The Burlish Park Primary School site offers the perfect conditions on which to design a fully infiltrating SuDS scheme, one of the first of its kind in the country. Waterflow is managed through small-scale and large-scale features throughout the landscape, giving it a distinctive character.
The existing site at Burlish Park Primary School is effectively flat. It is also very free draining.
The site design strategy is to collect rainwater at the surface and direct it to shallow basins around the school building and next to paths and roadways to collect runoff. These small basins are generally designed as ’raingardens’ and will deal with modest rainfall with very little water visible at the surface. Car parking and frequently-used roads collect, treat and infiltrate rainfall by using either permeable pavement or an arrangement of filter strip and filter drain.
After heavy rain, water will overflow into grassy swales, carrying the water to larger basins that allow water to soak into the ground over several hours. This method replicates the way water would behave naturally on the site, and has the benefit of watering the soil and flora at the same time.
The school preferred not to have standing open water on their site as part of this SuDS scheme as they already have a small pond. They opted for flexible and accessible open spaces wherever possible.
Working closely with the school, we produced a series of connected, soft landscape spaces that children can access on a day-to-day basis and make their own through the addition of planting. Some SuDS features provide large, open spaces available for everyday play, e.g the shallow wildflower detention basins between grass sports pitches and informal outdoor classroom space within the amenity detention basin, enclosed by tree planting.
A series of overground channels allow the children to see the SuDS system in action as it collects rainwater from the roof and transports it through the hard landscape and into a swale or basin. It should be possible to see the first raingarden fill up gradually and the water flow into the next feature along the system. We have introduced attractive planting to features, creating colour and microhabitats. A bridge crossing over a swale to the pitch allows a further element of interaction with the rainwater management train.
An innovative approach has been used to maximize the infiltration potential across the site and provide a transparent methodology for the calculation of storage and exceedance in any basin on the site based on the 1 in 100 year return period event + 30% allowance for climate change.
The principle developed for this flat site calculates the volume of rainfall that can be managed by each square metre of infiltration basin. After the critical rainfall event was determined, a supplementary check was carried out to check half empty time is achieved within 24 hours, as this becomes the critical case for low infiltration soils.
The infiltration structures located close to the school generally deal with day to day rainfall allowing larger rainfall events to fill the shallow basins and overflow along paved channels or swales to large dedicated grass infiltration areas that are not critical to school use at all times.
Location: Stourport-on-Severn, nr. Kidderminster
Return period Attenuated : 1 in 100 year return period event + 30% climate change
Techiniques : Planted raingardens, large wildflower detention basins, grassed collection basins, linear infiltration or conveyance swales, and permeable paving.
Discharge destination: All water infiltrated on site
Infiltration rate : 0.072m/hr
Client : Worcestershire County Council