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Geographic Information System

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Geographic Information System (GIS) is a vital instrument for making use of remotely sensed data for disaster mitigation. High resolution visible and SAR images are good for extracting topography and preparing land use maps of any area. Digital Elevation Model (DEM) and land use map are important inputs to flood simulation models.

Lanza and Conti (1994) have discussed the potential of joining remotely sensed information and hydrologically oriented GIS structures to assist in flood forecasting. The remaining issues include different resolution scales, which are associated with data observed by the available sensors and their hydrological interpretation. The joint use of the various sensors is proposed in order to address the problem of quantitative precipitation forecasting at the small scale. The GIS data handling capability plays a major role in supporting the effectiveness of automated procedures eventually developed for flood hazard control in highly urbanized areas. Studies addressing the role of remotely sensed geographic information in mitigating “instantaneous” disasters, such as floods, have resulted in the following list of potential applications (Verstappen, 1995):

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  • Establishment of susceptibility of the land and vulnerability of the society;
  • Mapping potential hazard areas for use in physical planning (hazard zoning maps);
  • Monitoring potentially hazardous situations and processes, providing advanced warning; and
  • Improvement in management of emergency situations following a disaster.

Flooding poses a serious threat to the Fiji Islands. In recent years, inundation of the towns of Ba and Nadi in western Viti Levu in January 1999 resulted in an estimated damage bill of F$40 million (~US$20 million) and the loss of six lives (Yeo, 2000). Flooding of mostly rural areas in northern Vanua Levu in April 2000 is estimated to have caused financial losses of F$3 million (~US$1.5 million), a figure that obscures substantial losses incurred at the household level (Yeo, 2001). Severe flooding associated with Tropical Cyclone Ami in January 2003 cost tens of millions of dollars and left 17 people dead near Labasa (NDMO, 2003; Terry et al., 2004). Another 10 people drowned as a result of flooding in eastern Viti Levu in April 2004 (Fiji Government Online, 2004). A popular view is that the frequency of flooding in Fiji has increased over recent decades. Some attribute this increase to the sedimentation of river channels (e.g. Cochrane, 1969; Morrison et al., 1990). Indeed, to address the issue, the Government of Fiji has adopted a policy of river dredging—a policy which has been widely regarded as the panacea to the flooding problem (Yeo, 1997). Accurate assessment of flooding frequency has been inhibited by the short and incomplete nature of Fiji’s instrumental hydrological records.”

“On the other hand rural drainage area will have some water absorbed in the soil till it reaches saturation level sending the rest to contribute to direct runoff. Soil erosion, too, is greatly controlled by vegetation. Dense vegetation provides vegetal retarder to overland flow (Bruynzeel, 1990). Hence, land use classes, as determined by remote sensing, have an implicit hydrological significance in terms of water yield, peak flows and soil erosion (Gorte, 2000). Continuing deforestation leads to more sediment yield downstream causing damages in flood plain agricultural fields (Meijerink and Maathuis, 1997). Since, sudden increase in river flows might also cause floods, the stakeholders here are not only the watershed management agencies and people living in the region but also insurance agencies who provide insurance against flood damages.”

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