Flood, Drainage and SuDS – Page 12
Flood risk assessments, sequential and exception tests, drainage strategies and SuDS design.
Flood, Drainage and SuDS articles – page 12
290 articlesChoosing the right climate change allowance epoch
Most climate change allowance errors are selection errors rather than modelling errors. Getting the epoch, the catchment and the category right first time avoids a rerun.
Culverting a watercourse and the presumption against it
Regulators start from the position that a watercourse should stay open. Understanding riparian duties, the consent regime and the deculverting argument saves a layout that would otherwise be redesigned late.
Schedule 3 SuDS approval: where the law stands and what to do now
No SuDS Approving Body exists in England and the automatic right to connect survives. Here is what actually controls drainage design now, and what changes if Schedule 3 is brought into force.
Water neutrality: what applicants have to show in affected areas
In affected water resource zones a scheme has to cut per person water demand and offset what is left, with the offset secured before permission can be granted.
Basement development and flood risk: the tests to satisfy
The flood risk vulnerability class decides most basement schemes before any modelling starts. Here is how the Sequential Test, the Exception Test and groundwater evidence fit together.
SuDS adoption and maintenance: who holds it long term
Who maintains a SuDS scheme in 30 years is a design decision, not a handover decision. Here is how the adoption routes work and what each one demands of the layout.
What the lead local flood authority checks in a drainage strategy
Lead local flood authorities audit drainage strategies against a fairly consistent checklist. Here is what they look for, and the omissions that produce a holding objection.
Flood risk activity permits for works near a main river
A flood risk activity permit sits alongside planning permission, not inside it. Here is which works trigger one, the byelaw distances that matter and how to design the requirement out.
Ordinary watercourse consent: when planning is not enough
Building a culvert or an outfall in a ditch needs consent under the Land Drainage Act 1991, from the lead local flood authority. Planning permission does not authorise it, and building first is an enforcement risk.
Foul drainage on unsewered sites: package plants and permits
On a site with no mains sewer, the drainage answer has to satisfy building regulations, the general binding rules and the planning officer. Percolation testing is the step that decides most of it.
Getting a sewer connection agreement under the Water Industry Act
Planning permission does not give you a sewer connection. The right to connect comes from section 106 of the Water Industry Act 1991, and capacity, adoption and requisition all run on their own clocks.
The surface water discharge hierarchy and how to evidence it
The hierarchy runs ground, watercourse, surface water sewer, combined sewer. Applications stall on missing evidence that the higher options were tested, not on the design itself.
Permeable paving in a planning drainage strategy
Permeable paving removes impermeable area, provides subbase storage and treats runoff. It fails when it is drawn as a hatch with no section and no maintenance regime.
Attenuation storage sizing: durations, uplifts and volume
Attenuation volume is set by a matrix of return periods and durations, not a single storm. The uplifts, the critical duration and the drain down check decide the number.
Infiltration testing to BRE 365 and when it is worth doing
A low cost test with an expensive consequence. How to run BRE 365 properly, why summer results mislead, and the options when the ground will not take water.
The SuDS treatment train explained for planning applications
Officers test drainage strategies against the treatment train and the four pillars. How the stages work, how components are matched to pollution hazard and where space comes from.
Brownfield runoff betterment: how much reduction is expected
The national standards require improvement rather than restoration on brownfield sites. How to prove the existing positive drainage rate and what the local percentage really means.
Calculating greenfield runoff rates for a drainage strategy
The greenfield rate is the benchmark every discharge is judged against. Most holding objections come from the inputs, not the method.
Assessing surface water flood risk from the national map
The national surface water map is a screening tool, not a site model. Used properly it tells you where water crosses the site and what the drainage strategy has to do about it.
Flood resistance and resilience a council will condition
Resistance keeps water out to a limited depth. Resilience accepts it in and speeds the drying out. Councils condition both, and the wording decides who maintains them.
Safe access and egress in a flood event
A scheme can have floor levels well above the flood and still fail on access. The assessment is about people leaving, arriving and being reached during the event.
Setting finished floor levels and freeboard on a flood site
Floor levels on a flood risk site are a design decision with a paper trail behind them. Here is where the number comes from and how to reconcile it with access and drainage.
The flood exception test: evidencing both limbs
Sequential test done, exception test next. The two limbs need different evidence from different people, and most failures come from treating them as one argument.
Defining the search area for a flood sequential test
Most failed sequential tests fail on the search area rather than on the sites. Agree the geography with the authority first, then argue about availability.
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