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SIMULATING SCENARIO FLOODS FOR HAZARD
ASSESSMENT ON THE LOWER BICOL FLOODPLAIN,
THE PHILIPPINES
MUHIBUDDIN BIN USAMAH and DINAND ALKEMA
∗
Int. Institute for Geo-Information Science and Earth Observation (ITC)
PO Box 6, 7500 AA Enschede, The Netherlands
∗
alkema@itc.nl
This paper describes the first results from a study to the behavior of floods in
the lower Bicol area, the Philippines. A 1D2D dynamic hydraulic model was
applied to simulate a set of scenario floods through the complex topography of
the city Naga and surrounding area. The simulation results are integrated into
a multi-parameter hazard zonation for the five scenario floods.
Introduction
The Bicol floodplain is located on Luzon Island, the Philippines (Fig. 1).
Floods are the most serious natural hazard in this area. They occur almost
every year and cause substantial suffering, loss of life and economic damage.
This is especially true for the city of Naga, that is located at confluence of
the Bicol river with the Naga river. Simulation of flood events in this region
using a two-dimensional (2D) flood model can contribute to minimizing the
loss of life and damages to property and can be a helpful support for flood
risk management.
Flood Modeling
This research applies a 1D2D flood propagation model SOBEK, in the
Lower Bicol Floodplain to simulate flood events with a return period of
2, 5, 10, 25, and 50 years. In combined 1D2D flood modeling, the flow of
water within the riverbanks, is modeled as one-dimensional (1D) flow. At
the moment that overland flow occurs (because one of the banks is over-
topped), the flow is computed using a 2D solution of the flow equations
(Fig. 2). SOBEK is a grid based inundation model that uses the finite
difference method. The calculation scheme is based upon the following
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