Flood, Drainage and SuDS – Page 4
Flood risk assessments, sequential and exception tests, drainage strategies and SuDS design.
Flood, Drainage and SuDS articles – page 4
290 articlesInfiltration testing and when a soakaway will not work
The infiltration rate is only half the test. Depth, the number of pits and the seasonal groundwater maximum decide whether a soakaway is deliverable at all.
Blockage scenarios a flood risk assessment has to test
The design event assumes the asset works. Blockage assumes it does not, and the two produce different flood extents. What regulators expect in the blocked run and how to report it.
Finished floor levels and how a council fixes them
The level in the condition is the design flood level plus freeboard, in metres above Ordnance Datum. Survey it before the slab is designed, not after permission.
Separating surface water from a combined sewer
Taking roof and yard drainage out of a combined sewer is often the only betterment available on a tight urban site. It starts with dye testing, not drawings.
Condition or obligation for long term SuDS maintenance
A condition can require an approved maintenance plan but cannot carry money or a step-in right. On shared estate drainage that pushes you towards a section 106 obligation.
Finished floor levels and freeboard above the flood level
The design flood level is not the colour on the flood map. How to establish it, what freeboard to add, and every opening that has to sit above the result.
SuDS treatment stages and the simple index approach
Water quality is assessed by comparing pollution hazard indices with the mitigation indices of your treatment train. Where the calculation usually goes wrong.
Who adopts an attenuation tank and what that costs
Whether a tank goes to the sewerage undertaker or a management company decides the design standard, the whole-life cost and whether the drainage condition clears.
Permeable paving maintenance in a drainage plan
Permeable paving clogs in the top 20 millimetres of jointing grit. The plan that discharges the condition names the trigger, the equipment and who pays in year 12.
Blue roof attenuation and the evidence a condition needs
A blue roof turns the deck into the attenuation tank. The submission that gets approved covers the stored water load, the flow control performance curve and who maintains it.
Proving infiltration is unfeasible before discharging
Surface water strategies fail because the applicant jumped to a sewer without showing why infiltration could not work. Here is the evidence that discounts each rung properly.
Riparian ownership: the duties that come with a stream
Own land beside a stream and you own to the centre line, with duties to maintain the channel and pass flow on. What needs consent, and what a development site must record.
Drainage information for a minor planning application
The national requirements do not include a drainage strategy. What a proportionate drainage note for a small site contains, and the queries that delay validation.
Foul pumping stations: design, adoption and objections
A foul pumping station costs land, a standoff from dwellings, emergency storage and an adoption agreement. What the undertaker expects and which alternatives to test first.
Who adopts a SuDS scheme, and what that decides
Adoption is a design decision, not a paperwork exercise. The four routes for surface water drainage in England each dictate different slopes, access, treatment and long-term cost.
Blue roofs and podium attenuation on constrained sites
Roof level storage solves a site with no ground to work with, and it introduces loading, warranty and maintenance questions that a below-ground tank never raises.
When the sequential test applies to a householder extension
If you are extending a house in Flood Zone 2 or 3, you do not need to pass the sequential test. You do need to show the council how the extension deals with flood risk.
Overland flow from farmland onto a new development site
Water arriving from higher agricultural land is a separate problem from on-site attenuation, and it is the one most often missed until the layout is fixed. Here is how to find the flow path and design for it.
Silt management and pre-treatment before infiltration
Construction phase sediment is the main reason soakaways and infiltration basins fail. Catch silt upstream in features that can be cleaned, and protect the infiltration surface until the site is finished.
Pond and basin design: slopes, safety and maintenance
Hydraulic sizing is arithmetic. Side slopes, depths, access routes and the absence of a vertical drop into water are what the flood authority and the future management company actually judge.
Drainage evidence for a change of use with no new build
The test is not whether you are building, but whether the new use puts more or something different into the sewer. Most no-build changes of use need two to four pages, not a drainage strategy.
Internal drainage board districts and drainage rates
Internal drainage boards consent works to the watercourses they maintain, enforce a byelaw strip for maintenance access, set surface water discharge rates and raise drainage rates or a special levy. None of it is delivered by a planning condition.
Groundwater flooding in chalk and limestone catchments
The water table rises through winter until it reaches the ground and stays for weeks. Why the flood maps miss it, where it recurs, and how to design for it.
Soakaway design for a householder extension
Rainwater from a new extension roof is a Building Regulations question, not a planning one. The 5 m separation, the percolation test, BRE sizing and the alternatives when clay defeats you.
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