Solving Diverters' Headaches To Provide Peace Of Mind And Help Stay Out Of Trouble
Category: Accurate, Lasting Devices
There are standard measurement devices on the lower end of cost: weirs, orifices, and flumes. They can be easily purchased pre-fabricated, saving you time and money. Accuracy and speed of measurement make these great for reporting and for defending your diversion against challenges. High tech options like acoustic Dopplers, magnetic meters, and propeller meters cost more but save time for larger diversions. All are good to +/- 5% or better when installed, easily meeting any standard for field measurements.
If you have a circular headgate, how can you use that as an orifice to measure flow? It’s easy if the gate is fully open – orifice equations from the USBR Water Measurement Manual can be used. The area of a circle is PI*r^2.
Here are the orifice equations for a rectangular headgate – the same equations are used for a circular headgate, or really a headgate of any shape:
A = the area of the orifice g = gravity, 32.2 ft/sec^2 h1 = the upstream depth in feet h2 = the downstream depth in feet
The first equation with the coefficient of 0.61 is for a gate on a wall. The second with the coefficient of 0.70 is for a circular gate at the end of a pipe.
The difference between h1 and h2 can also be measured down from the top of a wall with a level top.
There you go. Based on the change of stem height, you can calculate how much the headgate is open. Convert that to a percentage. For example. A 2.0′ diameter headgate open 0.5′ is 25% open. Then use the table’s 50% row to where it intersects the 2.00 foot diameter column to get an area of 1.913 square feet.
What if you have a small diversion, but grass or debris would interfere with a standard weir? A weir has to have unobstructed, free-flowing water over
Weir with debris and grass on crest
the crest so measured depths accurately relate to a calculated flow. A weir with debris problems has to be cleared whenever flow is measured, which increases the time requirement.
When weirs have low flows, they trap debris more frequently, and they are less accurate when the depth over the crest drops below 0.2 feet (2.4 inches). Then the only way to measure flow is with a narrow suppressed weir, or with a contracted weir, typically half or less the maximum width. A V-notch weir can be used for measurement of low flows.
Changing the weir boards for different flows requires someone with experience,
Contracted weir
who will recognize when the depth over the weir is 0.2 feet or less and then use a contracted weir board. However, people are busy when irrigating, and even busier when flows drop. Weirs are often neglected during the time they need more frequent maintenance visits.
A good flume for passing debris and measuring low flows is the HS flume. These are accurate right down to zero flow. For the maximum flow, they require more
1.0-foot HS flume, for flows of 0.00 to 0.80 cfs
material than a rectangular Winflume, Montana, or Parshall flume. However, they are more accurate than other flumes at very low flows – testing by the University of Minnesota found an average accuracy to be +/- 3.2% for ideal approach conditions. They will pass debris down to zero flow – the flume shown here has an opening of 0.05 feet, or 5/8 inch at the flat bottom, and the opening increases with height.
HS flume for flows up to 0.8 cfs HS flume at 0.025 cfs
Why aren’t HS flumes common in California? I suspect that the early adoption of Parshall flumes here established the standard. I have seen a few hundred flumes, but I had never seen an operating HL (wide, high flow), H, or HS flume, prior to my installations.
Why go to the trouble of using an HS flume, if Parshall flumes are readily
New Parshall Flume
available? A Parshall flume may be +/- 10% accurate down to perhaps 5% of its maximum flow. Below that, the accuracy decreases. An HS flume is +/- 10% accurate down to 1% to 2% of its maximum flow. If the flow regime is predominantly low with occasional high flows, it is important to measure those low flows with the best possible accuracy. Some places where low flow measurement is critical include field runoff where pollution is proportional to flow, small water rights, and dam leakage.
HS flumes are easier to construct than a Parshall, too. The HS flume bottom is flat, and it has 3 vertical planes. The photos of the Parshall flume here show
Bottom of Parshall flume
that it has 3 horizontal planes, and 5 vertical planes. An HS flume takes less time to build, and can be put together fairly quickly in any farm or ranch shop. Parshalls are complex enough that they are purchased, including design and shipping costs.
