Demo Measuring Weir and Orifice; & Who To Call At The Board?

On January 16, we set up boards, this time videos show measuring flows over a weir and through an orifice!

Simple to set up weirs and orifices

Measuring Weir On Youtube:

Measuring Orifice On Youtube:

Last time, on January 16, we looked at how to set up weir and orifice boards in a dry diversion.  This is more exciting – now we’re actually measuring flow over a weir and through an orifice!


Shawn_Sticking_WeirStanding in front of the Wigno Weir, getting ready to “stick the weir” with an engineering ruler.  The ruler has inches on one side and tenths and hundredths of a foot on the other side – which is how engineers and surveyors measure the world in English (non-metric) units.



Sticking the weir with the ruler face-on shows that the depth is 0.31′, the same as the depth in the upstream pool.  The weir is 3.30′ wide and is suppressed or flat-sided – the water does not have to turn the corner while going over the weir.




With these measurements in hand, it’s a quick calculation using the suppressed weir equation:Supp_Weir_Eq_2

to find 1.90 cfs.

Here is the same weir, before being set up with orifice boards.  Flow is measured through a hole instead of over the top of the boards


The same engineering ruler is used, but this time measuring from the center of the hole, up to the top of the upstream water surface.


Actually, it’s easier to measurefrom the bottom of the hole and subtract off half the height of the hole.  The hole is 1.00′ wide, 0.30′ high, and the water height is 0.25′.


This time, the flow is less, at 0.73 cfs, using the equation: Supp_Orifice_Eq  WHY?  I did not wait the 5 minutes it would take for the upstream head to stabilize.  It was cold and about to get dark and the videographer was patient but getting cold.  🙂

A question I hear all the time is, “Hey, I got this letter from the ‘State Water Resources Control Board‘.  What am I supposed to do about measuring my flow?  How do I keep from getting in trouble?”  The main number for the Water Board is (916) 341-5300 – and these folks have much more work to do than time to do it.  Several calls may be required to reach a knowledgeable person who isn’t already talking to two telephone calls, or making three investigations in the field.  Since the most calls I get are about enforcement letters, calls, or visits from the Board, it’s probably most useful to have the phone numbers and emails from Enforcement Program Staff.  Here they are, from:

Enforcement Program Staff

Katherine Mrowka, Manager
(916) 341-5363

Enforcement Unit 1 Enforcement Unit 2

Laura Lavallee, Supervisor
(916) 341-5422

Ramon Ruiz
(916) 341-5411

Kyle Wooldridge
(916) 323-9405

Janelle Heinzler
(916) 323-9406

Dave LaBrie
(916) 341-5343

Paul Wells
(916) 323-5195

Brian Coats, Supervisor
(916) 341-5389

Chuck Arnold
(916) 341-5634

Matt Quint
(916) 341-5380

Samuel Cole
(916) 341-5345

Jeff Yeazell
(916) 341-5322

Enforcement Unit 3 Enforcement Unit 4

Victor Vasquez, Supervisor
(916) 323-9407

Michael Contreras
(916) 341-5307

Kathy Bare
(916) 327-3113

Oxcar Macias
(916) 341-5637

Natalie Stork
(916) 322-8425

Tomas Eggers

Taro Murano, Supervisor
(916) 341-5399

Michael Vella
(916) 327-3114

Skyler Anderson
(916) 341-5355

Kevin Porzio
(916) 323-9391

Bill Rigby
(916) 341-5376

Stephanie Ponce
(916) 319-8107

How Good Is Good Enough? Water Board Required Accuracy of Your Measurement Device

How accurate does your measurement device have to be?  The Water Board gives those numbers in the Fact Sheet at; see the bottom of this post for the excerpt on accuracy.

