POLYACRYLAMIDE AND GYPSIFEROUS MATERIAL EFFECTS ON RUNOFF AND EROSION UNDER SIMULATED RAINFALL

Abstract

An indoor laboratory study was conducted to compare the dry versus sprayed application of polyacrylamide(PAM) and the use of different gypsiferous materials (gypsum and a class C ponded fly ash) on runoff and sediment yield. Thesix treatments incorporated in this study were: control, NutraAsh (NA), gypsum (G), sprayed PAM plus NA (PAMW+NA),sprayed PAM plus G (PAMW+G), and granular PAM plus G (PAMD+G). Simulated rainfall at an intensity of 70 mm hr1 wasapplied for 2 hours to a silty clay loam soil packed into erosion pans. Only one of the two liquid PAM treatments (PAMW+G)significantly reduced runoff (35%), while both liquid PAM treatments (PAMW+G and PAMW+NA) significantly reducedsediment yield (74% and 77%) compared to the control.<br><br>Sprayed PAM was more effective than granular application in terms of total runoff, but there was no statistical differencewith regard to total sediment yield. Differences between the effects of sprayed and granular PAM are explained by themechanisms by which they reduce erosion. Sprayed PAM, in combination with gypsum, increases infiltration during the firstpart of a rainfall event until sufficient rainfall has occurred to break down the PAMtreated aggregates, at which time runoffrate and sediment yield rate approach those of the control. Runoff and sediment yield rates from the granular PAM applicationwere initially similar to those from the control. However, as time increased, sediment yield reached a maximum and thendecreased without a corresponding decrease in runoff. This likely occurred because the PAM particles became activatedduring the rainfall and acted as a mortar to stabilize the soil matrix.<br><br>Gypsum was a better source of electrolyte than a class C ponded fly ash, commercially known as NutraAsh (NA), likelydue to its greater solubility. Addition of PAM decreased soil erodibility and may be a viable erosion control practice for soilssusceptible to flow detachment. Choice of application method should be based on the expected amount and severity ofprecipitation before vegetation establishment. These results indicate that sprayed PAM, in combination with gypsum orNutraAsh, provides immediate erosion control, but its effectiveness decreases over time, as indicated by steadily increasingsediment yield rate. Dry PAM application was not as effective in the beginning of the experiment, but after sufficient rainfallit became activated and sediment yield continuously decreased over the remainder of the experiment.