What Lies Beneath
How to construct a bowling green…
Those of you who have been following my articles over the years in Bowls International must often wonder why we go through the procedures of maintenance at certain times of the year.
Therefore, over the next few issues, I intend to produce a series of illustrated construction techniques to help you appreciate what goes on beneath the turf and why.
Shown in the photograph is a section through the bowling green from the paving slab to the earth base, which, in this instance, is chalk. The green was constructed for the Loudwater club close to the M40 in Buckinghamshire many years ago and I helped with its construction.
The only area made available by the local council was a steep chalk area which needed a great deal of excavation into the chalk bank. The major problem otherwise would have been to use the ‘cut and fill’ method, but this can have serious consequences unless the base is very firm.
It goes without saying that with the above technique, the ‘filled’ part could have a tendency to slide or move further down the hill.
Stability is of the utmost importance and once the ground was firmed, four laser-levelled pegs were placed to correspond with the corners of the green and left for several months to see if there was any subsidence before further work was undertaken.
This was just as well because we realised that we needed to dig further into the chalk to provide a really solid base with a slightly sloping floor that would save extensive drainage pipework, as the slope would counteract the need for sloping drains to carry excess water away from the site.
As can be seen from the photograph, we have a chalky base with figure number three a 100mm lamflex hose with thousands of little holes around the outside to enable water to get in and move away quickly. We could not leave to chance the fact that the chalk would absorb excess water because in storm conditions the water would have been moving quite quickly from the green, down through the holes and in the ditch to the broken stone beneath and so on down into the trap where the lamflex is surrounded by pea shingle, which then filters its way into the pipe and moves down to the outlet.
In the photograph, the raft system can be seen composed of broken stones which are incompressible and have voids between where the water can drain through quickly and covers the whole area, including the ditch.
The water in the system can move sideways as well as downwards, and when required by the plant, can move upwards by capillary action. In the past, this raft layer would have been of clinker and ashes, but when gasworks no longer produced clinker an alternative had to be found.
This stony raft would be approximately 200mm and in the ideal situation the bottom 100mm is 40mm broken stone, and the next 100mm is 20mm broken stone, the reason being that voids are getting smaller as we are building the green upwards. These voids store a moisture-filled atmosphere at these levels.
Our next stage (number eight) above the 200mm broken stone is a blinding layer of 30mm 5/10mm pea shingle. This layer of pea shingle covers the entire area beneath the green, reducing the size of the voids still further.
The pre-cast ditch unit is now placed into position on top of the raft system. These are levelled up, floating to get the level correct on a soft sand mix of nine parts sand to one part cement. This cement is only applied beneath the leading edge and the trailing edge, not in the middle, otherwise water will not pass through the section.
Finally, when all the sections are in position, the root zone is then applied, leaving just enough room for the turf, seed or liquid sod to be the final level.