5-25 Figure P-10 shows an aquifer in the form of a rectangle bounded by an impervious rock outcrop and by a river in contact with the aquifer. Water levels in the river vary linearly, with elevations at A, B, C at +6.5 m, + 7.0 m, and + 5.0 m, respectively. The sandy aquifer is underlain by a thin layer of loam (semipervious) under which a very highly permeable layer of gravel is present, with (approximately) a constant head at po = + 6.0 m. Required: (a) Draw (schematically) two cross sections showing the phreatic surface, equipotentials, and streamlines. (b) Present the problem of predicting water levels for a variable natural replenishment (no wells) in an exact mathematical form. (c) Repeat (b) assuming essentially horizontal flow in the aquifer. (d) With the assumption introduced in (c), add several wells scattered over the area and give a numerical scheme for solving the forecasting problem. Channel e f 1 B B'