Background Information
In 1960, during the period when concrete was considered the must-have look for most rivers, the entire confluence of the Green Lanes Stream with the Hogsmill River was dredged excessively deep, widened and entombed in a concrete cast. The best habitat within the Hogsmill has since been cut off to fish by a sloping 35-metre length of the uniformly wide concrete channel in conjunction with a small weir. The banks were also cloaked in one-metre high concrete and stonewall severely restricting any marginal habitat.
Scope of the Project
This work is a continuation of the Catchment Restoration Fund Project funded by Defra, addressing fish passage along the length of the river. In combination with other projects located in the Hogsmill Local Nature Reserve, this means that there is now a 1.5 km unobstructed stretch of river for fish to populate. The aim of this project would address both the issue of the lack of connectivity for fish and the modified channel. Fish passage would be returned to the upper Hogsmill with the removal of the concrete bed while a 150 m cumulative of riverbank would be naturalised.
Our Solution
The banks were naturalised with a combination of coarse woody debris, the site won brash, rock rolls and coir geotextile for temporary soil protection. A sinuous meandering channel form has now replaced the former straight and wide channel.
Variations in depth, width and the inclusion of gravel, small boulders and multiple pieces of Large Woody Debris and root wads have all provided a diversity of habitat and complex flows within the channel. The low-lying wetlands have been seeded with a mix of native species in addition to several hundred plants being introduced.
