usgs - hydrogeologic framework and …wa.water.usgs.gov › projects › chehalis ›...
TRANSCRIPT
U.S. Department of the InteriorU.S. Geological Survey
Hydrogeologic Framework and Groundwater/Surface-Water Interactions of the Chehalis River Basin, Washington Andrew S. Gendaszek, U.S. Geological Survey, Washington Water Science Center, Tacoma, Washington
IntroductionThe Chehalis River has the largest drainage basin (fig. 1) of any river entirely contained within the state of Washington with a watershed of about 2,700 mi2 and has diverse geology, land uses, and demands for water resources. Local citizens and governments of the Chehalis River basin have coordinated with Federal, state and tribal agencies through the Chehalis Basin Partnership to develop a long-term watershed management plan. The recognition of the interdependence of groundwater and surface-water resources of the Chehalis River basin and their complex interaction became the impetus for this study, the purpose of which is to describe the hydrogeologic framework and groundwater-surface water interactions of the basin. The basin-wide hydrogeologic framework was generalized by combining surficial geologic maps with more than 372 drillers’ lithostratigraphic logs. The framework consists of five hydrogeologic units that include aquifers within unconsolidated glacial
and alluvial sediments separated by discontinuous confining units. These five units are bounded by a basal confining unit comprised of Tertiary bedrock. Generalized groundwater flow directions in the surficial aquifers were delineated from water-levels measured in wells between August and September 2009. Synoptic streamflows during August 2010 and water levels in wells during the 2010 water year were measured to characterize groundwater-surface water interactions in the Chehalis River basin. The streamflow mesurements revealed alternating gains and losses of streamflow, which became more pronounced on the Chehalis River downstream of its confluence with the Black River. Groundwater levels measured in wells fluctuated with changes in streamflow. These fluctuations were influenced by precipitation events in the upper Chehalis River basin and tidal effects from of the Pacific Ocean in the lower Chehalis River basin.
GRAYS HARBOR
GRAYS HARBOR
PACIFIC
KITSAP
JEFFERSON
MASON
PIERCE
THURSTON
WAHKIAKUM
LEWIS
COWLITZ
Cowlitz River Basin
Deschutes River Basin
KING
Montesano
Pe Ell
Doty
Hoquiam
Aberdeen
Chehalis
Porter
Centralia
Grand
Rochester
MoundBucoda
Tenino
Wyn
ooch
ee
R i
ver
Sats
op
Riv
er
M
iddl
e F
ork
Wes
t
Fo
rk
E ast
Fork
Wis
hk
ah
Riv
er
Hum
ptuli
ps
Riv
er
Wes
t
Fork
East
For
k
BigCr
Hoq
uiam R
iver
, East
For
k
Wes
t F
ork
Sk
ooku
mchuck River
Newaukum Riv
er,
North Fork
Newaukum R
iver,
South Fork
Cloq
uallu
m C
r
Chehalis River
South
For
k C
heha
lis
R i
ver
Che
halis
Riv
er
PAC
IFIC
OC
EAN
GraysHarbor
WillapaBay
47° 30'
47°
46° 30'
123°30' 124° 122°30' 123°
0 20 MILES 5 10 15
0 10 20 KILOMETERS 5 15
Scatter Creek
Bla
ck
Rive
r
Chehalis River
Base from U.S. Geological Survey Digital Data, 1:100,000, 1985Universal Transverse Mercator projection, Zone 10North American Datum of 1983
ConfederatedTribes of theChehalisReservation
Olympic Mountains
WASHINGTON
Location of �gure 4.
Location of �gure 5.
Figure 1. Location of the Chehalis River basin, Washington.
Groundwater/Surface-Water Interactions Surface-water bodies such as rivers and lakes can readily interact with groundwater and exchange appreciable quantities of water and solutes. This exchange, or seepage, provides both recharge of aquifers and maintenance of streamflows and has the potential to affect water quality of groundwater and surface water bodies. When the groundwater level in the underlying aquifer is higher
than the river stage, an upward hydraulic gradient drives the movement of water from the groundwater to the river resulting in a gaining river. Conversely, a downward hydraulic gradient exists when the river elevation is higher than the groundwater level causing the river to lose water to the underlying aquifer.
Well MonitoringWater levels in wells completed in the aquifers within several kilometers of the Chehalis River (fig. 2) fluctuated with the changes in river stage that were driven by precipitation events in the upper Chehalis River and tides within the lower Chehalis River. Wells completed in close proximity to the Chehalis River and its tributaries, notably well 14N/02W-07B02 (fig. 2A), fluctuated directly with river stage as measured at streamflow-gaging stations. The minimal delay in the peak of the well 14N/02W-07B02 hydrograph from the streamflow-gaging station in response to precipitation events was caused largely by the high hydrologic conductivities of the overlying sediments and lack of confining
layers. The well 15N/04W-03R02 (fig. 2B) fluctuated with the streamflow hydrograph, but the amplitude of the fluctuations is lower because it is farther away from the Chehalis River and other streams. The stage of the Chehalis River is influenced by ocean tides downstream of the confluence of the Chehalis River with the Satsop River. Water levels of well 17N/07W-08K02 (fig. 3) which is completed in the unit A (fig. 4) fluctuate closely with the stage measured at a nearby USGS streamflow-gaging station (12035100). These well hydrograph fluctuations are attenuated approximately 75 percent from stream hydrograph fluctuations.
