Recovery of coastal reserves after the 2013 surge

The storm surge dramatically illustrated the dynamic nature of our coastal landscape. Coastal nature reserves are, by their very nature, environments that change as tides and winds deposit or erode sand, shingle and rock.

The Lincolnshire coast has always been in a considerable state of flux since its creation as part of the island of Great Britain some 8,000 years ago at the end of the last Ice age. Great minds had conjectured our island’s creation, none more so than Sir Joseph Banks and his friend Joseph Correa de Serra (a Portuguese Abbott) as they walked along the beach at Huttoft in the late 18th Century. The source of their fascination was the remains of the submerged forest, their conclusion that it must have been left high and dry by an earthquake owing to “the level of the waters in our globe is much below what it was in former periods”, a clear reference to the Biblical flood!

Considerable coastal research and study has followed, particularly following the surge tide of 1953 and its tragic consequences. Even in half a lifetime, Barrie Wilkinson’s fixed-point photographs of Gibraltar Point have shown the dramatic changes that can take place, making our coast the most natural and fascinating of the county’s habitats.

Of course these issues have been brought right up to date with windstorm Xaver that struck the coast on the evening of 5 December 2013. It had been well predicted and anticipated for several days, preparations had been put in place, but the height above the 1953 event had not been fully anticipated. Whilst in the intervening years the improved flood defence and early warning meant no lives were lost, there was still considerable property damage.

The mechanism of the storm was studied and the scenario for a major storm surge – winds from the north west, deep low pressure system over Norway and the surge coinciding with a high spring tide – means that all future events will be well predicted.

Staff at Far Ings, Donna Nook and Gibraltar Point spent a fraught few hours in the dark on the early evening of 5 December; the full extent of the damage being revealed the following morning after Xaver had passed through. Fortunately at the time of the high tide the winds had abated, but the three NNR reserves had all suffered damage from flooding. Moulton Marsh was the only other Trust site that was damaged, but the national news focussed on the property damage in Hull, Boston and flooded villages along the Humber.

Time, and a relatively short time at that, has shown the flooded habitats to be remarkably resilient for the most part, or if ‘damaged’, the subsequent re-setting of the habitat back to more primary colonisation stages has been interesting.

Fences and basic infrastructure were quickly rebuilt, but the fate of Bulldog Bank (and hence the Freshwater Marsh) at Gibraltar Point still lies in the hands of the Environment Agency and the County Council. Other flood banks, particularly on the Humber, were quickly repaired. The building damage to the visitor centres at Far Ings and particularly Gibraltar Point have been problematic in terms of education and visitor facilities, but both sites should be up and running at full capacity again in 2016.

Xaver has certainly focussed the attention on the future of coastal defences and the habitats that are protected by them, particularly the vulnerability of freshwater systems immediately behind the defences. For the big estuaries of the Humber and the Wash the debate over soft defences will continue; the maintenance of the beaches and sand dunes of the open coast will have the engineers scratching their heads for some time.

There are great opportunities for the Trust to make the case for large, natural coastal ecosystems to offer flood protection and long-term resilience for sea level rise both on the grounds of economics and habitat/species protection.

In the immediate aftermath of the December storm surge, things looked alarming at Far Ings NNR in the north, round the coast at Donna Nook NNR, down to Gibraltar Point NNR and into the Wash at Moulton Marsh. Initial reports were of “catastrophic” flooding. This was most obvious from the man-made features: buildings and sea defences were damaged and fences washed out. But the habitat damage was more subtle with standing sea water on freshwater marshes, freshwater pools flooded and some impressive debris and strandlines left behind on all four sites. While some of the floodwater drained away quickly, it persisted for weeks elsewhere. Work started quickly to repair the physical infrastructure, but the habitat recovery was going to be more of a waiting game.

Dave Bromwich, Head of Nature Reserves, November 2015

There follows below some observations from the Field Staff at the four affected sites:

Far Ings

Eighteen months since the tidal surge of December 2013, the new visitor to any of the South Humber Bank nature reserves would not be aware that anything untoward had ever taken place. This remarkable recovery has been due to the resilience of nature and also to the hard work of many people.

