Drainage Strategy

Creating a Surface Water Drainage Strategy

In any proposed development, it’s important to have enough of an emphasis on surface water management.

As rainfall patterns continue to be as unpredictable as ever, new developments need to address rainfall safely without causing downstream flooding.

A structured drainage strategy makes sure that your planning project aligns with the national planning policy framework (NPPF) from day one.

What a Drainage Strategy Does

A drainage strategy is a comprehensive technical planning document that sets out a clear and structured blueprint for managing surface water runoff and foul sewage across a development site.

It shows how heavy rainfall will be safely managed, ensuring that your planning project will not increase flood risk to neighbouring properties or worsen any existing flood risk issues in the local area.

By incorporating sustainable drainage systems, the strategy aims to mimic natural hydrology, utilising natural processes to slow and clean water throughout the lifetime of the development on your proposed site.

Elements of Drainage Strategies

A robust strategy brings together several essential site components:

• Hierarchy Assessment: Applying both the SuDS hierarchy and the overarching drainage hierarchy in the following order of priority: discharge to ground – surface water body – surface water sewer – combined sewer.
• Outfall Selection: Assessing nearby options such as existing watercourses, a local surface water body or receiving water bodies, as well as routes to a regional wastewater treatment works.
• Runoff and Connection Mapping: Calculating the total impermeable area and identifying suitable connection points, whether to a public foul sewer or an existing public sewer.
• Site Data Integration: Incorporating results from a detailed topographical survey and site slope profile, often tested using advanced hydraulic modelling software.
• Treatment and Site Design: Implementing a structured SuDS management train alongside a comprehensive surface water management plan that integrates seamlessly into the overall site layout.

Importance of Drainage Discharge Flow Rates

Regulating discharge rates is essential to prevent overwhelming local infrastructure.

Local planning authorities need surface water discharge from a site to match natural greenfield runoff rates wherever possible.

By designing systems using appropriate climate change allowances to manage peak flow and overall volume control, you can stop excess runoff from flooding nearby land.

On brownfield sites, comparing proposed outputs to how previous land performances helps to reverse the effects of urban creep.

To achieve this, factors like soil geology and local ground conditions dictate the installation of flow control devices and attenuation structures such as detention basins.

What a Drainage Strategy is Used For

A drainage strategy services critical statutory functions:

Meeting Regulatory Mandates

Satisfying requirements set by your local planning authority, lead local flood authorities, the Environment Agency (EA), and other risk management authorities.

It also ensures full compliance with guidelines enforced by your overarching local authority.

Planning Submissions

Forming a crucial element of the planning application process for both outline applications and full proposals, usually alongside a detailed flood risk assessment.

Site-Specific Risk Mitigation

Essential for major developments, large residential developments or any site situated within a designated flood zone or an area identified with elevated development risk.

Tailored Solutions

Addressing any specific requirements flagged during pre-application discussions.

Advantages of Drainage Strategies

Investing in a well-conceived strategy offers substantial advantages for site developers:

• Enhanced Site Value: Using multifunctional benefits based on a natural approach using SuDS features improves visual appeal, such as via the use of green roofs and permeable paving.
• Environmental Protection: Safeguarding local water quality, directly supporting goals under the Water Framework Directive and delivering long-term biodiversity benefits.
• Resilience and Viability: Confirming clear exceedance routes to protect against extreme surface water flooding, showing that your site’s suitability for development and complying with local policy.
• Smooth Consenting: Accelerating the process of securing planning approval and grants of formal planning permission by avoiding costly application refusals or delays.

Assembling a Strategy for Your Site

Working out an effective strategy needs close collaboration between your design team, civil engineers and planning specialists.

It needs everyone involved to work together in order to evaluate all physical drainage features, identifying drainage issues early and checking connections to the surrounding surface water networks.

More than anything, the process confirms if outfalls cross third-party land or remain strictly within the site boundary.

Steps to Formulate a Strategy

1. Feasibility and Fieldwork

In the early stages, engineers carry out site-specific ground investigations to measure infiltration capacity and verify seasonal groundwater levels.

2. Concept and Alignment

With reference to the national standards and statutory practice guidance, an initial SuDS design can be created.

3. Formal Specification

Using calculations to ensure that the systems have sufficient capacity, the engineer can assemble a detailed design.

4. Submission and Discharge

After the strategy has been finalised, a report from the process can be submitted to the local planning authority to secure approval and discharge post-permission planning conditions.

Get a Professional Drainage Referral

If you need help with your proposed development on any matters affecting surface water runoff, sustainable drainage systems, factors that could increase flood risk and related national or local policy, 24Housing works with a high-quality service provider for all flood risk and drainage services.

By speaking to our team about the issues on your development site, we can work out what you need and put you in touch with the right people. In the case of needing a surface water drainage strategy, we will happily refer you to the drainage consultants we frequently partner with.

Contact Our Team for a Quote

Reach out to our team by calling us, emailing us or filling out a quote form at the top of this page or on our contact page. At this point, give us as much information as possible, as it will help us with pricing up what you need and speed up the process.

From there, we can refer you to the flood risk and drainage consultancy we work with and get your planning project moving forward, creating a drainage strategy and boosting your application for planning permission.