# Berms and water management



## HarryCallahan (Nov 2, 2004)

Lately I've been noticing berms cropping up on a lot of the local trails (Santa Cruz area). Seems that the trail elves are busy out there.

That got me wondering. The berms can be fun to ride, but are they good overall for the trails? I thought one aspect of good trail durability and management was to knock down berms where they keep water on the trail, to prevent mud and ersion caused by water standing or running down the trail. So wouldn't that mean a high berm on the outslope of a corner isn't a good thing as we head into the rainy season?


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## zrm (Oct 11, 2006)

Bermed turns may be fun to ride, but they are more often than not add a lot of maintenance. Generally berms do hold water and what I've seen is that when bermed turns are holding water people will often avoid the mud puddle and go next to the turn which widens the trail. Bermed corners can drain if they are properly built and have a place to drain the water to. The tendency though is for a rut to develope -especially if motos are using the trail - which feeds on itself
If you can build a drain on either side of the berm it should keep water from collecting but will require a lot of attention to keep the drains from clogging.


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## indytrekracer (Feb 13, 2004)

*Berms can be good*

Berms themselves aren't bad, it depends on how they impact water flow.

I often hear the term "deberming" a trail. I think this is specific to ensuring there is not a Lip on the out side edge of a bench cut trail. The lip or "Berm" would prevent water from flowing off the trail.

The Trail I support has areas where we could not avoid building in flat areas. Riders tend to skid through flat turns, which digs a low spot in the middle of the turn. 

Our solution was to berm the turns with mud hole issues. The dirt used to build the berm is dug from the inside of the turn, creating a drain for the water. The Berm reduces the amount of skidding and provides grade to send the water towards the drain.

I would say that Berms that hold water on the trail are bad. Berms that send water off the trail are fine. 

I would ride the trails with berms a day or two after a rain and see if the berms created any drainage issues. Thats the best way to figure out if these specific Berms are good or bad.


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## seenvic (Sep 9, 2003)

The bermed turns built here seperate the water flow from the rider flow. 

The rider is up high on the turn, while the water is low and in a bunch of rock to slow the water down and catch the sediment. 

Picture a french drain in the low spot of the berm, a rider in the high spot and an armored flat section of trail where the two come together. 

Works good, I think.


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## balfabiker22 (Feb 26, 2006)

All berms = good.

Please, If you see some work going to a trail (Santa Cruz ones) don't kill it just cuz you don't like it.

Now if the berm is like a pile of dirt then screw it, take it down and rebuild it and pack it down good.


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## HarryCallahan (Nov 2, 2004)

indytrekracer said:


> Berms themselves aren't bad, it depends on how they impact water flow.
> 
> I often hear the term "deberming" a trail. I think this is specific to ensuring there is not a Lip on the out side edge of a bench cut trail. The lip or "Berm" would prevent water from flowing off the trail.
> ...edit...
> ...


Thanks for posting that. I've been a little busy and just saw it. I took the liberty of editing it a little to be generic as I re-posted it above. My understanding of de-berming is a little broader than just bench cuts, but in line with the above: don't pool water on the trail, nor channel water downhill on the trail.

What I'm seeing is built berms on formerly flat ( as in unbermed, unbanked) trails. Now I'm not likely to go out running through the woods with a McCleod tearing down berms. But it concerns me that some of the berms I see look like they are going to turn certain trail corners into ponds, and turn whole sections of other trails into downhill canals.


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## Fattirewilly (Dec 10, 2001)

HarryCallahan said:


> What I'm seeing is built berms on formerly flat ( as in unbermed, unbanked) trails. Now I'm not likely to go out running through the woods with a McCleod tearing down berms. But it concerns me that some of the berms I see look like they are going to turn certain trail corners into ponds, and turn whole sections of other trails into downhill canals.


I'm familiar with what you're talking about. Unlike burm turns or inslope turns that are an acceptable alternative to a switchback in some locations, the trail you describe probably already has a fall line orientation. When it takes a turn, the water has half a chance of sheeting off the trail, and someone comes along and builds a burm to carry more momentum. Probably dug a hole two feet away from the burm. The bum causes a mud hole and sends water straight down the trail.

