The River Calder Restoration Project

Reviving the riparian ecosystem by fostering new native woodland habitat along the River Calder and restoring the river channel to enhance biodiversity and protect against climate change impacts.

This project was supported by the NatureScot Biodiversity Challenge Fund, SEPA and the Woodland Trust.

The River Calder, an upland tributary of the Spey, is undergoing a transformation. An ambitious, landscape scale project to restore the river and re-wood the riparian zone was delivered in 2020 and 2021. The Calder is a large upland tributary of the River Spey, typical of many of the headwaters in the upper catchment, and the project was a response to increasing concern about its ecological health, especially the low numbers of juvenile salmon and trout.

The first phase addressed the relatively uniform habitat in the river channel which lacked the diversity of gravel deposits, pools, riffles and refuge areas needed to support a thriving freshwater ecosytem. The aim was to install Large Woody Structures (LWS) to mimic natural dead wood in the channel to restore natural processes and encourage a more diverse physical structure in the channel. The second phase was creation of up to 15 hectares of riparian woodland along 3.5 km of the Calder which was largely bare of trees, to establish riparian woodland ensuring not only a future supply of dead wood into the river, but also shading to control rising water temperature and slowing flows into the river to help reduce flood risk downstream.

This project is an example of using integrated nature-based solutions to future-proof against the impacts of climate change while significantly expanding and improving habitat for aquatic and terrestrial species. The project was planned and delivered with the full support of the landowner Pitmain and Glenbanchor Estates, and this ensured that impact on estate activities such as farming and stalking was kept to a minimum.

Project Delivery: What did we do?

The project was completed in March 2021. Here are the main features of this project:

1. LWS installed

After careful mapping and design work, 29 LWS were installed along 1.6km of the Calder. The structures were formed from locally sourced plantation trees harvested with their root balls attached and embedded securely into the bed and banks of the river.

2. Deer Fencing Installed

To protect young trees from browsing by deer and sheep, three separate woodland enclosures were built, straddling both banks of the river. Approximately 5.5 km of deer fencing and seven water gates were installed. As the Calder is a large, spatey river, a robust, innovative design was required for the water gates. Swing fencing was used on areas of the flood plain to avoid flood damage.

3. Tree Planting

Over 15,000 trees made up of a diverse mix of native tree species were planted, to kick-start re-establishment of natural woodland.

4. Natural Regeneration

Alongside planting, natural regrowth is now occurring within the protected areas. There are seed sources from older trees in the glen and substantial regeneration of pioneer species such as birch and rowan is taking hold.

What are the Benefits of this Project?

1. An increase in availability and diversity of terrestrial habitat

The project has diversified the habitat available in the area, creating new riparian woodland which not only benefits terrestrial species but will also, over time, continue to improve in-stream habitat through addition of more deadwood and nutrients to the river, and the stabilising of the banks by tree root systems. By creating up to 15 hectares of new woodland in three separate enclosures, a new native woodland corridor will be formed along the glen, allowing for enhanced movement of bird, mammal and invertebrate species, crucial for ecological connectivity and resilience against climate change.

2. Improved in-channel habitat

The LWS will diversify flows in the river, encouraging formation of new pools, shallower areas and riffles and deposits of finer gravels. These all provide a much bigger variety of habitats for all river life, and particularly for fish to support all stages of their life cycle, from eggs to juveniles and adults returning from the sea to breed. Cooler, deeper areas of water are important refuges for fish when water temperatures rise, and sheltered nooks protect fish and invertebrates being washed out during spates – all improving resilience to climate change challenges.

3. Shading to keep water cool

As our summers continue to get hotter, more woodland along our river banks is going to be essential to safeguard threatened species which are susceptible to heat stress and even heat-induced mortality, such as Atlantic salmon and trout. The shade provided by the new woodland will help to regulate water temperature, and bankside trees along with deadwood in the river will create cooler refuge areas for fish to escape to in peak temperature conditions.

4. Natural Flood Management

Woodland can act as a sponge during heavy rainfall, holding water for longer in this upland glen and smoothing out peak flows. This contributes to reducing the risk of flooding downstream, protecting land and communities along the Spey.

Project Updates

2024 Update (3 years after delivery)

Three years after delivery we are seeing real improvements on the Calder. Salmon have spawned in the new gravels forming around the LWS, and although more data is needed to show long term impact, we are optimistic that fish breeding in the river has improved. The Spey Fishery Board carry out electrofishing to monitor salmon and trout juvenile numbers.

The planted native trees have taken well, and excitingly we are seeing substantial amounts of healthy natural tree regeneration in the woodland enclosures. We will continue monitoring water temperature, fish, invertebrates, birds and tree growth along the river to measure success in future.