Hillingdon Council’s Engineer wrote a report in April 1992 advising of the risks of flooding to homes in the flood plain of the Cannon Brook, below the dam at Ruislip Lido. This report included the following information and recommendations:
“During the past 15 years two instances of serious flooding have occurred in the area south of the reservoir. In 1977 and 1988 houses were inundated with flood water to depths approaching 1 metre above floor level and the safety of residents was threatened. It is known that ... high volumes of water from the reservoir contributed greatly towards the damaging flooding.”
“The depth that would prevent this type of flooding ... is 1.5 metres below spillway [datum] and the engineering recommendation would be that the lake level be returned to that level after any storm.” (The full report can be read on the next page, please follow link at the bottom of this page)
This recommendation was accepted by the Council at the time with the result that swimming, boating, dinghy sailing and water-skiing ceased.
However, the Council has now confirmed that “from 1998 to 2008 the water level was maintained at around 1.0m below datum”. After receiving representations from the Friends of Ruislip Lido in 2008 the Council decided to reduce the safety margin to “0.65m below datum ... with the proviso that the situation would be monitored closely”.
Early in 2010, following a request from the Friends of Ruislip Lido to refrain from releasing more water as this would have an adverse effect on the spawning frog population, the Council agreed not to release any further water for 6 weeks from March. This was stated to be “on the understanding that levels would be assessed and weather conditions monitored daily to ensure that any risk could be identified quickly and dealt with efficiently.” The Council's own water level records show that for the first 6 months of 2010 the Lido water levels were maintained at or close to the lower spillway level with little or no margin for safety.
Hillingdon Council now wishes to implement an 'improvement' programme for the Lido including new toilets, changing rooms, a new woodland centre, angling, a 160 space car park in the Lido grounds and, subject to raising the Lido water level, the reintroduction of swimming and boating.
The Council has commissioned a Flood Risk Assessment, which has been referred to the Environment Agency for consultation, and submitted a planning application for the proposed car park.