Sediment Balance Estimation of the ‘Cuvette Centrale’ of the Congo River Basin Using the SWAT Hydrological Model

Pankyes Datok,Sylvain Ouillon,Guy Moukandi N’Kaya,José-Miguel Sanchez-Perez,Clément Fabre,Sabine Sauvage,Alain Laraque

doi:10.3390/w13101388

Abstract

In this study, the SWAT hydrological model was used to estimate the sediment yields in the principal drainage basins of the Congo River Basin. The model was run for the 2000–2012 period and calibrated using measured values obtained at the basins principal gauging station that controls 98% of the basin area. Sediment yield rates of 4.01, 5.91, 7.88 and 8.68 t km−2 yr−1 were estimated for the areas upstream of the Ubangi at Bangui, Sangha at Ouesso, Lualaba at Kisangani, and Kasai at Kuto-Moke, respectively—the first three of which supply the Cuvette Centrale. The loads contributed into the Cuvette Centrale by eight tributaries were estimated to be worth 0.04, 0.07, 0.09, 0.18, 0.94, 1.50, 1.60, and 26.98 × 106 t yr−1 from the Likouala Mossaka at Makoua, Likouala aux Herbes at Botouali, Kouyou at Linnegue, Alima at Tchikapika, Sangha at Ouesso, Ubangi at Mongoumba, Ruki at Bokuma and Congo at Mbandaka, respectively. The upper Congo supplies up to 85% of the fluxes in the Cuvette Centrale, with the Ubangi and the Ruki contributing approximately 5% each. The Cuvette Centrale acts like a big sink trapping up to 23 megatons of sediment produced upstream (75%) annually.

Highlights

The most important agent transporting sediment across the land is river transport, while relief and runoff are the most important factors determining the sediment load of rivers [1] (Hay, 1998)
The validation of the daily simulations highlighted that Soil and Water Assessment Tool (SWAT) can be calibrated at a monthly time step and validated at a daily time step
The differences in the evaluation criteria show the effect of the regionalization in the calibration as well as the level of complexity of each sub-basin

Summary

Introduction

The most important agent transporting sediment across the land is river transport, while relief and runoff are the most important factors determining the sediment load of rivers [1] (Hay, 1998). The suspended sediment load transported by a river or stream is a mixture of sediment derived from different areas in a catchment that comprise source types with different erosional processes depending on the time and place [2,3] (Walling, 2006; Haddadchi et al, 2013). Sediment fluxes and their variability are important and merit study because drastic changes in their amounts and patterns usually indicate additional human impacts on the basin [4,5] (NKounkou & Probst, 1987; Walling, 2009). The hydrodynamic characteristics of wetland ecosystems, including the water inputs, outputs, water flow, and seasonality, can influence organic deposition and material fluxes [7] (Gosselink & Turner, 1978). [8] Novitzki (1979) characterized wetlands with regard to water source and landform as surface or groundwater depressions or slopes, which are defined by whether or not they receive a greater amount

Objectives

Methods

Results

Discussion

Conclusion