Hydrologic Model for Flooding in Manupali Watershed and Its Implications to Land-Use Policies

Abstract

Flooding has become a recurring event in the Province of Bukidnon causing severe destruction to houses, buildings, infrastructure and livelihood. Since the province is not exempted to flooding events as an impact of the typhoon, understanding the watershed hydrologic behavior is essential for vulnerability and risk assessment as to disaster preparedness and risk reduction. The study aims to analyze the hydrologic response of Manupali watershed through flood hazard maps, hydrologic and hydraulic models. This paper presents the combination of geographic information system, high -resolution digital elevation model, land cover, observed hydro-meteorological data and the combined Hydrologic Engineering Center-Hydrologic Modeling System and River Analysis System models. The hydrologic model assesses the relationship between rainfall and discharge of the watershed and the hydraulic model computes the flood depth and flow pattern in the floodplain. Upon calibration, the over-all performance of the hydrologic model is “very good” performance rating based on the standards set by Moriasi et.al. (2015) with index values of 0.89, 0.75, 0.46 for Nash-Sutcliffe Coefficient of Model Efficiency, Percentage Bias, and Root Mean Square Error, respectively. The calibrated hydrographs were used to produce flood hazard maps in 2, 5, 10, 25, 50, and 100-year return periods as well as determined the number of flooded buildings in each flood hazard level per return period. The flood hazard maps may contribute to science-based land-use policy formulation, land-use zoning, planning and management to mitigate extreme rainfall-induced flood risks in the affected Barangays in the Manupali watershed.