Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: Norman Castle on 15/06/2006 23:39:06
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I wish to make a brief statement about underground water, for reasons that are too complex to go into here.
I'm not a geologist, I've done some reading on the subject. I want to make sure that I'm correct before shooting my mouth off.
Please, geology experts, can you comment on the following statement, correct any details I've got wrong, etc. Thank you very much.
i) Streams that flowed on the surface in prehistoric times have been buried by geological activity over tens of thousands of years. In the present day, water continues to flow underground in narrow channels along the path of the ancient stream, many metres below current ground level. Ground either side of the channel may be virtually dry. True underground rivers are very common in karst formations.
ii) Water flows underground through various structures, including: underground rivers, ancient burried rivers, beds of sand, or gravel, minute fractures in rock, lava tubes and others.
iii) Underground water is comparatively rare and hard to find. Locating a suitable spot for a well is a job for an expert. Random drilling by someone without proper expertise is highly likely to hit a dry spot.
iv) Water supply is extremely variable over a short distance. It is perfectly possible to locate a well that produces several hundred gallons per minute (GPM) while a second well just a few metres away can produce very little or nothing at all.
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Originally posted by Norman Castle
i) Streams that flowed on the surface in prehistoric times have been buried by geological activity over tens of thousands of years. In the present day, water continues to flow underground in narrow channels along the path of the ancient stream, many metres below current ground level. Ground either side of the channel may be virtually dry. True underground rivers are very common in karst formations.
Underground water depends on porosity and permeability- porosity is the amount of pore (open) space in rocks and permeability is the measure of how easily water can flow through rocks. There are few true underground rivers- you noted one of the exceptions in karst (cave) formations. Underground rivers require large, interconnected open space- which as you can imagine is rare in rock formations. Ancient rivers buried by geologic activity may well boast impressive underground flows- usually because the stream channels are filled with gravel, which has both high porosity and permeability.
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ii) Water flows underground through various structures, including: underground rivers, ancient burried rivers, beds of sand, or gravel, minute fractures in rock, lava tubes and others.
correct. Again, all of your examples exhibit high porosity and permeability.
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iii) Underground water is comparatively rare and hard to find. Locating a suitable spot for a well is a job for an expert. Random drilling by someone without proper expertise is highly likely to hit a dry spot.
Rather than being rare, underground water (groundwater) exists almost everywhere and can be found in almost any hole drilled deep enough to pierce the water table. Abundant, rechargable groundwater is more difficult to find- but I wouldn't consider it rare. Not sure what you mean by "expert"- hydrologist, geophysicist, dowser, driller, Uncle Looney? Many people are relatively successful at finding water- but in places "dry" holes can be frustrating.
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iv) Water supply is extremely variable over a short distance. It is perfectly possible to locate a well that produces several hundred gallons per minute (GPM) while a second well just a few metres away can produce very little or nothing at all.
correct- but in places, adjacent wells will produce similar results.
Subduction causes orogeny.
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Rather than being rare, underground water (groundwater) exists almost everywhere and can be found in almost any hole drilled deep enough to pierce the water table. Abundant, rechargable groundwater is more difficult to find- but I wouldn't consider it rare. Not sure what you mean by "expert"- hydrologist, geophysicist, dowser, driller, Uncle Looney? Many people are relatively successful at finding water- but in places "dry" holes can be frustrating.
Thank you for your kind reply.
By expert, I mean qualified geologist with considerable training and experience.
Can you comment on this map of the aquifers around the Great Lakes.
http://pubs.usgs.gov/sir/2005/5141/images/Fig2.gif
For example, Map B shows an aquifer that covers about 1/3 of Indianna, and about 2/3 of Indianna doesn't have an aquifer under it, right? So how would this area be described accurately? Would it be true to say that a well drilled in this area is unlikely to hit water?
What about the granite around Lake Superior? Would this be dry? Or the shale between Michigan and Huron?
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Let me preface this by saying I am not a hydrologist.
If you look at the accompanying article to the map, Map B shows the extent of the deep carbonate aquifer in Ohio and Indiana. Water still can be found outside of the area shown- but the deep carbonate aquifer will be missing. Other aquifers, including shallower surficial aquifers (glacial depostis), surely contain water.
Granite typically makes for poor aquifers, since it has low porosity and permeability. Fractures in the granite may create local water sources. Likewise, the shale would make a poor aquifer- but the shale overlies better aquifers in the Great Lakes Basin, so drilling through the shales to the deeper aquifers would probably yield good water.
Subduction causes orogeny.
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Nornam -
Do not let Bass kid you, he is a qualified mining geologist. I am more inclined to the study of softer rocks but I cannot add much to Bass's reply. I only want to point out that the Michigan Basin with the ring of carbonates around it is the shape of a shallow tea cup.
The mind is like a parachute. It works best when open. -- A. Einstein
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So, lets just say that a certain farmer owns a field in Indianna, outside the area of the major aquifer shown. He want to grow crops on his field and needs water to irrigate.
