Option 2: Full Weir Removal with Pre-Barrages / Step-Pools
Solution
Further down the hierarchy of suitable solutions to improve fish passage along river systems, Option 2 would consist of completely removing one or both weirs associated with Shepley Mill. This would be combined with regrading the bed, desilting, installing trash screens at the entrance of one or both culverts to minimise the risk of debris entering/blocking the culvert; and constructing pre-barrages / step-pools along both the Carshalton and Croydon branches of the River Wandle. In addition, to ensure the successful migration of fish through either of the culverts, fish friendly modifications to the culverts, such as baffles, could be implemented.
Concept Design
Appraisal
Option 2 has the potential to allow for the safe passage of fish and eels through Shepley Mill, contribute to GEP under the WFD and comply with the Eels Regulations. It is also predicted that the construction of the pre-barrages along the Carshalton and Croydon branches, if one or both weirs were removed, would maintain the upstream water levels and head drop differences of the west and east weirs i.e. maintain hydrological status quo. As such, it is anticipated this option would not impact upstream water levels, fish passage and existing habitats of Wilderness Island, in particular during low flow conditions. Overall the suitability of this option to meet the project objectives is considered High (if the west weir only is removed).