Study on the western tributaries of Qara-Chay River on the basis of river type and sedimentary facies

Rivers are one of the most important fresh-water resources of the earth; in addition, many constructions are located on or adjacent to rivers. The most authentic method about river pattern is based on quantitative (non-descriptive) data; sedimentary facies give us important information about the river energy and its transportation processes as well. In this research, the channel pattern of the western tributaries of Qara-Chay river on the basis of morphological parameters (Levels I and II of Rosgen classification and some other parameters) and sedimentary facies (Miall classification) were studied. The Qara-Chay drainage basin (area=14455 Km2) is one of the sub-basins of the Qom salt lake (central Iran); more than 76% of its area is located in Hamedan Province. This river is mainly single channel, its sinuosity is 1-1.5, entranchment ratio is 1.1-2, W/D varies between less than 10 to 70 and slope is 0.02-0.001. In the mountainous part, the channel is entrenched and V-shaped (A and G types). It becomes wider (W/D >10) in the plain; in this part of the basin, B, C and F types (downstream) are present; in some short distances the multi channel type (D) may occur. The Qara-Chay bed in mountainous part gravelly facies (Gms and Gm) are present; sandy facies (Sm, Sh and St) are more abundant in the plain. Muddy facies (Fl and Fm) persist in distal parts. These facies were mainly deposited in the lower-flow and the primitive stage of the upper-flow regime.