Don Catchment Rivers Trust, with the support and advice from Derbyshire Council, Chesterfield Council, Environment Agency and the Wild Trout Trust recently embarked on a project to improve the River Hipper as it runs through Somersall Park, Chesterfield for wildlife and park users through the introduction of ‘woody debris’.
This project was fully-funded by the Environment Agency’s Fishery Improvement Program (FIP) which sees fees from rod licences reinvested to generate positive outcomes for anglers and fish stocks through projects such as this one which also included the design and installation of an interpretation board to inform park users of the work.
The River Hipper starts life as the Hipper Sick on Beeley Moor, high above Chesterfield. The river is a typical small, rain-fed Derbyshire stream, which passes through Holymoorside village before entering Chesterfield and flowing into the River Rother near Horns Bridge Roundabout.
It has a semi-natural feel to it however, this and many other stretches have been modified through straightening and the construction of barriers (weirs), restricting many of the natural river processes that would otherwise occur. In addition, the practice of removing windblown trees or branches from the river channel in public parks limits its ability form structurally-diverse habitats.
What is woody debris?
Woody debris is any woody plant material that has entered the river channel. It can range from twigs caught in a tree’s root system to whole large trees that have fallen into the river.
Wood that has fallen into the channel is often tidied up and removed as it is thought to look “unsightly” or can snag the fishing lines of anglers. They can also cause problems when swept up against bridges or culverts when blockages cause flooding.
Naturally, woody debris would be abundant and a very important part of the river ecosystem, so we now replicate this feature in a safe manner by carefully anchoring pieces of wood in place with metal fixings– as pictured. Appropriate consents from local agencies are also required to ensure work does not increase flood risk.
Benefits of woody debris?
The introduction of woody debris to the river will:
- Creates bends, pools and riffles in rivers – important aspects of a heathy river (as pictured).
- Promotes ‘sediment sorting’ – different plants and animals like different sizes of rock and sands
- e.g. burrowing mayflies like sand whereas flat-headed mayflies prefer flat stones and trout like to spawn in gravels.
- Provides a ‘home’ for fish and other life
- A place for them to hide from predators such as heron or kingfisher giving them a fair chance to escape – balancing predator-prey relationships.
- When the river floods – provide somewhere to hide so they don’t get washed downstream
- Traps leaves, twigs and encourages a biofilm (algea and bacteria) to form – food for insects that other invertebrates.
- ‘Cleans’ rivers
- Speeds up flow to clean gravel meaning more oxygen will flow over eggs in fish nests (redds) and greater hatching success.
- Takes fine bits of dirt out of the water and deposits behind debris meaning water is clearer