Earlier this month I had to pleasure of taking the Caledonian Sleeper up to Scotland for our third Members Site Visit of the year. We were visiting the Allt Lorgy which is a tributary of the River Dulnain in the Spey Catchment.
The day started in Scottish Natural Heritage’s Aviemore office, where 14 attendees enjoyed presentations from Hamish Moir (cbec), Eric Gillies (cbec) and Liz Henderson (Spey Catchment Initiative). The presentations put the site into a wider context and provided an insight into the design and delivery of the project. We couldn’t wait to get out and see it ourselves.
 |
 |
 |
||
| Out on site | ||||
| ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ | ||||
| The site visit started with lunch at the bottom end of the site. Hamish and Duncan Ferguson (Spey Fishery Board) then led us upstream to see some of the improvements that have allowed the river to become more dynamic and varied. |  |
|
This section of the Allt Lorgy used to be heavily constrained by high banks which were created to protect the adjacent land. The channel was straight and relatively uniform instead of being a highly dynamic and naturally braided system. |
| The works |
| ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ |
| Many restoration projects of this nature and scale require a detailed channel design. However, the landowner’s co-operation and the energy in the system meant that the project’s objectives could be achieved by reinstating natural processes and allowing the river to dictate its own course. |
The high banks that constrained the river were made up of previously dredged bed material. These were removed and the sediment was put back into the channel at a suitable site further upstream. Locally sourced trees were also placed in locations where the river was already trying to migrate.
Lowering the banks has allowed the river to flood and erode the banks with more ease. The additional sediment has been deposited, especially in areas where trees were placed. This is forcing the flow towards the outer banks resulting in an impressive amount of lateral migration. In general the channel is much more dynamic with a network of small bars and channels forming. Hamish remarked that it changes every time he visits.
It will be fascinating to see how the site develops over the coming years, there are already signs that the river is breaking out into palaeochannels during high flow events. I would fully recommend a visit to this site if you are ever in the area.
| After the visit |
| ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ |
| In the afternoon Hamish kindly agreed to take me out to see a couple of potential projects that cbec have been working on. The first was just down the road on the Allt Sluggan, a much smaller tributary of the Dulnain which has also been straightened and dredged. Here cbec have produced some conceptual designs in the past but the project has not been funded as of yet. |  |
 |
The second site was in Upper Nairnside. Here the river is straight, constrained by banks on either side and perched on a high point in the flood plain. This is another high energy system with a large supply of sediment from upstream. The project, which is in the final design phase, will give the river more room and allow it to make its own course through a lower area of the valley. It’s an exciting project with around 2km of the river set to be improved. |
I’d like to thank Liz, Hamish, Eric and Duncan for their help in organising a great day!
You can find more photos from the day here
We have one more site visit this year – Find out more
Add new comment