[Show abstract][Hide abstract] ABSTRACT: Salmonid embryos depend on the adequate flow of oxygenated water to survive and in- terstitial 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 distribu- tions 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.
[Show abstract][Hide abstract] ABSTRACT: This paper summarizes our current understanding of the effects of timber harvesting on erosion. Rates of erosion on mountain watersheds vary widely but the relative importance of different types of erosion and the consequences of distur- bances remain fairly consistent. Therefore these conclusions seem to be valid for most circumstances: Most of man's activities will increase erosion to some extent in forested watersheds; erosion rarely occurs uniformly; sediment production declines rapidly following disturbance; landslides and creep are the chief forms of natural erosion in mountainous regions; cutting of trees does not significantly increase erosion, but clearcutting on steep unstable slopes may lead to increased mass erosion; accelerated erosion is a possible undesirable side effect of use of fire in conjunction with logging; the road system built for timber harvesting far overshadows logging or fire as a cause of increased erosion; and potentially hazardous areas can be identified in advance of the timber harvest.
[Show abstract][Hide abstract] ABSTRACT: The maximum height for the salt pile in a circular dome with a 4ft retaining wall was determined by two methods. The first method used rigid-body physics; in this model, the critical angel, the maximum angle of inclination allowed while maintaining static equilibrium, was determined using only the external coefficient of friction for salt. Because the static equilibrium also depended upon internal friction, a second model was developed. Development of the second model utilized particle physics, fluid mechanics and soil stress analysis. Mohr's circle, the internal coefficient of friction for salt and its angle of repose were used to determine the critical angle. These results were combined to form our solution model, Model II, which consisted of two submodels:Model II(a) provides a general solution where the front-end loader is allowed to freely travel to any location on the salt pile. This model yields a maximum height of 17.4ft for a symmetric cone with a critical angle of 14.6°.Model II(b) provides a volume-maximizing solution if the loader's travel is restricted. This model yields a maximum height of 23.7ft for a wedge shape with a ramp slope of 14.6° and a back edge slope of 35.9°, where the loader must not cross the peak.Therefore, the authors recommend that Model II(a) be used in the general situation, since the loader is allowed to drive anywhere on the salt pile in this case. When the maximum volume provided is insufficient, Model II(b) can be utilized to increase the capacity of the dome. (Note: The loader must not cross the peak in this model.)
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