U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2006–5291

Prepared in cooperation with the County of Kauai Department of Water

Effects of Irrigation, Drought, and Ground-Water 

Withdrawals on Ground-Water Levels in the 

Southern Lihue Basin, Kauai, Hawaii

50

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50

100

150

150 100

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COVER

Simulated difference in ground-water levels between pre-development and 1981 conditions in the southern 

Lihue Basin, Kauai, Hawaii.
Effects of Irrigation, Drought, and 

Ground-Water Withdrawals on 

Ground-Water Levels in the Southern Lihue 

Basin, Kauai, Hawaii

By Scot K. Izuka

Prepared in cooperation with the County of Kauai Department of Water

Scientific Investigations Report 2006–5291

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: 2006

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Suggested citation:

Izuka, Scot K., 2006, Effects of irrigation, drought, and ground-water withdrawals on ground-water levels in the southern Lihue Basin, Kauai, Hawaii: U.S. Geological Survey Scientific Investigations Report 2006-5291, 42 p. 

Catalog-in-publication data are on file with the Library of Congress (URL http://www.loc.gov)

Manuscript approved for publication, October 26, 2006
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................3

Acknowledgments................................................................................................................................3

Setting .............................................................................................................................................................3

Hydrogeology .................................................................................................................................................3

Stratigraphy and Hydraulic Properties .............................................................................................8

Ground-Water Occurrence and Movement.....................................................................................9

Effects of Irrigation and Drought on Ground-Water Recharge...................................................11

Effects of Irrigation, Drought, and Ground-Water Withdrawal on Ground-Water Levels...............13

Original Southern Lihue Basin Model ............................................................................................13

Adjusting the Model to Revised Recharge Estimates ..................................................................15

Result of Model Adjustment.....................................................................................................15

Simulation of the Effects of Irrigation, Drought, and Ground-Water Withdrawal....................20

Steady-State Simulations.........................................................................................................23

Transient Simulations................................................................................................................23

Study Implications and Limitations...........................................................................................................28

Summary and Conclusions.........................................................................................................................29

References Cited..........................................................................................................................................30

Appendix: Estimating Ground-Water Recharge for Areas Outside the Lihue Basin........................32

Figures

1. Map showing the Lihue Basin....................................................................................................2

2. Map showing mean annual rainfall in the Lihue Basin..........................................................4

3. Map showing sugarcane fields in 1981 and 1998 in the Lihue Basin...................................5

4. Geologic map and block diagram of the Lihue Basin.............................................................7

5. Map showing vents of the Koloa Volcanics.............................................................................8

6. Diagram of conceptual model of ground-water occurrence in the 

southern Lihue Basin ...................................................................................................................9

7. Generalized ground-water table map for the southern Lihue Basin .................................10

8. Graphs showing water levels in Kilohana well I, ditch flows, and 

rainfall in the southern Lihue Basin.........................................................................................11

9. Diagram showing boundaries of the numerical ground-water-flow model of 

the southern Lihue Basin...........................................................................................................14

10. Diagram showing cells used to simulate streams, submarine areas, wells, 

and water tunnels in the adjusted model of the southern Lihue Basin.............................16

11. Diagram showing distribution of hydraulic conductivities in the adjusted 

model of the southern Lihue Basin ..........................................................................................18

12. Graphs comparing observed ground-water levels and stream base flows with 

simulated ground-water levels and stream base flows in the 

adjusted model of the southern Lihue Basin..........................................................................20

13. Diagram showing distribution of simulated ground-water levels in the 

upper layer of the adjusted model of the southern Lihue Basin.........................................21
iv

14. Diagram showing difference in simulated steady-state ground-water 

levels between pre-development and 1981 conditions in the 

adjusted model of the southern Lihue Basin..........................................................................24

15. Diagram showing difference in simulated steady-state ground-water 

levels between 1981 and 1998 conditions in the adjusted model of 

the southern Lihue Basin...........................................................................................................25

16. Graph showing simulated changes in ground-water level in the Kilohana-Puhi 

well field resulting from irrigation reduction and changes in ground-water 

withdrawals that occurred between 1981 and 1998 .............................................................27

17. Graphs comparing measured water levels in Kilohana well I with model-simulated 

changes in water level at the Kilohana-Puhi well field........................................................28

18. Graphs showing projected changes in water level in the Kilohana-Puhi well field, 

assuming conditions that existed in 2003 remain unchanged ........................................... 29

Tables

1. Estimates of ground-water recharge from water-budget analysis for 

various irrigation and rainfall conditions in the Lihue Basin...............................................12

2. Comparison of recharge estimates from previous water-budget studies ........................13

3. Recharge rates used in model simulations of various drought and irrigation 

scenarios in the ground-water-flow model of the southern Lihue Basin .........................15

