The marsh water levels are not a constant, they vary continuously; not only as a result of extrodinary natural events such as drought and flooding, but also as a response to normal everyday weather. We also control the marsh water levels for management reasons, conservation aims, and to facilitate safer grazing. By changing the height of sluice boards we alter water levels to make the marsh more attractive to wading birds, and to control the proliferation of aquatic plants. Managing the marsh water levels is a balancing act, with some areas requiring wet conditions and other habitats need to be damp or dry; it’s difficult to get the balance right. There is often a long time lag between lowering a sluice board and the water levels dropping. Lowering the sluice for too long a period can end up with the loss of too much water, and raising the boards too early can result in the retainment of too much water. Local weather conditions can make a big difference, as can weather condition thirty miles away. The River Stour can go from low water to flood conditions in a matter of a few hours. So through the judicious manipulation of sluice boards heights we aim to achieve low level muddy margined pools in spring and summer and maxium water levels in autumn and winter. Drainage ditches can slow the flow of water through the marsh when they are full of reeds, bull rushes, yellow flag irises and silt. Achieving optimal water levels on Wilden Marsh is a nightmare! Having too much water is prefferable to not having enough, though.
The north marsh, including the Swamp, drain through the North Pond Chain into the River Stour midway along the North Pasture. These natural spring waters, rain and flood waters are not drained through an adjustable sluice, they overflow the riverbank at its lowest point.
I saw a lesser spotted Mike Averill on the north marsh this afternoon, doing its water level measurements.