Can metal posts sided with metal roofing, along one side, support the water weight of a pond?

Site:  Eastern Coast of Mid Vancouver Island, BC, Canada (clueless as to what zone that might be).  I have a 20 foot wide, 30 foot long unused sliver of land, on a fairly significant slope (five feet over 20 feet) between the house/deck and the 6 foot fence (8 ft Chain link fence posts, pounded in 2 feet, sided with metal roofing).  Neighbor has very large, overhanging maples, along this southwest facing section, the only shade we get.  Between the height of the house and roofed deck, and the fence and trees, neither I nor this strip seem to be much good for "growing", so envision turning it into a wildlife oasis, and chill spot.  I think the bottom of this slope is begging for a long, skinny (8-10 foot wide, 30 foot long, 3-4 foot deep) pond, that should be land predator proof, due to existing climb proof fencing, and this long narrow strip, being unfavorable to avian predators.  Hopefully haven to songbirds, amphibians, and likely used as a "wilding" area for some of the wildlife patients.

Pond Vision:  I imagine a 35 foot long, 3-4 foot deep, 8-10 feet wide "trough" covered with pond liner, full of water.  Now think pollinator garden plants (tough in the shade, so maybe instead rhodo's or some such???), established in the ponds "retaining walls".  Now plop in several dirt filled 150 gallon Rubbermaid stock tanks that will also be planted pollinator style, bingo, islands.  Add underwater plant ledges for the pond plants, interspersed with long narrow trays holding pebbles to create "shallows" for the birds and create a 'beach access' for snakes, frogs etc.

Construction Advice:  BIG question, how do I figure out the "strength" of the existing "wall"?  My thought is alone it will not be strong enough, so plan to run a second row of posts, every three feet, pounded at least 4 feet down, also surfaced with metal roofing panels, 12 inches from the fence, back fill with gravel/dirt, for planting, and do the on the down slope end.  Would this be solid enough to withstand the weight of the water?  Am I completely entering "overkill" mode; or sadly delusional about the weight of water, and what is needed to support it?

Planting Advice: I really want this to be a carefree space both in actuality and looks.  Truth is, I am a great 'starter' but a lousy finisher when it comes to growing, anything.  Baby season for me runs pretty much March to October, with April-August the season of all nighters, doing 2hr bottle feeds, around the clock.  No matter my intentions, by June, any hopes of successfully growing anything edible is long gone; due to neglect.  So consider me a complete newbie, who needs the kindergarten plan, if not the toddler plan!  Ideally there would be some sort of edible berries or some such, but if it is just pollinator attractants, that is just fine, the hummers will love it.  In my mind there is low shrubs/bushes along the fence wall, and in the 'islands', reeds, iris's, water lily type stuff for the water and pebble shelves, and over hanging/dangling fruiting/flowering stuff on the second 'retaining wall' closest to the deck.  I do not want this to be a dead zone come winter, so plants, shrubs, etc. that keep their greenery all winter should be high on the list (California lilac?).  Watering will be done by soaker hose with collected rainwater, as will pond supplementation.

Filter:  In baby duck season I just MIGHT let them use this pond...so with the over hanging leaves, bird poop, etc., a solid but simple filter system will be required, and you guessed it, I know diddley squat about ponds or filters.

I do have several "pond experts" (friends with ponds to landscape professionals) coming in the next few weeks, but am really wanting to go a lot more permie than I suspect ANY of these folks will.  I would rather hit the swamp for water plants, or the forest for other plants, than a nursery (which I get may not be practical) and I absolutely will not use chemicals.  Basically I want to make this tiny oasis as natural, and self sufficient as possible; a self sustaining ecosystem, that does not turn into a sludge filled, mosquito breeding swamp.

Winter temps here will hit -10c for a few days to a few weeks; other than that it stays in the -5c to +15c range.  Summers are 25c - 35c range.  Rain is pretty regular, October to June, but we could go 3-6 weeks of no rain through July-Sept.

Thanks for any input you can offer...

