Case study
A drainage strategy for 2 dwellings in Ovingdean, prepared for planning and approved.
The constraint
Infiltration testing confirmed the ground would take water, so the scheme could discharge at the top of the drainage hierarchy rather than relying on a restricted discharge.
What we did
The scheme uses rainwater harvesting, a green roof, infiltration, permeable paving and attenuation storage.
Attenuation storage of 16m³ was provided for the 1-in-100-year event including a 40% climate change allowance.
The numbers
| Attenuation storage | 16m³ |
| Climate change allowance, 1 in 30 year | 45% |
| Climate change allowance, 1 in 100 year | 40% |
| Management catchment | Adur and Ouse |
Every SuDS option, and why
Each option in the SuDS hierarchy was considered for this site. This is the assessment as it went into the report:
| Option | Used | Why |
|---|---|---|
| Green Roofs | Yes | Green roofs have been proposed onsite as demonstrated on our proposed drainage layout. |
| Infiltration Systems | Yes | Cellular Soakaways crates have been proposed as means of discharge of surface water into the ground. |
| Proprietary Treatment Systems | No | The use of proprietary treatment systems is not considered required. |
| Filter Strips | No | Filter strips have not been considered the most effective proposal for this site due to the proposed site layout. |
| Filter Drains | No | Filter Drains have not been considered the most effective proposal for this site due to the proposed site layout. |
| Swales | No | Swales have not been proposed due to the site levels constraint. |
| Porous Pavements | Yes | It is proposed that all hard surfaces are to be of permeable construction. |
| Attenuation Storage | Yes | Attenuation storage has been provided in the form of cellular soakaway crates. |
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, based on sustainable drainage principles and an assessment of the hydrological and hydrogeological context of the development, including infiltration testing carried out in accordance with BRE Digest 365, has been submitted to and approved in writing by the Local Planning Authority.
The infiltration testing and the soakaway sizing 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.
More on drainage design in Ovingdean, browse the rest of our case studies, or see what a drainage strategy involves.