How To Survey A Reservoir

Pond In Mountains, Photo Credit: Pixabay
Pond In Mountains,  Credit: Pixabay

If you have a reservoir, the Water Board requires you to measure and report: how much you divert to it, how much water you store in it by month, and how much water you release if the pond has a controllable outlet.  It is usually not possible (or at least not feasible) to measure the inflow, so what is actually reported is the monthly positive change in storage, the amount that fills it up.

If your reservoir is less than 10 acre-feet (AF) per year, you only have to report it.  Measurement is not required.

How do you know how much is stored in your reservoir?  Each pond needs an elevation-storage table or curve, as the Water Board calls it.  Engineers call it an area-capacity table or curve – that’s what I created during part of my career as a water bureaucrat.  I’ll use the Water Board’s terminology here since water diversions and storage are reported to them.

First check to see if the Water Board or Division of Safety of Dams has an inspection report for your reservoir.  If not that, then an elevation-storage table or curve may be available.  You can have it emailed as a PDF.  If there is no information for your reservoir, then you have to create the table and curve yourself.

First a reservoir has to be surveyed, so you know how full it is for any given elevation of water.  The elevations start at zero storage.  The figure below shows a cross section and the contour map for a reservoir with a minimum elevation of 86 feet.

Pond Contours. Photo Credit:
          Pond Contours,  Credit:

How do you survey a reservoir?  You could hire an engineer or surveyor to survey it.  Depending on your budget and your need for accuracy, the elevation-storage table from a survey could be anywhere from +/- 5%, to +/- 10% accurate.  The Water Board requires +/- 10% for larger reservoirs, and +/- 15% for 100 acre-foot (AF) or smaller reservoirs.  I recommend aiming for +/- 5% in case you have significant errors elsewhere in the measurement system.

On the high end, the survey could be done using GPS survey instruments, so the result could be accurate and could overlay other digital maps.  Almost as high a cost is to have a transit with EDM (electronic distance measurement).  Robotic units only require one person acting as the rodman, and the instrument “follows” by keeping pointed at the laser prism reflector.

At the bottom end of the scale, a survey level or possibly a hand level, and a couple of 100′, 200′, or 300′ tapes can be used.  Many survey levels can read horizontal angles within a degree or two, so the instrument person can note angle and distance to every point.  If angles are not used, then two tapes are used, one to measure the distance along a side, the other to measure perpendiculars out to the rodman.  In the boat, the rodman measures depths, and on land he has a telescoping level rod to get elevations above the Photo_0188water level.  This way you measure X and Y distances that are plotted on a grid along with each point’s elevation or depth.

With plotted points, now you can draw contours for every foot, or every two feet, or every five feet, depending on the size of your reservoir.  Then calculate the area for each contour, and the volume between each set of contours.

Here’s where Google Earth can be your best friend.  Navigate to your property and reservoir in Google Earth.  Then take a digital photo of your contour map, and import it into Google Earth as an image overlay.  Make it 50 percent transparent, and move and resize the image until it fits over your reservoir.  Now you can use the polygon tool, trace over your contours, and let Google Earth calculate the areas for you!  Make sure to get those areas in square feet or acres and not square miles.

An alternative way of doing this is to print out a map of your reservoir from Google Earth, then draw your survey points and contours right on that map.  Then when you import the scanned or photographed, edited map, it will be a lot easier to overlay on your reservoir.

Make an elevation-storage table and draw an elevation-storage curve like the one below.

Let’s look at an example.  To get the reservoir volume, add the areas of two adjacent contours, say, the 90-foot contour and the 92-foot contour, divide by 2, then multiply by the elevation difference (in this case, 2 feet).  If the 90-foot contour has an area of 6.1 acres, and the 92-foot contour has an area of 7.6 acres, the calculation is [(6.1 + 7.6)  / 2] * 2 = 13.7 AF.

