Case study:Houghton 'trout stream' enhancements
Project overview
| Status | Complete |
|---|---|
| Project web site | |
| Themes | Fisheries, Hydromorphology |
| Country | England |
| Main contact forename | Rob |
| Main contact surname | Clapham |
| Main contact user ID | |
| Contact organisation | Environment Agency |
| Contact organisation web site | http://www.gov.uk/government/organisations/environment-agency |
| Partner organisations | |
| Parent multi-site project | |
| This is a parent project encompassing the following projects |
No |
Project summary
The Environment Agency worked with local stakeholders to improve habitat quality on a side-channel of the Great Ouse.
Like many of our rivers, the Houghton 'trout' stream, has been significantly modified over many years. These modifications include impoundment, channelization and tree clearance. These pressures have reduced the resilience of the channel to wider catchment scale pressures from water quality and sediment.
As a result of these modifications, there is insufficient flow and energy within the channel at many times of the year to move and redistribute sediment within the channel. This has meant that this 'naturally' gravelly river has an overlying layer of fine sediment. This significantly reduces the likelihood of successful spawning by species such as chub, dace and barbel, the latter of which has not been seen on the river for over a decade.
Such habitats are particularly important to retain on this side channel, as the main river is navigable, heavily impounded, and cannot provide the diversity of habitats found on this channel, all of which are vital to many species at different points in their life cycle. Furthermore, due to navigation on the main channel, options to enhance or restore it are limited.
The Environment Agency surveyed the side channel and put together a series of enhancement options to address the deterioration, which were then shared and discussed with the local Angling club and landowners. These included: Improving flow over an upstream weir, tree planting, retaining woody material, fencing, gravel jetting, and installing deflectors to keep areas of spawning gravels free from silt and excessive vegetation growth. Both landowners and Angling Club were keen to see these improvements made and offered both their time and money to see them implemented.
Partnership was vital to success of the project. Very little money was spent on these enhancements with most contributions coming from volunteer time. The angling club have helped with planting of trees (willow whips sourced from local trees), gravel jetting (using agency equipment), and will share the cost of installing fencing with the local landowners Smith & Smith. The Agencies Fisheries and biodiversity team cleared vegetation blocking an upstream weir and installed flow deflectors, again using wood sourced from locally fallen tree that identified for removal as it was blocking a nearby drainage channel.
While enhancements such as tree planting will take many years until benefits from increased cover, shelter shading, and supply of woody material to the channel are realized. Already, the benefits of the gravel jetting and flow deflectors can be seen. Following the work, the areas of clean gravels have remained, while other areas in the channel (not yet enhanced) have become covered with sediment and clogged with reed growth.
For the first time in many years, large numbers of fish have been seen congregating around the deflectors in preparation to spawn, including many large chub. Furthermore, we have also seen River Lamprey (a formerly declining species) making use of the clean gravels for spawning.
This project demonstrates that correctly targeted low-cost measures, undertaken in partnership with committed stakeholders, can make significant improvement to river channel habitat and fisheries value.
Follow link for YouTube video of spawning gravel enhancements: http://www.youtube.com/watch?v=ubVX4pla10Y&list=UU8XLubOua8P9B1hT0Qb5Tbg
Monitoring surveys and results
Pre-enhancement fish surveys have been undertaken
The Environment Agency will continue to monitor this site through electric fishing surveys.
Lessons learnt
Wood for construction of deflectors was sourced locally and work was undertaken by hand. Therefore the size of deflectors were limited to what could be manoeuvred by hand. Despite their size, careful consideration of the prevailing flow and sediment conditions meant they could be placed to achieve optimum benefit.
In November 2014 some of the wooden posts, used to hold deflectors in place, had to be replaced. The posts were 75 mm diameter and it is thought that the staples and screws used to secure wire to these posts were too large, causing the post to be weakened and split under load. We have since replaced posts with 20 mm re-bar drilled through the deflectors. Post diameter and staple size should be considered when planning how to secure LWD.
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