U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2006–5177

Prepared in Cooperation with the County of Maui Department of Water Supply

Numerical Simulation of the Hydrologic Effects of 

Redistributed and Additional Ground-Water Withdrawal, 

Island of Molokai, Hawaii

Cape

Halawa

Ilio Point 

Laau

Point

0.05 A

A 0.1

−0.01

−0.02

−0.050.2

0.01

0.02

Cape

Halawa

Ilio Point 

Laau

Point

A

−0.01

−0.02

−0.05

Cape

Halawa

Ilio Point 

Laau

Point 0.01

0.02

0.05

0.1

0.2

A
COVER: Redistributed ground-water withdrawals on the Island of Molokai 

will cause a redistribution of water levels and coastal discharge. Water levels 

increase near sites of reduced withdrawal (blue triangles), and decrease near 

sites of increased withdrawal (red triangles), as shown by the contours of 

water-level change (in feet). Similarly, coastal discharge increases near sites 

of reduced withdrawal (blue squares), and decreases near sites of increased 

withdrawal (brown squares), as shown by the colored boxes. Ground-water 

discharge to coastal fishponds may be affected by a redistribution of groundwater withdrawals.
Numerical Simulation of the Hydrologic 

Effects of Redistributed and Additional 

Ground-Water Withdrawal, Island of 

Molokai, Hawaii

By Delwyn S. Oki

Prepared in Cooperation with the County of Maui Department of Water Supply

Scientific Investigations Report 2006–5177

U.S. Department of the Interior

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

Dirk Kempthorne, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2006

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1–888–ASK–USGS

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment:

World Wide Web: http://www.usgs.gov/

Telephone: 1–888–ASK–USGS

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Oki, D.S., 2006, Numerical simulation of the hydrologic effects of redistributed and additional ground-water 

withdrawal, Island of Molokai, Hawaii: U.S. Geological Survey Scientific Investigations Report 2006–5177, 49 p.
iii

Contents

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

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

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

Setting .............................................................................................................................................................4

Climate....................................................................................................................................................4

Rainfall....................................................................................................................................................4

Evaporation............................................................................................................................................7

Geology............................................................................................................................................................8

West Molokai Volcano.........................................................................................................................8

East Molokai Volcano.........................................................................................................................10

Coastal Deposits .................................................................................................................................10

Hydraulic Conductivity of the Rocks................................................................................................10

Lava Flows...................................................................................................................................10

Dikes .........................................................................................................................................10

Weathering .................................................................................................................................10

Coastal Deposits ........................................................................................................................11

Regional Ground-Water-Flow System......................................................................................................11

Recharge..............................................................................................................................................11

Discharge to Streams.........................................................................................................................11

Water Levels........................................................................................................................................11

Freshwater Lens.........................................................................................................................14

Dike-Impounded Ground Water ..............................................................................................15

Depth to Saline Water........................................................................................................................15

Chloride Concentration......................................................................................................................15

Withdrawals.........................................................................................................................................18

Numerical Simulation of Additional Ground-Water Withdrawal .........................................................18

Model Description ..............................................................................................................................18

Model Application...............................................................................................................................18

Description of Model Scenarios .............................................................................................24

Model Results......................................................................................................................................24

Scenarios 1 Through 8—Redistribution of Withdrawals ....................................................25

Scenarios 9 Through 13—Additional Ground-Water Withdrawal.....................................38

Scenario 14—the DHHL Reservation .....................................................................................44

Scenario 15—Natural Conditions (Zero Withdrawals) .......................................................44

Model Limitations.........................................................................................................................................44

Summary........................................................................................................................................................47

References Cited..........................................................................................................................................47
iv

Figures

1. Island of Molokai, Hawaii, showing selected geographic features ....................................2

2. Aquifer systems designated by the Hawaii Commission on Water Resource

Management and sites for additional ground-water withdrawal proposed by the

County of Maui Department of Water Supply, Island of Molokai, Hawaii...........................3

3. Mean annual rainfall on the Island of Molokai, Hawaii .........................................................6

4. Annual rainfall at selected rain-gaging stations on the Island of Molokai, Hawaii,

for the period 1975–2004..............................................................................................................7

5. Generalized geologic map of the Island of Molokai, Hawaii.................................................9

6. Locations of selected wells on the Island of Molokai, Hawaii ...........................................12

7. Average measured water levels for period 1938–97, water levels from resistivity

measurements, and altitude of top of saline water body determined from timedomain electromagnetic survey, Island of Molokai, Hawaii ...............................................13

8. Schematic cross section of the ground-water-flow system on the Island of

Molokai, Hawaii ..........................................................................................................................14

9. Fluid-conductivity (A) and fluid-temperature (B) profiles in the Kualapuu deep

monitor well (0800–01) on the Island of Molokai, Hawaii.....................................................16

10. Chloride concentrations of water pumped from selected wells on the Island of

Molokai, Hawaii ..........................................................................................................................17

11. Reported ground-water withdrawal from selected wells on the Island of Molokai,

Hawaii...........................................................................................................................................19

12. Model mesh and hydraulic-conductivity zones used in the ground-water-flow

model for the Island of Molokai, Hawaii .................................................................................23

13. Simulated changes in water level and coastal discharge (relative to base-case

conditions) caused by decreasing withdrawal by 0.232 million gallons per day from

the existing Kualapuu well (0801–03), Island of Molokai, Hawaii.......................................26

14. Simulated changes in water level and coastal discharge (relative to base-case

conditions) caused by withdrawing 0.232 million gallons per day from proposed site

1 (Manawainui), Island of Molokai, Hawaii............................................................................27

15. Scenario 1 of ground-water-flow model for the Island of Molokai, Hawaii .....................28

16. Scenario 2 of ground-water-flow model for the Island of Molokai, Hawaii .....................30

17. Scenario 3 of ground-water-flow model for the Island of Molokai, Hawaii .....................31

18. Scenario 4 of ground-water-flow model for the Island of Molokai, Hawaii .....................32

19. Scenario 5 of ground-water-flow model for the Island of Molokai, Hawaii .....................33

20. Scenario 6 of ground-water-flow model for the Island of Molokai, Hawaii .....................34

21. Scenario 7 of ground-water-flow model for the Island of Molokai, Hawaii .....................35

22. Scenario 8 of ground-water-flow model for the Island of Molokai, Hawaii .....................36

23. Scenario 9 of ground-water-flow model for the Island of Molokai, Hawaii .....................39

24. Scenario 10 of ground-water-flow model for the Island of Molokai, Hawaii ...................40

25. Scenario 11 of ground-water-flow model for the Island of Molokai, Hawaii ...................41

26. Scenario 12 of ground-water-flow model for the Island of Molokai, Hawaii ...................42

27. Scenario 13 of ground-water-flow model for the Island of Molokai, Hawaii ...................43

28. Scenario 14 of ground-water-flow model for the Island of Molokai, Hawaii ...................45

29. Scenario 15 of ground-water-flow model for the Island of Molokai, Hawaii ...................46
v

Tables

1. Ground-water-use permits effective in 2005 on the Island of Molokai, Hawaii.................5

2. Proposed ground-water-withdrawal sites on the Island of Molokai, Hawaii ..................24

3. Summary of withdrawal scenarios simulated with the ground-water-flow model for

the Island of Molokai, Hawaii ...................................................................................................25

4. Summary of water-level changes simulated with the ground-water-flow model for

the Island of Molokai, Hawaii ...................................................................................................37

5. Summary of coastal-discharge changes simulated with the ground-water-flow

model for the Island of Molokai, Hawaii .................................................................................38
vi

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

square foot (ft2

) 0.09290 square meter (m2)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3

) 

million gallons (Mgal) 3,785 cubic meter (m3

)

cubic foot (ft3

) 0.02832 cubic meter (m3) 

Flow rate

gallon per day (gal/d) 0.003785 cubic meter per day (m3

/d)

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

/s)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

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 mean sea level.

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

Altitude, as used in this report, refers to distance above the vertical datum.

Fluid conductivity is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25°C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).
Abstract

Because of increased demand for water associated with 

a growing population, projected increases in demand over 

the next few decades, and rising salinity of the water pumped 

from some existing wells, the County of Maui Department of 

Water Supply (DWS) is currently (2006) considering drilling 

additional wells to replace or supplement existing wells on 

the Island of Molokai, Hawaii. Redistributed and additional 

ground-water withdrawals will affect ground-water levels, 

discharge of ground water to the nearshore environment, and, 

possibly, salinity of the water pumped from existing wells.

For this study, an existing numerical ground-water-flow 

model was used to estimate water-level and coastal-discharge 

changes, relative to 2005 base-case conditions, caused by 

withdrawals in the area between Kualapuu and Ualapue on 

Molokai. For most of the scenarios tested, total withdrawals 

were either equal to or 0.28 million gallons per day greater 

than those in the 2005 base case. Model results indicate that a 

redistribution of withdrawals causes a corresponding redistribution of water levels and coastal discharge. Water levels rose 

and coastal discharge increased near sites of reduced withdrawal, whereas water levels declined and coastal discharge 

decreased near sites of increased withdrawal. The magnitude 

and areal extent of hydrologic changes caused by a redistribution of withdrawals increased with larger changes in withdrawal rates. Simulated water-level changes were greatest at 

withdrawal sites and decreased outward with distance elsewhere. Simulated water-level declines at proposed withdrawal 

sites generally were less than 0.5 feet. The low-permeability 

dike complex of East Molokai Volcano impeded the spread of 

water-level changes to perennial streams in the northeastern 

part of the island, and discharge to these streams in the dike 

complex therefore was unaffected by the proposed withdrawals.

Simulated coastal-discharge changes generally were 

greatest immediately downgradient from sites of withdrawal 

change. Simulated coastal-discharge reductions generally were 

less than 30,000 gallons per day (and everywhere less than 

75,000 gallons per day) within model elements for scenarios 

that excluded the Hawaii Department of Hawaiian Home 

Lands reservation (2.905 million gallons per day). (Model 

elements cover discrete 1,640- by 1,640-foot-square areas.) 

Simulated coastal-discharge reductions generally represented 

less than 5 percent change relative to 2005 base-case conditions. Simulated discharge to some fishponds and springs 

increased in response to decreased withdrawal at upgradient 

sites, and simulated discharge to other fishponds and springs 

decreased in response to increased withdrawal. Simulated 

water-level declines associated with the Hawaii Department 

of Hawaiian Home Lands reservation were as much as 4 feet 

at three arbitrarily selected withdrawal sites, and simulated 

reductions in coastal discharge between Umipaa and Kamiloloa along the south coast exceeded 200,000 gallons per day 

from several model elements.

Introduction

The resident population of the Island of Molokai, 

Hawaii (fig. 1), has grown by more than 20 percent from 

1980 (population 6,049) to 2000 (population 7,404) (Hawaii 

Department of Business, Economic Development & Tourism, 

2006). Because of increased demand for water associated with 

the growing population, projected increases in demand over 

the next few decades, and rising salinity of the water pumped 

from some existing wells, the County of Maui Department of 

Water Supply (DWS) is currently (2006) considering drilling 

additional wells to replace or supplement existing wells on 

Molokai.

In response to concerns over the water resources of 

Molokai, the Hawaii Commission on Water Resource Management (CWRM) designated the entire island as a Ground Water 

Management Area in 1992. This action authorized the State 

to manage ground-water withdrawals on Molokai through a 

permitting process to protect the island’s water resources. The 

CWRM has divided the island into 16 management areas or 

aquifer systems, primarily defined on the basis of geologic 

conditions and topographic divides (Mink and Lau, 1992) 

(fig. 2). Ground-water withdrawals on the island currently 

Numerical Simulation of the Hydrologic Effects of 

Redistributed and Additional Ground-Water Withdrawal, 

Island of Molokai, Hawaii

By Delwyn S. Oki
South

Fk

North Fk

Kakaako

Gl

Kaunala

G

l

Ka

l

uapeelua

Gl

Manawainui

Gl

Kaunakakai

Gl

East

Fk

Kawela Gl

Punaula

G

l

Kamiloloa

Gl

W

a

w

a

i

a

G

l

M

a

na

l

o

Gl

Papohaku Gl

H

akina

Gl

O

n

o

p

a

lan

i

Gl Wa ai

kane

G

l

Waiahewahewa

Gl

West

Fk

Wa

Kahawaiiki Str H

W 

ailau

Str

Pelek

u

n

u

Str

Waioh

ooka

l

o

S

t

r

Waikolu

Str

Waialeia Str

Waihan

a

u

Str

Kawainui

Str

Pelekunu 

Bay

Moomomi

Kahiu Point 

KalaupapaPeninsula

Ilio Point 

Laau

Point

Kalaupapa

Kalae

Kualapuu 

Maunaloa

Kaunakakai Kamiloloa

Kamalo

Ualapue

Umipaa Coconut

Grove

Kawela Mapulehu

! !

!

!

!

!

!

!

!

00

2 4 MILES 

2 4 KILOMETERS 

157o05'

157o15'

156o55' 156o50'

157o10'

21o10'

157o

21o05'

EXPLANATION 

FISHPOND—Modified from Hawaii Office of Planning (2006)MOLOKAI IRRIGATION SYSTEM PIPELINEMOLOKAI IRRIGATION SYSTEM TUNNELFISHPOND LOCATION—Modified from Hawaii Office of Planning (2006)SPRING—Modified from Stearns and Macdonald (1947)ACTIVE (2006) U.S. GEOLOGICAL SURVEY SPRING-DISCHARGE-MEASUREMENT SITE

Base modified from U.S. Geological Survey digital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21o04'50" and 21o12'10", central meridian 

157o00'45". Relief from U.S. Geological Survey

digital elevation models, scale 1:250,000

Q

22o20o

158o 15

160o

Kauai

Niihau

Oahu

Molokai

Lanai

Kahoolawe

Hawaii

HAWAII 

LOCATION MAP

PACIFIC OCEAN

Q

Q

1,381 ft 

4,961 ft 

EAST MOLOKAI VOLCANO 

WEST MOLOKAI VOLCANO 

HOOLEHUA

PLAIN

Kualapuu 

Reservoir

Kalokoeli Pond 

Ooia Pond 

Kamahuehue Pond 

Keawanui Pond 

Puhaloa Pond 

Alii Pond 

Kaoaini Pond 

Kanoa Pond 

Q

Q

Figure 1. Island of Molokai, Hawaii, showing selected geographic features.
Figure 2. Aquifer systems designated by the Hawaii Commission on Water Resource Management and sites for additional ground-water withdrawa

Maui Department of Water Supply, Island of Molokai, Hawaii.

Ilio Point 

Laau

Point

00

Kalaupapa

Palaau 

Umipaa

Kaunakakai

Kawela 

Kamalo

Puk

Mapulehu

Ualapue

!

!

!

!

!

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

21°05'

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

Kualapuu 

KalaupapaPeninsula

26

WAIKOLU 

(5 Mgal/d) 

HAUPU

(2 Mgal/d) WAILAU 

(15 Mgal/d) 

H

(8 W(8 

UALAPUE

(8 Mgal/d) 

KAWELA 

(5 Mgal/d) 

KAMILOLOA

(3 Mgal/d) 

MANAWAINUI 

(2 Mgal/d) 

PUNAKOU

(2 Mgal/d) 

KALUAKOI

(2 Mgal/d) HOOLEHUA

(2 Mgal/d) 

KUALAPUU

(5 Mgal/d) 

KUALAPUU

(5 Mgal/d) 

KALAUPAPA 

(2 Mgal/d) 

KAHANUI

(3 Mgal/d) 

PELEKUNU

(9 Mgal/d) 

EXPLANATION 

AQUIFER-SYSTEM BOUNDARY, AND NAME OF AQUIFER SYSTEM—State  sustainable-yield estimate, in million gallons per day (Mgal/d), shown in parentheses.PROPOSED SITE FOR ADDITIONAL GROUND-WATER WITHDRAWAL AND SITE NUMBERARBITRARY GROUND-WATER-WITHDRAWAL SITE FOR  HAWAII DEPARTMENT OF HAWAIIAN HOME LANDS  RESERVATION AND SITE NUMBER

H

H

H

H

H

H

1

6 7 8

3

4

5

2

A

A

A A
are limited by sustainable-yield estimates for each of the 16 

aquifer systems. As of May 2005, the CWRM had issued 

water-use permits authorizing a total of 8.077 million gallons 

per day (Mgal/d) of ground-water withdrawals from wells and 

tunnels on the island (table 1). In addition, the Hawaii Department of Hawaiian Home Lands (DHHL) has a reservation for 

2.905 Mgal/d of ground water from the Kualapuu area (fig. 2; 

table 1).

