Watershed: The topography of any region may be subdivided into several
ecological units, each of which drains to a common point. Each such ecological
unit is referred to as watershed. Strictly speaking, the higher land that separates
each such unit is called a watershed, and the unit itself being termed as the
catchment area. However, it has become fairly common now to speak of
catchment area and watershed in identical terms. The size of a watershed may
vary from a few hectares to thousands of square kilometers. Table (following the
diagram) provides a system of classifying watersheds at different levels of
aggregation.
Causes of watershed deterioration:
Agricultural land: Cultivation on sloping land without adequate precautions;
cultivation along naala; cultivation of erosion permitting crops; over cropping
areas without replenishing soil fertility.
Forestland: Clear felling on steep slopes; drastic thinning of plants along slopes; faulty logging roads and disturbance of forest floors during removal of the felled trees.
Grasslands: Excessive grazing resulting in disappearance of protective cover development of cattle tracts into channels; compaction of soil resulting in lower infiltration rates etc.
Fire- Intentional or accidental fire resulting in loss of vegetation, organic matter, and microorganisms.
Consequences of watershed deterioration
Low productivity of land with respect to food, fuel, forge, fiber and fruits.
• Erosion and denudation within and adjoin watershed.
• Quick siltation of reservoir, lakes etc.
• Deterioration of water quality due to heavy sedimentation.
• Increased incidence of floods and droughts
• Poor health of people and cattle.
Water erosion
Water erosion is the detachment and removal of soil material by water. The process may be natural or accelerated by human activity. The rate of erosion may be very slow to very rapid, depending on the soil, the local landscape, and weather conditions. Water erosion wears away the earth's surface.
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