Ok. I cant explain physics to you. If you want to believe water is weightless, that we live in zero gravity, that concrete structures last forever, or that their deterioration doesn’t compromise the reason they were built in the first place, go for it
If you want to believe that a college professor with connections to Disney leadership is (wrong? misinformed? deliberately peddling Disney propaganda?) go for it
We have constantly wet man-made retention ponds all over Florida that manage to hold water year-round despite having 100% natural bottoms. Most are not there for decorative purposes. Compacted earth below and saturation limits on the soil tend to prevent the water from draining faster than they're refilled by local drainage and rain, even during "dry" months.
Within WDW there are many large bodies of water all over property that are man-made with diverted water that do not have sealed pool-like bottoms the way you're suggesting ROA works.
You understand that most of the land the Magic Kingom was built on had no problem retaining water before it was developed and that they had to build canals and ditches all over the place to drain the shallow swamp-like land that was already there, right? If I'm not mistaken, that's what Seven Seas lagoon was made from.
I admittedly got the water level of ROA wrong but them pumping water to keep it higher would not, I don't believe change these factors from being true.
Water evaporates if kept in the sun for too long, so why doesn't the water in lakes evaporate? Or else, why doesn’t that water seep into the ground? After all, it just sits there, right?
www.scienceabc.com
It’s all about permeability.
www.iflscience.com
I don't claim to be an expert in the field but the weight of the water and whatever is floating on top of it, simply isn't the issue you think it is because again, the cement isn't some sort of bowl or tank holding it.
How do you think they've managed to keep the water in the World Showcase lagoon all these years when it has a natural bottom?
What laws of physics do you think they break to manage that?
Anyway, my driving point is, the river is going because Disney has decided they want something else there. This and a number of other arguments are just distractions from that to somehow make it seem like this was something that had to happen and not something that they've purposely decided to do.
You can agree with their choice for the space or not.