Em4885 irrigation management practices to protect ground water
Em4885 irrigation management practices to protect ground water
Em4885 irrigation management practices to protect ground water
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4 CHAPTER<br />
These include:<br />
1. Flumes, weirs, and orifice gates for streams, ditches, and canals.<br />
2. Propeller flow meters and orifices for pipelines.<br />
Main <strong>water</strong> delivery pumps should always have a flow meter installed. In addition <strong>to</strong> moni<strong>to</strong>ring<br />
<strong>irrigation</strong> applications flow meters can serve as early warnings as <strong>to</strong> problems with a well or pump.<br />
Propeller flow meters can also measure <strong>to</strong>tal volume of <strong>water</strong> pumped as well as <strong>water</strong> flow.<br />
A flow meter does not have <strong>to</strong> be a permanent installation. Depending on the configuration of the<br />
conveyance system, portable meters may be utilized. And, there are several types of flow meters<br />
available besides propeller types.<br />
On pressurized systems (sprinkle, trickle) a flow meter in conjunction with a pressure gauge can<br />
indicate whether the system is performing as designed. Local <strong>irrigation</strong> supply companies are a<br />
source for flowmeters or information concerning manufacturers. Note that there are important<br />
restrictions concerning the installation of flow meters. Most important is that there must be clear,<br />
smooth flow in<strong>to</strong> the metering device for an accurate measurement. Recommendations usually range<br />
from five <strong>to</strong> eight pipe diameters of smooth straight pipe upstream of a propeller meter and two <strong>to</strong><br />
four pipe diameters clear downstream (refer <strong>to</strong> Figure 4-5). Follow manufacturer’s recommendations<br />
whenever installing a flowmeter in either open channels or pipelines.<br />
Meter gates for delivering <strong>water</strong> <strong>to</strong> a field or farm ditch come with fac<strong>to</strong>ry calibration curves.<br />
Two simple measurements are all that are needed <strong>to</strong> estimate flow through a meter gate: (1) the<br />
head at the gate and (2) the amount of gate opening.<br />
"Sounding Tube"<br />
1 / " Screw Type Cap<br />
1 4<br />
1 1/ 4 " Pipe Welded <strong>to</strong> Casing<br />
(Pipe should Have<br />
A Smooth Edge)<br />
Column<br />
Mo<strong>to</strong>r<br />
Pump Head<br />
FIGURE 4-5. Schematic of <strong>water</strong> well showing recommended configuration of discharge piping in order <strong>to</strong> test<br />
flow accurately (flow tested by pi<strong>to</strong>t tube) - after Pacific Gas & Electric Company publication 62-8953<br />
20<br />
Eight Times<br />
Diameter<br />
Discharge Pipe<br />
Casing<br />
Ground Surface<br />
Two Times Diamete<br />
1 4<br />
Hole for Pi<strong>to</strong>t / Tube /<br />
3 4
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