 
is in a relatively natural condition versus 
how much is developed or disturbed. 
Information on changes in land use is 
available for most areas west of the Cascade 
Range on the Washington Department 
of Ecology: 
http://www.ecy.wa.gov/programs/sea/sma/atlas_home.html 

. 
Determine what river-control structures 
have been built in your watershed. (For 
example: dikes, levees, dams, floodwalls, 
channels hardened by concrete, reservoirs, 
water diversions) Determine what 
control structures located in your immediate 
vicinity may affect your section 
of the river. 

. 
Pinpoint on the watershed map where 
your home or business is located. 
. Investigate the Geologic and 
Hydrologic Features at Your 
Location 

Are you in an area where there may be a 

river flood hazard? 

. 
Is there a flowing river within a quarter 
mile? 

Observations: ______________________ 

. 
If you walk from the river towards your 
home or worksite, is there much change 
in elevation? Is it noticeably flat or do 
you sometimes climb uphill? 
Observations: ______________________ 

. 
If you walk from the river towards your 
home or worksite, do you cross wetlands, 
swales, or old, overgrown river 
channels? 
Observations: ______________________ 

. 
Does ice form in the river in winter? 
Have you seen ice on the river sometimes 
break-up, pile up and back up the 
river’s flow? 
Observations: ______________________ 

. 
When you dig in the upper layer of your 
ground, what material do you find? 

Well-formed organic soil? Or mainly 

sand, silt, gravel and cobbles? 

Observations: ______________________ 


Learning About Your Watershed and River • 


. 
Is there a gravel mining pit nearby in a 
river’s floodplain? 

Observations: ______________________ 

. 
How deep must you drill to reach the 
water table? 
Observations: ______________________ 

Are you in an area where there may be 

a debris flow or alluvial fan hazard? 

. 
Do you see mountain foothills, a canyon, 
a narrow valley or a steep slope close by 
when you look around the property? 
Observations: ______________________ 

. 
Is there a fan-shaped, low-lying hill that 
sits at the base of the canyon or narrow 
valley? 
Observations: ______________________ 

. 
Are there large boulders scattered 
amongst trees nearby? 
Observations: ______________________ 

. 
Are there trees on the hill-slope that may 
have been crushed by rockfalls or rock-
slides in the past? Are there trees that 
are growing at a leaning 
angle? Are there trees 
growing with a noticeable 
angle in their trunk? 
Observations: __________ 


. 
When you dig a garden or dig a post 
hole, do you encounter a lot of gravel 
and larger rounded cobble rock near the 
surface? 
Observations: ______________________ 

. 
Do you see large rounded rocks in road-
cuts nearby? 
Observations: ______________________ 

. 
Is there a gravel mining pit in the area 
located near the base of a narrow mountain 
valley or canyon? 
Observations: ______________________ 

After you have gathered general information 
about your watershed and specific information 
about your location, some answers about 

the type and degree of flood hazard may 
become clear to you. An important final step 
to understand your flood hazards is to hire 

a professional geologist, geomorphologist or 

hydrologist. Professionals in these fields can 

look at maps, aerial photographs, technical 
reports and then walk the property with you 

to identify and discuss your flood hazards. 

With this background information you can 
now plan carefully whether you should 
build or live in the area. If you already have 
a home or building in the area, you can still 
benefit greatly from gathering accurate watershed 
and local site information so you can 

reduce your risks to flood and river erosion 

hazards. 

2 


.Living With the River 
Sources of Information on Floods and Floodplains 


mArvIN NAUmAN - fEmA 
Drawing 
Boundaries of 
the Floodplain 

The word 

“floodplain” is 

used in different 
ways by different 
groups of 
people. To a hydrologist, 
floodplain 
refers to 
the extent of the 
lowland along a 

river that periodically floods 

within a given frequency of 

time. This definition is based 

on river science and statistics. 
A hydrologist uses this numerical 
approach to delineate 

a floodplain boundary. 

Local, State and Federal 
regulatory agencies may 

define a floodplain from the 

viewpoint of zoning and 
managing the growth of 
their community. Science 

and statistical definitions of 
floodplain may be adopted 

by regulatory agencies to 

determine a “regulatory 
floodplain” but the two types 
of floodplain definitions are 

not necessarily the same. 
A regulatory floodplain is of


ten not as wide as the river’s 

known natural floodplain. 

