Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí lâm nghiệp đề tài: Forest watershed runoff changes determined using the unit hydrograph method. | JOURNAL OF FOREST SCIENCE 55 2009 2 89-95 Forest watershed runoff changes determined using the unit hydrograph method V. Cernohous1 P. Kovar2 1Forestry and Game Management Research Institute Strnady Opocno Research Station Opocno Czech Republic Faculty of Environmental Sciences Czech University of Life Sciences in Prague Prague Czech Republic ABSTRACT Unit hydrograph is a basic method to show changes in runoff in the watershed. The investigation of runoff changes was carried out in the U Dvou loucek watershed situated at the summit part of the Orlické hory Mts. East Bohemia. The waveform ordinates of recession limbs of unit hydrographs obtained using a common approach had to be approximated by the least-squares method. Final hydrographs reflected both drainage treatment and forest stand growth influencing the runoff from the watershed. Both factors increase culmination in synergy and reduce runoff on the recession limb of the hydrograph. We confirmed increased maximum runoff taking up 25-30 of the total runoff time when waterlogged sites were drained. The culmination increased by mm hour indicates the runoff increased by 2-8 m3 ha hr. Keywords forest watershed drainage runoff double-mass curve unit hydrograph Unit hydrograph is meant to describe basic runoff components reflecting changes in watersheds. Waveforms of hydrographs shape of runoff curve depend on the particular duration of rainfall and amount of precipitation since both physical and terrain conditions of watershed are considered constant. Therefore when the watershed changes in terms of these stable conditions a subsequent change in hydrograph showing a difference of runoff is expected as well Sherman 1932 . That was the reason why the described method has been often used to develop hydrological models Chow et al. 1988 Kovar 2000 . Chow et al. 1988 described the unit hydrograph as a simple linear model that can be used to derive the hydrograph resulting from any amount of excess rainfall though
