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Hanawi Stream near Nahiku, Maui, Hawaii.

DATA CENTER

Recent hydrologic conditions, West Hawaii

Last updated September 19, 2010

Introduction

West Hawaii Island area

The West Hawaii area comprises Hualalai Volcano, the western parts of Mauna Loa and Mauna Kea Volcanoes, and the southern part of Kohala Volcano on the Big Island of Hawaii. West Hawaii has both public and private sources of potable and irrigation water. In the Waimea area, water is obtained primarily from diversions of Waikoloa and Kohakohau Streams. Elsewhere, water is obtained from groundwater wells that tap volcanic-rock aquifers. Recent population growth has placed increased demand on the water resources of the region.

In collaboration with the County of Hawaii Department of Water Supply (HDWS) and the State of Hawaii Commission on Water Resource Management (CWRM), pumpage, water-level, chloride-concentration, deep monitor well, streamflow, and rainfall data for West Hawaii through the second quarter 2010 are displayed here (click on the tabs above to see each section). These web pages are prepared to provide water-resource managers, scientists, and the public with timely information on the status and trends of hydrologic conditions in west Hawaii. Pumpage data are current through May 2010 from some users and earlier from others. Chloride-concentration data are current through the end of June 2010. Rainfall data are current through the end of May 2010. Water-level data are current through August 2010. Kahaluu deep monitor well was last profiled in March 2010. Streamflow information is updated through June 2010.

Summary of recent conditions

The 12-month moving mean of reported pumping in the Waimea, Anaehoomalu, Kiholo, Keauhou, and Kealakekua aquifer systems based on the most recent complete reported values was 12.33, 4.36, 4.09, 12.93, and 2.41 Mgal/d, respectively. These totals are from February 2010 due to incomplete reporting of pumpage from some users. Recent chloride concentrations were as high as 360 mg/l at Kahaluu Shaft. The 12-month moving means of rainfall are below the long-term means at all of the available rain gages used for these quarterly updates. Streamflow was below the median during April-June 2010 at the gaging station on Waikoloa Stream.

Background information about West Hawaii

The West Hawaii area is characterized by a generally smooth, sloping land surface of consistent grade, marked by numerous cinder cones along the volcanic rift zones. Water erosion of the surface is nearly non-existent. Within West Hawaii, the boundaries of five aquifer systems have been defined by the Commission on Water Resource Management (1990) and Mink and Lau (1990). These are the Waimea, Anaehoomalu, Kiholo, Keauhou, and Kealakekua aquifer systems.

In West Hawaii, fresh groundwater tends to move from the mountainous interior of the island toward the coast and to the ocean. Groundwater is withdrawn from areas: (1) near the coast, where a thin, shallow lens of freshwater or brackish water floats on denser saltwater within highly permeable lavas and (2) inland farther than about 2 to 5 miles, where fresh groundwater is partially impounded by a feature with lower aquifer permeability and exists at altitudes greater than about 25 ft above mean sea level.

No perennial streams exist in West Hawaii, except on the southern slopes of Kohala Volcano. However, these streams rapidly lose their water downslope of Waimea and flow to the ocean only during heavy rain events.

Additional information about West Hawaii can be found in:

Geohydrology and numerical simulation of the groundwater flow system of Kona, island of Hawaii: U.S. Geological Survey Water Resources Investigations Report 99–4073, 70 p. by Oki, D.S., 1999.

"Preliminary report on the water resources of the Kona Area, Hawaii", Department of Land and Natural Resources, Division of Water and Land Development, Circular C46, 22 p. by D.A. Davis and George Yamanaga, 1968.

"Preliminary report on the water resources of Kohala Mountain and Mauna Kea, Hawaii", Department of Land and Natural Resources, Division of Water and Land Development, Circular C14, 44 p. by D.A. Davis and George Yamanaga, 1963.

References:

Commission on Water Resource Management, 1990, Water Resources Protection Plan: prepared by George A.L. Yuen and Associates, Inc., for Department of Land and Natural Resources, State of Hawaii, 262 p.

Mink, J.F., and Lau, L.S., 1990, Aquifer identification and classification for Maui: groundwater protection strategy for Hawaii: Honolulu, Hawaii, University of Hawaii Water Resources Research Center, Technical Report no. 185, 47 p.

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