Hello WEAP experts,

In my WEAP model, the reservoir is the first node on the river. How should I determine and define Headflow in this situation?

My simulation period starts in October 2002. The reservoir began filling in 2006, and measured reservoir inflow and outflow data are available from 2009 onward. However, observed streamflow data from a hydrometric station downstream of the reservoir are available for the entire simulation period.

How should I define Headflow for the years before 2009, when reservoir inflow data are unavailable?

Thank you.