Studying the Spatial Distribution of Physiographic Gravity Centers in Dewatering Iran's Internal Holes

Lakes act as a system. Climate, mathematical position, physiographic features (including basin area, perimeter, length, shape, slope, aspect and time of concentration), rugged topography and gravity center (geometric gravity center of basin, geometric gravity center of lake, hydrological gravity center and geomorphological gravity center) are among the affecting factors of lakes survival or destruction. With regard to the peaks, the topographic lines and waterways of the 14 Iranian basins (Urmia, Gavkhoni, Maharloo, Meighan, Qom, Duranjyr, Jazmurian, Abarkuh, Bafegh, Ardestān, Yazd, Qatruyeh, Sirjan and Lut) have been delineated according to the peaks, topography and drainage lines in 1/50000 topographic maps and by the use of Arc GIS software. Altitude of water and dry equilibrium line in some of lakes such as Urmia, Gavkhoni, Meighan, Qom and Maharloo was extracted from the source documents. For the rest of basin lakes, reflected evidence in topographic maps was used. In climatic calculations, temperature and precipitation of the database Asfezari with 50 years duration was used. Lake water volume was calculated according to the altitude of water and dry equilibrium line and the volume of annual rainfall was computed based on basin area in geographic information system. By dividing the volume of lake's water by the volume of precipitation, runoff coefficients have been estimated. Afterwards, geomorphological gravity center and lake and basin's geometric gravity center were determined. Hydrological gravity center was estimated based on river's discharge data. Analyzing the result of holes, runoff coefficient showed the fact that Lut, Dranjyr, Gavkhoni, Abarkuh and Qom basins have allocated the lowest runoff coefficient. The similar coefficients of Gavkhoni and Qom basin's with Lute basin, represent how distanse between basins’ topographic center and geometric center can affect the amount of runoff coefficient. High runoff of Qatruyeh, Ardestān and Sirjan watersheds are as the result of complaining the lowest part of topography with geometric center of the basin. Gravity center of lake have located in the topographic center of Bafgh basin and, this affected the location of Meighan and Maharloo basins accordingly.