Sensitivity of Modeled Channel Hydraulic Variables to Invasive and Native Riparian Vegetation

Quantifying the roughness of riparian vegetation is important where it plays a dominant role by reducing water velocity. Vegetation roughness was calculated based on the plant characteristics of three dominant herbaceous plants, including one invasive, along the Sprague River, Oregon. E. palustris and invasive P. arundinacea exhibit higher and similar roughness values whereas C. vesicaria is lower. To determine differences, hydraulic channel conditions were modeled within NAYS 2DH. First, current conditions were modeled by populating the channel banks with roughness, plant density, and height of vegetation patches. Next, along the same reach, monocultures were modeled assuming dominance of individual species. In comparing the two native species to the invasive species, monoculture conditions show that plant density and roughness causes the native E. palustris to have the highest ability to decrease stream velocity. In areas where the invasive species is outcompeting E. palustris, such changes could cause increases in velocity and less stable bank surfaces.