Assessment of the Quality of Sediments and Agricultural Soils: Case of the Ity-Floleu Area in the Prefecture of Zouan-Hounien, Western Côte d’Ivoire

The objective of this study is to assess the level of metal contamination of sediments and agricultural soils in the Ity-Floleu zone. The concentrations of trace elements (Fe, Mn, As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) were measured in different seasons over two successive years. The sediment pollution index made it possible to note that the sediments and agricultural soils of the various stations studied are highly polluted in all seasons. The calculation of the geoaccumulation index indicates that surface water sediments most often experience extreme or moderate pollution in As, Cd, Cu, Hg and Zn in the dry or rainy season except in Pb in some cases. We observed that the sediments of the Cavally river present a serious pollution due to extreme anthropic activities carried out along the river. Over the entire region, the results of the potential ecological risk index (RI) indicate that all the sediments and agricultural soils analysed present a moderate ecological risk in terms of Pb and Zn in certain cases and an ecological risk is observed low bound to other metals in all seasons. This metallic pollution generated by human activities in this region can have consequences for the environment and biodiversity.

Evaluation of Pollution Due to Gold Mining at Ity-Floleu Area in Sub-Prefecture of Zouan-Hounien, Western Côte d’Ivoire

This study aims to evaluate the mineral pollution of a gold mining environment in the sub-Prefecture of Zouan-Hounien (C?;te d’Ivoire). Samples were taken from surface water and flesh and skin samples of the Cavally River fish species over a period of two successive years. Concentrations in major elements, trace elements (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn), nutrients () and physico-chemical parameters in situ were measured. The results obtained show that the surface waters have very low pH with an average of 5.70. For nutrient salts, the deterioration of water quality in the study area is mainly related to alterations by nitrates, phosphates and sulphates. The concentrations of Fe, Cu, Hg and Pb are above the existing standards (international, FAO/WHO) for the majority of the stations, thus causing the deterioration of the surface water quality. Therefore, their use for agricultural irrigation could have negative impact on the health of the population and on biodiversity. Regarding the bioindicating species, the results obtained after analysis of samples showed that the fish (carp and machoiron) have Fe, Cu, Hg and Pb concentrations higher than the existing standards (international, FAO/WHO) exposing consumers to high health risks. This study showed good correlation between the high values of surface water turbidity and the proximity of gold washing sites. The use of the principal component analysis (PCA) of the physicochemical dataset revealed comparable behaviors for certain minerals within the groups (Fe, K, Mg, Mn and Na) and (As, Cd, Cu, Ni, Pb, Zn and Ca) in water. The Ascending Hierarchical Classification (AHC) analysis has defined three different classes of surface water in the study area. The presence of mineral trace elements in these receiving environments is of natural origin but would be strongly accentuated by human activities.

1D-2D Hydraulic Modeling of a Diversion Channel on the Cavally River in Zouan-Hounien,Cote d’Ivoire

On the Cavally River, located on the border between C?te d’Ivoire and Liberia, several hydraulic structures such as bridges and diversion channels are planned to be made in recent years in the operating perimeter of the Ity mining company. A 1D-2D hydraulic model was developed to design a diversion channel to cut a meander of the Cavally River in order to ensure hydraulic operation similar to the initial conditions of the river (water levels, flow and velocities). This model was designed with a flow rate of 240 m3/s and a Manning coefficient of 0.052 m1/3·s-1 for the minor bed and 0.06 m1/3·s-1 for the major bed. The results from the hydraulic model show that the hydraulic conditions (water levels, velocities) in the channel before and after the diversion remain almost like those of the Cavally River.

Rain-Flow Modeling Using a Multi-Layer Artificial Neural Network on the Watershed of the Cavally River(Cote d’Ivoire)

Water resources management is nowadays a significant stake for the world. However, missing or bad quality of the hydro-climatic historical data available of the studied area makes sometimes hydrological studies difficult. Generally, conceptual rain-flow models are designed to bring an appropriate answer with the correction of gaps and prediction of the flows. Historical hydro-climatic data of the Ity station, located on Cavally River, contain gaps which must be bridged. This study aims to establish a rainfall-runoff model through artificial neural networks for filling the gaps into the flow data series of the hydrometric station of Ity on the watershed of Cavally River. A multi-layer perceptron of feed forwards with two entries (monthly average rain and evapotranspiration) and an exit (flows) was established with flow evapotranspiration data. Comparison of the criteria of performance of the various architectures of the neural network model showed that architecture 2-3-1 gives best results. This architecture provides Nash coefficients of 75.79% and correlation linear coefficient of 95.64% for the calibration and Nash coefficients of 73.32% and correlation linear coefficient of 98.33% for the validation. The correlations between simulated flows and observed flows are strong. The correlation coefficients are 83.89% and 83.08% respectively for the calibration and validation.