Examine the potential constraints, risks and costs of removing three weirs from the Tonge River.
The River Tonge is a 4.8km long tributary of the River Croal, located within the WFD Irwell Croal operational catchment, which is part of the wider WFD Irwell Management catchment in the Mersey Basin. The River Tonge is a heavily modified water body under the Water Framework Directive, flowing through a highly urbanized area of the metropolitan borough of Bolton, with a catchment area of 3.54 km2.
The River Tonge Water Framework Directive Water Body is currently at Moderate Ecological Status. Despite having Good to High water quality, the fish status remains moderate due to the presence of three weirs acting as a barrier to fish migration, particularly for brown trout and coarse fish populations in an important spawning and juvenile fish headwater habitat.
The project aims to conduct a feasibility study to remove three small weirs in a 0.6km stretch of the River Tonge in Bolton, Greater Manchester, UK. The weir removals are part of a larger strategy to remove fish barriers within the Irwell Catchment Plan, which is a part of the North West River Basin District Water Framework Directive River Basin Management Plan. This strategy is supported by over 30 local partners in the Irwell Catchment Partnership, with the Mersey Rivers Trust leading the removal program in close collaboration with the regulatory body, the Environment Agency.
|Potential km to be opened
|Dam removal (pre-demolition)
Like many rivers in the Mersey Basin, the River Tonge and the wider River Irwell system is an ecologically “recovering” river following nearly two centuries of ecological damage from industrialisation and urbanisation in the Greater Manchester conurbation in North West England. The damage to rivers was extensive, with the river nearly biologically dead by the late 1960s. However, nascent brown trout and migratory European eel populations are gradually returning to the River Irwell system, including the River Tonge, following extensive investment in modern sewage treatment over the last 25 years, which has led to improved water quality. However, more investment is still needed to tackle sewer overflows and leachate from old waste tips and improve the in-river habitat required to restore the river to good ecological health.
With fish populations recovering, we must tackle the barriers to fish migration to improve in-river habitat. An extensive fish removal strategy is in place in the River Irwell, with some success already, including on the River Tonge upstream of the project site. Removing three more weirs will further open the River Tonge for fish migration.
The goal is the removal of three weirs located in a series along the River Tonge, which vary in height between 1.5m and 1.85m. Therefore, a feasibility phase of work is being funded to examine the potential constraints, risks and costs of removing the weirs from the river.
Removing these weirs will open up the upstream section of the River Tonge and its two tributary streams, amounting to some 12km of the river (as other upstream fish barriers have already been removed as part of earlier work under the Irwell fish barriers strategy). Removal of these weirs will accompany river restoration measures working with local angling and river conservation groups to optimise fish spawning habitat.