HYDROLOGICAL PICTURE OF NISAVA TRANS- BOUNDARY CATCHMENT

This work focuses on hydrographic and hydrological specific of Nisava River. It uses all hydrometric and cartographic information for the Bulgarian part of the catchment. Transboundary catchment of Nisava River includes four sub-basins, which are trans-borders too. There are a lot of karst areas in the river basin. The drainage density is 1.09 km/km(2). Water resources of Nisava River are 170 million m(3). They vary between 300.0 and 84.0 million m(3). The period of high water appears in March/April and finishes in June. The frequency of monthly maximum is biggest in April or May. The monthly minimum appears most often in September or October. Floods in the catchment of the river Nisava are most often in March, May and June. Some of the rivers lose its waters in the karst areas and dries up during the summer. The average number of days with ice is between 10 and 70. The chemical and ecological status of river water is good.