If you were building a circular pond in this manner, no problem.
Here are some quite good instructions for this:
https://www.instructables.com/How-to-Build-a-6000-gallon-Water-Tank/

Are you aware of ferrocement construction? It can be used for making strong water proof stuctures for ponds and tanks. I think it may be a better bet for what you are suggesting. I'd be worried by the weight of water collapsing that wall structure. 2ft deep isn't that much for the post, considering the depth of water it is supporting above. I seem to remember seeing recommendations for retaining walls for soil of 2/3 below ground for 1/3 above ground, or the posts will shift over time.

For a start look at this link permies topic about ponds on steep land

and Building ponds and dams

2ft deep isn't that much for the post, considering the depth of water it is supporting above.  

 I agree, that is why my thought is to run a second wall, a foot or so away from the existing fence with the 8 foot posts pounded down at least halfway, and placing them every three feet, instead of every six feet as the existing fence is.  The space between the two "walls" would be filled with dirt for planting.  I am unsure if this would be sufficient or if it is over kill.  The metal panels are 12 feet by just over three feet; so pond depth would match the height of the panels.

 For a start look at this link permies topic about ponds on steep land

and Building ponds and dams

Looks like I put this in the wrong place maybe...

I took a look, but found nothing to help me determine if the wall method I am thinking of will be sufficient.

 Are you aware of ferrocement construction?  

 I am vaguely familiar with ferrocement.  I AM trying to avoid any concrete/cement, if possible... it's heavy work, and we are in an earthquake zone, so not keen on something this large developing a crack when the ground shakes, even with the metal reinforcement, I don't know that I would trust it. But I do realize that is the 'normal' way to build a pond.

I have dozens and dozens of these roofing panels, left over from the fencing project, so am hoping to utilize what I have on hand, if it would be at all possible.  I have a tendency to use products in ways they are 'not advertised' for...

Based on your concept,the volume is about 35x4x10=1400 cu.ft. 1400x62 lbs/cu.ft. = 86,800 lbs. total weight. (1400ft³= 39.64358m³, so 39 tonnes if memory serves.)

It's a lot of weight. Most of that weight is supported by the base. But with a liquid, there is also substantial pressure on the sidewall. Any gearheads out there who know the math on this?

Edit 2: Apologies for posting, then mulling, and posting again. That's unnecessarily confusing.

If the fence/dam fails, will the water destroy anything on your neighbor's side?

Could you do the double fence and then pile soil against it so that your pond starts 3' away from the fence?  Then the pressure on the fence might no be so bad...

Mike Haasl wrote:Could you do the double fence and then pile soil against it so that your pond starts 3' away from the fence?  Then the pressure on the fence might no be so bad...

I agree, a soil berm would be helpful. Even if the fence holds the water now, I wonder if it would bow out over time (in a very wet or very dry year, for example).

Douglas Alpenstock wrote:
I agree, a soil berm would be helpful. Even if the fence holds the water now, I wonder if it would bow out over time (in a very wet or very dry year, for example).

Architects and engineers are taught that anything they build is going to fail (eventually or rather quickly if they do a bad job designing it).

With that in mind... What will happen when your dam fails? If it is just a matter of some downhill trees and vegetation gets a short but strong bath, if so, you have some freedom to play. If that water is going to do some serious damage, then you gotta do it right. But even if you do it right, eventually, it will fail. So you gotta ask yourself if you should.

Chickens love narrow strips of land, as do many other birds. Perhaps stuff could grow there with some soil amendments. Perhaps it would be a good place for an unsightly compost pile (which might leach some love into that soil and amend it for you). I’m not trying to suggest you do anything specific, I’m just trying to offer some thoughts to consider.

Good Luck!

Architects and engineers are taught that anything they build is going to fail (eventually or rather quickly if they do a bad job designing it).

As a Civil Engineer, I reckon your comment is the strangest thing I have ever read.
Where is the evidence behind such a comment?

Let us start with the Pyramids, Parthenon in Greece both of which have had thieves steal lots from them.
Hoover Dam, Golden Gate bridge, Eddystone Lighthouse.

