RELATIONS BETWEEN GROUNDWATER AND STREAMFLOW DEPLETIONS

Major aquifers of the United States are generally exhibiting net depletions of groundwater due to heavy pumping. Groundwater theory indicates that streamflows should be decreasing in response to groundwater use and storage depletion. To advance the understanding of the relation between groundwater depletion and streamflow, this study provides a systematic, empirical analysis of changes in streamflow across multiple principal aquifers of the United States and correlates changes in streamflow to groundwater pumpage. Using ten principal aquifers that have undergone substantial long-term changes in groundwater storage, trends in streamflow are related to groundwater depletion. To ensure that observed streamflows have been subject to the same conditions as the aquifer, streamgages selected for inclusion in this study generally have at least 50 percent of their contributing area contained within the area overlying each of the respective principal aquifers and minimal storage or regulation above the gage. Trends in the number of zero days of streamflow and the maximum-daily, mean-daily, and 7-day-minimum streamflow values are evaluated and compared to the time series of annual groundwater depletion for each principal aquifer. Trends were further categorized by cultural features, similar geologic settings, and depletion intensity. Results clearly show that in some cases streamflow depletion is related to (and probably caused by) groundwater depletion.