Prepared in cooperation with the

STATE OF HAWAII OFFICE OF HAWAIIAN AFFAIRS

Availability and Distribution of Base Flow in 

Lower Honokohau Stream, Island of Maui

Honokohau 

Bay

PACIFIC OCEAN

200

400

600

800

400

600

800

400

1800

1800

2400

1600

1800

1400

1000

Honokohau Stream

156°37' 156°36'

21°

20°59'

21°01'

Chun's

Dam

MacDonald's

Dam

MacDonald's Dam

Taro Gate

Release

Taro Gate Release

Honokohau Ditch

diversion dam

Honokohau Ditch diversion dam

MacDonald's

Dam

Chun's

Dam

Taro Gate

Release

Honokohau Ditch

Diversion Dam

U.S. Department of the Interior

U.S. Geological Survey

Water-Resources Investigations Report 03-4060
Availability and Distribution of Base Flow in Lower 

Honokohau Stream, Island of Maui, Hawaii

By Richard A. Fontaine

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 03-4060

Prepared in cooperation with the

STATE OF HAWAII OFFICE OF HAWAIIAN AFFAIRS

Honolulu, Hawaii

2003
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes 

only and does not constitute endorsement by the U.S. Geological Survey.

For additional information write to: Copies of this report can be purchased

from:

District Chief U.S. Geological Survey

U.S. Geological Survey Information Services

677 Ala Moana Blvd., Suite 415 Box 25286

Honolulu, HI 96813 Denver, CO 80225-0286

http://hi.water.usgs.gov

U. S. DEPARTMENT OF THE INTERIO

R

MARCH 3, 1849
Contents iii

CONTENTS

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Description of Study Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Physical Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Geologic Setting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Hydrologic Setting and Water Diversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Data Collection and Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Streamflow-Gaging Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Low-Flow Partial-Record Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Historic Discharge Measurements at Miscellaneous Sites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Base-Flow Availability and Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Seepage Runs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Effect of Honokohau Ditch Diversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Taro Gate Releases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Extrapolation of Base-Flow Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Base-Flow Water-Accounting Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Accuracy of Data and Base-Flow Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
iv Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui 

FIGURES

1–4. Maps showing: 

1. The Hawaiian islands, island of Maui, and the Honokohau Stream study area, Hawaii . . . . . . . . . . . . . . . 3

2. Mean annual rainfall in west Maui, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3. Geology of the West Maui Volcano, Hawaii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4. Streamflow measurement sites in, and geology of, Honokohau Valley, island of Maui . . . . . . . . . . . . . . . 9

5–13. Graphs showing:

5. Annual mean and average discharge at streamflow-gaging station 16620000 on Honokohau Stream,

Maui, water years 1914–2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6. Mean monthly and maximum and minimum monthly mean discharges at streamflow-gaging station

16220000 on Honokohau Stream, Maui, water years 1914–2000. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

7. Flow-duration curves for total flow, base flow, and direct runoff at streamflow-gaging station 16620000 

on Honokohau Stream, Maui, for 82 water years with complete record during 1913–2000 . . . . . . . . . 13

8. Relative contributions of direct runoff and base flow to annual mean streamflow at gaging station

16620000 on Honokohau Stream, Maui . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

9. Discharge on Honokohau Stream, Maui, during three seepage runs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

10. Stream temperature on Honokohau Stream, Maui, during August 13, 1997 seepage run . . . . . . . . . . . . . . 23

11. Specific conductance on Honokohau Stream, Maui, during the August 13, 1997 seepage run . . . . . . . . . . 23

12. Flow-duration curves for estimates of daily discharges upstream and downstream of the Honokohau 

Ditch diversion at altitude 825 feet, water years 1913–2000, Honokohau Stream, Maui . . . . . . . . . . . . 27

13. Scatterplot of computed Taro Gate flow releases from Honokohau Ditch into Honokohau Stream at 

altitude 405 feet, Maui. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

14. Discharge on Honokohau Stream, Maui, during August 13, 1997 seepage run and for selected flowduration percentiles under current practices of 1.05 ft3

/s Taro Gate release and 0.46 ft3/s hydropower

plant release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

15. Map showing discharge on Honokohau Stream, Maui, for the 95th percentile flow duration 

under current practices of 1.05 ft3/s Taro Gate release and 0.46 ft3/s hydropower plant release . . . . . . . . . 32
Contents v

TABLES 

1. Selected flow-duration discharges for total flow, base flow, and direct runoff at streamflow-gaging station 

16620000 on Honokohau Stream, Maui, water years 1913–2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2. Long-term and partial-record data-collection stations and miscellaneous sites on Honokohau Stream, Maui . . . . . 15

3. Discharge measurements at low-flow partial-record stations and concurrent daily mean discharges at gaging 

station 16620000, Honokohau Stream, Maui . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4. Computed statistics for concurrent daily mean discharges at index station 16620000 and discharge 

measurements at low-flow partial-record stations, Honokohau Stream, Maui. . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5. Estimated flow-duration discharges for low-flow partial-record stations, Honokohau Stream, Maui . . . . . . . . . . . . 17

6. Historic discharge measurements made by the U.S. Geological Survey at miscellaneous sites on Honokohau 

Stream, Maui. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

7. Discharge during seepage runs on Honokohau Stream, Maui . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

8. Stream temperature during seepage runs on Honokohau Stream, Maui. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

9. Specific conductance during seepage runs on Honokohau Stream, Maui . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

10. Selected flow-duration discharges at gaging station 16620000 and estimates of development tunnel discharge

and discharges upstream and downstream from the Honokohau Ditch diversion at altitude 825 feet, water

years 1913–2000, Honokohau Stream, Maui . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

11. Average, median, and minimum daily discharges for selected locations in the vicinity of the Honokohau Ditch 

diversion at altitude 825 feet, water years 1913–2000, Honokohau Stream, Maui . . . . . . . . . . . . . . . . . . . . . . . . 26

12. Computed Taro Gate flow releases from Honokohau Ditch into Honokohau Stream at altitude 405 feet, Maui. . . . 29

13. Computed flow-duration discharges for selected locations on lower Honokohau Stream, Maui, under 

current diversion and return-flow practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

14. Reductions in base flow for selected flow-duration discharges in the losing reach of Honokohau Stream, 

Maui, between MacDonald’s Dam and the ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

15. Variation in computed flow-duration discharges upstream from Chun’s Dam on Honokohau Stream, Maui, 

associated with variable flow-release rates at the Taro Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
vi Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui 

CONVERSION FACTORS AND DATUMS

Datums

Vertical coordinate information is referenced relative to mean sea level.

Horizontal coordinate information is referenced to the Northern American Datum of 1983 (NAD 83).

Multiply By To obtain

inch (in) 2.54 centimeter

foot (ft) 0.3048 meter

foot per mile (ft/mi) 0.1895 meter per kilometer

mile (mi) 1.609 kilometer

acres 4,047 square meter

square mile (mi2) 2.590 square kilometer

square mile (mi2) 640 acre

cubic foot per second (ft3/s) 0.02832 cubic meter per second

million gallons per day (Mgal/d) 0.04381 cubic meter per second
Introduction 1

Abstract

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 lowflow partial-record discharge measurements made 

for this study, and (4) current (2003) water diversion and return-flow practices. These flowduration 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 (MacDonald’s and Chun’s 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 MacDonald’s Dam and 80 percent of the 

time at Chun’s 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 MacDonald’s 

Dam. At Chun’s Dam the relation between Taro 

Gate releases and base flow varies with flowduration percentiles. At the 95th and 60th percentiles, differences in base flow at Chun’s Dam 

would equal about 50 and 90 percent of the change 

at the Taro Gate. 

INTRODUCTION

Honokohau Stream is one of only three streams in 

the Lahaina District (fig. 1) that flows perennially to the 

sea (Hawaii Commission on Water Resource Management, 1990, p. 23). The perennial nature of Honokohau 

streamflow makes it a valuable resource for meeting the 

Availability and Distribution of Base Flow in Lower 

Honokohau Stream, Island of Maui, Hawaii

By Richard A. Fontaine
2 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

often conflicting needs of in-stream, near-stream, and 

off-stream water users in the area. These conflicts are 

most evident during periods of minimal streamflow, or 

base flow, when water in the stream is derived primarily 

from ground-water sources. 

Starting in June 1904, with the completion of the 

Honokohau Ditch (also known as the Honolua Ditch), 

most of the flow in Honokohau Stream at an altitude of 

700 ft (the ditch intake was relocated upstream to an 

altitude of 825 ft in November 1913) was diverted for 

off-stream uses. During periods of base flow, the stream 

reach between the ditch intake and the springs, located 

at an altitude of 600 ft, is considered dry (Hawaii 

Department of Land and Natural Resources, 1977, 

p. 30; and Mink, 1990). The stream reach between the 

springs and the ocean is considered perennial. Previous 

estimates indicated that at least 2.32 ft3

/s (1.5 Mgal/d) 

of base flow [0.77 ft3

/s (0.5 Mgal/d) from the spring at 

an altitude of 600 ft and 1.55 ft3

/s (1.0 Mgal/d) released 

from Honokohau Ditch] were available to meet the 

water needs in lower Honokohau Stream (Hawaii 

Department of Land and Natural Resources, 1977, 

p. iv). 

The U.S. Geological Survey (USGS) operates a 

streamflow-gaging station, upstream of the Honokohau 

Ditch intake, at an altitude of 870 ft on Honokohau 

Stream. As of October 1, 2000, a total of 82 water years 

of streamflow data were available to describe hydrologic conditions at the gage. Only limited data were 

available to assess base flow and the effects of streamflow diversions downstream from the gage. 

In cooperation with the Office of Hawaiian Affairs 

(OHA), the USGS investigated how base flow in lower 

Honokohau Stream varies both with time and location 

along the stream. Historic and new data were collected 

and analyzed to evaluate the effects associated with 

human manipulations of streamflow as well as natural 

variability. These data are needed to better manage the 

limited resource.

PURPOSE AND SCOPE

The purpose of this report is to (1) quantify the 

amount of water available in lower Honokohau Stream 

during periods of base flow, (2) describe how the base 

flow varies both with time and location along the 

stream, and (3) quantify the effects that streamflow 

diversions and return flows have on base-flow availability.

To achieve the purposes of this report, both historic 

and new streamflow data and field observations were 

analyzed. Historic data included (1) 82 years of streamflow data collected by the USGS at streamflow-gaging 

station 16620000 on Honokohau Stream at altitude 870 

ft, (2) published summaries of Maui Land & Pineapple 

Company, Inc. flow data for the Honokohau ditch diversion and development tunnels T-21 and T-22 upstream 

from the diversion (fig. 4), (3) estimates of Honokohau 

ditch diversion capacity and ditch-flow release practices from Maui Land & Pineapple Company, Inc., and 

(4) historic discharge measurements made by the USGS 

along Honokohau Stream. New streamflow data and 

field observations included (1) three seepage runs made 

on the lower reach of Honokohau Stream (from station 

16620000 downstream to the ocean), (2) a minimum of 

10 discharge measurements at each of three low-flow 

partial-record stations on the lower reach of Honokohau 

Stream, and (3) field observations of streamflow (or 

lack of it) and diversion and return-flow practices.

ACKNOWLEDGMENTS

Mr. Wesley Nohara and other Maui Land & Pineapple Company, Inc. (ML&P) employees were most 

generous with their time and detailed knowledge of the 

study area. In addition they allowed USGS personnel 

access to ML&P’s properties in Honokohau Valley to 

collect new data. We also appreciate the information 

and access to privately owned lands provided by numerous residents of Honokohau Valley and members of the 

Honokohau Valley Association. 

DESCRIPTION OF STUDY AREA

Physical Setting

The island of Maui is formed by two volcanoes 

(fig. 1). The Honokohau Stream watershed lies on the 

northwest side of the western volcano and has a total 

drainage area estimated to be 8.12 square miles (mi2

) at 

its mouth (Chiu Yeung, U.S. Geological Survey, Honolulu, Hawaii, oral commun., 2002). The total drainage 

area of the Honokohau Stream watershed upstream 

from station 16620000 (fig. 4) is 4.11 mi2 (Taogoshi 

and others, 2001, p. 206). Honokohau is the longest 

stream in West Maui, traversing a nearly straight line 
Description of Study Area 3

Figure 1. The Hawaiian islands, island of Maui, and the Honokohau Stream study area, Hawaii.

West Maui Mo untain Crest

Honokohau Stream

Wailuku

Waikapu

Maalaea

Olowalu

Kahului

Bay

Lahaina

Kaanapali

Honokowai

Kahana

Napili

Waihee

Waiehu

Base modified from U.S. Geological Survey

digital data, 1:24,000, 1983, Albers equal area 

projection, standard parallels 20°35' and 21°00', 

central meridian 156°20'

Maalaea Bay

PACIFIC

OCEAN

Puu Kukui

Honokowai Str

Kahoma

Str

Kanaha

Str

Kauaula

Str

Launiupoko

Str

Olowalu Str

Ukumehame Str

Poohahoahoa Str

Nakalaloa Str

Waikapu Str

Waiehu Str

Iao Str

Iao Str

Waihee

River

South Waie

No

hu Str

rth Waiehu Str

Honokowai Tunnel

Honokohau Ditch

Honokohau Ditch

Mahinahina Gl

Kalepa Gulch

Evere tt Ditch

Manian i a Ditch Waihee Ditch

Spreckels Ditch

156°40'

21°

20°50'

156°30'

0

0

1 2 3 MILES

1 3 KILOMETERS 2

WAILUKU

DISTRICT

LAHAIN

A

DISTRICT

22°

20°

160° 158° 156°

PACIFIC OCEAN

Kauai

Niihau

Oahu

Maui

Molokai

Lanai

Kahoolawe

Hawaii

HAWAII

Area

of map

Kahului

Bay

EXPLANATION

DITCH OR TUNNEL

STREAM

INTERMITTENT STREAM
4 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

about 9.5 mi long from its headwaters at Puu Kukui to 

the ocean (Hawaii Department of Land and Natural 

Resources, 1977, p. 29). Starting from the summit of 

Puu Kukui (altitude of 5,788 ft) Honokohau Stream 

descends about 900 ft over its first 1.2 mi or an average 

slope of about 720 feet per mile (ft/mi). At Honokohau 

Falls the stream cuts down through the Wailuku Basalt 

about 2,300 ft, forming an impressive amphitheatreshaped valley (Stearns and Macdonald, 1942, pl. 28). 

Over the remaining 8.3 mi of its course to the ocean, 

Honokohau Stream flows through a relatively wide valley and has a fairly uniform slope that averages about 

310 ft/mi.

The Honokohau Stream watershed drains an area 

that has a steep rainfall gradient (fig. 2) (Giambelluca 

and others, 1986, p. 112). The mean annual rainfall at 

the head of the watershed (Puu Kukui) is greater than 

355 in. (9,000 millimeters), which is the second highest 

total in Hawaii (Meyer and Presley, 2001, p. 8). Mean 

annual rainfall near the mouth of Honokohau Stream is 

about 40 in. (1,000 millimeters). The weighted-average 

mean annual rainfall for the part of the Honokohau 

watershed upstream from station 16620000 was estimated to be about 241 in. (Hawaii Department of Land 

and Natural Resources, 1977, p. 19). 

