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The northeastern region of Bangladesh is characterized by expansive and round-shaped floodplain depressions referred to as Haors. These areas face significant challenges, including sedimentation, flood inundation, poor navigability, and drainage congestion. A considerable portion of these issues stem from heavy rainfall in the hilly terrain of Meghalaya, resulting in a substantial runoff that swiftly descends towards the lower elevations of Bangladesh. This rapid flow transports a substantial load of sediment, ultimately depositing it onto the riverbeds and floodplains of the Haor regions. Among the severely affected areas in the northeastern Haor region is the Om-Piyan-Dawki river system, where sedimentation poses significant threats to food security (agricultural, livestock, and fishery production) and the livelihoods of the Haor inhabitants. Despite the evident risks posed by sedimentation, previous assessments of flood-induced risk in the region have primarily relied on qualitative methodologies, lacking a comprehensive quantitative approach. In an effort to address this gap, this study employs a geospatial multi-index model to evaluate sedimentation-induced risk, specifically in the Gowainghat and Companiganj upazilas of Sylhet. The objectives encompass an assessment of sedimentation-induced risk on food security and their socio-economic implications. The methodology integrates Landsat imagery with a 30-meter resolution (1996-2021), subsequently validated through field observations to ascertain sedimentation-induced alterations in land and water features. Additionally, flood water depth estimation is conducted utilizing the FwDET v-2 tool and FABDEM within Haor waterbodies. Findings from the study reveal a substantial increase in silted-up land, totaling a 903.87% expansion across the study area between 1996 and 2021. Moreover, 41.85% of the water body area has been lost due to excessive sedimentation during the same period. This accelerated sedimentation process is attributed to elevated Suspended Sediment Concentration (SSC) values, with areas exhibiting SSC levels exceeding 200mg/L, expanding from 4% in 1996 to 44% in 2021. Due to excessive siltation on the riverbed, water carrying capacity of the Sari-Gowain River decreased three times from 2014 to 2018, while the Piyan River is almost dead, resulting in bio-diversity destruction in adjacent rivers and wetlands. On the other hand, mean rainfall during the pre-monsoon (March-May) gradually increased (Sen’s slope = 0.270), while a decrease in trend (Sen’s slope = -0.022) is observed in the monsoon (June-September) mean rainfall for the last three decades. As a result, the severity of flash floods increased, resulting in the loss of Boro crop production, and the production of the Aman crop was hampered due to irrigation water scarcity. As per the study, the productivity of the Boro crop and the Aman crop was reduced, respectively, to 8.42% and 24% between 1996 and 2021. This agricultural disturbance, coupled with disruptions in natural livestock feed production due to prolonged waterlogging, has elevated the risk in food security from a low to a medium range. Specifically, in 2021, the agricultural sector faces a high-risk level (6.27), while the livestock and fishery sectors encounter medium risk levels (4.62 and 5.31, respectively) on a scale of 0 to 10. Over the period of 1996-2021, the agricultural and livestock sectors experienced the highest increments in risk, while the fishery sector exhibited comparatively lower risk growth. Consequently, the resiliency power of the study area farmers and fishers decreased respectively to 15% and 42% throughout the period (1996-2021). The findings underscore the escalating risks posed by sedimentation, including loss of land and waterbodies and diminished water-carrying capacity in rivers. Additionally, changes in precipitation patterns exacerbate the situation, further threatening crop production and exacerbating vulnerabilities in the agricultural, livestock, and fishery sectors. Ultimately, the study emphasizes the pressing need for comprehensive mitigation strategies to address these challenges and enhance the resilience of communities in the affected areas. |
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