To fulfil the identified adaptive pathways, it is essential that clear responsibilities and liabilities are understood, and it is necessary to categorise the assets requiring ongoing management and upgrade. The harbour and esplanade assets can be split into three categories as follows;.
Harbour Sea Defence Walls
A significant number of harbour walls (approximately 2.5km in plan length) form not only a functional harbour quay wall but also provide a flood risk function to mitigate tidal flooding to residential and commercial property.
It is therefore essential that these walls are replaced and/or raised at the appropriate intervention timings to ensure the desired standard of protection is maintained. In addition, a number of locations are known to suffer from tidal water rising up behind the defences contributing to the flood risk.
An example of such an asset is Wall 7 (spanning part Commercial Road and part Custom House Quay)
Whilst the concrete flood wall was added in the early 2000’s by the Environment Agency, the supporting harbour wall itself has a residual life of around twenty years. In addition, the current crest height of 2.30mOD would be exceeded even in a present day (2020) 1 in 200-year tidal flood event.
It should be noted that the present-day flood levels are based on the most up-to-date guidance which has changed significantly since the Environment Agency scheme was designed in 2001.
Harbour Walls General
A further number of harbour walls (approximately 2.0km in plan length) provide limited Flood and Coastal erosion Risk Management (FCRM) benefit. However, in order to consider the total harbour wall requirements and to ensure coherent and efficient delivery, they should be included within the strategic approach.
An example of such an asset is Wall G (northern side of the Pavilion Peninsula).
The condition of this wall is poor and has reached the end of its effective design life. When it is replaced, it will not need its crest level raising for flood defence purposes.
However, should development be brought forward on the peninsula, mitigation measures funded by developers may be required.
Esplanade Sea Defences
The Esplanade Sea Defences provide a dual purpose in terms of offering flood risk benefit and also mitigating erosion risk. They are important to protect against wave overtopping for the low-lying areas of the town set behind the Esplanade frontage.
An example of such an asset is the seawall and beach along the frontage of the Esplanade within Section 2 (Jubilee Clock to the Pier Bandstand).
Here, future interventions are anticipated in approximately 45 years with the installation of set-back defences to manage flood risk. If the beach levels lower, further structural measures may be required including potential replacement of the Promenade seawall.
Other Esplanade assets such as Section 3 (Pier Bandstand to Greenhill Groyne) are impacted to a greater extent by coastal erosion. As such, interventions here include for considering undermining and erosion of the wall structures.
Current beach management activities should continue which includes recycling of sand and reprofiling of the beach. This provides a cost-effective measure of delaying more significant capital interventions.