Eutrophication in the Lobo watershed remains a major problem. The work carried out has focused on chemical and biological analyses in the lake or in its immediate environment: they did not sufficiently take into account the diffuse transfer of nutrients over the entire watershed. This study aims to assess the nutrient (N and P) loads in the Lobo watershed, an agricultural area, to understand the spatio-temporal impacts of land management practices on eutrophication. The methodology uses two steps: streamflow calibration and nutrient (N and P) estimation using the Soil and Water Assessment Tool (SWAT) watershed model. Thus, the nutrient inputs were estimated based on the levels of N and P in every kilogram of Nitrogen-phosphorus-Potassium (NPK) type fertilizers applied by farmers. The average quantities of N and P applied to the crops were 47.24 kg ha⁻¹ and 21.25 kg ha⁻¹. Results show a good performance on flow calibration as evidenced using evaluation criteria R², Nash–Sutcliffe Efficiency (NSE), and Percent Bias (PBIAS) of 0.63, 0.62, and −8.1, respectively. The yields of inorganic N and soluble P varied from 0 to 0.049 kg ha⁻¹ and from 0 to 0.31 kg ha⁻¹. These results show that the crops’ inorganic nitrogen requirements were higher than the demands for soluble phosphorus. Simulations relating to the organic N transfer revealed values ranging from 0.2 to 5 kg ha⁻¹, while the transport of organic phosphorus was estimated to vary from 0.3 to 1.3 kg ha⁻¹.

Eutrophication in the Lobo watershed remains a major problem. The work carried out has focused on chemical and biological analyzes in the lake or in its immediate environment: they did not sufficiently take into account the diffuse transfer of nutrients over the entire watershed. This study aims to assess the nutrient (N and P) loads in the Lobo watershed, an agricultural area, to understand the spatio-temporal impacts of land management practices on eutrophication. The methodology uses two steps: streamflow calibration and nutrient (N and P) estimation using the Soil and Water Assessment Tool (SWAT) watershed model. Thus, the nutrient inputs were estimated based on the levels of N and P in every kilogram of NPK-type fertilizers applied by farmers. The average quantities of N and P applied to the crops were 47.24 kg N/ha and 21.25 kg P/ha. Results show a good performance on flow calibration as evidenced by evaluation criteria R2, NSE and PBIAS of 0.63, 0.62 and -8.1, respectively. The yields of inorganic N and soluble P varied from 0 to 0.049 kg N/ha and from 0 to 0.31 kg P/ha. These results show that the crops’ in-organic nitrogen requirements were higher than the demands for soluble phosphorus. Simulations relating to the organic N transfer revealed values ranging from 0.2 to 5 kg N/ha, while the transport of organic phosphorus was estimated to vary from 0.3 to 1.3 kg P/ha.

This study aims to analyze the input data of the semi-distributed SWAT model that can be used as a hydrological study of the Lobo water reservoir. The adopted approach includes two major steps: The input data estimation and the watershed configuration. The estimation of input data consists in the collection and calculation of input data necessary for the watershed configuration. The input data collected and estimated were a digital elevation model (DEM), a soil map, soil physico-chemical parameters (grain size, K erodibility coefficient, exchangeable anions, soil density, organic carbon, soil electrical conductivity), a land cover map, information on agricultural practices and daily climate data (Temperature, Rainfall, Sunshine, Wind Speed ​​and Relative Humidity). The watershed configuration consisted of the extraction of watershed boundaries and watershed network, the integration of data, the calculation of hydrological response units (HRU) and the watershed configuration. The SWAT model permitted to extract a single type of soil for Lobo water reservoir watershed. The watershed has a dense drainage system which means that the area is heavily drained. The degraded forest occupies 37% of the watershed followed by agricultural land (30% of the territory). 213 HRU from 39 sub-watersheds were also obtained. These data are an indispensable tool for the hydrological simulation of the Lobo reservoir.

The Lobo reservoir, designed to supply water to the Daloa city population (central west of Côte d’Ivoire), is facing the phenomenon of eutrophication due to the agricultural plots located upstream of the reservoir inputs. Studies have highlighted the reservoir pollution and sedimentation problems. This study was initiated to test the effectiveness of a transfer model in the fight against the eutrophication problem. The objective of this study was to determine the optimal width of a vegetative filter strip on the banks of the Lobo reservoir, where the water intake installations of the drunk water company SODECI are located, using the VFSMOD model. The methodological approach is structured into four (4) main stages: 1—Evaluation of runoff from the source of pollution (contributing surface) during a rainy episode; 2—Calculation of the incoming runoff volume and the sediment load; 3—Simulation of runoff reduction and incoming sediments within the grassy filter strip; and 4—Determination of the optimal width of the grassy strip. The results obtained showed a contributing source area of 13.5 ha and 2% as the average slope. A runoff volume of 4680 m³ coming from the source of pollution is reduced by 1119 m³ (24%) through a grassy strip that is 3 m wide. The sediment load goes from 132 kg to 33 kg, a reduction of 75% in the quantity of sediment entering. The scenarios tested showed that a grassy strip width equal to 3 m should allow for a reduction of 75% of upstream sediments. This grassy strip width of 3 m should be considered for implementing a vegetative filter strip around the Lobo reservoir.

The Lobo reservoir designed to supply water to the Daloa city populations (Central west of Côte d'Ivoire) is facing the phenomenon of eutrophication due to the agricultural plots located upstream the reservoir inputs. Studies have highlighted the reservoir pollution and sedimentation problem. This study was initiated to provide a simple and effective solution to the eutrophication problem. The main objective is to determine the potential optimal dimensions of a grassed strip in order to limit the eutrophication phenomenon of the Lobo reservoir. The sizing of this grassed strip was done using the VFSMOD model. The flow from the pollution source plots was simulated and integrated into the model. The different scenarios tested from the band width variation have concerned the return periods of 1 and 2 years. The results obtained revealed that for the one-year return period, the grassed strip to be installed should have a width of 12.70 m in order to reduce by 70% the flow entering the strip considering the diffuse runoff over a length of 300 m. For the two-year return period, a width of 22.95 m should be required with the same length. The scenarios showed that a grassy strip width equal to 3 m should allow a reduction of 75% of upstream sediments.