190-AF Reservoir Capacity Chart

Here’s the great thing about simple methods: anyone can measure his own reservoir by reading up on it first (Google, Bing, or DuckDuckGo) and then taking some care (and good notes) to do the job well.  If the topography is difficult, or the pond is too large for tapes, or you are just too busy doing the work you have to get done, then talk with an engineer and negotiate cost vs. quality and accuracy.


Great AB 589 Self-Certification Training!

I attended the Flow Measurement Devices and Methods course in Cottonwood yesterday, for diverters to become a “qualified individual” per AB 589.  What a great class!  All my appreciation and applause to Larry Forero, Allan Fulton, and Khaled Bali of the UC Division of Agriculture and Natural Resources, who taught the course.  They laid out the requirements and the details of several ways to comply with SB 88, including weirs, flumes, water level loggers (pressure transducers with data collectors), in-line meters, in-line differential pressure, how to determine and track reservoir volume, and how to report changes in volume.

There were specific examples of how to size a weir to install the correct device, how to convert measured flow rates to the volumes that must be reported to the Water Board, and how to select an inline meter if your diversion is piped.  There were detailed examples of how to comply with the Water Board’s reporting requirements, and discussion of the most relevant parts of SB 88.

I hope that Larry and Allan will make their Powerpoint presentation available online for public use.  It is well done and really helps understand how to comply with SB 88, both in the field and online at the Water Board.

Update:  Allan Fulton contacted me and let me know that this course IS accepted by the Water Board!  So sign up, take the 3-4 hour course, and you will be certified to install your own measurement device(s).

I heard a week ago that it isn’t a 100 percent lock that completion of the course will be accepted by the Water Board.  However, the course is more than adequate in my estimation, and I don’t think the Water Board has any alternatives to comply with AB 589.  It is going to be accepted!

AB 589 says, in part:

“…any diverter who has completed an instructional course regarding the devices or measurement method included in the course administered by the University of California Cooperative Extension, including passage of a proficiency test before the completion of the course, shall be considered a qualified individual when installing and maintaining devices or implementing methods of measurement that were taught in the course for the diverter’s diversion.”

Thanks to the Shasta Livestock Auction Yard for providing the location – my guess is that there were 140 people attending, a good crowd for this narrow subject.  The Cattlemen’s Association got the word out and provided refreshments.  It was hundreds of hours of work among 8 people or so to pull this off.  Job well done, everyone!

Converting water logger pressures to depths to storage or flows

How are water pressure logger measurements converted to diverted flows or reservoir storage?  Why does anyone even have to have an electronic pressure logger?  PMC, Onset Computer, 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?

Most “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 7.00 psi, then the calculation to get depth is 7.00 psi / 0.4335 psi per foot = 16.15 feet of depth.

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.

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: 

[Update/Repost] Do Something Wrong, Instead Of Nothing!

Do something wrong, rather than nothing at all. Have you ever heard that before? I have heard it from Army veteran friends, a boss, even an elder of a church.

What it means to you and me is, if action is necessary, do something, maybe ANYthing, rather than freezing in place or ignoring a problem. This is obvious when you see a tornado 5 miles away, for example; either drive away from it if you are in a car, or take shelter if you are on foot. If you have a plumbing leak in the house and no parts to replace broken pipe, then put a bucket under it, or turn off the valve, and call a plumber. All of us have seen a TV show (or maybe had it happen to us) where a bad guy or an enemy pointed a rifle and said, “Don’t move.”. What do we all say to the TV? “Don’t just stand there, run!”. Doing nothing is a much worse choice!

Man working in ditch CostaDisc2-129 - EditedWhat about water rights – how does doing something wrong help? Everyone knows by now that surface water diverters need measurement devices, so put in a weir box and boards and try to measure flow if the Water Board, your watermaster, or your neighbor is promising painful consequences. Even stick boards in a ditch and seal the sides with gravel – something to take positive action to reduce future pain.

