Delagyle Backwater Channel Re-connection€¦ · salmonid spawning and endangered fresh water pearl mussel populations. Background Restoration of the Delagyle backwater channel was

Spey Catchment Initiative e: [email protected] t:01463 725110 m. 07909 533344

Delagyle Backwater Channel Re-connection

Project Report , June 2018

Summary

An artificially disconnected backwater of the River Spey has been re-connected to the main river by means of

a new culvert to restore increased, continual flow through the channel. The approximately 200m of restored

channel will provide a valuable high water refuge for juvenile fish and additional good quality habitat for

salmonid spawning and endangered fresh water pearl mussel populations.

Background

Restoration of the Delagyle backwater channel was investigated as part of a feasibility study into re-

connection of two backwater channels on the Spey commissioned under the EU LIFE+-funded Pearls in Peril

(PiP) project and undertaken by EnviroCentre Ltd in 2016. Funding granted to the Spey Fishery Board by

Speyburn Distilleries in 2017 for river enhancement along with a top-up contribution from Scottish Natural

Heritage enabled the Spey Catchment Initiative to deliver the project in early 2018.

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Aim and Rationale

The Spey is designated as a Special Area of Conservation (SAC) for freshwater pearl mussel, Atlantic salmon,

otter and sea lamprey. Monitoring of freshwater pearl mussels by Scottish Natural Heritage (SNH) and

salmon by the Spey Fishery Board in recent years suggests that the populations of both have undergone

significant decline.

The project site is an artificially disconnected backwater of the River Spey approximately 3km upstream of

Aberlour at Delagyle (location map appended) and approximately 200m in length. The backwater had been

historically cut-off from the main channel by the installation of upstream bank protection, probably to

improve access for fishing. There was little significant flow in the channel except in spate events when the

banks of the Spey over-topped. At most water levels the channel contained only a small, intermittent flow

with pools of standing water, resulting in the absence of active hydro-morphological processes and good

quality ecological habitat. By re-connecting the backwater to the main river and restoring a continual flow at

a wide range of water levels, the project aimed to restore natural river processes and re-introduce suitable

habitat for fresh water pearl mussels and salmonid fish, especially valuable for spawning and as a high water

refuge for juveniles.

The feasibility study ascertained that during larger flow events the River Spey will overtop the existing banks

and the opening of the backwater channel would have no significant impact on flood levels or extents.

Delagyle Pool is a popular and commercially valuable fishing beat, and the design and implementation of the

re-connection works took into account the need to avoid any interference with access for fishing, protect

and enhance riparian trees and vegetation and maintain the attractive landscape qualities of the area.

Groundworks and re-instatement

Following hydrological and geomorphological survey

and assessment, habitat assessment and an options

appraisal, a 900mm twin pipe culvert was installed

through the retained surrounding bank protection.

This allows flow from the Spey into the backwater

channel at almost all water levels. At high flows the

volume of water entering the backwater is limited

by culvert capacity. As an additional control

measure, provision has been made for removable

sluice boards to be put in place at the culvert inlets

to protect the channel downstream of the culvert

from scouring and ensure the channel functions as a

refuge area for fish.

Some excavation was undertaken to connect the remnant channel with the culvert outlet and to slightly

lower the bed level in the upper reaches of the channel for around 80m downstream to achieve a continual

flow. Some features have been built into the upper end of the channel, such as meanders and larger

boulders, but the majority of the channel downstream has been left unaltered. In time, the channel will

naturally evolve its own course forming pools, riffles, runs and steps, providing a diverse range of hydraulic

and physical habitats.

Construction of culvert

Spey Catchment Initiative e: [email protected] t:01463 725110 m. 07909 533344

Turf was re-instated above the culvert site and disturbed ground re-seeded with grass. Around 30 broadleaf

trees of appropriate riparian species were planted close to the banks of the channel where vegetation had

been removed during construction works, to give a boost to natural tree regeneration.

Monitoring

Regular (at least annual) fixed point re-photography will be used to monitor morphological changes in the

channel and surrounding area.

The channel will be electro-fished during the summer of 2018 and annually thereafter to monitor species

and numbers of fish present, and it will also be surveyed for freshwater pearl mussel.

We would like to acknowledge the generous support of Speyburn Distilleries and Scottish Natural Heritage

and the kind permission of Delagyle Fishings, without which this project would not have been possible.

Penny Lawson, June 2018

Completed culverts showing exit and channel

Entrance to culverts from main river, near completion

Spey Catchment Initiative e: [email protected] t:01463 725110 m. 07909 533344

Downstream confluence of backwater with main river

before re-connection.

Confluence of re-watered channel with main river one

week after re-connection, showing channel starting to

erode its own course.

Channel post-re-connection, showing in-channel

features.

Backwater channel before re-connection.

Backwater channel before reconnection, middle section

with standing water.

Excavated section of channel downstream of culvert.

Spey Catchment Initiative e: [email protected] t:01463 725110 m. 07909 533344

Location Maps