Fluid Dynamics and Superstition

As Alice in Wonderland discovered, sometimes it helps to think backwards, especially when it comes to fluid dynamics. I admit that I've been confused about the pond and pump since we've moved in. Sometimes the water flows and sometimes it doesn't. Sometimes it quits altogether and then starts again hours later. Or it never starts again. To make it work again I go through a little ritual--I might as well be shaking chicken bones and chanting, but it works.

At the center of this mystery is a water pump that pulls (or pushes) water from the pond into the well where it bubbles to the top and flows over into the upper pond, then gravity pulls it to the lower pond, and finally back to the pump.

The water travels from right to left in this picture. The leaf skimmer is on the right and the actual pump is on the left.

My latest suspicion is that a few months ago one of my little fish somehow swam into the 1-inch pipe that goes to the pump and it got stuck and, little-by-little, other debris has piled up, like cholesterol in an artery, and now the water can barely get through. I got out my sewer snake (a long coiled wire) to see if I could sense the obstruction. Nothing. Even so, the theory was fixed into my brain. How could I dislodge that minnow?

I got it! Why not shove a garden hose into the pipe and turn it on full blast? Then I could just open the leaf catcher over and see if water comes out. I did, and of course the hose water just flowed out. There was no obstruction. Normally this sort of news would be encouraging, but it did not bring me closer to the truth.

I closed the leaf catcher and turned on the pump, with the water hose still going. I could sense a great rumbling the well, which is over 6 feet deep and full of lava rock (in plastic garment bags, so I can get them out). It was like a great volcano threatening to explode. Then it let loose. Water rushed to the top and over the edge.

I turned off the hose and the water continued to flow at a very fast rate. Suspicious. And this continued for hours until it went back to its old ways. More suspicious.

It was time to think backwards. What if the problem is at the bottom of the well. Maybe it is so full of goop that it slowly shuts off the flow?

I'm cleaning it today, and it is a messy, messy job.