The headwaters of Honokohau watershed are primarily forest covered. Downstream, the first evidence 

of artificial alterations in the Honokohau watershed are 

water development tunnels T-21 and T-22, which are 

located at altitudes of 880 and 900 ft (fig. 4). Just downstream at an altitude of 825 ft is the diversion dam and 

intake which marks the start of the Honokohau Ditch 

(fig. 4). Currently all residential housing in the valley is 

downstream from MacDonald’s Dam, which is located 

at an altitude of about 340 ft (fig. 4). Historically taro 

cultivation was estimated to encompass in excess of 10 

acres in Honokohau Valley (Hawaii Commission on 

Water Resource Management, 1990, p. 214). Field evidence indicated that this cultivation took place at stream 

altitudes up to about 600 ft. As of March 1992, 3.13 

acres of taro was under cultivation with an additional 

8.07 acres planned for future production (Bill Rozeboom, Hawaii Commission on Water Resource Management, written commun., 1992). Most of the existing 

taro cultivation takes place downstream from Chun’s 

Dam (fig. 4), which is at an altitude of about 90 ft. Most 

of the taro cultivation planned for the future is downstream from MacDonald’s Dam (fig. 4), however two 

parcels are near the Taro Gate release (fig. 4) at an altitude of about 405 ft. In addition to taro cultivation, a 

variety of other small-scale agricultural activities take 

place in the valley below the diversion at MacDonald’s 

Dam (fig. 4).

Geologic Setting

 The volcano that forms west Maui differs from 

most Hawaiian volcanoes in that it is nearly circular 

(Stearns and Macdonald, 1942, p. 156). This near circular shape is attributed to the radial pattern of dikes from 

the volcano summit. The structure of the volcano is 

characterized by its central caldera and two principal rift 

zones, which trend to the northwest and southeast (fig. 

3). Two less pronounced rift zones trend to the northeast 

and southwest (Macdonald and others, 1983, p. 381).

West Maui’s volcano is composed of three principal units: the Wailuku Basalt, the Honolua Volcanics, 

and the Lahaina Volcanics (Stearns and Macdonald, 

1942; and Langenheim and Clague, 1987). The 

Wailuku Basalt is the oldest of the three units and contains mostly thin pahoehoe and aa lava flows that built 

the shield volcano. Following the completion of the 

shield-building stage, a veneer estimated to range from 

50 to 500 ft thick was deposited over most of the basaltic dome. These post-shield building deposits were classified as the Honolua Volcanics. Subsequent to the 

eruption of the Honolua Volcanics there was an 

extended erosional period. During this time canyons up 

to 2,000 to 4,000 ft deep were cut. The Lahaina Volcanics were the result of eruptions that took place after this 

period. These eruptions were minor and were confined 

to the western slopes of the volcano.

The northwest trending rift zone of the West Maui 

Volcano runs roughly parallel to the linear Honokohau 

Stream Valley. Dikes have been identified along most 

of Honokohau Stream (fig. 3) with the majority of them 

having strikes that are approximately parallel to the 

direction of the stream. Dikes in the Wailuku Basalt 

have widths that average about 1.5 ft and range from a 

few inches to 10 ft in width (Stearns and Macdonald, 

1942, p. 163).

In the vicinity of Honokohau Valley the principal 

volcanic unit is the Wailuku Basalt. The limited areas of 

Honolua Volcanics found in the valley are located along 

the boundaries with adjacent watersheds. The Wailuku 

Basalt is one of the most permeable volcanic units on 

Maui. Dikes complexes in the Wailuku Basalt would be 
Description of Study Area 5

Figure 2. Mean annual rainfall in west Maui, Hawaii (modified from Giambelluca and others, 1986).

West Maui Mo untain Crest

Wailuku

Waikapu

Maalaea

Olowalu

Kahului

Bay

Lahaina

Kaanapali

Honokowai

Kahana

Napili

Waihee

Waiehu

Base modified from U.S. Geological Survey

digital data, 1:24,000, 1983, Albers equal area 

projection, standard parallels 20°35' and 21°00', 

central meridian 156°20'

Maalaea Bay

PACIFIC

OCEAN

Puu Kukui

Honokowai Str

Kahoma

Str

Kanaha

Str

Kauaula

Str

Launiupoko

Str

Olowalu Str

Ukumehame Str

Poohahoahoa Str

Nakalaloa Str

Waikapu Str

Waiehu Str

Iao Str

Iao Str

Waihee

River

South Waiehu Str

North Waiehu Str

Honokowai Tunnel

Honokohau Ditch

Mahinahina Gl

Kalepa Gulch

Evere tt Ditch

Manian i a Ditch Waihee Ditch Spreckels Ditch

156°40'

21°

20°50'

156°30'

0

0

1 2 3 MILES

1 3 KILOMETERS 2

20

16

30

30

40

60

80

100

120

160

40

60

80

100

120

160

200

200

235

235

275

315

355

20

16

Kahului

Bay

EXPLANATION

MEAN ANNUAL RAINFALL--

 Interval, in inches, is variable

DITCH OR TUNNEL

STREAM

INTERMITTENT STREAM

16

Honokohau

Stream
6 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

Figure 3. Geology of the West Maui Volcano, Hawaii (modified from Stearns and Macdonald, 1942, and Langenheim and Clague, 1987).

156°40'

21°

20°50'

156°30'

0

0

1 2 3 MILES

1 3 KILOMETERS 2

Wailuku Wailuku

Puu

Kukui

Puu

Kukui

Maalaea

Olowalu

Lahaina

Kaanapali Waihee

Waiehu

Kahului

Bay

Base modified from U.S. Geological Survey

digital data, 1:24,000, 1983, Albers equal area 

projection, standard parallels 20°35' and 21°00', 

central meridian 156°20'
Description of Study Area 7

EXPLANATION

SEDIMENTARY DEPOSITS

 Unconsolidated deposits, chiefly younger alluvium 

 Calcareous sand dunes

 Consolidated earthy deposits, chiefly older alluvium

VOLCANIC ROCKS

 Lahaina Volcanics

 Honolua Volcanics

 Kula Volcanics

 Wailuku Basalt

CONES, VENTS, DOMES, CRATERS, BOSSES, AND DIKES

 Cone or vent of Lahaina Volcanics

 Cones or domes of Honolua Volcanics

 Cones or vents of Wailuku Basalt

 Pit craters

 Bosses of Wailuku Basalt

 Dikes of either Wailuku Basalt or Honolua Volcanics

 Dikes, where too numerous to show individually

 Axis of main rift zones (from Macdonald and others, 1983)

 Caldera boundary, dotted where concealed, dashed where inferred
8 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

expected to contain significant quantities of high-level 

ground water. Streams cutting through these dike complexes would encounter perennial sources of water. The 

Honolua Volcanics has significantly lower permeabilities and would not be expected to carry significant volumes of water (Stearns and Macdonald, 1942, p. 157).

In Honokohau Valley unconsolidated alluvial 

deposits have been mapped along the stream channel at 

altitudes as high as about 800 ft (fig. 4). These alluvial 

materials are chiefly poorly-sorted lava-rock gravels 

that were deposited during periods when sea levels rose 

significantly higher than current levels. These unconsolidated deposits can be expected to contain water derived 

from perennial stream reaches. Consolidated deposits 

that consist chiefly of older alluvium underlie most of 

the unconsolidated deposits in west Maui (Stearns and 

Macdonald, 1942, p. 182). 

Hydrologic Setting and Water Diversions

Ground water in the Honokohau watershed occurs 

primarily as a freshwater lens or dike-impounded, highlevel water. The freshwater lens is ground water that 

floats on the denser, underlying saltwater. Dikeimpounded, high-level ground water is in direct contact 

with the freshwater lens but is distinguished from it primarily because it is found at higher altitudes. Honokohau Valley lacks a significant zone of low permeability 

material (or caprock) that would impede the discharge 

of ground water at the ocean. As a result the surface of 

the freshwater lens stands about 1 foot above sea level 

near the coast. The freshwater lens rises about 1.5 to 2.5 

ft/mi inland for about 2 to 3 mi (Stearns and Macdonald, 

1942, p. 189) where there is a transition from the freshwater lens to high-level water.

In Honokohau Valley the location of the transitional area from the freshwater lens to high-level ground 

water is poorly defined. Yamanaga and Huxel (1969, 

p. 14) infer that the transitional zone is located along the 

edge of the dike zone. In Honokohau Valley this zone 

was shown to be located between 2.2 and 3.5 mi 

upstream from the mouth (fig. 4). In the transitional 

area, ground-water levels can be a few tens of feet above 

sea level (Yamanaga and Huxel, 1969, p. 16).

In Honokohau Valley, high-level ground water is 

confined in compartments of permeable Wailuku Basalt 

by numerous intersecting dikes. The radial pattern of 

dikes in the West Maui Volcano results in an ovalshaped area of high-level water that underlies most of 

the volcano. The surface of the dike-impounded highlevel ground water rises from about 700 to 1,200 ft, near 

the inland edge of the transitional area, up to 3,500 ft, or 

more, inland (Stearns and Macdonald, 1942, p. 195). 

Heavy rainfall over the West Maui Volcano (fig. 2) provides an abundant source of recharge to these high-level 

water bodies.

Honokohau Stream has eroded a deep canyon, cutting down through the Wailuku Basalt and the confining 

dikes as much as 2,300 ft at Honokohau Falls (Stearns 

and Macdonald, 1942, pl. 28). This erosional activity, 

and to a lesser degree seepage through the confining 

dikes, allows Honokohau Stream to tap the significant 

volumes of water stored as high-level ground water. The 

result is that Honokohau Stream flows perennially in the 

zone of high-level ground water. The sustained perennial nature of this streamflow is apparent when analyzing flow records collected by the USGS at gaging 

station 16620000 on Honokohau Stream at an altitude 

of 870 ft. The minimum flow recorded during 82 years 

of data collected between 1913 and 2000 was 8.4 ft3

/s 

(5.4 Mgal/d) (Taogoshi and others, 2001, p. 206).

Large springs are located just downstream from 

station 16620000 and upstream from the Honokohau 

Ditch intake. Water development tunnels T-21 and T-22 

(fig. 4) were constructed starting in 1913 (they were 

later extended in the 1920’s), in an attempt to enhance 

the flow of the springs. However it is considered 

unlikely that perennial flow, in addition to that already 

being discharged naturally, was developed by the tunnels (Hawaii Department of Land and Natural 

Resources, 1977, p. 31). Tunnel T-21 is located on the 

west side of Honokohau Stream about 700 ft downstream from the USGS gage. The tunnel is about 850 ft 

long and cuts through 8 dikes (Mink, 1990). Tunnel 

T-22 is located on the east side of Honokohau Stream 

about 300 ft downstream from the USGS gage. The tunnel is 990 ft long and cuts through 10 dikes (Mink, 

1990). Tunnels T-21 and T-22 in combination contributed an average flow of about 6.2 ft3

/s (4.0 Mgal/d) to 

Honokohau Stream over the period 1926–41 (Yamanaga and Huxel, 1969, p. 30). This flow enters the stream 

in the reach between station 16620000, at an altitude of 

870 ft, and the current location of the Honokohau Ditch 

intake, at an altitude of 825 ft.
Description of Study Area 9

Figure 4. Streamflow measurement sites in, and geology of, lower Honokohau Valley, island of Maui (geology from Stearns and Macdonald, 1942, and Langenheim and Clague, 1987).

400

a 7.9

UNCONSOLIDATED DEPOSITS, 

 CHIEFLY OLDER ALLUVIUM

HONOLUA VOLCANICS

WAILUKU BASALT

CONES AND DOMES OF 

 WAILUKU BASALT

CONES AND DOMES OF 

 HONOLUA VOLCANICS

BOUNDARY AND TRANSITIONAL 

 AREA BETWEEN DIKE-IMPOUNDED

 HIGH-LEVEL AND FRESH-WATER- 

 LENS GROUND WATER (from 

 Yamanaga and Huxel, 1969)

TOPOGRAPHIC CONTOUR 

 Interval 200 feet. Datum is 

 mean sea level

STREAMFLOW MEASUREMENT 

 SITE AND NUMBER

WATER DEVELOPMENT TUNNEL

 AND NUMBER

EXPLANATION

Honokohau 

Bay

PACIFIC OCEAN

200

400

600

800

400

600

800

400

1800

1800

2400

1600

1800

1400

1000

Honokohau Stream

a

a

a

a

a a

a

a

a

a

a

aa

a

a

a b

a

b

0

0

1 MILE

1 KILOMETER

Base modified from U.S. Geological Survey

digital data, 1:24,000, 1983, Albers equal area 

projection, standard parallels 20°35' and 21°00', 

central meridian 156°20'

156°37' 156°36'

21°

20°59'

21°01'

PACIFIC OCEAN

Area

of map

Maui

Honokohau Ditch Honokohau Ditch

T-22

T-221

T-21

Chun's

Dam

9.1

8.0

7.9

7.6

7.1

7.0

6.2

6.1

5.9

5.0

4.0

3.1

3.0

2.0

1.0

station

16621000

station 16621000

station

16620000

station 16620000

MacDonald's

Dam

MacDonald's Dam

Taro Gate

Release

Taro Gate Release

Honokohau Ditch

diversion dam

Honokohau Ditch diversion dam

9.1

8.0

7.9

7.6

7.1

7.0

6.2

6.1

5.9

5.0

4.0

3.1

3.0

2.0

1.0

station

16621000

station

16620000

MacDonald's

Dam

Chun's

Dam

Taro Gate

Release

Honokohau Ditch

Diversion Dam

Honokohau Ditch

T-21 b
10 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

Starting in June 1904 with the completion of the 

first Honokohau Ditch (also known as the Honolua 

Ditch), most of the flow in Honokohau Stream at an altitude of 700 ft was diverted for off-stream uses. Honokohau Ditch was built twice and extensively renovated 

once during its first 20 years of operation (Wilcox, 

1996, p. 126). As a result of these changes the ditch 

intake was relocated upstream, from the initial altitude 

of 700 ft to the current location, at an altitude of 825 ft. 

Updates to the ditch also significantly increased the 

capacity, at the Honokohau Stream intakes, from the 

original range of 30 to 39 Mgal/d (Wilcox, 1996, p. 127) 

to the current range of 60 to 65 Mgal/d (Wesley Nohara, 

Maui Land and Pineapple Company, Inc., oral commun., 2002). The average flow diverted from Honokohau Stream has been estimated to be 37.2 ft3

/s (24 

Mgal/d) although it is not clear over which time period 

this average flow was computed (Hawaii Commission 

on Water Resource Management, 1992, p. D7).

During periods of base flow, Honokohau Ditch 

diverts all the flow in Honokohau Stream at the ditch 

intake. The stream reach extending about 1 mi downstream from the ditch intake to some springs, which 

start at an altitude of 600 ft (site 2.0 in figure 4), is dry 

during these periods (Hawaii Department of Land and 

Natural Resources, 1977; and Mink, 1990). The springs 

discharge into the stream along a reach that extends 

between altitudes of about 600 to 550 ft. This discharge 

is overflow from a dike compartment (Hawaii Department of Land and Natural Resources, 1977, p. 30). A 

variety of estimates have been given for the sustained 

discharge from the springs, ranging from about 0.77 

ft3

/s (0.5 Mgal/d) (Hawaii Department of Land and Natural Resources, 1977, p. iv) to about 3.1 ft3

/s (2.0 

Mgal/d) (Wesley Nohara, Maui Land and Pineapple 

Company, Inc., written commun., 1993). Flow estimates for the springs have been based on only limited 

historic data. The stream reach between the springs, 

which start at an altitude of 600 ft, and the ocean is 

perennial.

