Investigation of sedimentology, trend of changes in grain size and determination of Debi-sediment equation in Jajroud drainage basin

Filling sediments behind dams decrease their useful lifetime, so sedimentological investigations in bed of arriving rivers are very necessary for distinguish and determination of sediment producer sources of sediments. Latian dam and Jajroud river have a critical situation. Jajroud drainage basin has an extent about 710 km2. It is located in north east of Tehran. It has 7 sub basins include Fasham, Ahar, Meigoon, Lavarak, Emameh, Kond and Afjeh. Its shape is nearly ellipsoid from NW to SE. This braided river has gravely bed with single channel and dam parameter more than 1. Average slope of Jajroud river is 4 percent. This river flows on bicarbonate, silicate, calcium bicarbonate, sulfate and salt material as bed rocks. The size of bed sediments has very irregular changes due to specialized tectonic activities in this area, arriving minor branches, clastic inputs, and changes in slope. So density of drainage in this river is 1.6. Most of sedimentary bars in Jajroud river are longitude and they show shallow and claim conditions. Morphoscopy of grains doesn’t have any defined trend. Granulometric graphs are polymodal. Sorting of grains are bad mostly. The graphs of mean and median changes have not regular trend. Most of samples have negative skewness and they are platykortic. Branch coefficient of this basin is 3.081, so this basin is general basin. The hydrograph curve of flood is normal. Final model for Debi- sediment for Jajroud basin has calculated based on physiography factors of basin that is correlated in maximum of Debi and flooding sediments by power ministry of Iran.