Category: Accurate, Lasting Devices

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.

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.

For 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.

We 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 retired 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,
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 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 download 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 a 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.

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-16 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.

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!