Abstract

Water soluble anionic polyacrylamide (PAM) can be added to irrigation canal water in low concentrations (less than 100 ppm) to reduce seepage loss in unlined conveyance channels. PAM achieves this by flocculating suspended solids into much larger particles which readily settle to form a low-permeability film at the soil/water interface. This research will examine the effects of flow dynamics (water velocity, shear stress, and flow turbulence) on the duration and extent of hydraulic conductivity reduction due to PAM addition. We hypothesize that turbulent, high velocity flows will reduce the duration and effectiveness of PAM treatment by inhibiting both the pore clogging mechanism of PAM and causing interfacial solids erosion due to hydrodynamic scouring.

Lab-scale and field scale tests will be conducted to test our hypotheses. In the lab tests, PAM treated water will flow over a small column of porous media embedded in a customized flume. This controlled atmosphere will allow a thorough characterization of flow dynamics and effluent and seepage flow rates. Data from these experiments will be analyzed to quantify the effects of flow dynamics on PAM's ability to reduce porous media hydraulic conductivity.

In addition PAM application will be field tested on a canal reach in Wyoming to validate lab results. After collecting channel geometry and characterizing flow patterns and dynamics with tracer tests, natural seepage rates will be measured directly using falling head permeameter tests and confirmed by real-time inflow and outflow measurements. PAM will then be added, and seepage loss rates will be measured and compared to the background values.