CHEHALIS RIVER BASIN STUDIES INVENTORY AND EVALUATION Final Report

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CHEHALIS RIVER
BASIN
STUDIES
INVENTORY AND EVALUATION


Final Report


June 15
, 2012









LEWIS COUNTY CONSERVATION DISTRICT:




Dr. Frank Reckendorf,
G.
Fluvial Geomorphologist

Dean Renner, P.E.
Stream Mechanics Engineer

Robert Amrine, District Manager

Kelly Verd, Special Projects Coordinator

Nikki Wilson, CREP/GIS Specialists

And

Mark Stevens,

P.E.

SW Washington Area Engineer
,

Douglas Fenwick,

Engineering Tech.,
Clark Conservation District





Funded by:










TABLE OF CONTENTS


ACRONYMS




8


INTRODUCTION



10



Purpose

1
0


Objectives

1
0


Methodologies


11

SETTING



1
2


Location

1
2


Sub
-
basins

1
2


Population


1
2


Potential Flooded Areas

1
3


Physiography and Geolog
y


1
3


Local Topography


1
7


Land Use


18


Climate

18


Surface Water


18


Annual and Mean Monthly

18


Peak Flows

18


Historic Flooding

2
1


Water Bodies

2
4


Estuary

2
6


Drainage


28


Sedimentation

29


Upland Erosion Landslides


3
1


Accelerated Streambank Erosion


3
5


Ground Water

3
5


Water Quality

3
7


Fluvial Geomorphology

4
1


Wetland Habitat


4
3




Aquatic Habitat

4
7


Land Resource


5
2


Soils

5
2


Land Capability

5
3


Upland
Forestry
Vegetation

5
6


Clearcutting

5
6


Rate of Harvesting

57


Riparian Vegetation

57


Upland Forest Riparian

58


Riparian Management Zones
(RMZs) and Wetland Management
Zones (WMZs)

58


Shade Requirements to Maintain
Water Temperature

58


Cultural Resources

58

WATER AND RELATED LAND RESOURCES PROBLEMS

59


Flooding

59


Stage and Frequency at
Representative Gage

6
0


Bankfull Discharge

6
1


Previous Studies

6
2


Existing Flood Control Works

6
6


Potential Flood
Reduction

Solutions

69


Non
-
Structural

69


Instream Measures

7
2


Missing Data

7
2


Accelerated
Soil
Erosion

Reduction

7
3


Upland

7
3


Landslides and Debris Flows

74


Accelerated Streambank Erosion


7
5


Sedimentation Impacts


7
6


Estuary

79


Fluvial

Geomorphology

Needs

79




Drainage

81


Ground W
ater

8
1


Water Quality

8
1


Aquatic Habitat

85


Wetlands

87

CONCLUSION


8
7

SCOPE OF
FUTURE
WORK

90

REFERENCES

9
1

ABSTRAC
TS and MAPS






































TABLES


1.

Chehalis Basin
Watershed
-
County Land Areas

2a.

Sub
-
areas in Chehalis Basin

as shown in SCS River
Basin Report

2b.

Watershed Area by HUC and WRIA

2c.

Floodwater Hazard Classes for Chehalis Basin by
Watershed

3.

Annual Streamflow Data for Chehalis Basin

4
.

Monthly

Streamflow Data for the Chehalis Basin

5.

Daily Streamflow Data for Chehalis Basin


6
a.

Peak Discharge for Selected Frequencies

6
b.

Chehalis Basin Discontinued USGS Stream Gages

7
a
.


Dates of Historic Flood Events from 1930


2010

7
b
.

Dates of Historic Flood Events from 1930


2010

Peak Discharges and Corresponding Flood
Frequency

8.

Percent Riparian Cover

9
a
.

&
9b.

Water Bodies: Named Lakes and Dams and
Reservoirs

10.

Sediment Yield
for

Sub
-
basins

11.

Timing of
Salmon
Fresh
-
water
Life Phases

12.

Erosion Los between 2006 and 2009 by Site

13a.

Potential Food Reduction Projects & Policies

13b
.

Potential Flood Reduction Studies and
Methodologies











F
IGURES


1.

Overview of Chehalis Basin

2a.

Cheh
alis Basin WRIA 23 Watersheds

2b.

Chehalis Basin WRIA 22 Watersheds

3a.

Maximum Extent and Drainage Routes of the Vashon
Glacier


3b.

Chehalis River Profile
-

Lewis County Washington

3c.

Chehalis/Skookumchuck River Profile
-
Lewis County
Washington

3d.

Chehalis/Newaukum River
Profile
-
Lewis County
Washington

4.

Stage Discharge Wate
rshed
for Satsop River near
Satsop, WA gage

5.

Stage Discharge for Satsop River near Satsop gage

6a.

1938 Photo Centralia Area

6b.

2011 Photo Centralia Area

6c.

1938 Photo Porter Area

6d.

2011
Photo Porter Area

6e.

1938 Photo Stearns Creek Basin

6f.

2011 Photo Stearns Creek Basin

7a.

Generalized Conceptual Model of Groundwater Flow in
the Centralia
-
Chehalis Lowland

7b.

Water Quality Monitoring Sites

throughout the Chehalis
Basin

7c.

Core
Summer Salmonid Temperature Conditions

in the
Chehalis River Basin

8a.

The Key to the
Rosgen Stream Classification System

8b.

Channel Evolution Model

9.

Stream Planform
Montgomery and Buff
ington

10.

Pattern of Soils and Parent Material in the
Reed
-
Chehalis Map Unit

11.

Riparian Assessment for Newaukum River, Lewis


County

12.

Upper Chehalis and South Fork Chehalis River Erosion
Sites

determined by comparing 2006 to 2009 aerial
photos

13.

Side by S
ide Aerial Photos 2006
and 2009 Site 1

14.

Si
de by S
ide Aerial Photos 2006
and 2009 Site 2

15.

Side by S
ide Aerial Photos 2006
and 2009 Site 3

16.

Side by S
ide Aerial Photos 2006
and 2009 Site 4

17.

Side by S
ide Aerial Photos 2006
and 2009 Site 5

18.

Side by S
ide Aerial Photos 2006
and 2009 Site
6

19.

Side by S
ide Aerial Photos 2006
and 2009 Site 7

20.

Side by S
ide Aerial Photos 2006
and 2009 Site 8

























ACRONYMS



BMP’s

Best Management Practices

BP


Before Present

CAO


Critical Areas Ordinance


CB
P


Chehalis Basin Partnership



CFS


Cubic Feet per Second


CMER

Cooperative Monitoring and Evaluation Research



Committee

COE


United States Army Corps of Engineers

CREP


Conservation Reserve Enhancement Program

CRSP


Chehalis River Surge Plain

CWA


Clean Water Act

DNR


Washington State
Department of Natural Resources

DOE


Department of Ecology

State of Washington

EDT


Ecosystem Diagnosis and Treatment

EIS


Environmental Impact Statement

EPA


United States Environmental Protection Agency

ESA


Endanger
ed Species Act

FEMA

Federal Emergency Management Agency

FFR


Forest and Fish Rules


GIS


Geographical Information Systems


GMA


Growth Management Act


HUC


Hydrologic Unit Code


IACWD

Interagency
Advisory Committee on

Water Data


LCCD

Lewis County Conserva
tion District


LHZ


Landslide Hazard Zonation


LiDAR

Light Distance and Ranging


LWD


Large Woody Debris


MCD


Mason Conservation District


MLR


Multi
-
Linear Regression


MSL


Meters above Sea Level


NAP


Natural Area Preserve


NFIP Nati
onal Flood Insurance Program


NRCS

Natural Resources Conservation Service


NWIS


National Water Information System


OHWM

Ordinary High Water Mark


RCW


Revised Code of Washington


RCYBP

Radio Carbon Years Before Present


RMZ


Riparian Management Zone




RLIP


Regional Landform Identification Project


RM


River Mile


RMAP

Road Maintenance and Abandonment Plan


RPW


Relatively Permanent Water


SCS


Soil Conservation Service


SMA


Shoreline Management Act


TMDL

Total Maximum Daily Load


TNW


Traditional Navigabl
e Wate
r


USDA

United States Department of Agriculture


USFWS

United States Fish and Wildlife Service


USGS


United States Geological Survey


WAC


Washington Administrative Code


WAU


Washington Administrative Unit


WDFW

Washington Department of Fish and Wi
ldlife


WARSSS

Watershed Assessment of River Stability and Sediment



Supply


WMZ


Wetland Management Zone


WRIA

Water Resource Inventory Area


WSCC

Washington State Conservation Commission



















10


INTRODUCTION


Purpose


The purpose of this study was to collect, inventory and prepare a report on
existing technical studies and similar reports for the Chehalis River Basin in
order to identify study needs for evaluating flood reduction
alternatives that
could be implem
ented in the Chehalis Basin
. The report was written in the
style of a river basin report that is traditionally written by the Natural
Resources Conservation Service (NRCS). As such
,
it

looks at all of the soil
and water r
esources that would need to be considered in any future work

on
flood reduction in the Chehalis Basin.


