Steep Slopes: Part I. Simulated Rainfall Conditions

Steep slopes consisting of disturbed soil are very often found in construction, landfill, and surface mining situations. Although legislation and economics dictate that vegetative cover be established on these slopes as rapidly as possible, the occurrence of large rainfall events during critical periods of vegetation establishment can frequently cause extensive soil loss. Sediment generated from erosion can impair off–site water quality, and on–site damages to the eroded region can be so extensive that expensive earthmoving, regrading, reseeding, and remulching may be necessary. We evaluated the effectiveness of two soil treatments for reducing runoff and soil loss from a silt loam topsoil placed on a constructed 32% slope. The three treatments were an untreated control, 80 kg ha–1 anionic polyacrylamide (PAM) applied as a liquid spray, and 80 kg ha–1 PAM as a liquid spray combined with a dry granular application of 5 Mg ha–1 of gypsum. Replicated plots were subjected to a range of rainfall intensities under a programmable rainfall simulator, and resulting runoff and sediment loss were measured. In the first event of 69 mm h–1 uniform rainfall applied for one hour to initially dry soil, the PAM and PAM with gypsum treatments significantly reduced runoff by almost 90% and sediment yield by 99%, compared to the control. Total runoff through a series of simulated rainfall events was reduced by 40% to 52%, and sediment loss was reduced by 83% to 91% for the plots treated with PAM and PAM plus gypsum, respectively. These results indicate that the use of PAM alone or in combination with gypsum can significantly reduce runoff and soil loss from large storm events, and may be a cost–effective approach to protect the soil during critical periods of vegetation establishment, particularly for disturbed soils