Step 1: Understanding the Concept:
A contour interval is the vertical distance or difference in elevation between two consecutive contour lines on a map. The choice of contour interval depends on the purpose of the map, the scale of the map, and the nature of the terrain. A smaller interval is used for detailed design work in flat terrain, while a larger interval is used for large-scale mapping in steep terrain. The question asks for the typical range for large engineering projects like reservoirs and town planning.
Step 2: Detailed Explanation:
Let's consider the requirements for different projects:
Detailed Design / Flat Terrain: For tasks like building layout, landscape design, or earthwork calculations for roads in flat areas, a very small contour interval is needed to show the subtle changes in elevation. This is often in the range of 0.15 m to 0.50 m (Option A).
Engineering Projects (Reservoirs, Town Planning, Highways): These projects cover large areas and require a good representation of the topography for planning, location studies, and earthwork volume calculations. The terrain is often moderately hilly. A very small interval would make the map cluttered and expensive to produce. A very large interval would not provide enough detail. A contour interval in the range of 0.5 m to 2 m is standard for this type of work. It provides a good balance between detail and clarity on a typical engineering scale map (e.g., 1:5000 to 1:10000).
General Topographic Mapping / Hilly Terrain: For general-purpose topographic maps of large, hilly, or mountainous regions, a larger contour interval is used, such as 2 m, 3 m, 5 m, 10 m, or even up to 25 m or more (Options C and D). This is necessary to prevent the contour lines from merging into a single mass on the map.
The work described – construction of reservoirs and town planning – falls squarely into the category of major engineering projects requiring a moderate contour interval.
Step 3: Final Answer:
The typical contour interval for engineering projects like reservoir construction and town planning is in the range of 0.5 to 2 m. Therefore, option (B) is the correct answer.