Where we work
We are drainage engineers and civil engineering designers working across Surrey and South West London. We have delivered 34 projects here — drainage strategies, SuDS reports, flood risk assessments and highway design, prepared for planning and taken through to approval.
You do not need a consultant down the road from your site. This is desk work built on survey data, ground testing and the local authority’s own standards. What matters is that whoever does it knows what Surrey County Council, Kingston upon Thames and Croydon asks for, and what the ground in Surrey and South West London will actually do.
Our projects in Surrey and South West London, in red, against the rest of England. One dot per project, placed within its postcode area rather than at the exact site. Zoom out for the full picture, or ctrl and scroll to zoom.
Civil engineering design in Surrey and South West London
- Drainage design in Surrey and South West London — surface water and foul drainage strategies, attenuation, SuDS and outfall design, sized for your site and your discharge rate.
- Highway design — access, visibility splays, turning heads and adoptable road design, including Section 38 and Section 278 agreements.
- Flood risk assessments — site-specific flood risk assessments for sites in Flood Zones 2 and 3, and for sites over a hectare in Zone 1.
- SuDS design — sustainable drainage design and the SuDS statement your planning authority expects, with the drainage hierarchy worked through in order.
- Percolation testing — BRE 365 soakaway testing across Surrey and South West London, arranged through PT (West Midlands) Ltd so the design and the testing come from one place.
Ground conditions in Surrey and South West London
This area steps down from Bagshot Sands on the higher ground, through London Clay, onto river terrace gravels and alluvium along the Thames and Mole, with Lower Greensand and Weald Clay further south. It is one of the sharpest contrasts in England: a plot on the terrace gravels may infiltrate freely while one a few hundred metres away on London Clay or Weald Clay will not take water at all.
None of that tells us what is under your plot, and no report should pretend otherwise. It tells us what to expect, what to test for, and whether to plan for infiltration or for attenuation and a restricted discharge. A percolation test to BRE 365 settles it, and it is cheaper to do that before the design than to redesign afterwards.
Source: BGS Earthwise, London Quaternary. Requirements and ground conditions both change — we check them at the start of every job.
The drainage hierarchy
- 1InfiltrationSoakaway or infiltration basin, if the ground takes it
- 2WatercourseDischarge to a surface water body, usually rate-restricted
- 3Surface water sewerWhere a public surface water sewer exists and has capacity
- 4Combined sewerLast resort, and increasingly refused outright
Every scheme has to work down this list in order, and show why each option above the chosen one was ruled out. The ground is what decides whether you get to stop at step one.
Surrey and South West London at a glance
- Lead local flood authority
- Surrey County Council, Kingston upon Thames and Croydon
- Postcode areas
- CR, GU, KT, RH, SM, TW
- Projects delivered here
- 34
- Statutory consultee
- Yes, on surface water for major development
- Percolation testing
- BRE 365, via PT (West Midlands) Ltd
- Case studies
- 8
What Surrey County Council expects
Surrey publishes its standard planning conditions for surface water drainage, so you can read the exact wording likely to be attached before you submit. It also issues separate design guidance for major and non-major development, which is unusual — smaller schemes get their own route rather than being squeezed into the major one.
Where infiltration is not feasible, the maximum discharge rate is stated on the decision notice itself, and schemes are expected to match greenfield runoff rates and follow natural drainage routes. The London boroughs here act as their own lead local flood authorities.
Source: Surrey County Council. Requirements and ground conditions both change — we check them at the start of every job.
Highway design in Surrey and South West London
Drainage is the bulk of what we do, but in Surrey and South West London a large share of it comes with highway design attached — because tight urban plots make access and visibility the constraint that shapes the whole layout.
Access and visibility are usually settled before drainage, because they constrain the layout itself. We design accesses, visibility splays, turning heads and adoptable carriageways, and take them through Section 278 works to the existing highway and Section 38 adoption of new roads with the highway authority for Surrey and South West London. Leaving this late is expensive: it can mean redrawing the site plan and the drainage with it.
