IMSWES - The Integrated Manila Bay-Laguna Lake Environmental Study

Laguna de Bay is one of the largest inland freshwater bodies in Asia and is currently host to a number of industrial, aquaculture and other livelihood activities. Protection of the lake from environmental degradation requires constant and reliable monitoring at synoptic scales. Time-series satellite imagery from ASTER AM-1 sensor, were used to monitor the Laguna de Bay water quality condition. A bio-optical model was first developed specific for the waters of Laguna de Bay, which is shallow and often turbid. Special studies were carried out to estimate absorption and scattering properties as well as backscattering probability of suspended matter. The inversion of bio-optical model allows for direct retrieval of turbidity and chlorophyll-a from the visible-near infrared (VNIR) range sensor. Spatial distribution of temperature for the lake was extracted from the thermal infrared (TIR) sensor. Corresponding field surveys were conducted to parameterize the bio-optical model. In-situ measurements include suspended particle and chlorophyll-a concentrations profiles from nephelometric devices and water sampling and processing. Hyperspectral measurements were used to validate results of the bio-optical model and satellite-based estimation. This study provides a theoretical basis and a practical illustration in carrying out space-based measurements that can be performed on an operational basis. See full paper.

Key Words: Laguna de Bay, water quality, remote sensing, bio-optical model

FIELD SURVEY ON HYDRODYNAMICS AND WATER QUALITY IN MANILA BAY AND LAGUNA LAKE

Hitoshi Tamura, Kazuo Nadaoka, Enrico C. Paringit, Fernando P. Siringan, Guillermo Q. Tabios III, Cesar L. Villanoy, Ariel C. Blanco

A series of field surveys was conducted in Manila Bay and Laguna Lake to clarify their physical and hydrodynamic environments and to provide basic information, which will be used to develop numerical models for the bay/lake system, including watershed hydrology. Data collected includes temperature, salinity, water level fluctuations, turbidity, Chl-a, TN, TP, SS, DO and others. The field surveys took into consideration the effects of season, wind conditions, tidal fluctuations, presence of fish pens and period of measurement. Initial analysis of the data collected indicates intrusion of saltwater into the lake in spring tide and lower TN/TP ratio in the lake and river during dry season. In dry season, SS, TN and TP in Laguna Lake were much higher than that for the rainy season. In Manila Bay, TN/TP ratio is greater than 16 except at the mouth of the Pasig River. The mixed layer is affected by wind speed. Positive correlation exists between st and turbidity. Read full paper.

Key Words: Hydrodynamics, water quality, Manila Bay, Laguna Lake, field survey

LAGUNA LAKE 2D MODEL WITH SPATIALLY AND TEMPORALLY VARYING WIND STRESSES FROM AN ATMOSPHERIC MODEL

Guillermo Q. Tabios III, Kazuo Nadaoka and Manabu Kanda

This paper presents a simulation study using two-dimensional (2d) flow model of Laguna Lake in the Philippines developed at the National Hydraulic Research Center of the University of the Philippines at Diliman with spatially and temporally varying wind stresses generated from the Regional Atmospheric Modeling System (RAMS) used at Tokyo Institute of Technology. Specifically, this study investigates the differences of lake flow hydraulics using a spatially varying wind stress in contrast to a uniform one. A comparison of the grid size used to calculate the wind stress is also performed. As seen in this study, significant differences in lake flow hydraulics are observed especially the flow velocities with spatially varying wind field as opposed to uniform wind field. It is concluded that serious consideration must be given in the use of realistic wind field data in general, and in the particular case of Laguna Lake which is by surrounded by irregular topographic features so that definitely spatially and temporally varying wind field commonly prevails.

(Paper presented at Third Regional Symposium on Infrastructure Development in Civil Engineering, in December 4-6, 2000 at the Tokyo Institute of Technology, Japan)

MANILA BAY/LAGUNA LAKE LINKED OCEAN CIRCULATION/LAKE HYDRAULIC MODEL

Guillermo Q. Tabios III, Kazuo Nadaoka and Gaku Hanada

This brief report presents a linked ocean circulation model and lake hydraulic model of Manila Bay and Laguna Lake, respectively. Specifically, the Manila Bay process is modeled using a modified version of the Princeton ocean model of Blumberg and Mellor (1987) by Nadaoka et al (2000a, 2000b). The Laguna Lake hydraulic model based on the finite volume method was developed at the National Hydraulic Research Center of the University of the Philippines at Diliman (NHRC, 1999b). The detailed hydrologic watershed model (Morel-Seytoux et al., 1999) to generate the inflows to the Laguna Lake and portions of Manila Bay constitute a separate model which was likewise developed by NHRC (1999a, 1999b). To generate the spatially and temporally varying wind field for the sample simulation run illustrated in this report, the regional atmospheric model systems (RAMS) by Pielke et al. 1992 was used.

The model presented here is still preliminary since there are components in the model that are still incomplete and others require improvement. For instance, the watershed modeling of inflows from Bataan and Pampanga River Basin is not yet done. A more important issue is model calibration and validation. This would require observed data which are not quite available in this area such as velocity measurements in particular. Primary data collection must be done in the future to obtain the needed data. A more practical utility of this model is to include a solute transport model or water quality model. For instance, modeling of salinity and pollutant transport would have immediate applications to address certain management issues. This issues and future work are further discussed at the end of this report.