How is a staff gage installed in a reservoir? The typical way is to drive a piece of 2″ galvanized pipe into the ground, deep enough to so it isn’t easy to push over. If cattle will be in the reservoir to get water, then the pipe needs to be really well installed. A gas-powered post pounder can be rented at Rental Guys, Home Depot, or similar places.
Most reservoirs are deeper than six feet, so it’s best to maximize the length of pipe installed. The length of pipe that can be installed by hand is usually about 6 feet. For a 6-foot tall pipe, about 3 feet of pipe needs to be in the ground, so the total pipe length is 9 feet.
Then the staff gage is attached to a 2″ x 8″, using screws or small bolts. Staff gages vary in width from 1″ to 4″; the usual USGS Style C staff gages are 2-1/2″ wide. Once the staff gage is screwed on, the board is U-bolted to the pipe.
That’s it…except for the surveying part. The top of staff gage needs to be at the same level as the spillway crest, so the maximum water surface elevation can be measured. How is the surveying done? An autolevel is close enough for most reservoirs, or two installers can use a very accurate survey level.
If the reservoir is deeper than your staff gage length (6 feet as shown here), and most are, then staged staff gages will be needed. For example, a first gage is installed at the top, going from, say, 6 feet to 12 feet. The second, lower staff gage is installed from 0 feet to 6 feet, and 6 feet is exactly the same elevation on both staff gages. In the photo below, there are 3 staged staff gages to measure 18 feet in elevation: 0 to 6 feet, 6 feet to 12 feet, and 12 feet to 18 feet. The top of the third, lowest staff gage can be seen in the bottom right corner.
More commonly, staff gages like the USGS Style C are purchased in 3.33 foot lengths. This is convenient because staff gages are installed closer together.
What if a pond is full, or mostly full? It is still possible to install a staff gage, but it will be harder. Boats or rafts will be needed, and the pipe with the board already attached has to be put in place and held vertical while being driven. If the total depth is greater than 6 feet, then a longer pipe, board, and staff gage will be needed, and the combined weight will be that much greater. Hint: tie a rope and buoy to the pipe so when if it slips and sinks, it can be pulled up again.
What about installing a staff gage along the slope of a dam, to avoid having to wrestle a pipe and board for a deep installation? This can be done by attaching a length of rebar or pipe to the dam face using concrete stakes or similar method. The slope distances measured are converted to vertical depths. However, this won’t stand up well to cattle or elk traffic, and it is more liable to be vandalized if the reservoir has easy access.
If you have a pipeline as part of your diversion, then an in-line meter with an integrated data collector can be installed. The data files from these units are
McCrometer McPropeller inline meter with data collector
easily readable in Excel, and the files can be sent directly to the Water Board to meet the requirements of SB 88.
What if you don’t have a pipeline? Then your flow needs to be measured in the open ditch with a weir, flume, or orifice. These devices measure the flow but they don’t record the data. To continuously record data, a submersible logging instrument must be used to measure the water pressure at the bottom of the box. These logging instruments are commonly put into stilling wells that are inside or outside the measurement device.
Flume with attached stilling well for water level logger
How are water pressure logger measurements converted to diverted flows or reservoir storage? Why does anyone even have to have an electronic pressure logger? Onset Computer, PMC, In-Situ, , and other manufacturers sell data loggers and water level loggers, not pressure loggers, so why is this post talking about measuring pressures at all?
Bluetooth Hobo Logger, cabled to recorder and barometric compensator unit – least expensive option for a single location
Loggers record pressure, because that is the easiest physical attribute to measure. A data logger in water does not know how deep it is, and it does not
know how much flow is going by, or how much water is being stored in a reservoir. Pressures relate directly to static (standing) water depths, and then equations convert the depths to flows, or to reservoir storage volumes.
