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Can I water my lawn this way?
May 23, 2012 6:43 AM   Subscribe

A question about the lifting capacity of sponges, gravity, pvc tubing and whether my lawn can be irrigated.

The water table under my lawn is very high. That is, when I dig a hole for a fence post, at about the three foot mark, I hit water.

Please tell me if this is physically possible.

If I take a four foot length of PVC pipe that is 5 or so inches in diameter, fill the pipe with high quality sponges to the top, and then place the pipe vertically in the hole, with the top 12 inches sticking out of the hole, will the water seep out of the top of the pipe where it can be collected?

More technically, is a sponges lifting capacity eventually exceeded by the force of gravity?, and if so, is four feet to great of a distance for lifting capacity to exceed gravity?

Alternatively, suggest any other reasons this will not work.
posted by otto42 to Home & Garden (9 answers total)
 
Thinking about how trees obtain water at much greater heights, it seems theoretically possible at least.
posted by exogenous at 6:55 AM on May 23, 2012


My feeling is that you may be able to get a vertical tube filled with wet sponge, but that this is different from getting a vertical tube filled with wet sponge with a pool of water at the top. That is, there is no reason for water to leave the sponge once the sponge is soaked, so you would have to somehow wring out the top sponge repeatedly into a separate container.
posted by Comrade_robot at 7:13 AM on May 23, 2012


Entirely dependent on the pressure in your water table- sponges don't have any lifting capacity on their own, and a pressure differential's the only way you're going to passively get lift. If you were using a smaller pipe, and filled the pipe/sponges up with water before installation, I think you could get a small amount of lift by evaporation, as the cohesiveness of water pulls it up as it evaporates, but this requires the water you DO bring to the top to disappear anyway so kinda useless
posted by MangyCarface at 7:17 AM on May 23, 2012


I wonder if you could somehow collect the evaporated water from the top sponge over time, in some kind of condensation hood.
posted by grog at 8:46 AM on May 23, 2012


If you want to raise enough water from three feet down to water a lawn, you'll get nowhere fooling about with pipes and sponges. What you need is a ground cover with roots that grow deep enough to suck it up on their own. Plant clover.
posted by flabdablet at 9:45 AM on May 23, 2012


Your goal is to take from the huge supply of water at 3' below the surface, and spread it arround to irrigate the rest of your lawn?

Sponges work basically through capillary action. Capillaries are great for picking up liquid from one place, but all they do is automatically fill up, they don't empty themselves, either out the top of the tube or out the bottom.
Capillaries also describe the way the groundwater moves through the soil in the first place, i.e. how the water table at 3' below the surface leads to wet soil at 2.8' down, damp soil at 2' down, and faintly moist soil at 1' down. Imagine augmenting this by filling your yard full of tiny tubes that extend from a couple of inches below the surface down below the water table level - nice narrow tubes so capillary action slurps the water up into the tube and fills it to a level that the dry soil at the top then has access to the liquid water and slurps the water out. A nice idea in concept but creating a capillary mesh like that is best left hypothetical (3' long capillaries? tearing up your entire yard down to 3' deep? no.)

Here's another idea, but you'll have to check for mathematical errors and pure nonsense level: A 200W sump pump carries 3000 gallons per hour, or you could phrase it as pumping 3000 gallons for 0.2kWh of electricity, less than 10 cents. For my local costs, water and sewer total is ~$12 per 1000 gallons, so that's a big price win. BUT you'd have to buy a sump pump ($200) and a rain barrel to pump it into ($100) and some hosing to distribute the water around the yard. AND you'd have to dig a sump in the yard big enough to collect more than a couple of gallons at a time, and run power out to it, and maintain it. And if there's not a switch to shut it all off, you'd just be continuously pumping and flooding the yard. So that needs some refinement.
posted by aimedwander at 9:49 AM on May 23, 2012


Imagine augmenting this by filling your yard full of tiny tubes that extend from a couple of inches below the surface down below the water table level - nice narrow tubes so capillary action slurps the water up into the tube and fills it to a level that the dry soil at the top then has access to the liquid water and slurps the water out.

Then imagine that all these amazing tiny tubes are self-assembling, self-installing and self-maintaining!

Plant clover.
posted by flabdablet at 10:22 AM on May 23, 2012 [1 favorite]


The only way I could see you utilizing this is along the lines of aimedwander's suggestions - build a sump and put a pump of some kind in there hooked up to your irrigation lines. Three feet is not that far for a pump, but it is a huge distance for capillary action.

Here's the thing though - I'm a geologist, and if you have groundwater at three feet in your yard that brings to mind other issues. This water is likely perched, i.e. not part of a large body of water, and you aren't going to be able to get much out of it. Also I have concerns about the quality of this water - there may be chemical aspects of this that aren't great for irrigation. I'm not thinking hazardous (although...), more like pH/conductivity or other general quality. If you were close to a saline water body that water is probably saline for example. Would need more info about where this is, but I commend you on trying to utilize one of natures resources!
posted by Big_B at 11:26 AM on May 23, 2012


The only way I could see you utilizing this is along the lines of aimedwander's suggestions - build a sump and put a pump of some kind in there hooked up to your irrigation lines.

Do check your state and local water law, though -- there are generally quite strict rules and regulations about who can dig a well, how it needs to be built in order to prevent cross-contamination (hint: an open hole with a sump pump in it won't qualify), and with whom such activity needs to be registered.
posted by Forktine at 6:12 PM on May 23, 2012


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