Influence of Channel Width on Bed Load Transport Capacity

The influence of channel width on bedload capacity in river reaches of given slope, water discharge, and channel‐bed material is examined. The view that transport capacity is a decreasing function of width is shown to be dependent upon an invalid premise. A contrary view—that transport capacity increases as channel width increases—is also considered. Conclusions based on the second view are shown to be inconsistent with transport formulas or are restricted to channels at a near‐threshold state. The existence of an optimum width that maximizes capacity is demonstrated. This is a consequence of the nature of the relationship between bedload transport rates and flow intensity (notably a threshold condition) and of the relationship between flow resistance and depth. Expressions are derived for the optimum channel width and are shown to predict Gilbert's flume observations. Problems are considered in applying this approach to natural channels.