Too much drainage work has been installed on a hearsay basis, or as a result of over confident and unjustified recommendations
better the backfill, the quicker and farther the water moves. Also, the shorter the distance to the discharge points, the greater the drainage rate that is provided. Discharge is normally into the backfill over pipe drains. A common reason for unsatisfactory slit drainage is that these pipe drains are too far apart. For example, it is unrealistic to expect pipe drains at 10 metre centres to be adequate. Centres at 5 metres would only be at all feasible if the crossing Major Sand Slits were very substantial. Pipe drains at closer centres are more effective.
Maintenance
Apart from dealing with obvious points such as blocked outfalls, collapsed pipes, full silt traps, etc., an important requirement is the maintenance of good permeability in the back-fill. All drainage slowly deteriorates due to the infiltration of fine particles.
The continuing performance of slit drains depends directly on the continuing permeability of their backfill. Gradual capping of the slits by soil is
inevitable and this prevents the entry of surface water. Measures to counter this are an essential part of maintenance. Fortunately, specialised equipment is now available which can very quickly install new fine neat slits at 90 degrees across existing slits and re-connect them to the surface. Because these machines have a very high output, costs are moderate. For example, it is possible to install 40,000 linear metres (25 miles!) of these minor slits on a rugby pitch or golf fairway in as little as one, or sometimes two, days. The work is so neat that golf greens can also be dealt with.
Scheme Design
It is possible to calculate exactly what the optimum specifications of any drainage installation should be in order to provide the most cost effective design. Whilst theory has to pay due heed to practical experience, calculated figures are realistic facts, whereas words can be merely convenient. Hit-and-miss is a poor approach. Too much drainage work has been installed on a hearsay basis, or as a
deep at 250mm centres -g
result of over confident and unjustified recommendations.
Slit Drains
A Slit Drainage System can compare very favourably with much more expensive Profile Replacement installations. The use of natural soil gives a stronger, healthier turf and a better playing surface.
Although this is entirely true of well designed intensive slit drainage, it is not realistic to expect inadequate schemes to provide a similar high performance.
Geoffery Davison has for many years been a pioneer in evolving the theory and practice of the techniques which are now in general use in Britain, Europe, The United States,Australia, New Zealand, Canada and other countries world-wide. Always keenly interested, he is happy to be telephoned regarding any query or to provide further information. Telephone 01568 797024
Mini sand slits 150mm
games pitches, golf greens etc.
An AFT 45 on a compact tractor has two applications
AFT TRENCHERS LTD
Fitted with its chain and boom for wider and deeper trenches
OR
Fitted with its slitting wheel for narrow slit drainage
Rapid neat trenching with simultaneous spoil removal
Tel: 01787 311811 email:
info@trenchers.co.uk www.trenchers.co.uk 49
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