The longest river in South Africa is the Orange River. It meanders through the north of the country and draws a parallel to the border between Namibia and South Africa. Together with the Vaal, it explodes into the rich East Rand of the highlands and flows through the dry areas until it reaches the large Kalahari Desert. At the Augrabies Falls in Upington, the river falls over 160m into a deep ravine.   The Orange River, due to the heavy rainfalls throughout the year, supplies even the dry areas with water. Numerous dams regulate the water level in the river.   The change in wet and dry seasons can be seen clearly by the level of the rivers. Small rivulets can change into raging rivers in a matter of hours. This is often a disaster for farmers as it destroys the cultivated land.   Other rivers in South Africa are the Limpopo, the Olifant and the Fishriver, as well as the Unzimkuli, Tugela River, Buffalo River, Great Letaba and Crocodile River. Ships are not able to get onto these rivers.   South Africa only has a few lakes, which is why numerous dams were built to supply the population with water. South Africa, due to its high temperatures, has to battle a high evaporation rate that hinders farming.