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Biological, morphological, and chemical characteristics of Wailuku River, Hawaii

January 1, 1994

Biological, morphological, and chemical data on Wailuku River were collected to assess its water quality characteristics. Biological measurements included evaluation of benthic invertebrates, periphyton, phytoplankton and coliform bacteria. Morphological measurements consisted of channel surveys and particle size determination of bed materials. Chemical quality measurements, made monthly at two sampling stations, included water temperature, pH, specific conductance, dissolved solids concentration, turbidity, dissolved oxygen, nitrogen, phosphorus , and minor elements. Biological and chemical data indicated relatively clean water compared to similar streams in conterminous United States. The number and types of benthic organisms are low in Wailuku River. This is due mainly to channel gradient and flow velocities rather than to chemical toxicity. Periphyton data also indicate unpolluted water of low to moderate primary productivity. Diatoms are the dominant organisms observed in the periphyton samples. Coliform bacteria densities are typical of mountain streams in Hawaii that are essentially unaffected by human activities. The streambed is formed of lava flows from Mauna Loa volcano, and the stream channel is characterized by a series of plunge pools and waterfalls. The longitudinal slope ranges from 5% at midreaches to 8% at the headwater regions. There is no broad flood plain at the mouth of the stream. The stream channel is generally a narrow steep-sided trapezoid with an irregular base. Streambanks are composed of fine to very coarse-grained material. Channel depth increases from 6 ft at the headwaters to 40 ft at Hilo. The width also increases from 60 ft at the highest study site to 220 ft at the Hilo site near the mouth of the river. (Author 's abstract)