Water Exchange In Hyporeic Zone Between Groundwater And Stream, Tataling River

Hyporheic zone between stream and groundwater is the most active area of material and energy exchange in the river,and also is the sensitive area of river basin ecological environment,which controlled by many factors such as topography,meteorology.Especially in the arid region,surface water and groundwater transformation is more frequency,the spatial and temporal differences of water exchange in hyporeic zone between groundwater and stream directly affect the downstream ecological environment quality.Based on Tataling river,qaidam basin,with the measured water level and temperature data,this paper analyzed the spatial and temporal distribution characteristics of water exchange in hyporeic zone between groundwater and stream,calculated the the amount of water exchange and discussed its influence factors.By comparing the difference of water exchange results based on hydrodynamic method and heat tracing method,we analyzed the suitable conditions for the two methods.Finally the following understands are aquired:(1)The hydrodynamic condition of the hyporeic zone between groundwater and stream is obviously affected by the quantity of upstream water recharge.In the non-flood period,the difference between two hydraulic heads in the hyporeic zone is small,the quantity of upstream water recharge increases during the flood period,and the quantity of the groundwater discharge to the river is increase.The quantity of water exchange calculated by hydrodynamic method shows that most of the time groundwater dischange to river hyporeic zone,and the amount of hyporeic exchange gradually increases from riverside to river center.The average amount of hyporeic exchange of each monitoring point is-0.279m~3/m~2/d~0.082m~3/m~2/d.(2)In the Tataling River Basin,during the non-flood period,the temperature at different depths below the surface of the river bed varies greatly.When the flood comes,the temperature of the river bed decreases as a whole,and the temperature changes at different depths below the surface of the river bed are significantly reduced.In the vertical,riverbed temperature has a layering effect,according to the temperature distribution at different depths can be divided into three zones:abrupt change zone(0~-20cm),gradual change zone(-20~-50cm),and stable zone(-50cm).In the horizontal direction,the temperature in the center of the river is relatively stable,while the temperature on both sides varies greatly.The heat tracing method show that the average amount of hyporeic exchange of each monitoring point is between-0.27m~3/m~2/d~0.149m~3/m~2/d.(3)The flood process changes the hydrodynamic field in the hyporeic zone,thus affecting the water exchange.The hydraulic conductivity is the main factor affecting the water exchange in hyporeic zone.The water exchange rate is also relatively large at the monitoring point where the river bed hydraulic conductivity is relatively large.At the basin scale,the regional hydrodynamic characteristics have a significant control effect on the water exchange in hyporeic zone.However,due to the fluctuation of the riverbed topography,the distribution of pressure inside the riverbed changes,There is a certain difference on the river?groundwater exchange in the vertical direction between the smaller scale riverbed profile and the basin scale.(4)For water exchange direction,the results of hydrodynamic method and heat as tracing method are consistent,but the two methods show obvious spatial and temporal differences in quantitative the amount of water exchange.As a traditional research method,under the condition of accurate determination of river bed hydraulic conductivity,hydrodynamic method has wide applicability.In the center of the river with relatively flat topography,heat as tracer method can be applied on shallow riverbed(50cm or shallower)to obtain more stable amount of water exchange.