How to Divide Up a Decreed Water Right

Back in 2005, Arnold and Eileen Williamson bought property near South Cow Creek in Shasta County.  They live in San Bernardino and plan to retire early, and build a new house on their land.  The parcel is part of an old ranch just off Highway 44.

The Williamsons paid $220,000 for the 3.55 acre lot.  That seemed high compared to similar parcels in the area, but they were assured the land has adjudicated water rights from South Cow Creek.

Arnold and Eileen brought their travel trailer to live on the land while they are building a new house.  Their savings account is in good shape so they are going to build a nice 2,200 square foot, single story ranch house with a garage and a shop.  They talked to a well driller 10 years ago and he assured them it would be easy to put in a well, for a cost of around $18,000.Williamson_Overview

When Arnold and Eileen went to get a permit to drill a well, they ran into unexpected problems.  Parcels on either side have their septic systems close to the common property lines, so their possible well locations are few.  Maybe a bigger issue is the passage of the Sustainable Groundwater Management Act in 2014.  Will their pumping rate be limited, and will their well-drilling permit application get held up?

Now the Williamsons are checking into their surface water right.  Is it enough for some pasture for horses and a few cows, in addition to the house and garden?  The Turings who live on the east side say there are no water rights.  The Poulans, to the west, say they have lived here for 6 years and they have never had water – they think the water right was bought off the place, or lost because of non-use.Williamsons_and_neighbors  Now the Williamsons are upset and headed toward just plain mad.  The real estate agent said they had rights, and didn’t the title companies insure it??  After a few frantic calls, they found out that title companies don’t insure water rights.  But, their realtor gave them the number of some folks over on the north side of the highway, and they have a “decree map”.  Arnold and Eileen head over to the Winters’ place to look over the maps.  Brad and Jenny Winters even have a web address where the decree and maps can be downloaded:  https://allwaterrights.com/some-decrees-maps/  The Water Board’s web page has the decree, but no maps:  http://www.waterboards.ca.gov/waterrights/board_decisions/adopted_orders/judgments/docs/cowcreek_jd.pdf.

SCow_Sheet_5_screenshot

It turns out that the Cow Creek adjudication does not have maps, but an engineering report done a few years before the decree was issued does have the maps.  Brad and Jenny have that report, too, so they have Sheets 1 through 5 showing the “Diversions And Irrigated Lands” on Cow Creek.  Besides that, they have the link to where they can get the South Cow Creek decree, and a link to a blog that has the maps not on the Water Board’s web site:  https://allwaterrights.com/some-decrees-maps/  Sheet 5 covers the area including the Winters and Williamson places.  Sheet 5 has a lot of “irrigated lands”Leggett_Focus_Area according to the legend – the green areas.

By looking at the maps, and their Assessor Parcel Map they have in their escrow package, it sure looks like their property is completely within the green area.  Great!  Now, how do they figure out if they actually have a water right?

Arnold and Eileen wonder, can they figure this out themselves?  Brad and Jenny tell them, they sure can, and there is a document online that explains how to do it: https://water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/All-Programs/Watermaster-Services/Files/Water-Rights-Reapportionment-Method.pdf.  They take a look at it and see that, yes, the document fully explains the process, but it requires having either AutoCAD or GIS software.  Also, it will take deep familiarity with the decree – and it is starting to look like a 3-day job just to understand it enough for their parcel!  Arnold and Eileen don’t have the software or experience, so they decide it’s not worth their time to learn this…and they are not sure if they can do it right.

AP_Map_59-98_croppedAfter asking around, Arnold and Eileen figure out they will need to see an attorney.  They call around and find out there are a couple of engineering companies that can see them faster, and they might cost less.  They picked Rights To Water Engineering to help figure out their water rights.  Within a couple of weeks, they have a nice report in their hands and answers to their questions.  So what did they find out?  The map below is one of several from the report they got from the engineer, showing their property boundary on the 1965 decree map of irrigated lands:Ex_2_Williamson_Parcel_Outline_on_DecreeMap_reduced

The report cost $1,500.  The engineer warns them that if it gets contentious and they can’t work out access to the water with their neighbors, they may end up having to get legal help.  He recommends a couple of local water rights attorneys if it comes to that – there are some good lawyers who specialize in in water rights.  For now, though, they have documentation they can discuss with their neighbors to work on getting their water right to their property.

Their property is on land that back in 1968 belonged to Howard and Gladys Leggett.  It has an adjudicated second priority water right for irrigation equal to 0.063 cubic feet per second, or 28.5 gallons per minute, 24 hours a day, 7 days a week, from March through October.   This 2nd priority right is less than the second and third priorities on the upper creek and tributaries, but it is the highest irrigation priority on the lower creek.  Back when the property was flooded, that was usually enough to flood irrigate their entire lot to grow pasture or hay.  That’s great news!

As natural flows drop during the summer that amount is reduced and everyone with a lower creek second priority has to reduce their diversion by the same percentage.  In normal and wet years they could keep their pasture, hay, or whatever else they plant, irrigated for most or all of the irrigation season.  And whether or not they use the water, the right does stay with the land and protect their property value; there is no provision for the expiration of water rights in the decree (the same as for nearly all surface water rights decrees).

What else was in their report?  There was a cover letter, and next some excerpts from the decree.  Schedule 1 lists the places of use for all the original owners.  The Leggetts’ description takes up most of page 60; the Williamson’s property is on the 69.8 acres listed in the second paragraph for the Leggett land:

SCow_Sched1_Leggett_Places_Of_Use

 

Schedule 2 lists all the points of diversion, whether gravity diversions or pumps.  The Leggett property actually could get water from two diversions, a pump from the creek, and a proposed second, movable diversion on the creek.  That’s convenient – per the decree they could already divert their water from someone else’s existing diversion, or pump their water from Diversion 95, or they could get it from anywhere they can get agreement from the landowner!SCow_Sched2_Leggett_Points_Of_Diversion

SCow_Sched2_Leggett_Points_Of_Diversion_2

Schedule 6 lists the water rights for Lower Cow Creek – other schedules have rights for the upper creek and tributaries.  This is interesting: there are four priorities of rights and this part of the Leggetts’ property has

SCow_Sched6_LowerSCC_Leggett_Allots_second_page

 a 1st and a 2nd priority right.  What does that mean exactly?  The decree explains that 1st priority rights are domestic – houses and gardens.  It’s a very small right and it is not clear whether or how it should be divided up among the all the subdivided parcels that used to be the Leggett ranch.  The engineer noted it in the cover letter.

How was the water right calculated for the Williamsons?  Using a geographic information system, or GIS, the engineer used his training and years of experience to precisely overlay the Assessor Parcel Map on the decree map.  Then he measured the acreage for both, and prorated the water right by area.  The following screenshots of the Excel spreadsheet shows these calculations.

TractMgmtSheet_20151222_Arial_12_01_reduced

TractMgmtSheet_20151222_Arial_12_02_reduced

TractMgmtSheet_20151222_Arial_12_03_reduced

Time to fess up: this was a water right subdivision of a fictitious, made-up parcel of land, and the Williamsons don’t actually own it.  However, this story is one that happens every day, when a landowner asks “How much is my water right, really?  Can I divert for hay, stock, pasture, wildlife habitat, crops not mentioned in the decree, an orchard, ……… ?”  Having information before arguing with neighbors, seeing attorneys, sending legal letters, and going to court, can help smart people who generally have good relationships work out happy and agreeable solutions.  The Williamsons were smart and talked politely with their neighbors, the Turings and Poulens and Winters’s.  Now they have a good basis to live peacefully in their neighborhood for many years, and Arnold can borrow Charlie’s lawnmower until he gets his own.

Ex_2_Williamson_Parcel_Outline_on_Aerial_reduced

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?John_Headgate_edit

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.WMM_Table_A9-3_suppressed

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:

Susan_1_of_2_DecreeParaAvailWaterEqualsDiversionsSusan_2_of_2_DecreeParaAvailWaterEqualsDiversionsThe 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.

Submerged Orifices From a Turned-Over Weir Board

Weir With Good Nappe
  Weir With Good Nappe

A flow measurement weir has to have a nappe that springs free, leaving an air gap (photo on left).  What if your weir becomes submerged for some reason (photo below), and boards cannot be adjusted to make it work properly as a weir?

Submerged Weir
  Submerged Weir, not working

 

 

 

 

One thing you can do is turn the weir into a submerged orifice.  The weir board can be turned over, maybe

Weir Board As Orifice
  Weir Board As Orifice

moved down a board position, so the same board serves as a rectangular submerged orifice.

To do this, all the flow needs to pass through a hole cut into the boards.  The depth of the hole doesn’t matter* as long as all of the hole is underwater enough to make it fully contracted.  The area of the hole is very important – it could be in square inches, but squwmm_top_of_table_a9-2_subm_rect_orif-editedare-foot areas are much more convenient to read flows directly from the USBR Water Measurement Manual.  From Table A9-2, flows can be read directly if the area is a multiple of 1/4 square foot.  For example, a hole that is 0.5′ (6 inches) by 0.5′ results in a 0.25 square-foot hole, which is the first column of the cross-sectional area values.

*If the hole is on the bottom and full-width, use Table A9-3, since the bottom will be suppressed.

This is me with 01_At_Diversionweir boards, starting to stack the boards for a weir.  I am using02_One_Board_In 2″ x 6″ lumber from Home Depot.  The lengths are cut about 2″ short of the slot width, so when they swell they won’t get stuck in the slots.  Once the04_1_Ft_Weiry’re all in, I end up with a 0.3′ high, 1.0’long, contracted weir.  The board took 5 minutes to measure and cut with a saw.

shawn_sticking_weir fadedWhen we got flow in the ditch, there was too much flow to use the 1.0′ weir.  Instead, I used the full length of the board, 3.3′, to measure the flow.  Here I am sticking the weir to get an accurate depth.

I turned over the same 06_1_Ft_Orificeweir board to make an orifice of 0.3′ x 1.0′, or 0.3 square feet.  That’s an area not in the tables of the Water
Measurement Manual, so I had to use the equation for a contracted, submerged, rectangular orifice.

This is a submerged orifice – you can’t see the 0.75 square-foot hole because it is underneath the waterOrifice_Side_Top_2.  There are two staff gages, one on the upstream side, and one on the downstream side.  The difference between the depths shown on the staff gages gives the head.  In this photo the head differential is 0.10′, less than the acceptable 0.20′ or higher.  We’ll go ahead and read the flow from Table A9-2 above, 1.16 cfs.

A square or rectangular headgate makes a great rectangular submerged orifice, with bottom and side contractions suppressed (photo on left).  Table A9-3 is used to read the flow for this type of submerged orifice.  Weir boards can also be used this way, so the orifice iAdjusting_gate_orifices on the bottom instead of somewhere in the middle of the stack of boards.  I don’t use boards this way because it makes more work – all the boards have to be removed to reconfigure the orifice back to a weir instead of just one or two.

That’s all for now, and may all your flow measurements be accurate!  Please leave a comment below, on flow measurement devices or anything else:

Standard Units – Acre-Feet and CFS

“Mornin’ Lisa, this is Will.  Hey, my diversion dropped off last night.  You’re the next water user upstream, so I thought I’d check if you made a change last night.”

“Hey Will, how are you folks?  Yeah I did.  I was only taking 50, and my right is 112, so I bumped it up to my full right.”Aerial_Small

“112?!  How’s that work?  My farm is bigger than your place, and I only get 20!  Well Lisa, I think you’re taking too much and you better turn it down.  There’s no way you get that much!”

“Will, when we bought this place from the Sarco’s 4 years ago, they showed me in the deed where the ranch gets up to 112.  It’s right there in the deed….  Do you and Roberta have a deed or something, Will?  How ’bout me and Steve come over and talk about it.  Joe down on the bottom told me there’s been water wars here, and I don’t want hassle if we can avoid it.”Screenshot 2016-04-17 at 08.38.49

 

“Sure, come on over, we may end up talking to lawyers but let’s see if we can figure it out first.”

The next morning, Steve and Lisa went over and dropped in on Will and Roberta.  Lisa showed Will right in the deed where, sure enough, it said” …all water rights appurtenant to the parcel, in the amount of 112 gallons per minute…”  They also showed a Permit from the Water Board, for the same amount.

Will and Roberta laid out a copy of their 1882 filing with the county, wSenior Rightshere it showed their ranch, one of the original ranches in the decree, with a water right of 20 miners inches.
“Lisa, wait a minute, you guys divert in gallons?  How does that match up with miners inches??  Most everyone around here diverts in miners inches, not gallons.”

