A Simulation Model
نویسندگان
چکیده
Salmonid embryos depend on the adequate flow of oxygenated water to survive and interstitial 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 nfiltrate the porous substrate. In many gravel-bed channels used for spawning, most of the infiltrating sediment consists of sand and fine gravel that fall by the force of gravity through the framework of bed particles once the 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 simulates 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 creating the pore. As sediment lodges in each layer, the particle-size distribution of the layer is updated to give a new population of pores through which the next group of sedimentary particles attempts to infiltrate. Transformations of percentile-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 distributions from a natural channel show vertical variations 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 sediment. This agrees qualitatively with direct measurements of sediment infiltration in this channel. Simulations using other arbitrary distributions show that the total volume, depth, and particle-size distribution of infiltrating sediment vary with the particle-size distribution of the sediment and streambed.
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