4. Simulated ground-water discharge in the adjusted model of 

the southern Lihue Basin...........................................................................................................17

5. Water tunnels in the area simulated by the ground-water model of 

the southern Lihue Basin...........................................................................................................20

6. Production wells and estimated draft used in the numerical-model simulation of 

1981 conditions in the southern Lihue Basin..........................................................................22

7. Production wells and estimated draft used in the numerical-model simulation of 

1998 conditions in the southern Lihue Basin..........................................................................22

8. Periods of irrigation, ground-water withdrawal, and rainfall in 

transient simulations of the adjusted ground-water model of 

the southern Lihue Basin...........................................................................................................26
v

Conversion Factors

Multiply By To obtain

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

gallon (gal) 3.785 liter (L) 

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

cubic foot (ft3) 0.02832 cubic meter (m3) 

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

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

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

Vertical coordinate information is referenced to mean sea level.

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

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

Abstract 

A numerical ground-water-flow model was used to 

investigate the effects of irrigation on ground-water levels 

in the southern Lihue Basin, Kauai, Hawaii, and the relation 

between declining ground-water levels observed in the basin in 

the 1990s and early 2000s and concurrent drought, irrigation 

reduction, and changes in ground-water withdrawal. Results 

of steady-state model simulations indicate that changing from 

pre-development to 1981 irrigation and ground-water-withdrawal conditions could, given enough time for steady state 

to be achieved, raise ground-water levels in some areas of the 

southern Lihue Basin by as much as 200 feet, and that changing from 1981 to 1998 irrigation and ground-water-withdrawal 

conditions could lower ground-water levels in some areas 

by as much as 100 feet. Transient simulations combining 

drought, irrigation reduction, and changes in ground-water 

withdrawal show trends that correspond with those observed in 

measured water levels.

Results of this study indicate that irrigation reduction was 

the primary cause of the observed decline in ground-water-levels. In contrast, ground-water withdrawal had a long-duration 

but small-magnitude effect, and drought had a widespread, 

high-magnitude but short-duration effect. Inasmuch as irrigation in the future is unlikely to return to the same levels as 

during the period of peak sugarcane agriculture, the decline in 

ground-water levels resulting from the reduction and ultimate 

end of sugarcane irrigation can be considered permanent. 

Assuming that irrigation does not return to the southern 

Lihue Basin and that, on average, normal rainfall persists 

and ground-water withdrawal remains at 1998 rates, model 

projections indicate that average ground-water levels in the 

Kilohana-Puhi area will continue to recover from the drought 

of 1998–2002 and eventually rise to within about 4 feet of the 

pre-drought conditions. Long-term climate trends, increases 

in ground-water withdrawal, or other factors not simulated in 

the model could also affect ground-water levels in the southern 

Lihue Basin in the future.

Introduction

About 31,000 people reside in the Lihue Basin, Kauai, 

Hawaii (fig. 1; U.S. Census Bureau, 2006). Most of the public 

drinking water in the basin comes from wells and tunnels that 

develop ground water from a volcanic-rock aquifer, much of 

which has a low regional permeability (Izuka and Gingerich, 

1998). Ground-water levels in the Lihue Basin showed declining trends in the late 1990s and early 2000s. The declining 

water levels resulted in diminished yield from some wells and 

water tunnels, and raised questions about the causes of the 

decline and concerns about the future reliability of groundwater resources.

The observed decline in ground-water levels in the Lihue 

Basin was approximately concurrent with events that could 

have affected ground-water recharge, including a drought from 

1998 to 2002 and a decrease in the volume of water diverted 

from surface-water sources for irrigation between 1981 and 

2000. Analysis of the water budget of the Lihue Basin indicates that both events caused a substantial reduction in groundwater recharge (Izuka and others, 2005). The water-budget 

analysis did not, however, directly assess whether the recharge 

reductions actually caused the decline in ground-water levels 

that was observed in Lihue Basin wells in the late 1990s and 

early 2000s. Increases in ground-water withdrawals may also 

have contributed to this decline. 

Ground-water-modeling studies in the Lihue Basin have 

shown that the introduction of a new production well may 

cause ground-water levels to continue to decline for decades 

before a new equilibrium is reached (Izuka and Oki, 2002). 

Therefore, wells that began production as early as the 1970s 

could have contributed to the decline in ground-water levels 

that was observed in the 1990s. Most of the highly productive 

wells in the Kilohana-Puhi well field (fig. 1) were constructed 

after 1970. Determining whether increases in ground-water 

withdrawals, reduction in ground-water recharge, or both were 

the primary cause of the observed decline in ground-water 

levels requires a comprehensive method of analysis, such as 

a numerical ground-water-flow model, that simultaneously 

considers these factors together with the hydrogeology of the 

basin.

