Flood, Drainage and SuDS – Page 5
Flood risk assessments, sequential and exception tests, drainage strategies and SuDS design.
Flood, Drainage and SuDS articles – page 5
290 articlesInterception storage and the first few millimetres of rain
The first few millimetres of rain never leave a greenfield site. Interception puts that behaviour back, and on a self-build it is usually satisfied by paving, a soakaway and a rain garden.
Vortex flow controls and accuracy at low discharge rates
Low greenfield runoff rates sit at the awkward end of a flow control's operating range. Head, device curves, blockage risk and the as-built discrepancy that catches schemes out.
Reservoir inundation mapping and what it changes
Reservoir inundation extents are consequence maps drawn for emergency planners, not flood zones. How to describe the residual risk proportionately and which proposals deserve more.
Pumping stations: standards and amenity separation
A pumping station sits at the low point, needs separation from habitable buildings and takes a fenced compound with highway access. Fix it at concept stage or lose three plots.
Foul network reinforcement and Grampian conditions
A negative condition preventing occupation beyond a stated number of homes until off-site works are complete can make a constrained site developable, or it can strand the scheme at plot 60.
Sewer capacity enquiries: asking the right question
A red line and a unit count buys a generic answer. A point of connection, a peak flow and a phasing programme buys a response you can attach to the drainage strategy.
Residual flood risk: writing about breach and blockage
Residual risk is the section consultees read hardest. Naming each failure mechanism, testing it proportionately and saying who carries the duty afterwards.
Site-specific flood assessment against the strategic one
The council's strategic assessment and your own site-specific one do different jobs. How to use the first to cut the cost of the second, and where its data runs out.
Basement flood risk and pumped drainage
Basement dwellings sit in the highly vulnerable category, so the flood zone decides the principle and the pump design decides the detail. What to show in the assessment.
Building close to a flood defence: byelaws and clearances
Permanent works within eight metres of a main river bank or flood defence need an Environment Agency permit, sixteen metres on tidal defences. The maintenance strip usually decides the layout.
Riparian ownership and what the duty involves
Own land beside a ditch or stream and you probably own the channel to its centre line, with duties to pass on flow and keep the bed and banks clear. Here is what that means in practice.
Blue roofs and attenuation on a podium deck
Where there is no ground level storage left, attenuation moves onto the roof. Here is what blue roofs and podium decks demand in loading, outlet control, waterproofing and maintenance.
Infiltration testing to BRE Digest 365 in practice
A BRE Digest 365 test is three fills of a trial pit timed from 75 to 25 per cent of the effective depth, designed on the slowest. Here is how to get the fieldwork and the reporting right.
Proving the existing run-off rate on a brownfield site
Flood authorities test the existing run-off rate harder than any other input. Here is the evidence that proves connected impermeable area, and how betterment is applied to it.
Managing runoff on a steeply sloping site
On a sloping plot the drainage problem is speed rather than volume. Energy dissipation, terraced storage, infiltration and slope stability, and the levels a reviewer will ask for.
Modelling a partially blocked flow control
Lead local flood authorities expect a drainage strategy to show what happens when the flow control blocks. Here is how the scenario is run, what levels it produces and how to present it.
Planting specification for swales and wetland margins
A swale base and a wetland margin are different growing conditions two metres apart. Here is how to specify planting by zone, and what the maintenance regime has to say to keep it working.
Construction dewatering: the consents you actually need
Dewatering an excavation needs an abstraction licence for taking the water and a permit or consent for discharging it. Neither comes from the council, and both take longer than the site programme assumes.
Which rainfall dataset to cite in a drainage calculation
Name the rainfall model, the version, the grid reference and the extraction date. Here is how the Flood Estimation Handbook revisions differ, why storm profiles change the answer, and what a drainage reviewer checks first.
Outfall design, bank stability and scour protection
A surface water outfall is where a drainage strategy either works or quietly fails. Four things have to be settled together: invert level, scour protection, bank stability and maintenance.
Construction phase drainage and silt control
An operational drainage strategy describes a finished site. During construction the same site is bare earth discharging to the same watercourse with no permanent treatment in place, and it needs its own design.
Greenfield runoff rate: comparing the accepted methods
Two accepted methods applied to the same field can differ by a factor of two on a small site. Here is what drives the difference, how the 50 hectare scaling works, and how to present it.
Culvert capacity and trash screen design on a small site
A culverted watercourse on a small site raises two questions: can it carry the design flow with climate change added, and who will clean the screen. Here is how to answer both.
Overland flow arriving from neighbouring land
Water from the field above is your flood risk, not the neighbour's problem. Blocking it shifts the risk and creates liability, so the design has to carry it through the site.
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