TMA statement is a wake up call that we should look back

25Oct 2018
Editor
Dar es Salaam
The Guardian
TMA statement is a wake up call that we should look back

THE Tanzania Meteorological Agency (TMA) has announced that during the rainfall season in next month, this year several regions will experience above normal rains.

It will be recalled that in 2015  we witnessed flash floods killing at least 38 people in Shinyanga Region after strong winds and hail battered villages. 

We had also witnessed in 2011 at least 23 people  were killed and thousands displaced in the worst flooding to hit Tanzania in 50 years.

The statement from the agency is a wake up call that we should look back at what are the causes of flood and what to do in case of floods. Floods generally occur as a result of bad weather for example storms, cyclones, tornadoes or thunderstorms, heavy or persistent rain or the sudden discharge of water.

These events lead to a rise in the water level of major riverbeds or to an accumulation of flow water, to the resurgence of underground rivers or to thaws in low-lying areas adjoining stream banks or river estuaries. In mountainous areas, landslides, earthquakes, and avalanches can cause the overflowing or rupture of hydraulic dams or cause unstable blockages at certain points on rivers, and thus threaten or destroy people and the infrastructure located in the lower parts of valleys.

Bursting or overflowing of hydraulic dams, as well as seismic/tidal waves are special cases which require specific protective measures.

Damage caused by floods can vary greatly according to the nature of the phenomenon at the origin of the flood. They can affect whole regions or certain limited sectors. Moreover, their impact will vary according to whether the event is sudden and violent or a steady but relatively slow rise of flood waters which will inundate a vast area, especially plains situated near or at the mouth of rivers.

The danger is obviously highest in mountainous areas or steep valleys where depressions will be totally leveled or momentarily drowned then covered in debris carried by the flood water (rocks, sand, gravel); this will result in the destruction or burial of all or some of the dwellings, of the economic infrastructure and of vital installations (energy grids, communications and drinking water). This also happens when torrential rainstorms occur in arid regions and deserts where the water cannot penetrate the impermeable soil and depending on the topography, runs off as surface water destroying homes and settlements over a wide area.

All types of floods have grave consequences, mainly because of their secondary effects. Localised flood, or one involving a small rise in water level can lead to large-scale damage, to the interruption or destruction of communication routes (road, rail, etc.) or the loss of infrastructure and damage to the environment (economy, supplies, crops).

 

 

As opposed to other natural phenomenon (landslides) or the causes of certain floods (tidal waves, bad weather), the risk of flood from rising water levels is predictable, although it is difficult to know when it will occur. It is therefore possible to determine the areas at risk.