Land and Watershed Management - Practices of Irrigation and On-farm Water Management - page 197

cultivation, grazing, and deforestation of marginally productive lands compounds
the effects of land scarcity. These are often steep areas with shallow soils that expe-
rience accelerated surface and gully erosion, soil mass movement, and increased
sediment and storm flow damage to downstream communities. In the tropics, it is
estimated that about 0.5 ha of farmland is needed to feed one person (Pimental et al.
1995 ) . Lal ( 1997 ) indicated that by the year 2025, 45 countries in the tropics will
have less than 0.1 ha of arable land per capita. Globally, of the 8.7 billion ha of
agricultural land, forest, woodland, and rangelands, over 22% has been degraded
since mid-century, with 3.5% being severely degraded (Scherr and Yadav, 1996 ) .
Deforestation continues to gain worldwide attention with most of the concern
expressed in terms of lost biodiversity; of equal importance are the implications
of deforestation on watershed functions.
From overall consideration of

the watershed, the challenges include the

following:

• high population growth

• increasing land use intensity

• highly degraded or threatened river systems

• no legal protection for in-stream flow needs

• watersheds that are driven by glacially fed rivers and then flow into the driest part

of the province

• significant allocation to irrigation

• an extensive plumbing systems of canals and dams

• a highly uncertain water supply and

• emerging water conflicts.

6.3 Fundamental Aspects of Watershed Management

6.3.1 Elements of Watershed

Watershed management recognizes that the water quality of our streams, lakes, and
estuaries results from the interaction of upstream features. It unites social, economic,
and environmental concerns and the cumulative effects of site-specific actions on
rangelands, forests, agricultural lands, and rural communities.
Wetlands are important elements of a watershed because they serve as the link
between land and water resources. Oceans, coasts, and estuaries provide critical
natural habitat and recreational areas for our nations.
The term “watershed processes” connotes consideration of distributed sys-
tems with processes which are neither uniform in space nor constant in time.
Watershed processes also suggest processes such as mass flux (water, sediment, or
contaminant) relative to a specified contributing area.