Redistributed and additional ground-water withdrawals 

will affect ground-water levels and may cause the salinity of 

water pumped from existing wells to increase. Redistributed 

and additional ground-water withdrawals also will affect 

discharge of fresh and brackish water to the nearshore environment. Along the south coast, Native Hawaiians built dozens of 

fishponds in shallow coastal waters by constructing rock-wall 

enclosures extending from the shoreline (fig. 1). References to 

fishpond construction on Molokai date back to the 16th century, and the most recently constructed fishpond on the island 

was built about 1829 (Farber, 1997). Members of the community on Molokai have identified 31 fishponds that they would 

like to restore and maintain in a traditional manner for subsistence and small-business ventures (Farber, 1997). Discharge 

of fresh or brackish ground water to these fishponds may be a 

factor controlling productivity by providing nutrients for algae 

on which the fish feed (Farber, 1997). Stearns and Macdonald 

(1947, p. 56) suggested that fishponds along the south shore 

of Molokai indicate the presence of coastal springs, some 

of which discharge more than 0.5 Mgal/d. Thus, additional 

ground-water withdrawal may affect fishpond productivity.

In response to concerns over the possible effects of 

ground-water withdrawal on Molokai, the U.S. Geological Survey (USGS) undertook the present investigation, in 

cooperation with the DWS, to quantify the hydrologic effects 

of withdrawal from selected sites on ground-water levels and 

coastal discharge of ground water. An existing numerical 

ground-water-flow model (Oki, 1997) was used to estimate 

water-level declines and coastal-discharge reductions caused 

by redistributed and additional ground-water withdrawals in 

the area between Kualapuu and Ualapue on Molokai.

Purpose and Scope

The purpose of this report is to describe the results 

of model simulations that assess the hydrologic effects of 

redistributed or additional ground-water withdrawals relative 

to average or permitted 2005 withdrawal rates. No new data 

were collected as part of this study. An existing numerical 

ground-water-flow model (Oki, 1997) for Molokai was used 

to estimate the effects of different withdrawal scenarios on 

ground-water levels and coastal discharge.

Setting

The Island of Molokai, the fifth largest of the Hawaiian 

Islands, occupies an area of 260 mi2 (Juvik and Juvik, 1998) 

between latitude 21°00′–21°15′ N. and longitude 157°20′–

156°40′ W. (fig. 1). The island is composed mainly of two 

shield volcanoes (Stearns and Macdonald, 1947): the older 

West Molokai Volcano, which rises to an altitude of 1,381 ft, 

and the younger East Molokai Volcano, which rises to an altitude of 4,961 ft. The town of Kualapuu lies on the Hoolehua 

Plain in the central saddle area of the island.

Climate

The climate on Molokai is characterized by mild temperatures, cool and persistent trade winds, a rainy winter season 

from October through April, and a dry summer season from 

May through September (Blumenstock and Price, 1967; Sanderson, 1993). The climate is controlled primarily by topography and the position of the North Pacific anticyclone and 

other migratory weather systems relative to the island. During 

the dry season, the stability of the North Pacific anticyclone 

produces persistent northeasterly winds known locally as 

trade winds. Summer trade winds blow 80 to 95 percent of the 

time. During the rainy season, frequent passage of migratory 

high-pressure systems by the Hawaiian Islands results in less 

persistent trade winds. Winter trade winds blow 50 to 80 percent of the time. Southerly winds associated with low-pressure 

systems can bring heavy rains to the island. The dry western 

and southern coastal areas receive much of their rainfall as a 

result of these low-pressure systems.

Rainfall

The windward (northeast) side of Molokai is wettest, a 

pattern controlled by the orographic lifting of moisture-laden 

northeasterly trade winds along the windward slope of East 

Molokai Volcano. The moisture-laden air mass cools as it 

rises up the slopes of the volcano, resulting in condensation, 

cloud formation, and high rainfall near the topographic crest 

of the mountains. West Molokai Volcano is considerably drier 

because it does not extend upward into the cloud-forming zone 

at higher altitudes.

Rainfall on Molokai is characterized by maxima at 

high altitudes and steep spatial gradients (fig. 3). Maximum 

mean annual rainfall is more than 150 in. near the summit of 

East Molokai Volcano in the northeastern part of the island 

(Giambelluca and others, 1986). Over West Molokai Volcano, 

maximum mean annual rainfall is about 25 in., and along the 

coastal areas of the southern and western parts of the island, 

mean annual rainfall is less than 16 in. Annual rainfall at 

Molokai Airport (rain gage 524, fig. 3) ranged from about 11 

to 43 in. during the period 1975–2004 (fig. 4). In a wetter area 

to the east at Waikolu (rain gage 540, fig. 3), annual rainfall 

4 Numerical Simulation of the Hydrologic Effects of Redistributed and Additional Ground-Water Withdrawal, Molokai
Table 1. Ground-water-use permits effective in 2005 on the Island of Molokai, Hawaii.

[Data from the Hawaii Commission on Water Resource Management. Values in parentheses are 2005 mean annual withdrawal 

rates. Mgal/d, million gallons per day; --, no number available; MIS, Molokai Irrigation System] 

Well Name Water-use permit

(Mgal/d)

Aquifer 

system

0350–01 Keawanui salt 0.24 Ualapue

0350–05 Wescoatt 0.004 Ualapue

0350–07 Manawai No. 1 0.015 Ualapue

0350–09 Oceanic Institute salt 0.75 Ualapue

0352–09 Kamalo 0.01 Ualapue

0352–10 Kamalo-Curtis 0.012 Kawela

0352–11 Shige’s farm 0.004 Kawela

0352–12 Urauchi No. 1 0.001 Ualapue

0354–01 Meyer, Inc., No. 1 0.029 Kawela

0354–02 Meyer, Inc., No. 2 0.04 Kawela

0354–03 No. 3 0.017 Kawela

0354–04 Meyer, Inc., No. 4 0.005 Kawela

0354–07 Bostwick No. 1 0.045 Kawela

0447–02 Pukoo Farm 0.003 Ualapue

0448–01 Mapulehu Shaft No. 1 0.003 Ualapue

0448–03 Mapulehu Shaft 0.007 Ualapue

0449–01 Ualapue Shaft 0.185 (0.234) Ualapue

0449–06 Kaluaaha-Shephard 0.008 Ualapue

0456–04, 0457–04 Breadfruit and AG No. 1 0.285 Kawela

0456–06, 0456–08, 0456–09 Kawela Plantation DW1–DW3 0.285 Kawela

0456–16 Kawela-Iaea No. 3 0.017 Kawela

0456–17 Johnson 0.016 Kawela

0457–01 Kawela Shaft 0.33 (0.348) Kawela

0501–04 Kupa Shaft 0.056 Kamiloloa

0501–06 Home Pumehana 0.005 Kamiloloa

0501–07 Kaunakakai Park 0.075 Kamiloloa

0546–02 Puelelu 0.202 Waialua

0549–01 Mapulehu Tunnel 0.01 Ualapue

0601–01 Oloolo Kaunakakai 0.075 Kamiloloa

0602–03 Kalaiakamanu 0.005 Manawainui

0603–01 Umipaa 0.046 Manawainui

0605–01, 0605–02 ORCA Shaft Nos. 1 and 2 0.6 Manawainui

0605–03 ORCA No. 3 0.04 Manawainui

0705–05 Naiwa 0.012 Manawainui

0706–02 South Hoolehua 0.864 Manawainui

0706–03 Palaau salt 0.001 Manawainui

0759–01 Waiola No. 1 1 0.656 Kamiloloa

0801–01, 0801–02 Kualapuu Nos. 1 and 2 0.367 Kualapuu

0801–03 Kualapuu mauka 0.516 (0.605) Kualapuu

0844–01 Puu O Hoku No. 1 10.235 Waialua

0855–01, 0855–02, 0855–03 Waikolu Tunnel 22–24 0.853 Waikolu

0901–01 No. 17 1.018 Kualapuu

1058–01 Waihanau No. 239 0.094 Kahanui

1059–01 Waikalae Tunnel 0.036 Kualapuu

–– DHHL reservation 2.905 Kualapuu

MIS Tunnel Molokai Irrigation System Tunnel 21.822 Waikolu

1

Not simulated.

2

1992–96 average withdrawal (Oki, 1997), equally distributed to two model nodes.

Setting 5
Figure 3. Mean annual rainfall on the Island of Molokai, Hawaii (modified from Giambelluca and others, 1986).

Ilio Point 

Laau

Point

00

Kalaupapa

Palaau 

Umipaa

Kaunakakai

Kawela 

Kamalo

Puk

Mapulehu

Ualapue

!

!

!

!

!

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

21°05'

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

Kualapuu 

KalaupapaPeninsula

EXPLANATION 

LINE OF EQUAL MEAN ANNUAL RAINFALL—Interval,  in inches, is variable. Number in parentheses is rainfall, in  millimetersRAIN GAGE AND STATE KEY NUMBER

534

536

524

540

563

536

2 2

2

2

2

2

16

(400)

24

(600)

16

(400)

16

(400)

24 (600) 39 (1000)

32 (800)

160

(4000)

120 (3000) 79 (2000)

79

(2000)
ranged from about 46 to 185 in. during the same period (fig. 

4). In comparison, mean annual rainfall over the open ocean 

is estimated at 22 to 28 in. (Dorman and Bourke, 1979; Elliot 

and Reed, 1984).

Evaporation

Published pan-evaporation records for Molokai are available at only three sites, two in the Hoolehua Plain and one 

near the town of Maunaloa in the western part of the island. 

Mean annual pan evaporation at the three sites ranges from 81 

in. at Maunaloa to 118 in. near the Hoolehua Plain (Ekern and 

Chang, 1985). The high pan-evaporation rate on the dry, windy 

uplands of the central part of the island is attributed to extreme 

positive advection of heat from the dry surrounding areas 

(Ekern and Chang, 1985). Over the open ocean, the computed 

evaporation rate is about 65 in/yr (Seckel, 1962).

0

10

20

30

40

50

0

10

20

30

40

50

0

50

100

150

200

0

50

100

1975 1980 1985 1990

YEAR

1995 2000 2005

ANNUAL RAINFALL, IN INCHES 

Molokai Airport (State key 524) 

Kaunakakai (State key 536) 

Waikolu (State key 540) 

Kalaupapa (State key 563) 

Mean annual rainfall 

Figure 4. Annual rainfall at selected rain-gaging stations on the Island of Molokai, Hawaii, for the period 1975–2004. 

Mean annual rainfall values are for 1975–2004 and do not include missing or incomplete years (indicated as zero 

values). Data from National Climatic Data Center (2006).

Geology 7
Geology

The evolution of Hawaiian volcanoes generally progresses through four main eruptive stages: preshield, shield, 

postshield, and rejuvenated (Langenheim and Clague, 1987), 

although not all Hawaiian volcanoes have a postshield or 

rejuvenated stage. The preshield stage is the earliest, submarine phase of volcanic activity. Lava from this stage consists 

predominantly of alkalic basalt (basalt that is low in silica 

and rich in sodium and potassium). Lava from the principal, 

or shield, stage of volcano building consists of fluid tholeiitic 

basalt (silica saturated) that characteristically forms thin flows. 

This type of basalt forms during submarine and subaerial eruptions. A large central caldera can form during the shield stage 

and might later be partly or completely filled during subsequent eruptions. Typically, thousands of lava flows originate 

from the central caldera and from two or three rift zones that 

radiate out from the central part of the volcano. Intrusive 

dikes formed by rising magma penetrate the rift zones and 

caldera area. The shield stage is the most voluminous phase 

of eruptive activity, during which more than 95 percent of the 

volcano is formed. The postshield stage is marked by a change 

in lava chemistry and characteristics. Postshield-stage lava 

includes alkalic basalt and more viscous hawaiite, ankaramite, 

mugearite, and trachyte. Lava from this stage may erupt from 

sites outside the rift zones formed during the shield stage and 

form a veneer atop the shield-stage basalt. After a long period 

of quiescence, lava might issue from isolated vents on the 

volcano during the rejuvenated stage (also referred to as the 

posterosional stage).

Volcanic rocks of Hawaii can be divided into three main 

groups on the basis of their mode of emplacement: extrusive lava flows; intrusive dikes, sills, stocks, and plugs; and 

pyroclastic deposits. In general, lava flows that erupt from rift 

zones are less than 10 ft thick and consist of either pahoehoe, 

which is characterized by smooth or ropy surfaces, or aa, 

which contains a massive central core sandwiched between 

rubbly clinker layers (Wentworth and Macdonald, 1953). Aa 

flows are typically more abundant at greater distances from 

eruptive sources (Lockwood and Lipman, 1987).

Dikes are thin, near-vertical sheets of massive rock that 

intrude existing rocks, such as lava flows. Dikes are commonly 

exposed by erosion within the central and marginal parts of 

rift zones of older volcanoes (see Takasaki and Mink, 1985), 

including West and East Molokai Volcanoes.

In the central part of a rift zone, dikes can number as 

many as 1,000 per mile of horizontal distance and compose 

10 percent or more of the total rock volume (Takasaki and 

Mink, 1985). The number of dikes decreases toward the outer 

edges of a rift zone within the marginal dike zone, where dikes 

generally compose less than 5 percent of the total rock volume 

(Takasaki and Mink, 1985). Wentworth and Macdonald (1953) 

estimated that 200 dikes are needed to build 1,000 ft of a 

shield volcano.

Takasaki and Mink (1985, p. 5) define a dike complex as 

the “aggregates of dikes and the rocks they intrude...” By this 

definition, the marginal dike zone should be considered part 

of the dike complex. However, in their earlier description of a 

dike complex, Stearns and Vaksvik (1935, p. 97) recognized 

that dikes do occur outside the dike complex. Thus, for the 

purposes of this report, the dike complex is considered as the 

central part of the rift zone, where dikes compose 10 percent 

or more of the total rock volume, and the marginal dike zone is 

adjacent to the dike complex.

Pyroclastic rocks are formed by explosive volcanic 

activity and deposited by transport processes related to this 

activity. Pyroclastic rocks, such as ash, cinder, and spatter, can 

be deposited during all of the subaerial stages of eruption and 

probably form less than 1 percent of the total mass of a Hawaiian volcano (Wentworth and Macdonald, 1953). Cinder cones 

likely represent the surface expression of an intrusive body 

(dike) and may occur outside the central part of the rift zone.

The overall geology of Molokai has been described by 

numerous investigators (for example, Lindgren, 1903; Stearns 

and Macdonald, 1947; Beeson, 1976; Macdonald and others, 1983; Stearns, 1985). Langenheim and Clague (1987) 

described and renamed the stratigraphic framework of volcanic rocks on Molokai.

The Island of Molokai is formed primarily by shield- and 

postshield-stage volcanic rocks of the West and East Molokai 

Volcanoes, and secondarily by rejuvenated-stage volcanic 

rocks on the Kalaupapa Peninsula (Langenheim and Clague, 

1987). Intrusive volcanic rocks in the form of dikes associated 

with rift zones and volcanic vents occur on both West and East 

Molokai Volcanoes. Coastal deposits consisting of sedimentary material and limestone reefs occur along the south coast.

West Molokai Volcano

The primary rift zones of West Molokai Volcano trend 

approximately northwest and southwest (fig. 5) in the direction of broad ridges that extend from near the summit of the 

volcano. A positive gravity anomaly that extends from near 

the summit region through Laau Point at the southwest tip of 

the island (Moore and Krivoy, 1965) suggests the presence 

of dense intrusive dikes associated with the southwestern rift 

zone. A few southeast-trending dikes exposed near the south 

coast may be evidence of a third rift zone associated with West 

Molokai Volcano. No surface evidence of a summit caldera 

has been observed on West Molokai Volcano (Beeson, 1976; 

Langenheim and Clague, 1987). Numerous fault scarps, 100 

to 500 ft high, are exposed on the northeastern part of the 

volcano (Stearns and Macdonald, 1947). The exposed rocks of 

West Molokai are shield-stage tholeiitic basalt and postshieldstage hawaiite and alkalic basalt. Collectively, the volcanic 

rocks of West Molokai Volcano are known as the West Molokai Volcanics (Langenheim and Clague, 1987).

8 Numerical Simulation of the Hydrologic Effects of Redistributed and Additional Ground-Water Withdrawal, Molokai
Figure 5. Generalized geologic map of the Island of Molokai, Hawaii (modified from Stearns and Macdonald, 1947, and Langenheim and Clague, 1987

EXPLANATION 

SEDIMENTARY DEPOSITS (Holocene and Pleistocene)EAST MOLOKAI VOLCANO Kalaupapa Volcanics (Pleistocene) East Molokai Volcanics (Pleistocene and Pliocene) Upp er member Lower memberWEST MOLOKAI VOLCANO West Molokai Volcanics (Pleistocene and Pliocene)

CONTACTCALDERA BOUNDARYAXIS OF RIFT ZONE—ApproSEA-LEVEL LOCATION OF  MOLOKAI CONFINING UNVOLCANIC VENT DIKE

Ilio Point 

Laau

Point

00

Kalaupapa

Palaau 

Umipaa

Kaunakakai

Kawela 

Kamalo

Puk

Mapulehu

Ualapue

b

!

!

!

!

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

21°05'

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

Kualapuu 

KalaupapaPeninsula
East Molokai Volcano

The primary rift zones of East Molokai Volcano trend 

northwest and east from a central caldera complex (fig. 5). 

