Technical
toe of cut slopes with a pipe drain installed in the invert of the swale.
Any local sharp sand covering pea gravel in a pipe drain trench will serve the required need and enable satisfactory water inflow.
False. It is vital that the gravel and the sand are chosen with the particle size distribution of each material being such that the acceptable bridging factor is attained. Fine particles in the sand moving down into the gravel soon restrict the drainage performance by occupying the voids necessary to enable satisfactory downward water movement. Of particular concern is the fine material content in the sand (less than 0.25mm) – which ideally should be less than 10%.
Drainage design must be adequate enough to accommodate all water not retained after high intensity rainfall.
False. Only sand pitches can accommodate rainfall of 25mm/hour (considered the maximum expected intensity over a twenty year period). Heavy clay loam soils on pitches permit infiltration of upto 5mm/hour. Even the best maintained 1m spaced slit drained surface will not permit a drainage rate of much in excess of 7mm/hour after continual use - even if regular sand dressings are applied.
Hence, with rainfall intensity of 25mm in one hour, over half the water volume will be subject to run-off - and this water will simply flow to the lowest areas and off the pitch. In residential areas, with limited or no outfall locations, the solution is the creation of adequate attenuation - this can be achieved in a number of ways with the creation of swales, wetlands and underground temporary storage.
Average daily rainfall in the British Isles varies between 5
and 12mm. With this level of rainfall, even with the soil at field capacity most of the winter, more often than not there is very little surplus water to pass through the drainage system. Surface water is retained in the grass foliage and micro-depressions - and the aggregates within the drainage installation can hold the equivalent of around 4mm of rainfall.
Vertidraining or deep aeration into heavy subsoils will improve the drainage of a sports pitch.
False. When clay loam topsoil and clay subsoil is loosened by aerating and creating holes, this will only create more water retention which will develop into waterlogged areas. The main aim in maintaining heavy loam soils in a condition in which to play football must hinge on retaining a firm surface, with adequate removal of surplus water by means of a suitable by-pass system. Allowing the topsoil to become loose at the onset of winter promotes the development of soft areas that are prone to displacement and the
formation of puddles after rain.
A slit drainage system without annual sand dressings is still better than no drainage installation.
False. The system is entirely dependent on the slit drains being ‘open’ at the surface, and the sand topping remaining uncontaminated with surrounding clay topsoil spread with play activity. The only way this can be achieved is by applying sand dressings to create a sandy medium in the shortest period of time to at least 25mm thickness over the slit drains - at least with the application of annual dressings for five years or more. Without these dressings, the drains soon become capped with clay loam topsoil, and the installation cost has become a waste of money.
Multi-use Trailer Three way discharge:
Rear: To a spinner for topdressing Front: Trench filling in view of the driver
Side: Filling of trenches, filling other machines, placing sand into bunkers, etc.
TRENCHERS
01787 311811
info@trenchers.co.uk www.trenchers.co.uk
AFT45 for compact
tractors from 20hp With chain or slitting wheel, augers or conveyor to quickly install drainage systems, pipes or cables as and when needed. Ideal for sports turf, agricultural, domestic and industrial markets.
JUNE/JULY 2012 PC 123
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