Flood, Drainage and SuDS – Page 7
Flood risk assessments, sequential and exception tests, drainage strategies and SuDS design.
Flood, Drainage and SuDS articles – page 7
290 articlesDrainage strategy for a phased development
The permitted discharge rate belongs to the site, not to phase one. Here is how to allocate it, design interim arrangements and lock each phase to the drainage it depends on.
Water quality treatment for surface water runoff
Attenuation volume says nothing about water quality. Here is how pollution hazard and mitigation indices set the treatment train, sub-catchment by sub-catchment.
Requesting sewer flooding records from the undertaker
Sewer flooding records come from the undertaker, not the council. Here is what a pre-development enquiry returns, how accurate the asset plans are, and how to write the response into an FRA.
FEH13 rainfall against older depth curves in drainage design
The rainfall dataset behind a drainage design changes the storage volume required. Here is what separates the current FEH model from FEH99 and the older Flood Studies Report curves, and how to evidence the choice.
Proving no increase in flood risk to third parties
The burden sits with the applicant. Comparable baseline and proposed runs, difference plots at named receptors and proper sensitivity testing are what satisfy the test.
Vortex flow controls and minimum orifice size limits
A 2 litre per second orifice is about 28mm across and will block. How vortex flow controls work, what minimum discharge rates authorities set, and the effect on storage volume.
Tidal locking and what it does to an outfall design
On an estuary frontage a gravity outfall is shut for hours each tide. The locked duration sets the storage volume, the critical rainfall duration and whether a pump is needed.
Wave overtopping on a tidal frontage and freeboard
On a tidal frontage the design flood level is the still water level plus the wave component. Here is how overtopping discharge is calculated and how freeboard follows from it.
Change of use applications and when an FRA is still needed
The same water in the same building matters more when people sleep in it. Vulnerability classification, not physical works, decides which flood tests apply.
Pumped surface water drainage and answering objections
Do not argue that pumps are reliable. Prove gravity is unavailable with levels, then show the failure case, the storage behind it and who funds the upkeep.
Blue roofs or permeable paving: where each one works
Structural capacity at roof level and the ground beneath the hardstanding usually decide this. Where contamination or groundwater rules out the pavement, the roof carries the scheme.
Sustainable drainage on a small infill plot
Minor development does not need major-scheme attenuation design. It needs a measured impermeable area, a tested infiltration rate and a discharge route someone has the right to use.
SuDS adoption and the maintenance schedule councils expect
Schedule 3 of the Flood and Water Management Act 2010 was never brought into force, so every SuDS asset needs a negotiated adoption route, a written schedule and a mechanism that binds successors.
Surface water flood maps against a local model
National surface water mapping applies rainfall to a coarse terrain model with no real drainage network. This compares it with local hydraulic modelling and sets out how to reconcile conflicting sources.
Departing from the drainage hierarchy: evidence that works
A hierarchy justification stands on trial pit logs, level surveys and dated correspondence, not on professional opinion. This sets out what evidence closes each tier and how to present it.
Discharging surface water to a public sewer: the consent route
Connecting surface water to a public sewer runs on a separate track from planning permission. This covers the section 106 right to connect, the evidence an undertaker wants and how the discharge rate is negotiated.
How attenuation storage volume is actually derived
Attenuation volume is inflow minus permitted outflow at the worst storm duration. This explains critical duration, urban creep, long term storage and half drain time, and how to present the calculation for review.
Residual risk after a defence: breach and overtopping
Published flood zones ignore defences, so a defended site still needs the residual risk case. Breach and overtopping produce very different results.
Flood Zone 3b: what can be built in the functional floodplain
The 3a and 3b split comes from the council's strategic flood risk assessment, not the Environment Agency map. That is where most of the argument lives.
Climate change allowances for peak river flow in an FRA
The allowance you must assess depends on river basin district, management catchment, development lifetime and vulnerability class. Here is how to select and present it.
Discharging a drainage strategy condition
A surface water condition is usually a condition precedent. Starting before it is discharged can mean the permission was never lawfully implemented.
Modelling urban creep on a redevelopment
Urban creep is applied to contributing area, not to rainfall. Confusing it with the climate change allowance is how residential drainage systems end up undersized.
Drainage information required at outline stage
An outline application needs proof the site can be drained, enough land reserved to do it, and a deliverable discharge point. Detailed design belongs in a condition.
Flood risk assessment for a householder extension
Householder extensions count as minor development, so the flood risk assessment is two or three pages. Here is the structure, and the point at which it gets harder.
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