Identification of the Relationship between Rainfall and the CN Parameter in Western Carpathian Mountain Catchments in Poland

Abstract

The aim of this study was to identify the form of the dependence describing the relationship between rainfall (P) and the curve number (CN) parameter using the Natural Resources Conservation Service (NRCS-CN) method in the mountain catchments of the Western Carpathians. The study was carried out in 28 catchments areas in the Western Carpathians in the Upper Vistula Basin, Poland. The study was conducted in the following stages: determination of the volume of the direct runoff using the NRCS-CN method, determination of the P–CN relationship using asymptotic functions, kinetic equation and complementary error function; determination of the volume of the direct runoff from the catchment area, accounting for the correction of the decline; determination of the value of the efficiency coefficient of the analysed models. On the basis of the conducted study, a strong relationship was found between the direct runoff and the rainfall that caused it. The study showed that the empirical values of the CN parameter differed from the values determined on the basis of the volume of rainfall and runoff. The vast majority of study catchments were characterised by a standard P–CN relationship. The kinetic model was found to be the best model to describe the P–CN relationship. The asymptotic model showed the greatest stability for high rainfall episodes. It was shown that the application of the catchment slope correction improved the quality of the NRCS-CN model.