Contribution of GIS to Soil Landscape Mapping by Multi-Criteria Analysis Using Weighting: The Case of the Square Degrees of M’Bahiakro (Centre) and Daloa (Centre-West) in Ivory Coast

As part of the drive to improve coffee and cocoa production in Ivory Coast, studies are carried out to identify soils that are favourable for these crops. It is therefore necessary to orientate soil investigations based on reliable criteria that best discriminate soil cover. With this in mind, this study is being carried out to help improve survey methods by mapping soil landscapes. It uses GIS and weighted multicriteria analysis. To do this, satellite images were processed and the geological map of the square degrees of M’Bahiakro and Daloa was reclassified. The results show that relief is the main factor in soil landscape differentiation, with respective weights of 0.58 and 0.67 for the forest and pre-forest zones. In contrast, the weight of geological formation in soil landscape differentiation remains low (0.05 for the forest zone and 0.07 for the pre-forest zone). The criteria used on the base of aggregation sum methods have made it possible to formulate soil landscape mapping prediction functions according to agro-ecological environments in the humid intertropical zone. This is essential for the orientation of soil survey work. Nevertheless, other comparative methods, such as the coding mapping method, could provide elements for discussion to validate the models.

Multicriteria Analysis by Codification for the Determination of Soil Landscape Units in Forest and Pre-Forest Zones of Cote D’Ivoire: The Case of the Square Degrees of M’Bahiakro and Daloa

The present study, carried out in the forest (Daloa) and pre-forest (M’Bahiakro) zones of Cote d’Ivoire, aims to determine soil landscape units using the coding method. Geological maps and satellite images (SRTM and Landsat) were used for this purpose. The methodological approach adopted consisted in producing maps of slope, geology, land use and topography using the codification method. These various maps, integrated into a GIS using the coding aggregation method, were used to generate soil landscape maps. Twenty-seven (27) soil landscapes have been identified for the pre-forest zone (M’Bahiakro), with a strong dominance of acid rock over a moderate relief under savannah, forest/degraded forest and crops/fallow. However, the forest zone (Daloa), with forty-one (41) soil landscapes identified over the entire zone, is characterized by a majority of mafic rocks on a medium altitude under forest/degraded forest, water and crops/fallow. The criteria used from the codification method (sum of aggregations) made it possible to predict the spatial distribution of soil map units according to agro-ecological environments in the humid intertropical zone. This is essential for the orientation and reinforcement of soil survey tools. However, a comparative evaluation of the different multicriteria analysis methods for coding and weighting soil landscape unit mapping would enable us to identify the most suitable and efficient method for drawing up base maps for soil surveys.

Impact of the Condition of Drinking Water Supply Networks on the Quality of Water Intended for Consumption: The Case of the Network in the Commune of Daloa (Central West of Côte d’Ivoire)

The potability of drinking water depends not only on the source and the treatment system, but also on the quality of the waterworks. In fact, the quality of drinking water is considerably degraded by the dilapidated state and lack of maintenance of drinking water networks. In Côte d’Ivoire, the majority of drinking water networks in the various towns are ageing. In Daloa, despite the efforts made by the company in charge of water treatment and distribution to make the water drinkable, the water at consumers’ taps is often colored, has an unpleasant aftertaste and settles after collection. As a result, people are concerned about the potability of tap water, and some are turning to alternative sources of drinking water of unknown quality. In order to determine the factors responsible for the deterioration in water color and taste, as well as the sectors of the network most affected, a diagnosis of the network’s equipment was carried out. Water samples taken from the network were analyzed for color and turbidity. The diagnosis revealed that most of the equipment (suction pads, valves, drains and fire hydrants) is outdated and irregularly maintained. Analyses show that the water is more colored in cast-iron and PVC pipes than in asbestos cement pipes. Coloration values in the network range from 0 to 27 UVC for asbestos cement pipes, from 15 to 56 UCV for ductile iron pipes, and from 11 to 102 UCV for PVC pipes. On the over hand, turbidity values vary from 8.02 to 3.32 NTU for ductile cast iron pipes, 8.51 to 16.98 NTU for asbestos cement pipes and 0.9 to 6.98 NTU for PVC pipes. Old cast-iron pipes release ferric ions on contact with water, degrading their color. Old cast-iron pipes release ferric ions into the water, degrading its color. The high color values observed in the vicinity of drains are thought to be due to irregular maintenance of the network. In fact, after network maintenance, a reduction rate ranging from 2% to 73% is observed for turbidity, while for color, the rate varies from 5% to 72%. In short, the network’s obsolescence and irregular maintenance contribute significantly to the deterioration of water quality.

Typology of Crop Residues and Energy Recovery in Heavily Agricultural Areas: Case of the Departments of Soubré, Daloa, Issia and Sassandra (Côte d’Ivoire)

The valorization of crop residues could constitute an energy source (biogas) allowing to reduce the energy needs of populations in agricultural regions, improve their living conditions and slow down deforestation as well as greenhouse gas emissions. This work aims to determine the typology of agricultural waste in the departments of Soubré, Sassandra, Daloa and Issia, to determine the number of residues generated in these departments, and to assess the biogas potential of these departments said residues. Field observations were made to identify the different types of waste, then, based on agricultural statistical data from the Ministry of Agriculture and biogas productivity indexes, the quantities of agricultural residues and biogas were estimated. Agricultural residues consist of pods (50%), stalks (19%), cobs (3%), Straws (8%), stalks (2%), shells (9%), fibers (7%), husks (1%), and bunches (1%). In addition, these localities have 465266.3 t of pods, 173583.2 t of stalks, 84280.0 t of shells, 75,857 t of straws, 12,000 t of husks, 10,987 t of bunches and 6793.0 t of fibers. The departments of Soubré, Sassandra, Daloa and Issia contain a total potential energy of 235.87 × 106 m3 of biogas. However, this is unevenly distributed among the localities. The volume of biogas recorded is higher in the department of Soubré (74.91 × 106 m3) which is followed respectively by the departments of Daloa (62.27 × 106 m3), Issia (52.77 × 106 m3 and Sassandra (45.93 × 106 m3). The departments of Soubré, Sassandra, Daloa and Issia have a very large potential for the production of agricultural residues that may be of interest to economic operators for recovery in biogas production units.

Mineralization of Natural Spring Water in the City of Daloa (West-Central Côte d’Ivoire)

The water from natural springs in the city of Daloa is increasingly used by the population for its drinking water needs, even though its quality remains unknown. This study aims to determine the acquisition mechanism of the mineralization of these waters. Thus, physicochemical analyses were carried out on 10 spring water samples in February 2019. A summary statistical analysis of the results obtained shows that these waters are acidic (4.81 ≤ pH ≤ 5.39) and very weakly mineralised, with 50% of the conductivities below 100 μS·cm-1. The average iron (0.5 ± 1.02 mg/L) and manganese (0.61 ± 0.90 mg/L) contents show that these two parameters are increasing in the spring water. The Normalized Principal Component Analysis (NPCA) shows that mineralization is mainly controlled by surface inputs of elements (anthropogenic pollution), then the oxidation-reduction phenomenon and, finally, the water-rock contact (mineralization-residence time). Otherwise, the very low expression of water-rock contact (mineralization-residence time) in the acquisition of the mineralization reflects a short residence time of the water in the aquifer.