Coastal grazing marsh - Drainage

Accompanying the increase in stock levels is the use of drainage works, particularly to reduce the level of winter flooding. In many cases engineering works on floodplains have caused sites to dry out. This in turn can produce erratic flooding regimes which changes the nature of their invertebrate communities. Flooding at unusual times can create a temporary abundance of terrestrial invertebrates (drowned by the flooding) but will lead to a reduced density of soil invertebrates in the longer term.

Drainage has a significant effect on bird populations. Lower water tables, especially in winter decrease the availability of prey, particularly for waders. Efforts to redress this situation have been made at several sites including the Somerset Levels and at Holkam in North Norfolk.

Also important, at least to the interests associated with brackish water communities, is the repair or renewal of structures controlling sea water intrusion. When undertaken without consideration of the implications for brackish water invertebrates they can have a significant adverse impact on the populations.