Risk factors associated with floods, the WRC warns
Recent widespread flooding may increase the risk for outbreaks associated with the contamination of drinking water sources, warns the Water Research Commission (WRC). However, the risk of outbreaks can be minimized if the risk is well recognized and disaster-response addresses the provision of clean water as a priority.
Mr Jay Bhagwan, Director at the WRC, says “There is an increased risk of infection with water-borne diseases contracted through direct contact with polluted waters, such as wound infections, dermatitis, conjunctivitis, and ear, nose and throat infections”.
Floods may indirectly lead to an increase in vector-borne diseases through the expansion in the number and range of vector habitats. Standing water resulting from heavy rainfall or overflow of rivers can act as breeding sites for mosquitoes, and therefore enhance the potential for exposure of the disaster-affected population and emergency workers to infections.
Bhagwan further says “Flooding may initially flush out mosquito breeding, but it comes back when the waters recede. The lag time is usually around 6-8 weeks before the onset of a malaria epidemic”.
“Generally, floods contribute to the lessening or the dilution of pollutants provided there are no sewage and chemical spills. A bigger concern is the increase in the sediments, plants, trees, litter and other objects” Bhagwan adds.
Commenting on concerns regarding acid mine-water generation in the Central Witwatersrand, Dr Jo Burgess, WRC Research Manager, says “The rainfall we are having will enable the water table underground to rise more rapidly than in the dry season, so it will affect the daily rate of rise. However, the average rates of rise that are worked out per annum are not affected, as the average takes dry and wet season rates into account. The heavy rain will make the action on Acid Mine Drainage even more urgent, but it is never too late to do the right thing.”
According to Dr Backeberg, Director for Water Utilisation in Agriculture at the WRC, the obvious impact of the floods is damage to crops, irrigation equipment and farming infrastructure. This will place an additional financial burden on farmers over the short- to long-term.
WRC guidelines have been developed for flood damage assessments and cost functions in flood-prone areas of the Vaal and Orange Rivers. A WRC report entitled “Flood damage management aids for integrated sustainable development planning in South Africa”, by Prof MF Viljoen, Department of Agricultural Economics of the University of the Free State in Bloemfontein, as lead author, provides much-needed information about how to react during floods.
Apart from the abovementioned costs of flood damage, assessments of periodic floods in the Vaal River have also shown benefits. These are mainly the flushing out of accumulated salt loads, leading to an improvement of water quality, in terms of salt content.
This finding has been published in WRC Report No. 740/1/00, “The effect of water quality on irrigation farming along the lower Vaal River: The influence on soils and crops”, with Prof CC du Preez of the Department of Soil Science of the University of the Free State as lead author.
According to Dr Backeberg the natural cycle of floods therefore periodically improves the quality of water from an agricultural perspective. In the case of irrigation farming along the Orange River the opposite tends to occur: During high river flow periods salt loads in the soil accumulate, which are released with irrigation during low flow periods. The reason is that water tables in soils riparian to the river rise while drainage of water from higher-lying soils continues.
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