Sediment deposition in the flood detention area of the "23·7" super large flood in the Haihe River basin
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Abstract:
The catastrophic flood eventb "23·7" super large flood in the Haihe River basin resulted from a combination of meteorological and geographical factors. The residual circulation from Typhoon Doksuri, combined with subtropical high pressure and moisture transport from Typhoon Khanun, interacted with the local topography to create conditions that led to extreme rainfall. This intense rainfall event, which took place from July 28 to August 1, 2023, was the most severe since 1963, with a total accumulated area rainfall amounting to 155.3 mm. This situation led to unprecedented flooding across the region, with 22 rivers exceeding their warning levels and eight rivers experiencing the most significant floods recorded in their history. As a response to the emergency conditions, eight flood detention areas within the basin were activated, resulting in significant sediment deposition. This, in turn, severely impacted both agricultural production and daily life in these regions. In order to investigate and evaluate the sediment deposition characteristics within the flood detention areas following the event, a comprehensive study was conducted. This study was distinguished by its use of advanced technologies, including satellite remote sensing, drone imagery, and ground surveys, which were carried out on August 29, 2023. Remote sensing images acquired from ZY-1F and GF-2 satellites were meticulously interpreted to identify the extent and characteristics of sediment deposition within the eight flood detention areas. Additionally, field surveys were conducted to obtain precise measurements of sediment thickness, volume, and mass within these areas. The maximum inundation depth was determined using flood mark measurements, and from these measurements, the average inundation depth, flood storage capacity, utilization rate, and sediment concentration were calculated. The sediment thickness and concentration calculations' reliability and accuracy were assessed using the Root Mean Square Error (ERMS) and Nash-Sutcliffe Efficiency (ENS) metrics. The integration of field data and remote sensing technology facilitated a detailed analysis of the spatial distribution of sediment deposition and the dynamics of the flood across the affected regions. The study's results revealed that the spatial interpolation of sediment thickness achieved a ERMS of 1.32 and a ENS of 0.78, demonstrating both the feasibility and reliability of the calculation methods employed. The flood storage calculation yielded an ERMS of 0.75 and an ENS of 0.92, further confirming the accuracy and validity of obtained results. Collectively, the eight flood detention areas stored a total flood volume of 2.463 billion m3, achieving a utilization rate of approximately 36.90%. The average sediment deposition thickness across areas was found to be 2.60 cm, resulting in a total sediment mass of 7.67×107t. During flood event, the average sediment concentration was calculated to be 31.14 kg/m3?in the Haihe River basin. Notably, in the Daqing River and Yongding River systems, sediment concentrations reached levels that were 20 to 40 times higher than the average recorded over the past 20 years. The study also exhibited that the spatial distribution of sediment deposition was significantly influenced by both the timing and sequence of flood detention area activation and the upstream-downstream relationship within the basin. Sediment deposition was more severe in the western and northern mountainous regions of the Haihe River basin, where topography played a crucial role in the observed spatial variations. The detention areas located in the upper reaches, which were activated earlier during the flood event, exhibited higher sediment deposition compared to other areas. This comprehensive assessment provides valuable data and insights for evaluating the impact of the "23?7" flood event. The stduy underscores the critical importance of enhancing the management and utilization of flood detention areas to mitigate potential flood risks in the future. It emphasize the integration of remote sensing and field methods to enable rapid and accurate post-disaster assessments of sediment deposition and flood impacts, thus providing essential support for disaster response and management efforts.
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