Ground water extraction is likely responsible for the bulk of the 8 inches sea level rise over the last century.
http://www.globalwarmingart.com/
Land makes up 30% of the planet. Suppose that typical aquifer porosity was 30%. It would only take an average drop of the water table of about six feet to account for all observed sea level rise in the last century.
http://www.ncwater.org/Ground_Water/
In China, aquifers are dropping 20 feet per year. Alarmists of course have ignored the science, because all they care about is using CO2 as a prop to shove their socialist vision down everyone else’s throats.
But now that sea level is declining, they suddenly are interested in how much water there is on land.
Excellent point Steve….. it is something probably worth pursuing.
My understanding is that the maximum water retention capacity of soils is about 25% for clays and dropping to below 10% for sands etc. and of course, down to almost zero for solid rock. Most aquifers would be in the 10% range, which is why the land doesn’t suddenly drop when an aquifer is depleted in drought.
Caution should also be applied with assumptions of aquifer depth. On sloped land it may be only 50cm deep while on flood plains it could be 100m or more. So this is a topic that would need a whole lot of detailed geological survey before anyone could get anywhere near the ball park. Caveat emptor.
You are missing the point. They have completely ignored groundwater depletion. CU does a completely bogus positive GIA adjustment but doesn’t do a groundwater mining adjustment.
That’s why clay doesn’t make a good Aquifer, and it is used to line landfill sites.
Sitting on a shale mountain side that has veins of clay running through it along with veins of slate. I will say that Ian is wrong in his claim. When they drilled my well they hit water at 38ft and needed to go down over 300 ft to get a sufficient flow for the well. for the last 5 years I have had a one gallon per minute overflow from the well head. In the 1700 ft from road to ridge line on my property the elevation change is 600 ft at various degrees of slope. Due to the angle of the veins under the property and along the road I live on the water tends to be deeper. However on the other side of the road a recent well was drilled over 500 ft before they found enough water flow but 800 ft from where they drilled on the property next door is a year round spring bubbling out of the side of the mountain.
It depends on the structure of the subsurface. In the fifties there were artesian wells all over the Las Vegas Valley, but as the water was withdrawn / mined most of those dried up and the water table continued to drop. That was sand over bed rock. Because of the structure of the subsurface the water pooled in various regions and you could drill a well and hit water but come up dry 200 ft away.
Steven,
Very interesting – I have been thinking a lot about aquifers and aquifer recharge and I have some questions for anyone out there with a geology background or someone knowledgeable about aquifers. Mostly I have no idea how aquifers work. I have searched on the internet and not found clear answers.
We hear that our world’s great aquifers are being depleted for agricultural and other perfectly worthy and necessary purposes; but could aquifers recharge be enhanced? Is it feasible for example to dig great open excavations that would be deep enough and strategically placed such that rain water would be collected and routed directly into the aquifer? Imagine enormous man-made lakes and dams with tributary shallower catch basins all feeding to an aquifer.
Sorry for not figuring this out myself – but I thought there would be easy answers on the internet but was wrong. I have gone so far as to download an elementary text book on the topic but just haven’t had time to study it in detail.
Here in Phoenix, Arizona we have all kinds of shallow catch basins designed into every possible nook and cranny of landscaping presumably to collect rain water. I live directly across from a small community park and it, like many others here, is depressed in the middle, in fact you walk down a slight slope directly upon entering the park. When it rains hard enough, the entire park temporarily fills with water – every teenager in the neighborhood shows up with their boogy boards and surfs down the park slopes.
Greg,
You can recharge aquifers by pumping water in, if you have clean water available.
One of the dirty little secrets about where you live is that Motorola dumped hundreds of barrels of TCE in the desert off McKellips Road, and the state is in a constant battle to force the plume away from the drinking water supply.
http://www.scottsdaleaz.gov/Assets/Public+Website/water/Super+Fund+Fact+Sheet.pdf
BTW – My undergraduate degree was in geology at ASU.
Steven,
Thanks so much for this information. I am forwarding this post to everyone I know locally; I’m not sure how many people really pay attention to this…we never hear about it on the news; at least I haven’t. Thanks again.
Wow just wow! I had no idea. One has to wonder about priorities in a world where the UN flies people around the world to talk about harmless CO2 while aquifers are horribly polluted. IMO the UN should at least consider real as opposed to imaginary problems.
Thanks also for the answer that aquifers could be recharged but recharge location would have to be qualified based on location and possible requirements to sequester toxic contaminants.
Oh and since you are from here and know the area, the weather today is indescribably beautiful.
I’ve got lots more where that came from. Groundwater pumping in the Valley has caused large subsidence cracks to form in many subdivisions near the mountains. Developers just plow dirt into them and then sell the lots. Arizona has no laws preventing them from doing this. At least they didn’t in the past.
