Hydrodynamic Investigation of Laguna Lake, Philippines for Water Security and Flood Risk Management of Metro Manila

Abstract

Laguna Lake, strategically located at the center of urban development, Metro Manila, is the focal point of national development efforts for economic activities, including flood disaster operation. It is the most stressed inland water body at the same time however, with competing and conflicting water-users, and continued environmental degradation from anthropogenic-based stressors. The use of the lake as a source of raw water for domestic supply have become more significant and critical over the past recent years with the aggravating condition of water scarcity in Metro Manila. It also serves as an important flood-detention storage for Metro Manila during the rainy season, with flow diversions from upstream Marikina river basin. This study presents a three-dimensional hydrodynamic study of Laguna Lake to understand the physical processes that govern and influence lake hydraulics for various water uses. A hydrodynamic model was set-up incorporating spatial and temporal variations in wind forcing and watershed river discharges, and dynamic sea interaction. Simulation results reveal a significant increase in lake salinity concentration for incremental increases in lake water abstraction, particularly during the dry season. A numerical experiment on bathymetric evolution also showed various Pasig River hydraulic discharge features and an increase in hydraulic residence time of the lake. Modelling analysis on the lake's flood detention function on the other hand revealed different shore-land flood inundation areas and recession durations for varying lake-flood detention levels that warrants the need for a more comprehensive and sustainable flood management operation in the metropolis. Results from this study substantiate scientific information for outlining management approaches and conservation strategies especially for fast developing environments.