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Discussion: How to Best Navigate in Spur / Re-entrant Terrain

in: Orienteering; General

Nov 26, 2019 8:36 PM # 
gordhun:
If you were to advise orienteers who had never encountered it before how to best navigate over and through spur / reentrant (aka ridge/valley) terrain - you know the kind of terrain that dominates US orienteering from Georgia to Virginia and west to Arkansas (but not here in Florida) - what would be your advice on how to best get through and keep contact with the map, etc.
Do you have any 'tricks of the trade' you would like to share?
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Nov 26, 2019 10:16 PM # 
simmo:
Up spurs, down gullies (reentrants). Use saddles wherever possible.
Nov 27, 2019 1:22 AM # 
gordhun:
That's interesting about going down gullies. Why? I always felt it was better to stay higher in all cases. Attack from above, so to speak.
Nov 27, 2019 1:31 AM # 
jjcote:
Simmo is right. Reentrants branch as you're going up them, so you can get diverted into the wrong one, but going down, they merge together. The opposite applies for spurs. This advice applies in particular for what to use as a handrail as you're going cross country. When you're crossing a big ridge, for example, locate yourself in the bottom before you go up, pick a spur in front of you, and go up it. Then to go down the other side into the next valley, you go down a reentrant. If you do the opposite, you're less likely to arrive where you're hoping to.
Nov 27, 2019 2:20 AM # 
EricW:
The US has plenty of this stuff, but the Aussies are probably the world's leader in this terrain type. I'm listening.
Nov 27, 2019 3:07 AM # 
simmo:
In classic gully/spur terrain you can't always stay high, and good course planners will make sure that you can't! Attack from above doesn't always work, sometimes flags are more visible from below.

Further to JJ's post, going down the wrong spur or up the wrong reentrant can be classic parallel errors because any spur or gully can look very much like every other one, especially to the over-confident (or panicked!) mind. You can end up hundreds of metres off course before you realise, and then maybe have to cross several deep gullies and high ridges to get back on course.

If visibility is good, look far ahead to pick out a prominent saddle on or near your line, and aim for it.
Nov 27, 2019 6:57 AM # 
robplow:
Nov 27, 2019 7:35 AM # 
gordhun:
Thanks so much. That convinces me about the up and down. I think I'm a run down on a spur following the re-entrant kind of orienteer.
Now what about navigating along the line of the hills? I have been looking at Route Gadget entries from Quantico and Georgia. I cannot find a consistent rule of thumb among the routes entered as to when there are too many spurs and too many re-entrants to cross so the navigator chooses to go higher up or lower down to avoid having to cross too many of those erosion features.
Do you use the same rule when choosing an attack point? Up the spur, down the re-entrant?
Nov 27, 2019 8:22 AM # 
Terje Mathisen:
Personally I tend to look for the flattest option, this often means going either up or down to avoid a long hillside full of narrow spurs and gullies, but I also like to consider how to attack the control, i.e. small cliffs are almost always easier to spot from below while most other small features area easier from above.

When I feel strong I definitely like to climb a bit more in order to minimize risk, i.e. cross the peak of a hill and use as an attack point for a hillside control, vs (when I'm less fit) contour around to save climb but accept that this is more likely to result in a miss.
Nov 27, 2019 10:09 AM # 
blairtrewin:
In Australian terrain (it may be different in wetter climates), one disadvantage of the up spurs/down re-entrants (gullies in Australian parlance) approach is that gullies are often more heavily vegetated than higher ground, and sometimes more eroded too, so will often be slower running. I tend to stay high given the option - but if you do this, you need to be aware of the potential for branching spurs (making sure you see the top of the gully as the spurs branch is one way).

If going across slopes, other features, where they exist, are often good for keeping check of your height. In the Canberra terrain which I grew up on, termite mounds were often good for this. The top of small gullies can be good too. (Visibility in Australian gully-spur terrain is usually good, so you can see the shape of the ground from some distance away).
Nov 27, 2019 12:11 PM # 
cmpbllv:
@gordhun - you might also look at BAOC terrain on RG (Pacheco is a good example). Massive ridgeline / spur / reentrant systems with generally good visibility, and nothing more challenging than navigating up and over and having to come down on the right one when everything is parallel and there are few point features to be sure you've made the right choice (same thing simmo described).
Nov 27, 2019 2:54 PM # 
bmay:
This is a really good thread.
Nov 27, 2019 3:42 PM # 
dofishman:
I find the problem with re-entrants are they are hard to run with all the rocks and other things that collect in them. I try to follow along the edge.

