Groundwater pumping causes salinization of coastal streams due to baseflow depletion: Analytical framework and application to Savannah River, GA

A conceptual diagram showing coastal stream dynamics before (a) and after (b) groundwater pumping. The saltwater-freshwater interface is a balance of river discharge and ocean forcing (tides, waves, sea level) that can be shifted inland due to reduced baseflow from nearby pumping. [Display omitted] •Analytical models show groundwater pumping can cause coastal stream salinization.•We show an example of an analytical model for detecting vulnerable coastal systems.•Salt front shifts can reach a few kilometers with certain pumping schemes. Groundwater-surface water interactions and associated water management issues are complicated by the risk of salinization along coastlines. Groundwater pumping can be a driving factor of streamflow depletion and allow for increased stream saltwater intrusion. In this study, we develop an analytical framework combining two analytical approaches to calculate the length of saltwater intrusion at high slack water and the stream depletion rate due to groundwater pumping. We test this framework using data from the Savannah River in southeastern U.S and use it to explore saltwater intrusion in the surface water system. The analytical approach produces an accurate estimate of the position of the salt front at approximately 56 km inland. Current pumping rates decrease streamflow by less than 1%, resulting in an increase in the saltwater intrusion length of 100 m. Increased groundwater pumping scenarios, however, show a risk of extending the saltwater intrusion length up to 4 km inland. In these cases, effects from pumping-induced saltwater intrusion would equal or exceed the impacts of sea-level rise or geomorphic change. Salinity is a critical factor in the ecological balance of this estuarine ecosystem and this analytical approach allows for investigation of hypothetical groundwater development in the region. We show, for the first time, the direct link between groundwater pumping and coastal stream salinity that should be an important management consideration all along developed coastlines.