Knowing how surface water, or rainwater, is dealt with on your property or a property you are working on, can help immensely with dealing with flooding, leaks, or even damp and mold issues.
But it’s important to also know what the rules and regulations are to make sure any changes you make are legal and compliant, and also to maintain a high standard of work when designing and working on these parts of the drainage system.
Soakaways
A soakaway is an underground structure designed to manage rainwater and surface water runoff.
It allows water to gradually seep into the ground, reducing the risk of flooding and preventing water logging.
Typically, a soakaway is a pit filled with rubble or plastic crates, which creates voids for water to collect before dispersing into the surrounding soil. Soakaways are common in areas where the soil has good permeability and are often used in gardens and around buildings.
Typically, older soakaways tend tend to be pits of rubble or shingle, often with house bricks thrown in, and more recently built soakaways tend to be purpose-made crates, not unlike milk crates in size and shape.
Soakaway Regs
Building Regs Part H
Soakaways must comply with Building Regulations Part H, which provides guidance on the design and construction of drainage systems, including soakaways.
This includes ensuring proper siting, construction methods, and materials used.
Sizing
The size of a soakaway is determined by a percolation test, which measures the soil’s absorption rate. The results help calculate the required size to handle the expected volume of water. Generally, the soakaway should be large enough to accommodate a 1 in 10 year storm event.
Construction
Soakaways must be constructed using materials that ensure longevity and efficiency, such as rubble, plastic crates, or proprietary systems.
They should be located at least 5 meters away from buildings to prevent water logging of foundations.
Same for boundaries or curtilage.
Maintenance
Regular maintenance is essential to prevent blockages. This includes clearing debris from gutters and downpipes that feed into the soakaway, and periodic inspection to ensure it is functioning properly
How Soakaways Work
Collection of Water
Rainwater or surface water from roofs, driveways, or other surfaces is directed into the soakaway via a system of gutters, downpipes, and channels.
Temporary Storage
The collected water enters the soakaway chamber, which temporarily holds the water. This chamber can be filled with materials like rubble, gravel, or specialized plastic crates that create voids for water storage.
Gradual Infiltration
Water gradually seeps out of the soakaway chamber into the surrounding soil. The rate of infiltration depends on the soil’s permeability, which is determined by the percolation test conducted during the planning phase.
Discharge into the Ground
The water disperses into the soil, recharging groundwater and preventing surface water flooding. This natural filtration process also helps remove some contaminants from the water before it reaches the groundwater table.
Lifetime of a Soakaway
Depending on the design, age and wear & tear on a Soakaway, it eventually become exhausted. The better the design, and the more maintenance carried out, the longer it will last.
Once exhausted though, it may be time to relocate to a new Soakaway or consider diverting the surface water elsewhere.
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Soakaway Alternatives
Soakaways don’t always have to be the go-to for removing rainwater or groundwater from a property, and sometimes it just isn’t feasible.
Here are some alternatives that you may have on your property or wish to install as an alternative – or to take the pressure of an existing soakaway.
Surface Water Mains or Combined Sewers
Some areas will have a dedicated foul sewer system for waste, some will have a dedicated foul system with a parallel surface water system which could run into a mains later on, or may run to a culvert or other watercourse, depending on the local and regional area (and time period the original properties were developed).
And then some areas will have a combined sewer, where the rainwater mixes with the waste water and it all goes into a mains sewer before ending up in a treatment plant (not always 100% of the time under some circumstances…).
Quick Tip
One quick, visual way to identify if your drainage is combined is checking the inspection chambers for the amount of laterals, or connections they have, and the size of the main channel in the middle.
Because combined sewers are designed to handle the peak flows of foul and rainwater, they are usually up sized quicker than standalone foul systems, so if the main channel your’re looking at is 150mm (6″) instead of 100mm (4″), it is more likely to be combined.
It was only during the mid 20th Century, after increasing environmental awareness, that separating foul water from rainwater became a priority.
As cities and urban areas grew, heavy rains being directed into waste water systems were causing raw sewage to end up in rivers, oceans and watercourses. This is still a concern now partly because of the amount of leftover combined sewers still around.
Permeable Paving
Permeable paving is a method of paving that allows water to pass through the surface and infiltrate the ground below. This type of paving is particularly useful in urban areas where traditional impervious surfaces like concrete or asphalt can lead to water runoff and flooding. Permeable paving materials include porous asphalt, permeable concrete, and interlocking pavers.
These may just save having to take the run off from your drive to a new soakaway, but should not be relied upon solely to take larger volumes.
