Urban pond evaporation concern

I've been contemplating for a while on an urban backyard pond plan - and would love feedback. Most of my experimental projects are easily reversed if they go wrong - not so much with this one.

I'd like to have a small, sustainable yield of edible fish - a couple pounds a week would be ideal. Edible water plants are also desirable. My hope is to go natural - no filters/pumps/etc - if possible. I'm in no hurry, so if it takes a while to get things balanced, that's fine.
I'm in sunny SoCal on a small urban lot. My space allows about 8 x 15 ft surface area. My soil has a fair amount of clay, and I will supplement with bentonite as needed for a seal without plastic liner.
Maximizing depth will give more volume & thermal mass with less evaporation surface, so rather than just a natural slope, I will create block retaining walls to have shallow, medium and deep zones - with the deep zone being at least 6 feet. I'm estimating my volume will be about 3000 gal.

My biggest worry is evaporation. We have virtually no rain for 3-6 months in a typical summer, and of course the sun is pretty intense here. I really don't want a pond that dries out and reboots annually. I know the variables make it impossible to predict accurately, but I'm trying to make an informed go/no-go decision.
I'm harvesting rain water off my roof, so even in our drought it is no problem to start every spring with the pond topped off plus about 1000 gal in tanks. Grey water options are limited for practical, legal, and economic reasons - I will work toward it, but not including it in my calculations right now. Supplementing with municipal water is possible, but if I'm going to have to be adding thousands of gallons just to get through the summer, then maybe I should skip this and move on to my next crazy idea.

What do you think, permies?

Sounds like to me you have this pretty well thought out.

Might be best to hold off stocking it with fish for a year or so, so that you can observe the evaporation rate, let the pond settle in, get vegetation going,etc.


I'm kinda curious though, you are planning on block walls, but a clay bottom? It seems to me if you are going partially artificial anyways, then why not a liner bottom?

Cris Bessette wrote:
I'm kinda curious though, you are planning on block walls, but a clay bottom? It seems to me if you are going partially artificial anyways, then why not a liner bottom?

Thanks for the reply, and good question. My clay content is high enough that I probably don't need a liner at all - I'll do some testing to determine if I need to supplement with bentonite. So I don't need to buy a liner or worry about what to do when it fails eventually. So the block retaining walls are really independent of the liner question. All things being equal, I'd rather not use blocks, but it solves a problem. And I shouldn't need mortar/cement - I can drive some anchor posts into the underlying soil, stack the blocks over those, pack them with dirt/clay - so not totally artificial.

Or maybe I'm crazy.

Myron - you can check out what your possible evaporation rate might be here: http://www.wrcc.dri.edu/htmlfiles/westevap.final.html#CALIFORNIA Pick the station closest to where you live.

Thanks for the reply, and good question. My clay content is high enough that I probably don't need a liner at all - I'll do some testing to determine if I need to supplement with bentonite. So I don't need to buy a liner or worry about what to do when it fails eventually. So the block retaining walls are really independent of the liner question. All things being equal, I'd rather not use blocks, but it solves a problem. And I shouldn't need mortar/cement - I can drive some anchor posts into the underlying soil, stack the blocks over those, pack them with dirt/clay - so not totally artificial.

Plan, design, check, adjust, think hard, and then plan some more...(measure 100 times...cut once)

Hello Myron,

Like so many DIY Permies projects I see done...way to many involve incomplete planning (not saying that is you) and reinventing the well. Jennifer's suggestion is spot on, not to mention there is math that can do much of that for you with some really clear parameters of accuracy. You can also call the State Ag agency for additional information. Have you called, and/or visited any Zoos, fish farms, universities in your area with ponds? These are great resources for info.

I am seeing more "holes" (pun intended) in your block concept. "Pins" are going to error out, and a block just stuck up against a bank may or may not support the bank from caving in. Just clay may be more than enough, or wood and clay. There is much to consider, and at this point I have more questions than good answers. I would need plan view and elevation view drawings, photos, and soil analysis to really give good counsel. Over all, I think Tilapia and/or a species of Siluriformes would work well (among others) and think you have a really good plan started...just a ways to go first.

Regards, and excited to see more...

j

Jennifer Wadsworth wrote:Myron - you can check out what your possible evaporation rate might be here: http://www.wrcc.dri.edu/htmlfiles/westevap.final.html#CALIFORNIA Pick the station closest to where you live.

