LIBRARY COPY

U S. GEOLOGICAL SURVEY,

ftQUA, MlSSQUiL

Water Resources of 

North-Central Oahu, 

Hawaii

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1899-D

Prepared in cooperation with the 

State of Hawaii, Department of 

Land and Natural Resources, 

Division of Water and Land 

Development
Water Resources of

North-Centra

Hawaii

By J. C. ROSENAU, E. R. LUBKE, and R. H.

WATER RESOURCES DIVISION

ROUUA, MO. 

RECEIVED

AUG 131971

PM

CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1899-D

Prepared in cooperation with the 

State of Hawaii, Department of 

Land and Natural Resources, 

Division of Water and Land 

Development

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1971
UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY 

William T. Pecora, Director

Library of Congress catalog-card No. 76-609223

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402-Price 30 cents (paper cover)
CONTENTS

Page

Abstract ............................................................................................................. Dl

Introduction .......................... .. ............................................ ................_.......... 1

Geology ................................................................................................................ 3

Climate ............................................................................................................... 7

Water resources ................................................................................................ 9

Hydrologic setting .................................................................................... 9

Streamflow .................................................................................................. 13

Koolau Range . ................................................................................ 13

Waianae Range ................................................................................ 18

Ground water ............................................................................................ 20

Koolau Range .................................................................................... 24

Waianae Range . ....................................... ..................................... 24

Mokuleia area . ......... ......................................................... ..... 25

Schofield Plateau .............................................................................. 26

Waialua-Haleiwa area .................................................................... 27

Kawailoa area .................................................................................... 28

Salt-water intrusion .................................................................................. 29

Estimate of ground-water flow .............................................................. 31

Runoff .................................................................................................. 35

Evapotranspiration .......................................................................... 36

Recharge .............................................................................................. 37

Summary ............................................................................................................ 88

References .......................................................................................................... 39

ILLUSTRATIONS

FIGURE 1. Map of Oahu, Hawaii showing area of study..................

2. Aerial view of northern Oahu looking southeast.............

3. Generalized geologic map ......................................................

4. Geologic section through the coastal plain ................_.....

5. Graphs showing temperature and rainfall .......................

6. Map showing mean annual rainfall and the locations 

of rain-gage stations ..........................................................

7. Graph showing the annual pumpage of ground water 

in the study area ........................................ ... .. . . -.

8. Map showing location of hydrologic data sites. 

9. Graph of gage-height record of Opaeula Stream near 

Wahiawa January 31 through February 2, 1963

10. Flow-duration curve of the North Fork Kaukonahua 

Stream above Right Branch ...........................................

Page

D2

4

6

8

9

11

13

14

15

16

HI
IV CONTENTS

FIGURE 11. Graph showing rainfall and runoff in the Waianae 

Range ...... .......................................................................

12. Generalized geohydrologic section from Kaala east

through central Oahu and the Koolau Range .............

13. Generalized geohydrologic section from Waialua to the 

Schofield Plateau ................................................................

14. Map showing location and ground-water levels in volcanic rock ..............................................................................

15. Map showing distribution of chloride content of water 

in basaltic aquifers ..........................................................

16. Graph showing ground-water pumpage and chloride 

content of the water in Waialua ......................................

17. Graph showing relation of runoff to rainfall ...................

Page

D19

21

22

23

29

30

34

TABLES

TABLE 1. Monthly rainfall at selected stations in 1964 in northern 

Oahu .........................................................................................

2. Rain-gage stations in northern Oahu ...................................

3. Stream-gaging stations in northern Oahu ...........................

4. Average rainfall, runoff, evapotranspiration, and recharge by geologic environment and rainfall zones as 

estimated for north-central Oahu ......._............................

5. Average rainfall and runoff for major areas of the 

island of Oahu .......................................................................

Page

DIG 

12 

14

33

36
CONTRIBUTIONS TO THE HYDROLOGY OF THE 

UNITED STATES

WATER RESOURCES OF NORTHCENTRAL OAHU, HAWAII

By J. C. ROSENAU, E. R. LuBKE, and R. H. NAKAHARA

ABSTRACT

North-central Oahu consists of 152 square miles and includes mountainous 

terrain, the Schofield Plateau, and a narrow coastal plain. Half the area is 

above an altitude of 1,000 feet and receives 71 percent of the 580 mgd 

(million gallons per day) average annual precipitation. Recharge to groundwater reservoirs from precipitation is estimated to be about 225 mgd.

Streamflow to the ocean is negligible, except during floods, owing to diversions by way of numerous mountain ditches into reservoirs. As it is used 

for irrigation of sugarcane, a large part of the diverted water percolates 

into underlying ground-water reservoirs.

Ground water is available from wells drilled into lava flows of the Koolau 

and Waianae Volcanic Series and from shallow sedimentary material in the 

coastal plain. About 200 mgd discharges to the ocean from ground-water 

reservoirs underlying the coastal plain.

Water use in a dry year is about 93 mgd 75 mgd for irrigation and 18 

mgd for domestic, industrial, and miscellaneous uses. Two-thirds of the 

total is from ground-water sources, and one-third is from streams and reservoirs. Long-term ground-water pumpage for all uses averages 48 mgd, of 

which nearly 42 mgd is for irrigation. Average annual streamflow diversion 

is 57 mgd, and irrigation application is approximately 36 mgd.

Salt-water intrusion of the shallow sedimentary material or of the deeper 

water-bearing lava is not yet a major problem. Water from a few heavily 

pumped coastal wells has become moderately saline, but a reduction in 

pumping at these sites, a dispersal of wells, or an inland placement of new 

wells would minimize intrusion.

INTRODUCTION

This report summarizes the findings of a study of a part of 

northern Oahu (fig. 1). It briefly describes the distribution of rainDl
D2 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

158°00'

21° 

30'

Kahuku Point

10 MILES

Barbers Point'

FIGURE 1. Island of Oahu, Hawaii, showing areas of this study and of

related investigations.

fall and of irrigation water, outlines the geology, and discusses the 

occurrence, quality, and quantity of water available.

The demand for water for municipal and irrigation use is increasing in the Mokuleia-Waialua area. Subdivision development 

and other aspects of urbanization are shifting the pattern of water 

use. Information is needed, therefore, on the quantity and quality 

of water that is available for development.

The study was made by the U.S. Geological Survey in cooperation with the Division of Water and Land Development, Department of Land and Natural Resources, State of Hawaii. It is one 

of a series of studies on Oahu designed to provide information for 

use in the development and efficient management of the water 

supply of the island. Related studies have been made in southern 

Oahu (Visher and Mink, 1964), the Waianae area (Zones, 1963), 

windward Oahu (Takasaki and others, 1969), and the Kahuku 

area (Takasaki and others, 1966) (fig. 1). Other related studies 

are in progress.

Previous studies of Oahu were made by Stearns and Vaksvik 

(1935, 1938) and Stearns (1940). Geology and topography were
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D3

described, records of wells were given, and ground-water resources 

of the study area were discussed in a general way in reports resulting from these studies. The Board of Water Supply, City and 

County of Honolulu, and the Waialua Sugar Co. have, in their files, 

unpublished reports by D. C. Cox, H. S. Palmer, H. T. Stearns 

and G. A. Macdonald, and W. B. Thomas.

The writers are indebted to the Board of Water Supply, City 

and County of Honolulu, and to the Waialua Sugar Co. for making 

valuable hydrologic data available.

The study area includes 152 square miles. Figure 2 shows the 

northern half of Oahu, illustrated as seen from an altitude of 

about 10,000 feet and north of the island. The study area is 

bounded by the crest of the Koolau Range and the drainage basin 

of Kamananui Stream on the east, by the crest of the Waianae 

Range on the west, by the ocean on the north, and by the summit 

of the Schofield Plateau in the area of Wahiawa and Schofield 

Barracks on the south.

The Koolau Range, rising to 2,763 feet above sea level, dominates the physiography of northern Oahu. Its broad and gently 

sloping west side stretches to Schofield Barracks, to the base of the 

Waianae Range, and to the ocean, and is cut by many streams that 

converge into six major valleys. These deep and narrow valleys 

are separated by ridges planted to sugarcane and pineapple up to 

altitudes of about 1,600 feet.

The Waianae Range is higher than the Koolau Range, having 

a maximum altitude of 4,025 feet at Kaala. The north and east 

sides of the Waianae Range are steep and extensively gullied, and 

the ridges are generally too narrow for cultivation.

