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

Abstract

The 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.

Hydrological processes of reference watersheds in experimental forests, USA.

“…The analysis also revealed that larger watersheds do not necessarily yield higher baseflows and damped high flows. In addition, the presence of an argillic horizon, large topographic depressions and riparian area, preferential flowpaths, pipeflow, steep slopes and certain soil physical properties also significantly affect flowpaths, the magnitude and variation of runoff generation, and possibly the water balance (Weiler and McDonnell, 2004;Griffin et al, 2014;Gillin et al, 2015;Klaus et al, 2015). Furthermore, the results also demonstrate that a better hydrological understanding of low topographic relief sites such as MEF and SEF is needed because these areas are common but not well represented by EFR sites, which are mostly in mountainous terrain.…”

“…Although SEF is the lowest gradient watershed, the high flow range that occurs for less than 1% of the time is greater than at most of the other sites, except for HBEF, HJAEF and CCEW. The highest flows at this site result from storm runoff from saturated clay-rich soils (Epps et al, 2013;Griffin et al, 2014).…”

Evaluating SWAT Model Performance for Runoff, Percolation, and Sediment Loss Estimation in Low-Gradient Watersheds of the Atlantic Coastal Plain

“…Most of the soils in these areas are classified as hydrologic groups A or B, which have low to moderate runoff potential even when soils are thoroughly wetted. Runoff can be low to non-existent in flat, sandy upland areas within this region [68], and forested Coastal Plains watersheds have been shown to have no runoff except for when conditions were wet enough to raise the level of the water table above the level of the streambed [69]. For the soil to become saturated to this level, either a storm of large volume or duration would have to occur, or with the occurrence of a storm with a high antecedent soil water content.…”

Turkey Creek—A Case Study of Ecohydrology and Integrated Watershed Management in the Low-Gradient Atlantic Coastal Plain, USA

“…Many of the ecohydrologic and integrated water management issues on this freshwater system proposed/identified at earlier phase of the project have been addressed by collaborative approaches during last 10 years as reported recently [7]. For example, reports have been generated concerning issues on design peak and low flow discharges for various design storms and flow duration pattern including their scaling issues generally used in pre-development storm water management scenarios, design of cross-drainage structures, and allocation of environmental flows [44]; water budget components generally used in restoration and comparison with developed watersheds [3] [65]; storm event characterization in terms of their peak flow rates, time to peak, runoff volumes and duration, and runoff ratios also used in pre-development scenarios and design of the best management practices [12] [67]. A study on recharge rates into the underlying groundwater aquifer and its quality in this region was conducted [11], related publications on the interaction of precipitation, surface and groundwater flow and their relative contributions to stream flow dynamics in the riparian floodplain of this lowland forested watershed are also available [67]- [69].…”