Room for rivers: An integrative search strategy for floodplain restoration

Abstract

River restoration aims to re-establish the ecological integrity of a river ecosystem. However, restoration measures are nowadays mainly a reactive, site-by-site activity, driven by a single driver (e.g. fisheries, flood protection) rather than based on strategic planning. This study presents an integrated search strategy to identify stream systems where present environmental (e.g. natural flow, sufficient bed load material) and socio-economic (e.g. public attitude) template conditions favour the eco-morphological restoration of floodplains and their biocoenosis. This ‘pre-screening’ process reveals where the greatest benefits (judged according to ecological and socio-economic criteria) are to be expected and thus justify further specific and detailed investigations. It helps to set priorities and thus avoid inefficiency. The search strategy presented in this study is designed to perform a pre-screening process at national level. It is based particularly on spatially explicit information and is balanced between accuracy and costs. A hierarchical filter process combines the facilities of GIS with multiple criteria decision analysis (MCDA) to generate restoration suitability maps. The filter process is based on a list of criteria and indicators that capture the ecological key factors that drive floodplain restoration (hydrology, bed load, connectivity, biodiversity, water quality), as well as crucial socio-economic aspects (e.g. flood protection, public attitude) that need to be taken into account when planning for floodplain restoration. Inevitable limitations, arising from the transfer from theory into practice, are accepted, as the search strategy is dedicated to practical application. A modified Delphi process survey of nine river ecology experts was used to assess the appropriateness of each indicator and to estimate the single indicator suitability function. We used ModelBuilder 1.0a (an ArcView extension) to integrate different data layers into a single Ecological Restoration Suitability Index (ERSI) layer. The practical application of the integrative search strategy for floodplain restoration is illustrated through a case study from the Rhône-Thur Project in Switzerland.