Interception Point of Inflow and Outflow Hydrographs
To understand why the point of intersection of the inflow and outflow hydrographs coincides with the peak of the outflow hydrograph during flood routing, we need to consider the following key points:

Inflow and Outflow Hydrographs
- The inflow hydrograph represents the rate of flow entering a reach, while the outflow hydrograph represents the rate of flow leaving the reach.
- During flood routing, the goal is to determine how the inflow hydrograph transforms as it passes through the reach and results in the outflow hydrograph.

Peak of Outflow Hydrograph
- The peak of the outflow hydrograph occurs when the maximum flow rate is observed at the downstream end of the reach.
- This peak flow rate is influenced by factors such as the volume of water entering the reach, the channel characteristics, and the routing parameters.

Intersection Point of Inflow and Outflow Hydrographs
- The point of intersection of the inflow and outflow hydrographs occurs when the rate of inflow entering the reach equals the rate of outflow leaving the reach.
- This point signifies a balance between the volume of water entering the reach and the capacity of the reach to convey that water downstream.
- During flood routing, as the inflow hydrograph rises and falls, it eventually intersects with the rising limb of the outflow hydrograph at the peak flow rate.
Therefore, the point of intersection of the inflow and outflow hydrographs coincides with the peak of the outflow hydrograph during flood routing due to the balance between inflow and outflow rates at that specific moment in time.