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The Environment


Topography, rainfall, geology and soils, and vegetation cover determine the amount of water flowing down our creeks and rivers and out of our catchments. If water yield is to be manipulated it is usually through vegetation management.

At a catchment level, the total amount of rainfall is independent of the vegetation cover. The same amount will fall whether the catchment is covered entirely by trees or by grass.

If land is under trees a smaller proportion of this rainfall reaches the streams than if it were used for farming. Evaporation occurs from tree canopies before rain can enter the soils. Trees, with their larger crowns and deeper root systems, transpire more than most other types of vegetation.

However, pumping irrigation water from streams for intensive cropping or horticulture can leave less water than when the land was covered by forest.

The clearing of forest for agriculture by early settlers led to heavier run off and problems in the form of accelerated erosion and waterlogging, and latterly salinity, as water tables flush salt back to the root zone.

Many of these problems are being addressed by today's land managers through tree planting and governments are promoting better native vegetation management.

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