Aquaculture Engineering

Contour surveying - Characteristics of contour

Unit 1- Surveying

Contour surveying

Characteristics of contour

• Two contour lines of different elevation cannot cross each other. If they did, the point of intersection would have two different elevations which is absurd. However contour lines of different elevations can intersect only in the case of overhanging cliff or a cave

• Contour lines of different elevations can unite to form one line only in the case of a vertical cliff.
• Contour lines close together in indicate steep slope. (a) They indicate a gentle slope if they are far a part. (b) If they are equally spaced uniform slope is indicated.
• (c) A series of straight, parallel and equally spaced contours represent a plane surface.

A contour passing through any point is perpendicular to the line of steepest slope at that point. The perpendicular distance between contour lines is the shortest distance.

• A closed contour line with one or more higher inside it represent a hill. Similarly a closed contour line with one or more lower ones inside it indicates depression without an outlet.

Two contour lines having the same elevation cannot unite and continue as one line. Similarly a single contour cannot split into two lines.

• A contour line must close upon itself, though not necessarily within the limits of the map.
• Contour lines cross a water shed or ridge line at right angles. They form curves of U-shape round it with the concave side of the curve towards the higher ground (a).
  

• Contour lines cross a valley line at right angles. They form sharp curves of v-shape across it with convex side of the curve to words the higher ground. If there is a stream the contour on either side, turning upstream, may disappear in coincidence with the edge of the stream and cross underneath the water surface.