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5-4-1995

A Hydrologic Analysis of Government Island, Oregon A Hydrologic Analysis of Government Island, Oregon

Scott Gregory Bittinger Portland State University

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Recommended Citation Recommended Citation Bittinger, Scott Gregory, "A Hydrologic Analysis of Government Island, Oregon" (1995). Dissertations and Theses. Paper 4851. https://doi.org/10.15760/etd.6727

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An abstract and thesis of Scott Gregory Bittinger for the

Master of Science in Geology presented May 4, 1995 and

accepted by the thesis committee and the department.

COMMITTEE APPROVALS: , Chair

DEPARTMENT

Kenneth M. Cruikshank

JRepresentative of the Office of Graduate Studies

,Department of Geology

* * * * * * * * * * * * * * * * * * * * * * * * * * * * *

ACCEPTED FOR PORTLAND STATE UNIVERSITY BY THE LIBRARY

b Y C."? a, o~ '4n4c:,e .'![;t' /970

~)"

ABSTRACT

An abstract of the thesis of Scott Gregory Bittinger for

the Master of Science in Geology presented May 4, 1995.

Title: A Hydrologic Analysis of Government Island,

Oregon.

Government Island, located in the Columbia River

approximately 16 km (10 mi) upstream of the confluence

with the Willamette River, is a wetland mitigation site

prompted by expansion of the southwest quadrant of

Portland International Airport. The purpose of the study

is to predict water levels in two enclosed lowland areas,

Jewit Lake and Southeast Pond, based on levels of the

Columbia River, precipitation, and evapotranspiration.

Mitigation is intended to convert 1.13 km2 (237 acres) of

seasonally flooded wetland to 1.27 km2 (267 acres) of

semi-permanently flooded wetland and seasonally flooded

wetland.

Flooding of the wetland is most likely to occur

December through January and May through early June when

Columbia River water levels at Government Island exceed

3.6 m (12 ft) m.s.l. Flooding of Jewit Lake occurs

through a channel connecting the wetland to the Columbia

River.

A groundwater model (MODFLOW) was parameterized to

2

simulate the hydrology of the wetland. Observations of

the subsurface stratigraphy in 25 soil pits, bucket auger

cores, and during installation of water monitoring devices

were used to estimate thickness and lateral extent of a

confining unit that overlies an aquifer. Climatological

data for 1994 and water levels were entered into MODFLOW

to calibrate rates of water movement through the

subsurface. Periods of drying for Jewit Lake and

Southeast Pond were predicted based on precipitation and

actual evapotranspiration rates expected to be present in

the study area between June and December.

Results of groundwater modeling show that Jewit Lake

will maintain surface water above 3.6 m (12 ft) in most

years. Southeast Pond is expected to dry annually as

mitigation is unlikely to change the hydrology of

Southeast Pond.

Groundwater modeling predicted the types of wetlands

present at different elevations by evaluating periods of

drying within the wetland using the U.S. Fish and Wildlife

Service classification of wetlands method. Results

suggest that Jewit Lake will be converted to semi­

permanently flooded wetland below 3.6 m (12 ft) in

elevation. Southeast Pond will remain a seasonally flooded

wetland as a result of mitigation.

A HYDROLOGIC ANALYSIS OF GOVERNMENT ISLAND, OREGON

by

Scott Gregory Bittinger

A thesis submitted in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE in

GEOLOGY

Portland State University 1995

ACKNOWLEDGEMENTS

I would like to thank PSU faculty members Ansel

Johnson, Michael Cummings, and Kenneth Cruikshank for

their advice and extensive amount of time invested in this

project. Time and assistance by Stewart Ashbaugh, Greg

Briggs, Janine Boer, Taryn Eddy, Rand Fisher, Doann

Hamilton, Chris Humphrey, Jim Martin, Brian Petersen,

Michael Pollock, Sherry Spencer, Susan Stucker, Christy

Vockler, Ken Walsh, and Jennifer Whitebread are greatly

appreciated.

I would like to thank the Port of Portland for

selecting the Center for Science Education at PSU to study

and monitor the Government Island wetlands mitigation site

and for the funding provided to PSU.

TABLE OF CONTENTS

ACKNOWLEDGEMENTS PAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

TABLE OF CONTENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

LIST OF TABLES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

LIST OF FIGURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

The Columbia River.............................. 5 Late Pleistocene/Holocene geology............... 8 Historical changes on Government Island......... 11

PRESENT WETLAND CONDITIONS ON GOVERNMENT ISLAND...... 13

HYDROGEOLOGY OF THE GOVERNMENT ISLAND WETLAND........ 22

Columbia River levels.... . . . . . . . . . . . . . . . . . . . . . . . 22 Water level monitoring.......................... 26 Flow rates through the dam ...................... 32 Climatological data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 7 Sediment particle size analysis ................. 43 Seismic refraction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Summary of factors affecting the hydrogeology of the Government Island mitigation site ........... 51

GROUNDWATER MODELING ................................. 53 GROUNDWATER MODEL DESIGN ........................ 53

Stratigraphic representation in the groundwater model .......................... 53 Evapotranspiration in the groundwater model 62 Calibration of the groundwater model....... 66

RESULTS OF GROUNDWATER MODELING................. 71 Climate as a variable in groundwater modeling.......................... . . . . . . . . . 71 Hydraulic conductivity of the confining unit as a variable in groundwater modeling. 80 Aquifer transmissivity as a variable in groundwater modeling ....................... 86 Predictions of site conditions based on groundwater modeling ....................... 86 Summary of the groundwater model design parameters and the results of groundwater modeling....................... . . . . . . . . . . . . 91

DISCUSSION OF HYDROLOGY.............................. 94

iii

TABLE OF CONTENTS (Continued)

DISCUSSION OF EXPECTED WETLAND CONDITIONS FOLLOWING MITIGATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6

RECOMMENDATIONS FOR FUTURE WORK AND IMPROVEMENTS TO THE MITIGATION PLAN .................................. 110

REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

APPENDICES

1. HYDROGRAPHS OF THE COLUMBIA RIVER FROM 1973 TO 1989. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

2. PARTICLE SIZE DISTRIBUTIONS ................ 133

3. SEISMIC REFRACTION DATA .................... 149

4. STRATIGRAPHIC COLUMNS ...................... 160

LIST OF TABLES TABLE PAGE

I Approximate water depths in Southeast Pond between October 23rd and October 30th, 1993 ............................. 28

II Government Island water levels ......... 29

III The volume of water in Jewit Lake and Southeast Pond at lake levels between 3 . 2 m and 4 . 6 m ........................ 3 2

IV Flow rates through the dam as water flowed into Jewit Lake in January and February of 1995 ....................... 37

V The grain size percentages for 15 samples collected on Government Island ................................. 47

VI Seismic refraction on Government Island; May 7th and 8th, 1994 .......... 51

VII Approximate elevations of the aquifer top at the locations shown in Figure 28 ..................................... 61

VIII Actual and modeled water levels on Government Island for February, March, and April, 1994 ........................ 68

IX Simulation identifying months where water is absent in Jewit Lake and Southeast Pond for years when flooding occurs through the spillway channel ................................ 76

X Summary of the variables used in MODFLOW to simulate the hydrogeology of Government Island ................... 93

FIGURE 1.

2.

LIST OF FIGURES PAGE

Location of the Portland International Airport SW quadrant site .................... 2

Map showing Government Island, and the Portland, Oregon and Vancouver, Washington areas ....................................... 3

3. Map of Government Island, Oregon ............ 4

4. The stages of the development of a braid in a laboratory flume river ...................... 7

5. Geologic cross section based on drill holes across the I-205 bridge ..................... 10

6. Modern monthly adjusted flow of the Columbia River at Vancouver, Washington and at the mouth ....................................... 12

7. A one foot contour map of the mitigation site ........................................ 14

8. The Government Island mitigation site dam ... 15

9. Map of the predicted wetland areas resulting from mitigation ............................. 18

10. River stage at Government Island in 1993 .... 23

11. River stage at Government Island in 1994 .... 24

12. Mean Columbia River elevation at Government Is 1 and 19 7 3 - 19 8 O • • • • • • • • • • • • • • • • • • • • • • • • • • • • 2 5

13. Locations of water monitoring points ........ 30

14. Volume of water in Jewit Lake at water levels between 3.2 m (10.5 ft) and 4.6 m (15.0 ft) ................................... 33

15. Volume of water in Southeast Pond at water levels between 3.5 m (11.5 ft) and 4.6 m (15.0 ft) .................................. 34

16. River level, Jewit Lake level, and Southeast Pond level from November 1, 1994 to February 21, 1995 .................................... 35

FIGURE 17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

vi

LIST OF FIGURES (continued} PAGE

Time required to raise Jewit Lake from 3.6 m (12 ft) to 4.6 m (15 ft) based on flow rates through the dam in January and February, 1995 ........................................ 36

1993 precipitation .......................... 39

1994 precipitation .......................... 40

1993, 1994, and average monthly evapotranspiration in Vancouver, Washington.41

Evapotranspiration and lake evaporation for selected days in June, 1994 ................. 44

Hydrometer sampling site locations .......... 46

Seismic refraction sites .................... 49

MODFLOW node grid. Each node is 152 m by 152 m (500 ft by 500 ft) ........................ 54

Schematic diagram of cross section A-A' as entered into MODFLOW ........................ 55

Location of Jewit Lake and Southeast Pond in MODFLOW at elevations above 3.6 m (12 ft) ... 56

Locations of Jewit Lake and Southeast Pond in MODFLOW at elevations between 3.3 and 3.6 m ( 11 and 12 ft ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 8

Locations where the aquifer was located during fieldwork ............................ 60

Cross section A-A' .......................... 63

Cross section B-B' .......................... 64

Site locations used for cross section construction ................................ 65

Evapotranspiration as a function of head .... 67

Precipitation, evapotranspiration, and groundwater infiltration from June through December with average precipitation and evapotranspiration rates .................... 72

vii

LIST OF FIGURES (continued) FIGURE PAGE

34. Precipitation, evapotranspiration, and groundwater infiltration from June through December with above average precipitation and below average evapotranspiration rates .. 73

35. Precipitation, evapotranspiration, and groundwater infiltration from June through December with below average precipitation and above average evapotranspiration rates .. 74

36. Water levels in Jewit Lake from June through December with variable rates of precipitation in years when no flooding occurs through the spillway channel ......... 77

37. Water levels in Southeast Pond from June through December with variable rates of precipitation in years when no water flows overland from Jewit Lake to flood Southeast Pond .............................. 7 8

38. Monthly evapotranspiration entered into MODFLOW ..................................... 81

39. Variations in Southeast Pond water levels from June 1, 1994 to September 1, 1994 using hydraulic conductivity values given for silts ................................... 84

40. Variations in Jewit Lake water levels from June through November using hydraulic conductivity values given for silts ......... 85

41. Variations in Jewit Lake water levels from June through November using transmissivity values given for sands ...................... 87

42. Variations in Southeast Pond water levels from June through November using transmissivity values given for sands ....... 88

43. Jewit Lake levels from May 31st to December 31st with average precipitation ............. 89

44. Southeast Pond levels from May 31st to December 31st with average precipitation .... 90

FIGURE 45.

46.

viii

LIST OF FIGURES (continued} PAGE

Zone of higher hydraulic conductivity at seismic refraction station G-9 .............. 98

Locations of stratigraphic columns that were not used for cross section construction ............................... 161

INTRODUCTION

Wetlands are vital ecosystems that provide habitat

for wildlife, recharge of groundwater systems, and

temporary storage of water during periods of high

discharge. Concern over loss of wetlands prompted the

U.S. Congress to include provision 404b in the Clean Water

Act of 1980 (Experimental Laboratory, 1987). This

provision requires no net loss of wetlands and allows

development of new wetlands as a mitigation where existing

wetlands have been destroyed or modified. Expansion of

the southwest quadrant of Portland International Airport

(Figure 1) by the Port of Portland prompted development of

a mitigation site on Government Island in the Columbia

River.

Government Island is a 9.5 km2 (2000 acre) (SRI,

199la) alluvial river bar located between river mile 111.5

and 117.5 of the Columbia River, approximately 8 km (5 mi)

east of Portland, Oregon (Figure 2). The island is owned

and managed by the Port of Portland. One square kilometer

(237 acres) selected as the mitigation site (Figure 3) is

to be modified from seasonally flooded wetlands to a

combination of semi-permanently flooded and seasonally

flooded wetlands. Site modifications to produce the

desired results included construction of a dam at the end

of a channel that connects Jewit Lake, the largest area

subject to seasonal flooding, and the Columbia River. In

2

order to attain the desired mitigation, the hydrology of

Government Island plays a critical role. In June, 1993, a

program of field observations was implemented to obtain

'"~I """ .> ~.

ii

POX SW Quadrant Site

~ < 0

~ ,..,

------ 3 Was ------4

"' 0 N

N

Figure 1. Location of the Portland International Airport SW quadrant site (SRI, 1991a).

Multnomah Channel

West Portland

Willamette River

5 km Scale: ----~

North

Washington

Vancouver

Island

U.S.G.S. gauging station *Vancouver weather

station

East Portland River

Oregon Troutdale

Figure 2. Map showing Government Island, and the Portland, Oregon and Vancouver, Washington areas.

L>J

Washington North

Island

Lake

Columbia River

Southeast

Oregon McGuire Sandy '-River

Scale:

Figure 3. Map of Government Island, Oregon. ~

data for development of a groundwater model for the site.

Data collection continued during the next 20 months until

the end of February, 1995. These data were gathered from

Jewit Lake, Southeast Pond, and monitoring points within

the study area. The groundwater model relates the water

levels of Jewit Lake and Southeast Pond to levels of the

Columbia River, precipitation, and evapotranspiration.

The Columbia River

The drainage basin of the Columbia River covers an

area of 660,480 km2 (245,765 mi 2). The Columbia River has

a mean annual flow rate of approximately 6,800 m3 /s

(240,139 ft 3 /s) (Simenstad and others, 1990).

5

Construction of hydroelectric dams beginning in 1937

altered the natural rates and timing of river stage events

(Sherwood and others, 1990). Maximum flow rates of the

Columbia River are now significantly smaller than peak

flow rates prior to dam construction. Land tracts

adjacent to and within the Columbia River were once

seasonally inundated by the spring flooding of the

Columbia River. Since flow rates are now restricted, much

of this land area is no longer inundated on a yearly

basis.

The Lower Columbia River, where Government Island is

located, is a braided river characterized by channel

6

division around alluvial islands. The growth of an island

begins by the deposition of a channel bar due to sorting

and deposition of the coarser fractions of the bedload

which locally cannot be transported. The channel bar

grows downstream and in height by continued deposition,

forcing water into the flanking channels, which, to carry

the flow, deepen and cut laterally into the original banks

(Figure 4). Such deepening locally lowers the water

surf ace and the central bar emerges as an island

stabilized by vegetation (Leopold and Wolman, 1957) .

Figure 4 shows the stages of the development of a

braid in a laboratory flume experiment performed by

Leopold and Wolman (1957) . Comparison of a flume river to

a natural river is based on the principle that processes

occurring on a small scale are similar to those that occur

on a large scale. This model does not consider changes in

flow rates that rivers experience. The landforms found in

the Lower Columbia River (Figure 2) resemble those formed

in flume experiments (Figure 4). Continual shifting of

channels builds a heterogenous bar consisting of patches

of materials of different size and degrees of sorting

(Leopold and Wolman, 1957) .

Channel bar sediments in the Lower Columbia River

are likely to have a particle size distribution that is

coarser than fine sand since coarser fractions of the

D.:>!..~NATION

3 hOUfS

r-------22

_STATION __ _

l.l 18 JO

~~(/] ~D<X•t more co••~e tl'lan °''I'"•' s•nd

--------

' 6 hOu•~

Ftt!

I I

:~I I !

2t

lt>Ot.·<

9 l'tours

13 houts

Figure 4. laboratory

--~.-

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1nc1ptent b••

lsl•nd

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u ~

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0 2~

'"!'!11.•

lsl•nd 0t ••H "lel'ly out ol •1te1

-w~~dehned edge of bar

lll·de'•ned edge of bar

SUCCESSIVE CROSS SECTIONS

AT SUTION J4

Water su~ace

lnt11al

~ fttt

The stages of development of a braid in a flume experiment (Leopold and Wolman, 1957) .

7

8

bedload are more difficult to transport. Holocene

sediments in the Lower Columbia River Basin are dominantly

fine sands (Gates, 1994).

Late Pleistocene/Holocene Geology

Between 15,300 years and 12,700 years B.P. (Waitt,

1985) catastrophic flooding occurred in the Columbia River

Valley. These floods occurred periodically as glacial

Lake Missoula slowly filled and catastrophically emptied

its waters. Each filling of Lake Missoula contained over

2100 km3 (500 mi 3) of water. Within a few weeks, up to

1590 km3 (380 mi 3) of water would break away an ice dam

and flow towards the Columbia River Valley at velocities

of 49-81 kph (30-50 mph) (Allen and others, 1986). The

flood waters scoured the Columbia River valley between 40

and 100 times (Waitt, 1985). The last great flood

inundated the Portland basin to an elevation of 130 m (400

ft) 12,700 years ago (Allen and others, 1986).

In latest Pleistocene time, sea level began to rise

as continental ice sheets and polar ice caps began

melting. During Holocene time the lower Columbia basin

began infilling with sediment. Sea level rise has the

same general sedimentologic effect as damming a river

(Gates, 1994). The river adjusts to a higher base level

by aggrading sediments in an upstream direction. It was

during this aggradation that Government Island evolved as

an alluvial island in the Columbia River channel.

9

In the Portland area, the Troutdale Formation and the

Sandy River Mudstone form the basal contact of the post

Missoula Flood deposits of the lower Columbia River

(Gates, 1994). A cross section across the west end of

Government Island based on drill holes for the I-205 Glen

Jackson Bridge (Figure 5) constructed by Gates (1994)

shows the alluvial Troutdale Formation contact ranges

between -24 m (-80 ft) m.s.l. beneath the northern channel

of the Columbia River to -55 m (-180 ft) m.s.l. beneath

the Oregon shoreline of the Columbia River (Figure 5)

(Gates, 1994) . Beneath the Oregon shoreline of the

Columbia River, the Troutdale Formation pinches out. The

pinchout of the Troutdale Formation occurs at a 24 m (80

ft) scour channel cut into the upper Sandy River Mudstone

Formation (Gates, 1994). It is unknown whether this

channel eroded during the Missoula floods or is a feature

formed by the early Holocene Columbia River.

Government Island is part of the Horseshoe geomorphic

surface of Multnomah County, Oregon (Parsons and Green,

1982). The Horseshoe surface is one of low relief and

includes the stream channel and associated features (point

bar deposits, channel fillings, and abandoned meanders).

The surf ace is generally underlain by coarse-grained or

Washington (North)

~

I Oregon (South)

,,,--. __, ...... ...__,,.

c 0

__,

240

160

80

0 0 > <O

w -80

-160

-·240

G

'<t"I()" °' - ,.,, coco co co a en "f""f°..,...,...,. '<t"

tO OJ -1-97 ....

503

t

505

' l Government Island

i 6-4-9

'\.

6+8

G'

It) 6-4-0 ;;; /

240

160

80

0

-80

-160

-240 • . ··-··-·· ··-··-··-··-··-··L ' I ·- - ·-··- ·-··-··-[ -320- I I I I I I I I I l • I I I I I I I I I I I I I I I I I I i I I I I I I I I i I I I I I I I I I - J:2g 0 2000 4000 6000 8000 1 0000 :. 12000 14000

fit I '

~ .

. . . . . .

= . . . . . . . - . . . . . . . . .

~ Figure 5.

Silt and Mud; unconsolidated fine grained deposits.

Fine sands; . unconsolidated, well sorted alluvium .

Medium .to fine sands; unconsolidated alluvium with graded bedding •

Mazama ash; tephra layer occurs in drillholes 645, 64-6, 648, and 649.

.-;::1·::a:::q.

::8*::~:~::: ·:::.<?' ••• 'cJ ·::.o·::a:.:

.. + + + . + + +

(

+ + + + + +

+ + + + + +

Disla nee (Feet)

I .} t

Coarse sands with scattered gravel; unconsolidated Holocene alluvium, includes pre-Holocehe deposits above 40 feet elevation O'iJ the north shore •

I '

Boring Basalt; flows possibly interb~dded within · the Troutdale and S<:Indy River Mudstone Formation4. Found only in borehole 499. ~ ,

Troutdale Formation; lithified coarse conglomerate.

Vertical Exaggeration X5

[2] - .

.

Sandy River Mudstpne: lithified fine graindd mudstone .

Not.e::s - Solid line inalo:rta:s known No fine incfic:atoc irtfen-ed

ad. ct.

..;.J

<V <V ...__

0 0 N

::::E

0 <D

52.3

I [

1000 feet

300 Meters

Sore Hole Site

Base of Boring

Geologic cross section based on drill holes across the I~205 bridge (Gatas, 1994).

