Water Measurement Presentation by L. Niel Allen Extension Irrigation Specialist Utah State University to Utah State Engineer’s Office Division of Water Rights Salt Lake City, Utah December 11, 2013
Water Measurement
Presentation by
L. Niel Allen Extension Irrigation Specialist
Utah State University
to
Utah State Engineer’s Office Division of Water Rights
Salt Lake City, Utah December 11, 2013
Introduction
When a resource is measured, it is implied that it has significant value; when not measured, the implication is of little or no value. Water Measurement is Needed for:
•Water Rights
•Water Distribution (dividing the stream)
•Management of Irrigation and Industrial Processes
•Equity
•Billing
•Records
•Conservation/management
•Statutory Requirements
Topics for Discussion
Flow Measurement Fundamentals
Flow Measurement Methods and Devices
Open Channel Flow Measurements
Pipeline Flow Measurements
Design of Flumes
Flow Measurement Fundamentals Flow Rate or Discharge is Volume per Unit Time Cubic Feet per Second, Gallons per minute, etc.
Flow Rate (e.g. ft3 per second) is equal to Velocity (e.g. feet per second) times Area (e.g. square feet)
Conservation of Mass Flow upstream, through, and downstream of a flow
measurement device is equal.
Conservation of Energy (Energy Equation) For small areas Energy equals pressure (water pressure
or depth) plus velocity head (v2/2g).
Manual Flow Measurements
Need to Measure Velocity and Area Velocity is not uniform in an open channel or closed
conduit, due to drag on the channel and conduit boundaries and viscosity of water.
976 cfs in a 25-foot Parshall Flume, depth of flow is 6.3 feet and two-point velocity measurements. Reported by Tom Ley, et al. in USCID March 2013 proceedings
Manual Flow Measurements
Stage v. Discharge for stable channel or river location
The velocity can be taken two points - at 0.8 and 0.2 of the depth areas.
For shallow depths (less than 2 feet) the velocity is taken at 0.6 of the depth.
Manual Flow Measurements
Divide the flow cross-section into a grid and then measure the flow and velocity each grid section.
The total flow is the sum of the velocity times the area of all grid sections.
Manual Flow Measurements
Current Meter and Rod
Manual Flow Measurements Electromagnetic velocity measurements
Diaphragm type depth measurements in combination with electromagnetic velocity measurement. Absolute pressure with single point calibration
Manual Flow Measurements Electromagnetic Flow Meter
The sensor attaches to a wading rod like used with a propeller current meter
Velocities over a short time period can be averaged
Data can be recorded
Open Channel Flow Measuring Structures Flumes Forces the velocity to increase by reducing the area of
flow (ramps, converging sides, etc.)
Ideally the velocity increases to critical depth where upstream water depth is not influenced by downstream water depth. Also known as free-flow.
Critical flow condition means that for a single depth, there is a single flow rate associated with that depth.
As the velocity in increased the water level drops because the area decreases and some of the depth is required to increase the velocity based on the energy equation. E = v2/2g + h
Open Channel Flow Measuring Structures Generally need to slow down the water to get proper
approach velocity Results in increase depth (and/or width of channel) of
water in the channel. Adequate freeboard is needed.
Smooth or tranquil flow
Requires a straight uniform section upstream
May require a wider section
Results in some head loss across structure (Some very little (0.1 feet) others more (0.5 feet or more)
Open Channel Flow Measuring Structures
Free flow conditions exist if the down stream depth does not influence the upstream depth (non-submerged condition).
Free flow is important for measurement accuracy, using the standard tables, and only one depth measurement is required.
Free flow can be established in the design by maintaining the submergence below the transition between free flow and submerged conditions.
Open Channel Flow Measuring Structures
Flumes
Ramp Flumes work very well and there is design software available from the USBR - WinFlume
Long-throated (Ramp) Flume
Long-throated (Ramp) Flume
Rating tables can be accurately calculated for many configurations
Great flexibility in Design
Low head loss through flume
Generally Low Cost
Compute software available for design and creation of rating tables (USBR WinFlume)
Long-Throated (Ramp) Flumes
Long-throated Flumes Characteristics Accurate rating tables can be computed. Even for as-
built dimensions
Throat can be any shape in direction perpendicular to flow. Can be used in open flow pipe.
