If the trough is semi circular and has a 24 inch diameter, how can it be 16 inches deep?.
The radius is 12 inches and that is as deep as it can be when filled to the top.
Here is an example with a trough 24 inches in diameter filled to the top. Find the pressure on the end. I will say it is filled with water, which has a weight density of 62.4 lb/ft^3.
Now, integrate. You can change the values accordingly.