PNS/BAFS/PAES 220:2017 Conveyance Systems PDF
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Central Bicol State University of Agriculture
2017
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This is a Philippine national standard document detailing the process of evaluating open channel conveyance systems, particularly focusing on determining water loss through inflow-outflow methodology. The document outlines methods for measuring flows, selecting appropriate measurement structures, and interpreting data analyses.
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PHILIPPINE NATIONAL STANDARD PNS/BAFS/PAES 220:2017 ICS 65.060.35 Conveyance Systems – Performance Evaluation of Open Channels – Determination of Conveyan...
PHILIPPINE NATIONAL STANDARD PNS/BAFS/PAES 220:2017 ICS 65.060.35 Conveyance Systems – Performance Evaluation of Open Channels – Determination of Conveyance Loss by Inflow- Outflow Method BUREAU OF AGRICULTURE AND FISHERIES STANDARDS BPI Compound Visayas Avenue, Diliman, Quezon City 1101 Philippines Phone (632) 920-6131; (632) 455-2856; (632) 467-9039; Telefax (632) 455-2858 E-mail: [email protected] DEPARTMENT OF Website: www.bafps.da.gov.ph AGRICULTURE PHILIPPINES PHILIPPINE NATIONAL STANDARD PNS/BAFS/PAES 220:2017 Conveyance Systems – Performance Evaluation of Open Channels – Determination of Conveyance Loss by Inflow-Outflow Method Foreword The formulation of this national standard was initiated by the Agricultural Machinery Testing and Evaluation Center (AMTEC) under the project entitled “Enhancement of Nutrient and Water Use Efficiency Through Standardization of Engineering Support Systems for Precision Farming” funded by the Philippine Council for Agriculture, Aquaculture and Forestry and Natural Resources Research and Development - Department of Science and Technology (PCAARRD - DOST). As provided by the Republic Act 10601 also known as the Agricultural and Fisheries Mechanization Law (AFMech Law of 2013), the Bureau of Agriculture and Fisheries Standards (BAFS) is mandated to develop standard specifications and test procedures for agricultural and fisheries machinery and equipment. Consistent with its standards development process, BAFS has endorsed this standard for the approval of the DA Secretary through the Bureau of Agricultural and Fisheries Engineering (BAFE) and to the Bureau of Philippine Standards (BPS) for appropriate numbering and inclusion to the Philippine National Standard (PNS) repository. This standard has been technically prepared in accordance with BPS Directives Part 3:2003 – Rules for the Structure and Drafting of International Standards. The word “shall” is used to indicate mandatory requirements to conform to the standard. The word “should” is used to indicate that among several possibilities one is recommended as particularly suitable without mentioning or excluding others. PHILIPPINE NATIONAL STANDARD PNS/BAFS/PAES 220:2017 Conveyance Systems – Performance Evaluation of Open Channels – Determination of Conveyance Loss by Inflow-Outflow Method 1 Scope This standard specifies the method of determination of seepage and percolation in open channels by inflow-outflow. 2 References The following normative documents contain provisions, which, through reference in this text, constitute provisions of this National Standard: ISO 8368:1999 Flow Measurements in Open Channels Using Structures – Guidelines for Selection of Structure 3 Definitions For the purpose of this standard, the following terms shall apply: 3.1 conveyance loss loss of water from a channel during transport due to seepage and percolation 3.2 water balance accounting of water inflows, such as irrigation and rainfall, and outflows, such as evaporation, seepage and percolation 4 Principle of Inflow-Outflow Method Inflow-outflow is one of the methods used to measure the conveyance losses in open channels where a section of the selected channel shall be analyzed using the water balance approach as shown in Figure 1. The rates of flow of water in the selected channel shall be measured using one of the flow measuring devices/structures and an appropriate flow measurement technique. The difference in the inflow and outflow rates shall be identified as the conveyance losses. 