PGC Maps - Remote Small Stream Wild Trout Fishing/Watershed Size

[Swattie87]

Been messing around with the new PGC mapping features. There is a pretty neat draw/measure feature that allows you to VERY accurately estimate hiking distances into/out of streams. You can also trace the perimeter of a stream's watershed and calculate its square mileage. I find this is useful in determining whether a watershed is large enough to produce a stream worth exploring. This feature is VERY easy to use...In just messing around I traced the watershed based on the topo features of a watershed of known size (about 5 sq miles) and I came within 0.07 of a sq mile of the published figure for that watershed. Pretty cool.

Obviously there are other factors at play like gradient, the amount and type of spring sources, etc, but in general, for small streams, I find the following:

About 1.5-2 square miles is the minimum to produce a year round
stream of the minimum fishable size. This will still be tiny, you can easily step across it.

2-5 square miles will produce a stream that is still very small, but will start to have enough water to make some consistently decent habitat. It might take a big step, or one step in the stream to get across these.

5-10 square miles produces a nice sized, very fishable small stream. These are generally the ones that I seek out and are my favorite to fish. The best balance of small stream intimacy and plenty of water.

10-20 square miles and you have a good sized stream. Some of these can be very good, but some start to get too big and run into thermal issues at this size if they're not well forested.

Somewhere around 20 square miles usually you are approaching the border of what I'd call a "big" small stream and a "small" medium stream.

Anyone else use these kinds of features, thoughts?

 

[jbomb]

i haven't used these features before, but I find this very interesting. Thank you for sharing.

 

[lv2nymph]

Yes, thanks. I'm gonna have a look see at that myself.

 

[sandfly]

kinda like my delorme program, though on delorme I can add a lot more things like fish holes markers etc.

 

[k-bob]

good idea. I see streams being a bit wider relative to the number of square miles drained ... For example at about three square miles I see about three steps to get across a stream.

 

[BrentL]

Those are some interesting observations about watershed size. I do eyeball potential watersheds on the map and compare them to other streams I've fished, but you have a much more scientific approach.

If you like the PGC online map you may also like ArcGIS Explorer, it's a free GIS viewer by ESRI that you can download and run on your desktop and it has a lot of features. It's kind of like Google Earth but you can do more stuff. One of the biggest advantages over Google Earth is the ability to use a wide variety of different base maps (not just aerials), including USGS topo maps.

I've downloaded a bunch of GIS files of PFBC data like "Streams with Natural Trout Reproduction" off of the PASDA website and added the real-time USGS streamflow layer. I can trace a stream section that I've fished, assign a color to it, add a note and save it. I can trace a watershed area, determine the size, add a note and save it. I only really just started using it for this so I'm still finding new features.

 

[Foxgap239]

I just happened upon these maps about a week before your post. Love them but need to spend time doing the things you and Bob do with them.

 

[k-bob]

OP mentions elevation. Makes big difference when trying to guess pool size on streams with small drainage areas, imho.

I fish very small brookie streams.

I look at the gradient of small streams over a half mile, and then look at the steepest 60ft gradient section within those half mile stretches. (Using a garmin 1:24k topo.)

I look at half miles because that's a fishing section I might try. I also look at the steepest 60ft fall in elevation because that might be a waterfall or tough bit of climbing.

I like steeper streams - up to a point.

For streams with small drainage areas, say 1-1.5 sq mi, 7% gradient over a half mile section seems to lead to small plunges, 5ft, with pools below. 9% over half a mile, and there may be a 5-10ft waterfall in there. 10 or 11% gradient seems to lead to some combination of plunges and waterfalls, maybe a waterfall of more than 10 ft. And some climbing.

Of course some streams with only 3% gradient per half mile have waterfalls, too. But most 3% streams don't have falls, while any stream I can think of with 9% or more grade/ half mi does have a waterfall and some bigger pools.

(15% gradient over a 60 ft drop is probably a waterfall.)

There are some very nice tiny brookie streams with 5-7% gradient per half mile, and only 1-2 square mile drainage areas.

 

[pcray1231]

Very very cool.

I have always estimated watershed size using maps. And yeah, for freestoners it's almost a perfect predictor of stream size. But I've always eyeballed it and never got down to brass tacks like this. One thing it misses is that streams sometimes seem smaller than they actually are, especially in rock rubble where a good % of the flow is underground. But you could say it's a better estimate of size, as it shows you what the flow really is rather than just what it looks like at a glance. i.e. if it's a decent sized stream but most of it is underground, then there's likely to be pools and such where it ISN'T underground.

It probably works very well for limestoners too, though it would be much more difficult to determine what areas are in what watershed, as most of the flow is subsurface. You have a number of situations where the surface water flows one way and the groundwater another, as well.

Gradient, I think, is much less reliable, but still very useful. There are high gradient streams with poor habitat and low gradient ones with good habitat. I think a lot of that has to do with the type of rocks present, types of tree, history of land use (it may be forest now but may not always have been), etc. But still, there is some correlation there, with higher gradient in general being more likely to produce good habitat. Especially if compared to nearby streams which are likely to be similar in geology, flora, and historical land use.

 

[k-bob]

I will fish very tiny streams, even enjoyed a mini brookie stream this summer with only .4 sq mi drainage area but nutty 15% gradient over a half mile... only after some rain of course

 

[k-bob]

btw gradient numbers can be deceptive, I think. A stream with 10% grade over a half mile is plenty steep. the steepest place I can think of is glen onoko, so steep I'd never try to fish there (I wont even hike there), and even it is only a 25% grade per half mile.

http://gonehikin.blogspot.com/2011/05/glen-onoko-fallsbroad-mountain-lehigh.html