story by Dennis Hollier photo by Ann Cecil   “We’ve got clams,” says Knud Lingard, bending down to rake up a passel of corbicula—Pacific clams—from the mudflats of Nu‘uanu Reservoir. The clams are just one of the surprises here, high in Nu‘uanu Valley on O‘ahu. The lake, which once supplied drinking water to Honolulu, is also…