SUBSECTION-SECTION 4M.8

SUBSECTION-SECTION 4M.8

PUYALLUP TRIBE ALL HAZARD MITIGATION PLAN

FLOOD HAZARD

Table of Contents

IDENTIFICATION DESCRIPTION ................................................................................2

DEFINITION .............................................................................................................2

TYPES ....................................................................................................................2

PROFILE ...................................................................................................................3

LOCATION AND EXTENT ...............................................................................................3

OCCURRENCES ........................................................................................................ 14

VULNERABILITY ....................................................................................................... 17

IMPACTS ............................................................................................................... 19

RESOURCE DIRECTORY .......................................................................................... 28

REGIONAL ............................................................................................................. 28

NATIONAL ............................................................................................................. 28

ENDNOTES ............................................................................................................. 30

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Identification Description

Definition1

A flood is a general and temporary condition of partial or complete inundation of normally dry

land areas from:







The overflow of inland or tidal waters,

The unusual and rapid accumulation or runoff of surface waters from any source, or

Mudflows or the sudden collapse of shoreline land, see the Volcanic Hazard and

Landslide Sections or the Chapters of the Pierce County Hazard Identification and Risk

Assessment 2015.

Pierce County’s flood hazards are divided into two types: riverine and urban

stream/groundwater.2 These two types of flood hazards affect the Planning Area also.

Types3

Riverine Flood Hazard

Riverine flooding results from heavy and prolonged rainfall and may include substantial

snowmelt if, there is rise in freezing levels after a measurable snowfall. Flooding of this type can

last several days after the storm.

The most severe flooding on the Planning Area’s rivers and major streams results from low- to

moderate-elevation (1,000 to 3,800 feet) snowmelt runoff occurring in conjunction with a

prolonged moderate- to high-intensity rainfall event. This is commonly referred to as a rain-onsnow event. Accumulating snowfall usually occurs for brief periods (one to three days) and can

be followed by accelerated warming from warm Pacific frontal storm systems arriving from the

tropics and containing a significant amount of precipitation. Rain-on-snow events typically result

in sharp rise in river flow that can yield flood stages and can last for several days. The rise in

peak flow can occur quickly, making consistent monitoring of river flow gauges essential during

the flood season.

Urban Stream/Groundwater Flood Hazard

The second category of flood hazard in Pierce County occurs when runoff exceeds the

conveyance capacity of natural and manmade drainage systems. Surface water runoff volumes in

urban stream channels, closed depressions (potholes),4 roadway ditches, culverts and conveyance

pipe systems typically exceed the available conveyance and storage capacity of such systems

during the fall, winter, and early spring wet seasons. This typically occurs with moderate- to

high-intensity storms that can last for several days or occur in succession over a period of weeks.

These events are characterized as rainfall of three inches or more in a 24-hour period. Urban area

flooding generally occurs gradually and allows time for property owners to identify an

impending flood situation and prepare for it. In the some areas, however, flooding can occur

rapidly and may leave little time for preparation.

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In some cases, debris can accumulate in stormwater collection systems and reduce the capacity

of the system to convey flow. Such a reduction in capacity can lead to more frequent flooding

events. Regular maintenance, however, can ensure that the stormwater systems function as

designed.

Urban stream flooding is exacerbated by rain-on-snow events. During the winter months, these

events usually result in widespread flooding along streets, streams, ditches, culvert pipe systems,

and storm drains. Conditions in the basins can change rapidly and the onset of flooding can occur

at an accelerated rate.

Groundwater flooding is associated with a large amount of cumulative rain over several storms

or consecutive rainy seasons. High groundwater may occur weeks after the last significant

rainfall and can also shift locations as groundwater levels change throughout the region. This

type of flooding may last for several weeks or even months.

Profile

Location and Extent

Flooding directly affects less than 20% of the Pierce County and 21.3% of the Planning Area.

The location of the flooding is categorized by the five major watersheds in Pierce County: the

Puyallup/White River Watershed, the Nisqually River Watershed, the Chambers/Clover Creek

Watershed, the Kitsap Watershed, and the Cowlitz Watershed, see Map 4.8-1.

Map 4.8-2 illustrates the location and extent of the flood hazard for the Planning Area. The map

shows the extent of the 100-yr and 500-yr flooding areas based on the flood hazard areas from

the Flood Insurance Rate Maps (FIRMs). Maps 4.8-7 to 4.8-9 further illustrates in greater detail

the Tribal Trust Lands that would be affected during a flood. These maps will provide a more

comprehensive opportunity to address those properties within the identified flood hazard area for

possible future mitigation efforts as funding becomes available.

Areas of repetitive flood loss further illustrate the extent of the flood hazard, see Map 4.8-3.

Some individual jurisdictions may also have repetitive loss properties that are not marked on this

map. This analysis focuses primarily on those watersheds that contain these repetitive flood loss

areas—the Puyallup/White River Watershed, the Nisqually Watershed, and the Chambers/Clover

Creek Watershed—and more specifically, the basins in which the repetitive flood loss areas are

located. Also included is a description of each type of flooding that occurs.

Pierce County’s two categories of flood hazards are described in more detail below including

their location and extent.

Riverine Flood Hazard

The riverine flood hazard typically arises from the Puyallup, White, Carbon, Nisqually, South

Prairie Creek, Wilkeson Creek, and Mashel Rivers.

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Map 4.8-1 Pierce County Watersheds

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Map 4.8-2 Puyallup Tribe of Indians Flood Hazard

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Map 4.8-3 Pierce County Repetitive Loss Areas

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The White and Nisqually Rivers are regulated by dams that provide some flood control.

However, during major events, neither of these has been able to prevent all flooding downstream

from their facilities.

White River flows are regulated by the U.S. Army Corps of Engineers at Mud Mountain Dam.

Mud Mountain Dam is operated solely as a flood control facility. The dam’s primary goal is to

provide flood control to the lower reaches of the Puyallup River, from River Mile 10.3

downstream through the Port of Tacoma to Commencement Bay. On the other hand, some flood

control benefits can be seen within the entire reach of the White River downstream of the dam.

