Underground pumping drains surface streams

Posted on July 25, 2012

In many river valleys there’s an intimate connection between surface water and groundwater.  The pumped extraction of groundwater for irrigation depletes  surface streams as water moves downwards to replenish the aquifer.  Because of their close links, surface and underground waters are best managed as an integrated system rather than independently, with studies indicating that economic benefits can be doubled through conjunctive use.  Some options for conjunctive water management have been explored using the South Platte River in Colorado, U.S.A. as a case study.  Simulation modelling showed that fluctuations in stream depletion caused by groundwater pumping in the growing season can be minimised by moving wells further away from the stream.  This dampening effect increased with the width of the aquifer.   Because of the relatively slow responses of groundwater systems, it’s not feasible to increase stream flows in the short term by shutting wells down.   In a crisis such as a drought, a better plan is to pump to the stream from distant wells.  Once groundwater pumping is begun, most stream depletion occurs in the first few years of pumping but it takes 10-15 years of pumping for depletion rates to level off, and a similar length of time for stream levels to return to zero after pumping is discontinued.  The main message is the need for a long-term focus if conjunctive management of water resources is to be effective.

Reference:  Bredehoeft, J.  2011.  Hydrologic trade-offs in conjunctive use management.  Groundwater 49(4), 468-475. http://onlinelibrary.wiley.com/doi/10.1111/j.1745-6584.2010.00762.x/pdf