CHANNEL EVOLUTION AND EROSION IN PAM–TREATED AND UNTREATED EXPERIMENTAL WATERWAYS

Abstract

Unprotected earthen waterways (e.g., grassed waterways before vegetation) and ephemeral gullies are prone to severe erosion. Previous research has suggested that polyacrylamide (PAM) may reduce erosion in areas of concentrated flow. This research tested the hypothesis that a PAM–treated channel would result in significantly less erosion than untreated soil in a pre–formed, trapezoidal channel measuring 0.6 m at the top, 0.1 m at the bottom, 0.13 m deep, and 15.2 m long. Anionic PAM (30% charge density, 18 Mg mol–1 molecular weight) was applied in solution at a rate of 80 kg ha–1. The soil used in these experiments was red clay loam (37% sand, 35% silt, 28% clay). Channel geometry and sediment concentration were measured for each of four inflow rates (0.0016, 0.0032, 0.0063, and 0.0126 m3 s–1). A secondary objective was to measure the influence of PAM on headcut rate advance. Measured sediment yield rate was significantly less from PAM–treated channels than from the control. Reductions in sediment yield rate ranged from 93% to 98%. Channel incision depth was not different between the two treatments; however, effective flow widths (assuming rectangular channel geometry) were significantly greater for the untreated control channel. Headcut advance rates were greatly reduced in PAM–treated channels (0.06 to 0.6 m h–1) compared to the untreated channel (17.8 m h–1) in our limited data. These results show that PAM was an effective means of controlling erosion in experimental earth channels.