The branch of science which deals with stream flow measurement is known as Hydrometry( Science of Water) . The stream is an open channel where the surface runoff from the nearby catchment area ( drainage & basin) enters in it ( drains in it )

The stream flow measurement plays an important roles in ;

• To find the capacity of a reservoir
• To find the flood flow
• To find the depth of surface runoff which helps in finding the inflation capacity of the soil
• To find the Linear Water way (LWW), so that length of a bridge can be decided
• To find the elevation of weir (or)barrage across a river

There are 2 categories of stream flow Discharge measurement technique

Direct Measurement & Indirect Measurement

Direct Measurement :

Direct measurement consist of following methods

1. Area Velocity method
2. Dilution Method
3. Elector-Magnetic method
4. Ultra- Sonic method

Indirect Measurement :

Indirect measurement consist of following methods

1. Hydraulic structures methods like wier, Notch, gates
2. Slope Area Methods

Hydrograph

Hydrograph is a plot (Graph) is between the discharge of a river (Y – Axis) and the tome of flow of the river in chronological order (Increasing order in X- Axis). A Hydrograph is also known as flood hydrograph is also known as flood hydrograph (or) storm hydrograph which consist of direct runoff and basflow ( combine)

Types of Hydrograph:

1. Hydrograph (Flood Hydro graph – Storm Hydrogrpah) – A plot of graph between discharge of river and time of flow of river ( Direct runoff + Base flow)
2. Direct runoff hydrograph (DRH) – A plot of graph between the discharge of a river without base flow and time of flow of river
3. Unit Hydrograph – A plot of graph between river without baseflow having 1 cm depth of DRO and time of flow of river
4. Summation Hydrograph –  Graph between the discharge of a river due to infinte duration of rainfall and time of flow
5. Disrtribution hydrograph – A plot of graph between Percentage of Total runoff ( Y-Axis) and the time of flow)
6. Synthetic Hydrograph – A Plot of discharge based on unit depth of runoff on a catchment and he time of flow