Flood, Drainage and SuDS – Page 9
Flood risk assessments, sequential and exception tests, drainage strategies and SuDS design.
Flood, Drainage and SuDS articles – page 9
290 articlesEvidencing groundwater flooding in a flood risk assessment
Groundwater is a named source of flooding with no equivalent of the flood zones. Geology, borehole logs and a winter of standpipe readings are what an assessment actually needs.
Reading the surface water flood risk map without overstating it
The national surface water map identifies where the question arises. Depths, local drainage records and survey levels answer it, and confusing the two costs developable area or an approval.
Land drainage consent for works to an ordinary watercourse
Section 23 consent is separate from planning permission and from an Environment Agency permit. What counts as an ordinary watercourse, which works are caught and what riparian ownership obliges you to do.
Basements, flood risk and sleeping accommodation
Basement dwellings sit in the highly vulnerable category of the flood risk vulnerability classification. That single fact decides whether a conversion has a policy route, before any modelling starts.
Foul drainage with no mains sewer: what to show
Applications for package treatment plants fail on the first question rather than the last. How to evidence that mains connection is impractical, test the ground properly and identify the right regulatory route.
Schedule 3 SuDS approval: what is in force and what is not
SuDS approving bodies operate in Wales and not in England, where drainage remains a planning matter secured by condition. What Schedule 3 would introduce and how to design so a change would not break the scheme.
Sizing attenuation storage for the 100 year event
Attenuation volume is decided by the design events, the permitted discharge rate and the half drain down requirement. Here are the inputs to fix first and the results a lead local flood authority expects to see.
SuDS management trains that satisfy water quality tests
Lead local flood authorities check whether the treatment stages in a SuDS management train match the pollution hazard of what drains into them. Here is how to split catchments, apply the index approach and evidence it.
Infiltration testing: what a drainage authority expects
Infiltration has to be tested, not assumed. Three fillings per pit, testing at the soakaway depth, and an honest account of seasonal groundwater are what get a strategy accepted.
Surface water risk on a Flood Zone 1 site under one hectare
Four triggers require a Flood Risk Assessment in Flood Zone 1, and surface water is the one that catches small sites. The lead local flood authority, not the Environment Agency, is the consultee.
When a flood warning and evacuation plan is required
A flood evacuation plan answers the safety limb of the exception test. It needs a stated design event, a passable route out or a defensible refuge, and someone named to own it after occupation.
Sites partly in Flood Zone 1 and how to use the rest
Most sites of any size straddle a flood zone boundary. Which part of the red line is in which zone decides the layout, the tests that apply and the documents you need.
Culverting policy and opportunities to de-culvert
The presumption against culverting shapes site layouts before anyone looks at plot numbers. How the consents work, where a culvert is still accepted, and what opening a channel is worth in the balance.
Flood resistance and resilience measures in design
Sealing a house against a metre of water can damage it. Treating a shallow nuisance flood as inevitable wastes a kitchen. Depth and duration decide the approach.
Blue roofs and permeable paving on constrained urban sites
Blue roofs and permeable paving are what urban drainage strategies fall back on when there is no external space. Both carry structural and maintenance consequences that need settling early.
Non-mains drainage and the general binding rules
Private drainage is regulated twice, by the Environment Agency and by the council. What the binding rules cover, when a permit is needed, and what to submit.
Foul drainage capacity and pre-development enquiries
Capacity answers come from the water company, not the council, and they take weeks. What to ask for, how to read sewer records, and what to put in the application.
Environment Agency standing advice and when it does not apply
Flood risk standing advice removes the consultation, not the assessment. Here is where it applies, what triggers a bespoke Environment Agency response, and how to record your reliance on it.
The drainage hierarchy and justifying a departure
Surface water must go to ground unless infiltration can be shown to fail. Here is the evidence needed to move down each step of the drainage hierarchy without a holding objection.
Infiltration testing and when soakaways are ruled out
A soakaway cannot be designed without a proper infiltration test. This covers the BRE Digest 365 method, groundwater and contamination constraints, and how to present a failed test so the council accepts the alternative.
Surface water flood risk and critical drainage areas
Flood Zone 1 does not mean low risk from every source. This explains what the national surface water map shows, how critical drainage areas are defined, and the extra evidence they require.
The flood sequential test at application stage
The sequential test is a gateway, not a balance. Most failures trace back to an area of search the council never agreed, or a schedule with no dates.
Flood Map for Planning or the long term risk service
The planning flood map is undefended and river and sea only. The long term service includes defences, surface water and reservoirs. Use each for what it is built for.
Rainwater harvesting and whether it counts as attenuation
A harvesting tank is designed to be full and an attenuation tank has to be empty. Splitting the vessel is the design that survives a planning condition.
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