Restoration of urban rivers with water quality modeling approach (Case Study: Kan River, Tehran City, Iran)

Abstract

Abstract This research focused on the urban section of Kan river in Tehran and aimed to rehabilitate it through treated wastewater by using the HEC-RAS quality model. The study area was longitudinally divided into eight sections and the sampling stations were selected based on the research objectives, and the sampling procedure was performed during the water year 2021 (from October 2020 to September 2021. The results showed that the water quality in terms of BOD and DO was lower in Section G than in other sections. This indicates the critical status of the water quality due to the entry of sewage and surface runoff from Persian Gulf Residential Town and Behshahr industries. The results also indicated that the nitrate changes were high in sections, B, C, D, E and F because of agricultural activities, surface runoff, and human wastewater. The highest phosphate level was measured in Section E and then Section F, which can be attributed to the entry of detergents from the located buildings. The model result after the allocation of the effluent of Tehran's sixth water treatment plant demonstrated the increased water quality in all studied sections of Kan River. The vulnerability assessment of this river showed that sections B and C, with a score of 26.7 and 67.6, were exhibited the highest and the lowest restoration potential, respectively. Based on the zoning of Kan River for restoration measures, Section B fell into the nature utilization zone (NUZ) and Facility Use Zone (FUZ). In addition, sections C, D, and G fell into Artificially Development Zone (ADZ) and Facility Use Zone (FUZ), and Development and Nature Mix Zone (DNMZ) and Facility Use Zone (FUZ), respectively. Since all the sections exhibited development potential, ADZ was considered in all zones, except B. Finally, some management solutions such as Flood control, the construction of low-water channels and falls and, wastewater allocation as the main suggestion were proposed to improve the water quality, and restore Kan River.