Water supply gridlock

By JOHN NEWBY
AGI Technologies

Given the past four years of above average rainfall, it may be difficult to believe that our water supply is severely limited. However, there is a water supply gridlock in Washington with environmental and economic consequences that rival the gridlock on our roads and highways.

Washington's population has grown by over one million people in the last 10 years. In the area served by Seattle Public Utilities, residential and commercial water use is about 120 gallons per person per day - approximately 50 in-house, 30 in the yard, and 40 commercial. This does not include water requirements for farm irrigation. Therefore, our water demand has grown by over 120 million gallons per day over the last 10 years.

In the past, engineers' primary tasks involved the technical aspects of water supply. Today, we are involved in everything from public education, helping to set appropriate public policy and balancing technical challenges with environmental protection, to developing innovative, environmentally sound and workable solutions to water supply management.

As part of the balancing act, an essential environmental issue is the necessity of maintaining minimum instream flows throughout the year to protect and enhance beneficial stream uses for fish, wildlife habitat, navigation and recreation.

The flow of water in a stream can fluctuate widely during a year. Much of the fluctuation is natural and related to annual variations in surface runoff from rainfall and snowmelt. Generally, streams are sustained during dry periods by base flow that depends on influent groundwater.

Developing any water resource for a water supply ultimately removes part of the water from the hydrologic cycle. Reservoirs trap and divert surface runoff and water supply wells remove groundwater that either may be in direct communication with surface water or ultimately replenished by surface water infiltration. This water is eventually returned to the environment as irrigation runoff, treated or untreated wastewater, or through evaporation or transpiration - much of which does not replenish streams.

Seattle Public Utilities' Tolt Treatment Facility is being designed, built and operated for up to 25 years by CDM Philip, in association with Dillingham Construction, N.A. Photo by Helicam

By the early 70s, laws had been enacted requiring the Department of Ecology to establish minimum flows, lake levels and base flows to protect, and where possible, enhance instream beneficial uses including fish habitat. The recent listing of Puget Sound Chinook as an endangered species has resulted in an even greater requirement to protect minimum stream flow.

While no one can reasonably argue with the importance of minimum stream flow, numerous disputes related to disparate water laws and quantifying appropriate instream flows have erupted. Further, the techniques necessary to accurately predict the impact of groundwater withdrawal on base flow are very complicated and require substantial amounts of detailed data. Evaluations of hydraulic continuity between surface and groundwater and the impacts of extraction are therefore subject to considerable dispute.

As an example, from 1976 through 1994 the Northwest experienced a 18-year period in which the annual precipitation was generally below average. Rainfall has been above average every year since. Groundwater well levels have followed a similar pattern of decline and recharge. This means that long-term precipitation trends have significantly more impact on groundwater levels and stream base flow than groundwater withdrawals for water supply.

Issuing new water rights essentially dried up in the early 1990s and there are now about 7,000 water applications on file. Thus the 10-year, 22 percent growth in state population has occurred without the benefit of additional water supply and new water rights. In addition to jeopardizing the state's economic health, this results in conflict between regulations and governing agencies.

For example, the Department of Health requires public water supplies to hold water rights for their sources. Without rights, utilities can not add services or meet increased demands. At the same time, utilities are required to provide water to users within their service areas. Several utilities have been forced to enter a moratorium and stop issuing certificates of water availability to new or growing customers. Others have resorted to unusual means of obtaining additional water without obtaining new water rights such as:

Wells producing less than 5,000 gallons per day are exempt from the requirement to obtain water rights. Currently, the development of systems serving less than a dozen homes is flourishing and constitutes 90 percent of the new wells being installed. These small water systems often have trouble in meeting health and other regulatory requirements.

Water utilities are auditing their water rights in an attempt to identify opportunities to extract more water. If water wells are not capable of producing the full amount of the water right pumps are replaced, wells are rehabilitated, or water rights are transferred to existing or new wells.

Litigation over water rights has become common and ambiguous rulings have further complicated Washington's water law.

None of these contribute to effective management of our water resource.

Finding new ways to capture, store water

Creative engineering minds are focusing on new means to capture and store winter runoff for use in augmenting summer stream flows or recharging aquifers. The cities of Tacoma and Seattle have conducted aquifer recharge studies to determine the feasibility of artificially recharging surface water from the Green and Cedar rivers into aquifers during the winter months for use during the summer when demand is highest.

Sammamish Plateau Water & Sewer District and King County Water District No. 19 on Vashon Island have also conducted artificial recharge studies in an effort to find a means to store water for future use. A new water treatment plant is being constructed to allow continuous operation of Seattle's Tolt source through periods of high turbidity.

Besides seasonally balancing the water supply, there are also opportunities to regionally balance the supply through distribution between watersheds that have, or could develop, excess supply and those with deficits. This can be accomplished by identifying and transferring or trading unused water rights. Sharing water rights between watersheds is both a political and technical challenge.

If Ecology is successful in reclaiming unused water rights, it may preclude managing the supply problem by redistribution. Seattle, Tacoma, and Everett are looking at system inter-ties as a means of balancing supplies.

Water reuse is also being studied as a means of saving our water resources. Current water treatment technology can produce treated water from municipal wastewater treatment plants suitable for many uses other than human consumption including irrigation, aquifer recharge, and stream enhancement.

Before the 1992 drought, Seattle Public Utilities average water use was about 150 gallons per person per day but has decreased to the current 120-gallon average due to conservation, higher water rates and improved system operations. We have a heightened recognition of the need to protect the quantity and quality of our water resources.

The years of legislative inaction on resolving critical water policy issues are now further complicated by the recent Endangered Species Act salmon listings bringing a new layer of government regulation and oversight into the equation.

The abundant rainfall we are blessed with can be better managed to provide for growth and for the environment. Long-term solutions must be based on studies that gather good data to support the evaluation of water supply withdrawals and stream flow for entire watersheds. The better we understand the complex mechanism of the water cycle, the better we can engineer systems to provide for adequate water supplies and protect our environment.

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