Assessment of riparian zone dynamics and its flood-related implications in Eleyele area of Ibadan, Nigeria

Abstract

Abstract This study aims at assessing how riparian zones have been altered through various land use activities and the implications of its capacity to mitigate flood. The study focused mainly on examining the land use/land cover changes within the riparian zone over a period of 20 years. The vulnerability of the riparian zone to flood were analyzed using remote sensing datasets. Flood vulnerability models were created based on the elevation and land cover type. A Euclidean distance (700 m) was created using the shuttle radar topographical mapping (SRTM) digital elevation model (DEM) of the lake and its riparian zone. The flood attenuation (150 m buffer) and riparian habitat (500 m) zones (areas) within the riparian zone of the lake were then created using the extracted lake boundary. Landsat 7 (for 1999) and 8 (for 2019) covering both zones were classified using the Maximum Likelihood Classification method. The results revealed that the built-up area increased from 2.04 to 4.54 km 2 between 1999 and 2019 while water body, grassland, and forest decreased from 0.05 to 0.04 km 2 , 0.37 to 0.12 km 2 and 1.84 to 1.82 km 2 over the period of the study. The results further show that about 18.9% of built-up areas were within the very high vulnerability zone of flood as of the year 2019. The results reveal that the riparian area cover is declining in the study area, despite its ecological services in reducing the effect of floods by slowing down runoff, trapping sediments and enhancing infiltration. The pattern of distribution of the land cover classes at different flood vulnerability levels within zones indicates that the more the alteration of both zones’ landscape, the more vulnerable they are to flood. The study concluded that there is a significant level of structural change of the riparian zone which increases its vulnerability level to flooding.