Case study:River Somer channel enhancement, Midsomer Norton
This case study is pending approval by a RiverWiki administrator.
Project overview
| Status | Complete |
|---|---|
| Project web site | |
| Themes | Fisheries, Habitat and biodiversity, Social benefits |
| Country | England |
| Main contact forename | Luke |
| Main contact surname | Kozak |
| Main contact user ID | User:NickRRC |
| Contact organisation | Woodland, Water and Gardens |
| Contact organisation web site | |
| Partner organisations | |
| Parent multi-site project | |
| This is a parent project encompassing the following projects |
No |
Project summary
The reach of the River Somer flowing through Midsomer Morton had been a focus of concern for many years. A complete lack of vegetation, weir impoundment and large amounts of silt accumulation were severely effecting habitat and amenity potential of the channel. This was in stark contrast to the natural brook up and downstream of the town.
Local residents formed the River Somer Management Team (RSMT), with the aim of improving the channel based around the following project objectives: • Removal of three weirs • Build new channel based on the geomorphology of the “natural” stretches of the River Somer • To enhance the aesthetic value of the reach, including the development of vegetated margins, in channel flow regime and opportunities to engage with the public • Restore habitats and enhance ecological value • “bring trout to the town” • Use localised materials • Use construction techniques which are flood resistant • Community engagement for construction, long term maintenance and educational opportunities
The project was split into four stages: 1. Weir removal 2. Berm construction 3. Bed raising and fine adjustment 4. Planting aquatic margins
The RSMT commissioned Woodland, Water and Gardens (Luke Kozak) as project consultants, designers and construction managers. BANES were commissioned as the overall project managers.
Construction started in May 2011 taking three weeks to complete. The planting phase was completed by volunteer Midsomer Norton residents.
The berms were constructed from coarse interlocking local limestone which did not exceed 30cm high. This allowed flow to be released over the berms, increasing channel capacity when needed (2-stage channel design). Flow events shortly after construction demonstrated the effectiveness of this design.
In June 2012 the first formal assessment took place post-project completion. This encompassed fish, invertebrate and vegetation assessment. The report concluded that: berms were intact and in good condition despite several high flow events, plant communities had matured well providing a diverse habitat, maintenance carried out by volunteers has helped to keep the channel litter free. Diversity of aquatic organisms has increased, and although some small silt deposits have form in low energy areas the channel in generally self-cleansing.
The project has been given a civic “Pride of Place” award for environmental enhancement, and the establishment of the RSMT will ensure the success of the project into the future.
The River Restoration Centre would like to thank Luke Kozak (Woodland, Water and Gardens) as well as Dominic Longley for providing the information and photographs for this case study.
Monitoring surveys and results
Lessons learnt
Catchment and subcatchment
Site
| Name | River Somer at Midsomer Norton |
|---|---|
| WFD water body codes | |
| WFD (national) typology | |
| WFD water body name | |
| Pre-project morphology | Impounded, Over-widened, Straightened |
| Reference morphology | 2-stage channel, Pool-riffle, Sinuous |
| 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 | wild brown trout |
| Dominant hydrology | |
| Dominant substrate | Artificial |
| River corridor land use | Improved/semi-improved grassland/pasture, Intensive agriculture (arable) |
| 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
| Reach length directly affected (m) | 167167 m <br />0.167 km <br />16,700 cm <br /> |
|---|---|
| Project started | |
| Works started | 2011/05/02 |
| Works completed | 2011/05/23 |
| Project completed | |
| Total cost category | 10 - 50 k€ |
| Total cost (k€) | |
| Benefit to cost ratio | |
| Funding sources | fundraising by the River Somer Management Team |
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
Measures
Structural measures
| |
|---|---|
| Bank/bed modifications | Weir removal, Creation of berms, Bed raising, Planting of native species, silt removal |
| Floodplain / River corridor | |
| Planform / Channel pattern | Channel naturalisation; Creation of new meandering channel |
| Other | |
Non-structural measures
| |
| Management interventions | management of litter, management of undesirable plant species |
| Social measures (incl. engagement) | creation of River Somer Management Team, fundraising |
| Other | Participation in maintenance, Participation in works |
Monitoring
Hydromorphological quality elements
| Element | When monitored | Type of monitoring | Control site used | Result | ||
|---|---|---|---|---|---|---|
| Before measures | After measures | Qualitative | Quantitative | |||
Biological quality elements
| Element | When monitored | Type of monitoring | Control site used | Result | ||
|---|---|---|---|---|---|---|
| Before measures | After measures | Qualitative | Quantitative | |||
| Fish | Yes | Yes | No | No | No | Improvement |
| Invertebrates | Yes | Yes | No | No | No | Improvement |
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
| Element | When monitored | Type of monitoring | Control site used | Result | ||
|---|---|---|---|---|---|---|
| Before measures | After measures | Qualitative | Quantitative | |||
| general assessment of habitat quality and diversity | Yes | Yes | Yes | No | No | Improvement |
Monitoring documents
Image gallery
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Additional documents and videos
Additional links and references
| Link | Description |
|---|
Supplementary Information
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