The study was funded by a grant from NRCS to the
Washington State

Conservation Commission

(WSCC)
. The
WSCC
provided matching funds
and
designated the L
ewis County Conservation District

(LCCD)

as the lead
agency to do the study and prepare the report on behalf of the six county
conservation districts in the Chehalis Basin
.


Objectives


The objectives of the study were laid out in a plan of work and
an

ag
reement
was signed between the NRCS and the WSCC. The objectives were as
follows:

1.

Complete an inventory and evaluation of existing technical reports
and studie
s completed by Federal, State, County, and T
ribal
agencies.

2.

Pr
epare a report summarizing the
pe
rtinent studies and reports.

3.

Determine the technical adequacy of each inventoried report to
reflect a comprehensive basin study.

4.

Identify additional study needs necessary to encompass all
potential flood reduction alternatives.

5.

Develop a scope of work for
additional study needs that have been
identified within the Chehalis Basin.





11


Methodology


This study was undertaken to inventory all studies and other types of
documents that related to the Chehalis Basin. It is commonly thought that
the Chehalis Basin has been studied intensely but there was no
comprehensive database that existed of what had b
een completed. Using lists
put together by several sources, the
LCCD

sought out documents on the
internet, at various libraries, the
United States Army Corp of Engineers
(COE)
, other government agencies, and any other available source.

A total of 7
68

tit
les of documents were identified. The majority of the
documents were found but a few were unable to be located. They were left
on the list as they do relate to the Chehalis Basin and maybe found in the
future. There are a few documents that are not specif
ic to the Chehalis Basin
but contain information that would be useful. Although this is meant to be a
comprehensive list, it is possible there are some documents that we were
unaware of.


A unique identifying number was created for each document. An Acce
ss
database was created and abstracts were written for each document. Each
was assigned to one of the following categories: Bibliographies, EIS’s,
Fisheries and Habitat, Flood Reduction, Flood Studies, General, Geology
and Geotech, Grays Harbor Navigation,

Groundwater, Historical and Misc.,
Water Quality, Water Resources, or Wildlife. The documents were reviewed
for overall usefulness to the goal of flood reduction. The documents were
ranked as excellent, good, fair, or not relevant. They were also ranked f
or
relevance of study goals, relevance of analysis, relevance of information,
and relevance of findings. In the final report, the documents are sorted by
category, then overall usefulness, and then by the ID number.


SubB
asin maps were created for
each
report that showed which area of the
watershed the study covered. The maps are based on the 12 digit Hydrologic
Unit Codes (HUC’s).
This is a method
of dividing up the subwatersheds
developed by the United States Geologic S
urvey
. In a few instances
,

the 10

digit HUC was used to identify the watershed.
The maps are included
separately from the Access database.





12


SETTING


Location


The Chehalis Basin,
with the exception of the Columbia River
,
is

the largest
watershed in Washington. It is bounded on th
e east

by the Cascade
Mountains

and the Deschutes River Basin
,

on the north by
Puget

Sound and
the Olympic Mountains, on the south by the Willapa Hills and the Cowlitz
River Basin, and on the west by the Pacific Ocean. Elevations vary from sea
level at Grays Ha
rbor to 5,054 feet (Capitol Peak
)

in the Olympic
Mountains.
The
Chehalis Basin

drains

2,766

square miles
(Tetra Tech

/KCM
and Triangle
Associates
,
2004
).


Sub
-
basins


The Chehalis
River flows

through the Cascade,
Puget

Lowlands and Coast
Range Ecoregions

(Figure 1)
. The outlet is Grays Harbor near Aberdeen.
The basin can be divided into sub
-
basins designed by the Washington
Department of Natural Resources (DNR) as the Upper Chehalis Basin
(WRIA 23) and Lower Chehalis Basin
(
WRIA 22).
The
Chehalis Basin

a
rea
by counties is
shown

in Table 1 (Anchor

QEA,LLC
, 2012).

A different
system used

to characterize sub
-
basins is shown in Table 2. This system is
the Con
servation Needs Inventory
used by the Soil Conservation Service
(SCS) in their 1972 river basin report

(
USDA,
S
oil Conservation Service

(SCS)
, 1972
). Also shown in Table 2
,

is the 12 digit HUC number for each
sub
-
watershed.


The
C
hehalis Basin
lies

mostly in Lewis, Thurston
,

Mason
and Grays
Harbor Counties

as shown in Figure 1
,
but also

drains portions of Pacific,
Cowlitz, Wahkiakum
, and Jefferson Counties
. Figures 2a and 2b

show

how

the sub
-
basins are separated by HUC’s
.


Population


The total population of the basin is approximately 140,000 people. The
major population centers are Cheh
alis (~6,000), Centralia (~12,000), in
Lewis County in
the upper basin,

and Aberdeen (~16,000
)
and

Hoquiam
(~9,700
) in Grays Harbor
County in

the lower b
asin. The communities of
13


Chehal
i
s and Centralia have experience
d significant
flood problems o
ver

the
ye
ars. The major population center
s in Thurston County that lie

within the
basin
are
Tenino

and the community of Rochester.
The average rate of
population growth
in WRIA 23
from 200
0

to 2025 is
projected to be 52%
(
Tetra Tech
/KCM and Triangle Associates,
2004
). There are many rural
communities in the basin such as Adna,
Dody, Dryad,
Bois
t
fort,

Curtis,
Napavine, Pe Ell
, Te
nino,

and Bucoda

in WRIA 23,
and
Elma, Montesano,
Hoquiam, Aberdeen, Westport, and Ocean Shores

in WRIA 22
. Many of
these have experi
enced

significant

flood damage
.


Potential Flooded Areas


It is difficult to exactly quantify the damages to rural communities from
flooding.
The Lewis County 2007 Flood Disaster Recovery Strategy

(
Cowlitz
-
Wahkiakum Council of Governments
,
2009)
determined th
at there
were

nearly 15 million o
f Federal funds allocated to 22 units of government
or non
-
profit corporations

as a result of the December 2007 flood
. This
included six fire districts, and the rural co
mmunities in Adna, Napavine,
Pe

Ell

as we
ll as

the Boistfort School and Water District. Lewis County an
d the
larger cities of Chehalis

and Centralia, also received extensive federal
assistance as

did the Port of Chehalis, Chehalis
-
Centralia Airport, Centralia
Public School District, Centralia Ch
ristian School, and Providence Health
Care System.
The 2009 report indicated that there were 9,222 acres of
agricultural land flooded in unincorporated Lewis County
,

whi
ch is 23% of
the 39,
861 acres of agricultural land in Lewis County.


Physiography and

Geology


Vashon glac
iation, which is the third stage of Frazer glaciation (16
,000 yrs
to 12,000 yrs BP), deposited coarse sand and gravel in the central basin
surr
ounding what is now Centralia. The Pu
get Sound Lobe of the Cordillean
i
ce sheet, which
occupied the Puget Sou
nd lowlands, terminated just north of
Lewis County (Figure 3
a
).


As the Vashon glac
i
er rec
eded a series of proglacial lakes formed filling the
main t
r
ough of Puget Sound and inundating the southern lowlands. Glacial
Lake Russell was

the first such larg
e recessional lake. From the vi
cinity of
Seattle in the north
,

the lake extended south to the Black Hills, where it
drained south into the Chehalis
River. Sediments from

Lake Russell formed
14


the blue
-
clay identified as the Lawton Clay.
Lake Russell was thought by
Bretz (1913) to have had an elevation of 110 to 130 feet above sea level.
The second major recessional lake was the glacial Lake Bretz. It drained to
the Chehalis River until glacial ice in the Leland Valley between
present

da
y
Quilcene and Discovery Bay in the northeast Olympic Penninsula melted,
allowing the lake’s water to rapidly drain north into the Straits of Juan De
Fuca.


