For Mananga River, no rain gauge inside the catchment was yet installed by the Department of Science and Technology – Advanced Science and Technology Institute (DOST-ASTI). No nearby station was also available.
Historical rainfall data was available through the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAG-ASA). These historical data were represented through rainfall-intensity-duration frequency (RIDF). Simulation of different rainfall scenarios with different return periods was done using this RIDF. A network of stations throughout the country was already available through PAG-ASA, the boundaries of the representative area per station was determined using the Thiessen polygon method and this is shown in Figure 4 1.
Rainfall data for Mactan Station with 5-, 10-, 25-, 50, 100-return periods