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The River Basin  
Climate and Weather
 Principles of Hydrology
 Water Cycle
 Surface Water
 Streams and Rivers
 Lakes and Reservoirs
 SW/GW Interactions
 Water Balance
 Hydrology of the Orange-Senqu River Basin
 Surface Water
 SADC Hydrogeological Mapping Project
 Water Use/Water Balance
 Monitoring Flow
Water Quality
Ecology and Biodiversity


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Hydrology is the scientific study of water, seeking to explain the water balance equation in terms of time and space, and assessing the impact of physical and chemical processes and their role in ecosystems.

Life on Earth is sustained by water, which is available to plants, animals and other organisms in three states: solid, liquid and gas (water vapour). The continuous movement of water on and below the earth’s surface, and between the earth and the atmosphere is known as the water cycle or hydrologic cycle. Only a small fraction of the water in the hydrologic cycle is available fresh water. Freshwater is therefore a precious resource requiring careful management and protection.

Within the hydrologic cycle, rivers form the link between rainfall and snow melt over land, and waterbodies such as lakes, wetlands, and the sea. The timing, extent, and pathway of water movements are critical to biota, including people, that depend on specific sources of water. This chapter describes the processes and environmental features related to the movement of water across the landscape within a river basin.

River systems include the entire length of the main channel (from headwaters to the sea) and associated permanent or temporary wetlands (floodplains, lakes, pools, estuaries, and deltas). These components of the river system and the surrounding landscape it drains (its watershed), are interconnected and interdependent. Because of these linkages between upstream and downstream ecosystems, river basins provide a convenient and logical unit for considering and managing most environmental systems (Beekman et al. 2009).

Chapter Summary

This chapter covers the following concepts and material:

Sehlabathebe National Park, Lesotho.
Source:ŠiStockphoto/Ananiadis 2008
( click to enlarge )



Explore the sub-basins of the Orange-Senqu River

Tour video scenes along the Orange-Senqu River related to the River Basin

Investigate land cover and terrestrial ecoregions in the basin

Examine how the hydrologic cycle moves water through and around the earth

Explore the interactions of living organisms in aquatic environments

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