Spitalgate Heath, Grantham

THE CHALLENGE

Grantham was awarded Growth Point Status in 2006 following a successful bid by South Kesteven District Council and Lincolnshire County Council for additional funding from the Department of Communities and Local Government.

The Spitalgate Heath expansion, latterly badged as one of the ‘garden village’ schemes at the start of 2017, aims to provide up to 3,700 new homes and 11ha of commercial development.

The land was formally allocated for development under SKDC’s local plan in 2012. The area is dominated by the high limestone country typical around Grantham and by the River Witham’s valley, sheltering a highly-valuable riverine habitat. Water quality is key both in the river for its habitat value and for the underlying aquifer in the limestone that supports water-supply abstractions to the east.

SYSTRA’S ROLE

SYSTRA has been working on the flood-risk and drainage aspects of the scheme since 2007. The site is divided in two by the river and the ground conditions and topography vary across the site. SYSTRA has devised a site-wide surface drainage strategy which comprises both infiltration and attenuation and which seeks to adapt conventional SuDS features to suit the hillside slopes that form about half the site area as well as features that work on the high plateau with a shallow rockhead and a need to minimise depths of new infrastructure to avoid expensive construction works.

The SuDS concept designs involve a dispersed series of features throughout the residential area, using linear features as part of the development terraces on the valley hillsides or more compact features on the high plateau. The high permeability of the limestone creates a risk that pollution is passed too quickly with inflow into the fractured rock so infiltration features will be lined with finer material to control the passage of water and to permit those features to provide a water-quality control function. The commercial development will look to separate roof and trafficked areas’ run-off and maximise infiltration of the cleaner run-off so as to minimise the residual volumes that require control by attenuation and restricted discharge. Outline permission was granted in principle in July 2017.