Agriculture Reference
In-Depth Information
and to set the height of walls and other built landform elements, such as
the top of earth forms and the bottom elevations of depressions such as
ponds. The designer considers where to place spot elevations to clarify
the grading design intent, particularly in critical areas such as where the
direction of slope must be maintained on paved or landscape surfaces.
Spot elevations provide greater control to prevent the flooding or pond-
ing of storm water. Spot elevations take precedence over contours in a
site-grading plan.
Most firms have established rules about the placement of spot
elevations. Spot elevations are the primary means of communicating
grading design intent on hardscape surfaces, walls, fountains, and other
constructed features. Contours are the primary means of communi-
cating grading design intent on nonpaved surfaces including landscape
areas and nonpaved surfaces. Technical sections are also used to aug-
ment contours and spot elevations. Sections provide the construction
contractor with greater elevation accuracy in situations where the
designer feels it is necessary—for instance, heights of walls and struc-
tures with complex elevation changes or roadway or bicycle paths.
Spot elevations are shown on the grading plan in a set of construc-
tion drawings. Spot elevations may appear in other locations when
details and sections are placed on other sheets in a set of construction
drawings. Avoid redundancy; that is, avoid multiple spot elevations for
the same element in more than one location. If for some reason the
designer makes a spot elevation change on one sheet, there is a 50/50
chance that the change will not be made in the other locations, and this
discrepancy can cause a cost overrun for the contractor—or worse, that
could be considered a design error with potential legal consequences
in the eventuality of someone getting injured as a result of the error.
Contractors generally use spot elevations to construct both hardscape
(paved surfaces) and soft-scape landscape areas. In areas of the grading
plan where contours are primarily used, the contractor will establish a
grid and interpolate spot elevations at the grid intersections. The grid
will be established on the ground with surveyor's stakes, with spot ele-
vations surveyed and marked on each stake.
