Proper land drainage should therefore play a key part in the planning and construction of an equestrian arena and will influence everything from its location to the type of subsurface, drainage system, geotextile and surface layer.
In this blog post, we focus on some key points to consider before starting your horse menage construction project. There is, of course, no substitute for engaging experienced designers and contractors and we would always recommend you do so, but let’s look into why some features of the design are so important.
Locating your horse arena
There are six key factors to consider when choosing a site for a horse riding arena:
- Access
The arena must be easily accessed by materials delivery vehicles and heavy machinery during construction and by horse boxes and riders when it is ready for use. This includes ample turning space and safe access to and from the public highway.
- Drainage
Any water collected in and around the horse arena must be properly discharged to meet environmental requirements. If you are planning on discharging runoff to a soakaway system, make sure there is ample space for this and that the system is an appropriate size for the arena.
If you are discharging runoff to a natural watercourse, you will need to make sure there is one nearby and sufficiently downhill from the arena so that water flow naturally drains the pipework. You may also need to obtain permission from a local authority to use a natural watercourse for this purpose.
- Shelter
Materials such as silica sand and rubber crumb, used for the top surface of horse arenas, are at risk of being blown away by stronger winds.
Where possible, choose a site that offers protection from the elements. Natural land contours, nearby buildings, trees and hedges can provide excellent barriers for this purpose. If none of these is available, consider the cost of covering the arena with a roof or tent-like structure.
- Land contours
Choosing a location that is already reasonably flat will reduce the amount of excavation required to prepare the site. Placing it on higher ground will naturally improve site drainage.
- Purpose
Consider how you will be using the horse riding arena both immediately and in the future. Novice dressage will require an arena that measures 40 x 20 metres, while advanced dressage will increase this to 60 x 20 metres. A showjumping arena will need a width of at least 25 metres.
- Budget
Although you may have plenty of space for a large equestrian arena, your budget may restrict how large it can be, at least to begin with. If your long-term plans are to expand the arena, locate it on the site in a spot that will allow future expansion without having to rebuild. Consider also how you might need to extend the underground drainage system to include the additional floor area.
Preparing your horse arena site
For a horse arena to perform well, last a long time and ensure safety for horses and riders, it must include a stable, well-drained base layer and suitable top surface. To allow for these, the site must first be cleared and excavated.
Start by marking out the area to be excavated, extending this to at least one metre beyond the perimeter of the finished arena. Place wooden posts at the corners of the excavation and connect them with a string line to check the levels across the site. To help the excavator operator follow the perimeter line, use a line marking spray paint along the ground below the string line.
Remove the topsoil from the area and set it neatly to one side. some of this will be needed to finish off the site after construction, but if it is in good condition you may also be able to sell it and recoup some of your project costs.
Excavate the area deeply enough to accommodate the drainage system, base layer and surface layer. If the arena is being built on sloping land, a method known as cut and fill, which uses material from the higher side to raise the level on the lower side, can be used to minimise the excavation depth and the amount of material you will need to dispose of afterwards.
Ensure the base of the excavation is level, checking for and removing any large tree roots that may cause issues later on.
Woven geotextile – adding stability to your horse arena base
The aggregate used for a horse arena sub-base must be kept separate from the subsoil it rests on; not doing so can result in the aggregate sinking into the softer subsoil and losing its strength and stability.
Placing a layer of non-porous woven geotextile over the compacted subsoil of the excavation will not only maintain this separation but also prevent water from seeping through into the subsoil and eroding it. The geotextile will also direct water towards the drainage system, where it will be discharged away from the arena.
Installing a land drain under your horse arena
Once the site has been excavated and the woven geotextile membrane has been laid it’s time to install a drainage system.
Why does my horse arena need a drainage system?
Unless the horse arena is under cover it is likely to be exposed to large amounts of rainwater. This can result in water pooling and ground instability.
Even indoor horse arenas that don’t have this problem can still be subject to shearing. This is when the surface becomes uneven and corrugated, caused by dry patches of the arena’s surface migrating to damper areas. Shearing can cause horses to lose their footing, which puts them and their riders at risk.
While both problems are fundamentally different, a land drainage system can prevent them both.
What is the best drainage system for my horse arena?
The best land drainage design for horse arenas is called the herringbone drainage system. This is comprised of a main 100-150mm diameter pipe running across the centre of the arena, with lengths of 75-100mm diameter perforated pipe running from the edge of the arena and connecting to the main pipe at an angle of 45 degrees. Placed at 5-metre centres, the perforated pipes will ensure even drainage of the entire arena.
The diameter of the pipe used will depend on the average rainfall and natural drainage of the site. For well-drained sites where rainfall is low, installing perforated pipe around the perimeter of an arena that has a slight gradient may even be sufficient.
