One of the most difficult things about a drought is that we don’t know when it will end. Our stormy December was followed by a bone-dry January. We had some rain in February, but no one knows what the rest of the winter will bring.
It is a welcome sight to see some local reservoirs begin to fill, but what is not so visible is the state of our local groundwater basins. A groundwater basin is an underground reserve of water which may take the form of a single aquifer or a group of linked aquifers. The Santa Clara Valley Water District monitors water levels at 225 wells to estimate the amount of groundwater storage we have.
Our groundwater basins are an essential part of our local water supply. In a typical year, about half the water we use is pumped from the ground. However, due to the drought, we actually used more groundwater in 2014 than the year before. Our measurements showed that the groundwater storage was reduced by almost 80,000 acre-feet in 2014. To put that in perspective, all 10 of our local reservoirs combined held 68,000 acre-feet at the beginning of 2015.
In a normal year, the water district actively replenishes groundwater supplies year round. Water that originates as snowpack in the Sierra Nevada is imported through pipes and canals to Santa Clara County. It combines with local water stored in reservoirs and is released into streams and percolation ponds throughout the valley to replenish the groundwater basins. In 2014, the amount of water available for groundwater replenishment was just 25 percent of normal.
As a result of using more groundwater and replenishing less, groundwater levels in southern Santa Clara County, are about 30 feet lower than average levels over the last five years. In San Jose, the difference is about 40 feet.
Our groundwater reserves are not unlimited. In fact, if we use too much, we begin to run the risk of land subsidence, which is the sinking of the ground surface as a result of overdrawing groundwater. ISubsidence often results in costly damage to infrastructure such as levees, canals, roads and sewer systems. It can also result in increased flood risks and saltwater intrusion to the groundwater basin.
Aggressively protecting groundwater quality, securing imported water supplies, promoting conservation and increasing the use of recycled water all contribute to protecting our groundwater basins. Through a groundwater production charge, well users pay for the management services we provide.
When the community pitches in by being our eyes and ears about water waste or contamination, we can all contribute to keeping our water supplies safe and reliable. To learn more about the importance of our groundwater supplies, join us at an open house during National Groundwater Awareness Week on March 12. from 4 to 8 p.m. at 5700 Almaden Expressway in San Jose. For more information or to RSVP, email rsvp@valleywater.org.
Contact me with questions or comments at 408.234.7707.
Richard Santos represents District 3 on the Santa Clara Valley Water District board.