Effects of Irrigation, Drought, and Ground-Water 

Withdrawals on Ground-Water Levels in the Southern 

Lihue Basin, Kauai, Hawaii

By Scot K. Izuka
P A C I F I C O C E A N

Boundary of Lihue Basin

Makaleha Mountains

Lihue

Waialeale

5,148

Kilohana Volcano

1,133

Upper Lihue

Ditch

Hanamaulu Ditch

Kawaikini

5,243

Kilohana-Puhi

well field

Kilohana

well I

Reservoir or other water body

Irrigation ditch

Well

Elevation, in feet above mean 

 sea level 

EXPLANATION

Figure 1.

Shaded relief generated from U.S. Geological Survey 10-meter digital elevation model, 

Universal Transverse Mercator projection, zone 4, NAD83 datum. Base modified from 

U.S. Geological Survey National Hydrography Dataset, 1:24000 scale.

Area of

map KAUAI

PACIFIC

OCEAN

22 ̊

20 ̊

160 ̊ 158 ̊ 156 ̊

PACIFIC OCEAN

Kauai

Niihau

Oahu Maui

Molokai

Lanai

Kahoolawe

Hawaii

HAWAII

LOCATION MAP

S. Fork Wailua R.

N. Fork Wailua R.

Hanamaulu Str.

Huleia Str.

Kapaa Str.

Opaekaa Str. Kalepa Ridge

Nonou Ridge

Kawaikini

5,243

Haupu Ridge

159o30' 159o25' 159o20'

22o

22o05'

0 2 MILES

0 2 KILOMETERS

Figure 1. The Lihue Basin, Kauai, Hawaii.

2 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
Purpose and Scope

This report describes the results of a study, undertaken by 

the U.S. Geological Survey (USGS) in cooperation with the 

County of Kauai Department of Water (Kauai DOW), to assess 

the effects of drought, irrigation changes, and ground-water 

withdrawals on ground-water levels in the southern Lihue 

Basin. The southern Lihue Basin is the part of the basin that 

lies south of the South Fork Wailua River (fig. 1). A numerical ground-water model of the southern Lihue Basin was 

developed by Izuka and Gingerich (1998) and modified by 

Izuka and Oki (2002). 

In this study, ground-water recharge estimates of Izuka 

and others (2005) and updated ground-water-withdrawal data 

were incorporated into the existing model of the southern 

Lihue Basin. This study addresses (1) whether the timing 

and location of the recharge reduction are consistent with the 

observed decline in ground-water levels, considering the rate 

of aquifer response to pumping and recharge stresses; and (2) 

the degree to which changes in ground-water withdrawals also 

contributed to the observed decline in ground-water levels. 

The study also looked backward historically to address how a 

century of irrigation in the southern Lihue Basin had altered 

the ground-water levels from pre-development conditions, and 

forward into the future to assess how ground-water levels will 

respond to the absence of irrigation.

Acknowledgments

Wynne Ushigome, acting Manager and Chief Engineer, 

Edward Tschupp, former Manager and Chief Engineer, and 

the staff of the Kauai DOW provided critical support for this 

study. The State of Hawaii Commission on Water Resource 

Management (CWRM) provided data on ground-water withdrawals. Delwyn S. Oki, Randall T. Hanson, and Connie M. 

Hoong of the USGS assisted in the preparation of this report.

Setting

The Lihue Basin is a 127-mi2 semicircular depression 

on the eastern flank of Kauai, the fourth-largest (553 mi2) 

island in the tropical North Pacific archipelago of Hawaii 

(fig. 1). The Lihue Basin is bounded on the west by the high 

central mountains of Kauai, which include the highest point 

on Kauai (Kawaikini Peak, elevation 5,243 ft), on the north by 

the Makaleha Mountains, on the south by Haupu Ridge, and 

on the east by the Pacific Ocean. A chain of smaller ridges, 

including Kalepa Ridge (elevation 708 ft) and Nonou Ridge 

(elevation 1,241 ft), lie near the eastern coast. In the southcentral part of the basin lies the broad, dome-shaped Kilohana 

Volcano, which rises to an elevation of 1,133 ft. 

Rainfall distribution in the Lihue Basin is influenced by 

the orographic effect (fig. 2). Rainfall is heaviest where the 

prevailing northeasterly trade winds encounter the windward 

flanks of Kauai’s central mountains. Rainfall averages range 

from about 50 in/yr in low-lying coastal areas to more than 

400 in/yr near the crest of the central mountains (Giambelluca and others, 1986). Numerous perennial streams drain 

the Lihue Basin, especially near Kilohana Volcano, where 

many small streams flow radially off the flanks of the volcano 

(fig. 1). Most small streams, however, coalesce with a few 

principal watercourses, including Huleia Stream, Hanamaulu 

Stream, the Wailua River, and Kapaa Stream, before discharging into the Pacific Ocean. 

