Autumn Brings a Tidal Surge to Saltfleetby-Theddlethorpe NNR

Cliff Morrison

Natural England volunteer Cliff Morrison shares his latest update from the reserve in Lincolnshire, where an autumnal tidal surge floods the salt marsh and impacts wildlife, and demonstrates the natural dynamic nature of a dune system - adjusting and shifting with the weather and the seasons.

A tidal surge corresponded with an early morning high tide here flooding the salt marsh and overtopping parts of the foredunes.

Those who scan from the Rimac viewpoint will be familiar with the 3-5 roe deer to be seen feeding far out across the saltmarsh and taking advantage of the safety that the remoteness brings. However, they can be taken by surprise by occasional tidal surges and must swim back to the foredunes.

a black and yellow image of a deer swimming by some reeds silhouetted in the evening light

Mrs Stephanie Lee is a frequent visitor to the NNR and was lucky enough to get take a photo on her phone (above) of a buck roe deer making it back to the dunes. She was at Donna Nook the previous day and was delighted to see a grey seal pup being born, describing the two events as memorable experiences along our coast. It is excellent, being able to share a visitor personal experience and photograph in a blog for Dynamic Dunescapes.

An area of saltmarsh is pictured with the sky reflecting in the pooled water

Rimac saltmarsh totally flooded and tide well up foredunes. Photo: John Walker MBE, 07/11/21

Tidal surges occur following periods of strong SW gales that pile ocean water up between Scotland and Norway, which then flows down the North Sea. Very high tides can occur if the surge coincides with a spring tide, as happened on the 7th November, with +40cm height gain. If the winds subsequently blow from the north, then the surge swells significantly. This did happen, but fortunately they then turned to fresh SW before the surge arrived, so no damaged occurred.

However, on 5th December 2013, the worst scenario conditions occurred almost together and a +90cm surge arrived causing significant, flooding in Boston and Humber towns with dune erosion and significant overtopping here. Even so, the gale force winds had abated just hours before the high tide and surge, so the damage was less than it could have been.

Photos below (taken 05/12/2013) show massive dune erosion and previous kidding to stimulate dune formation exposed. Large volumes debris piled up in front foredune buckthorn. The dunes have now rebuilt.