As the water level behind the dam increases during major storms, and if there is no break in the

amount of water entering the dam, the Army Corps of Engineers has at times had to increase

releases to the point that some portions of the White/Stuck River have flooded. This was the

situation in January 2009 when the Town of Pacific on the Pierce/King County border flooded.

Much of this was due to deposited silt and gravel having raised the river bed. The increased flow

then overtopped the levees flooding large portions of Pacific. While the Puyallup River has been

impacted, the result has not been nearly as severe.

The middle and upper reaches of the Puyallup River and many of its tributaries constitute a

largely unregulated and naturally flowing river system. Rapid changes in the quantity of water

entering the system, either from heavy rain throughout the basin or rapid snow melt, usually

from warm rain on snow, can change the downstream flood potential in a very short time.

Because these rapid changes occur in remote areas within the basin, monitoring and forecasting,

rain and rain-on-snow events are critical.

The lower Nisqually River is regulated by Tacoma City Light’s Alder and La Grande Dams.5

Neither dam is managed as a flood control facility. Their main purpose is as power generating

facilities. As such they are managed to maximize power generation and therefore, flood control

benefits from them are reduced. However, during periods when there is a threat of flooding

Tacoma City Light does take into account the flood potential and will modify the flow of water

released from the dams.

Despite the regulation from the dams, flooding from both the White and Nisqually Rivers

downstream of the dams occurs when runoff exceeds their storage capacity and the dams must

release more water than the downstream channels can convey.

The floodplain maps indicate that flooding occurs along either side of the Puyallup River, from

Clear Creek (described below) to the South and along Wapato Creek to the north. Further north

of Wapato Creek and still in the valley are mapped flood areas along Hylebos Creek. This

includes two larger areas: 8th Street E to I-5 (north to south) and 62nd Ave E to 54th Ave E (east to

west); and a portion just to the east of I-5 where the freeway bends northward and exits the

Planning Area.

Urban Stream/Groundwater Flood Hazard

Urban stream/groundwater flooding occurs when runoff exceeds the conveyance capacity of

natural and manmade drainage systems. It typically occurs with moderate- to high-intensity

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storms that can last for several days or occur in succession over a period of weeks. Urban

flooding in the Clear and Clover Creek basins is consistent with flooding areas shown on current

FEMA Flood Insurance Rate Maps (FIRMs).

For some streams, flooding inundates broad areas for lengths of 1,000 to 3,500 feet, and longer

in some cases. Floodwater can be high and flooding can last for several days until rainfall and

saturated soil moisture conditions subside.

Repetitive Loss Areas

FEMA defines a repetitive loss property as being a National Flood Insurance Program (NFIP)

insured property that since 1978, regardless of changes in ownership, has experienced any of the

three following6:







Four or more paid losses greater than $1,000;

Two paid losses in excess of $1,000 within any 10 year rolling period since 1978;

Three or more paid losses that equal or exceed the current value of the insured

property.

To further illustrate the extent of the flooding hazard in the Planning Area and Pierce County,

this analysis focuses on those areas within the County that have experienced repetitive flood

losses (discussed further in the occurrences section). Based on FEMA records, the County has

identified repetitive loss areas in three of the basins: Clear/Clarks Creek, Clover Creek, and the

Middle Nisqually River, Map 4.8-4. These are discussed in further detail below, including a

description of each basin and a description of the flooding that occurs.

The Planning Area is located in the Puyallup Watershed, which the Clear/Clarks Creek Basin

repetitive loss area, see Map 4.8-5 is a part of. These three repetitive loss areas are discussed in

further detail below, including a description of each basin and a description of the flooding that

occurs. Although the Planning Area is not located within two of the watershed basin boundaries,

Clover Creek and the Middle Nisqually River they impact the Puyallup Tribe of Indians with

their Usual and Accustomed fishing rights and this can impact the Planning Area indirectly.

Puyallup Watershed: Clear Creek Basin7

Description of Basin

Clear Creek, a tributary to the Puyallup River, is a major source of repetitive and destructive

flooding in the Planning Area. The majority of repetitive loss properties within Pierce County

exist within this basin. Clear Creek and its tributaries drains an area of approximately 12.7

square miles, see Map 4.8-5. Most of the Clear Creek basin is in unincorporated Pierce County

and the Planning Area, but it also contains small portions of the Cities of Tacoma and Fife.

Topography in the basin is composed of level river bottom in the lower portion of the basin

along the Puyallup River and gently rolling hills and flatlands in the upper basin, with a steep

transition in between.

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Map 4.8-4 Puyallup Tribe of Indians Repetitive Loss Areas

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The Clear Creek Basin includes the East and West forks of Clear Creek (5.8 sq. mi.), Canyon

Creek (2.2 sq. mi.), Squally Creek (0.9 sq. mi.), and Swan Creek (3.8 sq. mi.), all of which are

narrow, relatively steep creeks, Squally Creek and Swan Creek both enter Clear Creek

downstream of the repetitive loss area. Clear Creek also drains a portion of the flat agricultural

floodplain south of the Puyallup River that contains the repetitive loss area. In addition to natural

drainage courses, many storm drains carry water to the creeks from roads, low-lying farmlands

north of Pioneer way and south of the Puyallup River8, and developments.9

Description of Flooding

The repetitive loss area is in the flatlands of the lower portion of the basin. Map 4.8-5 shows the

Clear Creek basin and repetitive loss study area.10 In addition, Map 4.8-9 shows the Puyallup

Tribe Trust Lands at risk for flooding in this area.