Through irrigation, sugarcane is cultivated in the dry coastal 

areas and part way up the slopes of the Koolau Range and the 

Schofield Plateau. Pineapple is grown without irrigation throughout most of the upper Schofield Plateau area. Aside from sugarcane, vegetal cover is controlled by the local climate. Kiawe 

(algaroba) covered dry areas and patches of pricklypear cactus 

border the shore and extend partly up the flanks of the adjacent 

mountains. The higher altitudes are generally wetter than the 

lower and are covered by guava, koa, and other plants of the 

wet-forest type.

GEOLOGY

The geologic history of the Hawaiian Archipelago was described 

by Stearns (1966 and 1967). Stearns and Vaksvik (1935) and 

Stearns (1939, 1940) mapped and described the geology of Oahu
Makaha

Laie

o 

o

O

*

co

H O

H

a

H

a

a

Kahuku Poin Kaena Point

FIGURE 2. A southeasterly aerial view of northern Oahu, showing the massive Koolau Range on the east and 

the more eroded Waianae Range on the west topped by the 4,025-foot Kaala. Sugarcane in north-central Oahu is grown on the lower gentle slopes (dark tone), and pineapple is grown on parts of the higher slopes 

(light tone).

CO
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D5

(fig. 3). Owing to the scarcity of outcrops, wells, and test holes 

in critical areas, additional detailed geologic information is lacking upon which to base hydrologic interpretations.

The oldest rocks of northern Oahu are lava flows of the Waianae 

volcano, which are partly overlapped by younger flows of the 

Koolau volcano and separated locally by alluvium from the 

younger flows. Erosion has diminished the Waianae and Koolau 

volcanoes, cutting deep, narrow valleys into their flanks. The 

eroded material forms extensive alluvial deposits in the lowlands.

The Waianae Range is built of the basaltic lava flows and dikes 

of the Waianae Volcanic Series of Pliocene (?) age (G. A. 

Macdonald and D. A. Davis, in Avias, 1956, p. 135-136). (For 

general description, see G. A. Macdonald, in Stearns, 1967, p. 110- 

112.) Stea-rns and Vaksvik (1935, p. 67) divided the series into 

three members: the lower consists of 2,000 feet of thin-bedded 

pahoehoe; the middle is similarly thick but contains more aa; the 

upper consists of 2,300 feet of massive aa flows. A dike-complex 

zone lies west of the present crest of the Waianae Range, but only 

a few dikes have been found on the east side, where vegetation 

is extensive and the surface is only lightly eroded. G. A. Macdonald 

(in Stearns, 1940, p. 63-91) modified and elaborated on part of the 

earlier work of Stearns and Vaksvik. He wrote that lava of the 

lower member was thinly bedded and gently dipping olivine basalt; 

that lava of the middle member was thicker, more massive, and 

nearly horizontal olivine basalt; and that lava of the upper member was similar to that of the middle member but typically consisted of basaltic andesite.

The northern part of the Koolau Range was formed by basaltic 

flows of the Koolau Volcanic Series, also of Pliocene (?) age 

(G. A. Macdonald and D. A. Davis, in Avias, 1956, p. 106-107). 

The series, which is more than 3,100 feet thick, consists of flows 

of pahoehoe and aa that range from 10 to 80 feet in thickness. 

Even the thick flows consist of several layers (Stearns and 

Vaksvik, 1935, p. 93). The flows were extremely fluid and succeeded one another fairly rapidly. The landward flanks of the 

two ranges are similar, as are the seaward flanks. The landward 

flanks, however, lack the outcrops, the dikes, and the na pali ku'i, 

or joined succession of cliffs, that are typical of the seaward flanks 

of both ranges (fig. 2).

Basaltic rocks of the island are generally permeable, but the 

Koolau rocks are more permeable than those of the Waianae. 

High permeability, the favorable geologic framework (Takasaki 

and others, 1962, p. 4-7), and high rates of precipitation and
EXPLANATION

Alluvium and marine sediments

Koolau Volcanic Series

Waianae Volcanic Series

^ahuku

Contact

0 1 2 3 4 5 MILES 

I I I I I I 

CONTOUR INTERVAL, IN FEET, IS VARIABLE

DATUM IS MEAN SEA LEVEL Halpiwa

Kaena MLLINGHAM Pojnt AIR FORCE BASE

" -v^./^ .,/1, ^c. . < rrf*&ZMa(Ha.// -A*"" " !-\\ ' riMN^L /' v^.£i/> »^\

BABSAClrf South Tor

FIGURE 3. Generalized geologic map; section A-A' shown in figure 4. (After Stearns, 1939.)

U 

en

Cd 

di-3

I I

o 2

GO

H 

O

HaH

a Hatd

o f 

o o
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D7

recharge make the Koolau Range the largest source of water on 

the island.

Alluvium and marine sediments of sand and coral are shown as 

a group in figure 3 because they are small in volume and areal 

extent and are limited mostly to nearshore locations. These materials overlie lava flows in the coastal plain (fig. 4) from Kaena 

Point eastward to the Waimea River and confine the underlying 

artesian aquifers. They are known to be as thick as 500 feet in 

the Mokuleia area and 200 feet at Waialua and to decrease in 

thickness to a variable veneer east of the Anahulu River.

CLIMATE

The climate of northern Oahu is characterized by mild temperatures (fig. 5), northeast trade winds, and between 25 and 300 

inches of rainfall annually (fig. 6). Rainfall gradients are steep. 

Orographic lifting of moisture-laden trade-wind air causes frequent light lowland showers and moderate to heavy mountain 

showers throughout the summer and part of the winter. Although 

trade-wind rainfall is the most consistent water source, storms are 

important to the replenishment of ground water in the Koolau 

Range and of even greater importance in the Waianae Range. As 

many as seven major storms may occur in 1 year, bringing torrential rains and perhaps violent winds (Blumenstock, 1961).

Figure 5 includes a group of graphs that shows the effect, at 

a low coastal station (847) and at a mountain station (844.4), of 

the winter storms in 1963. A comparison of 1963 rainfall with 

mean monthly rainfall at these stations shows that 1963 was a wet 

year because of the storms in January, March, April, and May 

in spite of near- or below-normal rainfall during the rest of the 

year.

The size and intensity of individual storms can be inferred 

from table 1. March 1964 rainfall at Wheeler Air Force Base 

(sta. 810, fig. 6) was large, even larger than that on top of Kaala 

(sta. 844.2), whereas December rainfall was large throughout the 

study area a third or more of annual rainfall at many stations.

Humidity is generally between 60 and 80 percent in northern 

Oahu. Air temperature has a small annual and daily range the 

difference between the coldest and warmest months averages only 

6.5°F (3.6°C). A curve of mean monthly temperature at the 

Waialua Sugar Co. office (sta. 847) is included in figure 5.

The authors established a group of storage-type rain gages in 

the watershed area of the Waianae Range. The gages were concentrated on the north and northeast slopes of the range, as rain-
D8 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D9 

82

78

5 5 74 ^ z < u u. t70

I I I T

Mean monthly temperatures 

at Waialua,station 847

i i i I I i I i i

JFMAMJJASOND

I o 

O 8

± 4 

_f

n. 0 

? 16 

tr

12

"1 I I I I I I T

Waialua

Station 847

Alt 32 ft

1963

Average, 4.6 inches

T i i n y ^ i i i

Station 847

mean monthly rainfall

1931-55

\ r \ \ i i i i i i

Station 844 

mean monthly rainfall _ 

1933-47

Average, 7.3 inches

J FMAMJJASOND JFMAMJJASOND

MONTHS

FIGURE 5. Mean monthly temperature at Waialua (sta. 847) and the monthly rainfall for 1963 and the mean monthly rainfall for the period of 

record at Waialua (sta. 847) and at Kaala (sta. 844.4 and 844).

fall data from there were sparse or nonexistent. Table 2 lists the 

number, name, and altitude of rain-gage stations shown in figure 6.

WATER RESOURCES 

HYDROLOGIC SETTING

Rain is the source of fresh water. Upon reaching the ground, 

part of the rain evaporates and part is transpired, a part flows to 

the sea in streams, and the remainder filters down through the 

soil and rock to the water table and recharges the ground-water 

reservoir.
DIG CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

TABLE 1. Monthly rainfall in inches, at selected stations in 1964 

in northern Oahu

[These rain-gage stations are identified by number, name, and 

altitude in table 2, and their locations are shown in figure 6]

Station number 

843.1 844.2 841.9 857.2 802.2 810 870 892 887

January . ..

February . ...

March ... ....

April ...

May ..........

June ......

July

August .........

September ... 

October ......

November ... 

December ...

