Storm‐event flow pathways in lower coastal plain forested watersheds of the southeastern United States

Abstract

AbstractThe landscape of the coastal plain of the southeastern United States is rapidly changing due to urbanization and climate‐change‐related impacts. In addition to the forecasted population increase, this region could experience significant changes in precipitation patterns making watershed management very challenging. In order to establish baseline data, storm‐event flow pathways were studied in three lower coastal plain (LCP) forested lowland watersheds of the southeastern United States between 2010 and 2011. Two of the watersheds had clay loam subsoils while the third had sandy soils throughout the profile. Stream flow and water samples from water‐table wells, piezometers, lysimeters, and rain gauges were analyzed for ion concentrations; ion trends were assessed using principal components analysis; and chemical hydrograph separation was performed for nine storm events using end‐member mixing analysis. End‐members consisted of lower concentration rainwater; a near‐stream source (riparian or streambed groundwater); and a distant or deep groundwater source. Storm‐event stream water on the clayey sites was composed primarily of rainwater (45–67% by volume) and shallow groundwater (21–55%), with small inputs from deep (below the clay‐rich soil horizon) groundwater (0.2–21%). At the sandy site, a greater proportion was groundwater (56–61%), with smaller inputs from rainwater (28–33%) and soil water (6–16%). Dry antecedent soil moisture (ASM) conditions and larger storms resulted in greater rainwater contribution at the clayey sites. Shallow groundwater was an important contributor even in dry ASM conditions, perhaps due to the high specific retention of the soils. The results from this study will inform researchers about stormwater routing in forested, shallow water table watersheds and provide land managers with baseline data as they plan stormwater mitigation practices.