Drainage system refers to the origin and development of streams through time. In a region, evolution of drainage system is determined by two factors- nature of slope and geological structure.

Based on adjustment of streams to the geological structure of region, drainage system is divided into two categories.

1. Sequent streams: Those streams which follow the regional slope and are well adjusted to the local geological structure.
   
   

They may be divided into-

• Consequent rivers: They are the ones that follow the general direction of the slope. For example- Godadvari, Krishna, Kaveri, etc.
  
  
• Subsequent streams: Are those streams which originate on the flank of anticlines and joins the master stream at right angle. For example- River Asan (tributary of Yamuna river), River Son.
  
  
• Obsequent Streams: The stream flowing in opposite direction to its master consequent stream is called so.
  
  
• Resequent Streams: They originate at much later date in comparison to master stream and flow in the same direction as of master consequent stream.
  
  

2. Insequent Streams: Those streams which do not follow the regional slope and are not adjusted to geological structure are called Insequent stream.

They are of two types-

• Antecedent Stream: These are those streams which are originated before the upliftment of land surface. They have maintained their present course through continuous downcutting of their valleys. E.g. Indus, Ganga, Satluj, etc.
  
  
• Superimposed Stream: Are those streams that have been established on an earlier surface (perhaps conformable with the immediately underlying strata, and standing well above the present landscape). Subsequently the pattern was lowered by river incision so it now lies across geologic structures to which it bears no relation. E.g. Damodar, Chambal, Banas, etc.
  
  

Thus the drainage system determined by the geographical structures and slope of the region contributes to the further development of the drainage pattern which is witnessed in form of rectangular, trellis, annular, radial etc.