Map 4.8-5 Clear Creek Basin11

Clear Creek

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Puyallup River flood elevations (stages) at the Clear Creek confluence are influenced by a

combination of tidal conditions and flow rates, which in turn influence Clear Creek stages. The

outlet structure of Clear Creek into the Puyallup is designed to close at a river stage of 9 feet and

reopen at a river stage of 8.5 feet. According to a September 26, 1995, Technical Information

Report prepared by the Port of Tacoma, the operating elevations of the gate were chosen so that

the gate would close or remain open as follows:









The gate remains open for the 2-year, 3-day average flow (this is the flow that lasts three

days at a magnitude that has a 50 percent chance of occurring in a given year).

The gate closes for the 2-year instantaneous flow (this is the peak flow that has a 50

percent chance of occurring within a given year).

The gate closes for the 10-year, 1-day average flow (this is the flow that lasts one day at a

magnitude that has a 10 percent chance of occurring in a given year).

The gate closes for the 10-year, 3-day average flow (this is the flow that lasts three days

at a magnitude that has a 10 percent chance of occurring in a given year).

Map 4.8-6 Repetitive Flood Loss Aerial Photo12

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The flooding in Clear Creek results predominately from backwater in the Creek and ponding

within the drainage basin. If Puyallup River water surface elevations are greater than the Creek’s,

water from the Puyallup River can back into Clear Creek. The operation of the flood gate

prevents major flooding. While closure of the floodgate prevents extreme flooding from the

Puyallup River, it eliminates the gravity outlet for Clear Creek, causing water to accumulate

behind the outlet structure. Since backwater from the creek and ponding within the basin is the

primary cause of the Creek’s flooding, the velocity of the water within the flooded area is low.

The aerial photo Map 4.8-6 displays the repetitive flood loss areas during the 1996 flood of

record and illustrates the extent of the Creek’s flooding.

The repetitive loss areas are concentrated along 47th Avenue East and 50th Avenue East, north

of Pioneer Way and South of 40th Street East.13

Chambers-Clover Creek Watershed: Clover Creek Basin14

Description of Basin

The Chambers-Clover Creek watershed consists of level flatlands in the lower portion of the

basin and gently rolling hills and flatlands in the uplands. Elevations within the watershed range

from approximately 210 feet at Steilacoom Lake to 600 feet in the eastern uplands. Terrain was

formed by glacial deposition or erosion. High-velocity glacial meltwater streams cut several

distinct channels through the area, including the Clover Creek channel. Many of these channels

have steep slopes or bluffs defining their boundaries. The Clover Creek channel starts near

Puyallup’s South Hill on the northeast boundary of the watershed and runs southwest to the

Brookdale and Canyon Road area and into the current floodplain of Clover Creek. The repetitive

loss areas are within the flatlands that floodplain in the lower portion of the basin.

The Clover Creek basin is part of the Chambers-Clover Creek watershed and contains portions of

unincorporated Pierce County, including the Parkland and Spanaway communities, significant

portions of the Lakewood incorporated area, a small portion of Tacoma, and portions of Joint

Base Lewis-McChord. Urban development is concentrated toward the northern and western areas

and near freeway and highway corridors. The basin’s land cover is dominated by developed area,

forest, and other natural cover, with water and non-vegetative cover over the remainder.

The Clover Creek basin covers approximately 47,400 acres, or 74 square miles. The main

channel of Clover Creek is 12.8 miles long. Clover Creek has several tributaries and lakes

including Morey and North Fork Clover Creeks, and Spanaway, Tule, and Steilacoom Lakes.

The natural drainage system is modified by collection, detention, discharge, and infiltration

facilities. There are many piped systems in the Clover Creek basin. Due to the high propensity of

porous surface soils from 50 to 60 percent of the basin’s precipitation is absorbed becoming

groundwater recharge.15 Taking advantage of this porosity, the County operates numerous dry

wells, excavated pits usually 3 to 12 feet deep filled with aggregate, to help control runoff. These

are particularly prevalent in the western half of the basin.16

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Description of Flooding

During high intensity or long duration rainfall, broad flooding occurs in two areas along Clover

Creek. Broad flooding occurs in the vicinity of 38th Avenue East and 152nd Street East (Clover

Creek South) and in the vicinity of A street/4th Avenue East and 133rd/138th Street East (Clover

Creek North), downstream of the confluences of Clover Creek and the North Fork of Clover

Creek. Residents in this loss area have filed flood insurance claims in 1996 and 1997. Five

homes have been identified as repetitive loss properties. Surrounding homes are also within the

flood hazard area.

Flooding in these areas typically results from overflow of the creek channel during or after large

rainfall events, coupled with high flows in the North Fork of Clover Creek. The scale and

occurrence of flooding depends on antecedent soil moisture conditions and the duration and

depth of the rainfall. The creek overflows when the combination of backwater, flows from

upstream, and runoff from surrounding areas exceeds the creek’s conveyance capacity. The

backwater often begins at constriction in the channel where the creek’s capacity is lowest. Water

begins to accumulate upstream of these constrictions, and propagates upstream as runoff into the

creek increases. Flooding problems occur when the creek water elevation exceeds the channel

banks and water overflows onto nearby improved property.17

Nisqually River Watershed: Mid Nisqually Basin18

Description of Basin

The Nisqually River flows northwest for approximately 80 miles from its origin at the southern

base of Mount Rainier to Puget Sound just north-east of Olympia. The repetitive loss area is

along a 14.5-mile reach of the river between the City of Centralia’s diversion dam and the

Nisqually Hydroelectric Project, which is owned by Tacoma Public Utilities. Four drainage

basins contribute to this reach: the Upper Nisqually River Basin; the Mid Nisqually River Basin;

the Mashel River Basin; and the Ohop Creek Basin. The repetitive loss area is in the Mid

Nisqually Basin, in the vicinity of Harts Lake.19 This basin and the flooding are described in the

following paragraphs. For more information on the other basins, they are referenced herein.

The Mid Nisqually Basin consists of level to rolling terrain. Land use in the basin consists of

medium development for agriculture purposes.

The Nisqually River flows northwest from the Upper Nisqually Basin for about 30 miles across

the Mid Nisqually Basin. Tanwax Creek, a tributary to the Nisqually River in this basin, conveys

flows that originate in several lakes in the eastern portion of the basin.