From the late 19th through 20th centuries, much of the 

Lihue Basin was used for sugarcane agriculture. At its peak, 

the sugarcane industry in the basin diverted tens of billions 

of gallons of stream water to irrigate fields in the drier parts 

of the basin (Shade, 1995; Wilcox, 1996; Izuka and others, 

2005). The water was diverted, transferred, and stored in a 

network of ditches, tunnels, and reservoirs that not only redistributed water within the Lihue Basin but also brought water 

in from, and took water out to, adjacent basins (fig. 1). Thus, 

throughout most of the 20th century, the natural drainage 

pattern of the Lihue Basin had been modified into a network 

of natural stream channels crossed by irrigation ditches, and 

in some areas, natural rainfall was supplemented by irrigation 

water (fig. 3). Hawaii’s sugarcane industry began to decline in 

the 1970s, and by the end of the 20th century, sugarcane was 

being grown commercially in Hawaii only on Kauai and Maui. 

Sugarcane agriculture in the Lihue Basin ceased at the end of 

2000, marking the end of sugarcane irrigation and a significant 

change in the water budget of the Lihue Basin. 

Hydrogeology 

The geology of Kauai and the Lihue Basin has been 

described by research spanning several decades, including 

studies by Stearns (1946, 1985), Macdonald and others (1960), 

Langenheim and Clague (1987), Clague and Dalrymple 

(1988), Holcomb and others, (1997), and Reiners and others 

(1999), which are summarized here. The bulk of Kauai was 

built by mid-oceanic-plate, hotspot volcanism that created 

one or more large shield volcanoes during the Miocene and 

Pliocene. Subsequent erosion and faulting of the shield volcanoes created large valleys, canyons, and other depressions, 

including the Lihue Basin. The eroded and faulted surface 

was partly filled with sediment and lava flows from rejuvenated-stage volcanism during the late Pliocene and Pleistocene. The rocks of rejuvenated-stage volcanism cover most 

of the surface of the Lihue Basin (fig. 4). Rejuvenated-stage 

volcanic vents generally follow two linear trends (fig. 5), one 

essentially north-south and the other approximately N. 60 ̊ E., 

that presumably correspond to rifts through which magma rose 

to supply the rejuvenated-stage eruptions. 

The origin of the Lihue Basin remains enigmatic. Stearns 

(1946, 1985) attributed its formation to advanced stream erosion, whereas later researchers (for example, Macdonald and 

Hydrogeology 3
P A C I F I C O C E A N 

Boundary of Lihue Basin

390

350

310

280

240

200

160

120

80

60

430

Reservoir or other water body

Irrigation ditch

Line of equal mean annual rainfall, in inches

Elevation, in feet above mean sea level

EXPLANATION 

5,243

Shaded relief generated from U.S. Geological Survey 10-meter digital elevation model, 

Universal Transverse Mercator projection, zone 4, NAD83 datum. Base modified from 

U.S. Geological Survey National Hydrography Dataset, 1:24000 scale.

5,148

5,243

120

159o30' 159o25' 159o20'

22o

22o05'

0 2 MILES

0 2 KILOMETERS

Figure 2. 

Figure 2. Mean annual rainfall in the Lihue Basin, Kauai, Hawaii. (Modified from Giambelluca and 

others, 1986.)

4 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
Irrigation ditch

Well

Elevation, in feet above mean sea level 

EXPLANATION 

Shaded relief generated from U.S. Geological Survey 10-meter digital elevation model, 

Universal Transverse Mercator projection, zone 4, NAD83 datum. Base modified from 

U.S. Geological Survey National Hydrography Dataset, 1:24000 scale.

Lihue

Kawaikini

5,243

IRRIGATION METHOD 

Drip

Drip and furrow 

Drip and unirrigated 

Furrow 

Unirrigated 

Unirrigated and furrow 

Unirrigated, furrow, and drip 

Figure 3.

Upper Lihue

Ditch

Hanamaulu Ditch

P A C I F I C O C E A N 

Boundary of Lihue Basin

Kilohana-Puhi

well field

159o30' 159o25' 159o20'

22o

22o05'

0 2 MILES

0 2 KILOMETERS

1981

Kilohana

well I

Waialeale

5,148

Kawaikini

5,243

Figure 3. Sugarcane fields (colored areas) in 1981 and 1998 in the Lihue Basin, Kauai, Hawaii. (From Izuka and 

others, 2005.)

Hydrogeology 5
P A C I F I C O C E A N

Boundary of Lihue Basin

159o30' 159o25' 159o20'

22o

22o05'

0 2 MILES

0 2 KILOMETERS

Upper Lihue

Ditch

Hanamaulu Ditch

Kilohana-Puhi

well field

Shaded relief generated from U.S. Geological Survey 10-meter digital elevation model, 

Universal Transverse Mercator projection, zone 4, NAD83 datum.Base modified from 

U.S. Geological Survey National Hydrography Dataset, 1:24000 scale.

