Estimation of environmental flows in semi-natural lowland rivers – the narew basin case study

This paper discusses a new environmental flow method based on the adapted building block approach. A four-step procedure is outlined in this paper: (1) selecting biota of interest and organizing a team of specialists (2) selecting river reaches of interest (3) defining flow requirements of selected biota (4) defining environmental flow indicators The focus is placed on two elements of river and wetland ecosystems: fish and floodplain wetland vegetation. The method is applied to identify changes in the environmental flow indicators between 1976-83 (“past”) and 2001-08 (“present”) in 16 selected river reaches of the Narew basin, a large semi-natural lowland catchment situated in northeastern Poland. The results indicate that hydrological conditions for fish and floodplain wetland vegetation were significantly better in the past period compared to the present.