Water Depth

Pools come in many shapes and sizes. Their length can vary as well as the water depth. Most competitions happen in either 25 yard pools or 50 meter pools. However, at lower levels of competition many other sizes of pools get used. Pools that are 25 meters long are some of the notable exceptions, but there have even been pools that have been made 100 feet long. Measuring a standard-length competition race can be tricky here since there is frequently not a wall for the swimmers to finish. The one pool I encountered at this length, required us to cross a finish line much like that at a track meet. Though, by far, the hardest job there was done by the timers. They had to stand at the side of the pool all bunched up (three per lane), and guess when a swimmer crossed that imaginary finish line.

Considering how many lengths pools come in, it's not much of a surprise then, that pools also come in a variety of depths. Most, being designed for wading and recreation swimming, change depth along their length. These changes of water depth can provide a variety of challenges to competitive swimmers. The best swimming pools in the world for competition swimming are uniformly near nine feet deep. At this depth the wake that a swimmer produces in the act of swimming is weak enough when it reaches the bottom of the pool, that it cannot impact the swimmer, or the water near the swimmer much at all. However, when a pool is shallower, say three or four feet deep, that impact is far greater.

A Swimmer's Natural Environment

When you watch a swimmer going through the water, you see a wake at the surface of the water, much like that of a boat. Well that wake also continues in three dimensions to the bottom of the pool. Now when you see that swimmer lane one, for instance, his wake bounces off the wall and returns back towards the swimmer. If this swimmer is close to the wall, this wake interferes more with the swimmer than if they are far away. This is why many swimmers who end up in lane one or eight, try to swim on the inside of their lane, to minimize the interference of their own wake. The exact same thing happens under the swimmer as well. In a shallow pool, your wake provides pressure on your body as it bounces back from the bottom of the pool.

When the water is around 5 feet deep, most swimmers may actually feel a benefit from this under-wake. The wake that bounces back from the bottom of the pool hits the swimmer below his waist and he feels like he's swimming downhill. A shallower pool, however will feel very different. The wake from the bottom of the pool hits the swimmer above the waist and makes the swimmer feel like he's swimming uphill.

Many long-course pools (50m pools) have diving wells at one end. When the pool is designed this way, it can start 4 feet deep at one end then progress down to 6 feet near the middle, but soon after that, will drop away to 14 feet or so. The visual cliff a swimmer encounters is not only daunting but can mess with your stroke. As you swim over the edge of this cliff, the wake that you had become used to on the way down the pool, suddenly drops away and your body position completely changes. You'll feel a drop-off in power as you cross this threshold if you don't adjust your body position to the new fluid dynamics.

So how does a swimmer handle these variations in water depth? In shallower pools, make sure that you take off from the walls after a turn, almost completely on your side. This orientation will keep the extra turbulence from your kick from interfering with your progress. You also want to make sure that your body position works with the interference you're getting form your wake bouncing off the bottom of the pool. Generally speaking, the deeper the pool, the higher in the water you'll want to feel in order to get the most benefit.

The diving well cliff though is a real challenge. As you approach the cliff, you will need to adjust your body position drastically because as soon as you cross over the threshold your wake will no longer have any contact with the bottom of the pool. From a normal competition body position, as you cross the threshold, power through the first few strokes over the boundary. Most swimmers will slow down at this point so you'll likely catch them unawares. Once you've done a few power strokes you can go back to what feels like your normal position but you will have made the adjustment.

Very few of us are lucky enough to swim in great swimming pools our entire career. Most of us have to make the cutoff times for the big events in sub-standard pools. The more you plan for the environment that you'll be swimming in, the better you'll do, and the more likely you'll get to swim in the best pools in the world.