I used something similar but it was deeper (file cabinet plastic box from Big Box Store) and cut two 1" vertical slits on either side and 12" long at the top, took a heat gun and warmed the narrow piece, then folded it perpendicular to form the weir. Make sure you have something solid and straight beneath when you bend or upon cooling, the weir blade will not uniformly distribute water over it and it'll pour more than sheet. My box had a top which was handy for hiding the weir box at the top of my waterfall with flat slate stone on it. I used 1-1/2" bulkheads for the inlet and attached to a feed from one of my pumps (I have 2 of these box weirs; one for each main waterfall). So, it can be done on the cheap.Well the savings go on then. Been saving my fun bux to order it. Going to be a bit longer.
If I find some plastic paper holder drawer with a flat front opening, can I use that as the waterfall box? Lol
Figure it can be like 4” deep to save room but maybe not.
View attachment 144764