منتظر پست بعدی باشید
About the new generation of
منتظر پست بعدی باشید
After completing this training module, and readings of the selected references, you should be able to answer the following study questions.
Anderson, H. W., M. D. Hoover, and K. G. Reinhart. 1976. Forests and water: Effects of forest management on floods, sedimentation, and water supply. USDA Forest Service, General Technical Report PSW18.
Blackburn, W. H. 1983. Livestock grazing impacts on watersheds. Rangelands 5:123-125.
Bosch, J. M., and J. D. Hewlett. 1982. A review of catchment experiments to determine the effect of vegetation changes on water yield and evapotranspiration. Journal of Hydrology 55:3-23.
Branson, F. A., G. F. Gifford, K. G. Renard, and R. F. Hadley. 1981. Rangeland hydrology. Kendall-Hunt Publishing Company, Dubuque, Iowa.
Brooks, K. N., P. F. Ffolliott, H. M. Gregersen, and L. F. DeBano. 1997. Hydrology and the management of watersheds. Iowa State University Press, Ames, Iowa.
DeBano, L. P., and L. J. Schmidt. 1990. Potential for enhancing riparian habitats in the southwestern United States with watershed practices. Forest Ecology and Management 33-34:385-403.
Heathcote, Fl L. 1983. The arid lands: Their use and abuse. Longman, London.
National Academy of Science. 1974. More water for arid lands. National Academy of Sciences, Washington, D.C.
Renard, K. G. 1970. The hydrology of semiarid rangeland watersheds. USDA ARS 41-162:26
There is clear evidence that a potential exists on earth to feed a much larger population than currently lives here. Despite this encouragement, it must also be remembered that the resources of individual regions and countries vary widely. Development of the resources on watershed lands also takes a long period of time before it yields benefits. Conversely, once degraded, watershed restoration also takes a long period of time. Unfortunately, political leaders often have short-term goals—they focus on immediate and popular concerns. Yet, the production and conservation of the resources on watershed lands are dependent upon long-term and extensive commitments. People must be ready to make this commitment to the development of the watershed lands if future land degradation is to be avoided.
It is important to recognize that the problems of managing resources on watershed lands do not arise necessarily from physical limitations nor from lack of technical knowledge. Wood harvesting practices, reforestation programs, and methods of livestock grazing have been developed to largely prevent adverse impacts on soil and water resources. Likewise, technology to solve many watershed problems is available. However, methods are needed to effectively demonstrate the benefits of instituting environmentally sound watershed management programs. The social and economic benefits from watershed management programs must be quantified and compared to the costs of not implementing these programs. Inhabitants of watersheds and their livelihoods must be considered as an integral part of any watershed management program, requiring integration of social, economic, and political factors in addition to biological and physical considerations
Manipulation of vegetation that accompanies management of natural ecosystems can affect the long-term productivity of watershed lands. Of particular concern are impacts on quantities and qualities of water that originates from upland watersheds. It is important, therefore, to recognize the environmental effects that watershed management practices frequently have on the hydrology of watershed lands.
Many watershed lands are subjected to grazing by livestock and wild ungulates, harvesting of trees and shrubs for fuel and other wood products, agricultural cultivation, and other forms of human intervention. The harvesting of trees or shrubs or converting from one vegetative type to another can enhance water supplies if the watersheds are managed properly. However, when managed improperly, these manipulations can also lead to:
Water limits much of what people can do. Stability of water supplies is critical to programs of development. Emphasis in water resource management in dryland regions generally is placed on developing or conserving water supplies. The usefulness of water supplies to people also depends largely upon their physical, chemical, and biological characteristics. It is important, therefore, that both quantity and quality be considered in the management of water resources.
Numerous methods have been used in developing water supplies in the dryland regions of the world. Water harvesting is one example of note. Water harvesting systems were used by people in the Negev Desert over 4,000 years ago, with applications of this technology continuing to the present. Not all of the systems have been successful, although some form of water harvesting has been necessary to sustain livestock and agricultural crop production and forestry, in many instances.
Water harvesting methods involve the collection and, in many instances, storage of rainfall until the water can be used beneficially. Components of water harvesting systems include:
Managers of watershed lands must address specific questions in relation to land use. These questions include:
در صورت تمایل بازدید کنندگان و وقت کافی ، ترجمه می شود .
By Peter Ffolliott, professor of Watershed Management and of Renewable Natural Resources at The University of Arizona