The Mid Nisqually basin contains the City of Centralia’s Yelm Project, which is west of Harts

Lake at the downstream end of the Mid Nisqually Basin. The Yelm Project is a “run-of-theriver” project and diverts water from the river to generate power. Because it is a “run-of-theriver” project, there is no capability to store flood water at the diversion structure. A diversion

dam directs water into two intake structures leading to an earthen power canal. The diverted

water can generate 12 megawatts of power, and reenters the river 13.6 miles downstream.

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Description of Flooding

Flooding in the Nisqually floodplain is extremely variable in terms of frequency, severity, and

extent. The river’s banks provide inadequate capacity to contain moderate to high flows. The

repetitive loss property is within the 100-year floodplain. Flow in the Nisqually River is

regulated by the Nisqually Hydroelectric Project. Using Alder Lake’s storage capacity to

regulate discharge, the project allows continuous power production while maintaining

downstream flows and provides incidental flood control and recreation benefits. Although one of

the dam’s stated objectives is to provide flood control, the dam has also been identified as a

possible cause of flooding downstream by holding back floodwaters as long as possible and then

passing more water than the river has capacity to contain.20

Occurrences21

Throughout the settled history of Pierce County there have been floods that impact the

population. Tribes living along the rivers learned to live with them. It was not until settlers with a

European agricultural background began to move into the area in the 1850s, cleared the land,

built homes and planted crops that the flooding became more than just a nuisance. Fort Maloney,

a blockhouse erected to protect a ford on the Puyallup River was washed away in 1867.22

Since the early 1960’s, Pierce County has experienced 21 federally declared disasters. Of these,

13 were either caused or exacerbated by flooding, see Table 4.8-1.

Table 4.8-1 Flood Hazard Declared Disasters

Federal Disaster

DR-4056-WA – 01/14-24/2012

DR-1817-WA—01/06-16/09

DR-1734-WA—12/1-17/2007

DR-1671-WA--11/5-6/2006

DR-1499-WA--10/2003

DR-1159-WA--12/96-2/1997

DR-1100-WA--1-2/1996

DR-1079-WA--11-12/1995

DR-896-WA--12/1990

DR-883-WA--11/1990

DR-852-WA--1/1990

Notes

Severe Winter Storm, Flooding, Landslides and

Mudslides. 11 counties declared.

Flooding from a severe storm throughout much of

Washington. 23 counties declared.

Flooding throughout most of W. Washington. Pierce

County was not declared.

Major flooding on the Puyallup, Carbon, White, Stuck

and Nisqually rivers.

Surface flooding

Ice storm, snow and flood. Stafford Act assistance - $83

million, SBA $31.7 million.

Three deaths in Washington. Stafford Act disaster

assistance provided – $113 million. SBA disaster loans

approved - $61.2 million

100-year flood at Alderton on the Puyallup and 50-year

flood at La Grande

Stafford Act assistance provided $5.1 million

Stafford Act assistance provided $57 million

Stafford Act assistance provided $17.8 million

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DR-784-WA--11/1986

Federal Disaster

DR-545-WA--12/1977

DR-545-WA--12/1977

DR-492-WA--12/1975

DR-328-WA--2/1972

DR-185-WA--12/1964

Two deaths. $11 million in private property damage and

$6 million in public damage

Notes

16 counties were declared. Very heavy rain in the upper

Nisqually caused significant damage.

16 counties were declared. Very heavy rain in the upper

Nisqually caused significant damage.

13 counties flooded

King, Pierce and Thurston counties flooding

Wide ranging flooding affected 19 counties in both

eastern and western Washington

The idea of channeling the Puyallup River began to take hold towards the end of the 19th century

and in 1906 local citizens began the process of putting in small levees. Various work continued

with both Pierce and King Counties joining forces, and later, the addition of the Army Corps of

Engineers became involved, allowing the levee work to be completed in 1950.

Between 2002 and 1989, more than $22.8 million in Stafford Act disaster assistance was

provided to Region 5 for repairs to public facilities following flood events.23

The floods of 2006, 1997, and 1996 will remain in memory as three of the worst in the County.

All of Pierce County’s major rivers reached flood stage or above. These included the largest

floods on record for the Puyallup and Carbon Rivers. Levees were destroyed or overtopped,

revetments eroded, homes damaged or destroyed and some migration of the river channels.

During the February 1996 flooding, the Nisqually River had an unprecedented recorded event.

The amount of water released from the Alder/LaGrande dams located on the Nisqually River

exceeded the capacity of the river channel. Throughout the County, surface water flooding

occurred and sandbagging continued for weeks.

The flooding of 1996-1997 will remain in memory as one of the worst in the region. All of major

rivers in the County reached flood stage or above. It was the largest flood on record for the

Puyallup River. There were 10,000 feet of levee partially damaged and 20,000 feet completely

destroyed. The Nisqually River also had an unprecedented recorded event. The amount of water

released from the Alder/LaGrande dams located on the Nisqually River exceeded the capacity of

the river channel. Throughout the County, surface water flooding occurred and sandbagging

continued for weeks.

In early January of 2009, a severe winter storm resulted in significant flooding, mudslides,

landslides, avalanches, high winds and freezing rain throughout western Washington. Snow

levels rose between 6,000 to 8,000 feet while there was heavy precipitation falling between 3 to

6 inches over the course of two days. This was a 100 year flooding event for the Puyallup River

Basin. Pierce County was declared a federal flood disaster area.24

Repetitive Flood Loss Areas

Clear Creek Basin

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Flooding has affected Pierce County and the Planning Area many times in the past. Map 4.8-4

illustrates the specific occurrences of repetitive flooding within the Clear Creek Basin. Clear

Creek is the source of most of this flooding. The flood of record produced by the creek in

February 1996 is illustrated from the aerial photo of the basin taken on February 8, 1996 (see

Figure 4.8-1). The other major flooding occurred in November, 1995, and largely affected 47th

Avenue East. The Creek produced widespread and destructive flooding in February 1996 and the

extent of this flood of record is shown.

