Ocena wpływu zmian użytkowania terenu na odpływy wezbraniowe przy użyciu metody SCS-CS

Estimation of influence of land use changes to flood outflows from areas of the Roztocze Srodkowe and of the Krajenskie Lakeland were 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. Present paper is focused on the idea of adaptation original method to forest conditions. 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 catchments. The dependence between 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 investigated 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 first analyzed catchment of the Krynica River (area 19.1 km(2), afforestation 49.3%) is representative for the,Tomaszow Lubelski Forest Division and quasi-representative to the Roztocze Srodkowe (Poland). The area of catchment is situated within the following units: macroregion - Roztocze, mesoregion - Roztocze Srodkowe; this area belong to IV Mazowiecko-Podlaska Land. On area of the Tomaszow Lubelski Forest Division predominate the rusty soils (42.65%) as well as the brown soils (26.51%). Associations of beech forests and oak-hornbeam forests predominate. Pine is the dominant species, covering 55.37% forested area, beech is found at 19.70%, oak at 11.07%, alder at 3.49%, fir at 3.24%, hornbeam at 1.73%, birch at 2.14% and larch at 1.19%, while other species constitute a highly valuable admixture in the biocenosis. On area of investigated catchment granulometric composition is following: loose sand 70%, loamy sand 15% and loamy sand on loamy gravel 15%. Average daily specific discharge (in investigation period 2009-2010) was on level 3.4 [1.s-1.km -2], and maximum to minimum suitably 17.2 to 1.0[1.s-1.km -2]. The second analyzed catchment of the river no. 17-86-1 is located in the III Wielkopolsko-Pomorska Land, the Two Krajenskie Lakeland District, the Wysoczyzna Krajenska 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 coniferous forest (sign Bsw - in Polish standards) and fresh mixed coniferous forest (BMsw) - about 90% of catchment afforestetion area. Main species at afforestation area is ordinary pine (Pinus sylvestris L.) (93% of forest area). Average daily specific discharge (in investigation period 2004-2006) was on level 6.4[1.s-1.km -2], and minimum to maximum suitably 2.5 to 25.5[1.s-1.km -2]. The calculation were conducted using data of measuring rainy flood waves. The values of CNemp ware a base for introducing scenarios how changes of land use at investigation catchments are influencing to flood outflows (changing water retention).