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Harkins Slough water project threatened by duckweed...

Donna Jones, Santa Cruz Sentinel
3/24/2011

http://www.santacruzsentinel.com/news/ci_17694592

Harkins Slough water project threatened by duckweed: P.V. officials seek county's help for clearing vegetation, sediment

WATSONVILLE - Sediment and an aquatic plant known as duckweed are threatening a water supply project on Harkins Slough.

Pajaro Valley Water Management Agency officials say the problem is a lack of maintenance, and they are pushing Santa Cruz County Public Works to clean it up.

But county officials say getting the necessary permits from regulatory agencies will taken time.

Mary Bannister, the agency's general manager, said the issue needs to be put on the front burner as sediment and vegetation are clogging pumps used to pull freshwater from the Harkins and Watsonville sloughs during the rainy season for irrigation use in the summer. If cleanup isn't done this year, the project may become inoperable.

"One big pump sucks nothing but mud," Bannister said. "We can't even use it."

Bruce Laclergue, the county's flood control manager, said the county is working on a short-term solution, possibly pulling out the pump and trying to clean sediment from around screens and also clear vegetation in the area.

But the problem extends throughout the slough system, he said, and the county is looking at the bigger picture, doing the work that needs to be done to get a master permit from regulatory agencies.

"It's going to take some time to review systemwide needs and assessments and the environmental documentation," Laclergue said.

Bannister said she's been trying to get the county to act for years, and she worries it will soon be too late.

"This issue is immediate," she said.

The groundwater basin provides nearly all the water used by Pajaro Valley agriculture, residents and businesses. But more water is pumped than is replenished by winter rains.

About 55,000 acre-feet are pumped annually. An acre-foot equals 325,000 gallons.

As basin water levels drop, seawater moves inland, contaminating coastal wells.

The Harkins Slough project, built in 2001 at a cost of $11 million, is part of an agency strategy to bring the basin back into balance. Historically, the county pumped winter storm flows from the sloughs to the Monterey Bay. The agency's project can divert as much as 2,000 acre-feet of water a year to a pond on Dairy Road instead. There, the water percolates into the groundwater basin. The idea was to recover the water from area wells when it's needed later in the year, though the recovery wells have not produced as much water as anticipated.

Recent research by Andy Fisher, earth and planetary sciences at UC Santa Cruz, showed the recovery wells aren't placed optimally to catch water flowing into the aquifer due to geologic factors not well understood when the project was designed. However, Fisher said the water isn't lost.

"The place where it's probably going is back into the main aquifer, where there's a huge deficit and not enough recharge," Fisher said. "Ultimately, the project is contributing to getting it back into balance."

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