Through the development of the strategy economics (according to guidance we have to use) we have looked at the benefits (what’s at risk if we did nothing) and the costs of doing something to combat risks.
In each ODU, the Benefit Cost Ratios (BCR’s) were calculated for the strategic options to demonstrate their economic viability. The costs of an option were estimated according to the defence types, lengths and heights. The flood and erosion benefits of a strategy option were determined by calculating the damages avoided compared to the baseline ‘Do Nothing’ scenario.
Generally speaking, the higher the BCR, the more economically viable the strategy option. The BCR was used as a tool to help inform the decision, and for Strategy purposes as long as the option had a BCR greater than 1 (i.e. the benefits outweigh the cost) it was deemed a cost effective option.
In reality, a BCR on or around 1 is very low and is unlikely to attract funding from national sources under the current funding rules and therefore classed as a low economic case.. Although strategic management options may be ‘economically viable’ for the purposes of the Strategy, it does not mean they will go ahead; the required funding to pay for the schemes must still be found.
Defra invests Grant in Aid wherever flood risk is highest across the country and where it will benefit the most people and property, using a consistent set of criteria to fund schemes proposed by all Risk Management Authorities (RMAs).
Road damages have been included in the economic appraisal. Flooding results in damage to the integrity of a road surface, so costs have been included to repair the road to ensure the safety of vehicle users. Flooding can also affect roads by leading to traffic disruption and increased journey durations. Traffic disruption depends on the duration of a road closure, length of diversion and volume of traffic. Under the Do-Nothing scenario, flooding of the following major roads is expected; the A3023, Havant Road, Northney Road and West Lane. Traffic disruption damages have been included for each of these roads except for the A3023.
The damages for the A3023 have been counted by the Langstone FCERM scheme economic assessment because this road floods on the mainland from similar return period events, and therefore cannot be included in the appraisal for this Strategy. Hence the low BCR for the A3023 frontage in the north.
The Strategy intent along this frontage is to continue to protect the A3023 access route onto the Island. A future scheme in this location may be able to attract some public (Grant in Aid) funding, however, with a low economic case, other contributions will be required to enable a scheme to progress. As it is a major road, there will be many other parties with an interest such as Highways, HBC, HCC etc. who we will need to partner with to progress and potentially contribute to a scheme in this location.
A recent storm analysis study, published in December 2020 assessed the sea level and wave data along the south coast of the UK. The study found that the average rate across key sites for the period of 1970 to 2019 is 2.66 mm/yr, which equates to approximately a 13 cm rise in mean sea level during that period. However, for the period between 1990 to 2019 the average rate is 2.78 mm/yr and for the period 2000 to 2019 the average rate is 3.18 mm/yr. This indicates a gradual acceleration in the rate of rise of mean sea level in recent years.
For more information on the study, please see the SCOPAC Storm Analysis Study by The Southern Coastal Group and SCOPAC.
The Environment Agency East Solent flood model (2018) was the most up to date model available at the time of Strategy development. This model was used to support the economic appraisal and option development. To consider sea level rise, the Strategy has incorporated the latest sea level rise projections (UK Climate Projections 2018) into the flood modelling to produce ‘Do Nothing’ flood scenarios for 2041, 2071 and 2121. Following these guidelines, under the ‘medium emissions’ sea level rise scenario, mean sea levels across the Strategy frontage are expected to increase by approximately 1m over the coming century.
As and when schemes are progressed following completion of the strategy, new flood modelling will be required to update the understanding or risk and inform defence designs. Any modelling undertaken in the future will be required to use the latest hydrodynamic model available and incorporate the current national sea level guidance available at that time.
We recognise the strategic importance of the main road network on Hayling Island, which is reflected in the recommendation of options to provide protection to the A3023 for the next 100 years, as well as Northney Road, subject to securing funding.
Coastal Partners are also working on the Langstone Coastal Flood and Erosion Risk Management Scheme which will also protect the integrity of the A3023 access route to Hayling Island.
For further information on this scheme, please visit: HERE
As part of the strategy, we recognise that surface water drainage is an important consideration going forwards in respect to residual flood risk and defence design. If and when a scheme is progressed following the strategy, surface water drainage will need to be considered and be integral to the defence scheme.
Through the development and appraisal of the overall leading options, the strategy has identified high level indicative capital and maintenance costs to deliver the draft strategy options around the island, including along privately owned frontages. However, given the current economic climate, defence construction and maintenance costs are rising at an unprecedented rate. Therefore the costs presented in the Strategy will need to be reassessed at the appropriate time, if and when a scheme is taken forward.
More information on the economics is available in the draft economics report available here.
Through the development and appraisal of the overall leading options, the strategy has identified high level indicative capital and maintenance costs to deliver the draft strategy options around the island, including along privately owned frontages. However, given the current economic climate, defence construction and maintenance costs are rising at an unprecedented rate. Therefore the costs presented in the Strategy will need to be reassessed at the appropriate time, if and when a scheme is taken forward.
More information on the economics is available in the draft economics report available here.
If you would like to get in contact with the project team regarding further questions, please email coastal.team@havant.gov.uk
As a service, Coastal Partners are more than happy to meet with landowners to discuss options, funding opportunities and provide advice in terms of what licences and consents may be required.