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
149.0
151.0
153.0
155.0
157.0
159.0
161.0
163.0
PREC
IPIT
ATIO
N, I
N IN
CHES
STRE
AM S
TAGE
, IN
FEE
T
GRO
UN
DWAT
ER E
LEVA
TIO
N,
IN F
EET
ABO
VE N
AVD8
8
A
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
80.0
83.0
86.0
89.0
92.0
95.0
98.0
101.0
PREC
IPIT
ATIO
N, I
N IN
CHES
STRE
AM S
TAGE
, IN
FEE
T
GRO
UN
DWAT
ER E
LEVA
TIO
N,
IN F
EET
ABO
VE N
AVD8
8
BWell Stage
Stream Stage
Monthly Precipitation
Well Stage
Stream Stage
Monthly Precipitation
precipitation at Centralia, September 2009 – September 2010 for wells 14N/02W-07B02 (A) and 15N/04W-03R02 (B).Figure 2. Continuous water levels in wells, stream stage at U.S. Geological Survey streamflow gaging station 120227500, Chehalis River at Grand Mound, and total monthly
0
2
4
6
8
10
12
2 4 6 8 10
GRO
UN
DWAT
ER E
LEVA
TIO
N A
ND
STRE
AMST
AGE,
IN F
EET
ABO
VE N
AVD8
8 Well Stage
Stream Stage
APRIL 2010
Figure 3. Water levels in well 17N/07W-08K02 and stream stage at U.S. Geological Survey streamflow-gaging station 12035100, Chehalis River at Montesano, April 1 – April 11, 2010.
Base from U.S. Geological Survey digital data, 1:100,000Universal Transverse Mercator ProjectionGeology compiled from Washington Division of Geology and Earth Resources (2005).
17N/07W-08K02
15N/04W-03R02
14N/02W-07B02
123°0'W123°30'W
47°0'N
SCALE 1:250,0000 2 4 6 8 101 MILES
0 2 4 6 8 101 KILOMETERS
A
A’
B’
B
12035100
12027500
25
50
125
100
175
150
75
225
300 52527
520
0
250
500
325
425400
375
350
25
275
125
50
150
325
50
25017
5
50200
7522520
0
175
100
150
15050
200
100 300
125
NAVD88
200
400
600
NAVD88
200
400
600
15N
/03W
-07J
01
15N
/03W
-10D
02P1
CHEH
ALI
S RI
VER
15N
/03W
-03A
2P1
16N
/03W
-36J
01
16N
/02W
-29L
02P1
16N
/02W
-29G
04
16N
/02W
-09N
01
16N
/02W
-09F
01
17N
/02W
-33K
02
17N
/02W
-28J
06
17N
/02W
-22F
03
SEC
TIO
NB-
B’
SEC
TIO
NBE
ND
IN
SCALE 1: 62,500 VERTICAL EXAGGERATION x20
A A’
??
?
500
!
!
!
!!
Explanation
A
B
C
D
E
BEDROCK!
BOUNDARY OF CHEHALIS RIVER BASIN
TRACE OF HYDROGEOLOGIC SECTION
INVENTORIED WELL AND NO.
UNIT
AUG-SEPT 2009 WATER TABLE, IN FEET ABOVE NAVD88USGS STREAMFLOW GAGING STATION
Figure 4. Map and cross sections showing hydrogeologic units within Chehalis River basin, Washington.
1.6
6.54 5.4
0.6
0
-6.5
3.2
-2
6.9
74.7
-3.8
-0.6
13.1
9.6
17.8
6.7
1.51.8
-1.2-41.9
-11.
3
-4.6
0
13.1
123°0'123°15'
46°45"
ExplanationSeepage measurement
Seepage reachesGain/loss (ft3/s/mi)
Loss: -41.9 - 0
0
Gain: 0 - 34.9
Base from U.S. Geological Survey Digital Data, 1:100,000Universal Transverse Mercator projection,Zone 10 North american Datum of 1983
0 1 2 3 4 5 MILES
0 1 2 3 4 5 KILOMETERS
Black River
SkookumchuckRiver
Chehalis River
Scatter Creek34.9
Figure 5. Streamflow gains and losses, August 2010.
