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Surface Runoff Modelling Using GIS and Remote Sensing. Case study in the Krapinica catchment, Croatia

A rainfall-runoff analysis and the evaluation of the SCS curve number method, using HEC-1 hydrologic model have been carried out in order to estimate the surface runoff from the Krapinica catchment. The rainfall analysis showed that the rainfall time series are consistent indicating that there were no significant natural changes or changes induced by man in the gauging stations and in the catchment. The rainfall gauging stations are well correlated showing uniform spatial distribution of the rainfall in the area. Correlation also depends on the time scale i.e. correlation coefficients are much higher on the monthly than the daily basis while it decreases again on the annual basis. The streamflow data shows very little variability and is mainly ruled by the baseflow. The correlation between rainfall and runoff is not well explained by the simple linear regression model used i.e. correlation coefficients between the two variables are very small, depending on the time scale. They increase as the time scale used increases. The runoff capacity of the catchment is described with the runoff coefficient on the annual and the seasonal basis. On the seasonal basis the cathcment shows better response to the rainfall having higher runoff coefficients than on the annual bases. To estimate the surface runoff from the catchment, the SCS czrve number method and the HEC-a hydrological package has been used. Three sets of curve numbers have been estimated, depending on the data used for hydrologic soil group classification (hydrologic groups based on the soil properties, soil properties corrected for the slope classes and terrain mapping units). The estimation of the direct runoff volume therefore varies for all three cases. Depending on the rainfall distribution used, and curve numbers, the runoff volume is either underestimated or overestimated. When using curve numbers for normal antecedent moisture conditions, the calculation results with the underestimation of the runoff, while the wet antecendent moisture condition results with the overestimation of the runoff volume.

Krapinica catchment; rainfall-runoff; SCS CN method; HEC-1 hydrologic model; surface runoff; hydrologic soil groups; rainfall distribution

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