Measurements of the size distribution of frazil ice particles in three Alberta rivers

The size distribution of frazil ice particles has been studied extensively in laboratory environments but has proven much more difficult to measure in rivers. To make accurate measurements of frazil ice particle sizes and shapes in rivers, a novel submersible imaging system, called the FrazilCam, was designed and custom-built. The FrazilCam consists of a Nikon D800 digital single-lens reflex (DSLR) camera contained in a waterproof housing and programmed to capture images of frazil ice particles as they pass between two glass cross-polarising filters. Throughout the winter of 2014-15, the FrazilCam was deployed a total of six times in three different Alberta streams: the North Saskatchewan River at Edmonton, the Peace River at Fairview, and the Kananaskis River near Kananaskis Village. The resulting images were processed using a MATLAB algorithm and the size distribution of the suspended particles was determined. These are the first quantitative measurements of frazil ice size distributions made in rivers. It was observed that the mean particle diameter was larger during the principal supercooling stage, ranging from 0.73 to 1.20 mm, and reached a smaller mean diameter during the residual supercooling phase, with mean diameters ranging from 0.32 to 0.61 mm observed. Each of the frazil ice size distributions was reasonably well described by a lognormal distribution, which has long been used to describe the distribution of frazil particles produced in laboratory settings but never before been confirmed in the field.