Introduction:
Check dams, as one of the most important engineering measures in watershed management, play a crucial role in reducing flood hazards, controlling erosion, and enhancing the stability of local ecosystems. These structures modify channel morphology and slope, reduce concentrated flow velocity, improve downstream water quality by trapping sediments, and stabilize streambeds. Despite numerous global and national studies, most hydrological assessments of check dams have remained descriptive and qualitative, while their quantitative impacts especially at large scales and over long time periods require further investigation. One underexplored topic is the impact of reduced storage capacity caused by sediment deposition on the hydrological performance of these structures. Sediment accumulation can limit the dams’ ability to regulate runoff and reduce flood peaks, raising key questions regarding the relationship between sedimentation rates and flow changes, the persistence of flood control efficiency, and the point at which a dam transitions from a controlling infrastructure to a potentially hazardous element. Therefore, this study aims to investigate the effect of sediment infilling on the hydrological performance of check dams using a scenario-based modeling approach in the Meymeh watershed in Ilam Province, Iran, and to propose optimal management strategies.
Materials and Methods:
The Meymeh watershed, covering 1,633 km², is located in southern Ilam Province and features diverse topography, including mountainous and hilly areas. Daily meteorological and hydrological data (precipitation, air temperature, relative humidity, wind speed, and river discharge) for the period 2010–2020 were obtained from the provincial meteorological organization and the regional water company. Soil and land-use characteristics (based on 2019 data) were extracted from previous studies and land-use maps. Hydrological simulations were conducted using the SWAT+ model, which allows subdivision into sub-basins and hydrological response units (HRUs) and simulates flow, sediment transport, and interactions with reservoirs such as ponds, storage dams, and small watershed structures. For calibration and validation, the model was calibrated for 2010–2018 and validated for 2019–2020, using Nash–Sutcliffe Efficiency (NSE) and R² as performance indicators. Based on empirical relationships between watershed area and reservoir volume derived from similar basins, an optimal total storage volume of 2,234,169 m³ was estimated for all proposed check dams in the watershed. This volume was distributed among 1,289 check dams located in 1st-, 2nd-, and 3rd-order streams and used as the baseline for analysis. Using the calibrated model, in addition to the “no-sedimentation” condition, three sediment-filling scenarios were designed representing 25%, 50%, and 75% reductions in storage capacity to analyze the hydrological consequences of progressive sedimentation. Key flow indices including mean, minimum, and maximum discharge were examined for each scenario.
Results and Discussion:
The model performance evaluation showed NSE = 0.70 and R² = 0.72 during calibration, and NSE = 0.77 and R² = 0.81 during validation, confirming the high capability of SWAT+ in simulating watershed hydrology. Simulation results indicated that storage reduction due to sedimentation significantly affects surface runoff. Under the no-sedimentation condition, mean flow was 2.76 m³/s. With 25%, 50%, and 75% storage loss, mean flow increased to 3.47, 4.53, and 5.33 m³/s, respectively. Similarly, peak flow increased from 152 m³/s to 261, 409, and 608 m³/s under the respective scenarios representing roughly 1.7, 2.7, and 4 times the original value while minimum flow remained largely unchanged. These results indicate that sedimentation in check dams intensifies concentrated runoff and downstream flood risk, while baseflows mostly sustained by upstream springs and observed during dry seasons remain relatively unaffected. Comparative analysis with global studies confirms that sediment infilling in reservoirs typically reduces effective capacity and alters downstream flow regimes, consistent with the findings of this study.
Conclusion:
The study demonstrated that gradual reduction of check dam storage capacity due to sedimentation has significant hydrological impacts. Scenario-based simulations with SWAT+ enabled quantitative assessment of these effects, revealing that as storage decreases, peak flows increase and runoff regulation declines, while minimum flow remains nearly constant. Nevertheless, even heavily sedimented check dams still exert a substantial influence on runoff and flood dynamics. These findings highlight the importance of continuous monitoring and sediment management to maintain hydrological efficiency and reduce downstream flood risk. From an applied perspective, the results provide valuable guidance for management decision-making, optimization of dam operations, and design of replacement structures or sediment removal strategies during dry seasons, thereby contributing to sustainable watershed management planning. |
