ESTIMATION OF SCS RUNOFF CURVE NUMBER FOR AGRICULTURAL RESERVOIR WATERSHED BY ANALYSIS OF RESERVOIR OPERATION RECORD

摘要

The rainfall-runoff potential of a agricultural reservoir watershed was studied based on SCSrn(Soil Conservation Service; now the NRCS, Natural Resources Conservation Service, USDA)rnrunoff curve number (CN) technique. The observed precipitation and the reservoir operationrndata such as irrigation amount, reservoir storage, river maintenance requirement, and floodrncontrol discharge were collected for ten years period and analyzed. The runoff of each stormrnevent from the watershed of the reservoir was estimated by reservoir water balance modelrnusing reservoir operation records. The maximum retention, S, for each storm event fromrnrainfall-runoff pair was estimated for selected storm events. The estimated S values werernarranged in descending order, then its probability distribution was determined as log-normalrndistribution, and associated CNs were found about probability levels of Pr=0.1, 0.5, andrn0.9, respectively. CNs determined from observed rainfall-runoff estimated by reservoir waterrnbalance analysis was compared to the suggested CNs by the method of SCS-NEH4. ThernCN-Ⅱ estimated from water balance analysis in this study were 80. However, the CN-Ⅱ, whichrnwas determined based on hydrologic soil group, land use was 67 indicating that actual runoffrnpotential of the reservoir watershed is higher than that evaluated by SCS-NEH4 method. Thernresults showed that watershed runoff potential for large scale agricultural reservoirs needs tornbe examined for efficient management of water resources and flood prevention.