Measuring Groundwater Velocity: Method Based on Groundwater Flow-Induced Cooling

Groundwater flow velocity, including its magnitude and direction, is a crucial aquifer characteristic that plays a significant role in developing and protecting groundwater resources. Current groundwater measurement technologies yield low flow velocity accuracy and are expensive. This study proposes a new method for in situ measurement of groundwater velocity based on groundwater flow-induced cooling. It utilizes the cooling capability of flowing groundwater on a closed circulation of heated fluid to establish a functional relationship between the temperature difference of heated fluid and groundwater velocity. A series of experiments were conducted in a sandbox to verify this approach. The result shows that the new method can measure the groundwater velocity's magnitude and direction. Within the designed flow rate range (0-1.055 mm/s), the correlation coefficient between the calculated values obtained by the new method and the actual values exceeds 0.97, with only a 0.017 root mean square error and a 0.040 mean absolute error. Further, the method finds a significant sine function relationship between the temperature difference of heated fluid and the direction of groundwater flow, with the correlation coefficient exceeding 0.97.