1 Figure 1. Water balance in an open channel 5 Site Selection 5.1 The channel section to be considered shall be accessible for measurement. 5.2 The channel section should be at least 50 m with uniform cross section and grade between the inflow and outflow measuring points. 5.3 Channels with adjoining depressions such as creeks or rivers shall be avoided. 5.4 Bends, steep slopes and segments containing turnouts, valves, gates and other structures shall be avoided. 6 Flow Measuring Structures and Devices The appropriate flow measuring structures and devices should be selected based on ISO 8368:1999 – Flow Measurements in Open Channels Using Structures – Guidelines for Selection of Structure. Various types of flow measuring structures and devices are presented in Annex A. 6.1.1 Weir - an overflow structure built perpendicular to an open channel axis to measure the rate of flow of water 6.1.2 Flume - in-line structure with a geometrically specified constriction built in an open channel such that the center line coincides with the center line of the channel in which the flow is to be measured 2 6.1.3 Orifice - measuring device with a well-defined, sharp-edged opening in a wall through which flow occurs such that the upstream water level is always well above the top of this opening 6.1.4 Current Meter - velocity measuring device used in a sample point through which partial discharge can be obtained 7 Flow Measuring Structure Installation (a) Trapezoidal-notch weir (b) Triangular-notch weir 3 (c) Parshall flume (d) Submerged orifice Figure 2. Installation of flow measuring structures SOURCE: FAO, Irrigation and Drainage Paper 26/2: Small Hydraulic Structures, Vol. 2, 1975 7.2.1 The flow measuring structures shall be installed at the beginning and end of the channel section. The length of this section shall be recorded. 7.2.2 The outflow measuring structure shall be located at a point where backwater does not affect the flow to the extent that false intake rates are measured. 7.2.3 It is recommended that the type and size of the flow measuring structures be of the same type and size to minimize errors. 7.2.4 The beginning and end of the channel section where measurement will be taken shall be marked with stakes. The length of this section shall be recorded. 7.2.5 Current meters can be mounted on rods for stationary measurement (Figure 3) or suspended by cables (Figure 4) to allow free movement vertically and horizontally. 4 Figure 3. Current meter mounted on a rod SOURCE: Turnipseed and Sauer, Discharge Measurements at Gaging Stations: US Geological Techniques and Methods Book 3, Chapter A8. 2010 Cableway Current Meter Water Flow Figure 4. Current meter suspended by a cable SOURCE: Turnipseed and Sauer, Discharge Measurements at Gaging Stations: US Geological Techniques and Methods Book 3, Chapter A8. 2010 7.3.3 Current meters mounted on rods are more suitable in gauging small sections and ditches while suspended cable are for gauging large sections. 7.3.4 When mounting a current meter in a rod, a vaned tail piece shall be used to keep the meter facing into the current. The rod shall be marked to easy determination of depth. 5 8 Flow Measurement 8.1 The length and width of selected channel section shall be determined and recorded. All measurements and time of readings shall be recorded. 