Rosalind said:
My plan is to build a rock thingy per the instructions given by Scott & Helen Nearing (build wood forms at a certain rise/run angle, dump in rocks + mortar, remove forms, make a nice surface using prettier rocks and mortar). Then I'm going to put a pond liner in there, that'll be my cistern.
You'll want to make *real* sure the walls are thick/braced enough to stand the horizontal force of the weight of the water.
To control the mosquito/mayfly/waterboatman population that occurs in all still water around here, I'm going to put in trout, bluegills, the local freshwater pond-type fish, also crayfish and freshwater shrimps.
Have you looked at the numbers for this. Trout, especially if you mean larger rather than 'eensy fingerling and then they die before getting bigger' type trout, need pretty cold water, which in most places requires DEEP water or a constant spring-fed creek. Centrarchids (bass, crappie, sunfish) are much more tolerant of warm water but even they may have trouble in a pond that's just a few feet deep and partly aboveground, especially if it's in the sun.
Also the fish will eat the freshwater shrimps (dunno if you mean REAL shrimps or amphipods, but, either way) and whatever the fish don't eat, chances are the crayfish will. If things are crowded and food is short, the crayfish and fish will also go after each other to some extent (unless you use small baby crayfish - then the fish will just eat the crayfish).
Finally, think about stocking densities - I do not know what volume pond you're contemplating but it's unlikely to have room for all *that* much fish biomass.
Then I'm going to dig a trench from the cistern to the boulders at the other end of the grassy yard. Fill trench with packed clay (soil is all clay around here) and yet another liner, then put rocks/pebbles in. In this trench will be planted reeds, comfrey, cattails, cress. Trench will be fed periodically by means of siphoning from the cistern when needed.
This part sounds reasonable as long as you tap off water frequently enough to keep the trench plants happy (because they will be growing on top of a liner, their *only* source of root moisture will be the water you add from the cistern, and even if there are a couple feet of soil over the liner that's still a pretty finite supply)
The trench creek will feed into a koi pond dug around the boulders. I can maybe make a sort of waterfall type thing using the boulders, too, to aerate the water. The idea is that the whole thing will be rainwater fed and gravity-driven--to recirculate water, all I have to do is start the siphon, which is easy.
Sorry, I am totally not understanding this part. How is it 'recirculating' -- what I am seeing is the rainwater-fed cistern is tapped into the trench, which runs into the koi pond and then that's it. You would need a pump to return koi pond water to the cistern to make it actually recirculate.
Recirculating or not, I fear that there are several serious problems with this part of the idea. First, you are going ot have to tap off a LOT of cistern water, pretty frequently/continually, to offset the very large amount of evaporation that the reed trench and koi pond will experience. (Reed trench especially). I can't see your rainfall posssibly providing that much!
Second, you wouldn't *want* a recirculating system I don't think, anyhow, because the water will be quite warm by the time it was pumped from koi pond back to cistern (too warm for trout) and also if you were recirculating it the proper order of operations would be cistern -> koi -> trench (using the trench plants to scrub out the excess nutreints from the koi part of the system before returning water to the cistern which needs to stay fairly low-nutrient).
Finally, I don't think that the waterfall for aerating water coming into the koi pond is necessary or desirable -- there will be very little water coming into the koi pond anyhow, unless you do have a big pump running the whole thing to recirculate (but as I say, bad idea) and with just a trickle, bouncing it off rocks will not aerate so much as *evaporate* your already-too-limited water. I would strongly suggest that, in this type of koi pond, you use an actual powered aerator (be it electric or solar, or even wind-powered although they are not usually useful in tiny ornamental ponds)
Sorry Rosalind, I am not trying to shoot holes in things, it's just that I really really don't see your system working anything like you are envisioning... :/
The big things to be aware of in pond design/mgmt are:
1) you WILL have to fiddle a lot with nutrient balances (so that you do not get overgrown with algae and other undesirables -- this is especially true if you are fertilizing plants in/near the pond or if you have fish being fed in the pond). Nutrient problems manifest as things like green skanky water (bad for fish and invertebrates as well as bad for aesthetics), green 'hair' all through pond, stink problems, pond filling in with nasty sediment, or death of some/all of your desired fish and invertebrates.
2) small and/or shallow and/or aboveground ponds get pretty warm; you can only stock them with things that can deal with those temperatures (and with each other).
3) evaporation is a real issue, especially the more surface area you have (and a planted trickling trench is the *ultimate* in evaporators). Waterfalls (or anything else that causes any splashing) cause substantially more evaporation yet.
If you could summarize what your main goal(s) would be in building a pond system, probably we could make some suggestions -- but unless you are leaving out some major information (like 'oh, and this would be fed by a high-volume cold spring') I hate to say it but your plan is really not going to work, sorry.
Good luck, sorry to be a downer,
Pat, aquatic community ecologist (specializing in critters of small [naturally occurring] ponds) before 'retiring' to mommyhood
, i was very sad about this but to look on the bright side i'll have more room to plant. I still want a pond so i might make an above ground one maybe, to see how that works. I'm thinking about using that 5' by 5' of garden space for strawberries and some flowers.
