Analysis of the relationship between morphometric properties and erodibility using topographic position index in the Pivehzhen binalod

The morphometric parameters of the catchment are very suitable indicators for the analysis of geomorphological processes. Erosion studies and sediment production are among the most important research carried out by geoscientists, especially geomorphologists, to implement soil and water conservation programs, reduce erosion, change the hydraulic flow of rivers, and prevent the reduction of reservoir dam lake capacity. To measure the geometric (geometric) characteristics of a river, the term morphometry or river shaping is used. In fact, morphometrics is the quantitative analysis of the geomorphic features of landforms in an area. Morphometric analysis is one of the effective methods for prioritizing sub-basins that can indicate the status of the drainage network of the basin. Investigation of morphometric features of the Piveh Gene watershed is based on morphometric and geomorphometric indices. Considering the importance of studying morphometric characteristics in watershed studies and examining the degree of erosion in this study, the aim is to analyze the morphometric features with the type of landform and predict the amount of erosion through landforms.

 In the present study, for morphometric analysis, ArcGIS software, a digital elevation model (DEM) with an accuracy of 20 meters, prepared from 1:50,000 digital topographic maps of the National Mapping Organization and Aster satellite images were used. Has been. To extract the number of waterways, ArcView software, a digital terrestrial model (DEM), has been used. For the slope parameter and the slope direction and height of the study area, we used a topographic map and a digital elevation model of the earth. In order to prepare the drainage density parameter, the existing elevation waterways were extracted from the digital elevation model using the module (Spectral indices) in Archydro and the digital elevation model of the Aster satellite. A threshold of 25-50 cells was selected for drainage network extraction and the drainage network was plotted. In the last step, waterways were classified by astral method and morphometric parameters were extracted. To separate the landforms of the region, a digital model of height with a resolution of 20 meters was used and then the type of landforms were identified based on TPI or topographic position index and according to equation TPIi = Z0 – Σ n-1 Zn/n (Z0 Model point height under evaluation, Zn The height of the grid, n The total number of surrounding points considered in the evaluation) comparing the height of each cell in a digital model TPI, Height is adjacent to the average height of the cells. Finally, the average height decreases from the height value in the center.

 Morphometric parameters studied in this paper include the number of streams (Nu), the rank of streams (U), the length of streams (L), bifurcation coefficient (Rb), roughness coefficient (Bb), drainage density (Dd), frequency of streams  (F), shape factor (Rf), roundness coefficient (Rc) and rectangle coefficient are equivalent (Re). The results showed that according to the number of waterways (184 waterways), the existence of first, second, and third-degree waterways, the length of waterways, the high ratio of waterway lengths to the area of the basin, and the high unevenness coefficient of the erodible area And requires optimal planning and management. Also, landform studies in the study area showed that with the help of morphometric features, they determined the susceptibility of landforms to erosion in the area. So that after preparing the landforms using the topographic position index (TPI) and considering erosion-sensitive areas through morphometric features, erosion-sensitive landforms in the study area were identified. By comparing the landform map and the erosion zoning map of the study area, it was found that Class 2 landforms (U-shaped valley) and Class 4 landforms (high drains) have the highest erosion. The results showed that with increasing the drainage density, the amount of erosion increases.

After mapping the landforms using the topographic position index (TPI) and considering erosion-sensitive areas through morphometric features, erosion-sensitive landforms in the study area were identified. So that the increase in the number of waterways and their length in the watershed indicates an increase in erosion. Then, the topographic position index (TPI), which distinguishes between hollow and bulge, was considered as one of the geomorphometric indicators. The lower and upper limits of the index (TPI) for the study area were calculated as -39.21 and 33.51, respectively. Areas with negative TPI indicate low topography (concavities and pits) while areas with positive TPI indicate high topography (convex or ridges). The presence of dimples and holes (in areas with low TPI) increases the latency of surface currents in the area and causes water infiltration, which in turn can have a significant impact on the storage of precipitation and surface runoff. Have. The results of studies of morphometric parameters indicate that the erodibility conditions of the region are more favorable and the situation is critical. Analysis of classified data showed that the area and length of the canal are effective in erosion. By comparing the landforms map and the waterways map of the study area, it was found that the 4th floor landforms (U-shaped valleys) and the 3rd-floor landforms (high drainages) have the highest erodibility. Also, with an increasing degree of unevenness, the amount of erosion in the area increases, which in landforms located at high altitudes, such as ridges (Class 8 and 10 landforms), the highest amount and, consequently, the highest sensitivity of these landforms are determined. Class 3 locations have the highest drainage density. Due to its natural features, morphometric and physiographic features, the study area is round, which makes the time of short concentration and literal peak larger and more prone to flooding. By examining other morphological components, we came to the conclusion that the study area is prone to erosion.