I have an Electrical Geophysical field trip tomorrow, and can you imagine, I am here and trust me, it helped a lot to understand the practical knowledge and I'll let you know tomorrow, how it goes. Thanks a bunch for this beautiful lecture.
Hi Deepak, glad you found it useful! What I have seen over the years is that some people misuse geophysics as a silver bullet, and are not honest about its strengths, and more importantly its limitations. This is mostly for monetary gain... All the best, Andreas
Hi George, thanks for your kind words! You are welcome to share my videos on your social networks. Many of the views nowadays are coming from links outside of UA-cam. All the best, Andreas
Good creation of 3D images in our mind, that means saved permanantly in our mind. Thankyou verymuch for practically field setup of what we actually need for this survey.
Thanks for your kind words! Yes, the old fashioned tools never go out of fashion, and often better and more reliable especially in remote areas. All the best, Andreas
Awesome video, Im currently studying for the FG ASBOG exam and I was thinking how I am going to retain all of this information and not get confused. This is what I came up with to remember the arrays. For Wenner: I think We in Wenner, We all move together and for Schlumberger: I think Im standing in the middle and the burger I want is far from me or moving away from me, if I lose the burger's signal, I gotta go chase it lol.
Thank you so lot for offering such wonderful explanation and visuals! It was easy to understand even for Architect like me ! My question is, Are you offering consultations?, Our project is in Syria and it will positively help 4 million needed people there
Thanks for your kind words Tareq! I'm a freelance consultant, so always interested in new projects, but at the moment I'am fully booked till well into 2024. All the best, Andreas
Hi Andreas, an excellent presentation and helped my a lot to understand the VES ! I want to build an automated machine that can take all measurements and give a final graph for the survey, your support is highly appreciated. Please, I have some questions about the resistivity surveys : 1-If I want to survey both desert (dry sand) and Wetland area to find (cavitations & metal) what is the best method I can use (Schlumberger array or wenner array) to detect it is depth, and it is size ? Note: the required depth is 5 meters and higher up to 30, 40 meter 2- What is the type of current is used (DC or AC), what is the range for each (Voltage & Amp) min & max ? 3-How we can determine the suitable setting for both current and voltage for different lands? 4-As per your explanation on the above video, what I understand we can determine the depth for each layer by it is resistivity. My question, if the inspected land is the same resistance (Symmetrical) like desert, how can I determine the Layers from the required object from the resistant reading? 5-The distance between the AB is determined the depth of the layer or not? What I see in the video when the distant between the AB is increase the current is going deeper , in this case we need to rise the current or not ? 6-During survey process do we change the voltage & Amp setting or keep it constant, if we change it how we put the correct values? Waiting for your Kind reply Thank
Hi Abdelrahman, Sorry I don't know enough about the physics of how resistivity meters are built to be able to advise you. Perhaps you can have a look online at some existing equipment and download their manuals for a better understanding. However, if you are looking for cavities, resistivity surveys will not help you. You need to use radar or microgravity. "Metal" may be detected best with a magnetometer or maybe EM. Good luck & all the best, Andreas
Thanks for this great video that clears all the concepts regarding ERS. Could you please record a video for IP survey using Dipole-Dipole and Pole Dipole Arrays. It would be very helpful
You are welcome Yasir! Sorry, I have never used IP for groundwater exploration surveys, only for mineral exploration in Ireland, so I am not an expert. All the best, Andreas
Yes, I am asking for mineral exploration. It's okay, but if you have any material regarding the IP, then please share the links with me, which might be helpful for me. Thanks
Sorry I am not up to date with IP. Some links: www.gfinstruments.cz/version_cz/downloads/ARES_Short_guide_Res_IP_Water_survey%202019-01-16.pdf hendragrandis.wordpress.com/wp-content/uploads/2008/03/electrical_surveying_ip.pdf
Sir Could you please cover all hydrogeology theory and as possible as practical videos also sir Your videos are very help for financial backwards students sir like me We except more more video in hydrogeology sir Thanks for you sir 🙏🙏🙏 🎉
First and foremost, I want to express my immense gratitude for your excellent-quality videos that are incredibly enriching. They serve as a valuable source of knowledge and inspiration, and I am truly grateful for the time and effort you put into creating and sharing them. Your work makes a significant and positive impact, and I wanted to express my appreciation and admiration. Keep up the fantastic work! I am in search of a Chinese equivalent to the ERT Syscal R1 system with 60 or 72 electrodes, suitable for agricultural water drilling exploration up to depths of 120 meters. Since the Syscal model is beyond my budget, I am exploring more affordable Chinese alternatives. Could you provide any advice or recommendations on available models that would meet my requirements in terms of performance and cost-effectiveness? I appreciate any information or suggestions you can offer. Best regards,
Thanks so much for your kind words. It means a lot to me!!! Regarding your equipment, my first question is do you really need to do resistivity imaging for your groundwater exploration? It is not just the equipment which is expensive. A multi core cable costs something like 25000 euros the last time I looked. It would be far cheaper to get a standard resistivity meter, and use it in profiling mode to find anomalies and then get more information using VES at specific locations. All the cables and electrodes can be made and repaired locally. This is the technology I am describing in this video. Also, sorry I don’t know any Chinese equipment, and as a rule I don’t recommend any particular supplier. Simple resistivity gear is quite affordable, if you consider the cost of drilling unsuccessful water wells. All the best, Andreas
I wish to express my profound gratitude for your insightful advice regarding groundwater exploration. Your recommendation to employ a more cost-effective approach for identifying potential drilling areas is enlightening and perfectly aligns with my needs. Your suggestion to start with anomaly detection using an affordable resistivity device seems like a very wise strategy. This would allow us to pinpoint areas of interest without immediately incurring significant costs. Following this, employing a Vertical Electrical Sounding (VES) system to ascertain the depth and quality of the identified aquifers appears to be both an effective and economical method. I fully understand that, despite the advantages of Electrical Resistivity Tomography (ERT) systems in terms of detail and coverage, their high cost does not necessarily fit the requirements of my project. Your advice to opt for more accessible solutions tailored to my specific needs is invaluable. I am currently researching and inquiring about the various resistivity devices available in the market. I am also consulting with suppliers and geophysical experts to find the most suitable equipment for my objectives. Thank you once again for your expertise and wise recommendations. Your pragmatic approach provides me with invaluable guidance for my research and investments, allowing me to proceed in a strategic and thoughtful manner. Sincerely,@@GeosearchInternational
Resistivity imaging or ERT is suitable for highly detailed studies like looking for the leachate plume from a landfill, or mapping the route of a tunnel. It has been used for mapping faults, but I have also managed that quite well using low cost resistivity traverses and VES. Which country / aquifer type are you planning to explore? Wish you best of luck looking for equipment. Another advice - try to rent the equipment before you buy it. Also renting is often cheaper than owning geophysical equipment, unless you have many months of work lined up for it. All the best, Andreas
Thank you for your insightful advice on groundwater prospecting techniques. I am currently involved in a project in Morocco, where we are facing unique challenges due to the particularly hard and dry nature of the soil. This geological specificity makes aquifer detection more complex and necessitates specially adapted equipment. We plan to probe aquifers at depths ranging from 30 to 150 meters, sometimes even deeper. Although ERT is appealing for its ability to cover vast areas, we have taken your recommendations into account and are now considering the use of a Resistivity Meter for rapid anomaly detection. This method seems ideal for the initial phase of our project, allowing for effective exploration despite the challenging soil conditions. For depth verification, we will use Vertical Electrical Sounding (VES). This combination of methods should enable us to accurately locate potential water drilling sites, while considering the challenges posed by the Moroccan soil. Regarding the acquisition of equipment, although renting is an interesting option, our need for regular use leads us towards purchasing. We are currently exploring available options to acquire equipment that can efficiently operate in the arid and compact conditions typical of Moroccan soil. Thank you again for your support and valuable advice, which have been a great help in refining our prospecting strategy. Sincerely,@@GeosearchInternational
Hi, I was born in Morocco so it always has a special place in my heart! ERT is actually very slow in dry environments as you need to set up all the electrodes and make sure that you have contact everywhere before you can start. I used it in Mali a couple of years ago, and it took about two hours just to set up one 600m profile. The best technique I have used in the desert is TDEM (time domain electro magnetic survey) as you induce the currents rather than having to inject them via electrodes. It works best in areas without any human activities - power cables and water pipes cause lots of interference. It is quite expensive, but very fast on flat terrain. For resistivity surveys, remember that you will need an AB of at least 3x the anticipated penetration depth. 150m means 450m+, so better budget with at least 600m of cables. To get through hard soil, go for rebars and sledge hammers and lots of salty water for better contact. I'm planning to make a video about this, but no time... All the best, Andreas
Thank you sir for your time and updating and sharing your knowledge with amazing of clear presentations. I'm Geologist I've got full information and practical about hydrology . So I want to start my own company for water survey . So You are an expert in this field and you have worked in many countries for many years. I would like to ask you to advise me on the following: 1-Which equipment for Groundwater exploration would you pointed to me? 2- through my little understanding about equipments I intrested to [River G water Detector] which attracted me, would advise me to use ? I would look forward to hearing from you ASAP . Thank you sir.
Hi Liban, Looking for groundwater using geophysics is something I have done for many years, in particular during the five years I spent in Oman & the UAE. Here is my advice: 1) I do not promote any particular manufacturer. I think it is best to use equipment from a manufacturer who has a representative in your country or region of the world. When it breaks down you will need someone who can get you the spare parts and/or repair it for you. If you watch my videos on resistivity surveys, you will see that it is not really important to have the latest/most expensive equipment. Even simple, old equipment can give excellent results if the operator knows what to do. 2) Regarding buying of equipment, I do not advise it as the first step. If you are just starting the business you should rent the equipment or work together with a contractor who already owns some equipment. Once your business is successful - and my definition of this is that you have at least 6 months worth of work lined up - then you can consider buying equipment. 3) Regarding River G water detector - there are often claims about magic equipment which can detect groundwater 1000s of metres away. What you need to look for is what part of physics it is relying on. If that is not clearly explained in the brochure, assume that it is a fake. If they do present some obscure theoretical approach which has never been proven in practise by scientific papers, not the claims of the manufacturer - also assume that it is a fake. In any case, if you are looking to make a business you will need to provide proven technology or else your business will soon close down. Remember that there is no free lunch & there is no simple way to find groundwater. All the best, Andreas
Hello sir is their any complete course offered on Hydrogeologist and any suggest books please sir Your explaination is extraordinary ways I loved it sir keep explain all remaining topics sir please
Hi Sardar, I have not seen any good free hydrogeology courses. That is the reason why I am making my videos. One resource you should look at is the groundwater project: gw-project.org where you can find many free books for download. All the best, Andreas
@@GeosearchInternational sir atleast make complete videos how Bore pointing in the field sir Like Schlumberger array method use take reading than after how to make points or location identify and said to farmers air
I would pick the season when the climate is the best, because it is difficult to work in the heat. During the monsoon your work will be interrupted by rain/thunder, so I guess the post-monsoon would be the best time. There is also the issue of the soil. If it is already wet, the current can enter more easily. However that can be mitigated by pouring water on the electrodes. All the best, Andreas
I have been doing hundreds of resistivity soundings in undulating hard rock terraines in South India for many years,and most time I don't get perfect VES curves all the time! I don't think it's because I am not doing the survey wrong.
