Determination of the amount of Sanitary Water Flow from Dams based on the Quality of Drinking Water: A Case Study, Taleghan River, Iran

Abstract

Background: Given the crisis of water shortage and the industrial development in Iran, comprehensive water-resource management and planning to handle the water quality of the rivers are the critical issues to tackle with. The concentration of river pollutants is a function of both the quantity and quality of the river flow regime. In this regard, the construction of large dams leads to quantitative and qualitative changes in downstream rivers. These changes are effective in the health of the river water for uses such as drinking, agriculture, and industry. Therefore, in addition to the quantity of water needs of rivers, their quality needs to be also considered. Objectives: This study aimed to analyze issues related to the sanitary water flow of large dams. Our case study was the Taleghan River dam, Alborz Province, Iran, on which Taleghan reservoir was built to supply some part of the water needed by Greater Tehran, Iran. Methods: This study examined a 22-km long section of the river at the riffle of Taleghan Dam in Alborz Province (103 km from Karaj), Iran. The average annual and monthly discharges of the river in four 6-km-apart stations were estimated. The statistics of eight hydrometric stations and a discharge-surface method were used to calculate the average annual discharge of each sub-basin downstream of Taleghan Dam. Moreover, the discharge non-dimensionalization method, along with the observational statistics of the index station, was used to calculate the average monthly discharge in the examined stations. The Hydrologic Engineering Centers River Analysis System (HEC-RAS) software (version 4.0) was then utilized to determine the values ​​of river flow rates hydraulically. Additionally, water quality parameters were compared with the standard concentrations proposed by the World Health Organization (WHO) for drinking-water quality to examine possible changes in pollutant concentrations during the study. Correlation and regression statistical tests in SPSS software (version 24) were then used to analyze the relationship between discharge and pollutant concentration. Results: The experimental equation of Q = 0.0372A0.8641 was obtained to estimate the discharge based on the sub-basins area using the discharge-surface method. The average annual discharge at stations 2, 3, and 4 (B, C, and D) were estimated at 1.39, 2.11, and 3.39 m3/s, respectively, using this equation. Subsequently, the average monthly discharges in the studied stations in September were calculated at 0.21, 0.29, and 0.46 m3/s, respectively. Afterward, the discharge was measured using HEC-RAS software (version 4.0) in the same month at 0.34, 0.44, 0, and 0.62 m3/s, respectively. The examination of water quality values from ​​among the 17 water quality parameters revealed that physicochemical elements, pH concentration, lead (Pb), and electrical conductivity were higher than the standard concentration of drinking water proposed by the WHO. Conclusion: A model was presented to estimate sanitary water flow by performing correlation tests and linear regression calculations between the river discharge at the dam downstream and the concentration of water quality parameters. According to the proposed model, the minimum flow of sanitary water was estimated at 1.82 m3/s to be considered to release from the dam in the driest month of the year. Therefore, the release of water as the minimum flow of sanitary water less than 1.82 m3/s was not allowed in any other month of the year.