Hydrology
There is a layer of sandstone rock beneath the whole of the catchment of the River Lymn, which is largely covered by a layer of chalk. The sandstone outcrops in only a few places, and where it does, the springs provide the base flow for the river. As the layers of rock continue to dip to the east, they are covered by boulder clay, gravel and alluvium.
Flow on the upper river is measured by a gauging station at Partney Mill, consisting of a Crump weir with a 16-foot (5 m) crest. The catchment area of the river above this point is 23.8 square miles (61.6 km2), and this area received annual rainfall of 27.4 inches (696 mm) in the 1960s. This produces an average daily flow of 9.5 million gallons (43.2 Megalitres (Ml)), although a peak flow of 253M gallons (1149 Ml) was recorded in April 1981.
Discharge to the North Sea is along the Burgh Sluice Relief Channel during the winter and at times of high flow, but when flows in the river are low, Wainfleet Clough Sluice is used as the discharge point.
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