PRACTICAL 2-1.pdf

# 5m 15m 25m 65m the calibration formula for the chosen

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A suitable propeller is chosen and seven measurement points are selected at 0.5m, 1.5m, 2.5m ......... 6,5m. The calibration formula for the chosen propeller is: v = 0.25n + 0.01 Measurements are taken as follows: VERTICAL DEPTH REVS REVS/SEC AV VEL DIST PROP D TIME VEL (m) (m) (m) (s) (m/s) (m/s) [1] [2] [3] Left Bank 0.0 0.0 1 0.5 0.5 0.3 100 50 2.0 0.51 0.51 2 1.5 0.8 0.16 130 50 2.6 0.66 0.48 120 50 2.4 0.61 0.61 0.64 110 50 2.2 0.56 3 2.5 1.0 0.2 178 50 3.56 0.9 0.8 140 50 2.8 0.71 0.805 4 3.5 1.1 0.22 160 40 4.0 1.01 0.66 150 40 3.75 0.948 0.948 0.88 140 40 3.5 0.885 5 4.5 1.3 0.26 180 40 4.5 1.135 0.78 160 40 4.0 1.01 1.01 1.04 140 40 3.5 0.885 6 5.5 0.9 0.18 111 40 2.775 0.704 0.54 92 40 2.3 0.585 0.588 0.72 75 40 1.875 0.479 7 6.5 0.5 0.25 95 50 1.9 0.485 0.466 Right Bank 7.0 0.1 [1] Revs/sec = Number of revolutions divided by time [2] Velocity = Revs/sec inserted in calibration formula [3] Average velocity = see 4a.

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69 SEGMENT AREA VELOCITY DISCHARGE (m 2 ) (m/s) (m 3 /s) [4] [5] [6] 0/1 0.125 0.5100 0.0637 1/2 0.650 0.5600 0.3640 2/3 0.900 0.7075 0.6367 3/4 1.050 0.8765 0.9203 4/5 1.200 0.9787 1.1745 5/6 1.100 0.7991 0.8790 6/7 0.700 0.5269 0.3688 7/8 0.150 0.4656 0.0670 TOTAL DISCHARGE = 4.474 m 3 /s = 4.47 m 3 /s [7] [4] Area for each segment = mean of adjoining verticals x the distance between them. [5] Velocity = mean of the adjoining average velocities [6] Discharge = Area x velocity [7] Total discharge = The total of the discharges calculated for each segment. (rounded to 2 significant figures)
70 PRACTICAL 2 CALCULATION OF DISCHARGE VELOCITY-AREA METHOD This practical is totally theoretical and will enable you to gain experience at doing the necessary calculations involved in computing discharge at a river site and aid you when it comes to do a gauging in the field. The following measurements were taken at a river: The calibration formula for the chosen propeller is: v = 0.??n + 0.05 (where ?? equals the last two NON ZERO digits of your student number - for example if your student number is 2012654 32 then your equation becomes v = 0. 32 n +0.05 but If your student number is 201265402 or 201265420 then your equation becomes v = 0.4 2 n +0.05) Width of river : 20 metres VERTICAL DIST WATER DEPTH PROP D REVS TIME (m) (m) (m) (s) Left Bank 0.0 0.2 1 1.0 0.2 0.1 60 100 2 3.0 0.8 0.16 86 100 0.64 62 100 3 5.0 1.1 0.22 135 100 0.66 126 100 0.88 118 100 4 7.0 1.2 0.24 96 60 0.72 88 60 0.96 74 60 5 9.0 0.8 0.16 100 100 0.64 88 100 6 11.0 0.5 0.25 82 100 7 13.0 1.2 0.24 108 100 0.72 102 100 0.96 97 100 8 15.0 2.0 0.40 86 60 1.20 80 60 1.60 74 60 9 17.0 1.8 0.36 108 60 1.08 100 60 1.44 96 60 10 19.0 1.0 0.20 120 100 0.60 110 100 0.80 100 100 Right Bank 20.0 0.0 1) Draw an accurate cross-section of the gauging site and mark the measurement points (use graph paper). 2) Use the table provided to show your calculations. 3) Calculate the discharge at the site.

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71 PRACTICAL 2 ANSWER SHEET (Fill in your answers and do not attach calculations) STUDENT NAME________________________ STUDENT NUMBER________________________ Calibration formula used v=0.____n + 0.05 Vertical Distance Water Depth Prop Depth Revs Time Revs/Sec Velocity Average Velocity 1 2 3 4 5 6 7 8 9 10 Segment Area Velocity Discharge 0/1 1/2 2/3 3/4 4/5 5/6 6/7 7/8 8/9 9/10 10/11 TOTAL DISCHARGE_______________________ Attach your cross section to this page
• Fall '19
• Velocity

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