Title: Understanding Hydrologic Processes at Landscape and Watershed Scales

Cooperators: J.M. Sheridan, A.W. Thomas

Problem:
There currently is concern regarding nonpoint source pollution of the nation's surface and groundwater supplies by agriculture and the subsequent detrimental effects to the natural resource base and to environmental quality. Consequently, there is a need for agricultural conservation and management practices that will support a productive, profitable agricultural economy while maintaining or improving the quality of surface and ground water supplies. The focus of this research is on developing improved understanding of hydrologic processes at landscape and watershed scales, particularly within the Gulf-Atlantic Coastal Plain of the southeastern U.S.; and, on development of alternative agricultural management strategies that will reduce agricultural nonpoint source pollutant contributions to the nation's surface and ground water supplies.

Approach:
OBJECTIVE (1). Improved methodologies for relating hydrologic response to quantitative drainage basin characteristics are critical needs for water resource and environmental quality planning and management. Relationships between drainage network structure and hydrologic response will be developed for agricultural watersheds in the humid Gulf-Atlantic Coastal Plain region. Specific approaches are: (a) to develop geomorphic and topologic information descriptive of drainage system and channel network structure for Little River Experimental Watersheds (LRW); and (b) to evaluate, test, and/or adapt concepts advanced in the geomorphologic/geomorphoclimatic instantaneous unit hydrograph (GIUH) approaches and the network link-based derivation of the GIUH approach (the network width function) for use in rainfall-runoff modeling.

OBJECTIVE (2). Improved hydrologic design and modeling relationships are needed by action and regulatory agencies for use in water resource planning, design and management and for environmental quality modeling, particularly for use on humid-region watersheds with low-gradient drainage systems and significant riparian storage. Specific approaches are: (a) to continue long-term hydrologic data collection on Little River Experimental Watersheds; and (b), using the LRW hydrologic data bases, to develop hydrologic design and modeling relationships for use by action and regulatory agencies.

OBJECTIVE (3). Improved capabilities are needed for predicting the rate of movement of water and transported nonpoint source pollutants via surface and subsurface flows on agricultural landscapes. Specific approaches are: (a) to evaluate the impact of alternative management practices within riparian forest buffer systems on surface runoff and sediment loads moving from agricultural production areas across riparian portions of agricultural landscapes into surface drainage features or, depending on local subsurface stratigraphy, to ground water recharge; and (b) to test and validate the Hydrology Component of the Riparian Ecosystem Management Model (REMM). REMM is a field-scale, process-based, computer simulation model that is being developed by an multidisciplinary team of USDA-ARS and University of Georgia scientists at Tifton, GA, and which will permit evaluation of the potential of riparian forest buffer systems for attenuating nonpoint source pollutants from upland agricultural areas.

Expected Results:
This research will provide new scientific and engineering information that will permit development of improved resource management and conservation guidelines for use by Federal and state action and regulatory agencies. Products will include improved hydrologic tools, including computer simulation models, for predicting natural resource and environmental quality responses which can be used in evaluation of current and alternative agricultural management practices. The benefits from these advances include development of improved management practices and sustainable agricultural production systems that are cost effective and that protect and enhance the quality of regional surface and ground water supplies.

Past accomplishments:
Previous research by this investigator and collaborators has demonstrated the impact of extensive floodplain/riparian areas and the surficial stream-channel depositional aquifer systems in determining the hydrologic response, and hence, the potential for transport of sediment and nutrients in streamflow from low-gradient, humid region watersheds. This work has explained the extreme range of seasonal storm response characteristics observed on Coastal Plain watersheds, and has demonstrated the impact of stream channel aquifer systems on the volume of storm runoff, peak rate of discharge, and relative timing of runoff peaks.

Evaluations of the effect of heavily-vegetated floodplain and other nearstream riparian areas on rates of sediment transport and delivery observed within Coastal Plain watersheds demonstrated that riparian areas in the region function essentially as sinks for deposition of materials eroded from adjacent upland agricultural areas, significantly reducing levels of suspended constituents transported in streamflow from Coastal Plain watersheds.

Recent investigations of hydrograph time parameters for flatland watersheds have provided relationships for determining hydrograph time parameters required for engineering design applications in low-gradient drainage basins. Other recent research has provided rainfall-streamflow relations needed by Federal action agencies for water quality screening and assessment required for water resource planning and management responsibilities in Coastal Plain region of the southeastern US.

His most recent research showed that riparian forest buffer systems under standard forestry management and harvest practices significantly reduce water and sediment movement from agricultural areas, thereby providing economic return to the landowner while maintaining the intended environmental enhancement function of the buffer system.