River navigation is a crucial part of the economy for countries that share the Congo Basin. River transport falls short of the role it could play in the region's development, and has declined in recent decades. River navigation charts are specialist maps designed to assist in the safe navigation of river traffic. In the DRC, navigation charts for the 1,734 km of river between Kinshasa and Kisangani are issued by RVF (Régie des Voies Fluviales), the state navigation authority. These charts originated in the early 1900s and have not been updated since 1931. As part of the Congo River users Hydraulics and Morphology (CRuHM) project, we use these old charts to study geomorphological change by comparing them with modern remote sensing images, which provides a unique opportunity to compare snapshots of the river separated by 85 years. This paper reports on the results of our initial analysis on a representative 120 km study reach, which we have used to test feasibility and develop the methodology. Our analysis shows that the old charts are impressively accurate, and provide a valuable and usable snapshot of the river planform. Planform change analysis shows that, while most banks and major vegetated islands are relatively stable, there has been a significant deposition in the river of 14 ± 2.9% (~100 ± 2.9 km 2 ), compared to the original planform area. Deposition is not spatially uniform and is exponentially correlated with effective river width. Wide shallow reaches, already difficult to navigate, show higher deposition (up to 31 ± 3.2% of original planform area). These changes imply a reduction in the river flow or an increase in sediment supply, and there is evidence that both may be the case. By quantifying planform change over the last century, this research will provide a useful baseline to monitor future changes in the Congo River.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)