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Measurement of Stream Discharge by Wading Water Resources Investigations Report 00-4036 By K. M. Nolan and R. R. Shields.

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Presentation on theme: "Measurement of Stream Discharge by Wading Water Resources Investigations Report 00-4036 By K. M. Nolan and R. R. Shields."— Presentation transcript:

1 Measurement of Stream Discharge by Wading Water Resources Investigations Report By K. M. Nolan and R. R. Shields

2 Agenda Water Resources Investigations Report Test How class works Instructions for viewing and navigating through this training class can be found in the “Intro.html” file, which is on the CD- ROM containing this presentation. “Intro.html”

3 Agenda Water Resources Investigations Report Test Class Credit Listed as Training Class SW1271 with the National Training Center of U.S. Geological Survey Supervisor may ask to see a copy of the completed test

4 Agenda Water Resources Investigations Report Test Links to reference materials sws/fieldmethods USGS memos Linked Text

5 Agenda Water Resources Investigations Report Test Agenda How this class works The velocity-area concept Making the measurement Measuring width Measuring depth Wading rod use Measuring velocity Site selection Safety Measurement notes Blackfoot River as an example Starting the measurement The front sheet Inside the note sheet Job Hazard Analysis Horizontal angle correction Computing subsection width and depthComputing subsection width and depth Recording velocity Recording discharge Finalizing measurement Mean Gage Height Accuracy The control Point of zero flow Plotting on rating Test References Acknowledgements

6 Agenda Water Resources Investigations Report Test x Water Velocity Cross section area Discharge = (Area of water in cross section) x (Water velocity) THE VELOCITY-AREA METHOD

7 Agenda Water Resources Investigations Report Test Discharge of each sub-section = Area x Average Water Velocity Channel cross section is divided into numerous sub sections

8 Agenda Water Resources Investigations Report Test Width Depth Area = Width x Depth Area of each sub-section determined by directly measuring width and depth

9 Agenda Water Resources Investigations Report Test Water velocity in each sub-section is estimated using a current meter to measure water velocity at selected locations

10 Agenda Water Resources Investigations Report Test Total Discharge = ((Area 1 x Velocity 1 ) + (Area 2 x Velocity 2 ) + ….. (Area n x Velocity n )) 123 Stream discharge is sum of discharges in all sub-sections n

11 Agenda Water Resources Investigations Report Test Making the Measurement Verticals should be spaced so no subsection has more than 10% of the total discharge Ideal measurement has no more than 5% of total discharge in any subsection Should have between 20 and 30 subsections Spacing between verticals should be closer in those parts of cross section with greater depths and velocities.

12 Agenda Water Resources Investigations Report Test Measuring Cross-Section Area Width

13 Agenda Water Resources Investigations Report Test Measuring Cross-Section Area Width (cont.) Taglines usually have marks One mark every 2 ft Some taglines have: Two marks every 10 ft Three marks every 100 ft. Distances between marks are estimated or measured

14 Agenda Water Resources Investigations Report Test Measuring Cross-Section Area Depth Wading rod is marked every 0.1 foot

15 Agenda Water Resources Investigations Report Test Wading Rod Use Top Setting Mechanism

16 Agenda Water Resources Investigations Report Test Depth 2.6 ft. Total Depth 0.8 Depth 0.2 depth Setting Rod Depth Scale Rod set so meter placed at 0.6 (2.6 ft) 2.08 ft ft ft. Wading Rod Use (cont.)

17 Agenda Water Resources Investigations Report Test Wading Rod Use (cont.) Must estimate depth when velocity causes “pile-up” on rod. Visually extend water surface to rod.

