U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007–5128

Prepared in cooperation with the U.S. Army Corps of Engineers and 

County of Maui Department of Public Works and Environmental Management

Effects of Ground-Water Withdrawal on Kaunakakai 

Stream Environmental Restoration Plan, Moloka‘i, 

Hawai‘i
COVER

The proposed habitat-restoration site near the mouth of Kaunakakai Stream will provide habitat 

for the native Hawaiian Stilt (Himantopus mexicanus knudseni). The U.S. Army Corps of 

Engineers is planning to create about 2.75 acres of wetland habitat in the area shown by 

removing sediment and lowering the streambed. 
Effects of Ground-Water 

Withdrawal on Kaunakakai Stream 

Environmental Restoration Plan, 

Moloka‘i, Hawai‘i

By Delwyn S. Oki

In Cooperation with the U.S. Army Corps of Engineers and 

County of Maui Department of Public Works and 

Environmental Management

Scientific Investigations Report 2007–5128

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

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

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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., 2007, Effects of ground-water withdrawal on Kaunakakai Stream environmental 

restoration plan, Moloka‘i, Hawai‘i: U.S. Geological Survey Scientific Investigations Report 

2007—5128, 25 p.
iii

Contents

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

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

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

Setting ............................................................................................................................2

Regional Hydrogeologic Setting..............................................................................2

Kaunakakai Hydrogeologic Setting .........................................................................5

Withdrawals.............................................................................................................7

Numerical Simulation of Additional Ground-Water Withdrawal.....................................11

Model Description..................................................................................................11

Model Application..................................................................................................11

Description of Model Scenarios .....................................................................12

Model Results........................................................................................................12

Scenario 1......................................................................................................13

Scenario 2......................................................................................................16

Scenario 3......................................................................................................16

Scenario 4......................................................................................................16

Scenario 5......................................................................................................19

Scenario 6......................................................................................................19

Effects on Kaunakakai Habitat-Restoration Site ............................................19

Model Limitations..........................................................................................................23

Summary ......................................................................................................................23

References Cited..........................................................................................................24

Figures

1. Map of Island of Moloka‘i, Hawai‘i, showing proposed Kaunakakai

habitat-restoration area and selected geographic features...............................3

2. Aerial photograph showing proposed Kaunakakai habitat-restoration area

near the mouth of Kaunakakai Stream, Island of Moloka‘i, Hawai‘i..................4

3. Map showing average measured ground-water levels for the period

1938–97, ground-water levels from resistivity measurements, and altitude

of top of saline water body determined from time-domain electromagnetic

survey, Island of Moloka‘i, Hawai‘i ....................................................................6

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

Moloka‘i, Hawai‘i ...............................................................................................8

5. Map showing aquifer systems designated by the State of Hawai‘i

Commission on Water Resource Management and locations of selected

wells on the Island of Moloka‘i, Hawai‘i.............................................................9

6. Scenario 1 of ground-water-flow model for the Island of 

Moloka‘i, Hawai‘i .............................................................................................14

7. Scenario 2 of ground-water-flow model for the Island of 

Moloka‘i, Hawai‘i .............................................................................................17
iv

8. Scenario 3 of ground-water-flow model for the Island of 

Moloka‘i, Hawai‘i .............................................................................................18

9. Scenario 4 of ground-water-flow model for the Island of 

Moloka‘i, Hawai‘i .............................................................................................20

10. Scenario 5 of ground-water-flow model for the Island of 

Moloka‘i, Hawai‘i .............................................................................................21

11. Scenario 6 of ground-water-flow model for the Island of 

Moloka‘i, Hawai‘i .............................................................................................22

Tables

1. May 2007 ground-water-use permits for the Island of Moloka‘i, Hawai‘i.........10

2. Summary of withdrawal scenarios simulated with the ground-water-flow

model for the Island of Moloka‘i, Hawai‘i.........................................................13

3. Summary of changes in steady-state ground-water level simulated with the

ground-water-flow model for the Island of Moloka‘i, Hawai‘i ...........................15

4. Summary of changes in steady-state coastal discharge simulated with the

ground-water-flow model for the Island of Moloka‘i, Hawai‘i ...........................15
Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2

)

square foot (ft2

) 0.09290 square meter (m2)

square mile (mi2

) 2.590 square kilometer (km2) 

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

cubic foot per second (ft3

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

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)

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.

Specific conductance 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).
This page left intentionally blank
Abstract

The U.S. Army Corps of Engineers, in coop- eration with the County of Maui Department of 

Public Works and Environmental Management, has 

proposed to construct 2.75 acres of shallow ponds 

and mudflats near the mouth of Kaunakakai Stream, 

Moloka‘i, Hawai‘i to restore habitat for the endan- gered native Hawaiian Stilt. Kaunakakai Stream is 

ephemeral upstream from the habitat-restoration 

site. Where the pond and wetland bottoms are below 

the water table, the ponds and wetland will be 

sustained by ground-water discharge during dryweather conditions. Because ground water is the 

main source of water for the proposed ponds and 

wetland, a reduction of ground-water level and dis- charge near the mouth of Kaunakakai Stream will 

have an effect on the availability of habitat.

In response to concerns about the possible 

effects of ground-water withdrawal on the habitatrestoration project near the mouth of Kaunakakai 

Stream, the U.S. Geological Survey undertook the 

present investigation to estimate, using an existing 

numerical ground-water-flow model, the changes in 

ground-water level and coastal discharge caused by 

redistributed and additional ground-water withdraw- als. Steady-state water-level and coastal-discharge 

changes, relative to recent base-case conditions, 

were estimated for each of six withdrawal scenarios. 

Redistributed and additional ground-water with- drawals in the six scenarios were simulated from 

selected sites in the area between Kualapu‘u and 

‘Ualapu‘e. For the scenarios tested, model results 

indicate that withdrawals from existing and pro- posed wells cause a water-level decline of about 

0.1 feet in the vicinity of the Kaunakakai habitatrestoration site. In addition, model results indicate 

a reduction of ground-water discharge, ranging 

from 98,000 to 170,000 gallons per day, to the 

model element containing the habitat-restoration 

site, although the existing spatial discretization 

in the model is too coarse to reliably estimate the 

reduction of ground-water discharge to the stream. 

Reduction in discharge to the habitat-restoration site 

is likely less than the total indicated by the model 

element because the site covers a small fraction 

(about 5 percent) of the area of a model element.

Ground-water-level declines near the habitatrestoration site will reduce (1) the available wetted 

habitat area by an amount that is dependent on the 

bottom slope of the ponds near their edges, (2) the 

maximum water depth of the ponds by about 0.1 

feet, and (3) the average water depth by an amount 

that is dependent on the bottom shape of the ponds. 

The salinity of ground water discharging into the 

wetland area likely will increase by an unknown 

amount in response to increased withdrawals upgradient from the site. A numerical model capable of 

simulating density-dependent flow and transport 

is needed to evaluate the effects of withdrawal on 

salinity in the area.

Introduction

The U.S. Army Corps of Engineers (USACE), 

Honolulu Engineering District, in cooperation with 

the County of Maui Department of Public Works 

and Environmental Management (DPWEM), has 

proposed improvements to the existing Kaunakakai 

Stream Flood Control Project near the mouth of 

Kaunakakai Stream, Moloka‘i, Hawai‘i (fig. 1) to 

restore habitat for the endangered native Hawaiian Stilt (Himantopus mexicanus knudseni). 

(Kaunakakai Stream also is commonly referred to 

as Kaunakakai Gulch, but for the purposes of this 

report it will be referred to as Kaunakakai Stream.) 

The Kaunakakai Stream Flood Control Project 

was completed in 1950 and consists of an enlarged 

Effects of Ground-Water Withdrawal on 

Kaunakakai Stream Environmental Restoration 

Plan, Moloka‘i, Hawai‘i

By Delwyn S. Oki
stream channel with rock-lined levees on the stream 

banks. About 2.75 acres of wetland habitat, including shallow ponds and mudflats, would be created 

within the flood-control project limits by removing 

sediment and lowering the streambed (U.S. Army 

Corps of Engineers, 2004). Under the proposal, 

about 9,800 cubic yards of material would be excavated to create three ponds: pond A would extend 

upstream from the existing highway (route 460) 

bridge and would be excavated to an altitude of 1 

ft below mean sea level; pond B would be adjacent 

to and extend upstream from pond A and would 

be excavated to mean sea level; pond C would 

extend upstream from pond B and be excavated to 

1 ft above mean sea level (fig. 2). The study area 

is within Kaunakakai Stream channel and extends 

about 1,000 ft upstream of the highway bridge, 

which is about 1,500 ft inland from the coast. 

Where the pond and wetland bottoms are below 

the water table, the ponds and wetland will be 

sustained by ground-water discharge during dryweather conditions. Because ocean tides indirectly 

affect ground-water levels, tides also will affect 

water levels in the ponds and wetland. Upstream 

of the lowland coastal area, Kaunakakai Stream 

is ephemeral. Because ground water is the main 

source of water for the proposed ponds and wetland, 

a reduction of ground-water level and discharge 

near the mouth of Kaunakakai Stream will have 

an effect on the efficacy of the habitat-restoration 

project. Redistributed and additional ground-water 

withdrawals will affect ground-water levels, pond 

water levels, and discharge of fresh and brackish 

water to the near-shore environment. 

Purpose and Scope

In response to concerns about the possible 

effects of ground-water withdrawal on the habitatrestoration project near the mouth of Kaunakakai 

Stream, the U.S. Geological Survey (USGS) undertook the present investigation, in cooperation with 

the USACE and DPWEM, 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 changes in 

water level and coastal discharge caused by redistributed and additional ground-water withdrawals 

in the area between Kualapu‘u and ‘Ualapu‘e on 

Moloka‘i. This report describes the results of model 

simulations that assess the hydrologic effects of 

redistributed or additional ground-water withdrawals relative to 2006 average or May 2007 permitted 

withdrawal rates. No new data were collected as 

part of this study. 

