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crazyt

erosion is not the same everywhere

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Austin environmentalists make a big deal about erosion, this idea probably started with environmentalists on the west coast.  Ive always wondered as we are mostly limestone and there is barely any erosion. 

This picture comes from a trail I ride in california which is closed because of erosion. The kind of erosion they have there is completely different because their mountains are almost like big piles of sand. When they erode, it is literally gouges that are feet deep. I think our environmentalists use the term erosion very liberally. Anyway, just something to think about.

 

image.thumb.png.c733b5d4633bf1e6c7ce03a1ed7966e0.png

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Just now, mack_turtle said:

So Californians are to blame for all the chaos along Shoal Creek?

Sounds legit!

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Token geologist here. All regions will vary, but yes locally here in Austin we (for the most part) don’t suffer from severe erosion. Where you do see it will be the lower lying areas which is pratically just at the surface level (shoal creek). We are lucky we have a solid foundation that is porus enough to drain and filter water but still has enough backbone to hold its own for many lifetimes. That’s the mythical of limestone. Love that shit. Sandstone, siltstone and mudstone among other fine grain sedimentary stones don’t provide that guarantee. Go ride Houston’s memorial park. Nothing but sandstone and super fine grain surface silt/sand. Eroded to shit. 

We are fortunate to have such a great foundation here. 

ETA: this may be a troll after I read it again with my first bourbon of the night. That said, I still feel I provided a decent rock nerd moment for the website. Good day. 

Edited by bestbike85
Knowledge
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CrazyT are you trolling? 😄

 

When I saw the title, I thought it was another post by someone many people have chosen to ignore on here.

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Not trolling

The city environmental group tried to close the cat trails due to "erosion" concerns and impervious cover. The city claimed that any trail used for biking becomes impervious cover. When you read environmental papers erosion appears everywhere. I couldnt understand why it was such a big deal when it is limestone and barely changes year to year. A lot of the concern in the BCP is due to erosion. If the warbler is delisted, they will cite erosion due to mtb as a reason not to open it up. 

I ride the trail in the picture in california and I got notice through a california group that the trail is closed due to erosion. When I looked at the picture, I realized their geology is completely different.

How do you fight "erosion" concerns with discussions about geology?

Edited by crazyt
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Make the discussion regionally relevant. If someone cites an erosion study that was done in a place with totally different geology. Challenge them to conduct a local study. Look at City Park. Years and years of motorcycle use should have leveled the whole place by now, but that limestone is tenacious stuff.

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Most erosion concerns regarding trails can be addressed through application of the 50% rule and of rolling grade dips in the trail design. Armoring, ladder bridges, and other methods are also available to the trail builder who places sustainability high on their list of design criteria. The same techniques can be applied to repair and improve existing trail, along with maintenance of trail tread to promote sheet flow across the trail, rather than water being channeled into a narrow path following the trail.

The fact that IMBA's preeminent tome on sustainable trail construction provides chapters of information specific to addressing this very topic quite literally speaks volumes to counter arguments toward these environmental concerns.

Additional studies have shown how MTB tires rolling on a trail actually help address damage done to the trail surface by nature, as well as that done by equestrian and human use, and further exemplifies how mountain bikes contribute to sustainability and erosion prevention in concert with a sustainable design.

Lastly, the significant impact of the biking community in volunteer efforts for construction and maintenance of trail systems when compared to participation by other user groups further places mountain bikers at the pinnacle of desired users for any trail system.

 

Edited by Ridenfool
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12 hours ago, Teamsloan said:

When I saw the title, I thought it was another post by someone many people have chosen to ignore on here.

 

Now that's a troll.

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I think in some places (and minds) displacement = erosion.

Slaughter Creek trail can be used as an example. It's been around for some eight or nine years I think, and is used for equestrian, mtb, and hiking purposes. No doubt the weight of the horse will dislodge large stones and loosen dirt, but I don't believe it's as obvious as what happens with mtb riding. If you look at any of the corners that can be taken at fairly high speed you'll see dirt thrown to the outside of the corner — in some cases, quite severely. This can lead other users, such as hikers, who tend to be more concerned about any level of trail damage, to think/conclude that mtbing produces erosion.

Additionally... From what I know, the trail at Slaughter Creek was cut by mtb trail builders, and any related problems, such as real erosion caused by the trail itself (definite directing of water along the trail), will be placed squarely at their feet. And erosion has taken place. In fact, the last two times I participated in trail maintenance days there was a focus on dealing with two areas of erosion that were related to the trail. Nothing big (certainly not on the scale of the OP photo), and quickly addressed. But still relatable to the mtbing activity.

Unfortunately, we humans are vain, and have preferences in support of our vanity. And one way we love to exercise our vanity is by pointing fingers at others in defense of, and to satiate our preferences/vanity. Which is why we often end up with contentions over things like erosion — real or perceived — and who is causing it.

