Hydrochemical and Geological Investigations of Some Gully Erosion- Prone Areas in Parts of Awka- Orlu Cuesta, Nigeria

Abstract

Gullies of the Awka-Orlu escarpment within Anambra State, Nigeria, were studied using hydrochemical and geological properties for understanding the geo-environmental problems which underlies the gully-prone areas. This was achieved by conducting fieldwork which includes mapping, hydrogeological surveys and samples collection, followed by laboratory analyses of soil and water samples. The soil samples were subjected to particle size analysis, compaction. Water samples were analyzed using atomic absorption spectrophotometer and titrimetric methods. The results of surface water and groundwater revealed pH average values of 5.99 and 6.3, indicating slightly acidic. Such slightly-acidic water facilitates decomposition of the cementing material in the soil. The chemical composition of surface water revealed average concentrations of magnesium (1.57 mg/l), calcium (3.40 mg/l), sodium (2.27 mg/l), chloride (22.28 mg/l), iron (0.38 mg/l), bicarbonates (37.85 mg/l), nitrate (4.73 mg/l), sulphate (3.81 mg/l), for groundwater magnesium (2.57 mg/l), calcium (3.50 mg/l), sodium (2.26 mg/l), chloride (15.09 mg/l), iron (0.23 mg/l), bicarbonates (25.46 mg/l), nitrate (11.61mg/l), sulphate (8.49mg/l) and total dissolved solid (TDS) average values of 63.16mg/ and 50.90mg/l. Using the cations and anions values to plot the piper trilinear diagram sodium bicarbonate (Na-HCO-3). This is attributed to geochemical reactions of ion-exchange and oxidation-reduction in the soil. These reactions contribute to soil disaggregation, erosion and destruction of engineering structures build to control gully erosion. water type was identified. The soil is permeable with good infiltration capacity. The investigations showed the vulnerability of the soil to gullying. These findings are important for any planned, well-designed and executed gully erosion control programmes.