“When we bought the place, Joe Sarco showed us how our farm was subdivided from the original parcel.  Will, Roberta, you guys know, his farm was split into 4 equal parcels.  When he did that, and the water rights were divided up equally too.  Well, the other 3 parcels got 111, and ours got 112 gallons per minute, almost equal.”

“Well, how much is gallons per minute, in miners inches.  Steve, do you know?”

“I have no idea.  I suppose we can figure it out.  I went and look at our box, and your headgate, Will, and it looks like you are diverting several times as much as we are.”

There are all kinds of ways to measure flow and storage.  Flow rates for agricultural diversions in California include gallons per minute (gpm), miners inches, inches of head, shares, heads, and acre-feet per day (AF/day).  Take a look at the following table from http://www.jennessent.com/unit_conv/manual/no_frame/flow1.htm – there is no lack of ways to measure flow!jennessent.com_FlowMeasUnits

Some of these are very precise, and some not so precise.  “Accurate” is different than “precise”, as STEM graduates are fond of pointing out.  A measurement of 4.25 gpm is very precise, to the second decimal…but if the actual flow going down the ditch is really 9 gpm, then the reading of 4.25 gpm is nowhere near accurate.

Anyway, how much is a gallon per minute, and a miners inch?  Let’s put them in the standard units we use for agricultural diversions today.  Volumes are measured in AF, or one acre of land with water one foot deep.  Flow is measured in cubic feet per second (CFS).  Here are the relationships:

1  CFS = 40 miners inches (except sometimes it’s 50 miners inches, and there are several other variations.  Check out https://www.google.com/?ion=1&espv=2#q=dr%20hydro%20miners%20inches….)

1 CFS  =  450 gpm  =  2 AF/day

More precisely, 1 CFS = 448.84 gpm = 1.983 AF/day, but using the rounded values above is plenty precise enough for field measurements.

What about Steve’s and Lisa’s 112 gpm, and Will’s and Roberta’s 20 miners inches?  It turns out they’re both right, fortunately.  112 gpm is 0.25 cfs, close enough for horse shoes, and 20 miners inches is 0.50 cfs at the 40-miners-inches-per-cfs standard.  So, Will and Roberta do have twice as big a right as Steve and Lisa, which is easy to see once the units agree!

Board Updates Proposed Regs March 2

March 2, the California Water Board has updated the proposed regulations for measurement of surface water diversions.  You have to move fast to beat the comment deadline!

The notice is required to be given “…at least five working days prior to submission of a proposed emergency action to the Office of Administrative Law (OAL).  Then, “After the submission of the proposed emergency to OAL, OAL shall allow interested persons five calendar days to submit comments on the proposed emergency regulations as set forth in Government Code section 11349.6. This document provides the required notice.”  I haven’t called to check, but this could mean there are only 4 more days, until either March 6 (Sunday) or March 8 if “days” are M-F.

The definition of qualified persons is expanded, which will greatly help people with small diversions to comply at less cost, and sooner!  Instead of just engineers, now contractors and “professionals” may install and certify measurement devices.  The deadlines are stretched out somewhat – the biggest diversions (equivalent to 1.40 cubic feet per second 24-7-365, or 5.60 cfs for 90 days straight) and storage over 1,000 acre-feet per year have20160302_BdPropReg_AcrcyFreqQualIndvto be done by January 1, 2017 – less than 10 months.  The diversions equivalent to 0.14 – 1.40 cfs year-round, get six more months, to 7/1/2017.  The smallest diversions, 0.014 cfs year-0.14 cfs year-round, get until January 2018.  That makes sense – the Board gets the most bang-for-the-regulations with the large diversions.

In addition, the Board gives some estimated costs, which helps to plan for the expenditures.  It can be expensive, but when done right, devices can last 10, 20, even 40 years in some cases:

20160302_BdPropReg_CostRange

That’s all for now.  If someone already passed along comments that represent your water right interests, that’s great.  If not, you have a few days to make your own comments.

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
Weir_Set_No_Backfill_edit_smallthe 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.WMM_Cover_small

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.

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.

Board_FactSheet_MeasurementAccuracy

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.