How is pressure converted to depth? It’s an easy calculation – water that is one foot deep has a pressure of 0.4335 psi at the bottom. So, if your logger measures 1.60 psi, then the calculation to get depth is 1.60 psi / 0.4335 psi per foot = 3.69 feet of depth.
Note that water level loggers can be of two types. The least expensive are completely submersible, and do not compensate for barometric pressure. For an idea of the readings of barometric pressure in a measurement device, a 2 foot deep logger records a pressure of 0.8670 psi. Atmospheric pressure at sea level is about 14.7 psi, and high in the mountains may be 12.0 psi. Air pressure is much greater than those measured in ditches. Usually two of these loggers are used at once, one in the water, and one out of the water measuring only air pressure. This also eliminates the variability in pressure due to weather changes.
Stilling well in a weir
The second type of data logger compensates for barometric pressure at the same time water pressure is being recorded. That way, the water and air pressure data sets do not have to be combined before conversion to depths. These loggers were always more expensive until the Bluetooth Hobo water level logger came along; as of February 2019 I found that it is the least expensive option for a single location.
Now that you can calculate any depth, how do you convert depths to reservoir storage? That requires an Area-Capacity curve, also known as an Elevation-Storage curve. The points can be picked off the curve. For example, in the curve below, a depth of 8.5 feet would correspond to an elevation of 2,802.5 feet, and a reservoir storage volume of 30 acre-feet.
An owner of a reservoir with a capacity over 10 acre-feet must collect monthly storage values. That’s easily done by hand. However, a reservoir with a capacity of 50 AF requires weekly measurement; over 200 AF requires daily measurement; and over 1,000 AF requires hourly measurement. That is really tedious to do by hand.
This is where an Excel spreadsheet can make the task a whole lot easier! The spreadsheets shown below are just for this. The first sheet helps translate a graph into a table of elevations and storage volumes. The second sheet translates collected pressure values into depth and storage values, for as many data points as needed.
For diversion ditches from a stream, how are pressures converted to flows? The logger is in a stilling well, usually a pipe connected to the inside or outside wall of the weir, flume, or orifice. It measures pressure, which is easily converted to depths.
As with reservoirs, Excel spreadsheets make the conversion process a whole lot easier. The sheets below have the rating curve for a suppressed weir, and the second sheet converts pressure to actual water depths over the weir boards. Even for thousands of hourly readings, the hourly flow volumes are quickly calculated and are ready to send to the Water Board:
SB 88 requires diverters to measure diverted water flow and/or volume, then report the measurements. For small to medium-sized diversions and reservoirs, there is a often transducer measuring and recording pressure. The pressure data has to be converted to depth and flow, or depth and volume. Data may be hourly, daily, weekly, or monthly. Whatever the frequency, the Water Board wants data files uploaded with annual Reports and Supplemental Statements.
Where’s the manual for how to do this, for any of several data loggers, and for meters, weirs, flumes, and orifices, and flumes? It exists in pieces and parts. Each data logger manufacturer has a manual for each product. Sometimes products are similar, and sometimes very different, as are the manuals. The long-existing measuring devices, weirs, flumes, and orifices, are described and general measurement instructions listed in the U.S. Bureau of Reclamation Water Measurement Manual.
When it comes right down to it, a person has to be a “data-head” to enjoy collecting the data, and going through all of it to find bad results, missing data, and odd trends. Then stage and flow have to be calculated and checked against periodic readings taken during visits to the reservoir or stream. Data have to be listed in a format to upload with the Report or Supplemental Statement to the Water Board, and summed monthly to fill out the online form.
If you enjoy educating yourself and taking on new tasks, then you can be a data-head. If not, then you’ll need to have an employee do it, or more likely hire an expert.
Who are the experts? There are engineering firms, manufacturers, vendors and others who can download data for you. It still comes down to the person helping you That person who does the work has to have done data reduction, calculations, checking, and quality control in the past.
Make sure you get help from someone who knows data inside and out! If the Water Board has any questions, your data-head can explain and defend every bit of it for you. He or she will already know the answers to any questions that come up.
