Methodology for flood frequency estimations in small catchments

Abstract. Estimations of flood frequencies in small catchments are difficult due to a lack of measured discharge data. This problem is usually solved in the Czech Republic by hydrologic modelling when there is a reason not to use the data provided by the Czech hydrometeorological institute, which are quite expensive and have a very low level of accuracy. Another way is to use a simple method which provides sufficient estimates of flood frequency based on the available spatial data. A new methodology is being developed considering all important factors affecting flood formation in small catchments. The relationship between catchment descriptors and flood characteristics has been analysed first to get an overview of the importance of each considered descriptor. The results for different descriptors vary from a highly correlated relationship of an expected shape to a relationship which is opposite to that expected, mainly in the case of land use. The parameterisation of the methodology is also presented, including the sensitivity tests on each involved catchment descriptor and cross-validation of achieved results. In its present form, the methodology achieves an R_adj² value of about 0.61 for 10- and 0.60 for 100-year return periods.