This ahupua`a, although practically continuous with Waihe`e, is sheltered for most of its shore length behind low coastal hills, and its area contours are quite broken by the winding Kahalu`u Stream and its tributaries, Waiola (Living-water), Ahulumanu (Discolored-and-broken), and Kalohaka (Hollow-taro). For this reason, despite the breadth of the stream valley, the lo`i sections of Kahalu`u are tucked away in pockets of land watered from the several streams; there are few large continuous areas, but the total area under cultivation in ancient times must have been very considerable...
The seaward flats of the three contiguous ahupua`a of Ka`alaea, Waihe`e, and Kahalu`u together make up one of the largest single areas of wet-taro land on the Ko`olau coast. It is a region of ample rainfall. One of Hi`iaka's chants on traversing this coast of Oahu (Ino Ko`olau, e, ino Ko`olau, "The Bad Ko`olau Weather") refers to "the whisking rain in Kahalu`u (N.B. Emerson, 1915, p. 91).