Lets also assume that the farmwer is an idiot, and hires a dowser rather than a geologist to advise him. So, the charlatan with a stick picks a spot at random, assures Farmer Muggins there's an underground river at that point, and scoots off with his fee.
If the farmer drills a well at that spot, what are the odds that the well will come up dry?
My undferstanding is that he's unlikely to get water. Am I right?
Same question for the areas marked on the main map as shale or granite.
You mention better aquifers underneath the shale. How easy or hard would it be to reach them? Reasonably easy and cheap, or hard and prohibitively expensive?
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While the "carbonate" aquifer may not exist in certain areas, other aquifers will be present. The shallower glacial till aquifers can be quite good in spots. As to dowsers- I've known some that were very successful at finding water.
There was a thread here not long ago on dowsing: http://www.thenakedscientists.com/forum/topic.asp?TOPIC_ID=4126
In the Michigan (or Great Lakes) Basin, the younger shales cover the main "carbonate" aquifer. Drilling through the shales should not be that difficult, but drilling is always expensive- deeper holes can be costly. I'm not familiar enough with the stratigraphy in that area to estimate depths.
Subduction causes orogeny.
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Alright. dowsing might be real. Let's just say that I am less than 100% convinced about it, though I am open minded and willing to be convinced.
Lets just say random drilling, then.
If a farmer selects a spot at random, no survey by either geologist or dowser, what chance does he have of the well coming up dry?
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That depends on the underlying geology and hydrology. In places where good aquifers exist, his chances of hitting water are almost certain. If the underlying geology is unfavorable- a dry hole is highly likely. In areas with spotty available water, he is more likely to drill a dry hole than find an ample supply of water. (Keep in mind that a "dry" hole will not be dry- rather it will not produce enough water to be useful)
Subduction causes orogeny.
-
So, lets just say that a certain farmer owns a field in Indianna, outside the area of the major aquifer shown. He want to grow crops on his field and needs water to irrigate.
Lets also assume that the farmwer is an idiot, and hires a dowser rather than a geologist to advise him. So, the charlatan with a stick picks a spot at random, assures Farmer Muggins there's an underground river at that point, and scoots off with his fee.
If the farmer drills a well at that spot, what are the odds that the well will come up dry?
My undferstanding is that he's unlikely to get water. Am I right?
Same question for the areas marked on the main map as shale or granite.
You mention better aquifers underneath the shale. How easy or hard would it be to reach them? Reasonably easy and cheap, or hard and prohibitively expensive?
-
While the "carbonate" aquifer may not exist in certain areas, other aquifers will be present. The shallower glacial till aquifers can be quite good in spots. As to dowsers- I've known some that were very successful at finding water.
There was a thread here not long ago on dowsing: http://www.thenakedscientists.com/forum/topic.asp?TOPIC_ID=4126
In the Michigan (or Great Lakes) Basin, the younger shales cover the main "carbonate" aquifer. Drilling through the shales should not be that difficult, but drilling is always expensive- deeper holes can be costly. I'm not familiar enough with the stratigraphy in that area to estimate depths.
Subduction causes orogeny.
-
Alright. dowsing might be real. Let's just say that I am less than 100% convinced about it, though I am open minded and willing to be convinced.
Lets just say random drilling, then.
If a farmer selects a spot at random, no survey by either geologist or dowser, what chance does he have of the well coming up dry?
-
That depends on the underlying geology and hydrology. In places where good aquifers exist, his chances of hitting water are almost certain. If the underlying geology is unfavorable- a dry hole is highly likely. In areas with spotty available water, he is more likely to drill a dry hole than find an ample supply of water. (Keep in mind that a "dry" hole will not be dry- rather it will not produce enough water to be useful)
Subduction causes orogeny.
-
hi.... im Charls I dont know what im doing..... Ummmm i love science and im 14 years old... I thought i had an advanced accelarated knowledge about science but reading about the forums you guys were talking about, screwed my mind.... I now realize that im dumb and stupid becase i never, never understand what you guys are doing i just feel so stupid.. IM SO SO SO SORRY... I want to go to yale but i cant anymore because im stupid Yale is too advance for me i even had a B twice in P.E> leading me with a yearly GPA of 3.917 yeah i know stupid P.E. i hate my self now... Well for any advised e mail me ihatemyself_windsor92@hotmail.com
charls Pasion
charls Pasion
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hi.... im Charls I dont know what im doing..... Ummmm i love science and im 14 years old... I thought i had an advanced accelarated knowledge about science but reading about the forums you guys were talking about, screwed my mind.... I now realize that im dumb and stupid becase i never, never understand what you guys are doing i just feel so stupid.. IM SO SO SO SORRY... I want to go to yale but i cant anymore because im stupid Yale is too advance for me i even had a B twice in P.E> leading me with a yearly GPA of 3.917 yeah i know stupid P.E. i hate my self now... Well for any advised e mail me ihatemyself_windsor92@hotmail.com
charls Pasion
charls Pasion