Flow measurement in streams using video imagery

Abstract

A video imagery technique for making flow measurements in streams and waterways is presented and used to estimate discharge for Clear Creek near Oxford, Iowa. A video camera was used to visualize the flow seeded with tracers. Measurements of free surface flow velocities were then made using particle image velocimetry (PIV) techniques. The velocity measurements were used as input to a hydraulic model, which uses kinematic principles (conservation of mass) to derive three-dimensional flow fields for discharge estimation. A survey of five channel cross sections over a 7.15 m length of stream were made to define the channel bathymetry for the hydraulic model. The average channel width was 5.7 m, and the average depth was 0.2 m. The discharge estimate using the video technique (0.183 m3/s) compares well with the current meter discharge measurement (0.192 m3/s with an estimated standard error of 6.4%). The root-mean square difference of the depth-averaged velocity at the locations of the current meter measurements was 0.032 m/s. Potential applications of the video imagery technique include measurements of flood flows at ungaged sites, river monitoring from a remote site, and estimation of two- and three-dimensional flow components.