18 Agenda Water Resources Investigations Report Test Wading Rod Use Stand beside and downstream of rod

19 Agenda Water Resources Investigations Report Test Velocity Determination USGS generally uses Price current meters AA for large depths Pygmy for shallow depths Standard AA Meter Pygmy Meter See OSW memos and

20 Agenda Water Resources Investigations Report Test Meter Use

21 Agenda Water Resources Investigations Report Test Spin Tests A spin test should be performed on all meters: Before each field trip When performance is suspect. Before and after repairs A log of all spin tests must be maintained See OSW memo for policy on spin testsmemo 89.07

22 Agenda Water Resources Investigations Report Test Meter Performance Meter performance should also be checked before and after each measurement Spin meter and note if meter spins freely and comes to gradual stop

23 Agenda Water Resources Investigations Report Test Meter Care Meter care and maintenance is discussed in OSW memorandum memorandum 99.06

24 Agenda Water Resources Investigations Report Test Headset and Stopwatch Velocity is determined by placing meter in stream and counting number of revolutions in a measured amount of time Stop Watch and Headset

25 Agenda Water Resources Investigations Report Test Digitizer, Aquacalc and DMX 1 Newer units are now available that compute velocity and/or discharge Digitizer Aquacalc DMX 1 Use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government

26 Agenda Water Resources Investigations Report Test Marking Meter Meter revolutions can sometimes be counted manually by marking one meter cup.

27 Agenda Water Resources Investigations Report Test Rating Table Velocity can then determined using a current-meter rating table Partial listing of standard rating #2

28 Agenda Water Resources Investigations Report Test Rating Table Equations Equations for standard Rating Tables: For AA meter V = R For pygmy meter V = R R = Revolutions per second See: OSW Memo 99.05Memo Standard rating table #2 for AA meterrating table #2 for AA meter Standard rating table #2 for Pygmy meterrating table #2 for Pygmy meter

29 Agenda Water Resources Investigations Report Test Velocity from Digitizer, Aquacalc, and DMX Current meter digitizers Aquacalcs and DMX units have equations for rating table built in. These devices provide direct computation of velocity

30 Agenda Water Resources Investigations Report Test Measure velocity for at least 40 seconds Velocity should be measured for at least 40 seconds Evens out short- term velocity fluctuations

31 Agenda Water Resources Investigations Report Test Average Velocity The goal is to represent the average velocity in the vertical Measured at 0.6 the depth when depths are shallow Measured at 0.2 and 0.8 the depth when depths are large. These two velocities are averaged to represent average velocity in the vertical Typical velocity profile

32 Agenda Water Resources Investigations Report Test Velocity Measurement Methods Guide to velocity-measurement methods

33 Agenda Water Resources Investigations Report Test Non Standard Conditions Use of 0.6 and 0.2/0.8 methods assume velocity profile is logarithmic. Velocity should decrease closer to bottom due to friction If velocity at 0.8 depth is greater than velocity at 0.2 depth or if velocity at 0.2 depth is twice the velocity at 0.8 depth then the velocity profile is considered abnormal and the three-point method must be used (see next slide).

34 Agenda Water Resources Investigations Report Test Three-Point Method Three-point method computed by averaging velocity measured at 0.2 and 0.8 the depth and averaging that result with velocity measured at 0.6 the depth.

35 Agenda Water Resources Investigations Report Test Site Selection Reach should be straight and uniform for a long enough distance to provide uniform flow through the measuring section Streambed should be stable and free of large rocks, weeds, and protruding obstructions. Upstream view of excellent measuring section, Little Blackfoot River

36 Agenda Water Resources Investigations Report Test ControlMeasurement Section W 5W2W Site Selection (cont.) Straight and uniform for a distance long enough to support uniform flow Riffle Flow

37 Agenda Water Resources Investigations Report Test Safety - First Standard PFD Throw Bag Inflatable PFD “Safety First, Every Job, Every Time” (Department of Interior Policy)

38 Agenda Water Resources Investigations Report Test Safety – On Line

39 Agenda Water Resources Investigations Report Test Safety – Memo Water Resources Division Memorandum 99.32

40 Agenda Water Resources Investigations Report Test Safety – miscellaneous memos Click on page image to view memo

41 Agenda Water Resources Investigations Report Test Safety – Responsibilities WRD Memo “Both supervisors and employees will be held accountable if safety policies are not followed.” Winter measurement Snake River near Moran, WY

