Assessing Relative Importance of Erosion Types in Sediment Yield (Case study: Ghara-aghaj Watershed, Makoo)

By determining relative importance and contributions of erosion types to sediment yield, erosion susceptible areas in a watershed will be identified, and sediment control and soil conservation projects can be focused on that areas. Because of many problems associated with traditional procedures for identifying sediment sources, fingerprinting techniques, based on physical, chemical and organic properties of sediment and source materials, are increasingly being used as valuable and effective approach to assemble such information. In this method, a suitable composite (set) of diagnostic properties and a multivariate mixing model are employed to estimate the relative contribution of sediment sources to sediments transported to basin outlet. In this study, using suitable composites of geochemical elements, radionuclides, organic Carbon, Nitrogen and Phosphorous, capable of discriminating two groups of erosions (namely, sheet and rill erosions, and gully, channel and river bank erosions) of the study basin, and a multivariate mixing model were used to determine contributions of that erosion types to sediment yield. The suitable composite fingerprints (elements) were obtained using discriminant analysis. The study basin is Ghara aghaj basin, located in Makoo township, West Azarbaijan province. The suitable composite fingerprints having capability to distinguish the above mentioned erosion types include, 137Cs, OC and Nb. Mean contributions from the two main erosion types, namely sheet and rill erosions, and gully, channel and river bank erosions were estimated as 34.6% and 65.4% respectively. Low mean absolute errors (less than 12%) showed high degree of correspondence between measured and predicted properties. High model efficiencies (greater than 0.99) confirmed the goodness of fit of the mixing models. Also it is argued that fingerprinting estimates for sediment sources are consistent with field observations.