Effects of Wet Meadow Riparian Vegetation on Streambank Erosion. 1. Remote Sensing Measurements of Streambank Migration and Erodibility

We quantified how rates of stream channel migration in a montane meadow vary as a function of the riparian vegetation community. The South Fork of the Kern River at Monache Meadow, located in California’s southern Sierra Nevada range, supports two distinct types of vegetation: a dry meadow community dominated by sagebrush and non-native grasses (xeric scrub and meadow), and a wet meadow community dominated by rushes and sedges (hydric graminoids). We measured rates of lateral stream migration for dry versus wet meadow reaches from aerial photographs spanning a 40-year period (1955–1995). While stream migration rates averaged only 0Ð24 š 0Ð02 m a 1 in the wet meadow, the dry meadow channel migrated an average of 1Ð4 š 0Ð3 m a 1. We used a linear model of meander migration to calculate coefficients that characterize bank migration potential, or bank erodibility, independent of channel curvature. These calculations demonstrate that, at Monache Meadow, banks without wet meadow vegetation are roughly ten times more susceptible to erosion than banks with wet meadow vegetation. Where stream bank heights consistently exceed 1 m, low water availability creates riparian habitats dominated by dry meadow vegetation. Thus, channel incision may reduce bank stability not only by increasing bank height, but also by converting banks from wet meadow to dry meadow vegetation. Copyright  2002 John Wiley & Sons, Ltd.