Houses in this grassland subdivision are coming in around $1,000,000 dollars these days. I expect this one on the edge of stream bed is little different. Water has some lessons in store for this home owner.
The concrete pad in front of the house is resting on loose, water-and-wind-borne silt and loess. They will be moving it again. The concrete slab between the front pillars was resting on air during the last year of construction, whenever the silt slipped away. It has been packed back in now, and the whole thing sprayed with grass seed to keep it in place. This was tried just down the road a couple years ago, and the slope has now eroded into a vertical cliff. So, here are water’s lessons:
- There is an angle, set by the gravity of the Earth and soil qualities, at which soil will sit in place, and an angle steeper than that at which it will flow away with water. The steeper slopes you see in this image are rock. The shallower ones are what the land is aiming for, easily 10 degrees shallower in angle than the silt pile below that house. Water will correct this difference. In fact, you can already see some slumping in the new slope.
- What is deposited by water can be moved by water again, and will be. These silts were deposited by a river at the end of the glacial period, and the wind that scoured the silts off the hills after the glaciers left.
- In a grassland slope, grass is bunchgrass, which holds water in baskets of roots below the soil surface. It does not make sods and, thus, does not stop erosion as readily as sods do. Sods don’t allow water to dig into the soil. Bunchgrass does. It’s more like the bunchgrass works with the ants, bees, voles and other creatures of the soil to move soil downhill until it can flatten out, and to hold water, so it can be used in the hot months of summer. If this slope has been seeded in sod, it will need irrigation through the summer. The saturated soil will slump.
- The slopes just up the hill, just down the hill, and throughout this development show just how this can happen, and that is water’s lesson, too: if you don’t look around to see what water is doing, it will still do it. Water does not live in a book, even if the book says “stabilize slopes with grass.”
- The reason there is a creek here is that the water has taken the soil away. It is a natural process on these slopes, and should not be considered erosion. It is part of the process of the sorting of glacial material that leaves fine soils where they can collect water, and coarse soil and stones where they can hide it or give it a channel. That much of that silt is in the valley bottom, and covered by houses, is not water’s concern. It will bury them eventually. Plugging into this nice pile of silt will help.
- Water has all the time in the world.
I feel sorry for the people who are soon going to be moving into this story. I doubt they are expecting to move into a problem.