IMBA Slope/Trail building guidelines

Cypher

Cypher

Likes Dirt
Could someone jot down what the IMBA guidelines are for trail building on slopes?

I'd like to know what the categories are - for instance a 3% slope you need to put in x features, for a 10% slope you need y.

Also do people prefer their slopes expressed in percents (such at a 50% slope is 45 degrees and a 100% slope is vertical) or in degrees?

Cheers! Julie

Confused as to what I am doing? I am classifying land based on slope for trail building. Darned if I can tell what degree or percent a slope is at. Slopes that seem gentle to me result in badly eroded trails. So the end result will be a map of an MTB area all coloured by slope type according to the IMBA guidelines...if I can get them :) Ta
 
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Olly76

Likes Dirt
One of IMBA's guide lines is the 50% rule.

Say 8% slope trail should not exceed 4%. It is a very rough guideline but would satisfy in most situations.
 
crank1979

crank1979

Likes Bikes and Dirt
Plenty of good resources around for trailbuilding but nothing beats having a go and experimenting a bit. The more background knowledge you have though the less mistakes you hopefully make.

10 most common trailbuilding mistakes

I've found the IMBA stuff to be a good start but Sydney soil/sand doesn't seem to agree exactly with how IMBA describe to do things. The Trail Solutions book makes almost no reference to dealing with sandy conditions, so while the basic principles can be applied a bit of creativity can be needed to slow erosion and reduce the need for frequent maintenance.

There are plenty of knowledgable people on RB spread around the state and country too. If possible it's good to have a chat with someone else about work that needs doing. Walking a track with someone might not always be possible, but maybe taking photos of an area requiring work and posting it up or emailing it to people for ideas would be benficial too. :)
 
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outtacontrol

outtacontrol

Likes Bikes and Dirt
Cypher said:
Could someone jot down what the IMBA guidelines are for trail building on slopes?

Darned if I can tell what degree or percent a slope is at.
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Get a hold of a clinometer. It is a very simple device that allows you to calculate the grade of a section of sideslope.

Once you have calculated the grade of sideslope, you know what grade the trail can't exceed. Eg. With a sideslope with a 15% grade, the trail should not exceed 7.5% or it runs the risk of becoming fall line, and vulnerable to erosion.

On most trails there will be sections that will exceed the half rule (like climbing turns), but they can be protected by reverse grades before and after the section, and rock armouring.
 
dcrofty

dcrofty

Eats Squid
Side rule is a good one.

They also recommend not exceeding a 10%grade on any section of trail as a general rule.
Exceptions apply for very short distances and if there is armouring but 10% is a good rule of thumb.
 
Cypher

Cypher

Likes Dirt
Attached (hopefully) is a first draft of a map of what I was considering above.

This is using the IMBA guidelines (such that I could find - thanks guys!)

Let us know your thoughts

Notes: The PDF version (3mb) allows you to turn off and on the individual layers, so you can get ride of the noisy contours or the noise slope layer. But I can only attach the PNG version here.
 

Attachments

crank1979

crank1979

Likes Bikes and Dirt
Are you able to upload it to the MTB Census page so we can see a larger version?
 
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outtacontrol

outtacontrol

Likes Bikes and Dirt
I am afraid I am technology illiterate but as an interesting aside, someone from our club mapped our trails which are cut into the foothills of a mountain. These trails have been built for a long time, but to IMBA guidelines.

Was interesting to see when overlayed onto a map with contour lines that the trails almost followed them exactly.

With the high volume of rainfall we get in a short period during our wet season, they have stood the test of time with only minimal maintenance required.
 
Cypher

Cypher

Likes Dirt
The Menai example here largely does that to.

However Menai is unregulated - it is acutally private land. I have noticed the odd track going straight down the hill. These trails don't last long in a good condition.

Also I have been looking at trail condition. Basically if it is not near dead flat, then there are some erosion problems - from minor on gentle slopes to significant on steeper (but not what I would consider steep) slopes.

Thats why I thought a map like this could help - with planning new trails sensibly. Of course, people have been making good trails without this sort of help, and you would still need to be on the ground to check it all out.

However map making is where my real skill lies. I'm not so good at building trail (I'm the unskilled labour) :)
 
Misplaced

Misplaced

Formerly Unfit
Cypher said:
The Menai example here largely does that to.

However Menai is unregulated - it is acutally private land. I have noticed the odd track going straight down the hill. These trails don't last long in a good condition.

Also I have been looking at trail condition. Basically if it is not near dead flat, then there are some erosion problems - from minor on gentle slopes to significant on steeper (but not what I would consider steep) slopes.

Thats why I thought a map like this could help - with planning new trails sensibly. Of course, people have been making good trails without this sort of help, and you would still need to be on the ground to check it all out.

However map making is where my real skill lies. I'm not so good at building trail (I'm the unskilled labour) :)
Click to expand...

You should really link in with Nick Bowman at IMBA Australia. your skills and enthusiasm matched with his knowledge and resources would be a great thing.
http://imba-au.com/
 
outtacontrol

outtacontrol

Likes Bikes and Dirt
Cypher said:
Also I have been looking at trail condition. Basically if it is not near dead flat, then there are some erosion problems - from minor on gentle slopes to significant on steeper (but not what I would consider steep) slopes.

However map making is where my real skill lies. I'm not so good at building trail (I'm the unskilled labour) :)
Click to expand...
There are a couple of simple techniques that help to prevent erosion from water, like reverse grades, rock armouring, and most importantly, not exceeding the half rule.

The grade of the sideslope does make trail building more difficult. Gentle sideslope is obviously ideal, but flat terrain is surprisingly troublematic.
We have one trail that is on flat terrain at the base of the hill and it is always the last one rideable after the wet, as it cops all the runoff from the hill, and unless the tread is higher than the surrounding terrain, the water will sit in or follow the trail.

It is great that you are educating yourself in what is required to build sustainable trails. When you are riding, take note of truoble areas, and ask yourself how you would fix it using the simple techniques above.

This is a great way of getting some practical experience to solving trail design problems.

Good luck.
 
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