Tuesday, April 30, 2013

Victoria Falls (Chapter 1: The Facts)

Victoria Falls and the Zambezi River Watershed

Victoria Falls is the largest waterfall in Africa and is one of the seven natural wonders of the world.  At more than 300 feet high (twice the height of Niagara Falls) and more than a mile wide, the Falls dominate the landscape of the surrounding plateau.

<--         Zimbabwe             |             Zambia      -->

Victoria Falls is fed by the Zambezi River, which starts in northern Zambia and runs southward to the border of Zimbabwe.  From its source, the river flows for about one thousand kilometers, gaining volume and surging towards the south-eastern wing of the country.  When it arrives at the border of Zambia and Zimbabwe, the river cuts into the level countryside and plummets into a wide chasm, smashing into a series of criss-crossed gorges before making a break for Mozambique.  The resulting waterfall, of course, is Victoria Falls.  In the Tonga language, it is known as Mosi-oa-Tunya—The Smoke that Thunders.

On average, the Zambezi River flows over Victoria Falls at a rate of over 1,000 cubic meters per second.  That’s 31,536,000,000 cubic meters of output in the course of one year, or 31 square kilometers of water (try, if you will, to imagine a square kilometer of water). 

The character of the Falls is defined by the season in which they are viewed.  The Falls are at their peak volume at the end of the rainy season, from February until April.  The volume of water then decreases steadily from May until November, revealing the stone riverbed and the wall behind the falls.  When the rains return in December, the water level swells again.  Since the falls are located some thousand kilometers from the source of the river, there is some lag between the bulk of the rains and the high-water mark.  Usually, the crest of the rain pours over in March or April of every year.  At this time of great output, the falls are thundering at over 3,000 cubic meters of water per second. 


But while that is a great figure, it doesn’t really capture the essence of this massive wall of water.  How can you imagine the rush and sound and weight of Victoria Falls?  I could try to describe it with words (Legendary!  Awe-Inspiring!  Monstrous!), but I think that I would do better with illustrations.  Let’s start with a few pictures.

First, we want to imagine 3,000 cubic meters of water per second. 

Well, what is a cubic meter of water?  Oh, here it is:

One cubic meter of water (or 1,000 kilograms)

So 3,000 of these blocks spill over the falls in one second. 

That’s a lot of water.  But how can we get a better visual of the output of Victoria Falls?   Let’s now try to imagine the capacity of Victoria Falls in terms of fully-loaded dump trucks.  If we assume that the average dump truck has a capacity of about 20 cubic meters (which is does), then we are imagining something like this:

20 metric tons of water

Then, if we divide the flow of water (3,000 meters per second) by the capacity of a dump truck (20 cubic meters), we can now take a second leap and visualize the rate of flow as the contents of 150 dump trucks / per second:


And if that imagery doesn't do the trick, you can simply pictures one of these tumbling over the falls:

An Olympic-sized swimming pool

At the height of the rainy-season flow, Victoria Falls releases the equivalent of 72 Olympic-sized swimming  pools in every passing minute.  That is just over one swimming pool per second.  

One every second

So how long would it take for Victoria Falls to fill the largest swimming pool in the world?

San Alfonso del Mar seawater pool, Algarrobo, Chile

The largest swimming pool in the world holds about 250,000 cubic meters of water.  If Victoria Falls is flowing at a rate of 3,000 cubic meters per second, it would take less than a minute and a half (83 seconds) to fill this entire pool. 

It’s no wonder that, at the height of the rainy season, even elephants and hippos get swept over the falls.

Is your interest piqued?  Read on!   Chapter 2: The Falls

1 comment:

  1. Sounds like you guys picked the right time of year to go!