Assessing River Hydrological Health Before and After Dam Construction: A Quantitative Flow Regime Analysis

Rivers are vital sources of water for various purposes, such as drinking, industry, and agriculture. Understanding each river’s condition is crucial for planning water resources, constructing hydraulic structures, and meeting the demands of various sectors. Man-made structures along rivers can cause significant hydrological changes in river regimes and ecosystems, necessitating a quantitative assessment of flow characteristics. Accordingly, this study evaluated changes in the hydrological health of the Iril River over two periods: before (1994–2005) and after the construction of the Saqhezchi Dam (2005–2019). Temporal changes in the Iril River’s health were assessed using Flow Health software. According to the results, the high flow index value in 2002 (after dam construction) showed a significant deviation, contrasting with pre-construction dam period when the river-maintained flow even during low-flow seasons. Of the nine indicators analyzed, the minimum flow continuity and minimum monthly flow showed only slight, non-significant changes in recent years. Conversely, the flood occurrence index deviated most notably from natural conditions, with an average score of 0.80, the lowest among the indicators. Additionally, precipitation showed a non-significant decreasing trend, while river health score exhibited a significant decreasing trend. These findings can inform assessments of storage and regulatory dam impacts on river flow regimes and hydrological indicators under conditions of both water scarcity and high flow conditions.