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The Impact of Mega-floods - how to identify mega-floods in palaeorecords
Casa Lisa, Bobole, Mozambique, November 1-5, 2004


This workshop, held under the auspices of three international projects: ICSU, Dark Nature; INQUA, Catastrophes and Recoveries in the Holocene; and IGCP 490, The Role of Holocene Environmental Catastrophes in Human History, with an input from the IUGS Geoindicators Initiative, was attended by 25 delegates from 9 countries, 17 from Mozambique and 1 each from Canada, India, Kenya, Norway, Poland, Uganda, UK and the USA.

The programme consisted of 2 days of formal presentations followed by 2 days of field excursions, rounded off by a final day of discussions.

Presentations

The presentations included invited keynote lectures and reports of recent or .in progress. work from delegates:

Haldorsen, Sylvi (keynote): Dark Nature: environmental catastrophes and recoveries in the Holocene
Haldorsen, Sylvi; Jakobsen, Lief; Jrgensen, Per & Stromme, Gaute (keynote): Geochemical flux from a mountain catchment in southeastern Norway during the 200 year (?) flood in 1995
Teller, Jim (keynote): Catastrophic floods and abrupt global change: how glacial Lake Agassiz changed the world
Teller, Jim (keynote): Great floods of the Red River, Manitoba, Canada: the 1997 flood
Teller, Jim (keynote): Great floods of the Red River, Manitoba, Canada: geoscientific insight in to past floods
Ridgway, John (keynote): An introduction to geoindicators and their relevance to flood studies
Ridgway, John (keynote): Sediment geochemistry in the interpretation of floodplain sediments
Graniczny, Marek (keynote): monitoring the catastrophic flood in Central Europe, in the summer of 1997, by means of modern cartographic techniques
Graniczny, Marek: Applications of SAR remote sensing in landslide and subsidence studies
Vasconcelos, Lopo: Floods in Mozambique, January . March 2000
Abuodha, Pamela and Omenge, John: Modern mega-flooding in Kenya, especially Budalangi Division and Tana River Districts.
Bamutaze, Yazidhi: An analysis of the impact of floods on the urban poor in Kampala
Kessarkar, Pratima, M.: Record of abrupt climate change during Early Holocene on the western continental margin of India
Famba, Sebasitao I.: The 2000 flood in the lower Limpopo River basin
Tembe, Mondlane: Seminario sobre Cheias (in Portugese)

Despite the talks being held chiefly in English instead of the Portugese commonly spoken in Mozambique, all of the presentations provoked a good deal of discussion with all the delegates contributing at one stage or another.

Field Excursions

The first day excursion took the participants across some the areas most affected by the flooding of the Limpopo River in 2000 to the town of Xai-Xai, an important regional centre. Xai-Xai was flooded up to a level of over 3 m, railway lines were disrupted and the bridge across the Limpopo at Xai-Xai partially swept away. Most of the damage has now been repaired, but there is probably little that can be done to protect the area from future floods of the same magnitude as in 2000 apart from moving houses and business to higher ground on the left bank of the Limpopo. People displaced by the flood are already moving back to the sites of their pre-flood homes.

On the second excusion, the morning was spent on the Incomati floodplain looking at coring and sampling techniques, whilst in the afternoon sites of flood damage in Maputo were visited. In Maputo damage was largely limited to rapid erosion during the heavy rains with whole streets being destroyed and houses further downstream buried by flood-borne sediment. Much of this damage has been deemed irreparable and the gullying in the streets has been protected from further erosion by the use of gabions and geotextiles. Many people from the flood devasted areas near Maputo were rehoused in a very large new development on the outskirts of Maputo. The housing was provided free of charge, but as in the Xia-Xai district people are moving back to their traditional homes, selling the newly built houses to raise capital.

Final Discussion

The final day was spent in discussions of how to interpret the sediment cores collected on the previous day and in a general discussion of the problems associated with mega-floods, their prediction and consequences.

The workshop was well organised and the venue well chosen for the size of the meeting. Discussion was lively throughout, both in the field and in the seminar room and touched on many aspects of geoindicators, including the difficult question of how to persuade people to take note of the evidence before them and act accordingly.

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