That’s wild. In my neighborhood, some of the floors (mine included) are cracked a little, and over time it seems like door jams move a bit and the doors won’t close. One of my neighbors stripped off the tile from his floor and had the concrete colored and sealed and now just ignores the cracks – hey they are interior design “features” now! I’m thinking of doing the same thing to my cracked floor.
During the 1970s I saw land developers filling in cracks that were five feet wide and a hundred feet deep, and then pouring foundations over the fill.
Florida toyed with the idea of injecting treated sewage water back into the aquifers. I vaguely remember some environmental group freaking out over the idea.
HILN:
That is already done in some regions but sewer water is returned to the water cycle in many ways.
GregO:
In the 60s Phoenix used irrigation to water their yards and most of the properties were below street level for that reason. I also recall, in the 70s visiting cities in Utah that had irrigation ditches running along the streets so people could water their gardens.
The Central Arizona Project is about recharging the underground water, or at least that was my understanding of it!
HILN,
I think LA California wanted to recycle grey water which I believe is treated potty water back into the drinking water and the usual know-nothings freaked out. A few years later, (if I have the story straight) LA did it anyway ’caused they needed to. Ha Ha!
GregO:
Las Vegas has wells where they pump “Recycled” water into the ground on the west side of the valley.
All the water that passes through Las Vegas drains into Lake Mead, through Lake Mojave, then into Havasu where CAP water is pulled out. That does not take into consideration the recycled water flowing out of Western Colorado and Utah.
I recall the problem Tucson was having when they introduced CAP water into their system. It was eating the pipes in the older homes, well that was one of the claims!
GregO:
You can get more information here:
http://www.cap-az.com/AboutUs.aspx
Mike,
Thanks for the information – bookmarked and I’ll study when I have time.
I agree, Steve, this is an issue that should not be ignored, particularly as it represents one of the key ways in which water supply can be increased, ie by increasing the cycling rate. The pre-settlement cycling rate of water in Australia’s Great Artesian Basin was well over 50,000 years but increased uptake of that water reduces the cycling interval (of both recharge and discharge) and in so doing allows greater use of the same volume of water.
We also need to distinguish between the moisture retention capacity of different strata and the lateral speed of flows in different strata in groundwater flow systems (GFS). Finer material like clay holds more moisture once saturated but it takes much longer to become saturated while courser material like sand holds less moisture but becomes saturated faster.
Mike, your local example of clay/shale overlays is neither atypical nor typical. I live in the basaltic foothills of an ancient shield volcano where impervious bedrock is often exposed on both ridgetops and valley floors. Geology is far too complex to be making generalisations from either.
That is what I was telling you!
I spent my earlier life in the Las Vegas Valley in the middle of a desert. The Las Vegas Valley is an ancient lake bed. I now live in the foot hills of the Appalachian mountains, which is considered the oldest mountain range on the North American continent. I can see the strata that was laid down before the mountains were pushed up from the ocean floor 480 million years ago. The soil here is very shallow due to erosion and the slope of the land.
The Las Vegas Valley was composed of dormant volcanoes as part of the foot hills as well as mountains created by thrust faults.
I was disagreeing with your generalized claim about shallow ground water on slopes and deeper ground water in valleys. I made the statement that it depends on the underlying makeup of the substrata rather than the surface conditions.
Rise in sea levels…..well there is another part of the whole equation that seems to be missing or is just being ignored for some reason. In Scientific America Some months or years back (my memory is slipping..lol) there was an article about the how they had computer models predicting the levels of the continents based on the internal temperatures of the underlying crustal magma. It seems that as the magma heats or cools the granite ie continents “float” on the this superhot rock not unlike ice in a glass of water the “models” predict significant changes in elevation based upon very small changes in superheated magma…interesting.
As far a Underground water in metro pheonix…egad where to start, our local cities have recharge sites (which I personally am opposed too) because the water they reinject into the aquifer is “cleaned”…but not to same level that came out…ie there is still residual birth control estrogens, antimicrobals soaps oh and don’t forget the lovely ammonium perchlorate from the colorado river contamination…the bottom line it ain’t sparkling mineral water anymore…..the more we pump out the higher contaminant level is per cubic volume just by simple math. I am far more worried about slow poisoning of our water supply than a few measily inches of continental subsidence…
Konikow (2011) looked at this (Konikow, L. F. (2011), Contribution of global groundwater depletion since 1900 to sea-level rise, Geophys. Res. Lett., 38, L17401, doi:10.1029/2011GL048604.) and found a contribution of about 6% to global sea level rise. Other (earlier) papers said up to 25%. You have a specific criticism of their methodology that leads you to believe the number should be larger?