3.2 Sediment Supply

Sediment dynamics exert important controls on channel morphology and texture that affect habitat quantity and quality for aquatic and riparian species. Aquatic habitat attributes such as spawning gravel availability and the amount of fine sediment in the channel bed are determined by the size distribution and rate of sediment input and by the capacity of stream channels to store and transport sediment. Sediment transport and storage characteristics control the average time required for sediment of various sizes to be routed through the channel network, influencing the sensitivity of channels to disturbances.

Drainage basin geology and geomorphology often control the volume and size distribution of sediment supply, longitudinal pattern of sediment input, and project effects on channel conditions. The preferred approach for characterizing sediment supply depends on the geologic setting and availability of existing information, including

  1. long-term records of suspended load and/or bedload flux in tributaries to project reservoirs and downstream reaches;
  2. erosion inventories in source areas;
  3. published estimates of erosion rates in or characteristic of the geology, geomorphology, climate, and land use in the project area; and
  4. estimates of reservoir sedimentation or availability of impoundments suitable for estimating sedimentation.

More than one approach may be required to corroborate results.

The following references are recommended for additional information on sediment supply approaches:

Grant, G. E., J. C. Schmidt, and S. L. Lewis. 2003. A geological framework for interpreting downstream effects of dams on rivers. Pages 209-225 in J. E. O'Connor and G. E. Grant, editors. A peculiar river: geology, geomorphology, and hydrology of the Deschutes River, Oregon. Water Science and Application Series No. 7. American Geophysical Union, Washington, D. C.

Petts, G. E. 1979. Complex response of river channel morphology subsequent to reservoir construction. Progress in Physical Geography 3: 329-362.

Williams, G. P., and M. G. Wolman. 1984. Downstream effects of dams on alluvial rivers. Geological Survey Professional Paper 1286. U. S. Geological Survey, Washington, D. C.

Chien, N. 1985. Changes in river regimes after the construction of upstream reservoirs. Earth Surface Processes and Landforms 10: 143-159.

Collier, M., R. H. Webb, and J. C. Schmidt. 1996. Dams and rivers: a primer on the downstream effects of dams. Circular No. 1126. U. S. Geological Survey.