With ridges and valleys I try to count each one as I pass, so I can stay in contact with the map.
Nov 27, 2019 6:11 PM # 
yurets:
Developing CRITICAL THINKING is the core requirement of navigation in spur/re-entrant terrain. Not following blindly any recipes, but rather reading the map and deciding case-by-case. As mentioned already a good course design will test this skill.

It is true often re-entrants are wet, soft, trashy, and your visibility of features around is limited. On the other hand a simple rule: left-right-left and you simplified navigation.

Good rule is to avoid steepest slopes when you climb, so you can actually run, and using a re-entrant often helps.

BTW, mountain foothill terrain is not really spur/gully. Navigation in the mountains is a different story
Nov 27, 2019 9:25 PM # 
Terje Mathisen:
@cmpbliv: I agree re Pacheco! I ran the shorter race last year (Golden Kid), most people who made serious mistakes did so by going up the wrong spur/gully.

https://tmsw.no/qr/show_map.php?user=terjem&ma...
Nov 27, 2019 10:33 PM # 
TheInvisibleLog:
And of course, any good spur-gully course setter is aware of these rules of thumb and so will set legs that make it hard to follow these rules. Controls being approached from above will be placed on spurs where they are not to obvious, or at the foot of cliffs. Controls approached from below will be placed in gullies that encourage parallel errors and demand decisions at sequential gully junctions. Traverses will rarely be level- descending to cliffs is a favourite. Another local (Bendigo) favourite is a leg across flat bland terrain into parallel gullies, with a route choice option of going round the long way along ridge tops... safety-distance trade-off. As said by Yurets, you need to know the rules of thumb and also know when not to use them.
Nov 28, 2019 11:45 PM # 
tRicky:
Spur/gully rolls off the tongue better than spure-entrant.
Nov 29, 2019 3:59 AM # 
EricW:
Apologies for the diversion from the worthwhile substance, but spur- reentrant is strange to my eyes and ears as well. I believe the most common American term is ridge & valley, with ridge & reentrant coming second, both of which have a better roll for my ears and tongue.
Nothing wrong with spur/gully or gully/spur, but as some might know, for us gully refers only to the line symbol 107, not the contour feature.
Nov 29, 2019 8:09 AM # 
Jagge:
Spurgu is common Finnish slang word https://en.wiktionary.org/wiki/spurgu
For our typical suffixes it may sound and look pretty similar, like spurgulla and spurgulle. Apologies for yet an other diversion.
Nov 29, 2019 8:35 AM # 
gordhun:
Two more questions (and I promise these might be the last two): 1) In traversing sections of spur / re-entrant there is a lot of off-aiming. That makes sense. Are there any personal rules as to how you decide whether to off-aim above or below the control site?
2) How often is a good attack point important in your spur / re-entrant orienteering and how is a good attack point chosen?
Nov 29, 2019 12:32 PM # 
tRicky:
Better to aim off low if you're already below the control, makes sense to avoid unnecessary climb.
Nov 29, 2019 6:26 PM # 
graeme:
Consider going round. The climb going up and down (+aimoff) can quickly add up to more than one big ascent. Plus it often gives you a better attack point, because the setter won't be making it easy to find one on the straight line.
Nov 29, 2019 11:50 PM # 
gordhun:
Graeme, I'm pretty sure I know what you mean but would you have an illustration of what you mean by going round that you could e-mail to me? gordhun at rogers dot com
Nov 30, 2019 12:11 AM # 
TheInvisibleLog:
My bathroom scales tell me I am getting better at going round.
Nov 30, 2019 3:36 AM # 
simmo:
Gordhun I was hoping that robplow had posted a classic S-G map and that he would get around to correcting his post. However, I will email you the first leg from an Oz Champs event several years ago - a 3km leg in classic terrain.

