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The hyporheic zone (HZ) has the capability to eliminate and attenuate nutrients and contaminants in riverine systems. Biogeochemical reactions and the potential elimination of contaminants are strongly controlled by the flow paths and dynamics in the HZ. Nevertheless, an easily applicable method for the field determination of flow patterns in the HZ is still lacking. Therefore, a heat pulse technique, which traces the movement of a short heat pulse in the upper part of the HZ and other sand beds, was developed. Five rods are vertically driven into the sediment of the streambed; one rod with a heater as point source located in about 10‐cm sediment depth and four rods with four temperature sensors in 3 cm distance, arranged concentrically with 7 cm diameter around the heating rod. Subsequently, a heat pulse is applied and the resulting breakthrough curves are indicative of flow velocities and flow directions in the streambed. A rough data analysis procedure is also suggested. In addition, laboratory experiments were performed to test the heat pulse technique. These experiments were validated based on coupled numerical modelling of flow and heat transport. First field tests of the method prove that the method is easily applicable under field conditions. These first field tests showed highly complex flow patterns with flow velocities from 1·8 to 4·9 cm min?1 and flow directions from parallel to surface flow to opposite to surface flow. This suggests the need for a robust method to quantify hyporheic flow patterns in situ. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Water exchange across the sediment–water interface of streams impresses a characteristic thermal pattern at the interface. The use of fibre optic distributed temperature sensing at the sediment–water interface in a small sand‐bed stream identifies such temperature patterns. Groundwater and interflow can be differentiated based on the temporal evolution of temperature patterns. Additionally, sudden temperature changes at the sediment–water interface observed during the transit of floods enable spatial identification of local up and downwelling. Electromagnetic induction geophysics can detect subsurface texture structures that support groundwater–surface water exchange. Our results show that areas of permanent temperature anomalies observed with fibre optic distributed temperature sensing match areas of comparatively homogeneous electrical conductivity. This indicates groundwater discharge and enables differentiating groundwater discharge from interflow and local downwelling. 相似文献
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The wave-induced motion of two vessels in close proximity is studied using traditional two-dimensional (2D) and three-dimensional (3D) boundary element methods. Added mass, damping, and the behavior of the free surface between the vessels are examined in some detail. As expected based on previous work, the response of the water between the vessels is found to have a profound effect on the hydrodynamic forces. At “critical frequencies” corresponding to standing waves between the hulls, the hydrodynamic forces undergo significant drastic changes. The 2D and 3D results are compared, and the effects of a skew angle between the vessels are examined. Some of the consequences of the behavior at the critical frequencies for simulations in the time domain are examined, the most significant of which is a very lightly damped impulse response. 相似文献
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Tabea Broecker Vahid Sobhi Gollo Aryeh Fox Jörg Lewandowski Gunnar Nützmann Shai Arnon Reinhard Hinkelmann 《Ground water》2021,59(4):488-502
Transport processes that lead to exchange of mass between surface water and groundwater play a significant role for the ecological functioning of aquatic systems, for hydrological processes and for biogeochemical transformations. In this study, we present a novel integral modeling approach for flow and transport at the sediment–water interface. The model allows us to simultaneously simulate turbulent surface and subsurface flow and transport with the same conceptual approach. For this purpose, a conservative transport equation was implemented to an existing approach that uses an extended version of the Navier–Stokes equations. Based on previous flume studies which investigated the spreading of a dye tracer under neutral, losing and gaining flow conditions the new solver is validated. Tracer distributions of the experiments are in close agreement with the simulations. The simulated flow paths are significantly affected by in- and outflowing groundwater flow. The highest velocities within the sediment are found for losing condition, which leads to shorter residence times compared to neutral and gaining conditions. The largest extent of the hyporheic exchange flow is observed under neutral condition. The new solver can be used for further examinations of cases that are not suitable for the conventional coupled models, for example, if Reynolds numbers are larger than 10. Moreover, results gained with the integral solver provide high-resolution information on pressure and velocity distributions at the rippled streambed, which can be used to improve flow predictions. This includes the extent of hyporheic exchange under varying ambient groundwater flow conditions. 相似文献
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Until recently, the Global Positioning System (GPS) was the only operational means of distributing time to an arbitrary number
of users and of synchronizing clocks over large distances with a high degree of precision and accuracy. Over the last few
years it has been shown that similar performance can be achieved using the Russian Global Navigation Satellite System (GLONASS).
GLONASS time transfer between continents was initially hampered by the lack of post-processed precise ephemerides. Results
from the International GLONASS Experiment (IGEX) campaign are now available, however, and this paper reports on the first
use of IGEX precise ephemerides for GLONASS P-code intercontinental time links. The results of GLONASS P-code and GPS C/A-code
time transfer are compared under similar conditions.
Received: 31 January 2000 / Accepted: 10 July 2000 相似文献
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