Percolation ponds

Percolation: One of many percolation ponds used to collect water and allow it to seep into the groundwater basin below.

According to an engineering investigation released by the San Bernardino Valley Water Conservation District on March 7, the Bunker Hill Basin, which stores the groundwater used by the San Bernardino Valley, remains 570,718 acre-feet below full water storage following the 2017-18 water year.

The district covers an area of approximately 50,000 acres, about 60 percent, of the basin and manages the recharging activities of the Bunker Hill Basin. As the area’s water conservation district, the district is required by the California Water Code to prepare an engineering investigation to compile and analyze the area’s precipitation and water storage levels each year.

The investigation reports data from the 2017-18 water year, July 1, 2017 to June 30, 2018. This does not include the current water year (July 1, 2018 to June 30, 2019), which has seen a wet winter.

The water year brought a reported 56 percent of average annual precipitation and 161,708 acre-feet of groundwater production.

According to the report, water storage in the basin decreased by 47,788 acre-feet between fall of 2017 and fall 2018. It is estimated to decrease by 77,559 acre-feet during the current water year and by 5,973 acre-feet the ensuing water year, presuming average precipitation. (One acre-foot would fill a football field one foot deep in water and can provide enough water for one family for up to two years.)

The basin would need a recharge of 784,822 acre-feet in the ensuing water year to reach a level considered full, and Basin Technical Advisory Committee recommends a maximum recharge of 282,000 acre-feet.

A “full basin” is based on the water levels recorded in 1993. The basin can store about 5 million acre-feet of water.

The basin first dipped more than 500,000 acre-feet below full in 2014 when the storage level was 535,877 acre-feet below full. The storage level reached its lowest level in 2015, 583,447 acre-feet below full. In 2017 the basin reached 522,930 acre-feet below full.

The basin rests in the valley, south of the San Gabriel and San Bernardino maintain ranges, north of Crafton Hills and the San Jacinto fault. It receives runoff water from the Santa Ana River, Mill Creek and a portion of Lytle Creek and serves as a major supply for water districts serving Highland, San Bernardino, Redlands, Colton, Loma Linda and Riverside.

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