10

moderately coarse-grained alluvium. Elevations are

generally less than 6 m (20 ft) .

11

Soils of the Horseshoe surface are too young to show

well developed weathering horizons on Government Island.

Four soils; the Rafton, Sauvie, Faloma silt loams and the

Pilchuck sand, are present (Soil Survey Staff, 1983). The

Rafton, Sauvie, and Faloma silt loams are distinguished by

vegetation, elevation, thickness of organic horizons,

depth to mottles, the presence or absence of gleying, and

the amount of time annually that water is present at the

ground surface (Soil Survey Staff, 1992).

Historical changes on Government Island

Following construction of hydroelectric dams on the

Columbia River beginning in 1937, the hydrology of

Government Island changed. Hydroelectric dams store water

at all times of the year, modifying the length and level

of peak river flows. The decreased level of peak river

flows prevents Government Island from being inundated with

water on an annual basis. Estimates of unregulated

average discharges of the Columbia River from 1969 through

1982 based on river level data are given in Figure 6

(Sherwood and others, 1990). Unregulated runoffs are

approximated by adjusting for monthly reservoir storage.

Figure 6 shows that highest average monthly river flows

12

would occur in April, May, and June if flow rates were

unregulated.

Inspection of aerial photographs show that trees

became established on Government Island following

construction of hydroelectric dams on the Columbia River.

Annual flooding of Government Island prior to regulation

of river flows likely prevented trees from becoming

established.

zoooo

19000

1&00] 14000 a [o

0 0 -'j 12000

(/) -400

x ,, ~ "j -10000 l/)

3 300 s 0

·-' 9000 -~ -a::: ~ w 0 :> eooo ...J ct( 200 u..

0:::: w

4000~ / -------- ~:·.·.::·.···:::::::::::::::::···:.:.::::::-:::·::.:::.-:·.:·:·.:·:·:-:·:::::::::::<~ I- ~ 0::::

100 2000

0 J I I I I I ··.··. j :::.: .. _::;: ··;·· . ·.· .. --;- ::·:·:: ·.-/. . .... i°.:·.·.· ...... j f 0

OCT NOV DEC JAN FEB MAR APR ~y JUN JUL AUG SEP

Figure 6. Modern monthly mean adjusted flow of the Columbia River at Vancouver, Washington and at the mouth. Monthly flows have been averaged for the period 1969-1982 and adjusted for reservoir storage to approximate natural runoff conditions (Sherwood and others, 1990).

PRESENT WETLAND CONDITIONS ON GOVERNMENT ISLAND

Figure 7, prepared by Oakley Engineering Inc. (1992),

shows the mitigation areas selected for this study. A

channel was excavated between 1937 and 1945 between the

north channel of the Columbia River and the northwest edge

of Jewit Lake (Figure 7) . The original purpose of this

channel was to drain Jewit Lake in the summer months to

allow grazing and agriculture. The channel is now being

used to flood Jewit Lake during peak flow events of the

Columbia River. A dam that allows water to flow into

Jewit Lake was constructed in October of 1993 by the Port

of Portland at the mouth of the channel to retain water in

Jewit Lake and prevent fish from entering Jewit Lake. A

schematic diagram of the inside face of the dam is shown

in Figure 8. The dam allows water to flow through spring­

loaded gates when the Columbia River reaches an elevation

at Government Island between 3.6 and 4.7 m (12 and 15.3

ft) m.s.l. The spring loaded gates close themselves when

the Columbia River drops below the water level in Jewit

Lake. At river levels above 4.7 m (15.3 ft), water may

flood Jewit lake by flowing through an open spillway

grating. If Jewit Lake reaches a level above 4.7 m (15.3

ft), water will flow back out into the Columbia River

through the open spillway grating. Thus the dam can

maintain a maximum water level of 4.7 m (15.3 ft) in Jewit

Lake.

Columbia Riv~r

\\·. ___ .. --~-

North

··.,°'··.

GOVERNMENT ISLAND

150 m Scale: r===---- --1

:-·-.... .. {

LAKE ., \ \

.. -...... --...._ ·· ... ----~- .. .... ·-- ....

. ! X LOWl'O«THi.....J. --

B.e'. Jl.7'

.......... •"'·· ........ .

'1

// \~:.~ --::;-.

--~-=--~

\, __

Figure 7. A one foot contour map of the mitigation

· ...........

_)

-~- ... ··

f-.l ~

7.2 m m.s.l.

4.7 m m.s.l.

3.6 m m.s.l. D

I

open spillway grates

spring­

loaded gates D ~ control valve

6 m.-------------------

Figure 8. Government Island mitigation site dam. This view is facing north (downstream) from the spillway channel.

15

16

Jewit Lake and Southeast Pond (labeled 'Pond' in

Figure 7), are ephemeral lakes which contain water 3 to 10

months of the year depending on levels of the Columbia

River, precipitation, and evapotranspiration. The

spillway weir and inlet spillway shown in Figure 7 have

not been constructed. The ditch plug shown in Figure 7

was placed in the channel in 1992. The ditch plug was

used to hold water in Jewit Lake before the darn at the

mouth of the channel was constructed. The ditch plug was

removed in November of 1993 following completion of the

darn.

Modification of the Government Island wetland from

seasonally flooded wetlands to a combination of semi­

permanently flooded and seasonally flooded wetlands should

change the times of the year that surface water is present

in the Government Island wetland. Seasonally flooded

wetlands in the Government Island area should contain

water early in the growing season (approximately May

through July) and have dry conditions late in the growing

season (approximately August through October) . Semi­

permanently flooded wetlands in the Government Island area

should contain water throughout the growing season

(approximately May through October) in most years

(Cowardin and others, 1979, Soil Survey Staff, 1983).

According to the U.S. Fish and Wildlife Service

17

Classification of Wetlands in the United States, the study

area on Government Island satisfies criteria for the

palustrine system at the broadest level of the

classification hierarchy (Cowardin and others, 1979).

Palustrine wetlands may be situated shoreward of lakes,

river channels, or estuaries; on river floodplains; in

isolated catchments; or on slopes. They may also occur as

islands in lakes or rivers.

Palustrine emergent and palustrine forested are the

two classes of wetland found in the study area.

Approximately 0.77 km2 (161 acres) of palustrine emergent

wetland and 0.36 km2 (76 acres) of palustrine forested

wetland are present within the pre-mitigated study area

(Galen and others, 1992). The mitigation plan of Galen

and others (1992) indicates that 1.07 km2 (225 acres) of

persistent emergent wetland and 0.20 km2 (42 acres) of

forested wetland are expected to be present following 5

years of mitigation. Figure 9 shows where the palustrine

emergent and palustrine forested wetland are expected to

be located following mitigation. The persistent emergent

wetland is expected to contain a submergent plant

community (0.34 km2, 73 acres) and an emergent plant

community (0.72 km2, 152 acres).

The emergent wetland subclass of the palustrine

emergent class is characterized by erect, rooted,

300 m Sc a 1 e : i-------~

persistent emergent wetland with a submergent plant community

persistent emergent wetland between 12 and 14.5 feet m.s.l.

14.5 and 16 feet m.s.l.

Figure 9. Map of the predicted wetland areas following mitigation.

North

/I""

f-l 00

19

herbaceous hydrophytes, excluding mosses and lichens. The

wetlands on Government Island are dominated by

Calamagrostis A. (reed canary grass), a perennial

herbaceous species that is not native to Oregon. Reed

canary grass is not a hydrophyte because it grows in

wetland and non-wetland conditions (S. Spencer, personal

communication, 1995) . Even though reed canary grass is

not a hydrophyte, 0.77 km2 (161 acres) have been

delineated as persistent emergent wetland (SRI, 1991b,

Galen and others, 1992). Plant associations and soil

characteristics were used to delineate the Government

Island wetland.

A submergent plant community is expected to be

present between elevations of 3.2 and 3.6 m (10.5 and 12

ft) as a result of mitigation (Galen and others, 1992).

Submergent plants lie entirely beneath the water surface

except for flowering parts in most species (Cowardin and

others, 1979). Periodic drying of the lakes below 3.6 m

(12 ft) was expected to effect the submergent plant

community. The submergent plant community is expected to

tolerate periodic drying of the lakes. Lake levels are

expected to remain above 3.6 m (12 ft) in most years after

mitigation (Oakley, 1992, Galen and others, 1992).

Persistent emergent plant communities are expected to

exist between 3.6 and 4.9 m (12 and 16 ft) in elevation.

20

The plant communities between 3.6 and 4.4 m (12 and 14.5

ft) are expected to differ from the plant communities

between 4.4 and 4.9 m (14.5 and 16 ft) in elevation.

Eleocharis R. Br. (spikerush), Scirpus L. (bulrush) ,

Bidens L. (beggars tick), Sagittaria L. (wapato), and

Typha L. (cattail) (Hitchcock and Cronquist, 1973) are

expected to become the dominant plant species between 3.6

and 4.4 m (12 and 14.5 ft) in elevation, with surface

water present 6-12 months of the year. Herbaceous

hydrophyte grasses are expected to be present between 4.4

and 4.9 m (14.5 and 16 ft) in elevation. Surface water is

expected to be present 6 months of the year to a maximum

depth of 0.5 m (1.5 ft) following mitigation (Galen and

others, 1992).

Sections of Jewit Lake and Southeast Pond are

nonpersistent emergent wetlands because at times of the

year there is no emergent vegetation. This type of

wetland is found below about 3.8 m (12.5 ft). The areas

within the lakes that have surface water present for the

greatest amount of time during the year are nonpersistent

emergent wetlands. Centunculus minimus (S. Spencer,

personal communication, 1995), an emergent vascular plant,

grows in these areas following lake drying during the

growing season. C. minimus is an annual mudflat species

that must germinate each year. C. minimus will not

germinate in standing water and does not occur in the

presence of surface water. The presence of C. minimus

below 3.8 m (12.5 ft) indicates that perennial surface

water must not have been present in the study area prior

to site mitigation.

21

Areas within the Government Island wetland that

support trees are classified as forested wetlands.

Forested wetland is characterized by woody vegetation that

is 6 m (19 ft) or taller. Salix lasiandra (Pacific

Willow) and Populus trichocarpa (Black Cottonwood) (Arno,

1977) are the dominant species in the Government Island

forested wetland. These species are characteristic of the

broad-leaved deciduous subclass of forested wetland.

Water regimes of wetlands are defined in terms of the

growing season since periods of flooding in the dormant

season may have little influence on the development of

plant communities. The growing season in the Government

Island area is from late spring through early fall (Soil

Survey Staff, 1983). The entire Government Island wetland

area has a seasonally flooded water regime prior to

mitigation. Seasonally flooded wetlands have surface

water present for extended periods early in the growing

season, but water is absent by the end of the growing

season in most years.

HYDROGEOLOGY OF THE GOVERNMENT ISLAND MITIGATION SITE

Columbia River Levels

The elevations (m.s.l.) of the Columbia River were

obtained from the U.S. Geological Survey gaging station in

Vancouver, Washington at river mile 106.5 (Figure 2). An

average river gradient of 0.07 m/km (0.38 ft/mi) (Don

Oakley, personal communication, 1993) was added to river

stage measurements to adjust for the level of the river at

Government Island (river mile 115.5).

Hydrographs of the daily maximum river stage of the

Columbia River at Government Island were constructed for

1993 and 1994 (Figures 10 and 11) . The elevations of the

Columbia River allow one to predict the flooding of Jewit

Lake through the dam. A minimum river stage of 3.6 m

(12.0 ft) m.s.l. is necessary for water to reach Jewit

Lake through the mitigation site dam (Figure 8). Figure

12 shows the 7 year daily average of the Columbia River

elevation at Government Island between 1973 and 1980. From

Figure 12, the time of year when flooding of Jewit Lake is

likely to occur can be determined by locating the time of

the year when river levels are highest. Flooding of Jewit

Lake is most likely to occur in December, January, May,

and June. Hydrographs of the Columbia River from 1973 to

1989 are presented in Appendix 1.

2 0 -, - - - . - - - -· - - - - - - - - - - -. - - - - - - - - - - - - - - - - - - - -·- 6.10 m I I I I I I I ---------------------------

18 I I _ _ _ . _ _ __ . _ _ _ . _ _ _ .-A- _ _ -. ___ , _ _ _ . _ _ _ -. _ _ _ . _ _ _ .- _ _ _. . 5 . 4 8 m I I

- - - t - - - -, - - - I - - - 1- - - I - - - "l - - - r - - - I - - - -1 - - - T - - - 1- - - - I ·

"d I I

s:: 16 _ _ _ 1- _ - -1 - - - ~ - - - :- - - :~ - - .J - - - L - - - I - - - -I - - - " - - - I- - I . 4 0 8 7 m m

_ _ _ I_ _ _ _ 1 _ _ 1 ! _ _ _ '- _ I _ _ _1 _ _ _ ~ _ _ - I _ .-I Ul H

.w 14 -t - - - ,- - - -, - - f-T ~ - - - :+ - -:-~\- - -, - - - ~ - - -,- - - -. - - - ~ - - -.- - - - 4.27 m s:: Q) s of spring~loaded gate H 12 - - -1 - ..J - - - L.. - - - I - - - -1 - - - J. - - - 1- -'· 3.66 m Q)

::> 0 CJ

.w 10 1 - i. -H 111\~·Jt1 - -~ - t - ,- - - - I - - - -, It.*_,,.~ n- , - - ;;; -, - -i. 7 - t. - ~ t i -1..· 3 . 0 5 m m

.w 4-l 8 J ---1- - - -1 - - - ~ - - - 1- - - - : - - - ~ -1- - L -'"' - -~ -~ -~ ~ -l~ :- *- - ~, · 2 . 4 4 m --.-I I I I I ---------------Q)

::> Q) 6 --------------------- ~ ---------------- 1. 83 m ...::i I I I I I I 1 I I I

H RIVER 'STAGE ( COLUMBI'A RIVER)

- - - t - - - - I - - - 'T - - - 1- - - - I - - - "l - - - r - - - I - - - -1 - - - T - - - 1-

Q) I AT GOVERNMENT ISLAND .w m 4 - - - I_ - - -I - - - ~ - - - :-19 §}: - - - .J - - - L - - - I - - - -I - - - " - - - I- - - - I . 1 • 2 2 m

:s: I I I I I I I I ------------------------------

I

2 I 0.61 m - - - - -- - -- - -- --- - - - - - ---I

---------I I I t I I

- - - I - - - - l - - - i - - - 1- - - - I - - - I - r - - I

0 0.00 m

J F M A M J J A s 0 N D Month

Figure 10. River stage at Government Island in 1993. N w

2 0 ----, - - - · - - - -· - - - - - - - - - - - · - - - - - - - - - - - - - - - - - - - - - - - - - -· · 6 . 1 O m _ _ _ _ 1 _ _ _ _!. _ _ _ t_ _ _ _ I _ _ _ _1 _ _ _ I_ _ _ _ I - _ _ _ 1 _ !. _ _ _ I - _

18 - - - I - - - - I - - - ~ - - - ,- - - - I - - - -, - - - j°" - - - I - - - - , - - - 7 - - - I - - - - • 5 • 4 8 m

- - - 1- - - -1 - - - i - - - I- - - - I - - - I - - - r - - - I - - - -i - - - T - - - 1- - - -1

'd s:: 1 6 - - - I - - - -1 - - - ~ - - - 1- - - - I - - - .J - - - I... - - - I - - - -1 - - - L - - - 1- - - - I • 4 • 8 7 m ro

r-1 I I I I Ul ---------------H

.W 14 --+ - - -I - - - - I - - - ~ - - - ,- - - - I - - - -, - - - ,- - - - , - - - - - - - - - 4 • 2 7 m s:: (1J

~ H 12 l 11 1

' ~ 1

I I rt I I. 3 • 6 6 ffi

~~ I w !!: ~ 1-t: 4Ji_: "'-'-'--'- -L: -,- ___ ! ~ _,_:_

0

~ l0---f-t-Hlfwt-l-,'\':tt~l1£ll-~--"'-l-,~ - -¥,friiJ-L- - - -,- - - -,- - - 71- - -,- - - - ·3.05 m

.w ~ 8 j -1- :- - 1-: ---~ -~ -1- - - - I - - - .J - - - I... - - i1:f y· v "* ! - L - - - 1- - - - I . 2 • 4 4 m ,--i I I I I I I I _t I I 1 (1J ----- ---------------- ----- -----------

::> (1J 6 - - - I - - - - , - - - ~ - - - ,- - - I - - -, - - - ;- - ! - - - - , - - - ~ - - - , - - - - : • 1 • 8 3 m ~ RIVER STAGE (COLUMBIA RIVER) ~ - - - ,- - - -: - AT t;ov-EF{NMENT- ISL)Nb - ~ .w ~ 4 - - - I - - - _I - - - ~ - - - l-19 9 4 I - - - .J - I... - - - I - - - -I - L - - - I_ - I • 1 • 2 2 m

I I I I ---------------

2 - - - I - - - - I - - - ~ - - - ,- - - - I - - - -, - - - ;- - - - I - - - -, - - - 7 - - - ,- - I • 0 • 61 m

- - - I - - - -1 - i - - - 1- - - - I - - - I - - - r - - - I - - - -I - - - T - - - 1- - - - 1 •

0 0. 00 m J F M A M J J A S 0 N D

Month

Figure 11. River stage at Government Island in 1994. t-...J ~

16 -----

14

12 .....-..

,....,

(J) 10 s

' .w ~

8 ,....,

~ /\ ~

I \ ~ Dtton of i sprin g loc: ded g-~e~

=IJ ' \_. I ~ ,f' \Al f\ J \ Be ;ttom Of L ewit LakE

- ~ \ I '*'../ ~ I ~ - . -

~ v -

~ --

~ \ ~ -J

-r '/V

OJ -:> -OJ -,...., -H 6 OJ -

:> -·r-1 -p:: -

-4

------

2 -----

0 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I

J F M A M J J A s 0 N D

Month

Figure 12. Mean Columbia River elevation at Government Island 1973-1980.

.. - ------- .. -------------~---------- ·-·---------·-----·

4.87 m

4.27 m

3.66 m

3.05 m

2.44 m

1.83 m

1.22 m

0.66 m

0 m

N l51

26

Water Level Monitoring

Water levels throughout the study area were monitored

in order to observe fluctuations during the study. Each

monitoring point was surveyed to a 0.03 m (0.1 ft)

accuracy so water elevations would be known at each point.

Locations of monitoring points are shown in Figure 13.

From these measurements, variations in water levels and

the direction of slope of the water table can be

determined. Water level measurements were compared to

Columbia River levels, precipitation, and

evapotranspiration so that the processes responsible for

water table fluctuation could be assessed.

Water level measurements were also used to

approximate the hydraulic conductivity of the sediments in

Southeast Pond. Table I records the water depths in

Southeast Pond between October 23, 1993 and October 30,

1993. Southeast Pond water levels decreased at an average

rate of 0.12 ft/day between October 23, 1993 and October

30, 1993. The infiltration rate is 3.0 cm/day (0.10

ft/day) when an evapotranspiration rate of 0.61 cm/day

(0.02 ft/day) is subtracted from the rate at which water

levels decreased. The evapotranspiration rate of 0.61

cm/day (0.02 ft/day) was measured at a weather station in

Vancouver, Washington. Using Darcy's law

vh=-K(oh/ol)

27

where vh is the specific discharge, bh/bl is the hydraulic

gradient, and K is the hydraulic conductivity, the

hydraulic conductivity of the sediments underlying

Southeast Pond can be approximated from infiltration rates

if the hydraulic gradient remains constant. The hydraulic

gradient present at Government Island will remain constant

if Columbia River levels remain constant. Figure 10 shows

that Columbia River levels remained at a nearly constant

level of 2.7 m (8.9 ft) in August, September, and October

of 1993. The hydraulic gradient at Government Island is

determined by subtracting the head of the Columbia River

(2.7 m, 8.9 ft) from water levels in Southeast Pond (3.7

m, 12 ft) . By approximating the bottom elevation of the

confining unit underneath Southeast Pond at 1.6 m (5 ft),

the thickness of the confining unit is approximately 2.1 m

(7 ft). By substituting values of 0.9 m (3.1 ft) for bh

and 2.1 m (7 ft) for bl, the hydraulic gradient is 0.45.

By substituting 0.45 for bh/bl in Darcy's law, the

hydraulic conductivity is 6.7 cm/day (0.22 ft/day).

Table II contains water level elevations at

monitoring points in the mitigation site during 1994.

Figure 13 shows the location of these monitoring points.

Values in Table II are given in feet, m.s.l. If no water

was present at a monitoring point, the point is labeled

I dry'• If the water level was not measured, the point is

28

Table I

Approximate water depths in Southeast Pond between October 23rd and October 30th, 1993.

Water Depth Date cm in 10-23-93 25.4 10 10-26-93 10.2 4 10-27-93 6.4 2.5 10-28-93 5.0 2 10-30-93 1. 3 0.5

labeled '?' . If a monitoring point had not been

established at the date shown, 'n/a' appears in Table II.

