Analysis of flooding in the south of Tabriz city and its effects on the implementation of the sixth section of freeway project of Urmia - Tabriz

 ABSTRACT
 
 
Estimating runoff potential is important in water resource management and designing transportation infrastructure and civil structures such as bridges and tunnels, especially at the intersection with natural surface water flow paths. In this study, the Tabriz-Urmia Freeway was designed in 6 sections to create a suitable route between Tabriz and Urmia and continue creating an east-west corridor from Tehran to the Bazargan border. The analysis of the impact of flooding on this project in the south of Tabriz is of particular importance as an applied research project. Therefore, in this study, the runoff generation capability, water flow capacity, and geometric dimensions of the embankments of the sixth section of the Tabriz-Urmia Freeway were evaluated for each sub-basin. To estimate the runoff, an inference method was used, and in the next step, considering the 100-year discharge, Manning coefficient 0.014, and longitudinal slope 0.025, the water flow capacity of the waterways was calculated, and finally the minimum standard of the waterways, including the length and width of the channel, was determined. The overall results indicate that considering the natural conditions of the sub-basins and the appropriate Manning coefficient and longitudinal slope, the dimensions of the channel should be considered for the discharge of the produced runoff. Accordingly, sub-basin number 10, with a larger area and a discharge of 38.29 cubic meters per second compared to other sub-basins, is proposed to have a wider depth and channel for guiding and discharging floods. It also shows that the area parameter has a greater effect on the flood potential among the parameters used in sub-basins.
Extended Abstract
Introduction
Given the importance of the water sector in the country's economic and social development, it is necessary to move water resources management towards integrated water resources management. For this purpose, we can only take steps towards integrated water management in the country by integrating hydrological and economic water information. Watershed management requires hydrological studies to understand the characteristics of the basin concerning the elements that constitute these characteristics and, in the meantime, to understand the characteristics of runoff in the basin as one of the most important ones. The shaping and impact of factors in the basin, as well as the prediction and estimation of surface flow discharge from it in geomorphology and the design of water transfer structures such as bridges, underpasses, etc., as well as finding a strong relationship between hydrological behavior and geological structure and using this relationship in studies, are important. Considering the design and implementation of the Tabriz-Urmia freeway and its passage through the mountainous watersheds south of Tabriz, as one of the most important and populous cities in the country, examining the flood situation of these basins and its impact on the aforementioned freeway is very important and doubles the necessity of carrying out the present project.
 
Methodology
The study area in Tabriz city, East Azerbaijan province, includes the watershed south of Tabriz city, which discharges runoff from the northern slopes of the Sahand mountain range towards Tabriz city. The Tabriz-Urmia freeway is designed in 6 sections to create a suitable route between Tabriz city (the center of East Azerbaijan province) and Urmia (the center of West Azerbaijan province) and create an east-west corridor from Tehran to the Bazargan border. Estimating the potential for runoff production in hydrogeomorphological studies has various applications, including floods. In this regard, watersheds are often studied as study units. In this study, the geometric dimensions of the embankments of the sixth section of the Tabriz-Urmia freeway, located south of Tabriz city, were investigated by evaluating the runoff production capability for each sub-basin and estimating the water passage capacity. For this purpose, the watershed leading to the freeway was extracted using a digital elevation model layer in the GIS software environment. Runoff for each sub-basin was estimated using an inference method using concentration time, runoff coefficient, and stream slope parameters. For 11 waterways along the route of this freeway, the minimum standard of waterways, including the dimensions of length, width, and depth in the construction of the freeway infrastructure, was determined.
In this regard, some of the basic data required are given below:

Geological layer (lithology);
ETM8 satellite image;
Digital Elevation model with 10 m resolution and 12.5 m palsar sensor;
Soil and vegetation layers.

 
Results and discussion
The results of the study show that the low slope of the main waterways and the length of the sub-basin reduce the flood capacity in terms of physiography, but due to the poor vegetation cover of the region and high rainfall, the occurrence of floods in this area should be considered.
Also, considering the uniformity of the basin runoff coefficient and the small difference in rainfall intensity for each sub-basin, it can be concluded that the area of the sub-basins has played a fundamental role in the volume of runoff produced. So, the larger the basin area, the greater the amount of runoff produced and vice versa. Comparing the results of the present study with other studies conducted in the Tabriz watershed confirms the relative consistency of the study results with the results of the aforementioned studies. For example, Mahmoudzadeh et al. (2016) studied flooding in Tabriz city using an empirical method and applying parameters such as land use, runoff coefficient, slope, etc. They concluded that Tabriz city is exposed to flooding due to being enclosed between the northern and southern mountains (Sahand). Several risk areas have been determined for Tabriz city, and the south of Tabriz city has also been introduced as flood-prone basins. An important point in this study is that after estimating the amount of runoff and carrying capacity of the waterways, the height and width of the waterways' mouths have been considered in proportion to the amount of runoff produced in each sub-basin, which has doubled its use in discussing basin flooding and development and road construction issues.
 
Conclusion
Based on their natural and geostatistical characteristics, sub-basins can have different hydrological behavior than other units and will naturally have different amounts of runoff production from other units. Planning will take an appropriate direction and be a better response to solve problems so that the success rate of measures such as combating sediment and erosion and preventing floods or reducing their destructive effects will increase, and the possibility of integrated and targeted management of basins will be provided. Extracting and using these units in the present study created a suitable working unit for examining the amount of runoff production and determining the geometric characteristics and dimensions of streams for the discharge of runoff calculated based on the maximum runoff production. In hydrogeomorphological studies, the use of watersheds as working units for analyses is recommended in order to focus and create a prioritization approach in studies. This can be a suitable approach, especially in third-world countries, due to the lack of specialized personnel and financial resources. In this context, the use of interdisciplinary studies, such as those used in this research, can pave the way for effective flood management strategies. This method provides a new perspective on watershed studies and is recommended for professionals in this field to enhance their work.
 
Funding
There is no funding support.