Abstract
The variability of the curve number (CN) and the retention parameter (S) of the Soil Conservation Service (SCS)-CN method in a small agricultural, lowland watershed (23.4 km2 to the gauging station) in central Poland has been assessed using the probabilistic approach: distribution fitting and confidence intervals (CIs). Empirical CNs and Ss were computed directly from recorded rainfall depths and direct runoff volumes. Two measures of the goodness of fit were used as selection criteria in the identification of the parent distribution function. The measures specified the generalized extreme value (GEV), normal and general logistic (GLO) distributions for 100-CN and GLO, lognormal and GEV distributions for S. The characteristics estimated from theoretical distribution (median, quantiles) were compared to the tabulated CN and to the antecedent runoff conditions of Hawkins and Hjelmfelt. The distribution fitting for the whole sample revealed a good agreement between the tabulated CN and the median and between the antecedent runoff conditions (ARCs) of Hawkins and Hjelmfelt, which certified a good calibration of the model. However, the division of the CN sample due to heavy and moderate rainfall depths revealed a serious inconsistency between the parameters mentioned. This analysis proves that the application of the SCS-CN method should rely on deep insight into the probabilistic properties of CN and S.
Highlights
IntroductionFor the estimation of design floods and volumes, often, event-based hydrological models are applied
For the estimation of design floods and volumes, often, event-based hydrological models are applied.As inputs, they often use the components of rainfall, infiltration, soil properties, land use, etc
To observe the curve number (CN) behavior in other catchments, similar investigations should be carried out using empirical CN values
Summary
For the estimation of design floods and volumes, often, event-based hydrological models are applied. As inputs, they often use the components of rainfall, infiltration, soil properties, land use, etc. They often use the components of rainfall, infiltration, soil properties, land use, etc The variability of these components can cause the instability of model parameters. Conservation Service)) to estimate the runoff depth from small catchments It is included in many complex models, e.g., for the estimation of the rainstorm-generated sediment yield [4] or SWAT [5], which predicts the impact of land use on water, sediment and chemicals
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