Hi Shajan, in hard rock areas the horizontal layered earth assumptions will not always apply so your measured VES curves can deviate from the model. In fact sometimes it will be almost impossible to fit a model to the data. However the curves should still be smooth. If you take each reading 3x without averaging & it always comes up with the same number then your data is good. Most VES I have seen which are noisy is just because the operators don't follow this simple approach. All the best, Andreas
Dear Andreas, Thanks a lot for explaining the concept very well, useful. I have used master curves to find out the resistivity and thickness of layers. Please guide on groundwater modelling. Thanks, Shiv Pratap
You are welcome Shiv. Groundwater modelling is only needed if you want to do very detailed investigations like designing a wellfield, where the manual calculations would take too much time. Mostly, you can understand groundwater using conceptual models & Darcy's law. So my advice is to not use models until you are very experienced in hydrogeology, and then also only if you absolutely have to. Usually it is more cost effective to hire a professional groundwater modeller who has specialised in this field. All the best, Andreas
Hi Anwar, Saline groundwater has a higher conductivity - ie lower resistivity than fresh groundwater. A higher clay content has the same effect, so you need to be careful with the interpretation and it is always good to have calibration wells. I have used resistivity surveys to map the fresh - saline interface in coastal aquifers. The change in resistivity is really clear. Usually the currents don’t penetrate much into/below saline groundwater so it may affect the depth of investigation. All the best, Andreas
Good question! The reason is that we are trying to inject current into the ground and about 90% of the total resistance is between the electrodes and the soil. Adding water and also salt (1kg/20L) reduces this contact resistance so more current can get into the ground and we have a stronger signal to measure at the potential electrodes, which also need some water. All the best, Andreas
Hi Attaur Rahman, My knowledge is mostly via more experienced geophysicists and several years of field geophysical surveys for groundwater exploration. I always found the books to be very theoretical but not so useful for field surveys. I think there are already some books on geophysics in the Groundwater Project, but not sure if it's about conventional geophysical surveys. Have a look at: gw-project.org/books/?_books_categories_facet_filter=investigation-techniques I'm planning a new video on field techniques for resistivity surveys... but am very busy. All the best, Andreas
In the link I sent you I saw a book on geophysical borehole logging. There is also a book by the IAH which can be downloaded free: iah.org/wp-content/uploads/2013/03/IAHbook_ICH9.zip
Hi Rathna, that is an important question. First of all why would you be doing groundwater exploration in a hilly area? If you are looking for alluvium aquifers, they would be located in the valleys which should be flat enough for a resistivity survey. If you are looking for fractures, they should be preferentially weathered and eroded - i.e., also located in the valleys. In the hills I would concentrate my efforts on mapping of springs, and seeing how to use them for water supply. The better exposure of the geology should also help you to map any aquifers, and their thicknesses using conventional geological mapping supported by remote sensing. Also, there tends to be higher precipitation in hilly areas so roof rainwater harvesting could be feasible. As for the resistivity survey itself, it should be carried out over flat ground. If you have a special type of project like doing a geoelectrical survey over a future tunnel, then you should use resistivity imaging, and survey in all your electrode locations and elevations in order to do a 2D or even 3D inversion of the data. Note that resistivity imaging is a much more costly type of survey, and I would only recommend it for specific projects. All the best, Andreas
Hi Rathna, it sounds more like a geotechnical investigation so the resistivity method described in my video would not be recommended. All the best, Andreas
Hi Claudio, the number of VES you do depends on how much time/money you have. You can always start with a few and then add more in between them later if you see a lot of variations between them. For the interpretation you can interpolate key data in QGIS (e.g., depth to base of aquifer, aquifer resistivity) or just do sections - it depends on what you want to show. All the best, Andreas
Sir, it was very concisely and well explained as a summary.. Sir I have a couple of doubts:- a) Sir, why does it become difficult to measure the voltage difference when the space between the potential electrodes are kept small while the current electrode spacings are increased b) why does a layer of infinite resistance has a curve of maximum 45 degrees and not more than that? Sir, have you made any videos on TDEM surveys as you had mentioned at te end of the videos, (used in Groundwater and contamination exploration).. if so please provide a link...Thank you
Dear Aniket, thanks for your questions! a) As the current electrodes are moved further apart (AB), the current will penetrate deeper into the earth. That means that less current will pass between the potential electrodes (MN), so the voltage difference between them becomes less and less as we increase AB spacing. When the voltage reading becomes too small, noise starts to take over and our reading becomes useless. When you plot the apparent resistivity, it will suddenly change up or down from the smooth line we expect. To increase the voltage, the first thing to do is to try to increase the amount of current being injected at A & B. For example, adding more salty water to the electrodes or hammering them deeper. If that does not work, we have to increase the MN spacing. When the potential electrodes are further apart, the voltage difference between them will be greater because of the larger distance, and also as they will be more influenced by the part of the current which is going deeper into the earth. A bigger MN means a deeper measurement. b) Sorry, I forgot where I put the reference about the 45 degree slope for infinite resistivity, but it is something I have observed many times in hard rock terrain & also you can try it your self by having a look at the effect of high resitivities. Above 10000 ohm-m the line is 45 degrees and does not become any steeper. c) Sorry, I have not made any TDEM videos. I have used it a lot in the Middle East and it is an excellent tool for the desert, but I don't promote it as it is expensive, more complicated to use and there are many problems with anthropogenic interference in urban areas. Also in agricultural areas like in Afghanistan it will be much easier to pull a vertical line along the edge of a field than to lay out a square loop. All the best, Andreas
Hi Aniket, I recommend the work of M.H. Loke. You can find papers, notes and other resources at Geotomo Software: www.geotomosoft.com/downloads.php Scroll down to the middle of the page. You can also use the demo version of RES2DINV to make some nice sections if you have standard resistivity profiling data, or a line of VES. All the best, Andreas
From ( 19:39 minutes ). The length shown in the figure and you say we get it from From Baseline survey How did this happen? What is the meaning of Baseline survey? Thanks Andreas.
Hi Bassem, Before we start doing geophysics we need to carry out a desk study (look at previous reports) and also carry out a baseline survey (field visit & check existing wells). If we don't do this the results of the geophysical survey can be interpreted in the wrong way. Check out my video on groundwater exploration strategy: ua-cam.com/video/3c0iPjM65JU/v-deo.html All the best, Andreas
Hi Shiv, As a rule of thumb your AB spacing should be at least 3x your depth of investigation. However depth of investigation also depends a lot on the resistivities of the different layers. Please have look at my GeoVES video: ua-cam.com/video/EN0-Fhan3fs/v-deo.html All the best, Andreas
Thanks so much, it was clear and informative. Excuse me, I inquire about the application of EM concerning groundwater exploration, you mentioned the TDEM method (Did you create a video about it) or any other useful material for that?
You are welcome Ahmed, sorry I have not yet made any videos about TDEM. It is more complicated to use than resistivity surveys, but the results are similar for the interpretation. TDEM is best in desert areas without any human interference - no cables, pipelines etc or the noise will be too high. All the best, Andreas
Hi Andreas, I am an engineering student part of a university team helping a charity in South Africa improve water access by researching and designing low-cost geophysical survey equipment. We are in the early stages of the project, but a simple resistivity survey seems the clear choice for us at the moment and I have some questions about the process. From hydrogeological maps and borehole logs we know groundwater in the area occurs in fractures in the crystalline basement rock (granite). With this in mind, how would you conduct the geophysical survey to identify the location of major fractures to know where to drill? In a previous video you mention a productive borehole in northern Mali you drilled by finding a regional fracture - is this a similar geological context, and how did you go about finding this fracture? In this geology, would it still be appropriate to complete a resistivity profile by moving the whole electrode setup to many points over a long distance, and then doing a VES at the lowest apparent resistivity ‘anomaly’ to determine the depth that you should drill to? From what I have learned, VES can produce inaccurate data when there are non-horizontal structures in the sub-surface - is this a problem in this fractured geological context? Also, what factors affect: (1) the spacing of electrodes when measuring points for the resistivity profile, and (2) the distance between each measurement on the profile (resolution)? I apologise for any misconceptions and misunderstandings, as engineers we are very new to this, and your videos have been an extremely useful introduction to hydrogeology! Thanks :)
Hi Harry, I have been planning a new video about the practical side of resistivity surveys, so thanks for your questions! Resistivity equipment: I'm sure that you can get the right design together. The best I have ever seen was made at a University in Switzerland - I think it was Laussane. They had a battery box where I had to connect many 9V batteries together. Light weight & very powerful. Survey equipment: For the VES - I recommend 4 reels so 1 team can already lay out the next VES sounding while you are busy with the current one. For the potential electrodes it is good to have stainless steel, or I have also used copper electrodes in Ghana. For the current electrodes I usually use 1m rebar and sledgehammers. Also, you need shovels & water in jerry cans (1kg salt/20L for best results). It is good to mark the cables at set distances (1,2 or 3 marks) to avoid mistakes on the ground. See link to field sheets below. For the resistivity traversing you need to make a dedicated traversing cable. This contains cables for the current and potential electrodes set up so that at each reading location (say every 10 m) you will make two readings - say AB/2 of 80m & 30m. The MN/2 = 5m for both readings. That means that you collect two data points AB = 160m & 60m. Take 1/3 as the measurement depth and you will be looking at 20m and 50m. After you measure these two points, the whole traversing cable moves forward 10 metres, and you take the next two readings. It is very fast. All the cables should be inside a heat shrink, so they don't get tangled up. You need to look at the depth to bedrock in your area before you design the AB/2 distances. What is important is that both AB/2 should be divisible by 10, so that the field team can hammer in the current electrodes in advance so that you can quickly move along the profile. Groundwater exploration: Please have a look at my video on the groundwater exploration strategy. You need to do a desk study & baseline survey of existing wells before you do any geophysics. Best if you team up with a hydrogeologist - there are many good ones in South Africa. For exploring fracture aquifers like a granite, you first need to think about long term sustainability. Basically, you want to drill into a fracture that is connected up with as many other fractures as possible, so you don't just end up draining a bathtub. From air photos and satellite images you can look for lineations, and select those that are in the right direction. Some fractures are better for high yielding wells than others - something to find out from the desk study. Also, you need to consider where the groundwater recharge is coming from. Sometimes you can target a fracture that is intersecting a wetland or other surface water course, so if you pump from that well it will draw in surface water (induced recharge). In all cases you should check the available recharge area upstream of the target location. It should be enough to sustain the well. There is no point drilling a well at the top of a hill, for example. So you need to do a water balance check. Let’s say that you have selected a good lineation and it’s quite long (kms?) and you are happy with the recharge area or other sources of water to sustain the well. Now you need to find the fracture on the ground. You should be able to find it quite accurately from air photos, but you need to do resistivity traversing at 90 degrees to the fracture to locate it exactly. I would always do at least 3 traverses - the more the better, let’s say one every hundred metres. You need to put in wooden pegs with numbers to find the correct place later - don't rely on GPS. From the resistivity profile (one shallow and one deep value) you can see where the weathered zone is the thickest. Granite has a high resistivity, so you will be looking for the widest and strongest low resistivity anomaly. Depending on the shape of the anomaly you may be able to see which way the fracture is dipping. So you want to drill down dip of the deepest weathered zone - ie not necessarily in the centre of the anomaly. Once you have found an interesting location, you want to know how deep the basement is. This will help to plan the well depth. That is the only function of the VES. Another, less know advantage is that with a VES you can also positively identify fractures. There will be a horizontal offset in the VES curve at the depth where the fracture occurs. VES assumes a horizontal layered earth, so that can mess things up. Normally I would do two VES at 90 degrees to each other to be really sure. If there is no time, just do one parallel to the fracture. In all cases you want to locate two separate drill sites. If the first one is not successful, the rig tries the second one. Even if you do everything right, there is no guarantee that you will have a successful well. From the desk study you should be able to get an idea about success rates. To do a good field survey, it is really important to not only record, but also plot all data in the field. This applies to the resistivity profile and the VES. That way you can see straight away if there is a bad data point. I always make 3 separate readings & never take averages. If the readings are not stable - hammer the electrodes deeper & add more salty water. Resistivity surveys are perfect tools to find groundwater. I have also done more advanced surveys using resistivity imaging, but it does not really improve the number of positive wells. It is far more important to have a good conceptual model of the hydrogeology. In all this we have not thought about groundwater quality, but that is just as important. There is no point in drilling wells that can become contaminated from e.g. landfills or graveyards. So as part of the baseline survey of the area you need to identify possible pollution sources, and drill upstream of them. I would never drill a well close to latrines, landfills etc especially in a fracture aquifer. In conclusion, there are many things to consider, and it takes several years to train a good groundwater exploration hydrogeologist. The most important thing is to think critically. Good luck & all the best, Andreas PDF Schlumberger VES Fieldsheet: bit.ly/3ziyeql XLSX Schlumberger VES Fieldsheet: bit.ly/3IXCDT2
