## Is John Stealing Water?? Orifices And Sum Of The Boxes

This is updated from a previous post, which was an example for a stream with adjudicated water rights.  However, it also works for any stream where there are water rights with legally defined diversion quantities, if all the diverters have headgates in good condition and/or measurement devices such as weirs, flumes, and pipe meters.

Is John Stealing Water??  John Casey has a cattle ranch near Adin, where he grows pasture and hay to raise about 70 Angus steers.  His ranch is 240 acres with lower irrigated land and forest on the higher part.  He has an a licensed water right of 2.00 cubic feet per second (cfs) from Preacher Creek, to irrigate 80 acres, from April 1 to November 1.

John’s downstream neighbors claim he steals water.  He says he can show that he takes only 2 cfs, or less when the flow drops down in the summer.  Can he prove it?

As we can see, he has a square headgate at the head of his ditch.  It is 2.0′ wide, and can open up to 1.5′ high.  Right now, John says he is diverting 1.05 cfs.  His evidence is that his gate is open 0.15′, the water is 0.57′ deep on the upstream side, and the water is 0.20′ deep on the downstream side.  Is that enough to check what he says?

The box in which the gate sits has smooth walls, and the gate closes flush with the bottom when John is not diverting.  The water continues in a straight path from upstream to downstream.  That means the weir has “suppressed” sides.

This is in contrast with, for example, a hole cut in the middle of a 2″ x 12″ weir board.  The water on the sides has to make the turn to go straight through, so the hole in the board is an example of a “contracted” orifice.

Let’s look at the tables for orifices in the back of the Water Measurement Manual.  Table A9-3 is for submerged, suppressed weirs.

We can’t see the downstream side of the weir, but the water is above the bottom of the edge of the gate, so it is submerged rather than free-flowing.

This table has flows calculated for a minimum area of 2.0 square feet (sq. ft.).  However, the area of the opening at John’s headgate is 2.0′ wide x 0.15′ high, or 0.30 sq. ft.  Fortunately, the equation, Q=0.70A(2g Δh)^0.5, is listed right at the top of the table.  We can calculate the flow using that.  Q is the flow in cfs, A is the area of the orifice hole, g = the acceleration due to gravity, or 32.2 ft/second^2 (feet per second squared), and Δh is the difference between the upstream and downstream water depth.

So the flow Q = 0.70 x (2.0′ x 0.30′) x (2 x 32.2 x 0.37′)^0.5 = 1.03 cfs.  So far so good – John is taking 52%, or just over half of his right when 100 percent of flows are available.  But, how much flow is actually available right now?

Let’s use the “sum of the boxes” method.  Instead of measuring the amount of water in Preacher Creek at the top, before any diversions, and then estimating how much flow is being lost to evaporation, transpiration, and infiltration, and then estimating how much flow is subsurface above John Casey’s ranch and “pops up” out of the ground below, we’ll look at what each diversion amount is, plus the amount still in the creek after the last diversion.  This is very useful because none of the instream losses have to be estimated – we just add the diversions and flow still in the creek, and that amount IS the available supply.

Water Board Permits and Licenses are usually not interrelated – they specify water rights without considering the other water rights on the stream.  This is different from adjudicated streams, whether done by the Water Board or the Department of Water Resources.  Some Superior Court judges in past decades were pretty smart and actually ordered that available flows be calculated by the sum of the boxes:

The paragraph above, from the Susan River Decree, defines available water supply as what is being diverted, plus the flow passing the last diversion.

There are 4 diversions on Preacher Creek, and here are the amounts being diverted:

• Diversion 1 (John Casey) 1.03 cfs  of a 1.60 cfs water right, 52% of his total right
• Diversion 2 (Amy Hoss) 1.67 cfs  of a 3.80 cfs water right, 44% of her total right
• Diversion 3 (Mark and Cindy Sample) 0.55 cfs  of a 0.88 cfs water right, 62% of their total right
• Diversion 4 (Quint and Marcie Minks) 1.32 cfs  of a 2.50 cfs water right, 53% of his total right
• Flow still in the creek past the Minks Diverison – Quint estimates about 0.7 cfs

The total diversion-plus-bypass flow is about 5.3 cfs.  The total rights on the creek are 9.48 cfs.  Therefore, the total available flow = 5.3 / 9.48 = 56%.