Total ...

- 2.6

.3

... 5.1

... 1.4

... .3

- .1

... 2.2

... .2

.2 

... 2.2

... 2.5 

... 17.0

... 34.1

8.6

3.9

14.3

4.8

4.4

1 R

Q 0

2.9

3.0 

8.5

12.6

27.2

101.0

4.00

9 70

9 10

1.21

qO

.11

1.34

.35

.36 

9 97

2.50 

11.60

28.92

O K

0

8.5

1.0

.4

q

1.2

.4

.4 

1.4

5.1 

10.0

32.2

q 7

q

8 1

1.7

q

0

1.4

.5

1.4

2.0

8.0 

16.0

44.3

3.74

2.24

16.63

1.85

1.00

.50

2.41

.74

.85 

1.46

10.60 

15.87

57.89

7 37

3.48

5.45

q 70

1.43

2.10

3.35

3.11

3.07 

2.28

8.79 

13.11

57.24

6.15

2.63

5.80

2.14

1.67

2.24

3.32

3.18

2.13 

2.59

5.85 

16.53

54.23

3.46

1.08

4 Qfi

1.52

.47

.28

1.25

.99

.48 

1.78

3.55 

15.50

35.32

Rain on the 152 square miles of the study area is equivalent to 

an average of 580 mgd (million gallons per day) , as determined 

from the data shown in figure 6. Of this quantity, 413 mgd, or 71 

percent, falls in the 80 square miles that lies above an altitude of 

1,000 feet. About 12 mgd falls in the 10 square miles between sea 

level and an altitude of 40 feet, and the remaining 155 mgd, or 

27 percent, falls in the area between.

Ground water sustains high-altitude streamflow during dry 

periods in the Waianae and Koolau Ranges. Most streamflow is 

diverted for irrigation or eventually infiltrates through the streambeds; streamflow reaches the ocean only after periods of intense 

or prolonged rainfall.

Near the coast a large part of the ground water reaches the 

ocean as underflow. Some of the water discharges at ground level 

from springs or as seepage into low-lying swamps. A considerable quantity of water also is pumped for irrigation from wells 

along the coast, but about 40 percent of the applied irrigation 

water reenters the ground- water body by deep percolation (Dale, 

1967) .

About 90 percent of the water diverted from streams and 

pumped from lava aquifers is used for irrigating approximately 

10,000 acres of sugarcane 3,000 acres with surface water and
EXPLANATION

^887

Rain-gage station and number

-20

Line of mean annual rainfall; 

interval, in inches, is variable

Waimea

Waimea Rivet

CONTOUR INTERVAL, IN FEET, IS VARIABLE 

DATUM IS MEAN SEA LEVEL

863.1 ' BARRACKS ftuufk

FIGURE 6. Mean annual rainfall and the locations of rain-gag

Honolulu Board of Water Supply, 1963
D12 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

TABLE 2. Rain-gage stations in northern Oahu

[Numbers assigned by Hawaii State Division of Water and Land 

Development. *, Maintained by the U.S. Geological Survey]

Station

796 ..... 

800.1... 

*802.2... 

*802.3... 

803 ..... 

810 .. ..

833 ..... 

841 ....

841.3...

*841.4... 

*841.5... 

*841.6... 

*841.7... 

*841.8... 

*841.9...

*841.11. 

*841.12. 

*841.13. 

*841.14. 

*841.15. 

*842.1... 

*842.2... 

*842.3... 

*842.4... 

*842.5... 

*842.6... 

*843.1... 

*843.2... 

844 ... 

*844.2. . 

*844.4... 

845 .. 

846 .....

Name

..KP-5 (Kaena Point) ......... 

..KP-4 (Kaena Point) ........

..KP-3 (Kaena Point) ........ 

..KP-2 (Kaena Point) ....... 

..KP-1 (Kaena Point) ........

..PFR 6 (Peacock Flat) ....

PFR 4 (Peacock Flat)

..PFR-2 (Peacock Flat)

..Makaha (USGS) .......... .....

..PFR-7 (Peacock Flat) . ..

.KR-3 (Kaala Rd.) .......

..KR 4 (Kaala Rd.) .......

..KR-5 (Kaala Rd.) ............

KR-1 (Kaala Rd.) .... ..

..KR-2 (Kaala Rd.) .........

.KR-7 (Kaala Rd.) .......

KR-8 (Kaala Rd.) .........

Ranch (Mokuleia) ..........

Altitude 

(ft.)

......... 25

...........1,580

...........1,350

1 F\7F\

........... 845

...........1,060

........... 20

........... 880

...........1,300 

........... 400 

. ......... 45

........... 60

...........1,610

Qt\

Q7ft

2 1 Qn

...........2,050

O -1 QA

2 700

OAfi

920

...........4,000

...........3,965

o Q£n

20

........... 190

Station

847 ..... 

848 ..... 

850 ...... 

851 ..... 

852 ...... 

853 ...... 

854 ...... 

855 ...... 

856 ......

856.1.... 

*857.2.... 

861 ...... 

863 ...... 

863.1.... 

870 ...... 

872 ...... 

876 ...... 

880.2... .

881 ......

882.1.... 

887 ......

888 ...... 

890 ...... 

891 ......

892 . ....

893 ...... 

894 ...... 

897 ......

900 ...... 

908 ...... 

910 ... .. 

912 ......

Name

..Waialua ...................... ..........

.Kemoo Camp 8 ..................

.McCarthy 5 (Schofield) ....

.Opaeula 8 .............................. 

.Wahiawa Dam .................... 

.Area BB (Schofleld) ..........

.North Fork Kaukonahua ..

.Kawailoa .................................

.Kawailoa 15 ..........................

.Kawailoa 19 ..........................

.Waimea Mauka .....................

.Malaekahana (Kahuku) .....

.Pump 4 (Waialee) .............

.Pump 10 (Kahuku) .............

.Kahuku ...................................

Altitude 

(ft.)

........... 32 

...........1,040

........... 45

........... 285

........... 180

........... 520

........... 310

........... 730

........... 470

........... 700

........... 960

........... 690 

........... 855 

...........1,160

...........1,060

........... 920

...........1,250

...........1,180

...........1,275

...........1,150

........... 110

........... 245

........... 170 

........... 320

........... 420

........... 520

........... 660

........... 920

........... 190

........... 40

........... 200

.......... 25

7,000 acres with ground water. About two-thirds of the water used 

is pumped from wells or shafts, and the remainder is diverted 

from streams in the Koolau Range.

Ground-water withdrawal in north-central Oahu has increased 

slightly since 1924. Average daily pumpage from year to year has 

fluctuated between 28 and 70 mgd (fig. 7). This fluctuation is the 

result of irrigation demands, which vary seasonally and annually 

according to rainfall.

Municipal pumpage has increased from less than 0.5 mgd in 

1938 to as much as 8 mgd in 1965. Most of the increase has been 

on the Schofield Plateau, where water is needed for both civilian 

and military uses. From 2 to 5 mgd is used for air conditioning 

and small-truck-farm and forage-crop irrigation.
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D13

£LO

<0

70

60 

50 

40

30

20

10 

0

EXPLANATION

-

-

~

-

-

Ave re

m

ge fo

m

r record.

I m

m

m£

-

m

-c

P

M*.

-i

-;1

 Other

"-Municipal

 Irrigation

-

*1

M

m

>

1

i

1

i

I

ii

H -£

1

* 

5

.jMiii

T pVf

^

-

 *t oiDoinomom c\j roro^-'^inmvDvD 

CTi OSCTiOiCTiOiCTiCTiCTi

FIGURE 7. Annual pumpage and the use of ground water in north-central 

Oahu, 1924-66. Municipal pumpage before 1938 was less than 0.5 mgd and 

is not shown.

STREAMFLOW

KOOLAU RANGE

About one-third of the water used in north-central Oahu is 

diverted from streams in the upper part of the Koolau Range. 

The streams are generally perennial in their upper reaches but 

dry in their lower reaches owing to water being diverted. Highly 

permeable streambeds facilitate infiltration of undiverted flows. 

Except for Kiikii Stream and Anahulu River, which are fed by 

spring flow near sea level, no streams flow to the sea unless rainfall is heavy and of long duration or is unusually intense.

The Geological Survey has maintained stream-gaging stations in 

north-central Oahu since 1911. Major stations are identified by 

number and name of stream-gaging station in table 3 (Hoffard 

and Vaudrey, 1966) and in figure 8.