What if you have a small diversion, but grass or debris would interfere with a standard weir? A weir has to have unobstructed, free-flowing water over
Weir with debris and grass on crest
the crest so measured depths accurately relate to a calculated flow. A weir with debris problems has to be cleared whenever flow is measured, which increases the time requirement.
When weirs have low flows, they trap debris more frequently, and they are less accurate when the depth over the crest drops below 0.2 feet (2.4 inches). Then the only way to measure flow is with a narrow suppressed weir, or with a contracted weir, typically half or less the maximum width. A V-notch weir can be used for measurement of low flows.
Changing the weir boards for different flows requires someone with experience,
Contracted weir
who will recognize when the depth over the weir is 0.2 feet or less and then use a contracted weir board. However, people are busy when irrigating, and even busier when flows drop. Weirs are often neglected during the time they need more frequent maintenance visits.
A good flume for passing debris and measuring low flows is the HS flume. These are accurate right down to zero flow. For the maximum flow, they require more
1.0-foot HS flume, for flows of 0.00 to 0.80 cfs
material than a rectangular Winflume, Montana, or Parshall flume. However, they are more accurate than other flumes at very low flows – testing by the University of Minnesota found an average accuracy to be +/- 3.2% for ideal approach conditions. They will pass debris down to zero flow – the flume shown here has an opening of 0.05 feet, or 5/8 inch at the flat bottom, and the opening increases with height.
HS flume for flows up to 0.8 cfs HS flume at 0.025 cfs
Why aren’t HS flumes common in California? I suspect that the early adoption of Parshall flumes here established the standard. I have seen a few hundred flumes, but I had never seen an operating HL (wide, high flow), H, or HS flume, prior to my installations.
Why go to the trouble of using an HS flume, if Parshall flumes are readily
New Parshall Flume
available? A Parshall flume may be +/- 10% accurate down to perhaps 5% of its maximum flow. Below that, the accuracy decreases. An HS flume is +/- 10% accurate down to 1% to 2% of its maximum flow. If the flow regime is predominantly low with occasional high flows, it is important to measure those low flows with the best possible accuracy. Some places where low flow measurement is critical include field runoff where pollution is proportional to flow, small water rights, and dam leakage.
HS flumes are easier to construct than a Parshall, too. The HS flume bottom is flat, and it has 3 vertical planes. The photos of the Parshall flume here show
Bottom of Parshall flume
that it has 3 horizontal planes, and 5 vertical planes. An HS flume takes less time to build, and can be put together fairly quickly in any farm or ranch shop. Parshalls are complex enough that they are purchased, including design and shipping costs.
Do you always have to have a purchased flow meter and data recorder for a pipeline? No you don’t. If you pump your flow, you can probably use a certified pump efficiency curve and your online 15-minute or hourly power records.
Call a pump shop that will produce a certified pump efficiency curve for you. The curve itself will cost $300 to $700, and there may be up to $1,000 in setup work to install gage access ports or create acoustic meter mounting points. The resultant curve will have a certified accuracy, in the range of +/- 2-3%, plus an accuracy range for changing pumping levels or variable pump flow rates. The ratings will be +/- 10% or better, and so satisfy the Water Board regulations.
Graphics credit: West Virginia University
The person doing the work can provide you a spreadsheet so you can paste in your power records and get hourly flow rates. The certification will be good for at least a couple of years, and when it is redone for you, will cost in the $300 to $700 range.
These costs look pretty good compared to a meter that will cost $1,500 to $4,000, and has to be recalibrated and maintained every couple of years. Another big benefit is that the pump curve lets your pump shop know what to recommend for you to get the most efficiency, and spend less money for your power!
Will this method work for groundwater as well as surface water pumps? Yes it will. SGMA requirements include well metering for a whole bunch of pumps, so this can be of use to you no matter how you pump your water.
