Analysis of Physiographic Characteristics of Zagros Sub-basins in Relation to Karstization Conditions

The external processes of the earth and the resulting forms are basically a function of the climatic conditions prevailing in each region (Ramesht & Kazemi, 2007). There is a special connection between the climate and the shape of the roughness. In other words, in each realm, the main face of the rugged forms is under the influence of an evolving system and that system has functioned as a prevailing climatic condition in that land (Mahmoudi, 2007, p. 19). Karst geomorphology studies the specific morphological and hydrological features of soluble rocks (mostly carbonate), (Zanganeh Asadi et al., 2002). Climate change is one of the characteristics of the Quaternary period that has led to changes in shaping systems and consequently in the land form (Nematollahi, 2003, p. 12). The change has occurred intermittently (Jafar Beigloo et al., 2014). In the cold periods of the Pleistocene in the northwestern part of the Zagros region, a glacial and adjacent glacial process, and in the southeast of the eastern part, the river process have been the causes of changes in the face of roughness. But now the northwestern part of Zagros has mountainous weather. For this reason, the adjacent glacier process at the level of the hills and the river process in the thalwegs are considered to be the main elements of the formation (Alaeetalaghani, 2012, p. 135). The present study aimed to investigate the physiographic characteristics of Zagros sub-basins in relation to karstization conditions.

Drainage systems and river landscapes react in various ways to the physical characteristics of the catchment. In this paper, according to karst characteristics and the effect of dissolution on the basin in terms of physiographic characteristics, sub-basin shape parameters such as slope and roughness coefficient, along with topographic parameters in Arc Map 10.3 environment were extracted. Basic parameters including environment, area, minimum and maximum, the height and length of the canals of the basins were estimated. The results were entered into Excel 2013 software and their status was analyzed at different altitudes and climates.

The most important factor for creating karst is the presence of carbonate dissolved masses. Therefore, in this study, calcareous areas were first identified in Zagros. In general, limestone in Zagros was approximately 43% of its area, equivalent to 121270.8 km2, which was the highest in the middle of Zagros. Due to the vast amount of the study area and its placement in the wet currents and the Mediterranean and Sudanese cyclones, the western slopes of Zagros received more rainfall and humidity than the eastern slopes (Alijani, 2003). According to the precipitation and temperature maps of Zagros, the annual precipitation varied between 250 to 900 mm and the annual temperature varied from -1 to 26 ° C. In order to study the conditions of Karsts of Zagros, temperature and precipitation maps were classified. The values of these parameters were classified into five classes according to the conditions of the basins. Parameters such as the ratio of rippling, slope, circle ratio, form factor, basin length, and elongation were placed in the best possible condition. This coefficient was closer to the 1. Geometrically, the basin was closer to the circle. In square-shaped basins, the shape and form factor of the basin was equal to one.

In general, the study of the physiographic characteristics of the sub-basins in the climatic classes showed that when the karstification conditions become more climatically favorable, the shapes and landforms become circular and take on an elongated shape. Due to the climatic differences of the classes and the shape of karst landforms, terms such as water-water basin and glacial-water basin can be used. This means that in higher areas where the climatic conditions are favorable and very favorable for the karstification system, under the influence of the glacier, the dissolution action was more concentrated and in-depth, and karst-glacial forms were created. And at lower altitudes, due to the greater role of runoff in the karst-fiction process, the dissolution was at a higher level than the depth. The roughness coefficient was reduced and the shape of the karst complication was closer to the circle.