Starting at Wootton Bassett to the east, areas of high ground run west towards Malmesbury along the route of the B4042, southwest to Lyneham along the A3102 and the airfield at RAF Lyneham.
Rainfall on a large percentage of Wootton Bassett and almost all of the land eventually drains down into the Bristol Avon through two main watercourses, Brinkworth Brook and Dauntsey Brook (also called The Bourne beyond Dauntsey).
Water south of the M4 has to flow north via both brooks. Brinkworth Brook flows north through a single (16’ wide x 7’ high) culvert while Dauntsey Brook flows north under the M4 (6’ wide x 7’ high), west under Church Lane (7’ wide x 7’ high), back south under the M4 (7’ wide x 7’ high) and finally north again west of Christian Malford (8’6” wide x 8’ high).
The M4 is raised above the surrounding land and, apart from these culverts, generally acts as an impenetrable barrier to floodwater. Largely due to the M4, Brinkworth Brook now regularly flows overland through Grittenham and into Dauntsey Brook.
Flooding in Dauntsey is complicated with multiple significant watercourses, fluvial (river) and surface water flooding. Many road culverts are undersized and, until these design errors are corrected, will remain sources of flooding.
Up to the middle of the 20th C, maintenance of watercourses was carried out annually by landowners and district councils. Farmers have reduced their workforces dramatically and routine ditch maintenance has largely stopped. Similarly watercourse maintenance has been reduced in priority and importance by local authorities, the Highways and Environment Agencies.
And, possibly most significantly, nobody knows (or has cared) how it all should work… at least until the advent of DDB.
The following are the major sources of Dauntsey’s floodwater: