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Water Measurement
Examples of Alternative Measurement Methods
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All methods discussed below require that a daily log book or other recording device be maintained.
- Electricity Records Dedicated to the Pump
- Total Facility Records minus Estimated Non-Pump Electricity
- Staff Gage and Storage-Capacity Curve
- Pressure Transducer and Storage Capacity Curve
- Power Generation Estimates
- Remote Satellite Imaging
- Crop Duty Estimates/Consumptive Use Estimates
- Other Water Duty Estimates Other than for Crops
- Pipe/Trajectory Method
- Modeled/Estimated Flows
- Bucket and Stopwatch
- Engine Fuel Use
- Staff Gage and Floodable Acreage
- Float and Stopwatch
Electricity Records Dedicated to the Pump
Description: If a pump has a dedicated meter, the electricity used on the meter, in kilowatt hours, can be correlated to a water volume using a pump test. If a dedicated meter is not present or available, a device called a sub-meter can be installed by qualified electrician. This method requires a log book and occasional data entry to track usage over time.
Accessories: Log book; sub-meters by Kill A Watt™, Leviton™ and other manufacturers.
Advantages: The Kill A Watt™ electrical meter shows how much power a pump is using.The Kill A Watt™ electrical meter is for various indoor uses with standard 110V 15A wiring systems.The meter costs about $20 at home improvement stores. Indoor/outdoor commercial-grade sub-meters are $200 to $300 with some more sophisticated (3phase-240V-200A) systems with monitoring data ports are $400. Once the kilowatt-hours to gallons relationship is determined and calibrated, accuracy is relatively good under steady-state conditions.
Disadvantages: Measurement is indirect. A change in source water level, pipe length, pump speed or other factors that change the pump pressure “head” will affect the calibration. Large capacity electrical sub-meters should be installed by a qualified electrician.
Total Facility Electricity Records minus Estimated Non-Pump Electricity
Description: This method involves estimating the amount of non-pump electricity used at a facility, and subtracting it from the total electricity recorded at the facility’s electrical meter. The difference is the power used by the pump, which can be correlated to a water volume.
Accessories: Electrical meter, “Smart” meter
Advantages: This method does not require an electrical meter “at the pump.”
Disadvantages: This method may not work well when the amount of electricity used by the pump is small relative to other electrical loads “on the meter”. A change in source water level, pipe length, pump speed or other factor that changes the pump pressure “head” will affect the calibration.
Staff Gage and Storage-Capacity Curve
Description: Reservoir staff gage are used to determine the depth of water in a reservoir and are mounted on a pole or other sturdy structure. Often, the staff gage is located in the deepest part of the reservoir. Staff gages are typically marked in 1/10 or 1/100-foot increments and are used in conjunction with storage-capacity rating curve or table. Variations to this method includes using a stilling well or bubbler pipe with pressure transducer to determine or record the water level.
Accessories: Electronic data logger, data telemetry
Advantages: Relatively easy method for determining change in reservoir volume, diversion-to-storage, and withdrawals from storage over time.
Disadvantages: Staff gages can become fouled, corroded, tilted, or vandalized requiring maintenance or replacement. A depth-area-capacity survey needs to be completed to establish the rating curve or table. For large surface-area reservoirs, gages may be difficult to read from the shoreline because of the distance. Strong winds and wave action can cause erroneous gage readings. The tank air supply for a bubbler pipe needs to be replenished.
Pressure Transducer and Storage-Capacity Curve
This method is similar to the method using a staff gage and storage-capacity curve described above except that a device called a pressure transducer, which measures water pressure, is used to determine the depth of water in a reservoir.
Power Generation Estimates
Description: Power generated in watts, kilowatts, or megawatts using a turbine is correlated to the volume of water flowing through the turbine at a given head pressure. This method requires power generation meters and record-keeping to track power generation.
Accessories: Electronic data logger, data telemetry.
Advantages: Flow rate and quantity of water used can be approximated without the purchase of a flow measuring device.
Disadvantages: Requires calibration to develop a rating curve(s). Turbine and generator efficiencies affect the accuracy of calculated flow rates and volumes.
Remote Satellite Imaging
Description: Use of satellite imagery to estimate consumptive use of crops.
Advantages: State-of-the-are method for approximating crop evapotranspiration of consumptive use.
Disadvantages: Commercial satellite imagery is often more costly than other types of measuring devices. Satellite imagery at the required resolution may not be available in a timely fashion to estimate water use for Statement reports by July 1 of the following year. This method provides an estimate of crop consumptive use, but not the amount diverted from the stream.
