Flood vulnerability analysis for the towns of Mabitac and Santa Maria, Laguna, Philippines / Romeo Catabay Pati ; Danielito T. Franco, chair, advisory committee.

Date

4-2011

Abstract

GIS [geographic information system] floodplain mapping and flow hydrograph modeling using HEC-RAS [Hydrological Engineering Center's River Analysis System], HEC-HMS and Arc Map were done to delineate the extent of flooding and to assess the social vulnerability of the flood prone barangays [villages] of Santa Maria and Mabitac, Laguna [Philippines]. Flood hydrographs of the different river networks, which served as inputs to flood simulation, were satisfactorily derived using land cover map, soil data and extreme rainfall data as inputs to the HEC-HMS modeling system. The simulated peak discharges of the different river networks contained in different sub basins increased as the rainfall intensity increased from 68.1 to 80.0 mm/hr. The highest discharge of 74.5 cum/s in the simulation was obtained immediately after the interaction of the tributary and the middle reach (R330). The river cross-section and simulated peak flow in combination with DEM [Digital Elevation Model] as input to the HEC-RAS modeling system, predicted the flood depths and delineated the inundated barangays of the two towns. There were however, circumstances where the model over-predicted the flood depths, particularly in areas where there had been extensive land-filling. These areas were found in Baranagays 1 in Santa Maria and Sinagtala and Nanguma in Mabitac. The simulated flood depths in Barangays 1 and Sinagtala were 1.9 and 4.6 meters, respectively. On the other hand, the actual flood depths in these areas were 0.8 and 3.5 meters only. The results of the flood simulation likewise indicated that the most flood-prone barangays are Brgy. Jose Rizal in Santa Maria, and Brgys San Antonio, Nanguma, Lambac, and Bayanihan in Mabitac. The flood depths in these areas may reach 3.5 meters and can be as high as 6.4 meters in swampy areas. Social vulnerability analysis is also an important concern for understanding the interaction of the natural processes and the built-in environment. The social vulnerability index is a comparative metric that compares the differences in vulnerability of the flood-prone barangays in the town of Mabitac and Santa Maria. It also shows the potential capacity and ability of communities in recovering from a flood disaster. Moreover, it is also indicative of the weaknesses of the different barangays in recovering from floods. The thematic map that was created provides a summary of the social vulnerability of populations in the flood-prone barangays in the towns of Mabitac and Santa Maria. It shows the barangays which are potentially vulnerable based on social parameters. Barangays Jose Rizal, Masinao, Adia and Coralan in Santa Maria and Brgys. San Antonio, Nanguma, Lambac and Pag-asa in Mabitac are socially very vulnerable to flooding. The results of the social vulnerability analysis indicated that all of the flood-prone barangays in Mabitac have weak possibilities of recovery. Low family incomes, unstable jobs, low educational attainment and health services are the primary social factors that must be looked into and resolved in order to increase the coping capacity and resilience of the identified barangays to flooding. Families that have lesser incomes and resources to use or spend on preventative measures, emergency supplies, and recovery efforts, are most vulnerable. On the other hand, those with higher family income and stable job can better absorb and recover from the impacts of flooding.

Document Type

Dissertation

Degree

Doctor of Philosophy in Environmental Science

College

Graduate School (GS)

Adviser/Committee Chair

Danielito T. Franco

Committee Member

Antonio J. Alcantara, Arsenio N. Resurreccion, Enrique P. Pacard

Language

English

LC Subject

Natural disasters -- Laguna (Philippines), Environmental risk assessment, Environmental science School of Environmental Science and ManagementNatural disasters -- Laguna (Philippines), Environmental risk assessment, Environmental science School of Environmental Science and Management

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

LG 996 2011 E8 P38

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