ࡱ> DFEB( / 0LDTimes New Roman̳0~0  @n?" dd@  @@`` $dO     c $@>g4MdMd~0 *ppp@  <4BdBdLg4:d:d~0 jp@ pp? %O =lIrrigation: Its Consequences in Basin Water Management and the Potential for Conserving Water for New Users Presented by Harald Fredericksen Characteristics on IrrigationLargest consumer in many arid regions Consumption (evapo-transportation) depends mostly upon crop and weather Additional Water Diverted Depends Upon Conveyance Losses Application Methods Soil Type and Uniformity Weather$GG32Most of this Additional Water Ultimately Flows to:NGroundwater Drainage Channels Adjacent Channels River/Stream Channels/Wetlands*Net Basin Losses Consist Only of Flow to: $Saline Groundwater Saline Lakes SeasOther ConsiderationsKMajor Portion of Rice crops irrigated when basin run-off exceeds total basin demands Native vegetation is largest consumer in most basins Example of California: Total Precipitation -- 200 MAF E/T Native Vegetation -- 130 MAF Total Surface Runoff - 71 MAF Flood Flow -- 21 MAF Utilization - 50 MAF (Environmental Over 50% of Runoff)8NDefinition of Irrigation  Efficiencies Ratio of evapo-transpiration to water diverted (irrigation system efficiency) Ratio of evapo-transpiration to water applied to field (field efficiency) Ratio of evapo-transpiration to total water removed from the surface water and groundwater sytems (irrigation sector efficiency)P IEM LTypical Irrigation  Efficiency ValuesIrrigation system- 20 to 80 percent Field- 50 to 85 percent Sector- 87 percent in USA 1981 (higher if flows to wetlands are credited as beneficial) <Urban Water Use  Efficiencies SDeveloped countries- 10 to15 percent (majority of water used to convey wastes away from cities) Developing countries- 25 to 80 percent (per-capita delivery low and conveyance losses are high) Factors affecting urban sector efficiency Proximity to sea Quality of urban effluent Quality of resultant stream flow Use of underlying groundwater8ji $Basin  Efficiency Defined as: ratio of consumed water (all uses) to total  utilizable basin runoff Determined by: Type and location of various users Degree of reuse/recycling within basin Examples of basin efficiencies during low flow season Yellow- 100 percent Ganges- 100 percent Nile- Essentially 100 percent Sacramento- 100 percent Colorado- 100 percent aJ6v`I5]   Conclusions<Improving irrigation  efficiencies will yield little additional water for new uses Further reduction in irrigation supply carries high social, economic and political risks for next several decades Per-capita urban supply in developing countries insufficient today Groundwater is overdrafted in most regions and desalting is unaffordable Seepage of irrigation water is primary source of groundwater in many regions {  Conclusions (continued)MDroughts in developing countries will be increasingly catastrophic, impacting neighboring and distant countries Efforts should focus on urban waste treatment and new sources of supply Only remaining un-utilized resource is floodwater flowing into the sea International community should inform public and commence dealing with reality/4  u ` ̙33` ` ff3333f` 333MMM` f` f` 3>?" dd@,|?" dd@   " @ ` n?" dd@   @@``PR    @ ` ` p>> c(    6T P   T Click to edit Master title style! !  0     RClick to edit Master text styles Second level Third level Fourth level Fifth level!     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