U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2006–5285

Prepared in cooperation with the

State of Hawaiÿi Department of Land and Natural Resources 

Commission on Water Resource Management

Natural and Diverted Low-Flow Duration Discharges 

for Streams Affected by the Waiähole Ditch System, 

Windward Oÿahu, Hawaiÿi
COVER

Waterfall at one of the water sources of Waiähole Stream, windward Oÿahu, Hawaiÿi.
Natural and Diverted Low-Flow 

Duration Discharges for Streams 

Affected by the Waiähole Ditch 

System, Windward Oÿahu, Hawaiÿi 

By Chiu W. Yeung and Richard A. Fontaine

Prepared in cooperation with the

State of Hawaiÿi Department of Land and Natural Resources 

Commission on Water Resource Management

Scientific Investigations Report 2006–5285

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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copyright owners to reproduce any copyrighted materials contained within this report.

Suggested citation:

Yeung, C.W., and Fontaine, R.A., 2007, Natural and Diverted Low-Flow Duration Discharges for 

Streams Affected by the Waiähole Ditch System, Windward Oÿahu, Hawaiÿi: U.S. Geological Survey Scientific Investigations Report 2006-5285, 75 p. 
iii

Contents

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

Introduction ....................................................................................................................2

Purpose and Scope.................................................................................................4

Acknowledgements .................................................................................................5

Description of Study Area ..............................................................................................5

Physical Setting.......................................................................................................5

Climate ....................................................................................................................5

Geology...................................................................................................................5

Dike-Impounded System..................................................................................9

Hydrologic Setting and Water Diversions ................................................................9

Available Discharge Data ............................................................................................10

Seepage Runs.......................................................................................................10

Waiähole Ditch Tunnel....................................................................................10

Waiähole and Waianu Streams ......................................................................14

Waikäne Stream.............................................................................................24

Kahana Stream ..............................................................................................25

Continuous-Record Stations ................................................................................25

Pre-ditch.........................................................................................................25

Post-ditch .......................................................................................................34

Low-Flow Partial-Record Stations .........................................................................35

Miscellaneous Measurement Sites........................................................................35

Approach and Methods for Estimating Natural Low-Flow Duration Discharges ...........37

Low-Flow Duration Discharges in Streams ..........................................................38

Selection of Index Stations.............................................................................41

Low-Flow Duration Discharges in Waiähole Ditch.................................................44

Ground Water Beyond the Koÿolau Crest Developed by the 

Waiähole Ditch System .......................................................................51

Distribution of Waiähole Ditch Flows Among Watersheds.....................................52

Wall Measurements........................................................................................52

Ditch Tunnel Seepage Runs...........................................................................52

Addition of Flow-Duration Discharges ...................................................................53

Estimates of Low-Flow Duration Discharges for Diverted and 

Natural Flow Conditions.....................................................................................54

Diverted Flow Conditions ......................................................................................54

Natural Flow Conditions .......................................................................................56

Estimates Based on Addition of Ditch and Stream Data................................58

Estimates Based on Pre-ditch Data ...............................................................58

Comparison of Estimates...............................................................................63

Effects of Diversions on Low-Flow Duration Discharges ..............................................64

Effects of Flow Releases on Low-Flow Duration Discharges .......................................67

Comparison of Post-release to Natural Flows .......................................................67

Comparison of Pre-release to Post-release Flows................................................69

Limitations of Approach................................................................................................69
iv

 Accuracy of Low-Flow Duration Estimates...........................................................70

Summary and Conclusions ..........................................................................................70

References Cited..........................................................................................................72

Appendix 1. Reconstructed daily time series of ditch flow at North Portal station 

16287000 near Waiähole, windward Oÿahu, 2003-04........................................74

Figures

1. Waiähole Ditch System and the location of the Kahana, Waikäne, and 

Waiähole Streams, windward Oÿahu, Hawaiÿi ...................................................3

2. Timeline of major events affecting low flows in the study area, windward

Oÿahu, Hawaiÿi...................................................................................................4

3. Land use and land cover in 1998 for the study area, windward Oÿahu,

Hawaiÿi ..............................................................................................................6

4. Mean annual rainfall for the study area, windward Oÿahu, Hawaiÿi....................7

5. Generalized surficial geology, island of Oÿahu, Hawaiÿi.....................................8

6. Results of seepage runs on Waiähole Ditch System, windward Oÿahu,

Hawaiÿi, 1959 and 2002-03 .............................................................................12

7. Results of seepage runs on Waiähole Stream, windward Oÿahu, Hawaiÿi,

March 1995 and June and September 1995...................................................16

8. Results of seepage runs on Waianu Stream, windward Oÿahu, Hawaiÿi, May

1995 and June and September 1995..............................................................18

9. Results of seepage runs on Waiähole Stream, windward Oÿahu, Hawaiÿi,

1911 and 1959-60...........................................................................................20

10. Results of seepage runs on Waianu Stream, windward Oÿahu, Hawaiÿi,

1959 and 1960-61...........................................................................................22

11. Results of seepage runs on Waikäne Stream, windward Oÿahu, Hawaiÿi,

2002-03...........................................................................................................27

12. Results of seepage runs on Waikäne Stream, windward Oÿahu, Hawaiÿi,

July 1959 and October 1959 and February 1960 ...........................................28

13. Results of seepage runs on Kahana Stream, windward Oÿahu, Hawaiÿi,

1960 and 1961-62...........................................................................................30

14. Continuous-record and low-flow partial-record streamflow stations in the

study area, windward Oÿahu, Hawaiÿi..............................................................33

15. Logarithmic plot of daily discharge at continuous-record streamflow

stations 16292000 and 16294000, Waiähole Stream, windward Oÿahu, 

Hawaiÿi, September 25, 1911 to June 30, 1916 ..............................................34

16. Graphical relation between flows at index station on Kalihi Stream and

low-flow partial-record station on Waikäne Stream, Oÿahu, Hawaiÿi................40

17. Unadjusted and adjusted flow-duration curves of daily mean discharge

at continuous-record streamflow station 16294100 on Waiähole Stream,

windward Oÿahu, Hawaiÿi, for post-release period 2002-2004.........................41

18. Unadjusted and adjusted flow-duration curves of daily mean discharge

at continuous-record streamflow station 16294900 on Waikäne Stream,

windward Oÿahu, Hawaiÿi, for pre-release period 1960-2002 and

post-release period 2003-04...........................................................................42
19. Flow-duration curve of daily mean discharge at continuous-record

streamflow station 16296500 on Kahana Stream, windward Oÿahu, Hawaiÿi,

for period 1960-2004.......................................................................................43

20. Flow-duration curves for base period and period of record of daily mean

discharge at continuous-record streamflow station 16200000 on North Fork

Kaukonahua Stream, Oÿahu, Hawaiÿi ..............................................................43

21. Locations of index streamflow stations and selected rainfall stations on

Oÿahu, Hawaiÿi.................................................................................................45

22. Graphical relation between flows at index station on Makawao Streams

and low-flow partial-record streamflow station on Waikäne Stream,

Oÿahu, Hawaiÿi.................................................................................................55

23. Graphical relations between flows at index station on Kalihi Stream and

low-flow partial-record streamflow station on Waianu Stream,

Oÿahu, Hawaiÿi.................................................................................................56

24. Graphical relations between flows at index stations on Kalihi and Makawao

Streams and low-flow partial-record streamflow stations on Kahana

and Käwä Streams, Oÿahu, Hawaiÿi ................................................................57

25. Daily discharge at continuous-record streamflow station 16296000,

Kahana Stream, windward Oÿahu, Hawaiÿi, June 19, 1914, to June 30,

1917................................................................................................................62

26. Annual rainfall at station 783 at Nuÿuanu Reservoir 4, Oÿahu, Hawaiÿi,

1905-1920.......................................................................................................62

27. Correlation between monthly rainfall at stations 783 and 837.1 for concurrent 

period January 1913 to May 1914 ..................................................................63

28. Correlation between annual rainfall at stations 783 and 837 for concurrent 

period 1917-1986............................................................................................64

29. Estimated low-flow duration discharges of natural streamflow using various

methods at Waiähole and Kahana Streams, windward Oÿahu, Hawaiÿi ..........65

30. Diverted flows compared to natural flows at stream-channel altitudes of 250 to 

320 feet, Waiähole Stream, windward Oÿahu, Hawaiÿi ....................................66

31. Diverted flows compared to natural flows at stream-channel altitudes of 10 to 

220 feet, Waikäne Stream, windward Oÿahu, Hawaiÿi .....................................66

32. Diverted flows compared to natural flows at stream-channel altitudes of 30 to 

80 feet, Kahana Stream, windward Oÿahu, Hawaiÿi.........................................67

33. Pre-release flows compared to post-release flows at

stream-channel altitudes of 10 to 220 feet, Waikäne Stream, windward

Oÿahu, Hawaiÿi.................................................................................................69

34. Daily flow releases at Gate 30, Gate 31, and Intake 23 on Waiähole

Ditch System, windward Oÿahu, Hawaiÿi .........................................................71

Tables

1. Average flows for Waiähole Ditch System development tunnels.......................2

2. Discharge measurements made during seepage runs in the connecting

tunnels of the Waiähole Ditch System, windward Oÿahu, Hawaiÿi, 2002-03....11

3. Discharge measurements made during seepage run in the connecting

tunnels of the Waiähole Ditch System, windward Oÿahu, Hawaiÿi, 1959 .........11
vi

4. Discharge measurements made during seepage runs in the Waiähole

Stream, windward Oÿahu, Hawaiÿi, 1995 .........................................................14

5. Discharge measurements made during seepage runs in the Waianu

Stream, windward Oÿahu, Hawaiÿi, 1995 .........................................................15

6. Discharge measurements made during seepage runs in the Waiähole

Stream, windward Oÿahu, Hawaiÿi, 1911 and 1959-60....................................24

7. Discharge measurements made during seepage runs in the Waianu

Stream, windward Oÿahu, Hawaiÿi, 1959-61....................................................24

8. Discharge measurements made during seepage runs in the Waikäne

Stream, windward Oÿahu, Hawaiÿi, 2002-03....................................................25

9. Discharge measurements made during seepage runs in the Waikäne

Stream, windward Oÿahu, Hawaiÿi, 1959-60....................................................26

10. Discharge measurements made during seepage runs in the Kahana

Stream, windward Oÿahu, Hawaiÿi, 1960-62....................................................26

11. Continuous-record streamflow stations in the Waiähole, Waikäne, and

Kahana watersheds, windward Oÿahu, Hawaiÿi...............................................32

12. Low-flow partial-record streamflow stations on Waiähole, Waikäne, and

Kahana Streams, windward Oÿahu, Hawaiÿi....................................................36

13. Average flows from weir observations in Waiähole, Waianu, Waikäne, and

Kahana Streams, windward Oÿahu, Hawaiÿi, for June and July, 1911, by

W.A. Wall (modified from Lippencott, 1911)....................................................37

14. Continuous-record streamflow stations considered as potential index

stations in the study ........................................................................................39

15. Low-flow statistics, variances, and standard errors adjusted to the base

period of 1960-2004 for the low-flow partial-record stations using

record-extension methods, windward Oÿahu, Hawaiÿi .....................................46

16. Low-flow statistics, variances, and standard errors adjusted to the base

period of 1960-2004 for the continuous-record streamflow stations using

record-extension methods, windward Oÿahu, Hawaiÿi .....................................49

17. Distribution percentages of total Waiähole Ditch flow contributed by

Waiähole, Waikäne, and Kahana Streams, windward Oÿahu, Hawaiÿi ............52

18. Recorded discharge and associated flow-duration percentiles for selected

continuous-record streamflow stations in windward Oÿahu, Hawaiÿi,

February 2002 and August 2003 ....................................................................53

19. Comparison of flow statistics computed for stream sites where natural

flows are estimated, using data from multiple time series of daily flow,

windward Oÿahu, Hawaiÿi.................................................................................54

20. Estimates of natural, pre-release, and post-release low-flow duration 

discharges for continuous-record and low-flow partial-record streamflow 

stations in Waianu and Waiähole Streams, windward Oÿahu, Hawaiÿi.............59

21. Estimates of natural, pre-release, and post-release low-flow duration discharges 

for continuous-record and low-flow partial-record streamflow stations in Waikäne 

Stream, windward Oÿahu, Hawaiÿi......................................................................60

22. Estimates of natural and diverted low-flow duration discharges for continuousrecord and low-flow partial-record streamflow stations in Kahana Stream, 

windward Oÿahu, Hawaiÿi...................................................................................61

23. Unit-area duration discharges representative of natural streamflow

originating in the marginal dike zone of windward Oÿahu, Hawaiÿi ..................61

24. Percent difference between estimates of natural and post-release low-flow

duration discharges for continuous-record and low-flow partial-record 

streamflow stations, windward Oÿahu, Hawaiÿi................................................68
vii

Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2

)

square foot (ft2

) 0.09290 square meter (m2)

square mile (mi2

) 2.590 square kilometer (km2) 

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3

/s)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as 

follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as 

follows:

°C=(°F-32)/1.8

Vertical coordinate information is referenced to the mean sea level.

Horizontal coordinate information is referenced to the Old Hawaiian Datum or the 

North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the mean sea level.

Abstract 

For nearly a century, the Waiähole Ditch System has 

diverted an average of approximately 27 million gallons per 

day of water from the wet, northeastern part of windward 

Oÿahu, Hawaiÿi, to the dry, central part of the island to meet 

irrigation needs. The system intercepts large amounts of dikeimpounded ground water at high altitudes (above approximately 700 to 800 ft) that previously discharged to Waiähole 

(and its tributaries Waianu and Uwao1), Waikäne, and Kahana 

Streams through seeps and springs. Diversion of this ground 

water has significantly diminished low flows in these streams. 

Estimates of natural and diverted flows are needed by water 

managers for (1) setting permanent instream flow standards 

to protect, enhance, and reestablish beneficial instream uses 

of water in the diverted streams and (2) allocating the diverted 

water for instream and offstream uses. 

Data collected before construction of the Waiähole Ditch 

System reflect natural (undiverted) flow conditions. Natural 

low-flow duration discharges for percentiles ranging from 50 

to 99 percent were estimated for four sites at altitudes of 75 

to 320 feet in Waiähole Stream (and its tributaries Waianu and 

Uwao Streams), for six sites at altitudes of 10 to 220 feet in 

Waikäne Stream, and for three sites at altitudes of 30 to 80 feet 

in Kahana Stream. Among the available low-flow estimates 

along each affected stream, the highest natural Q50 (median) 

flows on Waiähole (altitude 250 ft), Waianu (altitude 75 ft), 

Waikäne (altitude 75 ft), and Kahana Streams (altitude 30 ft) 

are 13, 7.0, 5.5, and 22 million gallons per day, respectively. 

Q50 (median) is just one of five duration percentiles presented 

in this report to quantify low-flow discharges. All flow-duration estimates were adjusted to a common period of 1960-

2004 (called the base period). Natural flow-duration estimates 

compared favorably with limited pre-ditch streamflow data 

available for Waiähole and Kahana Streams. 

Data collected since construction of the ditch system 

reflect diverted flow conditions, which can be further divided 

into pre-release and post-release periods—several flow 

releases to Waiähole, Waianu, and Waikäne Streams were initiated between December 1994 and October 2002. Comparison 

of pre-release to natural flows indicate that the effects of the 

Waiähole Ditch System diversion are consistently greater at 

lower low-flow conditions (Q99 to Q90) than at higher low-flow 

conditions (Q75 to Q50). Results also indicate that the effects of 

the diversion become less significant as the streams gain additional ground water at lower altitudes. For Waiähole Stream, 

pre-release flows range from 25 to 28 percent of natural flows 

at an altitude of 250 feet and from 19 to 20 percent at an altitude of 320 feet. For Waikäne Stream, pre-release flows range 

from 30 to 46 percent of natural flows at an altitude of 10 feet 

and from 7 to 19 percent at an altitude of 220 feet. For Kahana 

Stream, pre-release flows range from 65 to 72 percent of natural flows at an altitude of 30 feet and from 58 to 71 percent at 

an altitude of 80 feet. 

Estimates of post-release flows were compared with 

estimates of natural flows to assess how closely current 

streamflows are to natural conditions. For Waianu Stream, 

post-release flows at an altitude of 75 feet are 41 to 46 percent 

lower than corresponding natural flows. For Waikäne Stream, 

post-release flows at an altitude of 75 feet are within 12 percent of the corresponding natural flows.

Comparisons of pre-release and post-release flows for 

Waikäne Stream at altitudes of 10 to 220 feet were used to 

assess downstream changes in flow along the stream reach 

where flow releases were made. For a particular stream 

altitude, proportions of pre-release to post-release flows 

associated with median flows are consistently greater than 

proportions associated with lower low flows because the relative effect of the flow release is smaller at higher low flows. 

Similarly, for a particular flow-duration percentile, proportions of pre-release to post-release flows associated with 

lower altitudes are consistently greater than proportions at 

higher altitudes because the relative effect of the flow release 

is smaller as the stream gains ground water at lower altitudes. 

Proportions of pre-release to post-release flows for selected 

flow-duration percentiles at an altitude of 10 feet range from 

35 to 43 percent, whereas proportions at a higher altitude of 

220 feet range from 5 to 11 percent. 

Natural and Diverted Low-Flow Duration 

Discharges for Streams Affected by the Waiähole 

Ditch System, Windward Oÿahu, Hawaiÿi

By Chiu W. Yeung and Richard A. Fontaine

1

 The name of this stream was formerly spelled Uwau, but the Hawai‘i 

Board on Geographic Names decided in 2000 that Uwao should be the correct 

spelling.
Introduction 

In 1897, the Oahu Sugar Company established a largescale sugar plantation on the dry, southwestern side of Oÿahu. 

Irrigation water for the sugar-cane plantation was initially 

pumped from the Pearl Harbor aquifer (Wilcox, 1996). 

Because of the high pumping cost, the Oahu Sugar Company 

constructed the Waiähole Ditch System to transport, by gravity, surface water from the northeastern side of the Koÿolau 

Range (fig. 1). For nearly a century, the Waiähole Ditch System diverted an average of about 27 million gallons per day 

(Mgal/d) (Hawaiÿi Commission on Water Resource Management, 2001, table 1 on p.143) of water from windward Oÿahu 

to central Oÿahu to meet irrigation needs. This diverted flow 

consists of ground water gained from the connecting tunnels, 

the four development tunnels, and the trans-Koÿolau tunnel 

and of surface water gained primarily from Kahana Valley. 

The Waiähole Ditch collection and delivery system was 

initially constructed during 1913-1916. The collection system, 

on the windward side of Oÿahu, consists of 4 development 

tunnels, 27 connecting tunnels, and 37 stream intakes, one at 

each gulch. The collection system was originally designed to 

divert the abundant surface water of windward Oÿahu streams. 

The 4.7 mi of connecting tunnels begins in Kahana Valley at 

about 790 ft altitude and extends south through the Waikäne 

and Waiähole Valleys (fig. 1). At Waiähole Valley, a 2.7-milong trans-Koÿolau tunnel was bored through the Koÿolau 

Range. The delivery part of the ditch system begins at Adit 8, 

where the main tunnel exits the Koÿolau Range, and terminates 

at Reservoir 155 at Honouliuli (Water Resource Associates, 

2003). Reservoir 155 is located near the foot of the Waiÿanae 

Range at an altitude of about 600 ft (Wilcox, 1996). 

The main tunnel through the Koÿolau Range was primarily designed as a transmission tunnel. The success of 

this tunnel in intercepting large amounts of dike-impounded 

ground water in the Koÿolau Range led to the construction 

of additional high-level ground-water development tunnels. 

Between 1925 and 1935, six tunnels with headings directed 

into the Koÿolau Range were added to the ditch system to 

develop ground water stored in dike compartments. Four 

development tunnels (Uwao, Waikäne 1, Waikäne 2, and 

Kahana) were considered successful (fig. 1, table 1). The 

Uwao tunnel was extended in 1963-64 beyond the topographic 

divide of the Koÿolau Range for about 228 ft (Takasaki and 

others, 1969, p.114), which increased production by about 2-3 

Mgal/d (Takasaki and Mink, 1985, p.38). In 1992, a bulkhead 

was installed in the Kahana tunnel, which reduced production 

by an average of 1.5 Mgal/d (Hawaiÿi Commission on Water 

Resource Management, 2001, table 1 on p.143). Several major 

flow releases to windward Oÿahu streams from the Waiähole 

Ditch System were initiated between December 1994 and 

October 2002. Construction timelines for the Waiähole Ditch 

System and other events that affected flows in the windward 

Oÿahu streams are summarized in figure 2. 

Waiähole Ditch diversion of the dike-impounded ground 

water, which previously discharged to Waiähole, Waikäne, and 

Kahana Streams through seeps and springs, has significantly 

diminished base flows in these streams. Base flows of streams 

are sustained by ground-water discharge and may continue 

even during dry-weather conditions. The effects of Waiähole 

Ditch diversions received significant attention in 1993, when 

it became known that large amounts of diverted water were 

not being used for irrigation and instead were being released 

into streams on the leeward side of Oÿahu. This coincided 

with the Oahu Sugar Company announcement of the closure 

of its sugar-plantation operations. Releases of water into 

leeward streams initiated a legal proceeding (Waiähole Ditch 

Contested Case) before the Hawaiÿi Commission on Water 

Resource Management (CWRM) over rights to the water. 

In December 1997, the CWRM released its initial decision, 

Table 1. Average flows for Waiähole Ditch System 

development tunnels.

[Mgal/d, million gallons per day; --, not available]

Tunnel Period

Number

of 

years

Average

flow

(Mgal/d)

Standard

deviation

(Mgal/d)

Waikäne 1 1938-78d 41 4.6 0.97

1989-1993e 5 4.2 --

1999-2004f 5 4.3 1.16

Waikäne 2 1938-78d 41 1.1 0.16

1989-1993e 5 1.1 --

1999-2004f 5 1.1 0.16

Kahanaa 1938-78d 41 3.6 0.73

1989-1993e 5 2.6g --

1999-2004f 5 0.8h 0.02

Uwaob 1938-62d 25 10.2 2.01

1967-78d 12 13.0 1.77

1989-1993e 5 13.5 --

1999-2004f 5 13.4 1.41

Main

tunnelc

1938-78d 41 4.8 0.98

1989-1993e 5 3.7 --

1999-2004f 5 4.8 1.17

a

Bulkhead installed in Kahana tunnel in 1992.

b

Uwao tunnel was lengthened by 228 ft in 1963-64; Uwao was formerly 

spelled Uwau.

c

Values represent ground-water gain between North Portal and Adit 8 

stations.

d

Values obtained from Takasaki and Mink (1985).

e

Values obtained from Hawaiÿi Commission on Water Resource Management (2001, table 1 on p.143).

f

Data provided by Agribusiness Development Corporation.

g

Reflects flow reduction of 1.1 Mgal/d due to bulkhead.

h

Average flow computed on the basis of estimated data.

Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
Kahana

Bay

K

Pearl 

 Harbor

EXPLANATION

WAIAHOLE DITCH SYSTEMWATERSHED BOUNDARY

Waiawa Stream

0 5 

0 

Basemap modified from U.S. Geological Survey digital data, 1:24,000, 1983 & 1999, Albers equal area projection, standard parallels 21 ̊19’40” and 21 ̊38’20”, central meridian 157 ̊58’.relief from U.S. Geological Survey digital elevation models,1:24,000.

star

22 ̊20 ̊

160 ̊ 158 ̊ 156 ̊

Kauai

Niihau

Oahu

Maui

Molokai

Lanai

Kahoolawe

Hawaii

HAWAII

PACIFIC OCEAN

maparea

Reservoir 155

Waia

n

a

e

Range

Koola

u

Range

Koolau

Range

Kahanabulkheadtunnel

Waiahole Ditch

Uwautunnel

Waikanetunnel 2

Waikanetunnel 1

Intake 23

Waiahole Ditch

Gate 31

Gate 30

Adit 8

NorthPortal

Kahanabulkheadtunnel

Waiahole Ditch

Uwaotunnel

Waikanetunnel 2

Waikanetunnel 1

Intake 23

Waiahole Ditch

Gate 31

Adit 8

NorthPortal

Gate 30

Waiah

Waian

Uwao 

Waika

Waike

Kawa 

Kahan

Punaluu Stream

157 ̊40'W

21 ̊30 ̊N

21 ̊25'N

158 ̊W

21 ̊35'N

Figure 1. Waiähole Ditch System and the location of the Kahana, Waikäne, Waiähole Streams, windward Oÿahu, Hawaiÿi. Uwaspelled Uwau.
1910

191519201925193019351940194519501955196019651970197519801985199019952000

19169–1982: Average of 1.0 Mgal/d pumped daily upstream from Waiahole Stream into the ditch4

12/19/94: Began releasing 8 Mgal/d via gate 31 released to Waiahole Stream5

5/23/95: Began releasing 2 Mgal/d via Gate 30 to Waianu Stream and reduced flow release at Gate 305

10/1/2002: Began releasing 3 Mgal/d via intake 23 to Waikane Stream6

2005

8/1/1913–12/13/1915: Water from tunnel construction entering Waiahole Stream2

2/1913–5/27/1916: Construction of Waiahole Ditch System1, 8

1/1925–5/1927: Construction and extension of Waikane I tunnel at intake 223

11/1933–8/1934: Construction and extension of Waikane I tunnel at intake 223

6/1927–2/18/1929: Construction of Waikane II tunnel at intake 253

1992: Construction of Kahana tunnel and installation of bulkhead at intake 93

4/1929–1/1931: Construction of Kahana tunnel and installation of bulkhead at intake 93

7/5/1963–10/31/1963: Second extension of Uwao tunnel3

11/19/1934–12/4/1935: First extension of Uwao tunnel3

5/20/1932–6/29/1933: Construction of Uwao tunnel at intake 273

which was appealed to the State Supreme Court. In August 

2000, the Supreme Court vacated part of the initial decision and remanded several issues for additional findings. In 

December 2001, the CWRM revised the decision on remand, 

which was again appealed to the Supreme Court. In June 2004, 

the Supreme Court vacated part of the revised decision and 

remanded several issues for additional findings. As of February 2006, the Waiähole Ditch Contested Case has yet to be 

fully resolved. As an interim resolution, the CWRM ordered 

the restoration of water back into windward streams to meet 

instream-flow needs. Waiähole Ditch is currently maintained 

by the Agribusiness Development Corporation (ADC), a State 

agency. ADC began releasing water from the Waiähole Ditch 

System into Waiähole Stream at Gate 31 on December 19, 

1994, into Waianu Stream at Gate 30 on May 23, 1995, and 

into Waikäne Stream at Intake 23 starting on October 1, 2002 

(fig. 1). 

In 2004, the U.S. Geological Survey (USGS), in cooperation with the CWRM, undertook a study to estimate low flows 

representative of natural undiverted conditions in Waiähole, 

Waikäne, and Kahana Streams affected by the Waiähole Ditch 

System. These estimates are needed by the CWRM for setting 

permanent instream flow standards to protect, enhance, and 

reestablish, where practicable, beneficial instream uses of 

water. 

Purpose and Scope

This report (1) presents estimates of natural low-flow 

characteristics at selected locations in Waiähole, Waikäne, and 

Kahana Streams, (2) quantifies the effects of diversions by the 

Waiähole Ditch System on low flows, and (3) describes the 

effects of flow releases on flows in the streams. A combination of pre-ditch and post-ditch streamflow data and ditch-flow 

data were analyzed for this report. Data collected during the 

pre-ditch period reflect natural (undiverted) flow conditions 

before any effects from the construction of Waiähole Ditch 

System. Data collected during the post-ditch period reflect 

diverted flow conditions, which can be further divided into 

pre-release and post-release periods for Waiähole, Waianu, and 

Waikäne Streams where flow releases were made. 

Pre-ditch streamflow data include data collected before 

any effects on streamflow from the construction of Waiähole 

Ditch System at (1) continuous-record stations on Waiähole 

and Kahana Streams and (2) miscellaneous sites along 

Waiähole, Waikäne, and Kahana Streams. Post-ditch streamflow data include data collected at (1) continuous-record stations on Waiähole (1914-16, 1950-69, 2000-present), Waikäne 

(1959-present), and Kahana (1958-present) Streams and (2) 

miscellaneous sites along Waiähole, Waikäne, and Kahana 

Streams after the construction of the ditch system. Post-ditch 

Figure 2. Timeline of major events affecting low flows in the study area, windward Oÿahu, Hawaiÿi. Uwao 

was formerly spelled Uwau. 1Kluegel, 1916; 2Wilcox, 1996; 3Stearns and Vaksvik, 1935; 4table 22 in Takasaki 

and others, 1969; 5

Hawaiÿi Commission on Water Resource Management, 2001; 6assumes the pumping 

began after the opening of ditch system in 1916; 7

Takasaki and Mink, 1985; 8unpublished USGS letter to 

Hawaiÿi Commission on Water Resource Management, 1966; 9

Agribusiness Development Corporation, 

written commun., 2003.

Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
streamflow data collected specifically for this study include (1) 

low-flow measurements representative of existing diversion 

conditions at 12 sites on Waianu, Uwao, Waikäne, and Kahana 

Streams in 2002-03, (2) two sets of discharge measurements 

made at multiple sites along the connecting tunnel of the 

Waiähole Ditch System from Kahana Stream to the North 

Portal in 2002-03, and (3) two sets of discharge measurements 

made at multiple sites along Waikäne Stream in 2002-03. 

Ditch-flow data include (1) development-tunnel flows available in digital format for the period 1999–2004 provided by 

ADC and (2) ditch flows recorded at continuous-record stations for various periods along the connecting tunnel. 

Acknowledgements

The authors would like to thank Agribusiness Development Corporation (ADC) personnel for sharing their detailed 

knowledge of the ditch and for flow data collected in the 

Waiähole Ditch System. ADC also provided valuable cooperation and assistance in accessing the Waiähole Ditch System. 

Personnel from the U.S. Marine Corps escorted U.S. Geological Survey (USGS) personnel in Waikäne Valley during seepage runs conducted as part of this study. The authors would 

also like to acknowledge Delwyn Oki from the USGS for his 

technical assistance during this study and the employees from 

the USGS Honolulu field office for conducting seepage runs 

and making low-flow measurements. 

Description of Study Area 

Physical Setting

The island of Oÿahu, with an area of 604 square miles 

(mi2), is the third largest of the Hawaiian Islands. It is formed 

by the eroded remnants of two elongated shield volcanoes, 

the older Waiÿanae Volcano and the younger Koÿolau Volcano 

(Visher and Mink, 1964). The Waiÿanae Range forms the western part of the island, and the Koÿolau Range forms the eastern 

part. The study area, in the northeastern part of the island, lies 

on the eastern slope, or windward side, of the Koÿolau Range. 

The study area encompasses the three watersheds (Waiähole, 

Waikäne, and Kahana) that are affected by the Waiähole Ditch 

System (fig. 1). The three watersheds have a combined drainage area of about 14.95 mi2

. The drainage areas of Waiähole 

and Waikäne watersheds are 3.95 and 2.65 mi2, respectively. 

Kahana Stream, which has a drainage area of 8.35 mi2, is the 

largest drainage area and has the longest stream length in 

the study area. The land uses in the headwaters of the three 

watersheds are primarily classified as conservation undeveloped areas (Klasner and Mikami, 2003) (fig. 3). The ridge 

(topographic crest) of the Koÿolau Range forms the southwest 

boundary of these three watersheds. The topographic relief 

in the study area ranges from mean sea level at the coast to 

2,786 ft at the peak of the topographic divide of the Waiähole 

watershed. Headwater areas above ditch altitudes are in 

amphitheater-headed valleys, with steep slopes of about 45 ̊ 

to nearly 80 ̊ (Takasaki and others, 1969). The stream gradients decrease abruptly to less than 5 ̊ in the lower parts of the 

watersheds, which have flat-bottomed valleys near the shore 

(Takasaki and others, 1969).

In general, Waiähole, Waikäne, and Kahana Streams 

flow northeastward from the topographic crest of the Koÿolau 

Range to the coast. Many small tributaries contribute flow 

to the main streams, particularly at high altitudes. Waiähole 

Stream has one main tributary, Waianu Stream, on the north. 

Upper Waiähole Stream is formed by Waihï Stream (north 

fork of Waiähole Stream) and Hälona Stream (south fork of 

Waiähole Stream) (fig. 4). Waikäne watershed lies north of 

Waiähole watershed. Waikeÿekeÿe Stream is the main tributary 

of Waikäne Stream. Kahana watershed lies south of Punaluÿu 

watershed and north of Waikäne watershed. Käwä Stream, a 

major tributary to Kahana Stream, is not directly affected by 

the ditch system, because it originates below the ditch, mostly 

in the marginal dike zone. 

Climate

The climate of Oÿahu is semitropical and is characterized by mild temperatures, persistent northeasterly winds, 

a wet season from October through April, and a dry season 

from May through September (Blumenstock and Price, 1967; 

Sanderson, 1993). The prevailing northeasterly trade winds 

throughout most of the year and the mountainous topography are the main controls of the climate on Oÿahu. Average 

annual air temperature on Oÿahu ranges from about 74 ̊ F near 

the northeast coast to about 68 ̊ F at higher altitudes of the 

Koÿolau Range (Nullet and Sanderson, 1993). 

The Koÿolau Range extends along the northeastern side of 

the island and is oriented roughly perpendicular to the northeasterly trade winds. Orographic lifting of the moisture-laden 

air causes frequent and heavy rainfall on the windward side 

of the Koÿolau Range relative to the less frequent and lighter 

showers on the leeward side. This orographic effect causes 

significant differences in rainfall over short distances. Within 

the study area, the mean annual rainfall varies from less than 

40 in. along the coastal lowland areas to about 240 in. over the 

mountainous areas of the Kahana watershed (fig. 4).

Geology

The Koÿolau Range has been significantly modified by 

erosion (Stearns and Vaksvik, 1935). Eruptions during the 

mountain-building (shield) stage from the central caldera and 

two principal rift zones fed lava flows that formed the bulk 

of the island (fig. 5). The two principal rift zones are oriented 

in northwestern and southeastern directions from the central 

caldera; the northwest rift zone crosses the study area. Within 

Description of Study Area 
Kahana

Bay

Kaneohe

Bay

Kahana Stream

Kawa Stream

Punaluu Stream

Kaaawa Stream

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream

Waihi

Stream

Halona

Stream

Waiahole Ditch

Waiahole Ditch

Punaluu Ditch

Kahana

bulkhead

tunnel

Waikane

tunnel 1

Waikane

tunnel 2

Uwao

tunnel Intake 29

Tunnel B

Tunnel A

K o o l a u R a n g e

Kamehameha Hwy.

LAND USE

 Agriculture

 Developed

 Conservation undeveloped

DITCH SYSTEM

 WATERSHED BOUNDARY

Kahana

Waiahole

Waikane

157 ̊56'W 157 ̊54'W 157 ̊52'W 157 ̊50'W

21 ̊28'N

21 ̊30'N

21 ̊32'N

21 ̊34'N

0 1 2 Kilometers

0 1 2 Miles Base modified from U.S. Geological Survey,

1:24,000 digital data.

Waiawa Stream

EXPLANATION

Figure 3. Land use and land cover in 1998 for the study area, windward Oÿahu, Hawaiÿi (modified from 

Klasner and Mikami, 2003). Uwao was formerly spelled Uwau.

Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
Kahana

Bay

Kaneohe

Bay

Kahana Stream

Kawa Stream

Punaluu Stream

Kaaawa Stream

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream

Waihi

Stream

Halona

Stream

Waiahole Ditch

Waiahole Ditch

Punaluu Ditch

Kahana

bulkhead

tunnel

Waikane

tunnel 1

Waikane

tunnel 2

Uwao

tunnel Intake 29

Tunnel B

Tunnel A

K o o l a u R a n g e

Kamehameha Hwy.

236.2

(6,000)

275.6

(7,000)

157.5

(4,000)

157.5

(4,000)

118.1

(3,000)

118.1

(3,000)

78.7

(2,000)

39.4

(1,000)

196.9

(5,000)

118.1

(3,000)

LINE OF EQUAL MEAN ANNUAL RAINFALL--Interval, in inches, is variable. 

 Number in parentheses is value in millimeters.

 WATERSHED BOUNDARY

157 ̊56'W 157 ̊54'W 157 ̊52'W 157 ̊50'W

21 ̊28'N

21 ̊30'N

21 ̊32'N

21 ̊34'N

0 1 2 Kilometers

0 1 2 Miles Base modified from U.S. Geological Survey,

1:24,000 digital data.

Waiawa Stream

EXPLANATION

Figure 4. Mean annual rainfall for the study area, windward Oÿahu, Hawaiÿi (modified from Giambelluca 

and others, 1986). Uwao was formerly spelled Uwau.

Description of Study Area 
HONOLULU

Kailua

Kaneohe

Makaha

Waianae

Maili

Nanakuli

EwaBeach

Ewa

Waialua

Haleiwa

Sunset

Beach Kahuku

Laie

Kaaawa

Waimanalo

HawaiiKai

AinaHaina

Aiea

Waipahu

Schofield

Barracks

Wahiawa

158 ̊10'W

157 ̊50'W

157 ̊40'W

21 ̊40'N

21 ̊30'N

21 ̊20'N

158 ̊W

00

2 4 MILES

2 4 KILOMETERS

Kahuku Point

Makapuu

Point

Barbers

Point

Diamond

Head

Kaena

Point

Waimanalo

Bay

KANEOHE

BAY

Kahana

Bay

Pearl

 Harbor

MAMALA BAY

Maunalua Bay

Base modified from U.S. Geological Survey NationalHydrography Dataset, Albers equal area projection, standard parallels 21o19'40" and 21o38'20", central 

meridian 157o58', datum NAD83. Relief from U.S. 

Geological Survey digital elevation models, 1:24,000

Waikiki

Koko Head

EXPLANATION

SEDIMENTARY DEPOKOOLAU VOLCANO HONOLULU VOLC KOOLAU BASALTWAIANAE VOLCANO VOLCANICS) POSTSHIELD-STA KOLEKOLE MEMB PALEHUA MEMBE KAMAILEUNU ANBOUNDARY OF CALRIFT ZONE BOUNDADIKE COMPLEX BOU

!

!

!

!

!

!

! !

!

! !

!

!

!

! !

!

!

!

!

!

!

study area Northwest Rift Zone

Northwest Rift Zone Northeast Rift Zone

South Rift Zone

Southeast

Rift Zone

Kaau Rift Zone

Koolau Range Volcano

Figure 5. Generalized surficial geology, island of Oÿahu, Hawaiÿi (modified from Stearns, 1939; Langenheim and Clague, 1987; and 1997).
the caldera and rift-zone areas, rising magma that cooled in 

the subsurface solidified to form dikes (Stearns and Vaksvik, 

1935). The main period of eruptive activity was followed by 

a long period of extensive erosion, during which streams on 

the windward side removed more than a thousand feet of the 

original surface from the Koÿolau Volcano to form amphitheater-headed valleys (Stearns and Vaksvik, 1935). Following 

the period of extensive erosion, streams transported material to 

coastal areas and deposits of marine and terrestrial sediments 

formed the coastal plain (Oki and Brasher, 2003). 

Exposed rocks of the Koÿolau Range are composed of 

three principal units: Koÿolau Basalt, Honolulu Volcanics, and 

sedimentary deposits (fig 5). Within the study area, sedimentary deposits at low altitudes overlie Koÿolau Basalt. Koÿolau 

Basalt is highly permeable where free of dikes. Sedimentary 

deposits near the coastal areas consist of older and younger 

alluvium. Older alluvium, moderately to well consolidated and 

weathered, is at an altitude of about 600 ft to below sea level 

in the lower reaches of valleys. At lower altitudes, in valleys 

and along the coastal plain, younger and generally poorly 

consolidated alluvium overlies the older alluvium (Takasaki 

and others, 1969). 

Dike-Impounded System

Dikes in the rift zone are near-vertical, intrusive volcanic 

rocks that are hydrologically significant because of their low 

permeability and impounding effect on ground water. They are 

most abundant within the central area of the rift zone. Poorly 

permeable dikes tend to compartmentalize areas of permeable 

volcanic rocks and impede the flow of ground water. Dikes 

impound water to altitudes as much as 1,600 ft above sea level 

on Oÿahu (Gingerich and Oki, 2000). These high-level groundwater reservoirs accumulate and store rainfall recharge and 

discharge ground water to downgradient streams cutting into 

the dike-impounded reservoirs (Takasaki and Mink, 1985). 

The headwater areas of the three study-area watersheds 

lie mostly within the northwest rift zone of the Koÿolau 

Volcano (fig. 5). This rift zone is divided into a central dike 

complex and marginal dike zone. Dikes associated with the 

rift zones of the Koÿolau Volcano generally are numerous and 

closely spaced in the dike complex and widely scattered in the 

marginal dike zone. The volcanic rocks are highly permeable 

where free of dikes, moderately permeable in the marginal 

dike zone, and generally poorly permeable in the dike complex 

(Takasaki and others, 1969). Headwaters of the three studyarea watersheds at higher altitudes originate and are almost 

entirely in the dike complex. At lower altitudes, Kahana 

watershed lies in the marginal dike zone, whereas almost the 

entire area of Waikäne and Waiähole watersheds are in the 

dike complex. In areas where dikes and the ground water they 

impound have been exposed by erosion in stream channels, 

ground water discharges directly to the stream. Ground water 

also may discharge through sedimentary deposits into streams.

Hydrologic Setting and Water Diversions

Recharge to dike compartments follows the path with 

the least resistance, discharging to downgradient water bodies 

and directly to streams through seeps and springs. Waiähole, 

Waikäne, and Kahana Streams are naturally perennial throughout their entire courses because rainfall in the watersheds is 

persistent (fig. 4) and because these stream channels intersect 

high-level ground-water bodies in the interior, dike-intruded 

areas. Before the boring of the Waiähole Ditch System development tunnels, ground water discharged to springs above the 

level of the ditch. Streams received ground-water discharge 

where stream channels cut through dikes impounding ground 

water. Ground-water withdrawals by the main tunnel and the 

development tunnels caused a decline in ground-water levels 

in the high-level dike compartments and created new groundwater discharge points and flow paths (Takasaki and others, 

1969). The lowering of ground-water levels caused natural discharge at higher level springs and streams to decrease or cease 

(Hirashima, 1971). Base flows of streams therefore have been 

significantly reduced because ground water impounded by 

high-level dikes in the headwaters of the three diverted streams 

have been intercepted by the development tunnels and diverted 

by the ditch system. Although a significant source of ground 

water available for stream base flow was diverted, most of the 

lower reaches of the three diverted streams remained perennial 

because base flows in these streams are sustained by groundwater discharge from dike compartments at lower altitudes. 

Historic and recent field observations indicate that tributaries of all the diverted streams upgradient of the ditch system 

at about 750 ft altitude, except for Kahana Stream, flow 

intermittently. Stearns and Vaksvik (1935, p. 408) noted that 

the Kahana development tunnel did not cause the upgradient 

streams in Kahana Valley to become completely dry. It dried 

up a spring yielding a million gallons daily about 2,000 ft to 

the south of the tunnel but did not affect springs to the north. 

During the period 1989 to 1993 an average of 2.1 Mgal/d was 

estimated to enter the Waiähole Ditch System through surfacewater intakes in Kahana Valley (Edwin Sakoda, CWRM, written commun., 2005). Currently (2006), the intakes in Kahana 

Valley are not maintained; inflows of surface water through 

these intakes are less than 2.1 Mgal/d, as indicated by ditch 

seepage runs in 2002-03. The surface-water intakes feeding 

the Waiähole Ditch System were maintained until Oahu Sugar 

Company converted from furrow to drip irrigation during the 

mid-1980s. Surface water inflows contained higher levels of 

suspended sediments, which tended to clog drip-irrigation 

tubes—hence the shift to developing water primarily from 

ground-water sources. 

According to field observations from a USGS reconnaissance survey on August 23, 2002, the channel of South Fork 

Waikäne Stream above an altitude of 260 ft was dry. However, 

no historical information was found on the effects of the two 

Waikäne tunnels (one near intake 22 and one near intake 25) 

on high-altitude springs in upper Waikäne Valley. 

Description of Study Area 
Tributaries of Waiähole Stream upstream from the connecting tunnels are no longer perennial. Discharge measurements made during the 2002-03 ditch seepage run indicated 

insignificant surface-water flow coming from intakes in 

Waiähole Valley. According to Stearns and Vaksvik (1935, 

p. 403), the boring of the main tunnel dried up two springs 

in the upper Waiähole Valley. The two springs on Hälona 

Stream had an average flow during June-July, 1911, of 4.7 and 

1.04 Mgal/d (Lippencott, 1911, p.10; Stearns and Vaksvik, 

1935, p.403), which indicated that a combined spring flow 

of 5.7 Mgal/d was diverted by the main tunnel. The springs 

apparently dried up as the ground water was redirected to the 

main tunnel. It is commonly assumed that a portion of the 

ground water intercepted by the main tunnel leeward of the 

topographic crest of the Koÿolau Range naturally would have 

discharged to the windward side (Takasaki and others, 1969, 

p.74). The failure of tunnel A (735 ft south of the main tunnel) 

and tunnel B (1,400 ft north of the main tunnel) to develop 

ground water was attributed to their proximity to the main 

tunnel. Assuming Stearns and Vaksvik (1935, p.405) correctly 

interpreted the failure of these two tunnels, the main tunnel 

has completely drained the dike compartments to the level 

of the main tunnel for more than 2,000 ft on each side of the 

main tunnel. 

In addition to the development tunnels, other water 

diversions to or from Waiähole Ditch affected low flows in 

the Waiähole watershed. Between 1916 and 1982, an average flow of 1 Mgal/d (Takasaki and Mink, 1985) and as much 

as 3 Mgal/d (an estimate obtained from USGS continuousrecord station 16291000 documents) was pumped daily from 

Waiähole Stream at 450 ft altitude into the Waiähole Ditch. 

In addition, an average flow of 0.5 Mgal/d is delivered from 

the ditch to users in Waiähole Valley through the McCandless Pipeline in compliance with water rights purchased from 

McCandless (Hawaiÿi Commission on Water Resource Management, 2001). This 0.5 Mgal/d is being diverted into Waianu 

Stream near 400 ft altitude, and supposedly the same quantity 

is diverted out of the stream at a slightly lower altitude into a 

pipeline system that supplies downstream users. According to 

Agribusiness Development Corporation personnel (Alfredo 

Lee, oral commun., 2005), flow being released from Waiähole 

Ditch through the McCandless Pipeline is fairly steady.

Available Discharge Data 

Available discharge data for natural and diverted flow 

conditions were compiled from (1) seepage runs, (2) continuous-record stations, (3) low-flow partial-record (LFPR) stations, and (4) miscellaneous measurement sites. Seepage runs 

consist of a series of discharge measurements made at multiple 

locations on a stream or ditch at approximately the same time 

during a period of steady base flow. Measurements are made at 

about the same time to minimize the effect that any variability 

with time might introduce (Fontaine, 2003). Data from continuous-record stations consist of a record of stage, individual 

measurements of discharge throughout a range of stages, and 

notations regarding factors that may affect relations between 

stage and discharge. Discharge for any particular instant or 

for selected periods of time are computed from the continuous 

record of stage and the relation between stage and discharge 

at the station. LFPR stations are typically nonrecording gages 

where systematic, instantaneous measurements of discharge 

and stream elevation are made during times of low flow. 

The discharge measurements are used to make estimates of 

selected low-flow statistics, such as median streamflow, at the 

stations. Miscellaneous measurement sites are locations where 

only random, instantaneous measurements of discharge are 

made.

Seepage Runs

Seepage runs have been conducted historically and 

specifically for this study to identify reaches where gains and 

losses of flow take place and to quantify these changes along 

Waiähole, Waianu, Waikäne, and Kahana Streams and in the 

connecting Waiähole tunnels (figs. 6-13). Seepage runs done 

specifically for this study were conducted to determine how 

the releases of Waiähole ditch water into Waiähole, Waianu, 

and Waikäne Streams affect downstream base flows. Seepage 

runs were also conducted in the Waiähole tunnels to determine 

the amount of ground water intercepted by the development 

tunnels in Kahana, Waikäne, and Waiähole watersheds. It 

should be noted that gaining reaches in the streams during 

diverted (post-ditch) conditions likely were gaining reaches 

during natural (pre-ditch) conditions; losing stream reaches 

during post-ditch conditions may or may not have been losing 

reaches during the pre-ditch period. The channel gains and 

losses in stream or ditch reaches reported in this study exclude 

flow releases or diversions and inflows from intakes, tributaries, and return flows. For example, tributary flow was not considered to be a gain in stream. The reported values therefore 

reflect natural gains and losses in stream or ditch reaches.

