As the Utility canyon is one of our major run-off channels and has important potential to store water, it was decided that it was an ideal place to build check-dams.
The principle is simple. Each dam holds back water and prevents it flowing down the canyon. If there is a big rain, the excess water flows over a spillway, a lower area in the middle of the dam, to be then held back by the next check-dam further down. The size and spacing of the dams depends on the "drop" of the canyon and how much water has to be held. As the flow of water is stemmed, the topsoil carried by the water builds up behind each check dam and becomes a fertile seedbed for nature to sow in and regenerate.
Hopefully nature then takes over again, and roots start to speed up the rate of percolation of the harvested rainwater. The canyons are a special biotope for flora and fauna which we must protect, and not eliminate.