 At a stream altitude of about 405 ft, ML&P returns 

some Honokohau Ditch water back into the stream. This 

water is released at a location commonly known as the 

Taro Gate to help support downstream taro farmers. 

ML&P has historically sought to maintain a flow 

release of 1.55 ft3

/s (1.0 Mgal/d) at this location (Wesley Nohara, Maui Land and Pineapple Company, Inc., 

oral commun., 2003). Three water pipes connected to 

Honokohau Ditch extend along Honokohau Stream 

downstream from the Taro Gate. One pipe transports 

water out of the Honokohau watershed for irrigation of 

pineapple fields. A second pipe historically provided an 

average of about 0.31 ft3

/s (0.2 Mgal/d) of water to a 

Maui Department of Water Supply (Maui DWS) water 

tank in the valley. This water tank in turn provided the 

drinking water supply for residents in the valley. Currently (2002) this second pipe is not in use and the Maui 

DWS pumps water from tanker trucks to replenish the 

storage tank. A third pipe provides an average of 0.46 

ft3

/s (0.3 Mgal/d) of water to a small-scale hydropower 

generator located at MacDonald’s Dam at an altitude of 

340 ft (fig. 4). The 0.46 ft3

/s (0.3 Mgal/d) from the 

hydropower plant is subsequently released back into 

Honokohau Stream via the water diversion ditch that 

originates at MacDonald’s Dam.

Downstream from the Taro Gate release two diversion dams are in place, MacDonald’s Dam (altitude of 

340 ft) and Chun’s Dam (altitude of 90 ft). Both of these 

dams divert varying amounts of water into ditches that 

provide irrigation water in the valley. Excess water 

from these ditches is returned to Honokohau Stream, 

although the locations of the return flows are commonly 

widely dispersed. Numerous, smaller scale diversions, 

which usually involve small pipes set in the stream, can 

also be found in operation at various locations downstream between MacDonald’s Dam and the ocean.

DATA COLLECTION AND ANALYSIS

In this section of the report, site-specific streamflow data that have historically been collected by the 

USGS or that have been collected specifically for this 

study in the Honokohau watershed will be summarized. 

Included are data for two streamflow-gaging stations, 

three low-flow partial-record stations, and several miscellaneous discharge measurements.

Streamflow-Gaging Stations

The USGS operated streamflow-gaging station 

16621000 from March 1906 through August 1913. This 

station was located at the intake to the Honokohau Ditch 

and measured diversions from Honokohau Stream by 

the ditch. During this period, the original ditch, at the 

downstream location, was in operation and as a result 

these data have little applicability to present day conditions in the valley. It is interesting to note, however, that 

the maximum daily discharge recorded during this 

period was 48 ft3

/s (31 Mgal/d) and this value agrees 
Data Collection and Analysis 11

with the stated capacity of the ditch during this period 

of 30 to 39 Mgal/d. The average discharge at the ditch 

intake during the period when station 16621000 was in 

operation was 34.4 ft3

/s.

The USGS has operated streamflow-gaging station 

16620000 on Honokohau Stream for all or parts of the 

years 1913–1920, 1922–1988, and 1990 through the 

present (2003). This gaging station is part of the longterm-trend surface-water data network in Hawaii (Fontaine, 1996, p. 35) and will continue in operation for as 

long as possible. The station is located at an altitude of 

870 ft, upstream from water development tunnels T-21 

and T-22 and the diversion dam at the start of the 

Honokohau Ditch (fig. 4). Through the end of 2000, 82 

complete water years of streamflow data have been collected at the gaging station. Water years extend from 

October 1 through September 30 of the following year 

and are designated by the calendar year in which it ends. 

Therefore the water year ending September 30, 1999 is 

called the “1999 water year.” The long-term streamflow 

data from the Honokohau Stream gaging station represents the only extended data set of its kind in the 

Honokohau watershed and therefore represents the 

index or base gaging station that will be used to estimate 

base-flow conditions at other locations.

There are a number of ways 82 water years of 

streamflow data for Honokohau gaging station 

16620000 can be summarized. The following are some 

of the more common. All data summaries are for data 

collected through the end of water year 2000. Through 

water year 2000 the average discharge was 39.1 ft3

/s 

(25.3 Mgal/d). The maximum discharge recorded at any 

time was 7,260 ft3

/s (4,690 Mgal/d) and the minimum 

was 8.4 ft3

/s (5.4 Mgal/d). Annual mean discharge for 

all complete water years of record are shown in figure 

5. The highest annual mean discharge was 68.3 ft3

/s 

(44.1 Mgal/d) in 1914 and the lowest annual mean discharge was 24.1 ft3

/s (15.6 Mgal/d) in 1926. There is no 

significant trend in the annual mean discharge data 

although there were several periods when streamflow 

was below normal for extended periods including 

Figure 5. Annual mean and average discharge at streamflow-gaging station 16620000 on Honokohau Stream, 

Maui, water years 1914–2000.

0

10

20

30

40

50

60

70

80

1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

WATER YEAR

ANNUAL MEAN DISCHARGE IN CUBIC FEET PER SECOND

Average

discharge

NO DATANO DATA
12 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

1943–47, 1971–1978, 1983–85, and 1995–98. The differences in streamflow that take place over various, 

short-duration periods of time, such as those noted 

above, illustrate why it is important to have long-term 

data to provide accurate estimates of streamflow characteristics. Mean monthly discharges along with maximum and minimum values for each month are shown in 

figure 6. There is no distinctive seasonal pattern in 

monthly streamflow data evident and the maximum and 

minimum mean discharges for any month range from 

144 ft3

/s (93.0 Mgal/d) (March 1942) to 10.8 ft3/s (7.0 

Mgal/d) (October 1985). The minimum monthly mean 

discharges are quite uniform throughout the year, indicating that extended periods of minimum base-flows 

can take place during any month in the year.

 In this report the primary focus is on low, or baseflow, conditions. One of the most straightforward and 

useful ways to summarize streamflow data is through 

the use of flow-duration curves (Vogel and Fennessey, 

1995). A flow-duration curve is simply a cumulative 

frequency curve, which shows the percentage of time 

that specified discharges were equaled or exceeded during a given period of record (Searcy, 1959). For example, one of the most frequently used points on a flowduration curve is the 50th percentile, or median discharge. This is the discharge that is equaled or exceeded 

50 percent of the time. A flow-duration curve based on 

daily mean discharges for 82 water years with complete 

record from 1913 through 2000, for Honokohau Stream 

gaging station 16620000, is shown in figure 7. The 

smooth flow-duration curve for total flow indicates that 

there are no flow manipulations of significance affecting the discharge recorded at the gage (Ries, 1993, 

p. 23). Another prominent feature of the total flow curve 

is the way it nearly levels out at the higher percentiles, 

which is indicative of a significant, sustained source of 

base flow (Searcy, 1959, p. 22). The long-term average 

discharge at the gage, 39.1 ft3

/s (25.3 Mgal/d), represents a flow rate that is equaled or exceeded about 26 

percent of the time, indicating that average flow is not a 

representative measure of typical flow conditions in the

Figure 6. Mean monthly and maximum and minimum monthly mean discharges at streamflowgaging station 16620000 on Honokohau Stream, Maui, water years 1914–2000.

0

20

40

60

80

100

120

140

160

January

March

May

July

September

November

February

April

June

August

October

December

MONTH

DISCHARGE, IN CUBIC FEET PER SECOND

MEAN MONTHLY DISCHARGE

MAXIMUM MONTHLY MEAN DISCHARGE

MINIMUM MONTHLY MEAN DISCHARGE
Data Collection and Analysis 13

stream. The median discharge for total flow of 24 ft3/s 

(15.5 Mgal/d) would therefore be a preferred measure 

of typical flow conditions. 

Streamflow at a gaging station is frequently 

divided into two basic components: base flow and direct 

runoff (Maidment, 1992). Base flow is that part of 

streamflow derived from ground water. Direct runoff is 

that part of streamflow derived from surface and rapid 

subsurface flow, which occurs in response to excess 

rainfall. The base-flow component of Honokohau 

streamflow at gaging station 16620000 was estimated 

using an automated hydrograph separation method 

developed by Wahl and Wahl (1995). In the method, 

two variables must be input: N (number of days) and f

(turning-point test factor). The separation method 

divides the daily streamflow data into non-overlapping 

periods, each N-days long, and determines the minimum flow in each period. If the minimum flow within a 

period is less than f times the minimums for the adjacent 

periods, then the central period minimum is made a 

pivot (or turning point) on the base-flow hydrograph. 

Conceptually, the variable N represents the number of 

days following a storm before direct runoff generally 

ceases. Straight lines drawn on semilogarithmic paper 

between the turning points define the base-flow 

hydrograph. In this application N was determined to be 

4 days and f was set at the 0.9 value recommend by 

Wahl and Wahl (1995). The direct runoff component of 

the total streamflow was computed as the total flow 

minus the base flow computed with the hydrograph separation method.

Flow-duration curves for the base-flow and directrunoff components of streamflow at gaging station 

16620000 on Honokohau Stream are shown in figure 7 

and summarized in table 1. A striking feature of the 

curves in figure 7 is that direct runoff contributes to 

total flow only slightly more than 70 percent of the time. 

This also indicates the importance of the ground-water 

contribution to streamflow during periods of low flows 

and the interaction between ground water and surface 

water (Winter and others, 1998). The base-flow curve is 

much flatter than both the total-flow and direct-runoff 

curves, which indicates that base flow is not as variable 

at this gage. Of the total streamflow at gaging station

Figure 7. Flow-duration curves for total flow, base flow, and direct runoff at streamflow-gaging station 16620000 

on Honokohau Stream, Maui, for 82 water years with complete record during 1913–2000.

PERCENTAGE OF TIME INDICATED DISCHARGE WAS EQUALLED OR EXCEEDED

0.01 0.050.1 0.2 0.5 1 2 5 10 20 30 50 70 80 90 95 98 99 99.899.99.95 99.99

DAILY MEAN DISCHARGE, IN CUBIC FEET PER SECOND

0.1

1

10

100

1000

TOTAL FLOW

BASE FLOW

DIRECT RUNOFF
14 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

16620000, 49 percent is derived from base flow and 51 

percent is derived from direct runoff. The relative contributions of direct runoff and base flow to streamflow 

at gaging station 16620000 by water year are shown in 

figure 8.

Low-Flow Partial-Record Stations

If long-term streamflow data were available at 

multiple locations along Honokohau Stream it would be 

a relatively simple matter to describe the availability 

and distribution of base flow along the stream. However, operation of gaging stations to collect the required 

data is costly and requires long periods of time. For 

Honokohau Stream only one long-term gaging station is 

available (USGS station 16620000) so alternative techniques that are both inexpensive and timely are 

required. Operation of low-flow partial-record stations 

for use in estimating base flows at sites without longterm gaging stations has been demonstrated to be a viable alternative in Hawaii (Fontaine and others, 1992).

At low-flow partial-record stations, a minimum of 

10 discharge measurements (Rantz and others, 1982) 

are made during periods of base flow. These measurements should be made over a variety of base-flow conditions and during independent recessions following 

periods of direct runoff. The discharge measurements 

are then correlated with the concurrent daily discharges 

recorded at an index station. The index station is a 

nearby gaging station where long-term data are available that can be used to accurately estimate streamflow 

statistics. In this case the index station is station 

16620000 on Honokohau Stream. The type of correlation and the data analysis technique to be used is based 

on the shape of the log-log plot of discharge measurements at the low-flow partial-record station compared 

with daily mean discharges at the index station (Ries, 

1993, p. 24). When the plot indicates curvature, then the 

graphical correlation technique would be used (Searcy, 

1959, p. 17). When the plot indicates little or no curvature, then the Maintenance Of Variance Extension, 

Type I (MOVE.1) technique would be used (Hirsch, 

1982). Using the established correlation, between the 

discharges at the stations, base-flow statistics from the 

index station can then be used to provide estimates of 

the same statistic at the low-flow partial-record stations. 

In this study low-flow partial-record stations were 

established at sites 4.0, 5.9, and 9.1 (table 2 and fig. 4). 

Site 4.0 is just upstream from the Taro Gate release and 

data there would be indicative of gains in base flow 

associated with the springs which start at an altitude of 

600 ft and any additional gains in the stream reach prior 

to the inflow of water released from Honokohau Ditch 

at the Taro Gate. Site 5.9 is located just upstream from 

MacDonald’s Dam and data there would be indicative 

of total base flow available to meet the in-stream and 

near-stream water needs in lower Honokohau Stream. 

Table 1. Selected flow-duration discharges for total flow, base flow, and direct runoff at streamflowgaging station 16620000 on Honokohau Stream, Maui, water years 1913–2000

[ft3/s, cubic feet per second] 

Percentage of time 

indicated flow equaled or 

exceeded

Total flow

(ft3/s)

Base flow

(ft3/s)

Direct runoff

(ft3/s)

99 10 9.7 0

95 12 11 0

90 13 12 0

80 16 14 0

70 18 15 0.5

60 21 17 1.3

50 24 18 3.2

40 28 19 6.7

30 35 21 13

20 48 24 26

10 79 27 57

5 118 31 96

1 246 42 223
Data Collection and Analysis 15

Figure 8. Relative contributions of direct runoff and base flow to annual mean streamflow at gaging station 

16620000 on Honokohau Stream, Maui.

a

 Not shown in figure 4. See remarks for location.

Table 2. Long-term and partial-record data-collection stations and miscellaneous sites on Honokohau Stream, Maui

[n.a., not applicable]

Site number

(fig. 4)

USGS

station number

Altitude

(feet)

Distance upstream

from mouth

(feet) Remarks

16620000 16620000 870 25,150 long-term streamflow-gaging station

0.2a n.a. 830 23,950 upstream from Honokohau ditch intake

n.a. n.a. 825 23,900 Honokohau ditch intake

0.4a n.a. 820 23,850 downstream from Honokohau ditch intake

1.0 205830156353801 625 19,950

2.0 n.a. 600 18,950 upstream end of springs

3.0 205843156354101 560 18,650

3.1 205845156354201 540 18,150

4.0 205915156360001 410 14,300 low-flow partial-record station

n.a. n.a. 405 14,100 Taro Gate release

5.0 205922156360101 380 13,600

5.9 205928156360601 350 12,950 low-flow partial-record station

n.a. n.a. 340 12,600 McDonald’s Dam

6.1 205933156360801 330 12,400

6.2 205940156360901 310 11,600

7.0 205958156361701 235 9,980

7.1 210001156362101 200 9,120

7.6 210012156362801 180 7,800

n.a. n.a. 105 5,400 concrete road ford

7.9 210041156363001 100 5,050

n.a. n.a. 90 4,520 Chun’s Dam

8.0 210045156363301 80 4,500

9.1 210128156364201 5 40 low-flow partial-record station

0

10

20

30

40

50

60

70

80

1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

DATE

DISCHARGE, IN CUBIC FEET PER SECOND

DIRECT RUNOFF

BASE FLOW

NO DATANO DATA
16 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

Site 9.1 is located just upstream from the mouth of the 

stream and data there would be indicative of base-flow 

discharges to the ocean. Discharge measurements made 

at the low-flow partial-record stations and concurrent 

daily mean discharges at the index station (station 

16620000) are listed in table 3. All of these data have 

been published in the series of USGS annual data 

reports and the data are stored in USGS electronic data 

bases.

