Case study
A drainage strategy for 11 dwellings in Walsall, prepared for planning and approved.
The constraint
The first question on any site is whether the ground will take water, because that decides whether the scheme is a soakaway or attenuation with a restricted discharge.
What we did
The scheme uses permeable paving and attenuation storage.
Attenuation storage of 8.94m³ was provided for the 1-in-100-year event including a 40% climate change allowance.
The numbers
| Discharge rate | 3.5l/s |
| Attenuation storage | 8.94m³ |
| Climate change allowance, 1 in 30 year | 35% |
| Climate change allowance, 1 in 100 year | 40% |
The kind of condition this discharges
Wording differs between officers, but a scheme like this one is normally answering a condition along these lines:
No development shall commence until a detailed surface water drainage scheme, demonstrating that surface water will be restricted to greenfield run-off rates for all storm events up to and including the 1 in 100 year event plus an allowance for climate change, has been submitted to and approved in writing by the Local Planning Authority.
The greenfield run-off calculation and the attenuation volume are what answer this one. There is a fuller guide to discharging drainage planning conditions if you want to read up on the process.
Outcome
The scheme was approved at planning.
Every scheme in these case studies was approved — that is the point of the exercise. If you have a drainage condition to discharge, send us the wording and the site address and we will tell you exactly what is needed.
Browse the rest of our case studies, see what a drainage strategy involves, or find where we work.