Monitoring points 11, 12, 13, 32, 33, 34, and 40 (Figure

13) are used to constrain water elevations in the Jewit

Lake area. In February through June, the water elevations

in the Jewit Lake area were highest in the lake, and equal

to or lower than the lake level in the monitoring points

surrounding Jewit Lake. At monitoring points 23, 25, and

26 (Figure 13), the water table was consistently higher

than at any of the other monitoring points. Subsurface

water elevations in the Jewit Lake area are not known July

to November because the water table fell below the depths

of all of the monitoring devices. The water monitoring

devices extend 1 m (3.3 ft) below the ground surface. The

location of the water table in the vicinity of Southeast

Pond is poorly constrained during 1994 since only the

Southeast Pond staff gauge and monitoring point 20 are

present in that area.

Monitoring

point 2/6/94 3/6/94 4/2/94 4/3/94

# 11 dry 11. 05 10.46 10.4

# 12 n/a n/a 10.74 10.6

# 13 10.82 11. 93 10.76 10.66

# 20 dry 11.86 dry dry

# 23 14.26 15.35 15.18 15.16

# 25 dry 16.51 16.29 16.26

# 26 15.54 17.48 16.54 16.5

# 30 n/a n/a n/a n/a

# 31 n/a n/a n/a n/a

# 32 n/a n/a n/a n/a

# 33 n/a n/a n/a n/a

# 34 n/a n/a n/a n/a

# 3 5 n/a n/a n/a n/a

# 38 n/a n/a n/a n/a

# 39 n/a n/a n/a n/a

# 40 n/a n/a n/a n/a

Jewit dry 11. 21 11. 67 11. 62

Lake --S.E. n/a 13 .1 12.67 12.6

Pond

Table II

Government Island water levels

4/10/94 5/7/94 5/8/94 5/20/94 6/10/94

10.99 dry dry dry dry

11. 23 ? dry dry dry

11. 37 dry dry dry dry

dry ? 11. 2 dry dry

15.59 13.72 13. 6 dry dry

16.97 dry dry dry dry

17.42 dry dry dry dry

? dry ? dry dry

12.03 11. 76 ? 11. 46 dry

11. 09 ? 10.34 dry dry

11. 35 ? 9.48 9.2 dry

? ? 12 12. 15 ?

? ? dry dry ?

n/a n/a n/a n/a n/a

n/a n/a n/a n/a n/a

n/a n/a n/a n/a n/a

11. 66 dry dry dry dry

12.85 12 12 ? dry

7/8/94 8/16/94

dry dry

dry dry

dry dry

dry dry

dry dry

dry dry

dry dry

dry dry

dry dry

dry dry

dry dry

dry dry

dry dry

dry 5.5

dry 5.5

dry 4

dry dry

dry dry

10/30/94 12/21/94

dry

dry

dry ?

dry ?

dry ?

dry

dry

dry dry

dry

dry

dry

dry dry

dry ?

5. 5 ?

dry ?

4.5

dry

dry ?

12.88

12.69

17.32

17.78

16.45

13. 59

12.81

8.5

11. 71

--

N l...O

* 33

* staff gauge 38 *

Jewit Lake

300 m Scale:

* 35

Figure 13. Locations of water monitoring points.

Columbia River

* 30

North * 31

~

gauge

Columbia River w 0

31

To estimate the volume of water in Jewit Lake and

Southeast Pond, a topographic map (Oakley Engineering

Inc., 1992) was analyzed at the 3.3, 3.6, 4.0, 4.3, and

4.6 m (11, 12, 13, 14, and 15 ft) contours. Areas within

each contour were obtained using a planimeter. Volume

estimates of the amount of water contained between lake

levels of 3.2 and 4.6 m (10.5 and 15.0 ft) are given in

Table III. The cumulative volumes of water in Jewit Lake

and Southeast Pond with increasing water levels are shown

in Figures 14 and 15. Figure 14 shows that the volume of

water in Jewit Lake increases with lake level at a lesser

rate between 3.2 and 3.6 m (10.5 ft and 12 ft) than

between 3.6 and 4.6 m (12 ft and 15 ft). This occurs

because the surface area of the lake increases with lake

level at a lesser rate below 3.6 m (12 ft) than above 3.6

m (12 ft). Figure 15 shows that the volume of water in

Southeast Pond increases with lake level at a greater rate

between 3.6 and 4.0 m (12 and 13 ft) than between 4.0 and

4.6 m (13 and 15 ft). This occurs because the surface

area of the lake increases with lake level at a greater

rate below 4.0 m (13 ft) than above 4.0 m (13 ft).

32

Table III

The volume of water in Jewit Lake and Southeast Pond at lake levels between 3.2 and 4.6 m m.s.l.

Lake level Jewit Lake (m3} Southeast Pond (m3} 3.2 m (10.5 ft) 1290 3.3 m (11.0 ft) 3646 3.4 m (11.5 ft) 25195 3.6 m (12.0 ft) 62404 350 3.8 m (12.5 ft) 115560 2325 4.0 m (13.0 ft) 184857 5649 4.1 m (13.5 ft) 269139 9875 4. 3 m (14.0 ft) 367636 14707 4.5 m (14.5 ft) 480440 20294 4.6 m (15.0 ft) 607974 26737

Flow rates through the dam

Figure 16 shows the level of the Columbia River at

Government Island from November of 1994 to February of

1995. From January 14th to January 21st, the Columbia

River raised Jewit Lake 15 cm (6 in) as water flowed

through the spring loaded gates on the dam. From February

1st to February 4th and February 20th to February 22nd,

flow through the dam occurred through the spring loaded

gates and the open spillway grates.

The total volume of water present in Jewit Lake at

different lake levels can be used to estimate flow rates

through the dam. Table IV shows the flow rates through

the dam for peak events (Figure 16) in January and

February of 1995. Figure 17 shows estimates of the amount

of time required to fill Jewit Lake from 3.6 to 4.6 m (12

to 15 ft) based on flow rates through the dam in January

700000

600000

----M s 500000 -~ Q) J.J 400000 m ~

4-1 0 300000 Q)

s ~

r-1 200000 0 >

100000

0

3 3.5 4 4.5 5

Water level (m)

Figure 14. Volume of water in Jewit Lake at water levels between 3.2 m (10.5 ft) and 4.6 m (15.0 ft). w

w

30000 ,.---~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~---

25000

-M s - ~

20000 H Q)

..w ro ~ 15000 ~

0

Q)

s 10000 ::1

r-1 0 :>

5000

0 -r-~~~~~~~t--~---~~~~---+~~~~~~~----1-~~~~~~~-J

3 3.5 4 4.5 5

Water level (m)

Figure 15. Volume of water in Southeast Pond at water levels between 3.5 m (11.5 ft) and 4.6 m (15.0 ft).

VJ p

16.00 ----i I 4. 87 m Bottom of spillway grating

- 1-.w 4-1 -'O c m rl Ul -H

12.00 ~o~ of ~pring 14Ja_ed_gates I , l ~n \. /I I r --1 3.66 m

.w c OJ

~ H OJ ::> 0 CJ

.w m rl 8 . 0 0 ---f ' 1111111111. I I. I ~II Rd 1.1 llllU 11 II ' m~N n1m111.1 n~ I l~l~l'~~IM ~Ill' --1 2.44 m OJ ::> OJ rl

H OJ ::>

·rl p::;

4.00 I I I I

1.22 m

tj1 tj1 tj1 tj1 tj1 lJ1 lJ1 lJ1 lJ1 m m m m m m m m m .......... .......... .......... .......... .......... .......... .......... .......... .......... rl lJ1 m M r- 0 tj1 r- rl .......... rl N rl N rl N .......... N rl .......... .......... .......... .......... .......... .......... N .......... rl rl rl N N rl rl N

rl rl rl rl

Date

Figure 16. River level, Jewit Lake level, and Southeast Pond level from November 1, 1994 to February 21, 1995.

w U1

U)

~ '"d

~ 0

~ ())

1

120 ---~~~~~~~~~~~-~~~-~--~~~-~~~~~~~~~--

10 0 1 1 sj';jji;jjjj'jjjll!il I 80 +-- ;.;.·.;.·

60 I (:::;:;:::;:::

40 I 1:·1:1::-::1::··::11:1.::1-:::·1.1:::

20 -------,

0 -+------January 14-21 February 1-4 February 20-22

Date (1995)

Figure 17. Time required to raise Jewit Lake from 3.6 m (12 ft) to 4.6 m (15 ft) based on flow rates through the dam in January and February, 1995.

w (j\

37

and February of 1995. Figure 17 shows that less time is

required to fill Jewit Lake as flow rates through the dam

increase.

Table IV

Rates of flow through the dam as water flowed into Jewit Lake in January and February, 1995.

Flow rate through the Lake Date of 2eak event {dam {m3 /day) levels {m} 1-14 to 1-21 1363 3.7 to 3.9 2-1 to 2-4 25265 3.6 to 4.3 2-20 to 2-22 22084 4.3 to 4.4

Climatological Data

Daily precipitation and evapotranspiration values

were obtained from a weather station in east Vancouver,

Washington. The weather station is located approximately

3 km (2 mi) north of the study area. The weather station

is operated by the Irrigation Management District of

Vancouver. Daily precipitation was also obtained from the

National Weather Service at Portland International

Airport, approximately 8 km (5 mi) west of the study area.

Daily precipitation in 1993 and 1994 was averaged between

the Vancouver weather station and the National Weather

Service station to determine precipitation on Government

Island. Historical average monthly precipitation for the

Portland area was obtained from the National Weather

Service. Monthly 1993 and 1994 precipitation and

38

historical monthly average precipitation are shown in

Figures 18 and 19. The Vancouver weather station has an

incomplete precipitation record for some months.

Precipitation data are necessary for this study because

precipitation onto Government Island adds water into Jewit

Lake and Southeast Pond.

Evapotranspiration rates are necessary to estimate

evapotranspiration loss. Figure 20 shows monthly 1993,

1994, and average actual evapotranspiration at the

Vancouver weather station. Average evapotranspiration was

determined by averaging evapotranspiration data collected

from 1991 to 1994. Figure 20 indicates that

evapotranspiration rates were below average during the

summer months of 1993 and above average during the summer

months of 1994. The data collected from the Vancouver

weather station for the study do not contain the

parameters necessary to determine the method used by the

weather station to determine evapotranspiration by the

methods given in Dunne and Leopold (1978) and Chow (1964)

The Vancouver weather station reports measurements of

relative humidity, wind velocity, solar radiation,

precipitation, minimum daily temperature, maximum daily

temperature, and evapotranspiration. The Thornthwaite

method of determining evapotranspiration (Chow, 1964) and

Penman's energy balance of small pans and shallow lakes

1-1 \.0 \.0 w

'O ti <D () I-'· 'O I-'· rt SlJ rt I-'· 0 ::::1

6[

:s: 0 ::::1 rt ::r

Jan

Feb

Mar

April

May

June

July

Aug

Sept

Oct

Nov

Dec

Precipitation (cm)

0 co

D Ill m ~ < ~ SlJ (J) ::::1 (J)

()

SlJ 0 1-1

< c \.0 <D < \.0 ti <D w SlJ ti lQ <D 1-1

\.0 \.0 w

Jan

Feb

Mar

April

May

June ~ 0 ::::1 rt ::r

July

Aug

Sept

Oct

Nov

Dec

Ov

Precipitation (cm)

D • ~ < ~

(/) ::::1 ()

~ 0 < i:::: (D

< 11 (D ~ 11

IQ (D ~

'° '° ii:::.

r:v 0

ml

~ (/)

~

'° '° ii:::.

r:v U1

25---~~~~~~~~~~~~~~~~~~~~~~~~~~~,

s 20 u

II average s::

1s I I 0 ·rl 111993 .w m I ~

01994 ·rl ~ Ul s:: 10 rtS ~ .w 0

~ :> 5 µ:J

0-

J F M A M J J A s 0 N

Month

Figure 20. 1993, 1994, and average monthly evapotranspiration in Vancouver, Washington.

D

~ I-'

method of calculating evaporation (Dunne and Leopold,

1978) are the methods that can be used to estimate water

loss to the atmosphere using the data collected from the

Vancouver weather station. The formula

U= 1 . 6 * ( 10 * t /TE) a

42

where U is evapotranspiration in cm/day, t is mean monthly

temperature (°F), TE is Thornthwaite's temperature

efficiency index, and a is a heat index coefficient, is

used to calculate evapotranspiration using the

Thornthwaite method. The values obtained from

calculations using the Thornthwaite method are approximate

because the t and TE parameters require mean daily and

monthly temperatures, respectively. Mean temperatures

were estimated by averaging daily maximum and minimum

temperatures. The formula

E0 = [ (o/A.) H+Ea] I (o/A.) +1

where E0 is the evaporation rate in cm/day, 6/A is

Penman's dimensionless parameter for various temperatures,

H is net radiation in units of cm/day, and Ea is a term

describing the contribution of mass transfer to

evaporation, is used to calculate evaporation. Penman's

dimensionless parameter for various temperatures

43

represents a function relating windspeed, vapor pressure

of the water surface, and vapor pressure of the air to

evaporation rate. The terms 6 and A are not defined in

Dunne and Leopold (1978) . Figure 21 shows

evapotranspiration reported from the Vancouver weather

station, evapotranspiration calculated using the

Thornthwaite equation from data collected at the Vancouver

weather station, and evaporation at the Vancouver weather

station for selected days in June of 1994. Figure 21

indicates that evapotranspiration rates were higher than

lake evaporation rates for the days shown in Figure 21.

Figure 21 shows that calculations of evapotranspiration

using the Thornthwaite method are consistently higher than

calculations of evapotranspiration by the Vancouver

weather station. Values for evapotranspiration reported

by the Vancouver weather station were used to represent

evapotranspiration on Government Island.

Sediment Particle Size Analysis

Samples were selected for particle size analysis

based on field observations of sediment in soil pits,

during bucket auger excavations, and during the

installation of water monitoring devices. Observations

were made at depths of 1.0 to 3.2 m (3 to 10 ft),

depending on the instrument used to expose the subsurface.

>t ~o. 9 .............

fJ0.8 -cv0.7 ~ CV gio. 6 0 El .wO. 5 rO

~0.4 .w

0 0.3 .w

Ul0.2 Ul 0 r-i0.1 ~ CV

0 .w rO '<:jl $:

°' .............

r-i .............

\..0

Figure 21.

'<:jl '<:jl '<:jl

°' °' °' ............. ............. .............

\..0 r-i \..0 ............. r-i r-i \..0 ............. .............

\..0 \..0 Date

'<:jl

°' .............

r-i N .............

\..0

'<:jl

°' .............

\..0 N .............

\..0

mvancouver weather station evapotranspiration

BLake evaporation

DThornthwai te evapotranspiration

Evapotranspiration and lake evaporation for selected days in June, 1994.

H:::> H:::>

45

On the basis of visual inspection, the finest grain-size

fraction at each site was sampled since vertical

groundwater flow is controlled by the lowest conductivity

layer. Locations of sampling sites are shown in Figure

22. Stratigraphic columns at the sampling sites and the

location in the stratigraphic column where the sample was

collected are given in Appendix 4. Sampling sites were

selected to assess the variability in the grain-size

distribution of the low conductivity layers and to

determine whether the low conductivity layers had a grain­

size distribution that could be related to topography or a

geomorphic feature. Samples 1, 8, 9, and 15 were

collected from the nonpersistent emergent wetland at sites

below 3.6 m (12 ft) in elevation. Samples 2, 5, 7, 11,

12, and 14 were collected from the persistent emergent

wetland at sites between 3.6 and 4.9 m (12 and 16 ft) in

elevation. Samples 3, 4, 6, 10, and 13 were collected

outside the wetland area. Sediments were analyzed using

the hydrometer method of Day (1965) . The percentages of

sand, silt, clay, and colloids/organic matter are shown in

Table V. The Udden-Wentworth grain size scale for elastic

sediments was used to define the size ranges for the sand,

silt, and clay. The amount of organic matter/colloids

were not determined experimentally. The cumulative

percentages of sand, silt and clay were subtracted from

* Columbia River 8,9

* 10

300 m scale:

Figure 22. Hydrometer sampling site locations.

* 13

* 3

Columbia River

No rt

Cl

~ 01

47

100 percent of the mass of the sample to determine the

percentage of organic matter/colloids. Graphs showing

particle size distribution for each sample are presented

in Appendix 2.

The data indicate that a pattern in the particle size

distribution relative to topography is not present. The

sample from Southeast Pond (sample 2) contains 4 percent

more clay than any other sample analyzed. Samples 1

through 14 are silt loams and sample 15 is a loam (Soil

Survey Staff, 1992).

Table V

The grain size percentages for 15 samples collected on Government Island. Sand size material is larger than 0.0625mm, silt size material is between 0.0625 mm and 0.004 mm, and clay size material is smaller than 0.004 mm.

SAMPLE % SAND %SILT % CLAY % ORGANICSLCOLLOIDS Sam2les collected from the non2ersistent emergent wetland

1 1 74 14 11 8 1 56 19 24 9 4 76 8 12

15 39 46 3 12

Sam2les collected from the 2ersistent emergent wetland 2 1 67 23 10 5 1 69 14 16 7 3 65 18 14

11 1 70 17 12 12 0 64 16 20 14 3 67 17 13

Sam2les collected from outside the wetland area 3 0 78 15 7 4 0 66 17 17 6 4 66 17 13

10 4 72 14 14 13 12 70 10 8

48

Seismic Refraction

Seismic refraction is used to identify boundary and

density contrast conditions of subsurface units (Telford

and others, 1990). In this study, seismic refraction was

used to identify the depth to the water table on May 7th

and 8th, 1994. The water table is delineated from non-

saturated strata by its higher velocity signal. Five

east-west transects were performed (Stations G-1, G-5, G-

9, G-13, and G-14) (Figure 23). Receiver distances were

set at 1.0, 2.0, 4.0, and 5.0 m spacings to obtain the

optimum signals. Table VI shows the elevation of the

water table based upon interpretation of the seismic

refraction data and known depths of the water table from

field observations at monitoring points and in soil pits.

The fourth column in Table VI compares the depth to the

water table determined by seismic refraction to the depth

of the water table seen in soil pits and monitoring

points. At each station, the water table was calculated

to be deeper using seismic refraction data than was

determined by visual observation of the water table in

soil pits and monitoring points. Visual observation

indicates that the water table is lowest in elevation in

the topographically lowest areas (stations G-5, G-9, and

Southeast Pond) and highest in the upland areas (G-1 and

G-13) . Seismic refraction data indicate that the water

Wetland boundary line

Jewit Lake

300 m Scale: ----·-·--

Figure 23. Seismic refraction sites.

Columbia River

* G-5

CJ

* G-9

Southeast Pond

Columbia River

North

i.j:::::.

\.0

50

table is independent of topography with the exception of

station G-9. Receiver reception time data and selected

graphs of the plotted data are given in Appendix 3. Using

the refraction data for station G-13, the seismic wave

velocity in the unsaturated sediments is 212.5 m/s and the

seismic wave velocity in the saturated sediments is 1562.5

m/s.

The discrepancy between seismic refraction data and

visual observation of the water table may be caused by

changes in the amount of water present in the sediments.

Sand lenses located beneath the water table may refract

the seismic signal since the amount of water present in

the intergranular pore space of sand may be higher than

the amount of water in the intergranular pore space of

silt and clay. If sand lenses refract the seismic

signals, the elevation of the water table could be

inaccurate if the water table is located above the

refractor.

51

Table VI

Seismic Refraction on Government Island; May 7th and 8th, 1994. Distances are in meters.

STATION REFRACTOR KNOWN WATER TABLE ELEVATION DEPTH DEPTH ELEVATION*

G-1 west 4.9 1.44 0.710 3.42/4.11 (1-rn spacing)

G-5 west 6.2 3.34 1. 88 2.88/4.40 ( 5-rn spacing)

G-5 west 6.2 3.23 1. 88 2.99/4.40 ( 2 -rn spacing) G-9 spacing 4.0 1. 80 1. 27 2.22/2.75 ( 5-rn spacing) G-13 spacing 7.6 3.72 3.85 (4-rn spacing)

G-14 5.6 unclear ( 4 -rn spacing) G-14 5.6 unclear ( 2 -rn spacing) Southeast Pond 3.71

* In table VI, there are 2 numbers showing the elevation of the water table. The first number is obtained by subtracting the depth to the refractor from the station elevation. The second number is obtained by subtracting field observation depths to the water table from the station elevation.

Summary of factors affecting the hydrogeology of the Government Island mitigation site

The Columbia River must reach a minimum elevation of

3.6 m (12 ft) for water to reach Jewit Lake through the

darn and channel. Columbia River levels above 4.7 rn (15.3

ft) fill Jewit Lake approximately 15 to 20 times faster

than when Columbia River levels are below 4.7 rn (15.3 ft)

because water is able to flow through the open spillway

grating and the spring loaded gates on the darn. Flooding

52

of Jewit Lake is most likely to occur in December,

January, May, and June. The hydraulic conductivity of the

Southeast Pond sediments is approximately 6.7 cm/day (0.22

ft/day) . Precipitation and evapotranspiration affect

water levels on Government Island. A pattern in the

particle size distribution relative to topography is not

present.