Take a look at the blog posts here.  There is enough information and how-to directions, that you might be able to do it right!  Check out these posts:

There is a philosophy based in law and a lot of experience, that says don’t put any controls on yourself until the court or government makes you. Why remodel your house to accommodate the wiring or plumbing, if you aren’t selling the house and everything works okay? Who would put a lot of money into an old truck to make it pass smog, if it just might pass a smog check the next time it has to be done? What farmer would change how he irrigates or ranches if everything still operates and the bank will keep making operating loans?

Surface water and groundwater are getting 10 50 times the attention they were prior to 2009. If the Water Board, or California Fish and Wildlife, or any other agency comes along, do something, anything, to comply sooner, even if it’s not the ultimate solution. Two posts ago, bureaucrats were discussed – they are still human beings and most people appreciate some effort to “get with the program”.

Be proactive, take some inexpensive action, educate yourself for free with some time in the Internet. Even a small, less-than-perfect improvement in your measurement device, flow and water use record keeping, diversion practices, or acreening, can pay back a lot more when you have to deal with agencies, a court, or an angry neighbor in the future.

You Can Be Your Own Qualified Individual For Diversions! AB 589 Passed October 4 – Training Coming Soon

Good news for folks who want to install, certify, measure and maintain their own devices!  AB 589 passed on October 4, and now any landowner, or their lessee or employee, can take the class and do all the required stuff to measure and record his own diversion flows / volumes.

I have not heard what the class dates might be, or whether it is online, and so on.  As soon as I do, I will sure put the word out there.  Meanwhile, let’s hope for another wetter-than-average winter – abundant water solves most of the demand issues.


Assembly Bill No. 589


An act to add and repeal Section 1841.5 to, the Water Code, relating to water rights.

[ Approved by Governor  October 04, 2017. Filed with Secretary of State  October 04, 2017. ]


AB 589, Bigelow. Water diversion: monitoring and reporting: University of California Cooperative Extension.

Existing law requires a person who diverts 10 acre-feet of water or more per year under a permit or license to install and maintain a device or employ a method capable of measuring the rate of direct diversion, rate of collection to storage, and rate of withdrawal or release from storage, as specified and with certain exceptions. Existing law requires the measurements to be made using the best available technologies and best professional practices using a device or methods satisfactory to the State Water Resources Control Board. Existing law requires a permittee or licensee to demonstrate to the board at 5-year intervals that a measuring device is functioning properly, as specified.

Existing law authorizes the board to adopt regulations requiring measurement and reporting of water diversion and use by persons including, but not limited to, those authorized to appropriate water under a permit, license, or registration for small irrigation use or livestock stockpond use, or a certification for livestock stockpond use.

This bill, until January 1, 2023, would require any diverter, as defined, who has completed an instructional course regarding the devices or measurement method administered by the University of California Cooperative Extension, including passage of a proficiency test before the completion of the course, to be considered a qualified individual when installing and maintaining devices or implementing methods of measurement that were taught in the course for the diverter’s diversion. The bill would require the University of California Cooperative Extension and the board to develop the curriculum of the course and the proficiency test.

Vote: majority   Appropriation: no   Fiscal Committee: yes   Local Program: no




Section 1841.5 is added to the Water Code, to read:


(a) For the purposes of a device installed pursuant to Section 1840 or 1841 or a method of measurement proposed and adopted pursuant to Section 934 or 935 of Title 23 of the California Code of Regulations, any diverter who has completed an instructional course regarding the devices or measurement method included in the course administered by the University of California Cooperative Extension, including passage of a proficiency test before the completion of the course, shall be considered a qualified individual when installing and maintaining devices or implementing methods of measurement that were taught in the course for the diverter’s diversion. The proficiency test shall seek to certify that the diverter has a satisfactory understanding of the principles of measurement and the use of a measurement method included in the course or the installation of a device. The University of California Cooperative Extension and the board shall develop the curriculum of the course and the proficiency test. The University of California Cooperative Extension and the board shall ensure the course curriculum and the proficiency test do not conflict with any state licensing acts.

