D. Streamflow Measurement Procedures

D.1 Pre-Measurement Activities

D.1.1 Field Data Book and Forms

It is very important that the hydrometric field technician establish a record keeping system in the form of a field data book. All pertinent notes and information should be well organized in the field data book to facilitate planning, scheduling, decision making, equipment management, and overall record keeping.

The actual organization of the field data book is up to the individual, but it should be logically organized and kept up to date at all times. If for any reason a field technician can not undertake or complete the field work (e.g. due to illness or re-assignment), the field data book should give colleagues a clear understanding of the design, function, and history of the station.

The field data book should contain the following information for each gauging station:

• Form AQU-01 Description of Hydrometric Station
• Form AQU-02 Gauge Level Notes
• Form AQU-03 Discharge Measurement
• Form AQU-04 History of Gauge Level Check
• Form AQU-05 Summary of Discharge Measurements for the Year
• Form AQU-06 Water Stage Recorder - Station Record for the Year
• Form AQU-07 Station Analysis for the Year
• Form AQU-08 Stage-Discharge Rating Curve
• Special instructions regarding equipment, maintenance, techniques, conditions, etc. as an attachment to Form AQU-01 (see completed example, Figures B-10 and B-11 in Section B.2.3.2).
• Names of field staff, and contact information.

Appendix II at the end of this Manual contains blank forms and examples of completed forms.

D.1.2 Before Departing for the Field

Before departing on a field trip to gauging stations, the field technician should:

• Carefully review the information and notes in the field data book.
• Address all problems that were noted on previous field trips, and be prepared to handle them if they come up again.
• Gather all equipment that might be needed for all potential conditions, i.e. high, medium, or low flow, at all stations.
• Check and test all equipment to ensure that it is functioning correctly.

D.1.3 On Site Preparations

Prior to conducting the discharge measurement, the conditions of the watercourse must be assessed and recorded, and all the equipment must be checked and serviced if necessary.

D.1.3.1 Assessing Channel Conditions of the Watercourse

One purpose of assessing the overall conditions of the watercourse is to be aware of conditions that will affect the measurement, and to note conditions that could have affected the stage-discharge relationship since the last time the station was visited.

Also, assessing the conditions of the watercourse is important in deciding whether or not to go ahead with the measurement. In some conditions it will be unsafe or impractical to do the measurement.

To assess the conditions of the watercourse, look for the following conditions and make notes about them in the field data book:

• Weed growth at the metering section or on the control
• Debris floating or lodged in the proximity of the gauge
• Beaver activity
• Deposition of gravel or development of sand bars in the vicinity of the gauge
• Any obstructions in the vicinity of the gauge
• Erosion of the channel banks
• Overflow channels that are bypassing the metering section (must be measured or estimated)
• High winds
• Ice conditions

D.1.3.2 Gauges and Water-Level Recorder

After noting the conditions of the watercourse, read the gauges and water-level recorder:

1. Note the time and date in the field data book.
2. Record all the gauge readings. Or, obtain a water level by instrument. Note and record any differences (pen setting, gauge height, or water level).

Note: An accurate determination of the mean gauge height is essential for plotting the results of the discharge measurement. If the stage appears to change while the measurement is in progress, it is necessary to obtain additional readings during the progress of the measurement.

3. Flush the stilling well intakes and make certain they are not obstructed. Observe and record any differences that occur after the flushing.
4. Service the recorder (see Appendix III for details). Remove the stage record that has been accumulating since the last visit to the gauging station.
   Wind the clock drive mechanism of the recorder. Set the pen to the correct time and gauge height.
5. Level check the gauge or gauges if required.
6. Make thorough notes in field data book about observations and procedures.

After taking the discharge measurement, obtain another gauge reading and observe whether the recorder drive system is operating properly and if the pen is tracking correctly. By this time the recorder will have been operating for approximately one hour and any error in setting the pen should be apparent.

This is also the time to check the recorder drive system to make certain that the clock weight spring has not caught on the shelf, or that the ratchet and pawl of a negator spring-driven recorder is disengaged.

D.1.3.3 Current Meter

Before using a Price 622AA current meter, inspect it to be sure the bearing surfaces are in good order. This can be done quite easily:

1. Loosen the bucket wheel raising nut so that the pivot wheel bearing rests on the pivot.
2. Gently rotate the bucket wheel and observe it as it comes to a stop. If the stop is gradual, then the bearing surfaces and the pivot are in satisfactory condition. If the bucket wheel comes to an abrupt halt or the motion is abnormal in any way, the pivot and bearings should be closely inspected.
3. Inspect the pivot and bearings if necessary. If there is evidence of wear, the meter should not be used. Have the meter professionally serviced and re-calibrated.
4. If the pivot and bearings are in good order, then go ahead with the discharge measurement.
5. Horizontal shaft "propeller" meters should be spun to confirm that the bearings and shaft are in satisfactory condition. How to check the propeller meter is described in Section C.4.2.6.

D.1.3.4 Observing Velocity

The guidelines for observing velocity (Figure D-1) are:

• Allow sufficient time for the current meter to adjust to water conditions. The adjustment time will be a very few seconds at high velocities, and significantly longer at low velocities. This adjustment period is very important at low velocities, i.e. <0.3 m/s, and the failure to allow for it could produce errors.
• Observe velocities for 40 to 70 seconds.
• Observe time to the nearest 1/2 second (stopwatch/meter rating table use), or the exact displayed time, when using the meter calibration equation to determine the velocity.
• Where water depth in the vertical is >1.0 m the velocity is measured at both 0.2 and 0.8 depth (from the water surface) with the current meter, and the mean velocity is calculated.
• Where water depth in the vertical is <0.8 m, observations are made at 0.6 depth (from the water surface) only. Using the 0.2 and 0.8 depth method in shallow watercourses places the current meter too close to the water surface and the channel bed to give reliable results.
• Where water depth is between 0.8 m and 1.0 m, the technician can choose the method.
• Usually, depth should be recorded to the nearest 2 cm. However, when wading small or shallow watercourses (<20 cm depth), depths should be recorded to the nearest centimetre. The important concept here is the total cross sectional area.

Figure D-1. Example of typical vertical velocity curve.