[Tagging] Help required on tagging a "wadi"
johnw at mac.com
Wed Sep 7 11:55:55 UTC 2016
> On Sep 5, 2016, at 7:24 AM, Warin <61sundowner at gmail.com> wrote:
> In an ideal world;
> the wadi would be a way along the lowest path - where water would first flow.
> the track would be a separate way
While there (of course) are some wadis that are roughly the size of a car tracks, the wadis (washes) in Southern California require a Wadi at least 2-3x car width to be able to be passable by a car - rocks, smoke trees, irregularly shaped walls, and other obstacles in a wadi would quickly render such a narrow wadi impassable by car - so a car track is made in a much wider wadi where you can go around these obstacles, including irregularities in the river bed left by a storm.
That is the important part.
Every time there is a flash flood, the sand and obstacles move; the "lowest point" in terms of a mappable way line, may move, and because a larger width wadi was needed, we are talking a structure that is tens to hundreds of meters across.
A structure that subtly changes its terrain and obstacles with each rain.
Since there are known points along the sides of wadis (markers on hills) as well as places where wadis meet, those markers and intersections become the navigation aides, and since the tracks in the riverbed were completely erased, the next person to drive through uses their instinct and desire to reach a far navigation point - reacting solely to the new placement of obstacles to literally make a "new" track. The hard sand left by dried water means you can drive a street car in the wadi at that time - I have made new tracks in a wash in a New Beetle a few times in the past. This makes mapping the exact course of the track impossible but uncecessary; you are too busy looking for rocks sticking up in your path to worry about a 10m deviation from a course. Navigation aides like rough intersections and names of other wadis, springs, caves, landmarks, camp sites, survey markers, and entrances to the wadi area are much more important to spatial navigation.
Here is the area I used to go, with a point dropped on "Hollywood& Vine" - a fake street sign put on a hill to make it easier to find the area's rare survey point. The wadis in the area are larger than most motorway systems.
So, to me, large wadis are a geographic area - similar to how we would map a riverbank. The only time there is water is when the whole thing is an angry torrent.
Tracks meander across the wadi depending on obstacles, crossing centerline only when it is narrow and forced due to a pinch point.
Wadis also spend most of their life as a dry feature - like the storm spillway of a dam - it is a flood hazard that is normally dry and used by people only when dry - it is a feature used and enjoyed because it was shaped by water, like the Grand Canyon, or the Hudson River valley, but we would not call those valleys "water features" - wadis are where we cross into water features, so perhaps people interested in mapping them and dealing with their tracks think of them mainly as a canyon or valley that floods once or twice a year, rather than a river that is dry 99% of the time. Mapping a 200m wide "river" in the desert with some blue lines is disingenuous and dangerous - there sure as hell no water to drink unless it is there to kill you.
Narrow wadis will have a track right on top of the "low point", and that reflects reality - the track cannot be anywhere but the wadi because of terrain.
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