One positive thought was that the inundation would help arrest the process of succession which is the greatest enemy of land-locked wetlands. In some pits such as Barton Reedbed at the Far Ings NNR this proved to be the case: severe flooding washed away the accumulated litter layer and reinvigorated the reedbeds. This is the sort of thing we try to do with various conservation management techniques but rather less dramatically!

One fear at the time was that the huge amount of water deposited from the Humber would raise salinity levels, killing or preventing the freshwater fish from breeding and thereby affect piscivorous bird species. This did not occur as the brackish water quickly drained away within a few days before the salt had time to sink. One pit, “Western Approaches”, did suffer a latent effect: the slightly raised salinity plus hot sunshine in August 2014 triggered a toxic algal bloom causing a significant fish kill.

Though natural systems are quite robust not all species are. One big loss was the extinction of the healthy population of water voles in the Far Ings SSSI drain which has yet to be recolonised.

Lionel Grooby, South Humber Warden

Gibraltar Point 

Most of the immediate coastal habitats south of the fore-dunes and shingle ridges were well able to withstand the surge tide. Some of the ridge features were left rounded and some embryo dunes were swept off shingle ridges, which was to have later benefits for nesting shorebirds.

The breaching of Bulldog Bank led to the flooding of the Freshwater Marsh and scrubland to the north and east. The following spring (2014) it appeared that at least 80% of the mature hawthorns had been killed off in the flooded area. However, as the season progressed, some green shoots could be seen sprouting from within the dead looking canopy. Another year on and the recovering thorns have produced more living growth and we have revised our original estimate to around 60% dieback. All mature sallows were thought lost but again, in June, new growth has appeared from a few trunks.

This hawthorn epitomises the flood survival. It was only 50 metres from the Bulldog Bank breaches and must have taken the full force of the flood waters and would have subsequently been ‘drowned’ in salt water for a couple of weeks.
As you can see, it survived well. What looks like a birds nest is the remnants of the tidal debris that got caught up in the branches as the water receded.

 

 

 

 

There are many flowers and grasses that occurred on the Freshwater Meadow which are clearly less hardy and this event has had a catastrophic impact on the species rich ‘humid dune slack’ community that affords the special designation to the Freshwater Marsh. Up to 30 species per metre had been recorded prior to the flood.

When flood waters receded, the resulting patches of bare mud colonised with silverweed (a transitional specialist) but as the season progressed, the previous summer scene of 30,000 southern marsh orchids was replaced with a changed environment, superficially dominated by sea club rush and sea couch grass. Closer inspection revealed a somewhat confused environment where some relicts of the freshwater epoch (a few adder’s-tongue fern) were mixed with saltmarsh pioneers – sea aster, glasswort and scurvy grass.

The higher ridges that bisect the marsh were flooded to a lesser extent and here some cowslips appeared again in spring and, subsequently, yellow rattle has persisted well.

Amazingly, 424 southern marsh orchids flowered on these ridges in 2014 plus 26 common spotted orchids, mostly in the eastern side of the marsh which drained down earlier. If the Freshwater Marsh is to recover, these small populations of dune slack species that survived will propagate themselves back into the low lying areas.

In the meantime, mobile animals such as aquatic invertebrates and dragonflies have been appearing over the ponds and ditches of the Freshwater Marsh. Remarkably, at least two species of dragonfly were able to emerge from the salt-filled ponds in the spring of 2014. It seems that some of the Odonata have a remarkable salt-tolerance.

Even more remarkable were several sightings of water vole in the ditch system of the Freshwater Marsh in spring 2014 suggesting that one or two animals must have survived the tidal flood in situ.

Kevin Wilson, Gibraltar Point Warden

Donna Nook

The 2013 surge tide caused widespread disruption to the breeding seals at Donna Nook, rearranged the dune frontage and did widespread damage to the seal viewing area infrastructure.

The pup mortality in 2013 rose to 16%, but was followed in 2014 with a rate of 5.6%, similar to ‘normal’ years. Pup production was not affected by the surge tide, numbers increased by 10% in 2013 and by 7.3% in 2014. There appears to be no impact on the long term well-being of the colony.

The surge levelled some of the foredunes up to 15m inland but these have now partially reformed and revegetated. Dune slacks that suffered saline incursion have seen a slight change in vegetation but are recovering quickly and we have already started grazing them again. 

Rob Lidstone-Scott, Outer Humber and Coast Warden