Outline MeasurementofSurfaceFlows ADEQSWShortCourse...
Transcript of Outline MeasurementofSurfaceFlows ADEQSWShortCourse...
![Page 1: Outline MeasurementofSurfaceFlows ADEQSWShortCourse ...web.sahra.arizona.edu/education2/science/docs/ADEQ... · MeasurementofSurfaceFlows ADEQSWShortCourse June13,2013 Phoenix,AZ](https://reader033.fdocuments.net/reader033/viewer/2022050404/5f817adb749c864c664b7c29/html5/thumbnails/1.jpg)
Measurement�o
f�Surface�Flows
ADEQ
�SW�Sho
rt�Cou
rse
June
�13,�2013
Phoe
nix,�AZ
(most�slides�cou
rtesy�of�USG
S)AD
EQ�SW�Sho
rt�Cou
rse
The�University
�of�A
rizon
a1
Outline
• Measurement�of�streamflow– Velocity�Area– Velocity�measurement– Selection�of�cross�section
• Measurement�of�stage– Use�of�controls
• Gaging�stations�and�recorders– Staff�gages– Water�level�sensors�and�Transducers
ADEQ�SW�Short�Course The�University�of�Arizona 2
Bottom�line:�one�page�summary
• Discharge�is�Area�x�Velocity�(ft3/sec�=�cfs)• Method�to�measure�Velocity�depends�on�flow• Area�must�be�subdivided�into�>25�subsections• Stage�is�water�level�above�a�datum• “Controls”�are�necessary�to�control�x�section• Method�to�measure�Stage�depends�on�site
ADEQ�SW�Short�Course The�University�of�Arizona 3
water.usgs.gov
ADEQ�SW�Short�Course The�University�of�Arizona 4
USGS�Stream�Gauge�Network
ADEQ�SW�Short�Course The�University�of�Arizona 5
http://waterwatch.usgs.gov/?id=ww_current
NWS�– River�Forecast�Ctr View
ADEQ�SW�Short�Course The�University�of�Arizona 6
![Page 2: Outline MeasurementofSurfaceFlows ADEQSWShortCourse ...web.sahra.arizona.edu/education2/science/docs/ADEQ... · MeasurementofSurfaceFlows ADEQSWShortCourse June13,2013 Phoenix,AZ](https://reader033.fdocuments.net/reader033/viewer/2022050404/5f817adb749c864c664b7c29/html5/thumbnails/2.jpg)
ADEQ�SW�Short�Course The�University�of�Arizona 7
What�is�the�origin�of�this�data?
ADEQ�SW�Short�Course The�University�of�Arizona 8
U.S. Department of the InteriorU.S. Geological Survey
Measurement of Streamflow
Definition of Streamflow
� Streamflow, or discharge, is defined as the volumetric rate of flow of water (volume per unit time) in an open channel
� Streamflow in the USGS is usually expressed in English dimensions of cubic feet per second (ft3/s) or CFS.
Velocity-Area Method
Discharge = (Mean water velocity) x (Cross-section area of water)
orDischarge = (Water velocity) x ((Width) x (Depth))
![Page 3: Outline MeasurementofSurfaceFlows ADEQSWShortCourse ...web.sahra.arizona.edu/education2/science/docs/ADEQ... · MeasurementofSurfaceFlows ADEQSWShortCourse June13,2013 Phoenix,AZ](https://reader033.fdocuments.net/reader033/viewer/2022050404/5f817adb749c864c664b7c29/html5/thumbnails/3.jpg)
Velocity-Area Method
Discharge =
Cross Section Area
X Mean Water Velocity
The Current Meter
Price AA PricePygmy
Acoustic Current Meter
� SonTek/YSIFlowTracker
ADCPs
ADCPs The Current Meter Method
![Page 4: Outline MeasurementofSurfaceFlows ADEQSWShortCourse ...web.sahra.arizona.edu/education2/science/docs/ADEQ... · MeasurementofSurfaceFlows ADEQSWShortCourse June13,2013 Phoenix,AZ](https://reader033.fdocuments.net/reader033/viewer/2022050404/5f817adb749c864c664b7c29/html5/thumbnails/4.jpg)
Miscellaneous Measurement Methods
Miscellaneous Measurement Methods
Measuring High Flow Measuring High Flow
Conventional Current Meter-Method
• The USGS measures water depth and velocity in at least 20 locations or verticals (generally >25 verticals) across the channel.