Edited by RidingAgain

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The most laughable example I've seen regarding concerns over "erosion" is Walnut Creek.  IMBA goofs came through Austin looking to do some good deeds.  They closed one of my favorite sections of trail to "prevent erosion."  I rode that section for years and never saw any significant changes.  2 months later, a huge portion of cliff, just across the creek, collapsed - enough to literally dam the creek.  A few years later, all that fall-in is gone.  The force of the Creation is out of, and beyond, our control.  As George Carlin said:

https://www.youtube.com/watch?v=7W33HRc1A6c

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I have been trying to write something on this very topic. There are some very good posts already out there - http://www.lebanonhills.com/sustainable-trails/

The problem is that it needs to be  "sound bite" for some people to pay attention and long and detailed for other people to pay attention. The same description cannot serve both.

I have posted some things here before. Our soils are highly prone to damage by riding, hiking, horse back riding, etc when they are wet. Most of our soils are clay over a rocky (limestone) base. Lose the few inches of clay and the limestone is exposed. Now the stuff that holds the rocks in place is gone and the rocks start moving. You know all those loose golf ball to baseball sized rocks on most of our downhills. They used to be held in place by the black clay soil. 

All of our "soils" including the limestone gets soft when wet. The difficulty convincing people of that is they think "rock" is hard and never changes. Some of the limestone is like that. When you find a vertical ledge, the top layer is the hard limestone. The softer limestone that was under it has dissolved (eroded) away underneath the hard layer. There is a very illustrative spot near the start of the City Park loop that the limestone gets wet and turns to mush. We keep filling that area with small rocks to try to harden it. It works for a while. Then it gets really wet and the rocks get dug out or mashed so deep into the mush it doesn't help anymore. ETA - in the picture, you can see above the 'photo model' where the color changes. That is some of the rock we added to harden the surface. Below the model, you can see where the trail tread is once again forming a channel that focuses the water into an erosive channel flow. That channel did not exist when we filled it with rock.

I will try to finish up and post at least one of my attempts to educate people about wet trails.

One 2019-01-11.jpeg

Edited by cxagent
Added BOLD to highlight this paragraph was specifically about limestone is not always a hard impervious surface.

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seems like any discussion of the impacts of erosion need to differentiate between the impacts at the site of the erosion and the impact of the material that was eroded away on creeks and streams. I personally don't see well designed bike or foot trails causing much damage of either type. The worst erosion I see seems to only cause a trail to be less fun (fall line booshit).

Also, you can't generalize much since the blackland prairie stuff behaves differently from the hilly limestone stuff. 

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10 minutes ago, Anita Handle said:

seems like any discussion of the impacts of erosion need to differentiate between the impacts at the site of the erosion and the impact of the material that was eroded away on creeks and streams. I personally don't see well designed bike or foot trails causing much damage of either type. The worst erosion I see seems to only cause a trail to be less fun (fall line booshit).

Also, you can't generalize much since the blackland prairie stuff behaves differently from the hilly limestone stuff. 

yes Im mainly thinking of the trails west of mopac that is on limestone. Im not saying there is zero erosion, but Im wondering if the scale of it is several orders of magnitude less than the erosion that made environmentalists concerned about erosion in the first place. So cxagent cited a section that turns to mush, but that is very different than a trail causing 3 ft deep drains 1/4 mile long, that sent hundreds of tons of material into creeks. The water was channeled down the trail and in the SO cal rains they had recently, that channeled water grooved out huge gaps.

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yes Im mainly thinking of the trails west of mopac that is on limestone. Im not saying there is zero erosion, but Im wondering if the scale of it is several orders of magnitude less than the erosion that made environmentalists concerned about erosion in the first place. So cxagent cited a section that turns to mush, but that is very different than a trail causing 3 ft deep drains 1/4 mile long, that sent hundreds of tons of material into creeks. The water was channeled down the trail and in the SO cal rains they had recently, that channeled water grooved out huge gaps.
Yeah, I agree that it can't be that much of a measuresble impact. You can't judge by standing at a spot and going "ooooooh that looks bad". You have to have objective measurements.

Sent from my LG-H810 using Tapatalk

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1 hour ago, Anita Handle said:

Yeah, I agree that it can't be that much of a measuresble impact. You can't judge by standing at a spot and going "ooooooh that looks bad". You have to have objective measurements.

Sent from my LG-H810 using Tapatalk
 

Yes sir! We have been collecting such measurements. But with all such data - there is never enough data. Or it is in the wrong spot. Or you should have started measuring years ago. Etc. Etc. Etc.

