Water-Resources Investigations Report 03-4060
By Richard A. Fontaine
Prepared in cooperation with the
STATE OF HAWAII OFFICE OF HAWAIIAN AFFAIRS
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Honokohau Stream is one of the few perennial streams in the Lahaina District of West Maui. Current Honokohau water-use practices often lead to conflicts among water users, which are most evident during periods of base flow. To better manage the resource, data are needed that describe the availability and distribution of base flow in lower Honokohau Stream and how base flow is affected by streamflow diversion and return-flow practices.Flow-duration discharges for percentiles ranging from 50 to 95 percent were estimated at 13 locations on lower Honokohau Stream using data from a variety of sources. These sources included (1) available U.S. Geological Survey discharge data, (2) published summaries of Maui Land & Pineapple Company, Inc. diversion and water development-tunnel data, (3) seepage run and low-flow partial-record discharge measurements made for this study, and (4) current (2003) water diversion and return-flow practices. These flow-duration estimates provide a detailed characterization of the distribution and availability of base flow in lower Honokohau Stream.
Estimates of base-flow statistics indicate the significant effect of Honokohau Ditch diversions on flow in the stream. Eighty-six percent of the total flow upstream from the ditch is diverted from the stream. Immediately downstream from the diversion dam there is no flow in the stream 91.2 percent of the time, except for minor leakage through the dam. Flow releases at the Taro Gate, from Honokohau Ditch back into the stream, are inconsistent and were found to be less than the target release of 1.55 cubic feet per second on 9 of the 10 days on which measurements were made. Previous estimates of base-flow availability downstream from the Taro Gate release range from 2.32 to 4.6 cubic feet per second (1.5 to 3.0 million gallons per day). At the two principal sites where water is currently being diverted for agricultural use in the valley (MacDonalds and Chuns Dams), base flows of 2.32 cubic feet per second (1.5 million gallons per day) are available more than 95 percent of the time at MacDonalds Dam and 80 percent of the time at Chuns Dam. Base flows of 4.6 cubic feet per second (3.0 million gallons per day) are available 65 and 56 percent of the time, respectively.
A base-flow water-accounting model was developed to estimate how flow-duration discharges for 13 sites on Honokohau Stream would change in response to a variety of flow release and diversion practices. A sample application of the model indicates that there is a 1 to 1 relation between changes in flow release rates at the Taro Gate and base flow upstream from MacDonalds Dam. At Chuns Dam the relation between Taro Gate releases and base flow varies with flow-duration percentiles. At the 95th and 60th percentiles, differences in base flow at Chuns Dam would equal about 50 and 90 percent of the change at the Taro Gate.
Purpose and Scope
Description of Study Area
Hydrologic Setting and Water Diversions
Data Collection and Analysis
Low-Flow Partial-Record Stations
Historic Discharge Measurements at Miscellaneous Sites
Base-Flow Availability and Distribution
Effect of Honokohau Ditch Diversion
Taro Gate Releases
Extrapolation of Base-Flow Characteristics
Base-Flow Water-Accounting Model
Accuracy of Data and Base-Flow Estimates
Summary and Conclusions
For additional information write to:
U.S. Geological Survey
677 Ala Moana Blvd., Suite 415
Honolulu, HI 96813
Copies of this report can be purchased from:
U.S. Geological Survey
Denver, CO 80225-0286
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