We hiked here in Feb 2012 and wanted to share these tips:
1)The “dirt road” is almost non existant, look for a wide parking spot for about 3 cars just past the last house on the left as you come down Kapahi Road. You have just passed the “trailhead”. Its about an 18″ gap in the brush and hard to see.
2) Locals you meet on the trail do not want tourists there, so try to keep to yourself and not ask them questions. You’ll get along better as you share the swimming holes.
3) Some guide books mentioned crossing the stream and hikiing to the bottom of the lower (taller) falls on the north bank of Kapa’a stream. We did not try this as the fence line is right on the north bank and overgrown. There are signs on the north side right at the falls warning you not to go to the bottom, but due to high water we decided against the stream crossing.
4) The Hike is worth it….you can see both falls in about 1 hour RT, but we packed a lunch and swam so we did it in about 3 hours RT.