25.6 : Profile Leveling and Cross Sections

Profile leveling and cross-sections are surveying methods used to determine and document terrain elevations for infrastructure projects such as highways, railroads, canals, and pipelines. These methods provide data for earthwork planning and alignment of proposed routes.  
Profile leveling involves measuring elevations along a fixed line to create a vertical terrain profile. A surveyor sets up a leveling instrument at the benchmark (BM) and records a backsight (BS) to determine the instrument's height (HI). Intermediate foresights (IFS) are taken at regular intervals to capture elevation changes along the route. Points of significant elevation shifts, such as ditches, slopes, or riverbanks, are included to represent the terrain accurately.  
When the instrument's range is exceeded, it is repositioned, maintaining continuity by taking a foresight at the last observed station and a backsight at the new station. Notes typically document station locations, elevations, and significant features. Stations are marked as plus stations to identify their position relative to the start. 
Cross sections are measured perpendicular to the main route at regular intervals or locations of significant elevation change. Stakes are placed at specified distances from the centerline to capture ground slopes and features. Elevation differences between the centerline and outer points are recorded, often using a level or a Jacob staff for precision. This information is plotted to show cross-sectional terrain profiles, aiding in earthwork calculations for cuts and fills.
These techniques ensure infrastructure aligns with the natural topography, providing essential design and construction planning data.