• • • • • DQS hr oreTeUiest fAioa3 The University of Arizona ADEQ SW Short Course • DQS hr oreTeUiest fAioa5 The University of Arizona ADEQ SW Short Course Method to measure Stage depends on site “Controls” are necessary to control x section Stage is water le Area must be subdivided into >25 subsections Method to measure Velocity depends on flow Discharge is Area x Velocity (ft Bottom line: one page summary USGS Stream Gauge Network http://waterwatch.usgs.gov/?id=ww_current vel above a datum Measurement of Surface Flows
ADEQ SW Short Course June 13, 2013
3 Phoenix, AZ /sec = cfs)
(most slides courtesy of USGS)
ADEQ SW Short Course The University of Arizona 1 DQS hr oreTeUiest fAioa2 The University of Arizona ADEQ SW Short Course • • • DQS hr oreTeUiest fAioa6 The University of Arizona ADEQ SW Short Course 4 The University of Arizona ADEQ SW Short Course Gaging stations and recorders Measurement of stage Measurement of streamflow – – – – – – W ie oeatCrView River Forecast Ctr NWS – Water level sensors and Transducers Staff gages Use of controls Selection of cross section Velocity measurement Velocity Area water.usgs.gov Outline What is the origin of this data?
ADEQ SW Short Course The University of Arizona 7 ADEQ SW Short Course The University of Arizona 8
Measurement of Streamflow
U.S. Department of the Interior U.S. Geological Survey
Definition of Streamflow Velocity-Area Method
Streamflow, or discharge, is defined as the Discharge = (Mean water velocity) x (Cross-section volumetric rate of flow of water (volume per unit area of water) time) in an open channel Streamflow in the USGS is usually expressed in or English dimensions of cubic feet per second Discharge = (Water velocity) x ((Width) x (Depth)) (ft3/s) or CFS. Velocity-Area Method The Current Meter
Discharge =
X Mean Water Velocity
Price AA Price Cross Section Area Pygmy
Acoustic Current Meter ADCPs
SonTek/YSI FlowTracker
ADCPs The Current Meter Method Miscellaneous Measurement Miscellaneous Measurement Methods Methods
Measuring High Flow Measuring High Flow
Conventional Current Meter-Method Conventional Current Meter-Method
• The USGS measures water depth and velocity in at least 20 locations The places where depth and velocity are measured or verticals (generally >25 verticals) across the channel. (verticals) define subsections of the channel cross section. • Velocity is measured at each location at water depths that best represent average velocity at that location. Discharge is determined by summing discharge in these subsections using the “mid-section method” 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
Selection of Measurement Cross Surface-Velocity Method Section • In a natural channel a surface-velocity Cross section lies within a strait reach, and coefficient of 0.85 or 0.86 is used to compute streamlines are parallel to each other mean velocity Velocities are greater than 0.5 ft/s and depths are greater than 0.5 ft • In a smooth artificial channel a surface Streambed is relatively uniform and free of numerous velocity coefficient of 0.90 is used 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 Selection of Measurement Cross Spacing of Observation Verticals Section 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
Discharge measurements are used to Indirect Measurement of Discharge develop rating curves
100
Rating Curve
10 Stage (ft)
Discharge Measurements
1 1 10 100 1000 10000 100000 Discharge (cfs)
Primary Data Sources
Measurement of Stage
U.S. Department of the Interior U.S. Geological Survey Primary Data Sources Measurement of Stage
Explanation of Stage Gage Datum at a station
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.
Uses of Stage Controls
Stage records along with stream discharge The conversion of a record of stage to a measurements are used to develop stage- record of discharge is made by the use of a discharge relations stage-discharge relation. Stage records can be used to design The physical element or combination of structures affected by stream elevation and elements that controls the relation is known planning of floodplain use as a control. Stage records can be used to provide an There are artificial and natural controls index of surface area and volume of a water body Artificial Controls Artificial Control
Artificial Controls Artificial Controls
Natural Controls Natural Controls Natural Controls Point of Zero Flow
Discharge measurements are used to develop rating curves Datum of Gage
Gage datum – The zero elevation reference 100 surface at a gaging station to which all gages Rating Curve are set Datum could be of known elevation or an arbitrary elevation 10 Stage (ft) A permanent datum should be maintained for the life of the gage Discharge Measurements
1 1 10 100 1000 10000 100000 Discharge (cfs)
Reference mark Reference Points
A permanent marker, installed in the ground Objects, often bolts or screws that are or on a structure, whose elevation above a assigned an elevation in the gage datum. set datum is known. Used to obtain gage heights when necessary Used to check and make sure that all gages by measuring their distance to the water and reference points are properly set to gage surface. datum. Primary Data Source
Gaging Stations and Recorders
U.S. Department of the Interior U.S. Geological Survey
Stage Data Collection Nonrecording Gages
Stage data is collected through the use of Can be used as an auxiliary or reference gage to non-recording and recording gages. indicate the water-surface elevation in a Stage data is collected continuously through Stream or reservoir the use of recording gages 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 Wire Weight Gage Wire Weight Gage
Float-Tape Gage Electric Tape Gages
Water-level Sensors Float and Shaft Encoder
A device that automatically determines, or senses, the vertical position of the water surface. Submersible Pressure Transducers Noncontact Water-Level Sensors
Typical Gaging-Station Typical Gaging-Station Instrumentation Configurations Instrumentation Configurations
Crest Stage Gage Crest-Stage Gage