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If you have a question or query on a wet leisure project or product, contact SPATA / BISHTA via SPN, the UK industry’s longest established magazine. Email:
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“Why do we need to be aware of the water table level around pools?”
It is important that the ground conditions are known before any work commences on the pool tank construction, to avoid problems at a later stage.
The information on ground conditions should be provided by the main contractor and / or the structural engineer. If this information is not available, then as the pool contractor, you should confirm to the main contractor and / or client that you are progressing on the basis that the ground is fit for the purpose.
It is also important to understand that a high water table in the vicinity of the swimming pool, will be a problem, not only with the construction of the tank itself, but also in future if the pool has to be drained down for any reason.
Although a high water table in itself is not a problem when the pool is full of water, as the water in the pool and the water around the pool will be of equal pressure, when the pool is drained of water this could have an adverse effect on the integrity of the pool tank. It has been known, in a few cases, that the pool structure has ‘broken its back’ and also that the structure has partially raised itself out of the ground and it will also make it very difficult to construct the pool tank.
There are one or two ways to install permanent dewatering systems. One way is to install a drainage system under the pool base construction and the second way is to install a pool water dewatering system around the base of the pool tank. In both ways, there is a need for a drainage system using land drainage (surrounded with a water permeable material and / or pea gravel with clean stone fill) which will need to be drained to a dewatering chamber of sufficient diameter to accept a sump pump. It will also need to be deeper than the pool base and the chamber closed off at the top with a removable cover (manhole).
It is also worth pointing out that all pool tank structures should be backfilled with clean stone material and compacted in accordance with the relevant recommendations.
Please ensure that any dewatering system is noted in the O & M manual.
“Floor outlets and vacuum points are dangerous entrapment hazards – why do we have them?”
There are two reason s why we have floor outlets. First and foremost, so that the circulation system can be effective, indeed some would argue that the separation of the outlets to reduce the entrapment hazard actually increases the efficiency of the circulation system. Second, we have them to aid the emptying of the pool for cleaning. This is made much easier if the floor of the pool shell is laid with a fall to the outlet(s).
The introduction of a hydraulically operated pool cleaner called the ‘Poolsweep’, a machine which brushed the floor debris to a point equidistant from the deep end wall and the two sidewalls, required a flat leaf trap placed over an outlet so the suction held the debris in place. Vacuum points are dangerous, only if the cover is not placed over the opening after vacuuming and the appropriate valves are not altered in the plant room.
So could we do without these outlets?
In at least one American state, the Federal law prohibits floor outlets. Designers overcome this by having more skimmers and inlets, with the inlets positioned either in the floor or at varying levels downwards in the walls. Cascade have had their ‘Aquagenie™’ (which is a combined skimmer and return jet angled downwards toward the deepest point), for some years. Floor inlets have long been discussed as the most efficient way of distributing the pool heating. Vacuuming can easily be done through a skimmer and it would not be difficult to install a vacuum point in an overflow channel with a short length of grating above it for easy access. Currently, however, most recommendations and legislation say that we should have these outlets. Certainly they should be fitted in Type 1, 2, and 3 pools, but maybe we really need to think about the domestic pool situation?
JIM GORDON
Jim is an independent consultant, a SPATA Inspector and a Member of SPATA’s Technical Committee.
PETER LANG
Peter is an independent consultant and SPATA’s Technical Adviser. He is a SPATA Inspector and Chairman of SPATA’s Technical Committee.
36 February 2014 SPN
www.swimmingpoolnews.co.uk
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