Predicting Low Probability Streamflow Using Lidar Data and Hydraulic Geometry

Abstract

Predicting stream flow is essential for safe and economic planning and design of hydraulic structures. This study uses the observed channel cross-section from LiDAR data and physical concepts of shear stress to estimate bankfull discharge (Qbf). Assuming that Qbf is the median of the annual peak flow distribution, a 2-parameter Extreme Value Type I distribution was fitted to predict discharge to a 200-year return period. The method was compared with gauged sites in low-order streams (less than 90-meter bankfull width) resulting in SE/SY=1.31 for Qbf and SE/SY=1.90 for the 200-year return period discharge; model precision is poor. However, the relative bias (-15\% to +15\%) demonstrates that on average results are similar to gauged data. Relationships between flow and channel geometry assure a quick way to estimate stream data and can serve as a tool used prior to applying conventional hydrologic methods such as flow routing and regional regression equations.