For example, science may 

numerically define a very 
broad 500-year floodplain 
(0.2% chance of flooding in 

any year), however, a local 
government may designate 

a regulatory floodplain for 

development that is much 
narrower. 

Structural versus 
Non-Structural Flood 
Control 

Society has historically 

tackled flood control by 

building structures with the 
intent to direct and tame the 
river. Levees, dams, reser


voirs, dikes, floodwalls, and 

riprapping riverbanks are a 
few examples. These structures 
sometimes fail, causing 
a loss of life and property. 
The economic costs of failed 

flood control structures can 

be enormous to local, State 
and Federal taxpayers. More 
recently the environmental 
damages to rivers and floodplains 
from these structures 
have become apparent, as 
have the costs related to 
health, safety and a community’s 
quality of life. 


Sources of Information on Floods and Floodplains • 


Because of the great economic 
and environmental costs of 
failed flood control structures, 
society is now moving 
towards ways of reducing the 

likelihood of flood damage 

through other approaches -
better community planning, 
zoning and public education. 
These planning, zoning and 
educational approaches are 

called “non-structural”. 

Examples of non-structural 
approaches to reduce the risk 

of flood damage include: 

• 
Regulations to prevent 
new development in the 
floodplain 

• 
Elevation of buildings 
that already exist in the 
floodplain 

• 
Relocation of houses out 
of flood prone areas 

• 
Government purchase 
of houses in dangerous 
flood prone areas 

• 
Restoration of riverine 
wetlands to increase 
floodwater storage 

capacity 

• 
Control and detention of 
stormwater runoff from 
developed areas 
• 
Preservation of open 
space that supports natural 
river functions 

• 
Stricter zoning and 
building codes for new 
subdivisions 
• 
Education program for 
all community members 
on how to reduce flood 

hazards 

One of the most important things 

you can do to reduce your flood 

risk is to learn about your local and 

State floodplain programs. Listed 

below are sources of information on 

floodplain policies and regulations. 

Learning about these programs may 
save you a lot of money and heartache 
in the long run. 

Floodplain maps are produced 
by several government 
agencies. Some of 
these maps are geomorphic 

floodplain maps showing 

the full natural range of the 

floodplain while others are 
“regulatory floodplain” maps 

that are generally narrower 

than the natural floodplain 

delineation. 

A type of floodplain map is 

the Flood Insurance Rate 
Map (FIRM). FIRMs de


2 


.Living With the River 
Example of a Flood Insurance Rate Map. 


lineate flood 

hazards including 
the Special Flood 
Hazard Areas. 
A Special Flood 
Hazard Area is 
an area where 
there is a 1-in100 
chance that a 

certain size flood 

will occur in any 
year. (This type 

of flood is also 

often referred to 

as the 100-year flood or the 
1% flood). A Flood Insurance 
Study is produced along 
with each Flood Insurance 
Rate Map. The study contains 
information about flood his-

A Note About Flood Map Accuracy: 

Check the date when the flood map for your area was 
produced. Some maps may be decades old and produced 
with primitive technology compared to what is available 
today. There may be much better information now which 
could change flood predictions in your area. Significant land 
cover and land use changes may have occurred since your 
watershed was mapped -more highways and parking lots 
paved, new river control structures built, forest lands cleared. 
In addition to substantial land use changes that have occurred 
over decades, warming temperatures associated with climate 
change can affect the behavior of rivers. As discussed in the 
section “What Happens When a River Floods”, warming 
temperatures will likely increase the already heavy rainfall 
and frequent wintertime flooding in Western Washington. 

tory in a community and the 
engineering methods used to 

produce the flood map. 

FIRMs and Flood Insurance 
Studies are produced by the 
Federal Emergency Management 
Agency (FEMA) 

National Flood Insurance 
Program (NFIP). The 

NFIP sells flood insurance to 

property owners in 20,000 
communities in the U.S. who 
have adopted State and local 
floodplain management regulations. 
If your community 
participates in this program, 
FIRMs can be found on the 
web at FEMA’s Map Service 
Center (http://msc.fema.gov) and 

at your county’s floodplain 
management office. Some 

towns and counties, such as 
King County, produce their 

own detailed flood hazard 

maps which in turn are used 
by the Federal government 
to update the FIRMs for that 
county. 

