Using the flexible gated pipes (made of low density polyethylen) instead of the rigid pipes as a head ditch to distribute water evenly, especially in furrow irrigation, in order to increase in-farm distribution and application efficiencies, is becoming popular by manufacturing them in Iran. Hydraulics of the gated pipeline in some situations, especially in a flexible form, has not been fully investigated. One of the reasons is the temperal varied nature of these pipes due to materials used and its characteristics. In order to evaluate the hydraulic and technical characteristics of the flexible gated pipe made in Iran, experiment was conducted in the Water Research Laboratory of Irrigation and Reclamation Eng. Dept. at Tehran University. The head loss coefficients of this flexible gated pipe were determined under three different conditions such as: (1) flexible pipe w/o gate, (2) closes gated spacing of 1.5 and 0.75 meter, and (3) open gates spacing of 1.5 and 0.75 meter. The operating pressures were about 1.12 ,1.28 and 1.63 meter and discharge through gates were about 0.5 , 1.0, 1.5, and 2.0 lit/sec. The following relationships were developed under different conditions in order to determine head loss coefficients:
1. For flexible gated pipe w/o gates:
2*104
2. For flexible gated pipe with closed gates:
a. Gate spacing of 1.5 meter.
2*104
b. Gate spacing of 0.75 meter
f = 0.0349 1.5 10 < Re <6 , 105 CHW= 89.9
3. For flexible gated pipe with open gates:
In order to estimate the head loss coefficient by using Chu and Moe equation, the head loss reduction coefficients (k) for different conditions of discharge and gate spacing were determined.
)