Macdonald (1956) suggested a possible southern rift zone 

emanating from the caldera. Furthermore, Malahoff and 

Woollard (1966) interpreted results from a magnetic survey as 

indicating a possible southwestern rift zone emanating from 

the caldera complex. The northwestern and eastern rift zones 

are marked by numerous nearly vertical to vertical intrusive 

dikes (Stearns and Macdonald, 1947). The caldera complex 

of East Molokai Volcano is exposed in Pelekunu and Wailau 

stream valleys (fig. 5), and consists of stocks, plugs, crater 

fills, ponded lavas, and talus and fault breccias cut by dike 

swarms (Stearns and Macdonald, 1947).

Stearns and Macdonald (1947) mapped numerous vent 

features, including cinder and spatter cones, along the west 

and south flanks of East Molokai Volcano (fig. 5). Many of 

these features do not appear to lie along the trends of the two 

primary rift zones of the volcano, possibly indicating the presence of (1) a marginal dike zone or (2) more than two primary 

rift zones.

The exposed rocks of East Molokai Volcano are named 

the East Molokai Volcanics and the Kalaupapa Volcanics 

(Langenheim and Clague, 1987). The East Molokai Volcanics is divided into two informal members: a lower member 

consisting of shield-stage tholeiitic, olivine-tholeiitic, and 

picritic-tholeiitic basalts and postshield-stage alkalic basalt; 

and an upper member consisting of postshield-stage mugearite 

and lesser amounts of hawaiite and trachyte (Langenheim 

and Clague, 1987). The upper member forms a relatively 

thin (approx. 50–500 ft thick) veneer over the lower member (Stearns and Macdonald, 1947); the upper member may 

obscure vent features associated with the lower member. The 

Kalaupapa Volcanics includes the rejuvenated-stage alkalic 

basalt and basanite that form Kalaupapa Peninsula (Clague 

and others, 1982; Langenheim and Clague, 1987).

Estimated ages of the rocks of West and East Molokai 

Volcanoes (McDougall, 1964; Naughton and others, 1980; 

Langenheim and Clague, 1987) indicate that the volcanoes 

may have formed contemporaneously. Stearns and Macdonald 

(1947) noted, however, that an erosional unconformity, which 

dips about 10° E., is exposed at an altitude of 250 ft in the east 

bank of Waiahewahewa Gulch (fig. 1). At this site, East and 

West Molokai Volcanics are separated by 3 ft of soil and 6 ft 

of spheroidally weathered basalt, with the West Molokai Volcanics at the bottom of the sequence. This sequence indicates 

that the West Molokai Volcanics is older than the East Molokai Volcanics at the site of the exposed unconformity.

Coastal Deposits

Along the southern part of the island, a coral reef extends 

from the coast to about 1 mi offshore, and limestone also has 

been described in a geologic log from a well near the south 

coast (Lindgren, 1903). In addition, along the south shore 

of East Molokai Volcano and the Hoolehua Plain, an apron 

of alluvium has formed by deposition of eroded soil. Off 

the north coast of Molokai, a thin veneer of recent sediment 

derived from wave erosion covers the insular shelf (Mathewson, 1970).

Hydraulic Conductivity of the Rocks

Hydraulic conductivity is a quantitative measure of the 

capacity of a rock to transmit water and can be described 

qualitatively by permeability–the ease of fluid movement 

through a porous rock (see Domenico and Schwartz, 1990). 

The permeability of volcanic rocks varies with their mode of 

emplacement.

Lava Flows

In a layered sequence of subaerial, shield-stage lava flows 

of a volcano, where dike intrusions are absent, the overall 

permeability is high (Stearns and Macdonald, 1947). The main 

features of lava flows contributing to the high permeability are 

(1) clinker zones associated with aa flows, (2) voids along the 

contacts between flows, (3) cooling joints normal to flow surfaces, and (4) lava tubes associated with pahoehoe flows. On 

the basis of a numerical-model analysis, Oki (1997) estimated 

the horizontal hydraulic conductivity of the dike-free, shieldstage lava flows of Molokai at 1,000 ft/d.

Dikes

Although most dikes are less than 10 ft thick, they can 

extend vertically and laterally for thousands of feet and are 

hydrologically important because of their low permeability. Within a dike complex, dikes intersect at various angles 

and compartmentalize the more permeable intruded rock, 

impounding ground water to high altitudes. Because dikes 

lower overall rock porosity and permeability, the average 

hydraulic conductivity of a dike complex decreases as the 

number of dike intrusions increases. Although the geometry 

and local-scale hydrologic effects of the dikes that fed the 

scattered vents of East Molokai Volcano near Kualapuu are 

unknown, these dikes intrude the aquifer and probably lower 

the overall permeability of the aquifer.

On the basis of a numerical-model analysis, Oki (1997) 

esti­mated the overall hydraulic conductivity of the dike complexes of West and East Molokai Volcanoes at 2 and 0.02 ft/d, 

respectively, and the horizontal hydraulic conductivity of the 

marginal dike zone near Kualapuu at 100 ft/d.

Weathering

Weathering generally reduces the permeability of volcanic rocks. The zone of weathered West Molokai Volcanics 

10 Numerical Simulation of the Hydrologic Effects of Redistributed and Additional Ground-Water Withdrawal, Molokai
and soil beneath the contact of the West and East Molokai 

Volcanics likely impedes ground-water flow between East and 

West Molokai Volcanoes. In this report, this weathered zone 

is referred to as the West Molokai confining unit. No data are 

available to determine whether this unit is truly an effective 

barrier to ground-water flow; however, on the basis of information from Oahu (Oki, 1998) on weathered volcanic rocks 

and a similar geohydrologic barrier, Oki (1997) estimated the 

hydraulic conductivity of the West Molokai confining unit at 

1 ft/d.

Coastal Deposits

Coastal deposits and underlying weathered volcanic rocks 

impede the seaward discharge of freshwater near the southern 

part of the island. The permeability of the interbedded coastal 

deposits may vary widely, from low-permeability compacted 

alluvium to cavernous limestone deposits. Oki (1997) estimated the overall vertical hydraulic conductivity of the coastal 

deposits in the southern part of the island at 0.5–5 ft/d.

Regional Ground-Water-Flow System

Precipitation is the source of all freshwater on Molokai. The precipitation either (1) runs off, (2) evaporates or is 

transpired by vegetation, or (3) recharges the ground-water 

system. Water that recharges the ground-water system flows 

from zones of higher to lower hydraulic head, as measured by 

water level. Water levels are highest in the mountainous interior parts of the island, particularly in the northeast, and lowest 

near the coast. Thus, ground water flows from the mountainous interior areas to coastal discharge areas. Ground water 

originating from the eastern and western parts of the island 

also flows toward the central Hoolehua Plain, from where it 

flows to either the north or south coast.

Ground water that is not withdrawn from wells and tunnels discharges naturally from the aquifer at onshore springs 

and seeps in deeply incised valleys and at subaerial and submarine coastal springs and seeps. In the northeastern part of 

the island, springs form where stream erosion has cut through 

dike compartments below the level of the water table. Groundwater discharge at these springs contributes to the base flow of 

streams.

Ground water on Molokai is unconfined in inland areas. 

Along the south coast, ground water may be confined by 

sedimentary deposits that impede the seaward discharge of 

fresh ground water. Fresh ground water on the island occurs 

in two main forms: (1) as a lens-shaped body of freshwater, called a freshwater lens, floating on denser, underlying 

saltwater within permeable dike-free lava flows; and (2) as 

dike-impounded water ten to hundreds of feet above sea level. 

Stearns and Macdonald (1947) also suggested that perched 

water exists on Molokai.

Recharge

Ground water is recharged by direct infiltration of rainfall 

over much of the island. Over West Molokai Volcano and the 

Hoolehua Plain, however, ground-water-recharge rates are low 

because of low rainfall and high evaporation rates. The area of 

greatest recharge is near the topographic peak of East Molokai 

Volcano, where rainfall is greatest.

Ground-water recharge on Molokai was estimated at 144 

Mgal/d from an annual water budget (Hawaii Commission on 

Water Resource Management, 1990). More recently, Shade 

(1997) estimated ground-water recharge at 188.6 Mgal/d from 

a monthly water budget for natural-vegetation conditions, 

which represents an average of about 15 in/yr over the island. 

However, the ground-water recharge estimated by Shade varies areally from a minimum of near 0 in/yr in the western part 

to a maximum of about 100 in/yr in the northeastern part of 

the island.

Discharge to Streams

Streams on Molokai have steeper gradients in the mountainous, high-rainfall areas and flatter gradients near the coast. 

Streams in the windward, northeastern valleys are perennial 

throughout most of their lengths because they receive groundwater discharge from the dike-impounded ground-water body. 

In contrast, no perennial streams exist in the western part of 

the island or the central Hoolehua Plain. Most of the streams 

that drain to the south coast of East Molokai Volcano are 

perennial only in their upper reaches where rainfall is persistent or where water drains from marshes or springs. These 

streams generally are perennial only where they flow over 

lavas of the upper member of the East Molokai Volcanics. 

Where streams flow over more permeable lavas of the lower 

member, surface water is more readily lost to infiltration 

(Stearns and Macdonald, 1947, p. 47).

Water Levels

Measured water levels are available primarily in wells 

along the south coast and in the central plain (figs. 6, 7). In the 

vicinity of Kualapuu, water levels are about 8 to 12 ft above 

sea level; along the south shore, water levels are 1 to 3 ft above 

sea level between Umipaa and Kawela and 4 to 5 ft above sea 

level between Kamalo and Mapulehu.

Within the northwestern rift zone of East Molokai 

Volcano near Waikolu Stream, water levels in wells 0855–01, 

0855–02, and 0855–03 (figs. 6 and 7) were about 900 ft above 

sea level in 1961. At the northern margin of the dike complex, 

near Kalaupapa Peninsula, the water level in well 1058–01 

was reported to be 9 ft above sea level, which probably represents an upper limit for the water-table altitude in the Kalaupapa Volcanics. Results from an electrical-resistivity survey 

indicated that the freshwater zone in the Kalaupapa Volcanics 

is thin (Takasaki, 1986). In the West Molokai Volcanics, the 

Regional Ground-Water-Flow System 11
Figure 6. Locations of selected wells on the Island of Molokai, Hawaii.

Ilio Point

Laau

Point

00

Kalaupapa

Palaau

Umipaa

Kaunakakai

Kawela

Kamalo

Puk

Mapulehu

Ualapue

!

!

!

!

!

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

21°05'

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

Kualapuu

KalaupapaPeninsula

H

H

H

H

H H H H

H

H

H

H

H

H

H

H

H

HH

H

H

H H

H

H H

H

H

H

H H H H

H

H

H H

H

H

0902−01

0352−01

0352−100352−090352−05

0352−11

0352−12

0350−01

0350−09

0354−04

0354−020354−01

0448−03

0448−020448−010549−01

05

0447−02 0449−06 0449−01

0350−050350−07

0457−01

0456−060456−080456−09

0457−04

0457−020458−020458−03

0559−01

0600−01

0601−02

0601−010501−030602−03 0603−01

0705−05

0603−070604−03 0700−01

0705−04

0605−020605−010605−03

0706−02

0807−01

0508−01

0509−01

0510−01 0511−01

0759−01

0800−01

0801−01, −02

0801−03

0801−03

0855−01

Molokai Irrigation System Tunnel

0855−02

0855−03 0901−01

0902−01

0905−01

0915−01

0514−01

1058−01

1059−01 1011−01

1014−01

1114−02

1114−01

0356−010456−170456−010456−160456−040456−020456−03

0458−010459−050459−040459−020459−030459−01

0500−010501−060501−040500−03

0501−050501−07

0354−07

0354−03

H

H H

H

H

H

H

H

H

H H

HH

HHH

H

H

H

H

H HH

HH

H

HH

H

H HH

H

H

H

H

HH HH

HHH H

H

H

H

H H

H

H

H

HH

WELL WITH 2005 WATER-USE PERMIT AND NUMBERWELL WITH NO WATER-USE PERMIT AND NUMBER

EXPLANATION
Figure 7. Average measured water levels for period 1938–97, water levels from resistivity measurements, and altitude of top of saline water body de

electromagnetic survey, Island of Molokai, Hawaii.

Ilio Point

Laau

Point

00

Kalaupapa

Palaau

Umipaa

Kaunakakai

Kawela

Kamalo

Puk

Mapulehu

Ualapue

!

!

!

!

!

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

21°05'

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

Kualapuu

KalaupapaPeninsula

-200

-400 -600 -800 -1,000

-1,200

-200

EXPLANATION

LINE OF EQUAL WATER LEVEL AS DETERMINED BY RESISTIVITY MEASUREMENTS (MacCarthy, 1941)— Interval, 1 foot. Datum is mean sea level. Dashed where inferredLINE OF EQUAL ALTITUDE OF TOP OF SALINE WATER BODY AS DETERMINED  BY TIME-DOMAIN ELECTROMAGNETIC SURVEY (HAWAII  COMMISSION ON WATER RESOURCE MANAGEMENT, 1997)— Interval, 200 feet. Datum is mean sea level.APPROXIMATE DIRECTION OF GROUND-WATER FLOWWELL AND AVERAGE MEASURED WATER LEVEL, IN FEET ABOVE MEAN SEA LEVEL

4

9

10

11

12

13

8

7

6 7 6

2

1

1

5

5

5

4 3

2

4

4

3

4.63

4.97

4.28

4.20

1.81.832.5

1.031.771.96

1.22

1.251.171.19

1.63

1.141.101.131.17

1

2.34

2.502.661.272.45

2.46

6.22

8.5

5.21

12.24

11.67 5.69

3

5.65 6.7

5.7

0.6

7.3

989

867

947

9

2.46

1.391.72.00

9.887.89.15

H

H

H

H

H

H

H

H

H

H

H

H

H H

H

H

H

H

H

H

H

H

H

H

H

H

H H

H

H

HH

H

H

H

H

H

H

H

H

H

H

H H

H H

H

H

0800-01

H
reported the water level in well 1011–01 was 5.65 ft above sea 

level in 1946 (Stearns and Macdonald, 1947, p. 65).

A detailed contour map of water levels for the entire 

island cannot be drawn from existing well data. MacCarthy 

(1941) used electrical-resistivity measurements to determine 

the depth to saltwater, then applied the Ghyben-Herzberg 

relation (see subsection below entitled “Freshwater Lens”) to 

estimate the altitude of the water table in the western part of 

the island (fig. 7). MacCarthy estimated that the water-table 

altitude there ranges from about 1 to 14 ft above sea level. The 

water-level estimates made from resistivity measurements are 

only approximate because use of the Ghyben-Herzberg relation to predict water levels from estimated depths to saltwater 

(1) ignores the freshwater-saltwater transition zone and (2) 

does not account for dynamic conditions in the aquifer where 

vertical flow is present. Unquantified errors probably are associated with the resistivity measurements and the geophysical 

models used to represent actual subsurface conditions.

Freshwater Lens

Water levels measured in wells drilled into the permeable 

dike-free lava flows on the island generally are less than 15 ft 

above sea level. Within these dike-free lava flows, a freshwater 

lens floats on denser, underlying saltwater. The source of the 

freshwater is ground-water recharge from (1) the upgradient 

dike complex where water levels are high, (2) infiltration of 

rainfall, and (3) irrigation water. Fresh ground water flows 

from inland recharge areas to coastal discharge areas. A 

saltwater-circulation system exists beneath the freshwater lens 

(fig. 8; Cooper and others, 1964; Souza and Voss, 1987). Saltwater flows landward in the deeper parts of the aquifer, rises, 

and then mixes with seaward-flowing freshwater, creating a 

freshwater-saltwater transition zone.

Under hydrostatic conditions, the thickness of a freshwater lens can be estimated by using the Ghyben-Herzberg 

relation. If the specific gravities of freshwater and saltwater 

are assumed to be 1.000 and 1.025, respectively, and if the 

freshwater-saltwater transition zone is assumed to be a sharp 

interface, then the Ghyben-Herzberg relation predicts that 

every foot of freshwater above sea level must be balanced by 

FRESHWATER 

BRACKISH WATER 

SALTWATER 

WATER TABLE 

VOLCANIC ROCKS 

SEDIMENTARY DEPOSITS 

GENERAL DIRECTION OF 

 GROUND-WATER FLOW 

EXPLANATION Bend in section

DISTANCE FROM COASTLINE, IN MILES 

Vertical scale greatly exaggerated 

FRESHWATER 

BRACKISH WATER 

SALTWATER 

1 0 1 2 3 4 5 6 7

Line of section

A A’

A

A’

LOCATION MAP

Figure 8. Schematic cross section of the ground-water-flow system on the Island of 

Molokai, Hawaii.

14 Numerical Simulation of the Hydrologic Effects of Redistributed and Additional Ground-Water Withdrawal, Molokai
40 ft of freshwater below sea level. For dynamic conditions, 

the Ghyben-Herzberg relation generally underestimates the 

freshwater-lens thickness near the discharge zone and overestimates it near the recharge zone. The Ghyben-Herzberg relation 

is sometimes used to estimate the depth at which brackish 

water in the transition zone has a salinity about 50 percent that 

of seawater.

