Vol 5 Life in the Desert ... Introduction ... Water in the desert
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Introduction

Water in the desert

If the desert rainfall is received as a once-a-year downpour, a desert may temporarily become a very wet place indeed!
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Although deserts are dry places, they receive up to 10 inches of rain each year: if this rainfall is received as a once-a-year downpour, a desert may temporarily become a very wet place indeed!

Water is one of desert's great sculptors. The rain falling during brief storms in the mountains rushes into dried out stream beds or washes. With nothing to stop it, the water gains speed and roars onward to the plains between the mountains, producing one of nature's spectacular dangers - the flash flood. Flooding can produce a wall of water several feet high, which pushes anything in its way, including boulders, bushes and mud.

Flood waters eventually soak into the ground or may enter a river. In some cases the water may reach an undrained basin where it becomes a pool that quickly dries up or evaporates, leaving a dry lake called a playa. The extreme temperatures of desert regions quickly evaporates water in basins, and clay and salts are deposited. The southwestern part of the US features several playas including the Great Salt Lake Desert and part of the Death Valley National Monument.

Mountains can also be changed by storms. The storm water carries rocks, gravel, soil and other materials down the sides of the mountains. Although larger rocks are only carried a short distance, the water continues its descent and leaves the finer material farther down the mountainside. This material gradually forms a land delta, known as a bajada, at the base of the mountain. Bajadas are made up of sand and clay, ranging from coarse to fine-textured descending onto the plain. Near the large dry stream beds or wahses in center of the plains, there may be water below the surface, encouraging growth of different types of plants.

Some desert areas have large rivers running through them: these include the Indus river in India, the Rio Grande in the US and the Nile in Africa. These rivers have their sources outside of the the desert region, and they provide essential water for the peoples of these areas.

Water from deep layers of rock comes to the surface at oases, where crops such as date palms are cultivated. Groundwater is stored in spaces within rocks – water bearing rocks are known as aquifers, and they include sandstone and limestones. Water from aquifers may emerge at springs or it may be necessary to drill wells to tap the water source.

Today, vast areas of deserts have been irrigated by water pumped from deep bore wells.