IRRIGATION METHOD

Drip

Drip and furrow

Drip and unirrigated

Furrow

Unirrigated

EXPLANATION

Irrigation ditch

Well

Elevation, in feet above mean sea level Kawaikini

5,243

Waialeale

5,148

Kawaikini

5,243

1998

Figure 3. Continued

Kilohana

well I

Lihue

Figure 3.—Continued.

6 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
0 1 2 MILES

0 1 2 KILOMETERS

PA

CIFIC

OCEAN

159o30' 159o25' 159o20'

22o

21o 55'

22o05'

Lihue

Puhi b

Nawiliwili

Bay

Hanamaulu

Bay

Kalepa Ridge

Nonou Ridge

Haupu Ridge

Waialeale

5,148

Kawaikini

5,243

Base modified from U.S. Geological Survey digital data, 

1:24,000-scale, 1983, Albers Equal Area projection, standard 

parallels 21o 55'40" and 22o 10'20", central meridian 

159o 32'30"

Kilohana

Volcano

crater Kilohana-Puhi

well field

Area of 

map

KAUAI 

PACIFIC 

OCEAN

?

?

Kalepa Ridge

 Pacific

Ocean

Waialeale

Kalepa Ridge

Hanamaulu

Stream

North Fork Wailua River

South Fork Wailua River

Volcano Kilohana

Volcano Kilohan

Dike a

Kapaia

Reservoir

Figure 4. 

Boundary of Lihue Basin

EXPLANATION

SEDIMENTARY DEPOSITS -- Includes 

 surficial sediments and sediments underlying

 or intercalated within the Koloa Volcanics

KOLOA VOLCANICS -- Volcanic rocks 

 from rejuvenated-stage volcanism 

WAIMEA CANYON BASALT -- Volcanic 

 rocks from shield-building volcanism

GEOLOGIC CONTACT -- Dashed 

 where approximate

Boundary of the Lihue Basin

Well

Elevation, in feet above mean sea level Kawaikini

5,243

Figure 4. Geologic map and block diagram of the Lihue Basin, Kauai, Hawaii. (Modified from Macdonald and others, 1960, 

and Izuka and Gingerich, 2003.)

Hydrogeology 7
N

0

0

3 MILES

3 KILOMETERS

LINEAMENTS MARKING 

 TRENDS IN VENT 

 LOCATION -- dashed where

 approximate

KNOWN VENT LOCATION

INFERRED VENT LOCATION

EXPLANATION

Figure 5. Vents of the Koloa Volcanics. (Modified from Macdonald and others, 1960.)

others, 1960; Holcomb and others, 1997) postulated some 

form of collapse. Exploratory drilling indicates that in some 

parts of the basin, the contact between the underlying shield 

volcano and the overlying basin-filling sediment and rejuvenated-stage volcanic rocks is hundreds of feet below present 

sea level (Gingerich and Izuka, 1997; Izuka and Gingerich, 

1997a-d; Reiners and others, 1999). The broad, dome-shaped 

edifice of Kilohana Volcano in the southern Lihue Basin (fig. 

1) is the largest single rejuvenated-stage structure on Kauai. 

Deep borings into the volcano’s eastern flank penetrated 

marine and terrigenous sediment intercalated with lava flows 

(Izuka and Gingerich, 1997a, c), indicating that parts of the 

Lihue Basin had been submerged in the past and that multiple 

episodes of rejuvenated-stage volcanism built the floor of the 

basin above sea level. 

Stratigraphy and Hydraulic Properties

The rocks of the Lihue Basin are divided into two principal units of formational rank separated by an erosional unconformity (fig. 4). The Pliocene Waimea Canyon Basalt, which 

includes the rocks of the shield volcanoes that form the bulk 

of Kauai, constitutes the basement on which younger rocks 

lie (Macdonald and others, 1960; Langenheim and Clague, 

1987). Most of the Waimea Canyon Basalt consists of voluminous accumulations of thin lava flows that built the flanks 

of the shield volcanoes. In southern and western Kauai, flank 

lavas of the Waimea Canyon Basalt form some of the most 

permeable and productive aquifers on the island. Analogous 

flank lava flows on Oahu, Hawaii, have horizontal hydraulic 

conductivities (Kh) of hundreds to thousands of feet per day 

(Soroos, 1973). Vertical hydraulic conductivities (Kv) of aquifers in Hawaii are poorly known, but because of the distinctly 

layered structure of lava-flow aquifers, most investigators have 

presumed that the ratio of Kv to Kh is between 1:3 and 1:200 

(Hunt, 1996). 

