Alternative Index for Measuring Flood Risk and Its Application in Gombe Metropolis, Nigeria

Aim: There is no doubt that the world is now under a serious threat from the environmental hazards due to the fact that the frequency and intensity of hydrological hazards such as floods have been increasing in recent years. Flood risk is a probability of loss which depends on three elements or concepts, namely 1) hazard, 2) vulnerability, and 3) exposure. A clear understanding and distinction between the three elements that create risk- hazard, exposure and vulnerability - gives the necessary information for factoring in most flood-related aspects. This paper focuses on developing a new method for measuring flood risk using the main indicators for geophysical exposure of the risk (percent built-up density, proximity to floodplains and elevation). The new method was afterward applied to study flood risk in Gombe Metropolis using Remote Sensing and GIS so as to achieve the set objectives.

Methods: The residential areas, streams were digitized, Multi-temporal satellite images were obtained from Land sat 8 Enhance Thematic Mapper (ETM) for 2014 and used for classification of Land cover/use type in the study area. Furthermore, Digital Elevation Model (DEM) was also used to collect elevation data for the entire Gombe Metropolis residential areas. The classified 2014 land use/land cover type of Gombe metropolis was overlaid with the digitized Gombe Metropolis residential areas map. Subsequently, the Structured Query Language (SQL) functions and attribute table of the GIS Arc map was applied to calculate the area coverage for the percent of built up areas and building constructions within 50-meter stream buffer in Gombe metropolis.

Results: The result revealed a remarkable outcome necessary to mitigate flood risk and thereby improving the well-being of the vulnerable flood communities in the metropolis. The finding proves that seven residential areas in Gombe metropolis are within a very high to high flood risk zones. These residential areas include Government Residential Area/Gabuka, Jankai, Checheniya, Pantami, Barunde, Dawaki and Bolari/ Madaki. However, Tudun Wada, MUAK, New Developed Areas, Jekadafari, Herwagana and Urban Fringe residential areas fall within the moderate to low flood risk.

Conclusion: Thus, priorities for flood risk mitigations measures should be focused towards the very high and high flood risk areas in the metropolis.