Atmospheric Momentum Roughness Applied to Stage-Discharge Relationships in Flood Plains

Abstract

A numerical model is developed to determine the flow depth and discharge relationship for turbulent flows over vegetated flood plains. The model is based on the turbulent boundary layer similarity concepts developed for atmospheric and pipe flow hydraulics. Here, the Darcy–Weisbach formula is modified to account for vegetative resistance by application of surface roughness lengths developed from atmospheric methodologies. Such roughness lengths are well defined for many natural surfaces and can be determined from existing databases of vegetative surfaces or directly measured for specific sites. The model estimates of the flood flow discharges from a natural site are compared to observed data. The results show very good agreement with errors on the order of 7–8%. A sensitivity analysis was conducted to evaluate the effect of channel characteristics on discharge.