A common and widespread feature in reports about the 20 July flooding in Grove and the Hanneys is that, at one point, there was a surge in the water levels in Letcombe Brook. It would be valuable to learn more about the surge, e.g. does it simply reflect the fact Letcombe Brook water levels peaked two or three hours after the rain stopped? Such a surge could well be a perfectly natural effect, e.g. due to the time delay in water flowing from the Downs or from the failure of debris dam upstream from the affected areas.
One concrete piece of evidence for the surge is the double peak in the flood water levels on Vale Avenue. The first peak occurred during, and immediately after, the heavy rain and was clearly due to local surface water flooding. The water level then dropped significantly before rising again in sunny conditions after 17:00. This second peak was due to water spilling eastwards from Letcombe Brook. It shows that the surge occured after 17:00.