River transport, with more than 17,000 km of navigable channels in the Congo, is a crucial part of the economy for many of the countries sharing the river basin and allows the transport of many goods (timber, charcoal, minerals etc.) and enables access to many areas where roads do not exist. However, river transport falls short of the role it could play in development of the region and has actually declined since the Congo basin countries became independent in the 1960s. This is in part due to years of civil unrest, aging equipment, a lack of infrastructure maintenance, and the poor support and operation of public waterway agencies. River navigation maps are a specialist form of map specifically designed to allow safe navigation of river traffic such as for barges carrying cargo. Boat captains use them as they travel along the river to follow the advised navigation route and avoid hazards such as submerged rocks and shallow channels. The navigation maps for the 1,700 km of river between Kinshasa and Kisangani are issued by RVF (Régie de Voie Fluvial), the state river navigation authority, and are therefore used by all boat captains. These maps originate from the early 1900s and have not been updated since colonial times. As part of the CRuHM project we are exploring the possibility of updating these maps using modern remote sensing methods, together with RVFs experienced input. As part of the update process, RVF have provided us with detailed digital scans of the original navigation maps and we are geo-referencing these to modern geospatial projections, in line with the remote sensing data. This provides us with a unique opportunity to compare snapshots of the river system geomorphology separated by nearly 100 years. We will show the current state of the project and some of the river secrets we have discovered so far.

A reach-scale high resolution digital elevation model (DEM) of the Congo’s main stem bathymetry is presented. The Bathymetry DEM covers a multichannel reach of the main stem situated in the Cuvette Centrale, and is developed from a series of in-situ measurements of bathymetry, water surface elevation and discharge that were obtained during a CRuHM fieldtrip in summer 2017. The main stem’s complex network of channel threads requires a bathymetry modelling methodology that is capable of intelligently interpolating the raw bathymetry measurements. The methodology must also estimate a significant portion of the bathymetry, since it is not feasible to measure the entire extent of the massive and complex channel network that this study reach is comprised of. This methodology is also presented. Remote sensing from satellites is increasingly being used to resolve the scarcity of contemporary hydrological and hydrographic measurements in the Congo Basin. However, river channel bathymetry information cannot yet be reliably obtained from remote sensing methods. This is problematic since river channel representation has been shown to be an essential input into a hydraulic model. Analyses of satellite observations suggest that, relative to other global rivers, in-channel flows on the Congo’s main stem represent a relatively large proportion of total flows through the river-floodplain system. This implies the Congo’s in-channel bathymetry may play a relatively large role in controlling Congo main stem hydrodynamics. When used in a hydraulic model, the bathymetry DEM presented here will provide new information on Congo in-channel hydraulics and the extent to which bathymetry controls the Congo’s middle reach hydrodynamics. It will help better quantify the capacity of the Congo main stem channels through the Cuvette Centrale, and thus provide further insights into the extent to which the main stem channel floods in this region. It is also intended to be used for testing simplified methods of Congo bathymetry representation that are necessary for larger scale hydraulic models.