Extended Abstract
Introduction: Flooding is one of the most common and destructive natural hazards worldwide, with numerous economic, social, and environmental consequences. In fact, one-third of the costs associated with natural disasters are related to floods. Floods occur when river flow exceeds its carrying capacity, which can result from factors such as intense or prolonged rainfall, frozen ground during precipitation, sudden snowmelt, deforestation, river blockage, and dam failure. In Iran, poor economic conditions and the inability of livestock owners to provide sufficient forage have led to overgrazing, which exacerbates soil erosion and increases flood risk. Rainfall is a key factor in flood occurrence, exhibiting significant spatial and temporal variations influenced by elevation, slope, soil characteristics, land use, and geology. The concept of the Hydrological Response Unit (HRU) is a widely used approach in hydrological modeling. Therefore, defining and measuring key hydrological response indicators at the watershed scale is essential for effective water and soil resource management and for reducing flood risk.
Materials and Methods: This study analyzes hydrological data from the Balikhlouchay watershed. The research process includes the collection, processing, and analysis of river flow data. Five hydrometric stations with a common 20-year statistical period (2003–2023) were selected. Key hydrological response indicators, including base flow index, peak discharge, runoff depth, drainage density, and recession coefficient, were calculated. Base flow was extracted using the one-parameter digital filter method, and its index was calculated as the ratio of base flow to total streamflow. The recession coefficient was obtained from an exponential recession model. Spatial variations of the indicators were analyzed using GIS-based interpolation techniques. In addition, the Mann–Kendall test was applied using Pro UCL software to detect temporal trends in river flow changes.
Results and Discussion: Analysis of Hydrological Response Indicators in the Balikhlouchay Watershed revealed that geological conditions, topography, and physical characteristics of the basin have a significant impact on flood behavior and river flow stability. In particular, the high values of the base flow index at the Nir station indicate the influence of permeable geological structures and effective aquifer recharge. In contrast, the high drainage density at the Pol-e Almas station reflects the basin’s rapid response to rainfall and the occurrence of flash floods. These results are consistent with findings from similar studies in other Iranian watersheds and confirm the critical role of geological conditions and hydro-geomorphological structures in shaping the flood hydrograph pattern.
Conclusion: The analysis of hydrological response indicators in the Balikhlouchay watershed highlights the significant influence of geological, topographic, and land surface characteristics on flood behavior and flow regime. The spatial distribution of base flow index, drainage density, and runoff depth across the watershed indicates notable variability, driven by differences in permeability, land cover, and geomorphological structure. For instance, higher base flow index values in the Nir station emphasize the importance of permeable geological layers and sustained groundwater contributions, whereas areas with high drainage density, such as the Pol-e Almas station, demonstrate rapid hydrological response and increased susceptibility to flash flooding. These variations reflect the complex hydrological functioning of the watershed and underscore the need for location-specific flood management strategies. The use of GIS-based spatial analysis and the Mann–Kendall trend test provided valuable insights into the temporal dynamics of key hydrological indicators. The observed trends in river flow suggest that changes in land use, soil conditions, and climate variability may be contributing to increasing flood risks in certain sub-regions.