Dew pond

Having heard about dew ponds before in dry climates, has anyone tried to construct one?

www.sharingsustainablesolutions.org/air-wells-dew-ponds/

I've never built one, but my car operates that way. I have to squeegee dew off of the windows most mornings, even if dew hasn't fallen most other places.

It sounds like the most popular sorts of living roof would function as a dew pond, too.

a means for creating a [negative]
movement pressure, in the preferred form of a turbine, may be provided
on the output…

My "preferred embodiment" would be driven by a solar chimney, not a turbine. The chimney might also be a radiative cooler at night. Building the system on a slope, and having the top of the chimney be roughly at the same height as the rubble pile, would allow the flow to reverse at night, potentially bringing the stones down to below ground temperature in the hours before dawn.

From my metal roofs I collect a surprising amount of water from dew.

Solar chimney sounds as if it would work too.

  I am going to try pumping my hot greenhouse air through tubes in a raised bed this year. Running through the tubes it is reported to dehumidify and heat the bed as the air cools in the pipe manifold buried in the bed. I'm curious as to just how much water will condense out as it runs through the tube.

Little battery-powered humidity meters are expensive, but extremely easy to use. They would allow you to calculate the amount fairly accurately.

It would be a matter of finding the relative humidity & temperature of the greenhouse air, the temperature of air as it leaves the raised beds (presumably slightly warmer than the soil), and the flow rate. If you have some ballpark figures, you should be able to figure that all out reasonably quickly.

In the orchard here I use drip irrigation, the black poly on mornings drips(when irrigation is not on), thus I'm planting many drought hardier plants in the rows with the trees rather than deal with a plentiful crop of tumbleweeds again.

Am also tapping the moisture off roofs as it can be a significant amount.

Trying an experiment very soon with used hose set in concentric circles around some of my more drought tolerant trees.

Frank Herbert also discusses this sort of thing in fair detail in his novel, Dune.

Pat: will the hose be filled with anything, like water or soil? It sounds as though thermal mass is important.

The Lawrence Berkeley Laboratory has a whole thing about infrared & visible pigments. Their idea is to make roofing material any color the customer asks for, but with very low emissivity outside the visible spectrum. But the same information could be used to make a paint for dew traps that absorbs very little sunlight during the day, but is good at radiating IR energy to the sky at night (similar to Frank Herbert's color-changing plastics, but with physics that would actually work).

Hi Joel,
    They will be filled with water. I think at least half should do it, will need to do some experimenting to see what works best.

I'm also a long time fan of the Dune series. Every time I see Gary Nabhan's name/picture can't help but associate him with Dune! )

Hi everybody,
I built a dew pond a few years ago. It was just a "try it and see if it works" one, and not built for lasting, but it really worked.
here is how I made it.

I got a bale of straw and a large sheet of clear poly tarp.
There was a rather deep hole someone had started already on the property, so I started there and smoothed it out and added a wide shallow pond shape around the deep part.
Then I broke the straw into the square layers and put one layer deep all around then sort of filled the deep part with the rest.
Then I added the tarp.
The day was so hot, I could barely stand it. Oh, I added a liter of water to start it in case it needed that help from me. (I had to leave the following day and I wanted to see the results right away if possible.)
The next morning I was sorry I had added the water because I couldn't tell, but there was a lot of moisture dripping on the under side of the tarp.
I had to leave.

I returned 2 weeks later and the pond was full!!
This was the deep part and I was glad I had saved the deep shape because it acted as a sort of reservoir.

I calculated by dimensions and did this over and over because it was so hard to believe that I had over 700 gallons of water in that pond in 2 weeks.

I could even see it on google. It was a small black dot in the yellow desert surrounding the 'pond'

It was so cool.
I am moving so I won't be using that dew pond, but the experience was great and I am so glad I can share with everybody that it does work.

But don't use clear poly tarp, because the dew pond is broken up from the sun and nearly gone after 2 winters.

thank you,

jeanna

Thank you, Jeanna! That's inspiring, and makes me want to try it, once I have the space.

