In the desert wilderness of Namibia, on southern Africa's western coast, there is an unusual river that lies hidden beneath the scorching sand for most of the year. It is an ephemeral river - a river that flows above ground for only a few days a year. The water that feeds the Hoanib River collects in the mountains of north-western Namibia. Its course cuts through the desert, travelling mainly underground all the way to the Atlantic Ocean where its waters fan out into a lagoon that is separated from the sea by a pebbled dune. Only when exceptional rains fall over the mountains does the water in the lagoon rise enough to break through to the sea.\nThe animals that live here have learnt to adapt to the harshness of the desert where both food and water is scarce. But, although the river flows underground, it provides enough moisture close to the surface to support a thin oasis of trees and bushes. Giraffes and elephants reach in the trees to pick leaves and pods off the ana tree - a remarkable tree that produces nutrient-rich pods when all other desert plants lie dormant. Small creatures such as gerbils hide in the small bushes that line the river's course. Along the course, underlying bedrock forces the river to the surface in the form of natural springs where animals, such as the terrapin, otherwise not associated with the desert, can survive on the thin trickle of water. Elephant herds migrate along the river valley in constant search for fresh vegetation and water. \nWhen the rains fall over the mountains the gush of water replenishes the Hoanib. The abundance of water flowing over the desert is short-lived, in just a few days it all seeps into the ground and the plants and animals of the desert have to rely once more on their skills to survive in one of the harshest environments on Earth.

In the desert wilderness of Namibia, on southern Africa's western coast, there ...