Aquifer top elevation can be easily estimated based on the elevation of the top surface but how to estimate bottom elevation of the aquifer when one deals with approx. 50 sq. km area. It is not possible to physically determine the bottom elevation everywhere in the area under study. So it has to be estimated. But now the question arises whether the bottom elevation will follow the top elevation (i.e. top elevation minus fixed aquifer thickness) or the bottom of the aquifer will be flat (i.e. the variable aquifer thickness). How to deal with this problem. Can anybody help?
Manish, I do not think there is an easy answer to this one. The bottom elevation will be driven by many variables but mostly by geologic history. Was the area previously under the ocean ? Is the area generally flat topographically ? Is is seismically active ? Is this a karst limestone region ? All of these might affect the elevation of the aquifer bottom. I think first you need to go back and assess the geologic history of the area to help you with assumptions regarding the elevation disposition.
Thanks Dr. Christopher Brown for your response. Can you give me any reference for similar problem anywhere else where such details will be given like what are the things I should look for and how these will be related this problem.
Manish, I suggest you look at papers dealing with "depositional environment".
Depending on your site location, you may be able to identify the elevations of the bottom of the aquifer using well logs. Surface topography is not a good indicator of aquifer bottom elevation.
David Hyndman I agree with you but it is not practically feasible to have well logs everywhere. I was looking for some indirect method.
It is different, you can not depend on the surface terrain to reflect the aquifer bottom, it is a matter of the stratigraphic and structural aspects of the beds of the aquifer
Then how to proceed for that? Please let me know the sequence of steps.
One possibility is to use geophysical prospecting tools, such as resistivity or seismicity detection techniques, though they can be expensive if applied to an extensive area.
Zhonghe Pang thanks for the suggestion. but that may not be possible if depth of aquifer is high. otherwise also it will be difficult. Any other way?
For a first approximation you could do pumping tests to get transmissivity (K*b). You can use various models to estimate hydraulic conductivity (K) based on grain size distributions and sorting. These estimates of K are generally no better than an order of magnitude, sometime worse depending on the heterogeneity of your aquifer. From the transmissivity and K values you can get a very rough approximation of b. But your best bet (IMO) is geophysics... ground penetrating radar, resistivity, seismic, or other.
Dear Mnish. The way of mapping the bottom of the aquifer is by means of geophysical prospection, for example with electrical resistivity methods, is an excellent tool, quick low cost, and with this, you can define your aquifer lateral and vertical boundaries and build your conceptual model for modeling purposes.
it may follow the terrain at the time of deposition [but not necessary the case] but when geological processes [i.e. folding] occurred thereafter [in large scale], then aquifer bottoms may be determined by geological structure affecting them. Think of a case of eroded terrains_changes occurring but does not modify an aquifer bottom. In case where aquifer too deep to obtain this information in lower costs, most scientists depend on knowing the geology of an area VERY WELL [including geological processes occurred or structures] than assumptions are portrayed in a cross-sectional map format. And also [Agree with Reyes] geophysical studies i.e. ER can help.
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