Hello Everyone,
I am a hydrologist and want to model baseflow (i.e. surface-water groundwater interactions) via the development of a numerical groundwater model (GW model). One of the critical input parameters for the development of the GW model is the hydrogeology of the catchment in question.
Bore-well lithology datasets required for preparation of hydrogeology map or Fence Diagram is very limited (2 borewell logs only), Since, my study area lies in the headwater mountainous region. I am planning to do an electrical resistivity survey for mapping the hydro-geology of the basin in the catchment area of 102 Km2. I have a few questions, in planning Electrical survey in the basin-
1. What could be the optimum number of resistivity profiles required for appropriate representation of hydrogeology of the basin?
2. How to identify the most appropriate locations for Electrical resistivity profiling representative of the basin under consideration?
I request you all to give suggestions in this respect.
Thanking You.
Regards
Rajat
Ideally it would be good to do one test per grid cell. If your grid size is say 100 by 100 m then you can take one. Also it depends on your budget, if budge is limited you can use three of four resistivity points.
The appropriate locations is to capture areas of different terrains.
There are many factors to be taken into account when applying such models, and it is best to use machine learning, which gives more accurate results in such a case.
In general, try to classify the area into a grid and choose profiles that are perpendicular to each other to show the lateral and vertical variation of the sediment and the geometry of the aquifer
Include some profiles in the vicinity of your calibration well. Factor in surface access conditions in profile design. Across / along sedimentary axis. Mimic similar acquisition patterns.
if you want to cover 102 Km2 it will cost too much. anyway ERT needs grids of parallel and intersected lines of uniform spacing. ERT with higher electrode spacing will be useful for the area. you need to identify the required depth to know the method of ERT work and interpretation method.
In general, for this area of land, you must first try to drill at least 10 boreholes. This is so that you can have parametric soundings to calibrate and validate electrical soundings.
Now, and given that the number of drilling is very limited, it seems judicious to me to carry out a grid of 500 m and to carry out a sounding (SEV) with AB/2 of 1000 m in each point of the grid.
The solicited depth of the SEV depends on the increase in the depth of the aquifers (according to geological data). It is therefore necessary to increase the length of electrical soundings in the areas of increase in P and to add SEVs with AB/2 between 3000 and 5000 m (for example).
The establishment of the geo-electrical profiles can be distributed, according to the configuration of the ground, in the following way:
Total number of SEV Number of profile Number of SEV/profile
Zone 1 24 04 06
Zone 2 18 03 06
Zone 3 20 05 04
Best regards
Electrical resistivity profiling (ERP) is a geophysical method that is often used in groundwater modeling to map the subsurface geology and locate groundwater resources. It works by measuring the electrical resistivity of the subsurface materials and using this information to create a map of the subsurface geology.
ERP involves the use of an electrical current, which is passed through the subsurface materials using a pair of electrodes. The resistance to the flow of this current is measured and used to calculate the electrical resistivity of the subsurface materials. Different subsurface materials have different electrical resistivities, and by measuring these resistivities, it is possible to determine the types of materials present in the subsurface and their relative depths.
ERP is often used in conjunction with other geophysical methods, such as ground penetrating radar (GPR) and seismic reflection, to create a more comprehensive picture of the subsurface geology. This information is then used to create a groundwater model, which can be used to predict the location and quality of groundwater resources, as well as to evaluate the potential impacts of groundwater development on the environment.
The optimum number of ERS you can as much as you can take, it would be greatly influenced your model accuracy and more subsurface information.
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