BRE 365 testing, developed by the Building Research Establishment (BRE), is a method of testing the soil infiltration rate to see how it can manage surface water runoff. It’s key to designing sustainable drainage systems (SuDS) and meeting planning and environmental regulations. By knowing the capacity of the natural underground drainage system, BRE 365 testing helps prevent flood risk and allows for good design of surface water drainage solutions.
Why is BRE 365 Testing Important?
BRE 365 testing is important for designing good drainage for construction projects. Its main purposes are:
- Surface Water Management: To see if infiltration devices such as soakaways can take the storm event runoff.
- Flood Risk Mitigation: To support local flood authorities and local planning authorities in reducing flood risk during the planning process.
- Regulatory Compliance: To meet requirements of authorities like the Environment Agency and local flood authorities.
- Sustainable Urban Drainage Systems: To design to the SuDS hierarchy to support long term surface water networks.
When is BRE 365 Testing Required?
BRE 365 testing is usually done at the planning application stage for:
- Development Proposals: To see if the site can take a proposed infiltration device such as a soakaway.
- Surface Water Management Designs: To see if a drainage system can absorb water and not run off.
- Drainage Strategy Compliance: To meet SuDS requirements for drainage systems.
How is BRE 365 Testing Done?
The testing involves percolation testing using a trial pit or test hole. The process is:
- Excavation: A test hole or pit is dug to the depth of the proposed soakaway or other infiltration device.
- Water Introduction: The pit is filled with water to simulate a heavy rainfall or storm event.
- Monitoring: The water absorption rate is measured, and notes are taken to calculate the infiltration rate.
- Analysis: Data on soil conditions, underlying geology and ground conditions is used to inform the suds design.
Factors that Affect BRE 365 Testing Results
The following factors will affect the results:
- Soil Type: Gravel soils have higher infiltration rates, clay soils can’t take much water.
- High Water Table: A high water table will limit the amount of water that can be absorbed and affect the feasibility of a proposed soakaway.
- Site Layout: The space for drainage systems must be considered at design stage.
Benefits of BRE 365 Testing
Testing ensures:
- Good Drainage Design: Reduces risk of underperforming infiltration devices.
- Environmental Compliance: Supports local planning authorities in approving development proposals.
- Flood Risk Management: Surface water drainage systems can take heavy rainfall and runoff.
- Cost Effective Construction: Avoids costly changes after construction has started by getting it right in the first place.
Challenges and Actions
In cases where clay soils or high water table sites are involved, alternative infiltration devices may need to be considered. Requesting SuDS reports from local planning authorities will give you insight into what you need to do to comply. The drainage strategy must include provision for sufficient capacity to take surface water runoff in extreme conditions.
Additional BRE 365 Testing ConsiderationsSurface Water Networks and SuDS Hierarchy
When designing sustainable drainage systems you must prioritise the SuDS hierarchy which puts natural methods of surface water runoff management first. By integrating surface water networks into your drainage strategy you will get a long term solution that can take stormwater and meets environmental goals. Proper planning at design stage allows you to include features that enhance surface water management without affecting the surrounding area.
Why Percolation Testing in Development Proposals
BRE 365 testing is often accompanied by percolation testing to get a better understanding of the soil conditions. This will ensure the proposed soakaway design or other infiltration device is suitable for the underlying geology. Testing at planning application stage allows developers to address potential issues such as clay soils or lack of space that will affect the performance of the system.
Enough Capacity for Heavy Rainfall
Any drainage system must be able to take heavy rainfall. BRE 365 testing will see if the soil type and site layout can take a large volume of water in a storm event. This is critical to avoid overflow which can cause flooding or erosion. Testing will also ensure the surface water drainage system has the necessary measures to take excess water without affecting nearby structures or ecosystems.
Local Planning Authorities and Environment Agency
Both local planning authorities and the Environment Agency will approve the drainage strategy. They often request SuDS reports to confirm the design meets the regulations and reduces flood risk. Engage with them early in the planning process to stay compliant and avoid delays.
Soil Conditions and Drainage Design
Infiltration testing is dependent on the site ground conditions. Gravel soils are generally more favourable as they have a higher water absorption rate, clay soils often require alternative solutions. Understanding the soil infiltration rate through testing allows you to select the right infiltration device that matches the natural underground drainage system.
Site Specific Testing
Every development project has its own unique challenges that require site specific testing to determine the right solutions. BRE 365 testing gives you infiltration data to design a sustainable drainage system for the site. This will not only ensure compliance but also future proof the surface water management system against climate change and urbanisation.
Site Layout and SuDS Design
A soakaway test or other infiltration method often depends on the site layout. Limited space can affect the location and size of the proposed soakaway or other drainage features. At design stage you need to balance the drainage strategy with the site practicalities to get the best out of it.
Overcoming Infiltration Testing Challenges
Where the high water table or clay soils are a challenge, alternative solutions may be needed. For example combining infiltration systems with controlled discharge options will overcome these issues and keep you compliant with the local flood authority and planning authority.
Summary
BRE 365 testing is key to designing effective, sustainable drainage systems that follow the SuDS hierarchy. By ensuring the soakaway design and other infiltration devices are specific to the soil conditions and ground conditions, BRE 365 testing will reduce flood risk, compliance and sustainability. To ensure your BRE 365 testing is complete to professional standards contact a professional like Ibex Consultant.