So, John is right, he is not stealing water!  He is taking 52% of his water right, when he could be taking 56% according to the “sum of the boxes” method.  Not only that, but Amy could take more, the Samples should reduce their diversion, and the Minks’s could take a tad more.  Well, that’s theoretical – Quint and Marcie Minks probably cannot seal up their dam completely, so there may be a little bit less flow actually available for diversion.

## Update – Who To Call At The Board?

A question I often hear is, “Hey, I got this letter/a call from the State Water Resources Control Board.  What am I supposed to do about measuring my flow?”  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.  So, start with the main contact, Paul Wells, who is very knowledgeable and can get you the answers or the person you need to talk to.

By the way, Thank You to Kathy Mrowka, who has been reasonable in working with diverters who are trying to comply.  What she says often is true:  talk with her and/or others at the Water Board and you’ll likely get consideration, some more time to comply, and reduced (maybe greatly reduced) fines.

Since many 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 the Water Rights Enforcement Program Web Page:

## Enforcement Program Staff

 Katherine Mrowka, Manager (916) 341-5363 Paul Wells, Senior WRCE Specialist (916) 323-5195

Central Coast/So. Cal Unit San Joaquin Valley Unit
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

Brian Coats, Supervisor
(916) 341-5389

Chuck Arnold
(916) 341-5634

Matt Quint
(916) 341-5380

Damon Hess
(916) 341-5345

Jeff Yeazell
(916) 341-5322

Sacramento Valley Unit North Coast Unit
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
916-327-8039

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

Vacant

## How Do I …. ? (Determine My Water Rights, Measure Flows, Report Flows , Etc.)

See the new “How Do I … ?” link on the left.  There are so many posts on this blog, it is getting harder to find stuff.  Click on the link, or right-click then “Open link in new tab”, and the big questions are linked to the appropriate blog posts.

Another way to search is, as always, Google.  For example, googling “allwaterrights measure weir” brings up the following results:

## Accurate, Economical Flume for LARGE Diversions

Photo on the right:  Intermountain Environmental Inc. Nuway Ramp Flume with stilling well, 20 cubic feet per second (cfs) capacity.  Shipped disassembled including fasteners; stilling well not included (but inexpensive to add).

20 cfs irrigates 400 to 2,000 acres of crops, trees, pasture, or hay, depending on where you are.  As a Professional Engineer with wide experience installing and operating flow measurement devices, I can solve your headaches, heartburn, and trouble meeting the Water Board’s Regulations, diverting 20 cfs, for as little as \$6,000 with one of these flumes.  These flumes can go in an almost flat ditch, needing a water drop of less than 4″, and still maintaining accuracy of plus or minus 5%, twice what is needed by the Water Board.  Smaller flumes cost less; even larger diversions could use 2 of these side by side.

Frank Crowe, farmer/rancher and the neighbor of some readers of this blog, has been doing research for 7 months on all possible flow measurement and datalogging devices.  He has found some lower-cost options, including the Nuway flumes, that in past years, I did not think would work well. After checking into them, I know many of these can save you headaches, anguish, trouble, and some money.  Technology has improved and computing costs have come down to make smaller, less expensive data loggers very useful for diversions.  For example, the eTape sensor and Track-It datalogger shown here, and similar equipment from other manufacturers, will work well for many diversions:

Frank checked into the smallest Nuway flume, for 3.5 cfs, and found that the cost is fairly low at \$580.  With a size of about 12″ wide, 15″ high, and 48″ long, it will be easy for one person to assemble and would be possible to install by hand, without a backhoe.

Larry Forero, County Director of the Cooperative Extension in Shasta County, has been doing a great job of searching and asking the how diverters can comply with the law economically, particularly through alternative methods.  The “Alternative Compliance” form will be available any day now on the Water Board’s website.  Larry has also been checking on devices, costs, and applicability for particular locations and uses.

Most diversions will have to comply using standard, accepted methods of measurement and recording data.  Following up on Frank’s research, I contacted Intermountain Environmental, Inc. in Utah and asked Josh Hanks about their 10 cfs and 20 cfs galvanized flumes.   They cost \$1,017 and \$1,995 respectively.  Shipping would be less than \$300. Josh provided detailed information, including how these flumes have performed in the field.  They are designed and built to be plus or minus 5% accurate, well within the Water Board’s regulation of +/- 10% accuracy as certified in the field.  Many installations have worked with soil backfill only, instead of poured concrete.  Installations will probably require a mass-concrete anchor, and may need steel plate inlet wingwall extensions, or outlet wingwalls added.

