As a follow-up, for anyone else who might be curious:
The computer, bowling pin, and Hippy Dippy pool all have sections that are 3'3" deep. Those shallow areas seemed to be smallest at Hippy Dippy (which was always so crowded with teenagers that DD6 didn't want to swim there), and biggest at the computer pool, where two of the 4 sides were 3'3" along their entire length.
All 4 pools are 4'9" at the drain. The deepest spot along the edge is either 3'9" or 4'1" (I think the latter, but couldn't swear to it).
DD6, at 46" (never measured for EE or M:S; clearly far too short for PW and RnRC) was comfortable without a life jacket in the 3'3" areas, but preferred having a life jacket. She's not a swimmer, and the life jacket gave her the freedom to explore the pool independently.
5yo niece (probably 44" - she didn't want to ride the 44" rides) was not comfortable going off the steps without a life jacket, because the shallowest water was too deep for her.
Also, being a life guard at the Pop pools must be nerve-wracking. Overheard in the pool:
5yo (who was playing with our kids, so we knew her age rather than guessing), to her father, as he approached from the other end of the pool: Mom told me I had to wear a life jacket so she didn't have to watch me. Can you watch me so I can swim without it? (Mom was halfway down the pool, napping on a lounge chair.)
That same kid, who had been bragging to ours that she could swim and they couldn't, slipped out of her depth within arm's length of the stairs we were all sitting on, couldn't get her nose above the surface again, and had to be fished out by her father.