Ecogeomorphological Condition and Hydrological Indicators of the Self-Purification Capacity of Rivers: A Case Study of Siminehrood River in Northwestern Iran

Aims: 
The steady development of human communities and the spread of industrial activities are major contributors to environmental pollution, especially the contamination of water resources. Population growth and thus the acceleration of municipal, industrial, and agricultural wastewater release have adversely affected these inestimable resources and restricted their accessibility. This work attempts to identify the ecogeomorphological condition of rivers in drainage basins emphasizing the Siminehrood River in Northwestern Iran. The purpose is to study all nonpoint source (PS) and PS pollutions and circumstances that weaken and intensify the pollution rate and self-purification capacity of rivers, especially in the Siminehrood River.
Materials and Methods: 
All data and statistics were collected and their seasonal average was calculated. Maps and variables associated with the physical properties of drainage basins were then extracted through ArcGIS. The Schuler diagram was plotted through Chemistry software for all stations and each season to assess the type and chemical quality of the river's drinking water. HEC-RAS model, HEC-GEORAS extension, and ArcGIS were employed for simulation of river flow and calculation and determination of water surface profiles and other hydraulic characteristics of flow including water depth, water flow rate, stream shear stress, and stream power.
Results: 
According to the analyses and results, the improper ecogeomorphological condition of rivers and their low self-purification capacity are directly correlated with the mean river water depth, water flow rate, slope of the river basin, and environmental differences.
Conclusions: 
Within the study area, the highest environmental instability and the least self-purification capacity were observed downstream of the sub-basin in which the mean and maximum depth of water were, respectively, 3.10 m and 8.803 m. Insignificant water flow rate (0.86 m/s on average) and slope of <4% in the area have stagnated water flow in most areas and consequently declined the content of dissolved oxygen and the quality of water. Conclusively, this sub-basin can be reported as a region with an improper ecogeomorphological condition