Flood, Drainage and SuDS – Page 2
Flood risk assessments, sequential and exception tests, drainage strategies and SuDS design.
Flood, Drainage and SuDS articles – page 2
290 articlesReservoir flood risk and what an assessment covers
A site downstream of a large raised reservoir can sit in Flood Zone 1 and still appear on inundation mapping. Reservoir risk is residual risk, assessed through depth, velocity, arrival time and the evacuation strategy.
Non return valves and basement sewer surcharge
Sewer surcharge floods basements through their own drains rather than over the threshold. An anti flooding valve to BS EN 13564, a sealed sump and a pumped rising main are the usual answer.
Culverts, de-culverting and the riparian owner's duties
A culverted watercourse is the riparian owner's responsibility whether or not anything is built. This covers the duties, the consent regimes, capacity and blockage assessment, and what a drainage strategy should propose.
Blue roofs in the drainage calculation
The hydraulics of roof attenuation are straightforward; getting the volume credited is not. This covers storage depth against structural loading, flow control modelling, failure modes and the drawings reviewers expect.
Choosing between the central and upper end climate allowance
The Environment Agency publishes bands rather than a single climate uplift. This explains how vulnerability classification, flood zone and catchment select the allowance, and how to document the choice so a reviewer can check it.
Local resilience forums and flood emergency planning
Flood emergency planning sits with local resilience forums under the Civil Contingencies Act, not with the planning system. Here is how the two meet.
Sewerage design standards and sewer adoption approval
Adoptable sewers are designed to the sewerage undertaker's standards, not the council's. Here is what governs the layout, how the application runs and where the programme slips.
Flood Re and what buyers will ask about
Homes built on or after 1 January 2009 cannot use Flood Re, so new build insurance rests on the open market. What to hand over at completion and what not to promise.
Trash screens and the liability they create
Screens protect a culvert and introduce a new flood risk upstream. How blockage is modelled, which designs degrade gracefully, and who maintains the structure afterwards.
Car park change of use and surface water retrofit
An existing impermeable site protects you from a greenfield requirement but not from a betterment expectation. How to evidence the baseline discharge and what the strategy must show.
Attenuation under an adopted highway: what is allowed
Highway authorities rarely accept attenuation storage under an adopted carriageway. The reasons, the technical bar where it is considered, and the alternatives that keep storage inside the site.
Maintenance plans for drainage: content and author
Most drainage maintenance plans describe inspection frequencies well and then fail on the question of who is actually obliged to carry them out, and how it is funded.
SuDS features and double counting against net gain
A basin can attenuate water and carry habitat. What it cannot do is appear twice in the metric, or be credited with a condition the maintenance regime makes impossible.
Highway drainage connections and the authority's rules
A highway drain is sized for the road and sits nowhere in the drainage hierarchy. Connecting to it needs the highway authority's consent, and the default answer is no.
Pumping stations: standards, odour and adoption
A foul pumping station needs land, access, a separation distance from habitable rooms and an adoption agreement. Settle all four at layout stage, not after.
Detention basins designed as usable landscape
A basin that counts towards an open space requirement and one that appears as a fenced hollow are the same feature designed differently. Slopes, depth and inundation frequency decide which you get.
Swale design: gradients, side slopes and check dams
A swale is mostly geometry. Shallow gradients keep flow slow, gentle side slopes let a machine mow it, and check dams break a steeper fall into shallow steps.
Geocellular storage and designing access for cleaning
Modular cells hold a large volume in a small footprint, but silt that reaches the cells stays there. The maintenance channel and the upstream treatment stage decide whether the design is accepted.
Changing to a more vulnerable use in a flood zone
Flood risk policy classifies uses by vulnerability, and a conversion to residential moves a building up a class. What applies in Zones 2, 3a and 3b, and how prior approval routes are affected.
Downpipe disconnection and retrofit rain planters at home
Disconnecting one downpipe into a planter or rain garden keeps roof water on the plot. The sizing method, the overflow detail most people skip, and where consent is still needed.
Paving a front garden: the drainage rules that apply
Hard surfacing a front garden is permitted development only if it is porous or drains inside your boundary once it exceeds five square metres. The detail, plus dropped kerbs and conservation area traps.
One and two dimensional modelling: which is needed
Many site assessments need no new hydraulic model at all. Here is when one dimension is enough, when spreading demands two, and how to scope it with the regulator.
Breach and overtopping scenarios behind a defence
Flood zones ignore defences, so a defended site needs breach and overtopping scenarios. The outputs that matter are depth, velocity, hazard and the time before water arrives.
Rainfall data sets and which one to design with
The rainfall model behind a drainage calculation changes the storage volume, especially for short rare storms. Record which data set you used and where it came from.
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