Technically, I'm not sure we have fully addressed resolving the issue underlying the mystery. But we have solved the mystery of where did all the cistern water go last summer monsoon season.
Previously, your musist, it now appears incorrectly, ascribed a WHOLE LOT less water than we expected in the cistern at the conclusion of the monsoon season to JCQ demonstrating the passive rainwater harvesting dry wash. She figured out that by opening the hose bib on the cistern you can simulate a heavy rain so water flows into the wash. Really pretty clever way to do it and also a great way to drain the cistern when we get around to fixing a small leak in the plumbing. By draining into the dry wash, at least the water gets used.
So I figured, it now appears incorrectly, that beverages were involved and the open hose bib may have been forgotten and the cistern pretty much drained.
Well. It seems your musist owes JCQ an appology. Painful, but true.
The other day the cistern was about 90% full as I was missing. It had been awhile so this musist thought, let's bring up the cistern gauge cam and see where we are. Well. We were about 25% full and it was continuing to rain hard. I bellowed and Sweetie came to investigate. She changed into her tight fitting low cut female CSI investigator outfit. I put on a rain coat - didn't figure I'd one of those in the desert did you!? Actually she put on a rain coat too and out we went.
The cistern is actively overflowing. A trickle of water is also flowing through the back wall as designed. Cool. The Quail Lake Manor is full to the brim. Water is flowing as designed through the gap in the fence over to DnT's. Their incarnation of the passive rainwater harvesting dry wash is also full to the brim. Very cool.
But applying the raise the hose running water until it stops running technique, the gauge is confirmed correct, the cistern is about a quarter full. The overflow should sure as hell NOT be running. Very uncool.
Fortunately right before I put on the rain coat I grabbed my go pocket protector. The engineer's version of the tight and low cut female CSI investigator outfit. I keep one at the ready for emergencies just like this. And went full nerd. The freaking overflow is siphoning the cistern dry. I'll bet the fact there is no vent in the overflow is kind of a problem...
We capped the overflow to stop the bleeding. Took a whole bunch of pictures. And sought second opinions from my consulting engineering team. Applying algebra, he following equation was derived:
No Vent = Problem
Flowing water is a little tough to see in a still picture, but you can see the Quail Lake Manor easily enough! Interestingly, as much water was collected, we siphoned on the order of 1,600 gallons out of the cistern plus whatever fell, the dry wash was dry again in a very small number of hours. This soil percolates like crazy!
So. Armed with ideas ranging from simple to complex from the consulting engineering team, and gracious support from SWITBO (who is only a Geologist/Botanist) that was focused on do as little as possible, I went out to engineer the crap out of this overflow. When faced with the tedium of the task ahead, I instead went with SWITBO's idea and did as little as possible. I drilled a hole an appropriate size that I could run a self-tapping screw in it if things went south.
I drilled the hole. Which was followed but a big sucking sound as air rushed into the pipe. And water rushed out the bottom. First thought was uh oh, quick to the screw bin. Second thought was I think I just released the vacuum and that is water emptying from the down pipe of the overflow that should be empty anyway. The flow stopped.
I left it at that. Still not sure just how big the vent needs to be when the cistern is in full overflow mode. One of the consulting engineers will be here in a couple of weeks. So I'll march him down for an on-site consult. Maybe he knows enough math to determine the appropriate vent size. He IS a Professional Engineer after all. I am a mere keep trying until it works aspiring engineer.
Supposed to get a fair bit of rain the next couple of days so we should start refilling again. With luck we'll be full or at least close enough to full before we head back to Denver that I can throw a hose in and force an overflow to measure emperically if we are sufficiently vented.