Chapter x Surface Water

Surface water characteristics:

Fresh surface water provides drinking water, habitat, recreation, and power generation in San Juan County.  Forty percent of the county’s population depends on surface water for drinking water, most of which comes from the two largest watershed systems in the county: the False Bay watershed on San Juan Island and the Mountain Lake/Cascade Lake watersheds on Orcas.  (For more information on the county’s watersheds see the 2000 San Juan County Watershed Action Plan and Characterization Report.)

Several reports[1] have addressed surface water conditions in the county over the years, calculating the amount of runoff in streams and the capacity for storage in lakes and ponds. Stream gauging and hydrologic modeling are used to estimate runoff and storage potential in a watershed system by developing an equation that includes precipitation, evaporation/transpiration (loss of water through vegetation), recharge, and runoff.   Stream gauging by Ecology in 1975 included 28 sites, with two read daily and 26 read monthly.  USGS gauging in 1997-98 included six sites, with continuous recording by electronic recorders.  (Currently, there are xnine gauging sites on Orcas and San Juan islands with recorders.  This network was started in November 2003, and will provide long-term, accurate data for analysis.)

These reports show that the hydrology of San Juan County is characterized by low runoff compared to other areas in western Washington and this runoff occurs during winter and early spring, late October to early April.  During the summer months, San Juan County is typically in a phase of water deficit.  More water is lost from the soil due to evaporation and transpiration (uptake of water by plants) than is added from precipitation. The largest component of the hydrologic water budget in San Juan County is evaporation/transpiration, which uses 64-75% of rainfall annually (see Table x.1, below).  Runoff ranges from 14% of precipitation on Lopez (with low terrain and glacial deposits) to 31% on Orcas (with high elevations and bedrock conditions).

Most of San Juan County’s streams are intermittent, drying up during the summer months when plants and evaporation take up all the available rainfall.  The few perennial streams are maintained by groundwater discharge through seeps and springs and/or by diversions as part of irrigation or drinking water impoundments.  Most of the county’s streams, lakes, and ponds have been altered by ditching and dams for irrigation, drainage, drinking water, or hydroelectric plants. 

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Table x.1

Water budget components (in inches)

Source: Estimates of Ground-Water Recharge, USGS WRIR 02-4114.  This is a summary of annual water budget components using the deep percolation model for Lopez, San Juan, and Orcas, water years 1997-98.  Components may not exactly equal precipitation because of round-off errors.

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Stored surface water is an important resource in the county, capturing winter rainfall for use during dry summer months.  Over the years, studies have identified potential sites for additional storage and use.   However, as the county has grown the importance of wetland and recreational areas has increased as well as impacts on water quality in the watershed and many of these locations are no longer realistic.  In order to provide water to meet growth projections, the Town of Friday Harbor, Roche Harbor and Eastsound water systems are planning to increase storage by raising the height of their respective dams.  There also appears to be potential for additional diversions from the Mountain Lake/Cascade Lake system without impairing existing beneficial uses of water.

Xxstorage assessment adds

Water quality

The quality of San Juan County’s streams do not have specific water quality classifications (WAC 173-201A-130).  The receiving marine waters in the county are classified as AA marine waters; therefore, San Juan County streams are designated Class AA by default.   The 2000 Characterization Report and follow-up San Juan County Monitoring Project identified several fresh water sites that exceed Class AA standards, mostly during the summer and early fall.  Some of these results may reflect natural conditions; others appear to indicate impact from land use activities. 

In October 1999, Ecology issued a TMDL[2] ranking report for San Juan County using preliminary monitoring for the Characterization Report.  This study identified five priority watersheds to consider for future TMDLs, with the recommendation that additional monitoring be conducted[3].  Ecology did not follow up the recommendation to continue to work on the ranking, but additional monitoring has been conducted by the county.  A comprehensive follow-up study was done in 1999-2000, which resulted in the Monitoring Project Report, and then, in 2002, the San Juan County Conservation District began a watershed stewards educational program that includes a volunteer/student monitoring program.  This program has been very popular, resulting in active community participation in watershed protection.  Results of current monitoring are included in appendix x.

