Many environmental factors influence how viable are alternative uses of land. Decisions about land use must be made within the context of these factors. This section of the Trevey report is about how slope, an integral component of a total ecosystem, influences planning options on the land. Slope is the angle of of incline of the land surface. Slope maps can be readily produced by GISs and often data from them such as slope frequency (O'Neill and Mark 1987) can be more useful in landscape analyses than the map image. Slope steepness (expressed as degrees from the horizontal, as percent (45-degrees being 100-percent), or as a ratio (e.g., a 3:1 slope means 3 units along the horizontal for every 1 unit of measure along the vertical) is an important factor in wildland management. It effects the utility of land for many purposes, the velocity of running water, and the micro-climate of sites. Slope steepness is a dominant factor in models used to estimate potential soil loss or erosion. It is used as one of many "bands" of information in remote sensing analyses of landscapes. It relates to gravity and the costs of movement. It relates to ground slippage and mass wasting. It relates to solar radiation received within a map unit. Decisions about where to do field work and the impacts of doing so are influenced by knowledge of slope steepness.

Safety

Slope steepness in combination with soil and rock type, moisture, and disturbance influences whether surfaces will fail and rock or mud slides occur. Mining stability analyses depend on such knowledge for stability analyses of embankments, hollow-fills, dams, and spoil bank management. Siesmic activity and its consequences is affected by the slopes of the land. Roots and root decay after timber cuts can affect slope stability. Soil strenght tends to increase linearly as live root biomass increases Ziemer 1981).

Construction

Slope, in combination with geologic factors, can determine the suitability of land for constructing such facilities as buildings, roads, and utility lines. Foundation stability, construction costs, accessi-bility, and immediate and longterrn environmental impacts are also related to slope. Slope thus influences the feasibility of construction.

Water Supply

Slope directly influences the amount. of runoff, stored surface water, and ground water. If there are constant soil characteristics, the runoff of precipitation which will eventually enter a lake or stream will increase with increasing slope. Conversely, as the degree of slope decreases, more water is stored at the surface and percolates into the ground water system. These concepts are important in planning projects such as those for water supplies, or in the building and regulating ponds and storm water control structures.

Slope classes are frequently used but they tend to obscure information already avaialble. When there are appropriate limits and comparisons need to be made with past studies, slope classes may be appropriate. Classes are usually based on other factors such as interest in water movement. Whether slope classes, land form, or drainage classes may be a good question as for the following table:

Number	Soil Drainage Classes	Position and Slope
1	Very poorly drained	Flood plain < 2 %
2	Poorly drained	Toe slope - equal or greater than 6 %
3	Somewhat poorly drained	Toe slope and side - <6 %
4	Moderately well drained	Upper and lower side - Shoulder
5	Well drained	Side
6	Somewhat excessively drained	Side and steep shoulders
7	Excessively drained	Ridges

From information in column three about map cells, the other two columns can be estimated and the condition mapped.

Waste Disposal

Slope is a significant factor in planning both solid and liquid waste disposal facilities. Slope must be included in decisions for locating landfills since too steep an area is not economically feasible. In addition, the seepage of pollutants may contaminate local water supplies.

The efficiency of drainfield sewage disposal systems is correlated to slope. A steeper area loses efficiency in sewage effluent renovation due to the decreased retention time. Therefore, a relatively flat area makes a better location for a drain field.

Roads and Other Transportation Systems

Both the location of road networks and their extent are largely determined by slope. Accessibility decreases, and construction costs increase with increasing slope. The necessity of grading steeper slopes may greatly increase erosion by disturbing natural vegetation and drainage patterns. The necessity of cutting and filling steep grades adversely affects natural scenery. The removal of snow is less essential and more easily accomplished on gentler slopes. Recreational area parking lot construction is less expensive and less environmentally disruptive in areas of minimal slope.

Similarly, the degree of slope restricts the development and scale of air, rail, and even water transportation systems.

Streams

Slope directly affects the velocity of running water and therefore streamflow characteristics. Gradient is the fall in feet per mile, and is usually greater at the headwaters than at the stream mouth. The rate of peak stream discharge and the volume of sediment that a stream can carry increase as the slope or gradient increases. Erosion of the stream bed, both vertically and laterally, is greater where the water velocity is higher due to steep gradients. Many flat areas have that characteristic because of past flooding and the influences of water and beaver dams.

In addition to these properties, slope is also related to many other stream characteristics such as stream bed substrate, water temperature, the type of fishery thast is possible in a stream, and stream ecosystem energy relationships.

Life Spaces

Varying slopes produce a variety of microclimates and other microsite characteristics. Temperature, moisture, and wind are affected by slope, as are soil particle size distribution and the resulting soil characteristics. The energy coming into a site and that leaving at night and available water are also influenced by slope. The microsite conditions created by these factors strongly influence which plant and animal species will exist on the site, the more energy is required for mammals and reptiles to live there. Less steep areas typically have more wildlife but these same areas have other uses, thus conflicts occur.

