Sensitivity of unlined canal seepage to hydraulic properties of polyacrylamide-treated soil

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High-molecular-weight, anionic, linear polyacrylamide (PAM) is being evaluated as a means of sealing unlined water delivery canals to reduce seepage losses. In this study, we investigated water seepage loss reduction by using a two-layer one-dimensional steady-state conceptual model. The objectives of this study were twofold: (i) to examine the effectiveness and implications of a PAM-treated thin layer at the bottom of the water delivery canal in reducing water seepage loss, and (ii) to investigate the sensitivity of seepage reduction to the hydraulic parameters of both the untreated and PAM-treated thin layer. We incorporated laboratory-measured saturated soil hydraulic conductivity results into the model to examine the seepage ratio of PAM-treated vs. untreated soils and the sensitivity of the seepage ratio. In cases where PAM applications and suspended sediment concentration (SSC) treatment were effective, the uncertainty in the soil hydraulic parameter (sorptive number) {alpha} ratio of the PAM-treated soil layer over the original soil had a significant impact on the uncertainty in the seepage ratio. For cases where the seepage ratio was insensitive to PAM and SSC treatment, the {alpha} ratio of the treated soil layer over the original soil layer was not significant. For a canal underlain by coarse-textured material, uncertainty in the {alpha} ratio is propagated to the uncertainty in the seepage ratio and augmented more significantly, while for relatively fine-textured sand (reflected in the small {alpha} values used in this study) the uncertainty propagation and augmentation are relatively gradual. For coarse-textured sand, small uncertainty in the {alpha} ratio can lead to large uncertainty in the prediction of the seepage ratio.

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