8.2 Flow measurement and discharge evaluation using weirs, flumes and orifices are detailed in Annex B. 8.3 Flow measurements and discharge evaluation using current meters are detailed in Annex C. 9 Computation Seepage and percolation losses shall be determined using the formula: (𝑄𝑖 − 𝑄0 )⁄ (𝑆 & 𝑃)𝑙𝑜𝑠𝑠𝑒𝑠 = 𝐿 where: (S&P)losses is the seepage and percolation loss rate, m3/s-m Qi is the inflow rate, m3/s Qo is the outflow rate, m3/s L is the length of channel reach, m 10 Bibliography Food and Agriculture Organization. 1975. Irrigation and Drainage Paper 26/2: Small Hydraulic Structures, Vol. 2 Food and Agriculture Organization. 1993. Irrigation Water Management Training Manual No. 8 Structures for Water Control and Distribution International Institute for Land Reclamation and Improvement. 1989. Discharge Measurement Structures, 3rd Ed. Sarki, A., et al. 2008. Comparison of Different Methods for Computing Seepage Losses in an Earthen Watercourse. Agricultura Tropica et Subtropica, Vol. 41 (4). Sonnichsen, R.P. 1993. Seepage Rates from Irrigation Canals. Water Resources Program: Open-File Technical Report. United States Department of Agriculture. 1993. National Engineering Handbook United States Department of the Interior Bureau of Reclamation. 2001. Water Measurement Manual Turnipseed, D.P. and V.B. Sauer. 2010. Discharge Measurements at Gaging Stations: US Geological Techniques and Methods Book 3, Chapter A8. 6 ANNEX A (informative) Various Types of Commonly Used Flow Measurement Structures Table 1. Types of Weir, Description and Discharge Evaluation Classification Description Discharge Evaluation SHARP-CRESTED/ THIN-PLATE - weir constructed with a crest of vertical thin plate Q = 1.84 (L − 0.2H)H 3⁄2 Q = discharge, m3/s Contracted L = length of crest, m Rectangular H = head (difference between the elevation of the weir crest and the elevation of the water surface in the weir pool), m 2 Q = Cd LH√2gH 3 1 H 2 Cd = 0.615 ( 1 + ) [1 + 0.5 ( ) ] H + 1.6 H+D Q = discharge, m3/s Supressed Cd = discharge coefficient Rectangular L = length of crest, m g = gravitational acceleration, m2/s H = head, m (mm for computing µ) D = distance from the crest to the bottom of the approach channel, mm 7 Q = 1.86 LH 3⁄2 Q = discharge, m3/s Cipoletti L = length of crest, m Contracted H = head (difference between the elevation of the weir crest and the elevation of the water surface in the weir pool), m 8 Q= √2gCd H 5⁄2 15 Q = discharge, m3/s V-notch g = gravitational acceleration, m2/s Cd = discharge coefficient H = head (difference between the elevation of the weir crest and the elevation of the water surface in the weir pool), m 8 Table 2. Types of Flumes, Description and Discharge Evaluation Classification Description Discharge Evaluation Long-throated (Rectangular control 2 2 0.50 section) Q = Cd Cv ( g) bc H11.50 3 3 Q = discharge, m3/s g = gravitational acceleration, m2/s H1 = (3/2)yc = total upstream energy head over the weir crest, m Cd = coefficient of discharge Cv = coefficient due to approach velocity 9 Cut-throat Q = CHa n C = KW1.025 Q = discharge, m3/s C = free flow coefficient Ha = upstream gauge reading (2L/9 from throat) K = flume length coefficient W = throat width, m Parshall Q = kHa u Q = discharge, m3/s k = dimensional factor which is a function of throat width Ha = upstream gauge reading u = 1.522 to 1.60 10 Table 3. Types of Orifices, Description and Discharge Equation Classification Description Discharge Evaluation Circular Sharp-Edged Q = Cd Cv A√2g(h1 − h2 ) Q = Cd Cv A√2g∆h Q = discharge, m3/s Cd = discharge coefficient Cv = velocity coefficient A = area of the orifice, m2 h1-h2 = head differential across the orifice Rectangular Sharp-Edged ∆h = upstream head above the center of the orifice 11 Table 4. Types of Current Meters, Description and Discharge Evaluation Classification Description