Flood Routing

What is Flood Routing?

Flood Routing is the technique of determining the flood hydrograph at a section of a river by utilizing the data of flood flow at one or more upstream sections. It is used to predict the magnitude and timing of floods.

Reservoir Routing (Level Pool Routing)

Used for routing floods through reservoirs. The inflow hydrograph ($I$) is modified by the reservoir's storage ($S$) to produce an outflow hydrograph ($O$).

Discretized for a time interval $\Delta t$:

This is often solved using the Storage-Indication Method or Modified Puls Method.

Muskingum Method (Channel Routing)

Used for routing floods in river channels. Storage in a channel reach is a function of both inflow ($I$) and outflow ($O$).

Where:

• $K$ = Storage time constant (has units of time). Typically approximates the travel time through the reach.
• $x$ = Weighting factor (dimensionless, 0 to 0.5). Represents the relative importance of inflow vs outflow on storage.
  • $x=0$: Reservoir-type storage (function of outflow only).
  • $x=0.5$: Pure translation (wedge storage equals prism storage).

Routing Equation:

The outflow at the next time step ($O_2$) is calculated as:

Where the coefficients are:

Note that $C_0 + C_1 + C_2 = 1$.