Willmott Dixon Construction; a returning client, commissioned ELLUC Projects to undertake a flood risk assessment and concept drainage for a part greenfield, part brownfield site on Ullswater Road, Lowton, Wigan. The site was approximately 0.94 ha and had several watercourses and a pond within its proximity.
Initially, The Environment Agency Flood Maps were analysed to identify if the site was at risk of fluvial, surface and reservoir flooding. The EA maps showed that the site was not at risk of fluvial flooding. This was questioned as it was shown on the maps that there were several watercourses both in and around the site. ELLUC Projects noted that the EA maps indicate flooding from catchments above 3km². However, the watercourses on site had catchments of less than 3km² and so were not highlighted on the EA Flood Maps. Therefore, a site visit was undertaken to come to an accurate conclusion of the hydrology and flood risk on the site.
ELLUC Projects undertook the site visit and concluded that there was not at a high risk of fluvial flooding on site. This conclusion was made based on a visual analysis of the site and investigation of the secondary data, such as a topographical survey. Liaison with the Lead Local Flood Authority (LLFA) was required to understand if there were any past records of flooding on the site and if the construction works were acceptable. The LLFA initially responded that the proposed layout would have to be changed, this was due to the positioning of the main carpark being above the existing watercourse. In principle, the culverting of a watercourse is not allowed except for access. In response to this ELLUC Projects successfully argued an alternative method. This involved diverting the existing watercourse to flow around the carpark and then culverting the watercourse beneath the access road. This was accepted by the LLFA and the proposed layout was not altered by this.
The LLFA stated that previous records of sewer flooding were recorded on the site. ELLUC Projects incorporated this into the concept drainage to mitigate the risk. For the concept drainage, the client insisted on a pond to the South of the site. This meant pipe clashes were unavoidable on the concept design. ELLUC Projects resolved this issue by creating a functional concept drainage strategy which would meet all the client’s requests while staying within the guidelines stated by the Lead Local Flood Authority. This gave our client confidence in pricing from the beginning.
The efficiency, punctuality and professionalism of ELLUC Projects ensured that the job was successful. We were therefore commisioned for detailed civil and structural engineering design.