The bottom line, what does it cost for me to solve your problem, and to purchase, install, attach a datalogger, and certify the device to the satisfaction of the Water Board?  For the largest flume, which can measure up to 20 cfs, in a typical location with vehicle access, I can have these working right, logging data, and certified for you, for \$6,000 to \$9,000.  Telemetry and/or solar power, if needed or required by the Water Board, could add another \$1,000 to \$4,000.

Done!  No more headaches, turmoil, or trouble for you, and I will have the pleasure of helping you keeping your business working well.

## How Do I Comply With Water Board Regulations? Part 3

In Part 2, How Do I Comply With Water Board Regulations? Part 2, we considered the question:  Who has to have a certified, accurate device by January 1, 2017? How often is it monitored?  The answer is, those who divert 1,000 acre-feet (AF) per year or more, and it has to be monitored hourly.  What size diversion is this, really?  An irrigation diversion of 1,000 AF over 6 months, with flows starting at 100% of the water right, declining to 50% of the right by the end of the season (month 6) would calculate out to a water right of 3.68 cubic feet per second (cfs), or about 3.7 to 4.0 cfs (cfs).  Depending on where you are, that irrigates somewhere between 80 and 400 acres of hay or pasture.

In this post, I’ll answer 2 questions:

1. What if your water right is smaller than 3.7 cfs, diverting 100 AF to 1,000 AF per year?
2. A BIG question right now: What is “alternative compliance”, and how might it be done to meet the Water Board’s regulations?

To answer the first question, the next category down is 100 AF to 1,000 AF per year.  Using the example of a 6-month irrigation season, with a diversion that starts at 100% of the water right and gradually declines to 50%, the water right we’re talking about is about 0.37 to 3.7 cfs.  This category does not have to comply as quickly – the deadline is July 1, 2017, or nearly a year from now.  The measurement frequency is daily, which is possible to be done by a diligent person, if not not recorded automatically.  For a sense of how much water this is, depending on where you are, what the soils are like, and how efficient the diversion is, the acreage of hay or pasture irrigated ranges from about 8 to 370 acres.

What kind of measurement devices would meet the regulations?  The same types that we discussed in Part 2, but ranging down to smaller sizes:

• weirs as little as 0.5′ (0.5 feet, or 6″) wide, or wider with boards cut to make contracted weirs
• free-flowing orifices with holes down to 0.16 x 0.16′ (2″ x 2″) square and a piece of steel plate to adjust it smaller
• submerged orifices down to 0.25′ x 0.25′ (3″ x 3″) with an adjustment plate.
• small flumes and meters

The photos above show smaller-sized devices than the 4′ weirs shown in earlier posts.

The second, and these days much BIGGER question, what about alternative compliance?  The Water Board requires submission of alternative compliance plans on a form that is not yet available.  If it were my diversion, I would not worry about that; I would put together my plan and send it in.  The old rule applies that if you are not sure who to send it to, send it to several managers and maybe a Deputy Director.  Emailing documents is cheaper; most computers will let you print to PDFs that can be emailed.  Your submittal probably will not be accepted this way but the point is, the Water Board cannot say that you have not attempted to comply.  Not complying at all can be very expensive; “Do something wrong, instead of nothing at all.”

This screenshot is from an OLD, no longer valid Statement Of Use form, but it
gives some ideas of what options for alternative compliance the Water Board has in mind.

What has to be in your alternative compliance plan?  From the Water Board’s ADOPTED TEXT OF EMERGENCY REGULATION, the text gives 12 parts that must be in the plan (below).  The plan may be rejected – having a plan (instead of a standard, certified measurement device) is no guarantee that the Board will accept it.  In summary, the plan must detail contacts for all people on a ditch, Assessor Parcel Numbers, the water right(s), priority(ies), use(s), diversion(s), ditch(es) and/or pipe(s), measurement frequency and methods, dates for milestones and completion, permits required, financing plan, and map(s) showing the plan area including all physical features and place of use…and all of this must be signed by all water right holders on the ditch (the emphasized text in the bullet points is mine):

“…………  §935 Alternative Compliance for a Measuring Device or Measurement Method Requirement.

