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River Mun

The Mundesley Beck is a small river in north-east Norfolk, with a length of about 8 km. It has its headwaters at Northrepps, at circa 40 m (131 ft) OD, It flows in an east south-easterly direction parallel to the coastline before turning abruptly north-eastwards to discharge its waters into the sea at Mundesley.

The Beck drains the south-eastern slopes of the Cromer Ridge landform The Ridge is a complex stack of glacial and glaciofluvial sediments dating from the Anglian glaciation c.450,000 years ago, resting on an eroded surface of Cretaceous Chalk and Pleistocene Crag (mostly marine sands and gravels). The Ridge meets the sea between Overstrand and Trimingham, where the deposits of three separate ice advances are represented in the cliffs, including layers of chalk-rich till (a mixed, clayey sediment deposited directly beneath the ice). The main body of the Ridge is composed of a thick sequence of glaciofluvial outwash sands and gravels of the Briton’s Lane Formation, dating from the retreat phase of the Anglian ice sheet. These sediments underlie the higher ground in the catchment. A more complex sequence of sands and tills outcrops in the lower half of the catchment; locally the till may impede drainage and give rise to ponds on the valley sides. The soils in the catchment are deep, permeable and loamy, and belong to the Wick 2 Association. In common with large areas of north-east Norfolk, they contain much fine, wind-blown silt dating from the last (Devensian) glaciation.

There are many shallow dry valleys in the catchment, and these are floored with layers of fine slope-derived deposits, moved downhill into the valleys by hillwash or by frost-creep in the Ice Age. The sands, gravels and chalky clays of the Ridge act as a major local aquifer, holding water which discharges southwards into the Mundesley catchment, or northwards to the sea cliffs where it causes spectacular landslips. Because of the sandy soils, the water has a higher content of dissolved iron than many other rivers in Norfolk. There is very little direct contribution to it from Chalk bedrock; a borehole at Craft Lane, Northrepps, penetrated no less than 67 m (220 ft) of sands and clays before reaching it.