The flashiness of streams in the Koolau Range is illustrated in 

figure 9, which shows the gage-height record of Opaeula Stream 

(sta. 3450) during a 12-hour period on January 31, 1963. During
D14 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

TABLE 3. Stream-gaging stations in northern Oahn

[*, crest-stage gage site]

Station

2080 

2085

2000

2P40

2030

2109

2110

3450

*3500

*3400

3250

3300

*2113

Period

of 

record

1957- 

1958-

1913-53,

1946-

1947-

1958-

1947-

1959-

1955-

1957-

1963-

1958

1958-

Name of station

South Fork Kaukonahua Stream at 

East Pump Reservoir, near Waihiawa 

Right Branch South Fork Kaukonahua

North Fork Kaukonahua Stream above

North Fork Kaukonahua Stream near

Kamananui Stream at Pupukea Military

Altitude

(ft.)

860 

980

1,150

970

1,140

1,120

1,150

1,120

20

70

590

20

180

Drainage

(sq mi)

4.04 

.86

1.38

4.86

_

1.79

2.98

5.96

13.5

3.13

9.79

4.24

Peak 1

Mgd

3,530

880

3,550

3,010

10

128

1,710

1,810

2,660

2,500

844

2,230

2,352

flow

Cfs

5,460 

1.360

6,490

4,660

16

198

2,650

2,800

4,120

3,870

1,310

3,450

3,640

EXPLANATION

 330-7A

Well and number

158°00' ^Kahuku Point

01 2345 MILES 

I I I I I I 

CONTOUR INTERVAL, IN FEET. IS VARIABLE 

DATUM IS MEAN SEA LEVEL

FIGURE 8. Locations of hydrologic data sites.
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D15

JANUARY 31 FEBRUARY 1 

1963

FEBRUARY

FIGURE 9. Gage height of Opaeula Stream near Wahiawa (sta. 3450) for 

the period January 31 through February 2, 1963. Instantaneous discharges 

are given at various gage heights.
D16 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

PERCENTAGE OF TIME INDICATED 

DISCHARGE WAS EQUALED OR EXCEEDED

FIGURE 10. Flow-duration curve of the North Fork Kaukonahua Stream 

above Right Branch near Wahiawa. The period of record is 1927-53 and 

1961-62.
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D17

the passage of two storms 4i/£ inches of rain fell, causing instantaneous discharge as great as 525 mgd, or 812 cfs (cubic feet per 

second) . Similar storms are fairly common during the winter and 

can occur any time of year.

Variability of streamflow is illustrated in figure 10, which is 

a flow-duration curve for North Fork Kaukonahua Stream above 

Right Branch (sta. 2000). The steep slope throughout the curve 

reflects the extreme variability of flow resulting from a very small 

ground-water source and the rapid response of runoff to rainfall. 

The curve shows that average daily flow exceeded 1.1 mgd about 

90 percent of the time, 10 mgd about 25 percent of the time, and 

100 mgd less than 1 percent of the time.

The Waialua Sugar Co. diverts about 55 mgd of water from 

streams on the west side of the Koolau Range and applies about 

35 mgd for the irrigation of sugarcane through four diversioncollection-distribution systems. The Wahiawa Reservoir (fig. 8) 

is the largest reservoir in the system and in the islands. It has 

a storage capacity of 2.5 billion gallons and is formed by impounded water of the 17-square-mile Kaukonahua drainage system and the flood flow of the upper Poamoho system. Helemano 

Reservoir (fig. 8) receives the normal flow of Poamoho Stream 

and the flow of Helemano Stream above an altitude of 1,074 feet. 

Opaeula Reservoir receives Opaeula and Kawaiiki streamflow 

above altitudes of 1,100 and 1,160 feet, respectively. The Kamananui Reservoir receives water from Kawainui Stream above an 

altitude of 713 feet. The lower parts of Poamoho and Helemano 

Streams are not tapped, nor is any of the Waimea River complex, 

which is a part of the northeast boundary of the study area.

Rainfall variations cause annual fluctuations in the amount of 

streamflow available from the seven major drainage systems of 

north-central Oahu. The 5-year average annual streamflow of these 

systems, measured above the diversions, is 83 mgd. Streamflow in 

a dry year (1962) was only 53 percent of the 5-year average. The 

following tabulation compares streamflow and water diversions 

during that year with those during a 5-year period (1962-66).
D18 CONTRIBUTIONS TO THE HYDROLOGY OP THE UNITED STATES

Streamflow

5-year average annual 1962

Streams (mgd) (mgd)

Kaukonahua .............................................. 39 24

Helemano and Poamoho ........................ 5 5

Opaeula and Kawaiiki ............................ 16 8

Kawainui .................................................. 6 2

Kamananui .............................................. 9 5

Total ........ .................................... 83 44

Water diverted to reservoirs

5-year average annual 1962

Reservoirs (mgd) (mgd)

Wahiawa .................................................. 39 23

Helemano .................................................. 6 2

Opaeula .................................................... 8 4

Kamananui .............................................. 4 2

Total .............................................. 57 31

Sixty-nine percent of the 83 mgd average annual measured 

streamflow was diverted to reservoirs, and an average of 36 mgd 

was eventually applied to approximately 3,000 acres of sugarcane. 

The remaining 20 mgd and the 26 mgd that was not diverted recharged the aquifer, evaporated, ran off to the sea during storm 

periods, or was transpired.

WAIANAE RANGE

Streams in the higher part of the Waianae Range have perennial flow, which probably originates from perched springs at altitudes of about 2,000 feet. Except during periods of intense rainfall and excessive runoff, their flow infiltrates before the streams 

reach the ocean.

A small unnamed stream about a mile southeast of Peacock 

Flat (fig. 8, miscellaneous discharge site, lat 21°32'05" N., long 

158°10'50"W.) at an altitude of 2,040 feet was measured at regular intervals between April 1962 and February 1966 (fig. 11A). 

Streamflow at the gage site generally varies seasonally, and the 

surface-drainage area is about 0.01 square mile. The low-flow 

period normally occurs between September and November, but in 

1964 it began in June and continued until the first winter storm 

in late October (fig. 1LB) . That storm caused the 7.2-inch October
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D19

120

100

D

= 80

60

UJ

O

cr

I 40 

O

20

30

20

B

1,0

n

1962 1963 1964 1965 1966

FIGURE 11. Rainfall and runoff in the Waianae Range. A, Instantaneous 

stream-flow measurements obtained at miscellaneous discharge site near 

rain gage S42..2. B, Monthly rainfall at gage 842.2.
D20 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

rainfall at station 842.2. In September 1964, after 15 months during which average monthly rainfall was only 3 inches, the flow 

of the stream had declined to its record low of 2.9 gallons per 

minute (about 4,200 gpd). Flows exceeding 200,000 gpd (gallons 

per day) are known to have occurred in response to heavy rainfall.

Half a mile southeast of the previous site are a group of springs 

(lat 21°31'13" N., long 158°10'25" W.) that apparently are the 

source of the west branch of Makaleha Stream. Measured a short 

distance below the springs, at an altitude of 1,750 feet and where 

the surface-drainage area is 0.06 square mile, the stream has a 

low flow of 30,000 gpd and a maximum flow estimated to exceed 

1 mgd.

A mile and a half west of Dillingham Air Force Base, a small 

spring-fed stream (lat 21°34'40'/ N., long 158°14'15" W.) supplies 

water to the Bowman cottage (sta. 841.9, fig. 6). The spring is at 

an altitude of about 700 feet and has a drainage area of 0.01 

square mile. It has a low flow of 14,000 gpd, and a maximum flow 

estimated to exceed half a million gallons per day.

Streams on the lower slopes of the range are ephemeral and 

have occasional flows that last only hours or a few days, depending on duration and intensity of rainfall. Streamflow records have 

been kept for Makaleha Stream near Waialua (sta. 2113, fig. 8) 

since 1958. The stream has a surface-drainage area of 4.20 square 

miles, and the crest-stage gage is at an altitude of 160 feet. Although Makaleha Stream is dry most of the time, a peak flow of 

2,350 mgd (3,640 cfs) occurred on November 13, 1965.

GROUND WATER

Most ground water in northern Oahu is in permeable volcanic 

rock. It is impounded at high levels in compartments formed by 

dikes that cut lava flows in the central parts of the Koolau and 

Waianae Ranges (fig. 12). Ground water occurs similarly in compartments under the Schofield Plateau (fig. 13) and in small scattered bodies perched on weathered ash beds and dense lava flows.
FIGURE 12. Generalized geohydrologic section from Kaala east throug
D22 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D23

Under the lower slopes of the ranges and in coastal areas, the 

water table is near sea level. Near shore, the fresh-water lens is 

normally confined in lava flows by semipermeable alluvium interbedded with coralline limestone. Water in the sedimentary material is mostly brackish.

