نوع مقاله : مقاله پژوهشی
عنوان مقاله English
نویسندگان English
Providing environmental water requirements for rivers supporting commercial fish species is essential for sustaining valuable aquatic stocks and maintaining the integrity of associated ecosystems, particularly in basins experiencing increasing water abstraction pressures. The Chalusroud river, one of the most important rivers discharging into the southern Caspian Sea, provides critical habitats for economically valuable species such as Caspian Kutum (Rutilus frisii) and rainbow trout (Oncorhynchus mykiss), but has experienced a noticeable decline in base flow in recent years. The objective of this study was to determine an optimal ecological flow regime for conserving key habitats of commercial fish species using an integrated ecohydraulic approach. To this end, five widely used and advanced environmental flow assessment methods were comparatively applied, including hydrological methods (Tennant, flow duration curve, and aquatic base flow) and ecohydraulic methods (wetted perimeter and the Physical Habitat Simulation model, PHABSIM). The analysis was based on 45 years of hydrological data combined with detailed field surveys conducted across 12 river reaches. The results indicated that simple hydrological methods, yielding environmental flow estimates ranging from 0.34 to 15.13 cubic meters per second (cms), lack sufficient ecological resolution to effectively protect fish habitats. The wetted perimeter method produced a wide range of flow requirements (1.7 to 8.77 cms), highlighting the strong dependence of environmental flow needs on channel morphology. In contrast, PHABSIM provided the most ecologically robust results by identifying a dynamic, species-specific flow regime. For example, maintaining at least 85% of suitable spawning habitat for Caspian white fish requires a discharge of approximately 5.7 cms in downstream reaches. The mean environmental flow estimated by PHABSIM for the entire river was approximately 4.8 cms. Overall, the findings demonstrate that environmental water requirements cannot be represented by a single fixed discharge, but rather constitute a flow regime that varies with species and life stage. The combined application of PHABSIM and the wetted perimeter method is therefore recommended as a scientifically sound and practical framework for determining ecological water allocations in rivers with high fisheries value. The results further indicate that current river flows during several seasons, particularly summer, fall below the minimum ecological thresholds required to sustain commercial fish habitats, underscoring the urgent need to revise water allocation strategies toward ecosystem-based and integrated water resources management.
کلیدواژهها English
