Sorry this is another principles of water engineering question that I would like to be answered.

Sorry this is another principles of water engineering question that I would like to be answered. I do realise that this is question belongs to the topic called “Physical Modelling” but I am having difficulty in applying the logic into this question. Please help! It would be much much appreciated if you could provide a nicely written up solution.  Thank you!

Attachment 1
Attachment 2