|Nejadhashemi, Amir - UNIV. OF MARYLAND|
|Shirmohammadi, Adel - UNIV. OF MARYLAND|
|Montas, Hubert - UNIV. OF MARYLAND|
Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 12, 2006
Publication Date: N/A
Interpretive Summary: Water quality issues relating to pollutant transport by storm runoff are critical environmental concerns. Additionally, flooding is a common and widespread natural hazard that causes loss of life as well as billions of dollars of property damage each year. To develop effective approaches for utilization of water resources and for resolution of critical environmental issues, natural resource professionals and policy makers need more comprehensive information on the storage and movement of storm water and on the primary flow paths for pollutant transport. Specific needs include better understanding of the partitioning of storm flows into surface and groundwater, or baseflow, components B especially at larger spatial scales. The objective of this study was to develop improved methods for partitioning streamflow from ungaged watersheds into the respective stormflow and baseflow components. A prior study by the authors evaluated forty existing approaches to streamflow partitioning, concluding that an approximate method developed by Boughton produced the most consistent results. Accuracy of the method was determined to be dependant upon the capability to estimate the time when surface runoff ceased to occur and on estimation of a proportioning coefficient that is a function of watershed physical and hydrologic characteristics. In this paper, an automated Boughton-type approach to hydrograph separation was tested on twelve years of flow data from an instrumented, field-sized watershed and determined to be 87% accurate. An equation was also developed relating the required proportioning coefficient to key parameters including storm rainfall duration and intensity. The improved methods developed provide natural resource and environmental professionals with better capabilities for estimating the relative proportioning of streamflows and permit more accurate determination of the magnitudes of the respective flow components from unmonitored watersheds. This information should support more effective management and planning approaches for wise utilization of water resources, for reduction of damages and economic losses due to floods, and for reductions in the amounts of nutrients and other water-borne environmental pollutants transported in storm runoff. The methods also provide improved storm flow partitioning capabilities required for adaptation into computerized natural resource and environmental quality models currently being developed for use with Geographic Information Systems (GIS) approaches on large spatial scales.
Technical Abstract: Evaluating the relative amounts of stored or moving water through the different components of the hydrological cycle is required for precise management and planning of water resources. An important aspect of this evaluation is the partitioning of streamflow into surface and baseflow components. A prior study evaluated forty different approaches for hydrograph-partitioning on a field scale watershed in the Coastal Plain of the Southeastern United States and concluded that the Boughton method produced the most consistent and accurate results. However, its accuracy depends upon the proper estimation of: 1) the end of surface runoff, and 2) the fraction factor (') that is a function of many physical and hydrologic characteristics of a watershed. Proper identification of the end of surface runoff was accomplished by using a second derivative approach. Applying this approach to twelve years of streamflow data proved to be accurate 87% of the time. Estimation of the ' value was accomplished in this study using two steps; first, alpha was fitted to individual hydrographs, and, second, a regression equation that determines these alpha values based on watersheds hydrologic characteristics (e.g. rainfall, evaporation) was developed. Using these strategies improved the streamflow partitioning method=s performance significantly.