Multi-purpose moat - practical?

You can think of it as a moat or a pond with an island. The island would be used for growing veggies and chickens for family consumption. Let's say 5000 sq ft. (40' radius) Uses: (1) Keep away browsers and predators (effective against all?) without a fence (2) Use moat to grow fish (3) Moderate climate (4) Backup irrigation source.

To overwinter fish in Zone 5a, I'm assuming a max depth of 10 ft. Assuming an angle of 30 degrees for inner and outer walls, and maintaining the max depth for 6', we get an outer radius of 80'. Moat area comes to 15000 sq ft = 1/3 acre, the whole thing is 1/2 acre. (For a 10,000 sq ft island, the moat area goes up to only 20,000 sq ft.) Not terribly big. On my land, I think a liner wouldn't be needed, so that would keep the cost down.

Is this practical? Useful?

Here it would not keep chickens safe, the main predators we have to worry about are foxes (would be safe) and mink which swim quite happily, as will rats and they will take chicks.

Assuming you don't have any swimming or flying predators chickens would then be safe but chickens and gardens do not mix so there would need to be a fence to keep the chickens in their side and the garden on it's (or chicken tractors) which is starting to make the area pretty small. If you're going to go trough all the effort of making the thing it probably should be big enough to grow a decent amount of food. I think you would have to go for the bigger size as the area you can use inside will be smaller than your calculations, you need to build it up above the water level or it will be too wet to grow anything.

I'm thinking you are going to access it by a bridge with a drawbridge maybe? (I'll be upset if you don't style the chicken coop after a castle by the way!) because going out to chickens twice a day by boat and needing to get in a boat every time you want a carrot would soon get old.


For us around 1/2 acre will grow everything for a family of 4 including potatoes and large plants like squash, and things like strawberries for jam for the entire year. You many not wish to grow so much but space really is something you rarely wish you had less of.

I think that a lot of animals can actually swim either out of choice, desperation, accident or desire to get to what's on that island!

That said, I've read about a bunch of people who grow on floating pads in the middle of ponds quite effectively and it is a great way to clean water. It may not stop animals completely, but it may reduce the risk sufficiently to be worth it. There's a really large one in China, but I think I also saw a Geoff Lawton video about one. The "floating garden" provides shelter for fish from flying predators.

I can also see potential benefits in high fire risk areas.

It could also be downright prettier and improve reptile/amphibian/insect ecosystems and those groups are under great threat. In fact, you might want to have a way to move the fish from area to area within the moat (like a multi-paddock animal system) to protect areas during frog mating season for example and to allow areas to regenerate before letting the fish back in.

So I don't see a "one right answer" here, but lots of room for research and cost/benefit analysis!

Skandi Rogers wrote: you need to build it up above the water level or it will be too wet to grow anything.

Thanks, I hadn't thought of this. You think this would be a problem even if the pond walls are impermeable enough to hold water and are sloping away at 30 degrees?

Skandi Rogers wrote: I'm thinking you are going to access it by a bridge with a drawbridge maybe? (I'll be upset if you don't style the chicken coop after a castle by the way!) because going out to chickens twice a day by boat and needing to get in a boat every time you want a carrot would soon get old.

A bridge with a super secure gate should be the easiest I'd think. Also, right under the bridge, one could make the moat narrow and just deep enough to deter animals. It doesn't have to be deep enough for fish throughout. Though, of course, if the water level drops, you'll be vulnerable to attack.

Skandi Rogers wrote:For us around 1/2 acre will grow everything for a family of 4 including potatoes and large plants like squash, and things like strawberries for jam for the entire year. You many not wish to grow so much but space really is something you rarely wish you had less of.

The good thing is that mathematically the moat area increases much more slowly than the island area.

Jay Angler wrote:I think that a lot of animals can actually swim either out of choice, desperation, accident or desire to get to what's on that island!

I suppose it's worth doing it on a small scale to find out.

I'd love to know the downsides of the moat - if I anyway want a pond of that size, how does it hurt to make it in the moat shape?

Shayok Mukhopadhyay wrote:

I'd love to know the downsides of the moat - if I anyway want a pond of that size, how does it hurt to make it in the moat shape?

That's the hard part because so much of "permaculture" is trying to hold water on the land, I only see positive things. If you're willing and able to accept the "gifts" the moat-shaped pond will give you, rather than being disappointed when what you envisioned in advance doesn't quite happen, I think you will produce a net benefit. One "problem" with ponds is that the water will evaporate or seep into the ground (if it's not well enough sealed with clay etc) compared to holding the same amount of water in a sealed tank, but "problem" is in quotes because humidity is sometimes a good thing for plants and even in the "Greening the Desert" series (Geoff Lawton) you see "water features" because they grow biomass and clean grey-water.

Ideas:
1. Since permaculture is all about "edges", I would picture this not as two circles, but two wavy edges with the water being wider and narrower in areas, and the slope down and up being steeper and shallower in areas or at least a series of "steps".

2. To keep the "island" high enough above the water line I'd use the dirt I dug out to make the moat and pile it up protecting the top soil to put on the very top.

