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 that 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 ten of our local reservoirs combined held 68,000 acre-feet at the beginning of 2015.
It is not uncommon, especially in South County, to hear the statement: “I don’t need to conserve, I’m on a well.” How far from the truth this is. Well owners especially need to conserve. Well owners especially, need to understand how critical saving our precious underground water resource is. We cannot afford to continue to waste it.
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 have dropped throughout the county. In southern Santa Clara County, groundwater levels are about 30 feet lower than average levels over the last five years. In the San Jose area, the difference is about 40 feet. Even with normal rainfall, it will take some time for our groundwater basins to recover.
It is important to recognize that 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. Historically, land subsidence occurred in the 20th century until the early 1970s in our county. Up to 14 feet of permanent land subsidence was observed in San Jose due to groundwater overdraft. Subsidence 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 active groundwater management services we provide.
If you are interested in learning more about the importance of our groundwater supplies, you are invited to join us at an open house during National Groundwater Awareness Week on March 12. The open house will take place from 4 to 8 p.m. at 5700 Almaden Expressway in San Jose. For more information or to RSVP, please email rs**@va*********.org.
I hope to see you there.
Former Morgan Hill Mayor Dennis Kennedy is the Santa Clara Valley Water District Board Vice-Chairman and District 1 Director. He can be reached at dk******@va*********.org.