Crop Duty Estimates/Consumptive Use Estimates
Description: The total volume of irrigation water required to grow a particular type or variety of crop, including consumptive use, evaporation and seepage from ditches, canals and water application.
Accessories: Farm advisor contacts, publications, and resources (e.g.: University of California Division of Agriculture and Natural Resources).
Advantages: The water used can be estimated without purchasing a measuring device.
Disadvantages: Crop duties depend on a number of variables being consistent, if not constant, including: soil moisture, average daily temperature during the growing season, precipitation, method of irrigation, groundwater percolation, soil type, crop type and variety, and availability of nutrients. Since these factors vary seasonally and by location, a crop duty in one area may not be applicable in another area.
Other Water Duty Estimates Other Than for Crops
Description: The approximate amount of water used “per person” by occupants of a household, or some other unit, such as water use per head of livestock. Amounts for households vary depending on the structure, fixtures, weather, location, and whether there is ornamental lawn watering.
Accessories: Daily log book; Various duty estimates can be found in Appendices I, II and III of the Division of Water Right’s booklet, How to File an Application.
Advantages: Quantity of water can be estimated without the purchase of a measuring device.
Disadvantages: Housing structures have varying levels of plumbing fixtures, habitation, and use; therefore, a water duty for one household is often different than another.
Pipe/Trajectory Method
Description: If water is flowing fast enough, and has sufficient “drop” at the pipe outlet, measuring how far water shoots out the pipe can provide an estimate of how much discharge is flowing through the pipe. This method requires that the pipe diameter and water level in the pipe be known. See below for a diagram and flow formula.
Accessories: Daily log book, scientific calculator.
Advantages: Where appropriate, the flow rate can be approximated without the purchase with expensive measuring devices.
Disadvantages: Method requires steady-state discharge and extensive record keeping. Not effective where there is very low or very high discharge velocities.
The flow Q can be calculated using the following formula:
Q = 8.69 (1- a/d)1.88 d2.48
Where:
Q = the volumetric flow in cubic feet per second
d = the diameter of the pipe (ft)
a = the measured distance between the inside upper edge of the pipe and the top of the water surface (ft)
For this method of measurement, the ratio of a/d must be greater than 0.45.
Modeled/Estimated Flows
Description: Flow estimated using a computer model or estimated based on a water balance.
Accessories: Model or flow balance spreadsheet.
Advantages: Relatively easy to use.
Disadvantages: Flows are estimated.
Bucket and Stopwatch
Description: This method involves filling a bucket of known volume and using the stopwatch to determine the time the bucket takes to fills. The volume of the bucket divided by the time it takes to fill gives the flow.
Accessories: Daily Log Book; Bucket and stopwatch.Advantages: Easy to use.
Disadvantages: Provides the flow at one point in time.
Engine Fuel Use
Description: Water diversion pumps using diesel or gas engines that run continuously typically use x gallons of fuel to pump y amount of water. If the amount of fuel use can be correlated to the amount of water pumped using a calibration procedure, a relationship may be developed between the amount of fuel used and the amount of water pumped. This can give a reasonably good estimate of the amount of water pumped based on the amount of fuel used to run the diversion pump(s).
Accessories: Daily Log Book
Advantages: No special water measurement devices needed.
Disadvantages: Determination of the amount pumped based on fuel usage is an indirect measurement of the “amount of water taken from the source” and may or may not give an accurate rate of diversion. A water measurement device is needed to develop a fuel to water-volume relationship (calibration).
Staff Gage and Floodable Acreage
Description: For water use(s) involving the deep flooding of land (such as duck clubs or rice checks), the amount of water applied to the land can be determined volumetrically. For example, a 5-acre rice check filled 24 inches or 2 feet deep will take 10 acre-feet to fill (excluding the water used to saturate the soil).
Accessories: Daily Log Book and some type of permanent or temporary staff gages placed at key locations within the flooded area.
Advantages: No special water measurement devices used.
Disadvantages: Does not account for initial and ongoing soil percolation losses, resulting in the under-estimate of the volume of water diverted to fill the containment area; diminished accuracy and precision of water diversion measurement.
Float and Stopwatch
Description: This method involves using a float and a stopwatch to estimate the velocity of flow by measuring the time it takes for a float to move a given distance. Since the float is near the top of the cross-sectional flow, it does not represent average velocity. The average velocity can be determined by multiplying the velocity at the top of the cross-sectional flow by 0.8 (Vavg = Vfloat x 0.8). To determine the discharge, you will need to measure the area of flow in the channel and multiply times the average velocity (discharge = velocity x area).
Accessories: Daily Log Book; Float and stopwatch.
Advantages: Easy to use.
Disadvantages: Provides the flow or volume discharged at one point in time.
