Oil Spill Scenario Analysis

In addition to Pasig River’s function as the main conveyance channel of water quantity and quality between Manila Bay and Laguna Lake, it serves as a waterway for ferries, watercraft, and tankers that transport people, cargo, and petroleum products. This doesn’t spare Pasig River from incidents like oil spills from happening. The toxic compounds from the leaked oil can be harmful to the environment, and the damage it can cause to marine plants, animals, and wildlife habitats would be incalculable. In June 2013, a warehouse in Sta Ana spilled 15,000 liters of oil to Pasig River and was only reported after residents complained of foul smell within their vicinity. Authorities were able to put the situation under control and people were evacuated immediately. What if a similar oil spill incident happens anywhere along Pasig River and is left uncontained? How fast does it spread, and how will it affect the connected water bodies?

An accidental oil spill along Pasig River during the wet season will cause the oil particles to spread to Manila Bay and its coasts. This is due to the fact that during the wet season, the current along Pasig River flows mainly from Laguna Lake to Manila Bay. This flow direction is caused by the water level in Laguna Lake being much higher than the water in Manila Bay during this period. As we can see, a day after release, oil particles will immediately flush out through the mouth of Pasig River in Manila Bay. The oil particles will float across the center of the bay for four months until they stick to the coasts of Bulacan, Pampanga, Bataan, Corregidor, and some parts of the Cavite Spit. It will take 9 months for the oil particles to completely adhere to these coastlines, while some of the slick exits through the north channel of the bay mouth.

On the other hand, an accidental oil spill along Pasig River during the dry season will cause most of the oil particles to flow towards Laguna Lake. The water level of Laguna Lake is lower than Manila Bay during this period, therefore the flow direction along Pasig River is reversed. This will cause the oil particles to flow to Laguna Lake instead. As we can see, most of the oil particles will stick to the coasts of the West Bay of Laguna Lake where the entry of the oil particles is near. However, some oil particles will still flow towards Manila Bay until they stick to the coasts of Bulacan after 12 months. Most of the oil particles that enter Laguna Lake will float for about one and a half years before they completely adhere mainly along the coast of the West Bay, and some on the Central and South Bays, while some flow back through Pasig River. A few oil particles will even reach and stick to the farthest parts of Laguna Lake along the coast of the East Bay.

Ten thousand oil particles (density of oil set to 890 kilograms per cubic meter) with a total weight of 10,000 kg, which is equivalent to the volume of 56 standard drums, were released instantaneously at San Joaquin Ferry Station along Pasig River. The release dates were June 5, 2018, representing the dry season scenario where there is backflow from Pasig River to Laguna Lake, and November 1, 2018, representing the wet season scenario where there is high outflow from Laguna Lake to Pasig River. The oil spill scenario was simulated in DELFT3D using the conditions of the calibrated and validated hydrodynamics model of the Manila Bay-Pasig River-Laguna Lake system. Oil Spill Model calculates the transport, spreading, and dispersion of an oil patch which can either be floating on the water surface or can be transported as a dispersed phase in the water column. Natural obstructions such as mangroves and artificial structures like fish cages were not yet introduced in the model. Also, evaporation, decomposition, and chemical reactions of oil with water or land when exposed to sunlight were not yet considered. The model had a warm-up period before releasing the oil particles.

The economic and environmental effects of these scenarios can be devastating to Manila Bay and Laguna Lake. For an instance, Laguna Lake’s large aquaculture industry can suffer huge economic losses and the recovery of market confidence in the quality of seafood in this area may take some time. The lake may also become unsuitable for abstraction to be used for domestic water supply. Moreover, the chemical toxicity brought about by oil spills may bring about long-term damage to habitats and significant ecological and environmental changes on both Manila Bay and Laguna Lake. Simulations like these may help provide support information to prepare for interventions in case these scenarios were to happen.