Drainage patterns
Drainage systems vary and often a pattern is seen in the kind of drainage that an area presents on the topo sheet. An area drained by a single river is called its drainage basin or catchment area. It includes the various streams, tributaries and sub tributaries that join to create a network of the river. Thus the main river of an area along with its tributaries forms a drainage pattern. The pattern that is formed is dependent on the relief and the rocks that make up the surface of the area. It is logical that water will flow from higher to lower area and while doing so, it will cut through the surface of the land.
On the topo sheets the perennial water bodies are shown with blue lines. The seasonal streams are shown in black lines. Irregular streams are those which carry water for short spells, generally during and after rainfall, and then disappear or finish off. These are shown by dotted black lines.