42 Agenda Water Resources Investigations Report Test Safety - PFDs See WRD Memo Personal Flotation Devices (PFDs) must be worn unless the job hazard analysis states otherwise. Standard PFD Suspender-type PFD

43 Agenda Water Resources Investigations Report Test Protection against hypothermia is required when conditions warrant. WRD Safety Home Page contains information on protection against hypothermia protection against hypothermia Use of cold water protective Personal Flotation Devices increases protection against hypothermia Float Coat Safety- Hypothermia

44 Agenda Water Resources Investigations Report Test Safety - Rescue Look downstream and think rescue Downstream view of measurement section, Clark Fork, near Gold Cr., MT

45 Agenda Water Resources Investigations Report Test Safety - Rescue Throw bags contain a line that can be thrown to colleagues who need help. See Mississippi report on use of multi- person field tripsMississippi report

46 Agenda Water Resources Investigations Report Test Wading Safely When wading, proceed carefully Use wading rod to probe bottom ahead of you

47 Agenda Water Resources Investigations Report Test Wading Safely (cont.) Wade carefully and think about hazards downstream How would you execute a self-rescue at this site? Have a plan before you begin

48 Agenda Water Resources Investigations Report Test Safety – Conditions Around You Be aware of potentially dangerous conditions upstream and downstream Ice Debris Dam Releases Boats Snake River near Moran, WY

49 Agenda Water Resources Investigations Report Test Safety – Measuring Width Laser distance meter Use laser distance meter, rather than a tag line, to measure channel width and distances when boat traffic is possible

50 Agenda Water Resources Investigations Report Test Safety - Traction Use of felt soles or metal cleats on the bottom of your waders can significantly improve traction. Be careful, felt bottoms can become slick if algae is present.

51 Agenda Water Resources Investigations Report Test Safety - Waders Belts can prevent waders from rapidly filling with water, if you fall below the water level. Belt

52 Agenda Water Resources Investigations Report Test Safety--In-Pool Training

53 Agenda Water Resources Investigations Report Test Measurement Notes

54 Agenda Water Resources Investigations Report Test Measurement Notes -Example The process of filling out measurement note sheets will be examined by following a measurement made on the North Fork Blackfoot River on September 13, 1999 Upstream view, North Fork, Blackfoot River Gage House

55 Agenda Water Resources Investigations Report Test N. Fk. Blackfoot River Downstream ViewUpstream View

56 Agenda Water Resources Investigations Report Test Gage House

57 Agenda Water Resources Investigations Report Test Starting the Measurement N. Fork Blackfoot River Discussion of measurement Overview of gage site

58 Agenda Water Resources Investigations Report Test Selecting Measuring Section

59 Agenda Water Resources Investigations Report Test Measuring Section Downstream view showing control riffle

60 Agenda Water Resources Investigations Report Test Stringing Tagline

61 Agenda Water Resources Investigations Report Test Meter and Rod Setup

62 Agenda Water Resources Investigations Report Test Meter and Rod Setup (cont.)

63 Agenda Water Resources Investigations Report Test Determining Subsection Spacing Remember, try to have no more than 5% of flow in any one subsection

64 Agenda Water Resources Investigations Report Test Assessing Subsection Spacing Can keep track of sectioning by using rating to estimate what discharge will be.

65 Agenda Water Resources Investigations Report Test Assessing Subsection Spacing (cont.) Try to monitor flow in each section as you proceed. It is most important to monitor flow in the deepest/fastest subsections to judge compliance to the 5% rule.

66 Agenda Water Resources Investigations Report Test Starting the Measurement – The Second Subsection

67 Agenda Water Resources Investigations Report Test Job Hazard Analysis Job Hazard Analysis for North Fork Blackfoot River Site

68 Agenda Water Resources Investigations Report Test Front Sheet Summarizes: 1. Measurement results 2. Gage operation 3. Channel conditions 4. Evidence of high- water 5. Water Samples taken during visit

69 Agenda Water Resources Investigations Report Test Summary Information - Blackfoot Measurement

70 Agenda Water Resources Investigations Report Test Gage equipment 1 1 Use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government Summary Information - Blackfoot Measurement (cont.)

71 Agenda Water Resources Investigations Report Test Inside the note sheet

72 Agenda Water Resources Investigations Report Test Recording Width and Depth Distance from initial point - usually measured from left bank Depth - usually measured directly using a wading rod.

73 Agenda Water Resources Investigations Report Test Recording Angle Correction Angle coefficient- correction applied if flow is not perpendicular to the cross section Needed because we must determine flow normal to the stream cross section. Angle of the current can be assessed by observing floating particles in the water Correction can be determined using measurement note sheet as guide (see next slide)

74 Agenda Water Resources Investigations Report Test Determining a horizontal angle correction Point of origin Read angle correction here Tagline or tape Note Sheet

75 Agenda Water Resources Investigations Report Test Computing width and depth of individual subsections Example of computing sub-section width Assume the following measurements applied Starting point - 0 feet Next point - 1 feet Next point - 3 feet Next point - 5 feet 0135 Meter locations

76 Agenda Water Resources Investigations Report Test Recording Width Width at point 0 = (1 - 0)/2 = 0.5 Width at point 1 - (3 - 0)/2 = 1.5 Width at point 3 = (5 - 1)/2 = Meter locations (ft.) Widths 0.5 ?

77 Agenda Water Resources Investigations Report Test Recording Width and Depth Meter locations Widths 0.5 ? Depth, in this example, is zero, therefore no flow Note: See table from Rantz (1982) for help estimating velocity when edge of water is vertical.table

78 Agenda Water Resources Investigations Report Test Recording Width and Depth (cont.) Data from the North Fork Blackfoot River

79 Agenda Water Resources Investigations Report Test Recording Velocity Velocity measured for at least 40 sec. Rating table for meter is used to determine velocity “at point” Any needed horizontal angle correction is applied to velocity

80 Agenda Water Resources Investigations Report Test Recording Velocity (cont.) Velocity measured at a single point is entered in the “At Point” column If velocity is measured at more than one point in the vertical the mean must be computed.

81 Agenda Water Resources Investigations Report Test Checking Meter Condition Condition of meter should be checked periodically to make sure debris is not affecting performance

82 Agenda Water Resources Investigations Report Test Velocity from Rating Table See OSW memo for the most recent ratings for AA and pygmy meters. memo Partial listing of standard rating #2

83 Agenda Water Resources Investigations Report Test Recording Discharge Data from North Fork Measurement

84 Agenda Water Resources Investigations Report Test Finalizing Measurement Include finish time Finishtime Total width Total of all widths Total area Total discharge Sum width, area and discharge Intermediatetime

85 Agenda Water Resources Investigations Report Test Finalizing Measurement (cont.) Record left edge of water, finish time, etc. A check of the discharge computation later revealed a discharge of 205 cubic feet per second Illustrates value of checking measurements

86 Agenda Water Resources Investigations Report Test Finalizing Measurement (cont.) Fill in Width, Area, Velocity, Gage height, and Discharge on Front Sheet Average velocity is (Discharge / Area)

87 Agenda Water Resources Investigations Report Test Finalizing Measurement (cont.) Fill in Width, Area, Velocity, Gage height, and Discharge o Front Sheet Average velocity is (Discharge / Area)

88 Agenda Water Resources Investigations Report Test Finalizing Measurement (cont.) Read gage Record times and gage heights recorded during measurement on front sheet.

89 Agenda Water Resources Investigations Report Test Determining Mean Gage Height Compute mean gage height for measurement, if needed Mean gage height should be computed if change in stage is greater than 0.15 feet or if change in stage has not been uniform during measurement Weighting can be done using either partial discharge or time as the weighting factor See Discharge Measurements, Part 2 in training class SW4230 for a description of how weighting should be done.Discharge Measurements, Part 2

90 Agenda Water Resources Investigations Report Test Measurements During Rapidly Changing Stage Weighted mean gage height is not truly applicable when stage is changing rapidly You can reduce measurement time using the following procedures in the order listed: 1.Use only the 0.6-depth method 2.Reduce velocity-observation time to about seconds 3.Reduce the number of subsections to 15 – 18 Using any of the shortcuts listed above will reduce measurement accuracy See further discussion in SW4230SW4230

