Reading Usgs Gauges

[GloryDaze]

A while back Al posted a great read on understanding the data from usgs gauges. I cannot find it anywhere, could someone enlighten me where I may find it?

[ScottK]

Is this it?

[GloryDaze]

That's it- Kind of... I seem to remember there was one posting where he explained how to read the percentiles and how to correlate those with fishing and floating conditions for a stream you may not be familiar with or floated in the past. Included was the reading of the CFS graph and the little yellow triangles and how they indicate average flow for a given day.

I found it very helpful as I don't have a river within 3 hours and it can be risky business making that drive and not having a good sense of river levels.

Perfect example- I am leaving tomorrow for a 3 day trip on the Niangua, I am somewhat familiar with that river but do not have the gauges and levels memorized. So, I would like to have a general idea in the morning if conditions may be favorable for both fishing and floating.

Thanks for the help!

[Ozark Sweetwater]

It's starting to come up pretty quick. It will probably be muddy for a few days.

[Al Agnew]

Here's what I wrote back in 2007:

The U.S. Geological Survey real time river gages are a wonderful resource for the stream angler. You will find links to them at the top of each river forum here. But I've found that many anglers don't get full use of them. Most seem to not look at anything but the gage height. If you know your river well and watch the gage height closely whenever you go on a fishing trip, it can be very useful. But that information, by itself and without experience with which to relate it, is useless. For instance, you can see that the gage height is 4.5 feet, but unless you know you've fished that river at that gage height before and remember what the conditions were like, that number is useless.

However, you CAN learn a whole lot from the real time gages by looking at the other information on the same pages. From your computer desk at home, you can find out almost exactly the level of any stream that has gages, whether that level is higher or lower than normal, what the river has been doing not only in the last seven days, but any time period you wish to look up, and make very good educated guesses on whether any river, even one you are totally unfamiliar with, is high, low, floatable, runnable by jet boat, and possibly even whether it is clear or muddy.

So let's take a tour through the gages on one river, the Meramec, in order to show what you can find out and how.

First, when you click on link to river gages at the top of the Meramec River page here on OA, you'll see four gages, Steelville, Sullivan, Eureka, and Valley Park. The first gage is the farthest upstream, with the others in downstream order. The first thing you need to know is the exact location of each gage. So, click on the Steelville gage. Up near the top of the page, you'll see a drop down menu for "Available data for this site". Click on "site map" on the menu. The site map will show the gage to be just north of Steelville, downstream from the Highway 19 bridge (it's actually at the Birds Nest bridge, but the road is not actually shown on the site map).

So now you know where the gage is located. Go back to the previous page. As you scroll down the page, you'll see graphs for "gage height in feet" and "discharge in cubic feet per second", plus a table labeled "daily discharge statistics, in cfs, for (today's date) based on 83 years of record". As I'm typing this, it is late in the evening of Nov. 25.

The graphs, both the gage height and discharge ones, will show what the river has done in the last seven days up to within a couple of hours or less of the present time. As I said, the gage height graph has very little use unless you know what the river looks like at different height readings. But the discharge graph is much more useful. So let's examine it.

You'll see the blue line that shows the river discharge throughout the seven day period, which as of Nov. 25, has been dropping very slowly from about 175 cfs to a bit over 150 cfs. Again, that doesn't tell you too much in itself, but you'll also see a little triangle on each day. Those little triangles represent the median flow for that day, and you can consider them to be pretty much the "normal" flow for that day. So, normal flow throughout the seven day period before today runs around 225 cfs, and you can tell that the river at Steelville is well below normal and has been throughout the seven day period.

But even that graph doesn't have nearly all the info you can use. Drop on down to the daily discharge statistics table. The "based on 83 years of record" is important because it shows how many years the gage has been in operation. The more years the gage has been in operation, the more accurate the figures in the table will be. A gage that has only been in existence a few years will not have enough data to be really useful, but after 10-15 years of record, it will begin to be very useful.

The first figure on the table is "Min (1981)" and is 115. This means that the minimum flow ever recorded for Nov. 25 in 83 years is 115 cubic feet per second. If the present flow was anywhere close to the minimum ever recorded, you KNOW the river is very low! The second figure, however, is more useful. It is "20th percentile" and is 152. That means that, on 20% of those 83 years, the river was at 152 cfs or lower on Nov 25. The 20th percentile figure is, therefore, 152 cfs is a very low flow for the river at that point on Nov. 25.

