Assessment of Geologic Controls of Flooding in Parts of OBIO/AKPOR L.G.A., Rivers State, Nigeria

Assessment of Geologic Controls of Flooding in Parts of OBIO/AKPOR L.G.A., Rivers State, Nigeria

DOI: 

https://doi.org/10.30564/jgr.v3i2.2902

Abstract

Flooding of Municipal areas is a frequent environmental occurrence in Rivers State that occurs when rainfall runoff meets land surfaces with low water absorbing capacity or when it overwhelms drainage channels. In order to assess the flood situation in the study area, an integrated method which involves field-measurement, geographic information system (GIS),laboratory analysis of soil samples and topographic studies were employed.Digital elevation model of the study area reveals that the flooded areas are situated in areas with elevations lower than its surrounding, thereby acting as a natural basin to retain flood waters after rainfall.Four holes were drilled to depth of 3 m to obtain soil samples at 1 m sampling interval, from which laboratory analysis was carried out to determine some geotechnical parameters such as soil’s particle size, specific gravity, bulk density,porosity,moisture content, permeability and hydraulic conductivity. Results of the analysis show that permeability,hydraulic conductivity and porosity diminishes with respect to depth. The soil in the flooded areas have high fines content (silt and clay), high bulk density which increase with depth and a specific gravity that is typical of organic rich soils that contain sand mixed with a considerable amount of fines. At Nkpolu, mean permeability rates of 0.003 cm/sec, 0.009 cm/sec and 0.033 cm/sec were obtained at 1, 2 and 3 m respectively. At Eneka, mean permeability rates of 0.011 cm/sec,0.018 cm/sec and 0.014 cm/sec were obtained at 1, 2 and 3m respectively,while at Rukpokwu, mean Permeability rates of 0.021 cm/sec was obtained at 1 m, while 0.006 cm/sec was obtained at 2 and 3 m respectively. The mean hydraulic conductivity for the locations under study is of the order of 10-4 ft/day. This study has shown that the flooded areas are located in low lying urban areas which act as basins, therefore, the top soil is crusted with highly compacted soil horizons beneath. With high and frequent rainfall in the region which generates a lot of runoff, in addition to poor drainage system, flooding in the study area occurs frequently.Therefore,construction and maintenance of efficient drainage channels for an effective solution to urban pluvial flooding in the study area are thereby recommended.

Keywords: 

Pluvial flooding, Risk assessment, Soil sample, Soil properties, Topography

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