You are asked to conduct a study on a section of a river $($non Tidal$).$ The slope of the river is $50$ cm per km$.$ The section of concern is a $100$ m stretch that is $100$ meters wide and approximately $50$ cm deep $($assume rectangular cross section$).$ This section has water contamination present at a concentration of $1$ mg$/$L$.$ What is the mass flow $($kg$/$min$)$ of contamination in the river?