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<br />3373
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<br />Most irrigation within liD is accomplished with surface (gravIty) flow methods except
<br />for gemlination and establishment of specialty and high value crops (Jensen/Walter
<br />Supplement 2003, p. 10). Surface irrigation in the llD setting is economical, energy
<br />efficient, and water efficient when properly managed (NRCE 2002, p, ll-14, WAC:
<br />Gilley et ai, 2003, p. 76), Sprinkler irrigation is being used in liD for seed germin~tion,
<br />crop est~bljshment, land prepar~tion purposes, and occ~sionalJy for leaching (NRCE
<br />2002, p.ll-14 & ]5). Drip i'Tigation is used when it is detennined by fa.mers to have an
<br />economic advanlage, depending on such factors as crop type, water quality management,
<br />yield, and economic return (W AC: Gilley et ~L, 2003, p. 76; NRCE 2002, p. II-IS). One
<br />of the primary reasons why gravity irrigation is more conunonly used is that the cracking
<br />soils in the central portion of llD are more conducive to surface irrigation than to either
<br />sprinkler or drip irrigation systems (Id.).
<br />
<br />Surface irrigation can be relatively efficient on fine textured soils, provided attention is
<br />given to stream size, timely changing of irrigation sets, and full attention of irrigators
<br />during irrigations (Jensen/Walter Supplement 2003, p. 10). Experts mentioned above
<br />who have examined practices by irrigators within the District have found that this type of
<br />careful attention is not typical or widespread. (WAC 2003, p, 31, MWD Submittal p, 39
<br />& 40). Surface runoff (tailwater) from border strip or furrow irrigation comprises the bulk
<br />of outflows from liD (Id.).
<br />
<br />The current, less-controlled methods of irrigation management used to apply water to Ihe
<br />variety of soils within llD result in substantial amounts of surface runoff and subsurface
<br />drainage, Excess surface nmoff levels in liD are particularly apparent for irrigations of
<br />tight, clay soils with low infiltration rates. While some individual irrigators within the
<br />District are using more-controlled irrigation methods, most irrigation scientists generally
<br />agree that these less-controlled management practices are more conunon. Some experts
<br />contend that tailwater values as low as 5% are alt~inable with more efficient irrigation
<br />management practices (MET: Rhoades 2003, p, 32). Measured nmoff that result from the
<br />historic irrigation and water applic~tion methods within lID support the fact that less
<br />intensive management practices are common (Table 3, MET, Scott, 2003, p. 5-7). Nearly
<br />one-thIrd of the water diverted by liD flows out of the District (NRCE 2002, p. V-8),
<br />which is mostly from tai]water (JenservWalter Supplement 2003, p. 7),
<br />
<br />Therefore, this detemlination concludes that significant improvements in irrigation
<br />methods are possible, Matching appropriate methods for each combination of crop and
<br />soil types h~ve proven beneficial to reducing water requiremenls in both clay and sandy
<br />soil envirorunents, Reclamation concludes that there are no distinguishing differences
<br />that would limit the applicability of these methods of irrigation in lID and that specr fic
<br />improvements should be undertaken. Reclamation's reconunendations in this regard arc
<br />discussed in mo,'e detail in Section IV. which contains Reclamation's Part 4\7.3 water
<br />conservation recomrnendations.
<br />
<br />July 2, 2003
<br />
<br />22
<br />
<br />Detenninations and Recommendations
<br />For liD - Calendar Year 2003
<br />
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