Mountain Hydrology Workshop, Bucharest, Romania, 26 September 2003 FORMATION AND REGULARITY OF THE RIVER FLOW IN A FORESTED MOUNTAIN REGION G. Gergov1, E. Rafailova2 1 2 National Institute of Meteorology and Hydrology, Sofia, Bulgaria, [email protected] University of Forestry, Sofia, Bulgaria, [email protected] The hydrological role of the forest ecosystems regarding formation of the river flow has been a subject of various studies performed by numerous researchers during the past years. The review of the studies performed about the role of the forest in hydrological phenomena leads to the next two basic questions, not sufficiently revealed – the role of preliminary saturation in formation of the river flow and the formation of sediment load of rivers on forest mountain lands. The aim of this paper is to fill this gap partially. The studies have been carried out on the basis of rich hydro-meteorological data information collected in the ecological station, situated in “Undola” place, Rila Mountain in Bulgaria. The preliminary wetness of the sample plots has been estimated on the basis of the hodographs of the water discharges for several years by means of the analysis of the typical modes. As a result a multi-parametric relationship (co-variance) is composed, which reveals the formation of river floods depending on the preliminary saturation of the water catchments area and precipitation. The co-variance can be used for modeling and predicting the formation of outflow of the basin depending on its preliminary damping.