As more people enjoy local trails this summer, they may notice many of Valley Water’s percolation ponds in Santa Clara County are empty and dry.
There’s no reason to be alarmed. In fact, the absence of water in many of the 100 percolation ponds owned by Valley Water is a sign that our underground water basins are mostly full and healthy.
Percolation ponds are water supply facilities built in areas where permeable material such as gravel and sand allow water to seep into our aquifers. Their primary and most important purpose is to allow water to filter underground to maintain healthy groundwater conditions. The ponds were not created to support wildlife, although many types of birds, fish and other animals take advantage of these ponds when water is available. When the ponds are dry, animals often find other nearby bodies of water to enjoy.
Despite the below-average 2019-20 rainfall season experienced in Santa Clara County, our groundwater basins remain mostly full and healthy thanks to careful water management and abundant water supplies in 2017 and 2018. We do not want to overfill the groundwater basins, which would happen if we were to continue to release water into more percolation ponds at this time. We are only recharging (adding water to aquifers) to meet the current water demands of our community.
Refilling more percolation ponds under this condition could result in increased artesian pressure underground that could bring water to the surface via abandoned wells, which can cause localized flooding. This could cause problems in the cities of San Jose, Santa Clara, and neighboring cities on the valley floor. Click here to read more about artesian wells, which occur naturally over large areas of Santa Clara Valley and do not require a pump to bring water to the surface.
Valley Water continues to monitor the groundwater basins and currently there isn’t a need to fill many of our percolation ponds. We do not make this decision lightly. Our scientists, hydrogeologists, and engineers assess water supplies and needs often and regularly track the water levels in the aquifers. We will refill more ponds when the groundwater conditions warrant it.
However, some of Valley Water’s percolation ponds across Santa Clara County currently do have water, including:
- Oka Pond and all three Camden Ponds in Los Gatos
- McClellan Pond in Cupertino
- Coyote Percolation Pond (north of Metcalf Road) in south San Jose
- Madrone Channel and Main Avenue Ponds in Morgan Hill
- Two Guadalupe Ponds along Guadalupe River (off Highway 85) in San Jose that have some water in them due to seepage from the creek
Also, Valley Water anticipates filling the Dr. Robert W. Gross Ponds along Upper Penitencia Creek in mid-July. Some of the ponds at the facility were dried out in April to allow for repairs to a concrete spillway.
Valley Water expects additional percolation ponds in the valley to be refilled in 2021 based on projected groundwater levels.
We will continue to carefully manage our precious water supplies to ensure safe, clean water for the community.