got rid of pond...

[patandchickens]

Ok, so it is not going to recirculate, just store rainwater runoff and bleed that down to feed the trench and koi pond, yes?

(You could put in a tiny waterwheel if you feel like it, just for fun, but it's not going to run a pump sufficient to pump the water back up to the cistern -- that would be a perpetual motion machine, you know? and sadly, not going to work )

Let three months' of runoff (the "cool" months before it gets very hot and evaporation becomes An Issue) = ~ 10,000 gallons. That's not counting snowmelt BTW. Then my cistern has to be about 14 feet across. I can make the cistern as deep as 10 feet, but it will have to be 12 feet across at least.

Well, if you want to keep water in this thing year-round (?? - but if you don't, not only will you have to replace fish etc every year but you are likely to experience SUBSTANTIAL winter damage to the cistern, probably to the point of it no longer holding water) then you are going to need much larger than that, yes? You need excess capacity for 10,000 gallons, on top of whatever amount of water you keep in it routinely. Or am I misunderstanding something here?

10' deep seems reasonable as long as it's nearly all underground, but it is not clear to me how you would achieve vertical walls or anything like it, especially not if the ground is naturally wet as you describe -- how would you hold back the earth on the sides of the excavation for long enough to build a rock retaining wall? And unless you can build nearly vertical sides (or anyhow very steep such as large amounts of rock riprap on a super heavy-duty liner [you can get something approaching a 30-40 degree slope that way in experimental ponds] then the volume will be much smaller and you may develop a significant problem with stinking mudflats being exposed around the edges as pond is drawn down to water trench and koi.

Also be careful about digging a pond right near a building that you care about -- the resulting changes in water level and soil saturation can seriously mess up the building's foundation and stability. I have no idea what is safe vs not safe and I assume it depends on your soil, but it might be wise to chat up an engineer before digging a pond right near the barn if you care about the barn.

Your big evaporative loss is going to be the trench (I was thinking the cistern was going to be much larger across, my fault for not reading carefully enough!). I'm curious on what you're basing your estimate for that? I would have guessed higher, because it's both evaporation *and* plant transpiration. Plant transpiration is an incredibly powerful thing. I used to work in temporary (vernal) ponds that would be 2-3' deep for several months and then when the trees leaf out in the spring (these were wooded ponds) BANG most of the water drains away within a week like someone pulled the bathtub plug.

Is there a particular *reason* for the reed bed trench thing, btw? Usually they are used to improve water quality (nutrient load and bacteriological issues) for water coming from a skanky source like greywater systems or a pond with fish being fed in it. If the main point of the reed bed trench thing is just to be able to grow those plants there since the water is available, maybe it would be better to pipe things as a 'Y', with the koi pond and reed bed being separate endpoints from the cistern (could branch from a single feeder line coming off the cistern, of course). That way you have more ability to ration water. In fact you could plumb it this way for now, build a *section* of reed bed trench, then spend a couple years seeing how your water supply behaves and how much water the trench actually uses... after which it would be quite easy to convert the plumbing to run all the water through a fully-enlarged reed trench if that seemed feasible. Meanwhile it would preserve your flexibility.

Just some things to consider anyhow.

Have fun,

Pat

 

[wolftheef]

Hi all, After reading about your slimy green ponds, I wanted to let you all know that you can use a UV filter. I had a pond at my old house that my brother and i built, with waterfalls and all. After one summer of sliny green water and not being able to see my beautiful koi, I did some researcha nd found out about these filters. I bought it at a fish/pond supply store. It took all the algae out. The pond was crystal clear. Of course, It didnt stop the bird that swooped in one spring and ate all my fish and ripped my liner to shreds. But thats a different story.

 

[setter4]

Hi all, After reading about your slimy green ponds, I wanted to let you all know that you can use a UV filter. I had a pond at my old house that my brother and i built, with waterfalls and all. After one summer of sliny green water and not being able to see my beautiful koi, I did some researcha nd found out about these filters. I bought it at a fish/pond supply store. It took all the algae out. The pond was crystal clear. Of course, It didnt stop the bird that swooped in one spring and ate all my fish and ripped my liner to shreds. But thats a different story.

At the same time I had the slimy green pond I owned a pet supply store that sold pond supplies including UV filters. lol
I'm just not willing to put that much effort into a swimming pool for my dogs!

 

[Rosalind]

Ok, so it is not going to recirculate, just store rainwater runoff and bleed that down to feed the trench and koi pond, yes?

