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A Total Forest Management Plan and Wildland Management Decision Support System
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Available Relief

Thornbury (1969:120) defined available relief as the vertical distance from the initial upland to the level of adjacent graded valleys. The concept suggests that for large areas there is a general notion of land available for for cropland and other conventional development for human use. Some areas have much available relief, others not much. Available relief in no way is related to ownership, access, or barriers and is merely a geomorphic characteristic of an area. Nevertheless, it is likely to be shown to relate very positively to the economic potentials of a region and to how an ownership fits within it.

Available relief is a vertical distance measure. It contains many of the difficulties of geomorphic measurements developed by others and how or why they should be used in analyzing a tract. Perhaps horizontal distance may be more relevant? Perhaps slope maps are sufficient? Perhaps it is a measure useful only in coastal areas, perhaps only for vast regions?

For individual tracts of land of less than 100,000 acres we believe that the following measures and descriptors are useful in understanding a property, gaining explanatory power ofer many natural processes, beginning to gain predictive control over benefits and costs.

• Maximum elevation (M)
• Minimum elevation (m)
• The difference between the maximum and the minimum (called relief)
• The ratio m/M (since some areas may be very flat, the larger the ratio, or the closer to 1.0, the more flat the area is likely to be) (relative relief)
• Available relief
• Area of the tract
• Percent of the area of the tract within the characteristics of available relief
• Percent of the area of the tract in each of 10 slope classes (in sequence;low to steep slopes)
• Concavity and concavity index
• Elevation - to- relief ratio
• Drainage density (length to area ratio)

Since slope is an expression of "rise-over-run" and since rise is an expression of vertical distance, the measures of slope and relief are expressions of the same structure.

Hydrology has developed to the point where what may have been called the traditional or "classical" concepts for processes are no longer accepted as the norm for studying environments. Flow-generating processes from forest and wildland as well as structure of the surface needs to be studied and modeled.

Consider:

• Constant of channel maintenance
• Basin circularity ratio
• Basin hexagonality ratio
• Basin linearity ratio
• Ruggedness Index type 1 and 2
• Volumetric estimates

References

Strahler, A.N. and A.H. Strahler. 1973. Environmental geoscience: interaction between natural systems and man. Hamilton Pub. Co., Santa Barbara, Calif. ix + 511pp.

Thornbury, W.D. 1969. Principles of geomorphology. 2nd ed. John Wiley and Sons, Inc., New York, NY xi + 594pp.

Visher, S.s. 1945. Climatic maps of geologic interest. Bull. Geol. Soc. Am. 56: 713-736.

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This Web site is maintained by R. H. Giles, Jr.
Last revision January 17, 2000.