Logarithmic plots of the discharge measurements 

for the three low-flow partial-record stations compared 

with daily mean discharges at the index station indicated linear relationships and therefore the MOVE.1 

technique was used to make estimates of low-flow discharges for selected flow-duration percentiles. Correlation coefficients, which provide a measure of the 

strength of the linear relationship between the index and 

partial-record stations, are 0.826 for site 4.0, 0.305 for 

site 5.9, and 0.738 for site 9.1. The correlation coefficient for site 5.9 indicates that only a very weak relationship exists between discharge measurements there 

and daily mean discharges at gaging station 16620000 

and therefore MOVE.1 analysis was not conducted 

using the site 5.9 data.

In the MOVE.1 analysis technique the discharge 

measurements at the partial-record stations and the concurrent daily mean discharges at the index station are 

transformed to log base 10 values. The means and standard deviations for the transformed discharge data at the 

two sites are then calculated. Estimates of discharges 

corresponding to selected base-flow durations at the 

partial-record station are obtained by entering the logarithms of known base-flow duration discharges at the 

index station (Xi

) and the computed means and standard 

deviations into the MOVE.1 formula:

Yi = Y + sy/sx (Xi – X), (1)

where:

Yi is the logarithm of the estimated base-flow 

duration discharge at the partial-record 

station,

Xi is the logarithm of the computed base-flow 

duration discharge at the index station,

Y is the mean of the logarithms of the discharge 

measurements at the partial-record station,

X is the mean of the logarithms of the concurrent 

daily mean discharges at the index station,

sy is the standard deviation of the logarithms of the 

discharge measurements at the partialrecord station,

sx is the standard deviation of the logarithms of the 

concurrent daily mean discharges at the 

index station,

Estimates of discharges corresponding to selected baseflow durations for the partial-record stations are then 

converted back into their original units of measurement 

in cubic feet per second.

Computed statistics for the MOVE.1 analyses at 

low-flow partial-record sites 4.0 and 9.1 and index station 16620000 are summarized in table 4. In table 4, two 

sets of statistics are provided for the index station

a

 Site numbers correspond to sites listed in table 2 and shown in figure 4 b

 Historic discharge measurement made by USGS personnel prior to study

Table 3. Discharge measurements at low-flow partial-record stations and concurrent daily 

mean discharges at gaging station 16620000, Honokohau Stream, Maui

[ft3/s, cubic feet per second; --, no data available]

Date

Discharge

(ft3/s)

16620000a Site 4.0a Site 5.9a Site 9.1a

01/22/76 11 0.69b -- --

09/14/95 16 1.53 3.76 1.63

08/12/97 19 1.64 3.54 1.75

10/23/97 17 1.89 3.61 1.81

06/29/99 20 2.74 3.92 2.47

10/27/99 18 2.92 4.52 3.49

02/09/00 17 -- -- 1.73

03/17/00 17 1.22 3.01 1.98

05/24/00 14 1.55 2.92 1.59

07/11/00 20 2.16 3.15 2.98

08/25/00 21 2.29 3.01 3.92

12/19/00 16 1.18 1.85 1.13
Data Collection and Analysis 17

16620000 because discharge measurements were not 

made on the exact same days at the two partial-record 

sites. The statistics from table 4 along with the logarithms of selected flow-duration discharges for total 

flow at the index station 16620000 (table 1) were substituted into equation 1 to compute estimates for 

selected flow-duration discharges at the two partial 

record sites (table 5). Estimates were not provided for 

flow-duration percentiles less than 50 percent because 

in that flow range, surface runoff, or total flow minus 

base flow, starts becoming a significant part of the total 

flow (fig. 7 and table 1). Estimates were not provided 

for flow-duration percentiles greater than 95 percent 

because those estimates would fall too far beyond the 

range of the discharge measurements made during the 

study. 

Historic Discharge Measurements at Miscellaneous 

Sites

The USGS surface-water data-collection program 

in Hawaii officially began in 1909 (Fontaine, 1996, 

p. 7). Over the years, numerous discharge measurements have been made at miscellaneous sites where no 

continuous-record gaging stations were in operation. 

These data provide valuable information that can be 

used to supplement current analyses. Historic discharge 

measurements made by the USGS on Honokohau 

Stream are summarized in table 6. Particularly noteworthy are the measurements made on January 24, 1924, 

which documented the combined discharge from development tunnels T-21 and T-22 as 5.9 ft3

/s. At the time 

of these measurements the daily mean discharge at station 16620000 was 20 ft3

/s or about a 65 percentile flow 

(table 1). On January 22, 1976 a discharge of 0.69 ft3

/s 

was measured near the location of present day partialrecord station 4.0 and it was included in the MOVE.1 

analysis of the measurements at that site (table 3). This 

discharge measurement was significant because it was 

the lowest made at site 4.0. The concurrent, daily mean 

discharge at station 16620000 was 11 ft3

/s or about a 97 

percentile flow (table 1). On June 22–23, 1994, a seepage run was attempted but it is now known that these 

measurements were made during a period when direct 

runoff was taking place. This was determined by 

observing that rapid changes in discharge, which are 

indicative of periods of direct runoff, took place during 

this period at index station 16620000 on Honokohau 

Stream. Therefore, these measurements should not be 

used to indicate how base-flow conditions vary along 

the perennial reach of Honokohau Stream downstream 

from the springs at an altitude of 600 ft.

a Based on concurrent daily mean discharges associated with discharge measurements made at site 4.0

b Based on concurrent daily mean discharges associated with discharge measurements made at site 9.1

a

 Site numbers correspond to sites listed in table 2 and shown in figure 4

Table 4. Computed statistics for concurrent daily mean discharges at index station 

16620000 and discharge measurements at low-flow partial-record stations, Honokohau

Stream, Maui

Station Mean Standard deviation

16620000 1.229a 0.081

Site 4.0 0.224 0.182

16620000 1.246b 0.052b

Site 9.1 0.319 0.164

Table 5. Estimated flow-duration discharges for low-flow partial-record stations, Honokohau 

Stream, Maui

[ft3/s, cubic feet per second]

Percentage of time indicated 

flow equaled or exceeded

Site 4.0a

(ft3/s)

Site 9.1a

(ft3/s)

95 0.77 0.63

90 0.92 0.80

80 1.5 1.5

70 1.9 2.2

60 2.7 3.6

50 3.7 5.5
18 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

BASE-FLOW AVAILABILITY AND DISTRIBUTION

In this section of the report, the distribution of base 

flow in lower Honokohau Stream and how it is affected 

by streamflow diversions and return flows are evaluated. For the purposes of this report, lower Honokohau 

Stream has been defined as the stream reach extending 

from gaging station 16620000, at an altitude of 870 ft, 

to the ocean. Data evaluated in this analysis included 

that summarized in the previous section of the report 

(Data Collection and Analysis) as well as results from 

three seepage runs conducted as part of this study. In 

addition, published summaries of ML&P data, their 

estimates of Honokohau Ditch diversion practices, and 

policies for returning flow from the ditch to Honokohau 

Stream are utilized.

Seepage Runs

Streams reaches can be classified as gaining, losing, or both (Winter and others, 1998, p. 10). Gaining 

stream reaches are lengths of stream where base flows 

increase due to inflows of ground water. Losing stream 

reaches are lengths of stream where base flows decrease 

due to outflows through the streambed to the underlying 

ground-water body. In some stream reaches both gaining and losing segments exist. In gaining stream 

reaches, water in the stream is directly (hydraulically) 

connected to the ground-water system. In losing stream 

reaches, there is an unsaturated zone between water in 

the stream and the underlying ground-water system. 

The above concepts become difficult to analyze in systems such as Honokohau Stream, where water is 

diverted from and returned to the stream. 

In this study three seepage runs were conducted in 

an attempt to identify gaining and losing stream reaches 

and to determine how diversion and return-flow practices affect base flow. A seepage run is an intensive 

data-collection effort in which discharge measurements 

(Rantz and others, 1982) are made at several locations 

along a stream reach. These measurements are made 

during periods of base flow when flow rates at any 

given location in the stream are relatively constant. The 

time between the first and last measurement in a seepage run is minimized to further reduce the effect that 

any variability with time might introduce. During the 

seepage runs, measurements of water temperature and 

specific conductance also were made. In addition to the 

physical measurements, observations were made 

regarding a variety of factors including water diversion 

and return-flow practices, and streambed characteristics.

Table 6. Historic discharge measurements made by the U.S. Geological Survey at miscellaneous sites on Honokohau Stream, Maui

[ft3/s, cubic feet per second; n.a., not applicable; --, no data available]

Date

Discharge

(ft3/s)

Altitude

(feet)

Base-flow

conditions Remarks

10/20/21 11.3 870 yes at gaging station 16620000 during a period when it was not in operation

12.4 870 yes at gaging station 16620000 during a period when it was not in operation

01/24/24 2.1 n.a. yes discharge from development tunnel T-21

3.8 n.a. yes discharge from development tunnel T-22

08/29/68 2.78 580 yes

2.82 480 yes

2.95 300 yes

09/23/75 0.97 580 yes

01/22/76 0.76 580 yes

0.69 440 yes included in analysis of base-flow measurements at partial-record site 4.0

06/22/94 0.26 600 no

4.34 540 no

3.86 410 no

5.36 380 no

06/23/94 3.81 -- no site is downstream from McDonald’s Dam but exact location is unknown

3.04 20 no
Base-Flow Availability and Distribution 19

Discharge measurements made during seepage 

runs conducted on September 14, 1995, August 13, 

1997, and October 23, 1997 are summarized in table 7. 

A graphical summary of the discharge measurements 

compared with stream altitude is shown in figure 9. At 

the time of the seepage runs, daily-mean discharges at 

gaging station 16620000 corresponded to flow-duration 

percentiles of 80 percent, 66 percent, and 75 percent, 

respectively. Analysis of the continuous streamflow 

record at gaging station 16620000 indicates that each of 

the seepage runs was made during periods of base flow 

when the flows remained relatively constant.

A visual inspection of the data in table 7 and figure 

9 indicates that the pattern of streamflow in lower 

Honokohau Stream was similar during the three seepage runs. Streamflows in the reach upstream from the 

Honokohau Ditch diversion dam, at 825 ft, were several 

times greater than those measured at any location downstream from the diversion. The results from these seepage runs also confirm that during base-flow conditions, 

most of the reach is dry between the diversion dam at 

825 ft and the springs, which start at an altitude of about 

600 ft. Downstream from the springs flow is continuous 

in the stream. These results confirm earlier statements 

regarding the general nature of base flow in lower 

Honokohau Stream (Hawaii Department of Land and 

Natural Resources, 1977, p. 30; and Mink, 1990).

Discharge measurements and observations made 

during the seepage runs were used to provide the following information. A significant gain in base flow 

between gaging station 16620000 and the diversion 

dam at 825 ft was attributed primarily to discharge from 

development tunnels T-21 and T-22. During the seepage runs this gain was not measured directly. Discharge 

upstream from the diversion dam was computed as the 

flow rate at the gage plus estimated tunnel discharges. 

The method of estimation is discussed in greater detail 

in the following section of the report (Effect of Honokohau Ditch Diversion). During the seepage runs all the 

flow was diverted at the dam except for a minor amount 

of leakage, which was estimated to be about 0.1 ft3

/s. 

No suitable location was found to measure this small 

discharge directly. This minor flow persisted in a reach 

of the stream that is about 1,500 ft in length, ending at a 

location which corresponds with the upstream terminus 

of the unconsolidated alluvium in the channel (fig. 4). In 

this area the permeability of the streambed increases, 

allowing the minor flow to seep into the ground. Downstream from this location the channel remained dry in a 

reach that is several hundred feet in length, until it 

reached the start of the springs, at an altitude of 600 ft. 

These springs discharge into the stream over a reach of 

several tens of feet and discharge measurements were 

made downstream from this reach to insure that the total 

gain in flow was measured. 

During all three seepage runs, discharge measurements were made on Honokohau Stream at sites 4.0 and 

5.0, just upstream and downstream of the inflow from 

the Taro Gate release (fig. 4). The difference between 

these measurements can be used to quantify how much 

water was being released into Honokohau Stream. During the three runs, computed Taro Gate releases were 

1.67, 1.42, and 1.30 ft3

/s, respectively, and averaged 

1.46 ft3

/s. In only one instance was the computed 

release equal to or greater than the targeted release of 

1.55 ft3

/s (1.0 Mgal/d). Flow releases at the Taro Gate 

are discussed in greater detail in a subsequent section of 

the report (Taro Gate Releases). During all three seepage runs, the stream reach extending from downstream 

of the Taro Gate (site 5.0) to just upstream of MacDonald’s Dam (site 5.9) gained water (table 7). The 

magnitude of the gain ranged from 0.42 to 0.56 ft3

/s and 

averaged 0.49 ft3

/s. No flow is released in the reach of 

channel between sites 5.0 and 5.9 and the gains in flow 

are ground-water discharges into the stream. This is 

contrary to prior findings, which indicate that no natural 

increases in streamflow took place downstream from 

the springs near 600 ft (Hawaii Department of Land and 

Natural Resources, 1977, p. v). 

During the two seepage runs made in 1997, discharge measurements were made at sites 5.9 and 6.1 just 

upstream and downstream of MacDonald’s Dam (fig. 

4). Using these measurements the diversion at the dam 

was computed to be 0.89 and 1.00 ft3

/s during the seepage runs. During all three seepage runs the hydropower 

diversion at MacDonald’s Dam appeared to be operating at its maximum capacity, releasing 0.46 ft3

/s (0.3 

Mgal/d) into the diversion ditch just downstream from 

the dam. Downstream from MacDonald’s Dam through 

site 6.2 (altitude 310 ft) several return flows were noted, 

however they were not sufficient to account for all the 

water diverted at the dam plus the hydropower plant 

flow release. The returns of diverted water in this section of stream were diffuse and could not be accurately 

measured. The stream reach between sites 6.2 and 7.1 

contained no identified return flows or diversions. During the August 13, 1997 seepage run, a loss of base flow 

totaling 0.20 ft3

/s was measured in this 2,480-ft reach. 
20 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

a

 Site numbers correspond to sites listed in table 2 and shown in figure 4 (sites 0.2 and 0.4 not shown in figure 4; see remarks in table 2

for locations) b Daily mean discharge at gaging station 16620000 on day of seepage run c

 Data based on daily mean discharge at station 16620000 and estimated discharge from development tunnels T-21 and T-22 d

 Estimated leakage through the Honokohau Ditch diversion dam 

Figure 9. Discharge on Honokohau Stream, Maui, during three seepage runs.

