Some Debussy that could work:
Preludes: brouillards, le vent dans la plaine, la puerta del vino, minstrels, tierces alternees, bruyeres, cathedrale engloutie
Images: reflets dans l'eau, movement, cloches a travers les feuilles,
Estampes: jardins sous la pluie
Suite Pour le Piano: prelude
His 'Nocturne', 'Ballade', and 'Masques' are severely underplayed (and barely discussed on the forum) but are INCREDIBLE pieces. If you are thinking of a 'water piece' based on the Barque sur l'Ocean mention, Debussy has tons of water pieces, that might be a bit easier but just as rewarding as the Ravel. I've mentioned a bunch

I'm sure if you are playing the Chopin and Beethoven stuff that you said then you can probably tackle any of Debussy's stuff.
Some Ravel that could work:
Sonatine (great choice for starting Ravel; it was my first piece by him)
Tombeau de Couperin: Prelude, Rigaudon,
Valses Nobles et Sentimentales
'Miroirs' might be a pretty crazy starting Ravel... even the slow ones wouldn't really seem to available as a 'starter' Ravel piece.
...Of the ones I suggested, most of those could be an 'encore' although I don't see the original poster mentioning an encore (unless I skipped through it several times).
Griffes also has really cool music (I was thinking of the Roman Sketches, as also mentioned earlier)