GROUNDWATER MODELING

GROUNDWATER MODEL DESIGN

MODFLOW, a groundwater modeling program developed by

the U.S. Geological Survey in 1976 (McDonald and Harbaugh,

1984), was used to simulate the hydrology of Government

Island. PREMOD, a preprocessor for MODFLOW, was used to

enter all data into the groundwater model. A 15 node by

10 node matrix (Figure 24) was used to represent the study

area. Each node is 152.4 m by 152.4 m (500 ft by 500 ft),

covering 23,225 m2 (250,000 ft 2).

Stratigraphic representation in the groundwater model

The groundwater model was designed as a 4 layer

problem, with a confining unit overlying an aquifer.

Layers 1, 2, and 3 represent the confining unit and Jewit

Lake and Southeast Pond respectively; layer 4 represents

the aquifer. Figure 25 is a schematic diagram of the

groundwater model design. The thickness of the confining

unit was approximated using a 0.61-m (2-ft) contour map of

the site (SRI, 1991b). Areas with higher elevations are

assumed to have a thicker confining unit than areas at

lower elevations. Layers 1 and 2 were designed to

accomodate fluctuations in the area of Jewit Lake with

changes in lake levels. At elevations above 3.6 m (12

ft), Jewit Lake is represented by 31 nodes (Figure 26).

At elevations between 3.3 and 3.6 m (11 and 12 ft), Jewit

A' ~ Dam \ B'

~ - ~

\

\ ~ ---- \ etlan Ci bou h.dary ~ ~

Colt mbia River

-___, \

~ ~ \_ ~

__, .....__...... " \

-

~y ~

North \ \ \ l\-L-/' ~ A ,

\ \ -

\ / \,,J

) '\ \

~

~ I\ hJ

"' ""'----L./" \ -~

~~--~ " ~ \ .........___

~- t? ~ r-..."1 ~

- ~ ~ ~ <

\ ~ b~ \ - ~----- ~

)

a \

300 m \ \ Scale 1 l \

~- --- \A __.---/

Columbia =-:---River -- ~ l--------- c---

Figure 24. MODFLOW node grid. Each node is 152 m by 152 m (500 ft by 500 ft). A-A' and B-B' represent cross section (Figures 30 and 31) locations.

i~ _ _/""'

Lines LJl i+::..

()

ri 0 [/) [/)

[/) (J) ()

rt I-'· 0 ::1

~ I ~

Pl [/)

I-'· ::1 rt 0

SS

I CJ'\

s s [/)

I--'

................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . .................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . . . . . . . . . . . .

I-' w w

-J w CJ'\

s s s s s s [/) [/) [/)

I--' I--' I--'

11

nil LJ

~ -J

CJ'\ N

s s s s [/) [/)

I--' I--'

~ Dam

\: Wetla1 Ila 001

, --- ~;nP Colur iliia F iver I ~ .I

- ~ I -

~ ~ f..-.." r-----

" ~ ~ --"""'--1 2 3 4 5 6 7

~ D

North \ 8 9 10 11 12 13 14 15 \ vr ~ ~ / ~ -

'I\ / \.J

16 17 18 19 20 21 22 23 24 25 )

"" ~ ~

K. 27 28 29 30 31 v-- -

" ~

-" - '\ \ -y ~ - "" ~ ~

-

,"-, ~

-~ ......... ~ ) -'-

< -

~ ~~~ --a

30( m ~ Scale: ~ -- ~ -------Columbic: Rive r-- ------ -Figure 26. Location of Jewit Lake and Southeast Pond in MODFLOW at elevations above 3.6 m (12 ft). Numbers represent nodes containing Jewit Lake and Southeast Pond in MODFLOW above 3.6 m (12 ft). Ul

01

57

Lake is present in 7 nodes (Figure 27) . Southeast Pond is

represented by 2 nodes at all water levels. Nodes that

fall partially within the wetland boundary line were

included or omitted from the lake area based on elevation.

Nodes containing elevations predominantly below 4.9 m (16

ft) in elevation were included in the lake area. Nodes

containing elevations predominantly above 4.9 m (16 ft) in

elevation were not included in the lake area. Surface

water is represented in a node as an unconfined aquifer

with 100 percent porosity and a hydraulic conductivity of

30,400 m/day (10 6 ft/day). This hydraulic conductivity

value was used because PREMOD recommends that hydraulic

conductivity values not exceed 30,400 m/day (10 6 ft/day).

The remaining nodes in layers 1 and 2 have the same

hydraulic conductivities as layer 3.

Layer 3 is a heterogeneous confining unit composed

of silt and clay layers, sand lenses, and a one node

coarse-grained sand and gravel deposit. The unit has

thicknesses of 1.7 to 6.1 m (5 to 20 ft), depending on the

elevation of the land surface. Since layers in MODFLOW

cannot overlap vertically, variations in thickness within

a layer must be controlled mathematically. This is done

in MODFLOW using the VCONT parameter. VCONT is defined as

the hydraulic conductivity divided by the thickness of the

layer. By varying the VCONT parameter, the layer is

~ Dam

re WE et lane boun

-.! ............ Coll lrnbia River OaLy ,._ .- ...... _

r\. \ ------ , - -

~ I__,,--I-.-/ ~ ~ ~

~ -,_ - -~ D

\ 1 2 3 4 \ ~ ~ ~ -

'I\ ,,./ \.:>

North 5 6 7 ) / ~

~ -~ i----

~ v--

"' ~

-~ ~ ~

\ .......___ ty ~ ~ ~'I ~

""... ........ ~ "")' < -~ ~~~

-L

a

Sea .... e: 300 n

I ~~

~ r----

1---~ ~ Columbi, a RivE r r---

--------Figure 27. Locations of Jewit Lake and Southeast Pond in MODFLOW at elevations between 3.3 and 3.6 m (11 and 12 ft). Numbers represent nodes of Jewit Lake and Southeast Pond in MODFLOW between 3.3 and 3.6 m (11 and 12 ft). lJl

O'.)

-- ---·-----~·-- -----·-----·-------"-~---·-~-~---····------·-"--~~------·---~------·------'

59

distorted in the vertical direction to account for changes

in the thickness of the unit. Such distortion causes the

vertical dimension to vary at each cell within a layer.

Variations in the VCONT values of layer 3 control the

thickness of the entire confining unit. Despite

heterogeneities, the confining unit was modeled as one

layer in the groundwater model because groundwater flow is

expected to be vertical through the unit. Vertical

groundwater flow rates are controlled by the zone of

lowest hydraulic conductivity in the unit. Water cannot

flow through zones of higher hydraulic conductivity in the

vertical direction at any velocity different than the

velocity that water flows through the lowest conductivity

zone. Sand lenses interbedded within the silt and clay

have little influence on the rate of water movement

through the unit because the silt and clay layers

surrounding the sand layers have lower hydraulic

conductivities than the sands.

The top of the aquifer was assigned a uniform

elevation of 1.7 m (5 ft) m.s.l. The approximate

elevation of the top of the aquifer is known from 1

excavation in Southeast Pond, 4 excavations in Jewit Lake,

and 2 monitoring points (38 and 40) that penetrate the

unit (Figure 28). These observations were made on

November 11th, 1993, July 8th, 1994, and August 16th, 1994

Columbia River Wetland boundary lin\ ~

* 21 (5.5) North

* 3 (5.5)

* 17 (5.0) c,

Jewit Lake * 18 (5.0)

Scale: 300 m

Columbia River

Figure 28. Locations where the aquifer was located during fieldwork. A stratigraphic column of each point is given in Appendix 4. Elevations of each point are shown in parentheses (ft, m.s.l.).

m 0

61

respectively. The approximate elevations of the top of

the aquifer at the points in Figure 28 are shown in Table

VII. Stratigraphic columns of the points shown in Figure

28 are given in Appendix 4. Deviations from the 1.7 m (5

ft) m.s.l. elevation for the top of the aquifer are

expected and accepted as reasonable error.

Table VII

Approximate elevations of the aquifer top at the locations shown in Figure 28.

Monitoring Point 6 3 17 18 19 21 5

Mean

Approximate Aquifer m (m.s.l.)

1. 2 1. 7 1. 5 1. 5 1. 4 1. 7 2.1 1. 6

Top Elevation ft (m.s.l.)

4.0 5.5 5.0 5.0 4.5 5.5 7.0 5.2

Although the aquifer was modeled as a homogeneous,

isotropic layer, it is unlikely that these conditions are

present beneath the confining unit. Coarse-grained sands

and gravels are likely to be interbedded with finer-

grained sediments. Groundwater flow is likely to occur

predominantly through the zones of highest hydraulic

conductivity; thus groundwater flow is not likely to be

uniform throughout the unit. The aquifer was modeled as

homogenous and isotropic because variability within the

62

aquifer is poorly constrained. The elevation of the top

of the aquifer is known only in topographically low areas.

The elevation that was assigned to represent the top of

the aquifer is biased since the top elevation of the

aquifer is not well constrained in upland areas. It is

not known whether the aquifer is continuous throughout the

island.

Figures 29 and 30 are cross sections showing the

stratigraphy of the mitigation site. Figure 31 shows the

location of the cross sections and the sites used for

construction of the cross sections. Appendix 4 contains

the stratigraphic columns used in construction of the

cross sections. The location of the top of the aquifer

shown in Figures 29 and 30 has been inferred in the areas

where it was not located. Stratigraphic columns for

points that were not used for these cross sections and a

map showing the location of these points are given in

Appendix 4. Elevations were taken from a 0.61-m (2-ft)

contour interval map of the study area (SRI, 1991b).

Evapotranspiration in the groundwater model

Evapotranspiration was entered into MODFLOW using

data collected from the Vancouver weather station.

MODFLOW uses an evapotranspiration rate versus depth

function (Figure 32) to determine evapotranspiration from

s N

1 2 3 4

0 250 500 750 1000

Figure 29. Cross section A-A 1• The location of cross section A-A 1 is given in

Figure 31. Distances are in meters. Vertical exageration = 7.

1250

CJ'\ l>J

0

Figure 30. Figure 31.

s N

5 6 7 8 9

250 500 750 1000

Cross section B-B 1• The location of cross section B-B' is given in

Distances are in meters. Vertical exageration = 7.

12

6

O'I ~

Columbia River

B' Wetland boundary line

9

North

Jewit Lake c,

300 m Scale:

Southeast Pond

* 1

Columbia River

Figure 31. Site locations used for cross section construction.

O'\ Ul

66

a node. Figure 32 shows that maximum evapotranspiration

decreases with depth from a specified surface elevation in

MODFLOW. The approximate elevation of the ground surface

was entered as the elevation from which maximum

evapotranspiration occurs in the groundwater model.

Evapotranspiration from surf ace water occurs at the

maximum evapotranspiration rate because surf ace water is

located above the elevation of the ground surface. An

extinction depth of 1.7 m (5 ft) was used because plant

roots were observed extending from the ground surf ace to

this depth.

Calibration of the groundwater model

The groundwater model was calibrated using water

levels (Table II) collected at monitoring points in

February, March, and April of 1994. Water levels given in

Table II were compared to water levels in the groundwater

model at the appropriate nodes to ensure that water levels

in the groundwater model were similar to actual water

levels. Precipitation and evapotranspiration were entered

into MODFLOW using actual data collected from the National

Weather Service and the Vancouver weather station for

February, March and April of 1994. Table VIII shows

actual water levels collected in February, March, and

April of 1994 and water levels obtained in the groundwater

<l)

0 Q) ,--._

--= v co <l)

I

ET Surface

Maximum ET Rate

_t_,_ - - - - - - - - - - -I

c .2 .c C3 a. c al :;: 0 x w

_l_

0

Maximum ET Rate Slope= . .

Extinction Depth

Extinction Elevation

Evapotranspi ration (ET)

Fioure 32. Evapotranspiration as a function of head (McDonald and Harbaugh, 1984).

67

Table VIII

Actual and modeled water levels on Government Island for February, March, and April, 1994.

Field data (also given in Table II) Modeling results in the node

containing the monitoring point

monitoring point 2/6/94 3/6/94 4/2/94 4/3/94 4/10/94 Feb-94 Mar-94 Jl.pr-94 # 11 dry 11. 05 10.46 10.4 10.99 10.98 11. 4 11.92

# 12 n/a n/a 10.74 10.6 11. 23 10.98 11. 4 11.92 # 13 10.82 11.93 10.76 10.66 11. 37 11. 04 11. 4 11. 97

--# 20 dry 11. 86 dry dry dry 11.28 11. 32 11. 75 # 23 14.26 15.35 15.18 15.16 15.59 12.25 11. 3 11. 37 # 25 dry 16.51 16.29 16.26 16.97 12.25 11. 3 11. 37

-# 2 6 15.54 17.48 16.54 16.5 17.42 12.25 11. 3 11.37

# 30 n/a n/a n/a n/a ? 11. 7 10.86 11.06 # 31 n/a n/a n/a n/a 12. 03 11.09 11. 2 6 11. 6 # 32 n/a n/a n/a n/a 11.09 10.91 11. 15 11. 46 # 33 n/a n/a n/a n/a 11. 35 10.99 11.14 11. 39

Jewit Lake dry 11. 21 11. 67 11.62 11.66 11. 3 11. 71 11. 58 staff gauge

Southeast Pond n/a 13 .1 12.67 12.6 12.85 11.65 13. 4 12.94

staff gauge

NOTE: Jewit Lake levels were not perfectly flat across all of the nodes representing Jewit Lake

in the groundwater model. Water levels were taken from a node in the center of Jewit Lake.

()\

CD

69

model node where the appropriate water level was observed.

Table VIII shows that water levels obtained in the

groundwater model are mostly within 20 cm (8 in) of water

levels observed at monitoring points. Water levels

observed at monitoring points 23, 25, and 26 (1 node) were

consistently 1 to 1.3 m (3 to 4 ft) higher than water

levels obtained in groundwater modeling. Hydraulic

conductivities in the node containing monitoring points

23, 25, and 26 were not altered so that modeling results

would match actual water levels. Changes to the hydraulic

conductivity and VCONT values in the node containing

monitoring points 23, 25, and 26 caused unreasonable water

levels to be present when the groundwater model was run

from June through December.

Water levels from May 1994 to December 1994 were not

used to calibrate the groundwater model because

observations of the water table could not be made at many

of the monitoring points. Water table levels fell below

observable depths at many of the monitoring points. Jewit

Lake water levels were not modeled from May 1994 through

December 1994 because running the groundwater model with

beginning lake levels of 3.5 m (11.5 ft) would cause the

nodes in layer 1 to go to no-flow (inactive).

Precipitation cannot enter the model and

evapotranspiration cannot leave the model if the nodes in

70

layer 1 go to no-flow. Water levels in the groundwater

model would be inaccurate if the groundwater model was run

using actual data from June of 1994. In 1994, Jewit Lake

had a level of 3.5 m (11.5 ft) at the end of May. The

Columbia River in 1994 (Figure 11) maintained levels in

January through September that were lower than any year

between 1973 and 1989. Precipitation in January through

September was below average and evapotranspiration rates

were above average. Water levels from May 1994 through

December 1994 were chosen to represent the minimum amount

of water that will be present May through December in any

year at Government Island.

Inspection of hydrographs between 1973 and 1989

(Appendix 1, Figure 12) indicate that peak flows of the

Columbia River at Government Island usually occur in

December through January and May through June. One aspect

of groundwater modeling of the study area focused on

flooding of the island during peak flow events and the

levels of water retained after flooding as a function of

time. A river elevation greater than 3.6 m (12.0 ft)

m.s.l. is required to flood Jewit Lake through the dam

(Figure 8) and the spillway channel. This is known from

an observation of the Jewit Lak~ level at the staff gauge

on January 22, 1995. On January 22, 1995, Jewit Lake was

filling and draining as the level of the Columbia River

71

fluctuated throughout the day. A maximum water level of

4.7 rn (15.3 ft) rn.s.l. can be retained in Jewit Lake by

the darn once the Columbia River receeds following a high­

flow event.

RESULTS OF GROUNDWATER MODELING

Climate as a variable in groundwater modeling

The MODFLOW program was used to model lake levels for

the months of June through December. The model was run by

entering the beginning lake levels, Columbia River level,

precipitation, and evapotranspiration. Changes in lake

levels were observed at 30 day intervals. Figures 33, 34,

and 35 show precipitation, evapotranspiration, and

groundwater infiltration from June through December with

average precipitation and evapotranspiration; 50 percent

above average precipitation and 25 percent below average

evapotranspiration; and 50 percent below average

precipitation and 25 percent above average

evapotranspiration, respectively. Figures 18 and 19 show

that 1993 and 1994 monthly precipitation rates are usually

within 50 percent of the National Weather Service monthly

average precipitation. Figure 20 shows that 1993 and 1994

monthly evapotranspiration rates are usually within 25

percent of the monthly average evapotranspiration at the

30000 ---~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-

Ms

~ (]) ..w co

25000

~ 15000 4-1 0

(])

s 10000 ~ 0 :>

5000

stirnated range for June groundwater infiltration

_._Precipitation

---evapotranspiration --It-groundwater infiltration

0 -+-~~~~---+-~~~~~..,._~~~~---;.~~~~~-+-~~~~~~~~~~~ J J A s 0 N D

Month of the year

Figure 33. Precipitation, evapotranspiration, and groundwater infiltration from June through December with average precipitation and evapotranspiration rates.

-....]

N

M

s

~ (l) .w cO ~

4-1 0

(l)

12000 ----~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~--,

10000

8000

6000

Estimated range for June groundwater infiltration

-+-precipitation

-9-evapotranspiration

_._groundwater infiltration

s 4000 ,..._, 0 :>

2000

0 ~~~~~~~~~~~.....;-~~~~~,.__~~~~-+-~~~~~...._~~~~---1 J J A S 0 N D

Month of the year

Figure 34. Precipitation, evapotranspiration, and groundwater infiltration from June through December with above average precipitation and below average evapotranspiration rates.

.......]

w

50000 ----~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-,

40000

(V)s

~ 30000 .w m ~

4-1 0

<V 20000

~ r-l 0 >

10000

stimated range for June groundwater infiltration

[;!recipitation

vapotranspiration

roundwater infiltration

al ---;---- : ' • ~ J J A s 0 N D

Month of the year

Figure 35. Precipitation, evapotranspiration, and groundwater infiltration from June through December with below average precipitation and above average evapotranspiration~ rates. P

75

Vancouver weather station. Figures 33, 34, and 35 show

that the amount of groundwater infiltration is dependent

upon rates of precipitation and evapotranspiration. The

groundwater infiltration curves are inaccurate for the

month of June because water flows into storage during the

first iteration of each modeling simulation to achieve an

equilibrium condition in the model. Figures 33, 34, and

35 show approximations of groundwater infiltration for the

month of June. June groundwater infiltration is

approximated by extrapolating the slope of the line

representing groundwater infiltration for July and August

to the y-axis. The shaded rectangle in Figures 33, 34,

and 35 represents an estimation of the range for June

groundwater infiltration.

Groundwater modeling of the site is used to determine

the length of time that water will be absent from Jewit

Lake and Southeast Pond when lake levels of 4.0, 4.3 and

4.6 m (13, 14 and 15 ft) occur following late May/early

June flooding of the study area (Table IX) . Table IX shows

periods of drying in Jewit Lake and Southeast Pond based

on modeling. Columbia River levels are maintained at a

level of approximately 2.9 m (9.5 ft) m.s.l. during the

summer months in most years (Appendix 1). Thus the

groundwater model is set up to examine the time for Jewit

Lake and Southeast Pond to dry keeping the Columbia River

Table IX

Simulation identifying months where water is absent in Jewit Lake and Southeast Pond for years when flooding

occurs through the spillway channel.

MAY 31 LAKE LEVEL PRECIPITATION JEWIT LAKE SE POND

4.0 m AVERAGE AUG.-DEC. AUG. -OCT.

4.0 m ABOVE AVERAGE AUG. 15- AUG. 15-NOV. 15 SEPT.

4.0 m DOUBLE SEPT.- NONE OCT. 15

4.3 m NONE OCT. - SEPT.-

4.3 m AVERAGE OCT. OCT.

4.3 m ABOVE AVERAGE NONE NONE

4.6 m NONE OCT.- SEPT.-

4.6 m BELOW AVERAGE OCT.- OCT. 15-NOV 30 NOV. 15

4.6 m AVERAGE NONE NONE

level at 2.9 m (9.5 ft) m.s.l. Precipitation rates,

evapotranspiration rates, and beginning lake levels were

used as variables in the MODFLOW program based on actual

data given in Figures 18, 19, and 20 and Table II.

