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: 

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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.

WaterLevelLogger_wl300_1
Photo credit: globalw.com

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!

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How Do You Record Diversions? Water Level Loggers, Value Vs. All Component Costs – Update

My friend Steve Beall in the far north of the state brought something to my attention, regarding my comparison of four water level loggers (five with the In-Situ Troll 200 added).  I listed only the component costs, and not the data cable, data shuttle (Hobo), software, PVC/galvanaized pipe, or installation.  Good point, and thanks for suggesting that I address all costs, Steve.  The five loggers detailed farther on down in the post are, with component costs only, data transfer, installation, and certification not included:

  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 and shipping about $700)
  3. Global Water WL-16  ($1,000 per diversion, about $1,100 with tax and shipping)
  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…about $2,500 for one diversion; with tax and shipping about $2,800 per diversion)
  5. PMC Versaline VL4511 – WLS-31 ($1,370 per diversion, about $1,500 with tax and shipping)

The additional components you will need if you want to download and process your own data are:  a customized data cable (or shuttle for the Hobo), and software.  These add $250 to $350.  You also need a laptop, except for the Hobo, unless you temporarily remove the other loggers to download them on your desktop at the house.  Shipping and taxes will add $70 to $350, depending on which equipment and the location where it ships from.  Electronic tools and equipment, and various testers are useful, sometimes necessary, to chase down problems.  Extra connectors and wire might be needed – keep at least a simple kit.  Installation can cost $200 and up, depending on the difficulty, need for vandalism protection, access, and so on.  Certification by a professional, required for all but the smallest diversions, costs $300 to $500 if you have Rights To Water Engineering do the work.

*****  ORIGINAL POST, with a couple of edits:

Recording is the other half of measuring diversions from streams, under California’s new 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 most diverters don’t care about 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.

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.

WaterLevelLogger_wl300_1
Photo credit: globalw.com

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.  Add shipping, tax, logger-8-usb
and $60 in other parts and batteries, and for $450 you’ll have the parts you n
eed 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, not including tax and shipping.

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 plus tax and shipping.  This cost may be reduced somewhat if the cost of a calibration device can be shared between several diverters, or several diversions.

 

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.  They cost about $1,000, before tax and shipping.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 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 ($595) can run independently without telemetry, or be attached to the Tube 300R Telemetry System ($1,320).  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 cable and software for the Troll 200 are about $375.

The total unit cost for 2 Troll 200s, a Tube 300R, and accessories, is about $2,900.  Tax, shipping, and installation will add $600 and up, depending on location, elevation, and the length of the dirt road going in; and difficulty at the site and vandalism potential will add costs, too.  $3,500 + for telemetered water level logging 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.

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 VL2111 – WLS-31 Water Level Datalogger  (replaced by the same-priced, updated model:  PMC Versaline VL4511 – WLS-31).  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.

pmc_vl2111-with-wls-31-datalogger

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 VL2111 – 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!

*****  From the update post, Update – Recommended Water Level Logger: PMC Versaline VL4511 – WLS-31

The PMC guys had to make a change in the sensor, so now the recommended setup is the PMC Versaline VL4511 – WLS-31 Water Level Datalogger.  It will cost the same and be as durable.  Regarding the reason for the change, pmc_header-editedversaline-vl4511-and-wls-31-water-level-datalogger-specs-editedBob Foster at PMC wrote: “This system will come with our VL4511 level sensor and not the VL2000 that we initially spoke to you about.

The reason for the change is the VL2000 required slightly more power than what is available through the datalogger battery, so we decided to provide an upgraded sensor model, which uses much less power.

This upgraded sensor, our VL4511 also has the advantage of using:

  1. An all-welded Titanium housing, which has a 5-year corrosion warranty
  2. Significantly smaller diameter

Additionally, it still has anti-clog features near the sensing element to ensure reliability.”

 

There 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!

