CFS vs Gauge Height Debate

[Al Agnew]

11 hours ago, fishinwrench said:

I just don't compute it that way.  6" is 6" regardless of whether the stream is 10 feet across, or 1/2 mile across.

 

Sure it is, and I do use the height in feet to see how the river level has changed after a rain.  For instance, I look at the flow in cfs graph first (always).  It immediately tells me, for instance, that the river has been around normal flow (the little triangles on the graph signify normal flow) until yesterday, and then jumped up.  At that point, I look at the height in feet graph to see how high it jumped, because that's easier to visualize than knowing it jumped up 400 cfs.  But 1.5 feet as a given level right now on that stream is NOT the same as 1.5 feet on a different stream.  But 150 cfs on one stream is exactly the same flow as 150 cfs on any other stream.  Having used the flow in cfs for many years, I can picture in my mind what 150 cfs looks like--how deep the riffles will be and therefore how easy it will be to float.  I've gotten good enough at it that if I walk up to a stream and look at a riffle when it's normal or low or even somewhat high, I can tell you with about a 10% error margin how many cfs it's flowing.

[fishinwrench]

3 hours ago, Al Agnew said:

But 1.5 feet as a given level right now on that stream is NOT the same as 1.5 feet on a different stream.  But 150 cfs on one stream is exactly the same flow as 150 cfs on any other stream.  Having used the flow in cfs for many years, I can picture in my mind what 150 cfs looks like--how deep the riffles will be and therefore how easy it will be to float. 

Craziest thing I've ever heard you say. 😊 

I can tell you that any river with a guage height of 1.5 ft. is going to be low and barely floatable in spots.   There's no "minus" when measuring guage height.  Zero means DRY.  

When camping on the river I drive a steak in at the waterline or make a little rock pile.  Way easier to tell the degree of rise/drop by looking at that than it is to glance at the nearest riffle and guess the CFS flow compared to my memory of yesterday.

[Devan S.]

6 minutes ago, fishinwrench said:

Craziest thing I've ever heard you say. 😊 

I can tell you that any river with a guage height of 1.5 ft. is going to be low and barely floatable in spots.   There's no "minus" when measuring guage height.  Zero means DRY.  

Gage height would be highly dependent on the location measured which is only understood from first hand knowledge. There is no way to glean that information readily from the data publish on the USGS sites. Measure 1.5' in a "deep" hole and your in trouble, 1.5' in a shallow riffle no matter the width and your probably okay. The problem isn't necessarily related to gage height when it nears zero. It's what do you do when the water level is 2-4 ft. Most people with little to know reasonable knowledge would assume that 4ft would be an easy float but if that is measured in a hole then it may or may not mean anything since you could in theory have a hole 4 ft. deep with almost little to no flow in or out. 

Both measurements are useful but without the "rest" of the story gage height can and will be misleading. CFS is handy because they already give you the mean, median data to understand if flow is high or low compared to historical data. CFS easily translates all along a stream while gage height is highly localized. 

Once your familiar with a stream, then it ultimately doesn't matter what you use because you likely have enough knowledge to determine if something is float able or not. 

[Guest]

 

 

3

[fishinwrench]

5 minutes ago, Devan S. said:

Gage height would be highly dependent on the location measured which is only understood from first hand knowledge. There is no way to glean that information readily from the data publish on the USGS sites. Measure 1.5' in a "deep" hole and your in trouble, 1.5' in a shallow riffle no matter the width and your probably okay. The problem isn't necessarily related to gage height when it nears zero. It's what do you do when the water level is 2-4 ft. Most people with little to know reasonable knowledge would assume that 4ft would be an easy float but if that is measured in a hole then it may or may not mean anything since you could in theory have a hole 4 ft. deep with almost little to no flow in or out. 

Both measurements are useful but without the "rest" of the story gage height can and will be misleading. CFS is handy because they already give you the mean, median data to understand if flow is high or low compared to historical data. CFS easily translates all along a stream while gage height is highly localized. 

Once your familiar with a stream, then it ultimately doesn't matter what you use because you likely have enough knowledge to determine if something is float able or not. 

If you aren't familiar with the river then CFS is useless too.   Some streams are easily floatable at 95 cfs, while others aren't.    Same can be said about the median flow since some streams can only be floated when they are high.  

Floatability and fishing conditions don't always jive with each other.  My concern is always how the fishing conditions are going to be, not whether or not I can float it without a portage.

[fishinwrench]

25 minutes ago, siusaluki said:

They go negative on some rivers, especially large rivers like the Missouri and Mississippi.  When it’s -1.5 at one gauge the miss is still flowing 250,000 cfs or more.  One river near me would still be be 3.0 feet on the gauge if the riffles ran dry.  All that it tells you is the height of that gauge station and the water level in that location. Gauge heights are more useful in flood situations.

 

 I know what 150 cfs looks like anywhere I go.

Didn't know that, thanks.  

So having never seen the river......if you see 250k CFS you'd think "cool sounds perfect"....then you get to NFOW and come across a washed out bridge and flooded fields.  😂 

I don't care what you say.....you gotta be somewhat familiar with the river for any of it (guage height or CFS) to make any sense.  Most river guage apps don't even show what the median flow is, gotta go to the USGS site to get that info (and often FOR ME that site won't load).

150 CFS on the little Niangua is good (perfect) but 150 CFS on the Mississippi is a bummer.   We'd all be in big trouble if that happened. 😅

[snagged in outlet 3]

I keep notes on both cfs and gauge height for my trips.  Also notes about how the river was at that point.  For instance I can tell you for the middle Meramec if the Sullivan gauge is 385 CFS at 2' my notes say "Don't go".  That's the level a guy tore his transom off above Hwy K.  My gorilla tape got him back to the ramp.  I'm talking jet boats here.     