In the Lihue Basin, the Waimea Canyon Basalt is mostly 

covered by younger rocks, but where it is exposed in the surrounding mountains and in smaller ridges within the basin, 

the formation is intruded by dense, near-vertical, sheetlike 

volcanic dikes (Macdonald and others, 1960). Dikes tend to 

reduce the overall Kh of the lava flows into which they intrude 

(Takasaki and Mink, 1985). An aquifer test in Haupu Ridge 

indicated a Kh of about 16 ft/d (Gingerich, 1999), but this 

value is probably higher than the regional bulk Kh of the dikeintruded Waimea Canyon Basalt of which the ridge is composed (Izuka and Oki, 2002). Dikes probably also intrude, and 

reduce the bulk permeability of, the Waimea Canyon Basalt 

beneath the floor of the basin (Izuka and Gingerich, 1998). 

8 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
At the western boundary of the basin near Mount Waialeale (fig. 1, 4), the Waimea Canyon Basalt consists of thick 

lava flows that have been variously interpreted as caldera-filling lavas (Macdonald and others, 1960) or lavas that accumulated between multiple shield volcanoes (Holcomb and others, 

1997). The hydraulic properties of this part of the Waimea 

Canyon Basalt are not known, but rocks formed in the caldera 

of the Koolau shield volcano on Oahu have very low permeability, owing to dike intrusion, thick ponded lava, hydrothermal alteration, and secondary mineralization (Stearns and 

Vaksvik, 1935; Takasaki and Mink, 1985). 

Overlying the Waimea Canyon Basalt is the Koloa 

Volcanics, which is of Pliocene through Pleistocene age. The 

Koloa Volcanics consists mostly of rejuvenated-stage volcanic 

rocks but includes sediments that are intercalated with the lava 

flows, as well as sediments that lie directly over the eroded 

surface of the Waimea Canyon Basalt (Macdonald and others, 

1960; Langenheim and Clague, 1987). The Koloa Volcanics 

has heterogeneous aquifer properties, probably owing to the 

presence or absence of dikes or sediments, or to variations in 

the thickness, degree of alteration, or secondary mineralization of lava flows. It is likely that dikes intrude the formation 

along the trends delineated by vents of the Koloa Volcanics 

(fig. 5). The specific capacity (well discharge divided by 

pumping drawdown) of wells in the Koloa Volcanics indicates 

that permeability in this formation varies widely. Aquifer 

tests indicate, however, that in most places the Kh of the Koloa 

Volcanics is less than 1.5 ft/d and may be as low as 0.042 ft/d; 

storage coefficients range from about 10-3 to 10-1 ft-1 (Gingerich, 1999). 

Ground-Water Occurrence and Movement

Fresh ground water in Kauai, as in other oceanic islands, 

forms a lens-shaped body that is underlain by saltwater (fig. 

6). The freshwater lens is buoyed by the density difference between saltwater and freshwater. The transition from 

freshwater to saltwater is a diffuse zone of mixing, but for 

simplicity, especially in the Lihue Basin where the freshwater 

lens is thick, the mixing zone can be envisioned as a sharp 

interface. Fresh ground water in the lens flows continuously 

from recharge areas to discharge areas. In the Lihue Basin, 

the freshwater lens is recharged primarily by infiltration of 

rainfall, although fog drip and irrigation enhance ground-water 

recharge in some places. Ground water in the freshwater lens 

flows generally from inland areas, where rainfall and recharge 

are highest, toward the coast, where it discharges to springs, 

streams, and the ocean. 

Under pre-development conditions (that is, before the 

emplacement of wells or the application of irrigation), the 

freshwater lens is in a state of long-term average dynamic 

equilibrium in which the ground-water recharge rate is balanced by the ground-water discharge rate. This state of 

long-term equilibrium is commonly referred to as steady 

state. When the equilibrium is upset, whether by natural 

stresses such as prolonged droughts, or by artificial stresses 

such ground-water withdrawals (from production wells) or 

recharge from irrigation, the shape and size of the freshwater 

lens change. The rate of change depends on numerous factors, 

including the timing, location, and magnitude of the stresses 

and the hydraulic properties of the aquifer. During this period 

of change, the aquifer adjusts to the new stresses and is said to 

be in a transient state. Droughts and ground-water withdrawals cause the freshwater lens to shrink by lowering the water 

levels in the aquifer and by inducing the freshwater/saltwater 

interface to rise. On the other hand, enhancement of recharge 

by irrigation raises water levels and induces a downward shift 

of the freshwater/saltwater interface. Some stresses, such as 

droughts, will eventually pass, whereas other stresses, such as 

changes in ground-water withdrawal or irrigation, may persist 

for a long time. If stresses persist long enough, the freshwater lens will adjust toward a new steady state in which the 

total input (recharge from rainfall, fog, and irrigation) again 

equals the total output (ground-water withdrawal plus natural 

discharge). 