Predictions of the times of the year that water will be

absent from Jewit Lake and Southeast Pond are shown in

76

15

Table IX and Figures 36 and 37. In Table IX, simulations

that receive no precipitation indicate an indefinite

ending time for the drying period. This occurs because

4---~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~---.

3.75 r-f

rJl

E

E 3.5

r-f CV ::> CV

r-l

CV 3. 25 ~ rU

I-'.:!

+.J ·rl ~

~ 3

Minimum water level desired by mitigation

Minimum ~n of Jewit Lake

Water in the lake

2.75...-~~~~~+--~~~~--1~~~~~--i-~~~~~-+-~~~~~.-p.-~~~~~~

June July Aug Sept Oct Nov Dec

Month of the year

-+-average rain

-II-one and one half times the average rain

_,.._double the average rain

Figure 36. Water levels in Jewit Lake from June through December with variable rates of precipitation in years when no flooding occurs through the spillway channel. -....J

-....J

---~- -------- ---------~-

4.25--------------------------------------------------------- -+-average rain

-II-one and one half times the average rain

r-i

(/)

E

El

r-i QJ

::> QJ

r-i

'O

4

3.75

§ 3. 5 p..,

.µ (/)

rU QJ

..r: .µ

g 3 .25 Ul

Minimum water level desired by mitigation

i ~ --...____...---Lowest elevation in Sout Pond

3 ~ ~ I I I I ' une . uly Aug Sept Oct Nov Dec

Month of the year

_._double the average rain

Figure 37. Water levels in Southeast Pond from June through December with variable rates of precipitation in years when no water flows overland from Jewit Lake to Southeast Pond.

-......] (XJ

79

Columbia River levels are lower than the lowest point in

Jewit Lake and Southeast Pond. Jewit Lake and Southeast

Pond decrease in water level without receiving water from

precipitation or the Columbia River.

The Columbia River may not reach an elevation above

3.8 m (12.5 ft) m.s.l. in the months of May or June. If

this is the case, then Jewit Lake will not be flooded

through the spillway channel. A beginning lake level of

3.8 m (12.5 ft) m.s.l. was modeled receiving average,

above average, and twice the average precipitation in the

months of June through December. A lake level of 3.8 m

(12.5 ft) was chosen because Jewit Lake reached a level of

3.8 m (12.5 ft) in 1994 (Table II) though no flooding

through the spring loaded gates occurred. The purpose of

modeling lake levels that have not received water through

the spillway channel was to determine the length of time

that rainfall alone could prevent Jewit Lake or Southeast

Pond from drying. Results indicate that drying will occur

in both lakes in years when flooding through the spillway

channel does not occur (Figures 36 and 37) . Higher rates

of precipitation decrease the amount of time that dry

conditions are present in the lakes.

Water leaves the groundwater model by infiltration

into the aquifer which flows to the Columbia River and by

evapotranspiration. Evapotranspiration rates were altered

80

depending upon the amount of rainfall being modeled.

Above average and below average evapotranspiration rates

were estimated to be 25 percent above and below,

respectively, average evapotranspiration rates in

Vancouver, Washington. When above average rainfall for a

month was being simulated, below average

evapotranspiration rates were used. When below average or

no rainfall conditions were being simulated, above average

evapotranspiration rates were used. Figure 38 shows the

monthly evapotranspiration used in groundwater modeling.

Figure 20 indicates that the summer of 1993 had below

average evapotranspiration and the summer of 1994 had

above average evapotranspiration. Comparison of Figure 20

with Figure 38 indicates that the 25 percent variation

from average evapotranspiration is a reasonable

approximation of the variability in evapotranspiration

that is expected to occur at Government Island.

Hydraulic conductivity of the confining unit as a variable in groundwater modeling

Samples analyzed for particle size distribution

indicate that the confining unit is predominately silt,

with clay, fine sand, colloids, and organic matter (Table

V) . Sample 15 was collected from a disturbed area behind

the dam (Figure 22) and is not indicative of the

composition of the confining unit. The confining unit was

25--~~~~~~~~~~~~~~~~~~~~~~~,

e 20 ()

ID average s::

1s I I 0 ·r-1 111993 JJ ro I H I 01994

·r-1 Pi {/)

s:: 10 ro H JJ 0 Pi ro ~ 5 IJ:l

0

J F M A M J J A s 0 N D

Month

Figure 38. Monthly evapotranspiration entered into MODFLOW. OJ I-'

82

modeled using a hydraulic conductivity of 15.2 cm/day (0.5

ft/day) for all of the nodes except 3. The conductivity

of the confining unit at Southeast Pond (2 nodes) was

approximated at 6.1 cm/day (0.2 ft/day). Sediments

underlying Southeast Pond (2 nodes) contain 4 percent more

clay than any other sample analyzed from the confining

unit (Table V) . Variations in the hydraulic conductivity

of the confining unit outside of Southeast Pond was not

attempted as samples may not represent the lowest

conductivity zone in the layer at the sampling site. A

sand and gravel layer of unknown lateral extent located

approximately 40 m (131 ft) west of Southeast Pond was

assigned one node in the MODFLOW grid. The sand and

gravel layer was assigned one node because no other sand

and gravel layers were located in vicinity of Southeast

Pond. A conductivity value of 30.5 m/day (100 ft/day) was

assigned to the sand and gravel layer based on the values

of hydraulic conductivity given for gravels in (Freeze and

Cherry, 1979).

The hydraulic conductivity of the confining unit was

estimated at 15.2 cm/day (0.5 ft/day) because Southeast

Pond maintained surface water in October of 1993 (Table I)

when Jewit Lake was dry; thus the confining unit at

Southeast Pond has a lower hydraulic conductivity than the

remainder of the confining unit. A hydraulic conductivity

83

of 15.2 cm/day (0.5 ft/day) is in the upper-value range of

hydraulic conductivities given for silts in Freeze and

Cherry (1979).

Figure 39 shows modeling results of Southeast Pond

levels from June 1, 1994 through September 1, 1994 using

hydraulic conductivity values of 6 cm/day (0.2 ft/day),

2.7 cm/day (0.09 ft/day) and 0.4 cm/day (0.013 ft/day).

Figure 39 is used to validate the hydraulic conductivity

value of 0.2 ft/day used in modeling for the 2 nodes

representing Southeast Pond. Lake levels are highest as

hydraulic conductivity values are decreased (Figure 39) .

In order to assess the effect of the hydraulic

conductivity of the confining unit on lake levels, values

of 2.7 cm/day (0.09 ft/day) and 0.4 cm/day (0.013 ft/day)

were used in the groundwater model for the hydraulic

conductivity of the confining unit. These values are in

the middle and lower value range, respectively, of

hydraulic conductivities for silts (Freeze and Cherry,

1979) . Average precipitation and evapotranspiration are

held constant as hydraulic conductivity values are

altered. Figure 40 shows Jewit Lake levels based on

modeling from the end of June through November. Figure 40

shows that lake levels are highest when the hydraulic

conductivity of the confining unit is decreased.

14 4. 3 m

--+-K=O. 2 ft/day r--i

Ul 13 4. 0 m

---K=0.09 ft/day s Lowest water level desired from mitigation

.tl 12 l \ 3 . 6 m f~~-~

--.-K=0.013 ft/day

r--i Q) :::. ~ 11

ro s:: 0 ~ 10 ..w Ul ro Q)

fl 9 ;::1 0 Cll

_____________ J3. 3 m

2. 7 m

8 +-- --+2.4 m June 1 July 1 Aug 1 Sept 1

Month

Figure 39. Variations in Southeast Pond water levels from June 1,1994 to September 1, 1994 using hydraulic conductivity values given for silts (Freeze and Cherry, 1979).

··---------- ·----- ------

(X)

~

15 4.6 m

.-1

Ul 14 s

... ..j.J Q)

~ 13

.-1 Q)

~ Q)

.-1 12 Q) ~ ro

...:I

..j.J 11 ·r-1 ~ Q)

t-")

----------.-----------_._~~~~~--14.3 m

4. 0 m Lowest water level desired from mitigation

~ 3.6 m

-+-K=. 5 ft/ day

3. 3 m Lowest elevation

-11-K=. 09 ft/day

--.-K=.013 ft/day in~it Lake

10 - 3.0 m June July Aug Sept Oct Nov

Month

Figure 40. Variations in Jewit Lake water levels from June through November using hydraulic conductivity values given for silts (Freeze and Cherry, 1979). co

Ul

Aquifer transmissivity as a variable in groundwater modeling

The effect of aquifer transmissivity on lake levels

86

was modeled by using values of 259 m/day, 2590 m/day, and

25900 m/day (850 ft/day, 8500 ft/day, and 85000 ft/day)

for aquifer transmissivity. These values were derived

from the lower, middle, and upper range of values,

respectively, of the hydraulic conductivity for sands

(Freeze and Cherry, 1979). A hydraulic conductivity of

0.5 ft/day was used for the confining unit as the values

of transmissivity were changed. Figures 41 and 42 show

water levels in Jewit Lake and Southeast Pond from June

through December using transmissivity values of 259 m/day,

2590 m/day, and 25900 m/day (850 ft/day, 8500 ft/day, and

85000 ft/day) . Lake levels are highest when the values of

transmissivity are lowest (Figures 41 and 42). Site

monitoring in 1993 through 1995 indicates that water

levels in Jewit Lake and Southeast Pond are most likely to

approach water levels obtained using a transmissivity

value of 2590 m/day (8500 ft/day).

Predictions of the site conditions based on modeling results

Figures 43 and 44 show the levels of Jewit Lake and

Southeast Pond from May 31 to December 31 based on

modeling. A hydraulic conductivity of 15.2 cm/day (0.5

ft/day) and a transmissivity value of 2590 m/day (8500

15 4. 6 m

4.3 m 14

.--t

Ul

6 13 4.0 m

Lowest water level desired from mit1g ...

..µ 4-1

12 ~ 13.6 m

.--t (})

:> ~ 11 3. 3 m

(})

~ ro ~ 10

elevation w Jewit Lake 3.0 m

..µ

2. 7 m ·r-i ;3: (}) 9 t"')

-+-T=850 ft/day

-ll-T=8500 ft/day

-.-T=85000 ft/day

8 2.4 m +-~~~-;-~~~-t-~~~-1-~~~---1~~~~+-~~~-+-~~~-+-~~~-+-~~~__,~~~---r

June - - Nov July Aug Sept Oct Month

Figure 41. Variations in Jewit Lake water levels from June through November using transmissivity values given for sands (Freeze and Cherry, 1979).

-------- ------·-·-------- ---~-- - -·----

OJ -..J

15 4. 6 m

r; 14 Ul

s .w 13

4.0 m

~

l""'"i 12 Q)

::> I , =----- ~ ~

13.6 m " -----. ;:::::::::-----Q)

l""'"i

ro 11 + Lowes~evation in Southeast Pond ~ s:: .3 m

0 ~

.w 10 Ul ro Q)

9 t ~T=850 ft/day ,..q .w ::J ---T=8500 ft/day 0 ti) --.-T=85000 ft/day

2. 7 m

8 2.4 m June July Aug Sept Oct Nov

Month

Figure 42. Variations in Southeast Pond water levels from June through November using transrnissivity values given for sands (Freeze and Cherry, 1979).

CD CD

J.J 4-1 -Ul

.--1 Q)

~ Q)

i-=1

Q) ~ ro i-=1

16 ,--- 4.9 m

15' beginning lake level on May 31st

15 / 4.6 m

14 J__ .............._ 14.3 m

13 l. -~ 14. 0 m

12 I .... -----.------- 13. 6 m

I Lowest elevation in Jewit Lake

11 -t ""- 13 .3 m

10 ~~~~~~~JT.u~l~y-;---+~J.\t;g-~~f--~;\~~t-~;;t~~+-~N;:~~-t-1).;;;-~-- ' June Aug Sept Month

Oct Nov Dec .0 m

Figure 43. Jewit Lake levels from May 31 to December 31 with average precipitation. 00 '-0

15 4.6 m

14.5 14' beginning lake level on May 31st

14 4.3 m

"'-' ~ 13. 5

r--1 Q)

:> 13 Q) 4. 0 m

r--1

Q) 12.5 ~ m ....:I

12 3.6 m

11. 5

Lowest elevation in Southeast Pond~

11 3.3 m June July Aug Sept

Month Oct Nov Dec

Figure 44. Southeast Pond levels from May 31 to December 31 with average precipitation.

\..()

0

91

ft/day) were used for the confining unit and aquifer

parameters, respectively. Beginning lake levels of 4.6 m

(15 ft) and 4.3 m (14 ft) are shown for Jewit Lake and

Southeast Pond respectively. At a beginning water level

of 4.6 m (15 ft) on May 31, Jewit Lake is not expected to

dry. At a beginning water level of 4.3 m (14 ft),

Southeast Pond is expected to dry during October.

Summary of the groundwater model design parameters and the results of groundwater modeling

The groundwater model was designed as a 4 layer

problem, with a confining unit overlying an aquifer.

Layers 1, 2, and 3 represent the confining unit and Jewit

Lake and Southeast Pond, respectively; layer 4 represents

the aquifer. Precipitation and evapotranspiration were

entered into the groundwater model to simulate the

response of lake levels to climatalogical factors expected

to occur on Government Island. Water level measurements

in February, March, and April 1994 were compared with

modeling results so that the groundwater model could be

calibrated against real data. Hydraulic conductivity and

transmissivity values of the confining unit and the

aquifer were altered to assess the variability in lake

levels with changes in these parameters. Decreasing

values of hydraulic conductivity and transmissivity in the

confining unit increases water levels in Jewit Lake and

92

Southeast Pond. For a fixed set of hydraulic parameters,

water leaves the study area by evapotranspiration and

groundwater infiltration in volumes dependent upon rates

of precipitation and evapotranspiration. Modeling

indicates that with average precipitation and

evapotranspiration, Jewit Lake must reach a level of 4.6 m

(15 ft) during the spring flooding of the Columbia River

to ensure that water levels in Jewit Lake do not drop

below 3.6 m (12 ft) during the summer months. Modeling

indicates that with average precipitation and

evapotranspiration, Southeast Pond must exceed a water

level of 4.3 m (14 ft) in the spring months to ensure that

water levels in Southeast Pond do not drop below 3.6 m (12

ft) during the summer months.

93

Table X

Summary of the variables used in MODFLOW to simulate the hydrogeology of Government Island.

Node dimensions: 152.4 m by 152.4 m

Confining unit thickness: 1.7 to 6.1 m

Aquifer thickness: 7.5 m

Aquifer transmissivity: 259 m/day, 2590 m/day, 25900 m/day

Confining unit hydraulic conductivity (Southeast Pond) : 6 cm/day, 2.7 cm/day, 0.4 cm/day

Confining unit hydraulic conductivity (all nodes except Southeast Pond): 15 cm/day, 2.7 cm/day, 0.4 cm/day

Evapotranspiration (in/mo) :Jun Jly Aug Sep Oct Nov Dec average: 4.9 6.0 5.4 3.8 2.0 1.1 0.7 below average: 3.7 4.5 4.0 2.9 1.5 0.8 0.5 above average: 6.1 7.5 6.8 4.8 2.6 1. 3 0.9

Precipitation: (in/mo): Jun Jly Aug Sep Oct Nov Dec average: 1.5 0.4 1.1 1.7 3.0 5.2 6.4 below average: 0.7 0.2 0.5 0.8 1.5 2.6 3.2 above average: 2.2 0.6 1.6 2.6 4.5 7.8 9.6 double the average: 3.0 0.8 2.2 3.4 6.0 10.4 12.8

DISCUSSION OF HYDROLOGY

Flooding of Jewit Lake through the spillway channel

can occur between December and June, depending upon the

timing of water release from the Columbia-Snake River dam

system. Between 1973 and 1989, each year that the

Columbia River exceeded 4.7 m (15.3 ft} in elevation in

December or January, the Columbia River also exceeded 4.7

m (15.3 ft} in elevation in May or June. Approximately

once every three years, river levels exceed 4.7 (15.3 ft}

m.s.l. during February, March, or April, thus flooding

Jewit Lake.

Table IV shows estimates of inflow rates which

occurred through the dam in January and February of 1995

based on the volume of water present in Jewit Lake

following high river stages (Figure 16} . Water from the

peak flows occurring on February 1st through February 4th

and February 20th through February 22nd flowed through the

open spillway grates and the spring loaded gates. Water

from the January 14th through January 21st peak flow event

flowed only through the spring loaded gates. The rate of

water flow through the dam was approximately 15 to 20

times higher when water flow occurred through the spillway

grates as well as the spring loaded gates than when water

flow occurred only through the spring loaded gates. Thus

when the Columbia River exceeds 4.7 meters (15.3 ft} in

elevation at Government Island, the level of Jewit Lake

95

will increase much faster than when the Columbia River is

between 3.6 and 4.7 m (12 and 15.3 ft) elevation at

Government Island.

By examining the spatial distribution of hydraulic

head at observation points throughout the study area, the

direction of groundwater flow can be determined. If head

is higher near the Columbia River than the interior of the

island, groundwater flow is towards the interior of the

island. If head is higher in the interior of the island

than near the Columbia River, groundwater flow is from the

interior of the island towards the Columbia River.

Through aquifers, groundwater flow is predominately

horizontal, with a small vertical component, while through

confining units, groundwater flow is predominantly

vertical, with a small horizontal component (Freeze and

Cherry, 1979).

Maximum river levels on the Columbia River occur in

May or June in most years (Figure 12, Appendix 1). Water

can be retained in Jewit Lake to a maximum level of 4.7 m

(15.3 ft), creating head differences of up to 1.8 m (5.8

ft) between the lake levels maintained by the spillway

channel dam and the level of the Columbia River. Since

the filled lake and pond each lose water to the aquifer

that flows to the Columbia River, the water table must

slope away from the interior of the island towards the

96

Columbia River. The slope of the water table decreases as

the lake levels decrease since the head difference between

the lakes and the river at 2.9 m (9.5 ft) is lower.

Seismic refraction data collected on May 7th and 8th,

1994 (Table VI) show that the water table was nearly flat

in the north-south direction during the time of the

refraction study. The seismic refraction data show that

the water table was sloping gently towards the interior of

the island. The Columbia River changed little in level in

the month prior to the seismic refraction study. Figure

11 shows that Columbia River levels varied only 0.61 m (2

ft) in elevation from approximately April 15th to May 7th

and 8th, when the seismic refraction study was done. The

water table should flatten in response to nearly constant

Columbia River levels and be approximately the same

elevation as the Columbia River. Rainfall recharge allows

the water table to be located above the minimum level

maintained by the Columbia River (McDonald and Harbaugh,

1984).

Differences between field observations of the water

table and refraction depths are attributed to the

heterogeneity of the sediments and the velocity

differences in the sediments. The water table at station

G-9 (Figure 23) was 1 m (3 ft) lower than the water table

at any of the other stations (Table VI). This suggests

97

that the sediments underlying this station may have a

higher conductivity than the sediments at the other

stations (Figure 45) . Figure 45 shows that a zone of

higher hydraulic conductivity may cause the elevation of

the water table to be lower in the vicinity of station G-9

than at the other stations. A zone of higher hydraulic

conductivity would likely be sandy material deposited

within the Government Island channel bar. The extent of

this zone of higher conductivity is unknown.

Figure 10 shows that the Columbia River reached a

level of 5.5 m (18 ft) in May of 1993; thus Jewit Lake was

flooded. Jewit Lake was dry in early October of 1993.

The ditch plug (Figure 4) held water in Jewit Lake prior

to construction of the dam in October of 1993. By

estimating the elevation of the top of the ditch plug, the

maximum level of Jewit Lake in 1993 can be estimated. The

top of the ditch plug is estimated to have an elevation of

4.3 m (14 ft). It is unknown when drying of Jewit Lake

occurred in 1993. Jewit Lake was dry on October 23rd,

1993.

It is not known if Southeast Pond received overland

flow from Jewit Lake in 1993. If Southeast Pond did

receive overland flow from Jewit Lake in 1993, the drying

date of Southeast Pond in 1993 permits an estimation of

when drying could occur in future years. A drying date in

Ground Surface

J;,V~ ! /:VJ; lower conductivitylhigher conductivity I lower conductivity

r·················· ... -... ' .................................... '. ....... ·.·················1 ·························································································· ·························································································· ·························································································· ·························································································· ·························································································· ·························································································· ·························································································· : . : : . : . : . : . : . : : . : ... : . ;. : . : .: . ;.: ... : . ;.: . ; . :-: . : . ;. : . : -:-: . ;. ;. : : . : : . : . : . : . : . : . : . : . ;. : . ; . : . : . : . : . : : . : : . : . : .: : . : : . : ... : : . :-: . : : . : ... : : . : . ;. : . ; .: . : . : ... :-: . ;. ;-: ... ;. ;. ::

-V water table ! groundwater flow direction f:::J aquifer

Figure 45. A zone of higher hydraulic conductivity at seismic refraction station G-9 (Figure 23).

98

October or early November can be predicted based on a

drying date of October 30th in l993.