Ground water in the study area ranges from fresh to saline. 

Inland, chloride content is between 10 and 50 mg/1 (milligrams 

per liter). Near the shore, it ranges from less than 50 to more 

than 2,000 mg/1. This wide range is attributed largely to pumping, 

which causes mixing of fresh and salt water.

Six major ground-water reservoirs were identified, and their 

boundaries are shown in figure 14. They are in the upper parts of

EXPLANATION

FIGURE 14. Location and water levels of ground-water bodies in volcanic 

rock. Water-level contours are based on measurements made in wells 

during January 1963.
D24 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

the Koolau and Waianae Ranges, the Schofield Plateau, the 

Mokuleia area, the Waialua-Haleiwa area, and the Kawailoa area.

KOOLAU RANGE

The ground-water reservoir in the Koolau Range is in dikecompartmented lava flows of the Koolau Volcanic Series (fig. 14). 

It underlies the Koolau Range, and its west boundary is roughly 

parallel with and about 2 miles west of the crest. Dikes, which 

retard lateral movement of ground water within lava flows, 

cause the water table to stand about 1,000 feet above sea level 

near the crest.

Rainfall averages 491 mgd (table 5), and recharge to the lava 

reservoir may exceed 200 mgd (Dale, 1967). Water moves westward and northwestward from the intake area primarily the 

west flank of the Koolau Range to the Mokuleia, WaialuaHaleiwa, and Kawailoa areas and eventually to the sea by way 

of surface and subsurface springs.

As ground water maintains the flow of streams in the Koolau 

Range at altitudes above 1,000 feet, the chloride content of the 

stream water is probably similar to the chloride content of the 

ground water. Chloride content of water in streams west of the 

300-inch rainfall zone (fig. 6) ranges from 10 to 12 mg/1, and 

that in streams north of the 300-inch zone ranges from 16 to 

23 mg/1.

WAIANAE RANGE

Ground water is impounded by dense dike rock in permeable 

lava flows near the crest of the Waianae Range (fig. 14). Tunneling in the west side of the Waianae Range indicates that the 

water table near Kaala is above an altitude of 1,500 feet. About 

4 miles northeast, however, the water table is less than 30 feet 

above sea level. The ground-water body in the dike-compartmented lava is recharged by rainfall that averages about 60 mgd. 

Most of the recharged water probably reaches the sea as groundwater flow in the Mokuleia area, but some may move eastward 

into adjoining lava flows of the Koolau Range. The chloride 

content of ground water in the central part of the Waianae Range 

is from 16 to 31 mg/1.

Ground water in the northwest end of the Waianae Range is 

perched upon weathered ash beds, which are fairly extensive 

above an altitude of 200 feet. The quantity of this perched water
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D25

discharged by springs is small estimated by Stearns and Vaksvik 

(1935, p. 439) to be 70,000 gpd. Only a small quantity of the 

spring water, probably less than 10,000 gpd, is used. Chloride 

content ranges from 100 to 160 mg/1.

MOKULEIA AREA

A fresh-water reservoir occupies the lava under the lower 

north slope of the Waianae Range (fig. 14) from Waialua toward 

Kaena Point and borders that high-level water impounded in dikecompartmented lava flows. The east boundary of the fresh water 

is west of Waialua, and the boundary is probably formed by a 

nearly impermeable weathered surface of buried lava of the 

Waianae Volcanic Series or by overlying alluvium that impedes 

ground-water movement into overlapping lava of the Koolau 

Volcanic Series (fig. 12). Ground water along the coast near 

Mokuleia is partly confined by alluvium, which overlies the more 

permeable reservoir rock. Westward the alluvium is thin and 

has little effect on the movement of water, or it is missing.

The hydrostatic head of the fresh-water reservoir is highest in 

the southeastern part of the area and declines 1.5 to 2 feet per 

mile to the northwest. Water levels (fig. 14) suggest that ground 

water is entering the Mokuleia area from the west side of the 

Schofield Plateau. They also show that there is an 8-foot drop 

in head between the east and west ends of Dillingham Air Force 

Base and that head declines to less than 2 feet above sea level 

toward Kaena Point.

Ground water discharges directly into the ocean through the 

marine sedimentary material or from the deeper lava along the 

Mokuleia-Kaena Point shoreline. It originates from rainfall in 

the Waianae Range, from the Schofield Plateau area, and from 

downward-percolating irrigation water, most of which was originally pumped from rocks of the Koolau Volcanic Series. About 

half the irrigated canefields overlie the alluvium, in which ground 

water has a greater hydraulic head than in the underlying lava 

flows. Of an average of 28 mgd of irrigation water applied to the 

canefields, about 40 percent (Dale, 1967) recharges the underlying ground-water reservoir.

An average of 3 to 4 mgd of ground water is presently being 

withdrawn in the Mokuleia area, and Stearns and Vaksvik (1935, 

p. 375) estimated that pumpage in 1933 was 14 mgd. Reduced 

pumpage for irrigation and the sealing of leaking wells since 1945 

have resulted in a rise in ground-water level of about half a foot.
D26 CONTRIBUTIONS TO THE HYDROLOGY OP THE UNITED STATES

Aquifer testing in the Mokuleia area to determine transmissivity of the lava flows of the Waianae Volcanic Series gave abnormally high values, ranging from 15 to 25 mgd. Transmissivity 

results obtained in tests of the Koolau Volcanic Series in the 

Haleiwa and Kawailoa areas were even higher, ranging from 27 

to 63 mgd. The median was 40 mgd. If all rainfall in the area, 

about 89 mgd (table 4), became recharge and channeled through 

the aquifer at the gradient and within the existing boundaries, 

the transmissivity would have to be about 20 mgd.

Visher and Mink (1964, p. 44), in their work in the Koolau 

Volcanic Series of the Pearl Harbor area, were also unable to use 

individual pumping-test data, but they analyzed the pumpage 

". . . records for the local and regional centers of gravity of 

pumping." They obtained transmissivities ranging from 4.3 to 

4.6 mgd. Takasaki, Hirashima, and Lubke (1969) tested the same 

ground-water reservoir in the Punaluu area of windward Oahu 

and obtained a transmissivity of 4 mgd.

The average transmissivity of the Waianae Volcanic Series in 

the Mokuleia area can be estimated by using Darcy's law in the 

form Q = TIL (Ferris and others, 1962, p. 73). Let Q equal the 

14-mgd pumpage estimate given by Stearns and assume that it 

is total flow through the Mokuleia area under steady-state conditions; / is the hydraulic gradient, or 1.5 feet per mile (fig. 14) ; 

L is 3 miles, the cross-sectional area through which the water 

discharges; and the resulting T is 3 mgd. There are no indications 

that the 1933 pumpage represented the total discharge of the 

aquifer, or that steady state had been attained, so these figures 

can serve only to estimate a somewhat tenuous minimum flow 

through the Mokuleia area.

A thin body of fresh to brackish water, in which head averages 

1 to 2 feet above sea level, occupies permeable coralline limestone 

along the Mokuleia coast. The water has a chloride content of 

about 250 mg/1. Although this source of water is not being 

utilized, pumping tests of the reservoir indicate that limited supplies of shallow ground water are available for development.

SCHOFIELD PLATEAU

The Schofield Plateau lies between the Waianae and the Koolau 

Ranges and is the saddle that forms the south boundary of the 

project area. The plateau is underlain by a ground-water reservoir 

in lava of the Koolau Volcanic Series and probably of the Waianae 

Volcanic Series. Dikes or other unknown structural features form 

the reservoir boundaries. The reservoir has an area of about 15
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D27

square miles (fig. 14). The north and south limits are inferred, 

in part, from an electrical resistivity survey made by the Geological Survey in 1938. (See Swartz, 1939, fig. 4, and Swartz, in 

Stearns, 1940, p. 56-59.) The reservoir is recharged by subsurface 

leakage from dike-impounded water in the Koolau Range and by 

infiltration of rainfall and streamflow on the Schofield Plateau. 

All natural ground-water outflow is by subsurface percolation 

either northward into the adjoining Waialua-Haleiwa area or 

southward into the southern Oahu area (fig. 1).

The water table ranges in altitude from 187 to 300 feet and 

may decline in steps to the north, as it does to the south (fig. 14 

and Visher and Mink, 1964, fig. 11). Just south of Wheeler Air 

Force Base, the difference in water level is 100 feet between wells 

only 0.2 mile apart and is about 250-feet between wells 1.3 miles 

apart.