(b) For purposes of this section, “diverter” means an individual authorized to divert water under a valid water right, a lessee of property that is subject to a water right who is acting as a representative of the water right holder, or a bona fide employee of the water right holder or lessee.

(c) This section shall remain in effect only until January 1, 2023, and as of that date is repealed, unless a later enacted statute that is enacted before January 1, 2023, deletes or extends that date.

How Do You Record Diversions? Water Level Loggers, Value Vs. Costs

Recording is the other half of measuring diversions from streams, under the law per SB 88, and per the Water Board‘s water diversion measurement and reporting regulations.  Diverters are required by law to measure flows at frequencies based on the volume of water diverted in a year.  The flow has to be measured and recorded.  Of course many diverters don’t need the data – it costs money and it doesn’t add income…unless a farm or ranch is upgrading for efficiency or to increase acreage  What you and I want in all of our purchases is the best value for the money.

We’ll look at 5 different water level logging options.  The total cost given does not include installation – that adds $200 and up.  Certification for the logger and the measurement device itself, by a professional, required for all but the smallest diversions, costs $300 and up if you have Rights To Water Engineering do the work.

  1. Vegetronix Aqua-Plumb Water Level Sensor connected with the Logger-8-USB  ($400 per diversion, less if diversions are very close to one another – with tax and shipping, about $500 per diversion)
  2. Onset Hobo U20L-04 Water Level Logger  ($600, less for multiple diversions; with tax, shipping, and data shuttle, about $1,050 for the one diversion, $1,400 for two….)
  3. Global Water WL-16  ($1,000; with with tax, shipping, and cable, about $1,450 per diversion)
  4. In-Situ Rugged Troll 200 Data Logger and Tube 300 Telemetry System ($1,200 – less for multiple diversions, plus $1,300 for each telemetered diversion.  With tax, shipping, and cable, about $1,600 per diversion, and with telemetry and add-ons, about $3,300 for one diversion)
  5. PMC Versaline VL4511 – WLS-31 ($1,370 per diversion; with the cable, tax, and shipping, about $1,800 per diversion)

This is a long post since it is hard to summarize something this technical so here is the bottom line:  my top recommendation is the last of five in this post – for most diverters.

SWRCB Measurement and Recording Requirements for 2017 (diverters exempted where Watermaster reports)
SWRCB Measurement and Recording Requirements for 2017 (diverters exempted where Watermaster reports)

For very small diversions, flows have to be recorded monthly or weekly.  That is easy to do as long as someone goes to the diversion at least once a week.

Photo credit:

Shawn_Sticking_WeirFor medium-sized diversions, flows must be recorded daily.  This is possible, but
it doesn’t allow for the owner or employees to have time off, travel, and so on.  At this level of recording, an automatic recorder of some type is necessary.  Large diversions must be recorded hourly, and automatic recording is the only practical way to be sure flows are recorded.  That is the subject of today’s post: automatic recording of flows, or what is really done most of the time, recording water levels and using equations to calculate the flow.

About_1.4_cfs_over_weir_edited_smallWe will leave aside the discussion of propeller, acoustic Doppler, magnetic, and other in-line meters.  If you have a diversion that goes through a long length of straight pipe, one of these devices can be bolted in or strapped on.  This post is about open diversions into a ditch, where an instantaneous measurement device (weir, orifice, flume) already exists.  These open devices do not measure flow directly, they measure the water level.  An equation is used to convert levels to flows after data is downloaded.

There are hundreds of devices (ready to go) and components (connected parts) to measure water levels.  There are also hundreds of loggers that collect data.  Here, we will look at 5 water level sensors connected to data loggers, called water level loggers.