@@GeosearchInternational Hi Andreas, I'm another student working in the team with Harry. Your videos and responses have been really helpful in guiding our development - THANK YOU :) I have a few questions about the surveying process that I'd be very grateful if you could guide me on, if have the time/are willing to do so? My current understanding of the process is that its undertaken by a team of 5, with one team member on each electrode and the hydrogeologist in the center with the battery and resistivity meter. Is this correct? How long are the electrodes typically? How deep are they inserted? (We've read that inserting them 50% deeper results in a 40% reduction in Ground resistance) Are they always extracted after use? - if so, what method is used to do this? Do you feel the extraction process could be improved with a crowbar-like tool? We're based in the UK so have been unable to test the time taken to hammer in electrodes into dried/hardened soil (Thanks to some very persistent rain :) ). What percentage of the Res surveying process would you say is taken up by inserting, removing and handling the electrodes? How much saltwater is typically poured on each electrode? What is the typical mass of one of the VES cable spools? My current understanding of the process is that its very labor intensive, how is the equipment currently transported when profiling? We have been planning to develop a small golf push cart device to aid with transporting the water, electrodes, cables drums, batteries and resistivity device. I'd be really interested to hear your thoughts as to how valuable an addition to the process it could be? The idea being that it could also be used as a tool to help insert and extract electrodes at a faster rate Any help would be really appreciated, Best Wishes, Dani
@@DaniLipscombe Thanks for your message. Some comments below: Team: Yes 1 geophysicist at the centre & 4 field staff - one for each electrode. All the equipment is in the centre: resistivity meter, batteries, the 4 reels (2 for current & two for potential), sunshade, chair, cool box with drinking water/food & extra water for the electrodes, first aid, etc So the field staff just pull out the cables, & hammer in the electrodes & carry a small jerry can of salty water with them. Electrode length: I normally use steel rebars from construction sites for the current electrodes & stainless steel or copper for the potential electrodes. Current electrodes can be 1 metre long. You will also need some small sledgehammers to hammer them in & shovels to make the holes. You hammer them in as deep as they will go. 90% of resistance to getting current into the ground is at the electrodes. Extracting electrodes: To get them out you just hit them from the side & then wiggle them out. No need for any special equipment. If you are doing a VES, then after each successful reading they will be moved to the next location. If you are doing a resistivity traverse, they can stay for a while until the profile cable has moved on & they are no longer needed. ie you will need a larger number of electrodes. Time requirement: setting out the equipment takes most of the time in any survey. That includes pulling out the cables, getting the electrodes into the ground, waiting for the salty water to soak in, hitting them in further if there is too much contact resistance… all that is like 90% of the work. The geophysicist at the centre just pushes the button 3x & takes the reading/plots the data which is the easy work. The most important task is the field team and their motivation to do quite hard physical labour. Also don't forget that they need to collect all the equipment together at the end. 20 Litres of salty water should be enough for one VES. The idea is just to get the contact between the electrode and the ground wet, so you just need one or two cups worth. I guess it depends on the soil type. If it more permeable it may need more water. Weight of reel: depends on how much cable is on it. Sorry I forget the exact weight as I usually have other people to carry them. Transport during profiling: everything needs to be carried, so it’s best to make a dedicated profiling cable which can be pulled along the profile. So you just park your 4x4 at the end of the profile, unload everything do the profile & then pick it up at the other end. Golf pushcart: I would not bother. The terrain can be very rugged, so it is likely to get stuck/break. It is best to carry things by hand. If necessary, just employ more field staff. As I said, extracting electrodes is easy. The hard work is to hammer them into the ground. I suggest that you get a local geophysicist to show you how a resistivity survey goes. It is a practical skill, so just writing about it like I’m trying to do here may miss out some important issues. Good luck & all the best, Andreas
@@GeosearchInternational Thanks Andreas, Thats really useful information. I've got a few more follow up questions if you’d be willing to provide some additional assistance? You mention that 90% of the resistance of injecting current into the ground is at the electrodes, Are you aware of any research into optimizing's the design of the electrodes to reduce this? (I understand that for a cost effective system rebar is fine - but if money weren't a factor and they were being electrically optimised would the design be different than a standard rod?) Are you aware of any more advanced methods of inserting the electrodes beyond hammering? How is the profiling line kept straight across a 2km profile? I assume that for the VES 1/2 long sections of measuring tape are laid out and used by the team? I'm trying to make a time and motion study of the surveying process, do you have any footage of a survey taking place that I could potentially study? (We're trying to arrange a visit with a local geophysicist but have so far been unable to do so). It would also be really interesting if you had any images/videos of work done in sub-saharan Africa so we could get a better understanding of the terrain. If the geologist replaced one of the team on the potential electrodes and all other cables were drawn out from this position could the team numbers be reduced by one? Do you feel the nature of the current workflow, with large weights that need transporting by hand and very manual electrode insertion prevents women in the communities from being able to work in the team? Thanks again, Best Wishes, Dani
Hi Dani, Electrode design: of course, there are better electrodes. If you buy them, you may well end up with 60cm stainless steel electrodes. But that will not last long if you are working in the bush with a team of workers who may change all the time. For these conditions you need robust equipment which is as simple and as cheap as possible. You need to be able to find it and repair it in Africa. So, my advice is that you just make the resistivity meter at your university & then go to the country where you intend to work & make everything else there. That way it will be sustainable, rather than a white elephant. Advanced methods for inserting electrodes: why make life more complicated than it is? All you need is a shovel, a hammer, and some salty water. This has worked for >50 years. Complicated solutions cost more money, break easily and are not sustainable. Keeping profile lines straight: Unless you are working in the desert, most of the areas where the fractures are or where wells will be sustainable are covered in dense vegetation. That means that lines need to be cut through the bush before any geophysics begins. The start/end of the lines can be decided in advance using satellite / aerial images so to find the start you would just look for the GPS waypoint. Of course, they may decide to move the lines depending on conditions on the ground. Perhaps there is a maize field in the way which you don't want to cut down etc. The line cutters can work by GPS or more usually just using a compass. They will insert a numbered peg every 10 metres to locate the survey. For the distance all you need is a piece of rope that has the distances marked. No need for expensive measuring tape that may get torn in the bush. Pictures & videos: sorry I cannot help you. All locations are different & you need an experienced local geophysicist to work with. Also, if you have no experience, I advise you to be very careful. If you don't know an area, you will not see those snakes. Reducing the team: Why would you want to reduce the number of field staff? You need a minimum of four for the profiles anyway if you want to move fast. Also, this is a way to give people employment. The field staff are the cheapest expense of any survey, and they are the most critical. If you want to save money, just insist that the village who will benefit from the survey should provide workers as their contribution to the project. In any case they should pay for at least 5-10% of the costs/provide services in kind or there will be no ownership/sustainability of the project. Field team: All members of the field team need to be physically fit & be able to walk in straight line on a compass bearing. That is the nature of the business. If you want to have a winning football team, you will also pick the best players. The work is not hard because you need to carry some equipment. It is hard because you will spend the whole day in the hot sunshine, walking through the bush. The point of the exercise is to find water for the whole community, which includes women, children, the old, sick and handicapped. Some women are tougher than the men in Africa, but that is not the reason why I have never seen them on a geophysical team. There are social reasons why certain tasks are done by certain people. The field team is selected by the geophysicist & it is best to let them chose who they want to work with. All the best, Andreas
Dear Andreas, thanks for your videos. I want to request you some help with VES survey. I have some experience in well-developed soils zones but in the last four months, I have changed the study area. The stratigraphy is generally composed of 5 meters of dry gravel/boulders (without matrix), 3 meters of fresh water and then saline waters. Since I started to collect VES here, I cant get nice curves. They are all like your last slide "Garbage. Send the geophysicist back to the field". I have probed with different types of equipment, wires, arrays, electrode materials, DC current, AC current, different potentials, limited current, unlimited current, I have wettened the electrodes, etc. I cant get nice curves. Do you have any tips to solve this situation? It is driving me crazy. Thank you very much.
Hi! Thanks for your message. Sounds like you are either not getting enough current into the ground, or there is a problem with the equipment. The first thing I would do is to check that the equipment is working OK. Maybe you have a calibration box that comes with the gear? Or just make a sounding near your office where you know that it will work. If all is OK, then it's probably a resistance problem between your electrodes and the dry gravels you mentioned. Dig a hole for each electrode - say 0.5 metres deep, and then hammer in your electrodes as deep as they will go. In this kind of terrain I would use strong steel bars, say 1 metre long. Fill up the hole with salty water (1 kg of salt / 20 Lites of water). Wait a few minutes. When the water has drained away, add more salty water, and see how much current you can get into the ground. You should repeat each reading three times and if the three readings are not similar - add more water/hammer the electrodes deeper. Let me know how it goes! All the best, Andreas
@@GeosearchInternational Dear Andreas. We follow your recommendations. We begin by validating the equipment and continue with the detailed field procedure. Evidently, there was a contact problem between the gravel and the electrodes. We dug a hole, buried thick and long electrodes, used saline solution, and finally, we got the curves with very good values and fits!!!! Thank you so much for your help, it was extremely useful. All the best
That is wonderful news! So happy that it worked. Contact resistance at the ground surface is often a challenge, along with interference from human sources. All the best, Andreas
Hi John, you can see my e-mail in the About - Details section. However, for any questions related to these videos it is better to exchange comments here, so that other people may also benefit from them. All the best, Andreas
Hi Mohammed, for the resistivity method you need four electrodes. Two current electrodes to measure the current, and two potential electrodes to measure the voltage. For groundwater exploration I recommend that you only use the Schlumberger array. All the best, Andreas
Hi Kabeer, magnetotellurics has been around for over 50 years, and is used mostly for deep exploration for oil, gas and geothermal energy. I have not used it for groundwater exploration. All the best, Andreas
@@GeosearchInternational thankyou Andreas, we have just tried that equipment for locating potential ground water exploration studies for some agriculturists and it's results till date are upto expectations 👍
Hi @chingikz13 Please have a look at the groundwater project website: gw-project.org They are uploading free books all the time, and you can also have a look at their UA-cam channel. All the best, Andreas
It depends how big your voids are, but to find them you need a lot of measurement data. Maybe a 2D resistivity imaging survey would be better. Alternative is a radar survey, microgravity or seismic. All the best, Andreas
Allah God bless you for an excellent tutorial. Somaliland is where many poor communities need your help to get water to feed their children and livestock.
