Well lets go with that flooding then, in the years there are no floods can crops still be grown. In Egypt the flood have stopped, that means building walls on each side and the diverting the water onto the flood plains. Sounds expensive and the silt from the headwaters doesn't make it past the dam anyway. If that wheel could be made to be 100ft tall the the water can be piped inland to 50 ft above water level. I don't know how much more land that would open up but even pure sand can be turned into topsoil over a few decades. If fertilizers have to also be used in the early stages not a big deal and most of the Prairies is as lifeless as desert sand which sometimes only lacks water before something will grow there. These days weeping hoses stretch water resources a lot further than the spraying methods in use in some systems.You could consider recent events in Manitoba just a refreshing of the land.
I was under the impression money shortage also had much to do with people's ability to buy food rather than ther being none available. (to a certain degree) Growing cotton doesn't do much to lower the price of imported flour.