assessment the effect of gypsum on temporary soil stabilization

today's, adverse effects of off-site erosion, namely damages received from sediment, is a serious bioenvironmental problem. one of the methods for temporary soil stabilization before permanent rehabilitation of vegetation cover, especially on slopes, for mitigating of bioenvironmental contaminants, is using materials having property to cementate the dispersed particles on the soil surface. gypsum is a material having ability to flocculate and bind the separate particles and aggregates on the soil surface. it can also prevent from soil detachment against abrasive forces. the objective of this study is to evaluate the optimum application of gypsum to reduce runoff and sediment yield and enhancing shear strength of soil surface and aggregate stability on unstable sloping marly hills of zanjan province using small flume facility and rainfall simulator, torvane and wet sieving apparatus. these marly hills are overhang to one of the biggest water reservoirs of iran (sefidrood dam) and due to their large amounts of clay particles cause numerous problems for this area. results showed that mixing of different amounts of gypsum with upper 5 mm of soil surface reduced runoff and sediment rates between ranges of 0-13% and 11-92% respectively compared with the control treatment. also at 30% slope and under 75 mm h-1 rainfall, the effectiveness of 20 mg ha-1 gypsum in reducing sediment concentration diminished 35 min after runoff initiation. whereas, the effect of 30 mg ha-1 gypsum on sediment reduction in the same slope and rainfall intensity did not decrease even 60 min (1 hour) after initiation of runoff. in addition, it was revealed that using of gypsum because of improvement of soil physical properties and formation of water stable aggregates (wsa) on steep slopes reduced soil particle detachment and ultimately decreased soil erosion. therefore with respecting to relatively cheap purchasing price of gypsum, the dispersed particles of soil surface on sloping areas can be economically stabilize and this leads to reduce different pollutions related to dispersed particles.