Sorry I don't understand your question. Do you mean how to use a magnetic compass i.e., read the direction in degrees from magnetic North? All the best, Andreas
Hi Andreas, could you perhaps provide me with an average amount of time required for a 300m length vertical electrical sounding survey based on your experience. I can understand the time will vary greatly depending on site conditions etc
Hi Jack, for AB 300m you should be able to do 4 per day. Say 2 hours per VES. It depends mostly on how many field crew you have and how good they are. All the best, Andreas
Hi Jack, if you need 5 minutes per station, it would take you about two days. Don't forget that you will need to clear the profile first & also put some pegs to mark the stations. Do you really need such a long profile? Normally it is better to do 3 separate parallel lines over an area of interest. Also, I would do a pilot project first with your team to get a better idea on time and logistical issue. All the best, Andreas
Hi dear We have problem in abem sas 1000 /4000 ..when we want to convert data from abem to computer, the computer know serial port but don't connect with abem.. please any advice
Hi Youssef! Sounds like a problem with the Utility Software. Have you looked at page 54 of the manual? wwwguidelinegeoc.cdn.triggerfish.cloud/uploads/2018/10/Terrameter-SAS-1000_4000_Manual_Terrameter_GGEO-100049.pdf All the best, Andreas
Good question Osama! The resistivity survey does not tell us anything except how easily the current flows through the ground, so we need to interpret this together with what we know about the aquifer. The geophysical survey needs to be part of a systematic groundwater exploration project, starting with a baseline survey of the project area. Please have a look at my video on groundwater exploration strategy: ua-cam.com/video/3c0iPjM65JU/v-deo.html All the best, Andreas
Hi Naseem, I normally follow this groundwater exploration strategy: ua-cam.com/video/3c0iPjM65JU/v-deo.html It is also useful to have a good knowledge of geology and hydrogeology. All the best, Andreas
A good question Josephine! It is almost impossible to put the electrodes in exactly the same place, so two consecutive surveys will never be exactly the same as there are so many variations in the near-surface resistivity. However, we should get similar results unless there has been an event which has made a dramatic change to the resistivity. e.g., saline intrusion of seawater in coastal aquifers. If we leave the electrodes in the ground permanently we can use them to monitor changes in resistivity. There are systems which will take a measurement automatically at regular intervals. e.g., to monitor leakage of leachate from landfills. All the best, Andreas
Good question Josephine! I think that it depends on how quickly the aquifer thickness and resistivity change over distance, so there is no standard rule. The way to find out is to start off with VES on a big grid, and then add more VES if you start to see big changes between them. It would help to have a good conceptual model of the local geology, so you can predict how uniform the aquifer is likely to be. In most cases what actually controls the number of VES is time and budget, so you just decide what you can pay for and then pick the most important locations for VES in order of priority. All the best, Andreas
Hi Taylor, Great question, and important to think about this very important issue as it will help us in the interpretation of the results. The current is trying to get from A to B along all possible pathways at the same time. If the topsoil was a perfect conductor, I guess most of the current would just flow straight from A to B. In nature we can get this effect if we have a good linear conductor like pipeline or a fence between A and B which lets a lot of the current "short circuit" between them, so we need to be careful in urban areas. In the real world the topsoil is quite resistive, so most of the current needs to first go deeper into the ground before it can find a route back to the other electrode. The amount of current which can flow along a horizontal layer is controlled by the resistivity and thickness of that layer. So let's say we have a 5-metre thick conductor between 10 - 15 m depth. Any current which reaches that depth will try to use this layer to get to the other current electrode. The amount of current which can flow along this layer will be controlled by Ohm's Law, so unless the layer is very thick or has a very low resistivity not all the current can flow along it. The remaining current will first have to go deeper to find other pathways to reach the current electrode. In general, the current will try to get through resistive layer as fast as possible, so it flows +/- vertically through resistors and then +/- horizontally along conductors. In 3D, the current field looks like a half-sphere, as the current will not only flow downwards, but also around the direct line between A & B. We have to be careful when there are very good conductors in the ground, as the current may not get through them and therefore the earth beneath them ends up being "invisible" to the resistivity survey. I mentioned the interference from pipelines in urban areas. Another one is saline groundwater - for example the fresh-salt water interface near the sea, and also thick clay layers. The "depth of investigation" is determined not just by the A-B spacing, but a lot by the geology and hydrogeology of the sub-surface. I hope that answers your question. It may be easier to see some computer animations, but unfortunate all I have are the figures which are in the video. All the best, Andreas
The current will flow from A to B or from B to A, depending on which is positive. Current flows from the positive to the negative electrode. I guess it will try to flow in the direct route, and then expand outwards and downwards in whatever direction it encounters the least resistance. All the best, Andreas
Hi Salahuddin, You have to be careful with the terminology. Yes, electrons flow from negative to positive and that is called electron current. However, "Conventional current" or simply current flow is from positive to negative. This is just a convention that is followed for historical reasons, and it does not affect any calculations. Check out: web.engr.oregonstate.edu/~traylor/ece112/beamer_lectures/elect_flow_vs_conv_I.pdf en.wikipedia.org/wiki/Electrical_polarity
Hello sir Thank you for this excellent explanation I would like to know if the location of the underground caves and fissures is possible. How do I do that please
You are welcome نور نور ! For fissures/fractures you need to look for regional lineations on air photos or satellite images, followed by resistivity traverses to locate them on the ground. This is just a bit of hard work. However I think you are asking about looking for caves and fractures in a karstic aquifer e.g., limestone. It is possible, but quite expensive and time consuming. If the cave/cavity is large enough it will cause a gravity anomaly at the surface, which you may be able to pick up with a micro-gravity survey. Another exploration method would be 2D resistivity imaging surveys, or the kind of seismic imaging surveys normally done in the petroleum industry. These are all very expensive and you need to be careful about the depth of investigation. Some years ago I was involved with a GPR (radar) survey on a motorway in the Middle East to look for what had caused a sinkhole which had swallowed up seven cars. We could not find any other cavities, so we drilled several boreholes into and around the collapsed zone. It turned out that the cavity in the limestone was actually at about 20 m depth - so way below the depth of investigation of our survey. The cause of the collapse was dewatering of the aquifer by a building site nearby, so the solution was to better manage any dewatering operations in the future - e.g., to re-inject the water to maintain groundwater heads near sensitive infrastructure like the motorway. So to summarise - a difficult challenge & you need to think carefully about your conceptual hydrogeological model of the area and carry out some pilot studies before you commit to a larger project. All the best, Andreas
Hello Andreas Thank you for your video I would like to get an equipment to start a new project and if you could recommend me one I would really appreciate for your help This project is about to make a VES in a river bank which has an approximately 50m of depth. Kind regards Luisin
Hi Luisin, Sorry I cannot recommend any particular equipment supplier, but normally I would only buy geophysical equipment if I had a lot of work lined up for it (like 6 months worth). If it is just for one project it is normally better to either rent the equipment or hire someone who has it. If you do decide to buy, then the key criteria should be that the equipment supplier has a representative in your region or country who can fix it if there is a breakdown. Sending equipment internationally can be expensive and also waste a lot of time. Good luck with your project and all the best, Andreas
@@GeosearchInternational Thank you Andreas for your feedback Could you tell me according yours experiences, which equipment/brands/models, you can feel more comfortable working with Thanks a lot for your help Kind regards
Hi @@luisingeovanny, in my opinion the most important issue is after sales service and the ease of carrying out maintenance/repairs. I don't have any preference. In fact the best equipment I have worked with was some "home made" gear from a Swiss university & I also saw some excellent, simple and robust equipment in India and Iran where you would not recognise the brand name. Just try it out first by renting/borrowing. All the best, Andreas
It depends on the depth of investigation. Please see my video on GeoVES: ua-cam.com/video/EN0-Fhan3fs/v-deo.html If you download the Excel tool, there is an example of MN & AB spacings. All the best, Andreas
There are two things we need to estimate: 1) the amount of groundwater in storage which we can pump during the dry part of the year - before the wet season when there is groundwater recharge, and 2) the amount of groundwater recharge that will replenish the aquifer. There has to be a balance between recharge and discharge, otherwise the groundwater in storage will be depleted. The best way is to monitor as many wells as possible. If there is a balance between recharge and discharge you should see annual fluctuations in groundwater levels but no overall decline. Please watch some of the other videos in the Hydrogeology 101 playlist. All the best, Andreas
Sorry, I don't have time to respond to emails, but you are welcome to leave a message here. If you have a question about my videos I will try to answer as best as I can. All the best, Andreas
@@GeosearchInternational Thank you so much. I really love your videos. I just want to ask if there would be a higher possibility of groundwater in a marshland area? If yes, how would it affect the expected yield? Thank you!
Hi Eric, ultrasound frequencies are made for medical imaging. They have poor depth penetration, so would not be much use for groundwater exploration. We can use seismic surveys, for example refraction seismic, to find the thickness of gravels. However, resistivity surveys have been very popular because they are fast and cheap. Also you can easily pick up clay and saline layers, both of which are not good for productive aquifers. All the best, Andreas
I have an Electrical Geophysical field trip tomorrow, and can you imagine, I am here and trust me, it helped a lot to understand the practical knowledge and I'll let you know tomorrow, how it goes. Thanks a bunch for this beautiful lecture.
Hi Akash, thanks so much for your kind words & good luck with your field trip! All the best, Andreas
you are such a wonderful soul, I really appreciate your work. please don't stop you are an inspiration.
Thank you, I will! All the best, Andreas
Thank you sir for your simple and clear explanations, it helped me immensely with understanding the basics of VES surveys..
You are most welcome Rifiqi! All the best, Andreas
Your presentation effectively sheds light on one of the most misunderstood subjects.
Hi Deepak, glad you found it useful! What I have seen over the years is that some people misuse geophysics as a silver bullet, and are not honest about its strengths, and more importantly its limitations. This is mostly for monetary gain... All the best, Andreas
the best presentation i have found online. thankyou for your work, sir.
You are most welcome Lalduhawma! All the best, Andreas
Hi Andreas, an excellent presentation and the graphics are superb! This should be required viewing for all hydrogeologists.
Hi George, thanks for your kind words! You are welcome to share my videos on your social networks. Many of the views nowadays are coming from links outside of UA-cam. All the best, Andreas
This is a great video. Really learned a lot as an entry level hydrogeologist.
Glad you liked it Patricia! All the best, Andreas
This is pure gold. I am translating technical dcouments and needed to get a better understanding of the process. Thank you!!!!
You are welcome Mariana! All the best, Andreas
Good creation of 3D images in our mind, that means saved permanantly in our mind. Thankyou verymuch for practically field setup of what we actually need for this survey.
You are most welcome Afzal! All the best, Andreas
It's very effective for me and clear all my doubts. Thank you Sir.
You are most welcome Subhasmita! All the best, Andreas
Thank you for clear explanation. it's really seldom to find explanation manner like this ... Thanks again a lot
You are most welcome Saqer! All the best, Andreas
Sir learning a lots of things from your videos respects from Afghanistan
You are most welcome! All the best, Andreas
very good, an appreciable true method and true instruments for groundwater Exploration
Thanks for your kind words! Yes, the old fashioned tools never go out of fashion, and often better and more reliable especially in remote areas. All the best, Andreas
Thanks for such a wonderful explanation 😊
You are welcome abhishek! All the best, Andreas
I love your teaching very much sir and videos animation which perfect to sink in field areas sir
Thanks and welcome Satheesh! All the best, Andreas
Awesome video, Im currently studying for the FG ASBOG exam and I was thinking how I am going to retain all of this information and not get confused. This is what I came up with to remember the arrays. For Wenner: I think We in Wenner, We all move together and for Schlumberger: I think Im standing in the middle and the burger I want is far from me or moving away from me, if I lose the burger's signal, I gotta go chase it lol.
I like your memory stories. The funnier they are, the easiest you will remember them. Good luck with your exams and all the best, Andreas
Great explanation..completely understood..Thank u so much SIR
You are most welcome Shubham! All the best, Andreas
Thank you so lot for offering such wonderful explanation and visuals! It was easy to understand even for Architect like me !
My question is, Are you offering consultations?, Our project is in Syria and it will positively help 4 million needed people there
Thanks for your kind words Tareq! I'm a freelance consultant, so always interested in new projects, but at the moment I'am fully booked till well into 2024. All the best, Andreas
Excellent enjoyed very much - thanks
You are welcome Ali! All the best, Andreas
amazing explanation and visuals, thank you sooo much!
You're very welcome! All the best, Andreas
Thanks for sharing and I am so lucky to catch this video.🙏
My pleasure Sophia, All the best, Andreas
this is simple and clear sir. thank you
You are welcome Victor! All the best, Andreas
Would love to see a video about, "how to use a terrameter ?"
Hi Farhan, sorry I don't have time to make such a video at the moment. Hope you find a suitable one on UA-cam. All the best, Andreas
Great Job Sir, a very useful video with a nice presentation. good luck to you.
Thank you Eng. Lalzada! All the best, Andreas
thank you sir for the free benefit and appreciating this kind of paying
You are welcome Xirsi! All the best, Andreas
Great. Excellent presentation. Keep it up Sir.🙏
Thank you, I will! All the best, Andreas
Thanks a lot for sharing such a valuable lecture ❤
You are welcome Hakmatyar! all the best, Andreas
Hi Andreas, an excellent presentation and helped my a lot to understand the VES !
I want to build an automated machine that can take all measurements and give a final graph for the survey, your support is highly appreciated.
Please, I have some questions about the resistivity surveys :
1-If I want to survey both desert (dry sand) and Wetland area to find (cavitations & metal) what is the best method I can use (Schlumberger array or wenner array) to detect it is depth, and it is size ?
