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Streamflow, Suspended-Sediment, and Erosion Monitoring, Kahoolawe

Project Chief: Scot K. Izuka
Project Period: October 2005 through September 2010
Cooperator: Kahoolawe Island Reserve Commission
Location:Island of Kahoolawe

Problem

Aerial view of north coast of Kahoolawe showing bare soil in uplands and sediment plumes emanating from the mouths of streams

Since the 19th century the island of Kahoolawe has been the site of various land uses, including grazing by domesticated and feral animals and bombing practice by the U.S. military. These land uses ceased in the late 20th century, and title to the island was transferred to the State of Hawaii in 1994, but large areas of the island have been denuded of vegetation and show evidence of rapid erosion by wind and water. The Kahoolawe Island Reserve Commission began restoration efforts on parts of the island in 2001. The restoration includes planting of native plants to reestablish vegetation and control erosion. Information on soil erosion and sediment transport are needed to measure effectiveness of these restoration efforts.

Objectives

The objective of this study is to collect data needed to evaluate the effectiveness of revegetation efforts on reducing erosion in selected watersheds on Kahoolawe.

Approach

The objectives of this study will be met by monitoring streamflow and suspended-sediment loads in Hakioawa and Kaulana Gulches and soil erosion at approximately 77 transects in both treated areas (where planting of native vegetation is being used as an erosion-control measure), and untreated areas. Results from this study will be published following the completion of three years of data collection in September 2009.

Progress

Streamflow and suspended-sediment monitoring stations were installed on Kaulana and Hakioawa Gulches in August and September 2006, respectively. Real-time streamflow data for the Kaulana and Hakioawa stations are displayed on the internet. In addition, daily-mean streamflow and suspended-sediment concentration and load for Kaulana (PDF), site no. 16682000, and Hakioawa(PDF) , site no. 16681000, are published in Annual Water Data Reports on the Internet.

Soil-erosion transects were installed at 75 sites between August 2006 and January 2007. The erosion transects are divided among treated and non-treated areas, and areas that are flat or have small channels (rill) of erosion. These erosion transects were measured in January and September 2007. Two more transects were installed in March 2008.  All transects are measured on a semi-annual basis.  Measurements will continue until January 2010.

Preliminary results (4.4 Mb PDF) from this study were presented at the Hawaii Water Quality Conference in March 2008.

Publication

Izuka, S.K., and Abbott, L.L., 2010, Streamflow, suspended-sediment, and soil-erosion data from Kaulana and Hakioawa watersheds, Kaho'olawe, Hawai'i, 2006 to 2010: U.S. Geological Survey Open-File Report 2010-1182, 40 p.