Rayburn (1972) showed how slopes were used in estimating the energy requirement of white-tailed deer to ive in an area (the steeper, the more energy-costly).

Recreation

Steep slopes are essential for some forms of recreation and may enhance or detract from others. Skiing requires steep slopes and trail bikers and 4-wheel drive enthusiasts seek out steep, rugged terrain. The visual contrasts of varying slopes enhance visitor experiences on hiking trails and scenic drives. However, steep slopes also limit the types and location of developed public recreation areas by raising their construction and maintenance costs.

Resources

Excessive slopes restrict mining, agriculture, and forestry by increasing costs or limiting accessibility for certain types of machinery. Although very steep areas can be made accessible, the environmental costs may be very high at current technological levels.

Basic Research

Basic or not, studies have been interesting in landscape analyses and descriptions, and in modeling the land form. Concave profiles may be cycloidal or of exponential form. In one area, the cycloidal form seems associated with erosional processes and the exponential form with depositional processes (Bridge and Beckman 1977).

Analysis

The following is an analysis of the slopes of your area. These may be considered in light of the above remarks. They relate to recreational, forestry, fisheries, and other land use potentials. They also relate to access for emergencies. For some, they characterize land for agriculture, taxation, flood damage and insurance, and human settlement. Slopes suggest the characteristics of some watersheds.

From The Roanoke Times, June 3, 2006 with permission; from "Report #466 of the APA Planning Advisory Service" in an article by Olshansky. U.S. Geological Survey (Professional Paper 351)."

The following are planned:

• Color Maps (slopes. Slope classes (flat less than 2.5%, 10 percent classes to 70):erosion slope classes; SCS classes
• Distribution of slopes within pixels (normally distributed?)
• Predominant slope
• Bar graph frequency (vertical) and slope classes (horizontal)
• Skewness coefficient for the frequency distribution (where negative skew (tail to the left) indicates a greater proportion than normal in steeper slopes; positive coefficient indicates shallow slopes are more frequent)
• Proportion in each class (a table)
• Arc-sine transformations with mean, variance, standard deviation, skewness, and frequence curves
• Land capability classes (former SCS) ; also the following classes used in West Va. (Pohlman 1937): 1-level to gently rolling (0-12 percent); 2 - gently rolling to rolling (12-25 percent); 3- rolling to steep (25-40); 4- steep (more than 40 percent)
• Simpson index of the above proportions
• Comments on how slope controls agricultural land utilization in Virginia (Raisz and Henry)
• Pie chart- slope classes
• Slope classes by 8 aspects; also by easterly/westerly and N/S aspects with "wind rose" directiopnal diagram (automated)
• Cumulative graph (sigmoidal) of slopes starting at zero(flat) summing all cell to total within the boundary
• Analyses of flat lands (a non-aspect?) and all of its meanings and dimensions
• Mean and Standard deviation of slopes
• Interactive visual basic procedure to change percent slope to degrees (or reverse)
• Maximum and minimum within the area.
• Possible finite-element maps showing each map cell as influenced by the one above it; another for the cell below it.
• Relations to geomorphology units (JWM 47(4):1164)

Using the Topographic Abney level

To find E
E = A x B

To find A
A = C / slope distance for 1 chain on the horizontal

Giles' questions related to slopes in 1976 are available. Some may persist.

References

Bridge, B.J. and G.G. Beckman. 1977. Slope profiles of cycloidal form. Sci. 198:610-612.

Gregory, K.J. and D.E. Walling. 1974. Drainage basin form and process: a geomorphological approach. Halsted (Wiley), New York, NY 456pp.

Lee, R., M. Chang, and S.C. Hill. 1976. Land slope in West Virginia. West Va. Agric. And Forestry 6(3): 10-16

Mathur, Priti. 1997?. A comparison of slope estimation methods. MS Geography, Virginia Polytechnic Institute, Blacksburg, Va. 117p. [The methods can be used interchangeably for non-site-specific applications while for site-specific applications, the differences can be very significant.] S

O'Neill, M.P. and D.M. Mark 1987. On the frequency distribution of land slope. Earth Surface Processes and Landforms 12 :127-136 ALSO SEE THESE AUTHORS' PAPER 1985 pROC 16TH aNNUAL mODELING AND sIMULATION cONF, P.311-15.

Rayburn, E. B. 1972. A measure of land for supporting deer populations. Unpub. M.S. Thesis, Va. Poly. Inst. and State Univ., Blacksburg, Va. ix + 195 pp.

Pohlman, G.G. 1937. Land classification in West Virginia based on use and agricultural value. Bul. 284, Ag. Exp. Sta., West Va Univ., Morgantown 31pp