Flood risk management
Flood risk needs to be taken into account when planning for new development. Planning policy promotes development which will decrease the risk of flooding. Where a proposed development is at risk from flooding, or could create a risk of flooding elsewhere, a flood risk assessment must be submitted with the planning application.
Fluvial flood risk covers flooding from watercourses. Fluvial flooding is categorised under four flood zones:
- Zone 1 - Estimated less than 1 in 1000 year risk of flooding
- Zone 2 - Between 1 in 100 to 1 in 1000 year risk of flooding
- Zone 3a - Between 1 in 30 and 1 in 100 year risk of flooding
- Zone 3b - More than a 1 in 30 year risk of flooding
Pluvial flooding is flooding that comes from surface water. There are two categories of pluvial flooding in Leicester:
- Hotspots - flooding of roads and low lying parts of gardens, and some dwellings
- Critical drainage areas - areas which are unlikely to flood but where the rapid runoff of water leads to flooding in the hotspots.
Sustainable drainage systems
Sustainable drainage will contribute to lowering the city’s risk of flooding. It does this through a range of measure that slow down the rate at which water runs off across surfaces. It is the combined impact of surface water flows that leads to flooding. The city’s topography, soils and patterns of development make Leicester at a particular risk of flooding. So even if a development is proposed at the top of a hill it still needs to use sustainable drainage techniques to prevent their run off affecting others.
Development that can contribute to increased run off includes the construction of patios, shed bases, conservatories and footpaths. Anything that takes away open ground can make the problem worse.
Many landscape features help in slowing water run off; even grass slows down that rate of run off; allowing for some filtration and some water quality improvement. Trees are a very simple sustainable drainage feature. Their roots absorb water and help to create ground that water can seep into, and the tree intercepts rainfall and allows for water to evaporate back into the atmosphere.
Sustainable drainage systems mimic natural drainage systems. Compared with conventional drainage they typically have slower rates of water runoff and have other benefits such as providing a range of wildlife habitats, multi-use areas (typically combining drainage with play space), water quality, visual amenity, have low and simple maintenance requirements and pose less of a threat to safety.
More information is available in the document at the bottom of the page.
What information should I provide?
For some developments a flood risk assessment is required. More information is available at GOV.UK.
For all developments of new build dwellings and for other developments where the floor area is greater than 200sqm (including change of use) the development should reduce surface water runoff through the use of sustainable drainage systems.