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Riparian Ecosystem Creation and Restoration:
A Literature Summary

Functions

Erosion Control


Vegetation influences soil erosion in several ways: (1) foliage and leaf residues intercept rainfall and dissipate energy, (2) root systems physically bind or restrain soil particles, (3) residues increase surface roughness and slow velocity of runoff, (4) roots and residues increase infiltration by maintaining soil porosity and permeability, and (5) plants deplete soil moisture through transpiration, giving the ground a "sponge effect" to allow it to absorb water (Abbey 1988).

In the Pacific Northwest, increased flow from upper watershed disturbance aggravates channel shifting and accelerates meandering in the floodplain (Carlson 1979). In many cases, natural vegetation does not provide sufficient resistance to counteract this increased flow. Loss of riparian vegetation in the channel has little effect on bank erosion, but loss of riparian vegetation in the floodplain zone does have a major impact on bank erosion. Revegetation in this zone can provide significant resistance to bank scouring because lower velocities permit plant establishment on most of the streambank. If not carefully planned and implemented, stream channel alteration (e.g., narrowing, straightening, diverting) also can greatly increase bank erosion. Erosive forces within a channel alteration can preclude use of vegetation to stabilize streambanks. Streambank revegetation usually is limited to slower-moving reaches with relatively flat gradients (<1 m/km) or in combination with structural measures on somewhat faster streams. The plant's ability to resist erosive stream flows must be considered in riparian ecosystem creation/restoration efforts.


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