I forgot to mention in my last post on SB 88 compliance, https://allwaterrights.com/2019/02/27/hiding-from-the-water-board-dont-worry-get-compliant/, that you’re still okay if you comply with SB 88 now. The Water Board is not issuing Cease And Desist Orders (CDO) or fines for folks who catch up now, even though it’s late. This is true whether you have yet to install a measurement device, a data logger/recorder, or catch up your Reports Of Licensee or Supplemental Statements. I have seen no adverse action for anyone I know, or clients of other consultants. There are a couple of exceptions here:
You need to catch up before the Water Board contacts you. By that time, you’re probably getting or about to get a CDO with 30 days to comply and report.
If you’re already being contacted, if you received a CDO, if the Water Board is issuing you an Administrative Civil Liability (ACL), if you’re headed to an ACL hearing, then you still need to comply as quickly as possible. Your hassles and fines will not increased, or they may be significantly reduced, and you may still be able to stop the process before you get fined.
I don’t know what may happen in, say, 2020, for folks who have no data for 2018. The same logic applies: get a data logger in and collecting data as soon as possible, and there might be no hassles even for missing data.
Start with a Request For Additional Time. This is quick to fill out and buys you some instant grace. Also, if you had extenuating circumstances like the Carr, Camp, or Mendocino Complex Fires, or other disasters, send an email to Jeff Yeazell, the Water Board’s Public Contact official outside of the Delta. Jeff is very nice, and he is careful to respond back and to keep the emails he gets.
As always, explain in the Remarks and/or other text sections of your Reports Of Licensee or Supplemental Statements anything that helps explain your late compliance, and anything that shows even partial compliance.
And the best news right now is that the drought is over!
Are you hiding from the Water Board because your ditch or piped diversion does
Small Ditch In Meadow With No Measurement Device
not yet have a measurement device? Give me a call at (530) 526-0134 – you might find some workable answers in a 15-minute conversation that costs nothing. You want to get on with the important things in your life and business, and my mission is to help you by solving diverters’ headaches to provide peace of mind, and help stay out of trouble.
The installation deadlines were January 1, 2017 through January 1, 2018. Maybe you don’t want any more government oversight because you put up with a lot already. You could be losing sleep over the potential large fines. Or, what if you do install a device, and you worry that you will be in trouble and have to pay fines as soon as you report your new compliance with SB 88? You might not know what needs to be done, and you’re worried it will cost you $15,000, or $20,000, or more.
You might be thinking that the Water Board is plenty busy, and you’re right. The folks there are going through thousands of online forms for Measurement Methods, Alternative Compliance Plans, Reports Of Licensee and Supplemental Statements that have new measurement device information in the blanks, and Requests For Additional Time. My guess is that it could take as long as 5 years before the enforcement staff get out to the most far-flung corners of the State…but it could be as soon as a year, depending on how the to-do pile is sorted.
Diversion Ditch Before Measurement Device Installed
Diversion Dam and Ditch Before Measurement Device Installed
Diversion Ditch Before Measurement Device Installed
Diversion Ditch Before Measurement Device Installed
Sure, some measurement devices have to be big to handle large diversions. A direction of 20 cubic feet per second (9,000 gallons per minute) or more may require something like the first two flumes shown below. The Parshall Flume shown below may be a $20,000 installation, but the Watchman Flume might only be an $8,000 installation.
As the diversion size decreases, the size and cost of the measurement device go down, too. There may be a relatively temporary solution, like the pipe and board weir that costs only $1,000 or so including the water level logger if you do it yourself. A larger, more permanent measurement device can be installed later.
New Watchman Flume In Medium Sized Ditch
New Parshall Flume
New 3-Foot Wide Briggs Mfg Concrete Weir
New McCrometer McPropeller Inline Meter With Data Collector
If you have a pipeline as part of your diversion, then an in-line meter with an integrated data collector can be installed. The data files from these units are
McCrometer McPropeller inline meter with data collector
easily readable in Excel, and the files can be sent directly to the Water Board to meet the requirements of SB 88.