Figure 4.8-1 Feb 8, 1996 Flooding - Del Rio Mobile Homes Along Puyallup River

The repetitive loss areas are concentrated along 47th Avenue East and 50th Avenue East, north of

Pioneer Way and South of 40th Street East. About 20 homes in this area have been identified as

repetitive loss properties. Residents in the Clear Creek Repetitive loss area filed flood insurance

claims in 1997, 1996, 1995, 1991, 1990, 1986, and 1984. The frequency of these claims indicates

that each year there is approximately a 33 percent chance of flooding from Clear Creek. The

February, 1996 flood was one of the worst in recent history, producing the highest stage of the

Puyallup River since 1942. In this flood, the area of inundation greatly exceeded the previously

delineated floodplain, emphasizing the need for updated flood mapping.25

Clover Creek Basin

Map 4.8-5 illustrates the repetitive loss property and flood hazard area. Broad flooding occurs in

the vicinity of 38th Avenue East and 152nd Street East (Clover Creek South) and the vicinity of A

street/4th Avenue East and 133rd/138th Street East (Clover Creek North). Residents in this loss

area have filed flood insurance claims in 1997 and 1996.26

Mid-Nisqually River Basin

Map 4.8-3 illustrates the repetitive loss property and flood hazard area. The owner of the

repetitive loss property has filed flood insurance claims in 1996, 1995, 1994, 1991, 1990, 1982,

and 1980 and has indicated that his property also flooded in 1976, 1974, and 1972, although no

flood insurance claims were made. The flood history for this property indicates approximately a

33 percent chance of flood damage in any given year. According to the property owner, the

February 1996 flood was the most severe, with flood elevations as high as eight feet and rapidly

flowing water.

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A second area recently identified is in the Ohop Creek Basin. One property has been identified

and there is the potential for another five that lie in the same area.

Recurrence Rate

Table 4.8-1 Flood Hazard Declared Disasters lists 17 disasters that were either flood disasters or

were exacerbated by flooding that have impacted Pierce County over the past 44 years, or one

every 3.1 years. In between these individual federally declared disasters were other flood issues

that did not make it to the federal declaration level. It was then decided, based on the number of

incidents, that the probability of recurrence for the flood hazard in the Planning Area is five

years or less.

Vulnerability

The temperate marine climate of western Washington adds to the frequency and magnitude of

floods. Annual rainfall ranges from 40 inches in the Puget Sound lowland to 80 inches or more in

the Cascade foothills, with a large portion occurring during the winter months. Winter storms

usually bring several days of low intensity rainfall, rather than short, intense thunderstorms.

Average snowfall at Paradise on Mount Rainier is 680 inches. A warm, wet period with mid to

low level snowpack accumulation in the mountains can cause swollen rivers to pour over their

banks into the surrounding floodplains. Combined with a longer duration rainfall, saturated soils,

and an elevated water table, the potential for severe flooding is significant.

Human alteration of the landscape—including clearing, grading, paving, building construction,

and landscaping—has an impact on hydrologic processes. Soil compaction and paving reduce the

infiltration and storage capacity of the soils. This leads to a runoff process called Horton

Overland Flow, in which rainfall exceeds the infiltration rate and the excess precipitation flows

downhill over the soil surface. This type of flow rapidly transmits rainfall to a stream or

conveyance system, causing higher peak flow rates than would occur in the unaltered landscape.

Unmitigated land development increases not only peak flow rates, but also annual and seasonal

runoff volumes. The larger the percentage of an area covered with impervious surface such as

buildings and pavement, the greater the runoff generated for a given rainfall event.27 The

following is a description of the specific factors affecting vulnerability in the repetitive loss area.

Clear Creek Basin

Most of the land use within the Clear Creek basin is single-family residential, with smaller areas

of agricultural and resource lands, as well as some more heavily urbanized pockets. Urban

development is concentrated toward the southern and western areas and near freeway and

highway corridors; much of the flatland in the lower portion of the basin has a higher proportion

of agricultural use.28 The vulnerability in the Clear Creek Basin is influenced by the operation of

the flood control measures identified in the Location and Extent Section—namely the operation

of the flood gate.

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The effects of these factors are noted as follows. Past flooding in the repetitive loss areas

described above has impacted buildings, infrastructure, and public health and safety in a number

of ways.







Health Risks: Residents have indicated that floodwaters have, at times, flooded their

drinking water wells and supply pumps.

Public Health and Safety Risks: Resident accounts, public work documents, and

aerial photos indicate that local access roads and arterials can be rendered impassible

during flood events. Road flooding can limit emergency response access and poses

potential risks for public health and safety.

Property Damage: Buildings within the area suffer water damage. Since many

residents do not have flood insurance, and since flood insurance does not cover all

losses, damage can go unrepaired, resulting in lower property values.29

Flooding also results in a significant number of claims paid to property owners. Because flood

insurance does not cover all losses, and because many property owners have no flood insurance,

the actual financial impact of flooding is greater than the losses summarized in the tables above.

The actual impact that this financial drain has on the economy has not been quantified. Likely

impacts, however, include the following:







The local economy suffers as savings are depleted to make necessary home repairs.

The tax base is weakened as property values decrease in areas impacted by flooding.

Conflicts in the community can arise as new developments create or exacerbate

flooding problems.30

New construction to accommodate a growing population can lead to increased runoff if no

mitigating measures are implemented. As more homes are built, larger areas of impervious

surface are created. Impervious surfaces prevent rainfall from infiltrating into the ground. The

rainfall instead is concentrated and flows directly into local creeks and rivers, increasing their

flows. If currently proposed mitigation is not adequate, the number of repetitive loss properties is

expected to increase in the coming years as floodplains expand with the increased flows.31

The most recent flood event (disaster declaration 1499) illustrated the region’s increasing

vulnerability to the flood hazard. Most of the damage occurred in areas not identified on the

FIRMs. The majority of flooding was due to the urban flood hazard indicating an increasing

vulnerability to this category of flooding.

