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U.S. Geological Survey Scientific Investigations Report 2010-5011

Prepared in Cooperation with the County of Maui Office of Economic Development, County of Maui Department of Water Supply, State of Hawai‘i Commission on Water Resource Management, State of Hawai‘i Office of Hawaiian Affairs

Effects of Surface-Water Diversion on Streamflow, Recharge, Physical Habitat, and Temperature, Nā Wai ‘Ehā, Maui, Hawai‘i

By Delwyn S. Oki, Reuben H. Wolff, and Jeff A. Perreault

ABSTRACT

Thumbnail of and link to report PDF (100 MB)

The perennial flow provided by Waihe‘e River, Waiehu Stream, ‘Īao Stream, and Waikapū Stream, collectively known as Nā Wai ‘Ehā (“The Four Streams”), made it possible for widespread agricultural activities to flourish in the eastern part of West Maui, Hawai‘i. The streams of the Nā Wai ‘Ehā area flow in their upper reaches even during extended dry-weather conditions because of persistent groundwater discharge to the streams. Overall, the lower reaches of these streams lose water, which may contribute to groundwater recharge.

During climate years 1984–2007 (when complete streamflow records were available for Waihe‘e River and ‘Īao Stream), Waihe‘e River had the greatest median flow of the four streams upstream of the uppermost diversion on each stream. The median flows, in million gallons per day, during climate years 1984–2007 were: 34 for Waihe‘e River near an altitude of 605 feet; 25 for ‘Īao Stream near an altitude of 780 feet; and estimated to be 4.3 for Waikapū Stream near an altitude of 1,160 feet; 3.2 for North Waiehu Stream near an altitude of 880 feet; and 3.2 for South Waiehu Stream near an altitude of 870 feet. Existing stream diversions in the Nā Wai ‘Ehā area have a combined capacity exceeding at least 75 million gallons per day and are capable of diverting all or nearly all of the dry-weather flows of these streams, leaving some downstream reaches dry. Hourly photographs collected during 2006–2008 indicate that some stream reaches downstream of diversions are dry more than 50 percent of the time. Many of these reaches would be perennial or nearly perennial in the absence of diversions.

A lack of sufficient streamflow downstream of existing diversions has led to recent conflicts between those currently diverting or using the water and those desiring sufficient instream flows for protection of traditional and customary Hawaiian rights (including the cultivation of taro), maintenance of habitat for native stream fauna, recreation, aesthetics, and groundwater recharge from loss of water through the streambed. In response to a need for additional information, the U.S. Geological Survey (USGS) undertook the present investigation to characterize the effects of existing surface-water diversions on (1) streamflow, (2) potential groundwater recharge from the streams to the underlying groundwater body, (3) physical habitat for native stream fauna (fish, shrimp, and snails), and (4) instream temperatures.

Information collected for this study includes discharge measurements under different streamflow conditions to characterize streamflow and seepage losses, hourly photographs of stream conditions from mounted cameras, snorkel surveys of stream fauna, measurements of microhabitat (depth, velocity, and substrate) under different flow conditions, and measurements of water temperatures. Families of curves were developed to show the relations between surface-water diversion intake capacity (the maximum rate that an intake can divert) and (1) selected duration discharges for sites near the coast; (2) selected duration discharges for the diversions; (3) groundwater-recharge reduction; and (4) physical-habitat reduction for native stream fauna. These curves may be used by water managers to evaluate the effects of different diversion intake capacities on streamflow, water available for offstream use, groundwater recharge, and habitat for native stream fauna.

  • Report PDF (100 MB)
  • Table 12 folder. Table 12 is provided here as a large data spreadsheet in several file formats: U.S. Geological Survey miscellaneous discharge measurements during 2004-2009, sorted by Nā Wai ‘Ehā stream and from upstream to downstream, Maui, Hawai‘i. (872 kB total)
  • This report is also available in print from:

    USGS Information Services, Box 25286,
    Federal Center, Denver, CO 80225
    telephone: 888 ASK-USGS; e-mail: infoservices@usgs.gov

For additional information contact:
Center Director, Pacific Islands Water Science Center
U.S. Geological Survey
677 Ala Moana Blvd., Suite 415
Honolulu, HI 96813
http://hi.water.usgs.gov/

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Suggested citation:

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.



Contents

Executive Summary

Abstract

Introduction

Setting

Stream Fauna

Natural, Undiverted Low-Flow Characteristics

Recent Diverted Low-Flow Characteristics in Streams

Effects of Surface-Water Diversions on Streamflow

Ditch-Flow Relations

Effects of Surface-Water Diversions on Recharge

Effects of Surface-Water Diversions on Physical Habitat

Effects of Surface-Water Diversions on Water Temperature

Summary

References Cited

24 tables

2 appendixes


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