Reading Streamflow Data Tutorial

[MaxDrown]

So I've been trying to make heads and tails of the streamflow website, but I really have no idea how to understand the data. Would someone like to take a stab and explaining to the rookies like me out there?

[Phil Lilley]

Pick the water you want to check and click the blue, underlined number to the left of the water listed. That will take you to the water chart showing close to real time water levels.

[Gavin]

Every river is different so youll need to educate yourself every time you go fishing....and be careful...

However, here are some very general guidelines...100cfs...easilly wadeable, and you can probably canoe it if you dont mind some dragging..

300cfs, easy floating in a canoe....still comfortable wading......Over 500cfs, wading can be an adventure...best to float and hop out at good looking spots....

But everything depends on the characteristics of that individual stream, what the water level was before the rain..Sharp spikes of over a foot or two usually mean stained or sometimes muddy water, but it depends on the river. Youll get a feel for it in no time. Plus there are lots of posts about water levels for different spots in the archives of the river forums. Cheers.

[timinmo]

Max

I find it easier to use the regular USGS site and go to the real time water data. The info is basically the same but I just like the way it is laid out. In short the gage height doesn't tell you anything unless you know about what is normal. The discharge tells you how many cubic feet of water per second that is going past a certain spot.

The USGS site gives the gage height in graph form and you can chose the time period. The discharge summary will tell you how much water is going by, also in graph form. If you look at the 20% figure and the stream is under that you can bet the water is really low. The 80% figure is that 80% of the time the cfs are under that amount so if you are over the 80% figure it is very high and probably not fishable. In graph form you can see whether the stream is rising or falling and where the level is. By and large I usually will not go if it approaches the 80% level and much prefer rising water to falling water. If the water is under the 20% level and I am planning on fishing a small stream with a canoe, I better plan on some dragging. The streams which I fish often I will have some idea of what a good gage height is and can go by that. I also keep notes on streams so I know if I had to drag every riffle at a gage height of say 1.37 and it is running at 1.85 it will probably be a more enjoyable float

Hope this helps. Others have explained it better.

Tim

[Al Agnew]

Excellent info above. To kinda encapsulate all of it...

First thing you need to know is where the gages are on the stream. Take the Meramec River, for instance. Most upstream gage is at Cook Station, which is about 20 miles or so above where Maramec Spring enters the river. It's a good indicator of the river above Maramec Spring, only marginally useful for the river below the spring. Second gage is at Steelville. It's a good indicator of what the river is doing between the spring and the mouth of the Huzzah, the first major Meramec tributary. Third gage is near Sullivan--good indicator of the river below the Huzzah down to the mouth of the Bourbeuse, the second major trib. Then there are one or two gages downstream that I never pay attention to, since I don't fish much down there.

Some streams aren't as well-served by gages as the Meramec. On those, you have to make some guesses unless the stretch of river you're fishing is near one of the gages. The Bourbeuse only has a gage at the upper end of fishable water, and one at Union, many miles downstream.

Now...reading the gages. There are two graphs, one showing river level in feet, the other river flow in cubic feet per second. And there is a table that shows the 20th percentile flow, median flow, mean flow, 80th percentile flow, and record low and high water for that day of the year. Keep in mind that the table is ONLY talking about that particular date. So the record low for today's date, for instance, will be different from the record low for tomorrow's date. There is also one other important piece of info--the years of record for that gage. Some gages have been there for many years, others are pretty new. For instance, the Steelville gage on the Meramec has been there a long time, but the gage at Hwy. 8 on the Huzzah has only been there two or three years. This is important because the longer a gage has been there, the more accurate its median, 20th and 80th percentile flows are. If the gage has only been there for three years, and one of those years there happened to be a huge flood on that day, it's really going to skew the median and percentile flows, but if the gage has been there for 75 years, it will all even out.

If you are not familiar with the gage readings already, the river level in feet graph is only useful to you to tell you if the river has risen, and how much it has risen, in the last few days. So go to the flow in cfs graph first. On that graph, look for the little triangles, there should be seven of them, one for each of the last seven days. Those triangles show the median flow for those days. The triangle for today's flow will correspond to the median flow in cfs in the table. The median flow is the flow at which on today's date, 50% of the years of record the river was higher than that, 50% of the years it was lower than that. So median flow is a very good indicator of the "normal" river flow for today's date. Usually, sometime in the last week or so the flow was somewhere close to those triangles--although this month with all the continuing rain it probably wasn't. If it was, however, you can then refer to the level in feet graph, look at the same day on it, and see how the flow in cfs matches a certain river level in feet.

If the river has been consistently higher (or lower) than the triangles, look for a stretch of a few days when it was close to being level and not jumping up and down. A level flow usually means stable and fishable water. Sudden jumps mean a rain event and a sudden rise in river level. You can look at the level in feet graph to see how many inches or feet the river rose at that time. A rise of a foot on a larger river like the middle Meramec or Gasconade may mean murky but not muddy water. A rise of two feet or more usually means muddy water and tough fishing. Anything over a two foot rise on most rivers usually blows out the fishing for a few days. But it depends upon size and character of the river. A two foot rise on Current River at Van Buren will usually only make the river off-color. A two foot rise on Huzzah Creek will make for tough fishing that day, but it goes down so quick that the next day it will probably be fishable. But a two foot rise on the Gasconade at Jerome will usually mean muddy water for several days.

So the point is, look at the table for 20th and 80th percentile flows. Timinmo told you how they are important. Look at the level in feet graph for a sense of what the river has been doing as far as rises go, and judge fishability according to how much of a rise it has been, how long ago it was, and what you know of the character of the river. Look at the flow in cfs graph to get a sense of how close the river has been to normal for the time period, and whether or not it is too low to float or too high to float. Use all three sources of info to give you the most complete picture possible.

[MaxDrown]

Great information, guys. Exactly what I needed.