Document Type : Research Paper

Authors

• Samaneh Razavizadeh ¹
• Zahra Saedifar ²
• Mohammad Khosroshahi ³
• Fatemeh Dargahian ⁴
• Sara Teimouri ⁵
• Adel Jalili ⁶

¹ Assistant Professor, Desert Research Division, Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran

² Research Expert, Desert Research Division, Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran

³ Professor, Desert Research Division, Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran

⁴ Associate Professor, Desert Research Division, Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran

⁵ Assistant Professor, Poplar and Fast-Growing Plants Research Division, Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran

⁶ Professor, Botany Research Division, Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran

Abstract

Background and Objective
The environment harbors both valuable resources and potential hazards. Among these hazards, natural disasters—especially floods—pose a significant risk to society. Floods are recurring natural events that consistently lead to widespread destruction and considerable human and economic losses. Understanding the factors that influence river flood variability, particularly those related to water control infrastructure and drought occurrences, is therefore essential. This study aims to explore the effects of drought and dam construction on the fluctuations in the maximum flood levels of the Karun River.
Methodology
To investigate flood trends, data on instantaneous maximum discharge from the Ahvaz hydrometric station were analyzed over 50 years (1966–2016). Statistical methods, including analysis of variance, ranking of maximum discharges, and flood frequency analysis, were employed to assess the data. In addition, the study examined the status of dams within the Karun watershed and applied the SPEI drought index to explore the relationship between climate change and human interventions in shaping the river's flood regime.
Results
An assessment of dam construction trends within the Karun watershed indicates that the expansion of dam infrastructure significantly contributed to the reduction of peak discharges. The findings show that dam construction played a major role in decreasing downstream peak flood discharges, particularly during the last two decades (1996–2016). However, in some cases, improper reservoir management has worsened the intensity of flash floods. After the construction of key dams such as Karun 1, 3, and 4, there was a noticeable decrease in peak discharges at the Ahvaz hydrometric station. This reduction underscores the importance of water control structures in flood management and outflow regulation. Nevertheless, in certain instances, altered flow patterns and delayed reservoir emptying have escalated the risk of flash floods, especially when sedimentation reduced reservoir capacity. The SPEI drought index analysis further reveals that extended drought periods have increased the likelihood of flash floods by lowering soil permeability and intensifying surface runoff. For example, in the final decade of the study (2006–2016), 53% of the basin experienced severe drought, 13% faced very severe drought, and 29% endured moderate to weak drought conditions. A small portion of the basin—about 1%—experienced wet conditions, and less than 5% recorded normal conditions. In contrast, during the first decade of the study (1967–1976), 18% of the basin was affected by drought, 22% experienced normal conditions, and 60% of the area was classified as wet.
Conclusion
The impact of drought in the final decade has been associated with an increase in flood frequency. The majority of floods during this period were of low intensity, with short return periods (2 to 5 years). In contrast, earlier decades, characterized by less severe droughts, displayed lower flood frequencies but included events with longer return periods. These findings highlight the need to concurrently address both climatic and structural factors to improve water resource management and mitigate flood-related damages.

Keywords

• dam construction
• statistical Analysis
• droughts
• Karun river
• Floods
• water resource management