Is a swimming pool main drain necessary? Consider an average size public pool 85x100x4,5 ft with 288,000 gallons). A 6 hour turnover would require 800 GPM, which can be handled by a single 18x18 drain cover (tested to ASME A112 19.8 (2007) as safe, single suction - safety backup options allowed by the Virginia Graeme Baker Pool and Spa Safety Act include an automatic pump shut off, which has been tested to the ASME A112 19.17 SVRS standard).
Assuming all flow is going to the swimming pool main drain, what are the chances that debris on the floor will find it? Before you answer, consider that the drain has an area of 2.5 sqft and the pool is more than 8,500 sqft. A main drain is going to have little influence on dead spots some 100 or more feet away if it doesn't have significant effect at 11 inches!
What is also missing in 1928 is anything about "circular motion of the water." In fact, the writers went to great lengths to attempt to create "plug flow" where drains were used. They put limits on where the returns would be to encourage the water to flow toward the pool drain, moving dirty water on the way to the drain. It was a North American standard, so they did not consider Coriolis effect and toilets flushing in Australia. either (if you think the rotation of the earth has an effect - read this).
Not only is this 1928 language accurate and concise, it counters most, if not all, of the folklore that plagues the swimming pool industry today. Anecdotal evidence of cloudy pools associated with no drains, etc. don't really stand up when one actually goes out and measures what is going on; there are always other explanations.
The industry should not feel embarrassed by these blatant statements that counter what they were taught by codes and health departments. In the grand scheme of construction schedules, plaster, steel, gravel, tile, piping, can you save my sod, and the prized butterfly bush the crew just demolished, knowing the details and physics behind circulation is a low priority. One can't really do much with it in the field, and industry standards writing committees are working to update the basic guidelines in the next generation standards.
What I do have a problem with, especially in light of someone's husband, daughter, son, grand daughter, etc. dying, is the unwillingness to learn. All states should take note. This is not debatable with any scientific merit. There is not one person that is competent in fluid flow that would argue this point: Swimming pool main drains don't move water, pool water inlets do.
It's that simple. Drains can be used to receive water and should not be intended for anything else. Most of our standards would not let us build a pool following the water circulation language from 1928.
They were right then, we are wrong now.