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SCS Curve Number Loss Model - United States Army

WebbThe multi-stage outlets are nearly identical. Each use a standard 4′ x 4′ box riser and a couple of secondary orifices and/or weirs. The only significant difference is the SCS method needed a 30-inch culvert compared to 18’s … WebbQ=Precipitation excess (runoff) [inches] This allows the ordinates of the UH to be dimensioned based on the precipitation excess (Q), as previously determined by the SCS runoff equation. Convolution: The Heart of TR-20. The unit hydrograph, when dimensioned, tells us what the runoff will be for a single burst of rainfall. high country brewery

Curve Number for Antecedent Moisture Condition-III Calculator

WebbThe SCS Runoff Equation Studies by the SCS resulted in the following empirical relationship for runoff: (P-.2S)² Q=----------- (Q=0 if P<.2S) P+.8S 1000 where S=------- - 10 CN Q=Precipitation excess (runoff) [inches] P=Cumulative precipitation [inches] S=Potential maximum retention [inches] CN=SCS Curve Number WebbIn the SCS method, the time lag tL for the catchment is computed using the following expression: (4.131) where tL is the catchment time lag (h), L is the length of the main stream (m), CN is the SCS runoff curve number, and S is the catchment average slope (m/m). The selection criteria of the CN value are described in NEH-4. WebbTo match the runoff depth given by the SCS runoff equation, the time span must include all times at which runoff will occur. To "see" the entire runoff volume (and the equivalent runoff depth) the time span must end sometime after the end of the storm. For a 24-hour storm, a span of 0-30 hours will generally include all the runoff. how far to melksham