A methodology for low-flow gauging at channel-control stations with seasonal vegetation effects
Stream gauging stations typically measure water level and use a stage-discharge relationship to determine discharge. At some channel-control stations, this relationship changes seasonally as channel roughness varies with growth and decay of aquatic vegetation. Inaccuracies in the measured discharge may result if the stage-discharge relationship does not represent these effects. This thesis investigates improved techniques for discharge calculation at stations affected by aquatic vegetation. A field program was implemented in 2006 at two sites in Southern Ontario. Vegetation was monitored, discharge measured, and four methods of discharge calculation evaluated: time- and stage-based shifts to the rating curve, seasonal rating curves, velocity and stage calculations, and stage and slope calculations. Results were compared to the measured discharge. It was found that all four approaches provided improved discharge prediction compared to those of the existing rating curve. However, the method of velocity and stage was found to be superior to all others.