Natural Hazards and Disasters: Severe floods in Mwanza, Tanzania

Torrential rainfall on Tuesday 2^nd December caused devastating floods in Mwanza, Tanzania. Although surface water flooding does occur due to intense rain in a space of a few hours, the main cause of floods in the city of Mwanza is river flooding.

Mirongo River runs through the city and joins Lake Victoria as shown on the maps. The river has a history of causing frequent devastating floods which have not only destroyed homes and infrastructure such as bridges but also caused numerous fatalities.

When Mirongo flooded in 2000, 30 people were killed and 20 homes were destroyed. In 2011 the floods resulted in the closure of Mwanza Airport for a few hours due to the runway being inundated with flood water. Flights were cancelled until the water cleared.

Although there has been no official confirmation of fatalities from authorities in the recent flood event, according to locals there have been a few fatalities. Homes have also been damaged and a vehicle was swept away. The floods also inundated bridges and roads.

Mwanza City Council is currently carrying out an assessment of the damage. According to reports authorities will try to mitigate the impacts of future floods. There are claims that the floods are caused by the local population who cause obstruction and blockage of the drainage system in the city. In response to this an awareness campaign is going to be carried out in order to educate the local population.

There is currently no flood warning system in place to alert the local population of possible flooding. Even though The Tanzania Meteorology Agency did forecast heavy rainfall in the month of December, no measures exist to analyse the rivers response to the heavy rainfall. Due to the flashy nature of the catchment, the river responds rapidly to a few hours of intense rainfall.

The river itself has been modified greatly in the past adding to the problem of flooding. Drainage systems in parts of Mwanza link to the river, transporting additional water which worsens the situation during heavy rainfall events. There is also no record of a risk assessment of the city, it would therefore be of benefit if a flood risk assessment was carried out in order to better analyse, map and evaluate the nature of the river and the population and infrastructure at risk.

The city would also benefit from a flood warning system which could alert the authorities and population of possible or ongoing flood event. The population of Mwanza has lived with floods for years, they therefore have the awareness of how severe a flood event can become in a matter of a few minutes or hours. A community based warning system could be a start to reducing the impacts of the floods and preventing fatalities.

The population at risk should also be educated with regards to flood preparation. Simple measures such as knowing how to respond before or during a flood event and creating emergency plans can be taken. Awareness campaigns should also communicate flood safety. During floods, people on foot and in vehicles have on numerous occasions attempted to cross inundated bridges over the river not realising or appreciating that only 6 inches (15cm) of water can sweep a person of their feet and only 2 feet (60cm) of water can move vehicles. (Having personally witnessed this in Mwanza, it does make you wonder why people take the risk to cross bridges with fast flowing flood water, especially when the same bridges have been destroyed on numerous occasions during past flood events!)

As the rainy season continues, further flooding may occur in Mwanza. It is therefore hoped that the population stay vigilant and out of harms way.

Location of Mwanza, Tanzania