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GRO8

GRO8 - Dealing with flood risk

Overview

The Plan helps to manage flood risk to ensure that Plymouth's flood defence, coast protection, drainage and sewerage infrastructure is sustainable and meets the requirements placed upon it by population growth and climate change.

Policy

The city will manage risk in association with flooding by:

Working with South West Water, the Environment Agency and other relevant organisations including asset owners to ensure that Plymouth's flood defence, coast protection, drainage and sewerage infrastructure is sustainable and meets the requirements placed upon it by population growth and climate change. Flood defence, water supply, surface water and waste water infrastructure requirements should be put in place in tandem with planned growth to avoid adverse social, economic and environmental impacts.

  1. Working with the Environment Agency and South West Water to align priorities for the efficient and effective management of tidal, fluvial, surface water and sewer flood risk, and to improve and ensure the effective functioning of the city's sewerage and drainage infrastructure.
  2. Maintaining an emergency response plan, sufficient to address the risks to life and livelihood from extreme weather events.
  3. Using planning powers to ensure that development takes place in appropriate locations and with proper regard to flood risk.

Rationale

Changes in weather patterns could result in an increase in flooding in some parts of the city. Intense rainfall events are expected to continue to increase in frequency in the coming decades throughout the UK. Sea levels are rising and will continue to do so, and storms are expected to increase in frequency and severity. Flooding can come from a range of sources such as tidal inundation, flooding from rivers after heavy rainfall and flash flooding caused by rainfall running off hard surfaces or from fields in rural areas. Flooding can overload sewerage and drainage systems and increase the risk of pollution and nuisance. It is important that flood risk is carefully considered, including how new development is designed so as not to increase vulnerability, where areas are vulnerable, risks should be managed through suitable adaptation measures. The JLP identifies how the policy will be supported through the planning system.

National flood risk mapping indicates that there are more than 900 properties at high risk of flooding (Flood Zone 3) in Plymouth from the sea or main rivers. Over 3,000 properties are at risk from surface water flooding. There is also a risk of damage to key transport infrastructure and services that would have a significant economic cost. Plymouth's delivery plan for managing local flood risks includes maps of risk areas for sea, fluvial and surface water flooding and information on strategic flood risk management infrastructure requirements. The South Devon and Dorset Shoreline Management Plan has a policy of ‘hold the line’ for the majority of Plymouth’s coast, having considered and rejected the alternative options of no active intervention and retreating defences further inland.

In order to mitigate these risks, the policy will help to:

  • Reduce the amount of rainwater reaching the sewers and water courses in Plymouth.
  • Improve the capacity of particular water courses and sewers, so that flood risk is significantly reduced during storm events.
  • Restrict the volume and nature of development in risk areas, and ensure any development in these areas is resilient to flooding and coastal erosion/storm damage.
  • Secure financial contributions to the maintenance and improvement of strategic drainage infrastructure, fluvial and tidal flood defences, and erosion defences.

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