Abstract
Dams are reservoirs established for different reasons. Oyan dam, Ogun State, Nigeria was established and commissioned on the 29th March 1983 to supply water to Lagos State and Abeokuta for municipal uses, with power generation potentials to support Lower Ogun Irrigation Project. However, flooding has become an annual experience of downstream communities along Ogun river especially when the Oyan dam is opened; it has really becomes remarkable since the flood events of 2012. This project investigates the level of siltation and floods menace adjoining Oyan dam and its environ. An integrated methodology of bathymetric survey, total station traversing and satellite imagery were used to acquire geospatial locations of the dam features and other details within the dam through the process of traversing, heightening and detailing. The field investigation was conducted between January 2018 and January 2020 to determine dam bed topography with the deployment of integrated approach. The collected data were processed using Hydrologic Engineering Center’s River Analysis System (HEC-RAS), HYPACK software and ArcGIS 10.6 software. The maximum and minimum depth within the dam are -4.072m and -21.588m respectively. The cross sections are represented for each 200m length of the dam. Furthermore, volumetric analysis of sediment budget was computed to be 251.7x106m3 and compared with designed reservoir capacity of 270x106m3. From the study, a loss of about 18.2x106m3 approximately 6.7% was recorded. Satellite imagery shows the rate of change within Oyan dam and its catchment area downstream based on Triangulated Irregular Network (TIN) generated from Shuttle Radar Topography Mission (SRTM) the maximum and minimum elevation in the catchment are 29m and 182m respectively. The study recommends that deepen and training of Ogun river and all adjoining drainages system within the study corridor to retain more water when peak rainfall is recorded.
Highlights
Total station was used for traversing the dam catchment, while Echo sounder was used for bathymetric survey
Figure 3u is the Triangulated Irregular Network (TIN) generated from Shuttle Radar Topography Mission (SRTM) data of the subject site with details of drainage system and other land forms; Figures 3a- 3t shows longitudinal and vertical profiles that revealed depth changes within Oyan dam which was used to compute sediment accrued
This study demonstrates the ability of bathymetric survey, total station traversing and GIS techniques in capturing spatial data, monitoring, maintenance and management of the reservoir
Summary
It is one of the most valuable properties in the life of man and his environment. “WHO (2020) estimated that universal access to safe water and sanitation would result in $170 billion of economic benefits each year from reductions in healthcare cost and increased productivity from reduced illness. Flooding is regarded as the most ubiquitous natural disaster that affects people and urbanization in different dimensions globally. The effects of river floods and storm surges in urban area include: deaths, displacements, acute health impacts and huge economic losses. ‘From 1970 to 2008, over 95% of deaths from natural disasters occurred in developing countries’ (IPCC, 2012). UNEP (2016) estimated that adapting to climate changes and coping with damages will cost developing countries $140-300 billion per year by 2030 and between $280-$500 billion per year in 2050
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