Analysis of Physicochemical Properties of Sediments Trapped in Successive Check Dams

Check dams have been widely used in erosion control projects of upland areas especially in arid and semi arid regions. These structures control and reduce the amount of sediments entering main rivers by trapping the sediment load of floods. Trapped sediments by check dam systems reduce the slope of gully and provide ideal condition to starting biological measures of erosion control such as vegetation cover establishment. Physical and chemical properties of check dam sediments have major role in determining the different aspects of their behavior like water holding capacity, water infiltration rate, and controlling nutrient loss and pollutants transportation. This study aims to analyze physicochemical properties of sediments in some successive check dam systems. The study was carried out in four seasonal waterways from two different region of Urmia city, northwestern Iran. Results indicated that the average sand content of the sediments in waterways lies between 54.4 and 88.4 percent. Sediments samples with sandy and loamy sand texture were coarser than the original soils of the adjacent hillslopes. Sediments were poor in macronutrients in comparison with original soils and the enrichment ratio of the N, P, and K were 0.53, 0.66 and 0.60 respectively. In the partially filled check dam systems, as a result of selective sediment deposition, sediment characteristics change regularly and the amount of clay and macro nutrients were higher in the downstream dams than the upstream dams. Results indicated that the check dam systems are not able to trap all sediment sizes and the great amounts of particles smaller than 2 micrometer in diameter, passed through the system in the form of suspended load. Principle component analysis of sediment properties strongly suggested the importance of macronutrients with sand and silt content in characterization of sediment properties.