Assessment of the impact of water level management on flood risk

The Somerset Drainage Boards Consortium has undertaken an assessment of the role of water level management in the severity of flooding in Somerset.

Understandable concerns have been raised that the maintenance of seasonal water levels can increase the severity of flooding by occupying storage capacity in ditches.  Therefore, the Somerset Drainage Boards Consortium has assessed the effects of water level management on flooding in order to address these concerns.

Ditch and soil water storage capacities were calculated using the best available evidence and observations collected from Somerset and other low lying areas.  The storage occupied by seasonal water level management practices was also calculated and assessed in relation to the maximum flood volumes and levels experienced during winter 2013/14, as well as the volumes and levels of less extreme flood events.

The assessment finds that the volume of water maintained within ditches, and corresponding reduction in flood storage capacity, represents a very small fraction of the volume of flood water stored on the moors during major flood events.  Expressed both as a proportion of the maximum flood volume or change in flood level, the calculations indicate that winter raised water level areas have only a very minor impact on large flood events. Water levels for agriculture in summer occupy larger volumes, but these are still small compared to volumes of water stored on the moors during major flood events.

Cattle that were evacuated during the flooding are now back grazing on Northmoor.



Summary leaflet of the main findings of the assessment: Public-leaflet-water-level-flood-impacts

Full copy of the report:  Ditch-and-Soil-Storage-Report