CURRENT PROJECTSChristchurch Bay and Harbour FCERM Strategy
23 May 2022
Engagement Phase 2 – This phase closed on 26 June 2022. Thanks to all those who came to our face-to-face and online events or completed a survey and added comments/photos to our interactive map. We are assessing the responses and will share the results when available.
We have now gathered information, research and data to help us understand what would happen if we do nothing to defend our coast. We will use these findings to start developing options to do something to manage the risks of coastal flooding and erosion. We will ask for people’s views on all the potential viable options in Winter this year.
A new coastal Strategy
Bournemouth, Christchurch and Poole Council (BCP) and New Forest District Council (NFDC) are working together with the Environment Agency (EA) to produce a strategy for Christchurch Bay and Harbour. It will identify where, when and broadly what type of works are needed to manage the risks of coastal flooding and erosion and what they may cost. It will also consider the effects of predicted climate change on coastal communities, including sea level rise and the increased levels of storminess.
As Coast Protection Authorities, BCP and NFDC do not have a statutory duty to undertake coast protection work, but we can use permissive powers to protect the coastline and work with communities to help them adapt to future coastal change. In addition, along with the EA, BCP (as Lead Local Flood Authority – LLFA) has statutory responsibilities for managing flood risk; Hampshire County Council is the LLFA covering the NFDC area.
The coastal management approaches are indicated on the Poole and Christchurch Bays Shoreline Management Plan (SMP) Policy Map. They take account of existing defences and the natural and built environments.
Producing the Strategy – In Autumn 2020, BCP Council successfully secured £450,000 of government Flood Defence Grant in Aid (FDGiA) to produce the strategy on behalf of the partners. We have appointed specialist technical consultant AECOM to help support us in this work.
Coast protection schemes – The final adopted Strategy will enable us to bid for government funding to deliver viable and realistic coast protection schemes to implement SMP policy. Although there is no guarantee we’d receive 100% funding for schemes, it will help us to understand the level of partnership funding that may be required to deliver a scheme.
The Strategy area
The Strategy area stretches from the Hengistbury Head Long Groyne to the western end of Hurst Spit and encompasses Christchurch Harbour up to the tidal limits of Tuckton Bridge on the River Stour and Knapp Mill on the River Avon. We have divided the coastal frontage into five key geographical areas (see maps below) to help us identify how we can manage the flood and erosion risks in each of them.
We have also identified the need to work collaboratively with the Hurst Spit to Lymington Strategy, which borders our strategy area to the east. The two strategies are linked by Hurst Spit, an important coastal feature and landmark of the area. By working collaboratively, Hurst Spit can be fully integrated into both strategies:
Map 1 – Christchurch Harbour
The policy varies for the area around the harbour but it can be broadly summarised as continuing to defend the areas which are currently defended (on their existing or realigned positions) and allow the undefended areas, such as the river estuaries and marshes, to continue to evolve naturally. We aim to work collaboratively with the Environment Agency and private landowners to co-ordinate a programme of flood defence works on the River Stour and Avon and create new wildlife habitats where opportunities arise. We also need to address the issue of the historic landfill site at Stanpit Marsh.
Map 2 – Mudeford Sandbank
The policy is to prevent a breach of the sandbank and manage the natural rollback of it into Christchurch Harbour as sea levels rise. This will be supported by the planned repair and upgrade of Hengistbury Head long groyne, repositioning the existing beach huts and addressing and maintaining the entrance to Christchurch Harbour.
Map 3 – Christchurch beaches and cliffs
The policy along the length of coast from Mudeford Quay to Chewton Bunny is to hold the line which can be achieved by sustainably topping-up beach levels to reduce the risk of coastal erosion. However, Friars cliff may need additional measures to prevent the area from receding. We will also need to address cliff stabilisation at Highcliffe and the future outflanking risk of Highcliffe’s coastal defences caused by the continued recession of Naish Cliff.
Map 4 – Naish Cliff and Barton-on-Sea
The policy for this stretch of coastline’s policy is for managed realignment. It will underpin the potential to introduce schemes to help slow the rate of coastal erosion. Cliff top losses will continue to occur in the short and long-term so this will require adaption of the affected cliff top. We aim to work with private landowners to identify cost-effective actions and continue cliff monitoring at Barton-on-Sea to help inform future options.
Map 5 – Hordle Cliff and Milford-on-Sea
The policy for the western side of Milford-on-Sea is aimed at managing the transition between the retreating, undefended section and the defended areas to the east. To the east, at the strategy boundary, the policy is managing the transition to the Hurst to Lymington Project, as well ensuring coastal processes are strategically considered in the eastern side of Christchurch Bay and towards Hurst Spit.
Coastal flood risk
Coastal properties, infrastructure and assets can be at risk from flooding ie during periods of high tides combined with storm surges and wave overtopping. Due to climate change, sea level is predicted to rise by 1.03m over the next 100 years. This will increase the risk of coastal flooding by making extreme coastal water levels higher and more frequent. Flooding caused by storm events is expressed in terms of an Average Return Period in years, calculating the frequency and intensity of past events. It describes the severity of a storm event and these can sometimes occur more than once in the same year. A large storm event that occurs on average once every century is referred to as a 1 in 100 year event.
Coastal erosion risk
Coastal properties, infrastructure and assets can be at risk from erosion, ie potentially being lost to the sea through shoreline retreat or land sliding. Shoreline retreat is where coastline boundaries change because of waves and tides, sediment supply, precipitation levels and the effect of groundwater. Sea level rise alone will also significantly increase the risk of coastal erosion. Our risk modelling data shows that if we do nothing and let nature take its course, our coastline would on average* erode by up to 1m every year.
*Cliffs in the strategy area are complex (influenced by both toe erosion and groundwater) and tend to undergo infrequent but large-scale episodes of retreat by cliff slips and landslides. The losses to this type of erosion are averaged out to give a yearly retreat figure.
Defending the coast
To reduce the effects of coastal erosion on communities and the natural environment, a combination of various defence structures and natural features can be used. These measures fall into two main categories:
- Hard engineering uses man-made barriers such as sea walls, groynes and rock revetments to reduce the impact of waves on the coast.
- Soft engineering techniques such as beach renourishment, dunes and saltmarsh creation use natural materials, features and processes to absorb energy from the waves.
Many successful coastal management methods combine both hard and soft engineering techniques. In each case the effects upon coastal processes and the natural environment are fully explored before management decisions are made.
Despite everything that can be done there will always be some locations where it is not possible or appropriate to defend against coastal flooding/erosion or maintain existing defences. In these cases, communities need time and support to adapt to changes. It is also important to note that although property insurance against coastal flooding can be purchased, there is no insurance currently available against coastal erosion.
Coastal management can have a significant impact on geological features, wildlife habitats, coastal processes, landforms and heritage features. The conservation of these habitats and features in a changing environment remains a key aspect in terms of environmental sustainability. Future management of the coast needs to allow natural habitats and features to respond and adjust to change, such as accelerated sea level rise. It must also comply with the legislation relating to important conservation designations protecting many habitats along the coastal frontage.
The policy balances the risks with natural processes by assigning one of four different management approaches to each of the coastline areas:
- Hold the Line – maintain / upgrade / replace coastal defences in their current position where funding permits.
- Managed Realignment – manage coastal processes to realign the ‘natural’ coastline configuration, either seaward or landward of its present position.
- No Active Intervention (do nothing) – a decision not to invest in providing or maintaining defences or management of the coast.
- Advance the Line – a decision to build new defences seaward of the existing defence line where significant land reclamation is considered.