How to add two snowmelt rates to FEH boundaries

Winter storm estimates, such as the winter Probable Maximum Flood (PMF) estimate, include a rate for snowmelt. Studies have indicated a single snowmelt rate may lead to an underestimation due to the absence of rainfall during storm events being taken into consideration.

Within the Flood Modeller FEH unit, you can now provide two snowmelt rates; the rate during the antecedent period, together with the (usually increased) rate during the storm event itself. Further, these rates can be calculated automatically within Flood Modeller using the temperature, altitude, and geographic location, alongside the catchment descriptors and event parameters given.

To add two snowmelt rates to an FEH boundary:

1. Load your network in Flood Modeller v6.1 and open your FEH boundary. If adding a new FEH boundary, fill in all relevant fields as you would normally.
2. Snowmelt rates are only applicable if using winter events, so the winter storm option must be selected within the Storm Profile section on the Event Rainfall Data tab, and the relevant parameters provided.
3. For manual entry:
   1. On the Event Data tab, enter your snowmelt rates within the Antecedent Melt Rate and Snow Melt Rate (Storm) fields provided
   2. Ensure the checkbox Override input snowmelt rates with calculated values is unchecked
4. For automatic calculation:
   1. On the Catchment Details tab, enter the altitude in the Altbar field
   2. On the Catchment Details tab, ensure the Northing value provided is accurate. This will be automatically filled based on the node location, but the field can be overwritten as needed
      Note

      If using a catchment descriptors file, the Northing value will be imported from here automatically.
   3. On the Event Data tab, enter the mean temperature in the Temperature field and the 100-year snow depth water equivalent in the S100 field. 
   4. Ensure the checkbox Override input snowmelt rates with calculated values is checked to calculate the snowmelt rates at simulation runtime and override the values provided within the Antecedent Melt Rate and Snow Melt Rate (Storm) fields with these calculated values. Alternatively, click the button Populate melt rate fields and the calculated rates will be added within the Antecedent Melt Rate and Snow Melt Rate (Storm) fields (in this case it makes no difference if the Override input snowmelt rates with calculated values checkbox is checked or unchecked)
5. Ensure you Save your network to retain the changes made.

Download the sample dataset used in the video to try it yourself: