An Investigation on Selecting Cartographic Scales on Sediment Delivery Ratio in Jamash Watershed

Multiciplity inputs of different analysis of digital data in modern methods of map processing causes the changes in results of erosion and sediment models. In this context، selecting a cartographic scale as the major input of spatial data has become a challenge issue in erosion and sediment modeling. Therefore، in this study، using topographic maps and selecting to spatial scales (1:25000 and 1:50000) and nine pixel size (10، 15، 20، 25، 30، 50، 75، 80 and 100) in digital elevation model derived from two mentioned cartographic scales in Jamash watershed، we tested the hypothesis of non-uniform of output regarding to sediment delivery ratio. In this manner، first by entering raw data in ArcHydro extension and processing them، we ordered the stream by Strahler method. Then، by calculating the ratio of drainage area، we tested the relationship between drainage area and estimated sediment delivery ratio in each scale in a logarithmic model. The result show that changes in cartographic map scales and DEM pixel sizes، have significant effect on Jamash watershed sediment delivery ratio. Due to not having a definite and comprehensive basis in choosing the map scale in erosion and sediment studies، especially estimation of sediment delivery ratio، more over exact determination of sediment delivery ratio by means of observed data in watersheds with statistic، would not be challengeless; Consequently it seems that future researches should focus on defining the appropriate scale of erosion and sediment studies by analyzing physical processes of sediment، transport and deposition and it’s correspondence to cartographic scale in each watershed.