Hydromulch roots reduce rill detachment capacity by overland flow in deforested hillslopes

Deforestation, which removes soil protection by plant leafs and roots, causes severe soil erosion, since the beneficial effects of plant cover and root actions on soil erodibility are lost. Hydromulching has been found to be a suitable technique for erosion control, but little research has been carried out to evaluate the effectiveness of hydromulch roots in controlling rill erosion in deforested areas due to overland flow. This study has evaluated rill detachment capacity (D-c) and erodibility (K-r, which is the slope of the equation regressing D-c and critical shear stress) in hydromulched and bare plots (1.3-m long and 0.5-m wide) on soils sampled in deforested hillslopes of Northern Iran; the most important root parameters of the grass used for hydromulching were also measured, such as root density and diameter. Dc has been measured in a laboratory flume under four bed slopes (10, 15, 20, and 25%) and five water discharges (0.26, 0.35, 0.45, 0.56, and 0.67 L m(-1) s(-1)) with five replications per experiment. D-c was lower (on average - 44%, with a minimum reduction of 40% at a slope of 25% and a maximum -50% at a slope of 15%) in the hydromulched soils compared to the untreated plot. D-c was positively and negatively correlated, with diameter and density of hydromulch roots, respectively. Rill erodibility was noticeably lower (81%) in the hydromulched soil compared to the bare plot. By regressing D-c on shear stress, rill erodibility and critical shear stress for deforested hillslopes (treated with hydromulching or left bare) were given. These parameters are useful to hydrologists in applications of physically-based erosion models.