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DATA CENTER

Streamflow and Stream-Macrofauna Characteristics, Central Maui, Hawaii

Project Chief: Delwyn Oki
Project Period: May 2006 through December 2009
Cooperator: Maui County Department of Water Supply, Maui County Office of Economic Development, Hawaii Commission on Water Resource Management, and Office of Hawaiian Affairs
Location:Waikapu, Iao, and Waiehu Streams and Waihee River in the central part of Maui, collectively known as Na Wai Eha, "the four great waters of Maui".

Problem

For over a century, water has been diverted from streams in the central part of Maui, Hawaii, to meet irrigation needs for sugarcane and pineapple cultivation. In recent years, it has become increasingly apparent that competition exists for the limited surface-water resources in central Maui. However, quantitative instream flow standards for central Maui streams have not been established as of March 2006. Additional scientific information, including ecological information and streamflow data, is needed to establish technically defensible instream flow standards that will support equitable, reasonable, and beneficial allocation of the water resources.

Objectives

The objectives of this 4 1/2-year study on Waikapu, Iao, and Waiehu Streams and Waihee River are to (1) assess the effects of existing surface-water diversions on streamflow characteristics, (2) characterize the effects of diversions on potential recharge from the streams to the underlying Iao and Waihee aquifers, (3) characterize the effects of diversions on instream temperature variations, (4) survey the native stream fauna (fish, shrimp, and snails) present in the streams under diverted conditions, and (5) estimate the effects that streamflow restoration (full or partial) will have on habitat availability for native stream fauna. A critical component of this study is the need to partially restore flow to the streams from diversions for periods of up to a few weeks to create streams that flow along their entire length. These controlled releases will be designed to allow measurements of streamflow, infiltration, and potential aquatic habitat in sections of the stream that commonly are dry under diverted conditions. Cooperation between the users of the diverted water and the U.S. Geological Survey is necessary to insure that these controlled releases provide the needed data to help the study be successful.

Relevance and Benefits

The results from this study are necessary for the proper management of the surface waters in the State of Hawaii and, thus, the study is consistent with the mission of the USGS Strategic Plan to provide scientific information to manage water resources and to protect our quality of life. This study will provide information needed for water-use permitting and land-use planning. In addition, the information generated by this study will be useful for establishing technically based instream flow standards in central Maui by addressing the hydrologic and aquatic-habitat aspects of the standards.

Approach

Available discharge data from gaging stations at unregulated stream sites, existing seepage-run data, and additional discharge measurements made for this study in central Maui will be used to estimate pre-diversion streamflow characteristics at regulated sites and the effects of the diversions on streamflow characteristics. Relations among streamflow, habitat, and native stream macrofauna will be used to estimate the effects that streamflow restoration will have on habitat availability for native stream macrofauna.

Progress

Since May 2006, we have compiled existing hydrologic data, performed baseline reconnaissance surveys of the streams, purchased and installed equipment needed to monitor stream temperature, frequency of dry days, and stream stage in selected reaches of the diverted streams, selected stream reaches for studying physical habitat, and began making streamflow and habitat measurements at selected sites upstream and downstream of diversions. In August 2006, a workshop was held on Maui to refine the scope of work related to the biological aspects of the study. The workshop was attended by experts in aquatic biology from Federal, State, and County agencies, Universities, and private consulting firms.

Fiscal Year 2008

A stakeholders meeting will be held to provide an update on the study and describe the need for controlled releases. We plan to collect additional data on streamflow, physical habitat, and frequency of dry days. Discharge measurements will be made at selected sites to characterize current flow conditions. If water is released back to the streams or if flow conditions permit, discharge measurements will be made to estimate streamflow losses along selected stream reaches. Presence/absence surveys of stream fauna in diverted reaches of the study-area streams will be made. Water-temperature data collected for the study will be checked and entered into a national database.

Publication

Oki, D.S., Wolff, R.H., and Perreault, J.A., 2010, Effects of surface-water diversion on streamflow, recharge, physical habitat, and temperature, Nā Wai ‘Ehā, Maui, Hawai‘i: U.S. Geological Survey Scientific Investigations Report 2010-5011, 154 p.

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