نقش پارامترهای ژئومورفیک مخروط افکنه ها بر تغییرات آب زیرزمینی ( محدوده مطالعاتی: شرق و مرکز استان گیلان)

Introduction

Gilan province is one of the most populous regions of the country, with a population of 2,530,696, making it the twelfth most populous province of Iran. These areas have become unstable due to factors such as the increase in immigration and the lack of recognition of the effective landforms in the quality and quantity of groundwater, especially in coastal areas, and require proper management and potential. Alluvial fans are an important landform in the plains that start from the mouths of the rivers coming out of the mountains and continue to the lowlands of the plains. In the present research, after identifying the boundaries of alluvial fans in the low-altitude eastern and central plains of Gilan province, the morphometric characteristics of each alluvial cone were calculated independently and quantitative analyzes of the geomorphic features of alluvial fans were provided. Therefore, in this article, we have tried to identify the boundary of the morphometric changes of alluvial fans according to statistical classification, and determine the ratio of changes in underground water parameters, so that the results of this research will help to identify underground water sources according to the morphometric characteristics of alluvial fans. Also, the results of this study show that geomorphic studies before carrying out implementation plans can be the basis for reducing errors in determining the right place to feed an aquifer or dig an underground water well.

Methodology

The alluvial fans in the east and center of Gilan province are located in the geographical range of 40.50° to 49.00° east longitude and 30.36° to 25.37° north latitude (Figure 1) and are influenced by the Anzali and Darya lagoon catchments. These areas, with an area of 3820 square kilometers, start from the west of the city of Masal and continue to the city of Chabaksar (originally the political border of Mazandaran province) in the east.

In this research, first, information on the depth of water table, standard deviation of time changes of water level, well discharge and electrical conductivity of 23559 rings of drinking, agricultural and urban wells were obtained from Iran Water Resources Organization. Also, the border of 28 alluvial cones was drawn using Landsat 8 satellite images, Sentinel 2 satellite and 1:50000 topographic maps in Arc Gis software. The parameters used and how to calculate them in this study for alluvial fans are: area of alluvial cone in kilometers, radius of the cone, sweep angle, height of the top of alluvial cone, height of the base of alluvial cone, degree of roughness of the cone, length of the cone, slope of the alluvial cone, concavity of the cone Alluvium, the length of the base of the cone, the volume of the alluvial cone

After extracting morphometric data and groundwater data for each alluvial cone, statistical methods and tests were used to make decisions about the impact of morphometry on groundwater parameters. For this purpose, SPSS version 23 software was used to classify the morphometrics of alluvial fans using cluster rank-order cluster analysis and its tree diagram was drawn. In the current cluster analysis, Euclidean geometry was used to determine the distance of members from each other.

Then, each separated cluster was evaluated separately by Pearson's correlation test, and the correlation of the morphometric parameters of each cluster with the changes in the groundwater parameters of that cluster was measured. In the end, RFFLOW software was used to draw the model of the influence of geomorphic parameters.

Results and Discussion



Due to the fact that the flow rate of the wells in the alluvial cone largely indicates the stable or unstable potential of underground water in the direction of exploiting these resources. Therefore, the results of the correlation test of flow rate with alluvial cone morphometry show that the area, length and total volume of alluvial cone in the study area have a positive correlation of 99% with the groundwater discharge of the area. In fact, with the increase in the area, length and volume of alluvial cones, the amount of water that can be extracted from the wells increases. This point has a positive and strong correlation of 99% with the height of the top and base of the cones, which indicates that in alluvial cones whose morphometry is higher than others, the amount of groundwater flow is also at that time. Alluvial cones are more. The slope of the alluvial cone, as an important factor in the duration and degree of water infiltration in the soil, has a negative and strong correlation of 99% with the flow rate, which indicates that by reducing the slope, the water flow rate has been reduced to a minimum. underground increases.

Conclusion

The results showed that the changes in discharge, electrical conductivity and depth of the sedimentation surface from the total of 11 morphometric parameters of the alluvial cone are affected by the morphometric characteristics with the amount of 82%, 45% and 45% respectively. are considered important for identifying and zoning the appropriate potential of underground water on a larger and local scale. Based on this, the highest amount of discharge can be observed in the alluvial cone of the third cluster. The reason for this issue is the direct relationship between the volume and area of the cone with the changes in the underground water flow. Also, in the third cluster, with the increase in the area of the cone from the average (19.3 km) to the maximum area (71.3), the flow rate of the wells also increases. The depth of the water table is also not significant because of the same conditions in the entire region and the water table depth of all three clusters is close to the total average .In general, the results of this research showed that geomorphological landforms and the difference in their morphometric characteristics can be used as an important indicator in evaluating the potential of underground water and can be used as a model in the studies of underground water in areas with the climatic characteristics of the studied region.