Migration of Biodegradable Organic Matter in Underlying Soils of Household Waste Dumpsites: A Case Study in Abomey-Calavi, Benin

This paper presented the first part of the studies about the development of a tool for groundwater contamination prediction, conducted by the Laboratory of Sciences and Technology of Water (UAC/Benin). The investigation made consisted in estimating the combined effect of retardation factor and biodegradation on migration processes of leachate, in the underlying soils of household waste dumpsites, without active safety barrier. Leachate infiltration tests for different initial conditions were made on soil columns and the breakthrough curves were traced for electrical conductivity, the 5 day biochemical oxygen demand (BOD5) and total kjeldahl nitrogen TKN. A mathematical migration model was developed and solved numerically by finite difference method and implemented with Matlab R2013a. Thus, the calibration of the model was made with electric conductivity data by determining the dispersion coefficient of the studied soils (D = 0.96 cm2/min). Simulations for model verification showed that the established model can perfectly predict the migration of biodegradable organic pollution (BOD5) but did not give conclusive results for the monitoring of nitrogenous organic matter (TKN). The influence of the retardation factor on the migration of biodegradable organic pollutants in soils was linear, while the biodegradation rate of the organic material on migration showed an exponential pattern.

Steady-State Radial Flow Modeling through the Production Well in the Confined Aquifer of Monzoungoudo,Benin

This study aims to develop a mathematical analysis for one-dimensional modeling of a radial flow through a production well drilled in a confined aquifer, in the case of steady-state flow conditions. An analytical solution has derived from that expression for estimation of drawdowns according to different flowrates. Through that process, the evaluation of static pressure, the calculation of hydraulic charge due to the waterflow through the well is evaluated, the drawdowns curves are drawn and at last, the obtained curves are analyzed. The curves obtained for the different flow rates have an asymptotic direction, the axis of the hydraulic charges. The variation of the hydraulic charge depends on the radial distance for different flow rates. The P point, is a common point of all curves obtained for different production flowrates in the well. This point is where the well production flowrate is optimum for the optimal hydraulic charge.

Modelling Estimation of the Available Rainwater Resource in Gbedji-Kotovi Clay Area for Supplying Dikes and Dams

Floods and flows data are useful for dimensioning of dikes and dams which often include evacuation devices that regulate flows to ensure the volumes of water. The objective of this study is to estimate the available water resource in the village of Gbédji-Kotovi, located in the watershed of Couffo river in Benin by using sequentially, the HBV (Hydrologiska Byrans Vattenbalansavdelning) and GR4J (Rural Engineering model with 4 daily parameters) climate models. Hydrographs of water levels are simulated according to the calibration period (1994-1999) different from the validation one (1982-1988). Considering the Nash-Sutcliffe model Efficiency coefficient (NSE), the performance of GR4J model during calibration is slightly higher than the performance of the HBV model, while during the validation, the contrary is noticed. The annual rainfall average simulated is 1117.7 mm/year while the average observed is 1104.6 mm/year over the period 1981-2005. By 2050, on one hand, the annual flow rate values will vary from -19.2 to -11.9%, while the actual evapotranspiration will vary between 0.5 and -5.8;on another hand, the potential evapotranspiration and the annual precipitation remain constant. An average flow of 187 millions m3/year for annual average water depth of 1094 mm is obtained at Lanta rain station, which covers an area of 1664.47 km2, while this flow enabled an average flow of 327.5 millons m3/year to be obtained at the virtual station of our study area of 2908.15 km2. The flow rates corresponding to the return periods of 10, 25 and 50 years vary from 5.51 to 12.67 m3/s at the outlet of the virtual station;while those at the outlet of Lanta station vary from 3.6 to 6.6 m3/s. However, the simulated water quantiles cannot be fully mobilized;because of the uses, they undergo upstream and downstream. Thus, Gbédji-Kotovi locality requires the implementation of an integrated water resource management strategy that includes the construction of dikes and dams.

Accessibility Index of Aquatic Environments as an Indicator of Surface Water Vulnerability in Urban Areas:Case of the Okpara Basin(Benin)

Physiographic differences and conditions of use of water resources in anthropogenic basins explain the variability of risk to surface water. Based on the multi-criteria analysis of Saaty, the present work proposes an assessment of the vulnerability of surface water through a three-factor accessibility index: the slope, the subdivision rate and the drainage density of the basin. It is observed that the topographic (slope) and urbanistic (subdivision) conditions are the most important (weighting of 59%, 34%) in front of the hydrographic condition (drainage 6%) with an overall consistency of 2%. Thus, in the Okpara basin in the city of Parakou, the analysis of the vulnerability of surface waters by the accessibility index highlights two groups. The Ganré and Kokouro basins with about 30% of their areas in the low and moderate classes and the Wonka and Dama basins in the very strong class at more than 50% of their areas.

Seasonal Variation of Nutrient Pollution and Suspended Solids in the Drainage Network of Okpara Basin in Parakou(North-East of Benin)

This work presents mainly, the seasonal variation of pollution by nutrients and suspended solids thresholds between the old urban core and the peripheral areas of the city of Parakou on the Okpara basin. The city of Parakou has been experiencing strong demographic and socio-economic growth for about two decades. A total of sixty wastewater samples from twelve sampling sites were collected in 2016 according to the AFNOR standards, between the months of March and April in the dry season, then August, September and October in the rainy season. The descriptive statistic of data (minima-maxima) indicates variations of the parameters as follows: The temperature varies between 27.05 and 30.82, the water is a highly variable pH in the dry season (5.84 < pH < 9.14;mean = 7.17) and wet (6.28 < pH < 9.38;mean = 7.45). The reduction potential is lower in rainy season (-89.50 5 respectively reach the highest ratio (55 mg/L O2 and 232.08 mg/LO2) in the dry season than in the wet season (12.00 mg/L O2 and 202.40 mg/L O2). Nitrates have reached a maximum of 12.60 mg/L in the rainy season against 5.40 mg/L in the dry season. For nitrite, yielded 3.34 mg/L against 0.45 mg/L for conversely, phosphates are at 6.45 mg/L in the dry season against 2.32 mg/L in the rainy season. The mean concentrations of suspended solids are between 40 mg/L in the rainy season and 0.52 mg/L in the dry season. From the physico-chemical characterization and the chi-square independent test, this work shows mainly two results: On the one hand, apart from phosphates, concentrations of nitrates, nitrites and suspended solids on the Okpara basin in Parakou, are higher in the rainy season than in dry season. This can be explained by the variability of soil leaching and thus shows a relative link between the quality of surface water and the hydrogeomorphic basin conditions shown by the independence test (0.456 < CC < 0.856). In addition, pollutant concentrations vary according to a decreasing gradient between the former urban core, the periphery zone and the exit of the peripheral zone.