TECHNOLOGICAL APPROACH FOR WATER RESOURCES DETERMINATION IN ISKAR RIVER WATER BODIES.

The main goal of presented study is a demonstration of technological approach to determine the water resources of surface water bodies, using a sparse hydrological monitoring network not covering many of them. Resource of the water body is a flow formed in the catchment area above the studied one including the additional inflow in the frame of the same water body. Practically the flow is changing in each sector of the water body but average annual resources are specified at the final section. The water resources for the river water bodies are determined using information from the monitoring network of the National Institute of Meteorology and Hydrology (NIMH) for the Iskar River. The investigation is preceded by hydrological analysis of the information: the referent period, homogenous and suitable data set selection for statistical procedures reflecting the actual conditions in the surface water. The transfer of information from observed river stretches to non-observed ones requires a special hydrological investigation and methodological decision. In the world practice there are two main methodological approaches for flow determination in the nonobserved river stretches - regionalization of characteristic flows depending on catchment characteristics and a balance method. The balance method requires a very big amount of information linked to the various water consumptions as: water supply, irrigation, power engineering, reservoir management and water accumulation very often missing or not reliable. That is the reason for the acceptance of regionalization of characteristic flows as a suitable approach for Bulgarian conditions based on the real and reliable measured data from the monitoring network in NIMH. In the case of water accumulation after dams, where practically the flow is interrupted, the water resource determination can be based only on the information from reservoir management authorities (if this information exists). Iskar River has a biggest watershed in the Danube catchment area in Bulgaria, where the capital Sofia is located, with important economic significance and big anthropogenic impacts on the flow regime. In the study is used a GIS information for the water bodies delineation presented by the Ministry of Environment and Water. [ABSTRACT FROM AUTHOR]