Summary:

Estimation of influence of land use changes to flood outflows from affor-estation areas of the Krajeńskie Lakeland was worked out basing on SCS-CN method. This method permits calculation from total rainfall a direct runoff as equivalent to effective rainfall. The original SCS-CN method in principle was worked out for catchments of cultivated areas [National Engineering Handbook 1956, 1985]. Present paper is focused on the idea of adaptation original method to forest conditions [Okoński 2006; Okoński, Miler 2010]. The main parameter of this method - CN is a function e.g. of land use. The empirical values of parameter CNemp were calculated basing on hydro-meteorological data of flood outflows at representative catchment of river no. 17-86-1 in the Krajeńskie Lakeland, in the area of the Lipka Forest District, the Biskupice Forest Range. The dependence be-tween empirical value of parameter CNemp and his equivalent's value from original method is a basis idea of adaptation method SCS-CN to characteristics of investi-gated catchment. In consequence it gives then possibility to prognoses how the change of land use, e.g. forest stand reconstruction, afforestation, deforestation, change of field culture, significant change in infrastructure etc., will influence to flood outflows (change to water retention) at a representative areas (a quasi-homogeneous in relation to investigated catchment). The analyzed catchment is located in the III Wielkopolsko-Pomorska Land, the Two Krajeńskie Lakeland Dis-trict, the Wysoczyzna Krajeńska mesoregion (Poland). The investigated catchment cover the area of 182.26ha; 174.02ha - 95% covered by forests, and 8.24ha - 5% arable land and meadows. The dominant soils are rusty soils (about 86% of catchment area) and similar. The dominant forest habitat types are: fresh conifer-ous forest (sign Bśw - in Polish standards) and fresh mixed coniferous forest (BMśw) - about 90% of catchment afforestetion area. Main species at afforestation area is ordinary pine (Pinus sylvestris L.) (93% of forest area). The length of the watercourse no. 17-86-1 channelling the water from the catchment is 1540m. Average daily specific discharge (in investigation period 2004-2006) was on level 6.4 [l•s-1•km-2], and minimum to maximum suitably 2.5 to 25.5 [l•s-1•km-2]. The calculation was conducted using data of 14 measuring rainy flood waves. The values of CNemp ware a base for introducing scenarios how changes of land use at investigation catchment are influencing to flood outflows (changing water retention).