320-HW7

# 320-HW7 - BRAE 340 Irrig Water Management HW 7 IE DU Name...

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BRAE 340 Irrig. Water Management Name: HW 7 - IE & DU (only odd numbered problems will be graded) [F] 1. T/F: Spray loses for under tree sprinklers range from 4-6%. Explanation See page E-5. Spray losses from hand move sprinklers are 4-6% [F] 2. T/F: Excess costs for water and energy, but decreased costs for drainage, are likely consequences of low on-farm AE's. Explanation Low AE's mean applying excess water. Water and energy costs would increase. More deep percolation would mean an increase drainage costs as well. [F] 3. T/F: DU must be at least 90% to have an IE above 100%. Explanation It is impossible to have an AE above 100% [T] 4. T/F: If an entire field is under-irrigated, the water beneficially used is equal to the average depth applied. Explanation If all is under-irrigated, Dmax is less than SMD --> no deep percolation So beneficial use = amount stored = all that infiltrates = Dave. Solution Key

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[D] 5. Given: Soil moisture depletion = 6.01 inches; average infiltration = 8.49 inches; DU = 61.8%. Which one of the phrases below best describes the irrigation on this field? A) impossible to tell B) perfect irrigation timing C) entire field is under irrigated D) field has both under and over irrigation E) entire field is over irrigated Explanation Dave = 8.49 inches Dmin = Dave x DU/100 = 8.49 x 61.8% = 5.25 inches Dave - Dmin = 8.49 - 5.25 = 3.24 inches Dmax = Dave + 3.24 = 8.49 + 3.24 = 11.73 inches SMD = 6.01 in --> SMD is between Dmin and Dmax Some over irrigation, Some under irrigation -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 0 100 % Area -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 SMD = 6.01 Infiltrated Amounts Dmin = 5.25 Dave = 8.49 Dmax = 11.73
[D] 6. Given: Soil moisture depletion = 5.25 inches; average infiltration = 8.02 inches; DU = 65.5%. Which one of the phrases below best describes the irrigation on this field? A) entire field is under irrigated B) entire field is over irrigated C) impossible to tell D) perfect irrigation timing E) field has both under and over irrigation Explanation Dave = 8.02 inches Dmin = Dave x DU/100 = 8.02 x 65.5% = 5.25 inches Dave - Dmin = 8.02 - 5.25 = 2.77 inches Dmax = Dave + 2.77 = 8.02 + 2.77 = 10.79 inches Dmin = 5.25 = SMD Since SMD = Dmin --> Perfect Irrigation Timing -1 0 1 2 3 4 5 6 7 8 9 10 11 12 0 100 % Area -1 0 1 2 3 4 5 6 7 8 9 10 11 12 SMD = 5.25 Infiltrated Depths Dmin = 5.25 Dave = 8.02 Dmax = 10.79

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[B] 7. Given: Applied water = 8.4 inches, evaporation loss = 4 %, DU = 77 %, Average infiltration = 5.7 inches, ETc = 0.24 in/day, SMD = 3.51 inches. What is the runoff expressed in inches? A) 1.94 inches B) 2.36 inches C) 2.65 inches D) 1.29 inches E) 1.54 inches Solution: Total loss = gross application - average infiltrated Total loss = 8.4 - 5.7 = 2.70 inches Also, total loss = evap loss + runoff loss So, runoff loss = total loss - evap loss evap loss = 4 % x gross = 4 % x 8.4 inches = 0.34 in runoff = total loss - evap loss = 2.70 - 0.34 inches = 2.36 in [D]
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