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Soil and Water Conservation District

 
 
 

Projects

Waipio Valley Flood Damage Reduction and Stream Stabilization Preliminary Investigation


Waipi‘o Valley, on the northern coast of the Island of Hawai’i, is an important cultural and economic resource to native Hawaiians, the County of Hawai‘i, and the State of Hawai‘i. Native Hawaiian cultural traditions place Waipi‘o as the wellspring of the political dynasties that consolidated power in the islands, and as the source of the traditional kalo-based society and economy. The Wailoa Stream system, which winds through Waipi‘o Valley and outlets at Waipi‘o Bay, is one of the most managed stream segments in the state. Hawaiians have cultivated kalo for over 1,000 years in Waipi‘o, sustaining populations in the thousands. Management of the dynamic stream processes and equitable allocation of water for irrigation required intensive and sophisticated management to successfully continue kalo production for a millennium. The decline of traditional cultural practices and conversion to modern forms of kalo cultivation came with the transition to single farmers with less communal involvement in farming. The traditional methods to manage the stream and to make and implement water allocation decisions also have suffered. A number of damaging floods in the past 50 years have made farmers keenly aware of the need to manage the river system to protect their fields against severe flood effects and to recover quickly from inevitable flood events. Floods in 1979, 1986, and 1989 caused considerable damage to taro lo‘i by avulsion of the stream and deposition of bed load in the lo‘i.


During much of the 20th century, farmers used heavy equipment, such as bulldozers, in the river
system to remove gravel bars and to repair stream banks following a storm for flood protection of the taro lo‘i. In the 1990s, complaints to the United States (U.S.) Army Corps of Engineers (USACE), under provisions of the Clean Water Act (CWA), halted the ability of farmers to manage the river with heavy equipment. Since the cessation of unpermitted mechanical stream maintenance, the natural stream tendencies for braiding in some reaches and meander in other reaches have increased the flooding and erosion problems for many taro farmers. The Waipi‘o kalo farmers are attempting to organize themselves and develop modern environmental principles to manage the streams in Waipi‘o to support kalo cultivation, while being mindful of traditional practices. They have requested stream analysis, sustainable solutions to flooding and bank erosion, and assistance to complete permit applications and execute the terms of the permits.


The U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS), in partnership with other organizations, such as Friends of the Future and the Mauna Kea Soil and Water Conservation District, has assisted the Waipi‘o farming community to progress toward their stream management goals. In 1999, at the request of the Waipi‘o Taro Farmers Association, Waipi‘o Valley was included in the project area for the NRCS’ Lower Hamakua Ditch (LHD) Watershed project. NRCS offered technical assistance to the Waipi‘o taro farming community for stream management and maintenance activities. In 2006, NRCS, with significant stakeholder input, completed the Waipi‘o Valley Stream Management Plan (SMP), which provides a framework for stream management to increase resilience of the taro lo‘i and farm improvements to flood damage. The SMP identified the major problem areas for Waipi‘o farmers. The problem areas included:

  • The blockage at the river mouth, which increased flooding in the lower part of the valley.
  • Gravel bars and islands in the midstream, approximately one mile upstream of the river mouth, are reducing flood capacity and are causing bank erosion, including bank erosion near the Kawashima farm.
  •  The unstable road crossing that requires constant maintenance.
  • The intake to the major ‘auwai system at the “Kūnaka split” is unstable and is threatening to direct the river into the ‘auwai system.
  • The meandering stream reach near the “Linda Beach Crossing”, which has caused considerable damage due to stream bank breaches that pour floodwater and bed load into neighboring taro lo‘i.


In 2009, NRCS  and Mauna Kea Soil & Water Conservation District (MKSWCD) assisted the Waipi‘o community in acquiring the necessary permits and approvals to clear the sand and rocks from the river mouth to reduce flood damage and lower the stream surface elevation by as much as 5 feet (ft). This effort was conducted in partnership with the State of Hawai’i Civil Defense, which was able to extend the State’s Emergency Declaration for the October 2006 earthquake.


In 2010 Valley residents approached MKSWCD and requested assistance to address heavy flooding that is occurring in the Valley due to damage from the 2006 earthquake. MKSWCD received funding through USDA/NRCS to study the flooding issue and produced the Waipi’o Valley Flood Damage Reduction and Stream Stabilization Preliminary Investigation. The present study focuses on two of the most severe problem areas identified in the SMP. The study will develop conceptual solutions or “alternatives” for the stream problems near Kawashima farm and at the Linda Beach Crossing.

Click here to download the Waipi‘o Valley Flood Damage Reduction and Stream Stabilization Preliminary Investigation Report.