Royal HaskoningDHV has been commissioned by the SES Water to undertake a feasibility assessment of making alterations to the west weir at Shepley Mill. This study aims to identify what alterations to the west weir are feasible from an engineering and fish passage perspective, but also whether the impact of the alteration on the upstream reaches are acceptable to stakeholders. It is acknowledged other habitat enhancements have been identified as part of wider works; however, this feasibility study predominantly focuses on fish passage improvements directly upstream and downstream of Shepley Mill, although benefits to geomorphology and in-channel habitats are also taken into consideration. Based on the outcomes of the study and stakeholder consultation, the following three options appear to be the most suitable fish passage solutions for this project, although further investigation on the options will be requited:

Option 2 – Full Weir Removal with pre-barrages / step-pools, with preference for only the west weir being removed combined with pre-barrages / step-pools. It should be noted this option would require the installation of a trash screen at the entrance of the west weir culvert.

Option 4: Weir Lowering and rock weirs, with the option of a single flight Larinier fish pass on the west weir.

Option 5 –Technical Larinier Fish Pass on west weir, with preference for a two flight over a one flight Larinier, to ensure upstream water levels are maintained along the Carshalton and Croydon branches of the River Wandle.

Based on the above three options and given the potential for high costs, Option 5 may be the most cost-effective solution, which would also have no impacts upon existing water levels, flood risk; and could be combined with complementary river restoration works; although there is also potential for a Hybrid Option in between Option 2,3 &4. However, further investigations and assessments, such as Hydraulic Modelling and Biodiversity Net Gain (BNG) Assessments will be required for the next phase to support the selection of the preferred fish passage option for the project. The Hydraulic Modelling will particularly focus on how the options may influence the hydrological connectivity between the Carshalton and Croydon branches; and the ecological features of Wildness Island such as the ponds and wetlands.