Aquatic Technology Pool & Spa, "Creating Water as Art."™

Aquatic Technology Pool & Spa, "Creating Water as Art."™
Pools as an art form - the way it should be!

Wednesday, November 9, 2011

Infinity Edge, Vanishing Edge, Negative Edge Pool Design Issues

A Pool with an Infinity Edge, Vanishing Edge, Negative Edge, Knife edge, Slot overflow, flooded deck, gutter, perimeter overflow... there are a multitude of names. But, they all share one basic premise... move the water from a catch basin (or hidden surge tank) to a visible vessel and create the illusion that it is overflowing one or more edges.

Sounds Simple Enough?

In every one of these pools there is a "dam wall." That is a wall that is supposed to be dry on one side & wet on the other - imagine the reservoir where you go water skiing. Some of these pools dam walls are 6-8 feet high, while others have low dam walls of only 4-8 inches high.

The other common element is that there is a catch basin for the water. Some have the basin attached to the pool, while others transport the water to a remote storage vessel. The remote vessels can be under the pool equipment room, adjacent to the pool, under the pool deck, a lawn or any place in between. There just needs to be access to the inside of the tank, so that the accumulated debris can be removed. I'll use the terms: storage tank, surge tank & catch basin interchangeably.

Common Problems

The most common problem that I see when consulting on construction defect cases, are surge tanks that are too small. There must be enough water in storage to (a) fill the pipes, (b) raise the level of the main pool so that it over flows, (c) complete the trip to the storage tank. Remotely located tanks usually have gravity lines from the pool to the tank, so this is the "trip back to the tank" (as in c). All totaled this is called the "water in transit."

There must also be a "reserve" of water left in the bottom of the tank to prevent the drains from vortexing (swirling) and ingesting air. This can cause the pump to lose prime, eventually damaging the pump seals & bearing and allow water to enter the motor.

The second most observed problem is the edge effects system (drains, pipes, pump & filter). Usually there are not enough drains of a design that will allow debris to pass through. Instead leaves accumulate on top, restricting the flow starving the pumps for water. The plumbing is usually undersized for the line velocity of the water (feet per minute). The pump is usually WAY TOO BIG to flood the edge. And there is usually no filter on the edge pump. 95+% of the debris in one of these pools ends up in the storage tank. So, why in the world would you want to grind up the leaves, earthworms, salamanders and snails & spit them back into the pool?

Improper placement of the return lines can cause unwanted surface turbulence, destroying the glassy mirror effect that these pools are know for. The primary causes are due to high flow rates, placement in the walls, incorrect elevations and poor aiming of the return flow. There are very simple techniques to guarantee that turbulence will not be a problem, but you have to have this knowledge & employ the solutions during construction!

The next most common issue is with the dam walls themselves. Oftentimes incorrect construction techniques result in a wall with voids, allowing water to seep through. Poor waterproofing techniques can result in tiles that weep. Inadequate expansion joints in the material on the "dry" side of the wall can cause the material to delaminate. After all, isn't this material constantly going through wet & dry, hot & cold, and expansion & contraction cycles? They are after all usually exposed to the direct sun & wind.

Other fatal mistakes are the discharge of excess water and backflow prevention. Rainwater simply cannot be dumped on the slope below the pool - a foolish mistake. One that will surely cause a landslide or in the least cause the pool to slip or tilt. One cannot simply rely on mechanical check valves to prevent water from back siphoning to the equipment pad or catch basin. Check valves flutter and the seals get worn or tear. Face the facts - not if, but when it fails... One needs to rely on physics - something like gravity that is never turned off!

The "Goal"

The goal with one of these pools is to create the flooding effect with the least amount of water in transit as possible. A vanishing edge pool with an exposed catch basin IS NOT SUPPOSED TO FUNCTION AS A WATERFALL. That will cost you many more pumps and a W-I-D-E basin to catch the splash & splatter. The back side of the wall is supposed to appear as a "glistening wet wall."

If the edge tolerances are maintained (how level the finish workmanship is), then you will be rewarded with a pool that can be flooded with the smallest pump. If the pool is "dead on level" you could create the effect with a garden hose! Granted, you would need a larger pump to return the water to the pool displaced by bathers, but this is where a VFD (variable frequency drive) pump could come in really handy. It could run at low speeds to provide the normal visual effect. When bathers are present, it could ramp up the flowrate to meet the need of returning the bather displacement to the main pool.

These pools are spectacular to look at. While on the surface they appear simple, they are actually quite complex.

Paolo Benedetti - Aquatic Artist
"Creating water as art."™
Aquatic Technology Pool & Spa©