Desert Sources of Water
- Rainfall is sporadic, however, rare substantial, intense flash floods generate considerable runoff
- These episodic flash floods arise from convectional storms in mountain ranges and flow as sheet floods or are confined within channels
- Despite being short-lived, large amounts of sediment are washed down from the mountains to be deposited on alluvial lowland plains
- There is a limited vegetative cover to absorb water and this limits humus levels, lowering plant root disturbance, making the soil dense and compact
- Rain is therefore, able to beat down on the surface with maximum impact, dislodging fine particles and blocking pore spaces, thereby further reducing the infiltration rate
- This minimal infiltration rate means that slopes of less than 2° experience extensive overland flow
Ephemeral rivers
- Snowmelt and episodic flash floods provide the water for these intermittent rivers and are also known as wadis, barrancas, washes or arroyos
- More typical of desert areas, streams flow intermittently or seasonally after rainstorms and are powerful forces of erosion
Endoreic rivers Exogenous rivers
- This is when a river flows into the desert but terminates in an inland lake or sea
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River Jordan into the Dead Sea, the Aral Sea, The Bear into the Great Salt Lake
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Exogenous rivers
- Large, perennial rivers with an external source
- They have sufficient discharge to flow continuously, despite high evaporative rates as they cross arid land
- The Blue Nile, the Nile's main tributary, originates in the Highlands of Ethiopia
