Garden Pools

Before constructing garden pools it is important to consult your local council bylaws.

Garden pools may be constructed in a number of ways using polythene and other modern films which act as a water retaining membrane.

Figure 1 shows the simplest way is to use polythene(250 micron, available up to 4m wide) to line a hole and then fill with water to the desired depth and trim the edges to suit, then pin the polythene down with soft wire just above the waterline. Planting will hide the edges. AT ALL TIMES MAKE SURE THERE IS NOTHING ON THE BOTTOM OF THE HOLE TO PUNCTURE THE LINER.

Figure 2 shows the next simple yet artistic finish. Lay the polythene in the hole and fill with water. When the water is to the desired depth, carefully cut out a ledge to sit bricks or pavers on. Care must be made so as not to puncture the membrane as well as allow enough overlap to bring up behind the edging pavers, so that if desired the water may come up to them, and allow some waterplants to grow between them. Incorporating ledges at different depths is a good way to grow a range of aquatic plants.

Figure 3 shows the ultimate design is the polythene liner overlaid with a concrete film about 4cm thick. This is a little more involved but well worth the effort since the finish can be quite natural looking and the shapes and possibilities are as endless as your imagination. THIS IS AN EXCELLENT METHOD TO REVAMP A LEAKY EXISTING POOL.
I recently consructed a series of 3 pools, 2 of which were informal, and the 3rd is brick supported on 2 sides, which has quite a formal effect. The concrete finish good for the odd adventurous dog who would otherwise upset the polythene.

The preparation is the same as the other pool systems, but once the liner is laid you start plastering a veneer of concrete about 4cm thick over it and up the edges. You have to work with a dryish mix of about 7:1 gravel to cement, so that it wont slump off the edges as you work your way up the walls of the pool. About an hour after the concrete is applied(longer in cool weather) it may be submerged by tying a cloth over the end of the hose and turning it on slowly- the water should stay quite clear as the water level rises, but a "scummy" film will often creep off the concrete onto the surface as it creeps up the edges. If the concrete starts to crumble once it is submerged, drop the level a bit and wait a while before resuming the filling process. This filling of the pool enables the concrete to settle into place before it actually sets, and tends to avoid cracks forming. The polythene liner avoids leaks if cracks do form for any reason.

If you haven't set a level to finish to with the excavation, you may finish the rim of the pool by carefully adding more concrete to the low spots around the top, but be careful not to submerge it too soon. At this time you can embed appropriate rocks to make the finished pool more natural looking. ONLY USE ONE TYPE OF STONE FOR A MORE NATURAL LOOK.Gently swab the cement stains off the stones used.

A brick outer frame may also be lined with polythene and concrete, but the more vertical the side, the more difficult theapplication of the concrete liner becomes.

Once the concrete has hardened after about a day or so, you should drain the pool and gently scrub any areas of pure cement that often form as you stand in the concrete to work the sides. By scrubbing these areas away, it will speed up the leaching process that is necessary to stabilize the pH of the water. To leach the pool it should be filled for 2 days then refilled with fresh water, repeating this process about three times before plants are introduced.

Once the ph has stabilised (when crystals stop forming on pots and plants) you may introduce fish.

Having just cleaned the autumn leaves from our pools, I have noticed the water snails doing better than they ever did in the polythene-only constructed pools. Perhaps it is the extra calcium available from the water.

Waterfalls: To create noise the best way is a "film fall" which is a thin sheet of water cascading over a lip in an even sheet.The formula is 1.5 litre per minute per centimetre of width of the fall. ( a cascade 10 cm wide needs 15litres/minute) The bigger the cavity behind the waterfall, the better the sound will be amplified, making it like a soundshell or an echo chamber.

Construct the fall then work out the size of pump required to give the lift and the flow rate.