daniel chigunwe
THE persistent rains falling for most of this month to the delight of farmers are also increasing dangers for the unwary, with at least 21 people reported drowned in mineshafts, flooded rivers and other traps.
The dangers of fast moving flows of water are repeated every year, and some people do not listen or refuse to accept that the flows in their nearest river, or across the bridge they normally use, could possibly be dangerous.
But people should apply that textbook knowledge they acquire in school as they grow up and they will quickly see that the less obvious aspects of river flow are the most dangerous, which should fit in with their own experience.
The energy of a flowing river, and so the force it exerts on an object like a human being walking across or a vehicle being driven through it is proportional to the mass of the water flowing, basically the depth of the water, but to the square of the speed of the flow. So a river flowing twice as fast has four times the energy, one flowing three times as fast, nine times the energy and one four times as fast, 16 times the energy.
This is why some people are fooled when they see a river is only twice as deep as it was last week, when it was a slow-flowing gentle stream and is now a raging torrent.
Despite being only twice as deep it might well hit you with more than 20 times the force and sweep you or your car away. So the danger is far more than just the modest danger of deeper water.
This is why everybody concerned about safety, from the police onwards, continually warn people not to cross flooded rivers and flooded bridges, no matter how benign they might look. They need to wait.
Low level bridges opened up in Zimbabwe as the first proper roads, the old strip roads, were driven across the country and people who had spent half a rainy season unable to cross a ford now revelled in having to wait just a few days before the bridge was usable in even the heaviest rainy season. Often now, with these bridges largely on the smaller rivers, drivers only have to wait a few hours or a day at the most before it is safe.
The problems for pedestrians are more numerous, it often being a walk of some length or several hours to get to the nearest bridge.
For some odd reason there are not many foot bridges in Zimbabwe, despite the problems of rivers and streams rising in flood for a few months each year. Yet an adequate footbridge is not very expensive and can easily be built from wood or a small quantity of metal.
We would think that standard designs could easily be drawn up and distributed through rural district councils to many communities, and even some of our cities that have a reasonable summer river running through them would benefit.
This is the sort of practical engineering that should be publicised.
Often local materials can be used and local labour, so the cost of a footbridge might be very low, just some hardware items or perhaps the hire of a tractor for a few hours to move tree trunks.
Many people take risks when crossing rivers because they do not want to divert, and in countries where it rains most months of the year these small bridges become ubiquitous over generations since crossing even the smallest rivers normally needs a bridge.
It is not just rural areas.
The Mukuvisi River in Harare becomes dangerous over part of the rainy season after some decent rains have fallen, and a city council on the ball would have found a suitable site for a foot and cycle bridge every half kilometre or so, instead of forcing pedestrians to take their lives in their hands or walk long distances to the half a dozen or so road bridges.
Artisanal miners take far too many risks at the best of times, but in the rainy season these risks escalate alarmingly and when storm water diverts down a mine shaft or into a mining tunnel then a whole lot of extra dangers emerge, from shaft walls being eroded away to the sheer force of water sweeping miners off their feet and drowning them.
Major established mines are aware of the dangers and take a great deal of care to properly collect and drain their storm water, making sure it is not a menace and a danger. But on many artisanal mines no one has even thought of that work for many years, so even if there were adequate drains at some stage these are probably blocked, eroded or simply non-functioning. Once again people die.
Property is often severely damaged because people have not thought of storm water drains when building a house or some other structure, and we have even seen that in Borrowdale Brook in the poshest Harare suburb, or have allowed drains to become blocked. Sometimes houses are just built in the wrong place, and that we have also seen.
What looks like a good building site between May and September might be quite dangerous after heavy rains near by, or even for the whole of a reasonable rainy season and people should be willing to look harder at the site, and preferably during a rainy season so they can see the dangers.
Even those who should be able to work out the drainage often forget that drains can block quite quickly and should make sure their drains can handle far higher loads than predicted, with big margins of safety.
We need to see every rainy season as the blessing it is, and that means we need to be able to deal with rising streams and rivers without much trouble since these are not new and unknown events but come with the rains.
