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• APPENDIX C MEASUREMENT OF FLOW <br />C. 1 STAFF GAGES <br />Staff gages are used to measure flow height in weirs, flumes and streams. <br />The gages are simply ruled staffs which are used to measure the height of <br />water above same arbitrary reference point. The staff gages are normally <br />ruled in intervals of 0.01 feet. The procedure for measuring a flow <br />height is as follows: <br />1. Clear any debris away from the staff gage and out of the flume <br />or weir. <br />2. Observe the height of the water relative to the gage. If the <br />water level is oscilating, note the mean water level. In <br />flumes, always measure the gage height on the upstream end of <br />the flume if there is more than one gage. In some situations, <br />the downstream gage height should also be measured. <br />3. Record the gage height to the nearest 0.01-foot on the Data <br />Collection Form. If appropriate, also record the calculated <br />flow rate. Flow through 60 deg. and 90 deg. V-notch weirs can <br />be obtained from Table C-1. Flow through a Cutthroat flume can <br />be obtained from the formulas on Table C-2. <br />• C. 2 TEMPORARY CUTTHROAT FLUME INSTALLATIONS <br />Portable cutthroat flumes can easily be installed in small stream and <br />spring discharges to get spot measurements of flow. The flume is made of <br />stainless steel, has interchangeable bottom sections for different flow <br />rate ranges, and is collapsible. From the top view, the flume is hour- <br />glass shaped with the longer section of the hour glass being the <br />downstream end. The flume can be set for either a 1-inch throat (2.5 to <br />125 gpm) or a 4-inch throat (10 to 500 gpm). The procedure for installing <br />and reading the flume is as follows: <br />1. Assemble the flume with the appropriate throat size. For most <br />of the cases the 1-inch flume will be suitable. <br />2. If possible, select an installation location with sufficient <br />slope to allow the water to freely discharge from the downstream <br />end of the flume. <br />3. Install the flume in the flow path. The flume must be level in <br />both the bank-to-bank and upstream-downstream directions. Use a <br />spirit level to level the flume. No water can be allowed to <br />flow under the flume, and side wall dams should be constructed <br />as required to prevent flow around the flume. <br />4. Wait for flow to stabilize before reading staff gage in flume. <br />Read both the upstream and downstream staff gages. As long as <br />the downstream gage height is 60Y or less of the upstream gage <br />height, the flow through the flume is "free flowing". Otherwise <br />. it is "submerged flow". <br />C-1 <br />