Sensitivity of SCS Models to Curve Number Variation¹

Abstract

The Soil Conservation Service (SCS) models, including the TR‐20 computer program and the simplified methods in TR‐55, are widely used in hydrologic design. The runoff curve number (CN), which is an important input parameter to SCS models, is defined in terms of land use tretments, hydrologic, condition, antecedent soil moisture, and soil type. The objective of this study was to evaluate the sensitivity of the SCS models to errors in CN estimates. The results show that the effects of CN variation decrease as the design rainfall depth increases, such as for the larger storm events. The value and use of the sensitivity curves are demonstrated using a comparison of Landsat and conventionally derived curve numbers for three watersheds in Pennsylvania.

Are estimates of catchment response time inconsistent as used in current flood hydrology practice in South Africa?

“…Various researchers (e.g. Bondelid et al 1982;McCuen et al 1984;McCuen 2009) demonstrated that as much as 75% of the total error in estimates of peak discharge could be ascribed to errors in the estimation of time parameters. Gericke and Smithers (2014) showed that the underestimation of time parameters by 80% or more could result in the overestimation of peak discharges of up to 200%, while the overestimation of time parameters beyond 800% could result in maximum peak discharge underestimations of up to 100%.…”

Review of methods used to estimate catchment response time for the purpose of peak discharge estimation

“…Consequently, the resulting peak discharges will be overestimated by between 30% and 50% (McCuen 2009). Bondelid et al (1982) indicated that as much as 75% of the total error in peak discharge estimates could be ascribed to errors in the estimation of time parameters. In addition, McCuen (2005) highlighted that there is, in general, no single time parameter estimation method that is superior to all other methods under the wide variety of climatological, geomorphological and hydrological response characteristics that are encountered in practice.…”

The influence of physical and geographical catchment parameters and precipitation characteristics on the runoff time of concentration

“…Według Bondelid i in. [4] błędnie oszacowane parametry związane z czasem reakcji zlewni mogą generować nawet 75%-owy błąd w wartości przepływu w kulminacji. Dlatego czas koncentracji należy szacować porównując różne metody i wybierając wartość optymalną w zależności od charakterystyki zlewni.…”