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

Abstract

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. Accurately detecting groundwater flow velocity, including its magnitude and direction, plays a significant role in developing and protecting groundwater resources. However, traditional methods for measuring groundwater flow velocity, such as isotope tracing and borehole dilution tests, have a problem: measurement accuracy is not high, measuring equipment is expensive, and there is a long measurement time. Thus, we propose a fast and accurate method for measuring groundwater velocity. The new method utilizes the cooling capability of flowing groundwater on a closed circulation of heated fluid. A theoretical analysis of the method yields a mathematical relationship between the temperature difference of heated fluid and groundwater velocity. Based on the theoretical analysis, we designed and tested a series of experiments in a sandbox. The result shows that the new method can simultaneously measure the groundwater velocity’s magnitude and direction and has the advantages of high accuracy and strong robustness, which provides a theoretical reference for in situ measurement of groundwater velocity.