English: Halstead: Flood Storage Area embankment Halstead has periodically suffered from flooding from the River Colne, the most recent damaging flood event being in October 2001, when about 300 properties were flooded. In order to alleviate this flooding the Environment Agency built this embankment in 2005 across the valley of the Colne, upstream of Halstead near Box Mill Plantation. In the distance is a twin sluice gate, seen in close-up in 1457081, which allows the river to flow normally through the embankment. However, if a flood threatens, the sluice gates can be either fully or partially shut and the flood water is then impounded behind the embankment, and allowed to flow down gradually and in a controlled manner through Halstead. In a very severe flood event the impounded water could reach the level of the top of the embankment, in which case the flow would again be partially alleviated, this time by spreading it out over the very wide spillway section of the embankment which is about 200 metres long. A severe flood event like this would be anticipated by the Environment Agency to occur, on average, once every 75 years or more.