Flood, Drainage and SuDS – Page 10
Flood risk assessments, sequential and exception tests, drainage strategies and SuDS design.
Flood, Drainage and SuDS articles – page 10
290 articlesDrainage evidence for a single new dwelling
One new house needs a short drainage statement, not a modelled design. Work down the surface water hierarchy with a reason at each step, and include a dated percolation test.
Basement development and the flood risk objection
Flood objections to basements start with vulnerability classification, and the use below ground decides the outcome rather than the waterproofing. Groundwater, surface water and sewer backflow each need separate answers.
Exception test evidence: the two limbs in practice
The exception test asks for wider sustainability benefits to the community and for a development that is safe for its lifetime. Most failures come from writing the first limb about the applicant rather than the community.
Groundwater flooding evidence and how to assess it
A site can sit in Flood Zone 1 and still flood from a rising water table. Characterising the risk means borehole monitoring through a recharge season, not map reading.
Culverts and the presumption against burying a stream
Culverting is resisted in policy, needs separate consent from the lead local flood authority or Environment Agency, and now carries a measurable cost in biodiversity units.
Climate change allowances: picking the right percentile
Four inputs decide which climate change allowance applies: catchment, variable, vulnerability and lifetime. Getting one wrong costs you the floor levels or the storage volume.
Half drain time and why attenuation designs get rejected
Attenuation storage that takes two days to half empty is not available for the next storm. What the half drain time criterion tests, and the design moves that fix a failing scheme.
Flood risk assessment for a change of use application
The walls stay where they are, but the people inside change. How vulnerability classification decides whether a conversion needs an assessment and an Exception Test.
Flood risk betterment as a planning benefit in the balance
Only the part of a drainage scheme that goes beyond what policy requires counts as a benefit. Here is how to identify that surplus, quantify it and secure it.
Raised access roads and refuge platforms on flood sites
Safe access is where flood affected schemes fail. Here is how hazard rating works along a route, what raising land does to levels elsewhere, and when refuge is defensible.
Trash screens, headwalls and maintenance access
A trash screen moves blockage risk from inside the culvert to the inlet. Here is how to choose a screen, detail a headwall, model blockage and secure clearance access.
Compensatory flood storage and level for level design
Floodplain compensation has to be level for level, volume for volume and hydraulically connected. Here is how the accounting works and what the Environment Agency checks.
What a consultee checks in a drainage model output
Drainage model outputs are reviewed quickly and rejected for predictable reasons. Here is what a consultee reads first, the checks to run before submission, and how to present results so they can be followed.
Estate road drainage and the section 38 adoption process
Highway drainage on a new estate is adopted under section 38 of the Highways Act 1980, not by the water company. What the authority takes, what it refuses, and how to close the gaps before they stall adoption.
Construction phase surface water pollution control
Construction sites pollute watercourses mostly through silt, and the controls have to be designed before the topsoil comes off. Temporary drainage, settlement, washout areas, permits and a construction management plan that an officer will approve.
Section 104 sewer adoption and the standards behind it
A section 104 agreement transfers your new sewers to the water company. Here is what it covers, the design standards applied, where sustainable drainage falls outside it, and how to sequence it against the build programme.
Flow control devices: orifice plates and vortex units
The device that sets your discharge rate decides the storage volume. How each type behaves, the small orifice problem, and what to check once it is installed.
Sustainable drainage on a householder extension
Extension drainage is a Building Regulations question more than a planning one. Soakaway sizing, separation distances, sewer connections and permeable paving.
Pumped surface water systems and why councils resist them
Pumped drainage meets resistance on resilience, adoption and long-term cost. Where it is unavoidable, and what a submission needs to contain to succeed.
Proving infiltration is not feasible in the drainage hierarchy
Moving down the surface water hierarchy takes site evidence, not a geology map. What to test, what to record and how to set out the justification a flood authority accepts.
Tidal flood risk, breach modelling and coastal change
A site behind a good sea wall still sits in Flood Zone 3, because the mapping is undefended. The safety case is made by breach modelling, hazard rating and the defence's residual life.
Groundwater flooding where there is no published map
The Flood Map for Planning covers rivers and the sea, not the water table. Where groundwater is the risk, the evidence has to be assembled plot by plot, and winter monitoring takes a season.
Permeable paving on clay soils: when it still works
A poor percolation test rules out full infiltration, not permeable paving. On clay the pavement becomes a shallow tanked attenuation structure with a controlled outlet, and it is sized on void ratio.
Blue roofs: design, attenuation credit and adoption
Roof level attenuation buys developable ground on tight urban sites. It also puts standing water above an occupied building and hands a maintenance duty to whoever owns it in year thirty.
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