Discharge Evaluation Anemometer and - uses anemometer cup and propellers Propeller Type for sensing velocity - rated by dragging through tanks of still water at known speeds - does not sense direction of velocity Electromagnetic - produces voltage proportional to the velocity - provides direct analog reading of velocity - provides directional measurements Doppler Type - measures velocity by the change of source light or sound frequency from Velocity-Area Method the frequency of reflections from Midsection Method moving particles Moving Boat Method - uses laser light (laser Doppler velocimeters) or sound (acoustic Doppler velocimeter) Optical Strobe - measures velocity using the strobe Velocity Meter effect with mirrors mounted around a polygon drum reflecting light coming from the water surface. The rate of rotation of the mirror drum is varied until images become steady. With the rate of rotation and the distance from the mirrors to the water surface known, surface velocity can be determined 12 ANNEX B (informative) Discharge Measurement Using Weirs, Flumes and Orifices B.1 Discharge Measurement Using Weirs The following measurement procedure described in this annex can be used for the following standard types of sharp-crested weirs: rectangular, Cipolleti and V-notch. Figure B.1. Dimensions for Discharge Measurement in Sharp-Crested Weirs SOURCE: FAO, Irrigation Water Management Training Manual No. 8 Structures for Water Control and Distribution, 1993 B.1.1 Establish the recommended dimensions shown in Figure B.1. B.1.2 Estimate the maximum discharge to be measured which will determine the corresponding maximum head of water over the weir crest. Tables B.1 to B.3 show the corresponding head, H based on the discharge. B.1.3 From the value of H, the level of the crest relative to the channel bed shall be at least twice higher than H. B.1.4 The distance between the gauge and weir shall be at least four times than H. B.1.5 The gauge’s zero mark shall be at the same elevation with the weir crest. B.1.6 Read the water level on the gauge and record as H. B.1.7 Compute for the discharge Q based on the type of weir using the discharge evaluation equations shown in Annex A. 13 Table B.1. Discharge-Head Relationship for a Rectangular Weir Discharge (Q), L/s Head Length of Crest (L), m (H), m 0.25 0.50 0.75 1.00 1.25 1.50 0.01 0 1 1 2 2 3 0.015 1 2 3 3 4 5 0.02 1 3 4 5 6 8 0.03 2 5 7 10 12 14 0.04 4 7 11 15 18 22 0.05 5 10 15 20 26 31 0.06 6 13 20 27 33 40 0.08 10 20 31 41 51 62 0.10 13 28 42 57 72 86 0.12 17 36 56 75 94 113 0.14 45 70 94 118 142 0.16 55 85 114 143 173 0.18 65 100 135 171 206 0.20 76 117 158 199 0.25 104 161 219 0.30 209 SOURCE: FAO, Irrigation Water Management Training Manual No. 8 Structures for Water Control and Distribution, 1993 Table B.2. Discharge-Head Relationship for a Cipoletti Weir Discharge (Q), L/s Head Length of Crest (L), m (H), m 0.25 0.50 0.75 1.00 1.25 1.50 0.01 0 1 1 2 2 3 0.015 1 2 3 3 4 5 0.02 1 3 4 5 7 8 0.03 2 5 7 10 12 14 0.04 4 7 11 15 19 22 0.05 5 10 16 21 26 31 0.06 7 14 21 27 34 41 0.08 11 21 32 42 53 63 0.10 15 29 44 59 74 88 0.12 19 39 58 77 97 116 0.14 49 73 97 122 146 0.16 60 89 119 149 179 0.18 71 107 142 178 213 0.20 83 125 166 208 0.25 116 174 233 0.30 229 SOURCE: FAO, Irrigation Water Management Training Manual No. 8 Structures for Water Control and Distribution, 1993 14 Table B.3. Discharge-Head Relationship for a 900 V-notch Weir H, m Q, L/s H, m Q, L/s H, m Q, L/s 0.01 0.0 0.08 2.5 0.15 12 0.02 0.1 0.09 3.3 0.16 14 0.03 0.2 0.10 4.3 0.17 16 0.04 0.4 0.11 5.5 0.18 19 0.05 0.8 0.12 6.8 0.19 22 0.06 1.2 0.13 8.3 0.20 24 0.07 1.8 0.14 10 SOURCE: FAO, Irrigation Water Management Training Manual No. 8 Structures for Water Control and Distribution, 1993 B.2 Discharge Measurement Using Flumes B.2.1 Determine