Hydrography

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Hydrography pertains to water and drainage features. Hydrographic features on aeronautical charts are represented in blue: Streams, rivers, or aqueducts are depicted by single blue lines; lakes and reservoirs are depicted by a blue tint. Small dots or “hatching” indicate where streams and lakes fan out (or are not perennial) or where reservoirs are under construction.

Figure shows how shorelines, lakes, streams, reservoirs, and aqueducts are depicted. Shorelines usually make excellent checkpoints, except where they are relatively straight without features. Pilots need to pay attention to shoreline orientation. For example, most people assume that California’s coastline is north-south; however, in certain areas, such as around Santa Barbara, the coast is actually east-west. This has led to much confusion for student pilots and others unfamiliar with the area. Lakes usually make good checkpoints, especially when their shape is unique or they are dammed.

Caution needs to be exercised with all lakes, perennial and nonperennial. A perennial lake contains water year round; a nonperennial lake is intermittently dry, usually during the dry season. There can be confusion during periods of drought when perennial lakes will be dry. Other discrepancies result from human decisions to drain, expand, or abandon reservoirs. If at all possible, streams should only be used to support other checkpoints. That is, there should be other landmarks that establish position that are supported by the position of the stream. Perennial and nonperennial streams should be treated with the same cautions as perennial and nonperennial lakes. Reservoirs are similar to lakes and can be treated in the same way; however, reservoirs are usually perennial.

Figure describes other hydrographical features contained on aeronautical charts. Among them are symbols for swamps, marshes, and bogs. A swamp is nothing more than a lake with trees growing out of it—an emergency landing there could be catastrophic. Pilots flying over unfamiliar terrain would be well advised to seek the advice of local pilots or the FSS that is responsible for that region.

Tundra describes a rolling, treeless, often marshy plain, usually associated with arctic regions. Hummocks and ridges describe a wooded tract of land that rises above an adjacent marsh or swamp. Mangroves are any of a number of evergreen shrubs and trees growing in marshy and coastal tropical areas; a nipa is a palm tree indigenous to these areas. Bogs are areas of moist, soggy ground, usually over deposits of peat. Flumes, penstocks, and similar features depict water channels used to carry water as a source of power, such as a waterwheel. Pilots flying in northwestern Montana and especially Alaska can expect to see glaciers and glacial moraines (debris carried by the glacier), ice cliffs, snow and ice fields, and ice caps. Other than canals, the other features in figure might be difficult to verify and should normally only be used to support other checkpoint features.

Figure depicts the remaining hydrographical features contained on aeronautical charts. Ice peaks, polar ice, and pack ice are features restricted to polar and arctic regions. Boulders, wrecks, reefs, and underwater features are displayed because they have certain landmark value. Some of these features might be small and difficult to identify.

One other topographical feature should be mentioned. Mountain passes are depicted by black curved lines outlining the pass. The name of the pass and its elevation are shown. Tioga Pass in figure, upper right, is shown with an elevation of 9943 feet MSL.

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