Monday, February 8, 2010

GCNP river boundary 2

Working on the Quartermaster Quad, map 47 in the Guide. Fairly simple: the goal was to remove the center line and the words "INDIAN RES BDY" from the river. This was an exercise in using the lasso. I am not particularly adept yet at gauging what size to make the first loop, that which captures the clean river, in order to match what needs to be covered up. So I have to take a lot of extra steps. In one sense it doesnt matter since when I do the Paste Into Selection, even though the shapes do not match, it does not paste over where I dont want it. I had to do a little repair of the rapids; they show up well only at certain magnifications.
  A peculiarity of this map; it shows river miles coming upstream marked by a black cross and sometimes, a number.
 And the maps in the section of the Canyon that Lake Mead can affect have a line on each side that seems to relate to some water line above the old river shore; perhaps the reservoir maximum. It is a bit disconcerting since in some places it has the appearance of a political boundary, not just a contour line.
 What is even more relevant will be the answer to the question of how to SHOW the boundary in that part of the channel where the reservoir can/has spread much farther than the old river channel. To go back to basics: the purpose served by the 1975 GCNP Act in setting the Park boundary "on south bank" was to put the "entire river/water surface" under a single jurisdiction. Throughout most of the Park, although the river does fluctuate due to changes in Glen Canyon Dam's operations, it is a matter of a few feet, and on the map poses no problem to drawing the boundary of the Park.*(see below)  However, once you get downstream of river mile (r.m.) 235 (Lake Mead's historical high water), the maps begin to depict the differences between reservoir line and old river shore, that is, the fluctuation of the water surface measured over years (above Mead, the fluctuation is rapid in comparison: diurnal, monthly, seasonally) can extend for many yards, particularly in side canyons/notches that start out flat. The extent of the fluctuation is limited, particularly on the left side/south shore, up to about r.m. 260. From there on, the flats along the river bring about a much more noticeable gap between reservoir high and low water. At present, with the continuing drought and the reservoir way down, the Park boundary approximates the old shore more closely (though silt deposition over the past 3/4-century changes this parameter).
  So, what to do to indicate a boundary that has two manifestations? Physically, at any given moment a person is there, it is obvious: If you are on the water (wet-foot), you are in the Park; when you step on the south bank (dry-foot), you are on Hualapai land. Cartographically, on the second hand, the desire is to draw a definitive line. This cannot be done, as shown when the two lines of the old river channel and the Mead high water line are quite far apart. One possibility is explanatory text, indicated perhaps by a phrase on the map. Another would be stippling. A third would be to not draw a line or perhaps give the appearance of a line by writing "on south bank" in very small type in the areas with enough space. Suggestions are welcomed. 
  Again, I want to stress that this is not a physically real, operational difficulty: on the spot, it is the wet-foot/dry-foot dichotomy. (Mud I leave to the lawyers.)

*See the next post for a comment on the Hualapai boundary 

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