Note: the required depth is 5 meters and higher up to 30, 40 meter
2- What is the type of current is used (DC or AC), what is the range for each (Voltage & Amp) min & max ?
3-How we can determine the suitable setting for both current and voltage for different lands?
4-As per your explanation on the above video, what I understand we can determine the depth for each layer by it is resistivity.
My question, if the inspected land is the same resistance (Symmetrical) like desert, how can I determine the Layers from the required object from the resistant reading?
5-The distance between the AB is determined the depth of the layer or not?
What I see in the video when the distant between the AB is increase the current is going deeper , in this case we need to rise the current or not ?
6-During survey process do we change the voltage & Amp setting or keep it constant, if we change it how we put the correct values?
Waiting for your Kind reply
Thank
Hi Abdelrahman, Sorry I don't know enough about the physics of how resistivity meters are built to be able to advise you. Perhaps you can have a look online at some existing equipment and download their manuals for a better understanding. However, if you are looking for cavities, resistivity surveys will not help you. You need to use radar or microgravity. "Metal" may be detected best with a magnetometer or maybe EM. Good luck & all the best, Andreas
This is such a very good video and explanation is crystal clear ❤❤ i love it. Looking forward to watch other videos of you
Glad you liked it Dirceu! All the best, Andreas
100% you given good information us for research purpose. Thanks
Thanks and welcome! All the best, Andreas
This was very informative just did a revision of my hydrogeology ⚡🤓
Glad you found it useful Emma! All the best, Andreas
Thanks for this great video that clears all the concepts regarding ERS. Could you please record a video for IP survey using Dipole-Dipole and Pole Dipole Arrays. It would be very helpful
You are welcome Yasir! Sorry, I have never used IP for groundwater exploration surveys, only for mineral exploration in Ireland, so I am not an expert. All the best, Andreas
Yes, I am asking for mineral exploration. It's okay, but if you have any material regarding the IP, then please share the links with me, which might be helpful for me. Thanks
Sorry I am not up to date with IP. Some links:
www.gfinstruments.cz/version_cz/downloads/ARES_Short_guide_Res_IP_Water_survey%202019-01-16.pdf
hendragrandis.wordpress.com/wp-content/uploads/2008/03/electrical_surveying_ip.pdf
very good presentation!!! Hi from Greece...
Thanks Bill! All the best, Andreas
This was a great presentation
Thanks John! All the best, Andreas
Thank you sir for clear explaination. 👍
You are welcome Abdikadir! All the best, Andreas
Sir
Could you please cover all hydrogeology theory and as possible as practical videos also sir
Your videos are very help for financial backwards students sir like me
We except more more video in hydrogeology sir
Thanks for you sir 🙏🙏🙏 🎉
I will try my best Satheesh! All the best, Andreas
Perfect research 👌
So nice of you Eng. Ruhullah! All the best, Andreas
i will really appreciate your efforts
It's my pleasure Eng. Jawid! All the best, Andreas
Very nice and interesting learning video
Many many thanks Eng. Fayez! All the best, Andreas
Thanks a lot for sharing this great informations
You are welcome Kam! All the best, Andreas
Very nice geophysic class professor, thanks from Venezuela
You are welcome Manuel, All the best from Jordan, Andreas
Thank you sir for your explanation
You are most welcome Eng. Mohamad! All the best, Andreas
very exciting lectures
Thank you Arif! All the best, Andreas
It is really excellent explanation. Even better than our user manual of our IP resistivity meter.😂
Glad it was helpful Sophia! All the best, Andreas
First and foremost, I want to express my immense gratitude for your excellent-quality videos that are incredibly enriching. They serve as a valuable source of knowledge and inspiration, and I am truly grateful for the time and effort you put into creating and sharing them. Your work makes a significant and positive impact, and I wanted to express my appreciation and admiration. Keep up the fantastic work!
I am in search of a Chinese equivalent to the ERT Syscal R1 system with 60 or 72 electrodes, suitable for agricultural water drilling exploration up to depths of 120 meters. Since the Syscal model is beyond my budget, I am exploring more affordable Chinese alternatives. Could you provide any advice or recommendations on available models that would meet my requirements in terms of performance and cost-effectiveness? I appreciate any information or suggestions you can offer.
Best regards,
Thanks so much for your kind words. It means a lot to me!!! Regarding your equipment, my first question is do you really need to do resistivity imaging for your groundwater exploration? It is not just the equipment which is expensive. A multi core cable costs something like 25000 euros the last time I looked. It would be far cheaper to get a standard resistivity meter, and use it in profiling mode to find anomalies and then get more information using VES at specific locations. All the cables and electrodes can be made and repaired locally. This is the technology I am describing in this video. Also, sorry I don’t know any Chinese equipment, and as a rule I don’t recommend any particular supplier. Simple resistivity gear is quite affordable, if you consider the cost of drilling unsuccessful water wells. All the best, Andreas
I wish to express my profound gratitude for your insightful advice regarding groundwater exploration. Your recommendation to employ a more cost-effective approach for identifying potential drilling areas is enlightening and perfectly aligns with my needs.
Your suggestion to start with anomaly detection using an affordable resistivity device seems like a very wise strategy. This would allow us to pinpoint areas of interest without immediately incurring significant costs. Following this, employing a Vertical Electrical Sounding (VES) system to ascertain the depth and quality of the identified aquifers appears to be both an effective and economical method.
I fully understand that, despite the advantages of Electrical Resistivity Tomography (ERT) systems in terms of detail and coverage, their high cost does not necessarily fit the requirements of my project. Your advice to opt for more accessible solutions tailored to my specific needs is invaluable.
I am currently researching and inquiring about the various resistivity devices available in the market. I am also consulting with suppliers and geophysical experts to find the most suitable equipment for my objectives.
Thank you once again for your expertise and wise recommendations. Your pragmatic approach provides me with invaluable guidance for my research and investments, allowing me to proceed in a strategic and thoughtful manner.
Sincerely,@@GeosearchInternational
Resistivity imaging or ERT is suitable for highly detailed studies like looking for the leachate plume from a landfill, or mapping the route of a tunnel. It has been used for mapping faults, but I have also managed that quite well using low cost resistivity traverses and VES. Which country / aquifer type are you planning to explore? Wish you best of luck looking for equipment. Another advice - try to rent the equipment before you buy it. Also renting is often cheaper than owning geophysical equipment, unless you have many months of work lined up for it. All the best, Andreas
Thank you for your insightful advice on groundwater prospecting techniques. I am currently involved in a project in Morocco, where we are facing unique challenges due to the particularly hard and dry nature of the soil. This geological specificity makes aquifer detection more complex and necessitates specially adapted equipment.
We plan to probe aquifers at depths ranging from 30 to 150 meters, sometimes even deeper. Although ERT is appealing for its ability to cover vast areas, we have taken your recommendations into account and are now considering the use of a Resistivity Meter for rapid anomaly detection. This method seems ideal for the initial phase of our project, allowing for effective exploration despite the challenging soil conditions.
For depth verification, we will use Vertical Electrical Sounding (VES). This combination of methods should enable us to accurately locate potential water drilling sites, while considering the challenges posed by the Moroccan soil.
Regarding the acquisition of equipment, although renting is an interesting option, our need for regular use leads us towards purchasing. We are currently exploring available options to acquire equipment that can efficiently operate in the arid and compact conditions typical of Moroccan soil.
Thank you again for your support and valuable advice, which have been a great help in refining our prospecting strategy.
Sincerely,@@GeosearchInternational
Hi, I was born in Morocco so it always has a special place in my heart!
ERT is actually very slow in dry environments as you need to set up all the electrodes and make sure that you have contact everywhere before you can start. I used it in Mali a couple of years ago, and it took about two hours just to set up one 600m profile.
The best technique I have used in the desert is TDEM (time domain electro magnetic survey) as you induce the currents rather than having to inject them via electrodes. It works best in areas without any human activities - power cables and water pipes cause lots of interference. It is quite expensive, but very fast on flat terrain.
For resistivity surveys, remember that you will need an AB of at least 3x the anticipated penetration depth. 150m means 450m+, so better budget with at least 600m of cables. To get through hard soil, go for rebars and sledge hammers and lots of salty water for better contact. I'm planning to make a video about this, but no time... All the best, Andreas
Thank you sir for your time and updating and sharing your knowledge with amazing of clear presentations.
I'm Geologist I've got full information and practical about hydrology .
So I want to start my own company for water survey .
So You are an expert in this field and you have worked in many countries for many years. I would like to ask you to advise me on the following:
1-Which equipment for Groundwater exploration would you pointed to me?
2- through my little understanding about equipments I intrested to [River G water Detector] which attracted me, would advise me to use ?
I would look forward to hearing from you ASAP .
Thank you sir.
Hi Liban, Looking for groundwater using geophysics is something I have done for many years, in particular during the five years I spent in Oman & the UAE. Here is my advice:
1) I do not promote any particular manufacturer. I think it is best to use equipment from a manufacturer who has a representative in your country or region of the world. When it breaks down you will need someone who can get you the spare parts and/or repair it for you. If you watch my videos on resistivity surveys, you will see that it is not really important to have the latest/most expensive equipment. Even simple, old equipment can give excellent results if the operator knows what to do.
2) Regarding buying of equipment, I do not advise it as the first step. If you are just starting the business you should rent the equipment or work together with a contractor who already owns some equipment. Once your business is successful - and my definition of this is that you have at least 6 months worth of work lined up - then you can consider buying equipment.
3) Regarding River G water detector - there are often claims about magic equipment which can detect groundwater 1000s of metres away. What you need to look for is what part of physics it is relying on. If that is not clearly explained in the brochure, assume that it is a fake. If they do present some obscure theoretical approach which has never been proven in practise by scientific papers, not the claims of the manufacturer - also assume that it is a fake. In any case, if you are looking to make a business you will need to provide proven technology or else your business will soon close down. Remember that there is no free lunch & there is no simple way to find groundwater. All the best, Andreas
Waaaw You've expanded my horizon.
I appreciate your Golden advice.!!!
Thank you sir for your support.
Hi Liban, You are most welcome! All the best, Andreas
This video is simple to understand and please. What year was this video uploaded as I want to reference it on my research work?
Hi Inodu, The video was uploaded on March 18th 2021.
Link to UA-cam Video: ua-cam.com/video/MvOR4xY1Mb8/v-deo.html
All the best, Andreas
Hello sir is their any complete course offered on Hydrogeologist and any suggest books please sir
Your explaination is extraordinary ways I loved it sir keep explain all remaining topics sir please
Hi Sardar, I have not seen any good free hydrogeology courses. That is the reason why I am making my videos. One resource you should look at is the groundwater project: gw-project.org where you can find many free books for download. All the best, Andreas
@@GeosearchInternational sir atleast make complete videos how Bore pointing in the field sir
Like Schlumberger array method use take reading than after how to make points or location identify and said to farmers air
Very helpful thank you
You are welcome Nadia! all the best, Andreas
What is the best season to do the resistivity survey?
Is it pre monsoon, monsoon or post monsoon?
I would pick the season when the climate is the best, because it is difficult to work in the heat. During the monsoon your work will be interrupted by rain/thunder, so I guess the post-monsoon would be the best time. There is also the issue of the soil. If it is already wet, the current can enter more easily. However that can be mitigated by pouring water on the electrodes. All the best, Andreas
I have been doing hundreds of resistivity soundings in undulating hard rock terraines in South India for many years,and most time I don't get perfect VES curves all the time! I don't think it's because I am not doing the survey wrong.
Hi Shajan, in hard rock areas the horizontal layered earth assumptions will not always apply so your measured VES curves can deviate from the model. In fact sometimes it will be almost impossible to fit a model to the data. However the curves should still be smooth. If you take each reading 3x without averaging & it always comes up with the same number then your data is good. Most VES I have seen which are noisy is just because the operators don't follow this simple approach. All the best, Andreas
Its remarkable video....
