Remeandering straightened rivers

Effectiveness for Biological Quality Elements

Studies of macroinvertebrates, fish fauna, and aquatic vegetation in the River Gelså and other remeandered Danish streams have shown some positive results (Iversen et al., 1993; Hansen, 1996; Friberg et al., 1998). Improvements in both physical habitat and fish species diversity have also been reported from an Austrian stream (Junwirth et al., 1995). The positive benefits of restoring or recreating meanders on stream morphology and hydrology and sediment transport have been documented (e.g. Rutherfurd et al., 2000; Janes et al., 2005). Similarly, recovery of macroinvertebrates and other biota from construction impacts appears to be relatively rapid. However, long-term studies conclusively documenting recovery or increase in fish production have not yet been completed. As with many structural manipulations of physical habitat, if potential water quality problems are not addressed, they can impair biotic responses to floodplain habitat rehabilitation.

Large-scale river-floodplain restoration projects, each of which involve an element of meander reconnection, include the River Rhine (Buise et al., 2002; Cais et al., 1998; Simons et al., 2001), the River Rhône (Henry et al., 2002), and the Cosumnes River (Ahearn et al., 2006). All of these projects are showing ecological gains ranging from improvements in fish populations to increases in macro-invertebrate densities, macrophyte numbers, algal biomass and numbers of wading birds. The evidence for ecological imrpovements offered by increased river-floodplain connectivity and reconnection of former side channels is thus steadily growing.

Evidence from the UK also demonstrates that remeandering has a benefitical impact on river ecology and morphology. Reconnected meanders on the River Erewash in Derbyshire have developed a good diversity of emergent marginal vegetation including sweet grass, reedmace and common club rush, and provide an improved habitat for bird species (Environment Agency, 2000). In addition, a restored meandering channel on the River Little Ouse in Norfolk is well used by a variety of fish species and provides spawning and nursery areas for a variety of fish including chubb and dace not found in the adjacent channelised reaches (Environment Agency, 2000).

Tockner et al. (1999) and Simons et al. (2001) suggest that cut-off meanders and oxbows often have distinct elements that add to overall diversity and should therefore not be reconnected as a matter of course. Careful consideration of the habitat value of any remnant features is therefore required before they are reinstated.

Academic references

Ahearn, D.S., Viers, J.H., Mount, J.F. and Dahlgren, R.A. (2006) Priming the productivity pump: flood pulse driven trends in suspended algal biomass distribution across a restored floodplain. Freshwater Biology, 51, 1417-1433.

Buise, A.D., Coops, H. and Stara, M. (2002) Restoration strategies for river floodplains along large lowland rivers in Europe. Freshwater Biology, 47, 889-907.

Cals, M.R.J., Postma, R., Buise, A.D. and Marteijn, E.C.L. (1998) Habitat restoration along the River Rhine in the Netherlands: putting ideas in practice. Aquatic Conservation: Marine and Freshwater Ecosystems, 8, 61-70.

Friberg, N., Kronvang, B., Hanse, H.O. and Svendsen, L.M. (1998) Long-term, habitat-specific response of a macroinvertebrate community to river restoration. Aquatic Conservation: Marine and Freshwater Ecosystems, 8, 87-99.

Hansen, H.O. (1996) River Restoration - Danish Experience and Examples. National Environmental Research Institute, Denmark, 99pp.

Henry, C.P., Amoros, C. and Roset, N. (2002) Restoration ecology of riverine wetlands: a 5-year post-operation survey on the Rhône River, France. Ecological Engineering, 18, 543-554.

Janes, M., Fisher, K., Mant, J. and de Smith, L. (2005) River Rehabilitation Guidance for Eastern England Rivers. Report to the Environment Agency Anglian Region. River Restoration Centre, Silsoe, 92pp.

Rutherfurd, I.D., Jerie, K. and Marsh, N. (2000) A Rehabilitation Manual for Australian Streams, Volume 2. Cooperative Research Centre for Catchment Hydrology, Land and Water Resources Research and Development Corporation, Canberra, 400pp.

Simons, J.H.E.J., Bakker, C., Schropp, M.H.I., Jans, L.H., Kok, F.R. and Grift, R.E. (2001) Man-made secondary channel along the River Rhine (The Netherlands); Results of post-project monitoring. Regulated Rivers Research and Management, 17, 473-491.

Tockner, K., Schiemer, F., Bauggartner, C., Kum, G., Weigand, E., Zweimuller, I. and Ward, J.V. (1999) The Danube restoration project: species diversity patterns across connectivity gradients in the floodplain system. Regulated Rivers: Research and Management, 15, 245-258.