Short Answer:

To conduct a contour survey, surveyors measure the elevation of points on the ground and then draw contour lines that connect points of equal height. The process starts with selecting the area, setting up instruments like a level or total station, and recording elevations at different locations.

These elevation points are then plotted on a map, and lines are drawn to join points of the same level. This creates a contour map that shows the shape, slope, and height differences of the land, which helps in planning construction and drainage systems.

Detailed Explanation:

How to conduct a contour survey

A contour survey helps represent the natural features of the ground in terms of height or elevation. It is commonly used in civil engineering for planning and designing roads, buildings, irrigation systems, and other projects that require detailed knowledge of land slopes and surface variation.

Step-by-step process to conduct a contour survey:

1. Selection of the survey area
   The first step is to clearly define the area that needs to be surveyed. This includes marking the boundaries and deciding the contour interval, which is the vertical distance between successive contour lines (e.g., 0.5 m, 1 m, or 2 m depending on the project).
2. Choosing the method
   Two main methods are used:

• Direct method: Elevation points of specific contour levels are located directly on the field using leveling instruments.
• Indirect method: Elevations are taken at grid points or along lines and contours are drawn later by interpolation.

3. Setup of instruments
   Use instruments like the dumpy level, auto level, total station, or theodolite mounted on a tripod. The instrument must be carefully leveled and centered to avoid error in height measurement.
4. Recording elevations

• A benchmark is used as a reference point with a known elevation.
• The instrument is used to measure the back sight (BS), intermediate sight (IS), and fore sight (FS) on a leveling staff placed at various ground points.
• The height of instrument (HI) is calculated and used to find Reduced Levels (RLs) of each point.

5. Marking ground points
   Points are selected either along a grid or along cross-sections. The more points surveyed, the more accurate the contour map will be. Each point’s RL is noted carefully.
6. Plotting contour lines
   Once all elevations are taken, the data is plotted on a sheet. Points with the same RL are connected to form contour lines. These lines show the terrain’s slope:

• Closely spaced lines = steep slope
• Widely spaced lines = gentle slope

7. Checking and adjustment
   Double-check the data for any major errors. If needed, field measurements may be repeated to confirm doubtful points.

Applications of contour survey:

• Planning roads, canals, and pipelines
• Deciding building levels and cut-fill volumes
• Drainage design to prevent water logging
• Identifying suitable areas for farming or development
• Estimating earthwork quantities

Conclusion

Conducting a contour survey involves measuring ground elevations, plotting those points, and drawing contour lines to represent equal heights. This process helps visualize the terrain and plan engineering works more accurately and efficiently. A well-conducted contour survey ensures safe, cost-effective, and practical construction and land use.