MSc ECE 2018/19 student Michalis Karas reports on the SOES3014/CENV6126 fieldtrip to Hengistbury Head and Christchurch Bay:
On Monday 5th of November a field trip was organised to introduce a variety of coastal environments, both natural and engineered. A group of MSc students from Coastal Sediment Dynamics and Coastal Morphodyamics courses visited the area where coastal processes and engineering interventions were mainly examined. The field trip was led by Dr Hachem Kassem, Professor Robert J. Nicholls, and Professor Ian Towenend. The team had the opportunity to meet Engineers from Bournemouth Council, currently working on the long Groyne at Hengistbury Head, and discuss any issues that could affect local transport of sediment and morphology. Then, we visited the barrier island (Mudeford Spit) and inlet of Christchurch Harbour and the coastal defenses of Christchurch bay. Finally, we had the chance to visit Highcliffe and Barton-on-Sea and contrast two shorelines with opposing management plans.
The Geology of the local cliffs at Hegnistbury Head was studied while walking along the shoreline. It consist a sandy gravel beach and the cliff is mainly made from Barton Clay with a thin layer of pebbles and iron stone. At the top of the cliff a gravel, deposited by the ancient river Solent, can be found. It can be seen that the headland has been eroded through the years with pebbles locally feeding the beach.
The Engineers from Bournemouth Council explained the current management plan to stabilise the headland. The Beach Management Scheme is a 17 year plan to protect Bournemouth’s coastline between 2015-2032. This will cost approximately £50 million and is mostly founded from Environment Agency (EA) with contribution from the Council. The plan includes:
- ement of the existing 53 groynes.
- Construction of an additional 3 new groynes.
- Replacement of the Long Groyne at Hengistburry Head.
- Replenish the beach every five years.
We then walked along Southbourne Beach towards the Long Groyne. The current groyne is:
- 120 meters long.
- Life span around 100 years.
- Recent re-Designed for future sea level rise.
- Cost of works on it will be £7-8 million (funded from EA)
However, the original construction of the long groyne in 1938 caused erosion of the sandy barrier island (spit) protecting Christchurch Bay, since materials are trapped in the west side. Therefore, the bay has being protected by stablising the spit with rock groynes to eliminate longshore drift, a sheet-pile seawall, beach recycling and fixing the inlet positon by hard structures. The beach here have sand dunes where sediments are mainly transported from wind. Eastward drift had contributed to the growth of Mudeford spit, which has deflected the harbour inlet channel to the northeast. If it were not fixed, the inlet would have migrated and reformed by breaching the barrier. Sediments entering the inlet are flushed seaward by dominant ebb tidal currents and accumulate within an ebb tidal delta.
Highcliffe and Barton-on-Sea
The second part of the trip included a visit in Highcliffe and Barton-on-Sea where two different approaches of coastline management were been applied by the local councils. At the west site rock groynes were been used to protect the cliff from erosion. However, on the east site the council did not use any coastal defense and the cliff is highly subjected to erosion.
This can be seen in the drone Footage below :