BIE 5110/6110
Sprinkle & Trickle Irrigation
Fall Semester, 2004
Assignment #5 (100 pts)
Minor Losses & Pumps
Due: 13 Oct 04
Given:
•
A rectangular field to be sprinkler irrigated
•
There will be four laterals, two on each side of the mainline
•
All of the periodic-move laterals will move in the same direction
•
At the beginning of an irrigation, two laterals are at the upstream end of the mainline
(first hydrant) and the other two are at the mid-point of the mainline
•
The nominal hydrant diameter, and the inside diameter, is 4 inches
•
Each lateral irrigates ¼ of the field area, and each is 600 ft in length
•
Required lateral inlet pressure head is P
l
= 44 psi
•
The mainline will be 5-inch aluminum (see Table 8.4), with hydrant values spaced at
S
l
= 30 ft along the 1,320-ft length of the mainline
•
The first hydrant is located 30 ft from the beginning of the mainline, and the last
hydrant is 1,320 ft from the beginning of the mainline
•
The sprinkler system will operate 12 hrs/day, and the irrigation interval during the
peak-use period is 7 days
•
The gross depth to apply per irrigation is 1.9 inches
•
The mainline slopes downhill at a uniform slope of 0.18%
•
See the table in Chapter 8 for the roughness height of aluminum pipe
•
See Table 11.1 for minor loss coefficients, K
r
Required:
•
What is the field area, in acres?
•
What is the system capacity, in gpm?
•
Will the velocity in the mainline acceptable, or too high?
•
Use the Darcy-Weisbach equation for pipe friction loss
•
Make a graph of required (minimum) pressure at the upstream end of the mainline
as a function of lateral position, such that the minimum lateral inlet pressure (for
each lateral position) is exactly 44 psi
•
This means that one pair of laterals will have exactly 44 psi inlet pressure, while the
other pair will have a slightly higher inlet pressure, and this will be the case for each
lateral position
•
Note that there will be 1,320/(2*30) = 22 different positions lateral for each pair of
laterals
•
On the graph, you can call the lateral positions “1,” “2,” “3,” … “21,” and “22.”
•
Make note of any assumptions and of references which you use to obtain data