The maximu
m extent of Vash
on Glaciation, and drainage

routes are shown
in Figure 3a. (
Noble and Wal
lace
,
1966). As shown in Figure 3a, glacial
meltwater flowed down the Skookumchuck River to the Chehalis River
where it dumped a large qua
n
tity of gravel. The Skookumchuck River has a
steeper gradient than the Chehalis (see Figures 3c verses 3b). The grav
els
which entered the Chehalis River valley at Centralia, constitute the most
southern advance of Vashon outwash in
to Pu
get Sound. The Chehalis Valley
was filled to an elevation of about 188 feet, which is considerably above the
pre
-
Vashon valley bottom.
Excavations of the gravel in Centralia exceed 75
feet of depth.


The gravel deposited at Centralia then created a dam across the Chehalis
River which created what Bretz cal
led “Lake Cheh
alis”.

The following is a
description of
the Lake Chehalis area by B
retz

(1913)
:
“The city of Chehalis
is about four miles up the river from Centralia, and stands at the same
altitude on the same flood plain. But whereas outwash gravels are at least 75
feet deep beneath Centralia, Chehalis is built of a valley fill of riv
er alluvium
and lacustrine deposits, and no trace of glacial gravel has been foun
d in the
region, except w
h
ere tr
ansported by
a
human
agency
. The region of the city
of Chehalis received no gravel

because the flowing water turned

downstream on entering Chehalis Valley at Centralia and the invading
gravels were carried back toward

the g
la
cier. Only standing water could
have e
xisted at the site of Chehalis when the gravels were de
posited, for the
valley was dammed by the outwash ab
out Centralia and water must have
backed up the Newaukum, Chehalis, and “Big Swamp” valley.” (Bretz,
1913)


Figure 3b shows the C
hehalis River in profile view.
The channel bottom at
the lower end shows the depos
i
tion from the Skookumchuck that causes th
e
river at low flow to run uphill. However, if one views the flood profile they
see the extensive flattened area starting at about Chehalis and extending
through to Centra
lia.

This flattening reflects
the lake formed
when the north
15


outlet of the Che
halis
River was blocked. Figure 3c
shows a profile of the
Skookumchuck River, without the flattening reflected in the Ch
ehalis
profile.
Some of the Chehalis Basin
streams have an irregular stair stepped
stream profile such as shown for th
e Newaukum River in Figu
re 3d.
At the
end of the ice age
,

me
ltwater from the glaciers in Pu
get Sound flowed down
the Black River and lower Chehalis River as shown in Figure 3a.


Bretz in 1913 (p.122 and 123), gave the following explanation for how the
dammed up gla
cial lakes d
rained: “But in Pu
get Sound all water escaping
from glacial lakes in the different valleys was forced to pass over the
Chehalis Sound divide into one drainage line. The result of this control of
glacial drainage by one pass was to limit subsidence of pond
ed waters whose
valleys had successively lower outlets exposed by ice retreat. Gradually
waters in the troughs and fjords of sufficient depth in the southern part of the
area united at a common level that was determined by the Chehalis Sound
divide east of

th
e Black Hills.
The water body
thus controlled was named
Lake Russell.” The common level of Bretz Lake was about 160 feet msl
and represents a lake level drained by way of the Black River.


During the t
ime that Vashon Ice occupied Pu
get Sound south o
f Everett,
most of western Washing
ton drainage that now enters Pu
get Sound from the
east, had to flow south through the Black River, past Gate, to the
Chehalis
River and the
n to the Pacific Ocean. After the Straits of Juan de Fuca
became free of ice
,

and n
orthward drainage
into Pu
get Sound returned,
the
Black River draining to the south became an underfit river. The river’s
drainage area became too small and the river’s cross section developed by
Pl
eistocene runoff, was too wide
to transport its available
sediment load.


The
older Chehalis
B
a
sin

before the most important
,

Pleistocene and
Holocene events that control the present physiograph includes
,


the Cascade
Mountains,
the Puget Lowlands, t
he Coast Range
and the Willapa Hills.
The

Cascade Range was formed by uplifting of tertiary age basaltic lavas,
pyroclastics, and sedimentary rocks. The uplift of the Cascade Range began
during the late Pliocene Epoc
h and continued on into the Ple
istocene Epoch,
a period of approximately six million years. Pleistocene glaciation has
modified the topography in the northern and eastern portions of the Chehalis
Basin.
The Cascade Mo
untains province is characteriz
ed by rough and
mountainous volcanic he
adlands and their foothills.
Much
of the

land is
above 2,000 feet.
Alpine glaciers in the Olympic Mountains had a major
impact in sculpturing the upland present topography.

16



The Willapa Hill Physiographic province extends from the Pacific Ocean
upstream to

the central basin. The Chehalis River sid
e hills, terraces and
flood plai
n make up the topography of this province. Exposed rock within
the Willapa province is composed of Tertiary age marine
and nonmarine
sedimentary rock
with interbed volcanic rocks.

These rocks were deformed
in the late Tertiary Period.


The Pu
get Sound Trough is a structural basin, an
d

extends into the foothills
of the Cascade Mountain,
the
Willa
pa Hills and Olympic Mountains of the
Washington Coast Range.
The Chehalis Valley i
s
in the southern end of the
Pu
g
et Trough and is
presently
characteris
ed by a broad, well developed
flood plain and low terraces surrounded by highly dis
s
ected uplands of low
to moderate relief that have broad rounded ridges. Valley bottoms are at an
elevation of
about 150 feet, a
nd uplands range from 300 to 600

feet.


The Chehalis River
is the main drain
a
g
e

in the C
hehalis Basin
. Its
tributaries
start in
the hills west of Doty, and flow generally eastward to Chehalis
where the river turns

abruptly to the north

(Figure 1)
.

The Chehalis flows
north into Thurston County near Centrali
a.

From near Grand Mound
,

the
ri
ver flows northwestward to Elma
, and the
n
flows west
ward to Grays
Harbor
.

A major tributary draining the Boistfort Valley

is

the South Fork
Chehalis River, which heads up in the hills southwest of Curtis.
Other large
tributaries are t
he Newaukum


River
which
has its
headwaters in the
f
oothills of

the Cascades

on the
south
eastern side of the basin
, and the
Skookumchuck
River that has it
s headwaters in the foothills of the northeast
portion of the basin.

In addition
,

t
he Wynoochee
, Satsop
and Hoquiam

Rivers are large tribu
taries
that
have headwate
rs in the south
ern

flank of the

Olympic Mountains

in Grays H
arbor County. The Humptulips
and Wishkah

Rivers

also have their headwaters in the O
lympic Mountains and flow into
G
rays Ha
rbor.

In the mi
d
-
basin
,
Black Lake

originates in wetlands

at the
northeast part of the the basin
.
Most of the Chehalis Basin
is lowlands
, with
elevation var
y
ing from sea level to 5,000 feet.


The 2003

US Army Corps of Engineers

r
eport states that geologic evidence
indicates that the Chehalis River has reworked
its valley since the deposition
of sand and gravel outwash that was derived from the glacial runoff. The
glacial sand and gravel can however still be found in the terraces alo
ng the
valley margin. The
US Army Corps of Engineers

(
2003
)

indicate
s

a time line
for the reworked river deposits
of 7,000

to 10,000 years old. The
17


reformation of the meandering river lateral and vertical accretion deposits to
form flood plains in the former lake beds is one of slow aggradation
dominated by silt cl
ay and o
rganic mud. The
US Army Corps of Engineers

(200
3) study noted that information they received from the
NRCS
,

f
ormerly
SCS
, showed that at least 50
% of the deposits in the upper five

feet of

valley
sediments are organic mud, silt or clay. This is consistent

with what is
reflected

in the block diagram (Figure 10
).


The
US Army Corps of Engineers

(2003
) report states that in 1890, the

main
stem

of
the Chehalis

River from RM 82 to the mouth became
progressively
shallower d
o
w
nstream and incr
easingly blocked by
snags.

Many shoals were
documented to be between .05 and 1.0 feet deep. This report (
US Army
Corps of Engineers
, 2003) also states that the survey plat noted “
Plat records
(1833
-
1860)
provide additional accounts of numerous side channels,
sloughs, and pond
s hydrologically connected to the Chehalis mainstem, the
Newaukum, and the Skookumchuck Rivers



Local Topography


There are m
ultiple

7.5 quad sheets th
a
t cover the basin. The USGS quad
sheets for

each county can be acquired electronically by doing a query

of t
he
GIS

(
Geographical Information Systems
)

data base in each county

(Lewis
County
,

2012
;

Thurston County
,

2012
;

Mason County, 2012
;

and Grays
Harbor County, 2012
)
.
A
erial photography of the Chehalis Basin includes at
least partial coverage in
1938, 1966,
and various flights from
1970 to
2002
,
and
2009
.
The Puget Sound LiDAR Consortium lists all LiDAR

data for the
Chehalis basin as collected by them and other entit
ies. The data is available
for
all of Thurston County and the mainstem of the
Chehalis River in Grays
Harbor County from 2000
-
2005, portions of Lewis County in 2005 and
2006, and the coastal areas and the Wynoochee River in 2009.