We do this as part of the same job, so the highway design and the drainage strategy agree with each other rather than being written by two firms who never spoke. More on highway design.
What you need, and when
The work is not one document handed in once. It arrives in stages, and sending the wrong level of detail at the wrong stage is one of the commonest reasons an application stalls with Surrey County Council.
- Outline application. A strategy showing the principle: where the water goes, roughly what it will take, and that the site can be drained at all. Detailed calculations are not expected yet, but a strategy that ignores the discharge hierarchy will be questioned.
- Full application. The full surface water and foul scheme with calculations, layout, attenuation volumes and the discharge rate you are asking for, evidenced.
- Reserved matters. The detail that was reserved at outline, now built out against the approved strategy — and it has to match it.
- Discharge of conditions. The final submission against the wording of the condition itself, with the maintenance and management arrangements Surrey County Council asks for. This is the stage most people reach us at, often with a condition already imposed.
Where the work lands
- OutlineDrainage strategy: the principle, not the detail
- FullFull scheme, with calculations and discharge rate
- Reserved mattersThe detail, matching the approved strategy
- DischargeSubmission against the condition wording itself
Most people reach us at the last step, with a condition already imposed. That is fine — it is just cheaper to have got the strategy right at the first.
Typical conditions we discharge in Surrey and South West London
Exact wording varies between officers and between applications, but conditions on sites here almost always fall into three shapes:
- Surface water drainage. “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, has been submitted to and approved in writing by the Local Planning Authority.” This is the one that needs the percolation results and the attenuation calculations.
- Foul drainage. A scheme for foul water disposal, agreed before occupation — straightforward on a mains connection, considerably less so on a package treatment plant or where the sewer is at capacity.
- Management and maintenance. A plan setting out who maintains the drainage for the lifetime of the development, and how. Often overlooked, and a common reason a discharge application comes back.
If you have a condition in front of you, send us the wording. We will tell you what it actually requires, before you commit to anything. There is a fuller guide to drainage planning conditions if you want to read up first.
Our work in Surrey and South West London
Past project locations here include Surbiton, Surrey, Alton, Purley, Oakhanger, Grayshott and South Bank Surbiton.
- A holiday park in Rudgwick Horsham
- A single dwelling in Mitcham
- An extension in Woking, Surrey
- 7 dwellings in Purley
- A single dwelling in Leatherhead
- A school in Surrey
- 84 Ditton Road, Surbiton
- Manor Cottage, Oakhanger
Questions we get asked in Surrey and South West London
Do you need to be local to do this work?
No. It is done from survey data, ground investigation and Surrey County Council’s own standards, none of which require us to be nearby. Being the right distance from your site has never discharged a condition; knowing what the authority wants has.
Who is the lead local flood authority for my site?
Surrey County Council, Kingston upon Thames and Croydon. They are a statutory consultee on surface water drainage for major development, and they set the local standards and the discharge rate your scheme is judged against.
Do I need a Section 38 or a Section 278 agreement?
Section 38 covers a new road you want adopted; Section 278 covers works to an existing highway, such as a new access. Many schemes in Surrey and South West London need both, and they run to different timescales.
How early does highway design need to start?
Earlier than most people expect. Access and visibility often constrain the layout itself, so settling them late can mean redrawing the site plan and the drainage with it.
What holds a drainage scheme up?
Usually the ground testing, and where one is needed, the response time from Surrey County Council or the water company — not the design itself. Getting the testing booked early is the single biggest thing you can do to keep a scheme moving.
I already have a planning condition. Can you deal with it?
Yes, and it is most of what we do. Send us the condition wording and the site address and we will tell you what is needed to discharge it.
Get a quote for your Surrey and South West London site
Send us the site address and the condition wording, or the planning reference, and we will tell you exactly what is needed. If you do not need us, we will say so.