the degree of submergence, which is the ratio of the downstream head, Hb to the upstream head, Ha. Hb Degree of Submergence (%) = × 100 Ha B.2.2 If the computed degree of submergence is equal to or below the free flow limit indicated in Table B.4, free flow condition exists. Read the free flow discharge (Qfree flow) from Table B.5 based on Ha and throat width, W. Table B.4. Free flow limits for various sizes of Parshall Flumes Width of throat (W) Free flow limit of Hb/Ha 15.2 cm to 23 cm (6 in to 9 in) 60% 30.5 cm to 244 cm (1 ft to 8 ft) 70% SOURCE: FAO, Irrigation and Drainage Paper 26/2: Small Hydraulic Structures, Vol. 2, 1975 B.2.3 If the computed degree of submergence is greater than the free flow limit indicated in Table B.4, B.2.3.1 If W = 15.2 cm (6 in), use Figure B.2 directly B.2.3.2 If W = 23 cm (9 in), use Figure B.3 directly B.2.3.3 If W = 30.5 cm (1 ft), use the correction diagram shown in Figure B.4 for Qcorrection B.2.3.4 If W > 30.5 cm (1ft), use Figure B.4 and the multiplying factor shown in Table B.6 based on the size of flume for Qcorrection B.2.4 Apply the negative correction to the free flow discharge to determine the discharge from the submerged flow (Qsubmerged flow). Qsubmerged flow = Qfree flow − Qcorrection 15 Table B.5. Free Flow Discharge Values for Parshall Flumes Discharge (Q), m3/s for Throat Widths (W) of- Head (Ha) 15.24 22.86 30.48 45.72 60.96 91.44 121.92 152.40 182.88 cm cm cm cm cm cm cm cm cm cm 0.50 ft 0.75 ft 1.00 ft 1.50 ft 2.00 ft 3.00 ft 4.00 ft 5.00 ft 6.00 ft 3.00 0.0015 0.0025 0.0033 0.0048 3.50 0.0019 0.0032 0.0042 0.0060 4.00 0.0024 0.0039 0.0052 0.0074 4.50 0.0028 0.0047 0.0062 0.0089 0.0116 0.0169 5.00 0.0034 0.0055 0.0072 0.0105 0.0137 0.0200 5.50 0.0039 0.0063 0.0084 0.0122 0.0159 0.0232 6.00 0.0045 0.0072 0.0096 0.0139 0.0182 0.0266 0.0348 0.0429 6.50 0.0051 0.0082 0.0108 0.0157 0.0206 0.0302 0.0395 0.0487 7.00 0.0057 0.0092 0.0121 0.0176 0.0231 0.0339 0.0444 0.0548 7.50 0.0064 0.0102 0.0134 0.0196 0.0257 0.0378 0.0495 0.0611 0.0726 8.00 0.0071 0.0112 0.0148 0.0217 0.0285 0.0418 0.0549 0.0677 0.0805 8.50 0.0078 0.0123 0.0162 0.0238 0.0313 0.0459 0.0604 0.0746 0.0887 9.00 0.0085 0.0135 0.0177 0.0260 0.0342 0.0503 0.0661 0.0817 0.0971 9.50 0.0093 0.0146 0.0192 0.0282 0.0372 0.0547 0.0720 0.0890 0.1059 10.00 0.0100 0.0158 0.0208 0.0306 0.0402 0.0593 0.0780 0.0965 0.1149 10.50 0.0108 0.0170 0.0224 0.0329 0.0434 0.0640 0.0843 0.1043 0.1242 11.00 0.0117 0.0183 0.0240 0.0354 0.0466 0.0688 0.0907 0.1123 0.1338 11.50 0.0125 0.0196 0.0254 0.0379 0.0500 0.0738 0.0973 0.1205 0.1436 12.00 0.0134 0.0209 0.0274 0.0405 0.0534 0.0789 0.1040 0.1290 0.1537 12.50 0.0143 0.0222 0.0292 0.0431 0.0569 0.0841 0.1110 0.1376 0.1640 13.00 0.0152 0.0236 0.031 0.0458 0.0604 0.0894 0.1181 0.1464 0.1746 13.50 0.0161 0.0250 0.0328 0.0485 0.0641 0.0949 0.1253 0.1555 0.1854 14.00 0.0171 0.0264 0.0347 0.0513 0.0678 0.1004 0.1327 0.1647 0.1965 14.50 0.0180 0.0279 0.0360 0.0541 0.0716 0.1061 0.1403 0.1741 0.2078 15.00 0.0190 0.0294 0.0385 0.0570 0.0755 0.1119 0.1480 0.1838 0.2194 15.50 0.0200 0.0309 0.4050 0.0600 0.0794 0.1178 0.1558 0.1936 0.2351 16.00 0.0211 0.0324 0.4250 0.0630 0.0834 0.1238 0.1638 0.2036 0.2431 16.50 0.0221 0.0340 0.0445 0.0661 0.0875 0.1299 0.1720 0.2138 0.2554 17.00 0.0232 0.0356 0.0466 0.0692 0.0916 0.1361 0.1803 0.2242 0.2678 17.50 0.0243 0.0372 0.0487 0.0723 0.0958 0.1425 0.1887 0.2347 0.2805 18.00 0.0254 0.0388 0.0508 0.0755 0.1001 0.1489 0.1973 0.2455 0.2934 18.50 0.0265 0.0405 0.0530 0.0788 0.1045 0.1554 0.2060 0.2564 0.3065 19.00 0.0276 0.0422 0.0552 0.0821 0.1089 0.1620 0.2149 0.2675 0.3198 19.50 0.0288 0.0439 0.0574 0.0854 0.1133 0.1688 0.2239 0.2787 0.3333 20.00 0.0300 0.0456 0.0597 0.0888 0.1179 0.1756 0.2330 0.2901 0.3471 20.50 0.0312 0.0474 0.0619 0.0923 0.1225 0.1825 0.2423 0.3017 0.3610 21.00 