Lewis,
Thurston
, Mason and Grays Harbor Counties all have
a
GIS
data
c
enter, for the purpose of prese
nting an interactive web site to allow users to
view tax lots, aerial photos, topographic maps, and flooded areas. Layers
included in the maps are parcels, urban growth areas, zoning, transportation,
streams, aerial photos,
topographic maps,
proposed

Fede
ral Emergency
Management Agency

(
FEMA
)

zones, and othe
r

layers (
Lewis County
,

2012
;

Thurston County
,
2012
;

Mason County, 2012
;

and Grays Harbor County,
2012
).

18





Land Use


The Chehalis Basin in 1966

(Glancy, 1971) was about 73% f
orestry, 13%
cropland
, 6%

pasture; 1% urban, and 10%

other. The Chehalis Basin
Partnership
,
(
CBP
) r
eported in 2004 (Tetra Tech
/KCM and Triangle
Associates
) that the
r
e

was 7% agriculture. This would be a drop of 12% in
agriculture in 40 years. Commercial dairy, livestock and cro
p farming
operations are located mainly in the low lying valleys adjacent to the
Chehalis
R
iver and tributaries.



Climate



The climate of the area is characterized by cool dry summers and mild moist
winters over most of the basin. The greatest amount of

precipitation falls
between the months of October and May. Precipitation varies from a
minimum of 40 inches
in
the central basin (Chehalis Area) to 220 inches in
the higher elevations in the Olympic Mountains (Wynoochee and
Humptulips) watersheds. Precip
itation usually occurs as rain o
r

snowfall at
higher elevations. However
,

snowfall does not accumulate over any
pr
olonged period below 2,500 ft. in

elevation. Maximum temperatures in the
warmest months are usually in
the 70’s occasionally

reaching 80 to 90
degrees. Winter temperatures are mild in the mid
-
basin agricultural areas
and generally ra
n
g
e from
the
mid 3
0’s to
5
0’s. River d
ischarges tend to peak
between December and March, but the Chehalis River flowed at or above
bankfull for muc
h of April in 2012.


Surface Water



Annual and Mean Flows


Surface
w
ater
a
nnual streamflow follows the variation of climate and annual
precipitation as is discussed above. Stream flow has been measured by the
U.S. Geological Survey (USGS) at stream g
aging stations located at various
locations in the basin since approximately 1929. The mean annual
streamflow measured at the existing stream gages over their period of record
varies from 3.14 cubic feet per second per square mile of drainage area
19


(csm),
or an annual mean runoff depth of 42 inches for the Skookumchuck
River, to 10.3 csm or 140.1 inches of mean annual runoff depth, for the
Humptulips River. Table 3, also shows the mean of the average annual
runoff for sites on the Chehalis River, Newaukum
River, Skookumchuck
River, Satsop River, Wynoochee River, and Humptulips River. The highest
annual mean streamflow and lowest annual mean stream flow for the period
of record of these sites are also shown on Table 3.


The streamflow rates vary throughout

the year as well as varying at different
locations in the Chehalis Basin. Table 4 shows mean monthly streamflow at
selected USGS stream gaging stations. Since for precipitation, winter is the
wet season and summer is the dry season, mean monthly stream
flow has the
same annual pattern as precipitation, with stream flows that are generally
highest in December and January and lowest in August. The maximum and
minimum mean monthly streamflow for each month is also shown at each
selected gaging station on T
able 4, for the period of record of the gage.


The mean annual and mean monthly stream flows are essentially a summary
of the mean of the daily measured streamflow. Table 5 shows the highest
and lowest mean daily stream discharges measured at each of the
selected
USGS stream gage stations. Also shown is the date on which those highest
and lowest mean daily flows were measured.
Additionally,
Table 5
presents
what streamflow rate at each site was exceeded 10 percent of the time, 50
percent of the time, and

90 percent of the time.


Regulatory minimum instream flows were established by
the
Department of
Ecology

(DOE)
for

31 control points in the

Chehalis Basin in 1976.
(
Tetra
T
ech
/KCM and Triangle Associates
,
2004). These 31 control points in the
Chehalis Basin were established to continue a healthy stream for fish. An
instream flow study in 2002 looked at streamflow where there was no
historical data, such as
the type of data shown in Table

4. This study foun
d
that flows were below the regulatory minimum stream flows for most of the
monitoring period for Chehalis River at
the
Highway 6
Bridge
, Black River,
Newskah Creek, East Fork Hoquiam River and East Fork Wishkah
River
.
Flows were above regulatory minimum f
lows before dropping below in
August at the following stations: South Fork Chehalis River, Middle Fork
Satsop River, and Wishkah Rivers. The following stations did not drop

below the regulatory minimum: C
edar Creek, Decker Creek, Johns River,
and West Fork

Hoquiam.


20


Since seasonal variations in streamflow are important for water quality and
fish habitat, it is important to be able to make estimates of flow that will
occur as well as what has occurred. As a basis for designing for the future,
flow informat
ion is usually presented in a probability format. Two methods
are especially useful for planning and designing:




Flow duration, the probability a given streamflow was equaled or
exceeded over a period of time.



Flow frequency, the probability a given strea
mflow will be exceeded in a
year.

The data presented in Table 5, and discussed above, relative to the
streamflow rate at each site was exceeded 10 percent of the time, 50 percent
of the time, and 90 percent of the time is an example of a “flow duration”
an
alysis.

The “flow frequency” is defined as the probability or percent
chance of a given flow being exceeded or not exceeded in a given year.
Flow frequency is often expressed in terms of recurrence interval or the
estimated number of years between exceed
ed or not exceeding the given
flows.

Guidelines for determining the frequency of peak flow events at a
particular location using streamflow records are documented by the Bulletin
17B

(
Interagency A
dvisory Committee on Water Data

(IACWD)
,
1982)
.



Peak
Flows


Table 6
a

presents estimates for selected frequencies of peak flow rates for
active USGS stream gaging stations in the Chehalis Basin. The relationship
between frequency and peak flow rates at these stream gage sites was
determined by the USGS and published in “Ma
gnitude and Frequency of
Floods in Washington”, USGS Water Resources Investigation Report 97
-
4277.
(Sumioka
, Kresch, and Kasnick
, 1998)

This report, which was
produced in 1997, included flow data through water year 1996 (October to
September). For the act
ive USGS stream gaging stations listed in Table 6
a
,
another 15 years of data has been collected since 1966
,

which changes the
peak flow rate versus frequency relationship. Thus for Table 6
a
, the Peak
Discharges for the various frequencies were either obta
ined from recent
Flood Insurance Studies or estimated using the current data and procedures
in Bulletin 17

(
IACWD
, 1982)
.


21


Table 6a
, includes estimates for the USGS stream gage on the Humptulips
River. This station operated from 1934 to 1979, and was then

discontinued.
Prior to 2003, a new site was installed on the Humptulips River 1.0 miles
downstream from the previous site. In order to present an estimate of peak
flow data for the Humptulips River, the gage records were combined for the
1934 to 1979 si
te and the 2003 to 2011 site. The drainage areas for the two
sites are similar, but there is a data gap between 1979 and 2003.

Table 6
b

provides a list of discontinued USGS stream gages in the Chehalis
Basin. Unfortunately, due to cut backs in government
programs, not all of
the USGS stream gages that have been installed in the Chehalis Basin are
still in operation. The peak discharges at these gages for various frequencies
are not included in Table 6
b
, because the lack of recent flow events would
affect t
he accuracy of the discharge versus frequency relationships. The
active s
tream gages, listed in Table 6a
, are co
-
funded by the following
cooperators:



Lewis County Public Works



Skookumchuck Dam, LLC



Thurston County



DOE



Tacoma Public Utilities



Grays Harbor
County


Historic
Flooding


The Chehalis and Skookumchuck Rivers were formed by runoff from the
Puget Glaciation and have probably been subject to periodic flows that rise
and over top the banks of these rivers and inundate normally dry land ever
since. The first people who lived in this region probably adapted to the
overbank flows and did not consider the floods as damaging.

