Case study:Burn of Mosset, Forres

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Location: 57° 35' 43.20" N, 3° 35' 30.93" W
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Project overview

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Status Complete
Project web site
Themes Fisheries, Flood risk management, Habitat and biodiversity, Hydromorphology
Country Scotland
Main contact forename Matthew
Main contact surname Hardwick
Main contact user ID
Contact organisation Royal HaskoningDHV
Contact organisation web site
Partner organisations
Parent multi-site project
This is a parent project
encompassing the following
projects
No
Burn of Mosset- sustainable sediment and flood management by reconnecting the river with its floodplain and working with natural processes

Project summary

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The Burn of Mosset is a small gravel bed stream draining an area of 49km2. A Tributary of the River Findhorn, it flows north through the town of Forres before entering Findhorn bay. The town of Forres has a long history of flooding from the burn, with six flood events causing serious damage to property or disruption in the last fifty years. The new Flood Alleviation Scheme (FAS) took two years to complete. It included the construction of an earth-filled embankment dam designed to allow for discharges up to 8.5 m3/s to flow through Forres, with excess floodwater temporarily stored behind the dam. In addition to this, the upstream storage area has been designed to create an extensive natural sediment accretion zone (for sand, gravel and large wood). This will reduce the risk of sediment or other debris blocking the dam control structure. The scheme also aimed to create a mosaic of river and floodplain habitats, by working with natural processes to develop a multi-thread (anabranched) system. This was achieved by breaching the existing embanked channel which ran around a field boundary at two points, allowing flow to spill out across the open field, before re-joining the original channel just upstream of the dam. Tress were planted across the site to create a wet woodland habitat. Since construction in 2008 the scheme is effectively storing large wood and sediment, with a large sediment outwash fan forming at the upstream breach. A small amount of adaptive management has been required at the upstream breach due to erosional events interacting with woody material in the channel. Measures were taken to ensure that a further breach of the old channel did not occur, as this could have led to flooding of a significant area of agricultural land. In 2010 the scheme was awarded an "environmentally sustainable construction" commendation by the Institute of Civil Engineers.

Monitoring surveys and results

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Lessons learnt

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Catchment and subcatchment

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Catchment

River basin district Scotland RBD
River basin Findhorn

Subcatchment

River name Burn of Mosset
Area category
Area (km2) 13001,300 km² <br />130,000 ha <br />
Maximum altitude category
Maximum altitude (m)
Dominant geology Organic
Ecoregion Great Britain
Dominant land cover Moorland/heathland, Woodland
Waterbody ID



Site

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Name Forres Flood Alleviation Scheme
WFD water body codes 23021
WFD (national) typology Lowland, Small, Siliceous
WFD water body name Mosset Burn Altyre to Forres
Pre-project morphology Straightened, Embanked, Over-widened
Reference morphology Anastomosing, Pool-riffle
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 Quick run-off
Dominant substrate Gravel, Cobble
River corridor land use Improved/semi-improved grassland/pasture, Moorland/heathland, Woodland
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

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Reach length directly affected (m) 500500 m <br />0.5 km <br />50,000 cm <br />
Project started 2008/01/01
Works started
Works completed
Project completed 2008/12/31
Total cost category
Total cost (k€) 116116 k€ <br />116,000 € <br />
Benefit to cost ratio
Funding sources

Cost for project phases

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Investigation and design
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Reasons for river restoration

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Mitigation of a pressure Flood risk management
Hydromorphology
Biology
Physico-chemical
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Measures

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Structural measures
Bank/bed modifications Create breaches in the bank
Floodplain / River corridor Floodplain reconnection, Riparian tree planting
Planform / Channel pattern Allow future natural channel changes to occur
Other
Non-structural measures
Management interventions
Social measures (incl. engagement)
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Monitoring

Hydromorphological quality elements

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quality elements
Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Biological quality elements

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quality elements
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Physico-chemical quality elements

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quality elements
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Monitoring documents

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Image gallery


Chapelton Dam control structure (2013)
The Burn management works (2013)


Additional documents and videos

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Additional links and references

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Supplementary Information

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