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Room for Rivers: an Integrative Search Strategy for Floodplain Restoration

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Room for Rivers: an Integrative Search Strategy for Floodplain Restoration Landscape and Urban Planning 78 (2006) 50–70 Room for rivers: An integrative search strategy for floodplain restoration S. Rohde a,∗, M. Hostmann b, A. Peter c, K.C. Ewald d a Swiss Federal Institute for Forest, Snow and Landscape Research WSL/ETH, 8903 Birmensdorf, Switzerland b Swiss Federal Institute for Environmental Science and Technology EAWAG/ETH, 8600 D¨ubendorf, Switzerland c Swiss Federal Institute for Environmental Science and Technology EAWAG/ETH, 6047 Kastanienbaum, Switzerland d Nature and Landscape Protection, Swiss Federal Institute of Technology (ETH), 8092 Zurich, Switzerland Received 25 March 2004; received in revised form 30 May 2005; accepted 30 May 2005 Available online 21 November 2005 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 Rhone-Thurˆ Project in Switzerland. © 2005 Elsevier B.V. All rights reserved. Keywords: River restoration; Priority setting; Restoration suitability; Indicators; Multiple criteria decision analysis; GIS ∗ Corresponding author. Tel.: +41 1 739 23 69; fax: +41 1 739 22 15. E-mail address: [email protected] (S. Rohde). 0169-2046/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.landurbplan.2005.05.006 S. Rohde et al. / Landscape and Urban Planning 78 (2006) 50–70 51 1. Introduction Answering these questions is not easy. They are key questions that arise also in related planning processes, River floodplains are widely acknowledged as e.g. the location of landfills (Kontos et al., 2003), the biodiversity hotspots (Malanson, 1995; Naiman et al., evaluation of alignments of motorways (Sadek et al., 1993; Ward et al., 2002). However, river canalisations 1999) or the design of reserve networks (Villa et al., have led to major ecological degradation (Erskine, 2002). 1992; Nilsson and Svedmark, 2002; Pedroli et al., 2002; Petts and Calow, 1996). Since the negative impacts of river canalisation have become more and more 2. Aims and scope apparent, several river restoration projects have been realized, for example, in The Netherlands (Neilsen, The integrative search strategy presented in this 2002; Nienhuis et al., 2002) and Switzerland (Rohde et paper is a framework for pro-active planning that moves al., 2004), the UK and Denmark (Holmes and Nielsen, away from the traditional view of river restoration as 1998). a reactive, site-by-site activity towards a framework Ecological restoration is the process of assisting the where restoration occurs at a landscape and catch- recovery of an ecosystem that has been degraded, dam- ment scale and becomes an important, strategic com- aged or destroyed (SER and Policy Working Group, ponent of landscape and regional planning as required, 2002). At present, restoration sites are often selected e.g. by the Water Framework Directive of the Euro- opportunistically and on an ad hoc basis rather than pean Union (Naveh, 1994; Webb, 1997). It focuses according to a strategic planning process (Clarke et on the restoration of riparian floodplains by widening al., 2003; Hobbs and Norton, 1996; Lamy et al., rivers or re-allocating flood levees to allow river braid- 2002). In many cases, restoration projects are not ing or meandering, and thus the re-establishment of a based on higher-level planning but react on local deci- wide array of in-stream and riparian habitats (riffles, sions, e.g. flood defence work or road development pools, gravel bars, willow woodlands, etc.). There are (Holmes, 1998; VAW, 1993). Thus, due attention is other components of the river system which may need not always given to the underlying ecological pro- restoration (e.g. reduction of hydropeaking, increase of cesses that form rivers and their floodplains. Conse- minimal flow). However, due to socio-economic con- quently, many projects have not been self-sustaining straints (e.g. long-term licenses) we regard them as and have required continued management input, for unchangeable framework, in which eco-morphological example, mimicking geomorphic processes with exca- floodplain restoration will take place. vating works. Clarke et al. (2003) argue that river The GIS-based, integrative search strategy pre- restoration will only be sustainable if it is undertaken sented here is: (1) designed as pragmatic decision within a process-driven and strategic framework with support tool, to assist government agencies and man- inputs from a wide range of specialists. agement authorities in identifying those stream systems In present day catchments including multiple forms (we follow the definition proposed by Frissell et al. of land use, it should be noted that restoration possibil- (1986)) on national and catchment level where flood- ities are restricted and that all sectors of society need to plain restoration is less likely to be undermined by be included in planning and decision-making. Limited poor environmental conditions and where the greatest financial and spatial resources launch a debate about benefits (judged according to ecological and socio- the efficiency of restoration measures. Two key ques- economic criteria) are to be expected. The search strat- tions arise: egy is balanced between accuracy and costs to account for practical application. Using objective ecological • Where are the more promising river stretches which and socio-economic criteria enables stream systems are less likely to be undermined by poor environ- to be selected for floodplain restoration in a transpar- mental conditions? ent and reproducible way. The search strategy is also • Where shall we spend our money and space to fulfill thought to (2) provide a checklist of ecological and the various social demands and ecological require- socio-economic criteria and (3) indicators that need ments concerning rivers and their floodplains? to be considered in the planning process of flood- 52 S. Rohde et al. / Landscape and Urban Planning 78 (2006) 50–70 plain restoration. The starting point of the proposed will be discussed in more detail in the following sec- search strategy is the ecological suitability of a river for tions. restoration. However, we are aware that, in many cases, ecological restoration is not necessarily the key driver 3.2. Filter 1: pre-selection based on limiting for floodplain restoration. Other drivers in day-to- constraints day restoration include ‘flood protection’ and ‘human recreation’. In the proposed search strategy, they are The first filter defines the minimum pre-requisites to included as socio-economic indicators. be met for eco-morphological floodplain restoration. It The search strategy is not designed to compare determines stream systems to be excluded from fur- different restoration sites within a single stream sys- ther consideration based on the attributes of selected tem. Once a promising stream system is identified, constraints. We considered the following two factors more detailed investigations are necessary to choose as constraints: a suitable location for restoration (site selection). Fur- thermore, different restoration alternatives should be (i) Slope >6%. A spatial analysis of the distribution of compared for the chosen restoration site (alternative floodplains in Switzerland showed that extended selection). It is beyond the scope of this study to address floodplains can only be found in areas with a the ‘site selection’ and ‘alternative selection’ project slope <6%, because steeper slopes naturally result phases. For a discussion of these phases and stake- in straight river courses,
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