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When planning a new driveway it can be easy to get carried away with material, design and style choices. However one of the most important components of installing a new driveway is drainage.
Many do not realise the impact driveway drainage has upon the wider, natural environment. This is especially so when it comes it to surface run-off from driveways and other impermeable surfaces. Getting your driveway drainage strategy wrong can lead to flash flooding, damp and costly alterations and repairs. In this article, I break down and summarise all the elements of driveway drainage. I explain why driveway drainage is so important and how it should be implemented correctly. Why is correct driveway drainage important?
Water run-off from driveways is some of the most polluted surface water produced by the urban environment. Driveways accumulate a dirty combination of brake dust, heavy metals oil, grease and rubber particles. During times of heavy rain these toxic materials can be washed from driveways into the local drainage network. These pollutants can then be washed into local watercourses and wetland habitats.
This can lead to the destruction of delicate ecosystems. Furthermore, continuous toxification of fresh water within the landscape is also detrimental to human health.
Consequently, installing an effective driveway drainage system is paramount. Not only is it important to collect surface water, it will have to be drained to an isolated drainage feature. The environmental cost of incorrect driveway drainage
Pollutants
In recent times there has been a growing awareness of micro pollutants such as micro plastics and chemical spillage.
Our driveways and paved surfaces collect many chemical compounds as well as metal and plastic particles. If surface water is not collected in a managed way these can wash into rivers and streams. These substances can kill animal life and pollute fresh water ecosystems. The ramifications of such for human health and longevity are not even yet fully understood. Flash flooding
When driveway drainage is not installed excess storm water can overwhelm drainage networks. This can lead to flash flooding causing damage to homes and property.
Sewage overflow
During times of excessive rainfall drainage networks can overflow into sewage systems. This can lead to raw sewage spilling out into rivers and watercourses. Not only can this cause a health risk it leads to high nutrient levels within water bodies. The result is excessive algae blooms, low oxygenation and habitat loss. Ecosystem destruction
The combination of toxic chemicals, waste particles and nutrients washing into watercourses destroys wetland ecosystems. These delicate food webs help to keep our natural environment balanced and healthy. If storm water from driveways is not mitigated on site it can lead to health consequences for local ecosystems and people. Driveway drainage: Law & Legislation
Any new driveway with impermeable surfacing above 5 square metres will require planning permission. Permission is unlikely to be granted without water being collected and reabsorbed by the ground within your property. This can be achieved by installing a driveway drainage system plumbed into a soak-away or bio-swale. Does my new driveway need drainage?
Any new driveway or hard surfacing installation will require sufficient run-off mitigation. This will ether include; permeable paving or the installation of a drainage collection system. Does my existing driveway need drainage?
If your existing driveway runs surface water onto your street then there is existing precedent. Therefore it is unlikely you will ‘have’ to install driveway drainage to an old driveway. However, rules from country to region do vary, so check with your local authority. Ethically it would be best to install a drainage system to driveways where surface water runs onto the street. How to install driveway drainage
There are two main ways of installing driveway drainage; permeable surfacing and impermeable surface water collection and storage. Below I will summarise both of these driveway drainage strategies. Permeable Paving
Permeable paving is paving which allows water to pass through and be absorbed by the underlying ground. Permeable surfaces include gravel, resin bound aggregate, and gapped block systems. However none of these surfacing methods are permeable if their sub-base is also not permeable.
If you want to install a permeable surface you must also base it with a free draining aggregate such as MOT type 3. This sub-base material has very fine particles washed out, this means water can pass through.
