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Unformatted text preview: Sprinkle & Trickle Irrigation Lectures Page 169 Merkley & Allen Lecture 14 enter Pivot Uniformity Evaluation C I. In o • take into account the irrigated area represented by each • It is more important to have better • n, the area II. E u te • or CU proposed by Heermann and Hein is (ASAE/ANSI S436): tr duction The calculation of an application uniformity term must catch container application uniformity further from the pivot point than nearer, because the catch containers at larger distances represent larger irrigated areas f the catch containers are equally spaced in the radial directio I represented by each is directly proportional to the radial distance q ation for Cen r Pivot CU The equation f ( ) ( ) n i i n i 1 i i n i 1 i i 1 n CU 100 r 1.0 = = ⎜ ⎟ = ⎜ ⎟ ⎝ ⎠ ⎜ ⎟ − ⎜ ⎟ ⎜ ⎝ ∑ (295) i i i 1 dr r d dr = = ⎛ ⎛ ⎜ ⎟ ⎜ ⎟ − ⎜ ⎟ ⎜ ⎟ ⎟ ⎠ ∑ ∑ ∑ ual i i i i 1 i 1 r and, dr = = ∑ ∑ (296) • Then, perform the outer summation to determine the CU value • That is, don’t recalculate the inner summation values for every iteration of the outer summation – it isn’t necessary • It is usually considered that a center pivot CU should be greater than 85% • If the radial distances, r i , are equal, the sequence number of the can (increasing with increasing radius) can be used instead of the actual distance for the purpose of calculating application uniformity • Consider the following two figures: ⎞ ⎞ where CU is the coefficient of uniformity; d i is the depth from an individ container; r i is the radial distance from the pivot point; and n is the number of containers • First calculate the summations: n n ( ) slope? catch containers l e g # 1 le g # 3 l e g # 2 R slope? catch containers R level field? no wind?... CU = 100% Merkley & Allen Page 170 Sprinkle & Trickle Irrigation Lectures Sprinkle & Trickle Irrigation Lectures Page 171 Merkley & Allen III. Sta • ou can also calculate the “standard” CU or DU if you weight each catch value by multiplying it by the corres • To obtain the low ¼, rank the unweighted catches, then start summing radii ning with the radius for the lowest catch value) until the cumulative value is approximately equal to ¼ of the total cumulative radius • This may or may not be equal to ¼ of the total catch values, because each catch represents a different annular area of the field • Finally, divide the sum of the catches times the radii for this approximately ¼ area by the cumulative radius • This gives the average catch of the low ¼ • Don’t ndard Uniformity Values Y ponding radial distance (begin rank the weighted catches (depth x radius) because you will mostly get the values from the low r values (unless the inner catches are relatively high for some reason), and your answer will be wrong • Don’t calculate the average of the low ¼ like this… (because the lowest ¼ of the catches generally represents something different than ¼ of the irrigated area):...
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 Fall '03
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