The rest have been dammed, drained, or diverted. It is about 1450 miles long, but is a mere trickle and is salt-encroached at its terminus. The rest is saltwater.
Longitudinal profiles are typically concave up in large rivers.
Like a thermostat, a river tends to adjust toward a dynamic equilibrium. In terms of change of gradient, etc. Completed in 1970 with full hydropower generation from all 12 turbines. Farmers now have to buy fertilizer. Saltwater incursion into Nile Delta because not flushed out by seasonal floods.