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United States Department of Agriculture

Agricultural Research Service

Title: Water Conservation Questions and Definitions from a Hydrologic Perspective

Authors
item Allen, Richard - UNIV OF ID, KIMBERLY
item Willardson, Lyman - UTAH STATE, LOGAN UT
item Burt, Charles - CALPOLY, SLO, CA
item Clemmens, Albert

Submitted to: International Irrigation Show
Publication Type: Proceedings
Publication Acceptance Date: June 1, 2003
Publication Date: November 18, 2003
Citation: Allen, R.G., Willardson, L.S., Burt, C., Clemmens, A.J. 2003. Water conservation questions and definitions from a hydrologic perspective. International Irrigation Show. p. 159-170.

Interpretive Summary: Water conservation activities are frequently encouraged within municipalities and irrigation systems, especially during periods of drought. The objectives of many irrigation water conservation programs have been to increase irrigation efficiencies with the expressed purpose of reducing gross diversion requirements. The intent during droughts is that less water will be depleted from a limited resource. In long-term conservation programs the intent is that more water will be made available for other users. However, the reasons for reducing diversion requirements must have both a regional and local interpretation from a hydrologic and conservation of mass viewpoint. Water management principles used to guide society's water use objectives require terms and definitions that clearly describe the effects of various water uses, both consumptive and nonconsumptive, within a hydrologic system. Some water use terms such as the evaporated fraction, reusable fraction, nonreusable fraction and consumed fraction are discussed in this paper. These terms are useful to both users and public in developing improved, rational and visual understandings of the hydrologic nature and impacts of water use and conservation programs. This paper will be of interest to all parties interested in water conservation: NRCS, Bureau of Reclamation, state water agencies, irrigation districts, consultants, and water user organizations.

Technical Abstract: Water conservation activities are frequently encouraged within municipalities and irrigation systems, especially during periods of drought. The objectives of many irrigation water conservation programs have been to increase irrigation efficiencies with the expressed purpose of reducing gross diversion requirements. The intent during droughts is that less water will be depleted from a limited resource. In long-term conservation programs the intent is that more water will be made available for other users. However, the reasons for reducing diversion requirements must have both a regional and local interpretation from a hydrologic and conservation of mass viewpoint. Water management principles used to guide society's water use objectives require terms and definitions that clearly describe the effects of various water uses, both consumptive and non-consumptive, within a hydrologic system. Some water use terms such as the evaporated fraction, reusable fraction, nonreusable fraction and consumed fraction are discussed in this paper. These terms are useful to both users and public in developing improved, rational and visual understandings of the hydrologic nature and impacts of water use and conservation programs. In situations where the nonevaporated components of irrigation diversions return to the fresh water resource for reuse by others, conservation programs may not stretch water supplies or "save" water in the region, especially in the long-term, and especially where the initial source is from ground-water. In some instances, where water is abstracted from streams, irrigation water conservation programs can actually be "ET sustainment" programs, since they may sustain a more "consumable" water supply for one city or project at the potential expense of downstream projects, cities and perhaps the environment. Water conservation programs should fundamentally be evaluated in the context that, in general, the only real loss of water from an irrigation project is by the process of evaporation from open water surfaces, evaporation from moist soil and transpiration from vegetation. Fundamental hydrologic concepts and questions are described that can help planners and managers to establish the context and impact of individual conservation programs in the near and long term.

Last Modified: 7/28/2014
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