Depth of water table

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One of the most crucial factors in drilling or digging a well in most arid part of world relies on water table level. Is there an effective minimally disruptive method of profiling water table depth for a potential well site? I am more interested in depth variables and its attendant factors for well evaluation. Thank you. 

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7 Answers

  1. Hi Michael:

     

    I have read the comments and I agree with everyone. Geophysics is the way to go, however the hard thing is to set up the surveys and find the correct locations. I will try to give you a walkthrough, that in a very general way I believe it applies to any case study:
     

    1. You have to start by analyzing geological maps to study the soil type and stratigraphy. So you can at least have a very broad image of whats happening down there and where the water could possible be stored.

    2. A very brief hidrological analysis will let you know where it rains and how much it does. You can compare it with stream flows and try to close the water balance. It is important that you define if it rains, how much of that rain can be going to groundwater. Later on, that will be your recharge. If you have no recharge, you will dry the acuifer and all the work is done pointless.

    3. By looking at a DTM and going on field trips you can start implying possible locations to perform geophysical surveys. First, start with Vertical Electric Sounding (VES) which are cheaper and give you one directional information. With the VES interpretation you will know better where you need to search deeper and plan on 2D ERT (Electric Resistivity Tomography), that is pretty much like x-rays of the ground. With a good interpretation, you can stop any time. 

    4. If things are not so clear this far, you will need to bore exploration wells, which are cheaper. Direct information can be compared with indirect data from ERT and VES. Just now you can start making decissions.

     

    I hope you can use this information. If you have any further question, please don't hesitate to contact me:
    evillagomez@live.com

     

    Have a great day,

    Eduardo.

    1 Comment

    1. I appreciate your extensive and detailed approach. Thank you.

  2. I have had some success with Vertical Electrical Sounding (VES). This uses electrodes driven into the ground and measures soil resistivity. Multiple readings give a profile of subsurface conditions. It isn't 100%, but improves odds considerably.  https://www.agiusa.com/1d-resistivity-survey-vertical-electrical-sounding

    1 Comment

    1. Thank you. I looked at article on VES.

  3. Michael, as Fidelis said, the starting point is understanding the geological environment, and whether you are seeking water in an extensive aquifer with intergranular flow, or in a hard rock, fracture dominated, environment. In either case actual observations in existing wells and boreholes, and identifying any flowing springs or baseflow supplied rivers. should be the first stage of an investigation. In many cases if there are enough existing data points you can extrapolate a water table with reasonable confidence and also gain understanding of the effects of existing abstractions on the aquifer. In environments without too much abstraction a good conceptual model of groundwater flow, coupled with estimates of recharge and aquifer properties, can let you 'model' likely water tables with remarkable accuracy.

    If there aren't nearby data points you can consider geophysical methods - Vertical electrical soundings (resistivity or conductivity) can 'see' water tables in intergranular aquifers, but accurate interpretation of the results requires a good knowledge of the geology and water quality, which brings one back to needing existing data points. Resistivity is probably the most widely used geophysical method, partly because it is relatively cheap. More expensive options include seismic methods and ground penetrating radar. In the latter case unless the area of interest is very arid, or the radar is very powerful, it is limited to relatively shallow depths.

    2 Comments

    2. Thank you Mr Andrew McKenzie for your detailed contribution.

      Yes, water table in arid zones are not shallow. Can you shed some light on the seismic method to map underground water table? Resistivity method is comparative. What other approaches can be used if there is no prevailing geological profile for a location?

      1 Comment reply

      1. The water table can act as a seismic reflector, so a shallow seismic reflection survey can be used, but there are a number of limitations to the method - it  needs the water table to lie within a relatively homogeneous stratigraphy, otherwise lithological reflections will make interpretation difficult. Seismic reflection surveys are expensive - in equipment, in data acquisition and in interpretation, and imaging with seismic reflection at depths of < 30 metres gets progressively harder. So it can be done, but whether it's economically worth doing is questionable.

        I think I would sum up as saying that there isn't a single ideal non-invasive method to determine depth to the water table, all (?) geophysical methods require interpretation within a geological context.  It's fairly rare for there not to be some data from a borehole or well in a similar geological and topographic context, even if not in the same location, and it's probably more valuable to make a real effort to find pre-existing data or survey existing water points than to conduct speculative geophysical surveys without geological context. If it truly is an 'unexplored' area, at some early stage it will be necessary to drill an exploration borehole to prove the lithological sequence, aquifer properties and water quality At which point you have the opportunity to design and calibrate an appropriate geophysical survey.

         

  4. I can help you i.e. I'm involved in an innovation that detects 3D water till 10 km depth. If you can provide me more details I will bring you in contact.

    1 Comment

    1. Thanks you Mr Nico. Will the 3D model be derived differently from the article referred by Mr Tom Jenkins above? It will help but I am more curious about extracting distinct transition water table signatures. 

  5. Happy new year!

    There are some solutions for it, but very rare to find professionals who will tell you the truths. Field visit are mandatory, the correct interpretation of drilling reports, alternated water-well production rate descriptions.  

    You may get more information by somebody who is in charge about it since 3 decades now.

     

    info@wewaco.com

     

    Regards

     

    Ulf

  7. In the search for  groundwater, what is basic is the knowledge of the prevailing  geology.This is the controlling factor that determines the feasibility of the water project and not the level of water in the hole when there is no pumping or by free flow.This applies any where whether in the arid zone or otherwise.The issue of water level comes in when the borehole is constructed assuming is not a free flow one,to give an estimation of the available column of water at that point in time that in turn guides you in selecting a submersible pump that may be alright for the safe operation of the water scheme.

    1 Comment

    1. Thank you Mr Fidelis. I am curious deriving table depth signatures. Is it possible to derive distinct transition signatures assuming you have the vertical geological data? What is the best method or approach to map the water table?