The temperature gradient play important role for deep water circulation and high geothermal system. Heat source in the deep level is also important which is such as fractional movement of hot rock masses/ exothermic reactions etc. In case of normal heat flow value of the area temperature gradient is considered as 30 degree/km. Thus in normal condition a deep water circulation of  3 to 4 km is needed. But it may be affected by mixing of shallow cold water also if any.

It is not too difficult to estimate depth of groundwater circulation assuming a normal thermal gradient. A further question related to the previous one is: what is the driving force of this circulation. If only gravity is considered then how much difference in elevation is required to sustain such a circulation cell?

The required circulation depth depends on the background goothermal regime to a large extent, in addition, the circulation depth is constrained by the terrain elevation difference.

You have to know the magnetic gravity of the area and correct the terrain elevation with the magnetic gravity because you have to determine the terrain difference first before determine the circulation depth

Thanks Emad for your answer to my question. If the difference in terrain elevation is known, how do you think the groundwater circulation depth can be worked out?

I have to know the temperature difference with the depth (if it is available), the type of subsurface geological layers and the properties of these rocks (the porosity, permeability etc.) including the aquifer. The analysis of the groundwater. Is there a high radiation in the groundwater. All of these things most be known