However, it
has been reported that legends of the Chehalis and Cowlitz Native
Americans include accounts of flooding that
occurred before written records
were kept

in what is now Lewis County
(
Cowlitz
-
Wahkiakum Council of
Governments
, 2009
)
.

However,
following settlement of the area by
emigrants from other parts of the United States, and the building of the
railroad,
flooding
was

consid
ered
damaging and events were documented in
written records.


The Centralia newspaper has documentation and reports of 34 flood events
from 1887 to 2007 in Lewis County, 27 of which included the Chehalis
22


Basin, (
The
Chronicle, 2008
;
Cowl
itz
-
Wahkiakum Council of Governments

January
,

2009). Table 7
a

lists reported flood events from 1930 to 2010 by
Water Year (October to September) from 9 different sources in the entire
Chehalis Basin. Thes
e sources include The Chronicle,

Lewis County 200
7
F
lood Disaster Recovery Strategy,

Comprehensive Flood Hazard
Management Plans for Lewis and Grays Harbor Counties
, and the Chehalis
Reservation
and Flood Insurance Studies for areas in Lewis and Grays
Harbor Counties. The first column of flood dates in
Table 7
a

only reports
the flood events by year, whereas the remaining columns report month and
year. Not all of the flood dates in the first column match up with a flood
date from another source. This indicates that the flood dates in the first
column ma
y include flood events in Lewis County outside the Chehalis
Basin.


The flood events in the Chehalis Basin are not evenly distributed across the
basin. Floods in Lewis County do not always occur in Grays Harbor
County, and likewise floods in Grays Harbor
County do not always also
occur in Lewis County.


Documentation of flood events extends back in time to 1887, but records on
the streamflow for the flood events in the Chehalis Basin only extends back
in time to the year 1929 for two of the existing stream

gages, and most of the
existing gages were installed much later. So for approximately the first 50
years of documented flood events, we have no stream gage data for
comparison with recent flood events.


As a point of reference, the oldest currently act
ive stream gage in
Washington State is on the Spokane River at Spokane, and this gage has
stream flow records that extend back to 1891. By the year 1919, there were
209 stream gaging stations operating in Washington State, but there were
none in the Cheha
lis Basin (
Parker and Lee,

1923).


Table 7
b

presents the Peak Discharge at selected Stream Gages for the 35
flood events shown in Table 7
a

which are listed by month and year. These
tables cover the
time period

from 1930 to 2010 because the stream flow
rec
ords of documented floods do not extend back to before 1930.
Unfortunately
,

not all of the gages listed have periods of record that extend
back to 1930. But the period of record for all the gages listed extends to
2010 or 2011. The Humptulips River gage does have a period where the
gage was discontinued that extends from 1979 t
o 2003.

23


The Peak Discharge for Selected Frequencies shown on Table 6
a
, was used
to determine the flood frequency range for the flood events in Table 7
b
.
Peak Discharge values alone allow the comparison of different flood events
at a single gage site. But

the flood frequency allows the comparison of a
single flood event at different gage sites.

There are flood events shown in Table 7
b

that do not have any peak
discharge or flood frequency listed for one or more of the stream gages
during the period of reco
rd for gage. That is because there is only one peak
annual discharge for each water year, and if peak annual discharge date does
not match the flood date
,

it is not listed. Thus on water years that have two
or more flood dates listed, there will only be
a flood discharge listed for one
of the flood dates at a gage.

As was stated above, Table 7
b

shows that flood events are not evenly
distributed across the Chehalis Basin. Even the December 2007 event varies
from a greater than 100
-
year event at some sites

to a less than 2
-
year event at
other sites.

One of the statements that have been made is that in the Chehalis Basin in
the last two decades, four 100
-
year floods have occurred: in January and
November 1990, February 1996, and December 2007. This statemen
t is
mathematically incorrect. There can only be one 100
-
year flood at a gage
site in less than a 100 year period. According to Table 7
b,

the December
2007 event was a 100
-
year flood at several of the gage sites and the
February 1996 flood was a 100
-
year

flood at the Newaukum River gage site.
But the January and November 1990 events were less than 100
-
year events
at all the gage sites in Table 7
b
. So it appears that the correct statement is
that two 100
-
year floods have occurred in the last decade.

The p
revious
statement about the four 100
-
year floods, may have been trying to point out
that successive flood events appear to be increasing. If the January and
November 1990 events were analyzed without considering the events in
1996 and 2007 they may be con
sidered to be 100
-
year events. Table 7
b

shows that at the Grand Mound gage site the top 5 peak flow events are the
January 1972, November 1986, January 1990, February 1996, and December
2007 and they successively increase in discharge rate, each one being

the
flood of record at the time of the event. There is also a general trend that is
similar at the other gages with floods after 1972 generally being

larger than
those before 1972.
This is a major area of concern t
hat has not been
investigated.


As show
n on Figures 4

and 5
,

and in Table 7
b

t
he gage station recorded a
peak flood of 79,100 cfs in the December 12, 2007 flood that had a
24


frequency
of
>
100 year. This flood caused millions of dollars in urban and
rural area damages.


Map 8 from the
Lewis Cou
nty 2007 Flood Disaster Recovery Strategy

(
Cowlitz
-
Wahkiakum Council of Governments
, 2009
)

shows that
most of

the agricultural land on the Lewis County bottomlands has a flood problem.

Based on soils
, there

were 277,560

acres (
SCS
,

1972)

that have a flood
problem

or drainage problem

or both
. This wetness
along with drainage
problems,
l
imits the agricultural
use mostly

to
pasture.
However
,

thousands
of acres have been drained so the actual area with a drainage problem in the
basin should b
e much less.


Water Bodies


Table 9
a

lists the number and total area of named lakes in the Chehalis Basin
and Table 9
b

lists the number, total area and total storage volume of the
dams and reservoirs.


Combining the two tables
gives a result of there being
117 lakes and
reservoirs with a total surface area of 5,362 acres in the Chehalis Basin.


The Southwest
ern
Washington River Basin Report

(
SCS
, 1972)

noted that
there were 7,146 acres of fresh water lakes and reservoirs in 1972
.
However
,

there was a gross error in the River Basin Report in that it reported
that Lake Sylvia in Grays Harbor County had a surface area of 3,327 acres.


According to
DOE
, Dam Safety Section, Inventory of Dams, Lake Sylvia is
a small reservoir in Gra
ys Harbor County with a surface area of 32 acres
behind a 32 foot high dam with a maximum storage volume of 510 acre
-
feet.
It is owned by the Washington State Parks.


Table 9a

shows that there are 49 named lakes in the Chehalis Basin
,

with a
total surface

area of 1569.2 acres. HUC 17100104 Lower Chehalis and
HUC 17100105 Grays Harbor (W
RI
A 22) contain 29 lakes and HUC
17100103 Upper Chehalis (W
RI
A 23) contains 20 lakes.


The largest lake in the Chehalis Basin is Black Lake in Thurston County
with a surfac
e area of 576.1 acres. Black Lake is unique in that it currently
drains to both the Chehalis Basin and to Puget Sound. This is both unusual
25


and unnatural. Black Lake originally only drained into the Black River and
the Chehalis Basin until 1922, when the

Black Lake Ditch was constructed
from the north end of Black Lake to Percival Creek which drains into Budd
Inlet of Puget Sound.


The second largest lake is Nahwatzel Lake in Mason County with a surface
area of 268.8 acres and drains to the East Fork of t
he Satsop River. The
third largest lake is Duck Lake in Grays Harbor County with a surface area
of 197.0 acres and it drains to Grays Harbor.


Thus
,

the three largest lakes constitute 66 percent of the total surface area of
the 49 named lakes reported on
Table 9
a
.


The named lakes for Table 9
a

were obtained from a 1961 inventory of water
resources in Washington State. The lakes listed in the Chehalis Basin were
then verified on recent US
GS 7.5 Minute Quadrangle Maps.
Some of the
lakes listed on the
1961 i
nventory were found to no longer exist.
Developing
an inventory of unnamed lakes was beyond the scope of this report,
especially since they would have a minimal impact on evaluating flood
reduction alternatives.


Table 9
b
shows that there are 68 dams and r
eservoirs in the Chehalis Basin
with a total reservoir surface area of 3,972 acres and a maximum storage
volume of 182,294 acre
-
feet. The Lower Chehalis and Grays Harbor
watersheds (W
RI
A 22) contain 16 dams and reservoirs and the Upper
Chehalis watershed
(W
RI
A 23) contains 52 dams and reservoirs.


