Index assessment of the water quality – a case study of Bulgarian rivers

Development and implementation of indexation methods used in the assessment of surface water quality (pollution)
is particularly relevant in recent years. Currently, hydrological practice actively uses several dozen indices. The
existence of so many indices offers the possibility of testing and choosing those that provide a complete and thorough
characterization of the anthropogenic impact as well as the types and forms of pollution inselected rivers in Bulgaria.We
calculated four indices: the Water Quality Index – WQI, the Combinatorial Index of Water Pollution – CIP, the Index
of Water Pollution – IWP and the Index of Oxygen Balance in river water – IOB for the Bulgarian rivers: the Topolnitsa
River, the Vacha River, the Lesnovska River and the Provadiyska River. The results show that complex (index) methods are
very effective methods for assessing the quality of river water, especially in the context of anthropogenic impact. Uniform
indices also allow to compare the water quality status of different rivers and regions.