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!

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AllWaterRights - Rights To Water Engineering

Solving Diverters' Headaches To Provide Peace Of Mind And Help Stay Out Of Trouble. Helping California residents understand, define, and protect their water rights since 2005.

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