After a multi-year drought, and low rainfall totals in 8 of the past 10 years, rainfall in the San Gabriel Valley has been trending above average this winter. These storms have provided nearly 28 inches of rain so far this season, with the Los Angeles County Flood Control District capturing all but peak flows for conservation, while still maintaining flood protection. These statistics are encouraging, and it is important to understand how these rains help restore much needed groundwater levels.
The San Gabriel Valley depends on the Main San Gabriel Basin (Basin) to provide nearly 80 percent of its water supply. In an average year, approximately 100,000 acre-feet (an acre-foot is equivalent to a football field one foot deep in water) of stormwater runoff enters the Basin as natural recharge. During the drought between 2012 and 2016, San Gabriel Valley water purveyors relied on groundwater stored in the Basin to meet demands resulting in a depletion of over 400,000 acre-feet of water. To put this into perspective, over this five-year period, the San Gabriel Valley only received about 135,000 acre-feet of runoff for recharge, where under normal conditions, would have received nearly 500,000 acre-feet. “San Gabriel Valley residents did a great job with water conservation during fiscal year 2015-16, reducing water usage to about 185,000 acre-feet, which is nearly 25,000 acre-feet below annual average,” said Main San Gabriel Basin Watermaster Executive Officer, Tony Zampiello. “It is critical that residents maximize all opportunities to conserve water, even in wet years to preserve long-term, local sustainability of our water supplies”. Zampiello also said that “the simplest way to relate to the Basin is to picture a piggy bank – we have been taking from the bank for over five years and now it is time to start putting it back”. “Remembering that even though the hillsides are green today, the water stored beneath our feet is our future.”