More than a hundred years ago Prof A.H. Keane exhaustively outlined in his book - The Gold of Ophir how in his long search for biblical Ophir he came to the conclusion that biblical Havilah was Zimbabwe.
The biblical book of Genesis 2:11 when speaking of the gold speaks of Havilah and a river issuing from Eden says…
‘…it then divides and becomes four branches. ; the one that winds through the whole land is Havilah, where the gold is. (The gold of that land is good; bdellium is there, and lapis lazuli). The name of the second river is Gihon, the one that winds through the whole land of Cush. The name of the third river is Hiddekel, the one that flows east of Asshur. And the fourth river is the Perat.’
Regarding the Garden of Eden, the predominant opinion among biblical scholars is that in Genesis 13:10, the garden is made independent of the vagaries of seasonal rainfall. Somewhere beyond the confines of the garden this single river separated into four branches that probably represent the four quarters of the inhabited world. Opinion is that the ‘River of Eden’ also nourished the rest of the world with its life-giving waters. Typical opinion has somehow related two rivers, the Tigris and Euphrates to have a connection with Eden. For example:
“While the Tigris and the Euphrates are of course well known, the other two names defy positive identification. They may stand for another great river civilization corresponding to that of the Mesopotamian plain, perhaps the Nile Valley.”
But the aforementioned is pure speculation of scholars (peering myopically at the present world) and generally assuming that only two of the rivers are either the Tigris or the Euphrates, or associated with these two well known Middle Eastern rivers associated with the ancient world and located in the Fertile Crescent where humans and religion have experienced enormous development. The fact is there were four rivers of Eden and not one of the rivers have ever been positively identified! There is not a shred of real evidence to support the contentions and theories that the Tigris and Euphrates are the rivers of Eden.
Rand Flem-Ath and Colin Wilson put an extremely good case in ‘The Atlantis Blueprint,’ for the equator once having formerly been directly over Giza presently 30°N (The then prime Meridian). If we consider that polar shift or reversal (coupled with earth crustal shift) has possibly occurred many times in the past (the most recent being the Hudson Bay North Pole) these rivers of Eden could have been anywhere.
Havilah means ‘sandy land’ in Hebrew. If, in the light of this possibility, we remember that, climatically and geologically things were very different a hundred thousand or even twenty thousand years ago and that a vast inland sea covered the present Kalahari Desert which spreads across Namibia, Botswana and Eastern Zimbabwe; of which the many dried salt lakes of Mgadikgadi Botswana and Etosha Namibia and the great Okavango Delta are the last remnants. And if we examine the Zambezi and African river systems in the light of Havilah and this inland sea – we suddenly find a far better and more likely fit to the Biblical quote:
‘The name of the first is Pishon; the one that winds through the whole land is Havilah, where the gold is. The gold of that land is good; bdellium is there, and lapis lazuli.’
More than two million years ago the land around the Makgadigadi salt pans experienced tectonic uplift (perhaps as part of what geologists call the African super swell) and a large lake formed, and extended east and the upper Zambezi River used to flow south through what is now the Makgadikgadi Pan to the Limpopo River. The land through which the ancient first Zambezi once ran (now the great sandy Kalahari) easily meets the description –
“... is the one (river) that winds through the whole land is Havilah, where the gold is. The gold of that land is good.”
The land along most of the Zambezi is sandy, ancient evidence of this mighty river’s sand and washed pebbles lies everywhere in the rift valley. I have personally, during years of military patrolling, frequently marvelled at smooth washed pebbles and boulders encased in great slabs of compressed river sandstone, lying as much as fifty miles from and a thousand feet or more higher than the river, in the dramatic escarpments through which the great river presently traverses. Admittedly Zimbabwe is not (now) a traditional source of bdellium (an aromatic gum like myrrh exuded from a tree which we shall discuss later) – but neither is the Fertile Crescent. If The Atlantis Blueprint is right – and crustal shift did occur; then when Egypt lay on the equator Zimbabwe once lay at about 45°S. Who is to say what was produced there?