The moist climate of the Lihue Basin and the low 

regional hydraulic conductivities of the Koloa Volcanics and 

the dike-intruded Waimea Canyon Basalt result in a freshwater 

lens that is thicker than in most other places in Hawaii (fig. 

6). Freshwater saturates the aquifer to higher elevations, such 

that even some small, youthful streams with relatively shallow 

incision intersect and drain water from the upper part of the 

freshwater lens. Streams in the Lihue Basin thus play a substantial role in discharging water from the aquifer and shaping the water table (fig. 7). The low hydraulic conductivities 

result in steep horizontal and vertical hydraulic-head gradients 

that also contribute to the large areal variation in water-table 

elevations (Izuka and Gingerich, 2003). 

Seepage to streams

Low-permeability volcanic rock and 

 sediments

High-permeability lava flows

General direction of ground-water flow

Freshwater

Saltwater

Dikes

Seepage to ocean

Ocean

Not to scale

EXPLANATION 

Figure 6. 

Figure 6. Conceptual model of ground-water occurrence in the 

southern Lihue Basin, Kauai, Hawaii. (From Izuka and Gingerich, 

2003.) 

Hydrogeology 9
0 1 2 MILES

0 1 2 KILOMETERS

PA

CIFIC

O

CEAN

Kalepa Ridge

Nonou Ridge

Haupu Ridge

EXPLANATION

22o 05’

159o 30’ 159o 25’ 159o 20’

22o 55’

22o

Line of equal water-table elevation,1910-96, in feet relative 

 to mean sea level

Boundary of the southern Lihue Basin

Base modified from U.S. Geological Survey digitial data,

1:24,000, 1983, Albers equal area projection, standard

parallels 21o 55’ 40” and 22o 10’ 20”, central meridian

159o 32’ 30”

100

100

200

300

400

600

800

700

500

1000

900

Area of

map

KAUAI

PACIFIC

OCEAN

Figure 7.

Figure 7. Generalized ground-water table map for the southern Lihue Basin, Kauai, Hawaii. (Modified from Izuka and 

Gingerich, 1998.) 

10 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
Most of the wells and tunnels that provide water to the 

southern Lihue Basin develop ground water from the Koloa 

Volcanics. Although most of the Koloa Volcanics has low 

bulk Kh, a few exceptional wells, such as those of the PuhiKilohana well field (fig. 1), can produce as much as 1 Mgal/d. 

These few high-producing wells and tunnels are critical to the 

public water supply in the southern Lihue Basin, but a recent 

decline in ground-water levels has resulted in diminished 

yield in some wells and water tunnels. The decline in water 

levels was approximately concurrent with an extended period 

of lower-than-average rainfall and a decline in diversion of 

stream water for irrigation (fig. 8). 

Effects of Irrigation and Drought on 

Ground-Water Recharge

Izuka and others (2005) used a daily soil-water-budget 

analysis to estimate ground-water recharge for various landuse and irrigation conditions that existed during hydrologically 

significant periods in the history of the Lihue Basin (table 

1). These periods included (1) conditions in 1981, when the 

sugarcane industry was diverting billions of gallons of surface 

water per year for irrigation; (2) conditions in 1998, just 

before cessation of the sugarcane agriculture in the basin; and 

(3) no-irrigation conditions, which represent both pre-development conditions and conditions that are likely to persist after 

the closure of the sugarcane plantations in 2000. 

1951 195319551957195919611963196519671969197119731975197719791981198319851987198919911993199519971999200120032005

YEAR

Drought of

1998-2002

-30

-20

-10

0

10

20

30

40

Lihue Airport

(Mean = 41.25 inches per year)

DEPARTURE FROM MEAN ANNUAL RAINFALL,

IN INCHES ANNUAL FLOW, IN BILLION GALLONS

0

5

10

15

20

25

30

35

No data No data

Plantation

closed

Combined flow of Upper Lihue

and Hanamaulu Ditches

2-5923-07 Kilohana Well I

USGS Number 215901159235201 

205

210

215

220

225

230

WATER LEVEL, IN FEET ABOVE MEAN SEA LEVEL 

Figure 8. Water levels in Kilohana well I, mean annual rainfall at the Lihue Airport, and irrigation-ditch flows in 

the southern Lihue Basin, Kauai, Hawaii. (Rainfall data from National Climatic Data Center, 2006; ditch-flow data 

from records of the Lihue Plantation Company.)

