Setting the Water Table Imagine That You Have Peeled Away the Top Layers of the Island and You Can’T See It, but There Are Hills of Groundwater Beneath Our Feet

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Map Orientation, Peel away the skin Setting the Water Table Imagine that you have peeled away the top layers of the Island and You can’t see it, but there are hills of groundwater beneath our feet. In are now looking at the sand and gravel that is our primary aquifer. The map below shows contour lines depicting the elevation above some locations on the Island, water infiltrates downward more easily sea level of the water table in this aquifer. The aquifer is saturated and begins to build up, forming mounds of water. These groundwater with water below the water table. The orange squares represent mounds will try to flatten out, so the water beneath our feet is always on wells with the water elevations denoted in black. the move.

LEGEND What is a “water table?” Roads In the diagram below, you can see that the ground below Streams the water table is saturated with water. Above the water Groundwater “Peaks” table there still is some water adhered to the soil and rock particles, but there is also air, so it is not totally saturated. Outline of Vashon Advance Outwash (Qva) 150 Water Table Contour Interval 50 feet

Approximate Flow Land Direction Unsaturated Zone Surface Water Table Surface Water 261.1 Monitored well sites in Saturated Zone the primary aquifer (Qva) Ground Water Gravel Air 150 w/watertable elevation Water (not groundwater) held by molecular attraction surrounds surfaces of rock particles Based on USGS Approximate level of the water table The graph depicts the daily 15-minute peak flows in Fisher “Water Science for Gravity reigns All openings below the water table Creek during water-year 2009. Winter flows are supplement- The dark yellow shading on the Schools” series. full of water ed by rain storms which cause the dramatic peaks, while water table map shows that we have summer flows are fed primarily by groundwa-

ter with an occasional shower contributing two “peaks” of groundwater. One

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surface water to the creek. is west of town and the other S S

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183.7 w is northwest of Burton. Water

H 179.5 198.1 n o obeys gravity and will move h

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k k downward, seeking sea

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e “water year?” r level. The arrows SW 156th St C

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Scientists who study water, i show the direction

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report data like “total g groundwater is moving. n n

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rainfall” during a h S “water year.” A water S

115th Ave SW year runs from 276.9 Water level October 1 through SW Cove Rd 200 monitoring September 30. Island volunteers have monitored the elevation SW Bank Rd ek e of the water in their well r 250 C since 2001. They do this by 301.1 l 261.1 l

a e measuring the “depth-to- B water” from the top of their

Thorsen Rd Sw W well. In water year 2009, S

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e e four of the five wells moni-

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R tored by volunteers showed Beall Rd SW a decrease in water table

181.4 elevation compared to k

SW Cemetery Rd k

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r baseline levels established C

Judd Creek C

r in 2002 and 2003.

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Vashon Hwy SW s

240.4 s

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Westside Hwy SW 240.5 Depth-to-water measurements 111th Ave SW 111th Ave 150 The graphs above depict depth-to-water measurements in feet taken from the top 250 of wells by volunteers since 2001. Note the seasonal variation of almost 10 feet in 200 Groundwater Level (GWL) in well 09. The gradual increase in the average depth-

310.4 SW 220th St to-water measurements from 2001 to 2007 shows the elevation of the water table 87.3

246.8 Monument Rd SW in the vicinity of this well was decreasing until 2008. There is much less varia- C 5 h SW 22 th St tion in GWL in well 06, but GWL in well 13 also shows a seasonal variation ris te n and a slight decline in the water table over the last two years. s e n

C 252.9 212.5 r e 265.8 SW 232nd St e S Groundwater con- k W

Po in t R nects neighbors o b in s 262.7 107th SWAve o It takes time, but groundwater F n

is R h SWSW Burton Burton Dr Dr d will find its way to a stream or e SW 240th St r

150 C Mile squirt out the side of the Island r ta e C e r as a spring or be captured by us k eek to drink. Because groundwater is on the move and does not respect property lines, what we throw on our property today could soon show up in our neigh- 84.6 SW Dock St bor’s well. 221.8 63.7 53.1 200 Why is Maury’s water table elevation

Wax Orchard Rd SW lower than Vashon’s?

200 99th Ave SW Ave 99th 99th Ave SW Ave 99th 60 The water table near Dockton appears to be only 80 feet above sea level 219.3 while the water table on Vashon reaches 300 feet above sea level. Why 210.0 the difference? Well, there’s up to 10 inches less rain annually on the 80 east side of the Island than on the west side. And, the clay layer below W

w the primary aquifer on southern Maury is below sea level. On Vashon,

230.1 n o this clay layer is in the range of 200-250 feet above sea level. Raindrops

V must dig deeper on Maury before they reach a clay aquitard and begin to

k saturate the sands and gravel above it.

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LIN h T K 150 O S a H

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q Creeks closed to water withdrawals e

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h The state Department of Ecology no longer issues new rights to withdraw water

a a T T from Christiansen Creek, Fisher Creek, Judd Creek and Shinglemill Creek in Want to know more? an effort to retain enough water in the creeks to support aquatic wildlife. In the To learn more about groundwater, see the summer, these creeks are fed primarily by groundwater. Keeping the water table Vashon-Maury Island Water Resources Evaluation Liquid high helps keep our creeks flowing in the summer. Project and Chapter 4 of the Vashon-Maury Island Assets Rapid Rural Reconnaissance Report. A Collaboration of Vashon-Maury Island Groundwater Protection Committee and King County Water and Land Resources Division 5