Table 7. Discharge during seepage runs on Honokohau Stream, Maui

[ft3/s, cubic feet per second; --, no data available]

Site 

numbera

Altitude

(feet)

Distance upstream 

from mouth

(feet)

Discharge

(ft3/s)

09/14/95 08/13/97 10/23/97

16620000 870 25,150 16b 19b 17b

0.2 830 23,950 21c 25c 21c

0.4 820 23,850 0.1d 0.1d 0.1d

1.0 625 19,950 0 0 0

2.0 600 18,950 0 0 0

3.0 560 18,650 1.29 -- --

3.1 540 18,150 -- 1.95 --

4.0 410 14,300 1.53 1.64 1.89

5.0 380 13,600 3.20 3.06 3.19

5.9 350 12,950 3.76 3.54 3.61

6.1 330 12,400 -- 2.65 2.61

6.2 310 11,600 -- 3.26 3.04

7.0 235 9,980 3.96 -- --

7.1 200 9,120 -- 3.06 --

7.6 180 7,800 -- 3.70 3.12

7.9 100 5,050 -- 2.76 2.50

8.0 80 4,500 1.05 1.25 1.81

9.1 5 40 1.63 1.75 1.81

5

0

10

15

20

25

30

1000 900 800 700 600 500 400 300 200 100 0

ALTITUDE, IN FEET

DISCHARGE, IN CUBIC FEET PER SECOND

SEPTEMBER 14, 1995

AUGUST 13, 1997

OCTOBER 23, 1997
Base-Flow Availability and Distribution 21

During the same seepage run, a loss of base flow 

totaling 0.94 ft3

/s was measured in the 2,750-ft reach 

between sites 7.6 and 7.9, another reach where no return 

flows or diversions were identified. This loss rate is 

greater than that measured upstream although no reasons to directly account for it, such as differences in 

streambed material, were identified. These data provide 

a range of possible rates at which base flow infiltrates 

through the bed of Honokohau Stream to the underlying 

ground-water body in losing reaches, downstream from 

MacDonald’s Dam. 

During the two seepage runs made in 1997, discharge measurements were made at sites 7.9 and 8.0 just 

upstream and downstream of Chun’s Dam (fig. 4). 

Using these measurements, the diversion at the dam was 

computed to be 1.51 and 0.69 ft3

/s during the seepage 

runs. Diversions at Chun’s Dam are not as consistent as 

those upstream at MacDonald’s Dam because of the 

variable nature of losses both through and over the dam. 

In the reach downstream from the dam several return 

flows were noted, however they were not sufficient to 

account for all the water diverted at Chun’s Dam.

During the three seepage runs, the stream reach 

between MacDonald’s Dam and the ocean loses water, 

although these losses are not of a magnitude that is sufficient to totally dry the stream. Total loss in streamflow 

can be computed as the discharge at site 5.9, plus the 

hydropower plant discharge of 0.46 ft3

/s, minus the discharge at site 9.1. Computed losses during the seepage 

runs were 2.59 ft3

/s (September 14, 1995), 2.25 ft3/s 

(August 13, 1997), and 2.26 ft3

/s (October 23, 1997) 

and the average loss was 2.37 ft3

/s. Base-flow losses in 

Honokohau Stream can be attributed primarily to infiltration through the streambed. Although losses due to 

consumptive use of water that was diverted at MacDonald’s Dam and Chun’s Dam could not be measured 

directly, they can be assumed to be secondary. Penn 

(1997, p. 83–86) indicated that consumptive use of 

water in Hawaiian taro fields ranged from 0.06 to 0.19 

ft3

/s per acre (0.04 to 0.12 Mgal/d per acre). Using the 

value of 3.13 acres as the amount of taro being irrigated 

in lower Honokohau Valley (Bill Rozeboom, Hawaii 

Commission on Water Resource Management, written 

commun., 1992), a range of possible consumptive water 

use can be estimated as 0.20 to 0.59 ft3

/s (0.13 to 0.38 

Mgal/d). The range of possible consumptive water use 

would therefore equal 8 to 25 percent of the average loss 

of 2.37 ft3

/s measured during the three seepage runs.

Water-temperature and specific-conductance measurements were made during the three seepage runs 

(tables 8 and 9). Variations in water-temperature and 

specific-conductance data for the August 13, 1997 seepage run are shown graphically in figures 10 and 11. 

Water temperatures at site 16620000 and site 3.1 are 

lower than temperatures at other locations along the 

stream reach, indicating the water originates from a 

colder source such as ground-water inflow. A previous 

measure of water temperature at the springs at 600 ft 

(Hawaii Department of Land and Natural Resources, 

1977, p. 30) was 18.9°C (66°F) and this agrees with 

results from this study. Water temperatures gradually 

increase as water flows downstream from the springs at 

600 ft. This gradual increase indicates that little or no 

colder ground-water inflow is taking place along this 

reach of stream. 

Specific-conductance values drop sharply between 

sites 4.0 and 5.0 (fig. 4). This drop is in response to the 

dilution effect associated with the inflow of lower conductivity water from the Taro Gate release between 

these sites. Water released from the Taro Gate would 

have characteristics similar to the water at gaging station 16620000. There is also a small drop in specificconductance values downstream from MacDonald’s 

Dam. This would be attributed to the dilution effect 

associated with the release of water from the hydropower plant. Hydropower plant releases come from the 

Honokohau Ditch and would also have characteristics 

similar to water at gaging station 16620000. Specificconductance values increase slightly near the coast and 

this would most likely be the result of saltwater sprays 

affecting conductivity readings at site 9.1, which is a 

short distance upstream from the ocean. 

Effect of Honokohau Ditch Diversion

The intake of Honokohau Ditch is located at an 

altitude of 825 ft and was constructed to divert essentially all of the base flow in Honokohau Stream. While 

the capacity of the ditch and intake has varied over the 

years (Wilcox, 1996), the current capacity at the intake 

on Honokohau Stream is estimated to be about 93 to 101 

ft3

/s (60 to 65 Mgal/d) (Wesley Nohara, Maui Land and 

Pineapple Company, Inc., oral commun., 2002). To 

evaluate the effect of the Honokohau Ditch diversion on 
22 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

a

 Site numbers correspond to sites listed in table 2 and shown in figure 4 (sites 0.2 and 0.4 not shown in figure 4; see remarks in table 2 

for locations)

a

 Site numbers correspond to sites listed in table 2 and shown in figure 4 (sites 0.2 and 0.4 not shown in figure 4; see remarks in table 2 

for locations)

Table 8. Stream temperature during seepage runs on Honokohau Stream, Maui

[--, no data available]

Site numbera

Altitude

(feet)

Distance upstream 

from mouth

(feet)

Stream temperature

(degrees Celsius)

09/14/95 08/13/97 10/23/97

16620000 870 25,150 -- 19.5 --

0.2 830 23,950 -- -- --

0.4 820 23,850 -- -- --

1.0 625 19,950 -- -- --

2.0 600 18,950 -- -- --

3.0 560 18,650 19.0 -- --

3.1 540 18,150 -- 19.5 --

4.0 410 14,300 20.0 21.0 20.5

5.0 380 13,600 20.5 21.0 20.5

5.9 350 12,950 21.5 21.0 21.5

6.1 330 12,400 -- 21.5 21.5

6.2 310 11,600 -- 21.5 22.0

7.0 235 9,980 21.0 -- --

7.1 200 9,120 -- 22.0 --

7.6 180 7,800 -- 22.0 22.0

7.9 100 5,050 -- 22.5 22.5

8.0 80 4,500 -- 22.0 23.0

9.1 5 40 25.0 24.5 24.5

Table 9. Specific conductance during seepage runs on Honokohau Stream, Maui

[--, no data available]

Site numbera

Altitude

(feet)

Distance upstream 

from mouth

(feet)

Specific conductance

(microsiemens per centimeter)

09/14/95 08/13/97 10/23/97

16620000 870 25,150 -- 68 --

0.2 830 23,950 -- -- --

0.4 820 23,850 -- -- --

1.0 625 19,950 -- -- --

2.0 600 18,950 -- -- --

3.0 560 18,650 -- -- --

3.1 540 18,150 -- 111 --

4.0 410 14,300 -- 114 120

5.0 380 13,600 -- 88 95

5.9 350 12,950 -- 92 95

6.1 330 12,400 -- 92 95

6.2 310 11,600 -- 90 92

7.0 235 9,980 -- -- --

7.1 200 9,120 -- 90 --

7.6 180 7,800 -- 90 94

7.9 100 5,050 -- 90 94

8.0 80 4,500 -- 92 95

9.1 5 40 -- 101 111
Base-Flow Availability and Distribution 23

Figure 10. Stream temperature on Honokohau Stream, Maui, during August 13, 1997 seepage run.

Figure 11. Specific conductance on Honokohau Stream, Maui, during August 13, 1997 seepage run.

15

16

17

18

19

20

21

22

23

24

25

600 500 400 300 200 100 0

ALTITUDE, IN FEET

TEMPERATURE, IN DEGREES CELSIUS 

40

60

80

100

120

140

600 500 400 300 200 100 0

ALTITUDE, IN FEET

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER
24 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

Honokohau Stream, estimates of long-term streamflow 

data upstream and downstream of the diversion intake 

are needed. In the stream reach between station 

16620000 and the diversion dam, significant inflow 

from development tunnels T-21 and T-22 enters 

Honokohau Stream. Inflow from the tunnels needs to be 

computed to provide estimates of long-term streamflow 

data upstream from the diversion.

ML&P gaged the outflow from development tunnels T-21 and T-22 for several years. However, the data 

have not been published, are of unknown accuracy, and 

are not stored in electronic format. Yamanaga and 

Huxel (1969, p. 30) indicated that for the period 1926–

41 the combined daily flow from development tunnels 

T-21 (1.81 Mgal/d) and T-22 (2.25 Mgal/d) was 6.28 

ft3

/s (4.06 Mgal/d) based on ML&P data. Mink (1990) 

used data for the tunnels, which was assumed to be from 

ML&P, for the period 1926–54 to compute an average 

discharge of 2.82 ft3

/s (1.82 Mgal/d) for tunnel T-21. 

Although ranges for minimum and maximum discharges for tunnel T-22 are computed by Mink (1990), 

no average discharge was given. The data given in 

Yamanaga and Huxel (1969, p. 30) are inconsistent with 

other sources (Mink, 1990; Stearns and Macdonald, 

1942) and appear to have the relative contributions of 

tunnels T-21 and T-22 reversed (results given above are 

revised to account for this assumed error). This assumption appears to be correct as the average discharges, 

cited above for tunnel T-21, are now essentially the 

same. Stearns and Macdonald (1942, p. 213) indicated 

that the combined discharge from the two tunnels was 

5.9 ft3

/s (3.75 Mgal/d) although this estimate was based 

on a single set of discharge measurements made by the 

USGS on January 24, 1924 (table 6).

The analyses summarized in the previous paragraph provide valuable background information; however, they are not directly compatible with data analyzed as part of this report. The available data are not in 

electronic format as a time series of daily discharges 

and are available for a much shorter period of time than 

data from gaging station 16620000. The importance of 

using long-term data is highlighted by the fact that average discharge for the period 1926–41, the period used 

by Yamanaga and Huxel (1969) in their analysis, at station 16620000 was 42.6 ft3

/s. This value is 9.0 percent 

greater than the average discharge computed for 82 

water years between 1913–2000 of 39.1 ft3

/s.

To account for limitations in available data it was 

decided to estimate a time series of daily discharge representing the combined discharge of development tunnels T-21 and T-22 into Honokohau Stream. In an 

earlier section of this report, estimates of the base-flow 

component of the total discharge at station 16620000 

were summarized (fig. 7 and table 1). Base flow at the 

gaging station comes primarily from high-level dikeimpounded ground water in the Wailuku Basalt. Discharge from the development tunnels is also primarily 

base flow from a comparable source. It is therefore reasonable to assume that some direct correlation between 

base flows at station 16620000 and development tunnels T-21 and T-22 exists. The only USGS data available to assess this correlation are discharge measurements of tunnel discharge made on January 24, 1924 

(table 6). On January 24, 1924, the daily mean discharge 

at station 16620000 was 20 ft3

/s, and all of this discharge was estimated to be base flow. The ratio of measured discharge from the tunnels to base flow at station 

16620000 on January 24, 1924 was multiplied by the 

time series of daily base flows at station 16620000 to 

generate a time series of tunnel discharges for the period 

of available data from 1913–2000. 

Comparisons with previously published tunnel discharge data were made to test the reasonableness of the 

estimated time series. As noted above, Yamanaga and 

Huxel (1969, p. 30) reported an average discharge from 

the tunnels for the period 1926–41 as 6.28 ft3

/s. Using 

the time series estimated for the current study, an average discharge for the same period was computed to be 

6.01 ft3

/s, a value that is within 4.4 percent of 6.28 ft3/s. 

Data presented by Mink (1990) indicate that the minimum discharge for the period 1926–54, from the two 

tunnels combined, was about 3.2 ft3

/s. Using the time 

series estimated for this study, a minimum discharge for 

the same time period was computed to be 2.8 ft3

/s. 

Although the time series computed for combined 

development-tunnel discharges can only be considered 

an estimate with unknown accuracy, the above comparisons indicate that the estimates are reasonable. 

The estimated time series of tunnel discharges 

were then combined with the daily-discharge time 

series from station 16620000 to provide estimates of 

daily discharges for the period 1913–2000 upstream 

from the Honokohau Ditch intake. Flow-duration data 

for estimated development tunnel discharges and total 

discharge of Honokohau Stream, upstream from the 
Base-Flow Availability and Distribution 25

diversion, are presented in table 10 and figure 12. Discharges from the development tunnels provide a significant portion of total base-flow discharge of Honokohau 

Stream, upstream from the diversion. For example, 

addition of development tunnel inflow increases the 

median, or 50th percentile, discharge of Honokohau 

Stream from 24 ft3

/s at gaging station 16620000 to 30 

ft3

/s upstream from the diversion (table 10), an increase 

of 25 percent. When viewing flow-duration data, such 

as that presented in table 10, it is important to understand that results for a given flow-duration percentile at 

two sites cannot be directly combined. To compute the 

flow-duration curve for total discharge upstream from 

the diversion, first, flow data must be combined from 

station 16620000 and the development tunnels for each 

individual day, and then, a flow-duration curve is computed based on the new time series. This is why direct 

combination of individual flow-duration discharges for 

station 16620000 and the development tunnels do not 

always exactly equal those presented for total discharge 

upstream from the diversion in table 10.

To determine the effect of Honokohau Ditch diversions on streamflow, a maximum capacity of the intake 

on Honokohau Stream (at an altitude of 825 ft) of 93 

ft3

/s (60 Mgal/d) was used. Although this value is at the 

low end of the estimated range provided by ML&P it 

was deemed to be the most reasonable value. Actual 

diversions tend to be lower than computed ditch capacities because of factors such as accumulation of debris 

on intake trash racks and deposits of sediment and 

aquatic growth in the ditch itself. These and other naturally occurring processes all tend to reduce magnitudes 

of streamflow diversions. Estimated daily discharges 

for the period 1913–2000, upstream from the diversion, 

were all reduced by a value equal to the lesser of the 

daily discharge upstream from the diversion and the 

assumed ditch capacity of 93 ft3

/s (60 Mgal/d). For all 

days a minimum leakage through the dam of 0.1 ft3

/s, 

based on leakage observed during the seepage runs 

(table 7), was assumed. The result of this analysis is a 

time series of estimated daily discharges for Honokohau 

Stream downstream from the diversion at an altitude of 

825 ft. A time series for the period 1913–2000 of estimated daily discharges for Honokohau Ditch just downstream from the intake on Honokohau Stream, was 

estimated as the daily discharge upstream from the 

diversion less the daily discharge downstream from the 

diversion. This is an estimate of what the time series 

would have been if a consistent pattern of ditch capacity 

and diversion dam leakage, as assumed in the analysis, 

existed over the entire period of time.

