Advancing Flood and Sediment Inflow Monitoring in Laguna Lake Through Basin-Scale Rainfall–Sediment Runoff Modeling

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The escalating turbidity in the eastern basin of Laguna Lake poses a critical challenge driven by excessive sediment inflow. This study addresses the issue by utilizing a basin-scale rainfall and sediment runoff model to enhance flood and sediment monitoring in the lake. It focused on one of the significant sediment contributors on the eastern basin of Laguna Lake, the Pagsanjan River basin, specifically the Balanac River. The model utilized satellite rainfall data, land cover, and topography. A key refinement involved incorporating distinct grain size distributions for the plain and mountain areas derived from field and laboratory analyses to accurately capture varied sediment transport behaviors. The model’s findings reveal a predominant suspended sediment load in the plain area of the Balanac River. Crucially, the study demonstrates that a significant portion of these sediments bypass in-river deposition and are transported directly into Laguna Lake, a process exacerbated during extreme rainfall events. Furthermore, anthropogenic modifications such as increased channel capacity, channel straightening, and concrete channel lining have significantly altered river channel conditions. These changes enhance shear stress during flood events, suppress suspended sediment deposition in the plain reach, thereby accelerating sediment delivery to Laguna Lake. This integrated modeling approach offers a valuable tool for understanding and predicting flood and sediment dynamics, providing crucial insights for water resource management, sediment control strategies, and informed decision-making to safeguard the health and functionality of Laguna Lake and similar vital water bodies.