Abstract

Third-dimensional channel characteristics, bed forms, sediment load, and discharge data are described for two suspended-load streams (Guadalupe and San Antonio Rivers) and a mixed-load stream (Coleto Creek) that together make up the suspended-load fluvial system of the Guadalupe delta of Texas. Discharge of the Guadalupe River is highly variable and increases downstream, but (1) percentage of sand and mean grain size of bed material, (2) channel gradient, (3) valley gradient, (4) channel sinuosity, and (5) channel width/depth ratio all decrease downstream. The most marked decreases in these parameters occur between the alluvial plain and the delta plain.

The relationships between percentage of silt-clay in channel perimeters, width/depth ratios, and sinuosities for these small coastal-plain rivers with single channels support the classification and empirical relationships established by Schumm for modern alluvial channels. One notable exception is that downstream increases in silt and clay from alluvial plains to delta plains do not necessarily yield higher sinuosity channels. The low channel sinuosities and lack of point-bar accretion along lower reaches of many suspended-load alluvial channels and delta distributaries are related to extremely low channel gradients and a natural gradient threshold below which meandering is minimal.

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