Gloucestershire Surface Water Management Plan

Surface Water Management Plan’s (SWMP’s) are a framework through which local partners work together to understand the
causes of surface water flooding and agree a cost effective way of managing that risk by making decisions that are evidence
based, risk based, future proofed and inclusive of stakeholder views.
RAA were involved in one of the First Edition Surface Water Management Plans acting as a sub-Consultant to Halcrow for the
Gloucestershire SWMP. RAA’s detailed knowledge of Gloucester’s sewerage network gained from modelling for Severn Trent Water
together with our pluvial and fluvial modelling expertise has enabled us to build a truly Integrated Urban Drainage model.
For the Gloucestershire SWMP we undertook 3 stages of modelling.
The initial ‘overview’ stage involved pluvial modelling of 5 major catchments covering nearly 30% of Gloucestershire. The second
‘intermediate’ stage involved more detailed pluvial modelling of the same catchments with sewers and culverts included. The third
and most complex stage was a fully integrated model with all the sewers in part of Gloucester with 3 major urban streams included.
This model was highly complex and was calibrated against the major flooding of 2007. The model was used to calculate the annualised
flood damage (AFD) costs and then a number of potential solutions were modelled and cost estimates prepared. The reduced AFD costs
were determined and a cost–benefit exercise was undertaken. A ‘Drainage Strategy’ and a ‘Supplementary Planning Document’ for
the study area were prepared as the final SWMP deliverables. The project was completed in 2009.