ABSTRACT: Magnetically tagged particles were used to investigate the effects of sockeye salmon (Oncorhynchus nerka) and floods on the dispersion of coarse bed material in the Stuart‐Takla region, British Columbia, Canada. The dominant annual sediment transporting event in the channels is the snowmelt flood events, with lesser activity usually accomplished during summer floods. Annually in August, the channel bed material is reworked by the Early Stuart sockeye salmon spawning, as the fish excavate the streambed to deposit and bury their eggs. These nesting cavities are called redds. Results from 67 tracer recovery experiments over five years were highly variable, subject to the magnitude of floods and the returning population of salmon. Overall, the depositional pattern from nival flood events usually demonstrated a high degree of clast mobilization, long travel distances (up to 150 m), and mean depths of burial up to 18 cm. Summer flood events showed somewhat lower rates of mobilization, distances of travel, and depths of burial. Although the fish did not move the tracers very far, their effect on the bed was generally quite pervasive ‐ up to 100 percent of the clasts were mobilized, and the depth of burial was considerable (mean burial depths up to 14 cm). The amount of vertical mixing of sediment by salmon was often on the same order of magnitude as flood events. The significant vertical mixing of sediments by the fish has important implications for the mobility of sediment in the stream. Since any armoring layer formed during high flows throughout the year is subject to the bioturbation of salmon, this suggests that the transport threshold in the creeks remains relatively low. Salmon likely play an integral role in the sediment transport dynamics and annual sediment budget of the lower reaches of these creeks. 相似文献
ABSTRACT: One-dimensional and two-dimensional modeling approaches were compared for their abilities in predicting overland runoff and sediment transport. Both 1-D and 2-D models were developed to test the hypothesis that the 2-D modeling approach could improve the model predictions over the 1-P approach, based on the same mathematical representations of physical processes for runoff and sediment transport. The models developed in this study were applied to overland areas with cross slopes. A hypothetical case and an experimental study reported by Storm (1991) were used. Based on the simulation results from the selected hypothetical case and experimental study, the 2-D model provided better representation of spatial distribution of flow depths and sediment concentrations than the 1-D model. However, no significant differences in predictions of total runoff volume and sediment yield at the outlet area were found between the 1-D and 2-D models. 相似文献
Objective: Though public transport vehicles are rarely involved in mass casualty accidents, when they are, the number of injuries and fatalities is usually high due to the high passenger capacity. Of the few studies that have been conducted on bus safety, the majority focused on vehicle safety features, road environmental factors, as well as driver characteristics. Nevertheless, few studies have attempted to investigate the underlying risk factors related to bus occupants. This article presents an investigation aimed at identifying the risk factors affecting injury severity of bus passengers with different movements.
Method: Three different passenger movement types including standing, seated, and boarding/alighting were analyzed individually using classification and regression tree (CART) method based on publicly available accident database of Great Britain.
Results: According to the results of exploratory analyses, passenger age and vehicle maneuver are associated with passenger injury severity in all 3 types of accidents. Moreover, the variable “skidding and overturning” is associated with injury severity of seated passengers and driver age is correlated with injury severity of standing and boarding/alighting passengers.
Conclusions: The CART method shows its ability to identify and easily explain the complicated patterns affecting passenger injury severity. Several countermeasures to reduce bus passenger injury severity are recommended. 相似文献
In order to understand the similarity or difference of inorganic As species uptake and transport related to phosphorus in As-hyperaccumulator,uptake and transport of arsenate(As(V))and arsenite(As(III))were studied using Pteris vittata L.under sandculture.Higher concentrations of phosphate were found to inhibit accumulation of arsenate and arsenite in the fronds of P.vittata.The reduction in As accumulation was greater in old fronds than in young fronds,and relatively weak in root and rhizome.Moderateincreases,from 0.05 to 0.3 mmol/L,in phosphate reduced uptake of As(III)more than As(V),while the reverse was observed at highconcentrations of phosphate(1.0 mmol/L).Phosphate apparently reduced As transport and the proportion of As accumulated in frondsof P.vittata when As was supplied as As(V).It may in part be due to competition between phosphorus and As(V)during transport.Incontrast,phosphate had a much smaller effect on As transport when the As was supplied as As(III).Therefore,the results from presentexperiments indicates that a higher concentration of phosphate suppressed As accumulation and transport in P.vittata,especially inthe fronds,when exposed to As(V);but the suppression of phosphate to As transport may be insignificant when P.vittata exposed toAs(III)under sand culture conditions.The finding will help to understand the interaction of P and As during their uptake process in P.vittata. 相似文献
The mechanism of flow turbulence, sediment supply conditions, and sediment transport patterns that affect the adsorption of cadmium ions onto sediment particles in natural waters are experimentally simulated and studied in this study both in batch reactors and in a turbulence simulation tank. By changing the agitation conditions, the sediment transport in batch reactors can be categorized into bottom sediment-dominated sediment and suspended sediment-dominated sediment. It is found that the adsorption rate of bottom sediment is much less than that of suspended sediment, but the sediment transport pattern does not affect the final (equilibrium) concentration of dissolved cadmium. This result indicates that the parameters of an adsorption isotherm are the same regardless of the sediment transport pattern. In the turbulence simulation tank, the turbulence is generated by harmonic grid-stirred motions, and the turbulence intensity is quantified in terms of eddy diffusivity, which is equal to 9.84F(F is the harmonic vibration frequency) and is comparable to natural surface water conditions.When the turbulence intensity of flow is low and sediment particles stay as bottom sediment, the adsorption rate is significantly low, and the adsorption quantity compared with that of suspended sediment is negligible in the 6 h duration of the experiment. This result greatly favors the simplification of the numerical modeling of heavy metal pollutant transformation in natural rivers. When the turbulence intensity is high but bottom sediment persists, the rate and extent of descent of the dissolved cadmium concentration in the tank noticeably increase, and the time that is required to reach adsorption equilibrium also increases considerably due to the continuous exchange that occurs between the suspended sediment and the bottom sediment.A comparison of the results of the experiments in the batch reactor and those in the turbulence simulation tank reveals that the adsorption ability of the sediment, and in particular the adsorption rate, is greatly over-estimated in the batch reactor. 相似文献