Hurst Castle Spit EarthCache
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Hurst Spit is a shingle bank at the easternmost point of Christchurch Bay, extending from the end of Milford beach into the Solent. It protects the Western Solent from flooding and shelters the designated area of saltmarsh to the north.
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The published coordinates are for the parking.
Background
A spit is a deposition landform found off coasts. At one end, spits connect to land, while at the far end they exist in open water. A spit is a type of bar or beach that develops where a re-entrant occurs, such as at cove's headlands, by the process of longshore drift. Longshore drift (also called littoral drift) occurs due to waves meeting the beach at an oblique angle, and backwashing perpendicular to the shore, moving sediment down the beach in a zigzag pattern.
Hurst Spit is an important coastal defence, aggradation feature (barrier beach). The flint beach shingle of Christchurch Bay (Highcliffe, Barton-on-Sea and Hordle Cliff) has been moved by the longshore drift. This transport is the result of the prevailing south-westerly winds. The light brown, flint gravel is present in most of the cliffs as a cap of Pleistocene periglacial clastics, overlying Eocene sands and clays. Not only is gravel on the spit, but also pieces of shelly siderite from Barton-on-Sea and fossils from the Barton Clay, particularly the gastropod Clavilithes.
Although originally formed by natural processes, Hurst Spit is now maintained by regular shingle recycling operations.
History
The Spit has been declining in volume, probably since the 1940's when coast protection works in Christchurch Bay first began to interrupt movement of the shingle that maintains its stability.
Coastal erosion problems are a characteristic feature of Christchurch Bay, famous for coastal retreat, especially at Barton and Highcliffe. Nearer to Hurst Spit, At Milford-on-Sea, the natural overall retreat of the coast caused concern at Milford-on-Sea in the 1950s, at about that time some defences were constructed there. The sea-defences have been strengthened since and now it is very difficult for shingle to pass eastward of Milford beach.
A consequence of the development of the coast of Christchurch Bay over the years and the human efforts to stop cliff erosion and loss of beach at places to the west was a dwindling of the quantity of shingle on Hurst Castle Spit. In February 1979, the sea almost breached the beach directly east of the sea-defences and the beach ridge was stepped back out of line. There was fear that if nothing was done the shingle ridge might permanently breach, letting large waves into the West Solent and isolating the Castle area of the spit as an island. Bulldozers were quickly brought in and the shingle beach was repaired.
Gravel has always been lost from the end of the spit and the whole spit has moved landwards by a "rollover" process. It has survived more or less unbroken for thousands of years, but not in the same place. Wash-over and temporary breaching has occurred because the delayed effects of the sea-defence works in Christchurch Bay finally stopped any significant natural transport of shingle to the beach. There was a crisis in 1989 when the shingle beach was extensively flattened and at risk of total destruction.
The reduction in sediment supply led to several breaches, and in 1996 major work was undertaken to replenish the spit with dredged gravel from the Shingles Bank, and to construct a rock breakwater and new rock revetment.
Today
The rock armour barrier at the landward end of Hurst Castle Spit is a more recent development which although apparently giving some protection to land behind the beach is yet another barrier to the transport of any remaining shingle transport eastward.
Salt marshes to the north of the spit are also eroding, with the seaward edge eroding at up to 3m/year.
The long stretch is now banked up to 7m in height. It does have its original natural appearance and is more like a railway embankment and it is also compacted. Nevertheless it still exists and to the casual observer may look fairly natural. Current management includes regular shingle replenishment with flint gravel and monitoring.
The far end has been less affected by erosion and has not been rebuilt and re-nourished. Much of the re-curved end of the spit is still in natural condition and its accretionary development can still be studied.
To claim this cache:
1) Estimate the length of the spit
2) What direction is the sediment in Christchurch Bay moving, due to longshore drift?
Email me with the answers to these questions & also take a photo of the spit with your GPSr in the foreground to upload to your log. Send an email with your team name to:
Hurst.Answer2@gmail.com (Email title Answer1)
E.g. If the sediment in Christchurch Bay is moving south, due to longshore drift, and the length of the spit was 100 metres, then send your answer to: Hurst.south@gmail.com (Email title 100 metres) With the right answers you will receive log permission.
Additional Hints
(Decrypt)
1) Hfr lbhe TCF naq jnyx gb gur raq bs gur fcvg.
2) Frr juvpu fvqr bs gur ornpu teblarf gur frqvzrag vf pbyyrpgvat ba.