Define water divide. What are the different patterns of flow made by a river?

Water divide: An elevated area such as a mountain or an upland that separates two drainage basins is known as water divide.
The four drainage patterns are as follows:
(i) Dendritic - The dendritic patterns develop where the river channels follows the slope terrain. The stream with its tributaries resembles the branches of a tree, thus the name dendritic.

(ii) Trellis - A river joined by its tributaries, at approximately right angles, develops a Trellis pattern. A Trellis drainage pattern develops where hard and soft rocks exist parallel to each other.

(iii) Rectangular - A rectangular drainage pattern develops on a strongly-jointed rocky terrain.

(iv) Radial - The radial pattern develops when streams flows in different directions from a central peak or dome-like structure.

Please refer link too 

https://www.askiitians.com/revision-notes/class-7-science/water-a-precious-resource/