To test the accuracy of the method used to assess 

the effect of ditch diversions, the average discharge, 

based on the estimated time series of discharge diverted 

by the ditch, was computed. Average ditch discharge 

was found to be 38.3 ft3

/s (24.7 Mgal/d) (table 11). This 

result compares favorably (within 2.9 percent) with the 

published value given for average ditch discharge of 

37.2 ft3

/s (24 Mgal/d) (Hawaii Commission on Water 

Resource Management, 1990, 1992). Average ditch discharge computed from the estimated time series was not 

expected to exactly replicate the value cited in the literature because the two values were not based on the same 

period of record and the published value is rounded off 

to the nearest million gallons. Also, no basis for the 

value of average ditch discharge cited in the literature is 

provided. Therefore it is assumed that the method used 

to estimate ditch diversions and Honokohau Stream discharges downstream from the diversion provides data 

values that are reasonable. The estimated time series of 

ditch flow data can be also used to compute the median 

flow in the ditch, which is 29.4 ft3

/s (19.0 Mgal/d). In 

most cases median flow is a more representative measure of typical flow magnitudes than average flow.

A flow-duration curve for Honokohau Stream, 

downstream from the ditch diversion, based on the estimated time series of daily discharges for the period 

1913–2000 was computed and is summarized in table 

10 and figure 12. Although average discharge for 

Honokohau Stream downstream from the ditch diversion is computed to be 6.3 ft3

/s, this number does not 

accurately describe the situation there. The flowduration curve (fig. 12) provides a simple method for 

quantifying the hydrologic effect of the ditch diversion. 

Using this analysis it can be estimated that for 91.2 percent of the days, flow in Honokohau Stream immediately downstream from the diversion is limited to the 

minor amount of leakage which takes place through the 

dam. In this analysis the volume of leakage was 

assumed to equal 0.1 ft3

/s based on observations made 

during three seepage runs (table 7). Streamflow of consequence exists downstream from the diversion dam 

only during 8.8 percent of all days and then only when 

significant surface-runoff events are ongoing. An alternate way to evaluate the hydrologic effect of the ditch 

diversion is through computation of average and minimum daily discharges (table 11). Average discharge 
26 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

a

 Based on the estimated time series for 82 complete water years of record from 1913–2000; daily estimates based on ratio of development 

tunnel discharge measured by the USGS on January 24, 1924 (5.9 ft3/s) to concurrent base flow at gage 16620000 (20 ft3/s) multiplied by daily 

estimates of base flow at gage 16620000

b

 Based on the estimated time series for 82 complete water years of record from 1913–2000; daily estimates equal the sum of the daily 

discharge at gage 16620000 plus the estimated daily discharge for the two development tunnels T-21 and T-22 c

 Based on estimated time series for 82 complete water years of record from 1913–2000; daily estimates based on estimated daily discharges 

upstream from the diversion minus 93 ft3/s (60 Mgal/d), the maximum diversion capacity of the ditch intake, plus an estimated 

0.1 ft3/s of leakage through the diversion dam

a Based on estimated daily discharges for period 1913–2000 computed as part of study

Table 10. Selected flow-duration discharges at gaging station 16620000 and estimates of development tunnel discharge and discharges 

upstream and downstream from the Honokohau Ditch diversion at altitude 825 feet, water years 1913–2000, Honokohau Stream, Maui

[ft3/s, cubic feet per second]

Percentage of time 

indicated discharge 

equaled or exceeded

USGS station 

16620000 discharge

(ft3

/s)

Total discharge from 

development tunnels 

T-21 and T-22a

(ft3

/s)

Total discharge 

upstream from diversion

at site 0.2b

(ft3/s)

Total discharge 

downstream from diversion

at site 0.4c 

(ft3/s)

99 10 2.8 13 0.1

95 12 3.2 15 0.1

90 13 3.5 17 0.1

80 16 4.0 20 0.1

70 18 4.4 23 0.1

60 21 4.8 26 0.1

50 24 5.2 30 0.1

40 28 5.6 34 0.1

30 35 6.1 41 0.1

20 48 6.9 55 0.1

10 79 7.9 86 0.1

5 118 9.0 126 32.8

1 246 12 252 160

Table 11. Average, median, and minimum daily discharges for selected locations in the vicinity of the Honokohau

Ditch diversion at altitude 825 feet, water years 1913–2000, Honokohau Stream, Maui

[ft3/s, cubic feet per second]

Site locations

Average discharge

(ft3/s)

Median discharge

(ft3/s)

Minimum daily 

discharge

(ft3/s)

USGS gaging station 16620000 39.1 24 8.4

Development tunnels T-21 and T-22a (total) 5.6 5.2 2.5

Upstream of diversion dam at site 0.2a 44.6 30 11

Downstream of diversion dam at site 0.4a 6.3 0.1 0.1

Honokohau Ditch just below intakea 38.3 29 11
Base-Flow Availability and Distribution 27

data can serve as a surrogate for total discharge and in 

this case average flow diverted in the Honokohau Ditch 

is 38.3 ft3

/s or 86 percent of the total flow of 44.6 ft3/s 

upstream from the diversion. Minimum daily discharge 

in the diversion ditch is 11 ft3

/s and only 0.1 ft3/s in the 

stream downstream from the diversion. Using most any 

measure, diversion of streamflow from Honokohau 

Stream at the ditch intake, located at an altitude of 825 

ft, significantly alters the pattern of streamflow downstream from that location.

Taro Gate Releases

An important source of sustained base flow in 

lower reaches of Honokohau Stream, downstream from 

the springs at altitude 600 ft, are flow releases at the 

Taro Gate. During periods of base flow in the lower 

reaches of Honokohau Stream, flow releases at the Taro 

Gate are base flows, or ground-water-derived flows that 

were diverted from Honokohau Stream at an altitude of 

825 ft by the Honokohau Ditch. ML&P currently targets 

a constant release of 1.55 ft3

/s (1.0 Mgal/d) from the 

Honokohau Ditch into the stream at an altitude of about 

405 ft through the Taro Gate. For example, during the 

three seepage runs (table 7) Taro Gate releases 

increased the base flow downstream from site 4.0 by 69 

to 109 percent. Flow releases from the Taro Gate during 

the three seepage runs were 1.67, 1.42, and 1.30 ft3

/s 

respectively, computed as the difference between measurements made at sites 4.0 and 5.0 (table 7). The availability of a constant release of 1.55 ft3

/s at the Taro Gate 

would have the greatest effect during periods of extreme 

low flows in Honokohau Stream. Using flow-duration 

data summarized for site 4.0 in table 5 it can be seen that 

at 95 and 90 percentile flow-duration discharges, constant inflow of 1.55 ft3

/s would increase base flow 

downstream from site 4.0 by 201 and 168 percent.

The availability of base flow in lower Honokohau 

Stream is therefore highly influenced and dependent on 

release of ditch water at the Taro Gate. As noted above, 

Taro Gate releases can be computed on the three days 

when seepage runs were conducted. During these seepage runs, discharge measurements were made just 

upstream and downstream of the flow release point. 

Flow releases from the Taro Gate can also be estimated 

at times when low-flow measurements at sites 4.0 and 

Figure 12. Flow-duration curves for estimates of daily discharges upstream and downstream of the Honokohau 

Ditch diversion at altitude 825 feet, water years 1913–2000, Honokohau Stream, Maui.

PERCENTAGE OF TIME INDICATED DISCHARGE WAS EQUAL OR EXCEEDED

0.01 0.05 0.1 0.2 0.5 1 2 5 10 20 30 50 70 80 90 95 98 99 99.8 99.9 99.95 99.99

DAILY MEAN DISCHARGE, IN CUBIC FEET PER SECOND

0.1

1

10

100

1000

TOTAL PLUS TUNNEL DISCHARGE

TOTAL PLUS TUNNEL DISCHARGE LESS 93 ft3

/s
28 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

5.9 (table 3) were made. To make these computations, 

estimates of discharge at site 5.0 are required for each 

day when discharge measurements were made at sites 

4.0 and 5.9. As noted in the analysis of seepage runs, the 

reach between sites 5.0 and 5.9 gained an average of 

0.49 ft3

/s from ground-water inflow during the three 

seepage runs. It can be expected that ground-water 

gains in this reach would be correlated to measured base 

flow at gaging station 16620000. To test this hypothesis, ratios of ground-water inflow between sites 5.0 and 

5.9 during the seepage runs to concurrent base flow at 

gaging station 16620000 were computed. The resultant 

ratios were 0.035, 0.025, and 0.028 with an average of 

0.029. The consistency of these ratios indicate that reasonable estimates of ground-water inflow for this reach 

can be made by multiplying the ratio 0.029 by the base 

flow at station 16620000. This computation was made 

for each day that low-flow partial-record measurements 

were made at sites 4.0 and 5.9. Estimates of discharge at 

site 5.0 on these days can be made by subtracting estimated ground-water inflow between sites 5.0 and 5.9 

from measured discharge at site 5.9. Flow releases from 

the Taro Gate can be computed as estimated discharges 

at site 5.0 minus measured discharges at site 4.0. The 

accuracy of the proposed method was tested using data 

from the three seepage runs. Estimated Taro Gate 

releases were within +6.0, -4.9, and -1.5 percent of the 

results computed using measured discharges at site 5.0, 

indicating the suitability of the proposed method. The 

computations of Taro Gate releases are summarized in 

table 12 and a scatterplot of the computed Taro Gate 

flow releases compared with time are shown in figure 

13.

The data in figure 13 and table 12 indicate that 

Taro Gate flow releases from Honokohau Ditch into 

Honokohau Stream are inconsistent and are frequently 

less than the targeted release of 1.55 ft3

/s. For the ten 

days when Taro Gate releases were computed, results 

ranged from a high of 1.67 ft3

/s to a low of 0.14 ft3/s. 

The median flow release was 1.05 ft3

/s and computed 

releases were less than the targeted level on 9 of 10 days 

when measurements were made. ML&P attributes the 

problem of maintaining consistent flow releases to periodic blockage of the Taro Gate by leaves and debris 

(Wesley Nohara, Maui Land and Pineapple Company, 

Inc., written commun., 1993). Blockages at the Taro 

Gate are currently scheduled to be removed by ML&P 

personnel during their routine month-end visits to the 

site (Wesley Nohara, Maui Land and Pineapple Company, Inc., oral commun., 2003).

In an earlier section of the report (Low-Flow 

Partial-Record Stations) it was noted that no estimates 

of flow-duration statistics would be made at site 5.9 

because the correlation coefficient between discharge 

measurements made there with daily mean discharges at 

station 16620000 was only 0.305. The variability of 

Taro Gate flow releases was likely the primary reason 

for this poor correlation. 

Extrapolation of Base-Flow Characteristics

Flow-duration discharges have been computed and 

summarized for gaging station 16620000 (table 1), for 

low-flow partial-record sites 4.0 and 9.1 (table 5), and 

for sites 0.2 and 0.4 located upstream and downstream 

of the Honokohau Ditch diversion (table 10). The purpose of this section of the report is to summarize these 

computations of base-flow characteristics and to use 

these and other data, such as the seepage run measurements (table 7), to extrapolate the results to other locations along the lower section of Honokohau Stream. 

Assuming current flow-diversion practices at 

Honokohau Ditch, at altitude 825 ft, (maximum of 93 

ft3

/s) and measured median-return-flow practices at the 

Taro Gate release (1.05 ft3

/s) and hydropower plant 

release (0.46 ft3

/s) are consistently followed, extrapolations of base-flow computations can be made at sites 

1.0, 2.0, 5.0, 5.9, 6.1, 7.6, 7.9, and 8.0 (table 2) using a 

variety of procedures. Flow-duration discharges for 

these sites as well as those for which results have been 

previously computed (tables 1, 5, and 10) are summarized in table 13. 

During base-flow conditions observed in the field 

primarily during seepage runs (table 7), there was no 

flow observed at sites 1.0 and 2.0. It is reasonable to 

assume that no-flow conditions will exist at these sites 

over the range of flow-durations summarized in table 

13. Flow-duration estimates can be made at site 5.0 by 

adding the measured median-flow release from the Taro 

Gate (1.05 ft3

/s) to site 4.0 flow-duration estimates. 

Flow-duration estimates for a single site can be manipulated directly when the adjustments made would be 

consistent (such as adding 1.05 ft3

/s of inflow) over the 

range of time and discharge being considered. Flowduration estimates can be made at site 5.9 by adding 

estimates of ground-water inflow in the reach between 

sites 5.0 and 5.9 to flow-duration estimates made for 

site 5.0. As noted in an earlier section of the report (Taro 

Gate Releases) the inflow can be estimated by multiplying 0.029 times corresponding base flow at station 

16620000.
Base-Flow Availability and Distribution 29

a

 Estimated ground-water inflow computed using the average ratio of measured ground-water inflow to base flow at station 16620000 determined for the

first three pairs of measurements at sites 5.0 and 5.9 shown above; ground-water inflow equals 0.029 times base flow at station 16620000 for the day b

 Taro Gate release determined as measured or estimated discharges at site 5.0 minus measured discharges at site 4.0 c

 Estimated discharge at site 5.0 computed as measured discharge at site 5.9 minus estimated ground-water inflow between sites 5.0 and 5.9 

Figure 13. Scatterplot of computed Taro Gate flow releases from Honokohau Ditch into 

Honokohau Stream at altitude 405 feet, Maui.

Table 12. Computed Taro Gate flow releases from Honokohau Ditch into Honokohau Stream at altitude of 405 feet, Maui

[Values in cubic feet per second]

Date

Measured discharge Estimated ground-water 

inflow between 

sites 5.0 and 5.9a

Computed Taro 

Gate releaseb Site 4.0 Site 5.0 Site 5.9

09/14/95 1.53 3.20 3.76 0.46 1.67

08/13/97 1.64 3.06 3.54 0.55 1.42

10/23/97 1.89 3.19 3.61 0.44 1.30

06/29/99 2.74 3.43c 3.92 0.49 0.69

10/27/99 2.92 4.06c 4.52 0.46 1.14

03/17/00 1.22 2.57c 3.01 0.44 1.35

05/24/00 1.55 2.51c 2.92 0.41 0.96

07/11/00 2.16 2.77c 3.15 0.38 0.61

08/25/00 2.29 2.43c 3.01 0.58 0.14

12/19/00 1.18 1.39c 1.85 0.46 0.21

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

1995 1996 1996 1997 1998 1999 2000 2001

DATE

TARO GATE FLOW RELEASE, IN CUBIC FEET PER SECOND

1.55 ft3/s--target release level
30 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

Flow-duration estimates can be made at site 6.1, 

downstream from MacDonald’s Dam, by subtracting 

the diversion at the dam from estimates for site 5.9. For 

the purposes of this work, diversion at the dam was 

assumed to be the maximum value of 1.00 ft3

/s 

observed during seepage runs (table 7). Flow-duration 

estimates at sites 7.6 and 7.9 were based on average percentages of flow losses between site 5.9 (plus the hydropower plant release of 0.46 ft3

/s) and the site (either site 

7.6 or 7.9) to total flow losses in the losing reach of 

Honokohau Stream (site 5.9 to 9.1). The percentages 

were computed using data from the two 1997 seepage 

runs (table 7) which indicated that on average, 28 percent of total losses between sites 5.9 and 9.1, takes place 

between sites 5.9 and 7.6, and 62 percent of total losses 

takes place between sites 5.9 and 7.9. Flow-duration 

estimates can be made at site 8.0, downstream from 

Chun’s Dam, by subtracting diversion at the dam from 

estimates for site 7.9. For purposes of this report, diversion at the dam was assumed to be the lesser of the flowduration estimate at site 7.9 (upstream from Chun’s 

Dam) less losses through and over the dam and the maximum diversion value of 1.51 ft3

/s observed during 

seepage runs (table 7). Losses through and over Chun’s 

Dam are variable and not easily controlled; therefore, 

minimum losses at the dam were assumed to equal 25 

percent of flow upstream from the dam at site 7.9.