The main pipe then discharges into a soakaway system or watercourse along a shallow trench with an evenly-falling gradient.
Installing your horse arena drainage system
Start by excavating a trench for the land drainage pipes – if you are using geotextile under the sub-base, the trench will need to be excavated before the geotextile is installed. Planning where the trench needs to go will be made easier if you lay out the preassembled system on the ground and use line marking spray paint to indicate where the excavation needs to be. Allow space around the pipes for backfilling with aggregate.
A bed of aggregate should now be placed in the trench to support the pipe. Install and connect the pipe and check its levels again to ensure water will flow evenly along its length to the discharge point, with no high spots that will allow water and silt to accumulate.
Now surround the pipes with more aggregate. This will act as a barrier to silt and small particles that might otherwise clog up the pipe and its perforations.
Laying your horse arena sub-base
The sub-base of a horse arena creates a strong and stable support for the surface layer, so it must be laid correctly.
A sub-base for a horse arena should ideally be 150-200mm thick and made of good-quality aggregate. While the availability of suitable material for the sub-base may be limited by your location, we would recommend crumbled limestone as this provides a perfect base. Other crushed rock materials such as granite are also suitable. Gravel may be used providing it has sharp edges; rounded gravel is too prone to movement.
We would advise against using recycled sub-base material as this will generally contain impurities that in the long term can affect the stability of the sub-base. However, if budget or availability means your choice is limited, some recycled material can be almost as pure as crushed rock, so don’t dismiss it out of hand.
To ensure effective drainage of the horse arena, the sub-base particles should be 75-40mm in size. If they are larger than this, water will pass straight through the sub-base and place too much pressure on the drainage system, but if they are too small they will hamper its ability to drain the arena effectively.
As the sub-base is laid it should be compacted with a roller and regularly checked with a laser level.
Non-woven geotextile – drainage and separation
The sub-base and surface layer are deliberately different in composition as they fulfil distinct roles, and must also be kept separate so they can do this efficiently. But unlike the sub-base and subsoil, water must be able to pass through this barrier so that it can reach the drainage system.
Non-woven geotextile is fine enough to stop fine particles and sediment but still allows water to pass through into the sub-base. For a horse arena, a non-woven geotextile that weighs at least 300gsm (grams per square metre) should be used for durability. the membrane should be securely fastened around its perimeter and any joints between strips of membrane must be correctly sealed. This will prevent the surface layer from penetrating the sub-base and creating a potentially dangerous uneven riding area.
Laying your horse arena surface layer
By far the most popular surface layer material for horse arenas is silica sand. This should be laid to a minimum thickness of 100mm.
When laying the surface layer, avoid passing across the geotextile membrane with any vehicles or construction equipment as this can damage the membrane. To prevent damage, create a path of sand across the arena for vehicles and equipment to access the rest of the arena. Once the membrane has been completely covered with a minimum thickness of sand, use a roller compactor and laser level to achieve the finished surface.
If your budget allows for it, add a 50mm layer of rubber chippings on top of the sand. This will serve two purposes: retaining moisture in the sand to prevent it from blowing away, and creating a more cushioned surface that will protect horses’ hooves, improve ride quality and provide a softer landing in the event of a fall.
Maintaining your horse riding arena
Once you have installed your horse arena there are a few simple measures you can take to ensure it is maintained in peak condition.
- Check your arena’s drainage system
Regularly checking the drainage system pipework for blockages will ensure the arena remains well drained. While a properly constructed arena should hinder silt from entering the drainage system this cannot be entirely prevented. Other causes of blockages can include ground movement dislodging pipe connections and fine tree roots (such as those of silver birch trees) entering through small gaps.
- Avoid using the arena immediately after a heavy rainfall
Your horse arena will be constructed to remove excess water from the surface layer and sub-base but this will take time, especially after a heavy rainstorm. Using the arena before the residual water has subsided risks disrupting the sub-base and riding surface.
- Look after the surface layer
Remove all horse waste immediately from the riding surface to maintain a clean and hygienic arena, and regularly rake the most-used areas of the surface to prevent compaction and maintain a level surface. Lightly dampen the surface during spells of dry weather.
We hope you have found this information helpful and interesting. If you have any further questions, you are always welcome to call the friendly team of drainage experts at Drainfast on 01420 555600 or email [email protected].
Also, look out for more articles in our ongoing series of blog posts, bringing you useful information, insights, guides and tips on all things drainage!
Written by
Vicki James
Sales & Marketing Coordinator
Vicki is a vital part of the marketing team; from reporting to copywriting, she ensures we complete projects on time.
