ท่า port; harbor; wharf; pier; landing

ถ้า if

These both sound like Thaa with the falling tone to me. How can you tell them apart?

You are right. They are true homophones (sound exactly the same even to Thais). You tell them apart by the context only, which is easy since they are different word classes.

There is no risk of confusion if you know Thai sentence structure.

Tell them apart from context or spelling. One may a bit longer than the other.

One may be a bit longer than the other.

I think I know what you mean, but I also believe that is an effect due to the context.

The one word that will typically sound a little longer than the other is ถ้า as in 'if', but this is probably due to the position of this word at the beginning of a sentence. When you want to emphasize the uncertainty of a statement, you will overdo the tone and perhaps slightly prolong the vowel sound.

When it comes to "jetty, wharf, pier", it is most often used as a prefix in combinations:

ท่าเรือ (insert name), and in these occasions will not be emphasized, as it is not the most important information in the sentence (the more important information being the name of the pier).

Thanks, this all makes sense.