(September 10, 2017 at 1:28 pm)Gawdzilla Sama Wrote: The water that evaporates will leave all it's minerals behind. The water that doesn't evaporate will leave some portion of its minerals behind. Drainage just delays the inevitable.
BTW, did you notice that all those river beds are under sand dunes?
The theory that all water create net deposition of minerals would apply to all farming, not just in Sahara. But luckily it is not always true. Initially all water deposited some minerals, but they also dissolve and carry away existing minerals. If there is through flow of water eventually an equilibrium will develope where the rate at which incoming water deposits minerals will be matched by the rate at which water already in the region willl dissolve existing mineral and carry it away. When that equilibrium is establish mineral and salt buildup stops.
The fact that previous river beds are under sand is no big obstacle. The fact that these riverbed exist at all indicates the overall topography facilitates drainage to a lower point outside the region. If sufficient water is delivered into the region again, erosion should clear out the blocked river beds in a few years and the pre-existing drainage pattern will reestablish itself.
Geological evidence shows natural drainage pattern over large regions are surprising durable. Existing Drainage patterns in areas not immediate impacted by large scale mountain building or volcanic activity can often be traced back with little change over tens of millions of years, over repeated cycles of wet periods and periods of deserfication.