Waiähole Ditch Tunnel

As part of this study, seepage runs along the connecting 

and main tunnels of the Waiähole Ditch System were made 

on February 27, 2002 (wet season), and August 20, 2003 (dry 

season) (table 2). The seepage-run reach is 4.8 mi in length 

and extends from Intake 1 in Kahana Valley to the North 

Portal gage (fig. 6B). Flow records from the North Portal gage 

(USGS station number 16287000) indicated that the discharge 

measurements were made during a period of steady base flow 

in the tunnel. Both seepage runs indicate that a short reach 

between Waikäne tunnel 2 (site 10) and Uwao development 

tunnel (site 11) loses water (fig. 6). The 2002 seepage run, 

made at the beginning of the wet season, indicates that the 

reach from downstream of Intake 29 to North Portal gage loses 

water. However, the 2003 seepage run, made at the begin10

Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
Table 2. Discharge measurements made during seepage runs in the connecting tunnels of the Waiähole Ditch System, 

windward Oÿahu, Hawaiÿi, 2002-03

[Mgal/d, million gallons per day; --, not measured]

Site

number

(fig. 6)

February 27, 

2002

August 20, 

2003 Site description

Mgal/d Mgal/d

1 0.03 -- Downstream of Intake 1

2 0.15 0.16 Upstream of Kahana development tunnel

3 1.14 0.99 Downstream of Kahana development tunnel

4 1.59 1.13 Downstream of Intake 17

5 1.80 1.14 Kahana/Waikäne watershed divide

6 2.37 1.78 Intake 21 gage

7 5.05 4.20 Downstream of Waikäne development tunnel 1 at Intake 22

8 -- 2.97b Intake 23 release

9 6.44 1.49 Upstream of Waikäne development tunnel 2

10 7.37 2.26 Downstream of Waikäne development tunnel 2; Waikäne/Waiähole divide

11 7.17 1.89 Upstream of Uwaoa

 development tunnel

12 19.2 12.1 Downstream of Uwaoa

 development tunnel

13 20.5 13.9 Gage 16285000; downstream of Intake 29

14 2.84 3.03b Gate 30 release

15 16.0b 6.98b Gate 31 release; Gage 16286000 

16 1.20b 4.94b North Portal gage 16287000

a

Uwao was formerly spelled Uwau.

b

Discharge from stage-discharge relationship.

ning of the dry season, indicates that the same reach gained 

rather than lost water. The two seepage runs indicate that the 

Waiähole Ditch System intercepted an average of 1.45, 4.85, 

and 12.7 Mgal/d from the Kahana, Waikäne, and Waiähole 

watersheds, respectively (fig. 6).

On September 2, 1959, a seepage run was made on a 

short reach of the Waiähole Ditch connecting tunnel in Kahana 

Valley. Discharge measurements were made at three locations 

from just upstream of Kahana development tunnel (site 2) to 

downstream of Intake 19 (site 4A) (fig. 6A, table 3). During the 2002 and 2003 seepage runs, 0.15 and 0.16 Mgal/d, 

respectively, were measured just upstream of the Kahana 

development tunnel at site 2. In contrast, during the 1959 

seepage run 0.61 Mgal/d was measured at site 2. The significant reduction (0.46 Mgal/d) in measured flow at site 2 can 

be attributed to the decreased role played by the surface water 

inflows to the Waiähole Ditch System. Subsequent to the mid 

1980’s, a majority of the surface-water intakes have not been 

maintained (Edwin Sakoda, CWRM, written commun., 2005). 

During the 2002 and 2003 seepage runs, only minor surface 

water inflows were observed at the Kahana intakes upstream 

from site 2.

Table 3. Discharge measurements made during seepage run in the connecting tunnels of the Waiähole Ditch System, 

windward Oÿahu, Hawaiÿi, 1959.

[These unpublished measurements are in the files of the USGS Pacific Islands Water Science Center; Mgal/d, million gallons per day]

Site

number

(fig. 6)

September 2, 1959

Site description Mgal/d

2 0.61 Upstream of Kahana development tunnel

3A 4.01 Downstream of Intake 15

4A 4.11 Downstream of Intake 19

Available Discharge Data 11
Kahana

Bay

KaneoheBay

EXPLANATION

A

Kahana Stream

Kawa Stream

Punaluu Stream

Kaaawa Stream

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

HalonaStream

157 ̊54'W 157 ̊52'W 157 ̊50'W

21 ̊28'N21 ̊30'N21 ̊32'N21 ̊34'N

Waiawa Stream 0 1 2 Kilometers

0 1 2 Miles

+1.8

09/02/1959

+0.1

+0.1

Intake 15

Intake 19

Kahanatunnel

2

3A 4A

4A

DITCH SECTION–Number shows wain million gallons per day. Dashed whChannel gains or losses in section exclor diversions and inflows from intakes, tributaries, and return flows. Losing section Gaining sectionDITCHWATERSHED BOUNDARYMEASUREMENT SITE AND IDENTNET GAIN FROM WATERSHED, IN  GALLONS PER DAY

Figure 6. Results of seepage runs on Waiähole Ditch System, windward Oÿahu, Hawaiÿi, 1959 (A) and 2002-03 (B). Uwao was 

Uwau.
Kahana

Bay

KahanaBay

KaneoheBay

B

Kahana Stream

Kawa Stream

Punaluu Stream

Kaaawa Stream

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

HalonaStream

Kahana Stream

Kawa Stream

Punaluu Stream

Kaaawa Stream

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

HalonaStream

157 ̊54'W 157 ̊52'W 

21 ̊28'N21 ̊30'N21 ̊32'N21 ̊34'N

Waiawa Stream

Base modified from U.S. Geological Survey,1:24,000 digital data.

Base modified from U.S. Geological Survey,1:24,000 digital data.

157 ̊54'W 157 ̊52'W 157 ̊50'W

21 ̊28'N21 ̊30'N21 ̊32'N21 ̊34'N

Waiawa Stream

North Portal North Portal

+1.1

+4.1

+12.7

08/20/2003

Intake 1

Intake 29

02/27/2002

+1.8

+5.6

+12.7

Intake 1

Intake 29

1

16

15

14

13

12

11

10 9

8

7

6 5 4

3

2

1

16

15

14

13

12

11

10 9

8

7

6 5 4

3

2

Figure 6.—Continued.
Waiähole and Waianu Streams

Seepage runs on Waiähole Stream and its tributary, 

Waianu Stream, have been made during three different hydrologic settings: (1) post-release, (2) post-ditch and pre-release, 

and (3) pre-ditch. To evaluate the effects of flow releases 

from Waiähole Ditch at Gate 31 into Waiähole Stream and at 

Gate 30 into Waianu Stream, seepage runs were conducted 

on Waiähole Stream on March 14, June 26, and September 

27, 1995 (fig. 7, table 4), and on Waianu Stream on May 

10, June 21, and September 26, 1995 (fig. 8, table 5). These 

seepage runs were conducted to identify natural gains or 

losses of water during post-release base-flow conditions. All 

of the seepage runs on the Waiähole and Waianu Streams 

were made after the flow releases began on December 19, 

1994, and May 23, 1995, respectively, except for the May 10, 

1995, seepage run on Waianu Stream. During the March 14, 

June 26, and September 27, 1995 seepage runs on Waiähole 

Stream, measured flow releases at Gate 31 were 14.4, 11.8, 

and 11.1 Mgal/d, respectively. Flow release at Gate 31 was 

reduced over time to account for the subsequent initiation of 

flow release at Gate 30. During the June 21 and September 26, 

1995, seepage runs on Waianu Stream, measured flow releases 

at Gate 30 were 1.71 and 1.07 Mgal/d, respectively.

Natural gains and losses on some Waiähole and Waianu 

Stream reaches were difficult to determine because of complex 

patterns of inflows and flow diversions. In general, seepage 

runs on both streams indicate small losses of water just downstream from the two flow-release points at Gates 30 and 31. 

Both of the losing reaches were dry during base-flow periods 

before the release of water. In general, Waiähole Stream gains 

water over the remaining reach down to the confluence with 

Waianu Stream. The three seepage runs on Waianu Stream 

also indicate a predominant pattern of gains between the Gate 

30 release point and the confluence with Waiähole Stream. A 

short losing reach exists on Waiähole Stream, just downstream 

of the confluence with Waianu Stream. 

Seepage runs made before the flow release on these 

two streams in 1959 and 1960 also indicate similar patterns. 

Discharge measurements for seepage runs in 1959 and 1960 

(tables 6, 7) were made as part of a water resources study of 

windward Oÿahu (Takasaki and others, 1969). These seepage runs were not as extensive as those done in 1995, and 

discharge measurements were only made on parts of the 

two streams over relatively short reaches. Seepage runs on 

Waiähole Stream were made on July 20, 1959, and July 19, 

1960, and seepage runs on Waianu Stream were made on July 

21, 1959, July 19, 1960, and March 28, 1961. The results of 

these seepage runs during pre-release flow conditions indicate 

mostly gaining reaches (figs. 9, 10). This also indicates that 

although the Waiähole Ditch System has reduced base flow in 

Waiähole Stream, ground-water discharge from the lower part 

of the dike complex is sufficient to sustain perennial flow. 

Before the ditch construction, two seepage runs were 

made on Waiähole and Waianu Streams over a period of two 

days from September 9 to 10, 1911 (Martin and Pierce, 1913). 

On Waiähole Stream, discharge measurements were made 

between altitudes 160 and 20 ft. On Waianu Stream, discharge 

Table 4. Discharge measurements made during seepage runs in the Waiähole Stream, windward Oÿahu, Hawaiÿi, 1995.

[n.a., not available; Mgal/d, million gallons per day; --, not measured]

Site

number

(fig. 7)

Altitude

(feet)

March 14, 

1995

Mgal/d

June 26,1995

Mgal/d

September 

27, 1995

Mgal/d

Site description

1 n.a. 14.4 11.8 11.1 Gate 31 release

1A 400 -- 11.1 9.50 Near pumping station

2 320 16.5 -- 12.0 Near Waiähole Camp

3 250 18.2 -- 13.4 Downstream from old USGS gage (16291000)

3A 110 -- 14.1 -- Upstream from chicken farm diversion

3C 105 -- 14.2 14.3 Downstream from chicken farm diversion

4A 70 16.5 15.1 13.8 Upstream from confluence, Waianu Stream

4B 75 0.67 0.60 0.81 Diversion upstream form site 4A

4C 75 0.71 3.01 2.35 Waianu Stream at mouth

5 65 17.1 16.9 14.7 Downstream from confluence, Waianu Stream

5A 40 -- -- 17.5 Downstream from diversion at site 5B

5B 40 -- 1.07 0.32 Diversion upstream form site 5A

5C 14 -- 0.87 0.08 Return flow downstream from site 6

6 20 18.1 16.5 15.8 Upstream from Kamehameha Highway

14  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
Table 5. Discharge measurements made during seepage runs in the Waianu Stream, windward Oÿahu, Hawaiÿi, 1995.

[Mgal/d, million gallons per day; --, not measured]

Site

number

(fig. 8)

May 10, 1995

Mgal/d

June 21, 

1995

Mgal/d

September 

26, 1995

Mgal/d

Site description

1 -- 1.71 1.07 Gate 30 release

1A 0.02 1.44 1.07 Upstream from McCandless Pipeline inflow

2 0.40 1.72 1.34 Downstream from McCandless Pipeline inflow

3A 0.52 2.00 1.25 Upstream from McCandless diversion

4 0.08 0.11 0.12 Tributary inflow (Gate 29) at mouth

å 0.41 0.14 0.63 McCandless diversion

6 0.32 1.63 1.25 Downstream from McCandless diversion

7 0.74 2.35 1.37 Upstream from confluence, Uwaoa

 Stream

8 0.37 0.13 0.19 Uwaoa

 Stream at mouth

9 1.01 -- -- Downstream from confluence, Uwaoa

 Stream and near diversion pond

9A -- 2.42 1.68 Downstream from diversion pond

10 0.08 0.29 0.18 Diversion upstream from site 11

11 1.22 2.38 1.56 Downstream from diversion at site 10

12 1.33 2.26 1.78 Downstream from field inflow

13 0.37 0.36 0.19 Diversion upstream from site 14

14 1.16 2.10 1.75 Downstream from diversion at site 13

14A -- 2.42 1.89 Downstream from stream ford

15 1.64 2.55 2.06 Waianu Stream at mouth

a

Uwao was formerly spelled Uwau.

measurements were made between altitudes of about 310 and 

75 ft. Because of the complex patterns of flow diversions and 

the difficulty in determining the exact locations of the measurements, natural gains and losses under pre-diversion conditions along the lower part of Waiähole and Waianu streams are 

difficult to determine with certainty. 

Other same-day discharge measurements made during 

the pre-ditch period also provide estimates of the magnitude 

of ground-water gains representative of natural (undiverted) 

flow conditions on certain reaches of Waiähole and Waianu 

Streams. On August 11, 1911, discharge measurements were 

made (Lippencott, 1911) near an altitude of 750 ft (near ditch 

level) on Hälona and Waihï Streams and at 225 ft altitude 

(site 4) just downstream of station 16291000 and upstream 

of all irrigation diversions (fig. 9). The combined flow of the 

upstream discharge measurements was 7.9 Mgal/d at 750 ft 

altitude (table 6), and the downstream measurement indicated 

a total flow of 16.5 Mgal/d at 225 ft altitude under natural flow 

conditions (table 6). Because the measurements were made 

upstream from all irrigation diversions, the gains in flow represented ground-water discharge to the stream, assuming baseflow conditions with no surface runoff. The measurements 

indicate the stream reach between altitudes 750 ft (near ditch 

level) and 225 ft gained about 8.6 Mgal/d of ground water (fig. 

9). Based on 19 concurrent low-flow days (September 25 to 

October 15, 1911) (Martin and Pierce, 1913), the differences 

between the combined daily discharges at Hälona and Waihï 

stations (16288000 and 16289000) and daily discharges at 

station 16292000 indicate an average gain of about 8 Mgal/d 

between altitudes 750 and 160 ft. 

During dry-weather post-ditch periods, all of the upper 

tributaries of Waiähole Stream upstream from the 750 ft 

altitude were dry. The net post-diversion ground-water gain 

within about the same reach of Waiähole Stream, between altitudes of 750 and 250 ft (sites 1 and 3 on fig. 7), was reduced to 

3.8 Mgal/d on March 14, 1995, and to 2.3 Mgal/d on September 27, 1995 (table 4). 

 Discharge measurements were made in Uwao and upper 

Waianu Streams on October 11, 1911 (Martin and Pierce, 

1913). Flow measured on the north, middle, and south forks of 

upper Waianu Stream at about 650 ft altitude were 1.5 Mgal/d, 

2.7 Mgal/d, and 1.2 Mgal/d, respectively, with a combined 

flow of 5.4 Mgal/d. On the same day, flow measured in 

Uwao Stream just upstream of the confluence with Waianu 

Stream was 1.4 Mgal/d and the daily flow recorded at station 

16293000 just downstream of the confluence was 7.8 Mgal/d. 

Available Discharge Data 15
Kaneohe

Bay

A

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

Kamehameha Hwy

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

+2.1

+1.7

-1.0

-0.1

-0.1

1

2

3

4A

4C

5

6

+1.0

+1.0

03/14/1995

Gate 31

STREAM SECTION–Number shows in million gallons per day. Dashed whChannel gains or losses in reach excluor diversions and inflows from intakestributaries, and return flows. Losing section Gaining sectionDITCHWATERSHED BOUNDARYMEASUREMENT SITE AND IDENT

EXPLANATION

0 1 2 Kilometers

0 1 2 Miles

Figure 7. Results of seepage runs on Waiähole Stream, windward Oÿahu, Hawaiÿi, March 1995 (A) and June and September 1

was formerly spelled Uwau.
KaneoheBay Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

B

+3.0

-0.7

-1.2

+1.5 1 1A 3A

4B

4A

4C 5 5B

6

5C

3C

+0.1

Gate 31

06/26/199506/26/1995

-1.6

+2.5

+1.4

+0.9 

1

1A

2

3

Gate 31

09/27/199509/27/1995

Kamehameha Hwy 

Figure 7.—Continued.
Kaneohe

Bay

A

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

Kamehameha Hwy

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

+0.1+0.4

-0.1

-0.1

+0.3 +0.5

+0.4

1A

2

3A-5 8

6 7 9 10

15

15

12

11

14

13

Gate 30

05/10/1995

+0.1

STREAM SECTION–Number shows in million gallons per day. Dashed whChannel gains or losses in section excor diversions and inflows from intakestributaries, and return flows Losing section Gaining sectionDITCHWATERSHED BOUNDARYMEASUREMENT SITE AND IDENT

EXPLANATION

0 1 2 Kilometers

0 1 2 Miles

Figure 8. Results of seepage runs on Waianu Stream, windward Oÿahu, Hawaiÿi, May 1995 (A) and June and September 1995 

formerly spelled Uwau.
KaneoheBay Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

B

-0.1 +0.3+0.8 +0.3

+0.3

+0.1

1A 2

3A-5 8

6 7 9A 10

15

12

11

14

13

1

14A

+0.3

Gate 30

+0.1

-0.1

+0.1 +0

1A 2

3A-5 8

6 7 9A 10

1

11

13

1

+0.1

Gate 30

06/21/1995 09/26/1995

Kamehameha Hwy 

Figure 8.—Continued.
Kaneohe

Bay

A

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

Kamehameha Hwy

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

+8.6

+8.6

1

2

4

08/11/1911

4

-0.1

STREAM SECTION–Number shows in million gallons per day. Dashed whChannel gains or losses in section excor diversions and inflows from intaketributaries, and return flows. Losing section Gaining sectionDITCHWATERSHED BOUNDARYMEASUREMENT SITE AND IDEN

EXPLANATION

0 1 2 Kilometers

0 1 2 Miles

Figure 9. Results of seepage runs on Waiähole Stream, windward Oÿahu, Hawaiÿi, 1911 (A) and 1959-60 (B). Uwao was forme

Uwau.
KaneoheBay Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

B

+2.2

3

5

+2.6

3

07/20/1959 07/19/1960

Kamehameha Hwy 

Figure 9.—Continued.
Kaneohe

Bay

A

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

Kamehameha Hwy

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

+0.2

+0.1 +0.2

+0.2

2

7

7

3 6

5

1

07/21/1959

EXPLANATION

STREAM SECTION–Number shows in million gallons per day. Dashed whChannel gains or losses in section excor diversions and inflows from intakestributaries, and return flows. Gaining sectionDITCHWATERSHED BOUNDARYMEASUREMENT SITE AND IDENT

0 1 2 Kilometers

0 1 2 Miles

Figure 10. Results of seepage runs on Waianu Stream, windward Oÿahu, Hawaiÿi, 1959 (A) and 1960-61 (B). Uwao was forme
KaneoheBay Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

B

+0.3

4

5

7

+0.3 +0.2

6

3 5

07/19/1960 03/28/1961

Kamehameha Hwy 

Figure 10.—Continued.
These measurements indicate a gain of about 1.0 Mgal/d of 

ground water in the 4,500-ft reach of Waianu Stream between 

altitudes 650 and 190 ft. This gain is much less than the gain 

of about 8.6 Mgal/d in the 4,000-ft reach between about the 

same altitudes in Waiähole Stream on August 11, 1911 (fig. 

9). Takasaki and Mink (1985, p. 35) provided an explanation 

for this larger gain in Waiähole Stream: Between altitudes of 

400 and 250 ft, “Waiähole Stream cuts deeper into saturated 

rock in this reach than streams in the other valleys, resulting in 

more leakage. The gains in the other valleys are steady in the 

downstream direction and seem to indicate slow and uniform 

drainage by the streams cutting into saturated rock.”

Waikäne Stream

As part of this study, seepage runs along Waikäne Stream 

were made on September 18, 2002, and May 12, 2003 (fig. 

11, table 8). These seepage runs document how base flow 

varies along the stream before and after flow releases from 

the ditch system began on October 11, 2002, at Intake 23. The 

reach on south fork of Waikäne Stream upstream of altitude 

260 ft was observed to be dry during a USGS reconnaissance 

on August 23, 2002. It also was observed that a high percentage of streamflow at altitudes 410 and 500 ft on north fork of 

Waikäne Stream was ground-water discharge from dike-fed 

Table 7. Discharge measurements made during seepage runs in the Waianu Stream, windward Oÿahu, Hawaiÿi, 1959-

61 (data and site descriptions from Takasaki and others, 1969).

[ft, feet; Mgal/d, million gallons per day; --, not measured]

Site

number

(fig. 10)

Takasaki

numbera

July 21, 

1959

Mgal/d

July 19, 

1960

Mgal/d

March 28, 

1961

Mgal/d

Site description (Takasaki and others, 1969)

1 179 0.22 -- -- Diversion by McCandless Pipeline

2 180 0.03 -- -- 100 ft downstream from confluence of right and left branches; 

water left in stream after diversion by pipeline

3 181 0.20 -- 0.26 At first ford; at trail crossing at altitude 320 ft

4 182 -- 0.51 -- Upstream of Uwaob

 confluence

5 183 0.08 0.24 0.15 80 ft upstream of road crossing - Uwaob

 Stream

6 184 0.38 -- 0.72 10 ft downstream of Uwaob

 confluence

7 185 0.62 1.06 0.92 Downstream of Waiähole road crossing on Waianu Stream

a

Station numbers used by Takasaki and others (1969).

b

Uwao was formerly spelled Uwau.

Table 6. Discharge measurements made during seepage runs in the Waiähole Stream, windward Oÿahu, Hawaiÿi, 1911 

(Lippencott, 1911) and 1959-60 (Takasaki and others, 1969).

[ft, feet; Mgal/d, million gallons per day; --, not measured]

Site

number

(fig. 9)

Takasaki

numbera

August 11, 

1911

Mgal/d

July 20, 

1959

Mgal/d

July 19, 

1960

Mgal/d

Site description (Takasaki and others, 1969)

1 -- 2.40 -- -- Waihï Stream at altitude 723 ft

2 -- 5.50 -- -- Hälona Stream at altitude 672 ft

3 176 -- 0.13 0.41 Downstream of pumping station and confluence of two streams; 

most of this water spills over weir at pump house--excess over 

pump capacity

4 -- 16.5 -- -- Old USGS station 16291000; upstream of all diversions

5 178 -- 2.34 2.96 Upstream of confluence with Waianu Stream

6 185 -- -- 1.06 Downstream of Waiähole road crossing on Waianu Stream

7 186 -- -- 3.90 Downstream of Waianu confluence; possibly some water being 

diverted to taro patches on right bank

a

Station numbers used by Takasaki and others (1969).

24  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
springs. In general, both seepage runs (before and after flow 

was released at Intake 23) indicate a pattern of gaining flow at 

upper altitudes. Both seepage runs indicate Waikäne Stream 

loses water downstream from about 35 ft altitude. Similar 

patterns also are evident in results from three separate seepage 

runs conducted in 1959-60 (fig. 12, table 9).

Kahana Stream

Kahana Stream differs from both Waiähole and Waikäne 

Streams because it is not affected by the recent flow releases 

from the Waiähole Ditch. The only seepage runs done on this 

stream were made on three occasions in 1960-62 as part of the 

water resources study of windward Oÿahu (Takasaki and others, 1969) (fig. 13, table 10). Discharge measurements made 

on August 23, 1960, indicate a pattern of gaining flow between 

altitudes of about 620 and 290 ft. Seepage runs on September 

6, 1961, and February 13, 1962, both indicate a pattern of 

gaining flow extending from an altitude of about 280 ft downstream to an altitude of about 120 ft. 

Continuous-Record Stations 

Numerous continuous-record stations have been operated by the USGS in the Waiähole, Waikäne, and Kahana 

watersheds of windward Oÿahu (table 11). Most of the stations 

measured streamflow, while others measured ditch flows. Only 

a few of the stations were operated before the construction of 

the Waiähole Ditch System.

Pre-ditch

A total of six continuous-record stations were operated 

in the Waiähole and Waikäne watersheds before the ditch 

construction. Four of the six stations were operated concurrently for several months. No continuous-record stations were 

operated in the Kahana watershed before the ditch-system 

construction; stations 16296000 and 16297000 were operated 

mostly during the construction period (table 11). Records collected at these pre-ditch stations are based on one gage reading 

per day, except for station 16292000, where records are based 

on two gage readings per day.

Continuous streamflow data are available for station 

16292000 on Waiähole Stream from September 25, 1911, to 

June 30, 1916. This station was located at an altitude of 160 

ft, above the confluence of Waiähole and Waianu Streams, 

and measured streamflow upstream of all irrigation diversions 

(fig. 14). Discharge data for the period before the construction of the ditch system are limited to those recorded from 

1911 through August 1, 1913. The average flow for this period 

is 15.4 Mgal/d. A sharp increase in daily discharge (fig. 15) 

indicates that after August 1, 1913, additional water that was 

developed during the boring of the main tunnel was being 

discharged into the stream upstream from the station. Data 

collected subsequent to this date were therefore not used to 

estimate natural flow-duration discharges in Waiähole Stream. 