0.0324 0.0492 0.0643 0.0957 0.1271 0.1896 0.2516 0.3135 0.3752 21.50 0.0336 0.0509 0.0666 0.0993 0.1319 0.1967 0.2612 0.3254 0.3895 16 Table B.5 (continued) 22.00 0.0349 0.0528 0.0690 0.1029 0.1366 0.2039 0.2708 0.3375 0.4040 22.50 0.0361 0.0546 0.0714 0.1065 0.1415 0.2112 0.2806 0.3498 0.4188 23.00 0.0374 0.0565 0.0738 0.1101 0.1464 0.2186 0.2905 0.3622 0.4337 23.50 0.0387 0.0584 0.0762 0.1138 0.1513 0.2261 0.3005 0.3748 0.4489 24.00 0.0400 0.0603 0.0787 0.1176 0.1564 0.2337 0.3107 0.3875 0.4642 24.50 0.0413 0.0622 0.0812 0.1214 0.1614 0.2413 0.3210 0.4004 0.4797 25.00 0.0427 0.0642 0.0838 0.1252 0.1666 0.2491 0.3314 0.4134 0.4954 25.50 0.0440 0.0661 0.0863 0.1291 0.1718 0.2569 0.3419 0.4267 0.5113 26.00 0.0454 0.0681 0.0889 0.1330 0.1770 0.2649 0.3525 0.4400 0.5274 26.50 0.0468 0.0701 0.0915 0.1370 0.1823 0.2729 0.3633 0.4535 0.5436 27.00 0.0460 0.0722 0.0942 0.1410 0.1877 0.2810 0.3741 0.4672 0.5601 27.50 0.0482 0.0742 0.0968 0.1450 0.1931 0.2892 0.3831 0.4810 0.5767 28.00 0.0496 0.0763 0.0995 0.1491 0.1986 0.2975 0.3962 0.4949 0.5935 28.50 0.0510 0.0784 0.1023 0.1532 0.2041 0.3058 0.4075 0.5090 0.6105 29.00 0.0525 0.0805 0.1050 0.1573 0.2097 0.3143 0.4188 0.5233 0.6277 29.50 0.0539 0.0826 0.1078 0.1615 0.2153 0.3228 0.4303 0.5377 0.6451 30.00 0.0554 0.0848 0.1106 0.1658 0.2210 0.3314 0.4418 0.5522 0.6626 30.50 0.0569 0.087 0.1134 0.1700 0.2267 0.3401 0.4535 0.5669 0.6803 31.00 0.0583 0.0892 0.1162 0.1743 0.2325 0.3489 0.4653 0.5817 0.6980 31.50 0.0599 0.0914 0.1191 0.1782 0.2383 0.3577 0.4772 0.5767 0.7162 32.00 0.0614 0.0936 0.1219 0.1831 0.2442 0.3667 0.4892 0.6118 0.7344 32.50 0.0629 0.0959 0.1248 0.1876 0.2502 0.3757 0.5013 0.6270 0.7528 33.00 0.0645 0.0981 0.1278 0.1919 0.2562 0.3848 0.5135 0.6424 0.7713 33.50 0.0661 0.1004 0.1307 0.1964 0.2622 0.3939 0.5259 0.6579 0.7901 34.00 0.0677 0.1027 0.1337 0.2010 0.2683 0.4052 0.5385 0.6736 0.8089 34.50 0.0693 0.105 0.1367 0.2055 0.2744 0.4125 0.5508 0.6893 0.8280 35.00 0.0709 0.1074 0.1398 0.2101 0.2806 0.4219 0.5635 0.7053 0.8472 35.50 0.0725 0.1097 0.1428 0.2145 0.2869 0.4314 0.5762 0.7213 0.8666 36.00 0.0742 0.1121 0.1459 0.2194 0.2932 0.4410 0.5891 0.7325 0.8861 36.50 0.0758 0.1145 0.149 0.2241 0.2995 0.4506 0.6021 0.7538 0.9051 37.00 0.0775 0.1169 0.1521 0.2289 0.3059 0.4603 0.6151 0.7703 0.9257 37.50 0.0792 0.1193 0.1552 0.2337 0.3123 0.4703 0.6283 0.7869 0.9457 38.00 0.0809 0.1218 0.1584 0.2385 0.3188 0.4799 0.6416 0.8036 0.9659 38.50 0.0826 0.1242 0.1616 0.2433 0.3253 0.4898 0.6549 0.8204 0.9863 39.00 0.0843 0.1267 0.1648 0.2482 0.3319 0.4998 0.6684 0.8374 1.007 39.50 0.0861 0.1292 0.168 0.2531 0.3385 0.5099 0.6820 0.8545 1.027 40.00 0.0878 0.1317 0.1713 0.2580 0.3452 0.5201 0.6957 0.8718 1.048 40.50 0.0896 0.1342 0.1745 0.2630 0.3519 0.5303 0.7094 0.8891 1.069 41.00 0.0914 0.1368 0.1778 0.2680 0.3586 0.5406 0.7233 0.9066 1.090 41.50 0.0932 0.1394 0.1811 0.2731 0.3654 0.5509 0.7373 0.9242 1.112 42.00 0.0950 0.1419 0.1845 0.2782 0.3783 0.5614 0.7513 0.9419 1.133 42.50 0.0968 0.1445 0.1878 0.2833 0.3792 0.5719 0.7655 0.9598 1.155 17 Table B.5 (continued) 43.00 0.0986 0.1471 0.1912 0.2884 0.3861 0.5824 0.7798 0.9778 1.176 43.50 0.1004 0.1498 0.1946 0.2936 0.3931 0.5931 0.7941 0.9959 1.198 44.00 0.1023 0.1524 0.198 0.2988 0.4001 0.6038 0.8086 1.014 1.220 44.50 0.1042 0.1551 0.2014 0.3040 0.4072 0.6140 0.8231 1.033 1.243 45.00 0.1060 0.1577 0.2049 0.3093 0.4143 0.6254 0.8377 1.051 1.265 45.50 0.1079 0.1604 0.2084 0.3146 0.4214 0.6363 0.8525 1.070 1.287 46.00 0.1631 0.2119 0.3199 0.4286 0.6473 0.8673 1.088 1.310 46.50 0.1659 0.2154 0.3253 0.4359 0.6384 0.8822 1.107 1.333 47.00 0.1686 0.2189 0.3307 0.4432 0.6695 0.8972 1.126 1.356 47.50 0.1713 0.2225 0.3361 0.4505 0.6807 0.9124 1.145 1.379 48.00 0.1741 0.2260 0.3416 0.4579 0.6919 0.9276 1.164 1.402 48.50 0.1769 0.2296 0.3471 0.4653 0.7033 0.9428 1.184 