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guesing width of small streams from maps

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I often try to guess the width of small streams from maps. Which of the tiny streams in this image might be the widest/have the greatest flow, and why? Often can't see them in satellite images through the trees thanks (image from backcountry navigator phone app)

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Posted on: 2013/8/20 16:48


Re: guesing width of small streams from maps
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The expanse of land being drained is the best indicator, I think. Cannot evaluate your maps, though.

Posted on: 2013/8/20 17:44
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Re: guesing width of small streams from maps

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if drained land is important, number 4 might be smaller than 3, even though number 4 appears to have a deeper ravine... thanks

Posted on: 2013/8/20 17:49


Re: guesing width of small streams from maps
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Well expanse of land probably determines the volume of water, but gradient will determine depth to a large extent. I'd guess knowing something about each factor would be helpful.

Posted on: 2013/8/20 17:55
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Re: guesing width of small streams from maps

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right I now look at gradient over half mi stretches I might fish. streams with say 5-6% grade over .5 mi more likely to have some pools. ones nearer to 10% have plunge pools maybe falls.

Posted on: 2013/8/20 18:31

Edited by k-bob on 2013/8/20 18:49:23


Re: guesing width of small streams from maps

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Nos. 1 and 2 look too small.

Both 3 and 4 look worth a try. I'd have trouble deciding between the two.

But I would probably choose 3. Larger watershed area, as already discussed. And longer stream channel length above the last road.

Posted on: 2013/8/20 19:26


Re: guesing width of small streams from maps

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I have a general rule of thumb when looking for "fishable" trout streams in the mountains of PA. If the catchment is 4 square miles or more it is generally fishable with a fly rod. Less than 4 sq. miles and the stream channel is generally too narrow and the stream side vegetation too tight. There may be trout in the stream, but getting at them is too much trouble. Based on your map, I'd say #3 comes closest, but still doesn't satisfy my catchment criterion, being approximately 2.5 to 3 sq. miles.


Posted on: 2013/8/20 20:00


Re: guesing width of small streams from maps

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I've looked at those streams on the map before! Never fished them though. I think stream width is a function of watershed size in combination with gradient. Steeper streams seem bigger than they actually are. I can think of several examples of streams that are small, but still plenty fishable when they're tumbling down a mountain...when they hit the valley floor and lose their gradient that same stream can look pretty dinky, overgrown, and unfishable.

Just based on the map (and not PFBC list info, access issues, etc) I like the look of 1 a lot, but would probably fish 3 and 4 first based on what I perceive to be a larger watershed, as the others have mentioned. They all have enough gradient.

Posted on: 2013/8/20 21:07


Re: guesing width of small streams from maps

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How do you estimate the square mileage of the catchment?

Posted on: 2013/8/20 21:08


Re: guesing width of small streams from maps

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Actually #3 is as deep as #4, the difference is #4 is steeper. They both start above 1600ft. and enter at approx enter the big creek at 800 ft.My guess is that # 3 is a bigger stream, but the difficulty of guessing from a map is that other factors contribute to stream size, such as aquifer and the size of springs and flow of springs that feed the 2 streams. Also from know the area, there may be AMD outflows there that could contribute water toany of the 4 streams making one bigger than an other.
Generally I go for streams that have longer flows and if there are tribs that enter I like to see that. Sometimes streams start out small and don't get any larger.
Gradient alone doesn't make 1 stream larger than an other.

Posted on: 2013/8/20 21:16


Re: guesing width of small streams from maps

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Troutbert: To estimate the area of the catchment, locate on the map the high points between the watershed divides. Draw a polygon (in your head if necessary) from point to point and close the traverse (so to speak). Use K-bob's scale to estimate the lengths of the "legs" of the polygon. Multiply length of polygon by its width and you should come up with a rough estimate of the catchment size (area).

Most of us tend to use the term "watershed" when what we are describing is the "catchment". A "watershed" by definition is the boundary line surrounding a catchment. A "catchment" is the area of land contributing runoff to a stream (i.e., the area within a stream's watershed boundary).

Posted on: 2013/8/20 21:36


Re: guesing width of small streams from maps

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http://pgcmaps.pa.gov/pgcpublicviewer/

The Game Commission's Mapping tool is very useful for estimating catchment size.

Posted on: 2013/8/20 21:56


Re: guesing width of small streams from maps

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Each is a first order stream flowing within the ridge and valley province, so there is a chance that they are not perennial streams but rather seasonal. They are just a bit too far off the I-81 corridor to be within the anthracite zone, so mine drainage is unlikely to be a factor in steam discharge. Also, I think it's safe to say that limestone springs are not a significant factor at this location (Catawissa drainage).

Posted on: 2013/8/20 22:32


Re: guesing width of small streams from maps

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From the satellite images on AcmeMapper it looks like there is a road running right along #3, Klingerman Run. I'd scratch that one.

Cranberry Run looks like real backcountry. It's likely to be real small though. It's only about 1 mile from the origin down to the road.

Posted on: 2013/8/20 22:57


Re: guesing width of small streams from maps

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thanks, interesting discussion. tups' thoughts on /4 sq mi to fish with a fly/ seem like a good fit here. I have fished #3 klingermanns, but I think it is smaller stream than most guys want to brother with... but not by that much. it might have 60-70% of 4 sq mi catchment as tups notes...thanks again all.

Posted on: 2013/8/20 23:10



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