How do sand and gravel pits cause impacts that can endanger lives and property?
When floodwater enters a pit, erosion occurs on the upstream lip of the pit. The erosion cuts away at the lip, moving it upstream in a process known as headcutting. Floodwater in natural streams in Maricopa County contains huge quantities of sand and gravel in motion. When these sediment-rich waters enter a large pit, the solids settle out, and the water leaving the pit is relatively clean. This cleaner water tends to pick up more sediment after leaving the pit and causes downstream erosion, or tailcutting. The inadequate embankment stabilization of deep pits causes the steep slopes to collapse into the pits as floodwater passes, causing lateral migration of the pit.
