Hydrographs and Flood Events
A hydrograph is a graphical representation of the flow rate or discharge of a river or channel over a specific period of time. It depicts the rise and fall of water levels in response to precipitation, and is commonly used in hydrology and hydraulic engineering to analyze flood events.

Isolated Storm and Flood Hydrograph
An isolated storm refers to a singular rainfall event that occurs over a relatively short period of time, typically within a few hours. When this storm occurs, it can produce a flood hydrograph that illustrates the changes in river discharge over time. The flood hydrograph resulting from an isolated storm typically consists of three distinct phases: surface runoff, interflow, and base flow.

Surface Runoff
Surface runoff is the portion of precipitation that flows over the ground surface and eventually enters streams or rivers. It occurs when the rate of rainfall exceeds the infiltration rate of the soil, causing excess water to flow overland. Surface runoff is a major contributor to flood events, as it can rapidly increase river discharge. In the flood hydrograph, the surface runoff phase is characterized by a steep rising limb, indicating a rapid increase in river discharge.

Interflow
Interflow refers to the lateral movement of water within the soil, just below the ground surface. It occurs when the soil becomes saturated and excess water starts to move horizontally through the soil layers. Interflow contributes to the overall flow of water towards streams or rivers, but its contribution to flood events is relatively smaller compared to surface runoff. In the flood hydrograph, the interflow phase is represented by a slower rising limb, indicating a gradual increase in river discharge.

Base Flow
Base flow is the portion of streamflow that is sustained by groundwater seepage into a river or channel. It represents the long-term average flow of a river under normal weather conditions, and it is typically lower than the peak flow associated with flood events. However, during a flood event, the base flow can contribute to the overall river discharge. In the flood hydrograph, the base flow phase is depicted by a relatively flat portion after the peak flow, indicating a gradual recession of river discharge.

Conclusion
In summary, the flood hydrograph resulting from an isolated storm consists of three phases: surface runoff, interflow, and base flow. Surface runoff is the primary contributor to flood events, as it represents the rapid increase in river discharge during heavy rainfall. Interflow and base flow play smaller roles in flood events but contribute to the overall hydrograph shape. Understanding the different phases of a flood hydrograph is crucial for analyzing and managing flood risk in hydraulic engineering and hydrology.