Drainage: The river system of an area is called drainage. The area drained by a single river system is called the drainage basin. Drainage Patterns: Depending on the slope of land, underlying rock structure and climate of an area, the streams in a drainage basin form certain patters. Different types of drainage pattern are as follows: a. Dendritic Drainage Pattern: When the river channel follows the slope of the terrain, it develops dendritic pattern. The stream and its tributaries resemble the branches of a tree. Hence, it is called dendritic pattern. b. Trellis Drainage Pattern: When a river is joined by its tributaries at almost right angles, it develops a trellis pattern. Trellis pattern develops where hard and soft rocks exist parallel to each other. c. Rectangular Drainage Pattern: When rocks are strongly joined, then rectangular pattern develops. d. Radial Drainage Pattern: When the streams flow in different directions from a central peak or dome like structure, a radial pattern is developed.