How Do I Comply With Water Board Regulations? Part 2

In Part 1, How Do I Comply With Water Board Regulations? , we looked at what water flow measurement devices will meet and exceed the Board’s requirements.  The questions right back to me were:  1) Yeah, but which dates apply to me?  and 2) Yeah, but what about monitoring and collecting data and reporting?  How do I do that?Board_2017_Table

  1.  Who has to have a certified, accurate device by January 1, 2017?  How often is it monitored?

This is the “worst case” if I am not already compliant – less than 6 months from today!  The first to have to report are those who divert 1,000 acre-feet or more per year, or store 1,000 acre-feet or more per year.  The reporting has to be hourly, or 8,760 data points per year.  The average rate of diversion for 365 days is 1.38 cubic feet per second (cfs) (which I had rounded to 1.40 cfs in previous posts).  That’s equal to 620 gallons per minute (gpm), or 2.74 AF/day.

What if all the flow is diverted just for the irrigation season?  Let’s use 6 months for simplicity – the average rate of flow is 2.76 cfs.  Available flows dropAbout_1.4_cfs_over_weir_edited_small as the summer proceeds, so what size of water right are we really looking at?  Let’s say flows decline evenly from 100% at the beginning, to 50% of available flows at the end of 6 months.  The right that would divert 1,000 AF per year under these conditions is 3.68 cfs.  The summary is, if my water right is, say, 4 cfs or more, then it is very likely I will be in this category.  The weir shown abovJohn_Headgate_edite is a 4′ weir, capable of measuring up to 4 cfs very accurately, at plus or minus 5% (sometimes better) accuracy with new lumber.  A headgate like the one to the left is easily capable of passing 4 cfs and, if the gate is used as a measurement orifice, the accuracy can be 5%, certainly within plus or minus 10% if care is used with an older gate.

I can get that 4′ weir shown above installed and working for somewhere between $2,000 and $10,000 – depending on how difficult the access is to the site, whether native materials can be used, or 3/4″ base rock and 12″ protective rock have to be hauled in, and whether I already have a backhoe or excavator to install it.  The headgate will cost more than that, maybe $3,000 to $12,000.  A larger bulkhead or box is required, and good gates can cost quite a bit.

A larger diversion will have to use a larger weir or orifice, or more likely a flume or acoustic measurement device.  That makes sense – the larger the flow, the more complicated it is to measure.

How do I report hourly flows?  I sure can’t run out to the diversion every hour, so that means I have to use some kind of automawl16ted flow GE_PT878measurement device.  The G.E. Panametrics acoustic Doppler meter on the left is an option, and it or an in-line propeller meter, or an inline mag-meter, will be necessary for some configurations of diversions (pumped or very flat).  The price starts at $5,000, though.  If I have enough fall (drop in water elevation), I would sure rather put in a weir, orifice, or flume.  A weir or flume can use a water level measurement device and data collector like the water level logger above on the right.  That Global Water device is relatively durable, takes readings as often as desired, and can store data for months.  It costs a little over $1,000.  Oh, and if the orifice is submerged, so that the hole is underwater both upstream and downstream, then I will need two water level loggers, for $2,000.

Some folks at the Water Board are talking about telemetered data, meaning the data is sent to a remote location, or even available online.  This would only be necessary if there were a great possibility FTS_GOES - Editedthat the diversion would be tampered with, or if it is a large diversion having a big impact on the amount of flow left in the stream.  This has little benefit for anyone at most diversions.  I would only install it if the need were very clear to me and everyone else.  The added cost can be anywhere from $1,000 for short-range radio, to $20,000 or more for a full-on gaging station like you see on streams.  The annual cost of operation and maintenance goes up, too.

How do I read the data on thesnotebook-405755_1280e devices, so I can report it to the Water Board?  Well, that takes some expertise.  If I have 5 diversions from a creek, I’ll make sure my foreman knows how to do it, and handle it myself.  If I have 1 or 2 diversions, then it’s more cost effective for me to have a professional do it, and to maintain it periodically.  Reading that data takes a laptop to hook up to the USB port, and the software that comes with the device, and the expertise to look at the data Sticking_Weirand make sure it’s reasonable.  The data that is recorded is “stage”, or water surface elevation.  Using the correct weir, orifice, or flume equation, or table from the Water Measurement Manual, the stages have to be converted to flows.  For hourly flows, that means 8,760 data points per year, which will require a spreadsheet like Excel to make the conversions.  A BIG caution is that if the boards are changed, it has to be written down WMM_Cover_smalland then a different zero-flow datum used to convert stages to flows starting when the change was made.

2.  Who has to have a certified, accurate device by July 1, 2017?  How often is it reported?

The “next worst case” is for those diversions from 100 AF to 1,000 AF per year – irrigation water rights of about 0.35 to 3.5 cfs.  These have to be recorded daily.  The measurement devices are the same, but smaller.  It is possible someone might grab a reading every day…but it is more likely that these will also have some kind of automated water level logger.  More on these later.  Have a great weekend!

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.