(a) Alternative Compliance – Generally. In circumstances where strict compliance with sections 933 or 934 of this title is not feasible, would be unreasonably expensive, would unreasonably affect public trust uses, or would result in the waste or unreasonable use of water, a diverter may submit an alternative compliance plan.

(b) Minimum Standards – an alternative compliance plan under subdivision (a) shall meet the following minimum standards:

(1) The plan shall include the following information:

(A) The name and contact information for all diverters covered by the plan;
(B) The name and contact information for the person designated to represent all diverters covered by the plan in matters before the board;
(C) Identification of each individual water right type and priority covered by the plan;
(D) A detailed description of the area served by the plan, including all points of diversion whether used or not used, all methods of diversion, any conveyance systems, all beneficial uses of water, and all acreage served;
(E) The assessor’s parcel numbers and ownership within the area covered by the plan;
(F) Identification of the proposed measurement frequency;
(G) Identification of the proposed measurement methodology;
(H) Topographic map(s) or aerial photograph(s) of the area covered by the plan that show the separate places of use authorized to be served by claimed water rights covered by the plan and showing the acreage served;
(I) An implementation schedule, including date-specific, objective milestones of plan implementation from date of filing through final implementation, including the estimated milestones for acquiring permits required for plan implementation and the estimated milestones for compliance with the California Environmental Quality Act, if required;
(J) Budget for implementation of the plan and the source(s) of financing for the plan;
(K) A list of any permits required for plan implementation, the agencies that will issue the permits, and expected dates for issuance;
(L)
An affirmation, signed by all diverters covered by the plan, that the plan will be implemented in accordance with the schedule contained therein and that all claimed water rights covered by the plan will not be exercised outside the scope of the plan  …………”

## How Do I Comply With Water Board Regulations? Part 1

Yesterday I met with some nice folks up in Hat Creek and Old Station.  A big question right now is, how do I comply with Water Board regulations?  Also, what exactly do I need to do for a measuring device?  And, where can I find out that what I do will be acceptable, so I don’t get dinged after I did what I was supposed to?

First: devices.  The most common, long-lasting, and cost effective devices for measurement of irrigation diversions are:  weirs, orifices, flumes, mag-meters, propeller meters, and acoustic Dopplers.

Weirs are the least expensive, long-lasting, accurate devices.  This weir was prefabricated and shipped from Briggs Manufacturing.  Installation takes a few hours, and with new 2″ lumber, accuracy is plus or minus 5 %.  That is better than the Water Board’s requirement of 10 % accuracy.

An orifice is often exactly the same as a weir, with the boards set as an orifice.  Instead of the water going over, it goes through an exactly-sized hole.  The accuracy is plus or minus 5 % if it is set up carefully.  The cost is the same as for installing and operating a weir.

Here is another kind of orifice – a headgate.  If it is a square headgate, or a new, round (Waterman) headgate, then the area of the opening can be determined with plus or minus 5% accuracy.  An older headgate or one with a less-than-perfect opening can still be 10% accurate, within the Boards’s standards.

This is a Parshall flume.  It uses no boards, so no debris can pile up.  It is nearly maintenance-free.  Flumes cost more to install, and if they settle and get out of level they lose accuracy.  However, you’ll see many of these in Northern California.  There are some prefabricated flumes just coming into production that will be easier to install and will include data collectors.

How do you know which one will work for a particular diversion?  Someone with expertise can check the ditch, grade, soil-type, flow range, and other information and tell you within a couple of days what will work best, with an engineering report and cost estimate.  Rights To Water Engineering does this for \$300 to \$500, and can install the device if you like, with an operations manual.

Filing Statements of Use with the Water Board is now all by computer through the Internet.  That’s one of the things Rights To Water Engineering, and some other folks do at a reasonable cost.  If that’s your worry then contact us and we can point you in the right direction or help you out with reporting.

This is the quick summary on compliance!  Contact me at (530) 526-0134 or RightsToWaterEng1@gmail.com, and read this blog for more detailed information.  Have a great weekend!

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

#### Simple to set up weirs and orifices

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!