Advantages
Installation Considerations
Regs and other Considerations on Permeable Paving
If you’re thinking about checking out your current drainage system or replacing it with permeable paving, here are some key points to keep in mind. Following these guidelines will help manage water sustainably, reduce flooding risks, and comply with Building Regulations Part H.
Proper planning, installing, and maintaining of permeable paving properly is the best way to get the most out of it.
Regulations on Permeable Paving
Permeable paving, also referred to as pervious or porous paving, is designed to allow water to infiltrate through the surface, helping to manage surface water runoff and reduce the risk of flooding.
Here are the key regulations and guidelines concerning permeable paving as outlined in the Building Regulations Part H:
Design and Construction Requirements
Surface and Subsurface Composition
Permeable paving consists of a porous or permeable surface overlying a granular layer that acts as a storage reservoir. This reservoir retains peak flows while the water soaks into the underlying subsoil.
The materials used for permeable paving should include porous asphalt, permeable concrete, or interlocking pavers designed specifically for water permeability.
Storage Layer
Drainage Requirements
Paths, driveways, and other narrow areas of paving should be free-draining to a pervious area such as grassland, ensuring that the water is not discharged adjacent to buildings where it could damage foundations. The soakage capacity of the ground must not be overloaded.
Where water is to be drained onto adjacent ground, the edge of the paving should be finished above or flush with the surrounding ground to allow runoff.
Site Suitability
Gradient Considerations
Surface gradients should direct water draining from a paved area away from buildings. In cases where levels would otherwise cause water to concentrate along a building’s wall, a reverse gradient should be created for at least 500mm from the wall to divert water away.
Gradients on impervious surfaces should be designed to permit quick drainage of water. A gradient of at least 1 in 60 is recommended, with the gradient across paths not exceeding 1 in 40.
Limitations on Use
Maintenance and Inspection
Regular Maintenance
Durability and Longevity
Regulatory References
If you’re thinking about checking out your current drainage system or replacing it with permeable paving, here are some key points to keep in mind. Following these guidelines will help manage water sustainably, reduce flooding risks, and comply with Building Regulations Part H. Planning, installing, and maintaining permeable paving properly is essential to get the most out of it.
Rainwater Harvesting Systems
Rainwater harvesting systems collect and store rainwater from roofs and other surfaces for later use. This can help reduce the amount of surface water that needs to be managed and can provide a sustainable water source for irrigation, flushing toilets, and other non-potable uses.
In the picture above, you can see a good example of a compact rainwater harvesting system. Image from tanks-direct.co.uk.
Components of a Rainwater Harvesting System
Collection Surface
Typically, the collection surface is the roof of a building. The type of roofing material can affect the quality of the collected water, so non-toxic, non-leaching materials are preferred.
Gutters and Downpipes
Gutters are installed along the edges of the roof to collect rainwater. Downpipes then transport the water from the gutters to the storage tank. It’s important to ensure that gutters and downpipes are clean and well-maintained to prevent blockages.
First Flush Diverter
This device ensures that the initial runoff, which may contain debris and contaminants, is diverted away from the storage tank. This helps improve the quality of the harvested rainwater.
Storage Tanks
Rainwater storage tanks can be above ground or below ground. The size and type of tank depend on the intended use of the water and the amount of rainfall in the area. Tanks should be made from materials that do not contaminate the water, such as polyethylene, fiberglass, or concrete.
Filtration System
Filters remove debris, leaves, and other contaminants from the water before it enters the storage tank. Multiple stages of filtration may be used, including coarse filters, fine filters, and UV purification systems for potable uses.
Pump and Distribution System
If the harvested rainwater is to be used for purposes such as irrigation, toilet flushing, or laundry, a pump and distribution system will be required. The system ensures adequate water pressure and delivery to the required fixtures.
Uses of Harvested Rainwater
Irrigation
Harvested rainwater is ideal for watering gardens, lawns, and landscape areas. This reduces the need for mains water and supports sustainable gardening practices.
Toilet Flushing
Using rainwater for flushing toilets can significantly reduce the consumption of treated mains water.
Laundry
With appropriate filtration, rainwater can be used in washing machines, providing soft water that is gentle on clothes and appliances.
Potable Uses
With advanced filtration and purification systems, harvested rainwater can be made safe for drinking and cooking, though this is less common in urban areas due to regulatory requirements.
Benefits of Rainwater Harvesting
Water Conservation
Reduces reliance on mains water supply, conserving a valuable resource.
Flood Mitigation:
By capturing rainwater, runoff is reduced, decreasing the risk of flooding and soil erosion.