Because homeowners’ insurance 
does not cover damage 

from floods, National Flood 

Insurance is essential to pro


tect property in flood prone 

areas. Anyone at the slight


est risk of flooding should 

purchase NFIP insurance. 
Information on NFIP can be 

2 


Sources of Information on Floods and Floodplains • 


found at FloodSmart.gov or 
at Washington State Department 
of Ecology regional 

offices that serve your area 

(http://www.ecy.wa.gov). 

Channel Migration Zone 
(CZM) Maps depict the area 
within which a river is likely 
to move horizontally over a 

defined period of time. In 

some rivers this can be a very 
wide distance, in other rivers 
that are more constricted 
by adjacent landforms, the 
migration zone may be 
relatively narrow. Channel 
migration zones are deter


mined through field studies 

and study of aerial photography 
and satellite images 
taken over decades. Studies 
suggest images of a river 
over the past 100 years can 
provide a meaningful picture 
of a river’s CMZ. 

As of 2004, seven counties 
in Washington have been 
actively determining and 
mapping channel migration 
zones. In 1999, King County 
enacted a Public Rule to 
regulate land use where CMZ 
maps have been completed. 
As of 2005, King County 
had mapped 49 river miles 
of CZMs. In those 49 miles 
alone, there were 389 struc-

Diagram of a channel migration towards the 100-year floodplain 
boundary 


tures, with a total assessed 
value of $179,228,513 (2006 
King County Flood Hazard 
Management Plan). 

Communities and tribes 
can chose to participate in 

a flood-prevention program 

called the Community 
Rating System (CRS). The 
community adopts practices 
and activities that go beyond 
the minimum requirements 
of the National Flood Insurance 
Program. There are 
four types of activities under 
which a community can 
receive CRS credits: map


ping and regulations; flood 

damage reduction; public 

information; and flood 

preparedness. Examples of 


.Living With the River 
activities where credit might 
be awarded to a community 

include acquisition of flood 

prone buildings and strict 

zoning regulations for flood 

hazard areas. 

A community is assigned 
to one of 10 classes based 
on their type and level of 

flood-prevention activities. 

The more a community 
demonstrates good practices, 
the higher the class rating 
they are assigned. Each time 
a community rises in its 

classification, there is a 5% 
reduction in flood insurance 
rates for policy holders 
in that jurisdiction. In 
2005 King County and Pierce 
County received two of the 
highest ratings in the nation. 
The rating for King County 
will be upgraded even further 
to Class 2 in 2007. The 
Lower Elwah Tribe is one of 
two tribes in the nation who 
actively participate in the 
Community Rating System. 

Hazard Mitigation Plans 

are written by local, State 
and Tribal governments 
to describe all the types of 

hazards, including floods, 

in their areas. The plans also 
describe the risk of the hazards 
and strategies to reduce 

the risks through community 
planning and projects. The 
intention of hazard mitigation 
planning is to break the 
cycle of repeated damages 
in the same area or to the 
same structures. The State 
of Washington has a Hazard 
Mitigation Plan which is updated 
every three years. Your 
county or local community 

may have a specific hazard 

mitigation plan for your area. 
It is important to have an updated 
hazard mitigation plan 
to qualify for certain types of 
mitigation grants. 

Comprehensive Flood Hazard 
Management Plans are 
prepared by local and Tribal 
governments in Washington. 
These plans describe in 

detail the flood threats to 

the community and how the 
community could prevent 
flood damage. Public participation 
in the development 
of the plan is required by 
law. The plan must address 
certain topics including: local 
topography and hydrology 

related to flooding; history of 
flooding in the area; current 
flood problems; alternatives 
for reducing flood effects; 

environmental impacts of the 
alternatives; and a priority 


Sources of Information on Floods and Floodplains • 


for recommended actions. 
A community or tribe is 
required to have a Comprehensive 
Flood Hazard Management 
Plan to be eligible 

to apply for flood control 

assistance grants through the 
Washington State Department 
of Ecology. 

The Washington Shoreline 
Management Act was 
passed in 1972 to prevent 

“harm associated with an 

uncoordinated, piecemeal 
development of the State’s 
shorelines” (http://www.dnr. 
wa.gov/htdocs/aqr/shoreline/index. 
html). This Act directs local 
communities to develop 
plans for all their shorelines, 
including shorelines of navigable 
rivers. These plans are 
reviewed by the Washington 
Department of Ecology. 

