Coefficient Routing

The Coefficient Routing method is a linear hydrologic routing method that describes the routing with a series of timesteps and coefficients (or factors). The coefficient method uses the following equation to compute outflow from the reach:

Where:

O = Outflow
I = Inflow
C = Coefficient
t = the current timestep
n = the number of rows in the table.

Each coefficient equates to the fraction of the flow entering the reach that will reach the downstream end at the end of each timestep in the table. The values in the table must sum up to 1. The coefficients represent the fraction of the flow entering the reach in the current timestep that will exit the reach in the current and subsequent timesteps.

"Figure: Coefficient Routing Edit Panel" shows the edit panel for the Coefficient Routing method. In the example, 75% of the flow entering the reach in the current timestep plus 25% of the previous timestep's inflow will exit the reach in the current timestep. The other 25% of the current timestep's inflow to the reach will exit the reach in the next timestep, along with 75% of the next timestep's flow into the reach.

If you enter a coefficient of 1.0 in the first row of the Coefficient Routing table and leave the rest of the table blank, you have defined a Null or instantaneous routing reach — all the flow entering the reach will exit the reach in the same timestep.