water measurement - utah state university...

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


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.


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.

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

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

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 flow meters utilize two transducers which function as both ultrasonic transmitters and receivers.

Pipe Diameter, Thickness, Material

Fluid Properties

Precise Location of Sensors

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)

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