Comparison Density and Fractal Dimension of Drainage Networks in Different Scales and Precision Different (Case Study: Ilam Watersheds)

Every phenomena in the nature, despite the complexity of the subject, has certain rules and regulations. River pattern and behavior as one of the most complex natural phenomena to this is not an exception. Depending on geomorphologic, climatic, topographic and erosive conditions, the waterways exhibit different patterns and behaviors. One of the parameters which can be achieved using the complexity of the pattern of the form of phenomena is fractal geometry. The purpose of this study is to calculate and compare the fractal dimension of hydrographic networks in Ilam watersheds, which were extracted from 50 m DEM and SRTM satellite data. Hydrographic networks that were derived from SRTM data with a precision of more than 5 meters are mapped by using Google Earth images. For this purpose, 12 watersheds were first selected in Ilam province (Ema, Tang-e-Sazbon, Doiraj, Holylan, Nazarabad, Chamgahs, Kolm, Siagav, Jafarabad, Chaviz, Jezman and Vargach) and after determining the units of 25 square kilometers in each of the areas and drawing and completing the drainage network patterns in the studied areas, their fractal dimension were calculated using Fractalys software. The results showed that the calculation and comparison of fractal dimension with visual methods is correct if the compared fields have the same area, and the accuracy and scale of the drawing of hydrographic networks is also the same. On the other hand, the drainage network drafted on Google Earth with a precision of more than five meters compared to the corresponding waterway network with a precision of 50m DEM in 5 × 5 square kilometers (25 square kilometers), has a very high accuracy. Also, the minimum fractal dimension before the modification of hydrographic networks is for Ema watershed (1/042) and the maximum amount is for Tang-e-Sazbon watershed (1,424). However, after the modification of hydrographic networks and calculating fractal dimension, the lowest fractal dimension is for Chaviz watershed (1.1) and the highest amount is for Nazarabad (1.49).