Chemical and Isotopic Approach to Groundwater Cycle in Western Qaidam Basin,China

Due to the extremely arid climate in the western Qaidam Basin,the groundwater almost becomes the single water source for local residents and industrial production.It is necessary to know the reliable information on the groundwater cycle in this region for reasonable and sustainable exploitation of the groundwater resources with the further execution of recycling economy policies.This study focused on the recharge,the flow rate and the discharge of groundwater in the western Qaidam Basin through investigations on water chemistry and isotopes.Hydrological,chemical and isotopic characteristics show that the groundwater in the western Qaidam Basin was recharged by meltwater from new surface snow and old bottom glaciers on the northern slope of the Kunlun Mountains.In addition,the results also prove that the source water is enough and stable,and the rates of the circulation and renewal of the groundwater are relatively quick.Therefore,it can be concluded that the groundwater resources would guarantee the regional requirement if the meltwater volume of the mountains has not a great changes in future,moreover,water exploitation should be limited to the renewable amount of the groundwater reservoir in the western Qaidam Basin.

Migration of Infiltrated NH_4 and NO_3 in a Soil and Groundwater System Simulated by a Soil Tank

The infiltration of water contaminants into soil and groundwater systems can greatly affect the quality of groundwater. A laboratory-designed large soil tank with periodic and continuous infiltration models,respectively,was used to simulate the migration of the contaminants NH4 and NO3 in a soil and groundwater system,including unsaturated and saturated zones. The unsaturated soil zone had a significant effect on removing NH4 and NO3 infiltrated from the surface water. The patterns of breakthrough curves of NH4 and NO3 in the unsaturated zone were related to the infiltration time. A short infiltration time resulted in a single sharp peak in the breakthrough curve,while a long infiltration time led to a plateau curve. When NH4 and NO3 migrated from the unsaturated zone to the saturated zone,an interfacial retardation was formed,resulting in an increased contaminant concentration on the interface. Under the infiuence of horizontal groundwater movement,the infiltrated contaminants formed a contamination-prone area downstream. As the contaminants migrated downstream,their concentrations were significantly reduced. Under the same infiltration concentration,the concentration of NO3 was greater than that of NH4 at every corresponding cross-section in the soil and groundwater tank,suggesting that the removal effciency of NH4 was greater than that of NO3 in the soil and groundwater system.

Propagation and Amplitude Decay Mechanisms of Internal Solitary Waves

In this paper, a modified dynamic coherent eddy model （DCEM） of large eddy simulation is applied to study internal solitary waves in a numerical flume. The model was verified by physical experiment and applied to investigate the potential influence factors on internal wave amplitude. In addition, we discussed the energy loss of internal solitary wave as well as hydrodynamics in the propagation. The results of our study show that （1） Step-depth is the most sensitive factor on wave amplitude for the ＂step-pool＂ internal wave generation method and the wave amplitudes obey a linear increase with step depth, and the increase rate is about 0.4. （2） Wave energy loss obeys a linear decrease with the propagation distance and its loss rate of large amplitude waves is smaller than that of small amplitude waves. （3） Loss of kinetic energy in wave valley is larger than that near the interface due to relative high fluctuating frequency. （4） Discovered boundary jet-flow can intensify the bottom shear, which might be one of the mechanisms of substance transportation, and the boundary layers of jet flows are easily influenced by the adjacent waves.

Hydrodynamic improvement of a goose-head pattern braided reach in lower Yangtze River

The Three Gorges Reservoir (TGR) began operation in 2003 with alterations in the natural hydrological regime and with severe environmental impacts. Baguazhou Reach, a goose-head pattern of braided channels in the lower Yangtze River has emerged due to a series of changes in the water and sediment conditions caused by the TGR. This paper makes simulations of the hydrodynamic characteristics under the condition of clear water releasing from the TGR and analyzes the features of deformation within the branches of the reach, as well as predicts the future development of the hydrodynamic improvement and the additional fluvial processes. The results show that the decline of the tributary is mainly due to the weakening of the inflow energy and the channel resistance. The particular protective measures can effectively improve the hydrodynamic performance and the present situation but, they all result in a deflection of the main water flow and increase the local velocity, and over the long term, leading to the deposition in the junction areas, where a special protection is required.