• Velocity is measured at each location at water depths that best represent average velocity at that location.
Conventional Current Meter-Method
� The places where depth and velocity are measured (verticals) define subsections of the channel cross section.
� Discharge is determined by summing discharge in these subsections using the “mid-section method”
![Page 5: Outline MeasurementofSurfaceFlows ADEQSWShortCourse ...web.sahra.arizona.edu/education2/science/docs/ADEQ... · MeasurementofSurfaceFlows ADEQSWShortCourse June13,2013 Phoenix,AZ](https://reader033.fdocuments.net/reader033/viewer/2022050404/5f817adb749c864c664b7c29/html5/thumbnails/5.jpg)
The Midsection Method Measurement of Velocity
� Current-meter measures velocity at a point� Discharge measurements require determination of
the mean velocity in each of the selected verticals� Mean velocity in a vertical can be approximated by
making velocity observations and using a known relation between those velocities and the mean in the vertical.
Velocity Curve Two-Point Method
� Generally used for depths greater than or equal to 2.5 ft
� Velocity observations are made at the 0.2 and 0.8 depth below the surface.
� The average of the two observations is used as the mean velocity in the vertical
Surface-Velocity Method
• In a natural channel a surface-velocity coefficient of 0.85 or 0.86 is used to compute mean velocity
• In a smooth artificial channel a surface velocity coefficient of 0.90 is used
Selection of Measurement Cross Section� Cross section lies within a strait reach, and
streamlines are parallel to each other� Velocities are greater than 0.5 ft/s and depths are
greater than 0.5 ft� Streambed is relatively uniform and free of numerous
boulders and heavy aquatic growth� Measurement section is relatively close to gaging-
station control to avoid the effect of tributary inflow, and storage during periods of rapidly changing stage
![Page 6: Outline MeasurementofSurfaceFlows ADEQSWShortCourse ...web.sahra.arizona.edu/education2/science/docs/ADEQ... · MeasurementofSurfaceFlows ADEQSWShortCourse June13,2013 Phoenix,AZ](https://reader033.fdocuments.net/reader033/viewer/2022050404/5f817adb749c864c664b7c29/html5/thumbnails/6.jpg)
Selection of Measurement Cross Section Spacing of Observation Verticals
� Spacing of verticals is determined to provide about 25 to 30 subsections or more
� No subsection should have more than 10 percent of the total discharge
� Ideal measurement has no subsection more than 5 percent of the total discharge
� Spacing between verticals should be closer in areas of the cross section that have greater depths and velocities
� Note: Ideal measurements are seldom achieved with 25 subsections
Indirect Measurement of Discharge
1
10
100
1 10 100 1000 10000 100000Discharge (cfs)
Stag
e (ft
)
Rating Curve
Discharge Measurements
Discharge measurements are used to develop rating curves
U.S. Department of the InteriorU.S. Geological Survey
Measurement of Stage
Primary Data Sources
![Page 7: Outline MeasurementofSurfaceFlows ADEQSWShortCourse ...web.sahra.arizona.edu/education2/science/docs/ADEQ... · MeasurementofSurfaceFlows ADEQSWShortCourse June13,2013 Phoenix,AZ](https://reader033.fdocuments.net/reader033/viewer/2022050404/5f817adb749c864c664b7c29/html5/thumbnails/7.jpg)
Primary Data Sources Measurement of Stage
Explanation of Stage
� The stage of a stream or lake is the height or elevation of the water surface above an established datum plane.
� Gage height – the height of the water surface above the gage datum.
� Gage height is often used interchangeably with the more general term stage.
� Stage or gage height is usually expressed in feet and hundredths of a foot.
Gage Datum at a station
Uses of Stage
� Stage records along with stream discharge measurements are used to develop stage-discharge relations
� Stage records can be used to design structures affected by stream elevation and planning of floodplain use
� Stage records can be used to provide an index of surface area and volume of a water body
Controls
� The conversion of a record of stage to a record of discharge is made by the use of a stage-discharge relation.
