The Hydro-Morphological Index of Diversity: a planning tool for river restoration projects

Flood protection and river engineering projects nowadays have to improve also the ecological condition of the river. Very often the space is not available for a full restoration of the river morphology. Therefore the hydro-morphological heterogeneity has to be optimized within certain space constraints. For such projects a tool for practitioners would be very helpful which allows to quantify the habitat heterogeneity enhancement for different project alternatives and to recommend the best alternative in view of eco-morphological perspective. In his research project Dr. Walter Gostner proposed a new Hydro-Morphological Index of Diversity (HMID), which allows a quantitative statement of the enhancement of habitat heterogeneity during the comparison of different project alternatives in the framework of river engineering projects. Compared to other existing habitat indices, which are mostly based on visual, qualitative assessment in the field and therefore influenced by the subjectivity of the observers, the new HMID is based on statistical parameters calculated by numerical 2D and 3D simulations during project planning and thus can be denoted fully objective. The HMID was developed on the basis of very extensive field campaigns by recording a large amount of hydraulic and geomorphic data as it has been done rarely before. In order to see clearly the hydro-morphological heterogeneity several very contrasting sites from fully natural to very channelized stretches have been analysed on three different gravel bed rivers in the Swiss Pre-alps (Bünz, Venoge, Sense). By comparing the variability of the numerous hydraulic and morphological parameters between the studied stretches a formula for the HMID could be proposed. Dr. Walter Gostner could show that the coefficients of variation of flow velocity and water depth alone are sufficient to obtain a reliable and predictive HMID. With the development of the HMID Dr. Walter Gostner made available a very useful predicting tool to evaluate the ecological potential of river engineering projects