I used contour lines of equal elevation on sectional and topo maps, rather than memory, to discuss down drainage egress from Angel Fire and other high elevation airports in past threads. It has been some time since I discussed topo map reading itself, so this brief rehash.

Scale, the number of units on the map over a much larger number of units on the ground, is fixed on quadriangle topo maps at one inch on the sheet equals 24,000 inches on the ground. One inch on the sectional equals 500,000 inches on the ground. I used a US Topo app and AOPA Airports sectionals on my computer tablet. Both allowed scale change by finger slide Jedi magic.

Contour interval, the distance between contour lines, doesn't change with Jedi scale change. In the mountains, tighter contour lines allow easy visualization of terrain. In lowlands, high parks, deserts without mountains, and calderas, distance between contour lines make visualization difficult. Caution! Computers screens allow us to change scale at will, but contour interval will not change. To get the bigger picture of the topo's 200' interval, we have to use a topo rather than a sectional.

The Army field manuel on land navigation points out an easy way to visualize terrain features. When out there, read from ground to map to mitigate projection. During map reconnaissance, however, imagine standing on the feature and looking in four directions. Read contour lines to visualize elevation change in each direction. Consider how many changes are down and how many are up.

HILL- Four down. From the top, we would be looking down in all four directions.

SADDLE or PASS- Two down, two up. From the pass we read descending terrain, valleys, ahead and behind. We read higher terrain, a mountain peak perhaps, left and right.

VALLEY- One down, three up. From stream or drainage bottom, read down drainage with the wine glass method to lower terrain (check contour lines elevations. ) Read higher terrain (ridges) either side of the valley. Read higher terrain up drainage toward the pass.

RIDGE- Three down, one up. On either side of the valley rising up to the pass, and on either side of the valley descending from the pass, will be a ridge. From ridge crest, read descending contour lines toward the valleys either side and down ridge. From the ridge crest, the only way up is toward the mountain or higher terrain beside the pass.

Valley or ridge? This is where pilots get confused. Read stream or...intermittent stream where available. Check elevation marked contour interval lines when no blue is available. Large contour interval, like on the sectional, makes this difficult.

DEPRESSION- Four up. Read whiskers all the way around. We're in a hole. Everything is up. Problem: we could be in a large unmarked (whiskers) caldera like Angel Fire or the entire Jemez Mountains Range west of Santa Fe.

Wine glass method to determine drainage direction- Imagine placing a wine glass over the map with the sides over two streams and the stem over the one stream beyond the confluence. Water cannot enter the vessel through the stem. Drainage is toward the stem. This wine glass method is critical in mostly level terrain, especially the high desert, parks, and calderas. High, flat, desert is dry except during short seasonal rains. If by miscalculation or "who knew," we are actually at ceiling, having used map reconnaissance to determine down drainage could have saved our bacon. If we head out up drainage, it is too late.

Contact I love you buddy but did you use the "wine glass" method to type this up? You seriously crack me up and leave me wondering how you come up with this stuff sometimes! Love it buddy! Stay fired up!

AKT

You face troops away from the sun, but they still nod off unless you come up with something.

Half the fun is in trying to figure out what it is you are saying, all cool

Thanks Contact, you saved me a stint in Army map reading...

I always wondered why they don’t just put arrows on rivers to show the flow direction? It’s not like they change...

Which direction does the Monongahela River flow?

Why make it so hard? I recently moved to Alpine, WY and still don’t know which way some of the many rivers and creeks around here flow.

Best,

Tommy

Tommy,

You know this, but lets get everybody to do a map recon. McKeesport is at the confluence of the Monongahela and Youghiogheny rivers. If you lay one wine glass edge over the Monongahela towards Glassport and the other edge over the Youghiogheny toward Liberty, the stem will lie over the Monongahela towards Duquesne. Drainage is toward the North. Pittsburgh is at the confluence of the Monongahela (edge) and Allegheny (edge) rivers. Stem is Over the Ohio River. Drainage is northwest.

Drainage lines are all continuously blue. Not so where you are now...

Contact

If we look west of Las Alamos, on Albuquerque sectional just across the Jemez Mountains, we find what remains of a 70,000' mountain. The Valles caldera is bordered by the San Antonio River (topo map) from the northwest around the rim to the southwest and the East Fork of the Jemez River from confluence with the San Antonio almost back to the headwaters of the San Antonio. It has filled in with a few hills, but was all magma thousands of years ago.

Anyway, large depression with egress south down the Jemez river. Wine glass sides on the San Antonio and the East Fork of the Jemez and the stem on the Jemez.

Contact, I think I get this. Are you saying that two rivers running together forming (more or less) a Y, the flow is always toward the bottom of the Y?

Does anyone know of a counter-example where a single river splits on its own where the flow is in the direction of the split flows?

Blue skies,

Tommy

Tommy,

Yes, nature is ripe with variations. We have to cross check. Contour line elevation will be listed somewhere. We have to run that down in flat country where streams meander.

In volcanic, fold and fault, plate moving under plate mountains formation, wine glass method is easy. Big rivers in flat country are pretty easy, because of the greater volume. Glacier carved mountains with steep slopes and flat drainages, even long lakes, are tough.

Where you are now is easy until you get out into the dry semi arid regions and desert. With large, rapid elevation change, we just have to wine glass the valley and drainage and work valley to ridge to valley, etc. Or ingress using ridge lift up to the pass and egress down drainage. GPS A to B requires expensive engines to be safe with normal fuel reserve. Orographic lift and constant egress route make valley ridge system flying "in the mountains" more comfortable in almost any small aircraft.

Contact

To me, the box canyon turn around was egress back down the valley when I couldn't safely make the pass. If you look on Denver sectional northwest of Gallup GUP, you will find Canyon de Chelly from Chinle east to college on the sectional. The college is Tsalie pronounced saylee. Chelly is pronounced shey.

On the sectional it looks pretty flyable down low. Check it out on the topo map. The walls are a couple thousand feet and there are many hairpin turns that would definitely stall a flat turn. Energy management turns would have to be started, the zoom portion, when the eventual target, bottom of the drainage beyond the hairpin was not visible.

Doug Rhinehart made a famous picture climbing out in his Rose Parakeet, but he wasn't that far in.

With 2,000' terrain difference in a very tight horizontal space available place, notice how easy topo navigation is and even the wine glass method in a desert.

Does anybody know what happened to Tommy N? Going back through stuff I realized I never answered his questions about a river flowing both ways and about a river splitting and continuing in two directions which would not work with the wine glass method. Anyway, I saw a documentary of two places in the Rocky Mountains where a lake on the divide drains from two directions one to Pacific and one to Gulf of Mexico. Also there is the situation in swampy deltas where the river flows in multiple veins, but the delta is so flat that it doesn't matter for down drainage egress.

I have a question about enlarging the sectional with Skyvector on a laptop or with Ipad. How do you visualize contour interval and altitude with so few elevation numbers on the contour lines. Getting up close and personal with scale helps us evaluate the terrain, but paper topos give us the big picture at the same time. Wipes out the cockpit, but a pilot driving and another navigating really helps. For the navigator, the closer we get the slower we need to go for him to keep up. Fine with helicopters, but not safe with airplanes. With airplanes, we really need to have a very extensive map recon before going.