Water erosion in Zonouz river basin

4This study focuses on the land erosion by water in Zonouz valley. It is located in the N.W. part of Iran which is surrounded by two mountain ranges and has very cold and snowy weather in winter and cool summers. River terraces and alluvial fans which were built by Zonouz river are considerably important in the area. The main river of the area which flows from east to the west covers an area of 4630 km. The highest point of this basin is Soltan Sanjar Mt with 3200 meter elevation in the east and the lowest point is on the basin outlet in boundary city of Jolfa 300m elevation. It derives from Soltan- Sanjar Mt.in the east and flows to the west. In Cher- Cher area, it joins to Zilber river in Marand plain and finally enters into Aras river at border between Iran and Azerbaijan, finally reaches to the Caspian sea. This paper based on GIS methods, topographic map 1:50.000 and geologic map 1:100.000 scale in order to find out, the elevations, gradients, hydrographic layers, lithologic layers and orogenic movements which have affected on degradation of Zonouz valley. The precipitation, type of soil, gradient of land, effect of climate and hydrological cycles are the main factors that affect on land erosion. After eight years, a considerable change occurred in river discharge by making a dam on the river. The purpose of paper is to show the terraces and alluvial fans were formed before the construction of dam would be built on it. Flow of river in the area plays a major role on land degradation and creating various landforms. Thus, fluvial processes are the geomorphic process associated with running water. Therefore, fluvial landforms and landscapes are produced by currents of streams. Gradient of valley, the volume of water and form of valley play a major role on land degradation Rivers degrade (erode) and aggrade (deposit). Hence, the landscape contains degradational or erosional landforms which are created when gravels pebble and sands are removed. Depositional landforms are resulted from the accumulation of sediment. Bad land of Zonouz is an example of such an erosional landscape. Resistant material on hills has given a beautiful shape to the hills. (C) 2013 The Authors. Published by Elsevier Ltd.