Station 16294000 on Waiähole Stream at altitude 14 

ft was operated for much of the same time period as station 

16292000 and measured streamflow going into Käneÿohe Bay 

downstream from most irrigation diversions. Because of the 

numerous water diversions from the stream for irrigation of 

rice lands in the lower part of the valley, measurements made 

at this station are not representative of natural flow conditions 

and were not used in this study. 

Table 8. Discharge measurements made during seepage runs in the Waikäne Stream, windward Oÿahu, Hawaiÿi, 

2002-03.

[ft, feet; Mgal/d, million gallons per day; --, not measured]

Site

number

(fig. 11)

USGS

station number

September 18, 

2002

Mgal/d

May 12, 2003

Mgal/d Site description

1 213033157530801 0.19 0.19 North fork at altitude 500 ft

2 213030157525801 0.20 0.22 North fork at altitude 410 ft

3 16294400 0.36 0.49 North fork at altitude 220 ft, at mouth

4 213012157532601 -- 3.01 Intake 23 at altitude 760 ft

5 213015157524601 0.14 -- South fork at altitude 240 ft

6 16294500 0.16 3.36 South fork at altitude 220 ft, at mouth

7 16294800 0.93 4.24 At altitude 90 ft

8 16294700 0.03 0.22 Waikeÿekeÿe Stream at altitude 90 ft, at mouth

9 16294900 1.37 4.46a At altitude 75 ft

10 212950157514101 1.32 4.96 At altitude 35 ft

11 16295195 1.05 4.49 At altitude 10 ft, at Kamehameha Highway

a

 Discharge from stage-discharge relationship.

Available Discharge Data   25
Table 9. Discharge measurements made during seepage runs in the Waikäne Stream, windward Oÿahu, Hawaiÿi, 

1959-60.

[ft, feet; ft3/s, cubic feet per second; Mgal/d, million gallons per day; --, not measured]

Site

number

(fig. 12)

Takasaki

numbera

July 15, 

1959

Mgal/d

October 

19, 1959

Mgal/d

February 

9, 1960

Mgal/d

Site description (Takasaki and others, 1969)

1 188 0.39 -- 0.48 At altitude 240 ft, downstream of confluence of north and south 

forks

2 189 0.42 -- -- At altitude 220 ft

3 190 0.72 -- -- Waikäne Stream upstream of confluence with Waikeÿekeÿe Stream

4 191 0.06 -- 0.09 Waikeÿekeÿe Stream at altitude 100 ft, upstream of confluence with 

Waikäne Stream

5 192 -- 0.87 1.01 At altitude about 90 ft, downstream of confluence with 

Waikeÿekeÿe Stream

6 193 -- -- 1.23b USGS gaging station 16294900 at altitude 75 ft

7 194 -- 1.23 -- At altitude about 60 ft, downstream of ditch diversion and intake 

8 195 1.38 -- -- At altitude about 35 ft, downstream of ditch diversion

9 196 -- 1.18 -- At altitude about 30 ft, downstream of ditch diversion 

10 198 0.70 -- -- About 20 ft downstream of Kamehameha highway

a

Station numbers used by Takasaki and others (1969).

b

Daily mean discharge computed at gaging station.

Table 10. Discharge measurements made during seepage runs in the Kahana Stream, windward Oÿahu, Hawaiÿi, 1960-

62.

[ft, feet; Mgal/d, million gallons per day; --, not measured]

Site

number

(fig. 13)

Takasaki

numbera

August 23, 

1960

Mgal/d

September 6, 

1961

Mgal/d

February 13, 

1962

Mgal/d

Site description

1 210 0.08 -- -- Altitude 620 ft on eastern tributary

2 211 0.13 -- -- Altitude approximately 590 ft on eastern tributary

3 212 0.20 -- -- Altitude 560 ft on eastern tributary

4 213 0.81 -- -- Altitude 515 ft on eastern tributary

5 214 0.22 -- -- Altitude 500 ft on western tributary just above 

confluence

6 215 2.11 -- -- Altitude 380 ft on east branch

7 216 -- 2.57 1.95 East branch of Kahana Stream 100 ft upstream of 

confluence at altitude 280 ft

8 217 1.95 1.42 0.92 West branch of Kahana Strearm, 20 ft upstream of 

confluence at 280 ft altitude

9 218 5.55 -- 3.55 Kahana Stream about 30 ft downstream of confluence at altitude 280 ft

10 220 -- -- 3.83 Altitude 225 ft about 50 ft downstream of confluence with western tributary

11 221 -- 6.92 -- Below spring inflow about 1.0 mile (straight 

distance) upstream of USGS gaging station 

16296500.

12 224 -- 9.31 -- At 120 ft altitude

a

Station numbers used by Takasaki and others (1969).

26  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
KaneoheBay Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

B

+0.01 +0.2

+0.4

+0.4

-0.1

-0.3

11

10

9

8

7 6

3 2

1

5

4

intake 23

dry

+0.03

+0.3

+0.4

+0

+0

+0.4

8

7 6

3 2

1

4

intake 23

09/18/2002 05/12/2003

0 

0 

+0.4

-0.3

11

EXPLANATION

STREAM SECTION–Number shows water gain or loss, in million gallons per day. Dashed where uncertain. Channel gains or losses in section excludes flow releases or diversions and inflows from intakes, tunnels, and tributaries, and return flows. Losing section Gaining sectionDITCHWATERSHED BOUNDARYMEASUREMENT SITE AND IDENTIFICATION NUMBER

Kamehameha Hwy 

Figure 11. Results of seepage runs on Waikäne Stream, windward Oÿahu, Hawaiÿi, 2002-03. Uwao was formerly spelled Uwau.
Kaneohe

Bay

A

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

Kamehameha Hwy

157 ̊54'W 157 ̊52'W

21 ̊28'W21 ̊30'W +0.03 +0.3

+0.6 +0.6

-0.7

-0.7 3

8

10

10

 1

 2

 4

07/15/1959

EXPLANATION

STREAM SECTION–Number shows in million gallons per day. Dashed whChannel gains or losses in section excor diversions and inflows from intakestributaries, and return flows. Losing reach Gaining reachDITCHWATERSHED BOUNDARYMEASUREMENT SITE AND IDEN

0 1 2 Kilometers

0 1 2 Miles

Figure 12. Results of seepage runs on Waikäne Stream, windward Oÿahu, Hawaiÿi, July 1959 (A) and October 1959 and Febru

Uwao was formerly spelled Uwau.
KaneoheBay Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream Waihi

Stream

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

157 ̊54'W 157 ̊52'W

21 ̊28'N21 ̊30'N

B

 5

7

9

-0.1

+0.4

+0.4

+0

 1

4 5 

10/19/1959 02/09/1960

Kamehameha Hwy 

Figure 12.—Continued.
Kahana

Bay

EXPLANATION

A

Kahana Stream

Kawa Stream

Punaluu Stream

157 ̊54'W 157 ̊52'W

21 ̊32'N21 ̊34'N

08/23/1960

0 1 2 Kilometers

0 1 

+1.5

+1.5

+1.1

6

8

9

1

2

3 4

5

9

STREAM SECTION–Number shows wain million gallons per day. Dashed wherChannel gains or losses in reach excludeor diversions and inflows from intakes, ttributaries, and return flows. Gaining sectionDITCHWATERSHED BOUNDARYMEASUREMENT SITE AND IDENTIF

Figure 13. Results of seepage runs on Kahana Stream, windward Oÿahu, Hawaiÿi, 1960 (A) and 1961-62 (B). 
Kahana

Bay

B

Kahana Stream

Kawa Stream

Punaluu Stream

Kahana Stream

K

Punaluu Stream

Base modified from U.S. Geological Survey,1:24,000 digital data.

Base modified from U.S. Geological Survey,1:24,000 digital data.

157 ̊54'W 157 ̊52'W

21 ̊32'N21 ̊34'N

09/06/1961

157 ̊54'W 

21 ̊32'N21 ̊34'N

02/13/1962

+2.9

+2.4

7 8

11

12

+0.7

+0.2

7 8

9

10

Figure 13.—Continued.
Table 11. Continuous-record streamflow stations in the Waiähole, Waikäne, and Kahana watersheds, windward Oÿahu, Hawaiÿi.

[WWC, Waiähole Water Company; ADC, Agribusiness Development Corporation (took over the management of Waiähole Ditch System since 1999); stations operated before aWaiähole Ditch System are shown in bold; n.a., not available; P, present; LFPR low-flow partial-record]

Gagingstation

number

Station location

Station

altitude

(feet)

Period of record

operated by USGS Remarks

Waiähole

16285000 Waiähole tunnel at Waianu near Gate 30 n.a. 1950-69 Established by WWC in 19

operated by WWC; 1999

16286000 Waiähole tunnel wasteway at Intake 31 near Waiähole n.a. 1951-69 and 2000-03 Established by USGS in 19

WWC; 2003-P operated 

16287000 Waiähole tunnel at North portal near Waiähole n.a. 1951-69 and 2000-03 Established by WWC in 19

operated by WWC, and 2

16287200 Waiähole tunnel at Adit 8 near Waipahu n.a. 1956-69 and 2000-03 Established by WWC in 19

operated by WWC, and 2

16288000 Hälona Stream near Waikäne 750 8/9/1911 - 9/30/1911 Fragmentary record, only 

available

16289000 Waihï Stream near Waikäne 750 8/11/1911 - 10/19/1911 Fragmentary record, only 

available

16290000 Waiähole Stream downstream of powerhouse near 

Waiähole

420 1915

16291000 Waiähole Stream at altitude 250 feet near Waiähole 250 1955-68 Established as LFPR station 16292000 Waiähole Stream at Manianiaula, near Waikäne 160 10/1/1911 - 6/30/1916 Upstream of all diversion

8/1913 due to start of tu

16293000 Waiänu Stream near Waikäne 190 9/9/1911 - 11/22/1911 Fragmentary record; only 

able; upstream of all ir

16294000 Waiähole Stream at Waiähole, near Waikäne 20 9/25/1911 - 12/31/1912 Downstream of irrigation 16294100 Waiähole Stream upstream of Kamehameha Hwy 14 8/2001-Present Currently active; affected b

and 31

Waikäne

16294900 Waikäne Stream at altitude 75 ft at Waikäne 75 12/1959-Present Affected by flow release at 16295000 Waikäne Stream near Waikäne 30 1/27/1912 - 09/30/1912 No rating obtained; read 

of irrigation diversions

Kahana

16296000 Kahana Stream near Kahana 40 1914-17 Upstream of all irrigation 16296500 Kahana Stream at altitude 30 ft near Kahana 30 12/1958-Present Currently active16297000 Käwä Stream near Kahana 30 4/30/1914 - 3/8/1917 Upstream of all irrigation 

LFPR station since 10/6
Kahana

Bay

Kaneohe

Bay

Kahana Stream

Kawa Stream

Punaluu Stream

Kaaawa Stream

Waikane Stream

Waikeekee Stream

Uwao Stream

Waianu Stream

Waiahole Stream

Waihi

Stream

Halona

Stream

Waiahole Ditch

Waiahole Ditch

Punaluu Ditch

Kahana

bulkhead

tunnel

Waikane

tunnel 1

Waikane

tunnel 2

Uwao

tunnel Intake 29

Tunnel B

Tunnel A

K o o l a u R a n g e

Kamehameha Hwy.

2926

2850 29282928.9

2931

2929

2947

2948 2945

2944

2959.95

2970

2905

176-5

2951.95

EXPLANATION

2949

2890

ROADS

DITCH SYSTEM

 WATERSHED BOUNDARY

STATIONS AND ABBREVIATED NUMBER—Complete number for 2949 is 16294900. 

 Active continuous-record gaging station

 Inactive continuous-record gaging station

 Low-flow partial-record station

2949

2953

2950

2940

2941

2870

North

Portal

2890

2910

2920

2860

2872

Adit 8

Gate 31

Gate 30

2880

Intake 23

2930

2960 2965

3020

3030

2900

157 ̊56'W 157 ̊54'W 157 ̊52'W 157 ̊50'W

21 ̊28'N

21 ̊30'N

21 ̊32'N

21 ̊34'N

0 1 2 Kilometers

0 1 2 Miles Base modified from U.S. Geological Survey,

1:24,000 digital data.

Waiawa Stream

EXPLANATION

Figure 14. Continuous-record and low-flow partial-record streamflow stations in the study area, windward 

Oÿahu, Hawaiÿi. Uwao was formerly spelled Uwau.

Available Discharge Data   33
10

100

1000

1911 1912 1913 1914 1915 1916

DISCHARGE, IN MILLION GALLONS PER DAY

16294000

16292000

Beginning date for water from tunnel construction entering stream

Ending date for water from tunnel construction entering stream

A total of 22 daily flows were measured at station 

16293000 on Waianu Stream at an altitude of 190 ft from September to November of 1911. This station was upstream from 

all irrigation diversions and measured natural streamflow. The 

average of the 22 daily flow values is 8.1 Mgal/d. 

Streamflow records covering 31 and 27 days, during the 

period August through October 1911, are available for station 

16289000 on Waihï Stream and station 16288000 on Hälona 

Stream, respectively. These records indicate that base flows of 

these two streams at about 750 ft altitude were fairly steady 

before construction of the Waiähole Ditch System. The highest 

and lowest flows recorded in Waihï Stream were 2.9 and 2.4 

Mgal/d, respectively. The highest and lowest flows in Hälona 

Stream were 7.1 and 5.8 Mgal/d, respectively.

The earliest continuous streamflow data collected in the 

Kahana watershed were at stations 16296000 and 16297000 

between 1914 and 1917 (table 11), mainly during the period 

of ditch construction. Discharges measured during construction but before the opening of the ditch system may provide 

reasonable estimates of natural streamflow. The two bores of 

the main tunnel through the Koÿolau Range from the south and 

north portals met on December 13, 1915 (Stearns and Vaksvik, 

1935). The ditch system was officially opened on May 27, 

1916 (Wilcox, 1996). It is likely that the opening of the main 

tunnel coincided with the start of surface-water diversions by 

the Waiähole Ditch from the headwaters of Kahana Stream, 

which would reduce base flows in the stream. Flow data at 

station 16296000 indeed indicate that the median streamflow 

in 1915 and 1916 before the opening of the ditch was about 

24 Mgal/d; median streamflow after the ditch opened through 

1917 was 16 Mgal/d, a drop of about 8 Mgal/d. 

Post-ditch

Since completion of the Waiähole Ditch System on 

May 27, 1916 (Wilcox, 1996), numerous continuous-record 

stations have been operated for various periods of time (table 

11) on each of the diverted streams (fig. 14). These stations 

Figure 15. Logarithmic plot of daily discharge at continuous-record streamflow stations 16292000 

(altitude 160 ft) and 16294000 (altitude 14 ft), Waiähole Stream, windward Oÿahu, Hawaiÿi, September 

25, 1911 to June 30, 1916.

34  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
provide streamflow records representative of post-ditch 

(diverted) flow conditions in the Waiähole, Waikäne, and 

Kahana Streams. Three of the stations are currently active 

and useful for interpreting hydrologic conditions in the three 

diverted streams: station 16294100 on Waiähole Stream (altitude 14 ft), station 16294900 on Waikäne Stream (altitude 75 

ft), and station 16296500 on Kahana Stream (altitude 30 ft).

During the post-ditch period, two stations have been 

operated on Waiähole Stream. The currently active station 

16294100 has been operated from August 2001 to present, and 

is at an altitude of 14 ft, about 300 ft upstream from Kamehameha Highway (fig. 14). This station measures the combined flow from the Waiähole Stream and its principal tributary, Waianu Stream. Through 2004, the average discharge for 

station 16294100 was 28.3 Mgal/d. The highest annual mean 

discharge was 35.6 Mgal/d in 2004, and the lowest annual 

mean discharge was 18.7 Mgal/d in 2003. Station 16291000 

was operated from 1955 to 1968 on Waiähole Stream at an 

altitude of 250 ft and upstream from the confluence with 

Waianu Stream. Flow measured at this station was affected by 

upstream pumping to the Waiähole Ditch System and occasional flow releases from the ditch system through Gate 31. 

Station 16294900 on Waikäne Stream has been operated from December 1959 to present and is at an altitude of 

75 ft, about 0.3 mi downstream from the confluence with 

Waikeÿekeÿe Stream (fig. 14). Through 2004, the average 

discharge for station 16294900 was 5.7 Mgal/d. The highest 

annual mean discharge was 12.3 Mgal/d in 2004, and the lowest annual mean discharge was 2.2 Mgal/d in 1984. 

Station 16296500 on Kahana Stream has been operated 

from December 1958 to present and is at 30 ft altitude, just 

upstream from the confluence with Käwä Stream (fig. 14). 

Through 2004, the average discharge for station 16296500 

was 23.6 Mgal/d. The highest annual mean discharge was 43.4 

Mgal/d in 1982, and the lowest annual mean discharge was 

13.0 Mgal/d in 1984. 

Four continuous-record stations (16285000, 16286000, 

16287000, and 16287200) have been operated to monitor Waiähole Ditch flows at Gate 30, Gate 31, North Portal, 

and Adit 8, respectively. Responsibility for the operations 

of these stations has switched between the USGS, Waiähole 

Water Company, and ADC from time to time. Currently, 

these stations are operated by the ADC (fig. 14 and table 11). 

Station 16285000, located near Gate 30, measures total ditch 

flow leaving the Uwao area. Station 16286000, located at 

Waiähole Tunnel wasteway at Gate 31, monitors flow releases 

to Waiähole Stream. Station 16287000, commonly referred 

to as the North Portal gage, is in the main tunnel directly 

underneath the Koÿolau crest to measure the amount of water 

passing from the windward to the leeward side at the topographic divide. Station 16287200, commonly referred to as 

Adit 8, is at the southwest (leeward) portal of the main tunnel, 

about 2.8 mi downstream of the North Portal. This station was 

established to measure the ground-water inflow in the reach 

between the North Portal and the end of the Waiähole main 

tunnel at Adit 8. 

Low-Flow Partial-Record Stations

An individual continuous-recording station can be used 

to characterize flow conditions with time, but only at a single 

location on a stream. Streamflow data for a single location 

cannot be used to characterize an entire stream because flow 

conditions vary, both with time and location along a stream, as 

interactions between the surface and ground water vary. Some 

stream reaches may gain water from the adjacent groundwater body, whereas other reaches may lose water. Low-flow 

estimates at different locations on each stream are useful for 

describing the availability and distribution of base flow along 

the stream. Because continuous-recording stations cannot 

be operated at all locations where data are desired, low-flow 

partial-record (LFPR) stations were established as part of this 

study to provide low-flow estimates at ungaged sites. A series 

of discharge measurements were made at each LFPR station 

during periods of independent flow recessions and under various base-flow conditions. 

A total of 12 low-flow measurements representative of 

post-ditch conditions were made at each of 12 LFPR stations 

on Kahana, Waikäne, and Waiähole Streams and their significant tributaries (fig. 14, table 12) in 2002-03. In addition 

to data collected in 2002-03, low-flow measurements made 

in 1988-90 and during earlier periods at these LFPR stations 

were compiled for analysis. The range of discharge measured 

at a LFPR station varies depending on the objectives of the 

LFPR station. Historical streamflow measurements were 

checked, and only those measurements made during a period 

when no direct runoff was taking place were used. This was 

determined by checking the streamflow hydrographs at nearby 

continuous-record stations for rapid changes in discharge, 

which are indicative of periods of direct runoff. Fontaine and 

others (1992) used this screening approach to prevent potential 

bias that could be introduced by including high-flow measurements in the record-extension analysis discussed in the 

subsequent section “Low-flow duration discharges in streams.” 

All of the measurements made at the LFPR stations used in 

this study are stored in the USGS National Water Information 

System database.

Miscellaneous Measurement Sites

Numerous discharge measurements were made at 

selected sites on each of the diverted streams before the construction of the Waiähole Ditch System. Because exact locations of most of these miscellaneous discharge measurement 

sites are difficult to determine and irrigation diversion activities downstream of the Waiähole Ditch are not fully known, 

only measurements made upstream of all irrigation diversions 

were considered for use in estimating natural streamflow prior 

to the construction of the Waiähole Ditch System as part of 

this study. 

For Waikäne Stream, four pre-ditch discharge measurements were made in the lower reach of the stream below an 

Available Discharge Data   35
Table 12. Low-flow partial-record streamflow stations on Waiähole, Waikäne, and Kahana Streams, windward Oÿahu, Hawaiÿi.

[n.a., not applicable; --, not available; mi2, square mile]

USGS

station

number

Takasaki

numbera Station location

Altitude

(feet)

Latitudeb Longitudeb

Drainage

area

(mi2)

Period 

Waiähole Stream

19292600 -- Waianu Stream at Gate 30 release 820 21 ̊ 28’ 59” 157 ̊ 53’ 11” n.a 1995, 2

19292800 180 Waianu Stream 380 21 ̊ 29’ 08” 157 ̊ 52’ 51” 0.55 1959-6

19292890 182 Waianu Stream above confluence with Uwaoc Stream 200 21 ̊ 29’ 13” 157 ̊ 52’ 26” 0.67 1960, 1

16292900 183 Uwaoc Stream at mouth 200 21 ̊ 29’ 16” 157 ̊ 52’ 26” 0.56 1911, 1

16293100 185 Waianu Stream at mouth 75 21 ̊ 29’ 01” 157 ̊ 51’ 47” 1.65 1959-6

2002

16290500 176_5 Waiähole Stream 320 21 ̊ 28’ 29” 157 ̊ 52’ 39” 0.92 1988-9

Waikäne Stream

16294400 187_5 North Fork Waikäne Stream 220 21 ̊ 30’ 01” 157 ̊ 52’ 41” 0.58 1988-9

16294500 187_8 South Fork Waikäne Stream 220 21 ̊ 30’ 17” 157 ̊ 52’ 40” 0.67 1988-9

16294700 191 Waikeÿekeÿe Stream at mouth 90 21 ̊ 30’ 01” 157 ̊ 52’ 12” 0.43 1959-6

16294800 190 Waikäne Stream above confluence with Waikeÿekeÿe Stream 90 21 ̊ 30’ 04” 157 ̊ 52’ 10” 1.57 1959-6

16295195 198 Waikäne Stream at Kamehameha Highway 10 21 ̊ 29’ 41” 157 ̊ 51’ 12” 2.5 1988-9

Kahana Stream

16295995 224 Kahana Stream at mauka trail crossing 80 21 ̊ 32’ 17” 157 ̊ 53’ 29” 3.18 1960-6

1983

16297000 226 Käwä Stream at mouth 30 21 ̊ 32’ 33” 157 ̊ 53’ 00” 2.09 1914-1

19711988

aStation numbers used by Takasaki and others (1969), and Fontaine and others (1992).bCoordinates are referenced to Old Hawaiian Datum.cUwao was formerly spelled Uwau.
altitude of about 75 ft on October 9, 1911. The measurement 

made farthest upstream, about two miles from the mouth of 

the stream and near altitude 75 ft, was 6.0 Mgal/d (Martin and 

Pierce, 1913). This measurement represented natural streamflow upstream of all irrigation diversions. Because locations of 

other pre-ditch measurements for Waikäne Stream are difficult 

to determine, those measurements were not used in this study. 

Miscellaneous measurements were made on Kahana 

Stream and irrigation ditches on October 27, 1911 (Martin 

and Pierce, 1913). One measurement indicated a streamflow 

of 20.8 Mgal/d downstream of an irrigation ditch intake, and 

another measurement indicated a ditch flow of 3.0 Mgal/d. 

However, it is not clear if this is from the intake upstream of 

the stream measurement, and the exact location of the irrigation ditch is not known. 

As part of a feasibility study of bringing surface waters of 

the Waiähole, Waikäne, and Kahana Streams to a sugar-cane 

plantation in central Oÿahu (Lippencott, 1911), weirs were 

constructed to measure practically all of the spring flows at 

approximately 750 ft altitude from Kahana to Waiähole. During June and July 1911, W.A. Wall (Lippencott, 1911) made 

daily measurements at these weirs (table 13). These measurements will subsequently be referred to as the Wall measurements in this report. The total average flow measured by Wall 

for all the streams during June and July 1911 was 23.1 Mgal/d 

(Lippencott, 1911). 

Wall’s Waiähole Stream measurements compared closely 

with the limited and fragmentary daily flow data recorded 

at two currently inactive USGS continuous-record stations 

on Waihï (station 16289000) and Hälona (station 16288000) 

Streams. The USGS recorded daily flows in Waihï and Hälona 

Streams were 2.4 and 5.8 Mgal/d, respectively, and Wall’s corresponding measurements of average spring flows were about 

2.4 and 5.7 Mgal/d. 