It must be said however that in times of extreme rainfall many permeable surfaces can become overwhelmed. This can lead to some spill over into adjacent areas. Impermeable paving
Impermeable paving is hard surfacing which does not allow water pass through its surface. This type of paving constitutes the vast majority of driveway surfacing. Impermeable paving includes block paving and other types of pre-cast blocks and natural stone. There are some claims that block paving is permeable but I disagree! In any case such surface will produce run-off in times of heavy rainfall. Therefore, surface water must be collected and channelled into a drainage feature. In most scenarios this feature will be a buried soak-away crate system. Calculating storm water runoff volume
If you are installing driveway drainage for an impermeable surface you will need to channel water to a soak-away. For most driveways a cubic metre soak-away has enough storage capacity to contain run-off during heavy rain. However for larger surfaces you may want to check if a cubic metre is adequate. You will need to times the surface area of your driveway by 30mm of rainfall (about the UK ‘average’ highest rainfall for a 24 hour period). The calculation would be 30m x 0.030mm = 0.9 cubic metres So for a 30 square metre driveway a cubic metre is more than adequate. It is important to remember the ground around the soak-away will instantly start to absorb water. Even during times of extreme rainfall the water will fill a soak-away relatively slowly. Collecting storm water from impermeable paving
Channel drains & Slot drains
By far the most effective way to collect surface water from a driveway is with channel drains. Channel drains are linear channels that are laid into a driveway or patios surface. They often have metal or plastic grills which allow water to pass through and into the channel. The channels slot together to create continuous runs where water can be directed to drainage features. Slot drains are essentially the same concept as channel drains without the grills. Instead slot drains have a raised slot providing a flush drainage outlet within the paved surface. Ground pipesPvc plastic ground pipes are installed to pipe collected water from channel drains to drainage destinations. Typically 30-50mm diameter pipes with elbow sleeves are connected to the base of the channels. Water can then be channelled underground to soak-aways or other locations. Soak away systems for drivewaysSoakaway systems today are commonly constructed from reinforced plastic soakaway crates. These strong but lightweight crates slot together to create any sized soakaway you require. These are lowered into an excavation at with at least 100mm ground clearance either side.
The crates are then wrapped within a strong filtration membrane and backfilled with free draining 10mm pea gravel. Soakaways are the perfect system to channel away surface run-off from driveways.
Why not visit our full installation guide on how to install soak-away crates here. Retention vessels
Retention vessels are large water storage units submerged underneath the ground. These are particularly useful for climates which suffer from summer droughts. Instead of a soakaway which soaks water into the ground these retain it for later use. A submersible pump system can be activated in summer when water can be utilised for irrigation. The installation of underground retention tanks can be costly but a fantastic way to utilise surface water sustainably. Sustainable drainage for driveways
Seasonal flooding wetlands
Seasonal flooding wetlands are naturalistic, low lying, habitats which flood during winter and times of heavy rain.
In essence these are really natural soak-ways which can also create habitat for wildlife. These boggy looking depressions can be landscaped to become attractive features with rocks, pebbles and flowering plants.
Seasonal flooding wetlands are actually a nationally recognised endangered habitat. Seasonally flooded habitats provide nesting and feeding opportunities to rare and specialised species.
Consequently you can provide sustainable drainage for your driveway whilst also providing essential habitat for plants and animals. BioswalesBioswales are linear depressions in the ground that absorb surface runoff slowly and naturally. Very much like seasonal flooding wetlands these swales are planted with wetland plants. This creates great habitat for wildlife whilst also acting as a functional drainage solution for driveways. As storm water passes through the roots of wetland plants the water is oxygenated and cleaned. This makes bioswales one of the most ecological solutions for driveway drainage projects. Retention ponds
Retention ponds are effectively large wildlife ponds with extra capacity to accept surface run-off from hard surfaces. Typically ponds are created with pond liners but with sloping sides that reach up higher than the liner level. This creates a controlled flood zone which can fill during times of heavy rain. Surface water from driveways and other hard surfaces can be collected and piped into the ponds flood basin. The storm water is then retained and allowed to slowly be reabsorbed by the landscape. ConclusionImplementing a satisfactory driveway drainage system is not only crucial for functionality but also for minimising negative impacts on the environment. Incorrect driveway drainage can mean falling short of legal requirements and risking the threat of costly alterations and repairs. However by learning about the impact of urban runoff you can start to think about your driveway within its wider context. This will lead to better planning and inspiration when it comes to implementing a driveway drainage strategy. Perhaps you want to integrate seasonal flooding wetlands to your front yard to attract wildlife? Or perhaps install a drainage tank which can now be used for summer irrigation. Installing an effective driveway drainage system will not only save you hassle it will also provide you peace of mind. Who knows it may even make your front garden landscaping more interesting! FAQS
What is the best drainage for a driveway?
The best drainage for driveways is collection chambers such as a channel drains plumbed into a water storage vessel, soak-away or seasonally flooded wetland habitat. This allows you to collect all surface water and not contribute to flash flooding and environmental degradation. The second best drainage solution for driveway drainage is permeable surfacing with a permeable sub-base. What drainage do I need for a driveway?Fundamentally you need to keep surface water away from the walls of your home and prevent it flowing onto the street. The best way to achieve this is by installing channel drains and directing surface water to a soak-away,
Thank you for visiting our ultimate guide to driveway drainage! If you require driveway drainage, patio drainage or garden drainage services do not hesitate to contact us.
Based in Amersham, Buckinghamshire we undertake a range of landscaping services including land drainage and paving. We also now have a Norfolk office.
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