Why do the contour of different heights not cross each other?

How do the contour lines show the direction of the flow of rivers and streams?

Given below are some symbols and conventional signs, name each one:

Draw conventional symbols for the following using appropriate colours where necessary.

(i) Cart-track

(ii) Broken ground

(iii) Nala

(iv) Perennial tank

(v) Stream

(vi) Dry-stream