Case study:Burn of Mosset, Forres
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- 1 Project overview
- 2 Image gallery
- 3 Catchment and subcatchment
- 4 Site
- 5 Project background
- 6 Reasons for river restoration
- 7 Measures
- 8 Monitoring
- 9 Additional documents and videos
- 10 Additional links and references
- 11 Supplementary Information
|Project web site|
|Themes||Fisheries, Flood risk management, Habitat and biodiversity, Hydromorphology|
|Main contact forename||Paul|
|Main contact surname||Winfield|
|Main contact user ID|
|Contact organisation||Royal HaskoningDHV|
|Contact organisation web site|
|Parent multi-site project|
| This is a parent project
encompassing the following
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.
This project is part of the UK River Restoration Center's manual of river restoration techniques (update due to be published in late 2013).
Monitoring surveys and results
Approximately one year after the banks were breached in September 2009, the channel experienced an estimated 30m3/s flood flow (of the order of a 1 in 10 year event). The stone protection at the upstream breach was partially washed out, as anticipated. The breach enlarged such that the majority of the flow was diverted along the new route after the flow subsided. The result was rapid development of river features including the formation of an outwash fan. Some ecological degradation has occurred in the short term as the old channel is now dry except during very high flow events.
Small on-going adaptive management is predicted to be necessary in the short to medium term until this modified river system becomes better established.
Overall this scheme illustrates what can be achieved when working with natural sediment transport processes in flood storage zones. In 2010, the Saltire Society of Scotland in association with the Institution of Civil Engineers awarded the Forres Flood Alleviation Scheme its 'Environmental Sustainable Construction' commendation.
Catchment and subcatchment
Select a catchment/subcatchment
Cost for project phases
Reasons for river restoration
Hydromorphological quality elements
Biological quality elements
Physico-chemical quality elements
Additional documents and videos