Approach and Methods for 

Estimating Natural Low-Flow 

Duration Discharges

The Waiähole Ditch System intercepted large amounts 

of dike-impounded ground water, above an altitude of about 

750 ft, that previously fed Waiähole (and its tributaries Waianu 

and Uwao), Waikäne, and Kahana Streams through seeps and 

springs. Diversion of the dike-impounded ground water by 

Waiähole Ditch has significantly diminished base flows in 

Table 13. Average flows from weir observations in Waiähole, Waianu, Waikäne, and Kahana Streams, windward Oÿahu, 

Hawaiÿi, for June and July, 1911, by W.A. Wall (modified from Lippencott, 1911).

[--, not available; Mgal/d, million gallons per day]

Stream Weir

number

Average

Flow

(Mgal/d)

Total for 

stream

(Mgal/d)

Percentage

of

total flowa

(percent)

Total for 

watershed

(Mgal/d)

Waiähole 8.14 38.9 12.98

Hälona 1 4.7

Hälona 2 1.04

Waihï 3 2.4

Waianu 4.2 20.1

South Fork 1 0.53

Middle Fork 2 2.47

North Fork 3 1.2

Uwaob -- 0.64 0.64 3.1

Waikäne 2.57

Waikeÿekeÿe 12 0.92 0.92 4.4

South Fork 13 0.53

North Fork 14 1.12 1.65 7.9

Kahana -- 7.5 5.4a 25.8 5.4a

Total 100.0 20.95

a

Original average flow of 7.5 Mgal/d is reduced by 2.1 Mgal/d to account for Kahana surface water not diverted by Waiähole Ditch.

b

Uwao was formerly spelled Uwau.

Approach and Methods for Estimating Natural Low-Flow Duration Discharges  37
these streams. This section describes the overall approach used 

to estimate natural (undiverted) low-flow duration discharges 

for these streams during the common period of 1960-2004 

(called the base period). A combination of pre-ditch and postditch streamflow data, ditch-flow data, seepage runs in the 

ditch system, and low-flow estimates at data collection stations 

was used. 

Natural (undiverted) low flows were estimated using the 

following four-step approach:

Low-flow duration discharges representative of postditch (diverted) conditions were estimated for the LFPR 

and continuous-record stations located downstream from 

Waiähole Ditch. 

Low-flow duration discharges of flow diverted by 

Waiähole Ditch were computed. 

The relative distributions of flow diverted by Waiähole 

Ditch among Waiähole, Waikäne, and Kahana watersheds 

were estimated. 

Low-flow duration discharges for post-ditch (diverted) 

conditions (step 1) were combined with estimates of 

diversions from each watershed (step 3) to derive estimates of natural low-flow duration discharges.

Low-Flow Duration Discharges in 

Streams 

Discharge measurements made at LFPR stations were 

used to develop statistical relations with concurrent daily mean 

discharges at continuous-record index stations. These relations 

were then used to obtain estimates of various flow-duration 

discharges at LFPR stations corresponding to flow-duration 

discharges at the long-term index stations for the base period. 

The selection of the index stations will be discussed in the next 

section. To avoid bias associated with estimating low-flow 

duration discharges using ordinary least-squares regression 

statistical relations (Stedinger and Thomas, 1985), recordextension methods such as graphical correlation (Searcy, 

1959, p.14) and the Maintenance Of Variance Extension, 

Type I (MOVE.1) (Hirsch, 1982) were used. The two methods assume that the relation between discharges at the LFPR 

station and the index station remains constant with time (Ries, 

1993). The resulting low-flow estimates at LFPR stations 

therefore are representative of long-term conditions during the 

selected base period. Adjustment of short records to a common base period allows flow comparisons that reflect spatial 

differences in climate and drainage-basin characteristics rather 

than temporal differences in rainfall (Searcy, 1959). Because 

the majority of the potential index stations for this study (table 

14) have been operated concurrently from water year 1960 

to 2004, the period 1960 -2004 was therefore selected as the 

common base period for the record extension analyses for 

1.

2.

3.

4.

this study. Hydrologic conditions during the base period were 

assumed to be representative of long-term conditions. 

The following guidelines for the MOVE.1 and graphical record-extension methods are provided (USGS Office of 

Surface Water, in Technical Memorandum no. 86.02, December 16, 1985): (1) approximately 10 base-flow measurements 

should be available to use the MOVE.1 method, and (2) the 

graphical correlation technique should be used when there are 

fewer than 10 base-flow measurements or when there is a nonlinear relation between base-flow measurements and concurrent daily mean discharges at the index station. 

To summarize the application of the two record-extension 

methods, the initial procedure for both methods is to check 

for linearity in the relation between the concurrent discharges 

by the use of log-log plots (fig. 16). The use of logarithm 

(base 10) transformation normalizes the streamflow data and 

transforms the common curvilinear relation between continuous-record station records to straight lines (Searcy, 1959). The 

correlation coefficient was used as a measure of the strength of 

the linear relation between the index and LFPR stations. For 

stations with nonlinear relations and stations with less than 10 

measurements, the graphical method was used. For sites with 

linear relations and 10 or more low-flow measurements, the 

MOVE.1 method was used. 

In the MOVE.1 method, estimates of the low-flow 

statistics for the LFPR station are obtained by entering the 

logarithms of low-flow statistics 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 low-flow 

duration discharge at the low-flow partialrecord stations,

Xi is the logarithm of the computed low-flow 

duration discharge at the index station,

Y is the mean of the logarithms of the discharge 

measurements at the low-flow partialrecord 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, and

sx is the standard deviation of the logarithms of 

the concurrent daily mean discharges at the 

index station.

Both the MOVE.1 and graphical methods are thoroughly 

explained in the references cited, and a detailed example 

showing the application of the MOVE.1 method is provided by 

Ries (1993, p.28). 

The same record-extension techniques were used to 

extend records for short-term stations that were not in opera-

38  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
Table 14. Continuous-record streamflow stations considered as potential index stations in the study.

[n.a., not applicable; mi2, square mile]

USGS

station

number

Station name Latitudea Longitudea

Drainage

area

(mi2)

Period of rec

16200000 NF Kaukonahua Str abv RB, nr Wahiawa, Oÿahu, HI 21o 31’ 09” 157o 56’ 53” 1.38 1913-53, 1960-

16229000 Kalihi Str nr Honolulu, Oÿahu, HI 21o 22’ 00” 157o 50’ 49” 2.61 1914-Present16240500 Waiakeakua Str at Honolulu, Oÿahu, HI 21o 19’ 52” 157o 48’ 08” 1.06 1913-21, 1925-16254000 Makawao Str nr Kailua, Oÿahu, HI 21o 21’ 49” 157o 46’ 02” 2.04 1912-16, 1958-16294100 Waiähole Stream above Kamehameha Hwy, Oÿahu, HI 21o 29’ 05” 157o 50’ 57” 3.76 1988-1990b, 19

16294900 Waikäne Str at alt 75 ft at Waikäne, Oÿahu, HI 21o 30’ 00” 157o 51’ 54” 2.22 1959-Present

16296500 Kahana Str at alt 30 ft nr Kahana, Oÿahu, HI 21o 32’ 37” 157o 53’ 07” 3.74 1958-Present

16302000c Punaluÿu Ditch nr Punaluÿu, Oÿahu, HI 21o 33’ 41” 157o 54’ 10” n.a. 1953-Present16303000c Punaluÿu Str nr Punaluÿu, Oÿahu, HI 21o 33’ 33” 157o 54’ 06” 2.78 1953-Present

16304200 Kaluanui Str nr Punaluÿu, Oÿahu, HI 21o 35’ 22” 157o 54’ 38” 1.11 1967-Present

aLatitude and longitude are in Old Hawaiian Datum.bEstablished as miscellaneous measurements.cCombined records of stations 16302000 and 16303000 to reflect natural streamflow conditions.
tion through the entire base period. Application of the techniques varied slightly from the procedures used to extend 

records for LFPR stations. Instead of relating measured discharges at the station to concurrent daily discharges recorded 

at the index station, estimates for short-term continuous-record 

stations were obtained by relating computed duration discharges for the concurrent period of record between a shortterm continuous-record station and an index station. 

For the long-term continuous-record stations, flow-duration statistics were determined directly using standard USGS 

methods described in Searcy (1959). A flow-duration curve is 

a cumulative-frequency curve, which shows the percentage of 

time that a daily mean flow is equaled or exceeded (Searcy, 

1959). The median flow (Q50) and the 90th-percentile flow 

(Q90) are the daily mean flows equaled or exceeded 50 and 90 

percent of the time, respectively. 

Flow-duration curves for the three currently active continuous-record stations on Waiähole, Waikäne, and Kahana 

Streams were computed (figs. 17-19). The flow-duration curve 

for station 16294100 on Waiähole Stream, based on data for 

water years 2002 through 2004, is shown in figure 17. Streamflow at this station during this period was affected by flow 

releases through Waiähole Ditch System Gates 30 and 31. 

Flow conditions in Waikäne Stream also changed significantly 

after the flow release through Intake 23 started on October 11, 

2002; therefore data from station 16294900 are divided into 

pre-release and post-release periods. Flow-duration curves 

of daily mean discharge were constructed for water years 

1960 through 2002, representative of pre-release conditions 

(fig. 18A), and water years 2003 and 2004, representative of 

post-release conditions (fig. 18B). Post-release unadjusted 

flow-duration curves for both stations 16294100 (fig. 17) and 

16294900 (fig. 18B) exhibit sharp breaks or bends at the high 

ends, which may primarily be a reflection of the limited period 

of record. The flow-duration curve for station 16296500 on 

Kahana Stream (fig. 19), based on data for water years 1960 

through 2004, indicates that flows greater than or equal to 

8 Mgal/d occurred 99 percent of the days. The long-term average discharge at this station, 23.6 Mgal/d, represents a flow 

rate that is equaled or exceeded about 20 percent of the time. 

Flow-duration curves provide a convenient means for 

making comparison of the hydrologic conditions between 

watersheds. The low-flow end of a flow-duration curve also 

reflects the effect of geology on base flow. The sustained 

discharge of dike-impounded ground water to Waiähole, 

Waikäne, and Kahana Streams is reflected in the way the 

curves nearly flatten out at the higher percentile flows. In addition, a flow-duration curve is a summary of the flow characteristics of streams only for the period for which they are 

computed because climatic conditions and resulting streamflows during different periods may not be the same (Ries, 

1993, p. 20). The similarities between flow-duration curves 

0.1

1

10

0.1 1 10

DISCHARGE AT INDEX STATION 16229000 ON KALIHI STREAM,

IN MILLION GALLONS PER DAY

DISCHARGE AT LFPR STATION 16294400 ON NORTH FORK

WAIKANE STREAM, IN MILLION GALLONS PER DAY 

2003

2002

1988–90

Figure 16. Graphical relation between flows at index station on Kalihi Stream and low-flow 

partial-record (LFPR) station on Waikäne Stream, Oÿahu, Hawaiÿi.

40Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
at index station 16200000 on North Fork Kaukonahua Stream 

(table 14) for both the entire period of record and the base 

period indicate that hydrologic conditions during the selected 

base period of 1960-2004 were representative of long-term 

conditions (fig. 20). 

Selection of Index Stations

An index station is a nearby, hydrologically similar, 

continuous-record station with long-term data available that 

can be used to accurately compute streamflow statistics. 

Selection of index stations for establishing relations with 

LFPR and short-term stations was based on two criteria: (1) 

distance between the stations and (2) a minimum correlation 

coefficient of 0.80 between the discharge measurements (logtransformed) for the LFPR station and the concurrent daily 

discharges (log-transformed) at the index station. Nearby stations on the same stream as the LFPR station are obvious candidates for index stations because these stations generally are 

in hydrologically similar settings and provide better relations 

with the LFPR station than stations from distant watersheds 

(Searcy, 1959). The one currently active long-term continuousrecord gage on Waikäne Stream (station 16294900) therefore 

was considered as the primary index station for the five LFPR 

stations on Waikäne Stream because of its proximity to the 

LFPR stations (table 12). Although station 16296500 on 

Kahana Stream operated during the entire base period, this station was not used as an index station because flow conditions 

during this period may not have been uniform. The closure of 

surface-water intakes during the mid-1980s and the construction of a bulkhead in Kahana development tunnel in 1992 may 

have increased flow in the downgradient streams. 

Because the currently active station 16294100 on 

Waiähole Stream only has been operated since 2001, the 

selection of an index station for LFPR stations on Waianu 

Stream largely was based on the second criterion. As a result, 

long-term continuous-record stations outside of the study area 

were considered for use as index stations. High correlation 

coefficients for concurrent flows at the LFPR and index stations were assumed to reflect similar hydrogeological settings 

between the two watersheds.

16294100 Waiahole Stream

(post-release period)

PERCENTAGE OF TIME INDICATED DISCHARGE WAS EQUALED OR EXCEEDED

DAILY MEAN DISCHARGE, IN MILLION GALLONS PER DAY

10

100

1000

Unadjusted (2002-2004)

Adjusted to 1960-2004 base period

1 10 30 50 70 90 99

Figure 17. Unadjusted and adjusted flow-duration curves of daily mean discharge at 

continuous-record streamflow station 16294100 on Waiähole Stream, windward Oÿahu, 

Hawaiÿi, for post-release period 2002-2004.

Approach and Methods for Estimating Natural Low-Flow Duration Discharges  41
A 16294100 Waikane Stream

(pre-release period)

DAILY MEAN DISCHARGE, IN MILLION GALLONS PER DAY

1

10

100

1000

Unadjusted (1960-2002)

Adjusted to 1960-2004 base period

B 16294900 Waikane Stream

(post-release period)

PERCENTAGE OF TIME INDICATED DISCHARGE WAS EQUALED OR EXCEEDED

1 10 30 50 70 90 99

DAILY MEAN DISCHARGE, IN MILLION GALLONS PER DAY

10

1

100

1000

Unadjusted (2003-2004)

Adjusted to 1960-2004 base period

Figure 18. Unadjusted and adjusted flow-duration curves of daily mean 

discharge at continuous-record streamflow station 16294900 on Waikäne 

Stream, windward Oÿahu, Hawaiÿi, for pre-release period 1960-2002 (A) and 

post-release period 2003-04 (B).

42  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
Q 20

16296500 Kahana Stream

PERCENTAGE OF TIME INDICATED DISCHARGE WAS EQUALED OR EXCEEDED

1 10 30 50 70 90 99

DAILY MEAN DISCHARGE, IN MILLION GALLONS PER DAY

1

100

10

1000

Average discharge

23.6 Mgal/d

Base Period (water year 1960-2004)

16200000 North Fork Kaukonahua Stream

PERCENTAGE OF TIME INDICATED DISCHARGE WAS EQUALED OR EXCEEDED

DAILY MEAN DISCHARGE, IN MILLION GALLONS PER DAY

0.1

1000

100

10

1

Base period (1960-2004)

1914-52 and 1960-2004

1 10 30 50 70 90 99

Figure 19. Flow-duration curve of daily mean discharge at continuousrecord streamflow station 16296500 on Kahana Stream, windward Oÿahu, 

Hawaiÿi, for period 1960-2004.

Figure 20. Flow-duration curves for base period and period of record of daily 

mean discharge at continuous-record streamflow station 16200000 on North 

Fork Kaukonahua Stream, Oÿahu, Hawaiÿi.

Approach and Methods for Estimating Natural Low-Flow Duration Discharges  43
Potential windward Oÿahu index stations (table 14) 

considered were station 16254000 on Makawao Stream, station 16304200 on Kaluanui Stream, and station 16303000 

on Punaluÿu Stream (fig. 21). Streamflow data from station 

16303000 on Punaluÿu Stream, however, do not reflect natural 

flow conditions because of the Punaluÿu Ditch diversions 

immediately upstream of the station. Daily flow data for the 

Punaluÿu Ditch diversions at station 16302000 were therefore 

combined with daily flow measured at station 16303000 on 

Punaluÿu Stream to provide a measure of natural flow for 

Punaluÿu Stream. Potential leeward Oÿahu index stations 

considered were station 16200000 on North Fork Kaukonahua 

Stream, station 16240500 on Waiakeakua Stream and station 

16229000 on Kalihi Stream. These stations were selected 

because they were used as index stations for windward Oÿahu 

sites in a median streamflow study in Hawaiÿi (Fontaine and 

others, 1992). 

Ideally, flows at index stations should reflect entirely 

natural flow conditions. However, a few of the potential index 

stations considered for this study were affected to some extent 

by regulations, diversions, or both (table 14). Because regulations or diversions affecting flows at the potential index stations generally were consistent throughout the base period, the 

daily mean discharges and low-flow statistics computed for the 

potential index stations could be used for the analysis at LFPR 

stations (Ries, 1999). 

For cases in which correlation coefficients using the 

primary index stations were slightly less than 0.80, as for the 

LFPR station 16294400 on North Fork Waikäne Stream and 

station 16297000 on Käwä Stream (table 15), other potential 

index stations were incorporated in the analysis to increase 

the confidence in the low-flow estimates. For LFPR station 

16294400, the correlation coefficient using the primary index 

station is 0.78. Index continuous-record station 16229000 on 

Kalihi Stream, located outside of the study area, was used as 

a second index station for LFPR station 16294400. For LFPR 

station 16297000, none of the index stations produced a correlation coefficient greater than 0.80, and therefore all index 

stations with correlation coefficients greater than 0.74 were 

used. 

Multiple low-flow estimates were available for some of 

the LFPR and short-term stations that used more than one 

index station (tables 15 and 16). Estimates obtained from each 

of the index stations were averaged to obtain a single estimate 

of the selected duration discharge at the LFPR station. As suggested by Tasker (1975), a weighted average was computed for 

each of the low-flow estimates by weighting each individual 

estimate by its variance and averaging the weighted estimates. 

This procedure results in increased confidence in the final 

estimates because the variance of the final weighted estimate 

is less than or equal to the variances of each of the individual 

estimates (Ries, 1999). Standard errors (in percent) for lowflow estimates also were computed based on the equation 

developed by Stedinger and Thomas (1985, p.18). A detailed 

description of the computation procedures modified from 

Hardison and Moss (1972) was provided by Ries and Friesz 

(2000). 

Low-Flow Duration Discharges in 

Waiähole Ditch

A daily time series of total flow diverted by the Waiähole 

Ditch from windward Oÿahu was generated to estimate 

low-flow duration discharges of diverted water. Ditch flow 

recorded at the North Portal continuous-record station 

16287000 beneath the Koÿolau crest (fig. 14) measures (after 

adjustments described below) the amount of ground water 

diverted by the Waiähole Tunnel. Data in digital format for this 

station were available for the time periods 1951-69 and 1999-

2004 (table 11). 

Data for the period 1951-69 were not used in this analysis 

because (1) records for surface water that was pumped into 

the Waiähole Ditch System from Waiähole Stream during this 

period are not available, (2) occasional flow releases at Gate 

31 to Waiähole Stream also occurred, and (3) data collected 

during this period do not reflect current ditch-flow conditions 

following the extension of the Uwao development tunnel in 

1964, closure of surface-water intakes during the mid-1980s, 

and the construction of the Kahana development tunnel bulkhead in 1992. 

During the period 1999-2004, ditch flow was heavily regulated, primarily by flow releases at Intake 23 and 

Gates 30 and 31. ADC measured the flow releases at Intake 

23 and Gates 30 and 31 for all or parts of the period, and 

USGS measured flow at Gate 31 from 2000-2003 (table 11). 

Although flow releases at Gate 30 to Waianu Stream began in 

May 1995, data were recorded only since November 2002. In 

addition, water also was released at Intake 29 (a pipe extended 

to the stream) and through the McCandless Pipeline to Waianu 

Stream. The only available measurements made at the Intake 

29 release were during the three seepage runs in 1995. The 

measurements ranged from 0.08 to 0.12 Mgal/d and averaged 

0.10 Mgal/d (table 5). Flow released through the McCandless 

Pipeline has been fairly steady and estimated to be about 0.5 

Mgal/d (Hawaiÿi Commission on Water Resource Management, 2001). 

Because information on flow releases through Gate 

30 is available since November 2002, only flow data at the 

North Portal continuous-record station for the period 2003-

2004 were used to estimate water diverted from the Kahana, 

Waikäne, and Waiähole watersheds. The 2003-2004 time 

series of daily flows at North Portal was reconstructed to 

include flow releases at Intake 23, Gates 30 and 31, and the 

McCandless Pipeline. Because the pipe at Intake 29 was 

destroyed during a May 2002 flood, no flow releases at Intake 

29 occurred during the period of analysis. Although the period 

2003-2004 is of short duration, daily flow-release data are 

available to accurately reconstruct flow at North Portal station 

to reflect total ditch flow for the entire 2-year period. Also, 

ditch flow during this period is representative of homogeneous 

hydrologic conditions after the extension of Uwao tunnel, the 

installation of the Kahana bulkhead, and the closing of major 

surface-water intakes in Kahana Valley. 

44  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
Makaha

Waianae

Maili

Nanakuli

EwaBeach

Ewa

Waialua

Haleiwa

Sunset

Beach Kahuku

Laie

Kaaawa

Waima

HawaiiKai

AinaHaina

HONOLULU

Waipahu

Pearl

City

Aiea

KAILUA

KANEOHE

Schofield

Barracks

Wahiawa

Manini Gl

Waimea Gl

Paumalu Gl

Wa

ilupe

Gl

Huliwai

Gl

Kaloi

Gl

Honouliuli

Gl

Kuliouou

Vly

Kaunala

Gl

Malaekahana

Str

Ka

l

u

anui

Str

Ahuiman

u

S

He

e

ia S

Ka

w

a

S

Maunawili

Str

Manoa

Str

Waolani Str

Pauoa

Str

Kalihi

Str Moanalua

N Str Halawa Str Kalauao

Str

Waimalu

Str

Waikakalaua Str

Nanakuli

Str

Mailiilii

Str

Makua Str

Maka

leha

Str

Kaukonahua

Stream

Poamoho

Str

Opaeula

Str

Anahulu River

Makaha

Str

Kaupuni

Str

Waikele

St

re

a

m

Oio

S

t

r

Helemano

Str

S Halawa

Str

Inaole

Str

Kaelepulu

Str

Waimanalo Str

Waiman

Bay

KANEOHE

BAY

Kahana

Bay

Waialua

Bay

Pokai Bay 

Pearl

 Harbor 

MAMALA BAY

Maunalua Bay 

21 ̊20'N

158 ̊10'W

157 ̊50'W

21 ̊40'N

21 ̊30'N

158 ̊W

00

2 4 MILES

2 4 KILOMETERS

EXPLANATION

Kahuku Point 

Barbers

Point

Kaena

Point

3042

2000

2290

2405

2540

2949

2965

837 837.1

837.1

783

3020

3030

3042

STREAMFLOW-GAGINABBREVIATED STATIO (COMPLETE NUMBERAINFALL STATION A

study area

Figure 21. Locations of index streamflow stations and selected rainfall stations on Oÿahu, Hawaiÿi.
Table 15. Low-flow statistics, variances, and standard errors adjusted to the base period of 1960-2004 for the low-flow partial-record 

record-extension methods, windward Oÿahu, Hawaiÿi—Continued.

Site

Drainage

Area

(mi2)

Index

station

Number of

concurrent

data points

Record

extension

method

Correlation

coefficient Statistic Flow-dur

99 95 

Waiähole Stream

Pre-rel

16290500 Waiähole Stream at altitude 

320 ft

0.92 16291000 10 MOVE.1 0.87 Streamflow 1.5 1.6 1

16294900 10 MOVE.1 0.87 Streamflow 1.7 1.8 1

Weighted average streamflow 1.6 1.7 1

Variance 0.001 0.001 0

Standard error 7.0 6.1 5

Waianu Stream

Post-re

16292600 Waianu Stream at Gate 30 n.a. 16254000 11 MOVE.1 0.83 Streamflow 2.5 2.6 2

Variance 0.000 0.000 0

Standard error 4.2 3.2 2

Post-re

16292800 Waianu Stream at altitude 

330 ft near Waiähole

0.55 16254000 11 MOVE.1 0.88 Streamflow 2.1 2.3 2

Variance 0.000 0.000 0

Standard error 4.6 3.4 3

Post-re

16292890 Waianu Stream upstream 

from confluence

0.67 16254000 11 MOVE.1 0.90 Streamflow 2.0 2.2 2

Variance 0.001 0.000 0

Standard error 6.0 4.5 4

P

16292900 Uwaoa Stream at mouthb 0.56 16254000 16 MOVE.1 0.90 Streamflow 0.04 0.06 0

Variance 0.009 0.006 0

Standard error 22 18 1

Post-re

16293100 Waianu Stream at Waiähole 1.65 16254000 9 Graphical 0.74 Streamflow 2.7 2.9 3

Variance 0.000 0.000 0

Standard error 7.1 4.6 3

Pre-release 

16229000 13 MOVE.1 0.88 Streamflow 0.21 0.36 016294900 13 MOVE.1 0.95 Streamflow 0.57 0.68 0

Weighted average streamflow 0.53 0.63 0

Variance 0.002 0.001 0

Standard error 10 8.3 7

Table 15. Low-flow statistics, variances, and standard errors adjusted to the base period of 1960-2004 for the low-flow partial-record 

record-extension methods, windward Oÿahu, Hawaiÿi.