Low head loss across flume.
Can be operated in free flow with greater submergence than other critical flow devices.
With properly constructed gradual converging transition floating debris can usually pass through the flume.
Can be designed to pass sediments.
Economical to construct.
Adaptable to most existing canals.
Open Channel Flow Measurement - Weirs
Weirs are an overflow structure built perpendicular to the flow of the water.
Approach Velocity of about 0.5 ft/sec.
Cannot be submerged if using standard tables.
Submergence discouraged.
Open Channel Flow Measurement - Weirs
Standard Contracted Rectangular Weirs Q = 3.33h1
3/2(L-0.2h1)
Standard Suppressed Rectangular Weirs Q = 3.33Lh1
3/2
Fully Contracted Standard 90-Degree V-Notch Weir Q=2.49h1
2.48
Cipoletti Weirs Q = 3.367 L h1
3/2
Tables can also be used
Open Channel Flow Measurement - Weir
Duckbill Weir
Cipoletti Weir
Overshot Gates
Maintain Upstream Water Level
Provide Water Measurement
Overshot Gates
Depending on the angle of the gate, used as a water measurement device it resembles a weir, or free overflow, or flume under certain conditions.
Calibrated equations can be developed to get flow measurements accuracies of about 7 percent.
Clausen Weir Rule
Clausen Weir Rule
Open Channel Flow Measurement – Submerged Orifices
Flow is related to the difference between the upstream and downstream heads
V = C(2gh)0.5
Q= A*C(2gh)0.5
Open Channel Flow Measurement – Submerged Orifices
Submerged Orifice often Used for Headgate Measurement
Headgate Opening (Area) and
Difference in Head (Used to Estimate Velocity)
Transit Time Ultrasonic Flow Meters
Rubicon gates
Transit Time Ultrasonic Flow Meters
Selection of Water Measurement Device
Available Head Loss
Range of Flows
Adaptability to Site
Type of Record Needed (Recorder, Real-Time, etc.)
Cost of Structure or Device
User Acceptance
Ability to Pass Sediment or Debris
Selection of Water Measurement Device
Device Standardization and Calibration
Legal and Institutional Requirements
Maintenance Needs
Water Level and Recording Devices Water Level Staff gage
Float and Pulley (Potentiometer or mechanical)
Bubbler
Submersible Pressure Transducer
Optical
Ultrasonic Down-looker
Recorders Self Contained – need to be removed and data
downloaded
Datalogger or transmission of data (cell phone, radio, satellite, manual download, etc.)
Installation and Maintenance Upstream Conditions - Approach Velocity At 0.5 ft/sec the velocity head its .004 feet
At 4 ft/sec the velocity head is 0.248 feet.
Aquatic Vegetation impact on Measurement
Installation, Operation, and Maintenance of Weirs
Conditions Downstream of Weir No nappe for weir – can increase flows 25% of reading at
low flows.
Adjustments can be made for submerged weirs, but no submergence if much better.
Condition of Weir Edge
Upstream Flow Patterns Rough water
Turbulance
Width of channel
Length of straight channel
Installation and Maintenance What happens with excessive siltation
upstream of weir or flume? Is actual flow higher or lower than reading?
What happens when the weir or flume is submerged? Is actual flow higher or lower than reading?
How does the levelness of the flume impact the reading? For downstream falling slope is flow higher or
lower than reading?
For downstream rising slope is flow higher or lower than reading?
Installation and Maintenance Downstream
Condition Submergence (ex.
