Case study:River Somer channel enhancement, Midsomer Norton

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Location: 51° 17' 9", -2° 28' 56"
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Project overview

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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
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
River Somer on the high street post-restoration (Woodland water and gardens)

Project summary

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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

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Lessons learnt

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Image gallery


channel prior to restoration (woodland water and gardens)
channel one year after completion of works (woodland water and gardens)
local community group helping to complete the planting phase (woodland water and gardens)
channel during construction (woodland water and gardens)
laying out berm design (woodland water and gardens)
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Catchment and subcatchment

Catchment

River basin district Severn
River basin Bristol Avon and North Somerset Streams

Subcatchment

River name Wellow Bk - source to conf Snails Bk
Area category 10 - 100 km²
Area (km2)
Maximum altitude category 200 - 500 m
Maximum altitude (m) 220
220 m
0.22 km
22,000 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Improved grassland
Waterbody ID GB109053022250



Site

Name River Somer at Midsomer Norton
WFD water body codes GB109053022250
WFD (national) typology
WFD water body name Wellow Bk - source to conf Snails Bk
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) 167
167 m
0.167 km
16,700 cm
Project started 2011
Works started 2011/05/02
Works completed 2011/05/23
Project completed 2011/05/31
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

Mitigation of a pressure sediment accumulation, Barriers to fish migration, Urbanisation
Hydromorphology Continuity of sediment transport, Continuity for organisms
Biology Fish, Invertebrates
Physico-chemical
Other reasons for the project improving local town centre, Community demand


Measures

Structural measures
Bank/bed modifications Weir removal, Creation of berms, Bed raising, Planting of native species, Removal of sediment
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 (repeat photography) Yes Yes Yes No No Improvement


Monitoring documents



Additional documents and videos


Additional links and references

Link Description

Supplementary Information

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A public consultation meeting was held pre restoration in Midsomer Norton, roughly late 2010 – no documentation is available.


A project assessment report undertaken by Woodland, Water & Gardens (Luke Kozak) identified stakeholder engagement as a key part of the future of the project. Recommendations for this included:

-An increased presence of ornamental plants to please residents who dislike the "wild" look of channel vegetation

-Interpretation boards to identify in-channel plants and animals

-Sculptural representation of "creatures of the River Somer" constructed from local stone, wood or wrought iron

-Formal ecological tours of the channel, specifically for school children

-Regularly updated bulletin board including section to log "recent sightings"