Document Type : Original Article

Authors

• Somayeh Rostami ¹
• Hojjat Ahmadi ²
• Nasser Agh ³

¹ Department of Agriculture, Urmia University

² Associated professor, Department of water engineering, Urmia University, Urmia

³ Artemia research institute, Urmia University

Abstract

Introduction

Drying almost the whole of Lake Urmia is one of the main environmental crises of Iran nowadays. Despite great efforts to restoration of the lake since 2014, owing to the limitation of inlet flow to the lake, insignificant success has been reached. Actually, in the basin of Lake Urmia, the evaporation rate is very high and based on the reported data it is over 1000 mm annually, while the precipitation is about 330 mm. Hence, the pure evaporation height from the surface of the lake is higher than the lake water level rising during recent years. Therefore, in order to overcome the shortage of inlet flow to Lake Urmia, the evaporation area as well the surface of the water body must be equivalent to the evaporation rate. Samadzadeh et al. (2018), reported that by the construction of new dikes inside the lake, consequently by dividing the lake into some smaller parts and restore each part separately one by one, the lake could be restored with the available inflow of feeder rivers of the lake. However, difficulties of construction of causeway through lake Urmia confirmed that the sedimentary bed materials of the lake are classified as problematic material from a point of geotechnical view (Eslami et al., 2020). Henceforward, dividing the lake into smaller phases is not possible by using ordinary methods like earthen dikes which have been used in the restoration of the Aral Sea. In this regard, we explored the geotechnical properties of bed materials of Lake Urmia to choose a compatible method with the environment of the lake as well as the proper hydraulic structures to divide Lake Urmia into smaller regions proportional to annual discharges of its basin rivers.



Materials and Method

Lake Urmia is one of the largest hypersaline lakes located northwest of Iran. The area of the lake and its basin are about 5000 and 52000 km2. During las past two decades the lake has been faced with an intense drawing of water level, and almost the lake has vanished. Based on the published investigation regarding phases restoration of Lake Urmia, two different routes have been suggested by Samadzadeh et al., (2018) based on water balances of the lake. Therefore, we also followed the proposed routes to investigate the geotechnical properties of the bed materials. The first route complies with the constructed causeway. In this route, almost the total of the distance from the west to the east shore has been blocked by road dike, except the bridge with a span of around 1200m. The second route is located in the southern region of the lake and it started from Rashakan on the west coast to the east direction which intersects Espir and kaboodan islands. The length of the current route is about 19 km. For each route, three points with a distance of 200 m from each other (from the west coast) in the form of disturbed and undisturbed specimens have been prepared. Identification tests, shear strength tests include vane shear test, uniaxial shear test, and consolidation test have been carried out. In order to study the effect of salt and fresh water on the mechanical and physical properties of the bed and sedimentary material, some tests such as Aterberg limits have been conducted by using fresh and saltwater separately.

Results and Discussion

Based on the achieved results of laboratory tests, the bed materials of Lake Urmia in both routes were classified as OH and OL while treated with fresh and saltwater based on the Unified soil classification system, respectively. Also, shear strength tests showed a low strength of about 12 kg/cm2 for the bed materials of route 2 while the half is for the first route in direction of the causeway at the northern part of the lake. The content of organic materials was detected 3.54 and 4.67 for the first and second studied routs respectively. Odometer tests results revealed that the bed materials of the studied routs could be classified as soft or very soft soils. Therefore, construction of any heavy structure such as a levee to divide or isolate the lake is almost impossible with the ordinary techniques, however, light and thin structures like sheet piles could be a good alternative to the aim.

Keywords

• Phasing
• Shear strength
• Bed material
• compressibility

Main Subjects

• Geotechnic