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Dong P.,Key Laboratory of Groundwater Circulation and Evolution | Wang X.-S.,Water Resources University | Wan L.,Key Laboratory of Groundwater Circulation and Evolution | Kuang X.-X.,University of Hong Kong | Chen T.-F.,Water Resources University
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2013

The change of groundwater level drives air flow in the vadose zone, and the air flow in turn interacts with groundwater flow. This kind of coupling between groundwater level change and air flow becomes more apparent when the unconfined aquifer is covered by a low-permeability layer. Intake and drainage experiments were carried out in a double-layer sand column with fine sand over coarse sand, using the thin find sand layer as the low-permeability confining layer in this study. As the the water level declines in the drainage experiment, significant vacuum can be generated in the vadose zone and air flows from atmosphere into the column. In contrast to the drainage experiment, when the water level uplifts in the intake experiment, air pressure in the vadose zone increases and air flows outward. The change of vadose zone air pressure with time shows a single peak and is affected by the thickness of the fine sand layer. Based on the Darcy flow of groundwater in the saturated zone and the linear seepage of compressible air in the vadose zone, a simplified kinetic model is proposed to explain the air-water movement in the sand column and Runge-Kutta algorithm was used to solve the model, the observed vadose zone air pressure was reproduced. Simulation results show that the maximum air pressure in the vodose zone increases nonlinearly with the increasing of the thickness of the low-permeability layer.

Qian K.,Water Resources University | Qian K.,Key Laboratory of Groundwater Circulation and Evolution | Wang X.-S.,Water Resources University | Lv J.,Water Resources University | And 2 more authors.
International Journal of Climatology | Year: 2014

The source region of Yangtze River in China is a part of Tibet Plateau where the hydrological processes are sensitive to climatic change. The impacts of precipitation, air temperature and evapotranspiration on annual runoff in the source region of Yangtze River during 1957-2009 are investigated in the time-period domain using wavelet analysis method and multiple regression method. Annual evapotranspiration is calculated with data of precipitation and air temperature based on Takahashi's empirical equation. This approximation of actual evapotranspiration successfully matches the mean annual water balance. Significant periods of runoff, 7-8year, 20-21year and 42-43year, are revealed by using Morlet wavelet. Different significant periods are found for annual precipitation, air temperature and evapotranspiration, whereas the 7-8year and 42-43year periods are the same of the runoff. It is indicated by wavelet correlation coefficients that the correlations between runoff and these climatic components depends on periods. Change in the summation of runoff wavelet coefficients at different period can approximately represents the change pattern of real runoff and is correlated with the wavelet coefficients of the climatic components. The correlation can be expressed with a linear multiple regression equation which indicates that the change in annual runoff is contributed by change in annual precipitation rather than change in air temperature. This relationship between runoff and climatic components are different from that in the source region of Yellow River, in China. © 2013 Royal Meteorological Society.

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