1.423 49.00 0.1797 0.2333 0.3526 0.4727 0.7147 0.9582 1.203 1.449 49.50 0.1825 0.2369 0.3581 0.4802 0.7261 0.9737 1.223 1.473 50.00 0.1853 0.2405 0.3637 0.4878 0.7376 0.9893 1.242 1.496 50.50 0.1882 0.2442 0.3693 0.4953 0.7492 1.005 1.262 1.520 51.00 0.1910 0.2479 0.3750 0.5030 0.7609 1.021 1.282 1.544 51.50 0.1939 0.2516 0.3806 0.5106 0.7726 1.037 1.302 1.569 52.00 0.1968 0.2553 0.3863 0.5183 0.7844 1.052 1.322 1.593 52.50 0.1997 0.25911 0.3921 0.5261 0.7962 1.068 1.342 1.617 53.00 0.2026 0.2629 0.3978 0.5339 0.8081 1.085 1.363 1.642 53.50 0.2056 0.2666 0.4036 0.5417 0.8201 1.101 1.383 1.667 54.00 0.2085 0.2704 0.4094 0.5495 0.8321 1.117 1.404 1.692 54.50 0.2115 0.2743 0.4153 0.5575 0.8442 1.133 1.424 1.717 55.00 0.2144 0.2781 0.4212 0.5654 0.8564 1.150 1.445 1.742 55.50 0.2174 0.2820 0.4271 0.5734 0.8686 1.166 1.466 1.767 56.00 0.2204 0.2858 0.4330 0.5814 0.8809 1.183 1.487 1.793 56.50 0.2235 0.2897 0.4390 0.5895 0.8932 1.200 1.508 1.818 57.00 0.2265 0.2936 0.4449 0.5976 0.9057 1.217 1.529 1.844 57.50 0.2295 0.2976 0.4510 0.6057 0.9181 1.233 1.551 1.870 58.00 0.2326 0.3015 0.4570 0.6139 0.9307 1.250 1.572 1.896 58.50 0.2357 0.3055 0.4631 0.6221 0.9433 1.267 1.594 1.922 59.00 0.2388 0.3095 0.4692 0.6304 0.9559 1.285 1.615 1.948 59.50 0.2419 0.3135 0.4753 0.6387 0.9686 1.302 1.637 1.975 60.00 0.245 0.3175 0.4815 0.6470 0.9814 1.319 1.659 2.001 60.50 0.2481 0.3215 0.4877 0.6554 0.9943 1.336 1.681 2.028 61.00 0.2513 0.3256 0.4939 0.6638 1.007 1.354 1.703 2.055 61.50 0.3296 0.5001 0.6723 1.020 1.371 1.725 2.082 62.00 0.3337 0.5064 0.6808 1.033 1.389 1.748 2.109 62.50 0.3378 0.5127 0.6893 1.046 1.407 1.770 2.136 63.00 0.3420 0.5190 0.6978 1.059 1.425 1.793 2.163 63.50 0.3461 0.5254 0.7064 1.073 1.443 1.815 2.191 18 Table B.5 (continued) 64.00 0.3503 0.5317 0.7151 1.086 1.460 1.838 2.218 64.50 0.3544 0.5381 0.7238 1.099 1.479 1.861 2.246 65.00 0.3586 0.5446 0.7325 1.113 1.497 1.884 2.274 65.50 0.3628 0.5510 0.7412 1.126 1.515 1.907 2.302 66.00 0.3671 0.5575 0.7500 1.139 1.533 1.930 2.330 66.50 0.3713 0.5640 0.7588 1.153 1.552 1.953 2.538 67.00 0.3755 0.5706 0.7677 1.167 1.570 1.977 2.386 67.50 0.3798 0.5771 0.7766 1.180 1.588 2.000 2.415 68.00 0.3841 0.5837 0.7855 1.194 1.607 2.024 2.443 68.50 0.3884 0.5903 0.7945 1.208 1.626 2.047 2.472 69.00 0.3927 0.5970 0.8035 1.222 1.645 2.071 2.501 69.50 0.971 0.6036 0.8125 1.236 1.663 2.095 2.530 70.00 0.4014 0.6103 0.8216 1.249 1.682 2.119 2.559 70.50 0.4058 0.6170 0.8307 1.263 1.701 2.143 2.588 71.00 0.4102 0.6238 0.8399 1.278 1.720 2.167 2.617 71.50 0.4146 0.6306 0.8491 1.292 1.739 2.192 2.647 72.00 0.4190 0.6373 0.8583 1.306 1.759 2.216 2.676 72.50 0.4235 0.6442 0.8675 1.320 1.778 2.240 2.706 73.00 0.4279 0.6510 0.8768 1.334 1.797 2.265 2.736 73.50 0.4324 0.6579 0.8862 1.349 1.817 2.290 2.766 74.00 0.4369 0.6648 0.8955 1.363 1.836 2.314 2.796 74.50 0.4414 0.6717 0.9049 1.378 1.856 2.339 2.826 75.00 0.4459 0.6787 0.9143 1.392 1.876 2.364 2.856 SOURCE: FAO, Irrigation and Drainage Paper 26/2: Small Hydraulic Structures, Vol. 2, 1975 19 Figure B.2. Rate of Submerged Flow through a 15.2 cm (6 in) Parshall Flume SOURCE: FAO, Irrigation and Drainage Paper 26/2: Small Hydraulic Structures, Vol. 2, 1975 Figure B.3 – Rate of Submerged Flow through a 23 cm (9 in) Parshall Flume SOURCE: FAO, Irrigation and Drainage Paper 26/2: Small Hydraulic Structures, Vol. 2, 1975 20 Figure B.4. Correction Diagram for a 30.5 cm (1 ft) Parshall Flume SOURCE: FAO, Irrigation and Drainage Paper 26/2: Small Hydraulic Structures, Vol. 2, 1975 Table B.6. Multiplying Factor for Various Throat Widths Throat Width, W Multiplying Factor, M ft cm 1 30.5 1.0 1.5 45.7 1.4 2 61.0 1.8 3 91.5 2.4 4 122.0 3.1 5 152.5 3.7 6 183.0 4.3 SOURCE: FAO, Irrigation and Drainage Paper 26/2: Small Hydraulic Structures, Vol. 2, 1975 21 B.3 Discharge Measurement