Winter sports cause the most damage on natural turf fields due to wet weather, cool conditions and slow grass growth and recovery. Wet soils and high traffic cause rapid turf deterioration often resulting in a muddy and unstable surface. As the surface is damaged on poorly drained sports fields, the skills of the game are adversely affected as is the attractiveness of the game. Having adequate drainage is crucial in providing a dry and durable surface that has good recovery from wear and allows for a high standard of play. There is no substitute for a well-drained natural turf profile.
With the increasing demand for good quality community sports fields, the hours of use are increasing on most sports fields over the winter months. Many municipalities have wet weather policies where sports fields are closed for play if they become waterlogged. It is therefore important to have good drainage to minimise the loss of access to fields of play during wet weather.
While there are many forms of drainage, in this article, we will look at sand slit drainage system and how it can improve the drainage capability of an existing natural turf field. The sand slit drainage system is a means by which the drainage of a natural turf field can be improved without requiring a major reconstruction.
What is sand slit drainage?
A sand slit drainage system is a by-pass system installed into poor draining topsoils. Sand slit drains consist of vertical channels of high drainage rate sands and gravels that intercept water as it moves across the surface. The key to their functionality is having sand to the surface so there is an easy entry point for water to enter. The sand slits then intersect lateral pipe drains that ensure rapid removal of the drainage water. It is also important to have a sand topdressing layer of at least 20 – 25mm to protect the integrity of the sand slits.
Sand slit drainage is known by other terms such as sand banding, sand injection and sand grooving. While there are differences in the methodology, the principles remain the same in that the sand slits/bands/grooves intercept water and allow for easy passage of water through a low drainage rate topsoil. There are two types of sand slit drains:
- Excavated slit drains where the soil is removed and replaced with sand and gravel.
- Injected sand slits where the soil is forced apart and the groove is filled with sand. Injected sand slits are sometimes used to improve the drainage capability of an excavated slit drain system.
An excavated sand slit where a sand and gravel backfill is used has a much greater capacity to remove excess water compared to a sand injection method.
Why is sand slit drainage important?
Improved drainage in a natural turf field of play through the use of sand slit drainage has several important functions:
- Improves the infiltration rate of water into the surface of the sports field.
- Improves the playability of the sports field.
- Reduces the damage to the turf.
- Reduces the costs of expensive end of season renovations.
- Allows for better development of the skills of the game.
- A better surface will be a safer surface.
As an example, if a sports field with a topsoil that had a drainage rate of 5mm/hr and subsoil drains at 10m spacings, the drainage capability of the sports field will be about 0.2mm/day. If a sand slit drainage system with sand slits at 2 metre spacings was installed, the drainage capability of the sports field will be about:
- 2 – 3mm/day for sand slits without gravel.
- 200 – 300mm/day for sand slits that include gravel.
Designing a sand slit drainage system can have many variations and the sports field drainage capability can be manipulated through; altering the spacing of the sand slits and lateral drains and altering the depth of the gravel layer in the sand slit.
What are the advantages of sand slit drainage?
The advantages of installing a sand slit drainage system over a complete reconstruction are:
- Lower cost.
- Less work involved. While there is less work involved it does require specialised equipment and an experienced contractor.
- Less disruptive and allows for a quicker return to play.
- Useful for extending the short term life of a poorly drained sports field.
What are the disadvantages of sand slit drainage?
There several disadvantages of installing a sand slit drainage system that must be considered before selecting this option:
- Only affects about 5% of the playing surface.
- On reactive soils that swell and shrink the slits can open up and the sand/gravel backfill will sink. This can result in a loss of function and surface unevenness.
- Soil capping of the sand slit. Over time soil particles will be transferred across from the soil adjacent to the sand slit and seal the surface and is the most important reason for failure. Note: the sand slit only functions while it is connected to the surface with sand. Even a few millimetres of soil will stop the sand slit from functioning.
- Requires the turf to grow over the new slit.
Tips and reminders for sand slit drainage
In making a decision about sand slit drainage consider the following points:
- Is it the best option for the medium to long term improvement of the playing surface?
- What is the required standard for the playing surface?
- Do the calculations – compare the drainage capability of the sports field with different sand slit spacings and compare this against the local rainfall patterns. Once this is done the system can be designed and more accurately costed.
- Understand the ongoing maintenance requirements and costs i.e. annual sand topdressing, periodic renovation of drains etc.
Sand slit drainage is a by-pass system that is a low cost option for improving the drainage capability of an existing sports field. It is also a less disruptive process and allows a quicker return to play. SPORTENG can provide a detailed evaluation of your sports fields and assist in developing a strategy to improve the drainage rate of the field.