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Analysis of flood physical vulnerability in residential areas/Case study: Naga City, the Philippines.

Saut SAGALA student laureate
saut.sagala@gmail.com

°1979 Indonesia
Bachelor in Urban Planning, Institute of Technology Bandung, Indonesia, 2001

Analysis of flood physical vulnerability in residential areas/Case study: Naga City, the Philippines.

Mr Sagala spent six weeks carrying out fieldwork in the Philippines (Naga City) for this thesis. In fact this thesis is part of a co-operation project between the ITC and Naga City.
Naga is a medium-sized city (less than 150,000 inhabitants) comprising 17 administrative units. It lies less than 5m above sea-level and is regularly subjected to typhoons, which generate very heavy rainfall. Furthermore, some districts lie in the alluvial plain of two rivers and are regularly flooded.
Mr Sagala has focussed his study on two of these areas. He selected 245 buildings (non-random purposive sampling) which he located with a GIS* and which he visited in order to gather information regarding the height of the ground floor in relation to the street, the number of floors, the materials used for the walls and the roofs, whether the structure is on piles or not, etc.
Mr Sagala subsequently carried out surveys in order on the one hand to gather information about the level of the water during two floods (which recur more frequently than once every ten years) and on the other to establish the amount of damage caused during these floods; 68 owners were questioned. Stratified sampling was used to select the owners.
From these surveys he produced a map of the level the water reached during the floods in both districts. By combining this information with a scale of vulnerability (significance of damage), he created a series of graphs for the different types of buildings identified in his inventory, linking the significance of vulnerability to the level of submersion. According to the location of these buildings he then created a map of vulnerability.
Mr Sagala puts forwards and tests a simple but effective methodology, which can easily be transposed to urban environments in developing countries. These are often located in areas that are vulnerable to flooding and usually contain housing that is made of relatively fragile materials. Furthermore, Mr Sagala’s findings can be used in the future for the whole of Naga City. This will allow the risk of flooding to be better assessed, the damage to be properly estimated, and ultimately coping mechanisms to be developed.

*GIS: Geographic Information System
 

Report: Prof. F. Petit, Hydrography and Fluviatile Geomorphology Laboratory, Université de Liège, Belgium