The next figure is "most recent instantaneous value". So, right at the time I write this, the river is flowing at 154 cfs. That's right around the 20th percentile, so the river right now IS very low.

The next figure is "median", 225 cfs. The median flow is the flow at which, on Nov. 25 throughout those 83 years of record, half the time the river was higher, and half the time it was lower. So, "median", which corresponds to those little triangles on the discharge graph, is pretty much the "normal" flow of the river for that date.

The next figure is "Mean", 501 cfs. Mean is the average flow for Nov. 25. It is almost always considerably higher than median, because if there happens to be a big flood on that date sometime during the years of record, it will skew the average way upwards. "Mean" is of very little use to the angler wishing to understand the present river level.

The next figure is "80th percentile", 558 cfs. 80th percentile means that on 80 percent of the years of record, the river was at 558 cfs or lower. You can figure that the 80th percentile figure is a pretty good indication of the highest river level that would not be too high for the river to be good fishing. Anything much higher than that and the river would likely be muddy. This isn't a sure thing, because a lot depends upon what the river has been doing in the previous days. But generally if the river is higher than the 80th percentile figure, there's a chance it will be high and muddy.

The last figure is "Max (1974), 10200", which means that in 1974, the river was the highest ever recorded for Nov. 25 at 10,200 cfs. Max is interesting but of no use to the angler.

So now you see how you can look at the present river discharge in cfs and relate it to whether the river is high, low, very high, very low, or normal.

Now, there are other things you can learn about the river starting at this page. Go back up to the drop down menu for "available data for this site" at the top of the page, and click on "time series, daily data". This will bring you to a page with graphs showing what the river has done in the last year. You can also call up any time period during the 83 years of record by typing in the dates you wish at the "begin date" and "end date" spots near the top of the page.

So let's pick a period of time to look at more closely. You will note on the graph that the river had a rise around September 10, so let's type in "2007-09-07" for the begin date, and "2007-09-14" for the end date. This will give you graphs for discharge and height for the seven day period around the rise. On the graph for gage height, you'll see that the river was at about 1.8 feet on Sept. 7, and rose to 3.5 feet on the 8th. Then it steadily dropped to about 2.1 feet on the 11th, had a slight rise to 2.3 the next day, and then dropped steadily again to 1.8 feet on the 14th.

Now go down to the discharge graph, and you can start relating river height to discharge. On the 7th, the discharge was about 180 cfs, and rose to about 1050 cfs the next day. So, remember the levels the river is as I type this, 154 cfs? The river was a bit higher than that on Sep. 7, but still below the "normal" flow for today of 225 cfs. At the level it was on Sep. 7, a rise in discharge of 900 cfs was a rise in feet of about 1.7 feet. And in the morning of Sep. 10, the river dropped through 550 cfs, which was a river level of about 2.6 feet. If you'll remember, 558 cfs was the 89th percentile figure for Nov. 25, today's date, so now you know what the river level is at that flow. In the following days, the river dropped 1.4 feet in height, and 700 cfs from the high, down to about 350 cfs. Then it had that slight rise of 0.2 feet, which corresponded to about 25-30 cfs, and then dropped to a bit over 200 cfs by the 14th. That 200 plus cfs corresponded to a level of 1.8 feet. So...the normal flow for TODAY'S date, Nov. 25, of 225 cfs, is about the same as 1.8 feet on the height in feet graph. NOW, you know several things. You know what the "normal" river level in feet is on Nov. 25th. You know that, when the river is low in the autumn, a rise of about a foot will put it up at the 80th percentile and maybe be enough to get it murky or muddy. NOW, you can relate those pesky river levels to discharge in cfs, to whether the river is high or low, even to whether it might be murky or muddy.

Keep in mind several things. First, "normal" varies with the time of the year. Spring normals are much higher than summer and autumn normals. And a rise of a couple of feet might not have as much of an effect in the fall as it does in the spring, because the river is starting from a much lower level.

