Geoinformation for Disaster and Risk Management - ISPRS

The Philippine Atmospheric, Geophysical and
Astronomical Service Administration (PAGASA) is
responsible for weather and flood forecasts, and
does so with well instrumented and automated
systems for major rivers. However, such approaches
are not practical or affordable for smaller rivers,
most of which are consequently not being
monitored. For these areas a geodata-based system
may still be appropriate, although it has to be lowcost,
robust, sustainable and depend on strong
involvement of the local population. This best
practice example describes a system where the local
population is both involved in the data collection and
transmission, as well as in the early warning.
The Binahaan River basin flood early warning
system
The Binahaan River is located in the province of
Leyte in the Eastern Visayas of the Philippines
(Figure 1). It stretches from a mountain ridge in the
West to the Leyte Gulf in the East, covering an area of
272km2. It has a history of frequent flooding events
in the Eastern lowlands, with an average of more
than one damage-causing flood per year, and a small
number of people having drowned during floods that
occurred over the last 2 decades.
The reported damages are largely attributed to
reduced harvest due to submerged crops, mainly rice
and some vegetables, and also residential buildings
and infrastructure occasionally sustaining damages.
An increase in water-borne communicable diseases
has been observed as well. In the view of local
inhabitants the loss of crop, and as a result income, is
the most significant impact of the floods. Towards
the end of the monsoon periods, when the capacity
of the watershed to buffer more water is severely
reduced, events with a relatively small return period
may be especially serious by causing extensive and
widespread disruption.
Objectives and basic setup of the LFEWS
While not reducing the flood hazard, the
establishment of early warning systems allows
inhabitants of flood-prone areas to bring moveable
items susceptible to water damage, such as harvests,
livestock, household electronics, furniture and
motorized vehicles, to safety. This can be in higher
parts of buildings or elevated areas near their
dwellings. As a river basin sustaining frequent floods
(more than one per year) and with a relatively large
flood-prone area (64km2), the Binahaan was chosen
as the first site for the establishment of a local flood
early warning system (LFEWS) in Region VIII of the
Philippines. The LFEWS was developed in
accordance with basic principles of people-centred
early warning systems.
Rain + River
Level Gauges
Data
Transmission
Activities
It consists of rain and river level gauges, an
Operation Centre (OC) near the watershed where
data are received, analyzed and the decision about a
warning is taken. A communication chain down to
household level facilitates the transmission of the
warning. The LFEWS also includes evacuation
routes, evacuation centres and emergency response
capacity such as search and rescue teams (Figure 2).
The provincial government of Leyte is running the
system by setting up the OC, and coordinates the
efforts of the four involved municipalities. They, in
turn, contributed to the establishment of the system
with some community-based approaches. This
included hazard mapping with GPS and the
development of disaster preparedness plans at
village levels. The initial investments for the LFEWS
(15,000 Euro) were paid by GTZ, and all running
costs are covered by the provincial government. A
cost-benefit-analysis estimated that the investment
costs are recovered after eight years by reduced
losses due to timely warnings.
Generic Local Flood Early Warning System
Activities
Actors
Operation
Centre
Analysis and
Warning
Municipality
Village
Warning Warning
Household
Figure 2: Schematic overview of the Binahaan LFEWS
59