BATHYMETRIC ASSESSMENT AND WATERSHED LAND USE CHANGE ANALYSIS FOR ERELU RESERVOIR
Abstract
The sustainability of surface water reservoirs largely depends on continuous monitoring of
their bathymetric and watershed conditions. This study presents a comprehensive
bathymetric and land use/land cover (LULC) change analysis of the Erelu Reservoir, Oyo
State, Nigeria, aimed at assessing the impacts of human activities on the reservoir’s capacity
and surrounding watershed. Bathymetric data were collected using an echo sounder and
GARMIN Hand-Held GPS 78sc receiver, and processed in Hypack software (2023) to
generate a detailed bathymetric chart showing depth variations and sediment accumulation
zones. Satellite imageries for 1984, 2022, and 2024 were analyzed using ArcGIS to determine
LULC dynamics within the catchment. Results revealed a significant increase in built-up
areas from 33.5 km² in 1984 to 261.7 km² in 2024, while farmland and vegetation cover
decreased, indicating rapid urbanization and land conversion. The water surface area also
declined from 117.7 km² to 99.7 km², reflecting siltation and encroachment around the
reservoir. These changes demonstrate the increasing anthropogenic pressure on the
watershed, leading to reduced water storage potential and potential environmental
degradation. The study recommends effective catchment management practices, regular
bathymetric monitoring, and strict land use regulation to sustain the reservoir’s ecological
and socio-economic functions.
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