Two directives of the Shoreline 
Management Act are particularly 
applicable to river 

shorelines and floodplains: 

1) ensure environmental protection 
and 2) foster water-
dependent uses. Protection 
of floodplains from unregulated 
development is one way 
to ensure environmental 
protection. Recognizing 

floodplains as vital areas for 
floodwater storage and for 

GrAPhIC AdAPTEd frOm JIm O’CONNOr 
Channel migration over 120 years, Quinault River, Olympic Peninsula. 


river channel migration is an 
example of water-dependent 
uses. 

The Shoreline Management 
Act also requires communi


ties to generally define the 

channel migration zone in 
their area and defines activities 
that are not allowed in 
the zone. 

The Washington State 
Growth Management 
Act was passed in 1990 to 
increase local planning and 
to address regional planning 
issues as the State’s population 
rapidly increases. The 
Act was amended in 1995 to 


.Living With the River 
require protection of “critical 

areas”. Critical areas include: 

designated fish and wildlife 

habitat; wetlands; hazardous 
geologic areas; aquifer 
recharge areas; and fre


quently-flooded areas. When 

the Growth Management Act 

listed “frequently-flooded 

areas” as a type of critical 
area, the Act recognized that 

protecting floodplains and 

managing growth are im


portant ways to reduce flood 

damages. 

Sometimes when one type of 
critical area is protected, such 

as stream buffers for fish 
habitat, frequently-flooded 

COUrTEsy Of sEATTLE mUNICIPAL ArChIvEs Aerial view of the Skagit River near Concrete, showing a patchwork of land 
cover and land use. 


areas are also protected. In 
many cases local ordinances 
also serve to protect these 
same critical areas. 

County and municipal zon


ing and floodplain codes are 
in effect for Washington’s 
39 counties and for 143 
municipalities in the State. 
These codes set regulations 
for activities such as building 
and construction; subdivision 
allowances and restrictions; 

special flood hazard areas; 

setback requirements; and 
riparian landscaping. These 
county and municipal codes 
can be found on the web at 
the Municipal Research and 

Services Center for 
Washington (http://www. 
mrsc.org/codes.aspx#county). 

The International 
Building Code (IBC), 
published in 2000, has 
been adopted by all 
Washington State communities. 
Part of the 
code strives to reduce 
flood damage to buildings 
by integrating 
building design, building 
safety and floodplain 
management. 
The International 


Sources of Information on Floods and Floodplains • 


Building Codes Council, the 
American Society of Civil 
Engineers and the Federal 
Emergency Management 
Agency worked cooperatively 
on these flooding provisions 
to help communities 

meet floodplain management 

regulations as required by 
the National Flood Insurance 
Program. 

The Washington Shoreline Management Act, passed in 1971, 
can be found on the Washington Department of Ecology 
website. Sections of the Act and its amendments have 
requirements specific to rivers and streams: 

Critical Areas: Requires that Critical Areas, which includes 
aquatic habitat, will be managed and provided a level of 
protection WAC 173-26-221(2) 

Flood Hazard Reduction: Limits development that would 
affect channel migration zones; describes specific flood 
hazard prevention; generally prohibits new dikes and levees 
in channel migration zone WAC 173-26-221(3) 

Shoreline Modifications: Requires that fill design and 
location be placed so as to protect ecological functions of 
the shoreline; requires a conditional use permit for disposal 
of dredge material within channel migration zone; requires 
a conditional use permit for mining in the channel migration 
zone WAC 173-26-231(3) and WAC 173-26-241(3) 


.Living With the River 
How to Reduce Your Flood Hazard Risk 


Many people innocently buy, 
build or rent structures that 

are located in flood prone 
areas, not aware of the flood 

hazard around them. 

If you decide to buy, build or 
rent a structure, remember 

these five important rules: 

1. 
Learn about the flood 
hazards and flood history 
in your area 

2. 
Stay out of the currently 
defined flood hazard area

3. 
Elevate the structure off 
the ground 
4. 
Build with a flood-proofing 
design and materials 
5. 
Consider how climate 
change may affect your 
watershed in the future 
If you already own a build


ing in a flood prone area, 

there are still ways to reduce 

your flood hazard. Some of 

the following practices may 
be required by your municipal 
or county codes. 

