The designer would then select the arrows going from the quadrant corners (A) to the catch basin, indicating direction and percentage of slope (see Figure 12.10-C). Starting with a slope of 1 percent, the elevation of the catch basin would be established. To check to see if 1 percent is too steep, calculate the percent of slope from the midway CB points of the watershed outline 101.7’ to the catch basin. The calculated slope should be less than 2 percent. If it is more, then reduce the slope 102.0’ from the corners to the catch basin as low as .5 percent slope (paved areas in a plaza-like situation can work with .5 or 1 percent slopes). Figure 12.10-C Step Three The consideration for setting the catch basin elevation is to start by creating a .5 or 1 percent slope along the longest diagonal from the corners to the catch basin. If the slope along the longest diagonal is 1 percent, the shorter distances from the watershed outline to the catch basin will be slightly steeper. In order for the surface to appear “flat” or level—which would be an appropriate design intent in a plaza situation—the pavement where surface water travels the least distance should not be greater than 1 or 1.5 percent. If the slopes for the shorter distances are steeper than 1.5 percent, then revise the longest diagonal to less than 1 percent, say, to .5 percent of slope. In this example, the perimeter elevation is 102.0´, and the catch basin rim elevation is 101.7´.
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Creating a Sculpted Landform Site grading can be guided by practical considerations as well as the aesthetic goals of the designer. Successful site-grading solutions pay
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Landscape Site Grading Principles
