Low Flow Measurement in Streams Using Video

A video imagery technique for making discharge measurements in streams and waterways is presented and used to estimate low ow discharge for Clear Creek near Oxford, Iowa. A video camera was used to visualize the ow seeded with tracers. Estimates of free surface ow velocities were then made using particle image velocimetry (PIV) techniques. The velocity estimates were used as input to a hydraulic model, which uses kinematic principles (conservation of mass) to derive three-dimensional ow elds for discharge estimation. Measurements of ve channel cross-sections over a 7.15 m length of stream were made to deene the channel bathymetry for the hydraulic model. The average channel width was 5.7 m, and the average depth was 0.2 m. Discharge estimates using the video technique (0:187 cms) compare well with current meter discharge measurements (0:192 cms with an estimated standard error of 6.4%). The root mean square diierence of the depth-averaged velocity at the locations of the current meter measurements was 0:032 m/s. The video imagery technique is ideally suited for making repeated measurements (at low cost) for a surveyed site. 2