SPECIFICS IN DETERMINATION AND PROVISION OF ECOLOGICAL FLOW IN THE RIVERBEDS AFTER COMPLEX AND SIGNIFICANT DAMS IN BULGARIA

Abstract

Water resource of a given river basin is the main component of the ecosystem and water resources management system as well. Ecological flows are considered within the context of the Water Framework Directive (WFD) as �a hydrological regime consistent with the achievement of the environmental objectives of the WFD in natural surface water bodies as mentioned in Article 4(1). The so-called Heavily Modified Water Bodies (HMWB) or �regulated rivers� have modified flow, which is influenced by reservoir compensation releases and management. National Institute of Meteorology and Hydrology (NIMH) has responsibility and contributed to the implementation of the Eflow concept in Bulgaria. For the needs of the Ministry of Environment and Water (MoEW), a hydrological regionalization and a calculation scheme for the minimum acceptable flow in the rivers on the territory of Bulgaria are developed. In this report are represented the following researches: up-to-date assessment of the minimum acceptable flow (MAF) in the riverbeds after the complex dams, according to the Water Law (WL), a comparative analysis with the current state and definition of recommendations in support of the MoEW and the Basin Directorates (BD). The specificity of each reservoir in determining the MAF, the change during drought, etc. are highlighted. In the regulated rivers, the MAF is for the purpose of water ecosystems, groundwater and drinking water supply, wetlands, etc. The NIMH approach is applied and an up-to-date assessment of the MAF from the 52 complex and significant dams from Appendix 1 of the WL is carried out. The assessment is based on the results of hydrological development for the evaluation of the annual average flow and minimum monthly flows with 95% probability of exceedance of the own water catchment of dams. A comparative analysis was carried out between up-to-data assessed minimum acceptable flow (determined by NIMH) and current released MAF (by MoEW). The risks for ensuring the ecological flow are identified. Recommendations are given regarding the determination of ecological flow, definition of a minimum lower threshold, the specifics of reservoirs along the Black Sea or those for drinking water supply, etc. The research supports the MoEW and BD in determining the ecological flow in the riverbeds after the complex reservois, implementation of the Program of measures and the Eflow concept in Bulgaria.