The correct answer is option 'C': Hyetograph.

A hyetograph is a graphical representation of rainfall intensity over a specific period of time. It shows the variation in rainfall intensity with time. Hyetographs are commonly used in hydrology and civil engineering to analyze and design stormwater drainage systems, flood forecasting, and other related applications.

Here is a detailed explanation of the answer:

1. Hyetograph Definition:
A hyetograph is a plot that represents the rainfall intensity over a specific time period. It is derived from rainfall data collected at regular time intervals, such as hourly or 15-minute intervals. The intensity is usually measured in millimeters per hour or inches per hour.

2. Importance of Hyetograph:
Hyetographs are crucial in hydrological analysis and design as they provide valuable information about the temporal distribution of rainfall. By analyzing the hyetograph, engineers and hydrologists can understand the rainfall pattern during a storm event, estimate peak flows, and design hydraulic structures accordingly.

3. Construction of a Hyetograph:
To construct a hyetograph, rainfall data is collected at regular intervals using rain gauges. The data is then plotted on a graph, with time on the x-axis and rainfall intensity on the y-axis. The resulting plot shows how the intensity of rainfall varies over time.

4. Interpretation of a Hyetograph:
By analyzing the shape and characteristics of a hyetograph, several important parameters can be determined, including:
- Peak intensity: The maximum rainfall intensity during a storm event.
- Time of peak: The time at which the rainfall intensity reaches its maximum.
- Duration: The total time period over which rainfall occurs.
- Rising and falling limbs: The slopes of the hyetograph before and after the peak intensity, respectively.

5. Application of Hyetograph:
Hyetographs are widely used in hydrological studies and engineering design. They are used to estimate the runoff volume and peak flows for sizing stormwater management infrastructure, such as detention ponds, culverts, and storm sewers. Hyetographs are also used in flood forecasting to predict the timing and magnitude of floods.

In conclusion, a hyetograph is a graphical representation of rainfall intensity versus time. It provides valuable information about the temporal distribution of rainfall, which is crucial for various hydrological and engineering applications.