Distributed watershed modeling of design storms to identify nonpoint source loading areas

• Published in: Journal of environmental quality Vol. 28; no. 2; pp. 388 - 397
• Main Authors: Endreny, T. A., Wood, E. F.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Madison, WI American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America 01-03-1999; Crop Science Society of America; American Society of Agronomy
• Subjects: Agricultural management; Agronomy. Soil science and plant productions; Applied sciences; Basins; Biological and medical sciences; Design engineering; Design storms; Dynamics; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environment; Exact sciences and technology; Farmlands; Fundamental and applied biological sciences. Psychology; Groundwaters; Hydrology; Management; Mathematical models; Natural water pollution; Pollution; Pollution, environment geology; Precipitation; Runoff; Soil and water pollution; Soil science; Statics; Storms; Stress concentration; Water quality; Water treatment and pollution; Watersheds; Oklahoma; United States; North America; America; Water saturation; Cartography; Nonpoint source; Variable region; Cultivated soil; Modeling; Case study; Runoff; Watershed; Pollution source; Water pollution; Dynamic model; Ground water
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq1999.00472425002800020004x

Watershed areas that generate nonpoint source (NPS) polluted runoff need to be identified prior to the design of basin-wide water quality projects. Current watershed-scale NPS models lack a variable source area (VSA) hydrology routine, and are therefore unable to identify spatially dynamic runoff zones. The TOPLATS model used a watertable-driven VSA hydrology routine to identify runoff zones in a 17.5 km(2) agricultural watershed in central Oklahoma. Runoff areas were identified in a static modeling framework as a function of prestorm watertable depth and also in a dynamic modeling framework by basin response to 2, 10, and 25 yr return period 6 h design storms. Variable source area expansion occurred throughout the duration of each 6 h storm and total runoff area increased with design storm intensity. Basin-average runoff rates of 1 mm h(-1) provided little insight into runoff extremes while the spatially distributed analysis identified saturation excess zones with runoff rates equaling effective precipitation. The intersection of agricultural landcover areas with these saturation excess runoff zones targeted the priority potential NPS runoff zones that should be validated with field visits. These intersected areas, labeled as potential NPS runoff zones, were mapped within the watershed to demonstrate spatial analysis options available in TOPLATS for managing complex distributions of watershed runoff. TOPLATS concepts in spatial saturation excess runoff modeling should be incorporated into NPS management models.