Exploration of hydro-geomorphological indices for coastal floodplain characterization in Rivers State, Nigeria

Abstract

Flood is a reoccurring natural hazard in many parts of Nigeria, and is likely to increase in severity and frequency. Characterization of recently flooded areas was carried out using hydro-morphological indices to identify flood prone areas. In flood risk quantification and identification, hydrodynamic models require vast amounts of data, while contour delineation fails to account for the upstream contribution and accumulation at downstream locations. Data on recently flooded areas and elevation data were collated. Hydro-geomorphometric indices were computed and compared using the Mann-Whitney U test. Across the indices, the terrain roughness indices – vertical roughness measure (VRM) and topographic roughness index (TRI) were found to be significant but weakly correlated (r = 0.455, P<0.05). There was a significantly positive but moderate correlation between topographic wetness index (TWI) and VRM (r=-0.673) and TWI vs TRI (r=0.572). Topographic position index (TPI) displayed a weak but significant relation to VRM, TWI and TRI. Of these four indices, TWI and TRI have standardized test statistics of -6.11 and 10.00 respectively and a significant test value < 0.05. Results show that flooded and non-flooded areas can be distinguished for the study area using these indices. It is recommended that hydro-geomorphometric indices should be used, adding another layer of confidence in the identification of flood prone areas for disaster risk management in data poor environments.