Chronology of small dams sediments based on depth changes in sediment characteristics (case study: Hasan Abdal watershed, Zanjan province)

The age determination of sediments is usually performed by different methods, all of them need a lot of cost, effort and research facilities. The goal of this research is to compare the results of sediment granulometery with precipitation data to perform chronology of sediments. In this study four check dams were selected and profiles were drilled in their sediments. Then sediment sampling was performed in different horizons based on texture and color of the sediments. Granolumetric analyses were performned on samples and the results were analyzed by Gradistat Software. Long-term (45 years) rainfall statistics of Zanjan Station was obtained from Zanjan Meteorological Office for determination of low-water and high-water periods using PNPI (Percent of Normal Precipitation Index). The results of granolumeteric analyses were compared with the results of rainfall analyses which showed that sandy texture relates to high-water and silty texture to low-water periods. The results showed that in thirteen samples from seventeen samples, there is complete conformity between granolumetric and climatic results and that accurate recognition of high-water and low-water periods can be reached using granolumetric characteristics.The age of sediments in four small dams is as follow: Sediments of profile one were deposited between 2005 to 2011, profile 2 between 2006 to 2011, profile 3 between 2008 to 2011 and profile 4 between 2008 to 2011 years. Using sediment chronology of each horizon in sediment profiles, sediment yield potential of upland drainage basin of each small dam in different temporal phases can be estimated.