Assessing Runoff using Modified SME-CN Method for a Drained Forest Watershed on North Carolina Atlantic CoastalPlain

摘要

The NRCS curve number (CN) method is one of the widely used event-based models for estimating runoff using readily available watershed parameters and rainfall data from upland agricultural catchments. However, there is a limited literature on application of the CN method on drained forest systems. We propose herein an application of modified SME (Sahoo-Misra-Eldo)-CN method developed/tested in earlier studies. In this study the SME method was further modified by redefining the maximum potential retention to assess outflow (subsurface drainage + surface runoff) for a pine forest watershed with a high water table soil drained by 100-m apart ditches in Coastal North Carolina. We used measured rainfall and runoff data for 29 events from 1991-1993 periodfor the study watershed. Border conditions like initial abstraction, CN, percentage of saturated areas in the basin "a " were parameterized to assess subsurface drainage and surface runoff in the analysis performedfor all runoff events. Assuming measured outflow from the drained watershed was dominated by only subsurface drainage, computed event outflow using the modified SME-CN model showed a good agreement with the observed data (without extreme rainfall events) for the drained study watershed, yielding Nash-Sutcliffe coefficient of 0.97, R~2 = 0.98, and RMSE = 3.46 mm. These results were better than those obtained from the original SCS-CN method as well as the earlier reported study using modified-SCS work on tile-drained agricultural watershed inmid-West U.S. The SME-CN model, sensitive to input parameters like PET5, P, CN and a, need multi-site-year validation to gain more confidence.