Large-scale ground-water development in the Schofield Plateau 

began in 1938, and as much as 8 mgd has been pumped for municipal, industrial, and air-conditioning uses. Chloride content of the 

water ranges from 14 to 37 mg/1.

WAIALUA-HALEIWA AREA

Recharge from rainfall in the Koolau Range maintains an extensive fresh-water lens in uncompartmented Koolau lava flows 

in the northeastern part of the study area (fig. 14). The lens 

extends along the coast from Waialua to Waialee and is bounded 

on the inland side by dike-impounded ground-water reservoirs in 

lava of the Koolau and the Waianae Volcanic Series. Near the 

coast the lens is divided into two segments, the Waialua-Haleiwa 

and the Kawailoa, by the thick alluvial fill and weathered bedrock 

in the valley of the Anahulu River (fig. 4).

Ground water in the Waialua-Haleiwa area moves generally 

seaward (fig. 14) at a gradient of about 1 foot per mile and is 

confined by alluvium as far as 2 miles inland (fig. 3). The alluvium and marine sediments thicken seaward and extend to more 

than 200 feet below sea level at the coast. They generally confine 

ground water less effectively than the material in the Mokuleia 

area because there is more coralline limestone which allows water 

to discharge from the underlying basalt to the ocean. Stearns 

(1966, p. 14) watched the sea recede at Haleiwa, during the 

tsunami of March 9, 1957, and saw fresh ground water rising 

several inches to a foot above the surface ordinarily inundated by 

sea water.
D28 CONTRIBUTIONS TO THE HYDROLOGY OP THE UNITED STATES

Recent pumping of four shallow wells tapping a coral bed that 

underlies part of the Waialua area shows that fresh water is 

moving seaward through the coral and that infiltration of applied 

irrigation water is substantial. Pumping of wells 318-1 (fig. 8) 

to 318-4 began in 1966. The wells were drilled to depths of 25 

to 44 feet below sea level from a surface altitude of about 15 feet; 

they are 6 feet in diameter and are spaced 200 feet apart on a 

north-south line perpendicular to the shoreline. Wells 318-1 and 

318-4 are at the mill and shore ends of the line, respectively, and 

about equal distance (1,200 ft) from each end.

The Waialua Sugar Co. seasonally pumps about 10 mgd from 

these wells for cooling the mill condensers. Although detailed 

pumpage data are not available, the chloride data for a 3-year 

period show chlorides increasing with pumpage to as much as 

13,000 mg/1 in 4 months and decreasing to near prepumping levels 

shortly after pumping stops. Such rapid freshening results from 

fresh-water displacement of saline water by the seaward flow of 

ground water, by infiltration of irrigation water, or by a combination of both.

Most ground water discharges into the ocean by percolation 

through the semiconfining material, but some of it may move 

northward into the Kawailoa area. From 2 to 4 mgd discharges 

in the coastal area as seepage into low-lying swamps, or as spring 

flow; a part of this discharge is pumped or is diverted for irrigating sugarcane and other farm crops. Springs on the south bank 

of the Anahula River at Haleiwa discharge about 3 mgd from 

lava flows.

An average of 30 to 40 mgd is pumped from wells tapping 

the Koolau Volcanic Series, in the Waialua-Haleiwa area, about 

half of which is applied to canefields in the Mokuleia area. All 

but 2 mgd of the other half is used to irrigate canefields overlying 

lava flows in the Waialua-Haleiwa area, where as much as 10 

mgd (Dale, 1967) of the applied water may infiltrate back into 

the ground-water reservoir. Additional recharge originates from 

irrigation water diverted from Koolau streams. Total recharge 

from irrigation water is estimated to be 15 to 20 mgd.

KAWAILOA AREA

A 6-foot difference in water level across Anahulu River distinguishes the Kawailoa ground-water reservoir from that of the 

Waialua-Haleiwa area (fig. 14). Water levels are highest near 

the river and decline northeastward toward Waimea at about 1.5
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D29

feet per mile. The high water levels south of the river indicate 

that some ground water probably moves northeastward through 

or under the alluvium-filled valley of the Anahulu River.

A lack of confining alluvial material in the Kawailoa area allows free movement of ground water to the ocean. Fresh-water 

springs have been reported offshore, and water discharges from 

lava near shore and through sedimentary material into a large 

coastal swamp in the southwestern part of the area.

Ground-water development is restricted to the narrow coastal 

plain, where as much as 8 mgd is pumped from wells. About 7 

mgd is used for sugarcane irrigation. A part of this water plus 

irrigation water diverted from streams infiltrates to the groundwater reservoir.

SALT-WATER INTRUSION

Further development of fresh-water supplies in north-central 

Oahu is limited, in part by the possibility of increasing salt-water 

intrusion. Intrusion has occurred along the coast, where withdrawals are from lenses of fairly fresh water (fig. 15). Those

EXPLANATION

Line of equal chloride concentration 

Interval, in milligrams per liter, is variable

Approximate boundaries of ground-water bodies

2 3 MILES 

J____I

CONTOUR INTERVAL, IN FEET, IS VARIABLE 

DATUM IS MEAN SEA LEVEL

N

it

FIGURE 15. Chloride content, August 1964, of water in basaltic aquifers, 

Mokuleia, Waialua-Haleiwa, and Kawailoa areas.
D30 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

lenses, floating on salt water, exist because of density differences 

between fresh and salt water and extend to a depth of about 40 

times the height of the fresh-water head above sea level. Toward 

the bottom of the lens is a transition zone of mixed fresh and 

salt water, which becomes increasingly saline with depth. The 

extent to which salt water intrudes the lens is related to changes 

in fresh-water head caused by variations in recharge, in tidal and 

barometric fluctuations, and in pumping. The chloride content of 

water in lenses along the northern Oahu shore is generally greater 

than 250 mg/1.

Coastal pumping induces intrusion in direct relation to its rate. 

Pumping is generally cyclical during the year. Pumping and 

chloride content of the pumped water reach a maximum during 

the summer and fall. Increase in chloride content, however, seems 

to be largely localized at pumping wells, suggesting that movement of the underlying sea water is more vertical than horizontal. 

The relation of pumping to chloride content is shown in figure 16. 

Waialua Sugar Co. pumps 2 and 2A (wells 322A-N, fig. 8) are

400

II

lio:

ll

FMAMJ JASONDJFMAMJ 

1951

Pump 2

"Pump 2A

Well 326

JA SOND J 

1952

FMAMJ J ASOND 

1953

J FMAM J J ASON D 

1954

FIGURE 16. Relation of monthly average discharge of Waialua Sugar Co. 

pumps 2 and 2 A (wells 322A-N) and the chloride content in water at 

pumps 2 and 2A and at well 326, Waialua.
WATER RESOURCES OP NORTH-CENTRAL OAHU, HAWAII D31

within 100 feet of each other, and each withdraws water from 

separate batteries of wells at respective rates of about 11 and 9 

mgd. Although the overall range in chloride content is large, water 

withdrawn by the pump of smaller capacity, 2A, is less saline 

than that withdrawn by pump 2. The range in chloride content of 

water from well 326, which taps the same ground-water reservoir 

but is usually not pumped, is considerably smaller.

The seaward edge of the fresh-water lens is higher in chloride 

content and thinner in the eastern half of the Mokuleia area, 

where it underlies sedimentary material at great depth. The 

increase in chloride content of ground water near Dillingham Air 

Force Base (fig. 15) coincides with an abrupt decrease in head 

from 17 to 9.5 feet (fig. 14). The high chloride content of water 

in the Mokuleia area probably results from changes in the rate of 

recharge (from rainfall and irrigation) and from tidal fluctuations.

In the Waialua-Haleiwa area, the chloride content of the lens is 

generally less than 100 mg/1, but it is higher at pumping sites. It 

is also higher where the lens is confined to greater depths seaward from the town of Waialua, for example, where chloride content increases to more than 1,000 mg/1.

The seaward edge of the lens in the Kawailoa area is brackish, 

and ground water with a chloride content of more than 250 mg/1 

extends a mile inland from the coast. As much as 14 mgd is 

pumped from a battery of wells (fig. 8, wells 334A-W) only half 

a mile from the ocean, where, during the past 40 years, chloride 

content has ranged from 200 to 1,000 mg/1.

