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lines are drawn perpendicular to contour lines to indicate drainage divides. Once the perimeter of the watershed has been established, a planimeter is used to measure its area. Perimeter and length of the longest flow path are measured using a map wheel. Slope is calculated by taking the difference in elevation between map contours or from field survey data.

3.2.1

The Planimeter

A planimeter is an instrument used to trace around the perimeter of an object to determine its area. Planimeters are useful tools in determining surface areas from maps and aerial photos. A planimeter mechanically integrates an area,

and records this area as a tracing point moves along the

be

measured.

This

number

can

be

converted

to

an

planimeter reading by a constant called varies from planimeter to planimeter.

the

planimeter

boundary of the figure to area by multiplying the constant. This constant

A planimeter is composed of a graduated drum and disk, vernier, tracing arm and point, and anchor arm and point (anchored to table). An elbow connects the tracing arm and anchor arm, and bends and slides freely. Parallel to the elbow, which slides and bends freely, is a wheel with a scale (consisting of a disk, drum and vernier) that records how far the wheel has turned. Figure 3.2 is a picture of the planimeter used in this study (Kunkle, 2001).

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