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Hazelgreen Construction


Hungupagain

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7 hours ago, snagged in outlet 3 said:

The Meramec is the same way right now.  REAL low.  Jet scours on all the flats. 

@Al Agnew, you were talking about CFS in relation to gauge height and I watch and keep records on both for my trips.  This year the Sullivan gauge was 460 CFS at 2.2'.  Last year it was at 425 CFS and 2.5'.  No problems on those expansive flats last year but this year those same flats were covered in jet scours and a few of them had guys turning around and not even trying them. 

I don't know for sure if it's the case in this instance, but often the cfs changes in relation to gauge height when high water changes the bottom or banks of the river at the gauge.  For instance, say the gauge is at a pool that averages 4 feet deep at 2.5 feet on the gauge, and then a flood comes along and dumps a bunch of gravel in the pool, and now at 2.5 feet on the gauge the pool only averages 3 feet deep.  Then the same amount of flow that 2.5 feet used to represent now registers 3.something feet on the gauge.  It's why the USGS people often visit the gauge and actually measure the flow, to make sure it corresponds to the same level in feet that it used to.  Keep in mind that the flow in cfs is extrapolated from the level in feet.  So although the level in feet is what is actually measured at the gauge and recorded every 15 minutes, the algorithm converts the level to a flow.  If the shape of the bottom or banks changes, the algorithm has to change.  My example above is pretty extreme...usually this change amounts to only a tenth of a foot or less on the gauge, but even a tenth of a foot is enough to make a significant difference in the flow at lower water flows and levels.

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3 minutes ago, Al Agnew said:

I don't know for sure if it's the case in this instance, but often the cfs changes in relation to gauge height when high water changes the bottom or banks of the river at the gauge.  For instance, say the gauge is at a pool that averages 4 feet deep at 2.5 feet on the gauge, and then a flood comes along and dumps a bunch of gravel in the pool, and now at 2.5 feet on the gauge the pool only averages 3 feet deep.  Then the same amount of flow that 2.5 feet used to represent now registers 3.something feet on the gauge.  It's why the USGS people often visit the gauge and actually measure the flow, to make sure it corresponds to the same level in feet that it used to.  Keep in mind that the flow in cfs is extrapolated from the level in feet.  So although the level in feet is what is actually measured at the gauge and recorded every 15 minutes, the algorithm converts the level to a flow.  If the shape of the bottom or banks changes, the algorithm has to change.  My example above is pretty extreme...usually this change amounts to only a tenth of a foot or less on the gauge, but even a tenth of a foot is enough to make a significant difference in the flow at lower water flows and levels.

I can see that.  Between those two readings the river was flooded for a couple months.  That's why I look at both and keep them in my notes.  Especially if I haven't been in a while and I take off in low light. 

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1 minute ago, snagged in outlet 3 said:

I can see that.  Between those two readings the river was flooded for a couple months.  That's why I look at both and keep them in my notes.  Especially if I haven't been in a while and I take off in low light. 

That's a good idea for any river you know well.  Although the USGS people try to keep the gauges up to date on the correlation between height and flow, there might be several weeks after a flood before they get to the gauge, and in that several week period the height and flow can be off.  Whenever you look at the flow graph on a gauge and see a little red asterisk, that signifies when they came and checked the flow against the gauge height.

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By the way, there is a big difference in the median flow of the Gasconade at Hazelgreen in April compared to August.  Keep in mind that the median flow is a good approximation of the normal flow for the given time period.  In April, the median flow at Hazelgreen averages well over 900 cfs.  In August, it averages around 140 cfs.  So the river at Hazelgreen is easily runnable by jetboat in April, very seldom runnable in August.

The link Gavin came up with is interesting...cwc and I floated the stretch from Schlicht Spring to Hwy. 17 in very low water, and the river was probably flowing pretty close to what it showed in that graph.  I know we couldn't float the riffles without dragging every one, and the river at that time was choked with aquatic vegetation.  We caught a few fish before we got to the rockslide and the group of springs that comes out there, but after we passed that point we caught a lot of fish the rest of the float.

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27 minutes ago, fishinwrench said:

I thought gauge height was set (zeroed) by elevation (MSL).  Is that not the case?  

Surely they aren't just measuring the depth of water at a given location, as that information would be useless.

The gauge height is set by elevation and doesn't change, but if the shape of the river bottom and banks change, the same amount of water will register higher or lower on the gauge.  It would be like if you had a ditch 5 feet wide with a foot of water going through it at a speed of one foot per second, which registered at one foot on your gauge.  (And would be flowing 5 cubic feet per second.) Then you dug out the ditch 6 inches deeper.  Same amount of water, 5 cfs, going through it, but now it's only registering 0.5 feet on your gauge.  Or if you widened the ditch to ten feet.  Same amount of water again but it would only be 6 inches deep and would register 0.5 feet on your gauge.

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