91 Agenda Water Resources Investigations Report Test Finalizing Measurement (cont.) Downstream view through Blackfoot measuring reach

92 Agenda Water Resources Investigations Report Test Assessing Measurement Assessing accuracy of measurement Semi-quantitative based upon: 1. Cross section uniformity 2. Velocity uniformity 3. Stream bed conditions 4. Etc. See “Determination of Error in Individual Discharge Measurements” by Sauer and Meyer announced in OSW memo memo Blackfoot measuring section

93 Agenda Water Resources Investigations Report Test Assessing Measurement (cont.)

94 Agenda Water Resources Investigations Report Test Finalizing Measurement -- The Control Very important – Observations of control forms basis for developing shifts to ratings The control that is in effect during the measurement must be identified Channel Control Riffle Section Control Channel Control Water Surface Stream Bottom

95 Agenda Water Resources Investigations Report Test Finalizing Measurement -- The Control (cont.) Section Control Section Control drowning out-- Channel becoming control

96 Agenda Water Resources Investigations Report Test Finalizing Measurement – Describing channel conditions

97 Agenda Water Resources Investigations Report Test Finalizing measurement - Point of Zero Flow Point of zero flow (also called Gage Height of zero flow) Useful in developing stage-discharge relation (rating) First approximation for scale offset Can be used as another point on the rating Represented by the lowest (deepest) point on section control

98 Agenda Water Resources Investigations Report Test Point of Zero Flow (cont.) Gage Pool Include Velocity Head Deepest Point on Control Control Section Perpendicular to Flow Control Section Gage Pool Flow

99 Agenda Water Resources Investigations Report Test Point of Zero Flow (cont.) North Fork Blackfoot River

100 Agenda Water Resources Investigations Report Test Point of Zero Flow (cont.) Another example

101 Agenda Water Resources Investigations Report Test High Water Marks Look for high-water marks Important aid in working streamflow record Allow you to verify peak stages recorded between visits to site High-water marks on North Fork staff gage

102 Agenda Water Resources Investigations Report Test Measurement and the Stage-Discharge Relation Compute how far measurement plots from rating and plot on rating

103 Agenda Water Resources Investigations Report Test Click on image on the left to start Excel file containing the test. You will have to allow Excel the use of macros for the test to function properly You should open the Excel file as “read only”. You can install the Excel Viewer, if you do not have Excel on your computer Clicking here will start installationhere

104 Agenda Water Resources Investigations Report Test Wading Discharge Measurements Using the Mid-Section Method By K. Michael Nolan and Ronald R. Shields Listed as Training Class SW1271 with National Training Center of U.S. Geological Survey Quit View selected references Acknowledgements

105 Agenda Water Resources Investigations Report Test Selected References Buchanan, T.J., and Somers, W.P., 1969, Discharge measurements at gaging stations: USGS Techniques of Water-Resources Investigations, Book 3, Chapter A8, 65 p. (In revision) International Organization for Standardization, 1983, Measurement of liquid flow in open channels, Handbook 16, 518 p. Nolan, K.M. and others, Surface-water field techniques training class, USGS WRIR , (http://wwwrcamnl.wr.usgs.gov/sws/fieldmethods)wwwrcamnl.wr.usgs.gov/sws/fieldmethods Rantz, S.E., 1982, Measurement and Computation of Streamflow:Volumes I and II, USGS Water Supply Paper 2175, 631 p. V.B.Sauer and R.W. Meyer, Determination of Error in Individual Discharge Measurements”, USGS Open-file report Quit

106 Agenda Water Resources Investigations Report Test Acknowledgements The authors would like to thank Glen Hess, Vern Sauer, and Lucky Sultz for their review of preliminary versions of this report. We appreciated the help of Ken Thompson during field work at the North Fork Blackfoot River. Funding for production and distribution of this report was provided by the Safety Committee of the Water Resources Division. Quit


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