I live at the bottom of a hill on top of a big pile of gravel. They call it ‘alluvium’ on the geologic maps, but that’s just fancy-talk for rocks and sand that have been washed off the hillsides. A veneer of dirt sits on top. I hesitate to call it ‘soil’ because it’s barely that. If you want to grow anything besides juniper or star thistle you have to add nutrients and other organic matter. When you irrigate the water that doesn’t get retained by the soil percolates through the alluvium until it hits a clay layer. We call that clay layer ‘hardpan.’ It’s impermeable. It causes tree roots to turn sideways. When the rains come the water hits this layer and flows underground. We used to have a cellar that was below grade and it flooded every winter. In fact it would flood if my upstream neighbors watered their lawns.
It’s mostly desert around here. But there’s more water than you think. It’s just underground. I can dig a hole in my yard and a couple of feet down it’s saturated. Or not. It seems random. Dig a line of fence posts and there’s nothing. The next one over and you hit a pocket of water. When it really rains, and that happens sometimes, the hardpan will block the downward flow and the yard will fill with standing water. Over the next few days the water will soak into the ground and move on. I suppose it shows up in the creek beds below me, or joins an aquifer, or something. I don’t really know. It’s pretty damn dry around here, it’s not like this mysterious underground water is feeding a forest.
We had some digging done the other day for a concrete project. At one end of the dig there was standing water. Just a few inches, but it was there. Where did it come from? I don’t know. After spending all day panicking that I had another leak in my water line (we just had that fixed after much hassle and expense) I came to appreciate that it was perhaps just more of that anomalous water that regularly bedevils us.
I’d be willing to bet that if we could peel off the street and look beneath it we would see a web of rivulets. Capillaries of trickling water. Pockets of the stuff trapped in the aggregate sitting on top of the clay and just waiting to be freed. And a few feet one side or the other, not a drop. It’s vexing, this anomalous water. It’s not predictable. The gravel the town sits on is not uniform. It’s thick in some places and thin in other. Some spots are mostly big rocks and some spots are mostly pebbles and fine particles. It’s all jumbled up and mixed together. The hardpan varies as well. You can’t expect nature to erode mountains with any kind of regularity. It’s a big random conglomeration and that’s why we get this whack-a-mole water stuff.
My contractor is a very exacting fellow. He does not like surprises. When he forms up a concrete pour he does not want to worry that one end of it will be a soupy mess. And I’m writing the checks so I’m all for his careful approach. I want my concrete to last. So neither of us like this anomalous water. It appears here and there but not everywhere. It appears in odd places and at odd times. This is the first day of fall. That means we’ve just had summer. Why are there pockets of water under my feet after months of hot, dry weather? I don’t know.
Richard Feynman was quoted saying “I can live with doubt and uncertainty” and other stuff like “I don’t feel frightened by not knowing things.” He was usually talking about big problems in theoretical physics, not little problems like anomalous water in my yard. But I think the same attitude has to be applied here. I don’t understand what’s under the ground, but I guess can live with it.