The effects of pulsed pumping on land subsidence in the Santa Clara Valley, California

Abstract

Land subsidence caused by pulsed and constant pumping schemes was calculated, and the results were compared to determine the possible advantages of pulsed pumping in reducing land subsidence. Pulsed pumping refers to pumping strategies involving alternation between periods of pumping and recovery in a well. Subsidence was calculated using a numerical model based on the Santa Clara Valley, CA. The model accounts for delay in the release of water from storage in compressible interbeds as well as flow within aquifers. For these tests, the ratio of pumping period length to recovery period length was either 1 1 or 1 3 . Pulsing interval length (length of one pumping period plus one recovery period) ranged from 4 to 90 days. Pumping rates were adjusted so that pulsed pumping and constant pumping removed the same volume of water over the period under consideration. Pulsed pumping has the potential to ‘concentrate’ subsidence around the pumping well. For all simulations, pulsed pumping caused greater subsidence near the test well than constant pumping. Under some conditions a transition point was reached, beyond which pulsed pumping caused less subsidence than steady pumping. The distance from the test well to the transition point decreases for (a) decreasing aquifer transmissivity, (b) decreasing ratio of pumping period to recovery period, and (c) increasing pulsing interval length. The concentration of subsidence was reduced considerably when delay in release of water from storage in compressible aquitards was neglected, indicating the importance of including delay effects in subsidence studies. All pulsed pumping strategies caused a greater total volume of subsidence than steady pumping.