Setting

The Island of Moloka‘i, 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 Moloka‘i Volcano, which rises to an altitude 

of 1,381 ft, and the younger East Moloka‘i Volcano, 

which rises to an altitude of 4,961 ft. The town 

of Kaunakakai lies near the south coast of central 

Moloka‘i, about 0.25 mi east of Kaunakakai Stream, 

and on the south flank of East Moloka‘i Volcano 

(fig. 1). 

Regional Hydrogeologic Setting

The geologic setting of the island of Moloka‘i 

has been described in detail 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 Moloka‘i. 

The exposed rocks of East Moloka‘i Volcano are 

named the East Moloka‘i Volcanics and the Kalaupapa Volcanics (Langenheim and Clague, 1987). 

Kaunakakai Stream flows over the East Moloka‘i 

Volcanics, which is divided into two informal mem- bers—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 (approximately 

50–500 ft thick) veneer over the lower member 

(Stearns and Macdonald, 1947). The northeastern 

part of East Moloka‘i Volcano contains numerous 

intrusive volcanic dikes, which form a dike complex 

and reduce bulk permeability of the rocks in the 

area. The volcanic rocks of West Moloka‘i Volcano 

are known as the West Moloka‘i Volcanics (Langenheim and Clague, 1987) and are separated from 

the East Moloka‘i Volcanics by an erosional surface 

that forms a hydrologic confining unit over the West 

Moloka‘i Volcanics. 

Descriptions of the hydrologic setting and 

hydrologic data have been published previously 

(for example Lindgren, 1903; Stearns and Macdonald, 1947; Anthony, 1995; Oki, 1997, 2006; Oki 

and Bauer, 2001). Precipitation is the source of all 

freshwater on Moloka‘i. The windward (northeast) 

side of Moloka‘i is wettest, a pattern controlled by 

Effects of Ground-Water Withdrawal on Kaunakakai Stream, Moloka‘i, Hawai‘i 
Pelekunu

Bay

MoØomomi

KahiØu Point

KalaupapaPeninsula

Øìlio Point

LØau 

Point

16414200

16414000

South

Fk

North Fk

KakaØako

Gl

Kaunal

G

l

Kluape

Øelua

Gl

Manawainui

Gl

Kaunakakai Gl

East

Fk

Kawela Gl PunaØula

G

l 

Kamiloloa

Gl

W



w



Ø

a

i

Gl

M

na

l

o

Gl

Pphaku Gl

H

akina

Gl

O

n

opalani

Gl Wa ai

kne

G

l

Waiahewahewa

Gl

West

Fk

W

Kahawaiiki Str 

W 

ailau Str Pelekunu Str Wa oi hooka ol Str Waikolu Str WaiØaleØia Str

Waihnau

Str

Kawainui

Str

Kalaupapa

KalaØe

KualapuØu

Maunaloa

Kaunakakai Kamiloloa

Kamal

ØUalapuØe

ØUmipaØa PlØau Coconut

Grove

Kawela Mapulehu

00

2 4 MILES

2 4 KILOMETERS

157¡05'

157¡15'

156¡55' 156¡50'

157¡10'

21¡10'

157¡

21¡05'

EXPLANATION

MOLOKAØI IRRIGATION SYSTEM PIPELINEMOLOKAØI IRRIGATION SYSTEM TUNNELSTREAM-GAGING STATION AND NUMBERSPRINGÐModified from Stearns and Macdonald (1947)

Base modified from U.S. Geological Survey digital data, 1:24,000, 1983, Albers equal area projection, standard parallels 21¡04'50" and 21¡12'10", central meridian 157¡00'45", NAD83 datum. Relief from U.S. Geological Survey 10-meter digital elevation models.

16414000

22o20o

158o 1

160o

KauaØi

NiØihau

OØahu

Molok

LnaØi

KahoØolawe

HawaiØ

HAWA

LOCATION MAP

PACIFIC OCEAN

1,381 ft

4,961 ft

EAST MOLOKAØI VOLCANO

WEST MOLOKAØI VOLCANO

HOOLEHUA

PLAIN

KualapuØu

Reservoir

Approximate location of Kaunakakai 

habitat-restoration area

Figure 1. Map of Island of Moloka‘i, Hawai‘i, showing proposed Kaunakakai habitat-restoration area and selected geographic features

Gl, gulch; Fk, fork; Str, stream.
Pond A

Pond B

Pond C

157¡01'50" 157¡01'40" 157¡01'30" 157¡01'20" 157¡01'10" 

21¡05'10"21¡05'20"21¡05'30"21¡05'40"

0 500 1,000 FEET

Base modified from U.S. Department of Agriculture digital orthophoto quarter quadrangles, 2003, Universal TransverseMercator projection, zone 4, NAD83 datum.

Kaunakakai

Kaunakakai Stream

460

Figure 2. Aerial photograph showing proposed Kaunakakai habitat-restoration area near the mouth of Kaunakakai Stream, Island o(U.S. Army Corps of Engineers, 2004).
the orographic lifting of moisture-laden northeasterly trade winds along the windward slope of East 

Moloka‘i Volcano. West Moloka‘i Volcano is considerably drier because it does not extend upward 

into the cloud-forming zone at higher altitudes. 

Maximum mean annual rainfall is more than 150 

in. near the summit of East Moloka‘i Volcano in the 

northeastern part of the island (Giambelluca and 

others, 1986). Over West Moloka‘i 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. 

Rain that falls on the surface either (1) runs off, 

(2) evaporates or is transpired by vegetation, or (3) 

recharges the ground-water system. Total groundwater recharge on Moloka‘i was estimated from a 

monthly water budget to be 188.6 million gallons 

per day (Mgal/d), which represents an average 

of about 15 in/yr over the island (Shade, 1997). 

Ground-water recharge estimated by Shade (1997) 

varies spatially 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. 

Water that recharges the ground-water system 

flows from zones of higher to lower hydraulic head, 

as measured by ground-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 moun- tainous interior areas to coastal discharge areas. 

Measured water levels are available primar- ily in wells along the south coast and in the central 

plain (fig. 3). In the vicinity of Kualapu‘u, mea- sured 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 ‘Umipa‘a and Kawela 

and 4 to 5 ft above sea level between Kamalö and 

Püko‘o.

Available data are insufficient to develop a 

detailed contour map of water levels for the entire 

island. MacCarthy (1941) used electrical-resistivity 

measurements to determine the depth to saltwater, 

and then applied the Ghyben-Herzberg relation 

to estimate the altitude of the water table in the 

western part of the island (fig. 3). For hydrostatic 

conditions, and assuming a sharp interface between 

freshwater (specific gravity 1.000) and saltwater 

(specific gravity 1.025), the Ghyben-Herzberg relation predicts that every foot of freshwater above sea 

level must be balanced by 40 ft of freshwater below 

sea level. For dynamic conditions, the GhybenHerzberg 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. MacCarthy (1941) estimated that the 

water-table altitude in the western part of the island 

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.

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. Ground water on Moloka‘i 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 dikefree rocks; and (2) as dike-impounded water ten to 

hundreds of feet above sea level. 

Kaunakakai Hydrogeologic Setting

The Kaunakakai study area is located in the 

south-central coastal part of the island, where mean 

annual rainfall is less than 16 in. Near the inland 

reaches of Kaunakakai Stream, mean annual rainfall 

exceeds 120 in. (Giambelluca and others, 1986). 

Stearns and Macdonald (1947) observed small 

perched springs discharging from the upper member 

of the East Moloka‘i Volcanics in the north bank 

of the South Fork of Kaunakakai Stream, between 

altitudes of 2,450 and 3,150 ft, where the upper 

member overlies 3 to 5 ft of red ashy soil. Swamps 

upstream of the springs also may contribute flow to 

the South Fork of Kaunakakai Stream. During dry 

weather on October 9, 1945, total streamflow downstream of the springs was 0.12 ft3

/s; drainage from 

the swamps was 0.062 ft3/s and discharge from the 

springs was estimated to be 0.054 ft3/s (Stearns and 

Macdonald, 1947). On January 5, 1946, after three 

additional months of mostly dry weather, stream- flow downstream of the springs was estimated to 

be 0.019 ft3/s, all of which was attributed to the 

springs (Stearns and Macdonald, 1947). No springs 

have been mapped in the North Fork of Kaunakakai 

Stream. Discharge measurements are not available 

Setting
00

Kalaupapa

PlØau

ØUmipaØa

Kaunakakai

Kamal

P

ØUalapuØe

KualapuØu

KalaupapaPeninsula

Øìlio Point

LØau 

Point

157¡05'

157¡15'

156¡55' 156¡50'

157¡10'

21¡10'

157¡

21¡05'

Base modified from U.S. Geological Survey digital data, 1:24,000, 1983, Albers equal area projection, standard parallels 21¡04'50" and 21¡12'10", central meridian 157¡00'45", NAD83 datum. 

Mapulehu

Kawela

-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 DEPTH TO SALINE WATER BODY AS DETERMINED  BY TIME-DOMAIN ELECTROMAGNETIC SURVEY (HAWAIØI  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

0800Ð01

Figure 3. Map showing average measured ground-water levels for the period 1938–97, ground-water levels from resistivity measuremof top of saline water body determined from time-domain electromagnetic survey, Island of Moloka‘i, Hawai‘i (modified from Oki, 2006).
to characterize spring discharge for more recent 

conditions.

The North and South Forks of Kaunakakai 

Stream flow over the upper member of the East 

Moloka‘i Volcanics above altitudes of about 1,600 

and 3,000 ft, respectively. Below these altitudes, 

the North and South Forks flow over the more 

permeable rocks of the lower member of the East 

Moloka‘i Volcanics. Stearns and Macdonald (1947) 

indicated that several streams on the southern slope 

of East Moloka‘i Volcano are perennial in their 

upper reaches, but do not flow continuously to the 

coast because of seepage losses and evaporation. 

These streams generally are perennial where they 

flow over lavas of the upper member of the East 

Moloka‘i Volcanics and where water discharges 

from springs or drains swamps. Where streams flow 

over the more permeable lower member, surface 

water more readily may be lost to infiltration. The 

South Fork of Kaunakakai Stream was described as 

perennial above an altitude of 1,900 ft (Stearns and 

Macdonald, 1947). 