August 2010 Seepage RunA series of streamflow measurements to identify gaining and losing reaches, termed a seepage run, were made during summer base flow conditions in August 2010 when streamflow was at its lowest, and the relative contribution of groundwater was at its annual maximum, and the contribution of precipitation was minimal. Synoptic discharge measurements were made at 41 locations and streamflow gains and losses were calculated for 28 reaches from August 17 to 19, 2010 (fig. 5). The seepage run reveals a pattern of alternating gains and losses of streamflow throughout the extent of the river system. Of the 28 reaches, 17 (61 percent) gained streamflow, 9 (32 percent) lost streamflow and 2 (7 percent) had no net gain or loss of streamflow (fig. 5). Gains and losses of streamflow were minimal upstream of the confluence of the Chehalis and Black Rivers, but became more dynamic downstream with gains and losses as much as 34.9 ft3/s/mi and -41.9 ft3/s/mi, respectively. Most streamflow gains and losses were small relative to the compounded error in streamflow measurements demonstrating the difficulty in measuring streamflow gains and losses. Ungaged diversions and return flows between streamflow measurements may cause an overestimation or underestimation of loses or gains, respectively.
Hydrogeologic UnitsFive hydrogeologic units and bedrock were differentiated based on their lithologic and hydraulic characteristics (fig. 4).
Unit A - Alluvium and Vashon Recessional Outwash (Aquifer) – The Unit A aquifer extends throughout the major river valleys and lowland prairies of the Chehalis River and its tributaries and comprises the most areally extensive surficial aquifer. This aquifer interacts readily with surficial water features sustaining summer streamflows and recharging during winter. This unit contains alluvial sediments of glacial and non-glacial origins with silt, sand, gravel, and coarse materials. Significant heterogeneity exists within this aquifer including the presence of local confining layers.
Unit B - Vashon Till and Morainal Deposits (Confining Unit) – The B confining unit is distributed in the northern part of the Chehalis River basin and is comprised of unsorted and unstratified deposits with clay to boulder-sized particles although irregularly distributed layers of sand and gravel containing small amounts of groundwater occur locally. This unit was deposited during the last glacial advance at the southern margin of the Puget Lobe of the Cordilleran Ice Sheet.
Unit C - Vashon Advance Outwash (Aquifer) – Advance glacial outwash of Vashon age and pre-Vashon age outwash in hydrologic connection with each other form the C aquifer where they are confined by the B confining unit in the northern part of the Chehalis River basin.
Unit D - Quaternary Alpine Glacial Outwash (Aquifer) – Alpine glacial outwash emanating from the Cascade and Olympic Mountains comprises the Unit D aquifer on the bedrock uplands of the Chehalis River basin. Several episodes of alpine glaciation have been documented since the early Pleistocene and their deposits consist of Cascade and Olympic-derived Tertiary volcanic and sedimentary rocks. The top parts of these deposits have been extensively weathered into clay confining groundwater where this unit is saturated.
Unit E - Pre-Vashon Glacial Drift (Aquifers and Confining Units) – The E unit is comprised of Pre-Vashon tills and outwash sequences deposited in the northern Chehalis River basin as far south as Centralia. Groundwater within the E unit occurs under confined conditions within the coarse grained outwash sequences. The outwash is separated from stratigraphically higher A and C aquifers by till layers. Multiple aquifers and confining units within the E unit may exist where they have not been eroded.
Bedrock – The Tertiary sedimentary and volcanic bedrock forms the basal confining unit of the groundwater-flow system and is relatively impermeable in relation to the unconsolidated sediments stratigraphically above it. Bedrock locally yields water sufficient for domestic use through fracture flow.
References CitedWashington Division of Geology and Earth Resources, 2005, Digital 1:100,000-
scale geology of Washington State, version 1.0: Washington Division of Geology and Earth Resources Open-File Report 2005-3, accessed January 5, 2011, at http://www.dnr.wa.gov/ResearchScience/Topics/GeosciencesData/Pages/gis_data.asp.
For More Information:Andrew S. Gendaszek - [email protected]. Geological Survey, Washington Water Science Center934 Broadway Suite 300, Tacoma, Washington 98402http://wa.water.usgs.gov/
NAVD88
200
400
600
SCALE 1: 62,500 VERTICAL EXAGGERATION x20
B B’
NAVD88
200
400
600 SEC
TIO
N
SEC
TIO
NBE
ND
IN
A-A
’
16N
/03W
-29L
03P1
15N
/03W
-03A
2P1
15N
/03W
-02R
01P1
14N
/02W
-06C
02
14N
/02W
-39R
0114
N/0
2W-0
7B02
15N
/03W
-14E
01
15N
/03W
-25L
08
14N
/02W
-31P
01
14N
/02W
-31C
01
14N
/02W
-19H
06
14N
/02W
-17N
01
13N
/02W
-07Q
02
13N
/02W
-06K
01
15N
/03W
-24L
01
16N
/03W
-33F
05
?
CHEH
ALI
S RI
VER
CHEH
ALI
S RI
VER
BLAC
K RI
VER
CHEH
ALI
S RI
VER