Sure accidents and collapses have occurred through problems with design or materials.

The "pond" would be 4 feet deep (at the very deepest), rising with the natural grade to zero depth, over JUST 6 feet and run 30-50 feet long - 300 sq feet.  

This is NOT going to flood anything if the "dam" gives way, although the neighbors lawn may be the worse for wear, I doubt it would cause permanent damage.  Rainy season is not an issue, it is a pond, it will have an overflow that will join with the rain runoff from the asphalt shingles/galvanized roofing (toxic for fish etc.) and be sent to the ditch, where the plants and dirt can deal with it.  No, a berm is NOT an options as this area is only 20 feet wide; compost is NOT an option as this strip runs the entire length of the deck and is outside our and our neighbors bedroom window - the smell would be an issue.

Really, I am just trying to find out HOW to do the math on what sort of structural strength my three foot metal roofing wall will have.  Should the poles be at two or three foot intervals?  Is a six foot pole pounded in three feet enough; or should it be an eight foot pounded in five feet.  Then I am looking for plants that would be wildlife friendly, and love only 1 hour of sun a day, on the Wet Coast of Canada.

I think Paul has a point, in that catastrophic failure, however you build it, needs to be taken into account, whatever the specifics. There are issues of liability here, especially if there are things living beyond the overhanging maples.

Unless you structure the fill between metal walls so that it's not only self-supporting, but actually countering the sidewall pressure of the long pond you're constructing, it's just more debris to be washed towards your neighbour's property.

Is there a reason a shallower pond, or rill, if you will, couldn't serve the purposes to which you wish to put your narrow pond? If the water were only two feet deep rather than four, you not only cut the weight in half, but also the height at which it presses against the sidewall.

If you had a two-foot deep rill half-filled with large river stones, and maybe some type of solar-powered circulation, and maybe a slight decline from a "source" that would be the pump outlet, slightly uphill, and a slightly deeper, wider ponding area on the downhill end, you could work with a quarter of the original amount of water, and the stones taking up the balance of the volume could be stacked so their weight is supported entirely by the ground.

I suppose the question I am asking is, is the depth of water you want necessary for your purposes, or do you think it would just be nice to have?

-CK

Paul Eusey wrote:Architects and engineers are taught that anything they build is going to fail (eventually or rather quickly if they do a bad job designing it).

I'm a mechanical engineer.  In my education I don't recall being taught that anything I build is going to fail.  It was more along the line of how to calculate and predict if the thing you're building is or isn't going to fail in a given period of time.  

It's usually a matter of cost vs required lifetime.  A steel railroad bridge is often comprised of more air than metal.  If it was made from a solid block of cast iron (80' high by 200' long by 12' wide) I'm pretty sure it would not fail for 5-10 thousand years.

Building a pond that is supported by posts and metal roofing is likely a bit closer to the "low cost" side of the spectrum than it is towards the "10,000 year lifespan" side.

Lorinne Anderson wrote:

This is NOT going to flood anything if the "dam" gives way, although the neighbors lawn may be the worse for wear, I doubt it would cause permanent damage.  


Really, I am just trying to find out HOW to do the math on what sort of structural strength my three foot metal roofing wall will have.  Should the poles be at two or three foot intervals?  Is a six foot pole pounded in three feet enough; or should it be an eight foot pounded in five feet.  Then I am looking for plants that would be wildlife friendly, and love only 1 hour of sun a day, on the Wet Coast of Canada.

If you don’t have to worry about failure, then you are free to play.

In order to do the math you would need to know the numbers and I honestly don’t think you are going to find those numbers for metal roofing being used in a way it was never intended (or tested) for. Snow load may have been tested, but not for water pressure when repurposed as a dam (that most likely doesn’t exist). I recommend testing it to see if you can get it to fail and using common sense and a lot of caution to apply it to your intend use. Water is the most powerful and destructive force of nature and should never be underestimated.

So... No way to do a proper calculation and no danger from failure. So you gotta wing it if you want it.

I’m not going to go long winded with suggestions you may not want nor need. But I will add a few quick thoughts.