[mi2, square mile; duration discharge is in million gallons per day; variance is in units of base-10 logarithms; standard error is in percent; results shown in red represent a fairly s

extrapolation of the data; n.a, not applicable]
Table 15. Low-flow statistics, variances, and standard errors adjusted to the base period of 1960-2004 for the low-flow partial-record 

record-extension methods, windward Oÿahu, Hawaiÿi—Continued.

Site

Drainage

Area

(mi2)

Index

station

Number of

concurrent

data points

Record

extension

method

Correlation

coefficient Statistic Flow-dur

99 95 

Waikäne Stream

Na

16294400 North Fork Waikäne 

Streamb

0.58 16229000 21 MOVE.1 0.80 Streamflow 0.25 0.34 0

16294900 14 MOVE.1 0.78 Streamflow 0.25 0.31 0

Weighted average streamflowc 0.24 0.33 0

Variance 0.003 0.002 0

Standard error 12 9.3 7

Post-re

16294500 South Fork Waikäne 

Stream

0.67 16294900 6 Graphical 0.94 Streamflow 2.2 2.5 2

16200000 6 Graphical 0.80 Streamflow 2.1 2.4 2

Weighted average streamflow 2.2 2.5 2

Variance 0.001 0.001 0

Standard error 7.4 5.2 3

Pre-rele

16294900 14 MOVE.1 0.97 Streamflow 0.10 0.14 0

Variance 0.002 0.001 0

Standard error 9.0 7.3 5

P

16294700 Waikeÿekeÿe Streamb 0.43 16294900 26 MOVE.1 0.84 Streamflow 0.03 0.04 0

Variance 0.012 0.008 0

Standard error 26 21 1

Post-rele

16294800 Waikäne Stream 10 ft 

upstream from confluence with Waikeÿekeÿe Stream

1.57 16294900 8 Graphical 0.94 Streamflow 2.7 3.0 3

16254000 7 Graphical 0.85 Streamflow 2.9 3.2 3

Weighted average streamflow 2.7 3.1 3

Variance 0.001 0.000 0

Standard error 6.4 4.8 3

Pre-rele

16294900 24 MOVE.1 0.92 Streamflow 0.65 0.78 0

Variance 0.001 0.001 0

Standard error 7.7 6.4 5

Post-rele

16295195 Waikäne Stream at 

Kamehameha Highway

2.5 16294900 8 Graphical 0.93 Streamflow 2.6 3.0 3

16254000 7 Graphical 0.82 Streamflow 2.9 3.4 3

Weighted average streamflow 2.7 3.1 3

Variance 0.002 0.001 0

Standard error 9.2 7.0 5

Pre-rele

16294900 23 MOVE.1 0.96 Streamflow 0.90 1.1 1

Variance 0.001 0.001 0

Standard error 6.4 5.3 4
Table 15. Low-flow statistics, variances, and standard errors adjusted to the base period of 1960-2004 for the low-flow partial-record 

record-extension methods, windward Oÿahu, Hawaiÿi—Continued.

Site

Drainage

Area

(mi2)

Index

station

Number of

concurrent

data points

Record

extension

method

Correlation

coefficient Statistic Flow-dur

99 95 

Kahana Stream

Pos

16295995 Kahana Stream at mauka 

trail crossingb

3.18 16303000 9 Graphical 0.89 Streamflow 6.2 7.2 8

Variance 0.005 0.004 0

Standard error 17 14 1

Na

16297000 Käwä Stream (East Branch 

Kahana Str)b

2.09 16229000 48 MOVE.1 0.78 Streamflow 0.50 0.71 1

16254000 50 MOVE.1 0.74 Streamflow 0.47 0.58 0

Weighted average streamflowc 0.48 0.68 0

Variance 0.002 0.001 0

Standard error 9.7 7.6 6

aUwao was formerly spelled Uwau.bThis stream reach is not affected by flow releases.cLow-flow duration estimates are representative of natural flow conditions.
Table 16. Low-flow statistics, variances, and standard errors adjusted to the base period of 1960-2004 for the continuous-record stre

record-extension methods, windward Oÿahu, Hawaiÿi—Continued.

Site

Drainage

Area

(mi2)

Index

station

Concurrentdata period

Record

extension

method

Correlation

coefficient Statistic

Flow-duratio

99 95 9

Waiähole Ditch

Total di

16287000 Waiähole tunnel at 

North Portala

n.a. 16303000b 2003-04 MOVE.1 0.83 Streamflow 18 19 2

Variance 0.000 0.000 

Standard error 0.85 0.66 

Waiähole Stream

Pre-releas

16291000 Waiähole Stream at altitude 

250 ftc

0.99 16303000 1960-68 Graphical 0.99 Streamflow 2.4 2.5 

Variance 0.000 0.000 

Standard error 1.5 1.2 

Pre-

16292000 Waiähole Stream near 

Waiähole

1.22 16254000 11/12/12 

- 7/13/13

MOVE.1 0.42d Streamflow 11 11 1

Variance 0.000 0.000 

Standard error 2.2 1.9 

Post-releas

16294100 Waiähole Stream at 

Waiähole 

3.76 16303000 2002-04 MOVE.1 0.99 Streamflow 13 14 1

16229000 2002-04 MOVE.1 0.99 Streamflow 11 14 1

16240500 2002-04 MOVE.1 1.0 Streamflow 14 16 1

Weighted average streamflow 13 15 1

Variance 0.000 0.000 

Standard error 0.81 0.70 

Waikäne Stream

Post-releas

16294900 Waikäne Stream 2.22 16303000 2003-04 MOVE.1 0.92d Streamflow 2.9 3.2 

Variance 0.000 0.000 

Standard error 1.4 1.2 

Pre-releas

16303000 1961-2002 MOVE.1 0.99 Streamflow 1.0 1.2 

Variance 0.000 0.000 

Standard error 0.62 0.57 

Table 16. Low-flow statistics, variances, and standard errors adjusted to the base period of 1960-2004 for the continuous-record strearecord-extension methods, windward Oÿahu, Hawaiÿi.[mi2, square mile; duration discharge is in million gallons per day; variance is in units of base-10 logarithms; standard error is in percent; n.c., not computed because results repr

extension or extrapolation of the data and have high estimation errors; n.a., not applicable]
Table 16. Low-flow statistics, variances, and standard errors adjusted to the base period of 1960-2004 for the continuous-record stre

record-extension methods, windward Oÿahu, Hawaiÿi—Continued.

Site

Drainage

Area

(mi2)

Index

station

Concurrentdata period

Record

extension

method

Correlation

coefficient Statistic

Flow-duratio

99 95 9

Kahana Stream

Pre-

16296000 Kahana Stream near 

Kahana

3.2 16200000 12/16/14 to 

5/27/16

MOVE.1 0.68d Streamflow 8.7 12 1

16240500 12/16/14 to 

5/27/16

MOVE.1 0.75d Streamflow 8.7 11 1

Weighted average streamflow n.c n.c 

Variance 0.000 0.000 

Standard error 2.8 2.2 

Pre-bu

16296500 Kahana Stream 3.74 n.a. 1960-2002 n.a. n.a. Streamflow 7.8 9.1 

Post-b

16229000 2002-2004 Graphical 0.99 Streamflow 9.2 11 1

16303000 2002-2004 MOVE.1 0.94d Streamflow 7.4 8.3 

Weighted average streamflow 8.2 9.7 1

Variance 0.000 0.000 

Standard error 0.90 0.67 

aReconstructed to include flow releases at Gates 23, 30, 31, McCandless Pipeline inflow, and 55 percent of flow gained between North Portal and Adit 8 continuous-record stbBase-flow component.cTo reflect natural flow conditions, records were reconstructed to include upstream pumping and releases (recorded by station 16286000). Because pumping records were no

average rate of 1.0 Mgal/d was used (Takasaki and Mink, 1985).

dCorrelation coefficient computed based on concurrent daily discharges between two gaging stations.
The reconstructed time series was extended (using the 

record extension technique discussed previously) to estimate 

total ditch-flow duration statistics during the base period of 

1960-2004. The reconstructed time series was best correlated 

(correlation coefficient = 0.80) with the base-flow component 

of Punaluÿu Stream (combined records of stations 16302000 

and 16303000) (table 16). The base-flow component was 

estimated using an automated hydrograph separation method 

developed by Wahl and Wahl (1995). The method divides the 

daily streamflow record into non-overlapping N-day periods 

and determines the minimum flow within each N-day window. Parameter values for N (number of days) and f (turningpoint test factor) required for application of the method to the 

Punaluÿu station were 4 days and 0.9, respectively (Oki, 2003). 

Ground Water Beyond the Koÿolau Crest 

Developed by the Waiähole Ditch System

The reconstructed time series of ditch flow at North Portal also included a portion of the ground water gained beyond 

the Koÿolau crest to account for flow that was assumed to have 

discharged naturally to the windward streams. It is commonly 

thought that erosion of reentrant features at the head of windward Oÿahu valleys has resulted in diversion of ground water 

from the leeward side of the Koÿolau Range to the windward 

side. The Russ Smith Corporation (1980) suggested that the 

trend and strike of dikes in Waiähole Valley could naturally 

direct ground water from the leeward side to flow parallel to 

the dike structures and emerge as springs in Waiähole Valley. 

Stearns and Vaksvik (1935, p.28) indicated that the valleys of 

windward Oÿahu are deeper than leeward valleys; windward 

Oÿahu valleys captured ground water that naturally would have 

been tributary to leeward valleys. Takasaki and Mink (1985, 

p.35) stated that valleys leeward of the topographic crest of 

the Koÿolau Range have much lower gradients and are not 

cut deep enough to drain the dike-impounded reservoirs. It 

is therefore likely that the ground-water divide is leeward of 

the crest. The boring of the Waiähole Ditch System development tunnels provided lower outlets for the dike-impounded 

ground water to be discharged to windward Oÿahu streams. 

The lowered discharge outlets in the Waiähole Ditch System 

development tunnels may have shifted the ground-water divide 

even further leeward of the crest (Takasaki and others, 1969, 

p.65). However, data are not available to precisely locate the 

ground-water divide under natural (undiverted) conditions 

and to determine the effects of the development tunnels on the 

ground-water divide. Because of this uncertainty, the amount 

of ground water intercepted leeward of the Koÿolau crest in 

the main tunnel and Uwao development tunnel that naturally 

would have discharged to windward Oÿahu streams also is 

poorly known. 

Using available historical observations and recorded 

flows in the main tunnel, it is possible to estimate the percentage of ground water intercepted between the Adit 8 station 

16287200 (at the South Portal) and the North Portal station 

16287000 (beneath the topographic crest of the Koÿolau 

Range) that naturally would have discharged to windward 

Oÿahu. According to flow records collected by the Waiähole 

Water Company, the average ground-water gain leeward of the 

Koÿolau crest between the two stations during the period 1916-

32 was about 5.8 Mgal/d (Stearns and Vaksvik, 1935, p. 403). 

The average ground-water gain in the main tunnel windward 

of the Koÿolau crest was estimated to be 1.5 Mgal/d during 

dry weather and 3.0 Mgal/d during wet weather (Stearns and 

Vaksvik, 1935, p. 403). An average ground-water gain of 2.3 

Mgal/d was used in this study. Ground water gained in the 

entire length of Waiähole main tunnel was about 8.0 Mgal/d 

(Stearns and Vaksvik, 1935). Springs that flowed at a rate of 

5.7 Mgal/d in Waiähole Valley went dry following construction of the main tunnel (Stearns and Vaksvik, 1935). Thus, 3.4 

Mgal/d (5.7-2.3) of the flow at the springs was derived from 

the leeward part of the main tunnel. It is therefore estimated 

that about 59 percent (100x(5.7-2.3)/5.8) of ground water 

gained between the Adit 8 and North Portal continuous-record 

stations previously discharged naturally at the Waiähole 

springs. A similar calculation using flow measurements (figure 

16 in Takasaki and Mink, 1985) made at various locations 

along the main tunnel also indicates that about 55 percent of 

ground water gained between the Adit 8 and North Portal continuous-record stations previously discharged at the Waiähole 

springs. Takasaki and others (1969, p.74) estimated that half 

of the ground water gained between the south portal and the 

crest previously flowed to windward Oÿahu. An average of 

these three estimates (55 percent) will be used in this study to 

apportion ground-water gains in the main tunnel leeward of 

the Koÿolau crest to the windward streams.

In addition to the main tunnel, Uwao development tunnel 

also was bored beyond the Koÿolau crest. The original Uwao 

tunnel was driven to the crest and was subsequently extended 

about 228 ft beyond the Koÿolau crest in 1963-64. The actual 

amount of water intercepted from the extension that naturally 

would have discharged to the windward side is uncertain. 

According to flow measurements in the main Waiähole tunnel 

(figure 16 in Takasaki and Mink, 1985), ground water gained 

well beyond 500 ft leeward of the Koÿolau crest is needed to 

fully account for flow (5.7 Mgal/d) that previously discharged 

at the Waiähole springs. This could imply that the natural 

ground-water divide in the Uwao tunnel area is possibly well 

over 500 ft leeward of the Koÿolau crest. Assuming similar 

conditions near the Uwao development tunnel, all the ground 

water intercepted in the 228-ft Uwao tunnel extension may 

have naturally discharged to the windward side. This also is 

consistent with the assertion by Takasaki and Mink (1985, 

p. 29) that “the final equilibrium of base flow of the tunnel 

system is not appreciably different from the sum of the base 

flows of streams on the windward side before the tunnels were 

constructed.” The time series of North Portal daily ditch flows 

for 2003-04 was adjusted to include 55 percent of the main 

tunnel gain between the North Portal and Adit 8 continuousrecord stations and also includes gain from the Uwao tunnel 

extension. The reconstructed time series of ditch flow at North 

Portal is summarized in appendix 1.

Approach and Methods for Estimating Natural Low-Flow Duration Discharges  51
Distribution of Waiähole Ditch Flows 

Among Watersheds

At least two methods are available to estimate the relative distribution of water being diverted by Waiähole Ditch as 

natural streamflow in Waiähole, Waikäne, and Kahana Streams 

at the altitude of the connecting tunnel of the Waiähole Ditch 

System: (1) using historical (pre-ditch) Wall measurements 

(table 13) made at 750 ft altitude in each of the upper tributaries from Waiähole to Kahana Streams and (2) using measured 

changes in flow in the Waiähole Ditch between basin topographic divides obtained during tunnel seepage runs (table 2). 

The Wall measurements provide the best estimate because the 

measurements do not require the assumption that the groundwater divides are the same as the topographic divides. Use 

of a distribution based on tunnel seepage-runs assumes that 

ground-water divides coincide with topographic divides and is 

used only as a comparative estimate in this report.

Wall Measurements

On the basis of the Wall measurements (reduced to reflect 

2.1 Mgal/d of Kahana surface water not currently diverted by 

the Waiähole Ditch), Waiähole, Waikäne, and Kahana Streams 

contributed, respectively, 61.9, 12.3, and 25.8 percent of the 

total flow diverted by Waiähole Ditch at an altitude of 750 ft 

(table 17). Table 13 summarizes a further breakdown of these 

percentages among subwatersheds in Kahana, Waikäne, and 

Waiähole Streams. A set of weir measurements on August 10-

12, 1911, during a period of clear weather when normal flow 

of springs was observed indicated a similar distribution of 

flow (Lippencott, 1911). This indicates that the Wall measurements can reasonably be assumed to reflect natural base-flow 

conditions at 750 ft altitude on the three streams during the 

pre-ditch period. 

It should be noted that the distribution of flow computed 

using the Wall measurements represents base-flow conditions over a short, two-month period during June and July 

1911. No long-term streamflow data with concurrent record 

is available to evaluate hydrologic conditions when the Wall 

measurements were made. Because of the lack of data, the 

distribution of flows from the Wall measurements is assumed 

to apply over the range of flow-duration percentiles ranging from 50 to 99 percent. However, the distribution of flows 

diverted by the Waiähole Ditch System must reflect flow in 

Kahana Stream that is currently not diverted. The average flow 

in Kahana Stream that is not diverted at the level of the ditch is 

2.1 Mgal/d based on data collected from 1989-1993 (Hawaiÿi 

Commission on Water Resource Management, 2001, table 1 

on p. 143). The Wall measurement of 7.5 Mgal/d in Kahana 

Stream was therefore reduced by 2.1 Mgal/d to account for 

this flow, and the distribution of diverted flow from each 

watershed also is adjusted accordingly (table 17). 

Ditch Tunnel Seepage Runs

On the basis of ditch seepage runs in 2002-2003 (table 

2), adjusted to include 55 percent of the gain between North 

Portal and Adit 8, Waiähole, Waikäne, and Kahana Streams 

contributed, respectively, 70.7, 22.5, and 6.8 percent of the 

total flow diverted by Waiähole Ditch at an altitude of 750 ft 

(table 17). Within the connecting tunnel, discharge measurements were made beneath the topographic divides separating 

adjacent watersheds. These measurements made it possible to 

determine the ground-water contributions to the ditch system, 

after accounting for surface-water inflows and diversions, 

within each watershed (fig. 6). Flow-duration percentiles 

associated with daily-mean discharges at three nearby continuous-record stations (16287000 at North Portal, 16296500 on 

Kahana Stream, and 16303000 on Punaluÿu Stream; see fig. 

14) on the days of the seepage runs provide an estimate of 

Table 17. Distribution percentages of total Waiähole Ditch flow contributed by Waiähole, Waikäne, and Kahana 

Streams, windward Oÿahu, Hawaiÿi.

Stream

Relative distributions of ditch flow using different methods, in percent

Seepage

runs

Seepage

runs

(adjusted)a

Wall

measurements

Wall

measurements

(adjusted)b

Waiähole 67 70.7 56.3 61.9

Waikäne 25.3 22.5 11.2 12.3

Kahana 7.7 6.8 32.5 25.8

Total 100 100 100 100

a

Included Uwao extension tunnel flow and 55 percent of gain between North Portal and Adit 8

 gaging stations; Uwao was formerly spelled Uwau.

b

Reduced by 2.1 Mgal/d to account for Kahana surface water not diverted by Waiähole Ditch

 and selected as the relative distribution of streamflow in the natural flow computations.

52  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
ditch-flow conditions on these days (table 18). The February 

2002 seepage run was made under near-median flow conditions, when discharges recorded at the three nearby stations 

had duration percentiles ranging from 56 to 63 percent. The 

August 2003 seepage run was conducted at lower flow conditions, when flow at nearby stations had duration percentiles 

ranging from 83 to 91 percent. Although flow conditions during the two seepage runs were different, the relative distributions of flow are reasonably close. It is therefore reasonable to 

assume that similar distributions of ditch flow would exist over 

the range of flow durations from 56 to 91 percent and that the 

arithmetic average of the distributions based on the two seepage runs is representative over this range of flow conditions. 

Addition of Flow-Duration Discharges

Low-flow duration discharges based on the reconstructed 

time series of total ditch flow at North Portal are apportioned 

to each stream using the distribution percentages developed in 

the previous section (table 13). These apportioned low flows 

represent an estimate of the amount of dike-impounded ground 

water that would have naturally discharged to each stream 

at the level of the ditch system. To estimate natural low-flow 

duration discharges at downstream continuous-record and 

LFPR stations, the appropriate apportioned low-flow duration 

discharges from the ditch system are added to the corresponding low-flow duration discharges for pre-release conditions at 

the stations. Pre-release low-flow estimates are used because 

apportioned ditch flows reflect pre-release conditions. 

However, a limitation associated with adding flow-duration discharges directly is that the combination of individual 

flow statistics does not always exactly equal the corresponding flow statistic computed from the combined record of daily 

flows (Fontaine, 2003). In some cases, daily flows are available from two continuous-record stations, one monitoring flow 

diverted from a stream and the other monitoring streamflow 

downstream of the diversion. Flow-duration discharges for the 

natural, undiverted flow in the stream can be computed from 

the combined record of the two stations. Because a continuous 

record of daily flows is not available at LFPR stations, flowduration discharges cannot be computed from the combined 

record of daily flows from two stations if one of the stations 

is a LFPR station. In these cases, flow-duration discharges are 

sometimes added. Gingerich (2005) estimated possible errors 

associated with adding flow-duration discharges using data 

from two stations in northeast Maui, where flow is diverted 

from streams. Flow-duration discharges computed by adding 

individual flow-duration discharge were within about 10 percent of the corresponding flow-duration discharges computed 

using combined daily flows from the two stations. 

To evaluate if adding computed flow statistics directly is 

appropriate for this study, undiverted low-flow duration discharges in 2003-2004 for two stations (16269500 on Kahana 

Stream and 16294900 on Waikäne Stream) downstream of the 

Waiähole Ditch diversion were generated in two ways. First, 

low-flow duration discharges representing undiverted conditions at each station were computed based on the combined 

record of daily flows from the station and the appropriate 

Table 18. Recorded discharge and associated flow-duration percentiles for selected continuous-record streamflow 

stations in windward Oÿahu, Hawaiÿi, February 2002 and August 2003.

[Mgal/d, million gallons per day]

Date

Punaluÿu Stream

Station 16303000a

North Portal

Station 16287000

Kahana Stream

Station 16296500

Dischargeb

(Mgal/d)

(1960-2004)

Flow-duration

percentile

Dischargec

(Mgal/d)

(1960-2004)

Flow-duration

percentiled

Dischargeb

(Mgal/d)

(1960-2004)

Flow-duration

percentile

2/26/2002 12 58 14 58

2/27/2002 12 58 20 56 13 63

2/28/2002 12 58 13 63

8/19/2003 9.1 85 10 90

8/20/2003 8.4 91 18 83 10 90

8/21/2003 8.4 91 10 90

a

Combined records with station 16302000 at Punaluÿu Ditch to reflect natural streamflow conditions.

b

Daily mean discharge.

c

Discharge measurement adjusted to include measured flow releases at Gates 23, 30, and 31.

d

Computed using daily time series reconstructed to include flow releases at Gates 23, 30, and 31.

Approach and Methods for Estimating Natural Low-Flow Duration Discharges  53
daily ditch flows apportioned to the watershed. Daily ditch 

flows apportioned to a particular watershed were generated 

by multiplying the daily total ditch flows by the appropriate 

distribution percentage (table 17). Second, low-flow duration 

discharges were computed by combining the statistics from 

a station and the statistics based on apportioned ditch flows 

(table 19). The results of the two methods compare favorably, with a maximum relative error of 13 percent and average errors of 5 percent for Waikäne Stream and 2 percent for 

Kahana Stream (table 19). Natural flow statistics for stations 

on gaining streams downstream of the Waiähole Ditch System 

can be estimated reasonably well by adding flow statistics 

from two stations.

Estimates of Low-Flow Duration 

Discharges for Diverted and 

Natural Flow Conditions

Diverted Flow Conditions

Major flow releases to the Waiähole, Waianu, and 

Waikäne Streams from the Waiähole Ditch System started 

between December 1994 and October 2002 in response to 

court rulings and have significantly changed the diverted-flow 

conditions in these streams. Streamflow in Kahana Stream is 

not affected by flow releases from the Waiähole Ditch System. 

For Waiähole, Waianu, and Waikäne Streams, diverted-flow 

conditions can be divided into pre-release and post-release 

periods. Log-log plots of the concurrent discharges between 

the LFPR and index stations were used to identify changes in 

low-flow conditions at the LFPR stations along these streams. 

Pre-release and post-release low-flow estimates representative 

of base period conditions were computed using record-extension methods discussed in the previous section for the data 

collection stations where a sufficient number of low-flow 

measurements are available (tables 15 and 16). 

Six to eight low-flow measurements were made at the 

five LFPR stations on Waikäne Stream after the beginning 

of the flow release on October 11, 2002. Earlier discharge 

measurements at the LFPR stations provided information that 

was used to determine pre-release low-flow characteristics. 

The change in flow conditions associated with flow releases 

is clearly illustrated by two different groupings of the data 

points, as shown in the log-log plot of concurrent flows at the 

LFPR station 16294500 on South Fork Waikäne Stream and 

index station 16254000 on Makawao Stream (fig. 22). One 

group of data points describes the relation associated with 

post-release flow conditions and the second group describes 

the relation associated with pre-release flow conditions. 

Assuming flow conditions at the index station remain constant 

Table 19. Comparison of flow statistics computed for stream sites where natural flows are estimated, using data from 

multiple time series of daily flow, windward Oÿahu, Hawaiÿi.

