5:15 PM - 7:15 PM
[ACG51-P05] Implementation of a watershed model for developing an integrated land-ocean model in the Republic of Palau
Keywords:Republic of Palau, Land-based substances, watershed model, industrial structure transformation
In the Republic of Palau, efforts are underway to transition from a tourism-dependent economy to a more self-sustaining industrial structure. However, these industrial activities pose environmental risks, including the discharge of waste and pollutants into coastal waters and the overexploitation of coastal fishery resources. These factors raise concerns regarding the degradation of Palau’s critical natural assets, particularly its coral reef ecosystems. This study aims to develop a model to simulate the propagation of terrestrial materials, such as sediments and nutrients, into seawater to analyze the impacts of inland industrial structural changes on coastal ecosystems.
Focusing on the river systems in Aimeliik State, located on the western coast of Palau, and the adjacent marine area of Ngermaduu Bay, which features a well-developed lagoon, we simulated the influx of terrestrial materials into estuaries using a watershed model using the Soil and Water Assesment Tool plus (SWAT+; Bieger et al., 2017). To improve model accuracy, a field survey was conducted in Palau during the latter half of the rainy season, from September 11 to September 18, 2024. Water sampling, river cross-section surveys, velocity and discharge measurements, and temperature, salinity and turbidity using a multi-water quality profiler (AAQ-RINKO, JFE Advantech Co., Ltd.) were performed at some rivers. Additionally, flow velocity, water level and turbidity loggers were installed in one of the rivers in Aimeliik Stat. Furthermore, we conducted water sampling, multi-water quality profiling using AAQ, and depth measurements at multiple points in and around Ngermaduu Bay to understand terrestrial impacts on the adjacent coastal areas.
For developing a watershed model for the whole of Palau Island using SWAT+, the Hydrologic Response Units (HRUs), which serve as the fundamental computational units for material balance, were delineated using USGS degetal elevation model, the ESRI 10m Land Cover Map, and soil survey results from the USDA for soil data. The ERA5 reanalysis dataset was utilized to provide the necessary meteorological data for the simulation.
To estimate river discharge based on water levels in the target rivers of Aimeliik State, we developed a head-flow curve (H-Q curve) using both logger-recorded and manually measured values. The obtained equation was Q = 0.18e4.1H (R2=0.86). Analysis of meteorological data for runoff modeling showed an average precipitation of 10.1 mm, with a maximum of 286 mm and a minimum of 0 mm, indicating substantial variability. The mean air temperature was 28.3°C, with periodic fluctuations in maximum and minimum temperatures. These trends were also observed in solar radiation, humidity, and wind speed, suggesting seasonal differences between the wet and dry seasons. Vertical profiles obtained from AAQ measurements in the bay revealed a salt-wedge structure, characterized by higher salinity in the bottom layer and lower salinity in the surface layer. Additionally, a decreasing turbidity gradient and increasing salinity toward the open ocean were observed. Using SWAT+, we simulated the discharge of flow, sediments, and nutrients at the river mouths of Aimeliik State and Ngermaduu Bay.
Moving forward, we will refine and validate the model using calibration based on observed data, including nutrient concentrations from water samples. Furthermore, we will integrate field-measured oceanic parameters to advance the development of a hydrodynamic model for the region.
Focusing on the river systems in Aimeliik State, located on the western coast of Palau, and the adjacent marine area of Ngermaduu Bay, which features a well-developed lagoon, we simulated the influx of terrestrial materials into estuaries using a watershed model using the Soil and Water Assesment Tool plus (SWAT+; Bieger et al., 2017). To improve model accuracy, a field survey was conducted in Palau during the latter half of the rainy season, from September 11 to September 18, 2024. Water sampling, river cross-section surveys, velocity and discharge measurements, and temperature, salinity and turbidity using a multi-water quality profiler (AAQ-RINKO, JFE Advantech Co., Ltd.) were performed at some rivers. Additionally, flow velocity, water level and turbidity loggers were installed in one of the rivers in Aimeliik Stat. Furthermore, we conducted water sampling, multi-water quality profiling using AAQ, and depth measurements at multiple points in and around Ngermaduu Bay to understand terrestrial impacts on the adjacent coastal areas.
For developing a watershed model for the whole of Palau Island using SWAT+, the Hydrologic Response Units (HRUs), which serve as the fundamental computational units for material balance, were delineated using USGS degetal elevation model, the ESRI 10m Land Cover Map, and soil survey results from the USDA for soil data. The ERA5 reanalysis dataset was utilized to provide the necessary meteorological data for the simulation.
To estimate river discharge based on water levels in the target rivers of Aimeliik State, we developed a head-flow curve (H-Q curve) using both logger-recorded and manually measured values. The obtained equation was Q = 0.18e4.1H (R2=0.86). Analysis of meteorological data for runoff modeling showed an average precipitation of 10.1 mm, with a maximum of 286 mm and a minimum of 0 mm, indicating substantial variability. The mean air temperature was 28.3°C, with periodic fluctuations in maximum and minimum temperatures. These trends were also observed in solar radiation, humidity, and wind speed, suggesting seasonal differences between the wet and dry seasons. Vertical profiles obtained from AAQ measurements in the bay revealed a salt-wedge structure, characterized by higher salinity in the bottom layer and lower salinity in the surface layer. Additionally, a decreasing turbidity gradient and increasing salinity toward the open ocean were observed. Using SWAT+, we simulated the discharge of flow, sediments, and nutrients at the river mouths of Aimeliik State and Ngermaduu Bay.
Moving forward, we will refine and validate the model using calibration based on observed data, including nutrient concentrations from water samples. Furthermore, we will integrate field-measured oceanic parameters to advance the development of a hydrodynamic model for the region.