Water Soluble Polymers as a Means to Increase Flow Capacity: Field Experiment of Drag Reduction by Polymer Additives in an Irrigation Canal

Drag reduction method by polymer additives was tested for the first time in a large scale open-channel watercourse. Ten and a half tons of water soluble polymer were injected during 15 consecutive hours in the upstream section of an irrigation canal in permanent flow regime, leading to a 20ppm concentration of polymer in the water. The evolution of the water depth was measured every 10 min during 18 hr along ten sections further downstream, up to a distance of 26.3 km from the injection section. The water depth at all sections remained constant until the arrival of the polymer where it strongly decreased, with sometimes a slight water-depth increase beforehand, and finally remained constant as long as the polymer injection remained. A maximum of 26 cm water depth reduction (i.e. 17%) was measured at the first cross-section (2 km downstream from injection). The water depth reduction then decreased to 10% and 3% at, respectively, 10 km and 20 km downstream from the injection. However, further downstream the water depth increased by 5% at a distance of 26.3 km. The paper also discusses the environmental impacts of polymer injection through the analysis of samples taken in the water and bed material before and during the experiments.