Reducing Saturated Hydraulic Conductivity of Sandy Soils with Polyacrylamide

Abstract

Polyacrylamide (PAM) is being suggested as a new technology to reduce seepage losses in unlined canals. The goals of this research were to quantify the interactions of PAM and suspended sediment concentrations (SSCs) that reduced the saturated hydraulic conductivity (Ksat) of three sandy‐textured soils to the greatest degree, and to better understand the mechanisms contributing to reductions in Ksat Testing was conducted using a constant‐head method in soil columns. Suspended sediment was continuously added to a constant‐head water reservoir, into which PAM was added and mixed with an agitator. An unbalanced multifactorial design was used with soil type (fine [no. 70 mesh] sand, coarse [ASTM C33] sand, and loamy sand), PAM treatment level (0, 5.6, 11.2, 22.4, and 44.8 kg ha−1), and SSC (0, 150, and 300 mg L−1). Results showed that PAM treatment reduced Ksat 40 to 98% in the sands but reductions were much less in the loamy sand (0–56%). Combining suspended sediment and PAM in a 0.005 mol L−1 CaSO4 test solution reduced Ksat from 8 to 11 times more than adding PAM without suspended sediment. Mechanisms that reduced Ksat included higher viscosity from dissolved PAM and the plugging of larger soil pores near the soil surface. The latter mechanism dominated when the PAM treatment exceeded 5.6 kg ha−1 and when SSC was 150 mg L−1 or higher. Significant Ksat reductions were observed when tests were run on filter material (i.e., column experiments without soil), indicating that the creation of a thin soil seal, composed of PAM flocculates, could partially explain the observed Ksat reduction in soil.