Abstract

The surface water resource determination is an important issue related to most reliable water management, which in some districts of Bulgaria in some periods are not enough. In this aspect, the present work is part of the effort to create an operational tool to assess the annual resource. Annual, because this is one of the periods of planning the water use, on the other hand annual averaging significantly simplifies the water balance equation.
There are several methods in world practice for this purpose: modeling the process “rainfall – runoff”; regionalization in typical water quantities depending on physico-geographic factors; balance approach. The first one require a serious resource of information and time, mainly used to analyze the impact of decay factors and climate change rather than on operational purposes. The method of hydrological regionalization is already operational in use, but as far as it is based on registered river flow, it is important to clarify the influence of anthropogenic factors. The water balance method is widely used for the purposes of the Water Framework Directive, both for the assessment of the water bodies’ resources influenced by human activity, as well as for analysis of pressure and water stress, for water economic balances, for the management of water abstractions and river basins. It applies to WB category “lake” – large dams; WB with resource dependent on technological input from dams or derivations; WB with additional flow of water transfer, etc. Vit is one of the main bays in Northern Bulgaria, combining a mountainous, hilly and plain area, on average in area, presenting relatively well the characteristics of formation of the river flow. There are three significant dams, two irrigation systems, derivations and water transfers and a significant number of smaller consumers. In this sense, the basin is chosen as representative, with the opportunity to demonstrate the methods. The balance method is applied to typical sub-basins for the period 2015 -2017.
As a result, a hydrological evaluation of the surface water resource was made for the selected sub-basins based on the registered flow and the water balance assessment of the surface water resource for the same sub-basins. A comparison was made, conclusions were drawn about the advantages and disadvantages of the methods and their applicability in practice.