Sediment

Abstract: New data and new estimates from old data show that rivers with large sediment loads (annual discharges greater than about $15 \times 10^{6}$ tons) contribute about $7 \times 10^{9}$ tons of suspended sediment to the ocean yearly. Extrapolating available data for all drainage basins, the total suspended sediment delivered by all rivers to the oceans is about $13.5 \times 10^{9}$ tons annually; bedload and flood discharges may account for an additional $1-2 \times 10^{9}$ tons. About 70% of this total is derived from southern Asia and the larger islands in the Pacific and Indian Oceans, where sediment yields are much greater than for other drainage basins.

Abstract: Analysis of data from 280 rivers discharging to the ocean indicates that sediment loads/yields are a log-linear function of basin area and maximum elevation of the river basin. Other factors controlling sediment discharge (e.g., climate, runoff) appear to have secondary importance. A notable exception is the influence of human activity, climate, and geology on the rivers draining southern Asia and Oceania. Sediment fluxes from small mountainous rivers, many of which discharge directly onto active margins (e.g., western South and North America and most high-standing oceanic islands), have been greatly underestimated in previous global sediment budgets, perhaps by as much as a factor of three. In contrast, sediment fluxes to the ocean from large rivers (nearly all of which discharge onto passive margins or marginal seas) have been overestimated, as some of the sediment load is subaerially sequestered in subsiding deltas. Before the proliferation of dam construction in the latter half of this century, rivers...