Climate trends

In order to determine a sustainable capacity for surface water diversions, the impact of climate trends must be taken into account.  A sustainable yield from a surface water source must be based on drought conditions.  In 1975, Deitrich commented on the pattern of dry and wet years represented in the rainfall data from Olga on Orcas Island, one of the longest recorded rainfall sites in the state.  Climatologist now recognize the patterns as the PDO and ENSOx.  A comparison of Olga rainfall patterns and the PDO is represented in figure x.  (xBobM, explanation of exceedance values?)

Drought conditions during 1993-4 raised concerns about the sustainable capacity of surface water sources on San Juan Island.  The Town of Friday Harbor contracted a survey and analysis the capacity of Trout Lake and found that recharge to the lake occurred only after 18.5 inches of annual rainfall, out of an average of 27.6 inches.

An estimated water balance for average conditions can be calculated with the numbers above, but the Town found that estimates can vary dramatically with actual conditions.  A water balance for 1992 came up with the following results:

Source: Town of Friday Harbor Trout Lake Capacity Analysis, 1994

The rainfall pattern in 1992 was such that there were a limited number of storm events that resulted in significant enough rainfall to saturate the soil and allow for runoff to the lake.  As a result of this analysis, the Town decided to use a conservative number for sustainable yield from their watersheds, based on a 50-year drought cycle.

False Bay, Mountain Lake and Cascade Lake watersheds

Most of the surface water in the county is linked by ditches, diversions, and impoundments with a varied history of water rights and use.  The False Bay watershed is the largest single watershed in the county and includes the sources of water for the Town of Friday Harbor.  The Town owns 570 of the 840 acres that comprise the watershed for Trout Lake, its main source.  The Town also diverts water from two                                                                                                                                                                                                                                                                                        locations.  Augmentation 1 and 2 pump water from seasonal flows to the lake during winter months, supplementing the natural recharge to Trout Lake.   The Town shares rights to these stream flows with landowners who also use the water for irrigation.  The Town holds water rights for 480 MGY and estimates that the sustainable yield from its combined sources is 168 MGY.

The Mountain Lake and Cascade Lake watersheds are linked by Cascade Creek, which flows into Buck Bay.  These watersheds are located on the southwest slope of Mt. Constitution, inside Moran State Park, and include the wettest area in San Juan County. 

Moran State Park is a 5,252-acre pristine, forested, camping park with five freshwater lakes located on the 2,409-foot-high Mt. Constitution, the highest point on the San Juan Islands.  The popular park had a total of 868,995 visitors in 2003.

At the top of the Mountain Lake watershed is Moran Creek and Summit Lake.  Moran Creek is diverted to flow to Purdue Lake, Eastsound Water Users surface water supply  (xxTED?), and Summit Lake is formed by a small concrete dam that releases water into Mountain Lake.  Mountain Lake is impounded by a combination earthfill-concrete dam where Doe Bay Water Users diverts approximately 23.6 MGY (72.5afy) and holds water rights for a total of 59 MGY (181afy).  A five-inch pipe at the base of this dam discharges water into Cascade Creek.  Just above the bridge across Cascade Creek in Moran State Park, Olga Water Users Assoc. diverts about xx(30) acre/feet/year out of rights for 94 acre/feet.  Most of the flow in Cascade Creek below the bridge is then diverted by a dam, pipe, and cement canal to Cascade Lake.  Approximately, xx acre/feet/year is released to Cascade Creek from Mountain Lake and not diverted, maintaining stream flow throughout the year.  The Cascade Lake dam was built in 1884 to generate hydroelectric power. Rosario Resort holds rights for 92.2 MGY (283 afy) for domestic use and 518.5 MGY (1591 afy) for power generation from Cascade Lake and Cascade Creek and, in 2001 produced 37.4 MG of treated water (x#from diversion?).  The water rights in these lakes and creek were adjudicated in 1978.  The lower reach of Cascade Creek is documented as spawning habitat for salmon.

Surface Water Management Issues

·         Surface water provides drinking water to the majority of designated growth areas in the county.

·         There is a lack of coordinated, cooperative management of the county’s surface water resources.

·         In some areas, water rights to surface water sources exceed sustainable yield.

·         Planning for additional storage is essential to addressing growth and protection of habitat.

·         Long-term monitoring is needed to accurately calculate the county’s surface water characteristics.

X, maps of watersheds, aug1&2, lakes and c creek. Moran park, town boundary, contours.

xxMap, gauge sites from each study.  Rainfall at Olga.  PDO etc. graph. budget graphic, p67.

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Orcas Island Watershed Planning