Computations or estimates of flow-duration flows 

could not be made at a number of data sites used in this 

study (table 2). This was primarily attributed to variable 

ways by which flows diverted at MacDonald’s and 

Chun’s Dams were returned to the stream. Sites where 

flow-duration data could be computed provide a reasonable characterization of the distribution and availability 

of base flow in lower Honokohau Stream. In figure 14, 

flow-duration discharges for the 50th and 90th percentiles are plotted along with results from the August 13, 

1997 seepage run to illustrate the extent to which base 

flows can be characterized in lower Honokohau Stream. 

The variation of 95th percentile flow-duration discharges are also shown on the map in figure 15. A 

previous estimate indicated that at least 2.32 ft3/s

a

 Current practices include flow diversions up to 93 ft3/s at the Honokohau Ditch, and return-flow releases of 1.05 ft3/s at Taro Gate and 0.46 ft3/s at 

hydropower plant

b

 Site numbers correspond to sites listed in table 2 and shown in figure 4 (sites 0.2 and 0.4 not shown in figure 4; see remarks in table 2 for locations) c

 See table 1

d

 See table 10

e

 Discharge estimates based on field observations during seepage runs

f See table 5

g

 Discharge estimates based on site 4.0 data plus measured median-flow Taro Gate release of 1.05 ft3/s h

 Discharge estimates based on site 5.0 data plus estimated ground-water inflow in reach, see report section “Taro Gate Releases” i

 Discharge estimates based on upstream site data minus maximum diversion observed during seepage runs of 1.00 ft3/s at MacDonald’s Dam and 1.51 ft3/s at 

Chun’s Dam plus a minimum leakage of 0.10 ft3

/s at MacDonald’s Dam and 25 percent of discharge at Chun’s Dam

j Discharge estimates based on average percentage of total loss between sites 5.9 and 9.1; percentages based on average for two 1997 seepage runs

Table 13. Computed flow-duration discharges for selected locations on lower Honokohau Stream, Maui, under currenta diversion and

return-flow practices

Site numberb

Discharge equaled or exceeded indicated percentages of time

(cubic feet per second)

95 percent 90 percent 80 percent 70 percent 60 percent 50 percent

16620000c 12 13 16 18 21 24

0.2d 15 17 20 23 26 30

0.4d 0.1 0.1 0.1 0.1 0.1 0.1

1.0e 0 0 0 0 0 0

2.0e 0 0 0 0 0 0

4.0f 0.77 0.92 1.5 1.9 2.7 3.7

5.0g 1.8 2.0 2.5 3.0 3.8 4.7

5.9h 2.1 2.3 2.9 3.4 4.3 5.2

6.1i 1.1 1.3 1.9 2.4 3.3 4.2

7.6j 2.0 2.2 2.9 3.4 4.4 5.6

7.9j 1.4 1.6 2.2 2.9 4.0 5.6

8.0i 0.34 0.39 0.74 1.3 2.5 4.1

9.1f 0.63 0.80 1.5 2.2 3.6 5.5
Base-Flow Availability and Distribution 31

(1.5 Mgal/d) of base flow was available to meet water 

needs in lower Honokohau Stream (Hawaii Department 

of Land and Natural Resources, 1977, p. iv). Estimates 

from ML&P (Wesley Nohara, Maui Land and Pineapple Company, Inc., written commun., 1993) indicate 

that available base flow is in excess of 4.6 ft3

/s (3.0 

Mgal/d). Results in table 13 refine these estimates and 

indicate that base flows of 2.32 ft3

/s are available more 

than 95 percent of the time at MacDonald’s Dam (site 

5.9 plus the hydropower plant release) while flows in 

excess of 4.6 ft3

/s could be expected 65 percent of the 

time. Base flows of 2.32 and 4.6 ft3

/s are available 80 

and 56 percent of the time, respectively, at Chun’s Dam 

(site 7.9).

 Reductions in base flow are summarized in table 

14, both as absolute values and in terms of percentage 

for the entire losing reach of Honokohau Stream 

between MacDonald’s Dam and the ocean. Reductions 

in base flow include the losses associated with consumptive uses and infiltration through the streambed to 

the ground-water system. Base-flow losses are reduced 

by the volumes of diverted flows that are returned to the 

stream. Base-flow losses decrease with increasing discharges both in terms of absolute values and percentages. For example, between the 95th and 50th percentile 

flows, the percentage of flow losses decreases from 77 

to 4 percent. Some possible explanations for this process are (1) during higher flow conditions there is less 

need for irrigation water so that consumptive use of 

diverted water in the losing stream reach is lower, (2) 

during higher flow conditions, the freshwater lens is 

higher and as a result there is less seepage loss through 

the streambed, and (3) during higher flow conditions, 

contributions of flow from surface runoff start to 

become more significant. At gaging station 16620000 

surface runoff starts becoming a factor at about the 70th 

percentile on the flow-duration curve (table 1 and fig. 7) 

and this is the percentile at which absolute base-flow 

losses in the losing reach start to drop (table 14).

It is instructive to summarize how much water 

would actually be available to support current taro cultivation practices in Honokohau Valley. In an earlier 

section of the report (Seepage Runs) it was noted that 

possible consumptive water use associated with current 

taro cultivation ranged from 0.20 to 0.59 ft3

/s. Given 

Figure 14. Discharge on Honokohau Stream, Maui, during August 13, 1997 seepage run and 

for selected flow-duration percentiles under current practices of 1.05 ft3

/s Taro Gate release 

and 0.46 ft3

/s hydropower plant release (ft3/s, cubic feet per second).

0

5

10

15

20

25

30

35

1000 900 800 700 600 500 400 300 200 100 0

ALTITUDE, IN FEET

DISCHARGE, IN CUBIC FEET PER SECOND 

AUGUST 1997 SEEPAGE RUN

90TH PERCENTILE DISCHARGE

50TH PERCENTILE DISCHARGE
32 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

.

Figure 15. Discharge on Honokohau Stream, Maui, for the 95th percentile flow duration under current practices of 1.05 ft3/s

Taro Gate release and 0.46 ft3/s hydropower plant release (geology from Stearns and Macdonald, 1942, and Langenheim 

and Clague, 1987).

400

UNCONSOLIDATED DEPOSITS, 

 CHIEFLY OLDER ALLUVIUM

HONOLUA VOLCANICS

WAILUKU BASALT

CONES AND DOMES OF 

 WAILUKU BASALT

CONES AND DOMES OF 

 HONOLUA VOLCANICS

BOUNDARY AND TRANSITIONAL 

 AREA BETWEEN DIKE-IMPOUNDED

 HIGH-LEVEL AND FRESH-WATER- 

 LENS GROUND WATER (from 

 Yamanaga and Huxel, 1969)

TOPOGRAPHIC CONTOUR 

 Interval 200 feet. Datum is 

 mean sea level

RANGE OF 95 PERCENTILE--Flow

duration discharge (in ft3/s, cubic feet 

per second)

 0 – 0.5 ft3/s

 0.5 – 1.0 ft3/s

 1.0 – 2.0 ft3/s

 less than 10.0 ft3/s

EXPLANATION

Honokohau 

Bay

PACIFIC OCEAN

200

400

600

800

400

600

800

400

1800

1800

2400

1600

1800

1400

1000

Honokohau Stream

0

0

1 MILE

1 KILOMETER

Base modified from U.S. Geological Survey

digital data, 1:24,000, 1983, Albers equal area 

projection, standard parallels 20°35' and 21°00', 

central meridian 156°20'

156°37' 156°36'

21°

20°59'

21°01'
Base-Flow Availability and Distribution 33

that most of this cultivation is supported by Chun’s 

Dam, it is useful to see how much water is currently 

available for diversion at that location. The difference in 

flow-duration discharges between site 7.9 and 8.0 in 

table 13 is a measure of the volume of water that can 

reasonably be diverted at Chun’s Dam. These values 

range from about 1.1 ft3

/s at the 95th percentile discharge to the assumed maximum diversion capacity of 

1.5 ft3

/s for all percentiles of 70 percent and lower. 

These data indicate that currently available discharges 

for all flow-duration percentiles of 95 percent or less at 

site 7.9 would be sufficient to meet the estimates of consumptive use using water diverted at Chun’s Dam. 

Water diversions in excess of the volume of consumptive use are required to support taro cultivation; however, little or no consensus seems to exist as to what 

amounts of diversion, and therefore inflows, to taro 

fields are adequate. The Hawaii Commission on Water 

Resource Management, in its Waiahole decision (2001, 

p. 61), indicated that inflow rates in excess of 1.55 ft3

/s 

(1 Mgal/d) per acre of taro cultivation have been documented, but that in Waiahole Valley, a maximum rate of 

0.06 ft3

/s (0.04 Mgal/d) per acre was established as sufficient. Current base-flow discharges in lower Honokohau Valley would be sufficient to meet the inflow 

requirements set in the Waiahole decision, but would 

not be sufficient to meet the upper range of documented 

inflow requirements for significant percentages of the 

time.

Base-Flow Water-Accounting Model

The results describing the availability and distribution of base flow in lower Honokohau Stream (primarily 

summarized in table 13) are based on continuation of 

current diversion and return-flow practices which 

include (1) diversions of flows up to 93 ft3

/s at the 

Honokohau Ditch at 825 ft, (2) median-flow releases of 

1.05 ft3

/s from the Taro Gate at an altitude of 405 ft, (3) 

flow releases of 0.46 ft3

/s from the hydropower plant 

near MacDonald’s Dam, (4) continued operation of 

MacDonald’s and Chun’s Dams in a manner that is consistent with that observed during the seepage runs, and 

(5) no major changes in the patterns of near-stream consumptive use of water in lower Honokohau Valley. 

Using the data collected as part of this study, a baseflow water-accounting model was developed using a 

spreadsheet to compute flow-duration discharges for 

the percentiles and sites summarized in table 13 in 

response to changes in several factors including flow 

releases at the Taro Gate and the hydropower plant and 

diversion practices at MacDonald’s and Chun’s Dams. 

When the established diversion and return-flow practices are changed in the spreadsheet then results shown 

in table 13 are automatically recomputed.

To demonstrate the utility of the base-flow wateraccounting spreadsheet, changes in flow-duration discharges at MacDonald’s and Chun’s Dams were

a

 Data from table 13 

b

 Site 5.9 data plus targeted release of 0.46 ft3/s from hydropower plant c

 Data from table 13

d

 Computed as site 5.9 flow plus hydropower release flow minus site 9.1 flow e

 Computed as ratio of total base flow loss to site 5.9 flow plus hydropower release flow in percent

Table 14. Reductions in base flow for selected flow-duration discharges in the losing reach of Honokohau Stream, Maui, between 

MacDonald’s Dam and the ocean

[ft3/s, cubic feet per second]

Computation

Results for indicated flow-duration percentiles

95 percent 90 percent 80 percent 70 percent 60 percent 50 percent

Site 5.9a (ft3/s) 2.1 2.3 2.9 3.4 4.3 5.2

Site 5.9 plus hydropower 

releaseb (ft3

/s)

2.6 2.8 3.4 3.9 4.7 5.7

Site 9.1c (ft3/s) 0.63 0.80 1.5 2.2 3.6 5.5

Total base flow lossd (ft3/s) 2.0 2.0 1.9 1.7 1.1 0.2

Total base flow losse (percent) 77 71 56 44 23 4
34 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

computed in response to a variety of flow-release rates 

from the Taro Gate. Honokohau Stream, between the 

Taro Gate release and MacDonald’s Dam, was shown to 

be a gaining reach (described in section Seepage Runs). 

As a result there will be a 1 to 1 relation between 

changes in release rates at the Taro Gate and base flow 

upstream from MacDonald’s Dam. For example, at site 

5.9 (upstream from MacDonald’s Dam) the 95 percent 

flow-duration discharge is 2.1 ft3

/s under the current 

release practice at the Taro Gate (1.05 ft3

/s). If the flow 

release at the Taro Gate was decreased or increased by 

0.5 ft3

/s, the 95 percent flow-duration discharge would 

change to 1.6 or 2.6 ft3

/s, respectively. A similar 1 to 1 

relation would be expected for other changes in release 

rates and for other flow-duration percentiles. These 

results were correctly reproduced by the model. 

The response of flow-duration discharges 

upstream from Chun’s Dam (site 7.9) to changes in Taro 

Gate release rates is more complicated and therefore the 

model results are summarized in table 15. Downstream 

from MacDonald’s Dam, the stream loses base flow and 

therefore a 1 to 1 relation does not exist between variations in Taro Gate releases and base flow at site 7.9. As 

noted in table 14, rates of base-flow loss decrease from 

lower discharges to higher discharges and a similar pattern is evident in the variation of base-flow discharges 

with changes in flow-release rates at the Taro Gate. For 

example, if the release rate at the Taro Gate were to 

decrease from 1.00 to 0.0 ft3

/s, the 95th percentile 

discharge would decrease by 0.5 ft3/s (50 percent of the 

change at the Taro Gate) while the 60th percentile discharge would decrease by 0.9 ft3

/s (90 percent of the 

change at the Taro Gate) (table 15). The reverse case 

also holds true in that release-rate increases of 1.00 ft3

/s 

at the Taro Gate results in flow increases at Chun’s Dam 

that are variable with flow-duration percentile and less 

than 1.00 ft3

/s. 

ACCURACY OF DATA AND BASE-FLOW 

ESTIMATES

Users of this report should be aware of the accuracy, and therefore possible limitations, associated with 

the data and base-flow estimates provided. Primary data 

and computations summarized in this report are discharge measurements, daily mean streamflow and 

selected summary statistics (at one continuous record 

station), flow-duration estimates (at two low-flow 

partial-record stations), computations of diversions and 

flow releases, and extrapolation of base-flow estimates 

to additional locations. The purpose of this section of 

the report is to provide, where possible, statistical measures of the accuracy associated with the data mentioned above.