During water years 1951–98, mean discharge 

of Kaunakakai Stream near an altitude of 240 ft 

was 1.9 ft3

/s measured at USGS stream-gaging station 16414000 (Kaunakakai Gulch at Kaunakakai, 

Moloka‘i, Hawai‘i), downstream of the confluence 

of the North and South Forks. (Data from stream 

gaging-station 16414000 are available on the worldwide web at http://waterdata.usgs.gov/hi/nwis/

nwisman/?site_no=16414000&agency_cd=USGS.) 

Recorded daily mean discharge at gaging station 

16414000 was zero about 88 percent of the time 

during water years 1951–98, indicating that, at this 

site, Kaunakakai Stream probably flows only in 

response to rainfall. Farther downstream, recorded 

daily mean discharge at gaging station 16414200 

(Kaunakakai Gulch at 75 feet) was zero about 91 

percent of the time during water years 2004–6 

(http://waterdata.usgs.gov/hi/nwis/nwisman/?site_

no=16414200&agency_cd=USGS). No known 

diversions exist upstream from the gaging stations, 

although discharge from the Moloka‘i Irrigation 

System (MIS) Tunnel into Kaunakakai Stream 

sometimes may augment streamflow.

Near the mouth of Kaunakakai Stream, where 

habitat restoration is being proposed, Kaunakakai 

Stream is perennial where it is hydraulically connected to the ground-water system. Near the coast, 

the main ground-water-flow system consists of a 

freshwater-lens system (Gingerich and Oki, 2000) 

within dike-free rocks. In general, a freshwater-lens 

system includes a lens-shaped freshwater body, an 

intermediate transition zone of brackish water, and 

underlying saltwater (fig. 4). Within a freshwaterlens system, fresh ground water generally moves 

from inland areas to the coast. A saltwater circulation system exists beneath the freshwater lens 

(Cooper and others, 1964; Souza and Voss, 1987). 

Saltwater flows landward in the deeper parts of 

the aquifer, rises and mixes with seaward flowing 

freshwater forming a brackish-water transition zone, 

and then discharges to the ocean. The thicknesses 

of freshwater and the brackish-water transition zone 

are controlled by factors including aquifer permeability, recharge rate, ground-water-withdrawal 

rate, and extent of mixing between freshwater and 

underlying saltwater. The freshwater-lens system is 

recharged mainly by inflow from upgradient areas 

and also by direct infiltration of precipitation and 

irrigation water. Near the study area, discharge from 

the freshwater-lens system is by diffuse seepage 

near the coast, to springs, to Kaunakakai Stream, to 

the atmosphere by evapotranspiration, and to withdrawal wells.

In the study area, the freshwater-lens system 

exists in the dike-free volcanic rocks and sedimentary deposits near the coast. Alluvium overlies 

the volcanic rocks near the mouth of Kaunakakai 

Stream, where ground-water levels probably range 

from near sea level to about 2 ft above mean sea 

level (fig. 3). Both ground-water levels and stream 

stage are expected to be affected by ocean tides and 

longer-term variations in sea level. On the basis 

of water-quality information from nearby wells, 

the salinity of ground water near the mouth of 

Kaunakakai Stream is likely brackish because of 

mixing with saltwater from the ocean.

Withdrawals

In response to concerns about the water 

resources of Moloka‘i, the State of Hawai‘i 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 

Moloka‘i through a permitting process to protect the 

island’s water resources. The CWRM has divided 

the island into 16 management areas or aquifer 

systems (Hawai‘i Commission on Water Resource 

Management, 1990), primarily defined on the basis 

of geologic conditions and topographic divides 

(fig. 5) (Mink and Lau, 1992). Limits on groundwater withdrawals on the island currently are based 

on sustainable-yield estimates for each of the 16 

aquifer systems. As of May 2007, the CWRM had 

issued water-use permits authorizing a total of 8.077 

Mgal/d of ground-water withdrawals from wells and 

tunnels on the island (table 1), although reported 

withdrawals are less than this total. In addition to 

Setting
the 8.077 Mgal/d of water-use permits, the State 

of Hawai‘i Department of Hawaiian Home Lands 

(DHHL) has a reservation for 2.905 Mgal/d of 

ground water from the Kualapu‘u area (fig. 5; table 

1), and the MIS Tunnel develops ground water, 

estimated to be about 1.822 Mgal/d during 1992–96 

(Oki, 1997).

Most of the ground water withdrawn on 

Moloka‘i is from the Kualapu‘u area, the southeast 

coastal area, and the dike complex in the north- eastern part of the island. On the basis of complete 

monthly reports during 2006, the annual mean 

withdrawal from wells (excluding the MIS Tunnel) 

on Moloka‘i during 2006 was about 2.917 Mgal/d 

(computed from digital data supplied by Lenore 

Nakama, Hawai‘i Commission on Water Resource 

Management, written commun., 2007). This total is 

not representative of island-wide withdrawal during 

2006—incompletely reported monthly withdrawals 

from some wells and unreported withdrawals from 

other wells and tunnels would probably increase the 

total by several million gallons per day.

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

0801–03, 0901–01, and 0902–01, fig. 5) have been 

drilled in the Kualapu‘u 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 17 

(0901–01) has been used for domestic supply and 

irrigation in the western part of the island. During 

2006, mean withdrawal from Well 17 (0901–01) 

was 0.902 Mgal/d. Kualapu‘u wells 0801–01 

and 0801–02 (fig. 5) were completed in 1949 and 

1979, respectively, and well 0801–03 (Kualapu‘u 

Mauka) was drilled in 1987. During 2006, annual 

mean withdrawals from wells 0801–01, 0801–02, 

and 0801–03 were 0.213, 0.465, and 0.712 Mgal/d, 

respectively. 

FRESHWATER

BRACKISH WATER

SALTWATER

WATER TABLE

VOLCANIC ROCKS

SEDIMENTARY DEPOSITS

GENERAL DIRECTION OF

 GROUND-WATER FLOW

EXPLANATIONBend 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

MolokaØi

Figure 4. Schematic cross section of the ground-water-flow system on the Island of 

Moloka‘i, Hawai‘i (modified from Oki, 2006).

Effects of Ground-Water Withdrawal on Kaunakakai Stream, Moloka‘i, Hawai‘i 
00

Kalaupapa

PlØau

ØUmipaØa

Kaunakakai

Kamal

P

ØUalapuØe

KualapuØu

KalaupapaPeninsula

Øìlio Point

LØau 

Point

157¡05'

157¡15'

156¡55' 156¡50'

157¡10'

21¡10'

157¡

21¡05'

Base modified from U.S. Geological Survey digital data, 1:24,000, 1983, Albers equal area projection, standard parallels 21¡04'50" and 21¡12'10", central meridian 157¡00'45", NAD83 datum. 

WAIKOLU

(5 Mgal/d)

HØUPU

(2 Mgal/d) WAILAU

(15 Mgal/d)

ØUALAPUØE

(8 Mgal/d) KAWELA

(5 Mgal/d)

KAMILOLOA

(3 Mgal/d)

MANAWAINUI

(2 Mgal/d)

PUNAKOU

(2 Mgal/d)

KALUAKOØI

(2 Mgal/d) HOOLEHUA

(2 Mgal/d)

KUALAPUØU

(5 Mgal/d)

KUALAPUÔU

(5 Mgal/d)

KALAUPAPA

(2 Mgal/d)

KAHANUI

(3 Mgal/d)

PELEKUNU

(9 Mgal/d)

EXPLANATION

AQUIFER-SYSTEM BOUNDARY, AND NAME OF AQUIFER SYSTEMÐState  sustainable-yield estimate, in million gallons per day (Mgal/d), shown in parentheses.WELL WITH 2007 WATER-USE PERMIT AND NUMBERWELL WITH NO WATER-USE PERMIT AND NUMBERPROPOSED SITE FOR ADDITIONAL GROUND-WATER WITHDRAWAL AND SITE NAME

0902Ð01

0352Ð010352Ð100352Ð090352Ð05

0352Ð110352Ð12

0449Ð010350Ð050350Ð070350Ð010350Ð09

0448Ð0448Ð0448Ð

0354Ð040354Ð020354Ð01

0549Ð01

0447Ð0

0449Ð06

ØUalapuØe (proposed)

Manawainui

(proposed)

Kawela

(proposed)

Kawela

(proposed)

0457Ð010456Ð060456Ð080456Ð09 0559Ð01

0600Ð01

0601Ð020601Ð010501Ð030602Ð03 0603Ð01

0705Ð050603Ð070604Ð03

0700Ð01

0705Ð040605Ð020605Ð010605Ð03

0706Ð02

0807Ð01

0508Ð01

0509Ð01

0510Ð01 0511Ð01

0759Ð01

0801Ð01, Ð02

0801Ð03

0901-01

0855Ð01

Molokai Irrigation 

System Tunnel

0855Ð02

0855Ð03 0901Ð01

0902Ð01 0905Ð01

0915Ð01

0514Ð01

1058Ð01

1059Ð01 1011Ð01

1014Ð01

1114Ð02

1114Ð01

0356Ð010456Ð170456Ð010456Ð160456Ð040456Ð020456Ð030457Ð040457Ð020458Ð020458Ð030458Ð01

0500Ð010501Ð060501Ð040500Ð030459Ð010459Ð030459Ð020459Ð040459Ð05

0501Ð050501Ð07

0354Ð070354Ð03

Figure 5. Map showing aquifer systems designated by the State of Hawai‘i Commission on Water Resource Management and locatioon the Island of Moloka‘i, Hawai‘i.
Table 1. May 2007 ground-water-use permits for the Island of Moloka‘i, Hawai‘i.