3. I'd look carefully at the contours of the land looking for existing low or damp areas and consider if I dug there might I hit an existing water source.

4. I would *absolutely* figure out where that water will go if the storm of the century hits! You list your location as "New York". Have you ever heard about "Hurricane Hazel" and when it hit Toronto, Ontario in the 1950's? "Ravines" that people thought were just left overs from the last ice age were suddenly filled with water and washing houses away. I would have a way to lower the water level safely and consider if a larger than usual storm was coming, that I'd lower that level in advance of it, but at the very least I'd read about how to make a pond safely.

Maybe others can provide good reasons *not* to do this, but without seeing pictures of the land and ideally topo maps as well, there are many ways to make this a good thing, even if it doesn't end up being the veggie garden/chicken paddocks that you're picturing. Someone out your way is growing upland rice for example!

I look at this more from an "easy access to water/water retention/diversion" rather than a "safety from predation" situation. Short of acting as a possible deterrent to deer (who also will swim if properly motivated), I don't see it as providing any safety for garden OR chickens without at least an electric fence around the pond.

BUT with a solar powered pump feeding a container that would gravity feed the garden/chickens it would be a great time/labor saver.

Contamination from chicken feces in the pond might be an issue; accessing the chickens in winter may also be an issue.

A pressure release gate, in the event of high water/storm would be critical, as previously mentioned; along with an appropriately created and maintained sluiceway, in the event of an emergency could be life saving.

Hydroponics might be worth considering, instead of a dirt garden...on your island, perhaps within a greenhouse? Fish poop is great fertilizer, to my understanding.

I say go for it, at the very least it would be gorgeous as a picnic spot, or for a small one room cottage for visitors.

Goats. I’ve heard that goats are best confined by a moat (won’t cross water). I don’t know if it would help with predators, but I’ve had far more problems with goats that I can’t contain in a fence than I have with critters that want to get in to eat my goats.

It might not work perfectly but it would be awesome. Plus think about all the hugeling you could do elsewhere with the dirt you dig up. Gotta be thousands of yards!

If you have the means, do it. That's my professional advice.

Never considered a moat, but the property I owned at the time had such a high water table that at some point I planned to create a rather interesting flow path using solar powered DC pumps to put the water back into a ponded area (the property was 500 ft deep.) and "scape" a stream with a roundabout enough flow pattern to accomplish much of what you're talking about... except for the animals.  I know we had red fox, deer, and at least one larger predator in the area; I'm not sure if the groundhog(s) I saw were "in residence" or on the property next door.

Anyway, to the point:  had I been able to keep the property, we would have had chickens and goats... but close enough to the house to make the predators wary.  Plus enough outdoor cats and probably a sheepdog, etc.... naturally the kids thought I was an old meanie telling them if we did it, the dog would live outside!  I'm not quite sure how well my gardening ideas (combination of gardening in small spaces, square-foot-garden style boxes along the "streamside path", etc. would have worked given the interesting plant eaters, but I'd have loved to try.   Ultimately I think a balance would have been achievable between the human wants and garden goals and not trying to get rid of all the nearby wildlife, but one year is not enough to figure it all out! The enjoyable part of all of this is the challenge of figuring something out that we like, can live with, and doesn't break the bank.  Which is why I rejoined this site, by the way! I'm about ready to try whatever nifty again!

Since the Dark Ages, rabbitry in Europe relied on man-made islands planted with rabbit food, and with man-made warrens, to keep the nobles rich.  Its a tried and true practice.  

That being said, you realize by now, you have to provide shelter from predators.  Roosters and trained dogs  have the attitude to provide most protection.. Alas, cant mix in a garden.

There are a lot of useful aspects to your idea, even if not altogether what you were hoping when you first mentioned it.  I have a small pond on my property, and I've been thinking about putting an island in the middle of it, primarily to contain a clump of bamboo -- we are in zone 6b, and can grow several kinds here, but I don't want to turn running bamboo loose on the neighborhood, either.  It's just that it's such a useful plant, I'd really like to have some.  My pond is old and needs to be re-dug, and the material could just be dumped in the middle to form the island.  

Then you have all those edges where you could grow plants that like wet ground, like asparagus, rhubarb, horseradish, and many other edible marsh plants.  

All Technical and critical analysis aside, this is a brilliantly useful and interesting idea!  We see these around in our area, (probably not as big) mostly with park benches, landscaping plants, decor, gazebos what not.  If we had one we'd probably paddle the jonboat out to it 😄

... look up Irish ring fort! - larger than proposed project, but inspiring... every homestead needs a pond/ponds -  sounds like moat/ring pond would be even better idea... if original useage doesn't quite pan out many more will come to mind.      

My thought on this would be to make the garden a ‘land moat’, so you have the chickens in the very center, fenced in to keep them out of the garden. The ring of plants around the chickens acts as a buffer to keep the nitrogen from the chicken poop from leaching into the moat. Veggie scraps go into the middle to feed the birds, and waste comes out to fertilize the garden. If you had wood chip bedding and rotate the yard, the manure would cool off enough that it wouldn’t need to be composted. I’d still be inclined to fence the moat or the island, because water won’t keep predators out. You also have hawks to consider. Maybe a couple guard geese? As others have mentioned, solar floating pumps could water the garden if needed, though that may not be a problem if the moat raises the soil moisture. But if you have fish in the moat that water will contain nutrients.
Definitely sounds like a fun project to consider!