[Flysmallie]

I think it just depends on what you are used to. CFS works for me. 

[Al Agnew]

5 hours ago, fishinwrench said:

Didn't know that, thanks.  

So having never seen the river......if you see 250k CFS you'd think "cool sounds perfect"....then you get to NFOW and come across a washed out bridge and flooded fields.  😂 

I don't care what you say.....you gotta be somewhat familiar with the river for any of it (guage height or CFS) to make any sense.  Most river guage apps don't even show what the median flow is, gotta go to the USGS site to get that info (and often FOR ME that site won't load).

150 CFS on the little Niangua is good (perfect) but 150 CFS on the Mississippi is a bummer.   We'd all be in big trouble if that happened. 😅

Nope.  I can tell you whether any of the floatable rivers in the Ozarks are too low to float or not simply by looking at cfs and median flow.  I don't have to know anything else about them.  And here's another story...I floated the John Day River last summer.  The John Day is in Oregon and is a different river from any in the Ozarks, and it definitely gets too low to float by late summer, as the agricultural interests take most of the water in it.  We were worried it would be too low by the time our trip was planned.  So I kept watching the gauge.  I KNEW that we needed 150 cfs or more to float it in canoes.  Why?  Because I knew that it wasn't THAT much different from Ozark streams, a riffle/pool stream with riffles about the same width as the middle Meramec.  But the last time I'd floated it had been in 1998, and that was before I even knew about real time river gauges.  We also knew one other thing...it takes 500 cfs to be  able to get a raft down the one big rapid.  So as the time approached, the river was dropping below that 500 cfs figure, so we knew it was getting iffy for taking a raft, but it was still going to be plenty of water to float a canoe.  We ended up taking the raft, at 400 cfs, and yes, it was tough getting down that one rapid and a couple others, but we made it.  I never looked at the level in feet on the gauge.

And I'll make you a bet, although you'll have to remember it when the rivers get a little low.  PIck a river over on your side of the state, since I've only floated streams like the upper Niangua once or twice.  PIck a time when it may or may not be low.  Ask me if it's floatable.  I'll tell you almost exactly how easy it will be to float it just by looking at the cfs and median flow.  Here's how, if you don't care to make the bet:

As a rule of thumb, it takes 75 cfs for any stream in the Ozarks to be at least marginally floatable...that is, you can get down most riffles in a lightly loaded canoe without scraping bottom all the time.  150 cfs will make it easily floatable.  But the first thing I'll look at is the median flow for that date.  If the median flow is, say, 70 cfs, then I'll know that stream normally gets marginally floatable during that time of the year.  If the median is close to that 150 cfs mark, then I know that stream is normally easily floatable that time of year.  If the median is over 300 cfs, it's pretty much gonna be floatable year-round, and if it's over 500 cfs, it's normally jet-boatable that time of year.  So then I look at the cfs it's actually flowing.  Say it normally flows 70 cfs, and it's now flowing 75 cfs.  That means it's close to normal, and floatable without too much scraping bottom.  But if it's, say, 50 cfs, then I know it's low, and at 50 cfs I'm gonna be scraping bottom in a lot of the riffles and probably having to walk a few.  If it's 30 cfs I know I'll be scraping bottom or walking nearly every riffle.

But what if it normally flows 150 cfs, and now it's flowing 75 cfs?  Well, that means it's really low, and although you'd normally float it very easily, you might be having to really pick your lines and you'll still be scraping bottom  quite a bit, but you'll be able to get through it.

Note that we're not talking rivers the size of the Mississippi here, nor creeks that barely have enough water to wade.  We're only discussing actual streams that are floatable at least part of the year.  In the Ozarks, on every one of those streams my rule of thumb holds true.  

And by the way, you're wrong about 1.5 feet being enough water to float on every stream.  That does not mean that the riffles are 1.5 feet deep.  It doesn't mean that ANYWHERE on the river is necessarily 1.5 feet deep.  All it means is 1.5 feet on the gauge. Most real time river gauges, to simplify, use a tube attached to a vertical or steep surface, like a bridge piling, with the bottom of the tube in the water below the lowest level the river is ever expected to reach.  The bottom of the tube is 0.0 feet on the gauge.  There are openings below the waterline that allow water into the tube, and water pressure pushes the water within the tube up to the level of the stream's surface on the outside.  There is a float inside the tube that records the level, which goes to a remote recording station, usually updating every 15 minutes.  There are different mechanisms in some gauges, but they all give the level in feet at the gauge itself.  They don't measure depth, they measure level.  Depending upon the placement of the gauge, 1.5 feet might be a foot above dead low water, or 6 inches above dead low water, or it might be dead low water itself.

[tjm]

I can understand that a 2' pipe and a 6' pipe both having gate valves  6" open won't discharge equal volumes of fluid. Gage height is kinda like a gate valve.

Familiarity with a stream  certainly enhances the meaning of the USGS data, but so does standing on a bridge and looking down. As the gage rises in my local creek the velocity also increases and that is reflected in the CFS, I think. If the river bed fills in or is cut deeper or widened at the gage location that will also be reflected in the CFS graph eventually because the USGS checks those things out periodically.  Anyway March is usually too dang much water in these creeks. 

outside reading for the bored https://www.usgs.gov/special-topic/water-science-school/science/how-streamflow-measured?qt-science_center_objects=0#qt-science_center_objects