Hi Joel,
I wanted to add another part.
After being at permies a few days I understood the reason that the "roving groups of men" who used to build these dew ponds lined them with rocks.
I did not do that and it would be great. No matter how many rocks you can put in there the more the better. I guess it was one level of rocks deep.

jeanna

This looks like it is working on similar principles:

http://www.popsci.com/content/how-it-works-waterboxx

Jeanna,
Thank you for sharing your experience. I'm starting to dig a small (6x8' roughly) dew pond and will be modeling it after the description of yours, except that I hope to use a piece of pond liner or pool liner rather than a poly tarp. Just to clarify, you put down the straw, then one layer of the plastic, and that was it? Or did you have a second plastic layer somehow? I was a bit confused by the "water dripping on the underside" bit. Also, what benefits do the rocks give, just making it more resilient and less prone to puncturing, or something to do with thermal mass? Just wondering if I need them or if it would still work without.

Thanks again!
PJ

Mori no Niwa wrote:
Jeanna,
Thank you for sharing your experience. I'm starting to dig a small (6x8' roughly) dew pond and will be modeling it after the description of yours, except that I hope to use a piece of pond liner or pool liner rather than a poly tarp. Just to clarify, you put down the straw, then one layer of the plastic, and that was it? Or did you have a second plastic layer somehow? I was a bit confused by the "water dripping on the underside" bit. Also, what benefits do the rocks give, just making it more resilient and less prone to puncturing, or something to do with thermal mass? Just wondering if I need them or if it would still work without.

Thanks again!
PJ

I will try to find all the references I used to build this proof of concept.

I remember well puddled clay (white bentonite or sodium bentonite clay meaning umm clumping cat litter) which means well squished by the feet. That is what I replaced with the pond liner.
After the clay was well puddled the entire thing was lined with rocks.
In the article it was proposed that this was to keep the feet of the cows from cutting through the clay liner.

So, you see I had some concepts and theories about how this worked, so I substituted some modern equivalents.
Later, I saw Szep Holzer talking about how he uses the thermal mass of the big rocks, and I realized I had made a mistake. Well, I did have a working dew pond, so it was still OK.

To answer your questions.

I put the straw down first then the plastic.
The water underneath was the condensation of water from the ground that was NOT making it into the pond because it was on the wrong side!

What I would do now is this:

-site it at the top of a rise near the top of the hill if possible
-make it very shallow, like a dish.
-put down the pond liner
-cover that with a 6 inch layer of clay-soil to form the ground of the pond.
-place a single layer of stones over the entire pond area.

Sit back and watch it fill up.

It is a very big job to place a single layer of stones and I would start them in the center and add some every day. This way you will have some pond in the center from the beginning.
-----

It all has to do with the temperature of the pond at the coldest time of day which would be 3-5AM.
If you can prevent the pond and surrounding ground from heating up too much during the heat of the day, then when the night air is cool and the pond is cooler, the dew point just might be at the temperature of the pond.
It could help to add some cold water or package of ice on the first night just after dark, to start the cooling process.
It seems that once the pond has water in it, the water will help more dew to drop in. (  )
Here is another point. The condensation itself causes warmth above it, so placing this on a place where fast dissipation of that warmth will keep the dew formation happening.
------

I now understand the reason for the materials as I did not when I made it.
The rocks always collect ground moisture and condensation on their under sides.
Clay when being used for cob (different kind of clay) is mixed with straw. I believe this is how they made the liner. It was not so much a layer of straw followed by a layer of clay, but the mixture had both materials together.

Look at these links:
http://www.rexresearch.com/airwells/airwells.htm starting about 1/3 down the page where it says "air wells".

http://www.dewpond.co.uk/whoare.htm for a picture of one from the 16th century still working.

and
http://dewponds.co.uk/articles_dewponds_martin.htm
This last one helped me a lot. I found a piece of disinfo on the page, but you can find it yourself. (It was in the typical form where the summary is the opposite to the whole meaning of the article. So, read the article and ignore that stupid statement.)

enjoy and please send a pic or 2!

jeanna

Thanks Jeanna for the elaboration!

In my case, I don't have hills, clay, or even rocks readily available. My land is quite flat and the soil is dry and sandy, with very few rocks. The spot I've sited the pond is at one of the lowest points in the land (maybe only 1-2 ft lower than anywhere else), figuring that if it ever rained hard for a long time and the water started moving across the soil surface, it would go to the pond...but that may only happen once a year or less here. I could have stones and/or clay brought to the site, but I'd have to pay for that. With your method, maybe I could try w/o them first, and if it didn't work, add them later to see if it made the difference.

