IN-RIVER WORKS - RADLETT ROAD RECREATION GROUND
Radlett Road Recreation Ground provides a popular space for public recreation and sport, in addition to a wild river corridor with informal walking routes, giving people the opportunity to enjoy local wildlife. The land on the adjacent bank to the public park is not publicly accessible, but provides an important secluded refuge for wildlife. The section of the river is designated as a Local Wildlife Site 84/014 for Flowing waters (rivers and streams); species’. However the ecological value of the river corridor and surrounding habitats have declined over the past 20 years, meaning urgent intervention is required to ensure the site reaches its full ecological potential, which is what is being addressed by this programme.
Current site issues:
High sediment and pollution entering the River Colne
Lack of flow diversity, impacting sediment transportation and deposit
Lack of sunshine which negatively impacts floral biodiversity
Ditch systems which are dry for the majority of the year
Presence of non-native invasive species and water quality issues
The Hillfield Brook follows a straightened course, and is a major source of siltation and pollution (see image below) entering the River Colne during times of high flow. In addition, the backwaters have dried out since its creation in 1993, so that they are no longer connected to the main river channel and unable to act as refuges and spawning grounds for aquatic species. To address this, the Hillfield Brook is to be diverted to feed into the first backwater, before entering the River Colne. This will enable the settling of sediment and urban run-off, by ensuring the backwaters receive a constant feed of water (see diagram).
A backwater is the part of a river that is not reached by the current. The first backwater will allow for sedimentation and for pollution to drop out of suspension, whereas the second backwater will act a refuge for wildlife. The second backwater is to be desilted and reconnected to the main river, with consideration of the complicated network of utilities at this site. A low-lying marginal shelf, or berm, will be created to provide a complex littoral zone (the part of the river which is closest to the shore), which will in turn support a diversity of species. Small tree works will address the lack of sunshine over the river corridor, creating a healthy 60:40 balance ratio of sunshine to shade.