Summary:

Erosion processes apart from distruction of upper layer of soil, influences morphology and hydrology of streams. Devastation of upper soil layer decreases basin retention what increases surface runoff, flood discharges and decreases low flows. Particularly bad damages in mountains basins are caused by heavy rains that have local extent but are very violent. The Wielka Puszcza basin is located on two natural regions: Podkarpacie Właściwe and Beskid Mały that belong to the Karpaty district. The basin area amounts 19,30 km². Density of hydrographical network is 1,60 km⋅km^-2, slope index 0,3102. Mean height attaines 507,5 m npm. The basin has forestry degree 81,65%, and indicator of forestry development 0,87. In the investigated basin prevail slopes above 30% (62,1%) and 20-30% (20,7%). It is lack of slopes of 0- 3%. The mean slope of the basin is 25,47%. In land use prevail forests (81,65%). There is 16,54% of arable lands, and grasslands cover 1,81% of the area. The cross sections of the channel and discharge intensity curves before flood and after flood that took place on 28 August 2005 were presented. Disasterous flows caused significant cross section area, lowering channel bottom of about 0,5 m. The change of flow intensity curve took place either.