Using Orifice 𝑄 = 𝐶𝑑 𝐶𝑣 𝐴√2𝑔(ℎ1 − ℎ2 ) 𝑄 = 𝐶𝑑 𝐶𝑣 𝐴√2𝑔∆ℎ where: Q is the discharge (m3/s) Cd is the discharge coefficient Cv is the velocity coefficient A is the area of the orifice (m2) h1-h2 is the head differential across the orifice ∆h is the upstream head above the center of the orifice Table B.7. Average Discharge Coefficients for Circular Orifices (negligible approach velocity) Orifice Diameter (D), m Cd (free flow) Cd (submerged flow) 0.020 0.61 0.57 0.025 0.62 0.58 0.035 0.64 0.61 0.045 0.63 0.61 0.050 0.62 0.61 0.065 0.61 0.60 ≥ 0.075 0.60 0.60 SOURCE: ILRI, Discharge Measurement Structures, 3rd Ed. 1989 22 ANNEX C (informative) Discharge Measurement Using Current Meters C.1 Velocity-Area Method C.1.1 Select a measuring section and determine the overall width and depth. C.1.2 Layout the subsection verticals such that no subsection has more than 10% of the discharge in it. C.1.3 It is preferred that the width of the subsection lessens as depths and velocities increase. C.1.4 The initial point can be either bank and the edge of water is the first subsection. C.1.5 Measure and record the following for each subsection: distance from the initial point depth meter position number of revolutions time interval horizontal angle of flow C.1.6 Measure in succession until completed to the opposite bank. C.1.7 Compute for the discharge using the formula below. 𝑛 𝑄 = ∑ 𝑎𝑖 𝑣𝑖 𝑖=1 where: Q is the total discharge (m3/s) ai is the cross-section area for the ith segment of the n segments into which the cross section is divided (m2) vi is the corresponding mean velocity of the flow normal to the ith segment or vertical (m/s) C.2 Midsection Method C.2.1 This method assumes that the mean velocity in each vertical represents the mean velocity in a partial rectangular area. C.2.2 The cross-section area for a segment extends laterally from half the distance from the preceding vertical to half the distance to the next vertical, and vertically from the water surface to the channel bed. 23 C.2.3 Measure the velocity at one or more selected points in the vertical. C.2.4 Compute for the partial discharge using the formula below: (𝑏𝑖 − 𝑏(𝑖−1) ) (𝑏(𝑖+1) − 𝑏𝑖 ) 𝑏(𝑖+1) − 𝑏(𝑖−1) 𝑞𝑖 = 𝑣𝑖 [ + ] 𝑑𝑖 = 𝑣𝑖 [ ] 𝑑𝑖 2 2 2 where: qi is the discharge through partial section i (m3/s) vi is the mean velocity at location i (m/s) bi is the distance from initial point to location i (m) b(i-1) is the distance from initial point to preceding location (m) b(i+1) is the distance from initial point to next location (m) di is the depth of water at location i (m) Figure C.1. Cross-section measurements for the midsection method SOURCE: Turnipseed and Sauer, Discharge Measurements at Gaging Stations: US Geological Techniques and Methods Book 3, Chapter A8, 2010 24 Technical Working Group (TWG) for the Development of Philippine National Standard for Conveyance Systems – Performance Evaluation of Open Channels – Determination of Conveyance Loss by Inflow-Outflow Method Chair Engr. Bonifacio S. Labiano National Irrigation Administration Members Engr. Felimar M. Torizo Dr. Teresita S. Sandoval Board of Agricultural Engineering Bureau of Soils and Water Management Professional Regulation Commission Department of Agriculture Dr. Armando N. Espino Jr. Dr. Elmer D. Castillo Central Luzon State University Philippine Society of Agricultural Engineers Dr. Roger A. Luyun Jr. Engr. Francia M. Macalintal University of the Philippines Los Baños Philippine Council for Agriculture and Fisheries Department of Agriculture Project Managers Engr. Darwin C. Aranguren Engr. Romulo E. Eusebio Engr. Mary Louise P. Pascual Engr. Fidelina T. Flores Engr. Marie Jehosa B. Reyes Ms. Micah L. Araño Ms. Caroline D. Lat Mr. Gerald S. Trinidad University of the Philippines Los Baños – Agricultural Machinery Testing and Evaluation Center