Background Information
The Surbiton Stream or Tolworth Brook is a small waterbody approximately 5km in length. It spends much of its time culverted as it flows through Chessington and Surbiton where it emerges out of the culvert at the Hogsmill Public Open Space. From here it continues its journey before joining the Hogmill River a short distance downstream. This green space on the outskirts of London is a valuable host to a number of different and varied species of wildlife. As well as being a much-loved park and open space.
Scope of the Project
A predominantly concrete-lined channel with a series of step weirs. Almost vertical concrete banks on both sides of the channel meant there was very little bankside and marginal vegetation. The heavily modified stream lacks gradient and natural habitat due to its concrete bed. The abundance of concrete means in-stream macrophytes are rare and there was little habitat for fish and invertebrates. A series of step weirs along its course through the park had resulted in an impounded, over-wide and heavily silted stream in places. Approximately 100m from the confluence with the Hogsmill a stepped weir was present. This was impassable to fish wishing to migrate into the Surbiton Stream.
Our Solution
To create a diverse and varied habitat attractive to mammals, birds, reptiles, fish and invertebrates there were a number of in-channel works were carried out. The works included the removal of the concrete bed and step weirs. This allowed the installation of gravels to create a more natural river bed. Following the removal of the concrete and installation of gravels some simple in-stream habitat works to improve the sinuosity of the channel, creating pool and riffle sequences and increasing water velocity.
Channel naturalisation was undertaken by creating low-level vegetated berms and by the installation of woody debris and simple log deflectors to increase the habitat diversity. Tree works were carried out to allow penetration of sunlight to the watercourse increasing macrophyte growth. Planting of native aquatic macrophytes was carried out to aid establishment. The installation of a small rock ramp fish pass was carried out to create a series of pools, which increase the head level over the culvert.
The increased depth of water now allows fish to pass through the culvert. Dace has been recorded in the Surbiton Stream since the installation of the rock ramp fish pass. A footbridge was installed to provide connectivity around the park for members of the public and dog walkers.
