Original paper

A GIS approach to define the hydro-geomorphological regime for instream flow requirements using geomorphic response units (GRU)

Lindenschmidt, Karl-Erich; Long, Jeff


Instream Flow Requirement studies typically determine riverine flow needs based on the hydrology, water quality, connectivity, biology and geomorphology of lotic systems. This paper focuses on the geomorphology component, which can be explained as the processes that contribute to riverine channel structure, through the interaction of the hydrology of the system and the substrate through which the river bed is cut. We assume that the hydrological response is purely due to geomorphological effects, a statement first proposed and given its theoretical framework by Rodriguez-Iturbe and Valdes (1979). The theory states that the morphology of the network structure has a major contribution to the hydrologic response of a river and its basin. This study focuses on GIS and multi-variate derived geomorphic response unites (GRUs) to determine and classify groups of reaches along a riverine system that exhibit similar geomorphological structure. The model assumes that many of the factors utilised in other models can be captured and incorporated into higher-order variables thus reducing the need to measure many variables into a parsimonious dataset. Further validation of the model will provide better understanding of “like-for like“ habitat and allow better assessment of compensation requirements. Advantages of such an approach are (i) its reliance solely on parameters extracted from the stream network and stream characteristics and (ii) the direct relationship between GRUs and critical instream habitat. The model was developed for the Little Saskatchewan River in Manitoba, Canada.