I would use alternating metal and thick wood posts (4x6 or larger), both set in concrete (and give that concrete at least 30 days of wet curing, 60, 90, or 120 days would be better). You definitely want to go deeper than local building code for footers (below the frost line). I would go as deep as you can (I have no idea what kind of soil you have so that is all I can say).

You can also overlap the roofing panels (interlock roofing panels in layers to increase strength).

A pond liner is a must and make sure the ground around the footings for your dam posts are sloped to move water away (so that it will never become weak soggy ground).

Speaking of the frost line... Have you thought about freezing? If, or when (I should say), that pond becomes a solid block of ice and expands, it could get very interesting. (I envision a huge battering ram of ice racing down a hill, but I don’t even have a mental picture of your area so I don’t even know if that’s possible, but it’s an interesting thought).

In the end, it’s your project, do whatever you like. It could be a lot of fun, it could be challenging, it could be frustrating, etc.

Plants can be collected from nearby ponds, lakes, and streams. Streams are more likely to have the low light conditions that match yours.

Regardless, I wish you the best of luck and hope it turns out great!

Best wishes.

Mike Haasl wrote:
I'm a mechanical engineer.  In my education I don't recall being taught that anything I build is going to fail.

It's usually a matter of cost vs required lifetime.  A steel railroad bridge is often comprised of more air than metal.  If it was made from a solid block of cast iron (80' high by 200' long by 12' wide) I'm pretty sure it would not fail for 5-10 thousand years.

Hmmmm... That ideology was drilled in over and over in most of the engineering and architecture classes I took. It was intimately tied into the ethics of trying to make sure your skyscraper doesn’t kill too many people when it fails. That was back in the 1990s, many years prior to 9/11. So I imagine it is emphasized a lot more since then.

And I’m pretty sure that solid block of iron bridge would oxidize and rust away fairly quickly. I’ve seen 100 year old iron rust and flake into a pile of rust chips (if left outside). There are very few builds that are 5000 years old and not buried underground and of those few things that are above ground, all are monolithic. Newgrange And Stonehenge come to mind, heck, the pyramids in Egypt are only 4500 years old (but they are in a desert). I can’t imagine anything but fossils (and stone tools forgotten in caves) going past 10,000 years. Makes me wonder which school is teaching this kinda stuff...  5 to 10k years??? For engineering??? I don’t doubt they are teaching it, but that’s just nuts.

Thank you to everyone for your input...

...is the depth of water you want necessary for your purposes, or do you think it would just be nice to have?

 

Could you do the double fence and then pile soil against it so that your pond starts 3' away from the fence?  Then the pressure on the fence might no be so bad...

The depth of the pond is currently being determined by the slope of the land.  When we built, we had to elevate the level of the land the home was on, this raised us a good 4 feet above what WAS grade, and level with the neighbors on east.  This strip of land is on the west side.  The width of the area in question is small, I just measured it and it is even smaller than I thought at 14.5 feet; the last 7-8 feet, before the fence, it gradually drops almost 4 feet.  Rather than fill the area in, my thought was to USE the existing depression for the pond.  

So I am dealing with a gradual slope down; "grade" for about 4 feet, then about a 6-12 inch drop over 2 feet, then a further 3-4 foot drop over the final 8 feet.  I do intend to step the "pond wall" back from the existing fence, a couple of feet, and back fill with dirt to plant wildlife friendly plants, but certainly there would not be enough room for a full on berm - that would just bring me back to the "original" plan of fill it in with gravel and dirt, to bring it up to "grade"; about as expensive as a pond liner....

I would use alternating metal and thick wood posts (4x6 or larger), both set in concrete (and give that concrete at least 30 days of wet curing, 60, 90, or 120 days would be better). You definitely want to go deeper than local building code for footers (below the frost line).

 

I was under the impression that pounded posts were more structurally sound than dug/concreted posts as the soil was undisturbed.  Does anyone know if I am mistaken on this?

