West ditch 30 in e mail
Here is the actual valve installed in the concrete structure. Note the numbers on the right side angle. These are calibration marks used to set the desired flow through the valve. In our irrigation system we use units of Miner's Inches of water ("inches"). For those not familiar with this unit of measurement, it was developed during the gold rush era of the mid 1800's. Basically a valve having an area of opening of 10 square inches will flow 10 Miner's Inches of water. The amount of flow through the opening will vary depending on the depth of water above the opening due to increased pressure with increased depth. A more familiar unit of flow is Cubic Feet per Second (CFS) and different western states have defined a Miner's inch slightly differently. In Colorado, 38 Miners Inches equal one CFS, while other states use between 40-50 Miners inch per CFS. To put into another commonly used units of measure, 20 Miner's Inches of water flowing for 24 hours will result in about one Acre-Foot (1 foot deep over 1 Acre) or about 340,000 gallons. As mentioned elsewhere the actual flow depends on depth of water above the opening. The black line is about 6.5 inches above the bottom of the gate, and this seems like a reasonable depth to get at least an approximate calibration. When more than one valve is used with different settings, we tweak the settings until the water level is at the line for the valve that is open the furthest. Note that the openings are not rectangular, rather more like a half-moon shape. Surprisingly when opened up to about half open, the relationship between area and vertical movement is quite linear. For a 12 inch diameter opening like ours, each vertical movement of 1 1/8 inches produces an additional 10 Miner's Inches of water, or put another way, an additional 10 square inches of opening.
