You need a four-wheel-drive vehicle—or at least a vehicle with high clearance, carefully driven—to reach the somewhat obscure trailhead. It’s about a mile and a half down the Mohini Camp-10 Road, which you grab off Highway 550 in the vicinity of the Kokee Museum via a short jog on Waineke Road. The Mohini Camp-10 Road is a narrow, fairly rough track, so take it slow and be mindful of other drivers potentially coming from the other direction.
There’s a parking area at that roughly 1.5-mile mark; the unmarked trailhead is a few hundred feet back up the road from this, on the left. This Poomau Canyon Ditch Trail was originally blazed to service the Kokee Irrigation Ditch.
The path climbs, often brushy but otherwise easy enough to follow. It’s not particularly demanding, though there’s a stream crossing (nothing crazy) and you should be wary of thorns.
You’ll grab enticing views out over the canyon, but the payoff is the end of the trail. At this point, the path ventures out onto a marvelous knife ridge jutting, peninsula-like, out into the canyon gulf. On both sides, the land drops to stunning depths, here where multiple streams in their gorges run together into the upper Poomau Canyon.
Several waterfalls are visible, not least the spectacular Moeloa Falls with its several pour-offs and pools. The canyon walls are incredible, what with their many narrow lava flows stacked layer-cake-style.
The Poomau Canyon is one of the major arms of the Waimea Canyon system. Like the Waimea’s biggest tributary, the Koaie, part of the Poomau’s headwater drainage falls from the great Alakai Swamp. This boggy high-elevation wetland jungle provides the red-brown waters behind the Waimea River’s name. (Wai means “freshwater,” while mea means “reddish-brown.”)
And those waters soaking the Alakai bogs and partly draining out Waimea Canyon fall as rain on the shoulders of Mount Waialeale, by some measures the wettest place on the planet. On this skinny ridge crest at the end of the Poomau Canyon Ditch Trail, you’re close to where these two great Kauai landmarks—the Alakai Swamp and Waimea Canyon—connect.
The view’s great from the “End of Path” sign, but if you’re not too freaked out by heights you can venture a bit farther out on that knife-edge neck for even more whopping panoramas.
You’re unlikely to be sharing the Poomau Canyon Ditch Trail (or its big-finish vista) with many other hikers. Indeed, you may well have it completely to yourself. Compared with the busier overlooks of Waimea Canyon along the highway, it’s magically quiet and removed-feeling: definitely worth the effort if your vehicle can handle the access road!
If you can, bring a pair of binoculars with you on the Poomau Canyon Ditch Trail. It’s not uncommon to see feral goats clinging to steep slopes from the end-of-trail vantage.