RES Environmental Ltd were commissioned by ARC to assess external sewer flooding at 8 Scottish Water flood register (SFR) locations and to identify potential options.

A history of flooding is associated with properties on Belmont Road and Meadowpark. The rear of the properties sit at a lower level than the highway and this is the primary source of flooding. It was established during the Scoping Phase that the SFR is not representative of the extent and severity of the flooding issue and this was considered when designing solutions.

A review was conducted on the Meadowhead ICS model, which established the need for additional survey data and the addition of lateral connections to ensure the model accurately replicated reported flooding.

The existing ICS model was integrated with a mesh created from SEPA LiDAR data and converted to a 2D format in the area of concern. In addition, lateral connections were modelled, with one scenario also representing the NRVs currently offering protection for properties. Rainfall was applied to the 1D subcatchments and out of sewer flooding allowed to flow onto the 2D mesh. Predicted flooding compared reasonably well with the resident reports.

In addition, a 2D pluvial assessment was conducted over a wider area to confirm the main flow routes and ponding locations. The results of the pluvial assessment compared well with the SEPA Pluvial Food Risk maps.

The 1D and 2D models were uplifted to a future design horizon, to ensure the proposed solutions would be able to accommodate increases in population and impermeable surfaces.  The proposed solution consisted of a storage tank with Real Time Control elements to manage the rate of return flow back into the existing system. Additionally, a number of ‘low-cost’ options were investigated in the 1D-2D model such as the use of APNRVs, however unacceptable detriment was seen in the highway, which then subsequently entered the property boundary.

The report collated all findings including the flooding issue/mechanism, model updates, predicted flood volumes and developed solutions. This information was contextualised, with the legal requirements and construction costs, to inform Scottish Water of the flooding issue and the cost to resolve it.