Glad you like it Vivek, All the best, Andreas
Dear Andreas, Thanks a lot for explaining the concept very well, useful. I have used master curves to find out the resistivity and thickness of layers. Please guide on groundwater modelling. Thanks, Shiv Pratap
You are welcome Shiv. Groundwater modelling is only needed if you want to do very detailed investigations like designing a wellfield, where the manual calculations would take too much time. Mostly, you can understand groundwater using conceptual models & Darcy's law. So my advice is to not use models until you are very experienced in hydrogeology, and then also only if you absolutely have to. Usually it is more cost effective to hire a professional groundwater modeller who has specialised in this field. All the best, Andreas
Excellent content. How do saline aquifers affect the data readings in your experience? How to go about this survey in such cases?
Hi Anwar, Saline groundwater has a higher conductivity - ie lower resistivity than fresh groundwater. A higher clay content has the same effect, so you need to be careful with the interpretation and it is always good to have calibration wells. I have used resistivity surveys to map the fresh - saline interface in coastal aquifers. The change in resistivity is really clear. Usually the currents don’t penetrate much into/below saline groundwater so it may affect the depth of investigation. All the best, Andreas
Thank you for sharing your invaluable experience, Andreas.
@@anwarmaqsood9764 you are welcome! All the best, Andreas
best video on resistivity. sir why do we need water for the electrodes?
Good question! The reason is that we are trying to inject current into the ground and about 90% of the total resistance is between the electrodes and the soil. Adding water and also salt (1kg/20L) reduces this contact resistance so more current can get into the ground and we have a stronger signal to measure at the potential electrodes, which also need some water. All the best, Andreas
Thank you sir
Welcome! All the best, Andreas
Thank you very much,sir.
You are most welcome Farhad! All the best, Andreas
Great presentation. Can you please suggest reference books to study it more. Thanks.
Hi Attaur Rahman, My knowledge is mostly via more experienced geophysicists and several years of field geophysical surveys for groundwater exploration. I always found the books to be very theoretical but not so useful for field surveys. I think there are already some books on geophysics in the Groundwater Project, but not sure if it's about conventional geophysical surveys. Have a look at:
gw-project.org/books/?_books_categories_facet_filter=investigation-techniques
I'm planning a new video on field techniques for resistivity surveys... but am very busy. All the best, Andreas
@@GeosearchInternational many thanks. Please do share some stuff on bore well logging as well.
In the link I sent you I saw a book on geophysical borehole logging. There is also a book by the IAH which can be downloaded free: iah.org/wp-content/uploads/2013/03/IAHbook_ICH9.zip
How to do this in hilly area's
Hi Rathna, that is an important question. First of all why would you be doing groundwater exploration in a hilly area? If you are looking for alluvium aquifers, they would be located in the valleys which should be flat enough for a resistivity survey. If you are looking for fractures, they should be preferentially weathered and eroded - i.e., also located in the valleys. In the hills I would concentrate my efforts on mapping of springs, and seeing how to use them for water supply. The better exposure of the geology should also help you to map any aquifers, and their thicknesses using conventional geological mapping supported by remote sensing. Also, there tends to be higher precipitation in hilly areas so roof rainwater harvesting could be feasible.
As for the resistivity survey itself, it should be carried out over flat ground. If you have a special type of project like doing a geoelectrical survey over a future tunnel, then you should use resistivity imaging, and survey in all your electrode locations and elevations in order to do a 2D or even 3D inversion of the data. Note that resistivity imaging is a much more costly type of survey, and I would only recommend it for specific projects.
All the best, Andreas
@@GeosearchInternational geophysical investigations in hilly area not for ground water but to align the water conductor systems in power projects
Hi Rathna, it sounds more like a geotechnical investigation so the resistivity method described in my video would not be recommended. All the best, Andreas
@@GeosearchInternational okay sir noted
Welcome @@rathnakumarv3956 all the best, Andreas
Great analysis
Thank you Meta! I like your Ethiopian music. All the best, Andreas
@@GeosearchInternational thank you Andreas
Welcome! All the best, Andreas
Thank you very much sir.
Most welcome Naresh,
All the best, Andreas
Thank your and appreciate you.
You are most welcome Birhan! All the best, Andreas
Nice impormative, just a question how interpolate all made station
exp. 100 hectars i do 50 ves all over it? Thank you Sir..
Hi Claudio, the number of VES you do depends on how much time/money you have. You can always start with a few and then add more in between them later if you see a lot of variations between them. For the interpretation you can interpolate key data in QGIS (e.g., depth to base of aquifer, aquifer resistivity) or just do sections - it depends on what you want to show. All the best, Andreas
thanks sir very useful
Most welcome Eng. Hamadullah! All the best, Andreas
Sir, it was very concisely and well explained as a summary..
Sir I have a couple of doubts:-
a) Sir, why does it become difficult to measure the voltage difference when the space between the potential electrodes are kept small while the current electrode spacings are increased
b) why does a layer of infinite resistance has a curve of maximum 45 degrees and not more than that?
Sir, have you made any videos on TDEM surveys as you had mentioned at te end of the videos, (used in Groundwater and contamination exploration).. if so please provide a link...Thank you
Dear Aniket, thanks for your questions!
a) As the current electrodes are moved further apart (AB), the current will penetrate deeper into the earth. That means that less current will pass between the potential electrodes (MN), so the voltage difference between them becomes less and less as we increase AB spacing. When the voltage reading becomes too small, noise starts to take over and our reading becomes useless. When you plot the apparent resistivity, it will suddenly change up or down from the smooth line we expect. To increase the voltage, the first thing to do is to try to increase the amount of current being injected at A & B. For example, adding more salty water to the electrodes or hammering them deeper. If that does not work, we have to increase the MN spacing. When the potential electrodes are further apart, the voltage difference between them will be greater because of the larger distance, and also as they will be more influenced by the part of the current which is going deeper into the earth. A bigger MN means a deeper measurement.
b) Sorry, I forgot where I put the reference about the 45 degree slope for infinite resistivity, but it is something I have observed many times in hard rock terrain & also you can try it your self by having a look at the effect of high resitivities. Above 10000 ohm-m the line is 45 degrees and does not become any steeper.
c) Sorry, I have not made any TDEM videos. I have used it a lot in the Middle East and it is an excellent tool for the desert, but I don't promote it as it is expensive, more complicated to use and there are many problems with anthropogenic interference in urban areas. Also in agricultural areas like in Afghanistan it will be much easier to pull a vertical line along the edge of a field than to lay out a square loop.
All the best, Andreas
@@GeosearchInternational Thank you Sir..
Sir can you refer to me some.. videos/links of ERT survey techniques and inversion?
Hi Aniket, I recommend the work of M.H. Loke. You can find papers, notes and other resources at Geotomo Software: www.geotomosoft.com/downloads.php
Scroll down to the middle of the page. You can also use the demo version of RES2DINV to make some nice sections if you have standard resistivity profiling data, or a line of VES.
All the best, Andreas
Thanks a lot
You are welcome Resol! All the best, Andreas
From ( 19:39 minutes ).
The length shown in the figure and you say we get it from From Baseline survey How did this happen?
What is the meaning of Baseline survey?
Thanks Andreas.
Hi Bassem, Before we start doing geophysics we need to carry out a desk study (look at previous reports) and also carry out a baseline survey (field visit & check existing wells). If we don't do this the results of the geophysical survey can be interpreted in the wrong way. Check out my video on groundwater exploration strategy: ua-cam.com/video/3c0iPjM65JU/v-deo.html
All the best, Andreas
How can resistivity scanning can help manage fracking juice dispersement.
Sorry I do not understand your question. All the best, Andreas
Please suggest maximum depth which can be obtained by horizontal resistivity profiling and station arrangement ?
Hi Shiv, As a rule of thumb your AB spacing should be at least 3x your depth of investigation. However depth of investigation also depends a lot on the resistivities of the different layers. Please have look at my GeoVES video: ua-cam.com/video/EN0-Fhan3fs/v-deo.html
All the best, Andreas
Very nice
Thanks Asadullah! All the best, Andreas
Thank you Sir
Most welcome Mohammed,
All the best, Andreas
Thanks so much, it was clear and informative. Excuse me, I inquire about the application of EM concerning groundwater exploration, you mentioned the TDEM method (Did you create a video about it) or any other useful material for that?
You are welcome Ahmed, sorry I have not yet made any videos about TDEM. It is more complicated to use than resistivity surveys, but the results are similar for the interpretation. TDEM is best in desert areas without any human interference - no cables, pipelines etc or the noise will be too high. All the best, Andreas
Hi Andreas, I am an engineering student part of a university team helping a charity in South Africa improve water access by researching and designing low-cost geophysical survey equipment. We are in the early stages of the project, but a simple resistivity survey seems the clear choice for us at the moment and I have some questions about the process.
From hydrogeological maps and borehole logs we know groundwater in the area occurs in fractures in the crystalline basement rock (granite). With this in mind, how would you conduct the geophysical survey to identify the location of major fractures to know where to drill? In a previous video you mention a productive borehole in northern Mali you drilled by finding a regional fracture - is this a similar geological context, and how did you go about finding this fracture?
In this geology, would it still be appropriate to complete a resistivity profile by moving the whole electrode setup to many points over a long distance, and then doing a VES at the lowest apparent resistivity ‘anomaly’ to determine the depth that you should drill to?
From what I have learned, VES can produce inaccurate data when there are non-horizontal structures in the sub-surface - is this a problem in this fractured geological context?
Also, what factors affect: (1) the spacing of electrodes when measuring points for the resistivity profile, and (2) the distance between each measurement on the profile (resolution)?
I apologise for any misconceptions and misunderstandings, as engineers we are very new to this, and your videos have been an extremely useful introduction to hydrogeology! Thanks :)
Hi Harry, I have been planning a new video about the practical side of resistivity surveys, so thanks for your questions!
Resistivity equipment: I'm sure that you can get the right design together. The best I have ever seen was made at a University in Switzerland - I think it was Laussane. They had a battery box where I had to connect many 9V batteries together. Light weight & very powerful.
Survey equipment: For the VES - I recommend 4 reels so 1 team can already lay out the next VES sounding while you are busy with the current one. For the potential electrodes it is good to have stainless steel, or I have also used copper electrodes in Ghana. For the current electrodes I usually use 1m rebar and sledgehammers. Also, you need shovels & water in jerry cans (1kg salt/20L for best results). It is good to mark the cables at set distances (1,2 or 3 marks) to avoid mistakes on the ground. See link to field sheets below.
For the resistivity traversing you need to make a dedicated traversing cable. This contains cables for the current and potential electrodes set up so that at each reading location (say every 10 m) you will make two readings - say AB/2 of 80m & 30m. The MN/2 = 5m for both readings. That means that you collect two data points AB = 160m & 60m. Take 1/3 as the measurement depth and you will be looking at 20m and 50m. After you measure these two points, the whole traversing cable moves forward 10 metres, and you take the next two readings. It is very fast. All the cables should be inside a heat shrink, so they don't get tangled up. You need to look at the depth to bedrock in your area before you design the AB/2 distances. What is important is that both AB/2 should be divisible by 10, so that the field team can hammer in the current electrodes in advance so that you can quickly move along the profile.
Groundwater exploration: Please have a look at my video on the groundwater exploration strategy. You need to do a desk study & baseline survey of existing wells before you do any geophysics. Best if you team up with a hydrogeologist - there are many good ones in South Africa. For exploring fracture aquifers like a granite, you first need to think about long term sustainability. Basically, you want to drill into a fracture that is connected up with as many other fractures as possible, so you don't just end up draining a bathtub. From air photos and satellite images you can look for lineations, and select those that are in the right direction. Some fractures are better for high yielding wells than others - something to find out from the desk study. Also, you need to consider where the groundwater recharge is coming from. Sometimes you can target a fracture that is intersecting a wetland or other surface water course, so if you pump from that well it will draw in surface water (induced recharge). In all cases you should check the available recharge area upstream of the target location. It should be enough to sustain the well. There is no point drilling a well at the top of a hill, for example. So you need to do a water balance check.