[Mgal/d, million gallons per day; --, 2006 withdrawal information incomplete or not reported to the Hawai‘i Commission on Water Resource Management]

Well Name

May 2007 wateruse permit, 

in Mgal/d

2006 average 

reported withdrawal, 

in Mgal/d

Aquifer 

system

0350–01 Keawanui salt 0.240 -- ‘Ualapu‘e

0350–05 Wescoatt 0.004 -- ‘Ualapu‘e

0350–07 Manawai no. 1 0.015 -- ‘Ualapu‘e

0350–09 Oceanic Institute salt 0.750 -- ‘Ualapu‘e

0352–09 Kamalö 0.010 -- ‘Ualapu‘e

0352–10 Kamalö-Curtis 0.012 -- Kawela

0352–11 Shige’s farm 0.004 -- Kawela

0352–12 Urauchi No. 1 0.001 -- ‘Ualapu‘e

0354–01 Meyer, Inc., no. 1 0.029 -- Kawela

0354–02 Meyer, Inc., no. 2 0.040 -- Kawela

0354–03 Well no. 3 0.017 -- Kawela

0354–04 Meyer, Inc., no. 4 0.005 -- Kawela

0354–07 Keonekuino-Teves 0.045 -- Kawela

0447–02 Püko‘o Farm 0.003 -- ‘Ualapu‘e

0448–01 Mapulehu 0.003 -- ‘Ualapu‘e

0448–03 Mapulehu Shaft 0.007 -- ‘Ualapu‘e

0449–01 ‘Ualapu‘e Shaft 0.185 0.272 ‘Ualapu‘e

0449–06 Kalua‘aha-Shephard 0.008 -- ‘Ualapu‘e

0456–04, 0457–04 Breadfruit well 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 0.330 0.237 Kawela

0501–04 Kupa Shaft 0.056 0.035 Kamiloloa

0501–06 Home Pumehana 0.005 -- Kamiloloa

0501–07 Kaunakakai Park 0.075 -- Kamiloloa

0546–02 Pü‘elelü 0.202 -- Waialua

0549–01 Mapulehu Tunnel 0.010 -- ‘Ualapu‘e

0601–01 Oloolo 0.075 0.081 Kamiloloa

0602–03 Kalaiakamanu Hou 0.005 -- Manawainui

0603–01 ‘Umipa‘a 0.046 0.000 Manawainui

0605–01, 0605–02 ORCA Shaft no. 1 and no. 2 0.600 -- Manawainui

0605–03 ORCA no. 3 0.040 -- Manawainui

0705–05 Nä‘iwa 0.012 -- Manawainui

0706–02 South Hoolehua 0.864 -- Manawainui

0706–03 Pälä‘au salt 0.001 -- Manawainui

0759–01 Waiola no. 1 1

0.656 -- Kamiloloa

0801–01, 0801–02 Kualapu‘u DHHL 1 and 2 0.367 0.678 Kualapu‘u

0801–03 Kualapu‘u mauka 0.516 0.712 Kualapu‘u

0844–01 Pu‘u O Hoku no. 1 1

0.235 -- Waialua

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

0901–01 Well no. 17 1.018 0.902 Kualapu‘u

1058–01 Waihänau no. 239 0.094 -- Kahanui

1059–01 Waikalae Tunnel 0.036 0.00036 Kualapu‘u

DHHL reservation DHHL reservation 12.905 -- Kualapu‘u

MIS Tunnel Moloka‘i Irrigation System Tunnel 2

1.822 -- Waikolu

1

Not simulated.

2

No water-use permit; value is 1992–96 average withdrawal (Oki, 1997), equally distributed to two model nodes.

10Effects of Ground-Water Withdrawal on Kaunakakai Stream, Moloka‘i, Hawai‘i 
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. 5), near 

Kawela, was completed in 1921, and the other well 

(0449–01, fig. 5), near ‘Ualapu‘e, was completed in 

1936. During 2006, annual mean withdrawals from 

wells 0457–01 and 0449–01, respectively, were 

0.237 and 0.272 Mgal/d. Total reported annual mean 

withdrawals, on the basis of complete records, from 

other wells near the south coast were about 0.116 

Mgal/d. Incompletely reported and unreported withdrawals from drilled wells and numerous shallow 

dug wells along the south coast probably are less 

than a few million gallons per day.

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

and 0855–03, fig. 5) drilled in 1961 withdraw water 

from the dike complex in the northeastern part of 

the island. Water from these wells enters the MIS. 

Although withdrawals during 2006 from wells 

0855–01, 0855–02, and 0855–03 were not reported 

to the CWRM, from the most recently reported data 

during the period 2000–2, mean withdrawal from 

these three wells was 0.99 Mgal/d.

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 exist- ing wells, water purveyors on Moloka‘i have con- sidered increasing withdrawals from existing wells, 

drilling additional wells, and redistributing with- drawals among wells. The County of Maui Depart- ment of Water Supply (DWS) is considering drilling 

additional wells to (1) replace existing sources that 

have increasing salinity, (2) reduce withdrawals in 

the Kualapu‘u area, and (3) meet anticipated future 

water demand (Oki, 2006). Moloka‘i Properties 

Limited, the largest private landowner on Moloka‘i, 

is considering using brackish water from the exist- ing Käkalahale well (0700–01) for nonpotable 

needs and using water developed from Well 17 

(0901–01) for potable uses only (PBR Hawaii and 

Associates, Inc., 2006). Excess water available from 

Well 17 could be made available to communities 

outside of Moloka‘i Properties Limited lands (PBR 

Hawaii and Associates, Inc., 2006).

Numerical Simulation of 

Additional Ground-Water 

Withdrawal

A numerical ground-water-flow model previ- ously was constructed to simulate steady-state 

regional ground-water flow on Moloka‘i (Oki, 

1997). The model was used in another study to 

estimate changes in steady-state water level and 

coastal discharge caused by possible redistributed 

and additional ground-water withdrawals in the area 

between Kualapu‘u and ‘Ualapu‘e (Oki, 2006) and 

also is used for the present study. 

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 salt- water 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 simu- lates 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 

other details regarding development of the regional 

flow model.

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 domain 

includes the entire Island of Moloka‘i and offshore 

coastal-discharge zone. The model domain was 

discretized using a finite-element mesh consisting 

of 6,432 nodes and 6,251 square elements (1,640 ft 

on a side). The original mesh is valid for testing the 

scenarios described in this study.

A base case defined by 2006 annual mean with- drawal rates, if completely reported, and May 2007 

permitted withdrawal rates, otherwise, (table 1) was 

Numerical Simulation of Additional Ground-Water Withdrawal11
used to compute changes in water level and coastal 

discharge caused by redistributed or additional 

ground-water withdrawals. In the model, withdrawals were assigned to the node nearest to the 

withdrawal site. The hydraulic characteristics and 

the magnitude and distribution of long-term average recharge 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-dependentdischarge boundary conditions used to simulate 

ground-water discharge to the ocean and streams. 

Because ocean levels, coastal bathymetry, and 

stream-channel altitudes have not changed significantly, the original boundary conditions (Oki, 1997) 

were used in this study. Modification of model 

coastal leakance near the mouth of Kaunakakai 

Stream, where sediment will be excavated to create habitat, was considered unnecessary because 

(1) the excavated area represents less than 5 percent 

of the area of a model element, (2) the estimated 

confining-unit thickness (25 ft) in the excavated 

area likely would change by less than 10 percent, 

and (3) the resulting area-weighted confining-unit 

thickness and leakance value for the model element 

therefore would change by less than 1 percent.

The water level in Pu‘u O Hoku No. 1 well 

(0844–01, fig. 5), which was drilled after the origi- nal model was constructed, is about 9 ft above mean 

sea level (Hawai‘i Commission on Water Resource 

Management, unpub. data, 2006), indicating that 

the well site probably is not in the dike complex as 

originally modeled. Thus, the model is not used to 

specifically assess the hydrologic effects of groundwater withdrawal from this well, which is located 

near the east end of the island, outside the main area 

of withdrawals between Kualapu‘u and ‘Ualapu‘e. 

Description of Model Scenarios

The base-case scenario was used as a reference for computing changes in steady-state water 

level and coastal discharge caused by redistributed 

or additional ground-water withdrawals. The withdrawal rates used in the base case were 2006 mean 

reported withdrawal rates, if completely reported, an 

estimated 1.822 Mgal/d withdrawal from the MIS 

Tunnel (Oki, 1997), and May 2007 permitted withdrawal rates, otherwise (excluding Pu‘u O Hoku 

No. 1, Waiola No. 1, and the DHHL reservation). 

Pu‘u O Hoku No. 1 (0844–01) was not simulated 

because of uncertainty described previously. The 

proposed Waiola No. 1 well (0759–01) likely will 

not be drilled (Charley F. Ice, Hawai‘i Commission 

on Water Resource Management, written commun., 

2006), and was omitted from the model. The DHHL 

reservation was omitted from the base case because 

of uncertainty as to feasible well locations. The 

base-case withdrawal rates range from 0.001 Mgal/d 

(well 0352–12) to 1.822 Mgal/d (MIS Tunnel) and 

total 9.296 Mgal/d (table 1). Total withdrawal represented in the base case is 5 percent of recharge (187 

Mgal/d). Recharge in the model (187 Mgal/d) differs slightly from 188.6 Mgal/d estimated by Shade 

(1997) because discretization near the shoreline 

causes the modeled land area to differ slightly from 

the actual land area.

Withdrawal rates simulated in scenarios 

1–6 were determined during discussions with the 

USACE and were based on published information 

and preliminary plans of various water purveyors 

(table 2). In scenario 1, withdrawal from the Käkalahale well (0700–01) was increased from zero 

(base case) to 1.0 Mgal/d (PBR Hawaii and Associates, Inc., 2006). Scenario 2 is similar to scenario 

1 but includes increased withdrawal from Well 17 

(0901–01), increasing from 0.902 to 1.7 Mgal/d. 

Scenarios 3 and 5 are similar to scenario 1, but 

withdrawals from three existing wells (0449–01, 

0457–01, and 0801–03) were fully or partially 

redistributed to three proposed wells (‘Ualapu‘e, 

Kawela, and Manawainui) (Oki, 2006). Scenarios 

4 and 6 are similar to scenario 2, but withdrawals 

from three existing wells (0449–01, 0457–01, and 

0801–03) also were fully or partially redistributed 

to three proposed wells (‘Ualapu‘e, Kawela, and 

Manawainui). In scenarios 1, 3, and 5, total with- drawal exceeds the base-case withdrawal by 1.0 

Mgal/d, whereas in scenarios 2, 4, and 6, total with- drawal exceeds the base-case withdrawal by 1.798 

Mgal/d.

