Agenda item

The Panel considered the report of the Scrutiny Manager detailing the issues concerning flood risk management and the River Itchen Flood Alleviation Scheme (RIFAS).

The Panel received the following joint representations from Sam Foulds, Flood Risk Management Team Leader at Southampton City Council; Cara Brims, Flood Risk Officer at Southampton City Council; Blake Jones, Project Executive River Itchen Flood Alleviation Scheme at the Environment Agency; Dave Martin, Flood and Coastal Risk Management Partnership and Strategic Overview Team Leader for New Forest, Test and Itchen at the Environment Agency who summarised the key issues about flooding in Southampton around the River Itchen as:

Tidal Flooding

o  The key flood risk is tidal.  The Environment Agency is responsible for management of the flood risk from Main Rivers and the sea.

o  The greatest risk is to the River Itchen west bank as land levels are lower.

o  Southampton has a unique tidal pattern with a double high water – this extends the period where high water may occur with a surge. Rainfall and high tide can cause ‘tide locking’ of surface water sewers. 

o  Southampton has a number of areas that are vulnerable to flooding with a greater than 0.5% chance of flooding in any given year.  The city has been very fortunate that a 0.5% event has not occurred.

o  There are currently no formal raised flood defences in Southampton. There is currently a mix of engineered high ground, quay walls, low flood walls and embankments of varying condition and standard of protection.

o  Where standard of protection is lower than a potential flood level, water is likely to overtop, resulting in flooding to the ground behind.

o  The majority of the Itchen frontage is privately owned – landowners are responsible for maintenance of assets.

o  Through the impact of climate change and rising sea levels vulnerability to tidal flood risk will increase over time – more land areas, property and critical infrastructure will become at risk or experience more regular flooding.

o  Greatest increase will be seen in Northam and the City Centre – large areas are flat, low lying and reclaimed land. 

o  Increased risk includes flood extent (areas impacted) and depths of flooding. By 2120, flood depths during a 0.5% AEP (Annual Exceedance Probability) flood could reach up to 1.8m in some areas.

o  Southampton Coastal Flood and Erosion Risk Management Strategy (2012) – presents options for management of tidal risk on the west bank of the Itchen Estuary. The Strategy will be delivered in stages over time to create a continuous raised flood defence from Woodmill to Redbridge. 

o  Focus is on areas where risk and need for defences is greatest:

o  Phase 1 – River Itchen Flood Alleviation Scheme (RIFAS).

o  Phase 2 – Likely to be Woodmill to St Denys.

o  There are plans to revisit the Coastal Strategy to include examination of flood risk on the east bank.

o  All new development (including change of use) in a present day or future flood risk area must be accompanied by a Site-Specific Flood Risk Assessment.

o  Planning and development applications are reviewed by SCC Flood Risk Management and the Environment Agency.If not demonstrated to be safe, recommendations for refusal are presented to the Local Planning Authority.

o  Funding flood defences - Government funds are limited. All defence schemes must present a case to the Government to demonstrate that the benefits (flood damage prevented) outweigh the costs of the scheme. RIFAS has a 1:4 cost benefit ratio.

o  RIFAS is a flood defence scheme on the west bank of the Itchen Estuary between Mount Pleasant Industrial Estate to just south of the Itchen Bridge.

o  RIFAS is a partnership project between Southampton City Council (investment and communications) and the Environment Agency (design and construction) with delivery partners JBA Consulting (design), VolkerStevin (construction), Dalcour Maclaren (land agent) and Mott MacDonald (investment team).

o  Plans are for the RIFAS scheme to be delivered in two stages:

o  Phase one (present day) – Construct an interim height wall to provide a 0.5% AEP standard of protection by 2070.

o  Phase two (future, before 2070) – increase the height of the wall to provide a 0.5% AEP standard of protection by 2120.

o  This approach enables flexibility in the implementation of future interventions and reduces the immediate impact to business operations with a lower wall height.

o  Construction is provisionally planned to commence in January 2026 and conclude in Sept 2028.

o  The estimated scheme cost (January 2022) is £85.6m. Confirmed funding for this is currently £45.5m

o  Funding is being sought from alternative external funding streams to cover the outstanding estimated amount.  Funding challenges are standard for such projects.  If funding is not found consideration will be given to extending the timescales of the project to enable more time for funding to be sought.

o  Engagement has been ongoing with landowners and businesses that will be directly affected by the scheme. Engagement will continue to produce the detailed design over the next 3 years.

o  The scheme will require planning permission and anyone will have the ability to comment on the application through Southampton City Council planning processes.

o  Environmental and climate change considerations go hand in hand, and they are at the core of this project - RIFAS carbon forecast is about 60% lower as compared against the baseline.

o  The project includes a biodiversity net-gain target of 20% including whole life cost and climate resilience assessment.  A key focus is improving water quality and wildlife and habitats.

o  An environmental opportunities register has been created: 48 opportunities have been identified for consideration including carbon and pollution reduction e.g. bivalves; heritage, public realm and ecological improvements e.g. habitat creation.

o  A project objective is to facilitate sustainable growth along the west bank of the River Itchen (which includes parts of the City Centre) for businesses and residential purposes, including access.On completion, the RIFAS will remove the constraint of flood risk to many areas and increase regeneration and development opportunities.

o  The RIFAS will seek to improve public access and public realm along the waterfront – Including planned improvements to the Boardwalk and Crosshouse Hard car park.

o  To facilitate improvements a bid for £15.8m to the Levelling Up Fund was submitted in August 2022.  This was unsuccessful but another round, with objectives more aligned to the RIFAS scheme objectives, will commence next year.

o  The Council’s Flood Risk Team are working closely with Economic Development, Strategic Planning and the Masterplanning Team to align opportunities through RIFAS with the ambition outlined in the emerging City Vision Local Plan.

Surface Water Flooding

o  On 10 January 2023 the Government announced that it is committed to the enactment of Schedule 3 of the Flood and Water Management Act 2010 by the end of 2024.This will amend the Water Industry Act 1991 to end the automatic right to drain surface water to a public sewer.

o  It will become a requirement for all new developments of more than 1 dwelling house or where the construction area is 100 square meters or more, to include sustainable drainage systems (SuDS) for managing surface water.

o  The primary benefits will include - reducing surface water entering sewers; less combined sewer overflows; reusing water as a resource; improving habitat biodiversity and water quality; Improving amenity.

o  Once enacted, construction work which has drainage implications cannot be commenced unless the drainage system for the work has been approved by the SuDS Approval Body (Southampton City Council).