Dike-Impounded Ground Water

Within the dike complex of East Molokai Volcano, fresh 

ground water is impounded to high levels in the volcanic rocks 

between low-permeability dikes. In the valleys of the northeastern part of the island, the presence of springs indicates 

that ground water in the dike complex is probably impounded 

to altitudes higher than 2,000 ft above sea level (Stearns and 

Macdonald, 1947, p. 75). Because of low recharge rates in the 

western part of the island, water levels in the dike complex 

of West Molokai Volcano are probably less than about 15 ft 

above sea level (MacCarthy, 1941).

The abundance of dikes in a rift zone increases with 

depth, reducing the overall permeability of the dike complex 

with depth. No data exist that indicate the depth to which 

rocks are saturated with freshwater in the dike complex. In the 

marginal dike zone, where dike intrusions are few, freshwater 

floats on saltwater.

Depth to Saline Water

Salinity profiles from deep open boreholes (deep monitor 

wells) commonly are used in Hawaii to estimate the thicknesses of the freshwater lens and freshwater-saltwater transition zone. The USGS drilled a deep monitor well (0800–01, 

fig. 6) in the Kualapuu area (Oki and Bauer, 2001) and collected salinity profiles from this well during the period 2001–4 

(fig. 9). Measured salinity profiles indicate a freshwater lens, 

about 260 to 290 ft thick, defined by a fluid conductivity lower 

than 1,000 μS/cm. The thickness of this freshwater lens may 

vary over time because of changes in recharge or pumping 

rates. The upper part of the freshwater-saltwater transition 

zone, as indicated by fluid conductivity between 1,000 and 

25,000 μS/cm, generally is about 150 ft thick.

Salinity profiles from deep open boreholes, such as well 

0800–01 (fig. 6), may be affected by flow within the borehole (Paillet and others, 2002) caused by both natural and 

withdrawal-induced vertical-head differences in the aquifer. 

In areas where the head decreases with depth, downward 

borehole flow may occur, leading to an overestimate of the 

freshwater-lens thickness based on the recorded salinity 

profile. The head may increase with depth in the aquifer near 

partially penetrating pumped wells or coastal discharge areas, 

and an increase in head in the aquifer with depth may lead to 

upward flow within an open borehole. Upward borehole flow 

may cause saltwater to flow upward in the borehole, leading to 

an underestimate of the freshwater-lens thickness based on the 

recorded salinity profile.

The estimated thickness of the freshwater-saltwater 

transition zone may be unreliable if significant vertical flow 

causes mixing of water within the borehole. A flowmeter can 

be used to estimate the rate of vertical flow at different depths 

in an open borehole, although a flowmeter was not lowered 

into well 0800–01. Alternatively, the mixing effects caused by 

vertical flow can be eliminated by using a series of piezometers, each open at a different depth in the aquifer, rather than 

a single open borehole.

A time-domain electromagnetic survey in the Kualapuu 

area was conducted by Blackhawk Geosciences, Inc. (Hawaii 

Commission on Water Resource Management, 1997) to estimate the depth to saline water (unspecified salinity). Results 

of the survey indicate that the altitude of the saline-water 

zone in the aquifer rises to the southwest (fig. 7). The results 

of this survey are consistent with the expected southwesterly 

decrease in water level. However, the estimated altitude of 

the saline-water zone from the survey is about 800 to 1,000 ft 

below sea level near well 0800–01 (fig. 6), deeper than where 

measured salinity profiles indicate fluid conductivity of 25,000 

μS/cm (about 50 percent seawater) (fig. 9). In the Kualapuu 

area, estimated depths to saline water from the time-domain 

electromagnetic survey cannot be used to accurately predict 

water levels by using the Ghyben-Herzberg relation, mainly 

because the detected saline water does not correspond to 50 

percent seawater.

Chloride Concentration

Chloride concentration is commonly used as an indicator 

of salinity, which may increase as a result of saltwater intrusion into a fresh ground-water body. The chloride concentration of water pumped from wells in the Kualapuu area 

generally has been less than 200 mg/L except in well 0902–01 

(fig. 6). During the period 1950–61, the chloride concentration 

of water pumped from well 0902–01 ranged from 252 to 430 

mg/L (Oki, 1997). For comparison, the chloride concentration 

of rainfall is typically less than 10 to 20 mg/L (Swain, 1973), 

and that of seawater about 19,500 mg/L (Wentworth, 1939).

During the 1990s, chloride concentrations of water 

pumped from wells 0801–01, 0801–02, 0801–03, and 0901–

01 (fig. 6) in the Kualapuu area were less than 200 mg/L (fig. 

10). During the same period, chloride concentrations of water 

pumped from well 0901–01 generally were about 50 mg/L, 

whereas chloride concentrations of water pumped from wells 

0801–01, 0801–02, and 0801–03 generally ranged from 50 to 

150 mg/L.

Before the early 1980s, chloride concentrations of 

water pumped from the Kawela Shaft (well 0457–01, fig. 

6) were less than 100 mg/L (fig. 10). During 1996 through 

1998, chloride concentrations of water pumped from Kawela 

Shaft ranged from 100 to 200 mg/L, and since 2002 chloride 

concentrations generally have been greater than 200 mg/L. 

Regional Ground-Water-Flow System 15
08/12/2003

03/12/2003

12/05/2002

08/13/2002

04/30/2002

01/25/2002

07/13/2001

EXPLANATION 

0 10,000 20,000 30,000 40,000 50,000

-600

-550

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

0

CONDUCTIVITY, IN MICROSIEMENS PER CENTIMETER 

ALTITUDE, IN FEET RELATIVE TO MEAN SEA LEVEL 

20 21 22 23 24 25

TEMPERATURE, IN DEGREES CELSIUS 

A B

Figure 9. Fluid-conductivity (A) and fluid-temperature (B) profiles in the Kualapuu deep monitor well (0800–01) 

on the Island of Molokai, Hawaii.

16 Numerical Simulation of the Hydrologic Effects of Redistributed and Additional Ground-Water Withdrawal, Molokai
Chloride concentration 

Withdrawal

50

60

70

80

90

100

0

100

200

300

400

0

50

100

150

200

50

60

70

80

90

100

0

50

100

150

0

20

40

60

80

100

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.2

0.4

0.6

0.8

0.0

0.2

0.4

0.6

0.8

0.00

0.25

0.50

0.75

1.00

1.25

0.0

0.5

1.0

1.5

0.0

0.5

1.0

1.5

2.0

2.5

1975 1980 1985 1990

YEAR

1995 2000 2005

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER 

WITHDRAWAL RATE, IN MILLION GALLONS PER DAY 

Ualapue Shaft (0449−01)

Kawela Shaft (0457−01)

Kualapuu well 1 (0801−01)

Kualapuu well 2 (0801−02)

 Kualapuu Mauka well (0801−03)

Kaluakoi well (0901−01)

Figure 10. Chloride concentrations in water pumped from selected wells on the Island of Molokai, Hawaii (see 

fig. 6 for locations). Data from the U.S. Geological Survey and the County of Maui Department of Water Supply.

Regional Ground-Water-Flow System 17
Before 2002, chloride concentrations of water pumped from 

the Ualapue Shaft (well 0449–01) generally were less than 70 

mg/L (fig. 10); from 2003 through 2005, however, chloride 

concentrations generally were more than 70 mg/L, reaching a 

maximum of 100 mg/L during 2004.

Withdrawals

Most of the ground water withdrawn on Molokai is from 

the Kualapuu area, the southeast coastal area, and the dike 

complex in the northeastern part of the island. The reported 

mean annual withdrawal from wells (excluding the Molokai 

Irrigation System [MIS] Tunnel) on Molokai during the period 

2000–2 was about 4.2 Mgal/d (computed from digital data 

supplied by Kevin Gooding, CWRM, written commun., 2005).

Five production wells (0801–01, 0801–02, 0801–03, 

0901–01, and 0902–01, fig. 6) have been drilled in the 

Kualapuu area for either irrigation or domestic use. Wells 

0901–01 and 0902–01, drilled in 1950 and 1946, respectively, 

originally were used to irrigate pineapple fields in the Hoolehua Plain area. Well 0902–01 was abandoned in 1964 when 

surface water from the MIS Tunnel (fig. 1) became available. Since 1976, water from well 0901–01 has been used 

for domestic and irrigation purposes in the western part of 

the island. Before the MIS Tunnel was completed, combined 

withdrawals from wells 0901–01 and 0902–01 varied seasonally from near 0 to about 1 Mgal/d (fig. 11). Kualapuu wells 

0801–01 and 0801–02 (fig. 6) were completed in 1949 and 

1979, respectively, and well 0801–03 (Kualapuu Mauka) was 

drilled in 1987. Monthly mean withdrawal rates from each of 

these three wells (0801–01, 0801–02, and 0801–03) generally 

have remained below 1 Mgal/d (fig. 11). During the period 

2000–2, mean annual withdrawal from the four active wells in 

the Kualapuu area was about 2.2 Mgal/d. During 2005, mean 

annual withdrawal from well 0801–03 was 0.605 Mgal/d.

Near the south coast, ground-water withdrawals are 

mainly from two Maui-type wells (consisting of a shaft 

excavated to or below the water table, and one or more infiltration tunnels extending outward from the shaft); one well 

(0457–01, fig. 6), near Kawela, was completed in 1921, and 

the other well (0449–01, fig. 6), near Ualapue, was completed 

in 1936. During the period 2000–2, mean annual withdrawals 

from Kawela Shaft (well 0457–01) and Ualapue Shaft (well 

0449–01) were about 0.28 and 0.22 Mgal/d, respectively. During 2005, mean annual withdrawals from wells 0457–01 and 

0449–01, respectively, were 0.348 and 0.234 Mgal/d. Total 

reported mean annual withdrawals from other wells near the 

south coast were less than 0.5 Mgal/d. Total unreported withdrawals from drilled wells and numerous shallow dug wells 

along the south coast are probably small.

Three production wells (0855–01, 0855–02, and 0855–

03, fig. 6) drilled in 1961 withdraw water from the dike complex in the northeastern part of the island. Water from these 

wells enters the MIS. During the period 2000–2, mean annual 

withdrawal from these three wells was 0.99 Mgal/d.

Numerical Simulation of Additional 

Ground-Water Withdrawal

A numerical ground-water-flow model previously was 

constructed to simulate steady-state regional ground-water 

flow on Molokai (Oki, 1997). The same model was used in 

this study to estimate steady-state water-level and coastal-discharge changes caused by possible redistributed and additional 

ground-water withdrawals in the area between Kualapuu and 

Ualapue.

Model Description

The regional model uses the two-dimensional (areal), 

finite-element code AQUIFEM–SALT (Voss, 1984), which 

was designed to simulate the flow of confined or unconfined 

fresh ground water in systems that may have a freshwater 

lens. AQUIFEM–SALT simulates freshwater and saltwater 

as immiscible fluids separated by a sharp interface, the depth 

of which is determined by the Ghyben-Herzberg relation. In 

reality, a diffuse transition zone exists between the core of 

freshwater and underlying saltwater. AQUIFEM–SALT simulates the vertically averaged freshwater head in the aquifer and 

assumes that flow is entirely horizontal and that all wells fully 

penetrate the freshwater lens.

The model mesh, boundary conditions, hydraulic characteristics, and recharge used in this study are the same as 

those used in the original numerical model by Oki (1997), to 

which the reader is referred for a complete description of these 

features and construction details.

Model Application

The model by Oki (1997) was used in this study to 

estimate the steady-state hydrologic effects of ground-water 

withdrawals on ground-water levels and coastal discharge. The 

original model mesh consists of 6,432 nodes and 6,251 square 

elements (1,640 ft on a side). The mesh includes the entire 

Island of Molokai and extends offshore to include the entire 

coastal-discharge zone (fig. 12). The original mesh is therefore 

valid for testing the scenarios described in this study.

A base case defined mainly by 2005 mean annual withdrawal rates and May 2005 permitted withdrawal rates (table 

1) was used to compute the water-level and coastal-discharge 

changes caused by redistributed or additional ground-water 

withdrawals. In this model, withdrawals were assigned to the 

node nearest to the withdrawal site. The hydraulic characteristics and long-term average recharge distribution used in the 

original model (Oki, 1997) were used for all simulations in 

this study.

Boundary conditions used in the original model include 

a no-flow boundary condition coinciding with the perimeter 

of the mesh and head-dependent-discharge boundary conditions used to simulate ground-water discharge to the ocean and 

18 Numerical Simulation of the Hydrologic Effects of Redistributed and Additional Ground-Water Withdrawal, Molokai
Ualapue Shaft (0449−01) 

Breadfruit well (0456−04) 

Kawela Plantation DW3 (0456−06) 

Kawela Plantation DW2 (0456−08) 

1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Kawela Plantation DW1 (0456−09) 

0.2

0.4

0.6

0.8

1.0

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.0

WITHDRAWAL RATE, IN MILLION GALLONS PER DAY 

Figure 11. Reported ground-water withdrawal from selected wells on the Island of Molokai, Hawaii (see fig. 

6 for locations). Data from the U.S. Geological Survey, the County of Maui Department of Water Supply, and the 

Hawaii Commission on Water Resource Management.

Numerical Simulation of Additional Ground-Water Withdrawal 19
Kawela Shaft (0457−01) 

Kawela Plantation AG No. 1 (0457−04) 

Kupa Shaft (0501−04) 

Home Pumehana well (0501−06) 

Oloolo Kaunakakai well (0601−01) 

1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

0.2

0.4

0.6

0.8

1.0

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.02

0.04

0.06

0.08

0.10

0.00

0.1

0.2

0.3

0.4

0.5

0.0

WITHDRAWAL RATE, IN MILLION GALLONS PER DAY 

Figure 11. Reported ground-water withdrawal from selected wells on the Island of Molokai, Hawaii (see fig. 

6 for locations). Data from the U.S. Geological Survey, the County of Maui Department of Water Supply, and the 

Hawaii Commission on Water Resource Management—Continued.

20 Numerical Simulation of the Hydrologic Effects of Redistributed and Additional Ground-Water Withdrawal, Molokai
1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

0.1

0.2

0.3

0.4

0.5

0.0

0.02

0.04

0.06

0.08

0.10

0.00

0.2

0.4

0.6

0.8

1.0

0.0

0.5

1.0

1.5

2.0

0.0

0.5

1.0

1.5

2.0

0.0

WITHDRAWAL RATE, IN MILLION GALLONS PER DAY 

Umipaa well (0603−01) 

Naiawa well (0705−05) 

Kualapuu well 1 (0801−01) 

Kualapuu well 2 (0801−02) 

Kualapuu mauka well (0801−03) 

Figure 11. Reported ground-water withdrawal from selected wells on the Island of Molokai, Hawaii (see fig. 

6 for locations). Data from the U.S. Geological Survey, the County of Maui Department of Water Supply, and the 

Hawaii Commission on Water Resource Management—Continued.

Numerical Simulation of Additional Ground-Water Withdrawal 21
Waikolu Tunnel wells 22−24 (0855−01, 0855−02, and 0855−03) 

Well 17 (0901−01) 

Kualapuu (0902−01) 

Waihanau No. 239 (1058−01) 

1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

1

2

3

4

5

0

1

2

3

4

5

0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.0

WITHDRAWAL RATE, IN MILLION GALLONS PER DAY 

Figure 11. Reported ground-water withdrawal from selected wells on the Island of Molokai, Hawaii (see fig. 

6 for locations). Data from the U.S. Geological Survey, the County of Maui Department of Water Supply, and the 

Hawaii Commission on Water Resource Management—Continued.

22 Numerical Simulation of the Hydrologic Effects of Redistributed and Additional Ground-Water Withdrawal, Molokai
Figure 12. Model mesh and hydraulic-conductivity zones used in the ground-water-flow model for the Island of Molokai, Hawaii.

157°20' 157°10' 157° 156°50' 

21°10'

21°

00

2 

2 

WEST MOLOKAI VOLCANICS Dike free Dike complex Confining unit

EAST MOLOKAI VOLCANICS Dike free Dike complex Marginal dike zoneKALAUPAPA VOLCANICS

EXPLANATION

1 10 20 30 40 50 60 70 80 90 100 110 1

1

10203040

ROW

COLUMN

Ilio Point

Laau

Point

Kalaupapa

Kualapuu

Mapulehu

!

!

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula
streams. Because ocean levels, coastal bathymetry, and streamchannel altitudes have not changed sufficiently, the original 

boundary conditions (Oki, 1997) were used in this study.

The water level in Puu O Hoku No. 1 well (0844–01, 

fig. 6), which was drilled after the model was constructed, is 

about 9 ft above mean sea level (Hawaii Commission on Water 

Resource Management, unpub. data, 2006), indicating that 

the well site is probably not in the dike complex as originally 

modeled. Thus, the model is not used to specifically assess the 

hydrologic effects of ground-water withdrawal from this well, 

which is located near the east end of the island, outside the 

main area of interest between Kualapuu and Ualapue. 

