What flow depth is required in a turbulent river to support quartz grains of diameter 0.25 mm in suspension if the slope of the river is 1 m/km. Assume that the critical Rouse number for suspension is 2.5. Perform the same calculation for a 0.25 mm grain of gold. The density of gold is 19300 kg/m³, and of quartz is 2650 kg/m³. (You should find that gold is much less likely to be in suspension. This is the essence of the gold panning method.)