Model Results

For each of the scenarios tested, the changes 

in water level and coastal discharge were determined relative to the base case. Simulated waterlevel changes are greatest at withdrawal sites and 

decrease outward with distance elsewhere. Within 

the zone where water levels decline because of 

increased withdrawal, the salinity of water pumped 

from existing wells may increase, although the 

extent of the increase cannot be predicted accurately 

with the sharp-interface model used in this study. 

Similarly, within the zone where water levels rise 

because of decreased withdrawal, the salinity of 

water pumped from existing wells may decrease by 

an unknown amount. The change in the salinity of 

water pumped from existing wells is dependent on 

12  Effects of Ground-Water Withdrawal on Kaunakakai Stream, Moloka‘i, Hawai‘i 
the amount of water-level change and the location 

of the open interval of the well relative to the depth 

of the freshwater-saltwater transition zone. Greater 

water-level changes (all other factors being equal) 

are expected to cause 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 changes in coastal discharge generally are greatest immediately downgradient from 

sites of simulated changes in withdrawal. In general, 

changes in coastal discharge are difficult to measure 

directly except at onshore springs where discharge 

is channelized. Thus, the numerical model is used 

in this study to provide estimates of changes in 

coastal discharge caused by redistributed or additional ground-water withdrawals. In this study, 

the changes are represented over areas defined by 

model elements (1,640 by 1,640 ft). 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, changes greater than 1,000 gal/d 

generally account for about 95 percent of the total 

simulated change in discharge. Simulated changes 

in coastal discharge 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.

Scenario 1

In scenario 1, withdrawal of 1.0 Mgal/d from 

the Käkalahale well (0700–01) causes water levels 

and coastal discharge to decrease relative to 

base-case conditions (fig. 6, tables 3, 4). The simulated water-level decline at the Käkalahale well is 

0.61 ft, and water-level declines decrease outward 

from the well. The areal extent of simulated waterlevel decline, as indicated by the –0.01-ft line of 

equal water-level change, is from the Hoolehua 

Plain in the west to Kawela in the east (fig. 6). The 

areal extent of simulated water-level decline is 

limited in the northeast by the dike complex of East 

Moloka‘i Volcano and in the west by the confining unit separating the West and East Moloka‘i 

Volcanics. Near the Kaunakakai Stream habitatrestoration site, the simulated water-level decline is 

0.08 ft (table 3). 

Coastal discharge decreases mainly along the 

south coast from Päläÿau in the west to beyond 

Kawela in the east, but also along the north coast, 

northwest of the Käkalahale well. The total reduction in coastal discharge simulated in scenario 1 is 

equal to the withdrawal from the Käkalahale well 

(1.0 Mgal/d). In general, the simulated decrease 

in coastal discharge caused by withdrawal from 

the Käkalahale well is greatest in the coastal area 

immediately downgradient from the well. Within 

individual model elements, coastal discharge is 

reduced by as much as 110,000 gal/d south-southwest of the Käkalahale well and east of Kaunakakai Stream. Near the Kaunakakai Stream habitatrestoration site, the simulated reduction in coastal 

discharge from the model element closest to the site 

is 98,000 gal/d, which is a 7-percent reduction relative to base-case conditions (fig. 6, table 4). This 

reduction in coastal discharge may overestimate the 

reduction in ground-water discharge to Kaunaka- kai Stream, and thus the reduction in streamflow, 

because the stream covers a small fraction of the 

area represented by the model element.

Table 2. Summary of withdrawal scenarios simulated with the ground-water-flow model for the Island of Moloka‘i, 

Hawai‘i.

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

Scenario

Simulated withdrawal from selected wells (Mgal/d)

Käkalahale 

(0700–01)

Well 17

(0901–01)

Kualapu‘u

Mauka

(0801–03)

Kawela

Shaft

 (0457–01)

‘Ualapu‘e 

Shaft 

(0449–01)

Manawainui

proposed

Kawela

proposed

‘Ualapu‘e 

proposed Total

Base case 0 0.902 0.712 0.237 0.272 0 0 0 2.123

1 1.0 0.902 0.712 0.237 0.272 0 0 0 3.123

2 1.0 1.7 0.712 0.237 0.272 0 0 0 3.921

3 1.0 0.902 0.480 0 0 0.232 0.237 0.272 3.123

4 1.0 1.7 0.480 0 0 0.232 0.237 0.272 3.921

5 1.0 0.902 0.280 0 0 0.432 0.237 0.272 3.123

6 1.0 1.7 0.280 0 0 0.432 0.237 0.272 3.921

Numerical Simulation of Additional Ground-Water Withdrawal13
00

Kalaupapa

KualapuØu

Base modified from U.S. Geological Survey digital data, 1:24,000, 1983, Albers equal area projection, standard parallels 21¡04'50" and 21¡12'10", central meridian 157¡00'45", NAD83 datum. 

KahiØu Point

KalaupapaPeninsula

Øìlio Point

LØau 

Point

157¡05'

157¡15'

156¡55' 156¡50'

157¡10'

21¡10'

157¡

EXPLANATION

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET

0700Ð01

(Ð0.61)

0700Ð01

(Ð0.61)

Ð0.01

Ð0.02

Ð0.05

Ð0.05 Ð0.02 Ð0.01

Ð0.1

Ð0.1 Ð0.2

SITE OF SIMULATED WITHDRAWAL INCREASE AN NUMBERÐValue in parentheses is simulated water-le

Ð5,000 ≤ Q < Ð1,000

Ð15,000 ≤ Q < Ð5,000Ð50,000 ≤ Q < Ð15,000

Q < Ð50,000

CHANGE IN SIMULATED COASTAL 

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

Ð0.01Ð0.02Ð0.05Ð0.1Ð0.2

Discharge reductions greater than 50,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge). Negative change indicates reductionin coastal discharge relative to base-case conditions.

Ð63,000 gal/d (Ð5%)Ð83,000 gal/d (Ð6%)

(Kaunakakai habitat-restoration site) Ð98,000 gal/d (Ð7%)

Ð110,000 gal/d (Ð7%)

Ð75,000 gal/d (Ð8%)

Ð53,000 gal/d (Ð3%)Ð89,000 gal/d (Ð4%)

Figure 6. Scenario 1 of ground-water-flow model for the Island of Moloka‘i, Hawai‘i, showing simulated changes in steady-state grouncoastal discharge (relative to base-case conditions) caused by withdrawing 1.0 million gallons per day from the Käkalahale well (0700–
Table 3. Summary of changes in steady-state ground-water level simulated with the ground-water-flow model for the 

Island of Moloka‘i, Hawai‘i.

[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]

Simulated water-level change (feet)

Scenario Käkalahale 

(0700–01)

Well 17

(0901–01)

Kualapu‘u

Mauka

(0801–03)

Kawela

Shaft

(0457–01)

‘Ualapu‘e

Shaft

(0449–01)

Manawainui

proposed

Kawela

proposed

‘Ualapu‘e 

proposed

Kaunakakai 

Stream 

habitatrestoration 

site

1

Base case 5.98 6.89 7.34 2.95 3.64 6.13 4.86 4.75 1.38

1 –0.61 –0.09 –0.09 –0.01 0.00 –0.22 –0.04 0.00 –0.08

2 –0.71 –3.40 –1.45 –0.02 0.00 –0.38 –0.06 0.00 –0.12

3 –0.65 0.26 0.57 0.10 0.09 –0.49 –0.14 –0.08 –0.09

4 –0.74 –2.81 –0.65 0.10 0.09 –0.65 –0.16 –0.08 –0.13

5 –0.67 0.54 1.11 0.10 0.09 –0.72 –0.14 –0.08 –0.09

6 –0.77 –2.35 –0.03 0.10 0.09 –0.89 –0.16 –0.08 –0.13

1

Simulated base-case ground-water level, in feet.

Table 4. Summary of changes in steady-state coastal discharge simulated with the ground-water-flow model for the 

Island of Moloka‘i, Hawai‘i.

[Overall maximum changes in coastal discharge are within an individual model element. Model elements are square areas 1,640 feet on a side. Only 

model elements with base-case coastal discharge greater than 1,000 gal/d considered. gal/d, gallons per day; ‐‐, not applicable]

1

Reduction in 

coastal discharge 

near Kaunakakai 

Stream habitatrestoration site 

(gal/d)

Overall maximum absolute change in coastal 

discharge (gal/d)

Overall maximum relative change in coastal 

discharge (percent)

2

Number of model elements with coastaldischarge change 

greater than 5 percent

Scenario Increase Decrease Increase Decrease Increase Decrease

1 98,000 -- 110,000 -- 22 -- 13 (7)

2 149,000 -- 150,000 -- 63 -- 25 (12)

3 110,000 37,000 123,000 4 25 0 14 (8)

4 161,000 33,000 164,000 4 57 0 23 (12)

5 118,000 37,000 132,000 4 27 0 14 (9)

6 170,000 33,000 172,000 4 51 0 24 (12)

1

Simulated reduction in coastal discharge near Kaunakakai Stream habitat-restoration site is from the entire model element nearest the site. 

2

Values in parentheses indicate number of elements with change in steady-state coastal discharge greater than 5 percent and greater than 50,000 gal/d.

Numerical Simulation of Additional Ground-Water Withdrawal15
Scenario 2

Withdrawals simulated in scenario 2 are similar 

to those in scenario 1 except that withdrawal from 

Well 17 (0901–01) was increased from 0.902 to 1.7 

Mgal/d. Increased withdrawal from Well 17 causes 

greater declines in water level and greater reductions in coastal discharge relative to scenario 1 (fig. 

7, tables 3, 4). The simulated water-level decline 

is 3.40 ft at Well 17 and 0.71 ft at the Käkalahale 

well. The water-level declines decrease outward 

from Well 17 and the Käkalahale well (0700–01). 

In scenario 2, the areal extent of simulated waterlevel decline, as indicated by the –0.01-ft line of 

equal water-level change, is greater than the extent 

in scenario 1. Near the Kaunakakai Stream habitatrestoration site, the simulated water-level decline 

is 0.12 ft in scenario 2 (table 3), which is 0.04 ft 

greater than the simulated decline in scenario 1. 