Environmental Impact:
Lowers the demand on water treatment facilities and the energy required to treat and transport water.
Cost Savings
Reduces water bills for homeowners and businesses by providing an alternative water source.
Regulatory Considerations
Building Regulations Part H provides guidelines for the installation and use of rainwater harvesting systems to ensure they are safe and effective:
Maintenance:
Regular maintenance is essential to ensure the system operates efficiently. This includes cleaning gutters, checking filters, and inspecting tanks and pumps.
System Design:
The system should be designed to meet the needs of the property while ensuring water quality is maintained. The design must comply with local regulations and standards.
Backflow Prevention:
To protect the mains water supply, backflow prevention devices must be installed to prevent contamination.
Tank Siting:
Storage tanks should be placed in locations where they are protected from contamination and easily accessible for maintenance. Underground tanks should be checked for structural integrity and suitability for the site conditions.
Filtration and Treatment:
Systems should include appropriate filtration and treatment stages to ensure the water quality meets the intended use requirements.
Maintenance of Rainwater Harvesting Systems
Regular Inspection
Check gutters, downpipes, and filters regularly to ensure they are free from debris and functioning correctly.
Cleaning
Clean the collection surface and storage tanks periodically to prevent the buildup of contaminants.
System Testing
Periodically test the water quality, especially if the water is used for potable purposes.
Pump Maintenance
Ensure the pump and distribution system are maintained according to the manufacturer’s instructions to prevent breakdowns and ensure efficient operation.
By integrating rainwater harvesting systems, properties can effectively manage surface water, reduce dependency on mains water, and contribute to sustainable water management practices.
Proper design, installation, and maintenance are key to ensuring the system’s longevity and effectiveness.
French Drains
A French drain is a trench filled with gravel or rock containing a perforated pipe that redirects surface water and groundwater away from an area. These drains are effective in preventing water pooling and managing excess water in gardens and around buildings.
Design Considerations
- Slope the trench to ensure proper water flow.
- Use a perforated pipe for better drainage.
- Cover the trench with landscaping fabric to prevent soil from clogging the drain.
Swales
Swales are shallow, vegetated channels designed to slow down and capture runoff, allowing it to infiltrate the ground. Swales are often used in combination with other drainage systems like soakaways to manage larger volumes of water.
If you’ve been around any new builds in recent years, they all have some kind of swale system and they’re fitted in to the landscape, adding to biodiversity whilst also controlling the sudden flow of rain water from residential areas into the watercourses.
Benefits
- Enhance landscape aesthetics.
- Provide habitat for wildlife.
- Improve water quality by filtering runoff through vegetation.
Detention Basins and Ponds
Detention basins and ponds are designed to temporarily hold excess surface water during heavy rainfall events, releasing it slowly to prevent flooding. These structures can be dry or wet, with the latter providing additional environmental benefits such as habitat creation.
Key Features
- Sizing based on local rainfall data and runoff calculations.
- Proper outlet structures to control water release.
- Regular maintenance to ensure they function correctly.
Building Regulations Part H Compliance
According to Building Regulations Part H, all surface water drainage systems must comply with specific guidelines to ensure they are effective and safe. These regulations cover aspects such as siting, construction, and materials used for drainage systems.
Siting:
- Ensure drainage systems are located away from buildings and boundaries to prevent water logging.
Construction:
- Use durable materials that can withstand local conditions and expected loads.
- Properly grade and compact the soil to ensure stability.
Materials:
Use materials that are resistant to degradation and provide long-term performance.
Maintenance of Surface Water Drainage Systems
Over the last 20 years I’ve noticed one thing about floods affecting houses, commercial units and shops, especially driveways and car parks:
Lack of maintenance lets weeds grow and silt, mud, leaves, etc build up before you know, the gullies or slot drains can’t cope with light rain, let alone a sudden downpour.
I would recommend if you see anything growing out of these kinds of drains, deal with it straight away and you will save a fortune and loads of time.
Not to mention it will likely prevent property and furniture damage!
Regular maintenance is the best way of preserving long-term effectiveness of surface water drainage systems. This includes:
- Clearing debris from gutters, downpipes, and drains.
- Inspecting and cleaning permeable paving to prevent clogging.
- Checking rainwater harvesting systems for proper operation.
- Maintaining vegetation in swales and around detention basins.
- Inspecting and repairing any damage to drainage components.
By incorporating a combination of these surface water drainage systems, property owners and developers can effectively manage rainwater, reduce the risk of flooding, and comply with regulatory requirements. Proper planning, installation, and maintenance are essential to ensure these systems function optimally and provide lasting benefits.
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