Difference between revisions of "Moving bed test"
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Moving bed test required before each measurement, even if you are using GPS (GPS may fail and then you are stuck with bottom tracking). A 5-10 minute loop is the preferred method so the data can be easily corrected in LC software and it is faster than stationary. Otherwise stationary can be done if you do it multiple times across the channel (minimum 3 locations, 5-10 minutes each location) and use the SMBA software to correct data | Moving bed test required before each measurement, even if you are using GPS (GPS may fail and then you are stuck with bottom tracking). A 5-10 minute loop is the preferred method so the data can be easily corrected in LC software and it is faster than stationary. Otherwise stationary can be done if you do it multiple times across the channel (minimum 3 locations, 5-10 minutes each location) and use the SMBA software to correct data | ||
| − | Moving Bed test notes: Discharge will be biased low if there is a moving bed. There is a moving bed if there is a perceived upstream displacement in the ADCP position or the estimated bias error is above 1% (moving bed velocity / test site mean velocity > 0.01. Calculate the bias error by looking in [[ | + | Moving Bed test notes: Discharge will be biased low if there is a moving bed. There is a moving bed if there is a perceived upstream displacement in the ADCP position or the estimated bias error is above 1% (moving bed velocity / test site mean velocity > 0.01. Calculate the bias error by looking in [[Winriver II]] and calculate the distance made good / time of moving bed test to get your moving bed velocity. Then take the moving bed velocity / flow speed (the average velocity in the vertical profile). This number should not be greater than 1% or you have a bias. Stationary bed tests aren’t adequate, especially in large rivers. Conduct a loop test and use the USGS LC software to correct or use the GPS. If you can only conduct a stationary moving bed test, a minimum of 3 tests (5-10 mins each) across the channel should be done and use SMBA program to review/correct your data. |
It is good practice to do this for every measurement so you can correct the data for a moving bed (moving bed materials also include very fine sediments and organic materials). It is best to do a loop test (i.e go across the river and then come back to the exact same location where you started). Otherwise you can due a minimum of 3 stationary moving bed tests across the river. It will appear as if the boat has moved upstream. Stationary test for 10 minutes (5 minutes if anchored or tethered). If you have a moving bed, it will appear as if the boat is moving upstream. Use the USGS LC or SMBA test to correct. | It is good practice to do this for every measurement so you can correct the data for a moving bed (moving bed materials also include very fine sediments and organic materials). It is best to do a loop test (i.e go across the river and then come back to the exact same location where you started). Otherwise you can due a minimum of 3 stationary moving bed tests across the river. It will appear as if the boat has moved upstream. Stationary test for 10 minutes (5 minutes if anchored or tethered). If you have a moving bed, it will appear as if the boat is moving upstream. Use the USGS LC or SMBA test to correct. | ||
Latest revision as of 10:02, 2 April 2010
Moving bed test required before each measurement, even if you are using GPS (GPS may fail and then you are stuck with bottom tracking). A 5-10 minute loop is the preferred method so the data can be easily corrected in LC software and it is faster than stationary. Otherwise stationary can be done if you do it multiple times across the channel (minimum 3 locations, 5-10 minutes each location) and use the SMBA software to correct data
Moving Bed test notes: Discharge will be biased low if there is a moving bed. There is a moving bed if there is a perceived upstream displacement in the ADCP position or the estimated bias error is above 1% (moving bed velocity / test site mean velocity > 0.01. Calculate the bias error by looking in Winriver II and calculate the distance made good / time of moving bed test to get your moving bed velocity. Then take the moving bed velocity / flow speed (the average velocity in the vertical profile). This number should not be greater than 1% or you have a bias. Stationary bed tests aren’t adequate, especially in large rivers. Conduct a loop test and use the USGS LC software to correct or use the GPS. If you can only conduct a stationary moving bed test, a minimum of 3 tests (5-10 mins each) across the channel should be done and use SMBA program to review/correct your data.
It is good practice to do this for every measurement so you can correct the data for a moving bed (moving bed materials also include very fine sediments and organic materials). It is best to do a loop test (i.e go across the river and then come back to the exact same location where you started). Otherwise you can due a minimum of 3 stationary moving bed tests across the river. It will appear as if the boat has moved upstream. Stationary test for 10 minutes (5 minutes if anchored or tethered). If you have a moving bed, it will appear as if the boat is moving upstream. Use the USGS LC or SMBA test to correct.
