Case study:River Gelsa at Bevtoft

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Location: 55° 12' 3.48" N, 9° 12' 15.83" E

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Project overview

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Status	Complete
Project web site
Themes	Fisheries, Habitat and biodiversity
Country	Denmark
Main contact forename	Nick
Main contact surname	Elbourne
Main contact user ID
Contact organisation	River Restoration Centre
Contact organisation web site
Partner organisations
Parent multi-site project
This is a parent project encompassing the following projects	No

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Project summary

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From July to September 1989 a 1.3 km reach of the river which had historically been straightened and channelised, was restored to a 1.9 km meandering course. Rip-rap structures were created in the new meanders using 1000 m³ of stone. 740m³ of gravels were used to create new spawning grounds. In total sixteen new meanders were created, transforming the in stream morphology, decreasing channel width by 3-4m and reducing discharge capacity by around 50%. Sinuosity also increased from 1.15 and 1.60. A weir structure was also demolished just upstream of the project area as part of the restoration design. A similar upstream reach was left in the original channelised state to act as a benchmark against which improvements in the restored channel could be measured. An extensive maintenance regime of dredging and mechanical weed clearance was altered to weed clearance by scythe, and later to no human intervention. This reach represents an alternative option for restoration, which relies on natural processes to take over without human intervention. Post project monitoring was carried out in May in 1990, 1991, 1993 and 1995, as well as pre project monitoring. Results of monitoring showed nearly three times the macroinvertebrate population present post restoration. Numbers in the upstream reach which was left unaltered also increased between 1990 and 1995. Brown trout recovered to pre-restoration levels but not beyond. The results also showed that the River Gelsa had stabilised by 1993, with changes in substrate and macroinvertebrate composition mainly taking place between 1993 and 1995. The unaltered reach also showed impressive natural recovery, indicating that the termination of maintenance practices can have a substantial effect on the stream environment. Additional of gravels would further improve the channel and could provide a very cost effective restoration strategy. Nineteen years after restoration works were completed, hydromorphological conditions in the restored channel have developed in a very similar way to the unaltered channel. This supports the view that natural recovery without human intervention can be as effective as planned restoration.

Monitoring surveys and results

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Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this subcatchment) Catchment River basin district Ribe Å River basin Ribe Å Subcatchment River name Gelsa Area category Area (km2) 975975 km² <br />97,500 ha <br /> Maximum altitude category Maximum altitude (m) Dominant geology Ecoregion Dominant land cover Intensive agriculture (arable), Broadleaf/mixed woodland (semi natural) Waterbody ID Site Edit site Name Bevtoft WFD water body codes WFD (national) typology WFD water body name Pre-project morphology Straightened, Over-widened Reference morphology Low gradient passively meandering Desired post project morphology Heavily modified water body No National/international site designation Local/regional site designations Protected species present No Invasive species present No Species of interest Dominant hydrology Dominant substrate River corridor land use Intensive agriculture (arable), Improved/semi-improved grassland/pasture Average bankfull channel width category Average bankfull channel width (m) Average bankfull channel depth category Average bankfull channel depth (m) Mean discharge category Mean annual discharge (m3/s) Average channel gradient category Average channel gradient Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) 13001,300 m <br />1.3 km <br />130,000 cm <br /> Project started 1989/07/01 Works started Works completed 1989/09/01 Project completed 1989/09/01 Total cost category more than 10000 k€ Total cost (k€) Benefit to cost ratio Funding sources Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design Stakeholder engagement and communication Works and works supervision Post-project management and maintenance Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Riparian development, aquatic habitat development Hydromorphology Channel pattern/planform, Quantity & dynamics of flow Biology Fish, Invertebrates Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Floodplain / River corridor Planform / Channel pattern Channel naturalisation, Meandering channel, Creation of meanders Other Non-structural measures Management interventions ceased maintenance regime Social measures (incl. engagement) Other Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Invertebrates: Diversity Yes Yes No No Yes Improvement Invertebrates: Abundance Yes Yes No No Yes Improvement Physico-chemical quality elements Edit Physico-chemical quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Any other monitoring, e.g. social, economic Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit links and references Link Description http://www.youtube.com/watch?v=9JVpm G9yKU Supplementary Information Edit Supplementary Information Friberg, N., Kronvang, B., Svendsen, L.M., Hanse, H.O., Nielsen, N.B. (1994). Restoration of a channelized reach of the River Gelså, Denmark: Effects on the macroinvertebrate community. Aquatic Conservation: Marine and Freshwater Ecosystems, 4 (4), 289-296.