Navigable rivers were the foundation of trade and political power in Europe and much of Asia for centuries so it has always rankled that African rivers, with the exception of a moderate distance down
the Nile, have not given the same access, especially in East and Southern Africa.
Even rivers like the Congo and the Niger, with long navigable stretches in their middle reaches, do not give easy access from the sea into the deep interior.
The Zambezi, the fourth-largest African river, is particularly bad as a channel of communication and easily the worst of the big four.
A large delta at its mouth, four major sets of rapids, and the Victoria Falls, made the middle and lower reaches impassable to anything larger than a canoe, and even that had to be carried past the rapids.
The upper Zambezi, with its huge flood-plain, even more rapids and another two sets of waterfalls, is again hardly a barge captain's dream.
So bad was navigation along the Zambezi that early traders into the interior from the Indian Ocean preferred pushing up the Pungwe and Save Rivers instead and almost the first act of the British colonialists was to lay railways from South Africa and Beira to make trade viable.
And to this day the Zambezi is more famous for the bridges that carry roads and railways across the river, than for any traffic on the river.
But the dream of a navigable seaway persists. It received a major boost in the early 1970s as the new Cabora Bassa Dam was built, finally flooding the Kebrabasa rapids that had marked the limit of navigation up to then.
Dreamers started sketching lock gates at the dam, or else looking at transhipment of cargo to boats on the new lake, which started filling in December 1974. There were even suggestions of a Zimbabwean port where an arm of the lake entered the country in the north-east.
Others noticed that the river was almost navigable from Lake Cabora Basa to Lake Kariba, and the dreamers dreamed. The Batoka Gorge hydro scheme could even flood the one serious sets of rapids, allowing navigation almost to the Victoria Falls.
But so far all it has been is a dream, and a very expensive one. Now Public Works Deputy Minister Senator Aguy Georgias is reviving it.
He will find that, as others have found before him, it is technically possible to create a Zambezi seaway.
Given enough money, enough concrete and a fleet of dredgers in a mouth of the Zambezi, probably the Quelimane mouth, which is the only one not actually blocked by a sandbar and which has an existing port.
But there are a lot of obstacles in the way. The cost is likely to be immense. Although an investor is thinking about US$10 billion this is likely to be a small fraction of the final cost to allow even quite small ships up the river.
Locks at Cabora Basa and Kariba Dams will remove water that might be better used to generate power. This will require a major cost-benefit analysis. The Zambezi tends to fill the two dams when it floods and the levels fall for many months each year.
And the environmental impact is likely to be severe. Already the floodplain on the huge delta has been seriously damaged by the regulation of the floods done by the two dams. The Zambezi coastal floodplain, which is fed by the Zambezi, Buzi, Pungwe and Save Rivers, is the largest remaining in Africa. Precise trade-offs will have to be calculated. The works on the river will also have an impact on other areas of unique environments, including Mana Pools.
And finally there will have to be cargoes that would justify the costs of this huge project. Few people live in the Middle and Lower Zambezi Valleys, but from Hwange down to Tete large coal deposits have been found. But it would probably be cheaper to get this through to the sea either by a railway along the river, or even through a pipeline using dust of a slurry. There is not much else close to the river for bulk cargo. In any case the best way of moving coal energy around could well be as electricity on the regional grid.
And if miners, farmers and industrialists have to move their goods a few hundred kilometres by road or rail to the ports on the river, they might find it worthwhile to move them by road or rail all the way to the sea.
The large agricultural grain harvests on the plateaux north and south of the river tend to be sold within the region, distributed by the north-south rail lines and roads, rather than exported out of the region. High-value lower bulk goods, such as tobacco, will almost certainly find rail traffic cheaper since so much of the capital cost has already been paid off.
The seaway dream predates the railway lines that were actually used to open trade into the interior, and those railways tend to predate the roads that now dominate traffic. Moving goods from, say, Harare to Beira by rail would probably be faster and cheaper, once capital costs are factored in, than moving them by road to Port Chirundu and then down the seaway.
There is nothing wrong with dreaming. This is the way we all advance. But before dreams become reality the accountants have to be involved, and we have serious doubts that the costs would justify the results.
But for a start, why not begin doing the sums and see if they make sense; that initial step would cost little.