Michael Evans & Associates was approached by a local developer, wishing to regenerate a brownfield site that had been demolished ahead of redevelopment in the Amber Valley district of Derbyshire. Michael Evans & Associates was contracted to offer expertise in the design of both the foul and storm water drainage schemes for the site. The proposed development was to build a total of 13 houses, including a row of eight terrace houses, plus four semi-detached houses. The previous building had been connected to an existing combined sewer on the edge of the site.
A Previously-Undetected Issue Emerges
During the pre-design site visit, Michael Evans & Associates’ drainage engineer discovered an existing public lateral sewer which also crossed the site, serving a property outside of the boundaries of the redevelopment. This sewer had not been identified in the pre-planning stage and post-development would run under one of the proposed houses. As the location of the houses on the site had already been approved and included in the development plan, it was agreed by all parties that this sewer would need to be diverted.
Local water authority Severn Trent Water agreed that the existing connection to the brownfield site could be reused to serve the new development. However, following the diversion works it required the sewer’s flow rates to remain unchanged or be improved upon.
Modelling with Flow
Michael Evans & Associates used Causeway's Flow Essentials software to model the public lateral sewer along its existing line to evaluate the existing flows. They then used Flow to layout the diverted route and compare and demonstrate adequate capacity to maintain the previous flow rates and meet Severn Trent Water’s requirements. Flow Essentials was also used to design the foul networks servicing the properties.
Once the diversion and foul network designs were completed, Michael Evans & Associates used Flow to design the storm water network. Given the Flow rates and volumes they were required to meet – an increase of 30% against the existing brownfield rate – they established crate storage and Hydro Brake flow controls and incorporated these into the design. While also simultaneously analysing the network over a range of storm durations and return periods including climate change, the design was finalised.
Approval Is Granted
The designs results report was generated in the Flow software so that Michael Evans & Associates could collate the results and associated drawings. Finally, these were submitted for approval to Severn Trent Water and subsequently approved.