To pass NBE5, you'll need to confirm that at least one of the options listed below is being undertaken at this site.
You will be asked to provide evidence of the chosen options by uploading a submitted plan or document. You should make sure that the chosen option is feasible at the development.
In some cases, it may not be clear until later in the planning process whether the betterment proposed is viable. You will only have to do your back-up option if your first option proves not to be possible.
Any drainage device that allows runoff from a development to soak into the ground for example soakaway, permeable paving. Issues such as high groundwater levels and slow infiltration rates may mean that infiltration cannot be used at a site. Test results are needed to confirm that infiltration is possible and would be submitted anyway as part of getting the site’s drainage approved. If infiltration tests have been undertaken at submission, please indicate an alternative backup option.
Reducing impermeable area
Impermeable areas are hard surfaces where water will run off. This includes hardstanding, roofs and paving. By reducing impermeable surfacing and hardstanding, rainfall runoff will be reduced and flood risk is improved.
Reducing surface water discharge rates and/or volumes
This is ensuring that the amount of surface water leaving the site following a storm event post development is less than the amount that currently leaves the site.
Reducing the existing built footprint within a flooded area
Reducing the built footprint in an area that floods allows water to flow where it would naturally, reduces the risk to the building from the floodwaters and allows more water to be stored on the floodplain, helping to reduce downstream flood risk.
Rain garden planters
These divert rainfall from downpipes to garden planters before the water re-joins the drainage system. This creates storage, improves water quality and slows the rate at which water enters the drainage network.
Collect and store rainwater to be used in the garden.
Smart water butts
Water butts that will drain down between rainfall events.
This is a technical drainage term referring to the ‘greenfield’ (undeveloped) runoff rate that occurs during approximately the 1 in 2 year storm event. Discharging all storm events (including the 1 in 100 plus climate change storm event) at this rate is common technique for mitigating an increase in impermeable area. It has the advantage of reducing runoff rates overall from a site. This can be a harder technique to use on smaller sites where the greenfield QBAR rates are so low that there could be a risk of pipes blocking if the development discharge at this rate.
Rainwater harvesting system
This is where rainwater is collected for grey water re-use within the development e.g. for flushing toilets.
Foul sewer misconnections
This is when surface water is discharged into a foul sewer designed to take raw sewage only. This is a major cause of foul sewer flooding so removing these misconnections can help reduce flooding. In Hart there are no formal combined sewers and any surface water entering the foul sewer is a misconnection.
De-culvert a watercourse
A culverted watercourse is where a river or ditch has been piped. Piped watercourses can be difficult to clear if they block and often reduce the capacity of the ditch. In most circumstances removing the culvert would provide flood risk and environmental benefits. However, occasionally this may move flood risk to another area. Where the removing of a pipe does not increase the consequence of flooding, this would be considered a benefit. Works to watercourses are subject to Consent and Environmental Permits.
Set built development further back from a watercourse
Where building, garages, outbuildings, fences and roads are very close to a watercourse, this can:
- inhibit ease of access to the watercourse for maintenance
- disrupt green corridors used by wildlife
- increase the loading on the banks of watercourse making the bank more prone to failure
- expose the infrastructure to flooding.
Any opportunity to move existing structures away from a watercourse is encouraged. Moving these back by 0.5m or more would be considered a benefit and acceptable in this form. The ideal is to be at least 8m from the top of the bank of the main river and 5m from top of the bank of an ordinary watercourse where possible.
Sustainable drainage systems with water quality benefits
Sustainable drainage systems are a suite of drainage methods that mimic natural drainage. Some of these methods can remove pollutants in the water preventing these getting into river and other water environments. Further information can be found in the Ciria SuDS Manual C753 and the Simple index Criteria (Box 26.2).
Improving a failing septic tank or cesspit
To resolve existing flooding or pollution.
Increasing floodplain storage or space for an overland flow route
River floodplains store water in times of flooding. Surface water overland flow routes are where water will typically run over ground when it is raining heavily. Above ground structures in these locations occupy space that would otherwise store floodwaters. Opportunities to open the land up to receive floodwater prevent this water from being displaced downstream is welcome.
You can see if your site is in the floodplain or a surface water overland flow route by going to the Environment Agency’s online mapping.
Community access and egress routes
A pedestrian route across a flooded area that residents can safely use to get them to and from their house.
Reducing groundwater filtration into foul sewers
Groundwater getting into the foul sewer network can cause foul sewer flooding. This is a problem in areas prone to groundwater flooding or a shallow water table where there are poor joins or cracks in the pipe.
Reduce flood risk from any source
Any measures that reduce off site surface water, river, groundwater, or sewer flooding compared to the existing scenario.
Improving the environmental condition of a watercourse
Any measure that improves the water quality, river morphology or ecology of a river or ditch.
We recognise that the above list may not be exhaustive. Any measure providing a betterment to the water environment or flood risk that has not been covered in the list can be included here. This must be agreed with the Council’s drainage engineer