[All flows are in million gallons per day; relative error is (column 4 - column 5)/column 5 x 100]

Flow-duration

percentile

Downstream

gaging station

Upstream

ditch flow

time series

Sum of upstream

and downstream

flow statistics

Flow statistics 

based on combined 

upstream

and downstream 

daily flows

Relative error,

in percent

16296500 Kahana Stream near Kahana

99 8.6 4.6 13.2 13.7 -4

95 9.8 4.9 14.7 15.3 -3

90 10.4 5.1 15.5 15.9 -2

75 11.8 5.5 17.3 17.3 0

50 15.6 6.1 21.7 22.2 -2

average -2

16294900 Waikäne Stream at altitude 75 ft at Waikäne

99 0.4 2.2 2.6 2.9 -13

95 0.8 2.3 3.1 3.2 -4

90 0.9 2.5 3.4 3.4 -2

75 1.4 2.7 4.0 3.9 3

50 2.7 2.9 5.6 6.1 -7

average -5

54  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
through time, a change in the relation between the concurrent 

discharges measured at the two stations is most likely due to 

flow releases that significantly increased low flows in Waikäne 

Stream. At LFPR stations where low flow was significantly 

affected by flow releases, statistical relations associated with 

the post- and pre-release flow conditions were developed. At 

LFPR stations where base flow was unaffected by the flow 

releases, only one grouping of data points was evident (see station 16294400 on North Fork Waikäne Stream in figure 16). 

Of the five available LFPR stations on Waianu and Uwao 

Stream, only stations 16292900 and 16293100 had sufficient 

low-flow measurements, made before the start of flow releases 

(May 1995), available to estimate pre-release low-flow statistics. However, conflicting trends are evident in the log-log plot 

of concurrent discharges between the LFPR station 16293100 

and index station 16229000 on Kalihi Stream (fig. 23). More 

than one relation could be drawn from data collected during 

pre-release periods. For a particular flow at the index station, 

concurrent flows measured during 1988-90 were consistently 

higher than flows measured during the other two pre-release 

periods (1959-66 and 1995). These two relations represent 

different low-flow conditions, possibly associated with differences in water diversions or manipulations upstream of the 

LFPR station. In addition to flow releases through Gate 30, 

upstream diversions (for example, the McCandless diversion) 

or other water manipulations also may affect streamflow. 

The relation associated with discharges measured in 1995 

and 1959-66 was selected to estimate pre-release low-flow 

characteristics because this relation represents longer-term 

pre-release flow conditions in the stream extending over two 

different periods. This relation also reflects more current flow 

conditions, which include the 1995 pre-release discharge 

measurements.

Streamflow in Kahana Stream is not affected by flow 

releases from the Waiähole Ditch System but the close-off of 

the surface-water intakes during the mid-1980s and the construction of a bulkhead in Kahana development tunnel in 1992 

may have gradually increased flow in the lower part of Kahana 

Stream. The installation of the bulkhead was an attempt to 

restore ground-water storage in the dike compartments. Installation of the bulkhead reduced flow from the Kahana development tunnel into Waiähole Ditch by about 1.5 Mgal/d. According to the latest data, water pressure behind the bulkhead has 

stabilized, which indicates that ground-water outflow from the 

dike compartments behind the bulkhead seems to have stabilized (Edwin Sakoda, CWRM, written commun., 2005). It is 

assumed that the majority of the outflow discharges downgradient to Kahana Stream, but the exact effects of the bulkhead 

Figure 22. Graphical relation between flows at index station on Makawao Stream and low-flow 

partial-record (LFPR) streamflow station on Waikäne Stream, Oÿahu, Hawaiÿi.

0.1

1

10

0.1 1 10

DISCHARGE AT LFPR STATION 16294500 ON SOUTH FORK WAIKANE STREAM,

DISCHARGE AT INDEX STATION 16254000 ON MAKAWAO STREAM, IN MILLION GALLONS PER DAY

IN MILLION GALLONS PER DAY

2003

2002

1988-90

Estimates of Low-Flow Duration Discharges for Diverted and Natural Flow Conditions  55
on low flows in Kahana Stream are uncertain. Because the 

pressure behind the bulkhead probably increased gradually, the 

increase in outflow from the dike compartments also probably 

increased gradually. 

A log-log plot of the concurrent discharges between the 

LFPR station 16295995 on Kahana Stream and index station 

16229000 on Kalihi Stream was used to identify changes in 

low-flow conditions in Kahana Stream (fig. 24). The change 

in low-flow conditions is illustrated by three different groupings of the data points. The 1960-1984 data points describe 

the relation associated with pre-bulkhead flow conditions 

before the close-off of surface water intakes, the 1985-1990 

data points associate with pre-bulkhead flow conditions after 

the close-off of surface water intakes, and the 2002-2003 data 

points are used to estimate low-flow statistics representative of 

post-bulkhead flow conditions. Because data are not available 

to determine exactly when the pressure behind the bulkhead 

reached the approximate steady state, it will be assumed that 

the use of 2002 to 2004 data for computing current low-flow 

duration statistics at station 16296500 on Kahana Stream 

captures the effects of the bulkhead on low flows in Kahana 

Stream (table 16).

Natural Flow Conditions 

The Waiähole Ditch System intercepts dike-impounded 

ground water that would otherwise contribute to base flows of 

Waiähole, Waikäne, and Kahana Streams. Low flows measured at the downstream stations in the diverted streams are 

measures of ground water gained downstream of the Waiähole 

Ditch diversions. Natural low-flow duration discharges at the 

data collection stations were estimated by combining ditch 

and stream low-flow duration discharges. Natural low-flow 

estimates are limited to locations where pre-release lowflow estimates have been computed. Estimates of pre-release 

low-flow statistics could not be made at a number of LFPR 

stations. This is primarily attributed to the lack of pre-release 

0.1

1

10

0.1 1 10

DISCHARGE AT INDEX STATION 16229000 ON KALIHI STREAM,

 IN MILLION GALLONS PER DAY

DISCHARGE AT LFPR STATION 16293100 ON WAIANU STREAM,

IN MILLION GALLONS PER DAY

Fitting lines

Post-release

Pre-release

1957-66 & 1995 (pre-release period)

2002-03 (post-release period)

1988-90 (pre-release period)

Figure 23. Graphical relations between flows at index station on Kalihi Stream and low-flow 

partial-record (LFPR) streamflow station on Waianu Stream, Oÿahu, Hawaiÿi.

56  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
1

10

100

1.0 1 01

DISCHARGE AT INDEX STATION 16229000 ON KALIHI STREAM, IN MILLION GALLONS PER DAY

DISCHARGE AT LFPR STATION 16295995 ON KAHANA STREAM,

IN MILLION GALLONS PER DAY

1960-84 (pre-bulkhead period with open intakes)

1985-90 (pre-bulkhead period with closed intakes)

2002-03 (post-bulkhead period)

Fitting lines

0.1

1

10

1.0 1 01

DISCHARGE AT INDEX STATION 16254000 ON MAKAWAO STREAM, IN MILLION GALLONS PER DAY

DISCHARGE AT LFPR STATION 16297000 ON KAWA STREAM,

IN MILLION GALLONS PER DAY

2003 2002

1988-90 1980-84

1971-79 1960-66

1914-16

Fitting line

Figure 24. Graphical relations between flows at index stations on Kalihi and Makawao Streams and 

low-flow partial-record (LFPR) streamflow stations on Kahana and Käwä Streams, Oÿahu, Hawaiÿi.

Estimates of Low-Flow Duration Discharges for Diverted and Natural Flow Conditions  57
low-flow measurements available at those stations, which are 

mainly on Waianu Stream (table 15). Natural low-flow duration discharges also were estimated at selected locations where 

pre-ditch stream measurements were available. Comparisons 

of natural low-flow duration discharge estimates based on 

addition of ditch and stream data and estimates based on preditch stream flow measurements were made.

Estimates Based on Addition of Ditch and 

Stream Data

Natural (undiverted) low-flow duration discharges for 50 

to 99 percentiles were estimated for two stations on Waiähole 

Stream, one on Waianu Stream and one on its tributary Uwao 

Stream, five on Waikäne Stream and one on its tributary 

Waikeÿekeÿe Stream, and two on Kahana Stream and one on its 

tributary Käwä Stream (tables 20-22). To illustrate the computations, the apportioned Q50 ditch flow to station 16294700 

in Waikeÿekeÿe Stream (Waikäne watershed) is computed 

by multiplying the Q50 ditch flow of 24 Mgal/d (table 16) 

by the distribution percentage of 4.4 percent (table 13) for 

Waikeÿekeÿe Stream. Then, the apportioned ditch flow of 1.1 

Mgal/d (24 Mgal/d x 4.4 percent) is added to the low-flow 

Q50 estimate of 0.25 Mgal/d (table 15) at station 16294700 to 

estimate 50th-percentile natural flow-duration discharge of 

1.3 Mgal/d at station 16294700 (altitude 90 ft). For Waiähole 

Stream, natural Q50 (median) flows at altitudes of 320 and 250 

ft were estimated to be 12 and 13 Mgal/d, respectively. For 

Waianu Stream and its tributary Uwao Stream, natural Q50 

flows at altitudes of 200 and 75 ft were estimated to be 1.0 and 

7.0 Mgal/d, respectively. For Waikäne Stream and its tributary 

Waikeÿekeÿe Stream, natural Q50 flows between altitudes of 220 

and 10 ft range from 0.81 to 5.5 Mgal/d. Natural Q50 flows for 

Kahana Stream at altitudes of 80 and 30 ft were estimated to 

be 21 and 22 Mgal/d, respectively.

Low-flow duration discharge estimates under post-ditch 

conditions for North Fork Waikäne and Käwä Streams are also 

representative of natural (undiverted) flow conditions. Natural 

Q50 flow for Käwä Stream at an altitude of 30 ft is 2.0 Mgal/d, 

and natural Q50 flow for North Fork Waikäne Stream at an 

altitude of 220 ft is 0.81 Mgal/d. North Fork Waikäne and 

Käwä Streams are tributaries of the diverted streams, and both 

originate below tunnel level and receive negligible groundwater discharge from upper dike compartments. Streamflow 

in these two reaches is not affected by flow releases from 

Waiähole Ditch and not significantly affected by Waiähole 

Ditch diversions. A log-log plot of concurrent discharges 

between the LFPR station 16297000 on Käwä Stream and the 

index station 16254000 on Makawao Stream indicates that low 

flows in Käwä Stream were not likely to be affected by the 

construction of the Waiähole Ditch System (fig. 24). A single 

relation was developed for concurrent discharges covering a 

time period from 1914 to 2003 that spanned periods before 

and after the completion of Waiähole Ditch. 

In addition, the unit-area duration discharges (adjusted to 

base period) are similar and mostly under one for continuousrecord station 16295300 on Hakipuÿu Stream and both LFPR 

station 16297000 on Käwä Stream and station 16294400 on 

North Fork Waikäne Stream (table 23) which support the 

assumption that low-flow estimates under post-ditch conditions for these stream reaches are representative of natural 

(undiverted) flow conditions. Streamflow in Hakipuÿu Stream 

is assumed to be representative of natural streamflow for 

streams originating in the marginal dike zone of windward 

Oÿahu. Construction and operation of station 16295300 on 

Hakipuÿu Stream was initiated in 2002. This station provides 

streamflow data for a windward Oÿahu stream in the study 

area that is not diverted into the Waiähole Ditch System. 

Contrasting to streams that drain upper dike compartments, 

unit-area duration discharges for station 16296500 on Kahana 

Stream are much greater than one (table 23).

Estimates Based on Pre-ditch Data

The limited streamflow data collected before ditch construction cannot be used directly to estimate natural low flows 

for the common base period because of temporal differences in 

climatic and hydrologic conditions. For example, the Q90 flow 

during an extremely dry year could be much lower than Q90 

flow during a longer period like the base period used in this 

study. It is therefore critical to adjust the available pre-ditch 

flow record to represent the base period so that estimates of 

natural flows can be compared to other flow duration statistics 

computed for this same base period. 

The only continuous records of natural streamflows 

before the construction of Waiähole Ditch for the Waiähole 

and Kahana Streams were collected at stations 16292000 and 

16296000. These pre-ditch flow data were adjusted to the 

base period of 1960–2004 by using record-extension techniques described in a previous section (table 16). For station 

16292000 on Waiähole Stream, selection of an index station 

was limited to Makawao Stream station 16254000, the only 

active long-term streamflow station on the windward side of 

the island that has concurrent data. Concurrent pre-ditch flows 

for record extension are available on Waiähole and Makawao 

Streams from November 12, 1912, to July 31, 1913. For 

station 16296000 on Kahana Stream, there are uncertainties 

associated with the decline of flow in the later part of 1914 

(fig. 25). The 90th-percentile streamflow during 1914 was 

substantially higher than Q90 flow during subsequent years, 

and rainfall during 1914 was not significantly higher than 

during subsequent years (fig. 26). There is no written record of 

any event that was associated with this significant reduction in 

flow near the end of 1914. Flows recorded during 1914 therefore were not considered natural low flows and only concurrent records with index stations between December 16, 1914, 

and May 27, 1916, were used in the record extension analysis. 

Although correlation coefficients computed for the logarithms of the selected duration discharges from each pre-ditch 

58  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
Table 20. Estimates of natural, pre-release, and post-release low-flow 

duration discharges for continuous-record and low-flow partial-record (LFPR) streamflow stations in Waianu and Waiähole Streams, windward Oÿahu, Hawaiÿi.[Mgal/d, million gallons per day; --, not available; n.a., not applicable; estimates shown in redrepresent significant extension or extrapolation of the data and therefore have higher estimation errors]

Station

Station

altitude

(feet)

Duration

Percentile

Estimated

natural 

flow

at station

(Mgal/d)

Estimated

prerelease 

flow 

at station

(Mgal/d)

Estimated

postrelease 

flow

at station

(Mgal/d)

Waianu Stream

16292600 820 99 -- -- 2.5

95 -- -- 2.690 -- -- 2.775 -- -- 2.950 -- -- 3.2

Station

Station

altitude

(feet)

Duration

Percentile

Estimated

natural 

flow

at station

(Mgal/d)

E

pr

16292800 380 99 -- -- 2.1

95 -- -- 2.390 -- -- 2.375 -- -- 2.750 -- -- 3.0

Waiähole Stream

16292890 200 99 -- -- 2.0 16290500 320 99 8.4 

95 -- -- 2.2 95 9.3 

90 -- -- 2.3 90 9.6 

75 -- -- 2.7 75 10 

50 -- -- 3.4 50 12 

16292900a 200 99 0.57 0.04 n.a 16291000 250 99 9.2 

95 0.64 0.06 n.a 95 10 

90 0.67 0.08 n.a 90 11 

75 0.75 0.14 n.a 75 12 

50 1.0 0.32 n.a 50 13 

16293100 75 99 4.6 0.53 2.7 16294100 20 99 -- 

95 5.1 0.63 2.9 95 -- 

90 5.4 0.74 3.0 90 -- 

75 5.9 1.0 3.3 75 -- 

50 7.0 1.5 3.8 50 -- 

aStream reach is not affected by flow releases

Location of stations

16291000

16290500

16293100

16292900

16294100

16292600 16292800 16292890

Waiahole Stream

Waianu Stream

Uwao Stream

Waiahole Ditch
Table 21. Estimates of natural, pre-release, and post-release low-flow du

continuous-record and low-flow partial-record (LFPR) streamflow stations iwindward Oÿahu, Hawaiÿi.[Mgal/d, million gallons per day; --, not available; n.a., not applicable; estimates shown in red repextrapolation of the data and therefore have higher estimation errors]

Station

Station

altitude

(feet)

Duration

Percentile

Estimated

natural flow

at station

(Mgal/d)

Estimated

pre-release f

at

station

(Mgal/d)

Waikäne Stream

16294400a 220 99 0.24 -- 

95 0.33 -- 90 0.42 -- 75 0.56 -- 50 0.81 -- 

16294500 220 99 1.5 0.10 

95 1.7 0.14 90 1.8 0.17 75 2.0 0.27 50 2.3 0.43 

16294700b 90 99 0.80 -- 

95 0.90 -- 90 0.94 -- 75 1.1 -- 50 1.3 -- 

16294800 90 99 2.0 0.65 

95 2.3 0.78 90 2.5 0.90 75 2.8 1.2 50 3.5 1.6 

16294900 75 99 3.2 1.0 

95 3.7 1.2 90 3.9 1.4 75 4.5 1.9 

50 5.5 2.6 

16295195 10 99 3.1 0.90 

95 3.5 1.1 90 3.8 1.3 75 4.4 1.7 

50 5.5 2.5 

aStream reach is not affected by the Waiähole Ditch System diversionbStream reach is not affected by flow releases

Waikane Stream

16294900

16294800

16294700

16294500

16294400

16295195

Waikeekee Stream

Waiahole Ditch

Location of stations 
Table 22. Estimates of natural and diverted low-flow duration discharges for continuousrecord and low-flow partial-record (LFPR) streamflow stations in Kahana Stream, 

windward Oÿahu, Hawaiÿi.[Mgal/d, million gallons per day; --, not available; n.a., not applicable; estimates shown in red represent significant extension or extrapolation of the data and therefore have higher estimation errors]

Station

Station

altitude

(feet)

Duration

Percentile

Estimated

natural flow

at station

(Mgal/d)

Estimated

diverted flow

at station

(Mgal/d)

Kahana Stream

16295995a 80 99 11 6.2

95 12 7.2

90 13 8.2

75 17 11

50 21 15

16296500a 30 99 13 8.2

95 15 9.7

90 16 11

75 18 13

50 22 16

16297000b 30 99 0.48 n.a.

95 0.68 n.a.

90 0.87 n.a.

75 1.2 n.a.

50 2.0 n.a.

aStream reach is not affected by flow releasesbStream reach is not affected by the Waiähole Ditch System diversion

16296500

16297000

16295995

Kahana Stream

Kawa Stream

Waiahole Ditch

Location of stations

Table 23. Unit-area duration discharges representative of natural streamflow originating in the marginal dike zone of windward Oÿahu[mi2, square mile; duration discharge is in million gallons per day; unit-area duration discharge = duration discharge / drainage area] 

USGS

Station Stream

Drainage

area

(mi2)

Adjusted duration discharges

to base period (1960-2004)

at selected duration percentiles

Unit-area dura

at selected dur

99 95 90 75 50 99 95 

16297000 Käwä 2.09 0.48 0.68 0.87 1.24 1.95 0.23 0.33 0

16294400 North Fork Waikäne 0.58 0.24 0.33 0.42 0.56 0.81 0.42 0.57 0

16295300 Hakipuÿu 0.85 0.22 0.26 0.30 0.44 0.60 0.26 0.30 0

16296500 Kahana Streama 3.74 13 15 16 18 22 3.48 4.01 4

a Kahana Stream data are representative of natural streamflow originating in the upper dike zone
0

50

100

150

200

250

300

1914 1915 1916 1917 Significant reduction of Q90 flow Two bores of main tunnel met Official opening of Waiahole Ditch System

1914 Q90 flow

DISCHARGE, IN MILLION GALLONS PER DAY

0

50

100

150

200

250

1905190619071908190919101911191219131914191519161917191819191920

ANNUAL RAINFALL, IN INCHES

Figure 25. Daily discharge at continuous-record streamflow station 16296000, Kahana 

Stream, windward Oÿahu, Hawaiÿi, June 19, 1914, to June 30, 1917. The 1914 Q90 flow is 

the flow that was equaled or exceeded 90 percent of the time during 1914.

Figure 26. Annual rainfall at station 783 at Nuÿuanu Reservoir 4, Oÿahu, Hawaiÿi, 1905-

1920 (digital data from Hawaiÿi Commission on Water Resource Management).

62  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
station and its corresponding index station are above 0.80, 

complete years of record are recommended to compute flowduration statistics (Searcy, 1959). When plotting concurrent 

daily discharges to confirm a linear relation, the computed correlation coefficients for both stations are below 0.80. In addition to the poor correlation, it also is uncertain whether diversions that existed upstream of the index station on Makawao 

Stream remained consistent throughout all years. 

Long-term rainfall data collected at station 783 at 

Nuÿuanu Reservoir 4 (fig. 21) were used to determine whether 

streamflow data from the pre-ditch period were collected during dry or wet conditions. Station 783 is close to the study area 

and has long-term data extending from the pre-ditch period 

(1905) to present. Rainfall collected at this station in Nuÿuanu 

are reasonably correlated with concurrent rainfall collected at 

stations 837.1 and 837 in Waiähole (figs. 27 and 28), indicating similar rainfall conditions in the two areas. Station 837.1 

in Waiähole, at about 2,150 ft altitude, was operated during 

1911–14 and recorded the only pre-ditch rainfall data available in Waiähole near the topographic divide of Waiawa and 

Waiähole watersheds; station 837 in Waiähole at about 745 ft 

altitude was in operation during 1916–2004 (fig. 21). Exceedance probabilities (similar to flow-duration percentiles) for 

the annual rainfall values from station 783 indicate that annual 

rainfall values during 1911–16 have low percentiles and 

therefore that these are years of high rainfall. Although it is 

not possible to determine definitive flow-duration percentiles 

from these rainfall measurements, the percentiles associated 

with rainfall at least indicate that conditions were relatively 

wet when the pre-ditch flow data were collected, and flows 

measured during these periods may be higher than median 

flows. Oki (2004) also suggested that statistically significant 

downward trends in annual base flow as well as rainfall during 

1913–2002 were detected at seven long-term stations throughout the State. 

Comparison of Estimates

Estimates of natural low-flow statistics based on the 

adjusted pre-ditch streamflow data collected at station 

16292000 on Waiähole Stream and station 16296000 on 

Kahana Stream are compared with estimates computed at 

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35

Correlation coefficient = 0.68

MONTHLY RAINFALL AT STATION 837.1, IN INCHES 

MONTHLY RAINFALL AT STATION 783, IN INCHES

Fitting line

Figure 27. Correlation between monthly rainfall at stations 783 (Nuÿuanu Reservoir 

4) and 837.1 (Waiawa-Waiähole divide) for concurrent period January 1913 to May 

1914 (digital data from Hawaiÿi Commission on Water Resource Management).

Estimates of Low-Flow Duration Discharges for Diverted and Natural Flow Conditions  63
nearby station 16291000 on Waiähole Stream and station 

16296500 on Kahana Stream (fig. 29). For Waiähole Stream, 

natural low-flow estimates at station 16291000 based on 

the two distribution methods are reasonably similar to each 

other and to estimates based on pre-ditch flow data at station 16292000, which provides some measure of confidence 

in the estimates for this stream. Natural Q50 flows at station 

16291000 based on Wall measurement and ditch seepage run 

distribution methods are 13 and 14 Mgal/d, respectively, and 

natural Q50 flow at station 16292000 is 14 Mgal/d. Because 

Waiähole Stream is a gaining stream, natural low-flow estimates at downstream pre-ditch station 16292000 at 160-ft altitude are expected to be slightly higher than those at upstream 

station 16291000 at 250-ft altitude. Results based on the Wall 

measurement distribution, when compared with the pre-ditch 

flow data, are consistent with this pattern. Using the Wall measurement distribution, flow estimates for station 16291000 are 

on average about 1.1 Mgal/d lower than estimates made from 

station 16292000 (fig. 29). This 1.1 Mgal/d average difference 

also agrees with the gain in base flow in the 1-mi reach of 

Waiähole Stream between altitudes of 160 and 250 ft measured during the September 27, 1995 seepage run (table 4). 

For Kahana Stream, estimates at station 16296500 

are expected to be similar to estimates at station 16296000 

because of their proximity (fig. 14). Estimates of natural lowflow durations based on the Wall measurement distribution 

are again in agreement with the pre-ditch flow data (fig. 29). 

Natural Q50 flows at station 16296500 based on Wall measurement and ditch seepage run distribution methods are 22 

and 18 Mgal/d, respectively, and natural Q50 flows at station 

16296000 is 23 Mgal/d. It should be noted that estimates of 

higher duration percentiles (90, 95, and 99) based on pre-ditch 

flow at station 16296000 are not computed because the results 

represent a significant extrapolation of the data and therefore 

have higher estimation errors (table 16).

Effects of Diversions on 

Low-Flow Duration Discharges

Flow-duration discharges for natural and diverted (prerelease) conditions at the continuous-record and LFPR stations 

indicate significant effects of the diversion by Waiähole Ditch 

on the low-flow characteristics of streams. Diverted (prerelease) flows at the continuous-record and LFPR stations at 

0

50

100

150

200

250

300

350

0 50 100 150 200 250

ANNUAL RAINFALL AT STATION 783, IN INCHES

ANNUAL RAINFALL AT STATION 837, IN INCHES

Correlation coefficient = 0.80

Fitting line

Figure 28. Correlation between annual rainfall at stations 783 (Nuÿuanu 

Reservoir 4) and 837 (Waiähole) for concurrent period 1917-1986 (digital data from 

Hawaiÿi Commission on Water Resource Management).