Planning Area

The Planning Team determined that the Planning Area has a medium vulnerability to the flood

hazard because of the following factors: high probability of recurrence, portion of the

Reservation located in the 100-yr and 500-yr floodplain, the number of repetitive loss claims,

and the potential for urban flooding.32

The entire Planning Area, over 16,000 acres is vulnerable to the two types of flood hazards

(riverine and urban stream/groundwater) identified by the Planning Team. The total damage to

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the Planning Area could equal approximately $8 billion (the assessed value of all parcels in the

Planning Area, October 2016).

A more detailed vulnerability assessment by the Planning Team showed that approximately

5,588,000 acres (36% of the Planning Area) are located in FEMA mapped floodplain areas

making those acres even more vulnerable to the flood hazard. The total estimated losses to these

parcels would equal $2.7 billion (the assessed value of all parcels in the flood hazard area,

October 2016). The repetitive flood loss properties property owners in the floodplain have filed

65 claims to FEMA estimated at over $1,600,000 in damage since 1978.

Of the 485 Tribal Trust parcels in the Planning Area, 150 parcels (30.9%) are located in FEMA

mapped floodplain areas. The total estimated losses to these parcels would equal $167,822,500.

Maps 4.8-7 through 4.8-9 show a detailed vulnerability to flooding on a parcel level. Three

maps were scaled into to show the parcels at risk due to flooding in the Port of Tacoma area, the

downtown area and the Fife/Puyallup area. Most of the Tribal critical infrastructure is located

within these areas and scaling the map down to the parcel level will allow for critical mitigation

strategies to be potentially applied to the facilities at greatest risk or re-location of the buildings

as funding becomes available.

Impacts

Health and Safety of Persons in the Affected Area at the Time of the Incident

Flooding kills citizens throughout the United States every year. While that has not been a major

problem in Pierce County over the years, it very well could happen with any major flood we

have. The fact that Pierce County has had to do swift water rescues in the past with floods in

both 1996 and 2006 shows the potential for life threatening situations to evolve during a flood.

Pierce County streams and rivers run very fast, and can quickly overwhelm individuals or

vehicles caught in them. Persons caught in flood waters can be pinned under debris and drown.

They can receive trauma from

Figure 4.8-2 Nov. 2006 Flooding River Park Estates – Along Puyallup River

other debris being carried along

by the river or by impacting

rocks or other impediments in

the river itself.

During the fall and winter flood

season, rivers and streams are

comprised largely of cold rain

and snow, and for those

originating on Mt. Rainier, some

glacier melt. They are therefore

very cold. In addition, air

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Map 4.8-7 Puyallup Tribe of Indians Port of Tacoma Flood Hazard Area

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Map 4.8-8 Puyallup Tribe of Indians Downtown Flood Hazard Area

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Map 4.8-9 Puyallup Tribe of Indians Fife/Puyallup Flood Hazard Area

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temperature in the winter during flood season can also be in the thirty degree range, although not

usually below that during floods. The result is that persons caught in flood waters can drown not

just from direct action of the flood but also as a complication of hypothermia.

Other problems that can compromise a person’s health can develop after the flood waters have

receded. Mold will grow in wet material, be it clothing, bedding, the walls of a house or the

insulation under a floor. Sewage and hazardous chemicals may be present in homes, cars, or just

as a layer coating peoples’ property. Water and food may be contaminated. Heat and electricity

may be off for some time. All of these will contribute to a decrease in not just the quality of life

for individuals, but also their current and long-term health.

Health and Safety of Personnel Responding to the Incident

Response to flooding is response in hazardous conditions. Whether one is attempting swift water

rescue, adding sandbags to dikes, or cleaning up debris after the waters have receded, an

individual is working in a hazardous environment.

Impacts to responding personnel are similar to what can affect the citizens residing or working in

the flood area. They include death from drowning and/or hypothermia, and either death or injury

from trauma. Long-term, environmental hazards such as hazardous chemicals, sewage, etc. can

cause illness, either acute or chronic.

Continuity of Operations and Delivery of Services

Continuity of operations for most jurisdictions within Pierce County will not be compromised

due to flooding. However, those that have their main administration or critical components of

their operations within the flood zone could find their operational continuity at risk. If files,

paper or electronic, are damaged or destroyed, an organization may not be able to: contact

clients; assign work; complete scheduled jobs; meet deadlines; access, track, and pay accounts;

or pay staff. Without a Continuity of Operations Plan (COOP) that takes these issues into

account, they may not be able to operate in their normal mode. This would be especially true for

those jurisdictions like Orting, Sumner, Puyallup or Fife that lie directly on the river, or have a

significant portion of their infrastructure located close to the river.

The delivery of services by the local jurisdictions and agencies within Pierce County is directly

related to the degree of damage by the floods, to improved property, the infrastructure, and the

areas in which the damage occurs. A flood that closes roads, either with water over the road or a

washout, temporarily eliminates the ability of a local jurisdiction to repair other damaged

infrastructure, respond to emergencies in the affected area, or deliver the other normal goods and

services expected of it. Flooded electric substations, downed lines, contaminated wells, and

broken pipelines all have the same impact. In all of these cases the delivery of services will be at

least temporarily halted.

Damage to facilities, equipment, or files all could impact the delivery of services to citizens from

individual jurisdictions or agencies.

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Property, Facilities, and Infrastructure

Flooding is one of the major causes of damage to and destruction of property, facilities and

infrastructure throughout the country and it is no different in Pierce County. Individual property

has been destroyed in every major flood to hit the County. Over the years this has included

homes, barns, equipment, livestock, and transportation vehicles of various types.

Flood waters can damage or destroy a jurisdiction’s facilities. Buildings can be flooded.

Equipment, electronic or mechanical, ruined or in some cases made inaccessible due to flood

waters. Files, electronic or paper, can be destroyed. Both water and the contaminants it carries

can either damage or permanently ruin equipment.

