This redevelopment on the site of an old electricity substation, in the centre of Stamford remains the first high density SuDS scheme in the UK to demonstrate both a full ‘management train’ for urban runoff and the contribution of SuDS to defining the character of the landscape in a development.
The challenge of meeting SuDS requirements on a development of 106 units/hectare needed a radical design approach exploiting the full benefits of integrated SuDS design. The use of most of the site for cars and pedestrians precluded soft techniques like swales, basins and ponds. Instead, our approach made the most of permeable block paving to collect, clean, and store urban runoff as well as introducing design elements that mimic the more usual soft SuDS landscape features in an urban design form.
The loose arrangement of street and courtyard space largely paved with permeable block pavement provides an apparently conventional view of urban development to the visitor. Even closer inspection reveals only the grit joints to block pavement and a complete absence of road gullies.
The placemaking value of the main SuDS canal and bridge echoes the major river crossing of the Welland in Stamford. The stepped sides of the two canals mirror the safe 1 in 3 sloped sides of a grass swale. The base of the canal and rill contain a shallow (150mm) wetland with both aesthetic and biodiversity benefits. When it rains the canals and linking rill rise in anticipation of the river but empty before the main flood volumes reach the town. However, in the meantime the water has been cleaned and gives pleasure to residents as well as a home to wildlife.
Rain falling on the permeable roadway and car spaces filters slowly into crushed stone beneath the surface where it is cleaned and stored before it enters the canal and rill features. Roof water either flows underground into ‘diffuser boxes’, which are protected by silt trap chambers, or drops directly into the rills. In this way, the most polluted runoff from roads and car parks undergoes initial cleaning before it enters the open canals and rills. The treated road runoff together with cleaner roof water flows slowly through wetland vegetation before dropping quietly down a stepped rill into the River Welland. The design has control structures that ensure there is storage before water enters the river. The high runoff rate from the site ensures drain down before water arrives in the town from the Lincolnshire Wolds and ensures an unpolluted wetland habitat.
Location : Stamford, Lincolnshire
Return Period Attenuated : 1 in 100 + 30%
Techniques : permeable pavement; rills; canals; slot weir.
Discharge Destination : River Welland
Discharge Flow Rate : 40L/sec/Ha
Client : Taylor Woodrow