Let’s say that you have selected a good lineation and it’s quite long (kms?) and you are happy with the recharge area or other sources of water to sustain the well. Now you need to find the fracture on the ground. You should be able to find it quite accurately from air photos, but you need to do resistivity traversing at 90 degrees to the fracture to locate it exactly. I would always do at least 3 traverses - the more the better, let’s say one every hundred metres. You need to put in wooden pegs with numbers to find the correct place later - don't rely on GPS. From the resistivity profile (one shallow and one deep value) you can see where the weathered zone is the thickest. Granite has a high resistivity, so you will be looking for the widest and strongest low resistivity anomaly. Depending on the shape of the anomaly you may be able to see which way the fracture is dipping. So you want to drill down dip of the deepest weathered zone - ie not necessarily in the centre of the anomaly.
Once you have found an interesting location, you want to know how deep the basement is. This will help to plan the well depth. That is the only function of the VES. Another, less know advantage is that with a VES you can also positively identify fractures. There will be a horizontal offset in the VES curve at the depth where the fracture occurs. VES assumes a horizontal layered earth, so that can mess things up. Normally I would do two VES at 90 degrees to each other to be really sure. If there is no time, just do one parallel to the fracture. In all cases you want to locate two separate drill sites. If the first one is not successful, the rig tries the second one. Even if you do everything right, there is no guarantee that you will have a successful well. From the desk study you should be able to get an idea about success rates.
To do a good field survey, it is really important to not only record, but also plot all data in the field. This applies to the resistivity profile and the VES. That way you can see straight away if there is a bad data point. I always make 3 separate readings & never take averages. If the readings are not stable - hammer the electrodes deeper & add more salty water.
Resistivity surveys are perfect tools to find groundwater. I have also done more advanced surveys using resistivity imaging, but it does not really improve the number of positive wells. It is far more important to have a good conceptual model of the hydrogeology. In all this we have not thought about groundwater quality, but that is just as important. There is no point in drilling wells that can become contaminated from e.g. landfills or graveyards. So as part of the baseline survey of the area you need to identify possible pollution sources, and drill upstream of them. I would never drill a well close to latrines, landfills etc especially in a fracture aquifer.
In conclusion, there are many things to consider, and it takes several years to train a good groundwater exploration hydrogeologist. The most important thing is to think critically. Good luck & all the best, Andreas
PDF Schlumberger VES Fieldsheet: bit.ly/3ziyeql
XLSX Schlumberger VES Fieldsheet: bit.ly/3IXCDT2
@@GeosearchInternational Hi Andreas, I'm another student working in the team with Harry. Your videos and responses have been really helpful in guiding our development - THANK YOU :)
I have a few questions about the surveying process that I'd be very grateful if you could guide me on, if have the time/are willing to do so?
My current understanding of the process is that its undertaken by a team of 5, with one team member on each electrode and the hydrogeologist in the center with the battery and resistivity meter. Is this correct?
How long are the electrodes typically? How deep are they inserted? (We've read that inserting them 50% deeper results in a 40% reduction in Ground resistance) Are they always extracted after use? - if so, what method is used to do this? Do you feel the extraction process could be improved with a crowbar-like tool?
We're based in the UK so have been unable to test the time taken to hammer in electrodes into dried/hardened soil (Thanks to some very persistent rain :) ). What percentage of the Res surveying process would you say is taken up by inserting, removing and handling the electrodes?
How much saltwater is typically poured on each electrode?
What is the typical mass of one of the VES cable spools?
My current understanding of the process is that its very labor intensive, how is the equipment currently transported when profiling?
We have been planning to develop a small golf push cart device to aid with transporting the water, electrodes, cables drums, batteries and resistivity device. I'd be really interested to hear your thoughts as to how valuable an addition to the process it could be? The idea being that it could also be used as a tool to help insert and extract electrodes at a faster rate
Any help would be really appreciated,
Best Wishes,
Dani
@@DaniLipscombe Thanks for your message. Some comments below:
Team: Yes 1 geophysicist at the centre & 4 field staff - one for each electrode. All the equipment is in the centre: resistivity meter, batteries, the 4 reels (2 for current & two for potential), sunshade, chair, cool box with drinking water/food & extra water for the electrodes, first aid, etc
So the field staff just pull out the cables, & hammer in the electrodes & carry a small jerry can of salty water with them.
Electrode length: I normally use steel rebars from construction sites for the current electrodes & stainless steel or copper for the potential electrodes. Current electrodes can be 1 metre long. You will also need some small sledgehammers to hammer them in & shovels to make the holes. You hammer them in as deep as they will go. 90% of resistance to getting current into the ground is at the electrodes.
Extracting electrodes: To get them out you just hit them from the side & then wiggle them out. No need for any special equipment. If you are doing a VES, then after each successful reading they will be moved to the next location. If you are doing a resistivity traverse, they can stay for a while until the profile cable has moved on & they are no longer needed.
ie you will need a larger number of electrodes.
Time requirement: setting out the equipment takes most of the time in any survey. That includes pulling out the cables, getting the electrodes into the ground, waiting for the salty water to soak in, hitting them in further if there is too much contact resistance… all that is like 90% of the work. The geophysicist at the centre just pushes the button 3x & takes the reading/plots the data which is the easy work. The most important task is the field team and their motivation to do quite hard physical labour. Also don't forget that they need to collect all the equipment together at the end.
20 Litres of salty water should be enough for one VES. The idea is just to get the contact between the electrode and the ground wet, so you just need one or two cups worth. I guess it depends on the soil type. If it more permeable it may need more water.
Weight of reel: depends on how much cable is on it. Sorry I forget the exact weight as I usually have other people to carry them.
Transport during profiling: everything needs to be carried, so it’s best to make a dedicated profiling cable which can be pulled along the profile. So you just park your 4x4 at the end of the profile, unload everything do the profile & then pick it up at the other end.
Golf pushcart: I would not bother. The terrain can be very rugged, so it is likely to get stuck/break. It is best to carry things by hand. If necessary, just employ more field staff. As I said, extracting electrodes is easy. The hard work is to hammer them into the ground.
I suggest that you get a local geophysicist to show you how a resistivity survey goes. It is a practical skill, so just writing about it like I’m trying to do here may miss out some important issues.
Good luck & all the best, Andreas
@@GeosearchInternational Thanks Andreas,
Thats really useful information. I've got a few more follow up questions if you’d be willing to provide some additional assistance?
You mention that 90% of the resistance of injecting current into the ground is at the electrodes, Are you aware of any research into optimizing's the design of the electrodes to reduce this? (I understand that for a cost effective system rebar is fine - but if money weren't a factor and they were being electrically optimised would the design be different than a standard rod?)
Are you aware of any more advanced methods of inserting the electrodes beyond hammering?
How is the profiling line kept straight across a 2km profile? I assume that for the VES 1/2 long sections of measuring tape are laid out and used by the team?
I'm trying to make a time and motion study of the surveying process, do you have any footage of a survey taking place that I could potentially study? (We're trying to arrange a visit with a local geophysicist but have so far been unable to do so).
It would also be really interesting if you had any images/videos of work done in sub-saharan Africa so we could get a better understanding of the terrain.
If the geologist replaced one of the team on the potential electrodes and all other cables were drawn out from this position could the team numbers be reduced by one?
Do you feel the nature of the current workflow, with large weights that need transporting by hand and very manual electrode insertion prevents women in the communities from being able to work in the team?
Thanks again,
Best Wishes,
Dani
Hi Dani,
Electrode design: of course, there are better electrodes. If you buy them, you may well end up with 60cm stainless steel electrodes. But that will not last long if you are working in the bush with a team of workers who may change all the time. For these conditions you need robust equipment which is as simple and as cheap as possible. You need to be able to find it and repair it in Africa. So, my advice is that you just make the resistivity meter at your university & then go to the country where you intend to work & make everything else there. That way it will be sustainable, rather than a white elephant.
Advanced methods for inserting electrodes: why make life more complicated than it is? All you need is a shovel, a hammer, and some salty water. This has worked for >50 years. Complicated solutions cost more money, break easily and are not sustainable.
Keeping profile lines straight: Unless you are working in the desert, most of the areas where the fractures are or where wells will be sustainable are covered in dense vegetation. That means that lines need to be cut through the bush before any geophysics begins. The start/end of the lines can be decided in advance using satellite / aerial images so to find the start you would just look for the GPS waypoint. Of course, they may decide to move the lines depending on conditions on the ground. Perhaps there is a maize field in the way which you don't want to cut down etc. The line cutters can work by GPS or more usually just using a compass. They will insert a numbered peg every 10 metres to locate the survey. For the distance all you need is a piece of rope that has the distances marked. No need for expensive measuring tape that may get torn in the bush.
Pictures & videos: sorry I cannot help you. All locations are different & you need an experienced local geophysicist to work with. Also, if you have no experience, I advise you to be very careful. If you don't know an area, you will not see those snakes.
Reducing the team: Why would you want to reduce the number of field staff? You need a minimum of four for the profiles anyway if you want to move fast. Also, this is a way to give people employment. The field staff are the cheapest expense of any survey, and they are the most critical. If you want to save money, just insist that the village who will benefit from the survey should provide workers as their contribution to the project. In any case they should pay for at least 5-10% of the costs/provide services in kind or there will be no ownership/sustainability of the project.
Field team: All members of the field team need to be physically fit & be able to walk in straight line on a compass bearing. That is the nature of the business. If you want to have a winning football team, you will also pick the best players. The work is not hard because you need to carry some equipment. It is hard because you will spend the whole day in the hot sunshine, walking through the bush. The point of the exercise is to find water for the whole community, which includes women, children, the old, sick and handicapped. Some women are tougher than the men in Africa, but that is not the reason why I have never seen them on a geophysical team. There are social reasons why certain tasks are done by certain people. The field team is selected by the geophysicist & it is best to let them chose who they want to work with.
All the best, Andreas
Thankyou,
You're welcome Yusuf! All the best, Andreas
Dear Andreas, thanks for your videos.
I want to request you some help with VES survey. I have some experience in well-developed soils zones but in the last four months, I have changed the study area. The stratigraphy is generally composed of 5 meters of dry gravel/boulders (without matrix), 3 meters of fresh water and then saline waters. Since I started to collect VES here, I cant get nice curves. They are all like your last slide "Garbage. Send the geophysicist back to the field". I have probed with different types of equipment, wires, arrays, electrode materials, DC current, AC current, different potentials, limited current, unlimited current, I have wettened the electrodes, etc. I cant get nice curves. Do you have any tips to solve this situation? It is driving me crazy. Thank you very much.
Hi! Thanks for your message. Sounds like you are either not getting enough current into the ground, or there is a problem with the equipment. The first thing I would do is to check that the equipment is working OK. Maybe you have a calibration box that comes with the gear? Or just make a sounding near your office where you know that it will work.
If all is OK, then it's probably a resistance problem between your electrodes and the dry gravels you mentioned. Dig a hole for each electrode - say 0.5 metres deep, and then hammer in your electrodes as deep as they will go. In this kind of terrain I would use strong steel bars, say 1 metre long. Fill up the hole with salty water (1 kg of salt / 20 Lites of water). Wait a few minutes. When the water has drained away, add more salty water, and see how much current you can get into the ground. You should repeat each reading three times and if the three readings are not similar - add more water/hammer the electrodes deeper. Let me know how it goes! All the best, Andreas
@@GeosearchInternational Dear Andreas.
We follow your recommendations. We begin by validating the equipment and continue with the detailed field procedure. Evidently, there was a contact problem between the gravel and the electrodes. We dug a hole, buried thick and long electrodes, used saline solution, and finally, we got the curves with very good values and fits!!!!
Thank you so much for your help, it was extremely useful.
All the best
That is wonderful news! So happy that it worked. Contact resistance at the ground surface is often a challenge, along with interference from human sources. All the best, Andreas
You did great!
Thanks so much!!! All the best, Andreas
@@GeosearchInternational i am asking for your contacts i really want to get in touch with you.
Hi John, you can see my e-mail in the About - Details section. However, for any questions related to these videos it is better to exchange comments here, so that other people may also benefit from them. All the best, Andreas
Doctor what would be K factor if Iam using just 2 electrode method measure the source voltage and current.
