POLYACRYLAMIDE SOIL AMENDMENT EFFECTS ON RUNOFF AND SEDIMENT YIELD ON STEEP SLOPES: PART II. NATURAL RAINFALL CONDITIONS

Abstract

Soil loss from embankments at highway construction sites, sanitary landfills, and elsewhere can be extremely largedue to the loosened state of the soil and very steep slope gradients (typically 2:1 to 3:1). Soil amendments have the potentialto protect the soil during critical periods of vegetation establishment, thus reducing onsite damages and costs as well asreducing offsite impacts on water quality. In Part I of this study, results from a rainfall simulator experiment showed thatuse of an anionic polyacrylamide (PAM) could significantly reduce runoff and soil loss under the extreme condition of a largerainfall event occurring immediately after PAM application. In this part of the study, the same soil amendment treatmentswere tested in field situations on steep slopes under natural rainfall, to determine PAM effectiveness for typical constructedembankment conditions. One experiment was conducted on a highway cutslope on a clay loam subsoil placed at a 35% slope.The second experiment was in a surface sanitary landfill on a filled silt loam topsoil placed at a 45% slope, typical of a landfillcap. The soil amendment treatments used were an untreated control, an application of 80 kg ha1 anionic polyacrylamide(PAM) as a liquid spray, and 80 kg ha1 PAM applied as a liquid spray combined with a dry granular application of 5 Mgha1 of gypsum. A barrel collection system was used to measure total runoff volume and sediment loss. Total soil loss overall events at the two experiment sites for plots treated with PAM was reduced in the range of 40% to 54%, compared to thecontrol. The addition of gypsum had a significant effect on runoff volume only on the silt loam soil, possibly due to higherrainfall at that site and/or to the presence of substantial amounts of calcium in the clay loam subsoil at the other location.PAM and PAM with gypsum increased grass establishment and growth on treated plots compared to the control. These resultsindicate that the use of anionic polyacrylamide (with or without gypsum) can provide substantial benefits in reducing runoffand soil loss, and enhancing vegetation growth on very steep embankments.