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SINEX 2002

Water Flows Uphill To Money:
Case History of a Groundwater Recharge Project
in Coastal California

Joseph Hayes, ¹ Mary Bannister ²

The Pajaro Valley of Central California is a coastal valley with a history of abundant agricultural yield, supported by intensive pumping of groundwater. Numerous studies conducted over the past fifty years have documented that the Pajaro Valley groundwater basin is in an overdraft condition, with annual water pumping exceeding the amount of water recharging the basin. This trend has caused seawater intrusion, with high concentrations of chlorides in wells near the coast, and an expanding area of groundwater levels that have fallen below sea level. This threatens the coastal agricultural economy.

The local government agency with water management authority has projected that increases in water demand will cause further problems. The water agency has a goal of balancing water demand with a sustainable supply to protect the long term water quality, and so began a program to develop additional water supplies, or limit demand. Several years of technical studies, groundwater modeling, public hearings and a voter referendum on proposed water projects (and proposed increases in water cost) illustrate the difficulty in gaining a consensus on changes in water management.

A proposed regional water pipeline to connect the Pajaro Valley to a state-wide water project was denied, and instead a series of smaller local recharge projects, combined with water conservation and pumping management, were selected in the year 2000. An initial project to divert excess winter rainfall for groundwater recharge has now been constructed, called the Harkins Slough Recharge Basin.

The Harkins Slough Recharge Basin is located on an agricultural terrace near the Pacific Ocean, where intensive irrigation is conducted for strawberry and lettuce crops. This project includes 1) a pumping and filtration facility which collects water from the local drainage during wet winter months, 2) a pipeline to the recharge basin, and 3) a surface recharge basin. The recharge basin is surrounded by ten recovery wells, designed to recover the recharged water in summer for irrigation demand in the coastal zone.

Technical challenges encountered for the Harkins Slough Recharge Basin included:

• Endangered Species habitat in the surface water drainage limits water available.
• Low rainfall years may have no water available for recharge.
• Surface water filtration needed to remove sediments and prevent basin clogging.
• Soil Infiltration testing resulted in new basin location, with higher infiltration rates.
• Investigating the subsurface hydrogeology, to predict water flow after recharge.
• Limited yield of water from recovery wells, due to shallow aquifer conditions.

See Selected Slides.

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