Figure 7.18 presents a sequence of diagrams, each with the same set of three contour lines but different additional information. Diagram No. 1 in Figure 7.18 has simply three wavy lines but is absent of any additional graphic or alphanumeric information. Without any additional information, we can only guess what the three lines represent. For these contours to be useful or even recognizable as contour lines, additional information is required, as shown in diagram No. 2. The contours in diagram No. 2 include an elevation above each contour. Now we can see that the contours represent a partial slope with elevation 101 as the low point and elevation 103 two feet higher. With the addition of a scale (in this case 10˝ = 200´), the percent of slope can be calculated (see diagram No. 3). The steepness or degree of slope can be determined by dividing the vertical elevation difference between the contours (for instance, contour 101 and 102) by the horizontal distance between the two contours. In diagram No. 4 of Figure 7.18 a grid has been overlaid on the contour lines. The grid is useful in a several ways. Assuming the grid is referenced to site property lines, a contractor would be able to pinpoint the exact location of any existing or proposed object or feature, including a precise elevation at any intersection within the grid. The contractor would place stakes in the ground with the desired elevation for each grid intersection. This grid pattern of stakes would guide the earth-moving operations to achieve the grading shown in a site-grading plan prepared by the designer. The method used to calculate spot elevations and slope will be covered in the Chapter 10, "How to Calculate Spot Elevations."
Slope in Plan and Section One of the tools used in developing a site-grading plan is a section drawing. A section drawing aids the designer to quickly visualize existing terrain under study, as well as to see what one or more proposed grading strategies look like before deciding which design alternative is the better solution. A section should be drawn to show relations of the terrain
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Landscape Site Grading Principles
