V Notch Water Flow Measurement

Sharp crested weir background.

V notch water flow measurement. For a triangular or v notch weir the flow rate can be expressed as. Skrenter r instrumentation handbook water and wastewater treatment plants astm d 5242 92 2001. The triangular or v notch thin plate weir is an accurate flow measuring device particularly suited for small flows. Leakage measurement is one of the most important indicator of the overall performance of earth rock fill and concrete dams.

In other words a weir is essentially a partial dam. Quick ref table for v notch weir 0 to 125 l s53ov height above cease to flow point in mm discharge in l s litres per second if the water level when measured is say 65mm above the cease to flow level. It is used to meter flow of water in the channel by measuring the head of water over the v notch crest. V notch and flow meters reference products codes.

Water flow monitoring in open channels is widely employed in environmental and geotechnical field. θ v notch angle. The leakage rate is a function of the water level in the reservoir and depends either from the construction than the behaviour of the dam. Leakage measurement is one of the most important indicator of the overall performance of earth rock fill and concrete dam.

The v notch weir is especially good for measuring a low flow rate because the flow area decreases rapidly as the head over the v notch gets small. Triangular or v notch weir. It works by raising the water level upstream of the weir and then forcing the water to spill over. A weir as defined in the usbr measurement manual is simply an overflow structure built perpendicular to an open channel axis to measure the rate of flow of water.

Head h should be measured at a distance of at least 4h upstream of the weir. Q 8 15 c d 2 g 1 2 tan θ 2 h 5 2 2 where. Thicker than this the nappe may collapse against the downstream face of the weir due to insufficient aeration causing the weir to under indicate the actual flow rate. In order to allow the nappe body of water flowing over the weir crest to spring clear of the weir crest flow edge the crest should be no thicker than 3 mm 1 8 inch thick.

Usbr 1997 suggests using the v notch weir equations for the following conditions. Standard test method for open channel flow measurement of water with thin plate weirs nappe may cling to downstream weir face 90º v notch weir discharge table 2 5 accuracy channel floor 3 5 hmax hmax weir pool point of measurement. Go to the left column then come down the left column till you reach 60 then across to the right to the 5 column your now at 60 5 65. When water flows through some open channel then sometimes it is required to find the flow rate occurring through the channel.