The key to building a sound dam is the trench beneath it.
We are building a 400-foot dam to create a small lake for wildlife and irrigation. Mike, our contractor-artist, explains a dam needs to have a "key" of clay beneath it to arrest percolating water. Water has a mind of its own, and will find the weak spot in a structure sooner or later, unless the seal is foolproof. So, a key is excavated about 3 feet deep to make sure no lenses of sand are lurking underneath the dam. It is then refilled with packed clay, layer by layer, to the height of the dam. This dam will be about 15 feet tall at the lowest point of the topography. It tapers off at each end, as it ties into the two hills it is connecting.
|Topsoil is scraped off in search of clay, which is painful to witness. We have invested so much effort to build topsoil over the years, that it is counter-intuitive to remove it. But all is not lost, as it will be spread over the top and backside of the dam. |
We are also hauling dirt from the nearby streambank for the backside of the dam. We are embarking on another effort to renovate more streambanks on the property. This involves taking out the trees, hauling them away, pulling dirt back from the vertical bank to a 45 degree slope, hauling that dirt to another location, and finally replanting the streambank with willows and sycamores. Previously we hauled the dirt to a nearby hillside. We are currently hauling it to the backside of the new dam just across the field. The picture below shows topsoil and bank-fill being inventoried before it will be pushed forward to join with the dam.
|We can see the dam taking shape, as the streambank supplies much of the dirt. This represents about a week of work so far, involving multiple pieces of equipment. |