How does the Kasai River affect the Congo River system?

The Kasai River is the primary southern tributary of the Congo River, playing a significant role in the hydrology of the Congo River basin.1

As the longest river in the southern portion of the system, the Kasai empties into the Congo at Kwamouth, located approximately 125 miles above Malebo Pool. Its contribution to the main stream is substantial, as it delivers a volume of water approaching one-fifth of the Congo River's total volume. Before reaching this confluence, the Kasai undergoes various changes in character, transitioning from a series of rapids and waterfalls in its upper reaches to a broader, deeper, and navigable waterway in its lower sections.1

The river system is further supported by its own tributaries, such as the Sankuru River, which feeds into the Kasai, and the Fimi-Lukenie, which brings water from Lake Mai-Ndombe into the Kasai shortly before it joins the Congo.12