To connect or not to connect?: floods, fisheries and livelihoods in the Lower Rufiji floodplain lakes, Tanzania

For seven years, village-based recorders monitored fish catches and water levels in seven floodplainassociated lakes of the Lower Rufiji, Tanzania. The lakes differ in the number of days and volume of inflows from the river, and thus provide a natural experiment to explore the links between catch composition, income per hour of fishing (IPHF) and hydrological connectivity, and to analyse the response of the users. The fishers adapt their fishing mode and equipment to achieve a rather constant IPHF of between 0.2 and 0.8 US$/fisher/hour. In situations of low connectivity, during a series of drought years, the less well-connected lakes lost many species and became a virtual monoculture of Oreochromis urolepis. Only in one extreme case was average fish size significantly reduced, indicating a high fishing pressure. Catch was therefore highly resilient to shifts toward illegal, non-selective and active fishing techniques. Fish diversity and lake productivity were quickly re-established when the larger lakes reconnected. The potential impacts of changes in the flood hydrograph (through dams, increased abstraction or climate/land-use changes) are assessed, and management options discussed

Geomorphic classification of rivers and streams

deuxième éditionInternational audienceThis chapter discusses general philosophies of classifications in fluvial geomorphology, and reviews examples of geomorphic classification systems. It explores uses and limitations of classifications as a tool in fluvial geomorphology and river management. Buffington and Montgomery emphasize the distinction between descriptive and process‐based classifications, noting that descriptive classifications can be quantitative and process‐based classifications can be qualitative. Distinctions between mountain torrents and lowland rivers are perhaps the oldest form of river classification. A wide range of geomorphic river classification schemes have been proposed since the late 19th century, reflecting the diversity of environmental settings, the variety of potential approaches to ordering complex natural systems, the intellectual framework of the field and the diverse purposes for which the systems were developed. Classification can focus on spatial features such as river patterns, floodplains, in‐channel features, which can be separated according to a set of parameter