Concentration Distribution and Sampling of Suspended Matter

Abstract

Already the first recorded data on the concentration of suspended matter in rivers indicated a wide variation ranging from g.1^–1 in the Yellow River (Lyell 1830) to mg.1^–1 in the Elbe and Rhine rivers (Hübbe 1860; van der Toorn 1868). Since then, concentrations have been found to range from less that 0.5 mg.1^–1 in limestone areas to more than 10 g.1^–1 in the rivers draining the loess area in northern China. High concentrations are favoured by the presence of steep slopes, a semi-arid or glacial high-mountain climate, and loose sediments and soils that can be eroded easily. Concentrations above 500 mg. 1^–1 are therefore found in the rivers draining the Himalayas and the mountain ranges in and around the Pacific, the Chinese loess area, and some semi-arid areas in Asia (Godavari), Africa (Orange river), N. America (Brazos), and Australia (Murray). The Zaire (Congo) river, although it is, after the Amazon, the second largest river based on its discharge, has a relatively low suspended matter concentration (ca. 20–40 mg.1^–1) because the watersheds are low, the river basin is very flat and there are lakes where suspended sediment is trapped. The average concentration of suspended matter in rivers, obtained by dividing the total load by the total river discharge (using the data of Milliman and Meade 1983) is ca. 340 mg.1^–1. Of the total river supply, ca. 80% is transported by rivers with average concentrations of more than 500 mg.1^–1, whereas only 7.5% is transported by rivers with concentrations below 150 mg.1^–1. The highest concentrations ever recorded (≈ 1000 g.1^–1) are from the Puerco river in Arizona, an ephemeral stream flowing only a few days a year (Nordin 1985). The data of Table 2.1 give, for the rivers listed there, average concentrations of 4 g.1^–1 to 143 mg.1^–1. Many smaller rivers with much lower concentrations are not included in Table 2.1.