Graph the expected history of retreat of a river knickpoint in which the distribution of basin area is A=5(L-x)^1/2, where the length of the full channel is L, and x is the distance upstream from the mouth of the basin. The speed of the knickpoint as it is cast off from the basin exit is U=10 mm/yr. Plot the dimensionless knickpoint speed u/U as a function of non-dimensional distance upstream x/L. You will find it useful to stop your plot at say x/L = 0.9.