Defining environmentally acceptable flow downstream intake structures in Croatia

Determining minimum water flows that will continuously run through a natural channel downstream of a water intake (Q0) is a multidisciplinary problem. It is, however, not approached in a multidisciplinary way in most countries. This paper offers an overview of the main methods and proposes a practical and environmentally more acceptable way of determining the retained flow, namely the environmentally acceptable flow (EAF). It is proposed that until the conditions are created for use of more complex methods and/or biological response techniques, the EAF be defined by determining whether the retained flow is sufficient for sustaining and developing indigenous wildlife in the streams by ensuring of the essential living conditions for the bioindicator species. The proposed bioindicators are characteristic fish populations of a specific type of stream and stream reaches. Being the final link in the ecological food chain, fish species are reliable indicators of bioecological balance in a stream.