Drainage Strategies Making Sustainable Developments

Your planning application will benefit from a robust drainage system which is fully compliant with the national and local drainage guidance

Our experience in dealing with local drainage authorities, lead local flood authorities and planning departments put us in a great position to give you the best advice to get the planning application approved.

Our expertise allows us to give you the full range of services for drainage strategies including 2D surface water run-off modelling, approved drainage calculations using Micro Drainage and design of Sustainable Drainage Systems in complex site conditions such as:

Using our latest mapping, allow us to clearly examine the ground conditions at a desktop level and provide you with a robust design.

We work collaboratively with planners, landscape architects, architects to develop a design that meets the requirement of the developer and the local authority. We create developments that are more resilient to climate change.

You receive clear and specific advice which:

Trusted by over 100 developers, architects and planners in the UK to get their planning approvals

Our Reports

If you are uncertain about your requirements, give us a call, we are happy to talk you through the options.

During this process, we create Sustainable Drainage Systems –SuDS- strategy that focus on delivering projects which reduce water quantity, enhance water quality, allow space for water amenity, and provides biodiversity.

Our proactive approach allows the developers, landscape designers and architects to fully understand the benefits of using Sustainable Drainage Systems in their developments.

Frequently Asked Questions

A drainage consultant carries out the surface water drainage strategy in compliance with the local site condition and guidance by the Lead Local Flood Authority.

Who approves the sustainable drainage strategy report?

A drainage strategy is approved by the Lead Local Flood Authorities (LLFA’s). The LLFA is most likely to be the County Council where the development is located. In the near future, the may be a SuDS approving body (SAB) in England.

Why do I get a drainage planning condition after providing a drainage strategy?

The drainage is conditioned because the development can change between planning approval and construction.

It can also be conditioned if soakaway tests were not undertaken or discharge rates were not agreed with the Environment Agency or the local water company. The condition looks like this.

You can re-submit the same drainage strategy used at planning stage to clear the planning conditions and produce the detailed design for construction. This is assuming that there were not changes to the development.

Do I need to complete soakaway tests for my SuDS strategy?

It depends on the known soil characteristics and the flood risk.

In areas where the lead local flood authority is knowledgeable of the ground conditions, there is no need to carry out soakaway tests.

In councils where flooding is considered an issue or the ground conditions are unknown, the Lead Local Flood Authority or Local Council would request the following information:

How to do a soakaway test or percolation test for SuDS?

There are two types of percolation tests.

The first one is the percolation test to BRE365.

The soakaway tests can be undertaken by a site investigation company or your local builder or farmer or you can undertake them.

We will provide you with:

The second method is a deep borehole test, in which a hole is drilled into the ground and the discharge rate is calculated.

This method is used in areas where the permeable layers are underneath impermeable soils. For instance, clay overlaying chalk.

This type of soakaway test is undertaken by a site investigation company that has the equipment. If required, we can obtain quotes and organise this work.

What is a SuDS report or Drainage Report?

A SuDS report or Drainage Report is a document that sets out the drainage principles for the safe and sustainable disposal of surface water produced by a development. These reports are also called Drainage Strategies. The drainage strategy form part of the construction drainage design.

SuDS report or Drainage Report or Drainage Strategy contains the following items:

• The current site description including size, permeable and impermeable areas, flood risk and whether is a green or brownfield site

• An investigation of the possible discharge points such as infiltration, rivers, surface water sewer or combined sewer systems

• A full set of calculations for discharge rates of the existing site

• A drainage strategy drawing showing the location of the SuDS drainage

• An evaluation of the Sustainable Drainage Systems -SuDS- that can be used on the site

• The size of the sustainable drainage system based on drainage calculations

• The maintenance plan for each of the sustainable drainage elements

• A drainage report could also include the foul water drainage design strategy

What is a Sustainable Drainage System SuDS?

A SuDS is a surface water management approach that mimics the natural environment while providing resilience to climate change.

The aim is to revert the development site to their original water cycle state. It is achieve by reducing water quantity, enhancing water quality, allowing space for water amenity and providing biodiversity for your development.

In order to achieve this, the storm peaks are reduced by slowing down and diverting water away from sewers and into the ground. This is accomplished by using green roofs, permeable surfaces, soakaways, ponds and swales. These systems can be used for amenity spaces and for biodiversity.

In some cases is not possible to infiltrate all the water, then water is attenuated in a pond and discharged to a watercourse at the same flow rate than when the site was a green field.

When watercourses are not available, water can be discharge to a sewer and attenuated in tanks. This is the least sustainable approach to managing surface water.

This drainage strategy hierarchy is followed by Building regulations and the National Planning Policy.

How do sustainable urban drainage systems work?

Sustainable urban drainage systems work by making water closer to people and creating streetscapes for people and communities can interact.

The SuDS in urban environments also work by achieving the principles of controlling water volumes, reducing temperatures of surfaces, and making stable urban environments that a more resilient to drought and flooding.

These principles are achieved by introducing places where water interaction is possible by building green walls, rainwater gardens, street water gardens, reflective ponds, water playscapes, plant drills. Great examples of these works can be seen in the Bristol Harbour and in the Netherlands.

What does Building Regulations say about Sustainable drainage?

Sustainable drainage design is the preferred option for dealing with rainwater within Building Regulations. Building regulations follows this Drainage strategy hierarchy in order of priority:

Is the drainage Strategy the same as Detailed Drainage Design?

The drainage strategy is an outline design or stage 3 RIBA drainage design.

The drainage strategy gives the key elements of design such as type and size of Suds, minimum road build-ups etc. These designs would be fined tuned during detail design.

The detailed drainage design includes construction drawings or Stage 5 RIBA.

The detailed design contains all pipe sizes, pipe beddings, distribution chambers, setting out points for swales and 3D models for ponds.

In some special cases, the local council may request that all the levels, sizes and design up to stage RIBA 4 are determined before approval is given.

This can happen in areas of high flood risk or areas which are located in special zones such as source protection zones or in the proximity to Sites of Special Scientific Interest, Special Areas of Conservation, Special Protection Areas and Ramsar wetland sites.

What is a foul sewer strategy?

A foul sewer strategy determines:

A foul sewer strategy can be provided as part of the Surface Water Drainage Strategy if requested by the Lead Local Flood Authority.

How to undertake a percolation test for a treatment plant?

The percolation test should follow the requirements given in the BS6297.

The video below shows how to undertake the tests.

The soakaway tests can be undertaken by a site investigation company or your local builder or farmer can undertake them.

We will provide you with: