Hydraulic Properties of Polyacrylamide Treated Soils and Seepage Reduction in Unlined Canals.

High molecular weight, anionic, linear polyacrylamide (PAM) has been evaluated as a means of sealing unlined water delivery canals to reduce seepage losses. In this study, we investigate the mechanism of reducing water seepage loss by using PAM. The objectives are two-fold: (1) to examine the effectiveness of PAM-treated layer formed at the bottom of the water delivery canal in reducing water seepage loss, and (2) to investigate the sensitivity of seepage reduction to the hydraulic parameters of both the untreated and PAM-treated thin soil layer formed on the canal bottom. We incorporate laboratory measured saturated soil hydraulic conductivity results to examine the seepage ratio of PAM-treated versus untreated soils and the uncertainty of seepage ratio. Results indicate that, in cases when PAM applications and suspended sediment concentration (SSC) treatment are effective, the impact of soil hydraulic parameter ratio of the PAM-treated soil layer over the original soil on the uncertainty of the seepage ratio is significant. For cases when seepage ratio is insensitive to PAM and SSC, the hydraulic parameter ratio of the treated soil layer over the original soil layer is not significant. For a canal bottom with coarse-textured sand, uncertainty in the hydraulic parameter ratio is propagated to the uncertainty of seepage ratio and augmented more significantly, while for relatively fine-textured sand the uncertainty propagation and augmentation are relatively gradual. For coarse-textured sand, small uncertainty in the hydraulic parameter ratio can lead to large uncertainty in the prediction of seepage ratio.