Impact of Stream Hardening on Water Quality and Metabolic Characteristics of Waimanalo and Kane'ohe Streams, O'ahu, Hawaiian Islands

Abstract

Kane'ohe and Waimanalo Streams on the windward side of the island of O'ahu in the Hawaiian Islands have been hardened to prevent flooding. The hardening process has involved elimination of the natural riparian habitat and replacement of the natural stream channel with a concrete-lined conduit having vertical walls and a broad, flat bottom. The shallow depth of the water column and absence of shade have resulted in temperatures that average as much as 4-5C above ambient and rise as high as 32C during daylight hours. Unlike most low-order streams, the hardened sections of both streams are autotrophic, as evidenced by elevated pH values and O2 concentrations as high as 150 percent of saturation. Several allochthonous inputs, one from a storm sewer and the other from a natural spring, introduced water with anomalously low O2 concentrations rs is an unenlightened way to address flooding problems.