Analysis of Storm-wise Sedimentgraphs and Rating Loops in Galazchai Watershed, West-Azarbaijan, Iran

Studying sedimentgraph is an important tool in analyzing sediment behavior leading to success in watershed management projects. The present study was conducted in the Galaz Watershed in West-Azarbaijan Province، Iran، with an area of some 103 km2 to analyze sedimentgraph and rating loops of 13 observed storm events from 25 October 2011 to 25 November 2012. The water and sediment data were recorded with 1 h interval and corresponding sedimentgraphs and rating loops were developed. The results showed that the clockwise type-rating loops were occurred in 7 storm events due to early peak incidence of the sedimentgraphs (0. 5 to 4 h) with respect to peaks of hydrographs. However، other types of sediment rating loops were recognized for other storm events. The results indicated that the clockwise type of sediment rating loops were due to prompt contribution of steep slopes adjacent to the watershed outlet. Although، figure-eight and complex types of sediment rating loops could be attributed to sediment sources of the cropland areas with high sediment availability during autumn cultivation in the watershed upstream and confluence of rising and falling limbs of the hydrograph. The study also showed that 4 observed storm events had consequent storm events. So that، the total weights of total suspended sediment in the first events were respectively 1. 5، 3. 9، 10. 2 and 4. 6 times higher than the second events. The results further revealed that each individual storm events had two distinguished peaks، which proved the contribution of available sediments from agricultural lands located in upland areas.