Drainage Systems & SuDs

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Our design engineers are experienced in foul, surface water and highway drainage design for both existing environments and proposed developments. We support clients throughout their projects and deliver detailed design drawings, rainfall run-off calculation packages and complete Section 104 & 106 applications.
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Sustainable Drainage Systems (SuDS)

Legislation requires that new build homes incorporate Sustainable Drainage Design Systems (SuDS) and most councils are now advising the retro-fitting of SuDS as a simple and cost effective way of reducing flood risk. We include SuDS in all designs to maximise efficiency, to suit each development and support planning approval.

We can advise on the best form of SuDS for an area based on the infiltration of the ground and the potential impacts on ground stability. These SuDS solutions might include one or more of the following:
Drainage Design Audits

Waterco provides independent technical audits of drainage designs prepared by others, giving clients a trusted second opinion that highlights potential improvements. This ensures compliance and can often identify cost‑saving opportunities.

Expert review by engineers

With extensive design expertise, our experienced engineers scrutinise submitted schemes in detail, offering reassurance that drainage solutions are practical, efficient, and meet regulatory standards.

SuDS Approval Body (SAB) Wales

Under Schedule 3 of the Flood & Water Management Act, all new developments in Wales must secure SuDS approval alongside planning consent. This makes compliance a critical step in the development process.

Tailored SuDS Advice

We advise on the most appropriate SuDS solutions for each site, considering ground infiltration and stability to ensure designs are sustainable, effective, and aligned with local authority requirements.

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Surface Water Drainage Systems

Surface water drainage systems manage rainwater on development sites, helping to prevent flooding and ensure compliance with regulations. Our designs cover soakaway suitability, rainwater harvesting, flow control, and safe discharge to watercourses.

We also work with authorities to secure fair discharge rates, delivering efficient, sustainable, and cost‑effective solutions for developers.
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Tailored Design Packages

We incorporate soakaway suitability, rainwater harvesting, flow control, oil interception, adoption liaison, and full discharge specifications.

Outfall & Interface Design

Our expertise covers discharges to watercourses, outfall structures, and integration with headwalls and culverts.

Authority Engagement

We liaise with drainage authorities, NRW, SEPA, and the Environment Agency, challenging restrictions that are unreasonable or inappropriate.

Cost‑Saving Advocacy

Using advanced computer modelling, we have successfully reduced excessive discharge rates and storage requirements, saving developers thousands of pounds.

Sustainable drainage systems

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Foul Drainage

Using the latest micro-drainage and DH Mike Urban software, we establish optimum designs for third party approval, understanding the changing regulatory standards set. Additionally, where development costs appear to be prohibitive due to drainage problems, we review existing project / scheme designs.

Our detailed drainage design packages are tailored to benefit the value of a development, whilst ensuring regulatory and environmental standards are met. These can include:
Pipe specifications, layouts, and sewer connections

We design accurate pipe specifications and layouts to ensure efficient drainage flow. Connections to existing sewerage systems are planned to minimise disruption and guarantee compatibility with local infrastructure.

Connections to private systems

Our team develops safe and compliant links to private drainage networks. This ensures developments integrate seamlessly with non-public systems while meeting technical and environmental requirements.

Septic tanks, treatment plants, and pumping stations

We assess the suitability of septic tanks, package treatment plants, or pumping stations for each site. Recommendations are based on capacity, environmental impact and long-term sustainability.

S185 diversions, liaison, and statutory applications

We manage S185 sewer diversions and coordinate directly with Sewerage Operators and local environment agencies. Our service also covers Section 104 and Section 106 applications, ensuring all statutory approvals are secured efficiently.

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Drainage Strategy & Assessment

A Drainage Strategy or Preliminary Drainage Assessment ensures the most effective solutions for site drainage. Planning authorities expect strategies that are sustainable, practical, and capable of mitigating flood risk.

By addressing drainage early, developers can reduce costs and shape site layout more efficiently. We deliver clear, detailed reports to support planning applications and pre‑planning assessments, giving local authorities confidence in comprehensive and sustainable drainage solutions. Our assessments entail:
Waterco assessment
Initial Review & Testing Guidance

We review drainage records and advise on percolation test methods under Building Regulation Part H.

Analysis of Percolation Results

We assess test results to confirm soakaway suitability and calculate run‑off where they are not viable.

Run‑off Calculations & Solutions

We measure pre‑ and post‑development run‑off and recommend options such as infiltration, recycling, or discharge.

Reporting & Consultation

We submit developer enquiries and propose drainage solutions, consulting with all relevant authorities.

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Drainage Systems and SuDs Team

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Frequently Asked Questions

A Flood Risk Assessment checks if a site is suitable for development by evaluating its risk of flooding. Requirements vary by region, but usually depend on the site’s location, size, and type of development. In England and Scotland, it’s called a Flood Risk Assessment; in Wales, it’s a Flood Consequence Assessment.

A Flood Risk Assessment is typically required when any of the following applies:

1. The site is over 1ha.

2. Can be classed as a major development.

3. Located in Flood Zone 2 or 3.

4. Drainage area is classed as critical.

A Drainage Strategy (SuDS report) is needed if your site is over 1ha, a major development (10+ units), in Flood Zone 2 or 3, in a critical drainage area, or if building a new structure.

Local planning authorities may request one to ensure your project complies with regulations and avoids future issues. Checking early helps prevent delays, and our team can guide you through the process.

In certain areas the LLFA, EA, SEPA or NRW may not hold sufficient information for your site to inform their decision on flood risk, flood sources and flood hazards. We can support your Flood Risk Assessment in-house with hydrology assessments and detailed hydraulic modelling.

Hydraulic modelling simulates how water behaves under changing conditions to assess flood risks. Using software such as MIKE FLOOD, Flood Modeller Pro, TUFLOW, and HEC-RAS, we predict flood depths, velocities, inundation rates, and hazard ratings. These insights inform UK flood maps and help clients develop effective flood management strategies.