The Impact of Mega-floods in Mozambique
by
Achimo Mussa
Department of Geology, Faculty of Sciences, Universidade Eduardo Mondlane, C. Postal 257, Maputo, Mozambique
Coauthors: Fatima Mamade, Direcçâo Nacional de Geologia, Ministérios dos Recursos Minerais, Maputo, Mozambique; Joao Alberto Mugabe, Department of Geology, Faculty of Sciences, Universidade Eduardo Mondlane, C. Postal 257, Maputo, Mozambique; Fortunato Manuel Cuamba, Department of Geology, Faculty of Sciences, Universidade Eduardo Mondlane, C. Postal 257, Maputo, Mozambique; Sylvi Haldorsen, Department of Plant and Environmental Sciences, Agruculture University, Norway

Floods are the most common type of natural disaster in Mozambique due to its climate irregularity and unique drainage. The climate is predominantly tropical with two seasons: the wet and dry. Cyclones occasionally hit the country during the rain season exarbating the rainfall amounts, causing often widespread flood hazards. The catchments areas of the main Mozambican river basins extend over into the neighbouring southern African countries and these find their way to Indian Ocean through Mozambique. In early 2000, as it was world-wide broadcasted, the coastal and lowland of southern Mozambique experienced a period of catastrophic floods of the last 50 years, due to the heavy rains, Eline cyclone and high water flow from the upper catchments. The floods claimed more than 700 lives mainly along the Limpopo River, more than 250000 people were displaced from their homes, and economic infrastructure, such as roads, railways and agriculture land were lost. The total coast, flood damage and relief works were equivalent of about 25 % Mozambique's GPD. Floods are integral part of hydrologic cycle and they are recurrent events, therefore, they will strike over and over again. To estimate the frequency of these floods is very difficult due to limited time period covered by instrumental meteorological data, and uncertainties from sampling floods periods. One possibility to expand the record of past catastrophic floods is the analysis of the sediment record that has the potential to archive such event. Mozambique hosted the ICSU: Project Dark Nature workshop on the impact of mega-floods-how to identify mega-floods in palaeorecords in November 2004. The meeting focused in particular on the frequency and impact of recent and sub-recent mega-floods and flood action programmes, including field trip to 2000 flood plains of the Limpopo and Incomati flood plains, and the areas destroyed by fluvial erosion in Maputo, as well as the study of a sediment core from the Incomati flood plain. The coring site was selected due to the fact that Incomati River floodplain is inundated periodically by the overbank flow, and store sediments which are washed from the slopes of the red inland sand dunes. The retrieved core is predominantly grey to very dark grey in colour with organic matter (root leaves) at the surface, followed by sticky clay with brown mottling spots and buried reed fragments. The buried reeds were fresh, and were found pending to certain angle. The sediment pattern in the lowermost part of the core is predominantly sticky clay with a layer of organic matter at deep of 140-145 cm. The organic dark layers showed fire disturbance, and are interpreted as buried top soil. The pending reeds were forced by overtopping flow into the floodplain. The discussions in the field, as well as the study of the sediment core lead to an understanding of what kind of sediment to look for, and where to look for sediments.

Date received: July 15, 2005

Copyright © 2005 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caqy-37.