Chapter 12: Soils, Topography, and Land Use

Exercises
Links

Summary
Soils are a fundamental natural resource of the land that affects its capability to support vegetation and development. Land use is affected by soils’ strength and stability, drainability, erodibility, and agricultural and resource potential. Soil quality is subject to degradation by human activities, including compaction, erosion, and contamination, and can be improved through remediation.

For agricultural and development uses, the soil survey is the best source of information. Soil survey information can be used to map soil suitability for a variety of uses and as a basis for assessing agricultural suitability using the LESA technique. Soil suitability also depends on slope, which can be assessed for both site and areawide needs using topographic maps.

Techniques for assessing soil erosion potential, such as the RUSLE, are useful to identify problems and controls. Urban soils are subject to erosion and sedimentation from land construction practices and are also plagued by contamination and compaction problems. Most states require erosion and sediment control plans for construct. Federal agricultural programs, like the CRP, have been effective in reducing the nation’s soil erosion.

Chapter 12 Exercises

1. Posted as a pdf file is the soil survey base map for a portion of the Tom’s Creek Basin in Blacksburg (VA) bounded by Glade Road and Meadowbrook Rd. Also posted is a table from the Montogomery County Soil Survey. Using information in the table and this map, produce a hand-colored interpretive soils map for the area within the roads, showing limitations for septic tank absorption fields. Please provide a title and legend with the map, as well as a brief explanation along with any caveats or assumptions. Hint: consult Box 12.3.

2. Obtain a copy of a Soil Survey for your county or a neighboring one and prepare a soil suitability map for dwellings with basements for a selected portion of the area.

3. If the map scale is 1:12,000, contour lines are given for every 40 feet of elevation, and a certain area shows 6 contour intervals per inch, what is its percent slope?

4. In Giles County, VA, a three-acre pasture made up of soil that is about 30% silt, 55% clay, and 15% sand with about 2% organic content, is tilled and denuded of established grass. The slope of the site is 5% and 400 feet long.
a. Calculate the Erodibility Index for the site. Would you categorize the site as Highly Erodible Land (HEL) or Non-highly Erodible Land (NHEL)?
b. Estimate the potential for annual soil loss in tons that might result before and after the removal of vegetation, assuming no conservation practices.
c. What measures would you suggest to reduce the soil erosion potential?

5. Posted is information for a site in Montgomery County (VA) including a soils map and table giving the soils' acreage and Land Evaluation groups. A Site Assessment survey of the site, revealed the following information:
(1) 40% of the area within 1/2 mile of the site boundaries is in agriculture;
(2) 2 sides of the site is adjacent to non-agricultural uses;
(3) the site and two side properties are zoned for agriculture;
(4) one-half of land within 2 miles is less productive;
(5) the comprehensive plan calls for agriculture on this site;
(6) public water is adjacent to the site;
(7) public sewer is 1200 feet from the site;
(8) the site has access to a secondary road;
(9) the proposed use of the site is compatible with surrounding land use;
(10) the site is not in an Agricultural and Forestal District;
(11) but it does have a SCD plan;
(12) the farming family is the first generation on the site.
a. Compute the LE, SA and combined LESA score for the site. (Consult Table 12.6 for LE values and Table 12.7 for SA factors and adjusted weights for Montgomery County).
b. Comment on the site's suitability for agricultural use.
c. Comment on the merits and limitations of LESA as a local land evaluation tool.
6. Posted as a pdf file is a topographic map for a potion of Blacksburg (VA). At the top of the map determine the average slope from the site "x" to the right down to the farthest point on the 1800 foot elevation contour. For the portion of the map between Nellies’s Cave Road and Cedar Run Road, produce an areawide slope map showing four categories of steepness. Briefly describe the procedure you used to produce the map and include any gauges you used. (Hint: see Chapter 12, pages 335-340)
7. Obtain a topographic map for a location near you and for a selected area, produce an areawide slope map showing four categories of slope.
8. Soils may offer certain opportunities, concerns, or constraints for different land uses. For each of the following land uses, give two soil factors or characteristics that should be considered.
a. Onsite Wastewater (septic) systems:
b. Commercial Construction:
c. Stormwater infiltration basin:
d. Cultivated Cropland:
e. Sanitary Landfill: