| Abstract |
The Eastern Snake River Plain (ESRP) in southern Idaho is a region with significant potential as a geothermal energy resource. Deep boreholes in the region suggest generally high geothermal heat flux, of approximately 100 mW m-2, with a slight eastward increase across the plain (Blackwell 1989). Evidence of that vertical heat flux, however, is largely masked by the rapid flow of cold groundwater that originates in the Yellowstone Plateau and transports heat horizontally through the highly permeable basalts making up the aquifer. This masking means that spatial distribution of temperature and heat flux below the aquifer is only poorly known and that, in turn, reduces confidence in identification of areas most suitable for geothermal development. To improve understanding of temperature distribution below the aquifer and advance the general understanding of heat flux in the ESRP, we conducted groundwater heat transport simulations and compared results to mapped groundwater temperatures. Our heat transport model utilizes the groundwater flow model developed by the Eastern Snake Plain Hydrologic Modeling Committee, a MODFLOW-based model that has been well tested and calibrated for resource management. Heat flow was simulated using the MT3DMS software package that is compatible with MODFLOW. The model accounts for basal heat flow, conductive loss of heat from top of the aquifer through the vadose zone, and advective addition of heat through rivers, precipitation, irrigation, and injection wells. Simulations with constant basal heat flow capture many of the salient features of the measured temperature distribution. Results demonstrate the relative importance of advective transport in the aquifer. Viscous dissipation has been shown to be significant in the aquifer and that thermal input is being added to the model. The model is being calibrated against measured temperature profiles and heat flow measurements that have been taken below the aquifer. These vertical temperature profiles can also provide information about groundwater flux and mechanical dispersion within the aquifer, which is the subject of a companion paper. |