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Why swimming records stand, even with a broken pool floor

Despite the slightly shallower (and slower) Tollcross pool, Australia’s Daniel Fox set a world record in the Men’s 200m Freestyle S14 heat. Joe Giddens/PA Wire

Why swimming records stand, even with a broken pool floor

Despite the slightly shallower (and slower) Tollcross pool, Australia’s Daniel Fox set a world record in the Men’s 200m Freestyle S14 heat. Joe Giddens/PA Wire

You may have seen some controversy regarding water depth in the Tollcross International Swimming Centre being used for competition at the Glasgow Commonwealth Games.

The pool has a movable floor that allows water depth to be altered, but the hydraulic mechanism became caught just before competition began and wasn’t able to be fixed.

Instead of the planned constant depth of 2m, the pool starts at 2m, but rises to a depth of 1.88m at the 12m length, before then dropping back to 2m deep. This hump in the bottom has led some people to question the legality of records being set in the pool.

But how much of a problem is it, really?

Underwater reflections

FINA, the international swimming federation, only requires that competition pools be a minimum of 1.35m deep within 6m of the end walls, and they may be as shallow as 1m for the rest of the pool.

This contrasts with the requirements for Olympic Games and World Championships that specify a minimum depth of 2m throughout, and depths of 3m have been used at recent Olympic Games.

Water depth is of importance because it affects the reflection of waves within the water.

With a shallower pool, waves created by swimmers can reflect back off the pool bottom and create extra resistance on the swimmers. This increased wave drag would slow swimmers down and make it more difficult to achieve world record times.

There should, therefore, be no question about the validity of swimming records being set at the Glasgow Commonwealth Games.

The Australian women’s 4x100m freestyle team broke a world record. Joe Giddens/PA Wire

Although the pool does not correspond to Olympic standards, it greatly exceeds the minimum FINA requirements for other competitions, and the difference would actually be expected to make it more difficult to achieve fast swim times.

Building a ‘fast pool’

While the pool depth may not be optimal, other aspects of the Tollcross Pool correspond to the modern requirements for a “fast pool”:

  • rather than just having eight lanes for competition, the pool was built with ten lanes; the outer two lanes being left vacant during competition. Similar to the effect of pool depth, having a greater distance between swimmers and the pool depth reduces the effect of waves reflecting back off the edge
  • the side edges of the pool are slightly below water level so that waves flow over the edge into the drainage, rather than reflecting back
  • modern lane ropes resist the transmission of waves between lanes and the use of wider, 2.5m lanes further assist the isolation of waves moving between swimmers.
Danny Lawson/PA Wire

These aspects of pool design affect wave drag, which has been estimated to contribute between 5-12% of the total drag on a swimmer.

At the time of writing this article, new Commonwealth records have been set in 28 different events, about 74% of the total conducted thus far, and world records have been set for four events: the Women’s 4x100m Freestyle relay, Men’s 100 m Freestyle S9, Women’s 100m Freestyle S8 and the Men’s 200 m Freestyle S14.

There should be no suggestion that these records were assisted by the swimming pool floor malfunction. If anything, this would be more likely to have decreased performance than to have enhanced it.

The results here don’t seem remarkably different to the 26 Commonwealth records set in Delhi in 2010. It is a normal result for times to reduce each four years through increases in the capability of athletes.