Thanks, Jennifer. This is the sort of thing I was looking for, but my google-fu was failing me. [Sorry if this sounds weird, but I have to say, you are my favorite permie - thanks for all the amazing stuff you post on these forums.]

Myron Weber wrote:Sorry if this sounds weird, but I have to say, you are my favorite permie - thanks for all the amazing stuff you post on these forums.

Well gee, you make me feel all "aw shucks-y" now! (why is there no "blushy" emoti?) It was my post on dung beetles that won you over, yes?

In all seriousness though - thanks for the very kind words. And I wouldn't have found that page on evaporation rates if I hadn't come across the term "pan evaporation" somewhere in my late night wanderings into the dark and geeky corners of the web... I can dream though...

Jay C. White Cloud wrote:you have a really good plan started...just a ways to go first.

LOL. I don't know if I have a good plan or not - but I agree that I have a ways to go first. Before I work through the rest of the details, I'm focusing on feasibility from an evaporation standpoint. Thanks for your tips.

Jennifer Wadsworth wrote: I can dream though...

That's awesome.

Hi Myron,

I think you will be succesfully in this and will find that evap. is not going to be that large a challenge. There is tenting methods (like a greenhouse) that can mitigate the issue. You may also find some local fish farms for the pet trade that may inspire thoughts as well.

Good luck...

Jennifer...Google-Fu...that was awesome!

Some other thoughts I had, as I read the very well worded thoughts of others. When people want water to be warmer, they paint the background darker colors, so that it maintains the heat. Is it possible that raising the temperature of the water is going to increase the evaporation rate? Water evaporates from not only the heat of the sun but the wind as well, so the warmer the water is, the easier it will be for the wind to carry off. Maybe you can use some white stone for the bottom of the pond, though it might be hard on the eyes. Maybe some kind of sand?

You can design some kind of natural wind break around the pond, or at least in the areas that have the most/greatest wind, to minimize the damage that the wind will do. The greenhouse thing, as mentioned, would work. Another option would be shade trees, but have to consider the effect the leaves, etc of the trees would have on water chemistry. You can also put some kind of decking around the pond that overhangs the water significantly...but all of this stuff costs money. At some point you have to calculate the cost of lost water via evaporation over 10 years or so and the cost of preventing the water from evaporating. If I lived in a desert I would look into solar water distillation to process my gray water into pure water and waste, then use this (the pure water) in the pond.

Does the data source recommended here take into account only the air temperature? or does it include a wind factor as well?

I think you are wise at this stage to be concerned about evaporation drying it out. It seems to me to be a legitimate concern. Beyond sealing the pond itself, there are a lot of things you can do to slow evaporation, basically reducing air flow and temperature. Beyond just totally drying out, you will also need to worry about having enough water and oxygen to support the life you have in the pond. Other options might include a larger water reservoir (can you make the pond BIGGER at the bottom instead of smaller, perhaps a shelf for your shallow zone?), or more external storage.

I don't live in California, but spent a year in Cost Rica. My gut says if you get it sealed well, and keep it out of the sun and wind during the dry season, you will have something to work with, but it will dry out more than you want, totally exposing everything but the deepest zones. I imagine a water level drop of maybe 3-4 feet assuming there is no outside water coming in, and I think it could dry up completely if not sheltered. I would do some actual math on it though, and carefully take into account your specific circumstances.

On a pond that small, I would also take into account seepage through the clay liner.

Tom - some good thoughts, especially the white rock. Hadn't thought of that.

Tom Connolly wrote:Does the data source recommended here take into account only the air temperature? or does it include a wind factor as well?

http://en.wikipedia.org/wiki/Pan_evaporation
"Pan evaporation is a measurement that combines or integrates the effects of several climate elements: temperature, humidity, rain fall, drought dispersion, solar radiation, and wind."

Luke Townsley wrote:I would do some actual math on it though, and carefully take into account your specific circumstances.

On a pond that small, I would also take into account seepage through the clay liner.

Thanks for the insights. I'm still concerned about the evaporation, but not so much that I'm throwing in the towel by any means. My next step will be to get some empirical data by burying some 5-gal buckets up the rim in both sun and shade, and seeing how fast the water evaporates. That will give a baseline for the shallow parts independent of seepage.

