Application of Remote Sensing Techniques To Characterize Riparian Vegetation For Modeling Hydraulic Roughness

The influence of riparian vegetation on hydrodynamic processes can be modeled by means of hydraulic roughness. Riparian vegetation may decrease channel conveyance capacity by adding resistance to the flow. Traditionally, roughness is assigned based on land use types, photographs, and professional judgment, which generally disregard effects due to vegetation characteristics and local water depth and velocity. The objectives of this study were to implement numerical routines for simulating vegetation-induced roughness in a two-dimensional (2D) hydrodynamic model and to evaluate the performance of two vegetation roughness approaches compared to the standard user-assigned roughness approach. Two roughness algorithms were coupled to an existing 2D hydraulic solver, which requires vegetation parameters to calculate spatially-distributed roughness coefficients. Vegetation parameters such as vegetation height, density, and leaf area index were determined using LiDAR data for the San Joaquin River in California. Water surface elevations modeled using vegetation-based roughness approaches produced an acceptable overall performance. The results revealed the spatial variability of roughness based on discharge and vegetation species in the floodplain. This study incorporates the effect of vegetation characteristics on roughness instead of relying on the traditional roughness approaches. The method investigated here is beneficial for describing the hydraulic conditions for reaches and floodplains where vegetation characteristics vary spatially. In addition, the study improved the estimation of vegetation-induced roughness and its influence on hydraulic parameters such as water depth and velocity.