Description of Model Scenarios

The 2005 base-case scenario was used as a reference 

for computing steady-state water-level and coastal-discharge 

changes caused by redistributed or additional ground-water 

withdrawals. The withdrawal rates used in the 2005 base case 

were mean 2005 withdrawal rates at wells 0449–01 (Ualapue 

Shaft), 0457–01 (Kawela Shaft), and 0801–03 (Kualapuu 

Mauka), the May 2005 permitted withdrawal rates at other 

wells (excluding Puu O Hoku No. 1, Waiola No. 1, and the 

DHHL reservation), and the 1.822-Mgal/d withdrawal rate 

from the MIS Tunnel (Oki, 1997) near Waikolu Stream (fig. 6; 

table 1). Proposed Waiola No. 1 well (0759–01) is not likely 

to be drilled (Charley F. Ice, CWRM, written commun., 2006), 

and so it was omitted from the model. The DHHL reservation 

was omitted from the base case, although it was simulated in 

a scenario described below. The 2005 base-case withdrawal 

rates range from 0.001 Mgal/d (well 0352–12) to 1.822 

Mgal/d (MIS Tunnel) and total 9.164 Mgal/d (fig. 6; table 1). 

The total base-case withdrawal exclusive of the MIS Tunnel 

is 7.342 Mgal/d, or about 75 percent higher than the reported 

2000–2 mean annual withdrawal of 4.2 Mgal/d (excluding the 

MIS Tunnel). Total withdrawal represented in the base case is 

5 percent of recharge (187 Mgal/d).

The DWS provided five proposed withdrawal sites 

(Manawainui, Kawela 1, Kawela 2, Kamiloloa, and Ualapue) to be tested in the model (fig. 2; table 2). A total of 15 

scenarios, excluding the base case, were tested. In scenarios 1 

through 13, withdrawals from existing wells 0449–01, 0457–

01, and 0801–03 (fig. 6) were fully or partially redistributed 

to one to four of the proposed withdrawal sites. In scenarios 

1 through 8, the total withdrawal equals the base-case withdrawal, whereas in scenarios 9 through 13 the total withdrawal 

exceeds the base-case withdrawal by 0.28 Mgal/d. Scenarios 

9 through 13 incorporate an increased water demand forecast 

for 2030 by the DWS. Scenario 14 is similar to scenario 11 

but includes the 2.905-Mgal/d withdrawal from the DHHL 

reservation arbitrarily assigned to three sites in the Kualapuu 

area. Scenario 15 corresponds to natural conditions without 

any withdrawals. For all simulations, recharge in the model 

was 187 Mgal/d.

Model Results

For each of the scenarios tested, the steady-state distributions of water-level and coastal-discharge changes were determined relative to the 2005 base-case, steady-state distributions 

of water levels and coastal discharges. Simulated water-level 

changes are greatest at withdrawal sites and decrease outward 

with distance elsewhere. Within the zone where water levels 

rise because of decreased withdrawal, the salinity of water 

pumped from existing wells may decrease, although the extent 

of the decrease cannot be predicted accurately with the sharpinterface model used in this study. Similarly, within the zone 

where water levels decline because of increased withdrawal, 

the salinity of water pumped from existing wells may increase 

by an unknown amount. The change in the salinity of water 

pumped from existing wells is dependent on the amount of 

water-level change and the location of the well relative to 

the freshwater-saltwater transition zone. Greater water-level 

changes (all other factors being equal) are expected to cause 

Table 2. Proposed ground-water-withdrawal sites on the Island of Molokai, 

Hawaii.

[DHHL, Hawaii Department of Hawaiian Home Lands] 

Site Name Approximate

altitude (feet) Aquifer system

1 Manawainui 925 Manawainui

2 Kawela 1 700 Kawela

3 Kamiloloa 700 Kamiloloa

4 Kawela 2 700 Kawela

5 Ualapue 400 Ualapue

6 DHHL reservation 1 1,200 Kualapuu

7 DHHL reservation 2 1,600 Kualapuu

8 DHHL reservation 3 1,800 Kualapuu

24 Numerical Simulation of the Hydrologic Effects of Redistributed and Additional Ground-Water Withdrawal, Molokai
greater salinity changes. Deep wells or wells near the coast 

may be located near a source of brackish ground water (transition zone) and affected to a greater extent than shallow or 

inland wells.

Simulated coastal-discharge changes generally are 

greatest immediately downgradient from sites of withdrawal 

change, and areas of coastal-discharge changes may correspond to sites of mapped fishponds or springs (fig. 1). In general, coastal-discharge changes are difficult to directly measure 

except at onshore spring sites where discharge is channelized. 

Thus, the numerical model is used in this study to provide 

regional estimates of coastal-discharge changes caused by 

redistributed or additional ground-water withdrawals. In this 

study, coastal-discharge changes are represented over areas 

defined by model elements (1,640 by 1,640 ft). Coastal-discharge changes less than or equal to 1,000 gal/d within model 

elements are considered too small to be represented accurately 

by the regional model and therefore are not shown; however, 

coastal-discharge changes greater than 1,000 gal/d generally 

account for about 95 percent of the total simulated change in 

discharge. Simulated coastal-discharge changes may not accurately reflect actual local-scale changes because of the level of 

spatial discretization and because local-scale heterogeneities 

in the hydraulic characteristics of the rocks are not represented 

in the model.

Scenarios 1 Through 8—Redistribution of 

Withdrawals

In each of scenarios 1 through 8, withdrawals from 

existing wells 0449–01, 0457–01, and 0801–03 (fig. 6) were 

partially or fully redistributed to one to four proposed withdrawal sites (fig. 2; table 3), and the total withdrawal from all 

sites equals the total 2005 base-case withdrawal. In scenarios 

1 through 8, the total combined withdrawal from proposed 

withdrawal sites and wells 0449–01, 0457–01, and 0801–03 is 

1.187 Mgal/d. In these eight scenarios, withdrawal from well 

0801–03 was reduced by 0.232 or 0.432 Mgal/d, and withdrawals from wells 0449–01 and 0457–01 were maintained at 

2005 base-case rates or set equal to zero.

In scenario 1, in which the withdrawal from well 0801–

03 (fig. 6) is reduced by 0.232 Mgal/d and the withdrawal 

from proposed withdrawal site 1 is increased by the same 

amount, the hydrologic effects of each well are first simulated separately (figs. 13, 14) and then combined (fig. 15). 

Reducing the withdrawal from well 0801–03 by 0.232 Mgal/d 

without increasing the withdrawal from proposed withdrawal 

site 1 causes water levels and coastal discharge to increase 

(fig. 13). The water level at well 0801–03 rises by 0.63 ft, and 

water-level rises decrease outward with distance from well 

0801–03. Coastal discharge increases mainly along the south 

Table 3. Summary of withdrawal scenarios simulated with the ground-water-flow model for the Island of Molokai, Hawaii.

[Values in red bold indicate that withdrawal rate differs from base-case withdrawal at the site; Mgal/d, million gallons per day; DHHL, Hawaii Department 

of Hawaiian Home Lands]

Simulated withdrawal (Mgal/d)

Scenario

Well

0801–03

(Kualapuu

Mauka)

Well

0457–01

(Kawela

Shaft)

Well

0449–01

(Ualapue 

Shaft)

 Proposed

site 1

(Manawainui)

Proposed

site 2

(Kawela 1)

Proposed

site 3

(Kamiloloa)

Proposed

site 4

(Kawela 2)

Proposed

site 5

 (Ualapue)

DHHL Total

Base case 0.605 0.348 0.234 0 0 0 0 0 0 1.187

1 0.373 0.348 0.234 0.232 0 0 0 0 0 1.187

2 0.373 0 0.234 0.232 0.348 0 0 0 0 1.187

3 0.373 0 0 0.232 0.348 0 0 0.234 0 1.187

4 0.173 0.348 0.234 0.432 0 0 0 0 0 1.187

5 0.173 0 0.234 0.432 0.348 0 0 0 0 1.187

6 0.173 0 0 0.432 0.348 0 0 0.234 0 1.187

7 0.173 0 0 0.232 0.348 0.200 0 0.234 0 1.187

8 0.173 0 0 0.232 0.348 0 0.200 0.234 0 1.187

9 0.465 0.392 0.378 0.232 0 0 0 0 0 1.467

10 0.465 0 0.378 0.232 0.392 0 0 0 0 1.467

11 0.465 0 0 0.232 0.392 0 0 0.378 0 1.467

12 0.173 0 0 0.232 0.392 0.292 0 0.378 0 1.467

13 0.173 0 0 0.232 0.392 0 0.292 0.378 0 1.467

14 0.465 0 0 0.232 0.392 0 0 0.378 2.905 4.372

15 0 0 0 0 0 0 0 0 0 0

Numerical Simulation of Additional Ground-Water Withdrawal 25
Ilio Point 

Laau

Point

00

Kalaupapa

Kualapuu 

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

0.01

0.02

0.05 0.1 0.2

0801−03

(+0.63)

A

EXPLANATION 

A

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET 

0801−03

(+0.63) EXISTING WELL AND WELL NUMBER— 

 Value in parentheses is simulated water-level change, in feet

+0.01+0.02+0.05+0.1+0.2

 1,000 < Q ≤ 5,000  5,000 < Q ≤ 15,000  15,000 < Q ≤ 30,000 

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY

Figure 13. Simulated changes in water level and coastal discharge (relative to base-case conditions) caused by decreasing withdrawal by 0.232 milthe existing Kualapuu well (0801–03), Island of Molokai, Hawaii.
Ilio Point 

Laau

Point

00

Kalaupapa

Kualapuu 

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

A PROPOSED WITHDRAWAL SITE AND SIMULATED 

 WATER-LEVEL CHANGE, IN FEET 

EXPLANATION 

−0.30

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET 

−0.01−0.02−0.05−0.1

−0.30

A

−0.01 −0.02

−0.05

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000−30,000 ≤ Q < −15,000

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY

Figure 14. Simulated changes in water level and coastal discharge (relative to base-case conditions) caused by withdrawing 0.232 million gallons p(Manawainui), Island of Molokai, Hawaii.
Ilio Point 

Laau

Point

00

Kalaupapa

Kualapuu 

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

−0.02

−0.05

0.02 0.05

0.2 0.1

0.01 0.01

−0.01

0.02 0.05

A

EXPLANATION 

−0.25

−0.25

A

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET 

A

0801−03

(+0.59)

A

0801−03

(+0.59)

PROPOSED WITHDRAWAL SITE AND SIMULATED WATER-LEVEL CHANGE, IN FEETEXISTING WELL AND WELL NUMBER—  Value in parentheses is simulated water-level change, in feet

+0.01+0.02+0.05+0.1+0.2

−0.01−0.02−0.05

 1,000 < Q ≤ 5,000  5,000 < Q ≤ 15,000 

Scenario 1

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY

Figure 15. Scenario 1 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal dischargconditions) caused by decreasing withdrawal by 0.232 million gallons per day from the existing Kualapuu well (0801–03) and withdrawing 0.232 million proposed site 1 (Manawainui).
coast from Palaau to Kawela but also along the north coast, 

northwest of well 0801–03. Withdrawing 0.232 Mgal/d from 

proposed withdrawal site 1 without reducing the withdrawal 

from well 0801–03 causes water levels and coastal discharge 

to decrease (fig. 14). The water level at proposed withdrawal 

site 1 declines by 0.30 ft, and water-level declines decrease 

outward from proposed withdrawal site 1. Coastal discharge 

decreases along the south coast from Palaau to Kawela. The 

scenario 1 combination of reducing withdrawal from well 

0801–03 by 0.232 Mgal/d and withdrawing the same amount 

from proposed site 1 causes the water level at well 0801–03 to 

rise by 0.59 ft and the water level at proposed site 1 to decline 

by 0.25 ft (fig. 15). Thus, the water-level changes simulated 

in scenario 1 are reduced relative to those caused by the 

individual withdrawals. In addition, the zone where coastal 

discharge increases because of reduced withdrawal from well 

0801–03 is smaller if the withdrawal from proposed site 1 is 

0.232 Mgal/d rather than 0. Similarly, the zone where coastal 

discharge decreases because of increased withdrawal from 

proposed withdrawal site 1 is smaller if the withdrawal from 

well 0801–03 is reduced by 0.232 Mgal/d rather than 0.

In scenarios 1 through 8, simulation results indicate 

that a redistribution of withdrawals causes a corresponding 

redistribution of water levels and coastal discharge. Water 

levels rise and coastal discharge increases near sites of reduced 

withdrawal, whereas water levels decline and coastal discharge 

decreases near sites of increased withdrawal (figs. 15–22). 

The magnitude and areal extent of the hydrologic changes 

caused by redistributing ground-water withdrawals increase 

with larger withdrawal changes. The magnitude of hydrologic 

changes also generally decreases with distance from the withdrawal sites.

At existing wells where withdrawal rates are reduced, 

simulated water levels rise by 0.08 ft at well 0449–01 (Ualapue Shaft in scenarios 3, 6, 7, and 8) to 1.10 ft at well 0801–03 

(Kualapuu Mauka in scenarios 7 and 8) (table 4). At proposed 

sites where withdrawals are increased, simulated water levels 

decline by 0.07 ft at site 5 (Ualapue in scenarios 3, 6, 7, and 

8) to 0.48 ft at site 1 (Manawainui in scenarios 5 and 6) (table 

4). Simulated water-level changes decrease with distance from 

withdrawal sites. The magnitudes of simulated water-level 

changes increase with larger withdrawal changes. For example, simulated water-level changes (relative to the base case) 

in scenario 4 (fig. 18) are greater than those in scenario 1 (fig. 

15) because the magnitudes of withdrawal changes simulated 

in scenario 4 are greater than in scenario 1 at common sites. In 

scenario 1, the simulated water level at well 0801–03 rises by 

0.59 ft in response to a withdrawal reduction of 0.232 Mgal/d 

(fig. 15), whereas in scenario 4 the water level at well 0801–03 

rises by 1.08 ft in response to a withdrawal reduction of 

0.432 Mgal/d (fig. 18). Similarly, in scenario 1, the simulated 

water level at proposed withdrawal site 1 declines by 0.25 ft 

in response to withdrawal of 0.232 Mgal/d (fig. 15), whereas 

in scenario 4 the water level at site 1 declines by 0.47 ft in 

response to withdrawal of 0.432 Mgal/d (fig. 18).

The areal extent of simulated water-level change, as 

indicated by the ±0.01-ft line of equal water-level change, is 

dependent on the magnitude of the withdrawal change and the 

location of the withdrawal site relative to low-permeability 

features, the coast, and other withdrawal sites. Larger withdrawal changes cause more widespread water-level changes 

(for example, compare scenarios 1 and 4). Low-permeability 

features represented in the regional model affect the simulated distribution of water-level changes. The areal extent of 

simulated water-level changes is limited in the northeast by 

the dike complex of East Molokai Volcano and, in some cases, 

in the west by the confining unit separating the West and East 

Molokai Volcanics (for example, figs. 18–22). In general, 

withdrawal sites farther inland, away from areas of coastal 

discharge, create more extensive areas of water-level change. 

For example, a withdrawal reduction of 0.232 Mgal/d from 

well 0801–03 (scenario 1), located in the inland Kualapuu 

area, creates a more extensive area of water-level change than 

a withdrawal reduction of 0.234 Mgal/d from the Ualapue 

Shaft (scenario 3), located near the coast (figs. 15, 17). The 

areal extent of water-level rise caused by reduced withdrawal 

from an existing well is limited by the effects of increased 

withdrawal from nearby proposed sites. For example, in 

scenario 1, the areal extent of water-level rise caused by 

reduced withdrawal from well 0801–03 does not extend to the 

coast immediately south of the well because of the effects of 

increased withdrawal from proposed site 1 (fig. 15). Reducing 

the withdrawal from well 0801–03 by 0.232 Mgal/d without 

withdrawing 0.232 Mgal/d from proposed site 1 will create a 

larger areal extent of water-level rise relative to that simulated 

in scenario 1 (compare figs. 13 and 15). Reduced withdrawal 

from well 0801–03 may lead to decreased salinity of the water 

pumped from existing wells in the Kualapuu area, although the 

extent of improvement cannot be predicted accurately with a 

sharp-interface model.

For steady-state conditions, the zero net change in 

withdrawal simulated in scenarios 1 through 8 will cause a 

zero net change in coastal discharge. Local increases and 

decreases in coastal discharge are simulated in scenarios 1 

through 8, although the sum of the increases equals the sum 

of the decreases. In scenarios 1 through 8, coastal-discharge 

changes within model elements (1,640 ft on a side) do not 

exceed 70,000 gal/d (table 5). The simulated reductions in 

coastal discharge generally are less than 5 percent (table 5). In 

the regional model, the low-permeability dike complex of East 

Molokai Volcano impedes the simulated spreading of waterlevel changes to perennial streams in the northeastern part of 

the island, and discharge to these streams in the dike complex 

therefore is unaffected by proposed withdrawals.