99

The Columbia River did not flood Jewit Lake through

the channel in 1994. Thus all of the water in Jewit Lake

and Southeast Pond were derived from precipitation and

groundwater. Water levels in Southeast Pond were higher

than water levels in Jewit Lake throughout 1994 (Table

II) . The observation that water levels in Southeast Pond

were higher than water levels in Jewit Lake were used to

determine that infiltration rates are higher in Jewit Lake

than in Southeast Pond. Jewit Lake should have maintained

surface water longer into the fall of 1993 than Southeast

Pond if infiltration rates in the lakes were equal since

the bottom elevation of Jewit Lake is lower than the

bottom elevation of Southeast Pond. Since infiltration

rates into the sediments of Southeast Pond are lower than

infiltration rates into Jewit Lake, the hydraulic

conductivity of the Southeast Pond sediments must be lower

than the hydraulic conductivity of the Jewit Lake

sediments.

Groundwater modeling was used to determine if Jewit

Lake and Southeast Pond would maintain surface water

throughout the growing season in years when flooding of

the lake does not occur. Figures 36 and 37 indicate that

drying will occur in both lakes when flooding through the

100

dam does not occur. Figures 36 and 37 show that drying

times will fluctuate depending on precipitation rates

entered into the groundwater model. Analysis of

hydrographs of the Columbia River (Appendix 1) indicates

that the Columbia River did not reach 4.7 m (15.3 ft) in

elevation at Government Island in only 2 of the 16 years

between 1973 and 1989. The Columbia River reached 3.6 m

(12 ft) in elevation every year between 1973 and 1989. In

1994 (Figure 11), the Columbia River did not reach 3.6 (12

ft) in elevation, thus no flooding of Jewit Lake occurred.

In 1994, Jewit Lake dried in May and Southeast Pond dried

in June. It is unlikely that water will be absent from

Jewit Lake and Southeast Pond in future years for the

length of time that it was absent in 1994 because the

Columbia River maintained higher levels in the 16 years

prior to implementation of mitigation and 1994 had below

average precipitation. 1994 levels of the Columbia River

were extremely low and are not expected to occur of ten in

the future.

The length of time that water is absent from the

lakes depends upon the amount of precipitation occurring

at Government Island and the level of the lakes at the

beginning of the summer months. The years that the

Columbia River does not reach 3.6 m (12 ft) in elevation

at Government Island are likely to be years when below

101

average precipitation occurs in the Columbia River

drainage basin. Therefore, summer months with above

average or twice the average precipitation would not be

expected to occur on Government Island in years when the

Columbia River drainage basin recieves below average

precipitation.

The groundwater model was run using beginning lake

levels of 4.0, 4.3, and 4.6 m (13, 14, and 15 ft). The

lake and pond recieve variable amounts of precipitation

and undergo variable rates of evapotranspiration beginning

June 1st. Results of modeling (Table IX) indicate that

surface water will remain in Jewit Lake and Southeast Pond

when lake levels of 4.5 m (14.7 ft) are reached in May and

average precipitation and evapotranspiration rates occur.

Drying will occur for one month at the end of the growing

season when May lake levels reach 4.3 m (14 ft) in

elevation and average precipitation and evapotranspiration

rates occur. Unless twice the average precipitation

occurs in the summer months, dry conditions of greater

than one month during the growing season will occur in

both lakes when the lakes do not reach a level of 4.3 (14

ft) in May.

1994 water level observations (Table II) indicate

that Jewit Lake will dry before Southeast Pond when

flooding through the spillway channel does not occur.

Jewit Lake would be dry for longer periods of time than

indicated in Table IX if drying of Jewit Lake occurs

before drying of Southeast Pond. If water leaves Jewit

102

Lake and Southeast Pond at the same rate, Jewit Lake would

be expected to contain water longer each year than

Southeast Pond due to the elevation differences of the

bottom of the lakes. In order for water levels to be

lower in Jewit lake than Southeast Pond, water must leave

Jewit Lake at a faster rate than water leaves Southeast

Pond. In modeling, this would occur if the hydraulic

conductivity and VCONT of the confining unit under Jewit

Lake were increased or if the transmissivity of the

aquifer underlying Jewit Lake were increased.

In 1994, Jewit Lake and Southeast Pond had different

water levels, indicating that the hydrology of the lakes

are independent of each other. Water level measurements

(Table II) indicate that water in Jewit Lake and Southeast

Pond infiltrate at different rates; thus the rates of

groundwater flow through the subsurface sediments are

different. The transmissivity of the underlying aquifer

connecting to the Columbia River is assumed to be

homogenous since very little is known about the aquifer.

Differences in the hydraulic conductivity and the VCONT

parameters of the confining unit in MODFLOW allow

Southeast Pond and Jewit Lake to retain different water

levels.

103

The different water levels observed in the lakes

may not solely be caused by a difference in the hydraulic

conductivity of the confining unit. Variations in the

transmissivity of the underlying aquifer may be

contributing to differences in water levels of Jewit Lake

and Southeast Pond. The different levels in the lakes may

indicate that the aquifer is not continuous throughout the

island.

Precipitation which directly falls onto surface water

increases the lake to a level directly proportional to the

amount of water which falls on the lake. Water that falls

onto the ground surface infiltrates into the soil through

intergranular pore space or flows overland. Since water

occupies only intergranular pore space in the ground,

precipitation can raise the elevation of a subsurface

water table much more than when the water table is above

the ground surface. As the water table rises in elevation,

more of this water is exposed above ground as surf ace

water. Therefore, a given amount of precipitation has a

greater effect on the elevation of the water table in the

subsurface than when the water table is above the ground

surface.

In February of 1994 through May of 1994, water levels

in Southeast Pond were higher than water levels in Jewit

Lake. Since the ground surface of Southeast Pond is

104

higher than the ground surface in Jewit Lake, the water

table remains in the subsurface to a higher elevation in

Southeast Pond. Thus the water table is likely to be

higher in Southeast Pond than Jewit Lake if rainfall is

the source of water for both lakes.

Figures 33, 34, and 35 show precipitation,

evapotranspiration, and groundwater infiltration from June

through December under variable rates of precipitation.

These figures indicate that as precipitation increases,

groundwater infiltration increases and as

evapotranspiration increases, groundwater infiltration

decreases. When precipitation is average or above average

and evapotranspiration is average or below average, the

amount of water leaving the model by groundwater

infiltration is at least double the amount of water

leaving the model by evapotranspiration. More water

leaves the model by evapotranspiration in June, July,

August, and September than by groundwater infiltration

when precipitation is below average and evapotranspiration

is above average. Figures 33, 34, and 35 suggest that the

climate in June through December affects how much water

enters and leaves the study area by precipitation and

evapotranspiration, respectively; thus influencing the

amount of water available for groundwater infiltration.

Comparison of the periods of drying given for Jewit

105

Lake and Southeast Pond in Table IX indicate that

precipitation has a greater influence on the water level

of Southeast Pond than the water level of Jewit Lake.

This is because the sediments underlying Southeast Pond

have a lower hydraulic conductivity than the sediments

underlying Jewit Lake. The modeling results given in

Table IX show that dry conditions within the lakes end

before January. An average of 28 cm (11 in) of

precipitation (Figures 18 and 19) occurs in November and

December, contributing water to the lakes. Following a

period of drying, surface water should be present in the

lakes in November or December of an average precipitation

year.

DISCUSSION OF EXPECTED WETLAND CONDITIONS FOLLOWING MITIGATION

The data given in Appendix 1 show that flooding

through the spillway grating would have occurred in 14 of

16 years between 1973 and 1989. Based on observations of

the filling rates of Jewit Lake in February of 1995, Jewit

Lake levels above 4.2 m (14 ft) are expected to occur in

most years. The results given in Table IX indicate that

surface water will be present in Jewit Lake from late

spring to early fall in most years. Jewit Lake will have

a semipermanently flooded water regime following

mitigation in the 0.34 km2 (72 acres) below 3.8 m (12 ft)

in elevation if surface water is present from late spring

to early fall in most years.

Prior to mitigation, water flow from the Columbia

River into Jewit Lake was uninhibited above the elevation

of the ditch plug (4.3 m, 14 ft). The presence of

Centunculus minimus (Sherry Spencer, personal

communication, 1995) in Southeast Pond indicates that

neither flooding of Southeast Pond or high rates of summer

precipitation have maintained water in Southeast Pond

throughout the growing season in the past. Following

mitigation, flow rates into Jewit Lake are restricted to

flow through the dam. Southeast Pond is less likely to

recieve overland flow from Jewit Lake following mitigation

since a longer period of time is needed to flood Jewit

Lake to a level of 4.7 m (15.4 ft). Therefore Southeast

107

Pond will maintain a seasonally flooded water regime.

Galen and others (1992) predicted that a submergent

plant community would develop in 0.34 km2 (72 acres) of

Jewit Lake and Southeast Pond below an elevation of 3.8 m

(12 ft). Occasional drying of the lakes at the end of the

growing season was expected to affect this plant

community. Annual drying of Southeast Pond will prevent a

submergent plant community from establishing itself in

that area. A submergent plant community could become

established in Jewit Lake as a result of mitigation even

though drying is expected to occur in some years. The

nonpersistent emergent wetland that is currently present

in Jewit Lake should undergo changes in its plant

community as a result of mitigation.

Galen and others (1992) indicate that spikerush,

bulrush, beggars tick, wapato, and cattail will become

dominant plant species between 3.8 and 4.4 (12 and 14.5

ft) in elevation if surface water is present 6-12 months

of the year above 3.8 m (12 ft). The persistent emergent

wetland between elevations of 3.8 and 4.4 m (12 and 14.5

ft) will not meet the requirement of 6-12 months of

inundated conditions in years when flooding through the

spillway gates does not occur. Surface water will be

present 0-3 months of the year when this occurs. When

flooding through the spillway grates does occur, surface

108

water will be present 3 to 12 months of the year depending

on elevation of flooding. The persistent emergent plant

communities are more likely to become established between

3.8 and 4.0 m (12 and 13 ft) in elevation because standing

water will be present for longer periods of time. The

persistent emergent plant communities should not be

successful between 4.1 and 4.4 m (13.5 and 14.5 ft) in

elevation since surface water is not expected to be

present 6-12 months of the year.

Surf ace water cannot be expected to be present for 6

months of the year in areas with elevations between 4.4

and 4.9 m (14.5 and 16 ft). Using the rates of flow

through the dam given in Figure 17, a minimum of 7 days is

required to raise Jewit Lake to 14.5 ft. Surface water

may not reach these levels in years when flooding occurs

through the spillway grating and will not reach these

levels when flooding does not occur through the spillway

grating. The potential for herbaceous hydrophytes to

become established in areas with elevations between 4.4

and 4.9 m (14.5 and 16 ft) is low.

Galen and others (1992) indicate that 0.16 km2 (34

acres) of forested wetland will be converted to persistent

emergent wetland following mitigation. Surface water

inundation 6 to 12 months of the year is expected to

eliminate the present tree community between the

109

elevations of 3.6 to 4.1 m (12 to 13.5 ft) in elevation.

Persistent emergent wetland may not replace the forested

wetland present between 4.1 and 4.4 m (13.5 and 14.5 ft)

as Pacific Willow trees may continue to occupy these

areas. Approximately 0.10 km2 (22 acres) of forested

wetland are located between 4.1 and 4.6 m (14.5 and 16 ft)

and approximately 0.06 km2 (12 acres) of forested wetland

are located between 3.6 and 4.4 m (12 and 14.5 ft). Thus

only 0.06 of the 0.1 km2 (12 of the 34 acres) of forested

wetland are likely to be replaced by persistent emergent

wetland.

RECOMMENDATIONS FOR FUTURE WORK AND IMPROVEMENTS TO THE MITIGATION PLAN

Improvements to the groundwater model presented in

this study could be made if the sedimentology of the

island were better understood. Identification of the

geomorphic features and the lateral extent of these

features will improve the understanding of how the island

developed and how it behaves hydrologically. With this

understanding, a more detailed groundwater model could be

constructed to account for the variablity in conditions.

The node spacing for additional groundwater modeling could

be decreased so that smaller areas of particular interest

could be modeled with more precision. Many of the fluvial

geomorphic features examined in the study area were not

accounted for in this study because they only represented

a small area of an individual node in the groundwater

model.

More numerous water level measurements would allow

determination of hydrologic conditions in areas whose

depositional histories are different. At 3 to 6.1 m (10

to 20 ft) deep monitoring points, it could be determined

how much the water level in the aquifer changes with

fluctuations of the Columbia River. The approximate

relationship of the water table and the level of the

Columbia River could be determined.

A substantial quantity of water leaves Government

Island by evapotranspiration. Improved understanding of

the difference in evapotranspiration rates from wetland

and nonwetland areas would improve the understanding of

the water balance of the study area.

111

The forested wetland occurs in distinctly linear

trends and clusters that do not always follow changes in

elevation. Much can be learned from the vegetation in

this site because of the niche that each plant occupies.

Forested wetands may occur where shallow subsurface

drainage within sediments is higher than the drainage in

the non-forested wetland. Trees in the Government Island

wetland may occur at hydrologic boundaries caused by

changes in sediment composition in the shallow subsurface.

In order to maintain perennial surface water in

Southeast Pond, modifications to the mitigation plan need

to be developed. Southeast Pond could be connected to

Jewit Lake so that Southeast Lake would recieve water at

levels of flooding below the current 15.5 ft barrier.

Pumping of water into Southeast Pond could be effective in

maintaining perennial surface water in Southeast Pond.

Plant communities need to be monitored closely in order to

determine if the desired submerged species become

established in Jewit Lake despite periodic drying.

REFERENCES

Allen, J.E., Burns, M., and Sargent, S.C., 1986, Cataclysyms on the Columbia. Timber Press Publishing Co., Portland, Oregon. 211 p.

Arno, S.F., 1977, Northwest Trees. The Mountaineers, Seattle, Washington. 222 p.

Chow, V.T., 1964, Handbook of Applied Hydrology. McGraw­Hill, San Francisco, California, 1453 p.

Cowardin, L.M., Carter, V., Golet, F.C., and LaRoe, E.T., 1979, Classification of wetlands and deepwater habitats of the United States. U.S. Fish and Wildlife Service publ., 131 p.

Day, P.R., 1965, Particle fractionation and particle size analysis, in Black, C.A. ed., Methods of soil analysis, part 1, Madison, Wisconsin, American Society of Agronomy, Series in Agronomy, Number 9, p. 545-567.

Dunne, T., and Leopold, L., 1978, Water in environmental planning. W.H. Freeman Co., New York, New York. 818 p.

Experimental Laboratory, 1987, Corps of Engineers wetlands delineation manual. Technical Report Y-87-1. U.S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi, 100 p.

Freeze, R.A., and Cherry, J.A., 1979, Groundwater. Prentice Hall Publishing Co., Englewood Cliffs, New Jersey. 604 p.

Galen, C., Fishman, P., and Smith, D., 1992, Habitat evaluation of the Port of Portland PDX SW quadrant wetland fill site and Government Island mitigation site: Submitted to the Port of Portland, Portland, OR. Fishman Environmental Services, Portland, OR. 12 p.

Gates, E.B., 1994, The Holocene sedimentary framework of the Lower Columbia River: Unpublished M.S. Thesis, Portland State University, Portland OR. 210 p.

Hitchcock, C.L., and Cronquist, A., 1973, Flora of the Pacific Northwest. University of Washington Press, Seattle, Washington. 730 p.

113

Leopold, L.B., and Wolman, M.G., 1957, Physiographic and hydraulic studies of rivers; River channel Patterns: Braided, Meandering, and Straight. U.S. Geological Survey Professional Paper 282-B, p. 39-53.

McDonald, M., and Harbaugh, A., 1984, A modular three­dimensional finite-difference ground-water flow model. U.S. Department of Interior publ., Reston, Virginia. 528 p.

Oakley Engineering, 1992, Jewit Lake Hydrology: Submitted to the Port of Portland, Portland, OR. Oakley Engineering, Portland, OR., 89 p.

Parsons, R.B. and Green, G.L. 1982, Geomorphic surfaces and soils in Multnomah County, U.S. Department of Agriculture/Soil Conservation Service publ., 33 p.

SRI, 199la, Assessment of Wetland Mitigation Opportunity for Proposed Wetland Fill Associated with Development of the Southwest Quadrant Site at Portland International Airport: Submitted to the Port of Portland, Portland, Or. SRI, Lake Oswego, OR., 41 p.

SRI, 199lb, Wetland determination and delineation for the Jewit Lake area, Government Island, Portland, OR.: Submitted to the Port of Portland, Portland, OR. SRI, Lake Oswego, OR., 16 p.

Sherwood, C.R., Jay, D.A., Harvey, R.B., Hamilton, P., and Simenstad, C.A., 1990, Historical changes in the Columbia River Estuary: Progress in Oceanography, v. 25, p. 15-79.

Simenstad, C.A., Small, L.F., Mcintire, C.D., Jay, D.A., and Sherwood, C.R., 1990, An introduction to the Columbia River esturary: Brief history, prior studies, and the role of the CREDDP studies: Progress in Oceanography, v. 25, p. 175-210.

Soil Survey Staff, 1983, Soil Survey of Multnomah County, Oregon. U.S. Department of Agriculture, 225 p.

Soil Survey Staff, 1992, Keys to Soil Taxonomy. Pocahontas Press, Blacksburg, Virginia, 531 p.

Telford, W.M., Geldhart, L.P., and Sheriff, R.E., 1990, Applied Geophysics. Cambridge University Press, 770 p.

114

Waitt, R.B. Jr., 1985, Case for periodic jokulhaulps from Pleistocene glacial Lake Missoula: Geological Society of America Bulletin, v. 96, p. 1271-1286.

Appendix 1

Appendix 1 contains hydrographs of the Columbia River

from 1973 to 1989 (from Oakley, 1992). Levels of the

Columbia River were recorded at the U.S. Geological Survey

gauging station in Vancouver, Washington (Figure 2).

River elevations at Vancouver have been adjusted to

approximate the river elevations at Government Island by

adding 0.38 ft/mi to the water level readings.

Jewit Lake Hydrologic Analysis Estimated Lake Levels Based on ·1973 River Data

30- -i--·--.--··--·---·-··· 29 - - - - -·--·-·-----28 - - ----··-·-·-27--- -i-·-··-·-----26 --1-1-1---1-·-··------

25 -----·-·--··--24---- - 1 - 1-·-·----

23. - - - ·---i-·-·--··--------22 ---- ·- -·-·--·--·----

0 21-----·--·-·-··-·-­> (!) 20 --·--i-·-·-·--·-----6 19----· 1---1-1-·-·-·- ----···----·----· ----·-c: 0

~ > QJ [ij

18----·-·-·-·-·-- -·--·· ;!

LEGEND ---- ___ _

(] llivor lovol

() Lnlm Lcvol

ASSUMPTIONS OUTFALL s·1 nucrunE:

Woir Elov - 13.5', NGVD Wolr Length - 2..0' Pipo Diom ..... 15• CMP

I llGI I FLOW INLET Cl 11\flNEL Ovmllow Elcvntlon - M.5 Uolto111 WldU1 - 30' . Slopo - 0.0015 fl/It

SEEP/\Gt/EXCAVATION Ponnanblllty - 10 8 CM/S If Acres Exctwntcd ~ 6 Acrc3 lhlclmocs of Slit Lnyor,

Existing Arens - 4.0' ·1 hld<11oss of Slit Lnyor,

Excnvntcd /\rcD.!t - 1.5'

Dn6 (Jn~ 1 ,1.:! 031061091

0120150180 210~240 270 300 330 360 rom or ronTIAND to oc. Jan. March May July Sept. Nov. JEWITr LAJ<E ttYonotooY

Feb April June Aug. Oct. Dec. By ~aJ<gJy Enolneerrng, Inc. l\pnl, ·1902

1--1 1--1 CJ'\

~ CJ 6 c: 0

~ > QJ

iTI

Jewit Lal<e Hydrologic Analysis Estimated Lake Levels Based on ·197 4 River Data

30 - - - -,-----,-,-. ------. ------ -29--------·-·-----28- -1-- -1--1--1-,----1--------- 1-----1---1---·------·-27 -- ------- -----·------26-·-··-·-·--·----·-·-

-t---1 ·---·---·---·--·-· ----··-----. -----·---·---- ·---·-

l-t---1---1---1---1---·--- ·--- ·----·----·----·---·-

LEGEND ______ _

0 nivor lovol

LI Lnko Level

ASSUMPTIONS ou TTl\LL s 1 nucrunr::

Woir Flov - 13.5', NGVD Wolr Lc11glh - 2.0' Pipo Dinm .... 15• CMP

I llGI I rtow INLET Cl INIMEL Ov!!1 flow Elovollon - M.5 Bottom WldU1 .. 30' Slopo - 0.0015 fl/fl

SEEPAGE/EXCAVATION Pormonblllty - 1 O 8 CM/S . It /\crc!'I Excavnled ~ 6 Acrc!J ll1lcknocs of Siil Lnyor,

Existing /\tens - '1.0' l hlcknots <Jf Siii Lnyor,

Excnvnted Areo!J - 1.5'

90 120 150 180 2-1 O 2'10 270 300 330 360 ronr or- ronn.AND May July Sept. Nov. JEWITT LAJ<E 1tYonoLoaY

April June Aug. Oct. Dec. By ~akoly Englnoo1lng, Inc. /\prrl, 1002

1--' 1--' -...]

