The Wilts and Berks Canal is in the process of being restored. Currently isolated sections are “in water”, but it is likely to be many years before it is restored to full navigation (target date is 2025.)
The length between Old Sodom Lane and Dauntsey Lock receives a lot of water very quickly due to the steep slope of Lyneham Banks. Historically, water levels would have been limited by the weir action of the lock gates and the spillway. The canal is largely blocked at Dauntsey Lock with only a relatively small culvert under the B4069, so all flow has to take the spillway (intentionally) or an overland (unintentional) route under the railway bridge at Old Sodom Lane. This second route, along with general surface water flow, has created localised flooding problems around Corner Farm and Scots Smith Farm.
The canal spillway passes under the railway in a 1 m2 culvert, but the culvert under the road at St James is less than 0.3 m2 – this clearly presents a potential local flooding problem! The route of the spillway includes two sharp 900 bends and, at the first the water regularly comes out of bank and spreads across the land to join any pre-existing surface water. Modifying the watercourse to keep the flow in-bank would probably lead to flooding at St James (22 houses) unless Wiltshire Council increase the size of the culvert.
The current overland flow significantly impacts on 59 Dauntsey (the white thatched cottage just south of Good Monday’s Farm), Good Monday’s Farm and the road just east of Good Monday’s Farm (photograph with people standing in the water). This area again has undersized culverts under the road – until these culverts are increased in number and capacity, local properties will continue to flood and the road be closed to cars.
In the area for several hundred metres to the east of Trow Lane, the canal has been breached in several places. As a consequence it no longer either holds water or is capable of attenuating the overland flow down the hillside from the direction of the A3102.
Tockenham Reservoir was originally constructed to feed the canal in times of water shortage. The water control structures have been removed over the years and now, once the reservoir has reached its design level, all additional water is discharged with minimal attenuation. The flow then passes down the Lillybrook into Brinkworth Brook just before it passes under Whitehill Lane near the Ivy Lakes. As this is upstream of the Brinkworth Brook M4 culvert, in times of heavy rain this additional flow contributes to the overland flow into Dauntsey Brook.