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Soil and Water Conservation District

 
 
 

Projects

Waiulaula Watershed Management Project (2005-present)


The Waiulaula watershed encompasses about 32,000 acres, from the slopes of Kohala Mountain flowing down into inner Kawaihae Bay, a distance of less than 15 miles and including the town of Waimea.  The primary streams in the watershed are Waikoloa and Keanuiomano, which both originate in State lands at about 4,000-ft. elevation and flow relatively parallel to one another until they join at the 1,440-ft. elevation to form Waiulaula.  The waters of the Waiulaula watershed are not included on the State of Hawaii’s Section 303(d) list of impaired waters at this time because the water quality is generally thought to be good.  However, rapid development within the watershed threatens the water quality of the tributary streams. 

Very little water quality data exist for this watershed.  During heavy rainfall, visual assessments suggest the streams carry high loads of sediments into the near shore coastal waters.  Stream flow is generally perennial in the upper reaches of the streams and intermittent at lower elevations.  Annual rainfall in the watershed varies from about 120 inches in the upper elevations to 7 inches at the coast.  Currently, stream water from the upper reaches of Waikoloa and Kohakohau streams is diverted into reservoirs to provide the drinking water for Waimea town and environs, with a population of over 7,000 residents.

The Waiulaula stream system provides habitat for the five species of native stream fishes, known as o`opu: Lentipes concolor, Sicyopterus stimpsoni, Awaous guamensis, Stenogobius hawaiiensis, and Eleotris sandwicensis.  These fishes have an amphidromous life cycle and are specifically adapted to the rocky, steep, flashy-flow nature of Hawaiian streams.  Their distribution along the streams is believed to be influenced by their climbing ability.

There are mixed land uses within the watershed.  The upper portion of the watershed on the slopes of Kohala Mountain is contained within the State’s forest reserve, which protects native rainforest and bog ecosystems.  Other land uses within the watershed include urban, commercial, light industrial, and residential.  Almost the entire town of Waimea falls within the watershed.  Residential neighborhoods are expanding along Keanuiomano Stream.  Agricultural operations, both field crops and cattle grazing, occur in the upper to middle elevations.  There is much land that is currently undeveloped throughout the watershed, in particular in the dry lower elevations.  At the coast, there are luxury resort developments with hotels, homes, and associated golf courses.

The South Kohala District which encompasses this watershed has experienced tremendous growth over the past 20 years.  Between 1980 and 1990, the population increased by 98.4%, and between 1990 and 2000 it increased by a further 43.7% (County of Hawaii Databook 2001).  Much of this growth has occurred within the watershed.  No studies have been done on the impacts of this cumulative and ongoing development on the riparian and coral reef habitats, and stream and coastal water quality.  In addition, only preliminary biological surveys of the stream system have been conducted.  Expanding residential and urban development threatens riparian habitat by altering vegetation patterns and increasing the potential for flooding; it threatens the water quality of the streams and ocean by (a) increasing the potential for polluted runoff, and (b) changing natural freshwater flows as a result of legal and illegal diversions (reduced flow volume, increased water temperature) and the imperviousness of increasing amounts of hardened surfaces (increased flows impeding inland migration by native o`opu).  Agricultural operations may also contribute to polluted runoff, primarily in the form of excessive loss of sediments, chemicals, and nutrients.

Through the Waiulaula watershed management project, the District seeks to be proactive in the management of this important watershed, focusing on the prevention of pollution rather than waiting until there is a water quality problem downstream that requires an expensive and difficult clean-up.  Stakeholder involvement and community input is essential to the success of the project.  A Waiulaula Watershed Advisory Group advises the District on matters of concern to the community, contributes to the education of the residents of the watershed on water quality issues, helps identify contributing pollution sources in the watershed, recommends specific actions needed to effectively control sources of pollution, and will help develop a watershed management plan.

Monitoring is an important component of the watershed management project.  We expect our monitoring program to provide baseline information about the water quality of the streams and nearshore waters of the watershed, help identify types and sources of polluted runoff, and critical areas contributing runoff, and help develop watershed-specific coefficients for the N-SPECT model to generate pollutant load reduction estimates.  Monitoring will also provide education and community buy-in for the project, by engaging students and community members in volunteer biological and chemical monitoring.

Click here to download the Waiulaula Watershed Management Project Plan.