ESTIMATE OF GROUND-WATER FLOW

To manage the water resources of an area, the location, quality, 

and quantity of the resource must be known. It is possible to 

measure rainfall and its variations in time and space, and to gage 

the flow of streams, but it is impossible to measure directly the 

ground-water component of the hydrologic system. Major aquifers 

of north-central Oahu are identified and the quality of their waters 

is discussed in this report, but the quantity of ground water available can only be estimated.

The measured discharge from wells and springs in north-central 

Oahu is about 50 mgd, or about 9 percent of the estimated rainfall, 

580 mgd. In the adjacent Pearl Harbor area of southern Oahu, 

measured ground-water discharge is 50 percent of rainfall (Dale, 

1967). Owing to similarity in rainfall pattern, geology, and infil-
D32 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

tration capacity of the rocks of these two areas, it is reasonable 

to expect that the rainfall-discharge relations are similar or comparable. If the above assumption is correct, ground-water discharge now measurable in north-central Oahu, 50 mgd, is about 

one-fifth the total discharge; the remainder must discharge to 

sea as submarine springs.

To obtain the best estimate of the amount of water constituting 

total discharge, the water regimen of north-central Oahu was 

evaluated by determining rainfall means by zones (fig. 6) and obtaining runoff and evapotranspiration estimates (tables 4 and 5) 

from curves showing their relation to rainfall. The remainder is 

identified as recharge to the aquifer, most of which is considered 

to discharge as underflow to the sea.

The water regimen of an area may be delineated by the equation P=Rs -\-Rg + ET + &S, where rainfall (P) is balanced against 

surface runoff (Rs), recharge (Rg ) or ground-water flow, evapotranspiration (ET), and changes in ground-water storage (AS). 

Because long-term average annual data were used to determine 

recharge for north-central Oahu, it is assumed that storage 

changes (A<S) are negligible. The validity of this assumption is 

supported by the long-term stability of water levels and the continuing flow of springs. The use of the water-distribution equation, 

as written, results in recharge being available only after the demands of runoff and evapotranspiration are satisfied.

Table 4 gives estimates of rainfall, runoff, evapotranspiration, 

and recharge, other than that from irrigation, by rainfall zones. 

It is based on isohyetal (fig. 6) and on empirical relations developed for other areas on Oahu and verified by the few data and 

observations available in the study area. The zones between the 

isohyets were planimetered to determine their area. Rainfall was 

calculated for each zone and is shown in millions of gollons per day. 

Runoff, evapotranspiration, and recharge are similarly shown but 

with an additional column that shows the percentage of each in 

relation to total zone rainfall. Although runoff from each zone 

may contribute to the recharge in the adjacent topographically 

lower zone, this contribution and applied irrigation water are 

ignored in the analysis, so that computed recharge is less than 

actual recharge.
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D33

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D34 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

1UU IIII[III

50

20

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2260,

22301;

2270 o °2

2128,

 Station 3300 ~~ 

Kamananui Stream 

at Maunawai 

1280

°2160

5 

2 

'2130

NOTE

Stream names and station locations 

shown in Hirashima (1970)

20 30 100 

RAINFALL, IN INCHES

200 300

FIGURE 17. Relation of runoff to rainfall. (Developed by G. T. Hirashima.)
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D35

RUNOFF

Hirashima (1970) considered the problem of runoff from an 

area above Pearl Harbor that is predominantly underlain by lava 

of the Koolau Volcanic Series. He used long-term average annual 

rainfall and runoff from seven gaged streams in the Pearl Harbor 

area to develop a logarithmic curve relating rainfall to runoff 

(fig. 17). Only Kamananui Stream of north-central Oahu could 

be used as a check against Hirashima's Pearl Harbor data. An 

average rainfall of 119 inches on the basin above station 3300 and 

an adjusted 30-year discharge of 20 inches plots within 8 percent of the curve. Runoff from the Pearl Harbor area (table 5) 

averages about 13 percent (47 mgd) of average annual rainfall 

(355 mgd).

Mink (1962b, p. 155), in a study of a basin in the Pearl Harbor 

drainage area, found that mean annual runoff was 20 to 30 percent of the mean annual rainfall. He stated, however, that runoff 

might vary, depending on distribution and amount of rainfall 

and whether cyclonic or orographic rainfall predominated.

The U.S. Army Corps of Engineers x reported runoff from the 

upper half of Kalihi Valley (Honolulu area) to have a normal 

monthly range of 18 to 23 percent of rainfall and the lower half 

to have a range of 23 to 30 percent. Mean annual rainfall in the 

two halves is 101 and 69 inches, respectively.

Hirashima's rainfall-runoff relation seems more applicable to 

north-central Oahu, being based on 30^-year adjusted discharge 

records for a 90-square mile area, than do the other studies. Mink's 

study area was 4.3 square miles the upper one-third of Kipapa 

Stream basin and only 3 years of data were used. The Corps of 

Engineers study area was 5.24 square miles, 20 months of data 

were used, and the geohydrologic environment was different than 

that in north-central Oahu in that the area was underlain in part 

by rocks other than those of the Koolau Volcanic Series.

About 75 percent of north-central Oahu is underlain by lava 

flows of the Koolau Volcanic Series (table 5 and fig. 3). Under the

1 Unpub. report, Hydrologic relations in Hawaii, Project ES-182, Project Bull. 1, 30 November 1964.
D36 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES 

TABLE 5. Average rainfall and runoff for major areas of the island of Oahu

Rainfall Runoff

Area

Pearl Harbor area ..........

North-central Oahu area

Koolau Volcanic Series of

north-central Oahu ......

Waianae Volcanic Series

of north-central Oahu..

Square

miles

90

152

111

41

Inches

per

year

83

80

93

46

Mgd

355

580

491

89

Inches

per

year

11

12

15

5

Mgd

47

90

80

10

Percent

of

rainfall

13

15

16

11

assumption that rainfall-runoff characteristics are similar to those 

of the Pearl Harbor area as reported by Hirashima and that no 

major geohydrologic dissimilarities are known runoff from the 

Koolau Volcanic Series is 80 mgd, or 16 percent of runoff. Estimates for the area of the Waianae Volcanic Series and for northcentral Oahu, also based on Hirashima's work, are shown in 

table 5.

EVAPOTRANSPIRATION

Evapotranspiration in north-central Oahu is estimated to be 

265 mgd, or 46 percent of available rainfall (table 4). This loss, 

which may be satisfied by rainfall or by rainfall and irrigation, 

represents evaporation from soil and free-water surfaces and 

transpiration by plants in the cultivated and in the watershed 

areas.

Experimentation with lysimeters in the areas of sugarcane 

cultivation has shown that transpiration by sugarcane is equal 

to pan evaporation (Campbell and others, 1959, p. 643). Lacking 

experimental data for other than sugarcane areas, Cox wrote in 

the same paper (p. 648) : "In the watershed areas, evapotranspiration is a loss subtractive from the rainfall to obtain net water 

resources. The factors controlling evapotranspiration are to some 

extent correlative with rainfall, and hence it is possible to discuss 

evapotranspiration empirically as a function of rainfall." This is 

the approach used in developing the evapotranspiration of the 

study area.

Takasaki, Hirashima, and Lubke (1969) tabulated data from 

18 climatologic stations in the Hawaiian Islands that recorded 

wind movement, pan evaporation, rainfall, and temperature. Owing to the small range in temperature throughout the islands, the
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D37

effect of temperature variation was found to be negligible in the 

rainfall-evapotranspiration relation, but wind movement was 

found to be a major factor.

In his figure 9, Takasaki shows a logarithmic plot giving a relation of rainfall to pan evaporation and identifies those stations 

where annual wind movement is more than and less than 20,000 

miles. Those stations where annual wind movement was less than 

20,000 miles plot on the line represented by the equation logic E= 

1.9387 0.0035 R, where E is median annual pan evaporation and 

R is median annual rainfall.

Records of three stations, in addition to records of other partialrecord stations in the study area, indicate that there are no stations and that there may be no sites in north-central Oahu where 

wind movement exceeds 20,000 miles per year. The rainfall-panevaporation relation developed by Takasaki, therefore, can be 

applied. Using his formula, the estimates of evapotranspiration 

given in table 4 were developed for each of the rainfall zones. 

Potential evapotranspiration exceeds available rainfall by about 

100 percent in coastal and inland low areas. Evapotranspiration 

is less than rainfall only where rainfall exceeds 50 inches annually.

RECHARGE

Recharge, as used in this water regimen, represents that part 

of rainfall available for infiltration to the ground-water reservoir 

after subtraction of runoff and evapotranspiration. Using the 

figures shown in table 4, the maximum estimate of recharge for 

north-central Oahu is 225 mgd, or 39 percent of total rainfall. 

