Following on from our March 1st article on Hurst Castle, we’re publishing an on-line paper by SPS Council member and coastal engineer, Tim Kermode.
The Evolution of Hurst Spit
Following the collapse of a section of Hurst Castle it is interesting to consider the long-term evolution of Hurst Spit before coming to conclusions on the future of the spit and the castle that sits at the end.
The Coastline between Christchurch and Hurst Spit has been subject to much study, from geography students, serious academic research and major consultancies working for Local Authorities and the Environment Agency.
I have tried to distil some of this to give a fairly simple explanation of a complex situation. There are references to further reading on the internet at the end of this paper for those who wish to investigate further.
Spits are formed when there is a change in direction of a coastline that has littoral drift occurring. In the case of Hurst, littoral drift is from west to east, from Christchurch to Milford-on-Sea, and so the sands and gravels that are eroded from the soft cliffs, particularly at Barton-on-Sea become a shingle feed for the spit. There is quite a good explanation at this link. The recurve to the north at the end of the spit is caused by tidal flows in and out of the Solent and is formed, in simplistic terms, from an excess of the shingle needed to form the spit moving into deeper water before being carried back by tides. Shingle is also transported south and deposited on the Shingles Bank, where it is thought to remain rather than coming back into circulation.
Naturally, the spit will become dynamically stable, i.e. what is eroded from the spit is replaced from erosion of the cliffs between Barton-on-Sea and Milford-on-Sea. As the spit aligns with the beaches it will move landward (North in the case of Hurst) at the natural rate of erosion of the cliffs. There is much literature on these erosion rates and the quantity of material they produce but over the last 100 years the natural rate appears to be a little over 1 metre per year. It should be noted that this is not a linear process, but occurs in ‘chunks’ when there is a major storm after which the spit might roll back by 10’s of metres at a time.
In the case of Hurst Spit, the castle was first built between 1541 and 1544, at which time there would have been no coastal protection works between Christchurch and the spit, and it would have been in dynamic equilibrium, fed by erosion along the coast.
From the beginning of the 1800s till the start of the 20th century, there was a small community of houses on the spit around the castle, including a public house. This again suggests that at this time it was relatively stable.
The first groynes were built at Milford-on-Sea in 1857 and I have seen reference to drainage works for Highcliffe Castle gardens following construction of the “New Castle” there in 1830. The first coast protection works were constructed in Victorian times when the railway came, and coastal resorts started to be developed. As in most of Britain this part of the coastline started to be fixed, and although erosion still occurs and worries some, the result was a reduction in the feed of natural material to Hurst Spit.
Over the years, the coast protection works have become more intensive and although offering some protection to Barton-on-Sea and Milford-on-Sea have also over time reduced the feed of sand and shingle to the spit.
There is a very good record of the geological history on the website Hurst Spit History. This shows a number of interesting aspects. The 1958 and 1979 pictures when storms overwashed the spit show clearly the shingle deposited behind the spit. Had it been left alone, it would have reformed but in a new position, his comments suggest that the spit was pushed back by 12m in places in 1979, so taking both events into account it could be 25m total.
The spit was subsequently rebuilt using dredged shingle and bulldozers, with two significant effects:
- The spit is now probably about 25m seaward of its natural (dynamically stable) position.
- In a natural spit the shingle is graded by the waves depositing it. This has two advantages, firstly that it is more densely packed than can be achieved by bulldozer and secondly, that it has better natural drainage.
It is also worth noting that the financial justification for the rebuild was justified by the defence that the spit provides to the sea-wall from Keyhaven to Lymington and hence flood protection to Lymington and the surrounding area, rather than protection of the castle. This benefit would occur with or without the castle.
As a result of the lessening of the supply of shingle, and probably aggravated by higher sea levels and increased storminess (and perhaps slight changes in wind directions) due to climate change, the shingle to the east of the castle has disappeared and resulted in the undermining and subsequent collapse of part of the castle. This is clearly shown by the photos on our website.
The two Shoreline Management plans for this area The North Solent SMP and Poole and Christchurch Bay ( 2 Bays) SMP both have a “Hold the Line” (HTL) policy for Hurst Spit, but as outlined earlier this should not be taken to mean protection of the castle.
As owners of the Castle it will be up to English Heritage to determine its future, which could be to try to protect parts, move parts or simply walk away and leave it to the sea. This has of course happened to many villages in the past, including some quite nearby.
The SPS Council are actively discussing the developing situation and will, in due course, publishing further commentary.
Tim Kermode, March 5 2021