Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2002
Publication Date: 10/31/2002
Citation: Flanagan, D.C., Chaudhari, K., Norton, L.D. Polyacrylamide soil amendment effects on runoff and sediment yield on steepslopes II: Natural rainfall conditions. Transactions of the American Society of Agricultural Engineers. 2002. v. 45(5). p. 1339-1351. Interpretive Summary: Steep slopes such as embankments along highways and in landfills can have serious erosion and sediment loss problems. The slopes are often range from 2:1 (50%) to 3:1 (33%) because limited area is available for the highway overpass, landfill wall, etc. When the soil is that steep it is much easier for rainfall and runoff to erode the soil down the hill. The experiment that was done here used a chemical called polyacrylamide or PAM sprayed on the soil surface to try and reduce the runoff and soil loss at two experiment sites that were exposed to natural rainfall. Another chemical called gypsum, which is sometimes used as a fertilizer, was also applied in combination with the PAM. Grass seed was planted to see how the chemicals helped or hurt the grass growth. Two real-world sites were used: one on a steep (33%) highway slope and one on a very steep (50%) landfill embankment. The results showed that the PAM and PAM with gypsum could reduce runoff (up to 90%) and soil loss (up to 100%) in some rain storms. The PAM and PAM with gypsum also helped the grass that was planted to grow better. Use of these chemicals could help protect soils on steep embankments from erosion, either used alone or in combination with other control methods such as mulches. This research, of benefit to highway departments and other businesses, will result in better vegetation establishment and control of soil erosion and sediment yield on steep slopes, and it is less expensive than many alternatives.
Technical Abstract: Soil loss from embankments at highway construction sites, sanitary landfills, and elsewhere can be extremely large due to the loosened state of the soil and very steep slope gradients (typically 2:1 to 3:1). Soil amendments have the potential to protect the soil during critical periods of vegetation establishment, thus reducing on-site damages and costs as well as reducing off-site impacts on water quality. Two soil amendment treatments were tested in field situations on steep slopes under natural rainfall conditions, to determine their effectiveness under typical constructed embankment conditions. One experiment was conducted on a highway cut slope on a clay loam subsoil placed at a 33% slope. The second experiment was in a surface sanitary landfill on a filled silt loam topsoil placed at a 50% slope, typical of a landfill cap. The soil amendment treatments used were a control, an application of 80 kg/ha anionic polyacrylamide (PAM) as a liquid spray, and 80 kg/ha PAM applied as a liquid spray combined with a dry granular application of 5 Mg/ha of gypsum. Total soil loss over all events at the two experiment sites for plots treated with PAM was reduced in the range of 40% to 54%, compared to the control. The addition of gypsum had a significant effect on runoff volume only on the silt loam soil, most likely due to the presence of substantial amounts of calcium in the clay loam subsoil at the other location. Grass establishment and growth on the plots treated with PAM and PAM with gypsum was significantly increased compared to the control. These results indicate that anionic polyacrylamide (with or without gypsum) can provide substantial benefits in reducing runoff and soil loss, and enhancing vegetation growth.