The lack of even minor amounts of recharge in some of the low 

rainfall areas, although unrealistic, is the arithmetic result of 

evapotranspiration exceeding rainfall (fig. 6). Areas of no recharge are also those areas predominantly planted to sugarcane 

(fig. 2). Mink (1962a, p. 672), writing of the great quantity of 

water needed for effective irrigation of sugarcane in the Pearl 

Harbor area, stated: "On an annual basis, an average of 123 

inches is applied as irrigation, which when combined with average 

annual rainfall gives a total of 153 inches of water per year * * *" 

and that, "Hydrologic budgeting has indicated that between 50 

and 60 percent of this amount (153 in.) escapes evapotranspiration and returns to the ground water." The recharge estimates 

developed in this study do not include applied irrigation water.

Although 225 mgd for recharge is low (39 percent of rainfall) 

compared with recharge (50 percent) in the Pearl Harbor area,
D38 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

it permits determination of a reasonable estimate of the quantity 

of ground water available for development in north-central Oahu. 

Ground-water pumpage averages 42 mgd for irrigation, and 

stream-diverted water about 36 mgd. Of the 78 mgd applied, about 

31 mgd infiltrates the ground-water reservoir. Thus, present development leaves about 200 mgd of ground water discharging to 

sea. A major part of this water may be developed for future 

supplies.

SUMMARY

The geographic boundaries of the north-central Oahu study 

area are the Waianae Range on the west, the Waimea River and 

Koolau Range on the east, Wheeler Air Force Base on the south, 

and the Pacific Ocean on the north. The major water-bearing rocks 

are the lavas of the Koolau Volcanic Series, which are recharged 

by 491 mgd of rain falling on 111 square miles of the Koolau 

Range. The remaining 41 square miles of the study area receives

89 mgd as rainfall.

Runoff to the sea occurs only during prolonged periods of heavy 

rainfall, and the lower reaches of all streams are generally dry. 

Some streams gain water in their tidal reaches owing to discharge 

from springs. Runoff from north-central Oahu is estimated to be

90 mgd, or 15 percent of the 580 mgd total rainfall.

Evapotranspiration is high in the lowlands potentially approaching 200 percent of rainfall where rainfall is less than 40 

inches and of little significance in the wet upper parts of the 

Koolau and Waianae Ranges. It is estimated as 265 mgd, or 46 

percent of the total rainfall of north-central Oahu. Evapotranspiration is less than rainfall only where average rainfall is greater 

than 50 inches annually.

The amount of rain available to recharge the ground-water 

reservoirs of north-central Oahu is that remaining after runoff 

and evapotranspiration have been subtracted that is, about 225 

mgd, or 39 percent of average annual rainfall. Ground-water 

pumpage averages 48 mgd, and stream-diverted water 57 mgd. 

Of approximately 78 mgd applied for the irrigation of sugarcane, 

about 31 mgd infiltrates the ground-water reservoirs. Thus, present development leaves about 200 mgd of ground water available 

for future use. This water is discharging to the ocean in coastal 

seeps and springs and as submarine flows.

There are three main areas of discharge through Mokuleia on 

the west, through Waialua-Haleiwa in the central part, and
WATER RESOURCES OF NORTH-CENTRAL OAHU, HAWAII D39

through Kawailoa on the east. The shorelines, from Dillihgham 

Air Force Base on the west to the Waimea River on the east, is 

about 12 miles long and has an average discharge of about 17 mgd 

per mile. Owing to the high permeability of rocks of the Koolau 

compared with that of rocks of the Waianae Volcanic Series in 

the Mokuleia area, the Waialua-Haleiwa-Kawailoa areas are probably discharging more than the 17 mgd per mile average, and the 

Mokulei area somewhat less.

Future ground-water development should be inland of a line 

1% to 3 miles from the shoreline or, generally, above an altitude 

of 500 feet. Chloride content of the water inland of this line should 

be less than 50 mg/1. Water levels may range from 5 to as much 

as 300 feet above sea level, depending upon geographic location 

and the aquifer penetrated (basal water in the coastal area and 

basal and high-level water southward in the vicinity of the Schofield Plateau). The same area is in need of exploratory drilling 

owing to lack of available subsurface information for this 60 

square-mile area.

REFERENCES

Avias, Jacques, and others, 1956, Zone des Hawai, Chap. 2 in Oceanic proprement dite, Pt. 2 of Oceanie, v. 6 of Internat. Geol. Cong., Strat.

Comm., Lexique stratigraphique international: Paris, Centre Natl.

Recherche Sci., p. 71-143. 

Blumenstock, D. I., 1961, Climates of the states Hawaii: U.S. Weather

Bur., Climatology of the United States, No. 60-51, 20 p. 

Campbell, R. B., Chang, J., and Cox, D. C., 1959, Evapotranspiration of

surgarcane in Hawaii as measured by in-field lysimeters in relation to

climate: Internat. Soc. Sugarcane Technologistss Cong., 10th, Mauritius,

1959, Proc., p. 637-649. 

Dale, R. H., 1967, Land use and its effect on the basal water supply, Pearl

Harbor area, Oahu, Hawaii, 1931-65: U.S. Geol. Survey Hydrol. Inv.

Atlas HA-267, 2 sheets. 

Ferris, J. G., Knowles, D. B., Brown, R. H., and Stallman, R. W., 1962,

Theory of aquifer tests: U.S. Geol. Survey Water-Supply Paper 1536-E,

p. 69-174. 

Hirashima, G. T., 1970, Availability of streamflow for recharge of the basal

aquifer in the Pearl Harbor area, Hawaii: U.S. Geol. Survey WaterSupply Paper 1999-B (in press). 

Hoffard, S. H., and Vaudrey, W. C., 1966, An investigation of floods in

Hawaii through June 30, 1966: U.S. Geol. Survey Prog. Rept. No. 9,

Honolulu, issued annually, 169 p. 

Honolulu Board of Water Supply, 1963, Oahu water plan: City and County

of Honolulu, 68 p. 

Mink, John F., 1962a, Excessive irrigation and the soils and ground water

of Oahu, Hawaii: Science, v. 135, no. 3504, p. 672-673.
D40 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES'

 1962b, Rainfall and runoff in the leeward Koolau Mountains, Oahu,

Hawaii: Pacific Sci., v. 16, no. 2, p. 147-159. 

Stearns, H. T., 1939, Geologic map and guide of the island of Oahu, Hawaii:

Hawaii Div. Hydrography Bull. 2, 75 p., 6 pi.

 1940, Supplement to the geology and ground-water resources of the 

island of Oahu, Hawaii: Hawaii Div. Hydrography Bull. 5, 164 p.

 1966, Geology of the State of Hawaii: Palo Alto, Calif., Pacific Books, 

266 p.

.1967, Geology of the Hawaiian Islands, with supplement: Hawaii Div.

Hydrography Bull. 8, 112 p. 

Stearns, H. T., and Vaksvik, K. N., 1935, Geology and ground-water resources

of the island of Oahu, Hawaii: Hawaii Div. Hydrography Bull. 1, 479 p. 

 1938, Records of drilled wells on the island of Oahu, Hawaii: Hawaii

Div. Hydrography Bull. 4, 213 p. 

Swartz, J. H., 1939, Geophysical investigations in [the] Hawaiian Islands:

Am. Geophys. Union Trans., 20th Ann. Mtg. pt. 3, p. 292-298. 

Takasaki, K. J., Yamanaga, George, and Lubke, E. R., 1962. Preliminary

summary of findings in water-resources studies of windward Oahu,

Hawaii: Hawaii Div. Water and Land Devel. Circ. CIO, 15 p. 

Takasaki, K. J., Valenciano, Santos, and Ho, A. M., 1966, Preliminary report on the water resources of the Kahuku area, Oahu, Hawaii: Hawaii

Div. Water and Land Devel. Circ. C39, 33 p. 

Takasaki, K. J., Hirashima, G. T., and Lubke, E. R., 1969, Water resources

of windward Oahu, Hawaii: U.S. Geol. Survey Water-Supply Paper

1894, 119 p. 

Visher, F. N^., and Mink, J. F., 1964, Ground-water resources in southern

Oahu, Hawaii: U.S. Geol. Survey Water-Supply Paper 1778, 133 p. 

Zones, C. P., 1963, Preliminary report on the ground-water resources of the

Waianae area, Oahu, Hawaii: Hawaii Div. Water and Land Devel. Circ.

C16, 12 p.

U.S. GOVERNMENT PRINTING OFFICE: 1971 O 4O1 744