Question

The hydrograph is useful to estimate:

• A. runoff rate
• B. runoff rate, runoff volume
• C. rainfall rate, rainfall frequency
• D. rainfall rate, rainfall frequency, rainfall intensity

Hint:

Remember: \[ \textbf{Hydrograph} \Rightarrow \textbf{Runoff vs Time} \] while \[ \textbf{Hyetograph} \Rightarrow \textbf{Rainfall vs Time} \] Also:
• Height of hydrograph gives discharge rate
• Area under hydrograph gives runoff volume

Answer 1

The Correct Option is B

Concept: A hydrograph is a graphical representation showing variation of discharge or runoff with respect to time at a particular location in a river, stream, or watershed. It is one of the most fundamental and important concepts in hydrology and water resources engineering. Generally: \[ \text{Hydrograph} = \text{Discharge versus Time graph} \] Hydrographs are extensively used in:
• Flood analysis
• Reservoir design
• Drainage design
• Watershed management
• Runoff estimation
• Flood forecasting A hydrograph provides valuable information such as:
• Peak discharge
• Runoff rate
• Runoff volume
• Time to peak
• Base flow characteristics Thus, hydrographs are primarily associated with runoff behavior rather than rainfall characteristics.

Step 1: Understanding what a hydrograph represents. A hydrograph plots discharge \(Q\) on the vertical axis and time \(t\) on the horizontal axis. Thus it directly indicates: \[ \text{How runoff changes with time} \] From the graph we can determine:
• Instantaneous runoff rate
• Peak runoff
• Total runoff volume

Step 2: Understanding runoff volume estimation. The area under the hydrograph curve represents runoff volume. Mathematically: \[ \text{Runoff Volume} = \int Q\,dt \] Thus hydrographs are useful not only for runoff rate but also for total runoff volume estimation.

Step 3: Analyzing each option carefully. Option (A): Runoff rate A hydrograph indeed provides runoff rate information. However, it also provides runoff volume information. Hence this option is incomplete. Therefore: \[ \boxed{\text{Option (A) is incomplete}} \] Option (B): Runoff rate, runoff volume This option is correct because:
• Hydrograph gives runoff rate directly
• Area under hydrograph gives runoff volume Hence: \[ \boxed{\text{Option (B) is correct}} \] Option (C): Rainfall rate, rainfall frequency Hydrograph does not directly represent rainfall rate or rainfall frequency. Those are associated with rainfall analysis and hyetographs. Hence: \[ \boxed{\text{Option (C) is incorrect}} \] Option (D): Rainfall rate, rainfall frequency, rainfall intensity Hydrographs are not used for direct rainfall characteristic analysis. These parameters are obtained using rainfall records and hyetographs. Hence: \[ \boxed{\text{Option (D) is incorrect}} \] Final Conclusion: A hydrograph is mainly useful for estimating:
• Runoff rate
• Runoff volume Hence the correct answer is: \[ \boxed{(B)\ \text{runoff rate, runoff volume}} \]