The largest dam and reservoir in the Chehalis Basin is the Wynoochee Dam
on the Wynoochee River in Grays Harbor County with a maximum storage
of 76,000 acre
-
feet. This dam was constructed in 1972 by the U.S Army

Corps of Engineers to provide flood control, industrial water supply for the
City of Aberdeen, and to enhance fisheries. Ownership of the dam has been
transferred to the City of Aberdeen. In 1994
,
Tacoma Power added a
hydroelectric powerhouse one
-
quarter

mile downstream of the dam. The
industrial water supply is stored in the reservoir and released to flow 43.7
miles downstream to the City of Aberdeen diversion. This is the only dam
and reservoir in the Chehalis Basin that was designed to provide flood
protection.


26


The second largest dam and reservoir is the Skookumchuck Dam on the
Skookumchuck River in Thurston County with a maximum storage of
60,000 acre
-
feet. The Skookumchuck Dam was constructed in 1970 to
provide water to the Centralia Coal Power Pl
ant and is currently owned by
TransAlta. TransAlta also owns the Centralia Coal Power Plant and the
Centralia Coal Mine. The industrial water supply is stored in the reservoir
and released to flow 15 miles downstream to the Centralia Steam Electric
Proje
ct (Centralia Coal Power Plant) diversion. This dam was not designed
to provide flood protection.


Of the 52 dams and reservoirs shown in Table 9
b

for Thurston and Lewis
Counties (W
RI
A 23), 37 of these dams and reservoirs were constructed as
part of the o
peration of the Centralia Coal Mine and are owned by
them
.
Active mining at the Centralia Coal Mine stopped in November 2006 and
operations are now focused on compliance and reclamation activities.


The dams and reservoirs for Table 9
b

were obtained from
the “Inventory of
Dams in the State of Washington”

(
Department of Ecology

State of
Washington (DOE)
, 2011)
. Many of the dams inventoried have been
constructed since the Southwest River Basin Report was prepared in 1972.


Estuary


Grays Harbor is the major body of salt water in the basin. It is shaped like a
low
-
topped boot with the cities of Hoquiam, Aberdeen, and Cosmopolis
(Figure 1)
near the boots toe in the eastern part. The City of We
stport would
be at the boots hee
l, and the

City of Ocean Shores to the north, near the top
of the
boot.
Grays Harbor is approximately 15 miles long and six miles
wide.


Grays Harbor provides ocean
-
going vessels access to the Hoquiam
-
Aberdeen area, and is the main port for numerous fishing vessel
s. Grays
Harbor is the only coastal estuary in Washington with an authorized deep
water navigation channel. There are 26,603 acres of salt water within the
basin.


Work
by Peterson

and Phipps (1992) det
ermined the filling rate
of Grays

Harbor during the

Holocene (last 11,000 years),

as sea level rose. Grays
Harbor Valley was at a
depth 60

to 70 meters below present sea level. Their
(Peterson and Phipps, 1992) seismic studies and drill coring, established a
27


general textural sequence of sand and mud coars
ening upward to sand and
gravel in lower bay reaches, and gravelly sand and sandy gravel fining
upward to sand and mud in upper
-
bay reaches. Radiocarbon dating of core
sample wood, carbonate shells, and peaty mud yields help them develop
a
deposit age

curv
e beginning

at 57 meters depth,
at 10,760

+/
-

90 yrs.

(RCYBP, uncorrected). Average basin sedimentation rates decreased from
1.2 cm
. /
yr. about 11,000 years
BP
, to about 8,000
BP
.

By middle
Holocene (5,000 to 6
,
000 RCYBP) the filling rate in Grays
Harbor
decreased to about 0.1 cm
. /
yr. That trend corresponded to about a
fourfold

decrease in the average rate of basin fill (Peterson and Phipps, 1992). There
would have been episodic coastal uplift and subsidence events (1
-
2 meter of
vertical displace
ment) that influenced the Grays Harbor filling.

As
discussed

in Reckendorf
,

et al
.
,

(2003) the regional

average for 11 Cascadia
sub
-
su
b
duction events that likely caused subsidence and rebound uplift, is
450 yrs +/
-

150 years.


Twi
t
chell and Cross (200
2
)

r
eported very large volumes of sediment from
the Columbia River system were deposited in Grays Harbor Bay. The extent
and depth of the Holocene aged sediment deposits from the Columbia River
system were mapped and used to indicate how the Columbia River l
ittoral
cell evolved while the ocean levels rose during the last 11,000 years.


The COE in 188
2
noted (
Powell

and
Habersham, 1882
) that the entrance to
Grays Harbor did not need improvement. They stated
they compared the
entrance over

19 years and found that the entrance moved about 1,000 ft
.

southward. They al
so

said that the Chehalis River is noted for having gravel
bars, rafts, and snags that are obstructions to travel.
The first channel
enlargements w
ere

approved in 1892,
and
were

for deepening the channel
2.5 to 3.0 fe
et over three or four shoals. T
here were 401 snags removed from

the river in 1899
(
Secretary of War, 1900
). The COE in 1893 stated that
from the mouth of the Chehalis River
to Montesano,
for 15 miles
,

there is 18
fe
et of water depth at high water, and coasting vessels traverse this portion
of the river. From Mon
tesano to Elma, 16 miles, the river is slightly affected
by tides, and has a general sufficiency for light draft boats. Above Elma
,

the
river is practically

blockaded during the summer and fall by snags
and
shallow

water.


In 1933
,

the COE stated that
the existing

project
was 100

feet wide and 18
feet deep at mean low water from the mouth to the junction
of the

Lit
tle
Hoquiam and the East Branch
, a distance
of 2 miles. The
y

proposed that the
28


project be enlarged to 600 feet wide
at the mouth
and

30 feet deep. That
channel would decr
ease to 26 feet deep in Grays Ha
rbor
,
to the Union
Pacific Railroad Bridge in Aberdeen
,

and to be between 200 and 350 feet
wide. T
hey also proposed that there be a channel 150 feet wide and 16 feet
deep in the Chehalis River from Cosmopolis to
Montesano (
War
Department
,

Office of Chief of Engineers
,

1933
).


Maintenance dredging for a navigation channel
has

been continuous for 105
y
ears.

The COE has published numerous reports over the years on
maintenance dredging, and on the removal
of snags

and piles (A
bstracts 152
-
16
2
,
164,
307

and 523
, in Appendix
) In

1982
,

they proposed dredging 24
miles beginning at River Mile

(RM)

2.3 on the Chehalis River near
Cosmopolis and ending at Harbor Mile 22, which is 2.5 miles seaward of the
mouth of the estuary
.



The volume of materials removed
for channel enlargement or maintenance
dredging
and the problems related to ocean disposal h
ave increased over the
years.
To address some of the concerns for dredging and disposal, the COE
did a

study in 1977 (
DOE
, 1977
) evaluated the effects of pipeline dredging,
hopper dredging, disposal in upland dikes, disposal in unconfined

tidal areas,
and

disposal in an
d adjacent to the mouth of G
rays Harbor. The primary
effects of hopper dredging during the periods of observation wer
e

an
increase in turbidity,

which was a sediment plume that
caused a decrease in
light transmission.


Drainage


T
here is
an

extensive system of drainage and drainage ditches in the basin
that have substantially altered the natural wetlands.
An example of the
drainage alteration is shown as follows.
Figure
6a is

a 1938 aerial photo of
the Centralia area, showing extensive wet
lan
ds with Reed soil. Figure 6
b
shows the same area in 2011. A small area of the wetland was converted to
create Hays and Plummer Lake,
as both areas were used for borrow material
to build Interstate 5. However,

most of the wetland was drained for urban
d
evelopment. Interstate 5 was built across the center of the
wetland that

is
the center of former Bretz Lake. Two other com
parisons are shown in
Figures 6c and 6
d, nea
r the community of Porter, and 6e and 6
f in the
St
earns Creek Basin
.
The west part of th
e Porter area has been extensively
drained as shown by the drain ditches and light
er green

colors on the colored
29


photograph, verses the
wet
ter

past
ure and less drainage
in the
darker
green
areas to the right of

the state highway. In Figure 6
e the 1938 aer
ial photo
shows an extensive poorly drained dark area on the western (left) portion of
the aerial and d
ark grey to the north.
In

Figure 6
f

the 2011

photo

shows
many

drain
age

ditches and lighter colors for land drained for agricultural
purposes.


Sediment
ation


There is only one specific study of sediment transport in the Chehalis Basin.
This is the United States Geological Survey (USGS) study, Sediment
Transp
ort by Streams in the Chehalis R
iver Basin, Washington, October
1961 to
September 1965
. This study of suspended sediment
load measured

sediment at 19 different locations. Annual sediment loads varied from
270,000 tons to 690,000 tons. About 74

% of the sediment yield was
derived from Satsop and Wynoochee

Rivers
. Most of the sediment is
transported bet
ween October and April. Table
3 in

the USGS Water Supply
Paper 1798
-
H (Glancy, 1971)
,

shows
drainage area, approximate
topographic relief, and

the percent of time when suspended sedim
ent load
was transported
.
During the study period, 90% of

the suspended sedi
ment
discharge occurred in 5
-
10
% of the time from headwater streams sample
sites,
and 15
-
20
% of

the time at lower

main
-
stem sampling stations. The

short intervals are
likely
peak storm
and or landslide
related.

The Glancy

(1971)
,
USGS s
tudy suggests

that most of the sediment is derived from
streambank erosion. However
,

other s
tudies (Pease and Hoover,
1957)

have
suggested that sediment is also derived from erosion of landslide. Recent
studies of
landslides
(
Weyerhaeuser
, 1994
) also
indicate the importance of
landslide
s

as a contributor to the sediment load.


The suspended sediment yield
in the Glancy

(
1971
)

study

shows
considerable variation
. The yield can be expressed

in two ways as sh
own in
Table 10
. One way is in terms of tons

per square mile (t./sq.mi.). On that
basis (Glancy, 1971) estimated mean annual suspended

sediment

at Grand
Mound Gage (

895 sq.mi.) at about 150 t./sq.mi., but at o
nly 98 t/sq.mi at
Porter Gage ( 1,294
sq. mi
.). This can be interpreted
that additional
drainage
areas
tributary to the Chehalis River below the Grand Mound Gage
contribute a much lower sediment yield, for

the same drainage area, that
results in

a dilution effect at the Porter Gage.

In other words there is a much
lower sediment input from side tributaries to the Chehalis River, below
30


Grand
Mound compared

to above Grand Mound.

The Black River is the
main tributary between Grand Mound and
Porter and

joins the Chehalis
River upstream
from the community of Oakville. Glancy (1971)
acknowledged that the Black River contributed little runoff and sediment
yield to the main stem Chehalis River. This difference in sediment yield
betw
een Grand Mound and Porter is mo
st expressed during period
of high
runoff.


The

other method

(Table 10)
, such as in

the
USDA
,
Erosi
on, Sediment, and
Related Salt P
roblems and Treatments and Opportunities

(
USDA,
SCS
,
1975),

expresses

sediment
yield in

acre feet per square
mile
(ac.ft./sq.mi
.).

As shown in Table

10
, the

sediment yield varies
from .
07 ac
-
ft/sq.

mi. to
over 1.
0 ac.
f
t./s
q.mi
.

A background rate for a forested watershed with few
landslides i
s between 0.1 and 0.2 ac.ft/sq.
mi. (
USDA,
SCS
, 1975)
That rate
seems to fit

for many of the watershed
s

in the Chehalis Basin
. However,
the
upper Chehalis at Doty
(D.A
. of 113 sq. mi. at gage), which has an average
annual sedime
nt yield of 0.33 ac.ft./sq. mi.,

South Fork
Chehalis near
Bois
t
fort (D.A. 48 s
q. mi. at gage), which has a sediment yield of
0.37
a
c.ft./sq. mi.
and
for

Satsop River near Satsop (D.A. 209
ac.ft/
sq. mi. )
which has a sediment yield of 0.56 ac. ft./sq. mi. a
nd Middle Fork of Satsop

which has a sediment yield of 0.7 ac. ft./sq. mi.
,

are much higher than
the
background
rate for
forested watersheds.


The mean annual sediment yield of the Satsop River is about 44

% of that
for the entire study area. The suspended sediment yield measured near
Satsop,
is considerably greater
than

any other watershed in the basin except
the
Wynoochee

River

watershed.

The Glancy (1971)

study noted that some
of the higher sediment yield watershed
s

like the S
atsop (which was 90%
forested at the time of the

study)
had extensive clearcut areas, but ga
ve no
analysis of their impact. Glancy (1971)

indicates

that there is extensive
meander migration caus
ing streambank erosion on the S
atsop,
and the

sampled sediment was coarser

grained than many other tributaries evaluated.
However, the

contribution of sediment varies significantly among tributaries
of the Sat
sop
, from

0.06 ac. ft
. /
sq. mi on the East Fork of
Satsop

to greater
than 1.0 ac. ft
. /
sq. mi. on the West Fork
.


The forest practice regulations have become
stricter

since the work of
Glancy (1971). For example sidecast road construction on steep, uns
table
slop
es, which was common the time of the G
lancy study
,

and sediment
yields

likely reflect that practice,
is no longer permitted. In addition culvert
31


sizing and spacing has increased as well as limiting the size of clearcuts, and
widening the riparian buffer strips.



T
he Newaukum
River,
was

shown (Glancy,

1971) to have suspended
sediment
that
varied

between
tributaries from

.17 ac. ft/sq.

mi. to .22
ac.
ft./sq.mi. We noted that

the Newaukum
River

stream profile is stair stepped

(Figure 3d
)
,

rather than smooth
curve
d

as shown for the Skookumchuck

River
Figure 3
c, or U
pper Chehalis

Figure

3b
. A stair step profile is a
reflection
of the river down
-
cutt
ing and head
-
cutting reflecting an unstable
heading condition
, such as occurs in Stage II of the Channel Evolution
Model (
N
atural Resources Conservation Service

(NRCS)
, 2007
)
.
However
,

this potential condition would need to be field checked. In add
ition,
if
headcuts are found they

may have worked their way upstream because
of
downcutting

in the Chehalis River.
The bed material along the Newaukum is
mostly cobble showing that the finer fraction is being scoured out.

In
addition
,

the average percentage of c
oarse grained suspended load (particles
greater than 0.062 mm) of the Newaukum
River
is about twice that on the
Skookumchuck

River
.


Glancy
(
1971) noted
,

that there was a general decrease in average particle
size from Doty to Porter gages, wh
ich indicates

that: (1) the propo
rtions of
suspension of fine sediment increases in a downstream direction, (2) more of
the coarser material tends to move as bedload past the two stations

and is
therefore not reflected in the suspended sediment load measurements
, and
(
3) individual particle abrasion in a downstream direction effectively
decreases average particle size.


Upland Erosion


Landslides are a natural occurrence on the forest landscape of Washington
State, but improperly executed forest practices, including sidecast road
construction on steep slopes, poor water management along forest roads and
clearcut harvest of unstable slope
s can increase landslide rates. Forest
practices are regulated by WAC 222, which is administered by the
DNR
.
Most of the landslides in the Chehalis Basin occur on forestland. WAC 222
-
16
-
050 defines potentially unstable slopes and landforms

(Washington Stat
e
Legislature, 2012a)
.


32


The DNR has developed a Landslide Hazard Zonation (LHZ) project. The
goal of the LHZ project is to create an improved screening tool for DNR
regulatory personnel and foresters and landmanagers in identifying unstable
landforms. The

purpose is to eliminate error of omission, as much as
possible, for the forest practices permitting process.


Each LHZ consists of a map of known landslides, a map of landslide hazard
areas and a report detailing the landslide hazard findings for a part
icular
watershed administrative unit (WAU).
As
e
ach watershed is completed the
information is available to the public through the LH
Z completed products
web site.
The
landslide inventory and hazard z
one GIS is available at the
Forest Practices GIS special
Data Sets

page.


The following LHZ projects are completed in the Chehalis Basin:



1.

Upper North Fork and Upper South Fork Newaukum Rivers,
completed in 1994 and included in the Watershed Analysis report
produced by Weyerhaeuser (1999)

2.

Chehalis Slough (Se
r
dar

and Powell,

2008)

3.

Lower Wishkah (Othus

and Parks,

2009)

4.

Garrard Creek (Paulin
and Goetz
, 2008)


More dated landslide studies include a study in the Centralia
-
Chehalis area
of Lewis County (Fiksdal, 1978), and a slope stability map in Thurston
County
(Artim, 1976).


The following watershed analyses have been completed for WAUs in the
Chehalis Basin, following the protocol described in WAC 222
-
22
(Washington State Legislature, 2012a)
and the Forest Practices Board
Manual


Section 11:


1.

