Armoring stream banks can prevent erosion in one place, but may contribute to a lowered water table. Reduced ground water invites plant species that cannot tolerate floods to invade natural communities of the floodplain.
Photographer: Sam Sheline, courtesy of NatureServeRiprap (large, imported rocks that are used to armor stream banks) changes natural patterns of erosion. Floodwaters that are prevented from eroding stream banks will cut deeper into the bottom of the channel in a process called downcutting, which can eventually lower the adjacent water table. This tends to dry out the adjacent floodplain over time, leading to its invasion by plant species that don’t tolerate saturated soils, such as American beech. Furthermore, downcutting creates deep gully-like channels that increase water velocity, resulting in greater erosion downstream from the riprap.