� The physical element or combination of elements that controls the relation is known as a control.
� There are artificial and natural controls
![Page 8: Outline MeasurementofSurfaceFlows ADEQSWShortCourse ...web.sahra.arizona.edu/education2/science/docs/ADEQ... · MeasurementofSurfaceFlows ADEQSWShortCourse June13,2013 Phoenix,AZ](https://reader033.fdocuments.net/reader033/viewer/2022050404/5f817adb749c864c664b7c29/html5/thumbnails/8.jpg)
Artificial Controls Artificial Control
Artificial Controls Artificial Controls
Natural Controls Natural Controls
![Page 9: Outline MeasurementofSurfaceFlows ADEQSWShortCourse ...web.sahra.arizona.edu/education2/science/docs/ADEQ... · MeasurementofSurfaceFlows ADEQSWShortCourse June13,2013 Phoenix,AZ](https://reader033.fdocuments.net/reader033/viewer/2022050404/5f817adb749c864c664b7c29/html5/thumbnails/9.jpg)
Natural Controls Point of Zero Flow
1
10
100
1 10 100 1000 10000 100000Discharge (cfs)
Stag
e (ft
)
Rating Curve
Discharge Measurements
Discharge measurements are used to develop rating curves Datum of Gage
� Gage datum – The zero elevation reference surface at a gaging station to which all gages are set
� Datum could be of known elevation or an arbitrary elevation
� A permanent datum should be maintained for the life of the gage
Reference mark
� A permanent marker, installed in the ground or on a structure, whose elevation above a set datum is known.
� Used to check and make sure that all gages and reference points are properly set to gage datum.
Reference Points
� Objects, often bolts or screws that are assigned an elevation in the gage datum.
� Used to obtain gage heights when necessary by measuring their distance to the water surface.
![Page 10: Outline MeasurementofSurfaceFlows ADEQSWShortCourse ...web.sahra.arizona.edu/education2/science/docs/ADEQ... · MeasurementofSurfaceFlows ADEQSWShortCourse June13,2013 Phoenix,AZ](https://reader033.fdocuments.net/reader033/viewer/2022050404/5f817adb749c864c664b7c29/html5/thumbnails/10.jpg)
U.S. Department of the InteriorU.S. Geological Survey
Gaging Stations and Recorders
Primary Data Source
Stage Data Collection
� Stage data is collected through the use of non-recording and recording gages.
� Stage data is collected continuously through the use of recording gages
Nonrecording Gages
Can be used as an auxiliary or reference gage to indicate the water-surface elevation in a� Stream or reservoir� Stilling well
Can also be used as a temporary substitute for the recorder when the intakes are plugged or there is an equipment failure.
Vertical Staff Inclined Staff
![Page 11: Outline MeasurementofSurfaceFlows ADEQSWShortCourse ...web.sahra.arizona.edu/education2/science/docs/ADEQ... · MeasurementofSurfaceFlows ADEQSWShortCourse June13,2013 Phoenix,AZ](https://reader033.fdocuments.net/reader033/viewer/2022050404/5f817adb749c864c664b7c29/html5/thumbnails/11.jpg)
Wire Weight Gage Wire Weight Gage
Float-Tape Gage Electric Tape Gages
Water-level Sensors
� A device that automatically determines, or senses, the vertical position of the water surface.
Float and Shaft Encoder
![Page 12: Outline MeasurementofSurfaceFlows ADEQSWShortCourse ...web.sahra.arizona.edu/education2/science/docs/ADEQ... · MeasurementofSurfaceFlows ADEQSWShortCourse June13,2013 Phoenix,AZ](https://reader033.fdocuments.net/reader033/viewer/2022050404/5f817adb749c864c664b7c29/html5/thumbnails/12.jpg)
Submersible Pressure Transducers Noncontact Water-Level Sensors
Typical Gaging-Station Instrumentation Configurations
Typical Gaging-Station Instrumentation Configurations
Crest Stage Gage Crest-Stage Gage