General Santos City (GSC) serves as the catch basin of four major river systems that drain into Sarangani Bay and whose watershed areas are mostly outside of the City’s jurisdiction. Because of its location, the City is mostly affected by flood and flash floods due to runoff coming from these watersheds when heavy rains occur upstream. Out of these major rivers, Silway River poses the greatest risks of flood and flash floods to the settlements along the banks of the river, especially in the downstream portions where puroks of Barangays Labangal and Dadiangas West are situated.
Current hazard models for 25-, 50-, and 100-year flood return periods show nearby areas in Silway River as high-risk flood areas. A significant percentage of the City is exposed to flood hazards posed by the river. The floodplain of the river and its basin cover an area of about 30 square kilometers (km2) and are all within GSC, comprising 5% of the City’s total area. The barangays within this floodplain are those that have the highest population and population density among the City’s 26 barangays. The settlements that line Silway River’s banks are most at risk of flooding. Most of these settlements are informal settler families (ISFs) living in substandard housing which makes them more vulnerable to hazard impacts.
Water-level rise and flash flood events experienced in Silway River have also intensified in recent years. While the City is not typically hit and is sheltered from typhoons by the surrounding mountain ranges in the SOCCSKSARGEN region, heavy rains and runoff caught by the basins are conveyed by the river and drained as flood waters into Sarangani Bay. The prevailing effects of climate change may further intensify such hydrologic events and their adverse effects. Climate projections of the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) in SOCCSKSARGEN Region or Region XII for 2020 and 2050 show that an increase in rainfall intensity will be experienced in certain months. This, coupled with the continuing change of land use in the upstream areas of Silway River’s watershed may lead to an increase in runoff volume and velocity, and erosion/siltation if the latter is not controlled and managed, further exposing already-at-risk settlements to worse hazards.
As such, the protection of these vulnerable areas and population is in order and must be done soon. To address this, the Business Case Study on the Silway River Corridor Redevelopment Program is conducted as part of the scope of the GSC SUID MP.
The Silway River Corridor Redevelopment Program (referred to in this study as the Project) responds to the Master Plan goals of security/resiliency, livability/improved quality of life, and competitiveness. Along with protecting the settlements near the river from flood hazards, the Project also aims to include components that shall contribute to the development of the river’s East Corridor, which is within the Central Development Area.
The Silway River Corridor Redevelopment Program will also support the regional efforts to protect Sarangani Bay as a protected seascape. It complements the Urban Coastal Zone Redevelopment Program, another business case study selected for the endeavor, in conserving the surrounding environment while stimulating the economy by boosting business and tourism activities in the area.