What if you don’t have a pipeline? Then your flow needs to be measured in the open ditch with a weir, flume, or orifice. These devices measure the flow but they don’t record the data. To continuously record data, a submersible logging instrument must be used to measure the water pressure at the bottom of the box. These logging instruments are commonly put into stilling wells that are inside or outside the measurement device.
Flume with attached stilling well for water level logger
How are water pressure logger measurements converted to diverted flows or reservoir storage? Why does anyone even have to have an electronic pressure logger? Onset Computer, PMC, In-Situ, , and other manufacturers sell data loggers and water level loggers, not pressure loggers, so why is this post talking about measuring pressures at all?
Bluetooth Hobo Logger, cabled to recorder and barometric compensator unit – least expensive option for a single location
Loggers record pressure, because that is the easiest physical attribute to measure. A data logger in water does not know how deep it is, and it does not
know how much flow is going by, or how much water is being stored in a reservoir. Pressures relate directly to static (standing) water depths, and then equations convert the depths to flows, or to reservoir storage volumes.
How is pressure converted to depth? It’s an easy calculation – water that is one foot deep has a pressure of 0.4335 psi at the bottom. So, if your logger measures 1.60 psi, then the calculation to get depth is 1.60 psi / 0.4335 psi per foot = 3.69 feet of depth.
Note that water level loggers can be of two types. The least expensive are completely submersible, and do not compensate for barometric pressure. For an idea of the readings of barometric pressure in a measurement device, a 2 foot deep logger records a pressure of 0.8670 psi. Atmospheric pressure at sea level is about 14.7 psi, and high in the mountains may be 12.0 psi. Air pressure is much greater than those measured in ditches. Usually two of these loggers are used at once, one in the water, and one out of the water measuring only air pressure. This also eliminates the variability in pressure due to weather changes.
Stilling well in a weir
The second type of data logger compensates for barometric pressure at the same time water pressure is being recorded. That way, the water and air pressure data sets do not have to be combined before conversion to depths. These loggers were always more expensive until the Bluetooth Hobo water level logger came along; as of February 2019 I found that it is the least expensive option for a single location.
Now that you can calculate any depth, how do you convert depths to reservoir storage? That requires an Area-Capacity curve, also known as an Elevation-Storage curve. The points can be picked off the curve. For example, in the curve below, a depth of 8.5 feet would correspond to an elevation of 2,802.5 feet, and a reservoir storage volume of 30 acre-feet.
An owner of a reservoir with a capacity over 10 acre-feet must collect monthly storage values. That’s easily done by hand. However, a reservoir with a capacity of 50 AF requires weekly measurement; over 200 AF requires daily measurement; and over 1,000 AF requires hourly measurement. That is really tedious to do by hand.
This is where an Excel spreadsheet can make the task a whole lot easier! The spreadsheets shown below are just for this. The first sheet helps translate a graph into a table of elevations and storage volumes. The second sheet translates collected pressure values into depth and storage values, for as many data points as needed.
For diversion ditches from a stream, how are pressures converted to flows? The logger is in a stilling well, usually a pipe connected to the inside or outside wall of the weir, flume, or orifice. It measures pressure, which is easily converted to depths.
As with reservoirs, Excel spreadsheets make the conversion process a whole lot easier. The sheets below have the rating curve for a suppressed weir, and the second sheet converts pressure to actual water depths over the weir boards. Even for thousands of hourly readings, the hourly flow volumes are quickly calculated and are ready to send to the Water Board:
How is a staff gage installed in a reservoir? The typical way is to drive a piece of 2″ galvanized pipe into the ground, deep enough to so it isn’t easy to push over. If cattle will be in the reservoir to get water, then the pipe needs to be really well installed. A gas-powered post pounder can be rented at Rental Guys, Home Depot, or similar places.
already attached has to be put in place and held vertical while being driven. If the total depth is greater than 6 feet, then a longer pipe, board, and staff gage will be needed, and the combined weight will be that much greater. Hint: tie a rope and buoy to the pipe so 
is true whether you have yet to install a measurement device, a data logger/recorder, or catch up your 
