Can I substitute a Standard Acoustic Guitar for an Acoustic Bass/Bass with Amp?

I may be playing an acoustic set with my band at a local concert/festival, I play Bass, and it being an acoustic set, I don't think I will have access to an amp, and I do not have access to an acoustic Bass. Would it be practical to play the root bass notes, as power chords on a standard Acoustic guitar? I understand that the question has a lot of variables, but does anyone have any experience of this type of situation?

You can down-tune the guitar only so much, before it just starts to sound like a bag of rusty springs. Meaning, it's never really going to fill the role of a Bass. Like choosing a hotdog over a juicy slow-grilled porterhouse. You're going to get extra filler, not rich depth. My recommendation is to rent an instrument, or failing that, bring the electric Bass and your amp(s). Just don't drown out the others. Many music stores will be happy to rent you their gear, and for usually at reasonable prices. I can rent almost any guitar in my local shop for $20/day... Not bad considering the huge sticker price on some of them. Anyway, yes... you can play a bassline on a regular guitar. If you know the notes and how to play from notes, it's dead-easy to tranpose and translate. If you don't speak sheet-music, then I'm afraid it's best to have someone translate it for you. Just keep in mind what I said... that guitar is not going to ever go as low as your bass.

Try using a string bass. The type of bass used in an orchestra. Some Jazz Bands/Choirs use string basses instead of electric basses since they have the exact same tuning (EADG).

well, I would suggest, first see if you CAN get an amp, and just play electric Bass, just quietly. this is actually how quite a few "acoustic" bands do it.

if not, just imagine the bottom 4 strings of the guitar as the bass and play them as such; don't do power chords. it won't sound as low, but it will probably suffice.