Each mixture used the same gravel, and sand was added to produce mixtures containing 6, 15, 21, 27, and 34 % sand. Control of other variables allows us to isolate the effect of bed sand content on transport. As sand content increases, gravel transport rates increase by orders of magnitude, even though the proportion of gravel in the bed decreases.
Nov 22, 2019 · Sand is relatively common, mined in every state, and typically locally sourced due to high transportation costs, so deposits should be near populated areas where sand and gravel is in demand. Deposits should also be close to the ground surface, which makes sand and gravel easy and cheap to extract with openpit mines or dredging.