I don’t think our great river systems will die! I don’t think they will continue to supply us with our needs in the manner they have for most of recorded history either!
If you look at the largest of the river systems: Nile, Amazon, Mississippi, Missouri, Colorado, Rhine and so forth, it is readily evident that these systems are not now, today, the same quality as they were as recently as 50 years ago! I don’t think anyone would go to the mouth of any of the river systems noted above, dip a cup in the water and drink it! Before this class of water is usable, it must be processed to remove harmful chemicals, human waste, particulate matter and so forth before anyone would feel safe drinking it.
In all cases, the river systems of the world have been changed because of the acts of man and his efforts to utilize the river for purposes not conducive to good, clean, water. For the past 2-300 years we have been hellbent on utilizing the rivers to develop our coastal cities as centers of trade and not paying attention to how the rivers were being degraded. One badly mis-understood annual event in most river deltas interfacing with the oceans, is the spring runoff and flooding. Long cursed by the residents who built too close to the water and placed themselves in harms way, the flooding process maintains the rivers flow and allows it to pour rich soil on lands needing refreshing layers of soil.
The other fact of life that we continue to ignore are the vast underground rivers that exist completely around the world. We have accessed a few of them and found evidence of most of them with modern detection devices. Did these rivers once run on the surface, and but for a degrading environment would they still be here?
The vast deserts of the world should tell us that it is highly possible to have huge areas of the world totally unserved by any river. Think of the Sahara, Gobi and other large areas of totally arid land. Were they always that way? I think not! They had their time when water was more prevalent and sustained some sort of ecology. With the decrease of water available in this area, the land dries up, people move away and the cycle begins again.
The great rivers will always be there, but will we be able to use them?