Flood Control, Drainage and Irrigation
Flood Control and Drainage
The main receiving bodies of water for stormwater run-off in the city are the Santa Rosa River at the western boundary, the Diezmo and Cabuyao Rivers at the eastern side, and the Laguna de Bay. A system of storm drainage systems in the urban areas, residential areas and industrial estates convey runoff to these natural water bodies. These consist of reinforced-concrete pipes, open canals (either lined or unlined), and reinforced-concrete rectanqular culverts. Flooding is limited to tidal flooding in the lakeshore areas and river overflows. An area of around 50 hectares within the Diezmo River Irrigation System is prone to flooding.
Findings of the 2010 Site Investigation/Engineering Study for a Flood Control, Combined Drainage Sewerage System for the Santa Rosa Basin Project Interim Report, the existing drainage system in the 18 barangays of Santa Rosa City is a combination of circular pipe and rectangular channel. Most of the system is closed and about 90 is pipe. Based on the study, it reveals that most of the drainage structure are either insufficient to catch surface run-off due to structures are damaged. This condition coupled with encroachment of informal settlers along river banks resulting to flooding in the low lying areas. (p.13: 43-54). It was also observed during the field visit of the Study Team on February 12, 2016 that residential houses are found on the side of main canals.
In the recent study on "Participatory Watershed Land-use Management: An Approach for Integrated Climate Change Actions" of the University of the PhilippinesLos Banos and Institute of Global Environmental Strategies (IGES) of Japan, it is estimated that the flood extent area of Santa Rosa City will increase by 22 percent in 2025, reckoned from 2014 level, if the current urban development scenario is allowed to run its course without intervention. This translates to 1,180 hectares of flooded areas, compared to 970 hectares in 2014. Th is projection is based on the rapid land conversion from agricultural to residential and industrial, thereby increasing impervious areas. (Figures 7.1 and 7.2)
The flooding from new land development, particularly in the downstream areas, was articulated in the 2012 Sectoral Analysis Workshop.
Figure 7-1: Significant Development in Flood-Prone Areas in Selected Areasin Laguna
Source: UPLB-IGES Presentation
Figure 7-2: Land Use Changes Model: Do Nothing Scenario
Source: UPLB-IGES Presentation
One factor that contributes to the declining cultivation of agricultural lands is the lack of irrigation. As of 2013, there is only one antiquated irrigation facility, rehabilitated in 2010, in Sta. Rosa City (Table 7.2.)
Table 7·2: Irrigation System of the City of Sta. Rosa, 2013
Source. City Agriculture Office, City of Sta. Rosa, Laguna
In addition to its own system, the rice areas of Santa. Rosa City is also served by an irrigation facility in Cabuyao, Laguna (Figure 7.3).
Table 7-3: Irrigation Facilities servicing Rice Areas of the City of Sta. Rosa
Source: City Agnculture Office, City of Sta. Rosa. Laguna