Assessing the Restoration Success of River Widenin

Authors: Sigrun Rohde Felix Kienast Matthias Bürgi

Publish Date: 2004/10/22

Volume: 34, Issue: 4, Pages: 574-589

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Abstract

During the last 200 years many rivers in industrialized countries have been modified by canalization In the last two decades the philosophy of river management has changed considerably and restoration of ecological integrity has become an important management goal One appealing restoration approach is to create “river widenings” that permit braiding within a limited area This study presents a new and efficient framework for rapidly assessing such widening projects and offers a novel method to comparing restored sites with nearnatural stretches stencil technique The proposed framework evaluates spatial patterns of riparian habitat types using landscape metrics as indicators Three case studies from river restoration river widening in Switzerland are presented for demonstration purposesThe method compares restored sites with prerestoration conditions and nearnatural conditions which are assumed to represent the worst and best case states of a river system To take into account the limited spatial extent of the restored sites the socalled “stencil technique” was developed where the landscape metrics of the nearnatural reference sites are calculated for both the entire study area and smaller sections clips The clips are created by using a stencil that has the exact shape and size of the restored area random windowsampling technique Subsequently the calculated metrics for the restored sites are compared to the range of values calculated for the nearnatural data subsetOur studies show that the proposed method is easy to apply andprovides a valid way to assess the restoration success of river widenings We found that river widenings offer real opportunities for establishing riparian habitats However they promote mainly pioneer successional stages and the habitat mosaic of the restored section is more complex than at the nearnatural reference sitesWe thank P Englmaier and F Herzog for helpful feedback on an earlier draft and M W Doyle A R G Large M G Turner and two anonymous reviewers for their extended comments and suggestions which greatly improved the manuscript We are also grateful to C Ginzler for advice in the process of converting aerial photographs to orthophotosThis study is part of the RhoneThurProject funded by the Swiss Federal Research Institute WSL the Swiss Federal Institute for Environmental Science and Technology EAWAG the Swiss Federal Office for Water and Geology FOWG and the Swiss Agency for the Environment Forests and Landscape SAEFL

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