You might remember a local mtb rider by the name of Ross Martin. He was local until he earned his PhD at Texas State in 2017 before he moved away to be a university professor. His dissertation and many of the papers he wrote were about erosion, impact of bicycles vs hikers, measuring and documenting the impact, etc. He even did a 'radio type interview' with somebody like Pink Bike / MTBR / etc on the very subject. Again, he was saying the impact needs to be measured and documented so that is viewed in terms of facts as opposed to opinions.

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3 hours ago, El Gringo said:

The most laughable example I've seen regarding concerns over "erosion" is Walnut Creek.  IMBA goofs came through Austin looking to do some good deeds.  They closed one of my favorite sections of trail to "prevent erosion."  I rode that section for years and never saw any significant changes.  2 months later, a huge portion of cliff, just across the creek, collapsed - enough to literally dam the creek.  A few years later, all that fall-in is gone.  The force of the Creation is out of, and beyond, our control.  As George Carlin said:

https://www.youtube.com/watch?v=7W33HRc1A6c

LOVE George Carlin and especially that video. He was great at pointing out just how foolish and hypocritical we humans are.

As far as the part of the trail that was closed - that was more because of the City / PARD safety concerns than erosion. The City did not like that people were riding down that "ledge" picking up speed and then crossing blind intersection where cross traffic was picking up speed to hit the Wall Ride. They felt it was just a matter of time before there was a major crash there. They wanted to close that fall line trail and not opening any alternative. The IMBA Trail Crew pointed out that creating a dead end like that would never stay closed and the problem would not go away. So they offered a better solution of the longer and more flowy trail.

As far as the creek bank crashing into Walnut Creek - it has happened since probably before humans were on the earth. Look along Walnut Creek and not how deep below the 'nominal' ground surface it is. The same is found along Barton Creek. And Bull Creek. And the Colorado River. You don't have to look far to see that erosion is a natural process that has been going on since the earth's crust cooled. And to use George's example, it will go on long after humans are extinct.

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The growth of Austin (pavement and impervious cover) sends more water, more faster, through existing creeks and streams. Like at Roy G. Like what might happen to the Walnut wall ride. At Cat Mtn/Hill Country you loose topsoil until you hit rock. That Cali trail got trashed and should have been outsloped. What's this about again?

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17 hours ago, crazyt said:

Austin environmentalists make a big deal about erosion, this idea probably started with environmentalists on the west coast.  I've always wondered as we are mostly limestone and there is barely any erosion. 

I thought the first line of this thread was what it was about. Maybe I missed something along the way.

The "Austin environmentalist" is kind of a misnomer. Most of what I keep seeing is "Not In My Back Yard" stop anything I don't like. Use any reason / excuse but stop just it.

The part I was addressing is that limestone is not a hard surface that does not erode. It does erode and there are many examples visible on the trails all around town.

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1 hour ago, cxagent said:

They wanted to close that fall line trail and not opening any alternative. The IMBA Trail Crew pointed out that creating a dead end like that would never stay closed and the problem would not go away. So they offered a better solution of the longer and more flowy trail.

I miss that stair-step climb as well but I would trade it in a heartbeat for that longer, flowy trail from the top of Church Hill.

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Here is an example to illustrate the problem with riding wet trails.

IMBA published trail design guidance. Others, like the US Forestry Service, National Parks Service, and many others have published almost the same guidance because it works. The recommended trail design follows the Half Rule. That means that the trail slope is not more than half of the slope of the fall line (steepest slope of the hill). This is done intentionally so that water runs ACROSS the trail instead of down the trail.

Half Rule 180.jpg


 

The trail is also "outsloped" (see picture below). Again, this is done intentionally to drain water off the trail instead of down the trail. If the trail was "insloped" at least a portion of water running down to the trail from above would be trapped by the back slope and start running down the trail. The "berm" shown in the picture needs to be removed so it allows water to flow across the trail.

trailterms.jpg

 

So look what happens when a few riders ride on soft wet trails (red parts in picture). Some of the water is trapped on the trail and runs down the trail. That makes the whole trail softer. The a few more riders come thru and ride the softer trail. Now the trail is more like a drainage ditch than a trail. Then water is directed down the trail instead of across and off the trail. That water focuses all of the energy on washing away dirt and rock and everything in its path. Pretty soon the only thing left of the trail is a big erosion ditch like crazyt's picture. At some point the trail has to be repaired or the whole trail washes away.

Wet Trail Damage.jpg

Don't think that happens in Austin? How about this picture from City Park. You know that trail we all try to ride when everything else it too wet.

Seventeen 2019-01-11.jpeg

There are quite a few people who spend a whole lot of their time fixing trails so the trails stay open. I know I would rather spend that time riding or at least building new trails.

Edited by cxagent
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Thanks for educating us cxagent.  

If you guys ever get a chance to do trail work with cxagent, you will not be sorry.  He's always teaching.  

We got a chance to do some work with cxagent during Cranksgiving and my kids got a few lessons on trimming and such.

Edited by AntonioGG
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