Hi Mohammed, for the resistivity method you need four electrodes. Two current electrodes to measure the current, and two potential electrodes to measure the voltage. For groundwater exploration I recommend that you only use the Schlumberger array. All the best, Andreas
There is another equipment in trend these days. ADMT (audio magneto telluric ) can you please make a vedio for that too
Hi Kabeer, magnetotellurics has been around for over 50 years, and is used mostly for deep exploration for oil, gas and geothermal energy. I have not used it for groundwater exploration. All the best, Andreas
@@GeosearchInternational thankyou Andreas, we have just tried that equipment for locating potential ground water exploration studies for some agriculturists and it's results till date are upto expectations 👍
Thank you very much.
Could you recommend any literature to start learning hydrogeology?
Hi @chingikz13
Please have a look at the groundwater project website: gw-project.org They are uploading free books all the time, and you can also have a look at their UA-cam channel. All the best, Andreas
Can I use earth resistivity measure device for voids ground servay?
It depends how big your voids are, but to find them you need a lot of measurement data. Maybe a 2D resistivity imaging survey would be better. Alternative is a radar survey, microgravity or seismic. All the best, Andreas
@@GeosearchInternational I am very Thanks
You are welcome @kennany8! All the best, Andreas
Allah God bless you for an excellent tutorial. Somaliland is where many poor communities need your help to get water to feed their children and livestock.
Thank you for your kind words. All the best, Andreas
Thankyou❤❤❤
You're welcome Surafel! All the best, Andreas
Govt geologist uses magnetic compass , how they are doing ? Please do one video sir.
Sorry I don't understand your question. Do you mean how to use a magnetic compass i.e., read the direction in degrees from magnetic North? All the best, Andreas
Hi Andreas, could you perhaps provide me with an average amount of time required for a 300m length vertical electrical sounding survey based on your experience. I can understand the time will vary greatly depending on site conditions etc
Hi Jack, for AB 300m you should be able to do 4 per day. Say 2 hours per VES. It depends mostly on how many field crew you have and how good they are. All the best, Andreas
@@GeosearchInternational You are a legend, thank you sir
How long do you reckon a 2km horizontal electrical profile would take, using a separation of 10m? Again a rough estimate is more than helpful
Hi Jack, if you need 5 minutes per station, it would take you about two days. Don't forget that you will need to clear the profile first & also put some pegs to mark the stations. Do you really need such a long profile? Normally it is better to do 3 separate parallel lines over an area of interest. Also, I would do a pilot project first with your team to get a better idea on time and logistical issue. All the best, Andreas
Hi dear
We have problem in abem sas 1000 /4000 ..when we want to convert data from abem to computer, the computer know serial port but don't connect with abem.. please any advice
Hi Youssef! Sounds like a problem with the Utility Software. Have you looked at page 54 of the manual?
wwwguidelinegeoc.cdn.triggerfish.cloud/uploads/2018/10/Terrameter-SAS-1000_4000_Manual_Terrameter_GGEO-100049.pdf All the best, Andreas
thanks for the useful presentation, dear Andreas, how do you know we have water in the aquifer, just by evaluating the readings?
Good question Osama! The resistivity survey does not tell us anything except how easily the current flows through the ground, so we need to interpret this together with what we know about the aquifer. The geophysical survey needs to be part of a systematic groundwater exploration project, starting with a baseline survey of the project area. Please have a look at my video on groundwater exploration strategy: ua-cam.com/video/3c0iPjM65JU/v-deo.html
All the best, Andreas
@@GeosearchInternational thank you so much.
Welcome! all the best, Andreas
How can i identify the location of aquifer Sir
Hi Naseem, I normally follow this groundwater exploration strategy: ua-cam.com/video/3c0iPjM65JU/v-deo.html It is also useful to have a good knowledge of geology and hydrogeology. All the best, Andreas
Can the results of a geo-resistivity survey change from the previously conducted geo-resistivity survey
A good question Josephine! It is almost impossible to put the electrodes in exactly the same place, so two consecutive surveys will never be exactly the same as there are so many variations in the near-surface resistivity. However, we should get similar results unless there has been an event which has made a dramatic change to the resistivity. e.g., saline intrusion of seawater in coastal aquifers.
If we leave the electrodes in the ground permanently we can use them to monitor changes in resistivity. There are systems which will take a measurement automatically at regular intervals. e.g., to monitor leakage of leachate from landfills.
All the best, Andreas
@@GeosearchInternational thank you for your reply
@@GeosearchInternational Is there a standard rule as to how many VES points per area for the purpose of aquifer characterization? Thanks
Welcome! All the best, Andreas
Good question Josephine! I think that it depends on how quickly the aquifer thickness and resistivity change over distance, so there is no standard rule. The way to find out is to start off with VES on a big grid, and then add more VES if you start to see big changes between them. It would help to have a good conceptual model of the local geology, so you can predict how uniform the aquifer is likely to be. In most cases what actually controls the number of VES is time and budget, so you just decide what you can pay for and then pick the most important locations for VES in order of priority. All the best, Andreas
Question, why does the current arc in multiple depths, rather then just travel from electrode A straight to B?
Hi Taylor, Great question, and important to think about this very important issue as it will help us in the interpretation of the results.
The current is trying to get from A to B along all possible pathways at the same time. If the topsoil was a perfect conductor, I guess most of the current would just flow straight from A to B. In nature we can get this effect if we have a good linear conductor like pipeline or a fence between A and B which lets a lot of the current "short circuit" between them, so we need to be careful in urban areas.
In the real world the topsoil is quite resistive, so most of the current needs to first go deeper into the ground before it can find a route back to the other electrode. The amount of current which can flow along a horizontal layer is controlled by the resistivity and thickness of that layer. So let's say we have a 5-metre thick conductor between 10 - 15 m depth. Any current which reaches that depth will try to use this layer to get to the other current electrode. The amount of current which can flow along this layer will be controlled by Ohm's Law, so unless the layer is very thick or has a very low resistivity not all the current can flow along it.
The remaining current will first have to go deeper to find other pathways to reach the current electrode. In general, the current will try to get through resistive layer as fast as possible, so it flows +/- vertically through resistors and then +/- horizontally along conductors.
In 3D, the current field looks like a half-sphere, as the current will not only flow downwards, but also around the direct line between A & B.
We have to be careful when there are very good conductors in the ground, as the current may not get through them and therefore the earth beneath them ends up being "invisible" to the resistivity survey. I mentioned the interference from pipelines in urban areas. Another one is saline groundwater - for example the fresh-salt water interface near the sea, and also thick clay layers. The "depth of investigation" is determined not just by the A-B spacing, but a lot by the geology and hydrogeology of the sub-surface.
I hope that answers your question. It may be easier to see some computer animations, but unfortunate all I have are the figures which are in the video. All the best, Andreas
@@GeosearchInternationalSo the current flows away from A in ANY direction of the half-sphere, also away from B, doesnt it?
The current will flow from A to B or from B to A, depending on which is positive. Current flows from the positive to the negative electrode. I guess it will try to flow in the direct route, and then expand outwards and downwards in whatever direction it encounters the least resistance. All the best, Andreas
@@GeosearchInternational current will always flow from negative towards positive.
Hi Salahuddin, You have to be careful with the terminology. Yes, electrons flow from negative to positive and that is called electron current. However, "Conventional current" or simply current flow is from positive to negative. This is just a convention that is followed for historical reasons, and it does not affect any calculations.
Check out: web.engr.oregonstate.edu/~traylor/ece112/beamer_lectures/elect_flow_vs_conv_I.pdf
en.wikipedia.org/wiki/Electrical_polarity
Hello sir
Thank you for this excellent explanation
I would like to know if the location of the underground caves and fissures is possible. How do I do that please
You are welcome نور نور ! For fissures/fractures you need to look for regional lineations on air photos or satellite images, followed by resistivity traverses to locate them on the ground. This is just a bit of hard work.
However I think you are asking about looking for caves and fractures in a karstic aquifer e.g., limestone. It is possible, but quite expensive and time consuming. If the cave/cavity is large enough it will cause a gravity anomaly at the surface, which you may be able to pick up with a micro-gravity survey. Another exploration method would be 2D resistivity imaging surveys, or the kind of seismic imaging surveys normally done in the petroleum industry. These are all very expensive and you need to be careful about the depth of investigation.
Some years ago I was involved with a GPR (radar) survey on a motorway in the Middle East to look for what had caused a sinkhole which had swallowed up seven cars. We could not find any other cavities, so we drilled several boreholes into and around the collapsed zone. It turned out that the cavity in the limestone was actually at about 20 m depth - so way below the depth of investigation of our survey. The cause of the collapse was dewatering of the aquifer by a building site nearby, so the solution was to better manage any dewatering operations in the future - e.g., to re-inject the water to maintain groundwater heads near sensitive infrastructure like the motorway.
So to summarise - a difficult challenge & you need to think carefully about your conceptual hydrogeological model of the area and carry out some pilot studies before you commit to a larger project. All the best, Andreas
Hello Andreas
Thank you for your video
I would like to get an equipment to start a new project and if you could recommend me one I would really appreciate for your help
This project is about to make a VES in a river bank which has an approximately 50m of depth.
Kind regards
Luisin
Hi Luisin,
Sorry I cannot recommend any particular equipment supplier, but normally I would only buy geophysical equipment if I had a lot of work lined up for it (like 6 months worth). If it is just for one project it is normally better to either rent the equipment or hire someone who has it. If you do decide to buy, then the key criteria should be that the equipment supplier has a representative in your region or country who can fix it if there is a breakdown. Sending equipment internationally can be expensive and also waste a lot of time. Good luck with your project and all the best, Andreas
@@GeosearchInternational
Thank you Andreas for your feedback
Could you tell me according yours experiences, which equipment/brands/models, you can feel more comfortable working with
Thanks a lot for your help
Kind regards
Hi @@luisingeovanny, in my opinion the most important issue is after sales service and the ease of carrying out maintenance/repairs. I don't have any preference. In fact the best equipment I have worked with was some "home made" gear from a Swiss university & I also saw some excellent, simple and robust equipment in India and Iran where you would not recognise the brand name. Just try it out first by renting/borrowing. All the best, Andreas
Whats the usual spacing between electrodes
It depends on the depth of investigation. Please see my video on GeoVES: ua-cam.com/video/EN0-Fhan3fs/v-deo.html If you download the Excel tool, there is an example of MN & AB spacings. All the best, Andreas
Please sir , how do we estimate the volume of water present in the aquifer in such a way that water will last for a long period of time ?
There are two things we need to estimate: 1) the amount of groundwater in storage which we can pump during the dry part of the year - before the wet season when there is groundwater recharge, and 2) the amount of groundwater recharge that will replenish the aquifer. There has to be a balance between recharge and discharge, otherwise the groundwater in storage will be depleted. The best way is to monitor as many wells as possible. If there is a balance between recharge and discharge you should see annual fluctuations in groundwater levels but no overall decline. Please watch some of the other videos in the Hydrogeology 101 playlist. All the best, Andreas
Thank you sir
Welcome! All the best, Andreas
3 september 2023
Thank you sir 🤍
Most welcome! All the best, Andreas
Grlound water survey
Hi Rashid, what is your comment please? All the best, Andreas
Hello, I badly need your help. Thank you.
Hahahaha need some clarification on GEOVES
What is your question? All the best, Andreas
@@GeosearchInternational Can I email you sir? I am doing groundwater exploration in the Philippines
Sorry, I don't have time to respond to emails, but you are welcome to leave a message here. If you have a question about my videos I will try to answer as best as I can. All the best, Andreas
@@GeosearchInternational Thank you so much. I really love your videos. I just want to ask if there would be a higher possibility of groundwater in a marshland area? If yes, how would it affect the expected yield? Thank you!
Could ultrasound be better
Hi Eric, ultrasound frequencies are made for medical imaging. They have poor depth penetration, so would not be much use for groundwater exploration. We can use seismic surveys, for example refraction seismic, to find the thickness of gravels. However, resistivity surveys have been very popular because they are fast and cheap. Also you can easily pick up clay and saline layers, both of which are not good for productive aquifers. All the best, Andreas
Ves
Hi Naresh, what is your question? All the best, Andreas
Thank you very much
You are welcome! All the best, Andreas
thank you very much
Most welcome! All the best, Andreas
Thanks alot
You are most welcome Mohamed! All the best. Andreas