Thomas A. Cahan wrote:... look up Irish ring fort! - larger than proposed project, but inspiring... every homestead needs a pond/ponds -  sounds like moat/ring pond would be even better idea... if original useage doesn't quite pan out many more will come to mind.      

Time Team has any number of episodes about islands and such. Most episodes had demonstration of appropriate technology of the era. Hi-def versions of much of the 20 years is available on Amazon.

I think a racoon would wash your chickens before eating them in a moat.

Kathleen Sanderson wrote:There are a lot of useful aspects to your idea, even if not altogether what you were hoping when you first mentioned it.  I have a small pond on my property, and I've been thinking about putting an island in the middle of it, primarily to contain a clump of bamboo -- we are in zone 6b, and can grow several kinds here, but I don't want to turn running bamboo loose on the neighborhood, either.  It's just that it's such a useful plant, I'd really like to have some.  My pond is old and needs to be re-dug, and the material could just be dumped in the middle to form the island.  

Then you have all those edges where you could grow plants that like wet ground, like asparagus, rhubarb, horseradish, and many other edible marsh plants.  

I have exactly the same plan, an island of bamboo! We are probably a year or so from digging the pond in our lowest, wettest field, as the last and biggest of a series of water catching structures on our slope. The plan is that the island will be planted with edible and timber bamboo. I want cattails and other aquatic edibles in the pond itself.

2 thoughts to add to this.

1.  Do you need a true island for this to work?  There is an article in Farm Show Magazine for a large floating garden.  Can't link to it successfully but it is 2002 volume #26 issue #3 ""Floating Garden" Never needs watering" is the title.  Double its size an it would probably do what you want with no dirt in the middle of your pond.  It would still be half of your listed desire but if you garden intensively do you need that much?  Remember because your water supply is basic unlimited nutrients become your plant limit.

2.  I have done a floating tomato garden about 4 foot x nearly 7 foot.  It has worked incredibly well.   Only ever had 3 failures of moat affect.  1.  It floated in under the pier one night and the raccoons just walk right off the pier and onto the float and did serious damage.  2.  Had holes(looked like tooth holes) appearing in many the tomatoes.  Thought I had a rat or something.  Trapped like crazy.  Caught a small long billed bird.  Thought that was just bad luck.  About a week later caught a second one.  The tomato damage stopped.  So it was bill holes not tooth holes.  3.  Tomatoes that actually hang in the water take snail damage.

 From doing the float for about a decade and swimming around it  I know the water under the float is very noticeably cooler in summer.  Outside the float at a depth of up to a foot the water is warm to very warm.  Reach in under the float at the same depth and the water is cool.  So with it you could likely keep fish from some of their heat stress in summer by giving a cooler place to retreat to.  I assume the larger the float the more reliable the cool.  Add a bubbler under it to maintain the cool water solidly oxygenated as the other piece to help the fish as warm water loses oxygen.  Might get a double benefit here in that in aquaponics aerating the water in the floating part increases production.  Would the same thing apply if the water being drawn up into floating garden was solidly oxygenated?

Another benefit of a floating island planted with edible (or any) plants is that if the water is eutrophic (excess nutrients) these can be taken up by the plants. This is a remediation technique sometimes used in lakes with algal blooms or other issues associated with water being too high in nutrients. So in addition to feeding your flood plants on the floating island, you may be improving the water quality overall by tying up those nutrients in plants, especially if those will be harvested.

I think a similar effect of nutrient removal can be achieved using chinampas, which are a traditional gardening method  in Central America. So-called floating gardens but as I understand it, in reality they are stationary garden beds contained by reeds in a lake, the floating part is how you access them.

Edited to add: removing nutrients also improves oxygenation of the water, especially if there is overgrowth of algae. They photosynthesize and add oxygen during the day but respire and use oxygen/add carbon dioxide at night. Plus if they overshoot their sustainable population size and die off, that increases the biological oxygen demand and if the pond or lake goes anoxic that makes things even worse. So starving the algae of nutrients and preventing blooms is a good thing.

Cooler water also holds more oxygen than warm water. I don’t know whether the shading effect mentioned in previous message results in enough of a temperature change to make a difference in oxygen holding capacity, but it can’t hurt.

The Aztecs (Culhua-Mexica) were a nomadic tribe that settled in Tenochtitlan Islands (now Mexico city) because they were rebuffed by the more powerful local populations and forced to live where no one else would. There they developed their floating gardens and very likely owe their rise to the Chinampas.

Here are some pictures of the Mexico City Chinampas:









source

This might help explain:

https://en.wikipedia.org/wiki/Xochimilco

Anne Miller wrote:Here are some pictures of the Mexico City Chinampas:

There are people in Mexico who are trying to rehabilitate and revitalize some of the ancient chinampas. A way of producing food close to the population as well has improving water quality.