When talking about new weirs, orifices, flumes, mag-meters, and acoustic Doppler devices, plus or minus (+/-) 5% accuracy is expected of new, properly installed, regularly maintained, correctly operated devices.  What does that mean?  If your diversion rate is measured at 1.00 cubic feet per second (cfs), then you would expect the true value to be between 0.95 and 1.05 cfs.  If your diversion rate is 5.00 cfs, then the true value would be between 4.75 and 5.25 cfs.  The total accuracy is 10%, we just don’t know if measured values are really up to 5% less, or 5% more than calculated.

New devices might actually have better accuracy than +/- 5%.  Engineers never count on that because a bunch of factors, known and unknown, can stealthily make the accuracy worse.  Accuracy also depends on the measurer – some are better than others, some are better trained and experienced, and most take the job seriously but some do not.

Of course, accuracy gets worse as measurement devices age.  Why does this happen?  There are a number of reasons:

  • Settling, so the device is not level front to back, or side to side, or both
  • Cracking, so water leaks out, or the cracked wall is not straight (planar)
  • Wear, spalling, chipping, and other roughening in the device floor and walls
  • The ditch fills in downstream, causing submergence
  • Old boards that warp and leak
  • Installed staff gages wear, making them harder to read correctly
  • Etc.

The USBR Water Measurement Manual has 14 chapters, and all of Chapter 3 discusses accuracy in great detail.  That’s the “Bible” of water measurement so we would expect it to be, well, accurate in its discussion of accuracy.

It is not clear to me yet whether the Board’s accuracy numbers are +/- values, meaning the allowed accuracy is +/- 15% for diversions less than 100 acre-feet (AF) per year, and +/- 10% for diversions greater than 10 AF per year.  If so, that seems reasonable because that allows for some aging of measurement devices.  Otherwise, the Board would expect measurement devices to always be in new condition for diversions greater than 100 AF per year or storage greater than 200 AF per year.  That would be pretty expensive!

That brings up the subject of money – accuracy requirements hit your pocketbook.  First you have to either install or pay for a measurement device to be installed.  Hopefully the device will last 20 to 30 years, but high flows, getting walked on by cattle, freezing and thawing, settling faster than expected, and other events can wear them out faster.  The replacement cycle might be 10 years for some diversions, or even 5 if wear and tear is bad.


This post may be more than most people want to read on the subject of accuracy.  Still, it’s a lot shorter than Chapter 3 of the Water Measurement Manual!

That’s all for now, have a great rest of the week.

Summary of Water Rights, Flow Measurement Posts So Far

There have been 25 posts so far, on the types of California surface water rights, flow measurement devices, and how to measure diverted flows.  You’ll see new posts once or twice a week.  Please send suggestions for post topics!  We have discussed:

  1. All Water Rights, California
  2. Read Me My Rights (How do you know if you have a water right?)
  3. Reasonable And Beneficial Use Depends On Who You Are
  4. The Smartest Water Expert In California (Chuck Rich)
  5. Riparian Rules by Chuck Rich
  6. Water Rights – Why Do They Exist? Which Kinds Are There?
  7. Water Rights And Engineers
  8. California Water Right Holders Now Required To Have Measuring Device
  9. What Is Your Place Of Use?  (Where can you legally use your right?)
  10. Places Of Use – Adjudicated (Decreed) In The State Superior Court
  11. A Place For Permits And Licenses (Places of Use)
  12. Nothing Secret About It  (This is all public information.)
  13. Quick Change of Subjects: What’s a Water Right Permit Cost?
  14. Life Of Reilly: If You Can’t Measure It, You Can’t Manage It!
  15. How to Divide Up a Decreed Water Right – Part 1
  16. How to Divide Up a Decreed Water Right – Part 2
  17. Weirs – Planning, Building, Measuring Flows
  18. From weir to orifice in only an hour
  19. Chilean Water Rights at (darn near) the Driest Place on Earth
  20. Some Hope in Rain and Snow Totals
  21. Is John Stealing Water?? Orifices – Right Size and How to Measure
  22. Worried about SB 88? That’s what this blog is for! Get a device in, send a photo to the Board, record and report your diversions
  23. Flumes – installing for decades of flow measurement, Part 1
  24. Simple Weirs and Orifices, on video, and in photos!
  25. Diverters must report weekly, daily, or HOURLY starting 2017!

Simple Weirs and Orifices, on video, and in photos!

Simple to set up weirs and orifices!

On YouTube:

01a_EW_1922_01This is a corner of a diversion box built by my wife’s grandfather, Emil Wigno, in 1922.  The fleur de lis he brought with him from France.  🙂   Emil planted hay, peaches, prunes, and finally walnuts.




Hi, I’m Shawn Pike.  🙂

Now 2″ x 6″ boards, cut 1/2″ to 1″ shorter than the width of the board slots, are stacked up in the diversion box.










The weir board is cut 3-1/2″ deep.  There are 2 weirs, one 1.0′ wide, and the other 0.5′ wide.  These are contracted weirs, since water on the edge has to turn to go through.04_1_Ft_Weir


The small weir is blocked off, so the 1.0′ weir is left.  This is a 1.0′ contracted weir, and the flow can be read right out of the correct table in the Water Measurement Manual.





By simply flipping the weir board upside down, we have an orifice!  If the downstream water is higher than the hole, then the orifice is “submerged”.  If the flow out the orifice is free-flowing, then a different equation is used.  Either way, calculating the flow is pretty easy because we know the orifice area, and depths of water upstream and downstream.

Here’s the pretty photographer and videographer, in the gold-mining town of Bodie.  🙂Wiggy_At_Bodie

Flumes – installing for decades of flow measurement, Part 1

What is a flume?  Most people think of long flumes that carry water across a canyon, or along the edge of a mountAlong_Aqueductain, to get water through steep country.  These flumes are expensive and time-consuming to build so they have to make economic sense.  In early
California, flumes were used to get water from a stream to gold-bearing gravels Pipe_Flume_From_Endwhere there wasn’t water.  Gold was certainly worth the expense!  It takes water to wash gravel over a washboard so gold can settle out in the ribs or slats.  Flumes were then used to transport cut logs from the mountains down to mills in the valleys.  Lumber also brought in enough revenue to make flumes worth it.


The kind of flume for measuring flows is a concrete, metal, fiberglass, or wood structure built to exact dimensions.  The newly-built flume shown below is formed concrete.  It took 4 days for a crew of 5 people to make this.  This flume is 3.0′ wide, and will be used toFlume_newly_installed_edited measure diversions of up to about 16 cfs.  This device could last for 40 years before it becomes too worn to be accurate, or develops cracks that let parts of it settle.

Parshall_Flume_DimensionsFlumes are much more expensive than a weir box with boards.  It costs 3 or 4 times as much to install.  On the plus side, there are no boards to change, it measures a wide range of flows with good accuracy (+/- 5% in the first 10-15 years of its life), and it will pass debris and gravel through without clogging.

The photo below is of a flume that has been installed for 30 years.  It shows what can become a common problem: the ditch below has not been kept as deep as it should be, so the flume is “flooded out”.  The flow computed by using the staff gage depth is about 40% more than actually goes through the flume…so the ranchers who use theOld_Parshall_2 water could be shorting themselves.

Rehabilitating a flume is not impossible, but it is not often done.  The whole floor could be raised by pouring a higher concrete floor, making sure it slopes exactly the way the old floor sloped.  Usually a new measurement device is installed nearby, and the old flume is not used anymore.

More on the details and how-to’s of flumes later.  For now, we sure appreciate the snow and rain!

From weir to orifice in only an hour

Orifice devices are needed for flat ditches, where the fall may be as little as 0.20′ (2.4″) from upstream to downstream.  An orifice is simply a hole through which water flows, so it can be accurately measured.  The photo below shows a submerged weir, flowing from right to left.  The water in the ditch downstream (left) is above the hole in the boards.Orifice_Side_Top_2 You already noticed the amazing thing about this orifice, didn’t you?  I could tell you are savvy that way.  Yes, this is the same Briggs Manufacturing weir box as the ones in the previous post!  It has the same 2″ lumber in the upstream board slot.  Now the flow goes through a precisely cut hole in the boards, with a known area, instead of over the top of the boards.

Staff_GageInstallation is just like with the weir boxes installed in the previous post, too.  For convenience, staff gages may be attached to one side of the box so it is quick to read the water depths.  So the precast concrete box is versatile, it can be used as both a weir and an orifice.  Actually, some ditches need both a weir and an orifice.  This is especially true in a ditch where a gate or boards may be put in the ditch below the weir box, to flood hay or pasture just below the measurement device.  All it takes is a change of a couple of boards.







The big difference in measuring the flow is that, instead of “sticking” the weir boards, now the depth of the water must be measured upstream and downstream to use a weir equation or table.  The “difference in head”, or water surface elevation, gives us a value needed to read the table or use an equation to figure out the flow.  What tables or equations?  These are out of the water measurement bible, the Water Measurement Manual.  We will discuss these very soon in following posts.

This was a quick post to show how you can get 2 uses out of one device, to make your life simpler.  That’s all for now, hope you had a Merry Christmas!


Weirs – Planning, Building, And Measuring Flows

Tomorrow is Christmas 2015!  Merry Christmas all.

Weirs are the least expensive permanent measurement device you can install.  Materials will cost the diverter in the range of $300 to $2,000; hiring the backhoe to set it in place probably costs more than the materials, unless the diverter already has a backhoe or crane.

The weir below was precast by Briggs Manufacturing in Willows.  The weir is a cast concrete, 3-sided box with board slots for 2″ lumber.  It’s pretty simple, and relatively easy to install.  This particular weirWeir_Showing_Board_Slotsneeded metal wing-walls to keep the dirt on the sides from washing out.  Note that there are two board slots on each side, one for the boards to slide in, and the other to help make sure a nappe or air gap is created as water flows over the boards.

Step one is determining if there is enough fall in head from upstream to downstream.  A weir needs 0.7 feet (0.7′), or 8.4 inches (8.4″) of fall to be sure it will work correctly.  The 0.7′ figure is because the pool of water needs to be a maximum of 0.45′ above the top of the weir boards on the  upstream side.  Then, the water in the ditch downstream of the weir needs to be at least 0.25′ below the top of the boards so the water flows freely, separating from the boards and having an air gap on the downstream side.  0.45′ + 0.25′ = 0.70′.Sticking_Weir_sharpened

The photo above shows a ruler in tenths of a foot, held vertically on top of the weir boards.  This is called “sticking the weir”.  When the ruler is turned face-on to the flow, the water will climb up to the same level as the flat pool upstream of the boards.  It’s physics – standing water has an energy level equal to the height of the water surface.  Moving water has both potential and kinetic energy, so the energy level or line is above the surface of the

Sticking_Weir_zoom_sharpenedwater.  Moving water stalls behind the face of the ruler, giving the height of the water if it were standing still.  That is the water depth that has to be measured for weirs.  The photo is showing a water level of 0.31′ – it wobbles up and down just a little – so we know this weir is flowing at about 0.6 cfs per foot of width.

If the ditch is very flat and shows no ripples when flowing, it’s probably too flat, and an orifice or a flume will be needed instead of a weir.  Future posts will discuss those measurement devices, and others too.

Step 2 is figuring out how big a box is needed.  Fortunately, there is an easy rule.  1.0′ feet of width is needed for every cubic foot per second (cfs) that will be diverted.  For example, if the diversion will be a maximum of 3 cfs, then the diverter will need a 3′ wide weir.contracted_weir  If in doubt, get the next larger size since the cost is not much more.  The reason for this rule is that a weir can be accurate to plus or minus 5%, well within the accuracy needed for diversions in the field.  If the pool upstream of the weir boards is more than 0.45′ over the top of the boards (or less than about 0.1′ over the top of the boards), the accuracy of the weir is worse than the standard.

Measurement devices need to be planned and operated correctly to assure the diverter (and ditch-tender, and neighbors, and the State Water Resources Control Board, andsuppressed_weirpossibly 10 other state and federal agencies, and possibly even the Superior Court in the very worst case) that the flow measurement is correct.  It’s like a truck speedometer – they can get less accurate over time.  It’s no problem if they read faster than the driver is actually driving, but if they read slower, the driver is in danger of unknowingly speeding and getting a ticket.  Ouch.

The actual installation process is fairly simple to describe.  Get 1 to 4 yards of 3/4″ minus road base rock delivered on site, trucked from the gravel plant.  To save a lot of hassle, skip the forming up and pouring a concrete weir, and just call Briggs Manufacturing and order a weir to be delivered on site.  Dig a shallow, level (flat), square hole in the bottom of the ditch, about 8″ deep, and 1′ longer and wider than the bottom of the weir.  Shovel base rock into the hole about 2″ deep, and compact it.  Rent a gas-powered thumper, or use the bucket of the backhoe.  Pour another 2″ and compact it.  Use a level and make sure the top of the base rock is level side to side, and along the ditch.  Since it packed down during compacting, add the last 1″ and compact it, so the top of the road base is about 4″ below the bottom of the ditch upstream and downstream.

The installer needs to make sure to have a piece of 1″ steel bar that is about 1′ longer than the the width of the weir box.  There is one hole through the top of each side of the weir – stick the rod through that and hook onto it with a chain to lift the weir.  Set it in place, and make sure it is sitting level.  The installer might have to gently press down on one side with the backhoe to get it completely level.  Now the floor of the weir will be at the level of the bottom of the ditch.  Remove the steel bar, and fill the weir box inside about 2′ deep with some dirt.

Next, install the wing-walls, if needed.  These will keep the material on the outsides of the weir from washing out in a steeper ditch.  Then backfill with the remaining road base on the sides, compacting it for each 6″ of depth.  If tNew_Weirhe native soil holds water well, it could be used instead of base rock to backfill, saving a little bit of money.  Remember the dirt that was placed 2′ deep inside the weir?  This will keep the weir weighted down so it does not move during backfilling.  Also, it will keep the sides from being slightly bent in by the pressure of compacting the backfill.  The reinforced concrete weir boxes are strong but the walls can be bent in with enough force.

That’s it!  The weir box is installed and ready to go.  New weir boards, usually 2″ x 6″ or 2″ x 8″, should be cut about 1″ shorter than the width inside the board slots.  For example, a 3′-wide weir will have board slots about 2″ deep.  The full width from inside of board slot, to inside of the opposite board slot, is 3′-4″.  The boards should be cut about 3′-3″ long.  That way, when they swell a little bit, they won’t get impossibly stuck.

Happy measuring!  Good night to all, Merry Christmas, and blessings in the New Year.

Water Rights And Engineers

What is “water rights engineering”? It is not litigating as an attorney, since I am not a lawyer. It could include design and construction of dams, diversion works, pipelines, pumps, and other water-related work.

Concerning water rights, land ownership may change after a water right is defined. Parcels are split so children can each have a part of the original ranch, or because the owner needs income, and a panoply of other reasons. What happens to the original water right?

Well, it depends. In many court adjudications, or decrees, the irrigation water right gets split up by how much of the original place of use is in each smaller parcel. Decrees may also have rights for other uses like domestic (household) use, stock water, storage in a pond or lake, instream fisheries, frost protection, industry, fire protection, and from years past, filling the water tanks in a train steam engine.

What kinds of water rights are there and where do they come from? More on that later.