Individual discharge measurements are summarized in this report for low-flow partial-record stations 

(table 3), historic miscellaneous sites (table 6) and 

a 1.05 ft3

/s is the measured median-flow release rate and flow-duration discharges for this release rate are from table 13 site number 7.9

Table 15. Variation in computed flow-duration discharges upstream from Chun’s Dam on Honokohau Stream, Maui, associated with variable 

flow-release rates at the Taro Gate

[ft3/s, cubic feet per second]

Taro Gate

release rate 

(ft3/s)

Discharge equaled or exceeded indicated percentages of time

(ft3/s)

95 percent 90 percent 80 percent 70 percent 60 percent 50 percent

0.0 0.82 0.97 1.5 2.1 3.1 4.5

0.25 0.95 1.1 1.7 2.3 3.3 4.8

0.5 1.1 1.2 1.9 2.4 3.6 5.0

0.75 1.2 1.4 2.0 2.6 3.8 5.3

1.00 1.3 1.5 2.2 2.8 4.0 5.5

1.05a 1.4 1.6 2.2 2.9 4.0 5.6

1.25 1.5 1.7 2.4 3.0 4.2 5.7

1.50 1.6 1.8 2.5 3.2 4.4 6.0

1.75 1.7 1.9 2.7 3.4 4.6 6.2

2.00 1.9 2.1 2.9 3.5 4.8 6.5

3.00 2.4 2.6 3.5 4.3 5.7 7.5
Accuracy of Data and Base-Flow Estimates 35

seepage runs (table 7). Sauer and Meyer (1992) and 

Rantz and others (1982) provide a summary of the wide 

variety of factors that can influence the accuracy of 

individual discharge measurements. On the basis of 

findings summarized in those studies, USGS personnel 

assign accuracy ratings to each discharge measurement 

made. Measurements made as part of this study were 

primarily rated either good or fair. Good and fair measurements are considered to be within 5 and 8 percent of 

the actual “true” discharge (Sauer and Meyer, 1992, 

p. 2). 

Daily mean discharge data from long-term streamflow-gaging station 16620000 on Honokohau Stream 

and statistical summaries of the data are provided in 

tables 1 and 13 (flow-duration curve), table 3 (daily 

mean discharges for selected days), table 11 (average, 

median, and minimum daily discharges), figure 5 

(annual means), and figure 6 (monthly flow statistics). 

Daily mean discharge data published by the USGS are 

divided into one of four accuracy classifications 

(Novak, 1985, p. 65). These accuracy classifications 

take into account a broad variety of factors but depend 

primarily on the stability of the stage-discharge rating 

and the frequency and accuracy of stage and discharge 

measurements at the station. The majority of the daily 

mean discharge data for station 16620000 are rated 

good, which means that 95 percent of the daily mean 

discharges are within 10 percent of the actual “true” 

discharge (Novak, 1985, p. 65). Development of flowduration curves and computations of average, median, 

and minimum daily discharges for selected periods of 

record do not introduce additional sources of error 

beyond those inherent in the daily mean discharges data 

used to make the computations. 

The computed daily flow statistics are accurate 

measures for the period of record over which they have 

been computed. The question is how accurately does the 

period of record represent long-term conditions and 

future hydrologic conditions for the watershed. In this 

case 82 water years of streamflow data were available 

for Honokohau Stream gaging station 16620000. These 

data can be considered an excellent representation of 

long-term conditions given the length of record, the 

good rating for the majority of the daily mean discharge 

data, and the fact that no significant trends were evident 

in the data. Care must be used when extrapolating computed streamflow characteristics into the future, as there 

is no assurance that the relative stability of hydrologic 

conditions observed over the past 82 water years will 

continue.

Selected base-flow flow-duration discharges were 

computed for low-flow partial-record stations at sites 

4.0 and 9.1 and summarized in tables 5 and 13. Unlike 

the flow-duration discharges computed for station 

16620000, these statistics were not based on long-term 

daily discharge data and will therefore have additional 

errors associated with them. These errors are a function 

of a variety of factors, the two most important being the 

strength of the correlation between the discharge measurements at the low-flow partial-record stations and 

the daily mean discharges at the index station and the 

number of discharge measurements made. Using methods first developed by Hardison and Moss (1972) and 

later refined by Ries and Friesz (2000, p. 12) the total 

variance associated with the computations of each of the 

flow-duration discharges can be computed. Standard 

errors in percent were then computed based on the total 

variance using equations developed by Stedinger and 

Thomas (1985, p. 18). Standard errors at a low-flow 

partial-record station will differ slightly with the flowduration statistic being computed. In this report, average standard errors for the computed flow-duration discharges were determined to be 21 and 34 percent for 

sites 4.0 and 9.1. These errors should be considered 

minimum errors as the methods used to compute them 

do not take into account the potential errors inherent in 

the discharge measurements made at the low-flow 

partial-record sites or the daily mean discharges at the 

index station. 

Computations of flow-duration discharges and 

flow statistics upstream and downstream of Honokohau 

Ditch are provided in tables 10 and 11, flow releases 

from the Taro Gate are summarized in table 12, and 

flow-duration discharges that are extrapolated to additional locations are summarized in tables 13 and 15. 

Methods to estimate the errors associated with these 

computations are not available. Where possible, surrogate measures of accuracy were included in the report to 

provide some estimate of possible errors. For example, 

the computed discharge from development tunnels T-21 

and T-22 (tables 10 and 11) was compared to estimates 

provided by Yamanaga and Huxel (1969) and Mink 

(1990) and computed diversion in the Honokohau Ditch 

was compared to estimates summarized by the Hawaii 

Commission on Water Resource Management (1990, 

1992). The extrapolated flow-duration discharges were 

based on less data than were available to compute 
36 Availability and Distribution of Base Flow in Lower Honokohau Stream, Island of Maui, Hawaii

comparable discharges at low-flow partial-record site 

4.0 and 9.1. Standard errors associated with the extrapolations would, as a minimum, be greater than the 34 

percent value computed for site 9.1.

SUMMARY AND CONCLUSIONS

Results summarized in this report provide a 

detailed evaluation of the availability and distribution of 

base flow in lower Honokohau Stream and quantify 

how the base flow is affected by streamflow diversions 

and return flows located in the valley. The geology of 

Honokohau Valley plays a significant role because most 

of the naturally occurring base flow in the stream is 

derived from high-level water impounded by dikes in 

the Wailuku Basalt. At the only long-term USGS 

streamflow-gaging station in the valley (station 

16620000), a flow-duration analysis indicated that a 

sustained and stable base flow, which equals or exceeds 

10 ft3

/s is available at least 99 percent of the time.

Significant volumes of base flow, several times 

greater than those found downstream from Honokohau 

Ditch, are found upstream from the ditch. During base 

flow conditions, most of the stream, between the ditch 

diversion and the springs at an altitude of 600 feet, is 

dry. Starting with the springs and as far downstream as 

MacDonald’s Dam, at an altitude of 340 feet, the stream 

gains from ground-water discharges. Downstream from 

MacDonald’s Dam to the ocean the stream loses water 

as infiltration through the streambed. 

The Honokohau Ditch diversion has a significant 

effect on the flow in Honokohau Stream. The average 

flow diverted from Honokohau Stream into the ditch is 

38.3 ft3

/s or 86 percent of the total flow upstream from 

the ditch intake. Downstream from the diversion dam 

there is no flow in the stream 91.2 percent of the time, 

except for the minor amount of leakage taking place 

through the dam. At the Taro Gate, flow is returned 

from Honokohau Ditch into Honokohau Stream at an 

altitude of 405 feet. The flow release at this location is 

targeted to be 1.55 ft3

/s. The magnitude of the actual 

flow release was computed on ten separate occasions 

and the median value was determined to be 1.05 ft3

/s. 

Flow releases at the Taro Gate were found to be inconsistent and computed releases were less than the targeted level on 9 of the 10 days on which measurements 

were made.

Using current diversion and return-flow practices 

which include (1) diversion of up to 93 ft3

/s at Honokohau Ditch, (2) combined flow releases of 1.51 ft3

/s at the 

Taro Gate and the hydropower plant, and (3) continued 

operation of flow diversions at MacDonald’s and 

Chun’s Dams, flow-duration discharges for percentiles 

ranging from 50 to 95 percent were made at 13 locations 

between altitudes of 870 and 5 feet on Honokohau 

Stream. These flow-duration data provide detailed characterization of the distribution and availability of base 

flow in lower Honokohau Stream. Previous estimates 

indicated that base flows ranging from 2.32 to 4.6 ft3

/s 

were available to meet the water needs in lower Honokohau Stream. At the two principal water diversion sites 

in the lower valley (MacDonald’s and Chun’s Dams) 

data from this study indicate that base flows of 2.32 ft3

/s 

are available more than 95 percent of the time at MacDonald’s Dam and 80 percent of the time at Chun’s 

Dam. Base flows of 4.6 ft3

/s are available only 65 percent of the time at MacDonald’s Dam and only 56 percent of the time at Chun’s Dam. 

A base-flow water-accounting model was developed to determine how flow-duration discharges computed for the 13 sites, using current diversion and 

return-flow practices, would change in response to a 

variety of flow-release practices at the Taro Gate and 

hydropower plant and diversion practices at MacDonald’s and Chun’s Dams. Use of the model indicates 

that there is a 1 to 1 relation between changes in release 

rates at the Taro Gate and base flow upstream from 

MacDonald’s Dam. At Chun’s Dam the relation varies 

with flow-duration percentiles. At the 95th percentile, 

differences in flow at Chun’s Dam would equal 50 percent of the change at the Taro Gate. At the 60th percentile, differences in flow at Chun’s Dam would equal 90 

percent of the change at the Taro Gate. 

REFERENCES CITED

Fontaine, R.A., Wong, M.F., and Matsuoka, Iwao, 1992, Estimation of median streamflows at perennial stream sites 

in Hawaii: U.S. Geological Survey Water-Resources 

Investigations Report 92-4009, 37 p.

Fontaine, R.A., 1996, Evaluation of the surface-water quantity, surface-water quality, and rainfall data-collection 

programs in Hawaii, 1994: U.S. Geological Survey 

Water-Resources Investigations Report 95-4212, 125 p.

Giambelluca, T.W., Nullet, M.A., and Schroeder, T.A., 1986, 

Rainfall atlas of Hawaii: Hawaii Department of Land and 

Natural Resources Report R76, 267 p.
References Cited 37

Hardison, C.H., and Moss, M.E., 1972, Accuracy of low-flow 

characteristics estimated by correlation of base-flow 

measurements, in Manual of Hydrology—Part 2, LowFlow Techniques: U.S. Geological Survey Water-Supply 

Paper 1542-B, p. 35–55.

Hawaii Commission on Water Resource Management, 1990, 

Hawaii stream assessment, A preliminary appraisal of 

Hawaii’s stream resources: Hawaii Department of Land 

and Natural Resources Report R-84, 294 p.

Hawaii Commission on Water Resource Management, 1992, 

Water resources protection plan, volumes I and II: prepared by George A.L. Yuen and Associates Incorporated, Hawaii Department of Land and Natural 

Resources Report, variously paged.

Hawaii Commission on Water Resource Management, 2001, 

Legal framework, findings of fact, And decision and 

order; For the Waiahole Ditch combined contest case 

hearing: Commission on Water Resource Management 

Report, 158 p.

Hawaii Department of Land and Natural Resources, 1977, 

Kahakuloa water study: Prepared by Wilson Okamoto 

and Associates, Inc., Hawaii Department of Land and 

Natural Resources Report R-54, 84 p., 7 app.

Hirsch, R.M., 1982, A comparison of four streamflow record 

extension techniques: Water Resources Research, v. 18, 

no. 4, p. 1081–1088.

Langenheim,V.A.M., and Clague, D.A., 1987, The Hawaiian-Emperor volcanic chain: Stratigraphic framework of 

volcanic rocks of the Hawaiian islands, chap. 1 of

Decker, R.W., Wright, T.L., and Stauffer, P.H., eds., 

Volcanism in Hawaii: U.S. Geological Survey Professional Paper 1350, v. 1 p. 55–84.

Macdonald, G.A., Abbott, A.T., and Peterson, F.L., 1983, 

Volcanoes in the sea, the geology of Hawaii (2d ed.): 

Honolulu, Hawaii, University of Hawaii Press, 517 p.

Maidment, D.R., ed., 1992, Handbook of hydrology: San 

Francisco, Calif., McGraw-Hill, variously paged.

Meyer, William, and Presley, T.K., 2001, The response of the 

Iao aquifer to ground-water development, rainfall, and 

land-use practices between 1940 and 1998, island of 

Maui, Hawaii: U.S. Geological Survey Water-Resources 

Investigations Report 00-4223, 60 p.

Mink, J.F., 1990, West Maui water study, Lahaina district 

sources and systems, Honokohau to Launiupoko: Honolulu, Hawaii, variously paged.

Novak, C.E., 1985, WRD data reports preparation guide, 

1985 edition: U.S. Geological Survey Open-File Report 

85-480, 199 p., 2 app.

Penn, D.C., 1997, Water and energy flows in Hawaii taro 

pondfields: Honolulu, Hawaii, University of Hawaii at 

Manoa, Ph.D. dissertation, 376 p.

Rantz, S.E., and others, 1982, Measurement and computation 

of streamflow, volumes 1 and 2: U.S. Geological Survey 

Water-Supply Paper 2175, 631 p.

Ries, K.G., III, 1993, Estimation of low-flow duration discharges in Massachusetts: U.S. Geological Survey OpenFile Report 93-38, 59 p.

Ries, K.G., III, and Friesz, P.J., 2000, Methods for estimating 

low-flow statistics for Massachusetts streams: U.S. Geological Survey Water-Resources Investigations Report 

00-4135, 81 p.

Sauer, V.B., and Meyer, R.W., 1992, Determination of error 

in individual discharge measurements: U.S. Geological 

Survey Open-File Report 92-144, 21 p.

Searcy, J.K., 1959, Flow-duration curves, in manual of 

hydrology: part 2. low-flow techniques: U.S. Geological 

Survey Water-Supply Paper 1542-A, 33 p.

Stearns, H.T., and Macdonald, G.A., 1942, Geology and 

ground-water resources of the island of Maui, Hawaii: 

Hawaii Division of Hydrography Bulletin 7, 344 p., 2 pl.

Stedinger, J.R., and Thomas, W.O., 1985, Low-flow frequency estimation using base-flow measurements: U.S. 

Geological Survey Open-File Report 85-95, p. 22.

Taogoshi, R.I., Nishimoto, D.C., Fontaine, R.A., Wong, 

M.F., and Hill, B.R., 2001, Water Resources Data, 

Hawaii and other Pacific areas, water year 2000, volume 

1, Hawaii: U.S. Geological Survey Water-Data Report 

HI-00-1, 379 p.

Vogel, R.M., and Fennessey, N.M., 1995, Flow duration 

curves II: A review of applications in water resources 

planning: Water Resources Bulletin, v. 31, p. 1029–

1039.

Wahl, K.L., and Wahl, T.L., 1995, Determining the flow of 

Comal Springs at New Braunfels, Texas: Proceedings of 

Texas Water’95, A Component Conference of the First 

International Conference on Water Resources Engineering, American Society of Civil Engineers, August 16–17, 

1995, San Antonio, Tex., p. 77–86.

Wilcox, Carol, 1996, Sugar water, Hawaii’s plantation 

ditches: Honolulu, Hawaii, University of Hawaii Press, 

191 p.

Winter, T.C., Harvey, J.W., Franke, O.L., and Alley, W.M., 

1998, Ground water and surface water- a single resource: 

U.S. Geological Survey Circular 1139, 79 p. 

Yamanaga, George, and Huxel, C.J., 1969, Preliminary 

report on the water resources of the Lahaina district, 

Maui: State of Hawaii, Department of Land and Natural 

Resources, Division of Water and Land Development, 

Circular C51, 47 p.