6 cfs with reading of 20+ cfs)
4-foot Parshall -Reported by Tom Ley, et al. in USCID March 2013 proceedings
Recent Studies of Existing Flumes
Utah Water Research Lab conducted a study of 70 water measurement sites. Only one-third of the water measurement devices were within specification of design or manufacturer. Of those out of specs. 37% over estimated and 63% under estimated. Nearly all had installation or maintenance issues. (ASCE Irrigation & Drainage, June 2011)
Colorado DWR Study of 223 Parshall flumes (4,228 discharge measurements) found that 45% were within 5%, 16% were 5-8%, and 39% were more than 8% of measured discharge. Reported by Tom Ley, et al. in USCID March 2013 proceedings
Considerations for selection of measurement device
Accuracy Reliability Suitability to site Ease of data retrieval Maintenance needs Cost
Questions
Closed Conduit Flow
Fixed area (assumes full pipe flow) so velocity needs to be measured
Propeller Meter
Venturi Meters
Pitot Pipe Velocity Flow Meters
Discharge from Closed Conduits
Acoustic / Transit Time Ultrasonic Flow Meters (can also be used in open channel)
Propeller Flow Meters Instantaneous and tantalizer
Electronic recording
Upstream straight pipe -10 times pipe diameter, but swirls can travel 100 time pipe diameter. Can use straightening vanes.
Downstream straight pipe -1.5 to 2 times pipe diameter.
Saddle Meters need to be designed for exact pipe diameter (ID and OD)
Full pipe flow only
Maintained
Paddle Wheel Flow Meter
Makes velocity reading at only one point
Need uniform and straight section of pipe
Needs calibration for pipe diameter and material.
Needs correct installation
Venture Meter
Two unknown velocities, but we have two equations to solve for the velocities.
Venturi Meter
Made from PVC Pipe and Fittings (USBR has Designs Guidelines
Commercial Style
Collins Flow Meter Measures Velocity Head in Pipe
Pitot Tube Collins and Hall Manometer Flow Meters
Velocity Head
Vertical Discharge from Pipe
Based on H=velocity head
Horizontal Discharge from Pipe
Tables and formulas also exist for partially full pipe discharge.
Volume/Time and Pressure - Orifice Size Discharge Measurements
Measurement from sprinklers with bucket and stopwatch. (Volume (gallons)*60/time(seconds) equals gallons per minute)
Estimation of sprinkler discharge with pressure and orifice size.
Transit Time Ultrasonic Flow Meters
Transit time flow meters utilize two transducers which function as both ultrasonic transmitters and receivers.
Pipe Diameter, Thickness, Material
Fluid Properties
Precise Location of Sensors
Transit Time Ultrasonic Flow Meters
Transit Time Ultrasonic Flow Meters
Questions
WinFlume (simple design)
WinFlume Head-Discharge Table
C:\Program Files\WinFlume\Toone Flume vertical wall 2.5.Flm - Revision 9 Ditchrider's Rating Table, Printed: 12/5/2013 3:11:22 PM ------------------------------------------------------------------------------------- Head,h1 Discharges in cu. ft/s
ft 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 -- -- -- -- -- *0.43 *0.48 *0.52 0.57 0.62 0.2 0.67 0.73 0.78 0.84 0.89 0.95 1.01 1.07 1.14 1.20 0.3 1.27 1.33 1.40 1.47 1.54 1.61 1.68 1.76 1.83 1.91 0.4 1.99 2.07 2.15 2.23 2.31 2.39 2.48 2.57 2.65 2.74 0.5 2.83 2.92 3.01 3.10 3.20 3.29 3.39 3.48 3.58 3.68 0.6 3.78 3.88 3.98 4.09 4.19 4.29 4.40 4.51 4.61 4.72 0.7 4.83 4.94 5.06 5.17 5.28 5.40 5.51 5.63 5.75 5.87 0.8 5.99 6.11 6.23 6.35 6.47 6.60 6.72 6.85 6.98 7.10 0.9 7.23 7.36 7.49 7.62 7.76 7.89 8.02 8.16 8.30 8.43 1 8.57 8.71 8.85 8.99 9.13 9.27 9.42 9.56 9.70 9.85
1.1 10.00 10.14 10.29 10.44 10.59 10.74 10.89 11.04 11.20 11.35 1.2 11.51 -- -- -- -- -- -- -- -- --
Summary of Warning Messages (*'s indicate warnings) --------------------------------------------------- '5 - Upstream energy head / control section length is less than 0.07.
WinFlume (simple Design)