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93.
This study investigates spatial patterns and temporal dynamics of aquifer–river exchange flow at a reach of the River Leith, UK. Observations of sub‐channel vertical hydraulic gradients at the field site indicate the dominance of groundwater up‐welling into the river and the absence of groundwater recharge from surface water. However, observed hydraulic heads do not provide information on potential surface water infiltration into the top 0–15 cm of the streambed as these depths are not covered by the existing experimental infrastructure. In order to evaluate whether surface water infiltration is likely to occur outside the ‘window of detection’, i.e. the shallow streambed, a numerical groundwater model is used to simulate hydrological exchanges between the aquifer and the river. Transient simulations of the successfully validated model (Nash and Sutcliff efficiency of 0·91) suggest that surface water infiltration is marginal and that the possibility of significant volumes of surface water infiltrating into non‐monitored shallow streambed sediments can be excluded for the simulation period. Furthermore, the simulation results show that with increasing head differences between river and aquifer towards the end of the simulation period, the impact of streambed topography and hydraulic conductivity on spatial patterns of exchange flow rates decreases. A set of peak flow scenarios with altered groundwater‐surface water head gradients is simulated in order to quantify the potential for surface water infiltration during characteristic winter flow conditions following the observation period. The results indicate that, particularly at the beginning of peak flow conditions, head gradients are likely to cause substantial increase in surface water infiltration into the streambed. The study highlights the potential for the improvement of process understanding of hyporheic exchange flow patterns at the stream reach scale by simulating aquifer‐river exchange fluxes with a standard numerical groundwater model and a simple but robust model structure and parameterization. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
94.
Dead stranded sea turtles were recovered and examined to determine the impact of anthropogenic debris and fishery activities on sea turtles on the coast of Rio Grande do Sul State, Brazil. Esophagus/stomach contents of 38 juvenile green Chelonia mydas, 10 adults and sub-adults loggerhead Caretta caretta, and two leatherback Dermochelys coriacea turtles (adult or sub-adult) included plastic bags as the main debris ingested, predominated by white and colorless pieces. The ingestion of anthropogenic debris accounted for the death of 13.2% of the green turtles examined. Signs of damage over the body and carapace indicated that fishing activities caused the death of 13.6% (3/22) of loggerheads and 1.5% (1/56) of green turtles. Therefore, it appears that direct and indirect effects of fishing activities may pose a threat to these species in Brazilian waters. Other sources of plastic debris should be investigated as well as the direct impact of fisheries, especially bottom trawl and gill nets, in order to establish effective conservation action. 相似文献
95.
Tanguang Gao Shichang Kang Peter Krause Lan Cuo Santoch Nepal 《Environmental Earth Sciences》2012,65(6):1651-1659
In this paper, the application of a fully distributed hydrological model J2000 with limited hydrological data was investigated
in an alpine small and glacierized catchment, the Qugaqie (55 km2 with 7.3% glacier area), in the central Tibetan Plateau (TP). The J2000 was examined to investigate the influence on model
performance, as well as on data, parameters and sensitivities. The model was calibrated with time series of discharge at the
basin outlet for the summers of 2006 and 2007 and validated for the summer of 2008 by examining multiple objective functions.
The model coefficients of determination were 0.62 and 0.91 for the calibration periods in 2006 and 2007, respectively, and
0.56 for the validation period in 2008. Simulated discharge was generally less than the observed values for the calibration
and validation periods. The sensitivity to alteration in meteorological parameter has revealed that a change in air temperature
would cause a dramatic increase of discharge in the Qugaqie catchment. Hypothetical climate scenario experiments showed that
the increase of air temperature by 1°C resulted in 14% increase in runoff, whereas 20% increase in precipitation caused 9%
increase in runoff but 12% reduction in glacier melt. 相似文献
96.
The methods proposed in a foregoing paper are used for the derivation of the eddy viscosity of a two-dimensional homogeneous isotropic turbulence. In contrast to three-dimensional isotropic turbulence is shown that for the two-dimensional case the eddy viscosity (i) has no definite sign, (ii) tends to zero if the molecular viscosity tends to zero, (iii) is negative for special cases. However, the modes with large wave numbers decay in any case as is shown by investigating a dispersion relation. 相似文献