Abstract:

Temperature was used as a tracer to capture the hypothetic flow. Based on the equation of onedimensional steadystate water and heat transport in saturated porous medium, seepage velocities were estimated using time series thermal data. The application conditions and ranges, and the sensitivity to thermal properties of this method were analyzed. The vertical temperature at different depths in the riparian zone of the lower reach of Xin’an River, in Zhejiang Province, were monitored, and the changes in phase and amplitude of the temperature type curve were analyzed to quantify surface watergroundwater interactions. Results show that seepage velocity was sensitive to amplitude variation at low flow rates, and the greatest sensitivity of seepage rate to phase shift occurred near ±1×10^-5m/s. In the monitoring period, the seepage velocity fluctuated from 2.22×10^-5m/s to 4.39×10^-5m/s, and the values of the seepage velocity were all positive, which means that groundwater was recharged by surface water. The time series method which is insensitive to streambed scour and sedimentation, allows for application under a wide range of complex hydrodynamics conditions, and overcomes the effect of thermal dispersivity to some extent.

Key words: low temperature water discharged, seepage velocity, time series analysis, amplitude ratio, phase shift