Where we work
We are drainage engineers and civil engineering designers working across Wiltshire and the South West. We have delivered 17 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 Wiltshire Council, Somerset Council, Bristol City Council and Devon County Council asks for, and what the ground in Wiltshire and the South West will actually do.
Our projects in Wiltshire and the South West, 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 Wiltshire and the South West
- Drainage design in Wiltshire and the South West — surface water and foul drainage strategies, attenuation, SuDS and outfall design, sized for your site and your discharge rate.
- 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.
- Highway design — access, visibility splays, turning heads and adoptable road design, including Section 38 and Section 278 agreements.
- Percolation testing — BRE 365 soakaway testing across Wiltshire and the South West, arranged through PT (West Midlands) Ltd so the design and the testing come from one place.
Ground conditions in Wiltshire and the South West
Wiltshire has four distinct grounds: chalk downland, the stony Cotswold fringe toward Gloucestershire, sands following the chalk, and clay vales between them. Chalk can infiltrate but carries seasonal high groundwater; the clay-with-flints capping much of the downs, and the Oxford and Kimmeridge Clay vales, generally cannot. Soakaways here fail far more often from being put in the wrong ground than from being undersized.
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: County geological descriptions. 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.
Wiltshire and the South West at a glance
- Lead local flood authority
- Wiltshire Council, Somerset Council, Bristol City Council and Devon County Council
- Postcode areas
- BA, BH, BS, EX, PL, SN, SP
- Projects delivered here
- 17
- Statutory consultee
- Yes, on surface water for major development
- Percolation testing
- BRE 365, via PT (West Midlands) Ltd
- Case studies
- 7
What Wiltshire Council expects
Wiltshire requires a hydrogeological risk assessment where infiltration is proposed for anything other than clean roof water inside a Source Protection Zone 1. Given how much of this region sits on chalk and limestone, that catches a lot of otherwise straightforward soakaway schemes.
Wiltshire will adopt SuDS forming part of road drainage through a Section 38 agreement in its highway authority role, but does not adopt SuDS serving property drainage as lead local flood authority — so long-term maintenance has to be arranged privately. They publish a SuDS technical checklist that has to be submitted with the application.
Source: Wiltshire Council. Requirements and ground conditions both change — we check them at the start of every job.
Flood risk assessments in Wiltshire and the South West
Drainage is the bulk of what we do, but in Wiltshire and the South West a large share of it comes with flood risk assessment attached — because the Avon and Kennet valleys and a high winter water table put more sites in a flood zone than people expect.
A site-specific flood risk assessment applies the sequential and exception tests, works out the flood levels your site will actually see over its lifetime including an allowance for climate change, and sets finished floor levels, safe access and egress against them. Wiltshire Council and the Environment Agency both look at it, and the commonest reason one comes back is that it assessed fluvial risk and ignored surface water.
We do this as part of the same job, so the flood risk assessment and the drainage strategy agree with each other rather than being written by two firms who never spoke. More on flood risk assessment.
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 Wiltshire 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 Wiltshire 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 Wiltshire and the South West
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 Wiltshire and the South West
Past project locations here include Bristol, Salisbury, Gillingham, Dodford Lane, East Chinnok Somerset, Cricklade and Crickalde.
- A storage building in Cricklade, Wiltshire
- A storage building in Gillingham
- A single dwelling in Salisbury
- A single dwelling in Plymouth
- Animal pens in Salisbury
- A single dwelling in Bromham
- The Forty, Cricklade
Questions we get asked in Wiltshire and the South West
Do you need to be local to do this work?
No. It is done from survey data, ground investigation and Wiltshire 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?
Wiltshire Council, Somerset Council, Bristol City Council and Devon County Council. 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 definitely need a flood risk assessment?
If your site is in Flood Zone 2 or 3, or is over a hectare in Zone 1, yes. Smaller sites in Zone 1 can still need one where there is a record of surface water flooding — and in Wiltshire and the South West there often is. Send us the address and we will check the maps before you pay for anything.
Can a flood risk assessment get a refusal overturned?
Sometimes. An FRA that applies the sequential and exception tests properly, and shows safe access, egress and finished floor levels, can answer the objection that caused the refusal. It depends entirely on why it was refused.
What holds a drainage scheme up?
Usually the ground testing, and where one is needed, the response time from Wiltshire 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 Wiltshire and the South West 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.