In scenarios 1 and 4, the withdrawal from well 0801–03 

(fig. 6) is partly redistributed to proposed withdrawal site 1 

(Manawainui). Reducing the withdrawal from well 0801–03 

by 0.232 Mgal/d (scenario 1) or 0.432 Mgal/d (scenario 4) 

causes the simulated coastal discharge to increase along 

both the south and north coasts, southwest and northwest of 

well 0801–03 (figs. 15, 18). Within individual model eleNumerical Simulation of Additional Ground-Water Withdrawal 29
Ilio Point 

Laau

Point

00

Kalaupapa

Kualapuu 

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

+69,000 gal/d (9%) +60,000 gal/d (6%) 

A PROPOSED WITHDRAWAL SITE AND SIMULATED

 WATER-LEVEL CHANGE, IN FEETEXISTING WELL AND WELL NUMBER—  Value in parentheses is simulated water-level change, in feet

EXPLANATION 

−0.26

A

0801−03

(+0.59)

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY (gal/d)

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET 

−0.05

−0.05

0.02 0.05 0.1 0.2 0.01 0.01

−0.01 −0.02

0.02 0.05

−0.26

−0.15

−40,000 gal/d (−2%)

0457−01

(+0.17)

A

A

0801−03

(+0.59)

A

A

+0.01+0.02+0.05+0.1+0.2

−0.01−0.02−0.05

 1,000 < Q ≤ 5,000  5,000 < Q ≤ 15,000  15,000 < Q ≤ 30,000 30,000 < Q 

Scenario 2

Discharge changes greater than 30,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge)

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000−30,000 ≤ Q < −15,000

Q < −30,000

Figure 16. Scenario 2 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal dischargconditions) caused by decreasing withdrawal by 0.232 million gallons per day from the existing Kualapuu well (0801–03), decreasing withdrawal to zerShaft (well 0457–01), withdrawing 0.232 million gallons per day from proposed site 1 (Manawainui), and withdrawing 0.348 million gallons per day from 
Ilio Point 

Laau

Point

00

Kalaupapa

Kualapuu 

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

−0.05

0.02 0.05 0.1 0.2 0.01 0.01

−0.01 −0.02

0.02 0.05

−0.26

−0.07

−0.15

0457−01

(+0.17)

0449−01

(+0.08)

A

A

A

−0.05

0801−03

(+0.59)

A

EXPLANATION 

−0.26

A

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET 

PROPOSED WITHDRAWAL SITE AND SIMULATED WATER-LEVEL CHANGE, IN FEETEXISTING WELL AND WELL NUMBER—  Value in parentheses is simulated water-level change, in feet

0801−03

(+0.59)

A A

+0.01+0.02+0.05+0.1+0.2

−0.01−0.02−0.05

 1,000 < Q ≤ 5,000  5,000 < Q ≤ 15,000  15,000 < Q ≤ 30,000 30,000 < Q 

Scenario 3

A

+69,000 gal/d (9%) +60,000 gal/d (6%) 

−40,000 gal/d (−2%)

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000−30,000 ≤ Q < −15,000

Q < −30,000

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY (gal/d) 

Discharge changes greater than 30,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge)

Figure 17. Scenario 3 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal dischargconditions) caused by decreasing withdrawal by 0.232 million gallons per day from the existing Kualapuu well (0801–03), decreasing withdrawals to zeShaft (well 0457–01) and the existing Ualapue Shaft (well 0449–01), withdrawing 0.232 million gallons per day from proposed site 1 (Manawainui), withgallons per day from proposed site 2 (Kawela 1), and withdrawing 0.234 million gallons per day from proposed site 5 (Ualapue).
Ilio Point 

Laau

Point

00

Kalaupapa

Kualapuu 

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

A

+0.01+0.02+0.05+0.1+0.2+0.5

−0.47

A

 1,000 < Q ≤ 5,000  5,000 < Q ≤ 15,000 

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET 

PROPOSED WITHDRAWAL SITE AND SIMULATED WATER-LEVEL CHANGE, IN FEETEXISTING WELL AND WELL NUMBER—  Value in parentheses is simulated water-level change, in feet

0801−03

(+1.08)

−0.47

A

0801−03

(+1.08)

A

−0.01−0.02−0.05−0.1

0.02

0.05

0.01

0.01

−0.01 −0.02

−0.05

0.02 0.05 0.1 0.2

Scenario 4

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000−30,000 ≤ Q < −15,000

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY

Figure 18. Scenario 4 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal dischargconditions) caused by decreasing withdrawal by 0.432 million gallons per day from the existing Kualapuu well (0801–03) and withdrawing 0.432 million proposed site 1 (Manawainui).
Ilio Point 

Laau

Point

00

Kalaupapa

Kualapuu 

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

+69,000 gal/d (9%) +59,000 gal/d (6%) 

A

+0.01+0.02+0.05+0.1+0.2+0.5

EXPLANATION 

−0.01−0.02−0.05−0.1

−0.48

A

 1,000 < Q ≤ 5,000  5,000 < Q ≤ 15,000  15,000 < Q ≤ 30,000 30,000 < Q 

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET 

PROPOSED WITHDRAWAL SITE AND SIMULATED WATER-LEVEL CHANGE, IN FEETEXISTING WELL AND WELL NUMBER—  Value in parentheses is simulated water-level change, in feet

0801−03

(+1.07)

−0.48

−0.15

0457−01

(+0.17)

A

0801−03

(+1.07)

A

A

0.01

0.02

0.05

0.01

−0.01

−0.02 −0.05

0.02 0.05 0.1 0.2

A −32,000 gal/d (−1%)

−42,000 gal/d (−2%)

Scenario 5

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000−30,000 ≤ Q < −15,000

Q < −30,000

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY (gal/d) 

Discharge changes greater than 30,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge)

Figure 19. Scenario 5 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal dischargconditions) caused by decreasing withdrawal by 0.432 million gallons per day from the existing Kualapuu well (0801–03), decreasing withdrawal to zerShaft (well 0457–01), withdrawing 0.432 million gallons per day from proposed site 1 (Manawainui), and withdrawing 0.348 million gallons per day from 
Ilio Point 

Laau

Point

00

Kalaupapa

Kualapuu 

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

−0.48

−0.15

0457−01

(+0.17)

A

0801−03

(+1.07)

A

A

0.01

0.02

0.05

0.01

−0.01

−0.02

0.02 0.05 0.1 0.2

A

−0.05

A

+0.01+0.02+0.05+0.1+0.2+0.5

EXPLANATION 

−0.01−0.02−0.05−0.1

−0.48

A

 1,000 < Q ≤ 5,000  5,000 < Q ≤ 15,000  15,000 < Q ≤ 30,000 30,000 < Q 

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET 

PROPOSED WITHDRAWAL SITE AND SIMULATED WATER-LEVEL CHANGE, IN FEETEXISTING WELL AND WELL NUMBER—  Value in parentheses is simulated water-level change, in feet

0801−03

(+1.07)

−0.07

0449−01

(+0.08) AA

Scenario 6

−32,000 gal/d (−1%)−42,000 gal/d (−2%)

+69,000 gal/d (9%) +59,000 gal/d (6%) 

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000−30,000 ≤ Q < −15,000

Q < −30,000

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY (gal/d) 

Discharge changes greater than 30,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge)

Figure 20. Scenario 6 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal dischargconditions) caused by decreasing withdrawal by 0.432 million gallons per day from the existing Kualapuu well (0801–03), decreasing withdrawals to zeShaft (well 0457–01) and the existing Ualapue Shaft (well 0449–01), withdrawing 0.432 million gallons per day from proposed site 1 (Manawainui), withgallons per day from proposed site 2 (Kawela 1), and withdrawing 0.234 million gallons per day from proposed site 5 (Ualapue).
Ilio Point 

Laau

Point

00

Kalaupapa

Kualapuu 

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

+66,000 gal/d (8%) +57,000 gal/d (6%) 

−52,000 gal/d (−2%)−57,000 gal/d (−3%)−35,000 gal/d (−4%)

A

+0.01+0.02+0.05+0.1+0.2+0.5

EXPLANATION 

−0.01−0.02−0.05

−0.23

A

 1,000 < Q ≤ 5,000  5,000 < Q ≤ 15,000  15,000 < Q ≤ 30,000 30,000 < Q 

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET 

PROPOSED WITHDRAWAL SITE AND SIMULATED WATER-LEVEL CHANGE, IN FEETEXISTING WELL AND WELL NUMBER—  Value in parentheses is simulated water-level change, in feet

0801−03

(+1.10)

−0.23

−0.16

−0.11

0457−01

(+0.17)

A

0801−03

(+1.10)

A

A

A

0.01

0.02

0.05

0.01

−0.01 −0.02

0.02 0.05 0.1 0.2

A

−0.05

−0.07

0449−01

(+0.08)

Scenario 7

AA

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000−30,000 ≤ Q < −15,000

Q < −30,000

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY (gal/d) 

Discharge changes greater than 30,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge)

Figure 21. Scenario 7 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal dischargconditions) caused by decreasing withdrawal by 0.432 million gallons per day from the existing Kualapuu well (0801–03), decreasing withdrawals to zeShaft (well 0457–01) and the existing Ualapue Shaft (well 0449–01), withdrawing 0.232 million gallons per day from proposed site 1 (Manawainui), withper day from proposed site 2 (Kawela 1), withdrawing 0.200 million gallons per day from proposed site 3 (Kamiloloa), and withdrawing 0.234 million galsite 5 (Ualapue).
Ilio Point

Laau

Point

00

Kalaupapa

Kualapuu

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

A

0801−03

(+1.10)

0.05

0.01 0.02 0.05 0.1 0.2

−0.07

0449−01

(+0.08)

0457−01 A (+0.16) A

−0.21

−0.15

−0.08A

−0.01

−0.02

A

A

A

+0.01+0.02+0.05+0.1+0.2+0.5

EXPLANATION

−0.01−0.02−0.05

−0.21

A

 1,000 < Q ≤ 5,000 5,000 < Q ≤ 15,000 15,000 < Q ≤ 30,00030,000 < Q 

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET

PROPOSED WITHDRAWAL SITE AND SIMULATED WATER-LEVEL CHANGE, IN FEETEXISTING WELL AND WELL NUMBER—  Value in parentheses is simulated water-level change, in feet

0801−03

(+1.10)

0.01

0.02

−41,000 gal/d (−2%)−32,000 gal/d (−4%)

Scenario 8

A

+53,000 gal/d (7%)+51,000 gal/d (5%)

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000−30,000 ≤ Q < −15,000

Q < −30,000

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY (gal/d)

Discharge changes greater than 30,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge)

Figure 22. Scenario 8 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal dischargconditions) caused by decreasing withdrawal by 0.432 million gallons per day from the existing Kualapuu well (0801–03), decreasing withdrawals to zeShaft (well 0457–01) and the existing Ualapue Shaft (well 0449–01), withdrawing 0.232 million gallons per day from proposed site 1 (Manawainui), withper day from proposed site 2 (Kawela 1), withdrawing 0.200 million gallons per day from proposed site 4 (Kawela 2), and withdrawing 0.234 million gallsite 5 (Ualapue).
ments, coastal discharge increases by as much as 6,000 gal/d 

(scenario 1, fig. 15) and 12,000 gal/d (scenario 4, fig. 18). In 

general, the simulated increase in coastal discharge caused by 

reducing the withdrawal from well 0801–03 decreases with 

distance from the well. Increasing the withdrawal from proposed withdrawal site 1 causes coastal discharge to decrease 

along the south coast and limits the eastward extent of the 

zone where coastal discharge increases because of the reduced 

withdrawal from well 0801–03 (figs. 15, 18). Within individual model elements, coastal discharge decreases by as much as 

10,000 gal/d (scenario 1) and 18,000 gal/d (scenario 4) south 

of proposed withdrawal site 1.

Scenarios 2 and 5 (figs. 16, 19) include the redistributed 

withdrawals in scenarios 1 and 4, respectively, as well as the 

additional redistributed withdrawal from the Kawela Shaft 

(well 0457–01, fig. 6) to proposed withdrawal site 2 (Kawela 

1). In scenarios 2 and 5, withdrawal of 0.348 Mgal/d from the 

Kawela Shaft is entirely redistributed to proposed withdrawal 

site 2. Shutting off the Kawela Shaft causes water levels and 

coastal discharge to increase in the immediate vicinity of the 

shaft, and withdrawing 0.348 Mgal/d from proposed withdrawal site 2 causes water levels and coastal discharge to 

decrease in the vicinity of that site. In scenarios 2 and 5, water 

levels increase by 0.17 ft at the Kawela Shaft and decrease 

by 0.15 ft at proposed withdrawal site 2. In scenarios 2 and 5, 

coastal discharge within model elements increases by as much 

as 69,000 gal/d immediately south of the Kawela Shaft and 

decreases by as much as 40,000 gal/d (scenario 2, fig. 16) and 

42,000 gal/d (scenario 5, fig. 19) immediately southwest of 

proposed withdrawal site 2.

Scenarios 3 and 6 (figs. 17, 20) include the redistributed 

withdrawals in scenarios 2 and 5, respectively, as well as 

additional redistributed withdrawal from the Ualapue Shaft 

(well 0449–01, fig. 6) to proposed withdrawal site 5 (Ualapue), immediately inland from the shaft. In scenarios 3 and 

6, withdrawal of 0.234 Mgal/d from the Ualapue Shaft is 

entirely redistributed to proposed withdrawal site 5. Shutting 

off the Ualapue Shaft causes water levels and coastal discharge 

to increase in the immediate vicinity. Withdrawing 0.234 

Mgal/d from proposed withdrawal site 5 causes water levels 

to decrease in the immediate vicinity and coastal discharge to 

decrease to the southwest and southeast, bracketing the area 

where coastal discharge increases in response to shutting off 

the Ualapue Shaft (figs. 17, 20). The simulated hydrologic 

effects of redistributing withdrawal from the Ualapue Shaft 

to proposed withdrawal site 5 mainly are limited to the area 

between Kamalo and Pukoo. In scenarios 3 and 6, water levels 

Table 4. Summary of water-level changes simulated with the ground-water-flow model for the Island of Molokai, Hawaii.

[Values in red bold indicate that withdrawal rate differs from base-case withdrawal at the site; positive values indicate an increase in water level, whereas 

negative values indicate a decrease in water level; DHHL, Hawaii Department of Hawaiian Home Lands] 

Simulated water-level change (feet)

Scenario

Well

0801–03

(Kualapuu

Mauka)

Well

0457–01

(Kawela

Shaft)

Well

0449–01

(Ualapue

Shaft)

Proposed

site 1

(Manawainui)

Proposed

site 2

(Kawela 1)

Proposed

site 3

(Kamiloloa)

Proposed

site 4

(Kawela 2)

Proposed

site 5

(Ualapue)

DHHL

(range for

three sites)

1

Base 

case 8.38 2.89 3.66 6.19 4.87 5.37 5.67 4.76 12.48–16.75

1 0.59 0 0 −0.25 0 −0.01 0 0 0.04–0.10

2 0.59 0.17 0 −0.26 −0.15 −0.03 0 0 0.03–0.10

3 0.59 0.17 0.08 −0.26 −0.15 −0.03 0 −0.07 0.03–0.10

4 1.08 0 0 −0.47 0 −0.01 0 0 0.07–0.19

5 1.07 0.17 0 −0.48 −0.15 −0.03 0 0 0.07–0.18

6 1.07 0.17 0.08 −0.48 −0.15 −0.03 0 −0.07 0.07–0.18

7 1.10 0.17 0.08 −0.23 −0.16 −0.11 0 −0.07 0.08–0.20

8 1.10 0.16 0.08 −0.21 −0.15 −0.02 −0.08 −0.07 0.09–0.21

9 0.35 −0.03 −0.08 −0.27 0 −0.01 0 −0.02 0.01–0.05

10 0.35 0.17 −0.08 −0.28 −0.17 −0.04 0 −0.02 0.01–0.04

11 0.35 0.17 0.04 −0.28 −0.17 −0.04 0 −0.13 0.01–0.04

12 1.09 0.16 0.04 −0.24 −0.19 −0.16 −0.01 −0.13 0.08–0.20

13 1.10 0.15 0.04 −0.22 −0.18 −0.03 −0.12 −0.13 0.08–0.21

14 −1.89 0.12 0.04 −1.11 −0.30 −0.31 −0.05 −0.13 −3.64 to −3.99

15 3.51 0.29 0.18 0.45 0.14 0.19 0.12 0.08 0.63–1.07

1

Simulated base-case water level, in feet.

Numerical Simulation of Additional Ground-Water Withdrawal 37
increase by 0.08 ft at Ualapue Shaft and decrease by 0.07 ft at 

proposed withdrawal site 5. Coastal discharge within model 

elements increases by as much as 69,000 gal/d immediately 

south of the Ualapue Shaft and decreases by less than 5,000 

gal/d immediately southwest and southeast of proposed withdrawal site 5 (figs. 17, 20).

Scenarios 7 and 8 (figs. 21, 22) are similar to scenario 

3 but include a further reduction in the withdrawal (0.200 

Mgal/d) from well 0801–03, redistributed to either site 3 

(Kamiloloa in scenario 7) or site 4 (Kawela 2 in scenario 8). 

Scenarios 7 and 8 indicate a further increase in water levels in 

the Kualapuu area relative to scenario 3. The simulated water 

level at well 0801–03 increases by 1.10 ft (scenarios 7 and 8) 

compared to 0.59 ft (scenario 3) (table 1). In scenarios 7 and 8, 

the zone where coastal discharge increases because of reduced 

withdrawal from well 0801–03 extends farther eastward than 

in scenario 3, and the zone where coastal discharge decreases 

because of withdrawal from proposed withdrawal sites 1 

through 4 mainly is between Kaunakakai and Kamalo. Within 

model elements, coastal discharge decreases by as much as 

57,000 gal/d (scenario 7, fig. 21) and 41,000 gal/d (scenario 8, 

fig. 22) southwest of proposed withdrawal site 2.