In scenario 2, coastal discharge decreases 

mainly along the south coast from Päläÿau in the 

west to beyond Kawela in the east, but also along 

the north coast, northwest of Well 17. Because of 

increased withdrawal from Well 17 in scenario 2 relative to scenario 1, overall coastal-discharge reduction and reduction at common sites is greater in scenario 2. Within individual model elements, coastal 

discharge is reduced by as much as 150,000 gal/d 

along the south coast east of Kaunakakai Stream. 

Near the Kaunakakai Stream habitat-restoration site, 

the simulated reduction in coastal discharge from 

the model element closest to the site is 149,000 

gal/d in scenario 2, which is an 11-percent reduc- tion relative to base-case conditions (fig. 7, table 4) 

and which is greater than the simulated reduction in 

scenario 1 (98,000 gal/d). This reduction in coastal 

discharge may overestimate the discharge reduction 

in Kaunakakai Stream, which covers a small frac- tion of the area represented by the model element.

Scenario 3

Total withdrawal simulated in scenario 3 is 

equal to the total withdrawal simulated in scenario 

1, but scenario 3 includes a redistribution (full or 

partial) of withdrawals from existing wells to proposed wells. DWS is considering reducing withdrawal from well 0801–03 to reduce the possibility 

of saltwater intrusion in the Kualapuu area, where 

several existing wells are closely spaced. Because 

of increasing salinity in water pumped from wells 

0457–01 and 0449–01 (Oki, 2006), DWS also is 

considering replacing these wells with wells located 

farther inland. In scenario 3, withdrawal from well 

0801–03 was reduced by 0.232 Mgal/d, and withdrawal from the proposed Manawainui well was 

increased from zero to 0.232 Mgal/d; withdrawal 

from well 0457–01 was reduced from 0.237 Mgal/d 

to zero, and withdrawal from the proposed Kawela 

well was increased from zero to 0.237 Mgal/d; withdrawal from well 0449–01 was reduced from 0.272 

Mgal/d to zero, and withdrawal from the proposed 

‘Ualapu‘e well was increased from zero to 0.272 

Mgal/d.

Reduced withdrawal from well 0801–03 causes 

the water level near the well to increase by 0.57 

ft (fig. 8). Because of the increased withdrawals 

from the proposed Manawainui and Kawela wells, 

the simulated water-level decline at the Käkalahale well in scenario 3 (0.65 ft) is greater than the 

simulated decline in scenario 1 (0.61 ft). In scenario 3, the areal extent of simulated water-level 

decline around the Käkalahale well (0700–01), as 

indicated by the –0.01-ft line of equal water-level 

change, is less than the extent in scenario 1 because 

of the decreased withdrawal from well 0801–03. 

Near the Kaunakakai Stream habitat-restoration 

site, the simulated water-level decline is 0.09 ft in 

scenario 3 (table 3), which is 0.01 ft greater than 

the simulated decline in scenario 1. The effects of 

redistributing withdrawal from well 0449–01 to the 

proposed ‘Ualapu‘e well do not extend to Kaunakakai Stream.

In scenario 3, coastal discharge increases 

slightly along the north coast, northwest of well 

0801–03, because of the reduced withdrawal from 

that well. Local increases in coastal discharge also 

are simulated near other sites of reduced withdrawal 

(wells 0457–01 and 0449–01). Within individual 

model elements, coastal discharge is reduced by as 

much as 123,000 gal/d along the south coast east of 

Kaunakakai Stream. Near the Kaunakakai Stream 

habitat-restoration site, the simulated reduction in 

coastal discharge from the model element closest to 

the site is 110,000 gal/d in scenario 3 (fig. 8, table 

4), which is an 8-percent reduction relative to basecase conditions and which is greater than the simulated reduction in scenario 1 (98,000 gal/d). 

Scenario 4

Total withdrawal simulated in scenario 4 is 

equal to the total withdrawal simulated in scenario 2, but scenario 4 includes a redistribution 

(full or partial) of withdrawals from existing wells 

to proposed wells identical to the redistribution 

described in scenario 3. Reduced withdrawal from 

well 0801–03 causes the water-level decline at Well 

17 to decrease from 3.40 ft (scenario 2) to 2.81 ft 

(scenario 4). In contrast, the increased withdrawals 

from the proposed Manawainui and Kawela wells 

16  Effects of Ground-Water Withdrawal on Kaunakakai Stream, Moloka‘i, Hawai‘i 
00

Kalaupapa

KualapuØu

Base modified from U.S. Geological Survey digital data, 1:24,000, 1983, Albers equal area projection, standard parallels 21¡04'50" and 21¡12'10", central meridian 157¡00'45", NAD83 datum. 

KahiØu Point

KalaupapaPeninsula

Øìlio Point

LØau 

Point

157¡05'

157¡15'

156¡55' 156¡50'

157¡10'

21¡10'

157¡

EXPLANATION

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET

CHANGE IN SIMULATED COASTAL 

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

Ð0.01Ð0.02Ð0.05Ð0.1Ð0.2Ð0.5Ð1.0

Ð5,000 ≤ Q < Ð1,000

Ð15,000 ≤ Q < Ð5,000Ð50,000 ≤ Q < Ð15,000

Q < Ð50,000

0700Ð01

(Ð0.71)

0700Ð01

(Ð0.71)

0901Ð01

(Ð3.40)

Ð0.01 Ð0.02

Ð0.05

Ð0.1

Ð0.01 Ð0.02 Ð0.05 Ð0.1 Ð0.2

Ð0.5 Ð1

Discharge reductions greater than 50,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge). Negative change indicates reductionin coastal discharge relative to base-case conditions.

Ð58,000 gal/d (Ð63%)Ð74,000 gal/d (Ð11%)

Ð108,000 gal/d (Ð10%)Ð140,000 gal/d (Ð11%)Ð149,000 gal/d (Ð11%)

(Kaunakakai habitat-restoration site) Ð149,000 gal/d (Ð11%)

Ð150,000 gal/d ( Ð9%)

Ð98,000 gal/d (Ð11%)

Ð69,000 gal/d (Ð3%)

Ð115,000 gal/d (Ð5%)

Ð63,000 gal/d (Ð9%)Ð56,000 gal/d (Ð8%)

SITE OF SIMULATED WITHDRAWAL INCREASE AN NUMBERÐValue in parentheses is simulated water-le

Figure 7. Scenario 2 of ground-water-flow model for the Island of Moloka‘i, Hawai‘i, showing simulated changes in steady-state groundischarge (relative to base-case conditions) caused by withdrawing 1.0 million gallons per day (Mgal/d) from the Käkalahale well (0700–withdrawal from Well 17 (0901–01) from 0.902 to 1.7 Mgal/d.
00

Kalaupapa

KualapuØu

Base modified from U.S. Geological Survey digital data, 1:24,000, 1983, Albers equal area projection, standard parallels 21¡04'50" and 21¡12'10", central meridian 157¡00'45", NAD83 datum. 

KahiØu Point

KalaupapaPeninsula

Øìlio Point

LØau 

Point

157¡05'

157¡15'

156¡55' 156¡50'

157¡10'

21¡10'

157¡

EXPLANATION

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET

+0.01+0.02+0.05+0.1+0.2

Ð5,000 ≤ Q < Ð1,000

Ð15,000 ≤ Q < Ð5,000Ð50,000 ≤ Q < Ð15,000

Q < Ð50,000

CHANGE IN SIMULATED COASTAL 

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

Ð0.01Ð0.02Ð0.05Ð0.1Ð0.2

0700Ð01

(Ð0.65)

0457Ð01

(+0.10)

0801Ð03

(+0.57)

0449Ð01

(+0.09)

SITE OF SIMULATED WITHDRAWAL INCREASE AN NUMBER OR NAMEÐValue in parentheses is simulaSITE OF SIMULATED WITHDRAWAL DECREASE A NUMBERÐValue in parentheses is simulated water-le

0700Ð01

(Ð0.65)

Manawainui

(Ð0.49)

Kawela

(Ð0.14)

ØUalapuØe

(Ð0.08)

0803Ð01

(+0.57)

Ð0.01

0.01 0.02 0.05 0.1

Ð0.01

Ð0.01

Ð0.02

Ð0.02 Ð0.05

Ð0.05 Ð0.1 Ð0.1

Ð0.2

 1,000 < Q ≤ 5,000 5,000 < Q ≤ 15,000 15,000 < Q ≤ 40,000 

Discharge reductions greater than 50,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge). Negative change indicates reductionin coastal discharge relative to base-case conditions.

Ð65,000 gal/d (Ð5%)Ð90,000 gal/d (Ð7%)

(Kaunakakai habitat-restoration site) Ð110,000 gal/d (Ð8%)

Ð123,000 gal/d (Ð8%)

Ð84,000 gal/d (Ð9%)

Ð82,000 gal/d (Ð4%)

Ð110,000 gal/d (Ð5%)

Ð56,000 gal/d (Ð8%)

Figure 8. Scenario 3 of ground-water-flow model for the Island of Moloka‘i, Hawai‘i, showing simulated changes in steady-state groundischarge (relative to base-case conditions) caused by withdrawing 1.0 million gallons per day (Mgal/d) from the Käkalahale well (0700–(fully or partially) withdrawal from existing wells to proposed wells. Withdrawal from well 0801–03 was reduced by 0.232 Mgal/d, and witproposed Manawainui well was increased from zero to 0.232 Mgal/d; withdrawal from well 0457–01 was reduced from 0.237 Mgal/d to zthe proposed Kawela well was increased from zero to 0.237 Mgal/d; withdrawal from well 0449–01 was reduced from 0.272 Mgal/d to zthe proposed ‘Ualapu‘e well was increased from zero to 0.272 Mgal/d.
cause the water-level decline at the Käkalahale well 

(0700–01) to increase from 0.71 ft (scenario 2) to 

0.74 ft (scenario 4). Near the Kaunakakai Stream 

habitat-restoration site, the simulated water-level 

decline is 0.13 ft in scenario 4 (table 3), which is 

0.01 ft greater than the simulated decline in scenario 

2. 

In scenario 4, coastal discharge decreases 

mainly along the south coast, but also along the 

north coast, northwest of Well 17 (0901–01). 