Finally, how can you tell from these figures whether a river is navigable by canoe or jetboat? Well, you have to have some experience here...you have to get an idea of what the lowest floatable or runnable level is on a river you know well, and extrapolate it to other streams. I happen to know, because I was just on the Meramec a few days ago farther downstream, that a discharge at the Sullivan gage of about 250 cfs was at about the lowest flow I would consider running it. There were several riffles that day which gave me a significant "pucker factor" when running them, and I wouldn't want the river to be ANY lower than it was that day. So...you can figure that for a river the size of the middle Meramec, which would include such streams as the lower Niangua, middle Gasconade, and upper Current, somewhere around 250 cfs is about the lower limit of navigability for jetboats, unless you know the river VERY well or don't care if you bang rocks and suck gravel. And I know that, on most of the smaller Ozark streams, at a flow of about 75 cfs the river starts to become a little skinny and you'll start to scrape bottom on some riffles. At about 50 cfs, you'll scrape a lot of riffles and have to walk a few of them (this is in a lightly loaded canoe on a day trip). At 30 cfs you'll scrape most riffles and walk a lot of them. Anything under that and you'll walk nearly everything, although I've "floated" streams at flows of less than 20 cfs. As the "normal" size of the river goes up, those numbers also go up. For instance, on the lower Buffalo, you'll scrape quite a few riffles at 75 cfs. And you'll scrape MORE of them at that flow on the lower end than you will on the middle river, because the riffles are wider on the lower end and will be shallower with the same volume of water flowing through them.

There are other considerations, such as where gages are located. The Meramec is well covered, with the Steelville gage being downstream of Maramec Spring but upstream of the mouth of the Huzzah, the Sullivan gage being between the Huzzah and the mouth of the Bourbeuse, the Eureka gage being between the mouth of the Bourbeuse and the mouth of Big River, and the Valley Park gage being downstream of all major tributaries. So, for each gage you have a good idea of a fairly long section of stream--the Steelville gage covering from Maramec Spring to the Huzzah, the Sullivan gage from Huzzah to Bourbeuse, etc. But, some rivers aren't well covered. The Eleven Point only has one gage in MO, at the Hwy. 160 bridge. This is well below Greer Spring, so it doesn't give you much of an idea of the river levels above Greer. The highest gage on the Gasconade is at Hazelgreen, and there's a lot of river above there. The Osage Fork doesn't have ANY gages on it. My home river, Big River, has a gage on the upper end at Irondale, and the next gage is 70 miles downstream near De Soto. There are three significant tributary creeks and one large tributary that enter in that stretch, so the farther downstream you go the more water there is. I know by experience what a reading at Irondale and a reading at the next gage downstream means for the river at most points in between, but you have to do some educated guessing on a river you're not familiar with.

This is where looking at what the river has been doing at any gage available in the last few days comes in handy. If you have a significant rise on an upstream gage one day, and a rise the next day at a gage X number of miles downstream, you can get a good idea of how long it takes a rise to get to any point in between. If both gages show high water, you'll know the river is high in between. If there's a rise upstream on the day before you plan to fish, it'll probably either already be there or will hit you during the day. And if it's a stream that doesn't have a gage, you have to find a stream of similar size somewhere nearby and assume the levels are similar. For instance, a reading on the upper gage of the Niangua would give you a pretty good idea for the Osage Fork, which is a similar sized, nearby stream. But the upper Niangua gage doesn't show discharge in cfs at this time. So, an alternative would be to look at the discharge on the Gasconade at Hazelgreen, which is just a short distance downstream from where the Osage Fork enters the Gasconade. Since the Osage Fork normally flows just a little less water than the Gasconade above it, you can divide the flow at Hazelgreen in two, knock a bit off that, and guesstimate the flow of the Osage Fork. For example, the flow at Hazelgreen right now is 80 cfs, so the flow of the Osage Fork is probably about 35 cfs and the Gasconade 45 cfs above where the two come together.

So as you can see, it's not an exact science, but with a bit of knowledge and effort, you can plan your river trips very well with the USGS gages.

[GloryDaze]

Hell, no wonder I couldn't find it... 2007! Al, seriously thank you for that recap as it really helps me get an idea of what to expect.

Truly appreciate your knowledge.