A heat perturbation flow meter for application in soft sediments

A prototype flow meter has been developed, based upon the heat perturbation principle, to monitor groundwater specific discharge in soft sediments. The device is designed for use in spatially intensive, long-term monitoring campaigns in remote or inconvenient locations, and is cheap, robust and capable of being logged automatically. The results of the laboratory tests indicate that the heat perturbation principle is suitable for determining the magnitude of specific discharge to a degree of accuracy that would be useful in practical applications in dynamic groundwater systems with rapidly changing flows of approximately 1 md−1 or more and that the groundwater flow direction can generally be determined to a high level of precision. The accuracy and reliability of the estimates of specific discharge have been shown to depend strongly upon the geometrical precision of manufacture and the quality of the temperature monitoring system. These factors become most significant in the estimation of lower flows and further investigation is required to determine the detection limit of the device. Specific discharge estimates have been shown to be insensitive to dispersivity values appropriate to the scale of the device. Unlike the majority of heat perturbation devices, calibration is unnecessary.