You haven't told us how long the trough is, or how deep the water is in it.
If it's full to the rim ... 2-ft deep ... then there's 44.88 gallons for every foot of the trough's length.
20 gallons
7615 Gallons
If the container is 3ft x 3ft x 9ft, the answer is 81 cubic ft. There are approximately 607.5 gallons of water.
12,345 gallons
704.5 gallons (approx).
Approx 4892 Imperial gallons.
Not enough information. If it is a rectangular shape, you need to multiply length x width x height. The answer will be in cubic feet, which you would then have to convert to gallons (which is a great example of the benefits of the SI).
There are 907.9202769 feet2 of water, but you will have to convert that into gallons.
I believe trough is high tide but I'm not 100% sure A trough is the low part of a wave, the opposite of crest.
20 gallons
A cylinder 155mm diameter and 245mm high can hold up to 1.22 gallons of water.
50,000 gallons
1056 GALLONS
7615 Gallons
It isn't low tide, but part of the wave. Each wave in a tsunami has two parts: a crest of high water and a trough of low water. In many cases the trough comes first, resulting in the water receding.
If the container is 3ft x 3ft x 9ft, the answer is 81 cubic ft. There are approximately 607.5 gallons of water.
74.42 gallons.