Cobble

[JackM]

geebee wrote:
the wading stones I hate are the unexpectedly high pieces of granite that you don't know are there, and you go to step forward and over the cobbles you expect, and swing your foot into the side of it, sending yourself off balance or worse, forcing your right foot in front of your left leg leaving you cross legged with your body's momentum going forward....

This is when it is good to be known, as I am, as the Fred Astaire of the streambed.

 

[gulfgreyhound]

My nickname is splash! G g

 

[dc410]

JackM wrote:

geebee wrote:
the wading stones I hate are the unexpectedly high pieces of granite that you don't know are there, and you go to step forward and over the cobbles you expect, and swing your foot into the side of it, sending yourself off balance or worse, forcing your right foot in front of your left leg leaving you cross legged with your body's momentum going forward....

This is when it is good to be known, as I am, as the Fred Astaire of the streambed.

LMAO! We're all in this together. We've all been there, Jack.

 

[The_Sasquatch]

If I remember correctly, lots of cobblestone streams in Vermont

 

[troutbert]

The_Sasquatch wrote:
If I remember correctly, lots of cobblestone streams in Vermont

Lots in PA, too. Cobble are just rocks from 2.5 to 10" in diameter.

When fishing in PA, just look down and see what you are walking on. Much of the time it's rocks 2.5 to 10" in diameter.

I only have a little experience with streams in VT, but from what I saw there it seemed like boulders are a lot more common there than in streams in PA.

 

[Chaz]

Well Philly still has some cobblestone streets. Yes I knew what cobble is. Some of the roads the Romans built are still out there too.

 

[The_Sasquatch]

troutbert wrote:

The_Sasquatch wrote:
If I remember correctly, lots of cobblestone streams in Vermont

Lots in PA, too. Cobble are just rocks from 2.5 to 10" in diameter.

When fishing in PA, just look down and see what you are walking on. Much of the time it's rocks 2.5 to 10" in diameter.

I only have a little experience with streams in VT, but from what I saw there it seemed like boulders are a lot more common there than in streams in PA.

The streams I fished had bolder lined banks, but the stream bottoms themselves were cobblestone. What stood out was the density of the stone. Most stream bottoms were a lot more stone than bare soil. But I'm in Lancaster county and our streams are sandstoney silty messes!

 

[Maurice]

Cobble is bedload. High energy events carry many sizes of bedload. It takes 4x the energy to dislodge bedload than it does to carry it so once its in the flow, the flow has to drop x4 to settle it. Depending on where the suspended bedload is in the flow during the velocity decrease determines its resting place.

Sand and smaller pea gravel deposits on point bars (the inside of a bend) indicates these low energy areas where the smallest bedload falls out. While the larger cobbles will drop in pools and the tails of pools thereby creating elevation increases over the bedrock. The following stretch becomes the grade change or riffle into the next pool.

Its generally not the cobble that makes wading difficult it the rocks among them that are too large to dislodge during normal high water events. These are 18"-36" intermediate dimension stones, R-6 thru R-8 in a quarry.

When I am designing in-stream structures or fish habitat structures for streams I like to walk the stretch and see how big the stones are within the flow path. Then choose stones a size larger to ensure they are not carried away by normal high flows.

Cobbles are an intermediate indicator of velocity and sand the least. The sand and small gravel also indicate bank full elevations which are important for determining cut off sill levels on low flow channel devices and slope protection treatments.

My favorite stones to walk on in a stream are cobble a short time after a big storm before they become settled or cemented. That feeling of loose cobble below my boots is an interesting indicator that the stream just reset itself and likely so did the fish.

 

[afishinado]

^ Great post. Very interesting / informative. Thanks, Mo.

 

[gulfgreyhound]

Mo, that rocks. GG

 

[CRB]

RLeep2 wrote:
Additionally, when it comes to wading, there's cobble and then there's cobble. For example, some of the cobble substrate portions of Sugar Creek in Venango County can be pesky wading as a lot of the cobble is rather loose and/or a bit slime coated. More than once, I've done an imitation of an upper case K in mid-air trying to keep my footing on Sugar Creek.

On the other hand, there are many, many other stream sections of similar size across the northern tier with about the same size cobble substrate that are easy wading , even for somebody like me with pretty severely compromised balance functions. The cobble is more tightly packed or less coated or has more uniformity of size and shape than in Sugar Creek.

I have to agree on that stream. My feet always ache afterword, it is like wading on bowling balls with slime. Has to be hands down one of the most difficult streams to wade in nwpa.