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Update – Recommended Water Level Logger: PMC Versaline VL4511 – WLS-31

This is an update from my earlier post on my recommendation for a durable, set-it-and-forget-it water level logger.  Some kind of device is necessary to meet Water Board requirements; daily data must be recorded July 1, 2017 for those diversions of 100 to 1,000 acre-feet per year, and hourly data must be recorded starting January 1, 2017 for those 1,000 acre-feet and higher.  These roughly correspond to minimum irrigation season water rights of 0.37 to 3.7 cfs, and 3.7 cfs and higher.

To review, here is the Water Board’s table of measuring and monitoring requirements.  I added the 2 columns on the right to show the approximate water rights and year-round flow in CFS:

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

The PMC guys had to make a change in the sensor, so now the recommended setup is the PMC Versaline VL4511 – WLS-31 Water Level Datalogger.  It will cost the same and be as durable.  Regarding the reason for the change, pmc_header-editedversaline-vl4511-and-wls-31-water-level-datalogger-specs-editedBob Foster at PMC wrote: “This system will come with our VL4511 level sensor and not the VL2000 that we initially spoke to you about.

The reason for the change is the VL2000 required slightly more power than what is available through the datalogger battery, so we decided to provide an upgraded sensor model, which uses much less power.

This upgraded sensor, our VL4511 also has the advantage of using:

  1. An all-welded Titanium housing, which has a 5-year corrosion warranty
  2. Significantly smaller diameter

Additionally, it still has anti-clog features near the sensing element to ensure reliability.”

I also asked Bob about battery replacement.  Some well-known loggers have to be sent back to the manufacturer to have the batteries replaced.  The battery lives are 1 to 2 years.  What about the PMC Versaline VL4511 – WLS-31?

Bob reassured me that the PMC unit’s batteries are replaced in the field, by the landowner, or the engineer or technician acting for the diverter.  Battery lives are still only 1 to 2 years.  However, the batteries are inexpensive, about $7 each.  That keeps your costs and hassle to a minimum.

What about expected maintenance at the manufacturer?  While some better-known data loggers typically have to be sent in every 2 to 3 years, the PMC unit is expected to need no manufacturer’s maintenance for 10 years!

Original post:

This post is about the PMC Versaline VL2111 – WLS-31 Water Level Datalogger.  This looks much like the Global Water 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 a higher purchase cost than some alternatives, but it is my recommendation for durability, reliability, and low maintenance.

pmc_vl2111-with-wls-31-datalogger

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.  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 VL2111 – WLS-31 is three times the cost of the least-expensive option that I have seen so far.  However, it might be the least expensive in the long run…it sure is the most worry-free of all the options listed here! 

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

Recording is the other half of measuring diversions from streams, under California’s new 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 diverters don’t care about the data – it costs money and it doesn’t add income.  What you and I want in all of our purchases is the best value for the money.

This is a long post since it is hard to summarize something this technical so here is the bottom line:  my recommendation is the last of four in this post – for most diverters.  Click here for the simple, short post on my top recommendation.swrcb_flow_meas_frequency-edited

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

WaterLevelLogger_wl300_1
Photo credit: globalw.com

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 that level to a flow.

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 4 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.  Add shipping, tax, logger-8-usb
and $60 in other parts and batteries, and for $450 you’ll have the parts you n
eed 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, not including tax and shipping.

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.

Next, 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 100-square-mile area.

What I heard from colleagues is that these did not last for 10 years, and often not for five years.  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 plus tax and shipping.  This cost may be reduced somewhat if the cost of a calibration device can be shared between several diverters, or several diversions.

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.  They cost about $1,000, before tax and shipping.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 fourth and final water level logger discussed here is the PMC Versaline VL2111 – 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.

pmc_vl2111-with-wls-31-datalogger

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 VL2111 – 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!

Recommended Water Level Logger: PMC Versaline VL2111 – WLS-31

This post is about the PMC Versaline VL2111 – WLS-31 Water Level Datalogger.  This looks much like the Global Water 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 a higher purchase cost than some alternatives, but it is my recommendation for durability, reliability, and low maintenance.

pmc_vl2111-with-wls-31-datalogger

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.  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 VL2111 – WLS-31 is three times the cost of the least-expensive option that I have seen so far.  However, it might be the least expensive in the long run…it sure is the most worry-free of all the options listed here!