Standing 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:

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:   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:

http://www.waterboards.ca.gov/waterrights/water_issues/programs/enforcement/compliance/

## Enforcement Program Staff

Katherine Mrowka, Manager
(916) 341-5363
Kathy.Mrowka@waterboards.ca.gov

## Update to “Weirs – Planning, Building, & Measuring Flows”

This is an update and correction to the December 24 post, “Weirs – Planning, Building, & Measuring Flows“.  In that post explaining the essentials of installing a weir box, I had said to excavate the pad 4” deep and fill with base rock.  It should have said, excavate 8″.  I’m sure you already figured out why:  the weir bottom is about 4″ thick, so the weir floor would have been above the bottom of the ditch.  By excavating 8″, and then filling with 4″ and compacting a level pad of 3/4″-minus road base, when the weir is placed the floor of the weir will be level with the bottom of the ditch.  That way, the weir is not too high, where flow will undercut
the base, and it is not too low, requiring extra boards to get a still pool upstream of the weir.  The weir box in this photo is set – all it needs is for the water to be shut off, sides backfilled, and boards put in for easy measurement.

The important factor in figuring out where the weir gets placed along the ditch, is that the ditch needs to be straight upstream of the weir box.  You can see in the photo above that the weir is located in a straight section of the ditch.  When the box is placed in alignment with the straight ditch, the approaching water does not have to make a turn.  Water going around a bend rolls toward the outside of the bend, and rolling or turbulent water might give a false reading of depth over the weir boards.

How long does the straight section of ditch have to be?  The wider the weir, the longer the length of the ditch has to be straight.  For a 1.0 foot-wide (1.0′) weir, which would pass a maximum of 1.0 cubic feet per second (cfs) if it worked as a suppressed weir, the minimum distance should be about 10′.  For a wide weir box of 6.0′, the upstream distance should be 70′ or 80′.

How high do the boards have to be to provide an essentially still pool upstream of the weir?  Remember the rule that the static head going over a weir, or the height of water that climbs up a 1/2″ engineering ruler held face-on to the flow, should be a maximum of 0.45′.  A suppressed weir, with the flow width going from wall to wall as it goes over the weir, has to be 3 times that 0.45′, or 1.35′.  2  2″ x 8″ boards stacked up will get this height.  If the weir is contracted, or cut into the board, then the board height only has to be twice the static head, or 0.90′.  A 2″ x 12″ would take care of this.  However, to be sure, never use less than 2 2″ x 8″ boards.

One more thing – the weir has to keep from collecting dirt or sand behind the boards.  That means the boards may have to be lifted up every so often so the sediment can flush out.  Weeds have to be kept down all around the weir so they don’t affect the flow of water.  In the same way, sticks and grass have to be kept off the tops of the boards for the weir to work correctly.

Where can you find all this information yourself?  As always, check the bible for measuring flows, the USBR Water Measurement Manual.

That’s enough for now, more to come soon!  Have a great week and I hope it rains today where you are.

## Coming Soon, Free Ebooks on Measurement Device Installation and Flow Measurement

The All Water Rights Blog has most or all of the information needed for a farmer or rancher to install a simple measuring device that is compliant with the recent regulations of the State Water Resources Control Board.  I’ll have a couple of free ebooks by June, on how to install pre-cast weirs and orifices, as well as how to use them correctly, and report flows from small diversions to the Water Board.  Actually, the ebooks will apply to larger diversions, too, except for the necessary pressure transducer needed to report hourly (and some day, 15-minute) flows to the Board.

There are certainly more complicated devices that require help, such as cast-concrete
Parshall and other flumes, mag-meters, acoustic Dopplers, or full-on gaging stations on rated sections of streams or ditches.

However, most diverters can (and many do) comply with the law with relatively simple devices.  That’s it for now, I just wanted to get the word out on this.

Oh, and there will be an ebook some time around August, which has a working title of “Practical And Applied Water Rights In California – The Non-Attorney Book For Diverting Your Water”.  That book will be more complete and will cost something, yet to be determined.  Let me know what YOU want to see included in a book like this.

Have a great day, pray for more rain and snow!

## 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 http://www.swrcb.ca.gov/press_room/press_releases/2016/pr12016_measurement.pdf; 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.

http://www.usbr.gov/tsc/techreferences/mands/wmm/index.htm

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.