Local increases in coastal discharge are simulated 

near sites of reduced withdrawal (wells 0457–01 

and 0449–01). Within individual model elements, 

coastal discharge is reduced by as much as 164,000 

gal/d along the south coast east of Kaunakakai 

Stream. Near the Kaunakakai Stream habitatrestoration site, the simulated reduction in coastal 

discharge from the model element closest to the site 

is 161,000 gal/d in scenario 4 (fig. 9, table 4), which 

is an 11-percent reduction relative to base-case 

conditions and which is greater than the simulated 

reduction in scenario 2 (149,000 gal/d). 

Scenario 5

Simulated withdrawal in scenario 5 is similar 

to withdrawal in scenario 3, except that withdrawal 

from 0801–03 is further reduced by 0.2 Mgal/d and 

withdrawal from the proposed Manawainui well is 

increased by an equal amount. In scenario 5, the 

water level at well 0801–03 increases by 1.11 ft 

relative to the base case, compared to an increase 

of 0.57 ft in scenario 3. Because of the increased 

withdrawal from the proposed Manawainui well, 

the simulated water-level decline at the Manawainui 

well in scenario 5 (0.72 ft) is greater than the 

simulated decline in scenario 3 (0.49 ft). Near the 

Kaunakakai Stream habitat-restoration site, the 

simulated water-level decline is 0.09 ft in scenario 5 

(table 3), which is equal to the simulated decline in 

scenario 3. 

In scenario 5, coastal discharge increases 

slightly along the north coast, northwest of well 

0801–03, because of the reduced withdrawal from 

that well. Local increases in coastal discharge also 

are simulated near other sites of reduced withdrawal 

(wells 0457–01 and 0449–01). Within individual 

model elements, coastal discharge is reduced by as 

much as 132,000 gal/d along the south coast east of 

Kaunakakai Stream. Near the Kaunakakai Stream 

habitat-restoration site, the simulated reduction in 

coastal discharge from the model element closest to 

the site is 118,000 gal/d in scenario 5 (fig. 10, table 

4), which is an 8-percent reduction relative to basecase conditions and which is greater than the simulated reduction in scenario 3 (110,000 gal/d). 

Scenario 6

Simulated withdrawal in scenario 6 is similar 

to withdrawal in scenario 4, except that withdrawal 

from 0801–03 is further reduced by 0.2 Mgal/d and 

withdrawal from the proposed Manawainui well is 

increased by an equal amount. In scenario 6, the 

water level at well 0801–03 decreases by 0.03 ft 

relative to the base case, compared to a decrease 

of 0.65 ft in scenario 4. Because of the increased 

withdrawal from the proposed Manawainui well, 

the simulated water-level decline at the Manawainui 

well in scenario 6 (0.89 ft) is greater than the 

simulated decline in scenario 4 (0.65 ft). Near the 

Kaunakakai Stream habitat-restoration site, the 

simulated water-level decline is 0.13 ft in scenario 6 

(table 3), which is equal to the simulated decline in 

scenario 4. 

In scenario 6, coastal discharge decreases 

mainly along the south coast, but also along the 

north coast, northwest of Well 17 (0901–01). 

Local increases in coastal discharge are simulated 

near sites of reduced withdrawal (wells 0457–01 

and 0449–01). Within individual model elements, 

coastal discharge is reduced by as much as 172,000 

gal/d along the south coast east of Kaunakakai 

Stream. Near the Kaunakakai Stream habitatrestoration site, the simulated reduction in coastal 

discharge from the model element closest to the 

site is 170,000 gal/d in scenario 6 (fig. 11, table 4), 

which is a 12-percent reduction relative to base-case 

conditions and which is greater than the simulated 

reduction in scenario 4 (161,000 gal/d). 

Effects on Kaunakakai Habitat-Restoration 

Site

Model results indicate that withdrawals (within 

the ranges tested) from Well 17 (0901–01), the 

Käkalahale well (0700–01), and the proposed 

Manawainui and Kawela wells cause a waterlevel decline of about 0.1 ft in the vicinity of the 

Kaunakakai habitat-restoration site. This reduction in ground-water level will cause a reduction of 

ground-water discharge to Kaunakakai Stream, but 

the existing spatial discretization in the model is too 

coarse to reliably estimate the reduction. The simulated reductions of discharge in the model element 

containing the habitat-restoration site range from 

98,000 to 170,000 gal/d. Reduction in discharge 

to the habitat-restoration site likely is less than the 

total indicated by the model element because the 

Numerical Simulation of Additional Ground-Water Withdrawal19
00

Kalaupapa

KualapuØu

Base modified from U.S. Geological Survey digital data, 1:24,000, 1983, Albers equal area projection, standard parallels 21¡04'50" and 21¡12'10", central meridian 157¡00'45", NAD83 datum. 

KahiØu Point

KalaupapaPeninsula

Øìlio Point

LØau 

Point

157¡05'

157¡15'

156¡55' 156¡50'

157¡10'

21¡10'

157¡

EXPLANATION

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET

+0.01+0.02

 1,000 < Q ≤ 5,000 5,000 < Q ≤ 15,000 15,000 < Q ≤ 40,000 

Ð5,000 ≤ Q < Ð1,000

Ð15,000 ≤ Q < Ð5,000Ð50,000 ≤ Q < Ð15,000

Q < Ð50,000

CHANGE IN SIMULATED COASTAL 

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

Ð0.01Ð0.02Ð0.05Ð0.1Ð0.2Ð0.5Ð1.0

0457Ð01

(+0.10)

0801Ð03

(Ð0.65) 0901Ð01

(Ð2.81)

0449Ð01

(+0.09)

0700Ð01

(Ð0.74)

Manawainui

(Ð0.65)

Kawela

(Ð0.16)

ØUalapuØe

(Ð0.08)

0700Ð01

(Ð0.74)

0803Ð01

(Ð0.65)

Ð0.01 Ð0.02

Ð0.05

Ð0.1

Ð0.05 Ð0.02Ð0.01 Ð0.1 Ð0.2

Ð0.5

Ð0.01

Discharge reductions greater than 50,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge). Negative change indicates reductionin coastal discharge relative to base-case conditions.

Ð52,000 gal/d (Ð57%)Ð68,000 gal/d (Ð10%)

Ð104,000 gal/d (Ð10%)Ð141,000 gal/d (Ð12%)Ð157,000 gal/d (Ð12%)

(Kaunakakai habitat-restoration site) Ð161,000 gal/d (Ð11%)

Ð164,000 gal/d (Ð10%)Ð108,000 gal/d (Ð12%)

Ð97,000 gal/d ( Ð5%)

Ð135,000 gal/d ( Ð6%)

Ð70,000 gal/d (Ð10%)Ð62,000 gal/d ( Ð9%)

SITE OF SIMULATED WITHDRAWAL INCREASE AN NUMBER OR NAMEÐValue in parentheses is simulatSITE OF SIMULATED WITHDRAWAL DECREASE AN NUMBERÐValue in parentheses is simulated water-lev

Figure 9. Scenario 4 of ground-water-flow model for the Island of Moloka‘i, Hawai‘i, showing simulated changes in steady-state grouncoastal discharge (relative to base-case conditions) caused by withdrawing 1.0 million gallons per day (Mgal/d) from the Käkalahale wewithdrawal from Well 17 (0901–01) from 0.902 to 1.7 Mgal/d, and redistributing (fully or partially) withdrawal from existing wells to propofrom well 0801–03 was reduced by 0.232 Mgal/d, and withdrawal from the proposed Manawainui well was increased from zero to 0.232 well 0457–01 was reduced from 0.237 Mgal/d to zero, and withdrawal from the proposed Kawela well was increased from zero to 0.237 well 0449–01 was reduced from 0.272 Mgal/d to zero, and withdrawal from the proposed ‘Ualapu‘e well was increased from zero to 0.27
00

Kalaupapa

KualapuØu

Base modified from U.S. Geological Survey digital data, 1:24,000, 1983, Albers equal area projection, standard parallels 21¡04'50" and 21¡12'10", central meridian 157¡00'45", NAD83 datum. 

KahiØu Point

KalaupapaPeninsula

Øìlio Point

LØau 

Point

157¡05'

157¡15'

156¡55' 156¡50'

157¡10'

21¡10'

157¡

EXPLANATION

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET

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

CHANGE IN SIMULATED COASTAL 

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

Ð0.01Ð0.02Ð0.05Ð0.1Ð0.2

0457Ð01

(+0.10)

0801Ð03

(+1.11)

0449Ð01

(+0.09)

0700Ð01

(Ð0.67)

Manawainui

(Ð0.72)

Kawela

(Ð0.14)

ØUalapuØe

(Ð0.08)

0700Ð01

(Ð0.67)

0803Ð01

(+1.11)

Ð0.01

0.01 0.02 0.05

0.2 0.1

Ð0.01

Ð0.01

Ð0.02

Ð0.02 Ð0.05

Ð0.1Ð0.05

Ð0.1

Ð0.2

 1,000 < Q ≤ 5,000 5,000 < Q ≤ 15,000 15,000 < Q ≤ 40,000 

Ð5,000 ≤ Q < Ð1,000

Ð15,000 ≤ Q < Ð5,000Ð50,000 ≤ Q < Ð15,000

Q < Ð50,000

Discharge reductions greater than 50,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge). Negative change indicates reductionin coastal discharge relative to base-case conditions.