Yep.

Well, if you want to keep water in this thing year-round (?? - but if you don't, not only will you have to replace fish etc every year but you are likely to experience SUBSTANTIAL winter damage to the cistern, probably to the point of it no longer holding water) then you are going to need much larger than that, yes? You need excess capacity for 10,000 gallons, on top of whatever amount of water you keep in it routinely. Or am I misunderstanding something here?

Yep. But I figured I would manage the water volume same as I manage my swimming pool water volume--if it's getting kinda close to the top, pump some out into the reed bed. The idea being that even if there is a crack in the liner somewhere down there, it's so close to (or in) the water table that it's a non-issue. Sort of like building a catchment pond, but clean enough to hold water for a fish population.

10' deep seems reasonable as long as it's nearly all underground, but it is not clear to me how you would achieve vertical walls or anything like it, especially not if the ground is naturally wet as you describe -- how would you hold back the earth on the sides of the excavation for long enough to build a rock retaining wall? And unless you can build nearly vertical sides (or anyhow very steep such as large amounts of rock riprap on a super heavy-duty liner [you can get something approaching a 30-40 degree slope that way in experimental ponds] then the volume will be much smaller and you may develop a significant problem with stinking mudflats being exposed around the edges as pond is drawn down to water trench and koi.

There's where I am fortunate to work for Big Pharma. I can use the liner thing and rely on a stonework/rebar thing for structure (I know a guy who does that sort of thing), or I can get ginormous plastic or even steel tanks that are being discarded from old pharma manufacturing plants and build what is essentially decorative stonework around it. They don't crack, even when you fill them with 10,000 gallons of maple syrup and stick a giant marine turbine in to mix it. How much will be sunk underground...This is a bit difficult to explain without a picture, but you know those old 1800s bank barns, the kind with two levels--one where the cows go, one where the other critters go, and you're supposed to pitch hay down at them all through a sort of central gap in the floors? That's what I've got, built into the side of a slope. Originally, there were retaining walls on each side that kinda blocked off the lawn from the sheep pasture, and there still is one remaining retaining wall on t'other side. I want to put the cistern in on the side where once upon a time there was a retaining wall. So it will be buried on 3 sides, not on the 4th.

Also be careful about digging a pond right near a building that you care about -- the resulting changes in water level and soil saturation can seriously mess up the building's foundation and stability. I have no idea what is safe vs not safe and I assume it depends on your soil, but it might be wise to chat up an engineer before digging a pond right near the barn if you care about the barn.

Yeah, this plan is actually the result of that engineering conversation. I have to do something to control the water flow. The previous owner simply re-graded, which helped, but not enough.

I would have guessed higher, because it's both evaporation *and* plant transpiration.

Like, how much higher? I wasn't sure how to guesstimate that, because it has to depend on the type of plants, yes/no?

Is there a particular *reason* for the reed bed trench thing, btw? Usually they are used to improve water quality (nutrient load and bacteriological issues) for water coming from a skanky source like greywater systems or a pond with fish being fed in it.

Well, my understanding was that koi in particular need exceptionally pure water and that roof runoff really was not going to be acceptable to them; also that copper plumbing does a number on their little kidneys, and we just have too many gnawing critters that love to eat rubber and wire around here (ask me how I know... ) such that other methods of hard-plumbing a water source wouldn't really be feasible. But a siphon line that I can unhook after running it once in a while, that's more do-able and less prone to chewing critters. Another issue being, my property backs onto conservation land. On said conservation land is, you'll love this, the Blue Spotted Salamander, Wood Turtles, various endangered owls, two sorts of endangered snails, sticklebacks, and a truly impressive assortment of endangered dragonflies. I have to keep an easement open for the wildlife biologists to hike across my yard and do surveys. So, yeah, water quality, they will get a tad bit upset if the stuff I am putting in the soil is anything less than, you know, Evian.

 

[patandchickens]

Like, how much higher? I wasn't sure how to guesstimate that, because it has to depend on the type of plants, yes/no?

Yes. In general wet-ground type plants will have higher evapotranspiration (per unit biomass or leaf area, I am not sure which it scales best with) than plants typically living in drier areas. And plants can make a huge difference in drying out soil, so it is a much higher number than just evaporation alone.

If you google "rates of evapotranspiration", with or without another term such as marsh plants, you will find a bunch of hits involving actual numbers (many of them require online journal access which I lack but you would surely have) that may help you get a ballpark figure.

Good luck,

Pat