Have you ever wonder how water flow under the footing beneath your understructure ? We build a low - cost groundwater detection system in under twenty - four hour using uncouth cloth and shaft . Here ’s what we did , and how you could do it , too .
Top image : Puff the Science Dragonposing with the complete groundwater detection demo frame-up . Credit : Mika McKinnon
When I attendedScience Hack Day San Franciscoas a scientific discipline embassador , part of my role was to gear geoscience projects for attendees to take in a24 - hour volley of enthusiastic construction .
https://gizmodo.com/these-playful-science-projects-were-created-in-just-24-1656616408
consider the drudge day was in California , the on-going droughtwas ineluctable inspiration :
The rules on water - function are changing , withlimiting sale of irrigation water to residentssending hoi polloi to bore well to swear on groundwater rather . A low - cost groundwater spying organization could be used to explore subsurface pee dispersion , serve people reduce the endangerment of drilling a dry well or experiencing cost - overruns when the well need to be deeper than anticipated to reach the body of water mesa .
Monitoring groundwater levelsis tricker than monitoring reservoir level , yet is all-important to coordinating how much water supply can be safely withdrawn without peril the subsurface . While it would be lovely for this type of data point to be allow for substantial - prison term by supervisory regime agencies , that presently is n’t possible . A wide-eyed , downcast - price groundwater catching scheme could open up groundwater monitoring to citizen - scientists , taking important measurements while farm awareness about what ’s kick the bucket on with this buried water supply otherwise hidden from survey .
Alice Pevyhouse , Anita Hart , and Jeremy Wong were fascinate by the delivery of establish a groundwater monitoring organization out of promptly - available materials , so with 24 hours on the clock , we started building .
The Science of Groundwater Detection
geophysical science is the skill of characterizing the subsurface without in reality needing to go underground to look at it . The playing area is based on detecting physical property , then using those characteristics to deduce the underlaying geological properties . Between the use of anastrophe maths and the wide kitchen range of physical properties for geologic cloth , it can seem a scrap like voodoo even to other geoscientists . The most common way of using geophysical science to detect groundwater is through value the resistivity of the ground : dry dirt will resist the flow of electrical energy , while concentrated sediment will conduct electrical energy more pronto .
When detecting groundwater as a field of operation geophysicist , we use expensive resistivity equipment that is Laputan for mass use of goods and services . But the cathartic behind how the equipment works is relatively square :
institute equally - spaced electrically - conductive electrode in the primer coat . ( Other configuration are possible , but we stuck with thecommonly - used Wenner raiment . )
Inject current into the out duad of electrodes .
Measure voltage across the inner span of electrode .
PairOhm ’s Lawwith geometric scaling to determine the evident resistance at a deepness proportional to the electrode spacing .
throw in current into outer electrodes A and B while measuring potential drop across inner electrodes M and N. Image cite : Rhett Herman
Once you ’ve calculated the apparent electrical resistance , all that is provide is the rendering : impregnate deposit should have a low resistivity than dry versions of the same geological material . Change the spacing between electrodes to look shallower or deeper to do a vertical resistivity sound , or move the entire regalia to take measurements at the same deepness in different locations for a lateral traverse .
you could see more about the strong-arm principle behind groundwater detective work inthis fantabulous paper on building a resistivity scheme to expend in university geophysics laboratories and fieldwork .
Building a Low-Cost Groundwater Detection System
The required materials for a ohmic resistance setup are simple : electrically conductive wire and electrode , a major power supply , and a voltmeter .
require materials to build a resistivity system : wire , electrode , power germ , and voltmeter . Image course credit : Anita Hart
Wire is wire . While field surveys use thick , big - gauge wire to increase conductivity and reduce noise , for our simple tabletop prototype , we could practice electronics wires scavenged from the many other hardware project go on at Science Hack Day .
All we needed for our electrodes were four monovular electrically conductive rod . While in the field , these retinal rod are usually a quarter - inch to a half - column inch diam blade rods , for our test rig we commandeered four uncoated steel slacken off pins .
For a small-scale tabletop setup , a normal 9V shelling provide enough power to run a detectable current . In larger - plate app where a more hefty power source is necessary , even a railroad car battery can have enough juice .
While we could use a stock - bought multimeter to measure voltage , build our own voltmeter out of an Arduino appropriate us to create a system of rules with the capacity to eventually add on data - logging , while also challenging us to find out more about using the microprocessor . We usedthese Arduino digital voltmeter instructionsas a guide , spending an lewdly longsighted time fiddling with wires , debug deceivingly minor modifications , and otherwise have our lives complicated .
Building an Arduino voltmeter . Image acknowledgment : Anita Hart
While the rest of the team worked on building our voltmeter , I go under out to build us a tabletop test box . I find a plastic box that would n’t acquit electricity ( minimise weird current ) and would curb pee without making an epic mess . That the loge was transparent was an added fillip , giving us a transverse - sectioned view to peek at what was going on “ hugger-mugger . ”
The box needed to be filled with a homogeneous geological cloth . As we were build our paradigm in the urban fondness of San Francisco , this test more challenging than anticipated . After being rebuffed by a nearby dig site and unwilling to raid a decorative planter , all seemed lost until realizing that yet another neighbouring building site had a goodly supplying of sandbag . The site supervisor was more than unforced to contribute to the promotion of science , sending us off with a sandbag to transform our test loge into a sandpile .
Measuring Resistivity To Map Groundwater Distribution
With the rest of our materials acquired and equipment built , it was fourth dimension to test our epitome . We position the electrodes at three dissimilar separation distance , take in data in our altogether dry sandbox as a control mention .
Adding a water table to the sandbox to test out our homegrown resistivity system of rules . Image reference : Anita Hart
Next , we carefully pour tap body of water in a corner of the box to permeate through the sand to make a concentrated watertable . Once again , we read measure at each of the three distances .
The expectant lifting on the math expect to transform mensuration into apparent resistivity has already been done by others , making it a elementary matter of plugging the measurements into pre - established rule .
Measurement astuteness ( z ): For a Wenner array where the electrodes are evenly space at a distance ( a ) , the deepness of the measuring ( z ) is at or so half the interval distance : z = a/2 .
Apparent Resistivity ( ρ ): By Ohm ’s Law , the resistivity across the internal electrode ( roentgen ) is measure voltage ( Phoebe ) part by the the applied flow ( I ): R = V / I. The geometric scaling broker to get the apparent electric resistance ( ρ ) is proportional to the interval distance ( a ): ρ = 2πaR.
Happily , we saw the plain electric resistance drop between our dry control sandbox measurements , and once the same sandbox was impregnate with water . The prototype was functional !
The low - cost groundwater detection task succeed the Science Hack Day award for good economic consumption of down in the mouth - cost hardware .
Puff the Science Dragon posing with his Low Cost Hardware award . Image quotation : Mika McKinnon
More importantly , it was a proof of conception that we can work up groundwater monitoring systems without expend a stack of money or having a gamy stage of technical skill . This same system will be scaled up with heftier wire , electrodes , and power supplies forfield testingnext year . If it proceed to officiate well , the Arduino could theoretically be modified to also act as a information logger , even further simplifying the procedure of conducting a geophysical resume to supervise groundwater horizontal surface .
This is an experiment you could absolutely try at home . If you do n’t want to take on building your own voltmeter , you could apply a normal store - bought multimeter . Be careful when mixing electricity and body of water to not zap yourself ! If you try it out , check that to tell us about your experimentation !
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