Scenarios 9 Through 13—Additional GroundWater Withdrawal

In each of scenarios 9 through 13, the total withdrawal 

from all sites was 0.28 Mgal/d greater than the total 2005 

base-case withdrawal of 9.164 Mgal/d. In these five scenarios, 

the combined withdrawal from proposed sites and wells 

0449–01, 0457–01, and 0801–03 equals 1.467 Mgal/d (table 

3). In these scenarios, the withdrawal from well 0801–03 was 

reduced by 0.140 or 0.432 Mgal/d relative to the average 2005 

withdrawal rate, and the withdrawals from wells 0449–01 and 

0457–01 were increased by 0.044 and 0.144 Mgal/d, respectively, or set equal to zero.

At existing wells where withdrawals are changed, simulated water levels change by −0.08 ft at well 0449–01 (Ualapue Shaft in scenarios 9 and 10) to 1.10 ft at well 0801–03 

(Kualapuu Mauka in scenario 13) (figs. 23–27; table 4). At 

proposed withdrawal sites where withdrawals are increased, 

simulated water levels decline by 0.12 ft at site 4 (Kawela 2 in 

scenario 13) to 0.28 ft at site 1 (Manawainui in scenarios 10 

and 11) (table 3).

For the steady-state conditions simulated in scenarios 9 

through 13 (figs. 23–27), a net increase in withdrawal of 0.28 

Mgal/d relative to the 2005 base case causes a net decrease 

of 0.28 Mgal/d in coastal discharge. Local increases and 

Table 5. Summary of coastal-discharge changes simulated with the ground-water-flow model for the Island of Molokai, Hawaii.

[Maximum changes are within an individual model element. Model elements are square areas 1,640 feet on a side. gal/d, gallons per day; --, not 

applicable] 

Maximum absolute change

in coastal discharge (gal/d)

Maximum relative change

in coastal discharge (percent)

Number of model elements

with coastal-discharge change

greater than 5 percent

Scenario Increase Decrease Increase Decrease Increase Decrease

1 6,000 10,000 6 2 1 0

2 69,000 40,000 9 5 4 0

3 69,000 40,000 9 5 4 0

4 12,000 18,000 11 4 1 0

5 69,000 42,000 11 5 4 0

6 69,000 42,000 11 5 4 0

7 66,000 57,000 14 7 4 2

8 53,000 41,000 15 5 3 0

9 2,000 18,000 2 3 0 0

10 66,000 48,000 8 5 3 2

11 66,000 48,000 8 5 3 2

12 63,000 72,000 14 10 4 2

13 44,000 49,000 15 6 3 2

14 30,000 240,000 4 85 0 34

15 960,000 – – – 706 – – 68 – –

38 Numerical Simulation of the Hydrologic Effects of Redistributed and Additional Ground-Water Withdrawal, Molokai
Ilio Point

Laau

Point

00

Kalaupapa

Kualapuu

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

0801−03

(+0.35)

0449−01

(−0.08)

0457−01 A(−0.03)

A −0.27

A 0.01

−0.01

−0.01

−0.02

−0.02

−0.05

0.02

0.05 0.02 0.1

A

EXPLANATION

−0.27

A

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET

0801−03

(+0.35)

PROPOSED WITHDRAWAL SITE AND SIMULATED WATER-LEVEL CHANGE, IN FEETEXISTING WELL AND WELL NUMBER—  Value in parentheses is simulated water-level change, in feet

+0.01+0.02+0.05+0.1

−0.01−0.02−0.05

 1,000 < Q ≤ 5,000

Scenario 9

A

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000−30,000 ≤ Q < −15,000

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY

Figure 23. Scenario 9 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal dischargconditions) caused by decreasing withdrawal by 0.140 million gallons per day from the existing Kualapuu well (0801–03), increasing withdrawal by 0.0from the existing Kawela Shaft (well 0457–01), increasing withdrawal by 0.144 million gallons per day from the existing Ualapue Shaft (well 0449–01), amillion gallons per day from proposed site 1 (Manawainui).
Ilio Point

Laau

Point

00

Kalaupapa

Kualapuu

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

−35,000 gal/d (−2%)−48,000 gal/d (−2%)−35,000 gal/d (−4%)

+66,000 gal/d (8%)+57,000 gal/d (6%)

0449−01

(−0.08)

−0.01

−0.02 0457−01 (+0.17)

−0.28 −0.17

A

A

0801−03

(+0.35)

A

A

0.01 0.02

0.01

−0.01

−0.02 −0.05

−0.05

0.02 0.05 0.1

A

EXPLANATION

−0.28

A

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET

0801−03

(+0.35)

PROPOSED WITHDRAWAL SITE AND SIMULATED WATER-LEVEL CHANGE, IN FEETEXISTING WELL AND WELL NUMBER—  Value in parentheses is simulated water-level change, in feet

+0.01+0.02+0.05+0.1

−0.01−0.02−0.05

 1,000 < Q ≤ 5,000 5,000 < Q ≤ 15,000 15,000 < Q ≤ 30,00030,000 < Q 

Scenario 10

A

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000−30,000 ≤ Q < −15,000

Q < −30,000

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY (gal/d)

Discharge changes greater than 30,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge)

Figure 24. Scenario 10 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal discharconditions) caused by decreasing withdrawal by 0.140 million gallons per day from the existing Kualapuu well (0801–03), decreasing withdrawal to zerShaft (well 0457–01), increasing withdrawal by 0.144 million gallons per day from the existing Ualapue Shaft (well 0449–01), withdrawing 0.232 million gproposed site 1 (Manawainui), and withdrawing 0.392 million gallons per day from proposed site 2 (Kawela 1).
Ilio Point

Laau

Point

00

Kalaupapa

Kualapuu

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

+66,000 gal/d (8%)+57,000 gal/d (6%)

−0.28 −0.17

0457−01

(+0.17)

A

0801−03

(+0.35)

A

A

−0.13

0449−01

(+0.04) AA

A

0.01 0.02 0.05

−0.01

−0.01

−0.02

−0.02 −0.05

−0.05

0.1

A

EXPLANATION

−0.28

A

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET

0801−03

(+0.35)

PROPOSED WITHDRAWAL SITE AND SIMULATED WATER-LEVEL CHANGE, IN FEETEXISTING WELL AND WELL NUMBER—  Value in parentheses is simulated water-level change, in feet

+0.01+0.02+0.05+0.1

−0.01−0.02−0.05

 1,000 < Q ≤ 5,000 5,000 < Q ≤ 15,000 15,000 < Q ≤ 30,00030,000 < Q 

−35,000 gal/d (−2%)−48,000 gal/d (−2%)−35,000 gal/d (−4%)

Scenario 11

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000−30,000 ≤ Q < −15,000

Q < −30,000

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY (gal/d)

Discharge changes greater than 30,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge)

Figure 25. Scenario 11 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal discharconditions) caused by decreasing withdrawal by 0.140 million gallons per day from the existing Kualapuu well (0801–03), decreasing withdrawals to zeShaft (well 0457–01) and the existing Ualapue Shaft (well 0449–01), withdrawing 0.232 million gallons per day from proposed site 1 (Manawainui), withgallons per day from proposed site 2 (Kawela 1), and withdrawing 0.378 million gallons per day from proposed site 5 (Ualapue).
Ilio Point

Laau

Point

00

Kalaupapa

Kualapuu

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

+63,000 gal/d (8%)+54,000 gal/d (5%)

−70,000 gal/d (−3%)−72,000 gal/d (−4%)−37,000 gal/d (−1%)−43,000 gal/d (−5%)−36,000 gal/d (−4%)

−0.13

0449−01

(+0.04) AA

−0.01

−0.01 −0.02 −0.05

−0.02

0.01

0.02 0.05 0.1 0.2

0457−01

(+0.16) A

A

0801−03

(+1.09)

−0.24

A

−0.19

−0.16

A

A

A

EXPLANATION

−0.24

A

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET

0801−03

(+1.09)

PROPOSED WITHDRAWAL SITE AND SIMULATED WATER-LEVEL CHANGE, IN FEETEXISTING WELL AND WELL NUMBER—  Value in parentheses is simulated water-level change, in feet

+0.01+0.02+0.05+0.1+0.2+0.5

−0.01−0.02−0.05

 1,000 < Q ≤ 5,000 5,000 < Q ≤ 15,000 15,000 < Q ≤ 30,00030,000 < Q 

Scenario 12

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000−30,000 ≤ Q < −15,000

Q < −30,000

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY (gal/d)

Discharge changes greater than 30,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge)

Figure 26. Scenario 12 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal discharconditions) caused by decreasing withdrawal by 0.342 million gallons per day from the existing Kualapuu well (0801–03), decreasing withdrawals to zeShaft (well 0457–01) and the existing Ualapue Shaft (well 0449–01), withdrawing 0.232 million gallons per day from proposed site 1 (Manawainui), withgallons per day from proposed site 2 (Kawela 1), withdrawing 0.292 million gallons per day from proposed site 3 (Kamiloloa), and withdrawing 0.378 miproposed site 5 (Ualapue).
Ilio Point

Laau

Point

00

Kalaupapa

Kualapuu

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

+43,000 gal/d (5%)+44,000 gal/d (4%)

−49,000 gal/d (−2%)−32,000 gal/d (−3%)−39,000 gal/d (−4%)−42,000 gal/d (−2%) −43,000 gal/d (−1%)

−0.13

0449−01

(+0.04) A

0457−01

(+0.15)

A

0801−03

(+1.10)

−0.22

A

−0.18

A −0.12A

A A

A

EXPLANATION

−0.22

A

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET

0801−03

(+1.10)

PROPOSED WITHDRAWAL SITE AND SIMULATED WATER-LEVEL CHANGE, IN FEETEXISTING WELL AND WELL NUMBER—  Value in parentheses is simulated water-level change, in feet

+0.01+0.02+0.05+0.1+0.2+0.5

−0.01−0.02−0.05

 1,000 < Q ≤ 5,000 5,000 < Q ≤ 15,000 15,000 < Q ≤ 30,00030,000 < Q 

−0.01

−0.01

−0.02 −0.05 −0.02

0.01

0.02 0.05 0.1 0.2

Scenario 13

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000−30,000 ≤ Q < −15,000

Q < −30,000

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY (gal/d)

Discharge changes greater than 30,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge)

Figure 27. Scenario 13 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal discharconditions) caused by decreasing withdrawal by 0.342 million gallons per day from the existing Kualapuu well (0801–03), decreasing withdrawals to zeShaft (well 0457–01) and the existing Ualapue Shaft (well 0449–01), withdrawing 0.232 million gallons per day from proposed site 1 (Manawainui), withgallons per day from proposed site 2 (Kawela 1), withdrawing 0.292 million gallons per day from proposed site 4 (Kawela 2), and withdrawing 0.378 milproposed site 5 (Ualapue).
decreases in coastal discharge are simulated in these five 

scenarios, although the sum of the decreases exceeds the sum 

of the increases by 0.28 Mgal/d. Reducing withdrawal from 

well 0801–03 by 0.140 Mgal/d (scenarios 9–11) or 0.432 

Mgal/d (scenarios 12–13) causes simulated coastal discharge 

to increase along both the north and south coasts (figs. 23–27). 

Shutting off the Kawela Shaft and withdrawing 0.392 Mgal/d 

from site 2 (scenarios 10–13) causes coastal discharge immediately downgradient from Kawela Shaft to increase by as 

much 66,000 gal/d in model elements (scenarios 10, 11, figs. 

24–25). However, shutting off the Ualapue Shaft and withdrawing 0.378 Mgal/d from site 5 (scenarios 11–13, figs. 25–

27) does not result in an increase in coastal discharge immediately downgradient from the shaft. In scenarios 9 through 13, 

reductions in coastal discharge in model elements generally 

are less than 5 percent (table 5), and maximum reductions in 

coastal discharge in model elements range from 18,000 gal/d 

(scenario 9, fig. 23) to 72,000 gal/d (scenario 12, fig. 26).

Scenario 14—the DHHL Reservation

Scenario 14 is similar to scenario 11 with the addition 

of the 2.905-Mgal/d withdrawal from the DHHL reservation 

equally distributed among three arbitrary withdrawal sites in 

the Kualapuu area (fig. 28). In scenario 14, (1) simulated water 

levels at the three arbitrary withdrawal sites in the Kualapuu 

area are 3.64 to 3.99 ft lower than in the base case, (2) the 

simulated water level at well 0801–03 is 1.89 ft lower than in 

the base case and 1.54 (1.89 – 0.35) ft lower than in scenario 

11, and (3) simulated water levels at proposed withdrawal 

sites 1 and 2 are 1.11 and 0.30 ft lower than in the base case, 

respectively, and 0.83 and 0.25 ft lower than in scenario 11. In 

comparison, simulated water levels in scenarios 1 through 13 

decline less than 0.5 ft relative to the base case.

Total withdrawal in scenario 14 is 3.185 Mgal/d greater 

than in the base case. Thus, simulated steady-state coastal 

discharge in scenario 14 is 3.185 Mgal/d less than in the base 

case. In scenario 14, coastal discharge increases only in the 

area immediately downgradient from the Kawela Shaft (by as 

much as 30,000 gal/d in one model element; fig. 28). Coastal 

discharge decreases along both the north and south coasts. 

South of the Kualapuu area, between Umipaa and Kamiloloa 

(fig. 1), the reduction of coastal discharge in several model 

elements is greater than 200,000 gal/d (fig. 28). The simulated reduction of coastal discharge in model elements is less 

than 75,000 gal/d in scenarios 1 through 13. Comparison of 

scenarios 11 and 14 indicates that the 2.905-Mgal/d withdrawal from the DHHL reservation in the Kualapuu area at the 

three selected sites has little effect on water levels and coastal 

discharge east of Mapulehu.

Scenario 15—Natural Conditions (Zero 

Withdrawals)

In scenario 15, all withdrawals were set to zero, causing 

water levels and coastal discharge to increase over much of the 

central and eastern parts of the island relative to base-case conditions (fig. 29). Eliminating all withdrawal causes regional 

increases in water levels and coastal discharge to natural, 

predevelopment conditions. Water levels and coastal discharge 

increase along the south coast from Palaau eastward to Halawa 

(figs. 1, 29). Water levels and coastal discharge increase along 

the north coast from Moomomi eastward to Kalaupapa (fig. 

29). Simulated discharge to streams in the dike complex of 

East Molokai Volcano also increases in response to eliminating withdrawals from wells 0855–01, 0855–02, and 0855–03 

and the MIS Tunnel (fig. 29), which are located in the dike 

complex of East Molokai Volcano near Waikolu Stream.

Model Limitations

The ground-water-flow model of Molokai used in this 

study has several limitations. The number of monitor wells is 

insufficient to define the spatial distribution of water levels in 

inland areas in the southeastern part of the island, in the western part of the island, and in the dike complex in the northeastern part of the island. Thus, the distribution of simulated water 

levels is unverified in some places. Furthermore, the thickness 

of the freshwater lens is poorly known in most parts of the 

island, including areas of proposed additional ground-water 

withdrawal.

Because of a lack of sufficient water-level data used to 

constrain the simulations, the model used in this study is not 

unique—that is, different distributions of hydraulic conductivity could be used to construct a model that produces equally 

acceptable simulated water levels. The model used in this 

study can be refined, and the ground-water-flow system can be 

better represented, as more data become available to constrain 

the model.

Because the ground-water-flow model contains only a 

single layer, vertical hydraulic gradients cannot be simulated, 

and the simulated drawdown caused by additional withdrawal 

underestimates the actual drawdown near partially penetrating wells. In addition, the model should not be viewed as a 

quantitatively precise predictive tool because of the uncertainty in the hydraulic-conductivity distribution. The model is, 

nevertheless, the best available tool for analyzing the possible 

regional hydrologic effects of ground-water withdrawals on 

Molokai under steady-state conditions. Transient hydrologic 

effects of withdrawals were not considered in this study.