The name of the second is Gihon
The name of the second river is Gihon. (The one that winds through the whole land of Cush)
The River Nile is the one Biblical river which we can positively identify. The word Gihon in Hebrew means ‘gushing forth” – which is exactly what the Nile presently does as it gushes forth from an enormous inland sea (Lake Victoria) over a waterfall to instantly become one of the world’s great rivers. The word Cush means black – which technically is present day Ethiopia (or north Africa/S. Egypt.) The Nile is a prime candidate for having its source together with that of the R. Zambezi and the R. Congo - and its story is fascinating.
Today the Nile actually rises not on Lake Victoria but far to the south of that lake in the middle of Africa (in the E.Din or Abzu of the Sumerians) which Wikipedia tells us:
The present Nile is at least the fifth river that has flowed north from the Ethiopian Highlands. Satellite imagery was used to identify dry watercourses in the desert to the west of the Nile. An Eonile canyon, now filled by surface drift, represents an ancestral Nile called the Eonile that flowed during the later Miocene (23–5.3 million years before the present). The Eonile transported clastic sediments to the Mediterranean, where several gas fields have been discovered within these sediments. During the late-Miocene Messinian Salinity Crisis, when the Mediterranean Sea was a closed basin and evaporated empty or nearly so, the Nile cut its course down to the new base level until it was several hundred feet below world ocean level at Aswan and 8,000 feet (2,400 m) below Cairo. This huge canyon is now full of later sediment.
Formerly Lake Tanganyika drained northwards along the African Rift Valley into the Albert Nile, making the Nile about 900 miles (1,400 km) longer, until blocked in Miocene times by the bulk of the Virunga Volcanoes. Lake Tanganyika drained northwards into the Nile until the Virunga Volcanoes blocked its course in Rwanda. That would have made the Nile much longer, with its longest headwaters in northern Zambia.
End of Wikipedia extract
The name of the third river is Hiddekel, the one that flows east of Asshur.
The Hiddekel - is more complicated. This, the third river (‘that flows east of Asshur.’) leads scholars to assume a Fertile Crescent location, but Ashurr requires positive identification. The Lualaba, the main source of the mighty Zaire River (presently the 2nd greatest river in the world) also rises very close to the source of the Zambezi. In fact so near, that their sources are a watershed where literally one pace separates the waters flowing into either of these two great rivers. The mighty Zaire River could therefore conceivably have been the Hiddekel, with its source and that of the Zambezi not too far from the (ancient) source of the Nile. With three rivers rising from what could have once been “a single source,” this leaves only the Perat, the fourth river, generally believed to be (corrupted to) Euphrates.
And the fourth is Perat
A Portuguese writer de Barros, whom we shall frequently meet in the coming pages wrote these lines almost five hundred years ago. 
All the land which we include in the kingdom of Sofala is a great region, ruled by a heathen prince called Benomotapa; it is enclosed by two arms of a river which issues from the most considerable lake in all Africa which was much sought after by all the ancients as being the source of the whence also issues our Zaire – which flows by the kingdom of Congo. The river which flows towards Sofala which issues from this lake and has a long course divides into two branches
The lake of which De Barros was speaking was in all likelihood Nalubale (later Lake Victoria). The two arms of which De Barros was speaking were the Limpopo and the Zambezi. Perhaps the ancients knew all four biblical rivers emanated from one source- a great lake. When Livingstone and Moffat explored the Zambezi, Burke, Stanley, Grant and many others of the time, were still arguing about and seeking the source of the Nile, it is easy to see how they were confused. For climatically and geologically things were very different twelve thousand or more years ago. The Perat therefore (if earth crustal shift has occurred) could just as well be the Limpopo and or, the Sabi River - all once perhaps interconnected to a vast inland sea of which its remnants are now the Kalahari and the dried salt lakes of Mgadikgadi Botswana and Etosha Namibia.
So, as much as many biblical scholars wish it to be so - it is highly questionable that the Tigris and Euphrates are two of the four rivers of Eden - and this is why there has been so much scholarly speculation that another great river civilization existed somewhere.