(i) Direct runoff hydrograph
- Direct runoff hydrograph (DRH) is the hydrograph generated due to excess rainfall
- The surface runoff hydrograph obtained after the base flow separation is also known as direct runoff hydrograph.
- Direct runoff = Runoff – Base flow
(ii) Unit hydrograph
- It is a typical hydrograph of direct runoff which gets generated from one centimeter of effective rainfall falling at a uniform rate over the entire drainage basin uniformly during a specific duration.
- The unit hydrograph is a simple linear model that can be used to derive the hydrograph resulting from any amount of excess rainfall.
(iii) S-hydrograph
- A ‘S’ hydrograph is a hydrograph generated by a continuous effective rainfall occurring at an uniform rate for an indefinite period.
- It is called ‘S’ hydrograph because the shape of the hydrograph comes out like alphabet ‘S’ though slightly deformed.
