Case study:River Glyme Stratford Restoration
Project overview
| Status | Complete |
|---|---|
| Project web site | |
| Themes | Environmental flows and water resources, Fisheries, Flood risk management, Habitat and biodiversity, Monitoring, Social benefits, Water quality |
| Country | England |
| Main contact forename | Hilary |
| Main contact surname | Phillips |
| Main contact user ID | User:Hilary Phillips |
| Contact organisation | Wild Oxfordshire / Evenlode Catchment Partnership |
| Contact organisation web site | http://http://www.wildoxfordshire.org.uk/ |
| Partner organisations | |
| Parent multi-site project | |
| This is a parent project encompassing the following projects |
No |
Project summary
1. The project was to restore a stretch of the River Glyme with the following objectives:
• Enhancing the channel and floodplain habitat diversity
• Re-grading banks and re-planting with native species where needed
• Form pool-riffle sequences, raise the river-bed and provide a good medium for spawning fish
• Manipulate spatial structure of the channel form & hydraulics across the flow range
• Increase diversity of floodplains habitat
• Improve habitat downstream at Woodstock Water Meadows (WWM)
• Increase community engagement
2. The restoration took place on the reach between Stratford Bridge (444,645 218,482) and Woodstock Water Meadows (444,933 218,004), a 5 Ha site between Old and New Woodstock owned by Woodstock Town Council.
3. The river restoration was completed in late 2015, with WWM habitat and community engagement on-going until November 2016.
4. Prior to around 1890 the River Glyme at this location had a sinuous course. It was then extensively straightened and its bed lowered. More recently, the main channel has been heavily maintained by dredging, leaving it over-wide, significantly incised and very uniform in both cross section and plan-form. The majority of the hard bed has been removed, with little gravel remaining in a clay and silt dominated substrate. The river is now largely disconnected from its immediate floodplain except in times of high flow. This section of river should support a thriving wild brown trout population as well as other species; the lack of suitable spawning substrate had led to limited recruitment in this species.
Increased sediment input and diffuse pollution from upstream (agricultural run-off) and the lack of connectivity with the flood plain have contributed to substantial siltation and associated water quality issues in the Blenheim Lake SSSI and World Heritage site downstream.
Physical manipulation of channel planform, bed levels and flow patterns was undertaken to enhance the channel habitat diversity. This was achieved through the introduction of locally quarried stone, overlain with gravel to provide optimum conservation benefit for a range of species and spawning/juvenile brown trout. The introduction of Large Woody Debris (LWD) will help to maintain these new areas of gravel.
Meanders were excavated, banks re-graded and arisings redistributed behind brushwood faggot revetments. In combination with the excavation of scrapes this serves to increase the diversity of floodplain habitats.
An ongoing programme of habitat maintenance and community engagement is being led at WWM in collaboration with the ECP, Woodstock town council, Blenheim Estates and other local community groups and is due to finish in November 2016.
Management included a video to raise awareness and engagement.
Monitoring surveys and results
As with the project as a whole the monitoring and evaluation is a collaboration between partners. Project objectives were used to set the method and frequency for data collection with monitoring results collated and evaluated by the ECP. Methods used include:
• Fixed point and drone photography, habitat mapping, vegetative surveys, riverfly monitoring and electro-fishing to monitor increases in habitat diversity and change in macro-invertebrate and fish assemblages.
• Electro-fishing, catch returns, red counts to monitor increase in Brown trout spawning on gravels.
• Fixed point photography and cross-sections plus flow measurements to monitor channel and morphological changes.
Photographs will be georeferenced and stored. Evaluated after every set of photos (in-house) and included in final evaluation report alongside all other data. An initial evaluation report will be produced at the end of 2016, with 3 year monitoring reports contributing to a final project evaluation on 2019.
Despite the relatively small scale of this project on the Glyme at Stratford (>1000mtrs restored) the upstream EA gauging weir has been used to demonstrate how the water level throughout the whole system has been raised by the restoration of the river. The increase shown is in the region of 0.2m. This means that the river spills out onto its floodplain earlier, slowing the flow of water and providing natural flood management downstream. This will also help by settling sediment out earlier during the hydrographic peak, benefitting downstream habitats and communities.
The catchment-scale effects of the scheme are apparent in the water level record some 5km downstream, at the River Evenlode gauging station at Cassington. Changes in storage in the river channel are transmitted downstream as water level variations at the gauging station. This signal is recorded at low flows.
Further post-restoration channel measurements and monitoring will be taken and evaluated to better quantify this initial interpretation of data.
Lessons learnt
Too soon to say - this section will be updated when monitoring reults have been evaluated.
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