2014-01-29_HYDROLOGY - P2009025 (8)

Home Browse Search

Appendix D — SOP for Stream Flow Measurement — Hansen Project 19 width calculation. This is calculated as the quantity of the difference between the final distance and the second -to- the -last distance, divided by two. • Subsequent calculations will be performed as follows: - Calculate each discharge for each subsection by multiplying the width of the subsection times the depth times the velocity. - Sum the discharges for each subsection to arrive at total discharge for the entire cross - section. • Check your math by summing the subsection widths. Their total should equal the value obtained by taking the difference between the RL and the RR station measurements on the tape or tagline. • Initial at the line "Comp. by" to identify yourself as the person responsible for performing the discharge calculation. • Discharge calculations may be performed manually in the field or on a computer using software such as Microsoft Excel. 3.2.6 Maintenance and Calibration Procedures Before and after use of the current meter, spin tests will be conducted to ensure that the unit performs acceptably. The spin test will be performed in an enclosed area, such as in the cab of a truck or in the enclosed rear of a truck, to prevent wind interference. The test is to be performed prior to attaching the current meter to the wading rod. While holding the meter steady in an area sheltered from breezes, the technician will spin the rotor and then press the start button on the stop watch. The technician will observe the meter until the rotor ceases to spin. The duration of the spin for the Pygmy meter should be more than 40 seconds and for the Price AA meter should be more than 90 seconds. If the meter fails to meet the time -of -spin criteria, the meter will be cleaned and oiled before use. If the meter continues to spin well beyond these time limits, the record will indicate that the meter spun for 40+ seconds, in the case of the Pygmy meter, or for 90+ seconds, in the case of the Price AA meter. The Marsh- McBirney flow meter will be calibrated annually using a factory approved flow loop or tow tank. This procedure involves moving water past the meter at a known velocity or moving the meter at a known velocity through water. The velocity indicated by the meter is adjusted until the proper reading is obtained. To ensure reliable observations of velocity, it is necessary that the current meter be kept in good condition. Before and after each discharge measurement, the meter cups or vanes, pivot and bearing, and shaft should be examined for damage, wear, or faulty alignment. During measurements, the meter will be observed periodically when it is out of the water to be sure that the rotor spins freely. Meters will be cleaned and oiled daily when in use. If measurements are made in sediment -laden water, the meter will be cleaned immediately after each measurement. After oiling, the rotor will be spun to make sure that it operates freely. If the rotor stops abruptly, the cause of the trouble will be sought and corrected before using the meter. In addition to meter maintenance, the entire unit, consisting of current meter, wading rod, digital counter, and headset, will be checked before departure to the field each day as follows: 1. Attach the current meter and digital counter/headset to the wading rod. 2. Test the headset by: a) Spin the current meter to ensure that audible clicks occur. b) If audible clicks do not occur, the following steps should correct the problem: - Check that electronic connections are tight. - Check that the cat's whisker lightly contacts the upper part of the shaft. - Spin again. If audible clicks still do not occur, check that the battery in the headset is properly aligned. Replace the battery, if necessary. 4153A.140129 Whetstone Associates