Wyznaczenie wielkości opadu efektywnego i przepływów maksymalnych w małych zlewniach niezurbanizowanych

This paper presents application of HEC-HMS model that was used to calculate a pick flow for a small, non-urban catchment. The Debina catchment with 47.8 km2 area is located in a central part of Gnieznienskie Lakeland region. In this area Luvisol made from moraine materials (50%) and Brunic Arenosol (23%) under forest predominates. The rest of the catchment is covered by Histic Glyesol and Histosol. Obtained data from Corine Land Cover was used to quantify landuse structure in the studied catchment. The results showed that 77% of area is used as an arable land and around 20% as a belt of woodland with greens. Calculations of the effective rainfall were performed using four methods: SCS curve number (CN), Green and Ampt, initial and constant and deficit and constant method. The scale of the effective rainfall calculated by these four methods implemented in HEC-HMS hydrologic model showed a large divergence. Significant differences of the effective rainfall values translate into discharges values which are calculated on their basis. The peak flow of probability of exceedance of 10% in the Debina stream may have values which oscillate between 4.1 m3.s-1 and 0.6 m3.s-1 depending on the effective rainfall determination method. In case of 1% rainfall, peak discharges oscillate between 11.9 m 3.s-1 and 0.8 m 3.s-1. Flows calculated using SCS CN method are comparable to the values of maximum flow calculated using empirical formulas (Stachy and Fal and Debski and Stachy) which amount Q(1%) = 6.6 m3.s-1 and Q(10%) = 3.8 m3.s-1. Calculations of the peak flows in the Debina catchment indicate that the selection of methods that determine effective rainfall as a component of rainfall-runoff model has a significant influence on the maximum flow values.