THE FIRST is a setup that rancher and retiraqua-plumbed aircraft engineer Frank Crowe has been working on.  Frank’s desire is to save him and his neighbors money, so he has been working with the Vegetronix Aqua-Plumb Water Level Sensor connected with the Logger-8-USB.  Together these are $340, which is
the least cost of anything that I have seen.   With this you will have all thelogger-8-usb
parts you need for moderately durable, reliable, and accurate water level logger.  Not only that, but 
the Logger-8-USB has 8 channels altogether, so a diverter could measure up to 8 water levels at once by adding 7 more sensors at $95 apiece.  Wiith tax and shipping, this costs about $500 per diversion)

Here is Frank’s latest setup with his comments:  “Finally was able to put together a prototype package for the vegetronix_frank_1_p1300077vegetronix_frank_2_p1300078Vegetronix sensor.  The box is a little bigger than needed, but seems to work.  I’m trying to get the data to download into something I can analyze, but it seems to work very stable.

The pipe is 3/4″ mounted to the box, with the sensor wire going down to about an inch from the bottom and then returns up over 12″, therefore doubling the sensitivity.  The end is held by some wire at the moment, but would probably work better with a stainless steel spring.  The top of the pipe is not sealed, but should be to keep the humidity out of the box.  Of course if the data logger were in a separate box, the seal would not be necessary.

To exercise the thing, it is stuck into a 3″ pipe with a water drip going in and a drain at the bottom.  The overflow hole is 13″ above the bottom.”

So, what is the trade-off?  If you are handy, somewhat experienced with electronic components, and willing to spend some hours, you can set this up yourself.  Frank can help a few of his neighbors, but he has his family and ranch requiring his time, too.  Otherwise, it is going to cost a couple hundred dollars or so for someone to set this up for you.  It needs to be checked, maintained, and adjusted more often than the integrated water level loggers, too, so the maintenance and downloading cost can be $50 to $100 per year if everything is working well.


SECOND, the Onset Hobo U20L-04 Water Level Logger is $300 before shipping and tax.  The DWR Groundwater folks I worked with for years, use these in groundwater wells.  They are easy to set up – program one and place it in a stilling well.  Take it out once or twice a year to dowonset_hobo_u20l-04-editednload the data.  The battery life is 5 years, maybe more.

Why aren’t these automatically the cheapest option?  They may be the cheapest if a diverter has 3 diversions or more, or several neighbors are using the same Hobo U20L-04.  However, they are not vented, meaning that as atmospheric pressure changes due to low pressure areas and storms, the device’s pressure reading will not be as accurate.  Therefore  Onset recommends having a second U20L-04 set up outside the water to measure the pressure change over time.  The second device can be some miles away, so one outside calibration device could be used for several in the water within a 300-square-mile area.

What I heard from colleagues is that these did not last for 10 years, and sometimes not for five years, although the device is being improved over time.  Durability and reliability of a device are important for uninterrupted data, and therefore compliance with the Water Board’s regulations.  The more often onset_u20l-xx_handhelda device has to be replaced, the more it costs over time.

In summary, the cost of Onset Hobo U20L-04 devices is $600. This cost may be reduced somewhat if the cost of a calibration device can be shared between several diverters, or several diversions.  With tax, shipping, and data shuttle, the delivered cost for all parts is about $1,050 for the one diversion, $1,400 for two….)


THE THIRD device discussed here is the Global Water WL-16.  This is an integrated, vented device, designed to program and set in a pipe.  Watermasters have used these for years at various diversions.global_water_wl16-edited

The WL-16 has a stainless steel casing and is fairly tough.  They should last a good 5 years.  The problem is at the sensor end – it is relatively easy to clog up in warm-water conditions, with algae and/or silt.  In cool flowing water, it might operate for the whole irrigation season.  In warmer or still water, it will have to be checked and sprayed clean every 1 to 3 months.  Watermasters have put the sensor ends in distilled water in baby-bottle bags, and rubber-banded the tops of the bags closed to keep the sensors clean for the entire irrigation season.

One other concern which I have not discussed with the manufacturer – the manual for the WL-16globalwater_wl16_in_field was updated in 2009 and refers to Windows XP, not the current Windows 10.  I am sure that a newer manual is sent out with the device when it is purchased.  Overall, with some care to check the sensor end and clean it as necessary, this is a great drop-it-in-and-turn-it-on option.  The cost for a WL-16 is $1,000; with with tax, shipping, and cable, about $1,450 per diversion.


