Congo Basin Hydrology, Climate, and Biogeochemistry. Группа авторов

Photo 1.1 View of the Congo River and research boat in the Cuvette Centrale.

      Credit: CRREBaC/CRuHM.

Photo 1.2 Several chapter authors have collected new measurements on Congo Basin rivers. Photo taken on Lomami River at Isangi, where the Lomami River joins the Congo River.

      Credit: CRREBaC/CRuHM.

Photo 1.3 International collaborations are welcome in the Congo. Photo taken at Kisangani where the research team is traveling downstream from Kisangani to Kinshasa, collecting river measurements over 1700 km of flow distance.

      Credit: CRREBaC/CRuHM.

This monograph is a foundation for new collaborations. The 106 people who have contributed to the chapters in this book are open to building new research ventures (Photo 1.3). We anticipate that many readers will have studied the Amazon Basin and other tropical watersheds. They will recognize the similarities between the world’s two largest rivers and their basins and, importantly, find that the differences are significant and will likely lead to new discoveries. For example, the Amazon wetlands along the mainstem Solimoes River are marked by numerous floodplain channels and by water depths approaching ten meters, whereas the Congo’s Cuvette Centrale has no similar channelization and thus appears to have diffuse, shallow flows of only about a meter in depth (e.g., Alsdorf et al., 2016). What do these differences imply about water and sediment exchange between the mainstem river and its wetland, or about the related biogeochemical processes that include some of the world’s largest peatlands (Dargie et al., 2017), or about the fluvial geomorphic history of these two large river complexes? This monograph will hopefully inspire each reader to hypothesize testable ideas that they will use to forge new collaborations and hence new discoveries.

This monograph is a foundation for resource management. The Congo River is the lifeblood of more than one hundred and twenty million people who live in the basin. The river and its tributaries are the main and sometimes only transportation corridor (Photos 1.4, 1.5, 1.6). Challenges to maintaining river traffic include knowing water depths given that these change from shifting bathymetric dunes and change from seasonal to climatic variations in rainfall. Moreover, specific rivers will experience changes in flow if engineering projects are implemented, such as ideas expressed to channel flow away from the Ubangui River to Lake Chad. Perhaps, too, small hydroelectric generators such as those of the Kibali gold mine on the Nzoro River or larger generators such as the Inga Dam (Photo 1.7) need to know the long‐term expected rainfall and hence capability to provide peak electricity demand. Chapters in this book provide science foundations toward addressing resource management throughout the Congo Basin.

1.2. OVERVIEW OF THE CONGO BASIN

At 3.7M km² in size and 41,000 m³/s in average discharge, the Congo River Basin is second only to the Amazon in watershed area and flow rate (Figure 1.1; Alsdorf et al., 2016; Laraque et al., 2013, 2020; Tshimanga & Hughes, 2014). Goudie (2006) has suggested that sometime in the past 30 Myr stream capture by a small coastal river permanently linked the Congo River to the Atlantic Ocean, resulting in plunge pools with depths greater than 100 m. For example, just above Matadi approximately 150 km from the river’s mouth, Stanley (1885) reported depths of ninety fathoms (i.e., 165 m). Oberg et al. (2009) verified plunge pool depths of about 100 m in the reach below Kinshasa with one pool at 220 m deep. Given the land surface elevations, some of these pools bottom out below sea level. At the other end of the mainstem, where the Congo River is known as the Lualaba River, a number of cataracts and narrows likely indicate a variable channel bathymetry controlled by geology and tectonics. In between, the middle reaches of the mainstem have shallows of only a few meters depth (see Alsdorf et al., 2016). In summary, the hydraulics of the Congo River are variable and bely simple characterizations, especially for a massive river.

Photo 1.4 Waterways are major transportation routes in the Congo. Photo is taken in the Cuvette Centrale.

      Credit: CRREBaC/CRuHM.

Photo 1.5 Rivers serve commerce at small scales such as this boat. See Photo 1.6 for larger scales of commerce.

      Credit: CRREBaC/CRuHM.

Photo 1.6 Rivers serve commerce at large scales such as this boat moving logs. See Photo 1.5 for smaller scales of commerce.

      Credit: CRREBaC/CRuHM.

Photo 1.7 The Inga Dam. The Congo River is in the background. The canal in the foreground feeds penstocks just downstream of the photo.

      Credit: CICOS.

Precipitation in the Congo ranges from an average of about 1900 mm/yr in the central basin to about 1100 mm/yr at its northern and southern boundaries (Bultot, 1971). Rainfall generally follows a south to north migration with the southern parts of the basin experiencing their annual maximum precipitation in December to March, whereas rainfall peaks in the northern basin areas in July to October. The central basin areas experience two precipitation maxima with a smaller peak in March to May and a greater peak in September to November. Traditionally, the driver of this seasonally migrating precipitation was assigned to the InterTropical Convergence Zone (ITCZ), suggesting that it enhanced local convection. Recently, however, meteorologists have recognized mesoscale convective systems bounded by migrating jets that are a more likely driver of the migrating rainfall (Nicholson, 2009).

      The seasonally varying rainfall produces a bimodal river discharge on the mainstem Congo (see Alsdorf et al., 2016, for details). Because it takes between two weeks and two months, depending on flow distance, for local flood waves to migrate downstream, the timing of the flood peaks occur later than the associated rainfall maximums. At Kinshasa‐Brazzaville,