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The rates and styles of channel adjustments following an abrupt and voluminous sediment pulse are investigated in the context of site and valley characteristics and time-varying sediment transport regimes. Approximately 10.5 x 106m3 of stored gravel and sand was exposed when Barlin Dam failed during Typhoon WeiPa in 2007. The dam was located on the Dahan River, Taiwan, a system characterized by steep river gradients, typhoon- and monsoon-driven hydrology, high, episodic sediment supply, and highly variable hydraulic conditions. Topography, bulk sediment samples, aerial photos, and simulated hydraulic conditions are analyzed to investigate temporal and spatial patterns in morphology and likely sediment transport...
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Declining amphibian populations in the arid southwestern United States have prompted increased efforts to understand the reproductive behavior of desert anurans, particularly those species in restricted habitats (Sullivan 1989, Corn 1994). The Arizona toad, Bufo microscaphus, is confined in southwestern Utah to tributaries of the Virgin River drainage (Price and Sullivan 1988). Like most desert anurans, B. microscaphus is an explosive breeder (Wells 1977, Sullivan 1992); however, unlike many other toads, which deposit their eggs in still ponds and lakes, it prefers to lay eggs in the flowing water of a perennial or semi-permanent stream. Water quality and breeding behavior are influenced by many physical and biological...
Low-permeability, non-reactive barrier walls are often used to contain contaminants in an aquifer. Rates of solute transport through such barriers are typically many orders of magnitude slower than rates through the aquifer. Nevertheless, the success of remedial actions may be sensitive to these low rates of transport. Two numerical simulation methods for representing low-permeability barriers in a finite-difference groundwater-flow and transport model were tested. In the first method, the hydraulic properties of the barrier were represented directly on grid cells and in the second method, the intercell hydraulic-conductance values were adjusted to approximate the reduction in horizontal flow, allowing use of a...
Populations of chemotactic bacteria are able to sense and respond to chemical gradients in their surroundings and direct their migration toward increasing concentrations of chemicals that they perceive to be beneficial to their survival. It has been suggested that this phenomenon may facilitate bioremediation processes by bringing bacteria into closer proximity to the chemical contaminants that they degrade. To determine the significance of chemotaxis in these processes it is necessary to quantify the magnitude of the response and compare it to other groundwater processes that affect the fate and transport of bacteria. We present a systematic approach toward quantifying the chemotactic response of bacteria in laboratory...
    map background search result map search result map Egg mass deposition by Arizona toads, Bufo microscaphus, along a narrow canyon stream Egg mass deposition by Arizona toads, Bufo microscaphus, along a narrow canyon stream