Okavango Journal: I lay awake listening to the cacophony of the Okavango night. The sound was deafening, continuous and amazing. It was the sound of literally millions of tiny frogs serenading the floodwaters that had moved in recently. As I listened I pondered the phenomenon that is the seasonal flooding of the Okavango.
Text and images by Leigh Kemp
One of the earth's greatest natural phenomena happens in a tiny part of the great Kalahari Desert - in a place where a river flows into the sands and forms the world's largest inland delta. That the delta is in the middle of one of the largest deserts is extraordinary in itself but the real fascination lies in its behaviour through the seasons.
The happenings of the Okavango Delta
have gone on in relative obscurity for eons, with journals of early explorers and adventurers recording the spectacle in hushed whispers. More recently documentaries and travel brochures have been responsible for bringing part of the story to the forefront, with dramatic images and text, but these are generally geared at commercial gain and much of the story goes unrecorded.
The Kalahari is a vast place of many features, a place of red dunes, grass plains, tropical rain forest - and the Okavango Delta. Located in what would otherwise be a barren wilderness the Okavango plays host to one of nature's epic events - the seasonal flooding of the Kalahari
Part of a huge inland lake that once covered much of the central part of southern Africa the Okavango is all that remains of the ancient waterway. Signs of the lakes past can still be found in places such as the Makgadikgadi Salt Pans, the sand ridges of Savuti and in the ancient floodplains surrounding the delta.
The Okavango Flood by SeasonA time of the first drying
The waters of the delta begin to recede on the seasonal floodplains towards the end of the dry season, the drying up intensifying with the soaring temperatures of October.
It is now the hottest time in northern Botswana and usually there is no respite as the rains generally only start in November. The water on the floodplains shrinks away leaving only the deeper pools that have been deepened over previous seasons.
As the water shrinks fish can be seen in the clear water heading north to areas of more permanent water but there are thousands that will be trapped in the fast-dwindling pools. Together with other aquatic creatures those that are trapped will provide an orgy of feeding for countless birds and other predators. Even lions have been known to take advantage of this bounty.
Animals such as the lechwe will also begin to move away towards better watered areas, only returning to the same areas with the arrival of the new flood. Despite this move away by some species many animals remain on the floodplains as the grass greens for a time after the drying providing rich grazing.
With the drying up of the water the grass on the floodplains is initially green but dries quickly in the intense heat.
The floodplains may quickly turn to dust and even a small breeze or the hoofbeats of animals will stir a cloud into the air. But as anywhere in Africa there is a sense of expectation - an expectation that a new season is not far off.A time of respite - the rains
The clouds begin to build, a mere rumour at first but as the days pass the dust-greyed sky speaks of the promise until, after a time of intense anticipation, an evening may be touched by the sound of distant thunder and the scent of the season's first rains carried from a distance on the breeze.
The expectation grows by the day - until the rains bring relief from the dust and heat.
The results are almost immediate with greens shooting out on the floodplains and the dry reaches of the islands. Antelope give birth and the area turns from brown to all shades of green. Flowers carpet some parts with the devil thorns dominating in some areas, their beautiful flowers concealing their ultimate goal.
It is a time of plenty, the pans fill up and the grass is lush but the floodplains will see small change in the water levels. The local rains have a limited affect on the water levels of the Okavango, in most cases only raising the water table a little.A time of the second drying
With the end of the rainy season another period of drying up occurs as the dry season begins to take hold. This period happens from the time of the last rain to the time when the flood waters from the highlands of Angola arrive on the floodplains.
The vegetation growth slows and the greens of the rainy season begin to brown. The grass that has grown during the season of the rains now poses another problem - the threat of fire. Fires are an important part of the ecology of the Okavango and are necessary to clear old vegetation to stimulate new growth.
Although fires can occur in the delta at different times of the year they are more prevalent after the rainy season when the vegetation is dense. The sky is smudged grey from the numerous fires that burn around the delta at this time.
There is a sense of anticipation at this time - for the Okavango is about to show its uniqueness - an anticipation of the arrival of the flood waters from the highlands of Angola. It cannot be said when the waters will arrive in a particular area but an idea can be gained from the behavior of some species. Wattled cranes begin to arrive in numbers ahead of the water and lechwe, in particular the males become restless to move back to their territories if the previous season.
A time of fulfillment - arrival of the flood waters
And then on a day the water pushes in. It is called a flood although in reality it is a gentle push - no waves or rapids. It may take minutes, or even hours, for an area to fill up. The water deals with barriers by simply flowing around them - there is not enough force in the flow to push through.
Termite mounds and tree stands become islands as the water spreads on the floodplains. Lechwe move in and reclaim territories, birds follow the water while feeding on the small creatures that the flood rustles up. Crustaceans that have hidden in the mud since the last drying up resurface and insects get caught in the slow-moving water providing a feast for the birds.
The vegetation in the water quickly greens up providing a wonderful contrast to the dry season browns of the islands. It is the height of the dry season and yet much of the area is a lush green and water is everywhere and in the air a sense of peace prevails - as if a major project has been completed.
The waters from the distant highlands of Angola arrive in the Okavango Delta system months after leaving the highlands. The speed of the water's transfer depends on factors such as the amount of local rainfall in northern Botswana and the lower catchment areas and on how high the water table is at the time the water arrives.