Streamflow Records and the Determination of Sustainable Ground Water Use

Ground water often is a major source of supply for irrigation, industrial, and municipal development in the western United States.  Sustainability assessments of ground-water sources today often goes beyond a mere pumping rate or drawdown in the area of a well to include the effects on surface features such as streams and springs.  These effects may occur far from the pumping well and decades to centuries later in time.  Long-term streamflow records can be examined for evidence of influence from ground-water pumping, but the signal must be isolated from the inherent variability and/or climate change within the record.  The effects of ground-water pumping will be examined using three case examples. The San Pedro River at Charleston, Arizona, declined to zero flow in the summer of 2005 for the first time in 104 years of record at the U.S. Geological Survey’s Charleston streamflow-gaging station.  Ground-water pumping within the alluvial aquifer in the Upper San Pedro Basin was suspected to have reduced base flow. In another case study, Rapid Creek in Rapid City, South Dakota, is sustained by discharge from large carbonate springs sourced from the Madison aquifer, and water is withdrawn from the Madison aquifer in west Rapid City for municipal water supplies. Spring discharge has decreased by about 25 percent along with a reduction in the hydraulic head in the Madison aquifer at Jackson and Cleghorn Springs in the last 8 years.   Finally, streamflow gages on the Republican River in southern Nebraska show downward trends in discharge for the last 51 years in an area of extensive ground-water pumping for irrigation.  The utility and limitations of using streamflow records to evaluate the effects of ground-water withdrawals, and therefore the sustainability of the source, will be presented by use of hydroclimatic, streamflow, and ground-water records.