Another thing I should mention about the location is that it's almost entirely shaded, there's a deciduous tree overhead with a trunk maybe 12 ft. away. This means that I'm encountering some roots when I dig, but since it's small I don't think it will do any catastrophic damage to the tree. I thought about the pros and cons of this; leaves overhead mean that it might not get as much dew or rainfall as an exposed site, but it should also help keep it cooler and therefore less evaporative? If the main source of the water is from temp. differences between pond and surrounding areas (and not so much moisture "falling" down from directly overhead, as with rain), this may be an advantage...

But it's all an experiment and it could prove to be a bad idea/location. The experiment won't cost much to try (the pond liner is the only real expense, and I'm trying to find a salvaged pool liner to use for that for cheap or free). If it's a bust in this location I may try it elsewhere, but either way I'll share what I learn and take pics of the process. Once I get the liner I'll be in business and will let you all know how it works. Thanks for the great dialogue, I love these forums!
PJ

The whole idea with a dew pond is to build a watertight, shallow bowl exposed to the sky whose floor is insulated (by straw, foam sheets, etc.) from the earth's heat so that on clear nights its surface temperature drops below the dewpoint temperature and it starts condensing dew on its surface.  The water level in a dew pond is self-regulating, as the water level drops, more of the insulated pond floor is exposed to the night air, so it generates more dew.  As the water level rises, it covers more of the pond floor and as a result generates less moisture.  The construction materials you choose depends on your use of the pond (garden irrigation source or livestock waterer) and your climate (around here,termites would consume any hay left in contact with ground for a year or two).  If you get lots of fog, you can construct a dew pond partially under a tree to harvest the fog drip coming from the tree.

A couple more articles I've found on dew ponds which caught my interest:

http://www.balwois.com/balwois/administration/full_paper/ffp-587.pdf

http://www.independent.co.uk/news/education/education-news/rural-downland-newts-hope-for-small-pond-success-1292704.html ;

I'd love to know how the newt project went. There may be someone with a lot of experience at building modern dewponds associated with it.

Paul's presentation on Replacing Irrigation with Permaculture at the Inland Northwest Permaculture Convergence: http://www.richsoil.com/permaculture/508-podcast-087-replacing-irrigation-with-permaculture/

Paul talks about using dew ponds.

Suzy Bean wrote:
Paul's presentation on Replacing Irrigation with Permaculture at the Inland Northwest Permaculture Convergence: http://www.richsoil.com/permaculture/508-podcast-087-replacing-irrigation-with-permaculture/

Paul talks about using dew ponds.

I listened to the podcast last night and found it very enjoyable.  Then I started thinking about my property. I have a couple of seasonal ponds. They hold water due to hard pan clay.  This last year I watched them fill with water, then the tadpoles started growing. I was excited hoping for lots of frogs or toads, whatever they were.  But as spring turned hot on the Carrizo Plain as it always does, the ponds evaporated leaving the tadpoles squirming in mud concentrations. I felt so sorry for the little guys. Where I made a mistake driving through the pond when I got my truck stuck, I dug out a little channel deeper than the rest of the pond and some lucky tadpoles found that dip and those ones lasted a week or two longer than the rest but still they did not reach maturity.  The next door property has a much larger pond and that one had the same fate.

So I'm wondering what I can do to help facilitate this pond lasting long enough that the frogs/toads will mature.  Last night's podcast got me thinking about this topic again.  I feel casting a shadow with trees will be near impossible for the next 10 or so years because trees don't grow nicely in that hard pan clay (which is also riddled with sodium carbonate which is highly alkaline/salty).  So my next idea would be to dig out the pond so that it might accumulate more water and therefore last longer.

So my question to the readers at Permies.com is, what are some guidelines to consider when modifying dew ponds so that they still will hold water.  I'm sure if I dig down deep, I'lll pass through the hard pan clay and get to better clay beneath and I'm concerned that I might make the pond leaky like a swale. The end results would be more water getting back into the ground but also there'd be no frogs/toads.

If anyone has something useful for me to consider I'd appreciate if you shared it! Thanks!

Off The Grid wrote:

So my question to the readers at Permies.com is, what are some guidelines to consider when modifying dew ponds so that they still will hold water.  I'm sure if I dig down deep, I'lll pass through the hard pan clay and get to better clay beneath and I'm concerned that I might make the pond leaky like a swale. The end results would be more water getting back into the ground but also there'd be no frogs/toads.