THE FOURTH device, the In-Situ Troll, has the advantage of out-of-the-box options for telemetry.  The Groundwater folks at the Department of Water Resources have used these and a couple recommend these for the right application.  The In-Situ

in-situ_rugged_troll_200_loggerRugged Troll 200 Data Logger and Tube 300 Telemetry System.

The Troll 200 Data Logger can run independently without telemetry, or be attached to the Tube 300R Telemetry System.  The Troll 200 is non-vented, so like the Onset Hobo data loggers mentioned above, an extra unit is needed for air pressure to correct the water level (pressure) recorded by the unit in the water.

The total unit cost for 2 Troll 200s, a Tube 300R, and accessories, is about $2,900.  This is not cheap, but it is a lot less than a full-on gaging station with satellite radio, which costs $12,000 and up for components, and over $2,000 to install in easy locations.  Telemetry is expensive, there is no way of getting around that fact.  In summary, the cost for 2 Troll 200s is $1,200 to log a diversion – each additional, nearby diversion costs only another $600.  Telemetry addes $1,300 to the cost of parts for each telemetered diversion.  With tax, shipping, and cable, using Troll 200s costs about $1,600 per diversion, and with the Tube 300R telemetry and add-ons, the total parts cost is about $3,500 for one diversion)

The Tube 300R requires a separate phone number for each water in-situ_tube_300r_telemetrylevel logger, and cell service.  In-Situ offers the option of $35/month web hosting, on its HydroVu Cloud Data Services Plan.  This cost is in addition to the Tube 300R, cell phone service, and installation.


THE FIFTH and final water level logger discussed here is the PMC Versaline VL4511 – WLS-31 Water Level Datalogger.  This looks much like the WL-16, but instead of a silicon bladder at the end of sensor, it has a non-fouling ceramic sensor.  At $1,370 before tax and shipping, it has the highest purchase cost of the 4 listed in this post, but it is my recommendation for durability, reliability, and low maintenance.

The Versaline is made for wastewater; in other words, for sewer lines.  The datalogger end is vented and it is not supposed to be submerged, same as the Vegetronix components and the WL-16.  However, it is made to put inside manholes where it is very warm and humid.  The PMC guys have maintained the sensor end in rough environments with the equipment lasting 8 to 12 years.  If the sensor gets completely covered with algae (or something worse), it still works.  It can be cleaned off with a toothbrush if it seems so clogged it might prevent water from getting to the ceramic end.  The data logger and sensor are fairly new but are improvements on the older, long-lived versions.

The VL4511 – WLS-31 is three times the cost of the least-expensive option.  However, it might be the least expensive in the long run…it sure is the most worry-free of all the options listed here!  In summary, the VL4511 – WLS-31 costs about $1,370 per diversion; with the cable, tax, and shipping, about $1,800 per diversion.pmc_header-editedversaline-vl4511-and-wls-31-water-level-datalogger-specs-editedThere are many, many choices for logging water levels.  These are the ones I would install, either because I, my colleagues at DWR, or larger farms or ranches have used them; or because I have checked with other users.  One of these choices can serve you well!



What Does A Measurement Device Evaluation And Proposal Look Like?

When you call and ask, “What do I have to do to stay out of trouble with the Water Board?”, my reply is usually, “What’s your diversion or pond like?  How much and what type of water right(s) do you have?  When can I come and take a look at it?”  We’ll figure out a time, and I’ll visit for 2 hours or however long it takes to see how your diversion works, or how your pond fills and empties, and think of a few likely solutions.

Then I will write up an evaluation and proposal.  The proposals are good enough that, if you don’t choose me to install or certify it, then you, another engineer, or a contractor knows how to get the job done can install it and keep you out of trouble.  Of course, I would like the whole job, but you do have choices!

So, what does an evaluation and proposal look like?  Here is an example, just for a single measurement device for one diversion: