DYE-TRACER EXPERIMENTS ON A BRAIDED BRANCH OF THE MATANUSKA RIVER, ALASKA

Dye tracer studies have been conducted previously on glaciers to study subglacial hydrology. Multiple peaks of the concentration of the dye are interpreted to reflect a braided subglacial system. Dye experiments are also conducted on rivers to study the path of contaminates and as a method of calculating river discharge. Controlled dye tracer experiments, using Rhodomine dye, were conducted on a braided branch of the Matanuska River in August, 2000, in order to study the behavior of dye in water and to compare the results to subglacial hydrology tracer experiments.

Dye was injected directly downstream from a subglacial discharge vent, where the water flows in a single channel. Samples were collected at three localities downstream. Dye concentrations were measured in the lab using a fluorometer. The experiments were run multiple times and produced similar results. Each trial yielded a single dye peak, in contrast to glacial dye studies which often yield multiple peaks. In the first experiment, the greatest concentration of the dye took 7.5 minutes to travel approximately 60 meters to sampling site 1 and 45 minutes to travel 1050 meters to sampling site 3. The average concentration of the dye decreased dramatically downstream; at sampling site 3 the peak concentration was less than 1 percent of the concentration seen at sampling site 1. These data do not appear to accurately model subglacial hydrology during the melt season. Therefore, the subglacial path of water probably includes storage areas and/or very complex braided zones that are not accurately modeled by a comparatively simple braided river channel.