I am VERY leery of wood posts as we are on the West Coast, where it rains A LOT and just had to replace over 500 feet of fence due to rotten posts and lower portions of all the fence boards.  I want this to be a one time effort, BUT do have some six inch "pencil posts" that are pressure treated and could be repurposed to augment this; but I am concerned as they rotted, their structural integrity would slowly fail, and become useless.  I am also concerned about the toxic gick factor of pressure treated wood combined with the water and plants as this is to be a wildlife pond.

Speaking of the frost line... Have you thought about freezing? If, or when (I should say), that pond becomes a solid block of ice and expands, it could get very interesting. (I envision a huge battering ram of ice racing down a hill, but I don’t even have a mental picture of your area so I don’t even know if that’s possible, but it’s an interesting thought).

 

As we are on the west coast, freezing is not much of an issue.  With our mild winters we would be subzero, at best, for two weeks a year.  For those few weeks, it would be need to be kept open with a pump, aeration or some such measure or it will be useless to the wildlife.

Chickens love narrow strips of land, as do many other birds. Perhaps stuff could grow there with some soil amendments. Perhaps it would be a good place for an unsightly compost pile (which might leach some love into that soil and amend it for you). I’m not trying to suggest you do anything specific, I’m just trying to offer some thoughts to consider.

 

Sadly, as it only gets one hour of sunshine a day, between the house/deck on the east; 6 foot fence (with towering maples on the other side of it) to the west, massive firs/cedars to the south and massive willow to the north.  I do not think any domesticated birds would enjoy being "trapped" in this area (plus the resident Coopers hawk and other birds of prey already like the trees for perching and hunting songbirds); for the same reason, I am at a loss of what to plant, besides rhodo's and such.  Being directly between both the neighbors and our bedroom (total of 40 or so feet between us, at this spot) the bird or compost option is out due to noise and odor concerns...hence my thought to create a wildlife oasis, that us humans could also enjoy.

So, rather than pay someone to truck in loads and loads of gravel to level it up to grade, it seems more prudent, and environmentally friendly to spend that money on the pond liner, and use what nature gave me to create an oasis for her creatures.

So back to the original question:  anyone know how deep I should pound those metal posts, how wide to space them, and what sort of plants (land, semi aquatic and aquat would thrive with little to no direct sun, in a mild, damp climate, as we have on the south west coast of BC?

Lorinne Anderson wrote:
So back to the original question:  anyone know how deep I should pound those metal posts, how wide to space them, and what sort of plants (land, semi aquatic and aquat would thrive with little to no direct sun, in a mild, damp climate, as we have on the south west coast of BC?

Considering your dam would be less than 9 meters (from my understanding)... I think your best bet would be to contact one of the dam safety folks for your area. (Scroll down to the second table of contacts titled, “MINISTRY OF FORESTS, LANDS, NATURAL RESOURCE OPERATIONS AND RURAL DEVELOPMENT (FLNR) REGIONAL OPERATIONS (responsible for dams 9 metres or less in height)”

https://www2.gov.bc.ca/assets/gov/environment/air-land-water/water/dam-safety/2020-11-20_dam_safety_staff_contact_sheet_external.pdf

Good Luck!

Lorinne Anderson wrote:Thank you to everyone for your input...


So back to the original question:  anyone know how deep I should pound those metal posts, how wide to space them, and what sort of plants (land, semi aquatic and aquat would thrive with little to no direct sun, in a mild, damp climate, as we have on the south west coast of BC?

I can't answer any questions on pond construction, but water mint and possibly wasabi would like those conditions, water cress might manage as well depending on the light levels.

Lorinne Anderson wrote:So back to the original question:  anyone know how deep I should pound those metal posts, how wide to space them, and what sort of plants (land, semi aquatic and aquat would thrive with little to no direct sun, in a mild, damp climate, as we have on the south west coast of BC?

I'm not sure of the exact answer either, but I know that in pasture or other (mostly) dry land situations, a six foot post would typically be sunk two feet. In your case, the soil is likely wet all the time and therefore less stable. So, I'd want to sink them at least half the length of the post. Then I'd consider it an experiment until the test of time gave it a final score.