Correct burms are oriented with an apex that is about perpendicular to the topo lines. They also have a grade reversal shortly after them.


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## HarryCallahan (Nov 2, 2004)

*interesting post.*



Fattirewilly said:


> I'm familiar with what you're talking about. Unlike burm turns or inslope turns that are an acceptable alternative to a switchback in some locations, the trail you describe probably already has a fall line orientation. When it takes a turn, the water has half a chance of sheeting off the trail, and someone comes along and builds a burm to carry more momentum. Probably dug a hole two feet away from the burm. The bum causes a mud hole and sends water straight down the trail.
> 
> Correct burms are oriented with an apex that is about perpendicular to the topo lines. They also have a grade reversal shortly after them.


I think I get the essence of what you are saying, though I can't immediately picture building a berm as a switchback alternative. (I'll study up on that! :thumbsup: )

But you've definitely nailed the problem, namely that whoever is building the berms is doing it to carry momentum, without regard to drainage. And I'm seeing it on 2 types of trails, both ones that are more fall line oriented, and ones that are more XC. Yesterday I was on a more xc type trail that has had berms added. The trail is a very fun, tight, twisty one through the woods, with grade reversals, and outsloped corners to allow water to sheet of the trail. It's very challenging to ride fast and not smack a tree or wash out of a corner. But someone has been adding berms on the outslopes, which is going to lead to mud problems, and, in my opinion, dumbs down the trail as well.


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## Fattirewilly (Dec 10, 2001)

HarryCallahan said:


> I think I get the essence of what you are saying, though I can't immediately picture building a berm as a switchback alternative. (I'll study up on that! :thumbsup: )


I think Seenvic is describing a burm alternative to switchback as well. The rock/french drain is an interesting twist and sounds like a good idea.

I think IMBA calls it an "inslope turn" if you want to look it up.


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## NEPMTBA (Apr 7, 2007)

Berms are Great!

Providing we are talking about non motorized use here only

We build a berm turning into slope by first creating a water diversion(s) upstream. Depending on length of the straight coming into the turn you might have to use a few diversions. I don't mean water bars either. If you can do a few dips and slight turns upstream you will thus cut the water flow down into the turn. 
Now with that said, we make our berm with a drain in the center by cutting the berm wall and installing a rock culvert then matching the angle of the berm wall so it doesn't disturb the path of the tires. A flat rock to cover the hole a bit. Of course you have to have flat rocks around. Lot's here in Pa from old farm walls, bonus!
On the outside of the berm make the outflow clear of debris and angled away fron the berm. This will leave you with only one minor maintenance chore. Keeping the drain clear of leaves, and sticks. Please remember I have no way of knowing your location or soil. This works for us and I hope it helps others!:thumbsup:


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## justridnalong (Nov 1, 2004)

just lay some pvc pipe before building a berm. Not such a big deal and it's not very hard to maintain. Here's one thats 4' tall and drains fine.


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## HarryCallahan (Nov 2, 2004)

I appreciate all the posts here.

What I'm reading is that berms can be OK, IF, they are built and maintained in such a way that they allow water to flow off the trail. On the other hand, if a berm is built across an outslope turn grade reversal and there is no provision for drainage, then there may be a problem. Have I got that right?


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## mtb777 (Nov 6, 2005)

HarryCallahan said:


> I appreciate all the posts here.
> 
> What I'm reading is that berms can be OK, IF, they are built and maintained in such a way that they allow water to flow off the trail. On the other hand, if a berm is built across an outslope turn grade reversal and there is no provision for drainage, then there may be a problem. Have I got that right?


The IMBA Book has a couple of good ideas that work where if you look closely.....you enter the turn on an insloped surface that continues behind the turn and drains away further past the turn and the turn dips and turns back into a rolling dip to immediately drain the second half of the turn where it can rise up slightly to define the RD and continue in the same direction or turn back on itself again. If you stack them you need to offset or stagger them from the drainage or Rd's from above.

Drain away from the low inside of the turn to a lower area or create a drainage trench away from the trail. We are about to build something like that along a continuous section like a curved spine and drain water off of the trail to lower areas on both sides of the trail.


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