64  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
altitudes of 250 to 320 ft on Waiähole Stream, 10 to 220 ft on 

Waikäne Stream, and 30 to 80 ft on Kahana Stream were compared to natural flows to illustrate the effects of the diversions 

on streamflow. The diverted-flow values were expressed as 

percentages of the corresponding natural flows (figs. 30-32). 

Small percentages of diverted to natural flows indicate a relatively large effect of diversion on streamflow; higher percentages indicate a relatively smaller effect of diversion on streamflow. For Waiähole Stream, diverted (pre-release) flows for the 

selected duration percentiles at an altitude of 250 ft range from 

25 to 28 percent of natural flows, whereas at an altitude of 320 

ft they range from 19 to 20 percent of natural flows (fig. 30). 

For Waikäne Stream, diverted (pre-release) flows associated 

with the lower altitudes are consistently higher percentages 

of natural flows than at higher altitudes because the reduction 

in flow is less significant as the stream gains ground water 

at lower altitudes (fig. 31). Diverted (pre-release) flows for 

the selected duration percentiles at an altitude of 10 ft range 

from 30 to 46 percent of natural flows, whereas percentages 

at an altitude of 220 ft range from 7 to 19 percent. For Kahana 

Stream, the percentages for the selected duration percentiles 

at an altitude of 30 ft range from 65 to 72 percent, whereas 

percentages at an altitude of 80 ft range from 58 to 71 percent 

(fig. 32). At similar altitudes, therefore, diversion of water 

by the Waiähole Ditch System has caused a greater percentage reduction in streamflow in Waikäne Stream compared to 

Kahana Stream.

Station 16291000 in Waiahole Stream

7

8

9

10

11

12

13

14

15

16

NATURAL FLOW, IN 

MILLION GALLONS PER DAY

Wall measurement distribution (Lippencott, 1911)

Ditch seepage run distribution (2002-2003)

Station 16292000 pre-ditch flow (1912-1913)

Station 16296500 in Kahana Stream

5

7

9

11

13

15

17

19

21

23

25

0 10 20 30 40 50 60 70 80 90 100

DURATION PERCENTILE

NATURAL FLOW, IN 

MILLION GALLONS PER DAY

Wall measurement distribution (Lippencott, 1911)

Ditch Seepage Run Distribtion

Station 16296000 pre-ditch flow (1914-1916)

Figure 29. Estimated low-flow duration discharges of natural streamflow using various methods at Waiähole and 

Kahana Streams, windward Oÿahu, Hawaiÿi.

Effects of Diversions on Low-Flow Duration Discharges  65
10

12

14

16

18

20

22

24

26

28

30

200 220 240 260 280 300 320 340

STREAM-CHANNEL ALTITUDE, IN FEET

DIVERTED FLOW, AS A PERCENTAGE OF NATURAL FLOW

Q99 flow

Q95 flow

Q90 flow

Q75 flow

Q50 flow

0

5

10

15

20

25

30

35

40

45

50

0 50 100 150 200 250

STREAM-CHANNEL ALTITUDE, IN FEET

DIVERTED FLOW AS A PERCENTAGE OF NATURAL FLOW

Q99 flow

Q95 flow

Q90 flow

Q75 flow

Q50 flow

Figure 30. Diverted (pre-release) flows compared to natural flows (Q50

to Q99) at stream-channel altitudes of 250 to 320 feet, Waiähole Stream, 

windward Oÿahu, Hawaiÿi.

Figure 31. Diverted (pre-release) flows compared to natural flows (Q50

to Q99) at stream-channel altitudes of 10 to 220 feet, Waikäne Stream, 

windward Oÿahu, Hawaiÿi.

66  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
Effects of Flow Releases on 

Low-Flow Duration Discharges

Currently, flow releases from the Waiähole Ditch System 

are affecting streamflow in Waiähole, Waianu, and Waikäne 

Streams. This section compares estimates of post-release flows 

to estimates of natural flows and pre-release flows.

Comparison of Post-release to Natural 

Flows

Differences between the post-release and natural flow 

estimates were compared for continuous-record and LFPR 

stations along Waikäne and Waianu Streams to assess how 

current streamflows compare to natural conditions (table 24). 

Currently, flow is being released to one of the two tributaries to Waikäne Stream through Intake 23 (fig. 14). For the 

upper reach of Waikäne Stream at an altitude of 220 ft (at 

station 16294500), above the confluence with Waikeÿekeÿe 

Stream, the current post-release flows for selected flow-duration percentiles are from 48 to 62 percent higher than natural 

flows. At an altitude of 90 ft (at station 16294800), just above 

the confluence with Waikeÿekeÿe Stream, current post-release 

flows are 32 to 40 percent higher than natural flows. For the 

stream reach below the confluence with Waikeÿekeÿe Stream, 

the current post-release flows at altitudes of 75 and 10 ft (at 

stations 16294900 and 16295195, respectively) are within 12 

percent of natural flows. The results indicate that the current 

post-release flows are higher than natural flow along the upper 

reach of Waikäne Stream, but along the lower reach they are 

relatively close to natural flows. The post-release low-flow 

estimates for Waikäne Stream are mainly representative of 

flow-release conditions in 2003 because the estimates were 

made by correlating mostly 2003 low-flow discharge measurements and the concurrent daily discharges at index stations. 

For Waiähole Stream, the only station with available 

post-release and natural flow estimates is station 16293100 

on Waianu Stream (table 20). Post-release flows for selected 

flow-duration percentiles at an altitude of 75 ft (station 

16293100) are 41 to 46 percent lower than natural flows, 

which indicate that a higher flow release would be needed to 

restore flow at an altitude of 75 ft on Waianu Stream to natural 

flow conditions. 

50

55

60

65

70

75

0 20 40 60 80 100 120 140

STREAM-CHANNEL ALTITUDE, IN FEET

DIVERTED FLOW AS A PERCENTAGE OF NATURAL FLOW

Q99 flow

Q95 flow

Q90 flow

Q75 flow

Q50 flow

Figure 32. Diverted (pre-release) flows compared to natural flows (Q50 to Q99) 

at stream-channel altitudes of 30 to 80 feet, Kahana Stream, windward Oÿahu, 

Hawaiÿi.

Effects of Flow Releases on Low-Flow Duration Discharges  67
Table 24. Percent difference between estimates of natural and post-release low-flow duration discharges for 

continuous-record and low-flow partial-record (LFPR) streamflow stations, windward Oÿahu, Hawaiÿi.

[Mgal/d, million gallons per day; percentage of difference = 100 x (post-release flow - natural flow) / natural flow]

Station

Station

altitude

(feet)

Duration

percentile

Estimated

natural flow

at station

(Mgal/d)

Estimated

post-release flow

at station

(Mgal/d)

Percentage

of difference

Waianu Stream

16293100 75 99 4.6 2.7 -41

95 5.1 2.9 -43

90 5.4 3.0 -45

75 5.9 3.3 -44

50 7.0 3.8 -46

Waikäne Stream

16294500 220 99 1.5 2.2 49

95 1.7 2.5 48

90 1.8 2.7 52

75 2.0 3.2 62

50 2.3 3.5 51

16294700 90 99 0.80 0.03 -97

95 0.90 0.04 -95

90 0.94 0.06 -94

75 1.1 0.12 -89

50 1.3 0.25 -81

16294800 90 99 2.0 2.7 35

95 2.3 3.1 33

90 2.5 3.3 32

75 2.8 4.0 39

50 3.5 4.9 40

16294900 75 99 3.2 2.9 -10

95 3.7 3.2 -12

90 3.9 3.6 -7

75 4.5 4.7 4

50 5.5 5.9 7

16295195 10 99 3.1 2.7 -12

95 3.5 3.1 -11

90 3.8 3.4 -9

75 4.4 4.4 1

50 5.5 5.9 8

68  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
Comparison of Pre-release to 

Post-release Flows

Flow-duration discharge estimates at different locations 

make it possible to characterize the spatial distribution of low 

flows in the lower parts of the streams affected by upstream 

diversions and water releases. Effects of the flow releases 

can be assessed by comparing low-flow duration discharges 

between the pre-release and post-release periods. The comparison is limited to Waikäne Stream because insufficient 

pre-release discharge measurements are available for Waianu 

Stream and insufficient post-release discharge measurements 

are available for Waiähole Stream. 

Pre-release flows at the continuous-record and LFPR 

stations along Waikäne Stream at altitudes of 10 to 220 ft were 

compared to post-release flows in order to assess downstream 

changes in flow along the streams where releases were made 

(fig. 33). Pre-release flows for the selected duration percentiles 

at an altitude of 10 ft range from 35 to 43 percent of postrelease flows, whereas percentages at a higher altitude of 220 

ft range from 5 to 11 percent. At a particular stream altitude, 

Q50 (median) pre-release flows are consistently greater percentages of post-release flows than pre-release flows at higher 

duration percentiles because the relative effect of the added 

flow is smaller at higher flow conditions. Similarly, for a particular flow-duration percentile, pre-release flows associated 

with lower stream-channel altitudes are consistently greater 

percentages of post-release flows than those at higher streamchannel altitudes because the relative effect of the flow release 

is smaller as the stream gains ground water at lower altitudes. 

Limitations of Approach

The computation of natural low flows in streams using 

apportioned ditch flows assumes a one-to-one relation between 

water diverted by the Waiähole Ditch System and loss of flows 

from the streams. Takasaki and Mink (1985, p. 29) suggested 

that the final equilibrium base flow of the ditch system is not 

appreciably different from the total base flow of the diverted 

streams before the diversion system was constructed. The 

intercepted ground water was once discharged at springs 

above the level of the current ditch system; construction of 

the Waiähole Ditch System created new and lower points of 

discharge (Takasaki and others, 1969). The effect of tunneling 

is similar to an extension of a valley floor. If a tunnel is long 

enough, it may partly or completely replace a stream as the 

location where ground water will drain (Takasaki and others, 

1969, p.102). 

0

5

10

15

20

25

30

35

40

45

50

0 50 100 150 200 250

STREAM-CHANNEL ALTITUDE, IN FEET

Q99 flow

Q95 flow

Q90 flow

Q75 flow

Q50 flow

PRE-RELEASE FLOW AS A PERCENTAGE OF POST-RELEASE FLOW

Figure 33. Pre-release flows compared to post-release flows (Q50 to Q99) 

at stream-channel altitudes of 10 to 220 feet, Waikäne Stream, windward 

Oÿahu, Hawaiÿi. The Q50 flow is the median flow, and the Q99 flow is the flow 

that is equaled or exceeded 99 percent of the time.

Limitations of Approach  69
The computation of natural low flows in streams downstream from the Waiähole Ditch System assumes that intercepted base flows would have flowed naturally in streams 

above the level of the ditch system. As discussed in a previous 

section, the effect of tunneling largely affected ground-water 

discharge to stream reaches at higher altitudes, and effects at 

lower altitude reaches may be small. The uppermost LFPR station in the study area is station 16292800 at 380 ft altitude in 

Waianu Stream, well below the ditch altitude of approximately 

750 ft. Thus, for this study, it is reasonable to assume that 

all ground water intercepted by the Waiähole Ditch System 

would have discharged naturally to the stream reaches above 

the uppermost LFPR station. Low-flow estimates at the LFPR 

and continuous-record stations account for the current spatial 

distributions of gains and losses of water in the streams, and 

these distributions are assumed to be similar for both natural 

and diverted flow conditions.

Accuracy of Low-Flow Duration 

Estimates

The ranges of standard errors for the selected lowflow duration discharges at the LFPR stations on Waiähole, 

Waikäne, and Kahana Streams are 2.0 to 22, 1.8 to 26, and 5.0 

to 17 percent, respectively (table 15). The ranges of standard 

errors at the continuous-record stations on Waiähole, Waikäne, 

and Kahana Streams are 0.47 to 2.2, 0.38 to 1.4, and 0.59 to 

2.8 percent, respectively (table 16). The natural, pre-release, 

and post-release low-flow statistics at various locations on 

the diverted streams were computed using flow-duration 

analysis at continuous-record stations with long-term records 

and record extension techniques at stations with records 

shorter than the base period and at LFPR stations. Streamflow 

statistics for the long-term continuous-record stations were 

determined directly using the flow-duration analysis, and the 

computed daily flow statistics accurately represent flow conditions for the period of record over which they have been computed (Fontaine, 2003). Because low-flow estimates computed 

for short-term continuous-record stations and LFPR stations 

are not based on long-term data, they contain error. Accuracies 

associated with these low-flow estimates are largely related to 

the strength of the correlation between the discharges at the 

continuous-record and LFPR stations and the number of concurrent discharges available for the record-extension analysis. 

Accuracies associated with the pre-release low-flow estimates 

for station 16294900 are expected to be high because the available record from 1960 to 2002, representative of pre-release 

conditions, is only two years short of the base period (1960-

2004). The standard errors should be considered minimum 

errors because the methods used do not take into consideration 

the potential errors inherent in the discharge measurements 

made at the LFPR stations or the daily mean discharges at the 

index station (Fontaine, 2003). In addition, flow estimates at 

higher duration percentiles for some of the continuous-record 

and LFPR stations represent a significant extension or extrapolation of the data. 

 In general, accuracies associated with the pre-release 

flow estimates on Waikäne Stream are higher than accuracies 

associated with the post-release estimates. Flow releases at 

Intake 23 and Gates 30 and 31 were inconsistent and frequently higher than the targeted restoration flows (Hawaiÿi 

Commission on Water Resource Management, 2001) (fig. 34). 

The variability of flow releases in time reduces the reliability 

of the post-release flow estimates for this stream. In addition, 

because a small number of post-release discharge measurements at LFPR stations in Waikäne Stream were made during 

a relatively short period of time, the range of flows represented 

by these measurements was limited. 

For the natural flow estimates, the addition of flow 

statistics introduced additional errors. As discussed in an 

earlier section, the relative errors associated with adding flow 

statistics for stations on gaining streams downstream of the 

Waiähole Ditch System were estimated to average less than 5 

percent. 

Summary and Conclusions

Since 1916, the Waiähole Ditch System intercepted large 

amounts of dike-impounded ground water at high altitudes 

(above approximately 700 to 800 ft altitude) that previously 

discharged to Waiähole (and its tributaries Waianu and Uwao), 

Waikäne, and Kahana Streams through seeps and springs. 

Diversion of this ground water has significantly diminished 

low flows in these streams. Between December 1994 and 

October 2002, flow releases were initiated to Waikäne, 

Waianu, and Waiähole Streams from the Waiähole Ditch System. Natural (undiverted), pre-release, and post-release lowflow duration discharges for percentiles ranging from 50 to 99 

percent were estimated for continuous-record streamflow and 

LFPR stations along the affected streams. The computations 

involved the use of historical pre-ditch streamflow data and 

post-ditch streamflow data from USGS continuous-record stations, low-flow discharge measurements at LFPR stations, and 

seepage runs in the connecting tunnels and diverted streams. 

All flow estimates were adjusted to the base period of 1960-

2004, so that differences in flow reflect spatial differences in 

climate and drainage-basin characteristics rather than temporal 

differences in rainfall. 

Natural low-flow duration discharges were estimated for 

four sites at altitudes of 75 to 320 ft in Waiähole Stream (and 

its tributaries Waianu and Uwao Streams), for six sites at altitudes of 10 to 220 ft in Waikäne Stream, and for three sites at 

altitudes of 30 to 80 ft in Kahana Stream. Among the available 

low-flow estimates along each affected stream, the highest natural Q50 (median) flows on Waiähole (altitude 250 ft), 

Waianu (altitude 75 ft), Waikäne (altitude 75 ft), and Kahana 

(altitude 30 ft) Streams are 13, 7.0, 5.5, and 22 million gallons 

per day, respectively. The natural low-flow duration estimates 

compared favorably with limited pre-ditch streamflow data 

available for Waiähole and Kahana Streams. 

70Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
Gate 31 flow release to Waiahole Stream

0

5

10

15

20

25

30

35

40

45

50

DAILY DISCHARGE, 

IN MILLION GALLONS PER DAY

Gate 30 flow release to Waianu Stream

0

1

2

3

4

5

6

DAILY DISCHARGE, 

IN MILLION GALLONS PER DAY

Intake 23 flow release to Waikane Stream

0

1

2

3

4

5

6

1/1/1999 5/15/2000 9/27/2001 2/9/2003 6/23/2004

DAILY DISCHARGE, 

IN MILLION GALLONS PER DAY

Targeted flow restoration (4 Mgal/d)

Targeted flow restoration (3 Mgal/d)

Targeted flow restoration (2.1 Mgal/d)

(4.8 Mgal/d)

Figure 34. Daily flow releases at Gate 30, Gate 31, and Intake 23 on Waiähole Ditch System, 

windward Oÿahu, Hawaiÿi (daily flow data collected by Agribusiness Development Corporation and 

targeted flow restoration values issued by Hawaiÿi Commission on Water Resource Management 

(2001)).

Summary and Conclusions  71
Natural low-flow duration discharge estimates were 

compared with available current post-release flow duration 

discharge estimates at selected sites to assess how close current streamflows are to natural conditions. For Waianu Stream, 

current post-release flows at an altitude of 75 ft are 41 to 46 

percent lower than corresponding natural flows which indicate 

higher flow release would be needed to restore flow to natural 

conditions. For the upper reach of Waikäne Stream above the 

confluence with Waikeÿekeÿe Stream, current post-release low 

flows, at altitudes of 220 and 90 ft, are 32 to 62 percent higher 

than corresponding natural flows. For the stream reach below 

the confluence with Waikeÿekeÿe Stream, current post-release 

flows, at altitudes of 75 and 10 ft, are within 12 percent of 

corresponding natural flows. The results indicate that the current post-release flows are greater than natural flows along the 

upper reach of Waikäne Stream, but the current post-release 

flows along the lower reach are relatively close to natural 

flows. 

Pre-release flows and natural flows were compared at 

selected sites along the diverted streams from altitudes of 250 

to 320 ft in Waiähole Stream, 10 to 220 ft in Waikäne Stream, 

and 30 to 80 ft in Kahana Stream. The results indicate that the 

effects of the Waiähole Ditch System diversion are consistently greater at lower low-flow conditions (Q99 to Q90) than at 

higher low-flow conditions (Q75 to Q50). Results also indicate 

that the effects of the diversion become less significant as the 

streams gain additional ground water at lower altitudes. For 

Waiähole Stream, pre-release flows at an altitude of 250 ft 

range from 25 to 28 percent of natural flows, whereas at an 

altitude of 320 ft they range from 19 to 20 percent of natural 

flows. For Waikäne Stream, pre-release flows for selected 

flow-duration percentiles at an altitude of 10 ft range from 30 

to 46 percent of natural flows, whereas at an altitude of 220 ft 

they range from 7 to 19 percent of natural flows. For Kahana 

Stream, pre-release flows at an altitude of 30 ft range from 65 

to 72 percent of natural flows, whereas at an altitude of 80 ft 

they range from 58 to 71 percent of natural flows. 

Comparisons of pre-release and post-release flows at 

stations along Waikäne Stream at altitudes of 10 to 220 ft 

were used to assess downstream changes in flow along the 

stream reach where flow releases were made. At a particular 

stream altitude, pre-release flows associated with median 

flows are consistently greater percentages of median postrelease flows than those associated with lower low flows are 

of corresponding post-release flows because the relative effect 

of the added flow is smaller at higher low-flow conditions. 

Similarly, for a particular flow-duration percentile, pre-release 

flows associated with lower altitudes are consistently greater 

percentages of post-release flows than those at higher altitude 

because the relative effect of the flow release is smaller as 

the stream gains ground water at lower altitudes. Pre-release 

flows for selected duration percentiles at an altitude of 10 ft 

range from 35 to 43 percent of post-release flows, whereas at 

a higher altitude of 220 ft they range from 5 to 11 percent of 

post-release flows. 

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Appendix 1. Reconstructed daily time series of ditch flow at North 

Portal station 16287000 near Waiähole, windward Oÿahu, 2003-04. 

[Streamflow is in million gallons per day; --, not available]

2003

Day JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

1 24 25 22 23 22 21 21 21 21 19 19 21

2 24 24 23 23 22 21 21 22 20 19 17 22

3 24 24 22 22 22 21 20 22 20 19 18 23

4 24 24 22 24 22 21 21 21 20 19 19 27

5 24 23 22 23 21 22 21 22 20 19 19 28

6 24 23 23 24 21 21 22 21 22 20 18 24

7 23 23 24 23 23 21 21 22 22 19 19 29

8 23 23 23 23 22 22 21 22 20 20 19 25

9 23 23 23 24 22 22 21 22 20 20 19 25

10 23 23 22 26 22 22 21 20 21 20 18 25

11 23 23 23 24 22 21 21 21 31 20 17 25

12 23 23 22 23 22 21 21 20 24 20 18 25

13 23 22 22 23 22 20 21 20 23 19 18 25

14 24 31 22 23 22 21 21 21 22 20 18 25

15 24 25 22 22 22 22 20 20 21 20 17 25

16 23 23 27 22 22 22 21 21 21 19 17 23

17 24 23 24 22 22 21 21 22 20 20 18 23

18 24 23 22 22 22 21 21 20 21 19 19 23

19 24 23 22 22 22 21 21 20 21 20 18 23

20 25 23 22 23 21 21 22 20 21 19 18 23

21 24 23 22 22 22 21 21 20 22 19 18 23

22 24 24 22 22 22 21 20 20 20 19 18 23

23 23 23 22 22 22 21 21 21 20 19 18 23

24 23 23 22 22 22 21 21 21 20 19 18 23

25 23 22 22 22 22 22 23 20 20 19 18 23

26 23 23 22 22 22 21 26 20 20 19 18 23

27 23 23 24 21 21 21 23 20 20 19 18 23

28 23 23 23 21 21 22 25 20 20 19 18 23

29 23 -- 24 21 21 22 22 20 20 19 28 23

30 26 -- 24 21 21 21 21 21 20 19 25 24

31 28 -- 24 -- 21 -- 21 21 -- 19 -- 25

MEAN 24 23 23 23 22 21 21 21 21 19 19 24

74  Natural and Diverted Low-Flow Duration Discharges for Streams Affected by Waiähole Ditch System
Appendix 1. Reconstructed daily time series of ditch flow at North 

Portal station 16287000 near Waiähole, windward Oÿahu, 2003-04—

Continued.

[Streamflow is in million gallons per day; --, not available]

2004

Day JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

1 26 27 27 28 29 33 30 29 27 26 31 29

2 29 27 30 31 31 33 32 31 27 27 30 28

3 27 27 28 30 29 33 30 30 27 26 30 28

4 25 27 27 28 28 33 29 30 27 27 30 28

5 25 28 27 28 28 33 29 28 27 26 31 28

6 25 27 27 28 28 33 29 27 28 26 31 28

7 25 31 27 27 29 33 30 28 27 26 31 28

8 25 30 27 27 28 33 30 27 27 26 30 29

9 25 26 27 28 28 34 30 27 27 26 29 29

10 25 27 27 28 28 35 30 27 27 26 29 28

11 25 27 27 28 29 35 30 27 27 26 29 28

12 25 27 27 28 28 34 26 27 27 25 29 28

13 25 27 27 29 28 34 29 28 27 25 29 28

14 26 27 28 29 28 34 30 28 27 25 32 28

15 25 27 27 28 28 34 30 28 26 25 30 30

16 25 27 27 29 28 34 29 28 26 25 30 30

17 25 27 27 28 27 35 28 28 26 25 30 29

18 25 27 27 28 27 34 27 28 26 25 30 29

19 26 27 27 28 28 34 27 28 26 25 29 29

20 26 27 27 29 30 34 29 28 26 25 29 25

21 26 27 30 29 30 34 30 28 26 25 29 26

22 28 27 30 30 31 35 33 29 26 25 28 30

23 28 28 29 29 30 34 32 28 27 25 29 29

24 27 27 29 29 30 34 32 28 27 26 29 29

25 29 27 30 31 32 34 31 30 27 23 29 29

26 28 28 28 30 30 34 30 29 26 33 29 29

27 27 33 28 29 30 34 30 28 26 32 28 30

28 26 29 28 29 30 34 32 28 27 16 30 29

29 26 28 29 27 30 33 30 28 27 28 30 28

30 26 -- 30 31 28 34 28 26 27 29 28 28

31 27 -- 29 -- 30 -- 30 30 -- 35 -- 28

MEAN 26 28 28 29 29 34 30 28 27 26 30 28

Appendix 1  75

Yeung and Fontaine—Natural and Diverted Low-Flow Duration Discharges for Streams Affected by the Waiähole Ditch System, 

Windward Oÿahu, Hawaiÿi—Scientific Investigations Report 2006–5285

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