![]() This depth reading must be then converted to a flow in terms of cubic feet per second (CFS) using a rating table for the size of the flume being used. The staff gage reading then is simply the depth, not the amount, of the water flowing through the device. Most staff gages affixed to Parshall flumes are marked in tenths and hundredths of a foot. If the water cannot flow freely from the flume, the device will operate in a state of submergence which will give false high readings on the staff gage. Also, the site chosen for the device must permit the water to flow from the flume unimpeded. The water entering the device should have a uniform velocity and be relatively calm, not turbulent. However, the Parshall flume should not be placed too closely to the head gate or other water flow structures. The State Engineer’s Office requires that the measuring device be located in relatively close proximity to the head gate. It is best to re-establish the ditch’s uniform cross-section and gradient before installing the device to ensure the chosen location for the Parshall flume is suitable and that the finished elevation of the installed flume will be adequate to avoid operational problems.Ĥ. All debris and vegetation should be removed from the ditch where the Parshall flume is to be installed, as well as both up-ditch and down-ditch.ģ. All measuring devices are best installed in a dry, cleaned ditch. It may also allow the ditch to be cleaned less often.Ģ. Generally, a larger device will give you more latitude in site selection. Flat ditches often require larger flumes due to the head loss associated with the device. Also, consider the gradient of your ditch. Choose a Parshall flume that can easily pass that amount. Remember, during free river conditions, you may be able to divert a full ditch of water amounting to many times your total appropriation. While the cost of Parshall flumes usually increases with each larger size, you should not be too conservative in choosing the size suitable for your ditch. A properly installed and operating measuring device will help ensure that you are receiving all of the water you are rightfully entitled.ġ. This brief paper is meant to address the most common problems and concerns with Parshall flumes and offer guidance to water users with the installation, operation and maintenance of these measuring devices. Your livelihood depends on your getting all of the water you are entitled. Too often, water users do not know whether their Parshall flume is providing an accurate measurement of their ditch flow. Indeed, we often find where the water user is being shorted water due to an improperly installed or a poorly maintained measuring device. Our experience has been that the State is not always going to advise you if your measuring device is not accurately measuring your water. Properly installing and maintaining your Parshall flume or any other measuring device is the water user’s responsibility. In the course of our water rights work throughout Wyoming, we often see a variety of misconceptions, issues, and problems clients have concerning the measurement of their ditch water. Rhodes, PresidentĪs the State Engineer’s Office becomes more concerned over accurate water measurement for irrigation ditches throughout Wyoming, flow measuring devices are becoming a requirement. Points To Consider When Installing Parshall Flumes Todd A.
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