American Journal of Water Resources

Multiple Urban Wastewater Discharge Pathways as Drivers of Water Quality Degradation in the Cotonou Lagoon, Benin

2026-01-06

This study aimed to evaluate the physicochemical pollution levels in the Cotonou Lagoon, focusing on the dry season, when it receives raw wastewater through various stormwater sewers and drains in the city. Six stations were identified and monthly sampled on the lagoon for this purpose, taking into account the discharge point of the sewers. Temperature, pH, electrical conductivity, dissolved oxygen content, and water transparency of the lagoon waters were measured in situ. Turbidity, suspended solids, and nutrient concentrations, including ammonium, nitrites, nitrates, orthophosphates, and sulfates, of the water samples, were determined using molecular spectrophotometry. Through the assessed physico-chemical, the lagoon waters were found to be nutrient-rich, particularly with ammonium and orthophosphates (up to 10 mg L^-1 and 0.5 mg L^-1, respectively), detected at levels toxic to aquatic life and indicating early risk of eutrophication, despite the high dissolved oxygen levels recorded. The organic pollution index calculated (varying from 2.67 to 4.33), revealed a heterogenous a moderate organic pollution in most of the lagoon sectors, but a strong and a weak pollution level noticed in other sectors. An effective management of wastewater should be undertaken to significantly reduce the pollution of the lagoon, thereby preventing ecological disasters that may result from eutrophication.

Assessing the Impacts of Historical and Future Extreme Precipitations on Reservoir Sedimentation Dynamics: Insights from the Niger River Basin in Northern Benin

Djigbo Félicien BADOU, Audrey Merveille ADANGO, Chaim Vivien DOTO — 2026-01-27

This study assesses the relationship between extreme precipitations and reservoir sedimentation dynamics in the Beninese portion of the Niger River Basin. Historical daily rainfall data (1980-2020) and future climate projections (2021-2049) from the WRF regional climate model under the RCP 4.5 scenario were analyzed to assess trends in extreme rainfall using the Modified Mann-Kendall test and the Theil-Sen slope estimator. The impacts of changing heavy rainfall patterns on runoff and sediment yield were simulated using the Soil and Water Assessment Tool (SWAT), applied to the Sota catchment. The findings reveal mixed heavy rainfall trends across the study area, with a significant decrease projected under the RCP 4.5 scenario for several stations. The SWAT model showed satisfactory performance for streamflow simulation (NSE = 0.70 during calibration; 0.66 during validation). The historical mean sediment yield was estimated at 18.6 ton ha⁻¹yr⁻¹, exceeding commonly accepted sustainability thresholds. Spatial analysis revealed persistent sedimentation hotspots in the southwestern part of the catchment. Future simulations indicate an increase in runoff but a decline in sediment yield to 12.8 ton ha⁻¹ yr⁻¹ by 2049. This counterintuitive trend is attributed to a projected shift toward less erosive rainfall regimes coupled with temperature-driven changes in soil surface processes. While providing valuable insights into climate-sediment interactions, these projections are subject to uncertainties from the lack of measured sediment data, the use of a single climate scenario, and the assumption of static land use. Overall, the study highlights the sensitivity of reservoir sedimentation to changes in extreme rainfall and provides a scientific basis for improving sediment management strategies in small dams under future climate change.

Effects of Non-revenue Water on the Operational Efficiency of Water Utility in the Republic of Benin: A Case Study of SONEB in Parakou

Djigbo Félicien BADOU, Okombawa Adolphe SODJAHIN, Agnidé Emmanuel Lawin — 2026-02-03

Non-revenue water (NRW) presents a critical challenge to water security in Sub-Saharan Africa, directly undermining the financial viability and operational efficiency of public utilities. However, comprehensive studies quantifying its multifaceted impacts and root causes within specific utility contexts remain limited. This study addresses this gap through a mixed-methods assessment of the Société Nationale des Eaux du Bénin (SONEB) in Parakou, Benin. Analysis of utility records (2012-2024), household surveys (n=204), and semi-structured staff interviews (n=17) quantified NRW and evaluated its impacts across technical, commercial, financial, institutional, and customer-oriented performance dimensions. Results identify an NRW rate of 39% in 2024, significantly exceeding best-practice thresholds. While 96.6% of customers reported a reliable water supply, a critical service paradox exists: satisfaction is severely undermined by billing inefficiencies, with 54.1% experiencing delayed bills and 68.1% perceiving tariffs as excessive. Financially, the utility is crippled by a revenue collection efficiency averaging only 50.7%. The drivers are systemic, encompassing aging infrastructure, frequent leaks, absence of network sectorization, illegal connections, metering inaccuracies, and the critical institutional gap created by the dissolution of the dedicated NRW management unit. The study concludes by proposing evidence-based recommendations for SONEB, which are scalable to comparable utilities in the region to transition towards financial sustainability and improved service delivery.

Assessment of Water Quality from the Mani River, the Water Source of the Yalenzou Water Supply System in N'Zérékoré Prefecture, Guinea

2026-02-04

High concentrations of chemical elements and bacteria (enteropathogenic bacteria) in water can cause waterborne diseases that are potentially dangerous to humans without prior effective treatment. The aim of this study was to evaluate the physico-chemical and bacteriological quality of the water from the Mani River and the Yalenzou water supply system in order to establish the occasional presence of contaminants. Water was sampled from March to May 2025 (towards the end of the dry season and the beginning of the rainy season), which corresponds to the increase in surface water. Results showed significant differences (P<0.05) in conductivity, total dissolved solids (TDS), salinity and biological oxygen demand (BOD5) among the two sampling sites. Mani River recorded the highest mean value of BOD5 (191.33±1.52 mg/L versus 189±3.00 mg/L). Fecal coliforms in the Mani River and raw water of Yalenzou water supply system were 332.33±17.61 and 165±5.00 CFU/100mL respectively. These values were far above the minimum standards set by the World Health Organization (3 coliforms/100 mL of water). Iron, turbidity, nitrite, temperature and salinity characterized the raw water from the water supply system, whereas conductivity, turbidity, salinity, BOD5, fecal and total coliforms characterized water from the Mani River. This study highlights the level of contamination of the Mani River and the questionable quality of water consume in households of the forest region, Guinea.