Submitted to: Soil and Water Conservation Society
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2006
Publication Date: October 11, 2006
Citation: Bonta, J.V., Hicks, N.S., Morrison, M., Shipitalo, M.J., Owens, L.B. 2006. Potential use, limitations, and research needs for duration curves for evaluating the effectiveness of land management practices [abstract]. Soil and Water Conservation Society Meeting, "Managing Agricultural Landscapes for Environmental Quality - Strengthening the Science Base". Oct. 11-13, 2006, Kansas City, MO. Technical Abstract: Evaluations of changes in watershed behavior due to the implementation of land management practices are difficult because of scanty data, subtle watershed responses, and nonuniform responses through the range of stream flows. Duration curves (DCs), which are plots of percent of time that a flow, concentration, or load is exceeded, can be used to evaluate the effectiveness of conservation practices and to establish a TMDL. DCs can account for uncertainty in some relationships between flow and concentration, and stream-flow variability found in nature. DCs are a tool that can supplement watershed modeling, and they can sometimes be used when models are incapable of simulating watershed constituent loads. We used data from ARS and other experimental watersheds to explore factors that affect the construction of DCs such as sampling interval of data, incremental flow data, minimum number of water samples required, minimum number of years of runoff data, positive and negative slopes of regressions, and piecewise non-monotonic regressions. Experimental-watershed data are useful because of the short sampling interval of data, and the long watershed hydrology and water-quality records. Our analysis indicates that the log-normal distribution can be used to represent the flow duration curve in some instances. DCs can also be used to evaluate watershed model outputs. Two proposed methods of using DCs for quantifying effectiveness of a land-management practice are presented: 1.) as a measure of frequency reduction of a given flow, concentration, or load; and 2.) as a reduction of a flow, concentration, or load for a given frequency. Research needs and potential applications of the DC method are presented.