Source Control Technologies
A changing environment and increasing levels of new development covering soft landscaping are combining to create the increased occurance of flooding. A new sustainable approach to drainage design is under evolution within England. Such methods are already employed on mainland Europe and throughout Scotland and with future legislation and imminent publication and adoption of CIRIA RP637 as a guide for sustainable site drainage design, SEL have made a conscious effort to embrace techniques and systems that will soon become common place. Below are a selection of projects where such techniques have been employed with the purpose of dealing with storm water at source, where there are either inherent site problems or discharge restrictions imposed for storm water entering the sewer.
   
   
Scheme: New Housing Development, Verwood, Dorset
Client: Wimpey Homes Holdings Ltd
Scope of Works: Install 5No. shallow stormwater balancing tanks

 

Attenuation tanks with storage capacities of 10, 40, 35, 8 & 9cu.m were installed in various locations around site including under driveways and in soft landscaping zones to control the discharge into an adjacent watercourse.

 

 

The use of modular units to construct the storage tanks made it possible to achieve the various volume requirements.   The balancing tanks had to meet two criteria :-

1. The  close proximity of the new houses meant the tanks had to be able to fit into limited areas on site. 

2.   In order to keep costs to a minimum, the amount of exported dug material had to be kept to a low level.

 

The tanks were founded at shallow depths and were only 400mm in actual depth, cover of 1.0m was placed over the top which consisted of either as-dug and topsoil or as-dug and road construction. The modular units were encapsulated in a robust weldable membrane. The overall time for the installation of the 5 stormwater balancing tanks was only 4 days. The versatility of the modular infiltration units allows proposed storage tanks to be designed to meet the storage requirements and where there is a major deep excavation; a more economical shallow ‘flatter’ tank is a viable alternative. Consequently drainage pipework would not have to be founded at deep invert levels, reducing the amount of excavation necessary and the on-site installation time, creating considerable savings. 

   
   
   
   
Scheme: Shuttleworth Meads, Padiham, Burnley
Client: Graham & Brown
Scope of Works: To design, supply and install a stormwater management system

 

The site was low lying, with a fixed level outfall into an adjacent river that surcharged during periods of heavy rainfall. Large diameter pipes were unsuitable due to an insufficient gradient to attain required falls and recommended cover to the pipes could not be achieved. This was a brownfield site with high level contaminated groundwater. The total site area is 30,000m2.  Rainwater from the site was collected in a trench surrounding the perimeter of the building. The trench was constructed from modular units encapsulated in a robust weldable hydrocarbon resistant membrane to resist the aggressive contaminants within the existing made ground.  The trench is connected to an outlet which provided combined containment, storage and flow to the lagoon. The lagoon discharged into the River Calder over a weir.

 

 

The trench surrounding the perimeter of building is 1.5m wide x 0.4m deep. It was encapsulated in a robust weldable hydrocarbon resistant membrane.  The outlet from the trench to the lagoon is 3m wide x 0.4m deep x 90m long.  This has been designed to balance the storage requirements for the stormwater with outflow to prevent flooding occurring during periods of heavy rainfall.