BTW - I was a lifelong Indiana boy until I met a California girl and ended up here. I spent a lot of time in my early 20s driving around the Terre Haute, Vincennes, Bloomington areas, and actually know where Dugger IN is.

Myron Weber wrote:

Luke Townsley wrote:I would do some actual math on it though, and carefully take into account your specific circumstances.

On a pond that small, I would also take into account seepage through the clay liner.

Thanks for the insights. I'm still concerned about the evaporation, but not so much that I'm throwing in the towel by any means. My next step will be to get some empirical data by burying some 5-gal buckets up the rim in both sun and shade, and seeing how fast the water evaporates. That will give a baseline for the shallow parts independent of seepage.

BTW - I was a lifelong Indiana boy until I met a California girl and ended up here. I spent a lot of time in my early 20s driving around the Terre Haute, Vincennes, Bloomington areas, and actually know where Dugger IN is.

When you come back, you'll have to stop in! I was born here, but spent a lot of time away.

A shade sail will greatly reduce evaporation for very little money

R Scott wrote:A shade sail will greatly reduce evaporation for very little money

That's a great idea. I was puzzling over using trees for shade without root incursion - which I don't think would really work. But a shade sail could work great.

Depending on how big your pond is, you could also put a trellis with vines over it. I know Geoff Lawton puts trellises over his swales in Jordan. From: http://permaculturenews.org/2014/02/01/desert-oasis-4-years-jordan/

Jennifer Wadsworth wrote:Depending on how big your pond is, you could also put a trellis with vines over it. I know Geoff Lawton puts trellises over his swales in Jordan. From: http://permaculturenews.org/2014/02/01/desert-oasis-4-years-jordan/

When we lived in the Dominican Republic, we had a vine known locally as "Chinola" that bore orange-like fruits by the same name. I don't know what it is called in English, but it was an extremely growthy vine that was fairly hardy there and would be awesome for something like that if your climate supports it. The fruit was used widely for juice.

Edited to add: I believe this is it: http://en.wikipedia.org/wiki/Passiflora_edulis

Luke Townsley wrote:
When we lived in the Dominican Republic, we had a vine known locally as "Chinola" that bore orange-like fruits by the same name. I don't know what it is called in English, but it was an extremely growthy vine that was fairly hardy there and would be awesome for something like that if your climate supports it. The fruit was used widely for juice.

Edited to add: I believe this is it: http://en.wikipedia.org/wiki/Passiflora_edulis

Luke - great suggestion! In fact there is a version that does very well in hot drylands - the "Baja Passion Vine" - only problem is finding it for sale!

Hi, I would be interested in how your pond goes - if you do go ahead with it. I'm in Encinitas, not too far south from you, and have been thinking about ponds. Like you, I have the same concerns. There is also the question of how I would build it without inviting an earth compacting bulldozer and where would I find someone with the same Sepp Holzer magic of turning bulldozer into pond building pig? (Perhaps I can hand dig and then send my kids out - they are wilder than wild pigs sometimes). My soil was very clay and the subsoil is probably still the same. (I say was because I have added layers and layers of mulch to it and I think the top layers have improved). My parents own a house in Escondido, Ca (more inland). That house has a large pool and, if not for the pool cover blocking evaporation, loses 2 inches of water in a few days. Before they put a cover on, they would run water for almost 45 minutes to bring it up to the level needed so the pump won't burn. My area is milder, but that's a lot of evaporation. In short, I would love to hear your story and of your success!

(Hmmm, I think my kids would love to wallow in mud pit).

Hi Jackie and Myron,

I'd like to know if either of you do a pond because I'm thinking of doing the same thing.
I'm a bit north of Jackie in Carlsbad. And South of Myron by probably 60 miles.

Have either of you started on the pond?

By the way, I was just at Finch Frolic Gardens in Fallbrook (Diane Kennedy's place) for a tour - http://www.vegetariat.com/finch-frolic-gardens/
She has a few ponds (gorgeous and amazing ponds!) Jacob Hatch was around today during the tour and I am pretty sure he helped with the ponds and does a
lot of consulting about ponds. Hers was just packed clay - no liner.

Sheri

Sheri - My plan is to get started in Sept/Oct. Summer has been busy and not my favorite time to work on a major project in the sun.

Hi!

I haven't even started. Busy with PDC. That said, this link might prove useful: http://www.nwedible.com/2014/08/can-you-seal-a-pond-with-clay-kitty-litter-2-html.html

Jackie