Hi, I have used a constant value for headflow in my river, however, when I plot streamflow results(m3) there is a monthly variation. There is an abstraction, however, this abstraction is constant as well. What could be causing the variation? Many thanks.

Anabel,

This is likely due to different number of days in each month. If you look at the results in units of flow (CMS), you should see it as constant.

-Doug