Elevate 

Raising a building so that 

the lowest floor is above the 
typical flood level is a good 
way to reduce flood risk. 
The building may still flood 

in extreme events but much 
less so than before it was 
elevated. Learn the charac


teristics of typical floods in 

your area before you elevate 

a building. Important flood 

characteristics to understand 
include: how often flooding 
occurs; the depth and 

velocity of floodwaters; how 
fast floodwaters rise and 

fall; and the type of debris 
that might be carried by the 

flood. Ask yourself if you 

want to elevate your building 
to protect against the 1-in


100 chance flood, 1-in-500 
chance flood, or some other 
level of flooding. Once you 

have weighed these factors, 
discuss your options with 
your local building authorities 
and licensed contractor. 

Relocate 

Moving your house or build


ing out of the flood hazard 

area provides the greatest 

protection from flooding. It 

is, however, one of the most 
expensive options. If you are 


How to Reduce Your Flood Hazard Risk • 


planning to move a building, 
you need to evaluate its 
size, shape and its condition; 
routes available for the move; 
natural hazards at the new 
location; public utility connections 
at the new site; local 
zoning ordinances; and what 
work is needed to restore the 
old site to meet your local 
regulations. 

Demolish and Rebuild 

Demolition is sometimes the 
best and easiest option when 
a building has been severely 

damaged by floods. If the 

house is in the regulatory 
floodplain, trying to salvage 
it can be an expensive 
and complicated process. 

Rebuilding a new flood-

safe building on the same 
property is one option. The 
better option, though more 
expensive, is to rebuild on 

a different, more flood-safe 

property. 

Land and Vegetation 
Management 

Flood risk can be reduced 
through careful land management. 
If you remove 
impervious ground cover, 
such as asphalt and concrete, 
the natural ground will 

become available to absorb 

floodwater. Restoration of 

wetlands that were damaged 
or destroyed during building 
construction is another way 
to reduce flood risk. Wetland 
vegetation and soils have 
the ability to absorb and hold 
water. Restoration of wetland 
plants and native, hardy 
vegetation can also slow the 

velocity of floodwaters and 

act to capture debris that is 

moving with the floodwater. 

Build Small Flood-
Protection Structures 

Small flood-protection 

structures on a property, if 
properly designed and built, 

can reduce flood risk. These 

small structures can redi


rect floodwater and increase 

storage capacity. Examples 

of small flood-protection 

structures include: water 
detention ponds; diversion-
walls around a building; and 
drainage paths and culverts 

to guide floodwaters around 

and away from buildings. 
Check with your municipal 

and county code officials 

before building any of these 
small structures in to learn 
about any restrictions. 

Elevate 


Relocate 


Demolish 


Rebuild 


3 


.Living With the River 
Anchor Moveable Objects 

Floodwaters can lift and 
carry objects such as fuel 
tanks, storage sheds, playground 
equipment and trailers. 
Securing these objects is 
important not only to save 
the object but to prevent the 
object from ramming walls 
and causing severe building 
damage. A fuel spill is another 
possible hazard when 
an unanchored fuel tank is 
knocked over or shifted by a 

flood. Even a buried fuel tank 

can be pushed to the surface 
by the buoyant effect of saturated 
soil. A moveable object 
can be anchored by attaching 
it to a large concrete slab or 
by running metal straps over 
the object and attaching the 
straps to ground anchors. 

Remodel with Flood 
Resistant Materials 

You can reduce flood damage 
and make flood cleanup 
easier by using flood-resistant 
building materials 
when you remodel or put 
an addition on your building. 
Building materials are 

considered flood-resistant 

if they can withstand direct 

contact with flood waters 

for at least 72 hours without 

being significantly damaged. 

Flood-resistant materials can 

be used for walls, floors and 

other parts of a building. 

Commonly available flood-

resistant materials include: 
ceramic tile, clay tile, terrazzo 
tile, vinyl tile, rubber tile, 
concrete, brick, glass block, 
stone, pressure-treated wood, 
marine grade plywood, naturally 
decay-resistant lumber, 
cement board, foam insulation 
and metal doors. 

Flood-proof the Building 

One way to protect a building 
and its contents from 

flood damage is to seal the 
building so that floodwater 

cannot enter. Examples of 

flood-proofing measures 

include: application of a 
waterproof coating or membrane 
to the exterior walls 
of a building; installation of 
watertight shields over doors, 
windows, and other openings; 
installation of a sump 
pump and foundation drain 
system; and strengthening 
walls so they can withstand 

the pressures of floodwaters 

and impacts of rocks, trees 
and building debris en


trained in the flood. 


How to Reduce Your Flood Hazard Risk • 


Raise Electrical Units 

Electrical, heating, ventilation, 
plumbing and air conditioning 
units and wiring 
can be damaged or destroyed 
if they are inundated even 
for a short time. There is 

also a fire danger associated 
with short circuits in flooded 

electrical systems. Elevating 
electrical components at least 
1 foot above the 1-in-100chance 
flood level will significantly 
reduce your flood 
hazard. An added benefit 

to raising electrical units is 
that they might still function 

immediately after a flood, 

helping you to recover from 

other flood damages on your 

property. A less effective way 

of protecting electrical components 
is to leave the unit in 

place and build a floodwall 

with waterproof-membrane 
around the unit. 

Install Sewer Backflow 
Valves 

Flooding can cause sewage to 
back up through a building’s 

drain pipes and flow into 

the building. In addition 

to being a source of flood 

damage, sewage backup is 
also a serious health hazard. 
One way to protect your 
house or business from 
sewage backup is to install 

backflow valves. These valves 

are designed to block drain 
pipes temporarily, preventing 

JOsEf kUNzLEr 
Skagit River at floodstage, Mount Vernon, November 2006. 

3 


.Living With the River 
3 

flow into the building. There 
are several types of backflow 

valves on the market. 

Protect Wells from 
Contamination 

Floodwater often carries 
contaminants like sewage, 
animal waste, gasoline, 
and pesticides. A well can 
become contaminated by 
floodwater and these effects 
can last long after the 

flood has receded. A licensed 

well-drilling contractor can 
inspect your well and suggest 
ways to reduce the possibility 
of well contamination 

during floods. These changes 

might include: extending the 
well casing above the high


est known flood elevation; 

ground level by surrounding 
the well casing at ground 
level with a watertight seal; 
placing grout between the 
casing and the sides of 
the bore hole; installing a 

backflow valve in the water 

line; protecting well-pump 

electrical controls from flood 

water; or drilling a new well 
on higher ground. 

Build Flood Passageways 

Flood passageways are features 
that are intentionally 

built to allow floodwaters 

to pass through uninhabited 
areas of a building. When 

floodwaters are allowed to 

pass, pressure on the vertical 
surfaces of the building is 
released and the building is 
more likely to remain standing. 
Openings equipped with 
screens, louvers, breakaway 
walls, latticework or trellises 
on the ground level are examples 
of passageways where 
floodwaters can automatically 
enter and exit. 


Summary • 


Summary 

Rivers are in a constant state of change. Their 
powerful waters are always seeking balance - 
adjusting steepness, changing width and depth, 
picking up and dropping rock and sediment, re


shaping its channels and floodplain. The intent 
of this booklet, “Living With the River”, is to 

raise awareness about river behavior in Western 
Washington and to provide ideas on how to protect 
your property and yourself from the damag


ing effects of floods. 

Learn About Your Watershed and River 

An important step to reducing your flood hazard 
and increasing your personal safety is to learn about your 
watershed, the nearby river and your location within the watershed. 
There are a few basic hydrology concepts that can help 
make your river a more familiar, interesting and perhaps, more 
predictable, place. Understanding river behavior and potential 

flooding can help you prepare your land and buildings before a 
flood someday races through your area. 

Conduct a Flood Hazard Inventory of Your Land and 
Buildings 

It is fairly easy to gather information that can help you under


stand the flood hazards in your watershed and the more specific 

hazards near your land and buildings. After gathering this information, 
you may choose to consult with a professional geologist, 

geomorphologist or hydrologist to expand or interpret this flood 

hazard information. 

Learn About Programs Available to Help Reduce Flood 
Risk 

There are several local, State and Federal flood programs that 

provide guidance and sometimes funding to help you reduce 

NANCy dEsChU 
Lower Elwah River on north end of Olympic Peninsula. 



.Living With the River 
your flood hazards. After you have conducted your personal 
flood hazard inventory, you can then look into these government 

programs that may be able to help you carry out your plans for 

flood protection. 

Act to Reduce Your Flood Risk 

Once you have all your background information gathered, it is 

time to take action to reduce your risk to flood hazards. Your 
local zoning and code officials can provide useful information as 

you begin your work. If you engage contractors, be sure they are 
licensed and reputable. 

The most important rule to follow to reduce your risk of flood 
damage is simple: stay out of flood prone areas. If you are already 
in a flood prone area, there are still many ways to reduce the 
likelihood that you will face serious damages from flooding. 

It makes sense to reduce your risk to flooding. The next time a 
flood comes your way your building and property will be less 

vulnerable to damage and, importantly, you will be safer from 

the harm of destructive flooding. 


Glossary • 


Glossary 

Alluvial fan: 

A fan-shaped deposit of rock 
and sediment that forms at 
the base of a mountain range 
when a fast mountain stream 

flows out of the mountains to 

a less steep valley slope and 
suddenly slows, spreads out 
and drops its load; if two or 
more alluvial fans begin to 
overlap, it is referred to as a 
compound alluvial fan 

Aspect: 

The direction which a mountain 
slope faces 

Braided river: 

A river made of a network 
of small constantly shifting 
channels that are separated 
by shoals, bars and islands; 
braided streams commonly 
occur where a valley gradient 

significantly decreases and 

the river deposits its sediment 
load 

Channel migration: 

The lateral movement of a 
river channel within a valley 
due to the continual process 
of land and channel erosion 
and deposition of sediment 
and rock 

Channel migration zone 
(CMZ): 

The area within which a 
river channel moves laterally 
over time 

Channel capacity: 

The maximum flow of water 

that a channel is capable of 
carrying before its banks are 
overtopped 

Debris flow: 

A mixture of water-saturated 

earth that flows downslope, 

often very rapidly; debris 

flows can be destructive 

to buildings and deadly to 

people in the flow path 

Evaporation: 

The process of water moving 
from a liquid to a vapor state; 
evaporation includes vaporization 
from water body 
surfaces, land surfaces, and 

snow fields; “evaporation” 

does not include the vaporization 
of water released 
from the surface of vegetation 
(see transpiration) 

Floodplain: 

The relatively flat lowland 

that borders a river, stream 
or lake (formed under the 

current climate regime) 
which is usually dry but is 
subject to flooding; the sediment 
and rock materials on a 
floodplain are actually deposits 
from earlier floods 

Geomorphologist: 

A person who studies the 
topography, geology and 
geologic features of the surface 
of the Earth 

Gradient: 

A measure of the slope of 
the water surface of a river 
per unit distance; usually 
measured as a ratio of feet of 
change in water slope over 
feet of change of river length 
from a point upstream to a 
point downstream 

Groundwater: 

Water that is located beneath 
ground in soil pore spaces, 
among pebbles, cobbles and 
boulders, and in fractures of 
geologic formations 

Headwaters: 

The source (or sources) of 
a river or stream; headwater 
sources include lakes, 
springs, wetlands, glaciers or 
groundwater seeps 


.Living With the River 
Historic floodplain: 

The full width of a river’s lateral 
movement over geologic 
time 

Hydrologist: 

A scientist who studies the 
properties, distribution, and 
circulation of water on and 
below the earth’s surface and 
in the atmosphere 

Land Cover: 

That which physically covers 
the surface of the earth at a 
specific place; forests, glaciers, 
water surfaces, sandy 
beaches, irrigated croplands 
and major asphalt highways 
are examples of land cover; 
land cover is determined 

through field surveys and 

analysis of remote sensing 
imagery 

Land Use: 

A description of how people 
utilize land and the socioeconomic 
activity associated 
with how they utilize it; urban 
housing and agricultural 
are two common land uses 

Mitigation: 

Actions taken to reduce or 
eliminate the risk of a hazard 

such as flooding; mitigation 

actions attempt to prevent 

flood hazards from developing 
into disasters, or to 

reduce the effects of flooding 

when it occurs 

Meandering river: 

A river with distinct series of 
alternating bends that forms 

a snaking pattern as it flows 
through a wide valley or flat 

plain; the formation and the 
shape of the bends in a meandering 
stream are a result 
of erosion and deposition of 
sediment and rock 

Oxbow lake: 

The type of lake that is 
formed when a wide river 
meander is cut off from the 

main flow of the river 

Outburst flood: 

