What tense could I use when I write about a journey? Suppose if I write about a train journey and describe the countryside, would using a present tense create a deeper impact to the reader? I could make it appear as if I had been writing during the travel though the reality is I could have written it later. I would want the reader to feel the depiction and I was wondering if tense matters here.
I think you mix things up here. Present tense does not build immediacy, immediacy should be there if you use present tense. At least I expect it when present tense is used.
As Kate mentions the sense of immediacy is independent of the used tense. But if you use present tense, your writing should better have this sense. Just using present tense will not add it.
Though the tense does matter in combination with your viewpoint. You have to be consistent to avoid puzzling the reader.
As an example let me use a thriller playing in a train (for your journey ;). There is a murder committed in the compartment next to the person watching the scenery.
Using third person view (omniscient or not is only a matter of detail here) you can use present tense and write:
Sybil watches the mountains of Montana. In the compartment next to her a man slaughters a woman.
No problem with that (besides missing suspension).
First person, present tense:
I watch the mountain ranges of Montana while the guy in the next compartment is slashing his girl-friend.
Why do you know that? How could the first person narrator know what happens in the other compartment, or that it is his girl-friend and not his stepmother (or maybe both with one kill)?
For an opening scene of a book you can use this, if you answer these questions during the book. Otherwise it is an inconsistency in your perspective.
But now we try that with past tense:
He ripped apart her chest, while I was watching the snow on the shiny peaks of Montana. When I found the blood beneath the door one hour later, he had already left the train.
Using past tense this trick is possible, because it's plausible that the narrator knows more afterwards than he did when the crime happened. If it is good style or not, I leave open for discussion (well, I like it).
When you stay consistent, it does not matter if you use present tense or not. A deeper impact is not created by tense.
I know lots of people say that present tense creates immediacy, but as a reader I've never noticed any difference.
But if you want to give a better impression that the story is being written or told as it happens, present tense will help with that. That's not quite the same thing as the reader's sense immediacy. It's related, but not quite the same.
A few caveats for present tense:
If you want the piece to read as if it were written during the journey, you'll want to make sure you would have had a reason to write it during the journey. You may not need to express that reason directly in the text, but if you're writing in present tense, the reason to start writing can't come from events later in the text.
Also, you won't be able to foreshadow overtly. If you want to foreshadow, you'll have to do it subtly, perhaps via dramatic irony (describing things and events whose significance the reader understands, but the writer does not).
Choose the tense that suits the story you want to tell.
Like you say, if you want to create the impression that the description of the journey is from a diary, then present tense could work. However, even here you could write as past tense because perhaps you wrote in your diary at the end of the day looking back over the day's activities.
Or perhaps the story you're trying to tell is from the point of view of a changed, wiser person looking back at lessons learned from a particular journey, and you want to contrast between that younger self and the later, older one.
None of these options is any better or worse than the other as long as you tell the story well, and you're consistent. The possibilities are endless, but they all depend on the story you're trying to tell, and that's what you should use to dictate the tense.
Also, trust your instincts: if you feel more comfortable with first person, present tense as a writer, then do that. If you prefer past tense, third-person, do that. The only time I would suggest present tense would perhaps be with action novels, but even there, a story well told is a story well told.
In which tense do you feel most comfortable writing?
I think that a good writer can give a sense of immediacy and impact regardless of the tense chosen. This seems like one of those questions that we use to keep us from getting down to the hard work of actually writing - like 'what font should I use' or 'what's the best word processor'. It doesn't really matter. Chose one, and get going!