Jewil Lake Hydrologic /\pqlysis Estimated Lake Levels Based on 1975 River Data

3([) --·--~-------

29] 1=1=1==r-·---·------ ------------------ ------- ·----- LEGEND----

~~ J=1=1=1=1=1=1== i-:~----i------ i ---·----·-----·-26 -i---I- I----- I -- ---- l-------i---' - ----

25 ----i---l-l--o --

24- - ---- - - - --- I-·--·------·---

23- - --- -----------I --1----1 ---• --•-

22 -- - -- -- - -- -- -------- ,------,--,------l·fn---•-0 21 - - - - -- - -- --- ----- --------- ---- -----~ 2rn -----1------ 1-----1-·--­v v----

6 19---__.__ ___ t - - --- ----- --- -----,----,--,,11 c 10 --~----------- ------ ---- --- ,Ii_\ __ ,_ 0 v----

~ 17------,- - ---- ------ ---- -- ---~ 163--- -- ---- ---

1

1

- -, - ------ ----- ---l---rrr-·-15-- - --i __ ,,, - - -- ------

' l J I 14 - I I - l\b.--r·-1 ''11\trrm 13- - -

12-· 4-··-

11 -i----10 --·-·-

t--t---·---·---·---·---·--- ·----·---·----·---·-

0 nivor Lovol

[J Lulm lcvf!I

ASSUMPTIONS OU IFALL smuc1 unr::

Woir F:lov ... 13.5', NGVD Wnlr Lcnglh - 2-0' Pipo Dirun. - 15" CMP

I llGI I FLOW INLET Cl IAtmEL Ovcrrlow FJovntlon - M.5 · Bollom VVldU1 - 30' Slopo - 0.0015 rt/It

SEEP/\8E/EXCAVATION Ponnonblllly- 10 s CM/S , fl Acres Excnvotcd ... 6 Acre~ ·1 hlclmo&s of Siil Loyer,

Existing Arons - 4.0' -, hld<r1oc~ of Siil Loyor,

Excnvntod Arc03 - t .5'

90 120 150 180 21 O 240 270 300 330 360 ronr or- ronrtAND May - July Sept. Nov. JEWIJT LAJ~E uvonotoov

April June Aug. Oct. Dec. Dy ?nkoly Englnoorlng, In~ Apnl, 1992 f---l

f---l (X)

Jewit Lake Hydrologi9 Analysis Estimated Lake Levels Based on ·t 976 River Data

so -- r--,-------,--,----29 - - - - ----- ----·--28--- -i---l-l-•----

27-----i---i--i--·------

~~~===i==r=i=·-----···----- I - i-·- ·I ·--•-----•-

~~ ~ =--= = = =~1-----=~[=-~1=r=1=L 22 ----------- -- ---1 ----1------1-----1 - • ---·-

0 21 ---------- --,---1-··--1··---1--·--·-0 20 --------- ----;::;--- - - ---- ----- ---· ----. ----6 HJ-----· ---- ------ ----1--1----·---·-

g 18-- --·----i--·----·----

~ ~~:=~-=- .~---~1--=-----1-~----:=--~~ w 15 - ----- ---- -----. ·--·-

14 - -9 1 ~-\tre --- -1-1-r-mrn-nuof;, 13 -- l---------"--"--I I a ~·u~ -- --11111111RnDt'J __ -

12 _ __ _ -V: '"t~1 11101»111'' __ _

14 ------ • -- ---- ---- ---- ---- ---- I

10----------·---·-. 9 -1--1--1--1--1--1--·-·--·---

~ :i=I 1=:=:=:=:=·=:=;=;=;=;~ Dny (Jnn.1 _ O 30 60 90 120 150 180 2·l 0 240 270 300 330 360 to Dec.

31> Jan. March May July Sept. Nov.

Feb April June Aug. Oct. Dec.

LEGEND ·---------

() nivor lovol

I] Lnko Lbvol

ASSUMPTIONS ou1r-ALL smucrunr::

Wolr Elov .. 13.5', NGVD Wolr Lo11ull1 - 2.0' Pipo Dinm ... Hi" CMP

I llGI I rLOW INLET Cl 11\tUIEI Ovctllow Elcvnllon - M.5 Bottom WldU1 ... 30' Slope - 0.0015 ft/II

SEEPN3f'./EXCAVA1ION Pormonblllty - 10 rs CM/S II /\ems Excavntnd " 6 Acr<?s lhlckno&s of Siii Lnyor,

Exlsllng J\Jcns - 4.0' 1 hlcl<11oss or Slit Lnyor.

Excnvat~d Arf!fl!I - 1.5'

ronr or- romLAND JEWIH LAl<E I IYDnoLom By Oakoly Englnoorln(J, Inc. April, ·t 992 I-'

I-'

"°

Jewil Lake Hydrologic Analysis Estimated Lake Levels Based on ·1977 River Data

- . - . - . -·--~ - I --- LEGEND ------·

0 llivor Lovet

I_ I lJ1lm Lcvol

ASSUMPTIONS OUTFALL s1nuc·1 unr::

--- 1· - I r;i-~ --

<9 ?; ~ 0

Woir F:lov - 13.5', NGVD Wolr Length - 2.0' ripo Dicun .... 15• CMP

I llGI I FLOW INLET Cl IANMEL Ovo1flow Elovnllon - "1.5 Uottom WldU1 ... 30' ~ a;

iTI

· - . -· - -· -

Slopo - 0.00 I 5 fl/It

SEEP/\GF./EXCAVATION Ponnonblllty - 10 s CM/S II Acres Excnvntr.d "" 6 /\ere~ l hlckno&s of Siil Lnyot,

F_xlstlng Arens - 4.0' Thlcknot...-> of Siil Lny0r.

Excnvntcd l\ie03 - 1.5'

6 (Jn~1,1 7. 0 30 60 90 120 150 180 210 240 270 300 330 360 POnT or POOnAND ec. Jan. March May July Sept. Nov. JEWIH LAJ<E tlYDnOLOOY

Feb April June Aug. Oct. Dec. By ~;\koly Englnoertng. Inc. /\pnl, 1992 I-'

t-..J 0

Jewit Lake Hydrologic Analysis Estimated Lake Levels Based on ·1970 River Data

30 - ---1-r-·1---T-·------·------29 -- - ---1-- ---1--.---·------28- ---1----1-1---·---·---------

27 - - - - -- - -- -- ----·- ------- ------ ---- -----26 -- - - - - -- --- ------ --- ------- ------- ----- --25 - - - - - ----- ---- ·----- - -- --------- -·------- ------- -24 -~ - - -- - - --· ------- ------- ------- ---- -- -23 - - - - -- - -- ---- ---- ---------- ----· -------- -- --22 - - ------- - --- ------1----1--- ·----·-----·--

~ ~6:-====-==-=~~ -~~=-=·1-=:==:-=:~ 6 19---------- -----i-·--·----·-.g 1 8 - - - -- - --- -- ------ -----·-- -----1--1--·-~·-

~ ~ ~ ~ -= = = ~= =--=- =~~- -~=-= =-=1=:-w 15--

~ ~ ~ _ · "nf_ -~-.. i rn• 'ijm" ~r:~~~ .. ·~urtl, 1Ung~11" ___

1 ____

1_J_:;;;m;11,,11

1 I ton IJI """'I 1 2 - - - - - ~.:.- _lll11111 11- -m,pUIJ! --- IWllJllJI lr1•

11 -. --- -- -- ---- ---- --- --'il:'. ~ 10----------- •2fr\Jl-

~ :J=1=1=1=1=~=~=L-''.='.- 1

:=;=;: Dny (Jnn. 1 _ 0 30 60 90 120 150 180 210 240 270 300 330 360 to Dec.

31> Jan. March May July Sept. Nov.

Feb April June Aug. Oct. Dec.

----- LEGEND _____ _

0 nivor Lovol

[I Luko Lovel

. ASSUMPTIONS ou rrALL s muc·1unr::

Woir Elov - t 3.5', NGVD Wolr Length - 2.0' Pipo Uinm ... 15· CMP

1 llGI I r-LOW INLET CHANNEl Overflow EJcvotlon - M.5 l3otlom WldU1 - 30' Slopo - 0.0015 fl/ft

SEEPAQf'/EXCJ\VAllON Ponnonblllty - 10·8 CM/S fl /\crcg Excovntod r. 6 Acres ·111tcl<nocs of Slit Lnyor,

Exlstlog Arens - 4.0' Thlcknots of Siil Loyor;

Ex:cnvnted Aten~ - 1.5'

ronr or- romLAND JEWlTT LAl<E I IYDnoLom By Oakoly l:nglnoorlng; Inc. /\p1il, 1992

f--l N f--l

Jewit Lake Hydrplogir, Arialysis Estimated Lake Levels Based on ·1979 River Data

30) - - --,-,---,-,--. ,------·· - - . --- - - ·----------29 -- - - - ---- ----213 - - -·--· ----. --- . ---

27 - - --,---,---,--·-· -----26 -- -- -- --------·-----·------25------- --- ----·--- -- ---- --- ·--·--24- -------·- ---- --·--· --- -- -·-

~~-=======-= ====[ I ~~ _ • - · -~ ---~~-= ~~= 1 · ~:~: -< ~ :~ § 18--------- ---- --··-·--·-·--~ 17 - - - -· --- -- --- --- - ---- -- ------1 · -----·-1 ---- •·· ------. -> ~ 16- - - - - - - - -- -------- ----- - ---·----·-w ~~:~~I; Tnllj,llin n~~nno,-~,- --- ------ -- --·-·--·-- ------- ---- ·----- ·----·-

13- -- · -9-~ jX~ 12-1 i 1 OJ J-9 --V-l-1

8

pnf; (J~i~? 63106109101~0 1 ~01~o 2 f'024o 27o 3Qo 3Jo 3fio 0 ec. Jan.. March May July Sept. Nov.

Feb April June Aug. Oct. Dec.

LEGEND ________ _

() rlivorLovol

LJ L111<0 Level

ASSUMPTIONS OUTFALL Sl RUClURr::

Wolr Elov ... 13.5', NGVD Wolr Length - 2-0' Pipo Diurn .... 15• CMP

I llGI I FLOW INLET Cl IANMEI Ovorllow Elovollon - M.5 Bottom WldU1 .. 30' Slopo - 0.00 I 5 fl/fl

SEEPAOt=/EXCAVATION Ponnooblllly - 10 5 CM/S fl Acres E.xcuvnted "6 Acre~ Thlcknoss of Siil Lnyor. ·

Existing Arcos - '1.0' 1 hlcknocs of Slit lt\yor,

Excnvntcd Arcn3 - 1.5'

ronr or ronTLAND JEWnT LAJ<E I IYDrlOLOd't By Oakoly Enol11oorl110. Inc. April, 1002 I-'

t0 t0

Jewit Lake Hydrologic Analysis Estimated Lake Levels Based on ·1 gso River Data

3(1) -,-.-i-··-·---·--·-· 29. -1--1-··--·--·--213 -i-•-•--i ---i--•--27 -- - - - --·-·-----. -·-----26 - - -------1---- ·-----·-·-·-------

25---- - - - ------··

24----------· - ----,----·-,-----,--,--,-23-- -------------------

~ 21-----------'-----· ------ ---- ------·-·--·---22--------- -·--1-1-·--·-··-(!J 20--------------·---·----·-6 H~- ----- --------1----1--1-1-

_g H3-3--·-------------·1-1--·-·----·-ro 17 - --·-----·---·-·----- ·-- --·----i--·->

~ 16- -------·-- -----· ---------·-·---·-· w 15---

14- 11 i- I\ uum11ffinmm1 -01 1 ~~-l?t'-~tt\iq~-1··-----·1·---,-·1·--1-13 - - -- __ III llnu 1!_ ' rri;;:-- -- - ·-:;;ur;m 11 11--· • -' \hlln 111Jn11 r. 1 «") _ I _ _ -- -- __ (IJ\I mm·-- -:mnnOlf --'·- ,_

IC. • Ji\., •111111111 ,,,..

11 ----- • - I

T - _- ' _J- - Yl~~JiA:~---·---·-7-------------, ----1--1-1·------1-1-

~n6 (J~1;- 0 30 60 90 120 ·150 180 210 240 270 300 330 360 0

oc. Jan. March May July Sept. Nov. Feb April June Aug. Oct. Dec.

LEGEND ____ _

0 Jlivor lovol

LJ Lulm Level

/\SSUMPTIONS our FALL SlRUCTUnr::

Wolr Elov -13.5', NGVO Wolr Length - 2.0' Pipo Dinm. - 15• CMP

I llGI I FLOW INLET Cl IAflHEL Overflow Eovotlon - M.G Bottom VVldU1 .. 30' Slopo - 0.00 I 5 fl/rt

SEEPAOf/EXCA V ATION Ponnooblllly - 10·15 CM/S II Acres Excnvntnd " 6 Acr~~ lhlclmoss or Siil Lnyor,

Existing Arens - '1.0' lhlcl<110&s or Slit loyor,

Excnvnted Arne.!I - 1.5'

ronr or ronn.AND JEWIIT LN<E I IYDnOLOOY By Oakoly Englneotlno. Inc. April, 1992

f---l ~ w

Jewit Lake Hydrnlogic Analysis Estimated Lake Levels Based on ·t 981 River Data

3({) ·--- -- --·---·------ ----- -------· ----·--- ---

2B ----·-·-·----···----29 - - ---~--' =i_. ----. -----

~~ ~===r=i=i=i==---1------1----,--,---.---·--25 - --··-·-- ·-----·-- ---- I

24 1-1-·----23~ = = =t= ----- --·---22 ---------· -- -,- ----- ------ ---1--1 ---· --·-

--... I

~ 2i --------- - -- -------- -----------·----·--·-

·----- LEGEND----

0 nivor lovol

(] Lnko Lcvul

ASSUMPTIONS OUTFALL smuc1unE:

Wolr Elov .. 13.5', NGVD Wolr Lcnglh - 2.0'

CJ -- --- -- --- - I llGI I fLOW INLET Cl IAtlNEL 6 ---- -- -- ----- Ovcrllow EJovollon - 1'1.5

Pipe Dirun .... 15• CMP

c --------- ---- ------ ---- Ooltotn Width .. 30' a

~ ____ _____ ____ Sfopo - 0.0015 rl/U >

~ SEEPAGE/EXCAVATION W -- --- --- --- Ponnonblllly .. 1 O 15 CM/S

--- ~lto11

II Acres Excnvo.lcd "' 6 Acrc3 Thlcknoss of Slit Lnyot, .

ExlsUng Arens - '1.0' TI1lcknots of Siii Lnyor,

Excovnted ArcM - 1.5'

7 -1--1--1--1-1--1--1-1-----1--1---1--1-r ~Jn6 (Jn~;>1 - O 30 60 90 120 150 180 2-10 240 270 300 330 360 ronr OF ronTLAND 0

oc. Jan. March May July Sept. Nov. JEWnT LAJ<E 11vonotooY Feb April June Aug. Oct. Dec. By ~akoly Englnoerlno. Inc.

/\pnl, 1002

~ N ~

Jewit Lake Hydrologic Analysis Estimated Lake Levels Based on ·1982 River Data

~~~---==-==-:_-=-~-=-· == ·==r r-- LEGENlJ ____ _

28 - - - - -· --- -- ----- --·-- ----- ---. -

~~:====== = ····~-=·· ~.~~~ ~.:_-:-_ -=~ .:_-=:-1· 25 - - ------ - -- ---- ----· ·-·----. ----- ---- ·----

~i ~ == -= = = = = ~=~ -= -=-= =r - 22---- ----,--,---1----1-1----·-·-o 21------------~1------1·--1--1-·-> CJ 20--- 1

~ 1 ~ - - _J_li'--1--'X_,---t----.lt 0 1 :8 - - _! _ _\ft\, __ ll __

"+:' ro 17--~ 16- - -J-1~1-1-J!' l;~J-l\-/.-l-

1

-r·--1-----1-----1--1 --l-OY••-

15 - - --14 b

U ~J I /f 'lllJ 't~ - ft r - -. -- - _a:__ - \~\ ---i-±_ij_

13 - - - - ---- - -!lln11ou- - -- ·r.nn•IP11~'·-11 'no uun 111 · 12- 7 - ----- ----~ on_, ~-

1·1 -. --- ---- ---- ---- ---- ---- ---- M -.I:'Tr. i-~ f1.l .... -1 o -- - - - :J

9--------- --'tt~\~··-8- ---------l~-\-1---1-·-7------·--1-1---1-1--1-1-

Dny (Jnn. 1 _ 0 30 60 90 120 150 180 210 240 270 300 330 360 to Dec.

31) Jan. March May July Sept. Nov.

Feb April June Aug. Oct. Dec.

0 flivor Lovol

LJ Lnlm Level

/\SSUMPTIOMS OUlF/\LL S1RUG1UJ1E:

Wolr Elov ... 13.5', NGVD Weir Length - 2.0' P,ipo Dinm. - 15· CMP

I llGI I rLOW INLET Cl \At 11 IEI Ovmllow Elcvntlon - 14.5 Bottom WldU1 - 30' Slopo - 0.0015 ft/ll

SEEP/\Gl?/EXC/\ VAllON Pormonblllly- 10 8 CM/S fl /\CJes Excnvnlcd ~ 61\crcs Thlckt1o&s of Sill Lnyor,

E:xlsUng Arens - 4.0' lhlcktmts of Slit lnyor.

ExC'..nvntcd /\roM - 1.5'

ronr or rom LAND JC:WllT LAJ<E I IYDnotom By Oakoly Englnoorlng, Inc. April, 1992

1-1 t>-J Ul

~ <9 z -c:: 0

~ > ID ill

Jewit Lake Hydrologic Analysis Estimated Lake Levels Based on ·1983 River Data

LEGEMD -----~~ :==== .. .. -~. ••·~····· -~~- -- :=1--~r ·--LI nivor Lovol

0 lnlm Lovol 21 --- - -- - --- --·-- ------ ------- -------· 26 --------- -----, -··---,------·- I --------·r------• -·---

25 - - - - ·- - -- ---·· -----···-·------- ·--·--------· ----24 ---- ·-- -- - --, ------, -----1-~--,-----,--1-23-----------· ----- ---22-----------1--1----1--1----r---·---·-

---··----·-----·--·----· ----·-··----···----· ·~----·----·-

ASSUMPTIONS OUTFALL m nucrunr::

Wolr Elov ... 13.5', NGVO Weir umglh - 2.0' ripo Dinm. - 15• CMP

I llGI I FLOW INLE f Cl lAHUEI Ovmrtow Elovollon - M.5 l3onom WldU1 - 30' Slopo - 0.0015 fl/rt

SEEPAGl:fEXCl\Vl\TlON Ponnonblllly .. 10-s CM/S II Acee~ Excavated "6 Acre~ Thlcknm:s of Slit Lnyor.

Existing Arens - '1.0' lhlcknots of Siil Lnyor,

&.cnvnlcd AteC\3 - t .5'

Day (J~l}1? 0306'09'0120 150180 2fo 240 27o 3Qo 330 360 rom OF POnTlAND to Dec. Jan. March May July Sept. Nov. JEWHT LAJ<E ttYDnoLom

Feb April June Aug. Oct. Dec. By ~<\koly Enolnoorlng. Inc. Apnl, 1992 f--1

~

01

~ <9 z ...._ c: 0

~ > (1)

w

. Jewit Lake Hydrologic Analysis Estimated Lake Levels Based on 1984 River Data

---------- U:GEND - ____ _

lJ nivor Lovol

0 Uil<o Level

ASSUM Pl IONS ou-, FALL s 1 nuc1 unr::

Wolr Elov - 13.5', NGVD Wolr limglh -2.0' · Pipo IJin.m. - 15" CMP

I llGI I n.ow INLET Cl INlf lEI Ovmflow Elcvnllon - "1.5 Bollom WldU1 - 30' Slopo - 0.0015 fVH

SEEP /\GEJEXCAV Al ION Pormoo.blllty - 10-g CM/S II Acre~ Exctwflh!d ~ 6 Ac1c~ Thlcknocs of Sill Lnyor,

Existing /\Jens - '1.0' lhlckno&s of Siil Loyor,

r=xcnvntcd ArcO!J - 1.5'

Ponr or POnTLAND JEWllT LAJ<E llYDnOLOGl By Of\koly Engh1og1fno. Inc. April, ·1092

f-l t0 -...)

