A Simulation Model for the Infiltration of Heterogeneous Sediment into a Stream Bed

Roland H. Lamberson, Tim Lauck

Mathematics Department
Humboldt State University
Arcata, CA 95521

Thomas E. Lisle

U.S.Forest Service
Pacific Southwest Research Station
Arcata, CA 95521

Abstract:

Salmonid embryos depend on the adequate flow of oxygenated water to survive and interstial passageways to emerge from the gravel bed. Spawning gravels are initially cleaned by the spawning female, but sediment transported during subsequent high-runoff events can infiltrate the porous substrate. In many gravel-bed channels used for spawning, most of the infiltrating sediment consists of sand fine gravel that fall by the force of gravity through the framework of bed paeticles once thje sediment enters the streambed. The sediment comes to rest on the tops of large particles or lodges in pores created by bed particles in mutual contact.
We present a model that siulates the descent and deposition of heterogeneous spheres (sediment) into successive layers of a bed of heterogeneous spheres. Individual sedimentary particles may lodge or pass through a pore depending on its diameter relative to those of the bed particles creation the pore. As sediment lodges in each loyer, the particle size distrubution of the layer is updated to give a new population pf pores through which the next group of sedimentary particles attempts to ingiltrate. Transformations of percentil by weight distributions are used in the simulation both to generate random sediment particles and to simulate pores in the bed
Results using particle size distrjibution from a natural channel show vertical vareations in amount and particle size of infiltrating sediment. Top layers accumulate large amounts of relatively coarse sediment, middle layers accumulate little sediment, and bottom layers accumulate large amounts of fine seniment. This agrees qualitatively with direct measurements of sediment infiltration in this channel. Stimulations using other arbitrary distributions show that the total volume, depth, and particle size distribution of infiltration sediment vary with the particle size distribution of the sediment and streambed.

Advances in Hydro-Science and-Engineering, volume 1 Sam S.Y. Wang(ed.) ISBN 0-937099-02-3(2-Part Set)

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