Use of Tracer Minerals to Estimate Erosion in an Iranian Watershed

Abstract

The studied area in this research covers the upstream watershed area of the Dodar Ladiz dam in the southern part of Zahedan as well as northeast of the Taftan volcanic area in the eastern part of Iran. This area is located in flysch structural zone of eastern parts of Iran along with Taftan volcanic rocks and Quaternary alluviums. Hydrologic units were selected as the working congenial units in studying the erosion and determining the sedimentation rates. X-Ray diffraction analysis, performed on the samples of the hydrologic units, showed the presence of four main clay minerals including Kaolinite, Montmorillonite, Illite and Chlorite. Euclidian distance was used for clustering clay minerals and multi-variance cluster and also, statistical methods were applied for studying the relationship of changes in clay mineral types in the upstream area. Therefore, it was concluded that there is a meaningful difference between amplitude percentages of clay minerals of the samples with 95% confidence coefficients (P value < 0.05). Moreover, based on the statistical test of Kruskal Wallis, the groups were first divided and compared in order to distinguish mineral groups. In this case, the amplitude percentage of Montmorillonite, chlorite and Kaolinite minerals with a 95% confidence coefficient represent a meaningful difference between hydrologic units and the reservoir. Statistical analysis of data and study of clay minerals as a tracer for determining the erodibility rate of the upstream area of the Dodar Ladiz dam show that the maximum amount of erosion is present in the hydrologic area, i.e. a unit with the total surface area of 105.13 km². Although there is a good correlation between the results obtained from this model with geomorphological, sedimentological and field observation there are still some remaining points in this model for further surveys: 1- This model is based on fine-grain sediment and clay minerals; so in the watershed basin with coarser grain sediment, where most of the stream load is gravel and the river has a gravelly bed, there are some chances of error in this type of the basin. 2- In spite of the importance of factors that cause erosion in the basin area, the cause of erosion is not considered in this method. 3- The resulting materials of the erosion from the upstream areas will be deposited in downstream and with gentle slope, therefore they are not thoroughly analyzed. So, in order to avoid possible errors and to increase the confidence coefficient in applying this model for determining the erosional rate in the watershed areas, it is helpful to do further geomorphologic and sedimentological studies.