Document Type : Research Article
Authors
1
1Professor, Department of Geomorphology, Faculty of Planning and Environmental Sciences, University of Tabriz and Iranian Hazardology Association. Tabriz, Iran.
2
MSc. Department of Geomorphology, Faculty of Planning and Environmental Sciences, University of Tabriz. Tabriz, Iran.
3
Postdoctoral Researcher. Department of Geomorphology, Faculty of Planning and Environmental Sciences, University of Tabriz. Tabriz, Iran
4
PhD in Geomorphology, Department of Geomorphology, Faculty of Planning and Environmental Sciences, University of Tabriz. Tabriz, Iran
Abstract
Over the past few decades, significant changes have taken place in the Mardagh Chay watershed area with the aim of developing agricultural lands, expanding settlements, and other purposes. During this period, several events such as surface flows and river overflows have occurred, which have led to flooding in settlements and damage to infrastructure. Accordingly, the present study has studied and evaluated the impact of land use changes on flooding in the Mardagh Chay watershed in East Azerbaijan province. First, land use classification was performed using an artificial neural network model and land use maps were obtained in 2001, 2011, and 2021. Subsequently, the SWAT model was applied to the results of land use classification. According to the results, over a period of twenty years, with the exception of barren lands, other land use classes have had a dominant increasing trend, with the rangelands of the region experiencing the greatest growth in area. The results of the SWAT model also indicated that the runoff trend in the Mardagh Chay basin has largely been in line with the trend of land use changes in the region during this period, and the growth of pasture and built-up areas in the region has had a very direct impact on the increase in runoff in these southern areas. Considering the effect of the topography and slope of the basin on the flow trend and the more imperviousness of the land surface in the southern areas compared to other areas, the flood potential in these areas has been determined to be much higher than in other areas.
Introduction
Floods are considered one of the most important and abundant geomorphic hazards in the country, which cause a lot of damage every year. Recent events in the course of the Mordagh River have indicated the frequency and intensity of floods in the basin. However, the changes in hydrological and climatic regimes of the basin and what causes these changes in the basin have not been well studied. During the last few decades, significant developments have occurred in the Mordaghchay watershed with the aim of developing agricultural lands, expanding settlements and other purposes. During this period, several events have been observed in surface flows and river flooding, including the flooding of settlements and the destruction of infrastructure during the rainy season. The present research has evaluated the impact of land use changes on floods in Mordaq chai basin in East Azerbaijan province.
Material and Methods
Mordaq Chai basin is located at latitudes between 37° 16΄ and 37° 44΄ north, and at longitudes between 46° 21΄ and 46° 30΄ east. The basin area is about 332 Km2. The elevation variations of the basin range from 1567 meters at the outlet of the basin to 3693 meters in Sahand Mountain. In this study land use classification was done using artificial neural network model and land use map was obtained in 2001, 2011 and 2021. Then, the classification results were compared, for which the LCM model was used. The SWAT model has been implemented on the results of land use classification. In addition, the sensitivity assessment of the results has been considered in two phases of calibration and validation, in this regard, land use in 2001 was recalibrated in the statistical period of 1985-1999 and validated in the statistical period of 2000-2001. Also, the land use of 2011 was calibrated in the statistical period of 2002-2009 and validated in the statistical period of 2010-2011 and the land use of 2021 was calibrated in the statistical period of 2012-2019 and validated in the statistical period of 2020-2021.
Results and Discussion
Over the course of twenty years, with the exception of barren lands, other land use classes have shown a predominant upward trend, and the pastures in the region have witnessed the most significant expansion in terms of area. This shift highlights notable changes in land use patterns across the area. The increase in pastureland could be attributed to various factors, such as changes in agricultural practices, conservation policies, or even natural shifts in the ecosystem. This growth in pastures may have positive implications for biodiversity conservation, soil erosion prevention, and overall environmental improvement in the region. However, to fully understand the underlying reasons for these changes and their long-term impacts, a more detailed analysis and further data examination are required. According to the physiography and topography governing the basin, the situation is such that in the northern half of the region, we see more natural land cover (including snow, water, barren and pasture) than in the southern half, where human activities (gardens and built-up lands) dominate. The role of Mordaq Chai river in this field has also been significant and for example, most of the gardens of the region are distributed linearly next to this river and its branches, or the villages of the region that have the largest area of built-up land are located in the vicinity of these rivers. In 2001, wasteland, pastures, and gardens accounted for the largest share of existing land uses at 61.21%, 29.1%, and 8.01%, respectively, and snow, built-up areas, and water were next in rank at 1.59%, 0.073%, and 0.016%, respectively. In 2021, the relative share of barren lands has decreased sharply and reached 28.21% of the entire region, and on the other hand, pastures have grown a lot and their relative share in the region has become 54.45%.
Conclusions
The results of the SWAT model indicated that in some cases due to the location of the observed runoff outside the range of uncertainty, the calibration and validation of the model at the basin level with land use in different years was not favorable and the simulation of the surface runoff was not very satisfactory, which is the main reason for this. This is due to the improper estimation of runoff caused by snow melting, especially in late winter to late spring by the model. Also, the trend of runoff at the level of the Mordaghchay watershed has largely been in line with the trend of land use changes in the region during this period, and the growth of the area of pasture and built-up lands in the region has had a direct effect on the increase of runoff in these southern areas and due to the influence of topography and the slope of the basin on the flow process and the fact that the land surface is more impervious in the southern areas than in other areas, the flood potential in these areas is much higher than in other areas.
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