In the meantime, you may find several examples by searching Bruce's DOMA which you can access from his training log. Here is one example:. Leg 6-7 is a good illustration of going around.
Nov 30, 2019 3:48 AM # 
tRicky:
How did he navigate through the descriptions?
Nov 30, 2019 7:30 AM # 
robplow:
What could no one see my post? It looked fine on my laptop. But now when I tried to edit it it has disappeared for me too.


Trying to to link to a Google Photos photo - I give up.
Nov 30, 2019 7:38 AM # 
gordhun:
Thank you Simmo and thank you for the example sent by e-mail. That 3 km leg is far more complex than anything the students I will be helping will face, thankfully. But Wow!
The example you link to above, despite the unfortunately placed description shows on leg 6-7 just what I want to show - how going a little out of the way can cut out a lot of tiring climbing (about 50 m in all, I think) and difficult navigation. I also like how the rest of the course shows whether you go up or down the gully or up or down the spur all those ways can help funnel you to the control. Is it safe to say if the control is in the gully run the gully. If it is on a spur run the spur?
Nov 30, 2019 7:40 AM # 
robplow:
that 6-7 route is interesting. By my calculations going basically straight (a little bit left) has the same or less climb. I can't see going that wide being faster.

Often the case in this sort of terrain - when you actually count the contours you realise the route you chose to avoid climb didn't.
Nov 30, 2019 9:33 AM # 
TheInvisibleLog:
This afternoon was the Bendigo club end of season celebration. From here on its too hot to run in the forest, the risk of fire danger increases and the trees start suspending enormous webs with big golden orb spiders. As part pf the celebration of another season we ran a vote for two awards. One was the "Noodle", with about 16 contenders. The other was the Golden Leg, an award for the best route-choice leg for the year. There were 12 contenders and it was a close thing between first and second. This is the winning leg, shown for three courses as I can't work out how to combine them on livelox. The club members appreciated that all three hard courses shared the leg, and that there was a lot of variation in routes chosen. If on considering this leg you think there is only one obvious choice, remember that under race pressure, there was no concensus on the best choice amongst the runners. A good leg may have a best alternative, but a better leg will not make the best alternative clear to the competitor. Congratulations to Clare, who resides on AP as Clara.
Note- its the same map as linked by Simmo above. Some maps are made for route choice course setting.
Nov 30, 2019 10:06 AM # 
Uncle JiM:
Try this for going around (11 - 12) http://www.tulospalvelu.fi/gps/20191005olm21e/

While not classic Spur/Gully terrain, all terrain has spurs and gullies that you need to get past, sometimes you go up and over (straight) or you go around
Nov 30, 2019 11:28 AM # 
tRicky:
Is it safe to say if the control is in the gully run the gully. If it is on a spur run the spur?

Lots of factors to take into account. Is there green in the gully? Is the spur stony ground (happens often in Aus)?
Nov 30, 2019 1:09 PM # 
simmo:
@ IL and Gordun (and Bruce if he's listening): I have fond memories of Sedgwick as it was where I won the Oceania Championships, albeit tied with Steve F.
Nov 30, 2019 1:55 PM # 
tRicky:
Pretty good since Fletch is 31 years younger than you although he tends to do 180s on course.
Nov 30, 2019 10:05 PM # 
TheInvisibleLog:
> Is it safe to say if the control is in the gully run the gully. If it is on a spur run the spur?

From the examples above its clear that there will be no one decision about spur or gully. There will be lots of them. What you choose will be determined by the best way to tackle the leg as a whole. Often its a question of how to link the saddles.
Nov 30, 2019 10:59 PM # 
EricW:
Saddles- That's one difference between Aussie gully/spur, and most of our ridge & valley. Our version tends to have very few significant knolls, and therefore few saddles.
Dec 1, 2019 12:25 AM # 
tRicky:
Yet you have so many movies about the wild west.
Dec 1, 2019 12:35 AM # 
fossil:
but if you look closely you'll note that there are so few saddles that roughly half the horse riders in the movies didn't get one

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