Limitations of fibre optic distributed temperature sensing for quantifying surface water groundwater interactions

Abstract

Studies of surface water–groundwater interactions using fiber optic distributed temper-ature sensing (FO-DTS) has increased in recent years. However, only a few studies to date have explored the limitations of FO-DTS in detecting groundwater discharge to streams. A FO_DTS system was therefore tested in a flume under controlled laboratory 5 conditions for its ability to accurately measure the discharge of hot or cold groundwa-ter into a simulated surface water flow. In the experiment the surface water (SW) and groundwater (GW) velocities, expressed as ratios (v gw /v sw), were varied from 0.21 % to 61.7 %; temperature difference between SW-GW were varied from 2 to 10 • C; the direction of temperature gradient were varied with both cold and-hot water injection; 10 and two different bed materials were used to investigate their effects on FO_DTS's de-tection limit of groundwater discharge. The ability of the FO_DTS system to detect the discharge of groundwater of a different temperature in the laboratory environment was found to be mainly dependent upon the surface and groundwater flow velocities and their temperature difference. A correlation was proposed to estimate the groundwater 15 discharge from temperature. The correlation is valid when the ratio of the apparent temperature response to the source temperature difference is above 0.02.