Evolution and application of instream flow methodologies to small hydropower developments: an overview of the issues

ethods for evaluating instream flow needs have evolved over the last 30 years resulting in two categories which are defined as “standard-setting” and “incremental”. Standard-setting methodologies refer to those measurement and interpretative techniques designed to generate a flow value(s) which is intended to maintain the fishery at some acceptable level. Incremental methodologies on the other hand are organized and repeatable processes by which: (1) a fishery habitat/streamflow relationship and the hydrology of the stream are transformed into a baseline habitat time series; (2) proposed water management alternatives are quantified and compared with the baseline; and (3) project operating rules are negotiated. A hierarchical approach to small-hydro instream flow analysis is suggested.