On the Cavally River, located on the border between Côte 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 m 3 /s and a Manning coefficient of 0.052 m 1/3 •s −1 for the minor bed and 0.06 m 1/3 •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.

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.

<p>The aim of this paper is to characterize the bottom sediments of the Cavally River bed in order to determine the appropriate roughness coefficient of said river, in a context of clandestine gold panning in the locality of Zouan-Hounien. To achieve this, fifteen (15) sediment samples are periodically taken from the Cavally River bed, precisely in the area of influence of the activities of the Société des Mines de Ity (SMI). These samples are taken from the Bakatouo meander (upstream) to downstream of the Colline Sud meander. Sediment sampling is done with a Van Veen grab sampler. The collected sediments are carefully preserved in labeled bags. The granulometric analysis of these sediments is carried out at the laboratory using a column of sieves with AFNOR series. Analysis of the particle size curves of all samples suggests that Cavally sands are generally medium to heavy. Moreover, these particle size curves could show that the sands are transported mainly by bedload. However, these observations should be taken with great caution, since gold mining activities have a very great influence on the distribution of sediments in the river.</p>

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The Cavally watershed is covered by a large forest area, where for decades there has been intense agricultural and mining activity (modern and traditional). Anthropogenic pressures and hydro climatic variability can significantly alter the hydrological response of the Cavally River watershed. The objective of this study is to assess the impact of hydro climatic variability and land-use dynamics on the availability of water resources in the Cavally River basin. To achieve this objective, two methodological approaches were used, a first approach was used to calculate the rainfall and hydrometric indices to determine the different hydro-climatic trends of the watershed. The second approach consists in analyzing the inter-annual morphological evolution of the bed of the Cavally River by using Landsat images from 1986s, 2011s and 2018s. The results of this study show that several successive years of drought were observed in the Cavally Basin from 1970 to 1980. Analysis of hydro-climatic trends showed that rainfall has declined, and the land use map analysis showed that the vegetation cover has been significantly degraded (Four common land use classes were finally mapped. They are represented by dense vegetation with 13.11%; degraded vegetation and crops with 72.04%; water with 4.73%; built areas and bare soils with 10.12%). About the evolution of the Cavally River bed, illegal gold miners could be the cause of the increase in the surface area of the water body located between the SMI and the Floleu village (Section 3 where the morphology of the Cavally River bed has increased considerably by 13.70% between 1986 and 2011 and by 55.93% between 2011 and 2018). Indeed, this area is frequented daily by gold miners who carry out their activities both in the minor bed and on the banks of the river.