Flood waters can erode land containing infrastructure such as roads, power lines, natural gas,

fuel, water pipelines, and sewage control facilities. It can breach levees, erode revetments and

destroy bridges. Water overtopping dams can cause damage to the dam’s structure. Material

carried by the flood waters, if not screened out or removed can cause damage to the hydroelectric

generating components of a dam.

Figure 4.8-3 Nov. 2006 Flooding State Route 410 – Along Puyallup River

The Environment

The impacts to the environment from a major flood could include: erosion and scouring of

stream or river banks; loss of plants and animals; and contamination from chemicals, sewage,

and other noxious materials picked up, transported and deposited by the flood. The

contamination of both the river and the flooded landscape from the various chemicals and debris

picked up from farms, homes, and businesses along the river is a serious problem. Industrial

chemicals, oil and gas, sewage, old tires, etc. can all pollute the landscape where they come to

rest as the water recedes. Some of these materials may take years, decades or even longer to

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break down and become harmless. Until that happens they can continue to degrade the

environment where they have come to rest, in some cases leaching back into the water course or

into ground water spreading contamination away from the site. Without clean-up this may

continue for years.

However, from an environmental standpoint, not all flooding of rivers is bad. Floods are endemic

in these valleys and the low areas of the County. They have changed the course of rivers, flooded

low areas, uprooted or drowned vegetation, all as part of the natural environment. Areas where

the river has changed course, frequently during floods, and moved away from, form oxbow lakes

that attract water fowl and other animals. Where the river once ran the river gravels gradually

develop a layer of topsoil forming meadows and allowing willows, alders and other open area

bushes and trees to thrive. These species attract a growing diversity of animal life which

continues to change, as the forest itself changes, progressing from open area species to taller

trees like Douglas fir and eventually to shade resistant types like Western Hemlock.

Flood waters traditionally have replenished the soil. In bringing down silt from higher elevations

and depositing it across the landscape in the flat areas of the County, it adds a new quantity of

nutrients to the soil that is already there. This contributes to the fertility of the valley floors

aiding the growth of both natural vegetation and agricultural products.

Another development that occurs with flooding is the creation of snags within the river channel

itself. As the river erodes the banks, trees become uprooted, fall into the river and either create

coverage for fish at that spot or in many cases are transported by the flood down river and later

are snagged creating more fish habitat.

Economic and Financial Condition

Economically, the after effects will depend directly on how much damage was done to local

businesses, the local tax base, and the local infrastructure. While an individual home damaged by

a flood can be devastating to an individual or family, it has very little effect on the overall

economic condition of the

Figure 4.8-4 Nov. 2006 Flooding Rainier Manor – Along Puyallup River

community. However when a

large number of homes, and

businesses, are damaged or

destroyed it can negatively alter

the tax base decreasing the

ability of the local jurisdiction

to pay, not just for

infrastructure repair and

community restoration, but also

for the normal day to day

programs that make the

community a viable area in

which to live, work and play.

Related to this is the possibility

that many people may need

temporary relocation assistance.

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If homes are not salvageable families may have to look for alternate housing. Depending on what

is available, it could lead some to leave the County or Planning Area, moving to other areas.

Depending on the size of the flood and the resulting exodus, there could be a small loss of

population and tax revenue.

Damage to the business and industry sector does not only affect the tax base, but also removes

jobs from the local economy. The loss of jobs can escalate into other problems. The unemployed

may either move away, go on unemployment, or be forced to take a lower paying job all of

which further decreases the financial stability of the community. If the loss of financial stability

is not corrected there are other social problems that arise. Those out of work can develop a loss

of self esteem that can lead to an increase in crime, alcohol and drug abuse, spouse abuse, and an

increase in medical problems.

Flooding may damage the infrastructure by undercutting and washing out transportation

corridors such as roads, bridges and train tracks, downing power poles, damaging pipelines,

filling sewer lines with silt, and damaging levees and revetments. The time to repair these can

take from weeks to years depending on the amount of damage and the available resources to

repair them. This damage to the infrastructure will slow down the economic recovery for the

jurisdiction. Even further, damages can limit the reopening of businesses or it can force those

that may have had no damage, but operate on a just-in-time supply system, to close at least

temporarily. For some of these, the lack of commerce and therefore loss of income can prove

critical. With creditors needing payment and no revenue stream, some may not be able to recover

and could close permanently.

Flooding may have a significant impact on the fisheries due to the scouring of river beds, back

flooding of creeks and tributaries affecting salmon spawning and rearing habitats. The loss of

this critical habitat hinders the restoration recovery efforts for salmon species. The continued

loss of fish habitat not only affects recovery efforts but impacts the Puyallup Tribe who are

culturally connected the salmon.

Grocery stores, restaurants and food delivery systems may lose product because of the lack of

power. Large chains can recover, but small independent businesses may not. Those that have a

system of backup power should do much better than those that do not.

In summary, the economic viability of the community will depend on not just how much damage

is done, but also on how quickly the infrastructure can be repaired; how prepared businesses are

to operate in the post disaster environment; how prepared citizens are for the flood and its after

effects; and how well local governments and organizations can respond to the needs of the public

for support, cleanup, and if necessary relocation.

Public Confidence in the Jurisdiction’s Governance

The reputation of any individual jurisdiction within Pierce County or the public’s confidence in

the jurisdiction is highly dependent on the public’s perception on how well the response and

recovery were handled during and after the flood. A response that either shows or gives the

impression that a jurisdiction is prepared and responsive to the public’s needs and manages a

recovery to get services back and damage repaired in a timely manner will enhance a

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jurisdiction’s reputation. If however, the perception develops, rightly or wrongly, that the

jurisdiction is incompetent, slow to react, or ignores the needs of its citizens, then the reputation

of the jurisdiction and the confidence in its abilities will decline.

