The River Ash is a river in England and lies just outside of Greater London. More specifically, it flows from the River Colne, through the borough of Spelthorne, running through the towns of Ashford and Shepperton before finally joining the River Thames in the creek behind Sunbury Lock at Sunbury. It goes through many back-gardens in Old Charlton Road, Shepperton.
Many alterations have been made due to human action. There are maps dating back to medieval times to depict this. The earliest one shows the history of the Shepperton Studios site, more particularly Shepperton Manor. This dates to the Westiminster's monks, whom, it is suggested, may have done some widening still visible today.
In 1910, the Metropolitan Water Board made the Staines Aqueduct, with the purpose of supplying water from the River Thames at Hythe End to its works in Sunbury. This meant that the river was now in a siphon at three locations: Birch Green, Shortwood Allotments as well as adjacent to where the Queen Mary Reservoir is in Laleham.
More recently, the source of the river was moved quite a few metres south and some hundred metres of its length was diverted to make way for the Staines Bypass (the A30) in the early 1960s. Here it flows underground for 270 metres beneath the Crooked Billet roundabout.
Much of recent flood prevention is done by River Ash Flood Alleviation Scheme. A major upgrade of the water treatment works at Ashford Common was started by Thames Water Utilities during 1994 and 1995. There was an expected increases in flow and flood risk to properties along Old Charlton Road, Shepperton and Heriden Way because the works discharges to the lower River Ash near the M3. Consequently, a flood relief channel was suggested. This was built during the first five months in 1995 and cost a total of £450,000.