Underground Drainage Systems and Geothermal Flux

An analysis of the interaction between the geothermal fluxandthewaterorair-deepdrainagenetworks.Theproblem of geothermal power intercepted by deep structures and, in general, the temperature fieldcalculations,is converted to classical thermo-engineering problems in terms of shape factors. It is shown that the fluidflowin a conduit perturbs the whole deep rock temperature fielduntilthegeothermalfluxofa largeareaisfocalisedonto the conduit. It is shown that either small water masses flowingintoamountainareabletoperturbtherocktemperature up to the surface, on sizes that do not depend on water mass dimension, but on its depth, and then on enormous volumes. The introduction of the “geothermal cross section” of an underground drainage structure allows us to improve the classical formula of minimum provenance depth of geothermal water. Enlarging factors are applied to the classical estimation in dependence of the ratio between the actual average discharge and the critical discharge Qc, which depends on the conduit geothermal cross section. The geothermal “umbra cones”created in the overlying rock by deep underground structures are described. It is shown that the geothermal flux can play a significant role in the underground drainage phenomenology.