Tracing shallow groundwater systems by soil temperatures

Circulating water is known to affect the temperature of the rock through which it flows. Analysis of existing theoretical equations suggests that shallow groundwater flow will also affect the surface soil temperature. Soil temperatures therefore might be used to delineate small, shallow groundwater flow systems; both recharge and discharge zones might be distinguished. Temperature data taken in the field during summer and winter support the theoretical conclusions and agree with the groundwater flow patterns inferred from hydrologic data. In general, winter soil temperature profiles have less data scatter than profiles of summer temperatures. The greater the rate of groundwater flow, the greater the temperature difference between recharge and discharge zones. Temperature variations ranged from 0.75°C in clayey glacial till to 5°C in sand. The effect on soil temperature also decreases with increasing horizontal distance between the recharge and the discharge zone. The effect of horizontal flow in a shallow confined aquifer is also predictable from theoretical models and can be shown by field studies. The amount of heat redistributed depends on the thermal properties of the aquifer and on overburden and the velocity of fluid flow.