River mouths are useful indicators of coastal sediment transport. Often they are deflected in the direction of dominant longshore drift, sometimes with spits building up on their seaward side pointing in the prevalent direction of sediment transport.
Dramatic changes in the position of the mouth of the River North Esk are recorded in old Ordnance Survey maps dating from 1868 onward (represented in the diagram below). These bear testimony to the temporal dynamism of the shore, but they also allow us to make interpretations about local coastal processes when each of the maps were drawn.
In 1868, a long, narrow spit was shown to be deflecting the mouth of river to the north. This configuration likely reflects a dominance of northerly longshore sediment drift. However, in 1879 the narrow neck of the spit breached during a storm and as a result the river mouth shifted approximately 1500 meters to the south of its former position. Later, in 1904, the mouth was shown to be deflected in a slight southerly direction with an apparent formation of an incipient spit on the northern side of the estuary. This appears to suggest a stronger southerly drift alongshore at this time. However, from the 1920s onward, successive maps begin to show clues of a strengthening of northerly longshore drift as the mouth of the river was gradually deflected farther northwards. By 1976, it had reached the position that it roughly is at today, the river’s wandering seemingly having slowed down substantially in recent decades.
It is still possible to see the former course of the North Esk estuary during a visit to the St Cyrus Natural Nature Reserve where a wooden walkway crosses the abandoned channel. Several other clues point to the former existence of an estuary at this location, including rock outcrops smoothed by long-absent running water and an old piece of railway track which was used by 19th century fishermen to tie up their boats. Furthermore, the fantastic visitor centre at St Cyrus is housed in the old lifeboat station which, when it was built in the 1860s, enjoyed an estuary-side location well suited for rapid response to emergencies at sea. The channel avulsion of 1879 left the station high-and-dry, and unsurprisingly it was decommissioned a few years later!
Tidal inundation of the old channel occurred frequently up until the late 1980s, however this became gradually rarer due to ongoing accretion at St Cyrus. Seawater hasn’t encroached into the channel since 2001, but given the remarkable dynamism of our coastal landscapes this, of course, may just be a temporary reprieve!
St Cyrus Nature reserve Publications: http://www.nnr-scotland.org.uk/st-cyrus/publications/
Hansom J.D., Rennie A.F., Dunlop A. & Drummond J. (2011). A methodology to assess the causes and rates of change to Scotland’s beaches and sand dunes Phase1. Scottish Natural Heritage Commissioned Report No. 364. http://www.snh.org.uk/pdfs/publications/commissioned_reports/364.pdf
Milne, F.D., Dong, P. and Davidson, M. 2012 Natural variability and anthropogenic effects on the morphodynamics of a beach-dune system at Montrose Bay, Scotland. Journal of Coastal Research. 28 (2). 375-388.