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Resource Directory

Regional

o Pierce County Department of Emergency Management

http://www.co.pierce.wa.us/pc/abtus/ourorg/dem/abtusdem.htm

o Pierce County Department of Water Programs

http://www.co.pierce.wa.us/pc/services/home/environ/index.htm

o Washington State Department of Ecology

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

o Western Regional Climate Center

http://www.wrcc.dri.edu

o Corps of Engineers Northwest Division

http://www.nwd-wc.usace.army.mil

National

o Association of State Dam Safety Officials

http://crunch.tec.army.mil/nid/webpages/nid.cfm

o Copies of FIRMs, FISs, DFIRMs, Digital Q3 Flood Data, and FHBMs

http://msc.fema.gov/webapp/wcs/stores/servlet/FemaWelcomeView?storeId=10001&cata

logId=10001&langId=-1

o Flash-Flood Safety Rules

http://www.nws.noaa.gov/om/brochures/flashfld.shtml

o Flood Risk and Map Information

http://www.fema.gov/hazard/flood/index.shtm

o Flood Safety Rules

http://www.nws.noaa.gov/floodsafety/

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o Floodplain Management Association

http://www.floodplain.org

o General Flood Information

http://www.fema.gov/hazard/flood/index.shtm

o Guide to National Flood Insurance Program on the web

http://www.fema.gov/business/nfip/qanda.shtm

o Latest hydrological information (flooding, droughts, snow conditions,

etc.) http://www.nws.noaa.gov/oh/hic/current/

o FEMA Map Service Center

800.358.9616

www.msc.fema.gov/

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Endnotes

1 Modified from PC HIVA, Flood Section, September 5, 2002, p.29.

http://www.co.pierce.wa.us/xml/abuts/ourorg/dem/HIVAWEB.pdf

2 Pierce County Repetitive Loss Plan, Pierce County Water Programs. Prepared by Tetra Tech/KMC, Inc.,

Seattle, WA: July, 2001. p.6.

3 Pierce County Repetitive Loss Plan, Pierce County Water Programs. Prepared by Tetra Tech/KMC, Inc.,

Seattle, WA: July, 2001. p.1.

4 Closed Depression flooding occurs where water collects in low-lying areas with little to no drainage capacity.

Once flooding occurs, it can last for

the remainder of the wet season until evaporation or slow infiltration lowers the water level. (PC HIVA).

5 Tacoma Public Utilities Nisqually River Project.

http://www.tacomapower.com/parksandpower/hydro_power/nisqually_river_project.htm

6 Pierce County Flood Risk Assessment – Draft, June 2007, Pierce County Public Works & Utilities Water

Programs, TETRA TECH/KCM, p. 1-6.

7 Most information on the Clear/Clarks Creek Basin is taken from Pierce County Flood Risk Assessment –

Draft, June 2007, Pierce County Public

Works & Utilities Water Programs, Tetra Tech/KCM, pp.4-1 to 4-15.

8 Pierce County Flood Risk Assessment – Draft, June 2007, Pierce County Public Works & Utilities Water

Programs, Tetra Tech/KCM, p. 4-2

9 Pierce County Repetitive Loss Plan, Pierce County Water Programs. Prepared by Tetra Tech/KMC, Inc.,

Seattle, WA: July, 2001, p. 7.

10 Ibid. p. 7

11 Pierce County Repetitive Loss Plan, Pierce County Water Programs, Prepared by Tetra Tech/KMC, Inc.,

Seattle, WA. July, 2001. Figure 4-1.

12 Pierce County Water Programs, aerial photos for Clear Creek area, February 9, 1996.

13 Ibid, p. 1, 9, 10.

14 Most information on the Clover Creek Basin is taken from Pierce County Flood Risk Assessment – Draft,

June 2007, Pierce County Public

Works & Utilities Water Programs, Tetra Tech/KCM, pp.5-1 to 5-9.

15 Pierce County Flood Risk Assessment – Draft, June 2007, Pierce County Public Works & Utilities Water

Programs, Tetra Tech/KCM, p. 5-1.

16 Pierce County Repetitive Loss Plan, Pierce County Water Programs. Prepared by Tetra Tech/KMC, Inc.,

Seattle, WA: July, 2001. p. 10-11

17 Ibid. p.11-12

18 Some information on the Mid Nisqually Basin is taken from Pierce County Flood Risk Assessment – Draft,

June 2007, Pierce County Public

Works & Utilities Water Programs, TETRA TECH/KCM, pp.11-19 to 11-21.

19 Pierce County Repetitive Loss Plan, Pierce County Water Programs. Prepared by Tetra Tech/KMC, Inc.,

Seattle, WA: July, 2001, p.11-12

20 Ibid. p. 14

21 Modified from PC HIVA, Flood Section, September 5, 2002, p.29.

http://www.co.pierce.wa.us/xml/abtus/ourorg/dem/HIVAWEB.pdf

22 City of Puyallup Natural Hazard Mitigation Plan, March 2005, p. 4.5-8.

23 Washington State Hazard Mitigation Plan. Washington State Emergency Management Division, April, 2004.

Tab 7.2.5 p. 16.

24 Ordinance No. 2011-95s. Pierce County Code 11.06. Effective April 10, 2012.

http://www.co.pierce.wa.us/DocumentCenter/View/3334

25 Pierce County Repetitive Loss Plan, Pierce County Water Programs. Prepared by Tetra Tech/KMC, Inc.,

Seattle, WA: July, 2001. p. 9, 10.

26 Ibid. p.12

27 Ibid.

p. 8. For more information on percent-impervious analysis of the flood hazard areas, see the Pierce

County Repetitive Flood Loss Plan

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and the Guidance for Basin Planning.

28 Pierce County Repetitive Loss Plan, Pierce County Water Programs.

Prepared by Tetra Tech/KMC, Inc.,

Seattle, WA: July, 2001. p. 8

29 Ibid. p. 15.

30 Ibid, p. 15.

31 Ibid. p. 17

32 Pierce County Emergency Management. Spatial analysis using ArcGIS/CVPro to determine the

vulnerability for flood hazard.

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