~ (!J . z ...._ c: 0

~ 5'; w

Jewi1 Lake Hydrologic Analysis Estimated Lake Levels Based on ·1985 River Data

~---...---·---· -~-- ··---·----- ... -----

1--1---·----·---·---·----·---··• ---- ·----·----·---·---·-

LEGENO ---------

LI nivor Lovol

0 u1ko Lcvol

ASSUMPTIONS our FALL smuc-runr::

Wolr Elov .. 13.5', NGVD Weir Length - 2.0' f'ipo Dinm. - 15" CMI'

I llGI I FLOW INLET Cl lAMNEI Ovcsrlow Elovollon - M.5 Oottom WldUl - 30' Slopo - 0.0015 fl/It

SEEPAGE/EXCAVAllON rermanblllty- 10 11 CM/S II Acres Excnvo.led r. 6 Acres lhlcknoss of Siil Lnyor,

Existing Areas - 4.0' lhlcl<no&s of Siil U\yor.

Excnvntcd Atc03 - 1.5'

ronr or romtAND JEWIH LAl<E 1-IYDnOLOQ' By Oakofy Englnoorlng, Inc. April, ·t 092

f-1 N 00

0 > <!J z ....._,. c:: 0

"+:J ro > Cl> ill

Jewil Lake Hydrologic Analysis Estimated Lake Levels Based on 1986 River Data

30~,~---- ··--------- ---·----·--29 - - - ·- -- - - ----- -·-··- ------ -- - -- -26- - - -- - - -- ---- ----- --·--- ·--- --. ---- ·-

~~ ~ . ======--------~~~----= =~=--

---·---·---·---· ---- ·---- ·----·----·----·---·-90 120 150 180 210 240 270 300 330 360

May July Sept. Nov. April June Aug. Oct. Dec.

LEGEND --

0 nivor Lovol

0 IJtlm Lovol

ASSUMPTIONS OUTFALL SlAUClURE:

Wolr Elov - 13.5', NGVD Weir Length - 2.0' Pipo Dirun. - 15• CMP

I llGI I FLOW INLET Cl IANfm Overllow Elovollon - 14.5 · Bottom WldU1 - 30' Slopo - 0.0015 fl/It -

SEEPA<3 E/EXCAVATION Ponnonblllly .. 10-3 CM/S fl Acres Excavated ~ 6 Acre~ Thlcf~no&s of SIU Lnyor.

ExlsUng Arens - '1.0' Thlcknocs of Slit Ll\yer,

Excnvatcd Are113 - 1.5'

PORT OF PORTI.AND JEWITT LAJ<E f IYDnOLOGY By Oakaly Englnaorlng, Inc. April, 1902

1--l N \.D

Jewit Lake Hydrologir. Analysis Estimated Lake Levels Based on 1987 River Data

~~ _-- - -- -·-·- ------i·--· ·-28 ------·-27~-----------·- -·-==~ 2~ ---------·-25~---- ------ ------ ·----·-----. -24-====----- --- ---·-----=·~ 23 - - -- ---· -----2:2~-------·--· ---·-==1~

0 . -------·-----> 21------- ------~ 20- --~--- --=--=-1

-·--·--·-

...._ 19---~ -·-·-·--c ----0 18 - ------ --·--··---··---·-+:J ----~ 17--------- -- -- ------1--1·--·-·-

<1> 16 ---- --- ---- --w ___ )________ ------·-·--·-15 --- r- --- -- - ----- -- - --- -- --·-

14 ~ --------

-___ ·~---r&l--·- -- --------ljl-·-

13 - -·tt1J '-1\\ti... n. -- --------·--(

LEGEND-~

0 River Levol

0 Lnke Level

ASSUMPTIONS OUTFALL STRUCTURE: Woir Elov .. 13.5', NGVD Weir Length - 2.0' Pipe Diam. - 15• CMP

lflGlf FLOW INLET CHANNEL Overflow EJcvallon - 14.5 Bottom Width .. 30' Slope - 0.0015 ft/rt

SEEPAGE/EXCAVATION Ponnoablllty - 10·5 CM/S fl Acres Excavated ~ 6 Acres Thickness of Slit Layer,

Existing Areas - 4.0' - · lltlcknoss of Slit Layer,

Excnvatcd Are83 - 1.5'

PORT OF POnllAND JEWITT LAJ<E HYDROLOG) By Oakely Enolnoarlng, Inc. April, 1992

1-1 w 0

Jewit Lake Hydrplogic Analysis Estimated Lake Levels Based on ·t 988 River Data

LEGEND----~~:== -_ -~~:: -- ::::=---~-1=]~~-!~~T·------() fllvor 1.ovol

[] Luko Lovcl 21 -- -- - --- -- ---- --- ---- ---- ----- -----· ----·--26 -- - --- ___ : --- ----- -------- ---- -- ------·-·-25 - - --- - -- --- ----- --- --- -------- -- ----- ----· ~-·--

~~ · == = =~=·=~ -- -= ·=-= =1=: 22 --- -- - -- --- ---- --------- ------ ---- ----- ------·--·--

~ ~i. =-= = = = .~_.:. .:..= _::::.:.1=::::::.=~=:.:..-=.: 6 i g --- - -- -- --- ------ ------ ----- ---- ·----g H3----------

~ 17------·--1-1-·--> Q1 16- ------- ---·--[[j -15-=1------1-1-----1---·--·---·-·--·--

ASSUMPTIONS OU ITALL s I nuc rurn::

Wolr Elov ... 13,f,', NGVIJ Wel1 Lcnglh - 2.0' Pipo Dinm. - 15· CM!'

I llGI I FLOW IMLE r Cf 11\I IMEI Ove1llow ~lovntJon - "1.!i Bottom WldU1 - 30' Slopo - 0.0015 It/fl

SEEPAGE/EXCAVAI ION Ponnooblllty - 10 8 CM/S II Act cs Excnvntcd ,., 6 Ac1 C-' lhlcknocs of Siil Ll\yot,

Existing Arons - '1.0' Thlck11ocs of Siil Ll\yor,

ExcovntccJ Arcn' - 1.5'

nab (Jn~1J1? Q-3'Q6'Q9'012o 15~100 210240 2f 0 300 3SO 3BO Pom or romtAND 10 oc. Jan. March May July Sept. Nov. JEwrrr LAJ<E 11vnno1_om

Feb April June Aug. Oct. Dec. ~~1~af~~ Enolnoerlnn. Inc. ~ w ~

Jewit Lake Hydrologic /\nalysis Estimated Lake Levels Based 011 ·1989 Fliver Data

30 . -- ---1·-------i----·1·---·-----2'9- - -- - ----- -- ---·-------28. ---·--·--·--·----27-- -- --·------·-·~--26 --1-1---·--·-·--·----

25 -- -- -,--·--·-·------24. - - -- --·----·--·------23 --- - -·--·--·-·----22------,--,-·--·--~ 21 ------ --·-·----·--------

<.? 20----·--·--·---·--6 19 -- -1--1-1-1--··--·------e 0

~ > <lJ ill

HJ--- - --- -·-·-·-------

17 -- - - - -1-1-··------1 G - - - -- - -- --- ----· ______ _ 15 ---~----- --- 'l-- --- - . ------

---- LEGEND ________ _

0 nivor Lovol

LI IJ1!<0 Lovol

/\SSUMrTIONS OU ITf\ll Sl 11\IC1 unr::

Wolr f:lov - 13.5', NGVU Weir Lcnglh - 2.0' Pipe Dinm. - 15" CMP

I llGI I n.ow INlET Cl IANNEI Ovc11low Elc,votlon - M.5 Uoltotn VVldU1 - 30' Slopo - 0.0015 fl/It

SEEPAQE/8<CAVA1 ION Pormooblllty - 10-5 CMIS ff Acre~ Exccwo.tmJ <! O Aet c!t ·1 hlclmocs of Siil Lnyor, ·

Existing Arens - '1.0' ·1 hlck11ocs of Siil loyot,

Excnvnt~d AtctUJ - I .5'

Ony (Jon. 17_ o--3'Q6'09'01-2o 150100 2 I 0240270 30o-33o 3GO ronr or POntlAND 10 Voe.

31) Jan. March May July Sept. Nov. JEw1n LAl<E tlYDnoLom

Feb April June Aug. Oct. Dec. By ?<'kely Englnoorlng, hfc_ Apnl, -1092

1---' w N

Appendix 2

Plots of the grain size distribution were made based

on hydrometer readings taken at predetermined time

intervals. The hydrometer method of Day (1965) assumes

that a particle will fall to the bottom of a water column

in a time that is determined solely by its grain size.

The percentages of each size fraction are determined by

subtracting the mass of sediment present in the water

column at each reading from 100 percent of the total mass

of the sample. Each reading is shown with an asterisk in

the graphs of particle size distribution.

In the particle size distribution graphs, sand has

grain sizes larger than 0.0625 mm. Silts have grain sizes

between 0.004 mm and 0.0625 mm. Clay is represented by

the particles finer than 0.004 mm that fell out of the

water column. The remaining particles in the water column

are colloidal and organic material.

One hour is required for silt to begin settling out

of a water column. Twenty four hours are required for

clay to begin settling out of a water column (Day, 1965).

Using the United Soil Classification System (Soil

Survey Staff, 1992), samples 1 through 14 are silt loams.

Sample 15 is a loam.

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Appendix 3

Appendix 3 contains the seismic refraction receiver

time data at stations G-1, G-5, G-9, G-13, and G-14. A

change in slope in the reciever distance versus receiver

time graphs indicates that a change in seismic wave

velocity has occurred. The change in slope in the graph

likely differentiates saturated strata from unsaturated

strata. Depths to the water table are given in Table 6.

The depth at which the seismic wave velocity contrast

occurs was determined by the formula

z = x' /2 * [ (V2 -V1 ) I (V2 +V1 ) J 112

where z is the depth to the seismic wave velocity

contrast, x' is the crossover distance, V1 is the seismic

wave velocity in the unsaturated sediment, and V2 is the

seismic wave velocity in the saturated sediment. The

crossover distance value is taken from the time versus

reciever distance plots. The crossover distance is

extrapolated to the x-axis (receiver distance) from the

position on the graph where the best fit lines for V1 and

V2 intersect.

150

STATION RECIEVER SPACING {M} NORMAL{SEC} REVERSE{SEC} G-1 EAST 1 0.000 0.045

0.007 0.044 0.011 0.043 0.016 0.042 0.020 0.041 0.022 0.038 0.025 0.036 0.029 0.032 0.030 0.027 0.031 0.018 0.032 0.012 0.033 0.000

G-1 EAST 2 0.000 0.040 0.012 0.039 0.022 0.037 0.026 0.036 0.031 0.034 0.032 0.031 0.034 0.029 0.035 0.027 0.036 0.023 0.037 0.020 0.039 0.010 0.040 0.000

G-1 EAST 5 0.000 0.035 0.056 0.044 0.054 0.048 0.051 0.051 0.049 0.054 0.047 0.056 0.044 0.059 0.040 0.063 0.036

0.033 0.024 0.000

G-1 WEST 1 0.000 0.039 0.005 0.038 0.010 0.033 0.018 0.033 0.020 0.030 0.024 0.029 0.027 0.025 0.026 0.027 0.031 0.021 0.032 0.015

151

STATION RECIEVER SPACING {Ml NORMAL(SEC) REVERSE{SEC) 0.032 0.006 0.033 0.000

G-1 WEST 2 0.000 0.051 0.015 0.023 0.048 0.033 0.047 0.042 0.044 0.044 0.043 0.049 0.040 0.050 0.036 0.048 0.031 0.045 0.056 0.009

0.000

G-1 WEST 5 0.000 0.029 0.046 0.048 0.060 0.051 0.056

0.053 0.057 0.052 0.058 0.045 0.061 0.043 0.063 0.035 0.067 0.028

0.000

G-5 WEST 2 0.000 0.051 0.015 0.023 0.048 0.033 0.047 0.042 0.044 0.044 0.043 0.049 0.040 0.050 0.036 0.048 0.031 0.055 0.056 0.009

0.000

G-5 WEST 5 0.000 0.029 0.046 0.048 0.060 0.051 0.056 0.053 0.053 0.057 0.052

152

STATION RECIEVER SPACING {Ml_ NORMAL(SEC) REVERSE(SEC) 0.058 0.045 0.061 0.043 0.063 0.035 0.067 0.028

0.000

G-9 1 0.000 0.023 0.007 0.023 0.010 0.021 0.017 0.020 0.017 0.020 0.018 0.019 0.018 0.018 0.021 0.017 0.021 0.014 0.021 0.010 0.022 0.002 0.023 0.000

G-9 2 0.000 0.030 0.011 0.028 0.016 0.027 0.020 0.028 0.022 0.027 0.023 0.026 0.023 0.024 0.025 0.022 0.025 0.020 0.025 0.017 0.025 0.008 0.026 0.000

G-9 5 0.000 0.020 0.042 0.021 0.025 0.041 0.027 0.036 0.031 0.031 0.034 0.029 0.036 0.027 0.039 0.021 0.043 0.019 0.044 0.015 0.050 0.000

G-13 1 0.000 0.047 0.008 0.043

0.041 0.020 0.037

153

STATION RECIEVER SPACING {Ml NORMAL(SEC) REVERSE(SEC} 0.024 0.027 0.035 0.031 0.029 0.036 0.025 0.040 0.021 0.044 0.011 0.046 0.009 0.048 0.000

G-13 2 0.000 0.052 0.018 0.051 0.023 0.046

0.038 0.046 0.045 0.045 0.046 0.044 0.046 0.035 0.047 0.029 0.051 0.021 0.051 0.012 0.053 0.000

G-13 4 0.000 0.071 0.025 0.060 0.039 0.065 0.049 0.060 0.051 0.061 0.054 0.058 0.057 0.054 0.060 0.050 0.061 0.047 0.062 0.042 0.065 0.023 0.068 0.000

G-14 1 0.000 0.021 0.002 0.022 0.004 0.021 0.006 0.020 0.009 0.020 0.012 0.017 0.015 0.015 0.018 0.010 0.018 0.008 0.018 0.008 0.019 0.001 0.019 0.000

154

STATION RECIEVER SPACING (M} NORMAL(SEC} REVERSE(SEC} G-14 2 0.000 0.027

0.001 0.027 0.010 0.026 0.015 0.024 0.019 0.022 0.019 0.019 0.020 0.019 0.021 0.018 0.021 0.016 0.022 0.013 0.023 0.002 0.023 0.000

G-14 4 0.000 0.058 0.020 0.059 0.052 0.054 0.037 0.049 0.041 0.052 0.043 0.050 0.047 0.049 0.048 0.048 0.052 0.038 0.054 0.035 0.058 0.020 0.060 0.000

u Q) Ul ~

Q)

s ·~ E-i

G-1 East (5 m spacing)

0.07 .--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-

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0.03

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I II 0.01

0 ..-~~~~,.__~~~---1o~~~~---1-~~~~---1-~~~~--+-~----------.

0 10 20 30 40 50 60

Receiver spacing (m) f-1 lJ1 lJ1

u CD Cl) ~

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G-5 West (5 m spacing)

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0.03

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---reverse I II

0.01

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0 10 20 30 40 50 60

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0.05

0.045

I • 0.04

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e ·r-1 0.02 E-t

0.015

0.01

0.005

0

0

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-+-normal

---reverse

10 20 30 40

Receiver distance (m)

50 60

f-l lJl -.....]

-u CV Ul

CV s

·r-i E-t

G-13 (2 m spacing)

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0.05

0.04

0.03

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-+-normal

---reverse I I I

0.01

0 I

0 5 10 15 20 25

Receiver distance (m) I---' Ul OJ

-u Q) Ul

Q)

E ·r-1 8

G-14 (2 m spacing)

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0.025

0.02

0.015

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-+-normal

--m- reverse I II

0.005

0 ~~~~~~t--~~~~--+~~~~~-+~~~~~-+-~~---~~~

0 5 10 15 20 25

Receiver distance (m) 1--1 Vl

'°

Appendix 4

Appendix 4 gives the stratigraphic columns for 25

sites located within the study area. Sites 1 through 9

were used for cross section construction (Figures 29 and

30) . The locations of sites 1 through 9 are given in

Figure 31. Sites 10 through 25 were not used in the cross

sections of the study area. The locations of sites 10

through 25 are given in Appendix 4.

Elevations of the ground surface are given with the

stratigraphic columns. Some sites have been surveyed and

have established elevations. The elevations of the sites

that have not been surveyed are approximated. The

position in the stratigraphic columns where samples were

taken for particle size analysis are shown adjacent to the

stratigraphic columns.

* 22

* 17

Jewit Lake

300 m Scale:

Columbia River

Columbia River

*21

* 18

* 19

* 20

* 13 *

* 24

~

Southeast Po

Figure 46. Locations of stratigraphic columns that were not used for cross section construction.

North

/

f-l CJ\ f-l

ill 9·9

~91

3.6 m

4.0 m

~

163

Stratigraphic Column # 3

0-205 cm: muddy, organic rich, mottled silt

collected hydrometer sample # 12

205- cm.: medium sand, highly gleyed

Stratigraphic Column # 4

0-140 cm: dark, organic rich, mottled silt

141-170 cm: gray silt, highly gleyed

collected hydrometer sample 11

170-195 cm: tan silt/clay

3.8 rn

7.4 m

Stratigraphic Column # 5

0-140 cm: dark, organic rich silt/clay collected hydrometer sample 2

140 cm-: medium sand

Stratigraphic Column # 6

0-36 cm: organic rich silt

37-52 cm: tan, mottled silt and fine sand

53-90 cm: organic rich silt, highly mottled 75-90 cm.

90-115 cm: fine sand and silt

115 cm-: organic rich silt

164

4.0 m

4.8 m

Stratigraphic Column # 7

0-110 cm: dark, organic rich silt

111-116 cm: fine-medium sand

117- : organic rich silt

Stratigraphic Column # 8

0-170 cm: organic rich silt

171-250 cm: fine sand and silt, highly gleyed

165

6.1 m

Stratigraphic Column # 9

0-120 cm: dark, organic rich silt

121-145 cm: fine sand and silt

146-180 cm: mottled silt, gleyed 170-180 cm

166

4.1 m

4.0 m

5.8 m

167

Stratigraphic Column # 10

0-54 cm: dark, organic rich silt

54-66 cm: mottled fine sand 66-83 cm: mottled, organic rich silt 83-88 cm: mottled fine sand

88-108 cm: mottled, organic rich silt

Stratigraphic Column # 11

0-33 cm: organic rich silt

33-42 cm: mottled fine sand

42-?: mottled, organic rich silt

collected hydrometer sample # 5

Stratigraphic Column # 12

0-62 cm: unmottled silt

62-77 cm: fine sand

77-101 cm: slightly mottled silt

7.6 m

4.4 m

4.1 m

Stratigraphic Column # 13

0-56 cm: unmottled silt

56-65 cm: fine sand and silt 65-77cm: unmottled silt 77-85 cm: fine sand and silt 85-94 cm: unmottled silt

168

94-104 cm: slightly mottled fine sand

104-? cm: slightly mottled silt collected hydrometer sample # 6

Stratigraphic Column # 14

0-70 cm: dark, organic rich silt

collected hydrometer sample # 7

Stratigraphic Column # 15

0-125 cm: silt

125-270 cm: poorly sorted coarse sand

and gravel

4.2 m

3.5 m

169

Stratigraphic Column # 16

0-260 cm: organic rich silt with fine

sand lenses

260-270 cm: fine, medium, and coarse sand

Stratigraphic Column # 17

0-30 cm: mottled organic rich silt

30-33 cm: fine sand

33-70 cm: mottled organic rich silt

70-77 cm: fine sand

77-118 cm: mottled organic rich silt with

gleying increasing with depth

118-130 cm: medium sand

3.5 m

3.6 m

4. 6 m

Stratigraphic Column # 18

0-205 cm: organic rich silt, highly gleyed at 180 cm depth. Collected hydrometer sample 14

205-210 cm: well sorted medium sand

Stratigraphic Column # 19

0-180 cm: organic rich silt

Stratigraphic Column # 20

0-60 cm: slightly mottled organic rich silt

61-76 cm: slightly mottled fine and medium sand

76-103 cm: mottled organic rich silt collected hydrometer sample # 3

170

3.7 m

4.0 m

7 .3 m

3.4 m

171

Stratigraphic Column # 21

0-120 cm: organic rich silt

120-? cm: slightly gleyed fine sand

?-320 cm: mottled, organic rich silt below 240 cm, strong gleying is present

320-325 cm: sand

Stratigraphic Column # 22

0 to 90-110 cm: mottled, organic rich silt

90-110 cm to ?: gleyed, organic rich silt and clay

_ Stratigraphic Column # 23

dark, organic rich silt. Mottling increases with depth

ground surface in the spillway channel

25-73 cm: gleyed, organic rich silt and clay

73-85 cm: tan silt and clay

8.7 m

5.2 m

Stratigraphic Column # 24

0-280 cm: organic rich silt with fine sand

Stratigraphic Column # 25

0-280 cm: organic rich silt and fine sand. Strong gleying below 162 cm depth.

172