Evaluation of Environmental Flows in a River using Eco-hydrology and Hydraulic Methods based on the Natural Flow Regime (Case study: Darerud River,  Aras Basin)

Fakheri, Hossein; Yasi, Mehdi

doi:10.22059/ije.2026.414537.1914

Evaluation of Environmental Flows in a River using Eco-hydrology and Hydraulic Methods based on the Natural Flow Regime (Case study: Darerud River, Aras Basin)

Document Type : Research Article

Authors

Hossein Fakheri ¹
Mehdi Yasi ²

¹ Department of Irrigation and Reclamation Engineering, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran

² Department of Irrigation &amp; Reclamation Engineering, University of Tehran, Karaj Campus, Karaj 3158777871, IRAN

10.22059/ije.2026.414537.1914

Abstract

Objective: This study presents an integrated framework for environmental flow assessment by combining ecohydrological and hydraulic methods based on the reconstructed natural flow regime.

Method: Long-term hydrometric records from the Darerud River at the Moshiran hydrometric station were analyzed. The natural flow regime was first reconstructed, after which environmental flows were estimated using the Tennant, Modified Tennant, Tessman, Aquatic Base Flow, Flow Duration Curve (FDC), Flow Duration Curve Shifting (FDC-Shifting), Desktop Reserve Model (DRM), Range of Variability Approach (RVA), hydraulic Wetted Perimeter, and Water Quality methods.

Results: The observed mean annual discharge of the Darerud River at the Moshiran station is 11.8 m³/s, whereas the reconstructed natural flow regime yields a mean annual discharge of 21.6 m³/s. Using the Tennant method, the required environmental flow is 2.2 m³/s during the first six months of the water year, and 6.5 m³/s for the next six months. In contrast, the Modified Tennant, Tessman , Flow Duration Curve Shifting (FDC-Shifting), and Desktop Reserve Model (DRM) methods produce distributed monthly environmental flows that reflect the natural seasonal flow regime. The corresponding mean annual environmental flows are 4.7, 10.7, 7.5, and 7.6 m³/s. The Aquatic Base Flow, Flow Duration Curve (FDC), hydraulic method (wetted perimeter curve slope), hydraulic method (maximum curvature), and water quality methods estimate constant environmental flows of 8.3, 6.3, 12.5, 8.9, and 8.1 m³/s, respectively. The Range of Variability Approach (RVA), however, presents a yearly flexible environmental flow range between 9.6 and 27.6 m³/s, rather than prescribing a single discharge value.

Conclusions: The Modified Tennant, FDC-Shifting (Class D), DRM (Class B/C) methods are considered to be more reasonable approaches for the Darerud River. These three methods present the mean annual environmental flows of 4.7, 7.5, and 7.6 m³/s, respectively, corresponding to 22%, 35%, and 35% of the mean annual natural flow regime. The Spearman rank correlation coefficients are 0.99, 0.98, and 0.92, respectively. These three methods represent seasonal environmental flow variability in consistent with the hydrological characteristics of the natural river system. The findings of this study provide a flexible scientific tool for river management and the conservation of flow-dependent ecosystems in the Darerud watershed.

Keywords

Main Subjects

Ecohydrology

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