If anyone has something useful for me to consider I'd appreciate if you shared it! Thanks!

My first thought is to fill the pond or at least part of it with big rocks. These act as shade as well as something cool(er) for any water is the air to condense on. It seems to me this is one of those things talked about in one of the podcastes/threads but I can't remember which one. Rocks are also great to encourage wildlife... like your frogs... and the animals that eat them. The less you can see of your water, the longer it should last. It is hard for me to test this as I live in a less than dry climate.

Len Ovens wrote:My first thought is to fill the pond or at least part of it with big rocks. These act as shade as well as something cool(er) for any water is the air to condense on. It seems to me this is one of those things talked about in one of the podcastes/threads but I can't remember which one. Rocks are also great to encourage wildlife... like your frogs... and the animals that eat them. The less you can see of your water, the longer it should last. It is hard for me to test this as I live in a less than dry climate.

I have been considering your idea for a few days. It seems to me that the only way this could work is if there were several layers of rocks high because the sun on the Carrizo Plain is about the hottest sun I've ever felt. Honestly it's like hotter than other places for some reason the rays of the sun make it through the atmosphere more there (it's a fact actually). So I'm thinking if it were one layer of rocks then there'd be excessive evaporation during the days as soon as the first rock gets exposed to the air. My fear being it would evaporate more than it would condense. What do you think about that? Anyway, to bring rocks out there, that will cost me like probably a minimum of $1000 so I'll have to really consider this long and hard. I have maybe a week or two before they fill up. I was thinking next weekend, find the low spot in the large pond, and dig a trench in the center, going down 1 foot. If I do that the length of the pond I am thinking I will have enough water that frogs may reach maturity. That's a lot of digging bar muscles to make that work, but I'm thinking maybe 6 hours in the cooler weather... it'll be good exercise.

Off The Grid wrote:

Len Ovens wrote:My first thought is to fill the pond or at least part of it with big rocks. These act as shade as well as something cool(er) for any water is the air to condense on. It seems to me this is one of those things talked about in one of the podcastes/threads but I can't remember which one. Rocks are also great to encourage wildlife... like your frogs... and the animals that eat them. The less you can see of your water, the longer it should last. It is hard for me to test this as I live in a less than dry climate.

I have been considering your idea for a few days. It seems to me that the only way this could work is if there were several layers of rocks high because the sun on the Carrizo Plain is about the hottest sun I've ever felt. Honestly it's like hotter than other places for some reason the rays of the sun make it through the atmosphere more there (it's a fact actually). So I'm thinking if it were one layer of rocks then there'd be excessive evaporation during the days as soon as the first rock gets exposed to the air. My fear being it would evaporate more than it would condense. What do you think about that? Anyway, to bring rocks out there, that will cost me like probably a minimum of $1000 so I'll have to really consider this long and hard. I have maybe a week or two before they fill up. I was thinking next weekend, find the low spot in the large pond, and dig a trench in the center, going down 1 foot. If I do that the length of the pond I am thinking I will have enough water that frogs may reach maturity. That's a lot of digging bar muscles to make that work, but I'm thinking maybe 6 hours in the cooler weather... it'll be good exercise.

Instead of rocks could you use concrete rip-rap? When they tear up slabs and roadways its the busted up concrete waste. That might be a bit cheaper.

I know this thread is dead, but this may add some value to those looking in the future. This morning I awoke, as I do many mornings, to the sound of drops hitting my roof. I live in a desert (SoCal), and the drops are dew harvest from the leaves of my towering Sycamore. I spent a little time on the interwebs this morning researching the topic and found this inspiring gem:

http://wanderinggaia.com/2010/09/20/reforesting-the-desert/

Hope you like it. I did.
-greg

Robert Ray wrote:From my metal roofs I collect a surprising amount of water from dew.

Solar chimney sounds as if it would work too.

  I am going to try pumping my hot greenhouse air through tubes in a raised bed this year. Running through the tubes it is reported to dehumidify and heat the bed as the air cools in the pipe manifold buried in the bed. I'm curious as to just how much water will condense out as it runs through the tube.

Here in Alaska I get my water in the summer from the roof, filter it and store it in a 15 gallon tank. In the winter I just keep a metal bucket of snow near or on top of the wood stove.