Ð65,000 gal/d ( Ð5%)Ð96,000 gal/d ( Ð7%)

(Kaunakakai habitat-restoration site) Ð118,000 gal/d ( Ð8%)

Ð132,000 gal/d ( Ð8%)

Ð89,000 gal/d (Ð10%)

Ð84,000 gal/d (Ð4%)

Ð114,000 gal/d (Ð5%)

Ð59,000 gal/d (Ð9%)Ð52,000 gal/d (Ð7%)

SITE OF SIMULATED WITHDRAWAL INCREASE AN NUMBER OR NAMEÐValue in parentheses is simulaSITE OF SIMULATED WITHDRAWAL DECREASE A NUMBERÐValue in parentheses is simulated water-le

Figure 10. Scenario 5 of ground-water-flow model for the Island of Moloka‘i, Hawai‘i, showing simulated changes in steady-state groucoastal discharge (relative to base-case conditions) caused by withdrawing 1.0 million gallons per day (Mgal/d) from the Käkalahale weredistributing (fully or partially) withdrawal from existing wells to proposed wells. Withdrawal from well 0801–03 was reduced by 0.432 Mfrom the proposed Manawainui well was increased from zero to 0.432 Mgal/d; withdrawal from well 0457–01 was reduced from 0.237 Mwithdrawal from the proposed Kawela well was increased from zero to 0.237 Mgal/d; withdrawal from well 0449–01 was reduced from 0withdrawal from the proposed ‘Ualapu‘e well was increased from zero to 0.272 Mgal/d.
00

Kalaupapa

KualapuØu

Base modified from U.S. Geological Survey digital data, 1:24,000, 1983, Albers equal area projection, standard parallels 21¡04'50" and 21¡12'10", central meridian 157¡00'45", NAD83 datum. 

KahiØu Point

KalaupapaPeninsula

Øìlio Point

LØau 

Point

157¡05'

157¡15'

156¡55' 156¡50'

157¡10'

21¡10'

157¡

EXPLANATION

CHANGE IN SIMULATED COASTAL 

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

LINE OF EQUAL SIMULATED 

WATER-LEVEL CHANGE, IN FEET

+0.01+0.02

Ð0.01Ð0.02Ð0.05Ð0.1Ð0.2Ð0.5Ð1.0

Discharge reductions greater than 50,000 gal/d are indicated (values in parentheses are percentage change relative to base-case discharge). Negative change indicates reductionin coastal discharge relative to base-case conditions.

0457Ð01

(+0.10)

0801Ð03

(Ð0.03) 0901Ð01

(Ð2.35)

0449Ð01

(+0.09)

0700Ð01

(Ð0.77)

Manawainui

(Ð0.89)

Kawela

(Ð0.16)

ØUalapuØe

(Ð0.08)

0700Ð01

(Ð0.77)

0803Ð01

(Ð0.03)

Ð0.01 Ð0.02

Ð0.05

Ð0.1

Ð0.05 Ð0.02Ð0.01 Ð0.1 Ð0.2

Ð0.5

Ð0.01

 1,000 < Q ≤ 5,000 5,000 < Q ≤ 15,000 15,000 < Q ≤ 40,000 

Ð5,000 ≤ Q < Ð1,000

Ð15,000 ≤ Q < Ð5,000Ð50,000 ≤ Q < Ð15,000

Q < Ð50,000

Ð63,000 gal/d ( Ð9%)Ð99,000 gal/d ( Ð9%)

Ð142,000 gal/d (Ð12%)Ð162,000 gal/d (Ð12%)

(Kaunakakai habitat-restoration site) Ð170,000 gal/d (Ð12%)

Ð172,000 gal/d (Ð11%)Ð113,000 gal/d (Ð12%)

Ð65,000 gal/d ( Ð9%)

Ð50,000 gal/d ( Ð2%)

Ð100,000 gal/d ( Ð5%)Ð140,000 gal/d ( Ð6%)

Ð73,000 gal/d (Ð11%)

SITE OF SIMULATED WITHDRAWAL INCREASE AN NUMBER OR NAMEÐValue in parentheses is simulaSITE OF SIMULATED WITHDRAWAL DECREASE A NUMBERÐValue in parentheses is simulated water-lev

Figure 11. Scenario 6 of ground-water-flow model for the Island of Moloka‘i, Hawai‘i, showing simulated changes in steady-state groucoastal discharge (relative to base-case conditions) caused by withdrawing 1.0 million gallons per day (Mgal/d) from the Käkalahale wewithdrawal from Well 17 (0901–01) from 0.902 to 1.7 Mgal/d, and redistributing (fully or partially) withdrawal from existing wells to propofrom well 0801–03 was reduced by 0.432 Mgal/d, and withdrawal from the proposed Manawainui well was increased from zero to 0.432 well 0457–01 was reduced from 0.237 Mgal/d to zero, and withdrawal from the proposed Kawela well was increased from zero to 0.237 well 0449–01 was reduced from 0.272 Mgal/d to zero, and withdrawal from the proposed ‘Ualapu‘e well was increased from zero to 0.27
site covers a small fraction (about 5 percent) of the 

area of the model element.

 The reduction of ground-water level near the 

habitat-restoration site also may reduce the wetted habitat area available to the native species. The 

extent of reduction in wetted habitat area is controlled by the slope of the ponds near their edges, 

which will be affected by channel scour associated 

with large storms and sedimentation. The maximum water depth of the proposed ponds will be 

reduced by about 0.1 ft, and the average water depth 

also will be reduced by an amount that is dependent on the bottom shape of the ponds. The salinity of ground water discharging into the wetland 

area likely will increase by an unknown amount in 

response to increased withdrawals upgradient from 

the site. A numerical model capable of simulating 

density-dependent flow and transport is needed to 

evaluate the effects of withdrawal on salinity in the 

area.

Model Limitations

The ground-water-flow model of Moloka‘i 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 with- drawal.

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 distri- butions 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 distribu- tion. The model is, nevertheless, the best available 

tool for analyzing the possible regional hydrologic 

effects of ground-water withdrawals on Moloka‘i 

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. Simu- lated freshwater thickness from AQUIFEM–SALT 

overestimates the actual freshwater thickness. In 

reality, freshwater is separated from underlying 

saltwater by a freshwater-saltwater transition zone, 

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 relatively coarse spatial 

discretization and because local-scale heterogene- ities in the hydraulic characteristics of the rocks 

are not represented. Furthermore, changes to the 

hydraulic characteristics of the system, caused 

for example by excavation or filling near sites of 

ground‐water discharge, may not be represented 

accurately in the model.

Summary

The U.S. Army Corps of Engineers, in cooperation with the County of Maui Department of 

Public Works and Environmental Management, 

has proposed to construct 2.75 acres of shallow 

ponds and mudflats near the mouth of Kaunaka- kai Stream, Moloka‘i, Hawai‘i to restore habitat 

for the endangered native Hawaiian Stilt. Where 

the pond and wetland bottoms are below the water 

table, the ponds and wetland will be sustained by 

ground-water discharge during dry-weather condi- tions. Upstream of the lowland coastal area where 

Kaunakakai Stream is hydraulically connected 

to the ground-water system, Kaunakakai Stream 

is ephemeral. Because ground water is the main 

source of water for the proposed ponds and wetland, 

a reduction of ground-water level and discharge 

near the mouth of Kaunakakai Stream will have 

an effect on the efficacy of the habitat-restoration 

project. Redistributed and additional ground-water 

withdrawals will affect ground-water levels and discharge of fresh and brackish water near the project. 

In response to concerns about the possible 

effects of ground-water withdrawal on the habitatrestoration project near the mouth of Kaunakakai 

Stream, the USGS undertook the present investiga- tion to quantify the hydrologic effects of withdrawal 

Summary  23
from selected sites on ground-water levels and 

coastal discharge. An existing numerical groundwater-flow model was used to estimate changes in 

ground-water level and coastal discharge caused by 

redistributed and additional ground-water withdrawals in the area between Kualapu‘u and ‘Ualapu‘e. 

The ground-water-flow model was used to 

quantify changes, relative to base-case conditions, 

in steady-state ground-water level and coastal 

discharge for each of six withdrawal scenarios. 

Withdrawals simulated in the base case were average 2006 withdrawal rates, if completely reported, 

and May 2007 permitted rates otherwise. Simulated 

changes in ground-water level are greatest at withdrawal sites and decrease outward with distance 

elsewhere. Simulated changes in coastal discharge 

generally are greatest immediately downgradient 

from sites of withdrawal change. For the scenarios 

tested, hydrologic changes caused by withdrawals were limited to areas outside the low-permeability dike complex of East Moloka‘i Volcano and 

to areas east of the confining unit separating West 

and East Moloka‘i Volcanics. Water-level declines 

at withdrawal sites were as much as 3.40 ft at Well 

17 (0901–01), and coastal-discharge reductions in 

individual model elements (square areas 1,640 ft 

on a side) were as much as 170,000 gal/d along the 

south coast.

For the scenarios tested, model results indi- cate that withdrawals from existing and proposed 

wells cause a water-level decline of about 0.1 ft in 

the vicinity of the Kaunakakai habitat-restoration 

site. In addition, model results indicate a reduction 

of ground-water discharge to the stream, although 

the spatial discretization in the existing model is 

too coarse to accurately estimate the reduction 

of ground-water discharge to the stream. Reduc- tion of discharge in the model element containing 

the habitat-restoration site ranges from 98,000 to 

170,000 gal/d. Reduction in discharge to the habitatrestoration site is likely less than the total indicated 

because the site covers a small fraction (about 5 

percent) of the model element.

The reduction of ground-water level near the 

habitat-restoration site will reduce (1) the available 

wetted habitat area by an amount that is dependent 

on the bottom slope of the ponds near their edges, 

(2) the maximum water depth of the ponds by about 

0.1 ft, and (3) the average water depth by an amount 

that is dependent on the bottom shape of the ponds. 

The salinity of ground water discharging into the 

wetland area likely will increase by an unknown 

amount in response to increased withdrawals upgra- dient from the site. A numerical model capable of 

simulating density-dependent flow and transport 

is needed to evaluate the effects of withdrawal on 

salinity in the area.

The ground-water-flow model simulates the 

regional effects of additional withdrawal on water 

level and coastal discharge. The actual reduction in 

water level and coastal discharge on a local scale 

may not be accurately represented by the model 

because of the relatively coarse spatial discretization used in the model and because local-scale 

heterogeneities in the hydraulic characteristics of 

the rocks are not represented. Furthermore, humaninduced changes to the hydraulic characteristics of 

the system, caused for example by excavation or 

filling near sites of ground-water discharge, may not 

be represented accurately in the model.

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References Cited  25
Oki—Effects of Ground-Water Withdrawal on Kaunakakai Stream Environmental Restoration Plan, Moloka‘i, Hawai‘i—

Scientific Investigations Report 2007–5128

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