FLOODING

Different types of flooding (e.g. river floods, flash floods, dam-break floods or coastal floods) have different characteristics with respect to the time of occurrence, the magnitude, frequency, duration, flow velocity and the areal extension. Many factors play a role in the occurrence of flooding, such as the intensity and duration of rainfall, snowmelt, deforestation, land use practices, sedimentation in riverbeds, and natural or man-made obstructions. In the evaluation of flood hazard, the following parameters should be taken into account: depth of water during flood, the duration of flood, the flow velocity, the rate of rise and decline, and the frequency of occurrence.

Earth observation satellites can be used in the phase of disaster prevention, by mapping geomorphologic elements, historical events and sequential inundation phases, including duration, depth of inundation, and direction of current. The geomorphological approach consists of the geomorphological analysis of the landforms and the fluvial system, to be supported wherever possible by information on (past) floods and detailed topographic information. The procedures to be followed can be summarized as follows:

a) Detailed geomorphological terrain mapping, emphasizing fluvial landforms, such as floodplains, terraces, natural levees etc.

b) Mapping of historical floods by remote sensing image interpretation and field verification to define flooded zone outlines and characteristics.

c) Overlaying of the geomorphological map and the flood map to obtain indications for the susceptibility to flooding for each geomorphological unit.

d) Improving the predicting capacities of the method by combination of Geomorphological, hydrological, land use, and other data.

Remote sensing data for flood management should always be integrated with other data in a GIS. Especially on the local scale a large number of hydrological and hydraulic factors need to be integrated. One of the most important aspects in which GIS can contribute is the generation of detailed topographic information using high precision Digital Elevation Models, derived from geodetic surveys, aerial photography, SPOT, LIDAR (Light Detection and Ranging). These data are used in two and three dimensional finite element models for the prediction of floods in river channels and floodplains.

When satellite imagery is combined with other GIS data such as land use, population data, cadastral data, transportation and infrastructure networks, an analysis may be done of the high risk areas that may be subject to damage from disasters.


See also:

ENVIRONMENT
AGRICULTURE
HYDROLOGY
REMOTE SENSING OF ENVIRONMENT
NATURAL DISASTER MANAGEMENT