Some Fitzalan Road residents have been bemused by the shin-high wall that Mackley installed as part of the tidal flood defence works. “To prevent Hedgehogs falling into the River Arun?” was one suggestion. So we asked the Environment Agency to explain the thinking to us, and here is their response:
We understand that some residents have raised some questions over the design of the defences on Fitzalan Road South of the A27 Bridge, therefore we would like to clarify these for you.
The Environment Agency have undertaken works in order to achieve a 1 in 75 year standard of protection (SOP) from tidal flooding from the river Arun, as recommended by the Lower Tidal River Arun Strategy (LTRAS). This standard of protection means that there is a 1 in 75 (1.3%) chance of flooding within this area in any year, therefore the new defence will provide protection for these types of events.
In most locations (but not all) the embankment south of the A27 Bridge to the Windmill was already at the crest height required to achieve this level of protection. However we had identified that there were some localised ‘low spots’ which compromised the overall level of protection provided by the embankment. To inform the flood defence works we completed topographical (crest level) surveys over the entirety of the riverbanks. This identified the precise location and extent of these low spots.
We completed a robust options appraisal process to identify the best option to address these ‘low spots’. The preferred option that we have constructed was for a low level boarded wall over the section of embankment where the ‘low spots’ were identified. Additional topsoil was also placed along the embankment. This wall allows us to achieve the recommended a minimum 1 in 75 year SOP to residents. This also includes an allowance to manage increasing flood risk from climate change over the next 20 years.
Surveys were repeated after completion of the works. These confirmed that the required SOP has been achieved. We have not identified any areas where the height of the embankment is lower than before construction. This means that, working in combination, the existing river bank and new wall appropriately achieve the desired level of protection.
If you have any other questions, please feel free to email us at FloodRiskSussex@environment-agency.gov.uk