The use of thermal infrared imagery as a reconnaissance tool to identify bank seepage was investigated at Franklin D. Roosevelt Lake in northeastern Washington. The banks of the lake are generally composed of glacial lacustrine sediments deposited when the Cordilleran ice sheet dammed the Columbia River at least three times during the Pleistocene. The existence of a significant amount of bank storage was suspected. An airborne scanner having a spectral coverage of 8.5 to 11 micrometres and continuous filmstrip output was used in two test flights of March 27 and April 24, 1973. These flights were made during the reservoir drawdown when groundwater flow was from the banks to the reservoir and the ground water was warmer than the lake. The imagery shows temperatures in the lake ranging from 5° to 13° C. The lighter tones of the imagery show lake circulation patterns and extensive areas of bank seepage, spring discharge, stream inflow, and subsurface discharge which are all distinguishable from the darker tones of the colder lake surface. Bank seepage and ground-water discharge generally are evident where unconsolidated glacial sediment rather than bedrock is present.