The AQUIFEM–SALT model simulates a sharp interface between freshwater and saltwater. Simulated freshwater 

thickness from AQUIFEM–SALT overestimates the actual 

freshwater thickness. In reality, freshwater is separated from 

underlying saltwater by a freshwater-saltwater transition zone, 

44 Numerical Simulation of the Hydrologic Effects of Redistributed and Additional Ground-Water Withdrawal, Molokai
Ilio Point

Laau

Point

00

Kalaupapa

Kualapuu

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

−1.11

−3.98

−3.64

−3.99

−0.30

0457−01

(+0.12)

A

0801−03

(−1.89)

A

A

−0.13

0449−01

(+0.04)

AA

A

AAA

A

EXPLANATION

−1.11

A

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET

0801−03

(-1.89)

PROPOSED WITHDRAWAL SITE AND SIMULATED WATER-LEVEL CHANGE, IN FEETEXISTING WELL AND WELL NUMBER—  Value in parentheses is simulated water-level change, in feet

−0.2−0.5−1−2

 5,000 < Q ≤ 15,000 15,000 < Q ≤ 30,000

−0.01−0.02−0.05−0.1

−0.05

−0.02

−0.01

−0.1

−0.2

−0.5−1 −2

−1

−0.5

−0.2

−0.1

−0.05

−0.02 −0.01

−0.02 −230,000 gal/d (−18%)

−240,000 gal/d (−18%)−230,000 gal/d (−16%)−230,000 gal/d (−14%)−220,000 gal/d (−10%)

Scenario 14

Discharge reductions greater than 200,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge)

−5,000 ≤ Q < −1,000

−15,000 ≤ Q < −5,000−30,000 ≤ Q < −15,000

−200,000 ≤ Q < −30,000

Q < −200,000

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY (gal/d)

Figure 28. Scenario 14 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal discharconditions) caused by decreasing withdrawal by 0.140 million gallons per day from the existing Kualapuu well (0801–03), decreasing withdrawals to zeShaft (well 0457–01) and the existing Ualapue Shaft (well 0449–01), withdrawing 0.232 million gallons per day from proposed site 1 (Manawainui), withgallons per day from proposed site 2 (Kawela 1), withdrawing 0.378 million gallons per day from proposed site 5 (Ualapue), and withdrawing 0.968 millieach of three hypothetical wells in the Kualapuu area.
Ilio Point

Laau

Point

00

Kalaupapa

Kualapuu

Mapulehu

!

!

157°05'

157°15'

156°55'

156°50'

157°10'

21°10'

157°

Base modified from U.S. Geological Surveydigital data, scale 1:24,000, 1983, Albers equal-area projection, standard parallels 21°04'50" and 

21°12'10", central meridian 157°00'45"

KalaupapaPeninsula

EXPLANATION

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET

WITHDRAWAL SITE SIMULATED IN THE  2005 BASE CASEWITHDRAWAL SITE WITH 2005 WATER-USE PERMIT NOT SIMULATED IN THE 2005 BASE CASE

151050

0.010.050.10.5

0.5

0.01

0.01 0.05

0.1

0.05 0.05

0.1

0.5

1

510

50

0.1

1

H

H

340,000 gal/d (350%)240,000 gal/d (390%)740,000 gal/d (710%)

240,000 gal/d (32%)380,000 gal/d (30%)

960,000 gal/d (400%)

250,000 gal/d (19%)370,000 gal/d (45%)

240,000 gal/d (67%)

210,000 gal/d (13%)220,000 gal/d (16%)230,000 gal/d (18%)220,000 gal/d (21%)

 1,000 < Q ≤ 5,000 5,000 < Q ≤ 15,000 15,000 < Q ≤ 30,000 30,000 < Q ≤ 200,000 200,000 < Q

H

H

H

H

H

H

H

H H

HH

HHH

H

H

H

H

H HH

HH

H

HH

H

H

H

H

H

H

HH HH

HHH H

H

H

H

H H

H

H

H

HH

0759−01

H H

Scenario 15

CHANGE IN SIMULATED COASTAL 

DISCHARGE, Q, IN GALLONS PER DAY (gal/d)

Discharge reductions greater than 200,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge)

Figure 29. Scenario 15 of ground-water-flow model for the Island of Molokai, Hawaii, showing simulated changes in water level and coastal discharconditions) caused by setting all withdrawals to zero.
which can be represented by using a model capable of simulating density-dependent ground-water flow and transport.

The ground-water-flow model simulates the regional 

effects of additional withdrawal on coastal discharge. The 

actual reduction in coastal discharge on a local scale may not 

be accurately represented by the model because of the level of 

spatial discretization and because local-scale heterogeneities in 

the hydraulic characteristics of the rocks are not represented.

Summary

Because of the increasing demand for water associated 

with a growing population, projected increases in demand 

over the next few decades, and the increasing salinity of water 

pumped from some existing wells, the DWS is currently 

(2006) considering drilling additional wells to replace or 

supplement existing wells on Molokai. Redistributed and additional ground-water withdrawals would affect water levels, 

might affect the salinity of water pumped from existing wells, 

and would affect the discharge of ground water to the nearshore environment. In response to concerns over the possible 

effects of ground-water withdrawals on Molokai, the USGS 

undertook this investigation, in cooperation with the DWS, to 

quantify the hydrologic effects of ground-water withdrawal 

from selected sites on water levels and coastal discharge. An 

existing numerical ground-water-flow model was used to 

estimate water-level and coastal-discharge changes caused by 

redistributed and additional ground-water withdrawals in the 

area between Kualapuu and Ualapue.

The model by Oki (1997) was used in this study to 

estimate the steady-state hydrologic effects of redistributed 

and additional ground-water withdrawals. A base case defined 

by 2005 mean annual withdrawal rates from wells 0449–01 

(Ualapue Shaft), 0457–01 (Kawela Shaft), and 0801–03 

(Kualapuu Mauka), May 2005 permitted withdrawal rates 

from other wells (excluding Waiola No. 1, Puu O Hoku No. 1, 

and the DHHL reservation of 2.905 Mgal/d), and the 1.822-

Mgal/d withdrawal from the MIS Tunnel was used to calculate 

water-level and coastal-discharge changes caused by redistributed and additional ground-water withdrawals. The 2005 

base-case withdrawal rates range from 0.001 to 1.822 Mgal/d 

and total 9.164 Mgal/d. Total withdrawal represented in the 

base case is 5 percent of island recharge. The hydraulic characteristics and long-term average recharge distribution (187 

Mgal/d) used in the original numerical model were used for all 

the simulations in this study.

A total of 15 scenarios were tested. Results of the scenarios of redistributed and additional ground-water withdrawals indicate that (1) redistribution of ground-water withdrawals causes a corresponding redistribution of water levels and 

coastal discharge; (2) water levels rise and coastal discharge 

increases near sites of reduced withdrawal, whereas water 

levels decline and coastal discharge decreases near sites of 

increased withdrawal; (3) the magnitude and areal extent of 

hydrologic changes caused by redistributed ground-water 

withdrawals increase with larger withdrawal changes; (4) 

simulated hydrologic changes are greatest near and downgradient from withdrawal sites and decrease with distance 

elsewhere; (5) simulated water-level declines are less than 0.5 

ft (for scenarios in which the DHHL reservation is omitted); 

(6) simulated coastal-discharge reductions generally are less 

than 30,000 gal/d (and everywhere less than 75,000 gal/d) 

within discrete 1,640- by 1,640-ft-square areas (for scenarios 

in which the DHHL reservation is omitted), generally representing less than 5 percent change; (7) the low-permeability 

dike complex of East Molokai Volcano impedes the spread of 

water-level changes to perennial streams in the northeastern 

part of the island, and discharge to these streams in the dike 

complex therefore is unaffected by proposed withdrawals; 

and (8) discharge to some fishponds and springs increases 

in response to decreased withdrawal at upgradient sites, and 

discharge to other fishponds and springs decreases in response 

to increased withdrawal. Simulated withdrawal of the DHHL 

reservation (2.905 Mgal/d) causes water levels in the Kualapuu 

area to decline by almost 4 ft. Eliminating all withdrawal 

causes regional increases in water levels and coastal discharge 

to natural, predevelopment levels. In addition, eliminating 

withdrawals from existing wells and the MIS Tunnel in the 

dike complex increases ground-water discharge to streams in 

the northeastern part of the island.

The ground-water-flow model of Molokai used in this 

study has several limitations. Because of insufficient information on water levels in many areas, including areas of proposed 

withdrawal, the distribution of simulated water levels cannot be verified in some places. The regional model may not 

accurately represent local-scale reductions in coastal discharge 

caused by withdrawals. A better representation of the groundwater-flow system using a three-dimensional, density-dependent model can be constructed as more data become available.

References Cited

Beeson, M.H., 1976, Petrology, mineralogy, and geochemistry 

of the East Molokai Volcanic Series, Hawaii: U.S. Geological Survey Professional Paper 961, 53 p.

Blumenstock, D.I., and Price, Saul, 1967, Climate of Hawaii, 

in Climates of the States, no. 60–51, Climatography of the 

United States: Washington, D.C., U.S. Department of Commerce.

Clague, D.A., Dao-gong, Chen, Murnane, Richard, Beeson, 

M.H., Lanphere, M.A., Dalrymple, G.B., Friesen, Walter, 

and Holcomb, R.T., 1982, Age and petrology of the Kalaupapa Basalt, Molokai, Hawaii: Pacific Science, v. 36, no. 4, 

p. 411–420.

References Cited 47
Cooper, H.H., Jr., Kohout, F.A., Henry, H.R., and Glover, R.E., 

1964, Sea water in coastal aquifers: U.S. Geological Survey 

Water-Supply Paper 1613–C, 84 p.

Domenico, P.A., and Schwartz, F.W., 1990, Physical and 

chemical hydrogeology: New York, John Wiley, 824 p.

Dorman, C.E., and Bourke, R.H., 1979, Precipitation over the 

Pacific Ocean, 30°S to 60°N: Monthly Weather Review, v. 

107, no. 7, p. 896–910.

Ekern, P.C., and Chang, J.-H., 1985, Pan evaporation; State 

of Hawai‘i, 1894–1983: Hawaii Department of Land and 

Natural Resources Report R74, 172 p.

Elliot, W.P., and Reed, R.K., 1984, A climatological estimate 

of precipitation for the world ocean: Journal of Applied 

Meteorology, v. 23, no. 3, p. 434–439.

Farber, J.M., 1997, Ancient Hawaiian fishponds; can restoration succeed on Moloka‘i?: Encinitas, Calif., Neptune 

House, 99 p.

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

Rainfall atlas of Hawai‘i: Hawaii Department of Land and 

Natural Resources Report R76, 267 p.

Hawaii Commission on Water Resource Management, 1990, 

Hawaii water plan, v. 1–2 of Water resources protection 

plan: Honolulu, variously paginated.

Hawaii Commission on Water Resource Management, 1997, 

Contested case hearing on water use, well construction and 

pump installation permit applications filed by Wai‘ola O 

Molokai, Inc. and Molokai Ranch, Limited: case CCH–

MO96–1, exhibit A–18, 1 p.

Hawaii Department of Business, Economic Development & 

Tourism, 2006, 2004 State of Hawaii data book: URL http://

www.hawaii.gov/dbedt/info/economic/databook/db2004/ 

[accessed May 16, 2006].

Hawaii Office of Planning, 2006, Hawaii statewide GIS program: URL http://www.hawaii.gov/dbedt/gis/fishponds.htm 

[accessed Apr. 5, 2006].

Juvik, S.O., and Juvik, J.O., 1998, Atlas of Hawai‘i (3d ed.): 

Honolulu, University of Hawaii Press, 333 p.

Langenheim, V.A.M., and Clague, D.A., 1987, The HawaiianEmperor volcanic chain, part II, stratigraphic framework of 

volcanic rocks of the Hawaiian Islands, chap. 1 of Decker, 

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

Hawaii: U.S. Geological Survey Professional Paper 1350, v. 

1, p. 55–84.

Lindgren, Waldemar, 1903, The water resources of Molokai, 

Hawaiian Islands: U.S. Geological Survey Water-Supply 

and Irrigation Paper 77, 62 p.

Lockwood, J.P., and Lipman, P.W., 1987, Holocene eruptive 

history of Mauna Loa Volcano, chap. 18 of Decker, R.W., 

Wright, T.L., and Stauffer, P.H., eds., Volcanism in Hawaii: 

U.S. Geological Survey Professional Paper 1350, v. 1, p. 

509–535.

MacCarthy, G.R., 1941, Geophysical studies on the island of 

Molokai, Territory of Hawaii: U.S. Department of the Interior Press Release 160579, October 3, 1941, 2 p.

Macdonald, G.A., 1956, The structure of Hawaiian volcanoes: 

Verhandelingen Van Het Koninklijk Nederlandsh Geologisch Mijnbouwkundig Genootschap, v. 16, p. 1–22.

Macdonald, G.A., Abbott, A.T., and Peterson, F.L., 1983, Volcanoes in the sea; the geology of Hawaii (2d ed.): Honolulu, 

University of Hawaii Press, 517 p.

Malahoff, Alexander, and Woollard, G.P., 1966, Magnetic surveys over the Hawaiian Islands and their geologic implications: Pacific Science, v. 20, no. 3, p. 265–311.

Mathewson, C.C., 1970, Submarine canyons and the shelf 

along the north coast of Molokai Island, Hawaiian Ridge: 

Pacific Science, v. 24, no. 2, p. 235–244.

McDougall, Ian, 1964, Potassium-argon ages from lavas of the 

Hawaiian islands: Geological Society of America Bulletin, 

v. 75, no. 2, p. 107–128.

Mink, J.F., and Lau, L.S., 1992, Aquifer identification and 

classification for Moloka‘i; groundwater protection strategy for Hawaii: University of Hawaii, Water Resources 

Research Center Technical Report 187, 31 p.

Moore, J.G., and Krivoy, H.L., 1965, A reconnaissance gravity 

survey of the island of Molokai, Hawaii: Pacific Science, v. 

19, no. 3, p. 343–345.

National Climatic Data Center, 2006, Annual climatological 

summary: National Oceanic and Atmospheric Administration, URL http://hurricane.ncdc.noaa.gov/ancsum/ACS 

[accessed Apr. 12, 2006].

Naughton, J.J., Macdonald, G.A., and Greenberg, V.A., 1980, 

Some additional potassium-argon ages of Hawaiian rocks; 

the Maui Volcanic Complex of Molokai, Maui, Lanai 

and Kahoolawe: Journal of Volcanology and Geothermal 

Research, v. 7, no. 3–4, p. 339–355.

Oki, D.S., 1997, Geohydrology and numerical simulation of 

the ground-water flow system of Molokai, Hawaii: U.S. 

Geological Survey Water-Resources Investigations Report 

97–4176, 62 p.

Oki, D.S., 1998, Geohydrology of the central Oahu, Hawaii, 

ground-water flow system and numerical simulation of 

the effects of additional pumping: U.S. Geological Survey 

Water-Resources Investigations Report 97–4276, 132 p.

48 Numerical Simulation of the Hydrologic Effects of Redistributed and Additional Ground-Water Withdrawal, Molokai
Oki, D.S., and Bauer, G.R., 2001, Drilling, construction, 

water-level, and water-quality information for the Kualapuu 

deep monitor well 4–0800–01, Molokai, Hawaii: U.S. Geological Survey Open-File Report 01–350, 19 p.

Paillet, F.L., Williams, J.H., Oki, D.S., and Knutson, K.D., 

2002, Comparison of formation and fluid-column logs in a 

heterogeneous basalt aquifer: Ground Water, v. 40, no. 6, p. 

577–585.

Sanderson, Marie, ed., 1993, Prevailing trade winds; weather 

and climate in Hawai‘i: Honolulu, University of Hawaii 

Press, 126 p.

Seckel, G.R., 1962, Atlas of the oceanographic climate of the 

Hawaiian Islands region: U.S. Fish and Wildlife Service 

Fishery Bulletin 193, v. 61, p. 373–427.

Shade, P.J., 1997, Water budget for the island of Molokai, 

Hawaii: U.S. Geological Survey Water-Resources Investigations Report 97–4155, 20 p.

Souza, W.R., and Voss, C.I., 1987, Analysis of an anisotropic coastal aquifer system using variable-density flow and 

solute transport simulation: Journal of Hydrology, v. 92, p. 

17–41.

Stearns, H.T., 1985, Geology of the State of Hawaii (2d ed.): 

Palo Alto, Calif., Pacific Books, 335 p.

Stearns, H.T., and Macdonald, G.A., 1947, Geology and 

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

Hawaii Division of Hydrography Bulletin 11, 113 p.

Stearns, H.T., and Vaksvik, K.N., 1935, Geology and groundwater resources of the island of Oahu, Hawaii: Hawaii Division of Hydrography Bulletin 1, 479 p.

Swain, L.A., 1973, Chemical quality of ground water in 

Hawaii: Hawaii Department of Land and Natural Resources 

Report R48, 54 p.

Takasaki, K.J., 1986, Results of exploratory drilling for water 

in Waihanau Valley, Molokai, Hawaii: U.S. Geological Survey Water-Resources Investigations Report 85–4332, 26 p.

Takasaki, K.J., and Mink, J.F., 1985, Evaluation of major dikeimpounded ground-water reservoirs, island of Oahu: U.S. 

Geological Survey Water-Supply Paper 2217, 77 p.

Voss, C.I., 1984, AQUIFEM–SALT; a finite-element model for 

aquifers containing a seawater interface: U.S. Geological 

Survey Water-Resources Investigations Report 84–4263, 

37 p.

Wentworth, C.K., 1939, The specific gravity of sea water 

and the Ghyben-Herzberg ratio at Honolulu: University of 

Hawaii Bulletin, v. 18, no. 8, 24 p.

Wentworth, C.K., and Macdonald, G.A., 1953, Structures and 

forms of basaltic rocks in Hawaii: U.S. Geological Survey 

Bulletin 994, 98 p.

References Cited 49