Stillman Creek

(
Weyerha
e
user, 1994a)

2.

Chehalis Headwaters

(Weyerha
e
user, 1994b)

3.

Upper North Fork Newaukum

and
Upper South Fork Newaukum

(Weyer
haeuser, 1999)

4.

Upper Skookumchuck

(Weyerhaeuser, 1997)

5.

East/West Humptulips

(Lingley, Diem, and Schelmerdin
, 2003)

6.

West Fork
Satsop

(Weyerha
e
user and Simpson Timber, 199
6
)

7.

Upper Wynoochee

(U.S. Forest Service, 1996)

8.

Wishkah Headwaters (Bretherton
, et al.
, 1993)

33



One exampl
e of a watershed analysis,

is Stillman Creek
which
is shown
here.
Both a hydrologic assessment and a mass w
asting assessment
(
Weyerhaeuser
, 1994
b
) were conducted for Stillman Creek in Lewis County.

Four types of mass
wasting were identified in the S
tillman Creek basin. In
order of frequency they were shallow, rapid landslides (132); debris torrents
(40);
deep
-
seated slumps (14); and small sp
oradic deep seated slides (8)
(
Weyerhaeuser
, 1994
b
).


Deb
r
is torrents accounted for 21% of all landslides
and all of them delivered sediment to th
e stream system.

About 78% of the
debris torrents initiated as road fill

failures.

In general,
they star
ted as very
small to shallow, ra
pid slides on very steep slopes (~ 100%) in the higher
elevations of basins
.
They then

incorporate flood and spring w
ater and
become a viscous flow.
They have been observed to flow down creeks

a
s far
as 2,000 to 15,000 feet.
Fifteen of the debris torrents were concentrated in
the upper reaches of
the
West Fork of Stillman Creek.

Shallow rapid
landslides were categorized according to the land use a
ctiv
ity associated
with the instability such as
: road construction, timber harvesting, streamside
erosion, and natural forest instability. Road instability occurred on moderate
to steep slopes, gene
rally ranging from 30 to 75 % a
nd ranging in size from
very small to very large. Howe
ver the slope of t
he road fill was commonly
75 to 100%.
About 72% of these road related slides delivered sediment to
the stream. Road related slide
s

were predominantly (75%) associated with
un
-
compacted sidecast fill material placed on slopes. These fills were
mobilized
by saturation of the fill and debris by winter storms, both by direct
precipitation and channelization of surface water owing to the lack

of a
cul
vert
, poor placement

of the culvert

or poor maintenance of
the
culvert
.
Failures of cut slopes on the upper si
des of roads accounted f
or about 21

%
of roa
d
-
related failures.
Weyerhaeuser
(
1994) noted that such cut slope
failures resulted in the diversion of

ditch water across the road, which can

saturate and cause instability of the fill slope.




The Washington State Legislature passed a law that created
Road
Maintenance and Abandonment
Plan
(RMAP). The law became effective in
2000 and is administered by the DNR. The law was revised concerning
small landowners in 2006. The law covers only non
-
fed
eral land and
requires all large forest landowners, and most small forest
landowners,

to
submit RMAP’s to DNR.


The goal of
the
RMAP rule is

to have forest roads, excluding orphan roads,
on non
-
federal land brought up to the standards required by the fores
try
34


practices law (
Washington State Legislature, 2012a
). Originally, the date for
100 % compliance
was July 2016.

In October 2011, the legislature
authorized an extension of up to five years (2021).



According to the

WAC 222
-
24

(
Washington State Legislat
ure, 2012a)
all
forest roads, except orphan roads, must be maintained by the owner, until the
road is abandoned. The goals for forest road maintenance are spelled out in
WAC 222
-
24
-
010

(
Washington State Legislature, 2012a)
, and include:


1.

Providing fish pa
ssage.

2.

Preventing mass wasting.

3.

Limiting deliver of sediment and runoff to typed waters.

4.

Avoiding capture and redirection of surface and ground water.

5.

Providing for passage of some woody debris.

6.

Protecting streambank stability.

7.

Minimizing new roads.

8.

Assuring no net loss of wetland function.


In 2008

(
The Upslope Process Scientific Advisory Group
)

DNR initiated the
Mass Wasting Prescription
-
Scale Effectiveness Monitoring Project
to
determine if the Forest and F
ish Rules

(FFR)

for harvest on potentially
unstable slopes, road construction, and maintenance rules as well as the
RMAP rules, are effective at limiting landslides for forest practices.
Two
FFR

identified proj
ects have been designated to map

unstable landforms.
The R
egional Landform Identification Project (RLIP) has been completed
(
Dieu
, et al.
, 2011). That project identified and mapped regional landforms
at 1:24,000. Continuing is a
LHZ

project to

map landslides, and unstable
landforms. This mapping is performed at t
h
e watershed administrative unit
(WAU) scale, and the focus is on rule
-
identified landforms, RLIP identified
landforms, and other landforms of concern. Results of both of these projects
are being used as a screening too
l to determine unstable slopes
and
to

assist
with the implementatio
n of the unstable slopes rules
(
Dieu
, et al.
, 2011).


As stated in the 2009 Le
wis County 2007 Flood Disaster R
ecovery Strategy,

some
areas in the Chehalis Basin including

the Willapa Hills in the Upper
Chehalis watershed t
hat are relatively prone to landslides. Between
December 21, of 2007 and January 17, of 2008, Washi
ngton DNR mapped
1,
685 landslides. Of these
,

1,655 occurred in Lewis County. The DNR

(Sarikhan, et al., 200
8
)

states that the
ir
post 2007 storm runoff
sample
35


represents between 30

%

and 50

% of the landslides that occurred

statewide

during the December 2007 storm.


The DNR stated that from their sample
,

that the

most common landslides
were debris slides, many of which were transformed into debris flows
.
Sometimes deposits created temporary dams in streams that later burst,
creating a debris torrent or debris flow downstream. During the 2007 flood
landslide debris accumulated on the flood plains as both sediment and as
Large Woody Debris (
LWD
)
.


DNR (2
008
)

stated that debris flows created dams downstream from the
landslides
.
They also created large deposits of coarse material that did not
fully dam the river but obstructed flow. As pointed out by Benda and Dunne
(1997a
;b
)
and by

Reckendorf, (2008a
;b
)

t
he landslide deposit in streams are
reworked by large storms and progress in a downstream direction. These
landslide deposits move as a coarse mass in pulses with large runoff events
,
and

the streams usually find it easier to erode the streambanks than to

move
the coarse material from the landslide mass.




Accelerated
Streambank Erosion


Reports such as the
Glancy (
1971) study of sediment transport a
nd other
studies mention stream
bank erosion or show a few pictures, but there is no
comprehensive
streambank erosion inventory.

The LCCD

has done a
general study using aerial photos

of
a
sample area in the upper basin
, to

identify
stream bank

erosion locations. A
sample
map

of that study

is
presented as Figure

12
.



Gro
und Water



Ground water occurr
ence is variable within the basin, and depends on local
geology. Variation
s

are due to rock type, thickness, rock alteration and
deformation. In addition
,

the distribution and type of Pleistocene glacial
deposits

has a great influence on shallow ground water sources. The u
plands
of the Chehal
i
s Basin are
, in general, made up of shale, siltstone, s
andstone,
and volcanic rock of T
ertiary Age. These rock units have low ground water
yield,

and often the water is of l
ow drinking water quality becau
s
e of
mineral content (
USDA,
SCS,

1972). Most wells in Tertiary r
ocks yield only
enough water for domestic use. An exception to this is the Newaukum
36


Watershed that

has artesian wells that yield several hundred gallons a
minut
e. The Newaukum Artesian Basin has an area of 25 square miles, and
lies within a southeast trending syncline. Water taken from
the Newaukum
Artesian Basin is
from non
-
marine sedimentary rocks. These areas are
locally recharged from upland runoff.



Chehal
is Basin lowlands
t
end to have Quaternary Age deposits of coarse
grained materials, such as gravel, sand and conglomerate. These are mostly
glacial
Pleistocene glacial

outwash deposit, and are of major importance as a
source of useable ground water. Glaci
al
-
fluvial deposits of sand and
gravels

underlie upland plains and terraces to depths of 50 to 200 feet. Well tapping
these deposits usually yield 50 to 150 gallons per minute.

Outwash deposits

of sand and gravel deposited fr
om melting of the
Puget

Sound

Lobe are ver