Document Type : Research Paper
Authors
1 Scientific Board, Soil Conservation and Watershed Management Research Institute, Iran
2 PhD, AB Omran Pardisan Consulting Engineers, Iran
3 Associate Professor, Soil Conservation and Watershed Management Research Institute, Iran
Abstract
This study investigated the status of sediment transport and deposition in Khar-rud River, Qazvin province, Iran. The aim was to determine the possibility of construction of sand and gravel mining workshops in the margin of Khar-rud Flood-plain. Here with calculating sediment transport rate and specifying the distribution of sediment deposits in various parts of the river, an applied program for sand harvesting from the river bed, is developed. In this project, after preparing the basic information, such as information about river geometrical shape, roughness coefficients of different sections, information related to size gradation of suspended sediments and bed material, river hydrology data and boundary conditions of downstream hydraulic system, using HEC-RAS model, sediment loads and its distribution along the river was simulated. Simulation was done based on classified data from daily flow discharges during a 37-year period. After calibrating the HEC-RAS model and selecting Yang sediment transport equation as the closest relationship to the sedimentary data measured by regional Hydrometric stations, the average volume of sediment yield from the river was estimated 1.75 million tons per year. Finally, considering the changes in the river bed elevation for each cross-section, the amount of sediment passing during simulated 37-year was calculated. Using the results of the model and sedimentation changes along the study reaches, the volume of sediment transport in each river cross section, the river width and its private region and considering the maximum permissible depth of bed-material removal equal to 1 m, the most suitable mining length and period in the different reaches of river was determined, discussed and showed in ARC-GIS environment. Based on simulation results, the average depth of sand which can be taken safely from the river-bed was estimated to be 40cm and the most suitable period of time for sand mining along the river was recommended from January to May. It was determined that HEC_RAS hydraulic model, covers about %63 of initial engineering judgments for the amount and location of sand mining.
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