The abrupt, and often tremendous, 
release of water 
from a river or lake that has 
been blocked by a glacier, 
landslide, logjam, moraine or 
similar feature (also know as 

outbreak flood) 

Permeability: 

The ability of geologic material 
to transmit water 

Porosity: 

The ratio, expressed as a 
fraction or percentage, of the 
volume of the void spaces 

(pores) of a material (such as 
a rock, soil layer or sedimentary 
stratum) to the total 
volume of its mass 

Riparian zone: 

The interface between the 

land and a body of flowing 

surface water; vegetation 
along these river margins is 
referred to as riparian vegetation 


Riprap: 

A pile or layer of stones 
intended to prevent erosion, 
scour, or sloughing of an 
embankment, in efforts to 
protect or stabilize a structure 


Risk: 

The identification of a hazard 

and the mathematical analysis 
of the chances of that 
hazard occurring 

Runoff: 

Water from rainfall or melt


ing snow that flows across 

the surface of the ground but 

does not infiltrate into the 

ground 

Scree: 

Loose rock covering a slope, 
commonly found at the base 
of a cliff or steep incline 


Sediment: 

Particulate that is transported 

by flowing water and may 

be deposited on the riverbed 
during low flows and re-suspended 
in higher flows 

Sinuosity: 

A measure of the degree of 
meandering of a river; it is 
calculated as the ratio of the 
length of a river to the length 
of the river valley through 

which it flows 

Transpiration: 

The process where water 
absorbed by a plant (usually 
through its roots) is evaporated 
into the atmosphere from 
the surface of the plant; in 
plants with leaves, transpiration 
occurs through pores in 
the leaves 

Topography: 

The shape of the surface of 
an area of land including its 
relief and positions of natural 
and manmade features 

Watershed: 

A region of land, separated 
from adjacent basins by a 
ridge or mountain, that 
captures rain, snowmelt 
and glacier-melt and feeds 
it to a particular river; a 

watershed also includes the 
underground area that feeds 
groundwater to the river; 
a groundwater watershed, 
however, may differ in 
surface area from the surface-
water watershed that feeds 
same river 

Glossary • 



.Living With the River 
Recommended Reading 


Association of State Floodplain Managers and Interagency Floodplain Management Taskforce. 

1996. Addressing your Community’s Flood Problems: A Guide for Elected Officials. Prepared 

by The Floodplain Management Group, J. Wright, Knoxville, TN 54 pp 

Department of Ecology, State of Washington. March 2004. Floodplain Management in the State 
of Washington. Publication # 04-06-016. 12 pp Available at http://www.ecy.wa.gov/pubs.shtm 

Federal Emergency Management Agency. Floodplain Management: The National Flood Insurance 
Program. Available at http://online.fema.net/fima.htm 

Federal Emergency Management Agency. State and Local Mitigation Planning: Building Stronger 
and Safer. Available at http://online.fema.net/fima.htm 

Gori, P., C. Driedger and S. Randall. U.S. Geological Survey. 1999. Learning to Live with Geologic 
and Hydrologic Hazards. WRI Report 99-4182. 4pp Available at http: wa.water.usgs.gov 

Kresch, D. and K. Dinicola, U.S. Geological Survey. 1996. What Causes Floods in Washington 
State? Fact Sheet 228-96. 2 pp Available at http://wa.water.usgs.gov 

Leopold, L. B. 1994. A View of the River. Harvard University Press, Cambridge, MA, 298 pp 

Leopold, L.B., G. Wolman and J.P. Miller. 1995. Fluvial Processes in Geomorphology. Dover 
Publications, Inc., New York. 522 pp 

Rapp, C.F. and T.B. Abbe. 2003. A Framework for Delineating Channel Migration Zones State of 
Washington Department of Ecology Publication #03-06-027. 135 pp 
Available at http://www.ecy.wa.gov/pubs.shtm 

Stanley, S., J. Brown and S. Grigsby. 2005. Protecting Aquatic Ecosystems: A Guide for Puget 
Sound Planners to Understand Watershed Processes. State of Washington Department of Ecology 
Publication #05-06-027. 160 pp Available at http://www.ecy.wa.gov/pubs.shtm 

Task Force on the Natural and Beneficial Functions of the Floodplain. 2002. The Natural and 
Beneficial Functions of Floodplains: Reducing Flood Losses By Protecting and Restoring the 

Floodplain Environment. A Report for Congress. 84 pp