Hydrogeology 11
Results of the water-budget analysis indicate that, 

assuming normal rainfall, ground-water recharge in the Lihue 

Basin was 264 Mgal/d under 1981 irrigation conditions and 

246 Mgal/d under 1998 irrigation conditions (table 1). The 

decrease from 1981 to 1998 was partly due to a reduction in 

sugarcane irrigation as the industry in the basin neared its 

end. Also, some of the remaining fields were converted from 

furrow to drip irrigation, which significantly reduced the 

recharge-enhancing effect of irrigation. On the basis of irrigation-efficiency estimates used by the Hawaii Sugar Planters’ 

Association, Izuka and others (2005) considered drip irrigation 

to be 2.8 to 3.0 times more efficient than furrow irrigation. 

Fields that were converted to drip irrigation between 1981 and 

1998 included those near the Kilohana-Puhi well field, where 

declining ground-water levels were observed (fig. 3).

Results of the water-budget analysis also indicate that 

under no-irrigation conditions, ground-water recharge in 

the Lihue Basin was 212 Mgal/d (table 1). Comparison of 

this estimate with the recharge estimate for 1981 conditions 

indicates that irrigation had artificially increased ground-water 

recharge in the Lihue Basin by about 25 percent over no-irrigation conditions. The effects of irrigation on ground-water 

recharge were concentrated within the drier coastal areas, 

where irrigation was needed to supplement natural precipitation. All of the wells in the Lihue Basin that showed declining 

water levels are near irrigated areas. 

Izuka and others (2005) also estimated ground-water 

recharge for various combinations of drought and irrigation 

(table 1). The severity of one of the droughts simulated in 

their analysis was comparable to that of the drought of 1998-

2002 (fig. 8). Ground-water recharge under 1981 irrigation 

and drought conditions was estimated to be 131 Mgal/d (about 

50 percent lower than under 1981 irrigation and normal rainfall conditions). Ground-water recharge under 1998 irrigation 

and drought conditions was estimated to be 114 Mgal/d (about 

54 percent lower than under 1998 irrigation and normal rainfall conditions). Ground-water recharge under no-irrigation 

and drought conditions was estimated to be only 84 Mgal/d. 

These results indicate that a drought similar in magnitude to 

that of 1998-2002 could substantially reduce ground-water 

recharge in the Lihue Basin for a few years.

Unlike the effects of irrigation, the effects of drought on 

ground-water recharge in the Lihue Basin are widespread. 

Drought conditions in Hawaii are identified by statistically 

significant departures from normal rainfall, but the cause of 

droughts is commonly associated with quasi-periodic events, 

such as the El Niño Southern Oscillation (ENSO). Droughts 

are therefore expected to recur periodically but are balanced 

by higher-than-average rainfall periods. In contrast, irrigation 

in the Lihue Basin is not likely to return to the same magnitude as during the peak of sugarcane agriculture in the 20th 

century, when most sugarcane irrigation was by the furrow 

method. This inefficient and obsolete method returns much 

of the applied water to soil infiltration and ground-water 

recharge. Even if some form of agriculture replaces sugarcane in the Lihue Basin, it will probably use a more efficient 

method, such as drip irrigation, that contributes much less to 

ground-water recharge.

Ground-water recharge was significantly higher in the 

water-budget analysis of Izuka and others (2005) than it was in 

an earlier water-budget analysis by Shade (1995). Shade estimated that 19 percent of the total water input to the basin (sum 

of precipitation plus irrigation) went to ground-water recharge, 

whereas Izuka and others estimated that 34 percent of the total 

water input to the basin went to ground-water recharge (table 

2). This discrepancy was too large to be attributed to the difference in periods analyzed by the two studies; in the Lihue 

Basin, the 1990 conditions analyzed by Shade were comparable to the 1998 irrigation and normal rainfall conditions 

analyzed by Izuka and others. Izuka and others attributed the 

discrepancy to differences in the methods used to distinguish 

between base flow (the component of streamflow that comes 

from ground-water discharge) and direct runoff in streamgage records. Shade used a flow-duration analysis that can 

overestimate runoff, and in turn underestimate ground-water 

recharge, in areas such as the Lihue Basin where a substantial 

part of the total streamflow is ground-water discharge. Izuka 

and others used a hydrograph-separation technique that more 

accurately assesses the base-flow characteristics of each 

stream. To improve the accuracy of their recharge estimate 

even more, Izuka and others incorporated details of the sugarcane irrigation process and crop water demands, and used a 

smaller time step (daily) than did Shade (monthly). For these 

reasons, the recharge estimates of Izuka and others were used 

in the following analyses of the effects of drought, irrigation, 

and ground-water withdrawal on ground-water levels in the 

southern Lihue Basin.

Table 1. Estimates of ground-water recharge from water-budget 

analysis for various irrigation and rainfall conditions in the Lihue 

Basin, Kauai, Hawaii.

[From Izuka and others, 2005; Mgal/d, million gallons per day]

Scenario Recharge

(Mgal/d)

1981 irrigation, normal rainfall 264

1998 irrigation, normal rainfall 246

No irrigation, normal rainfall 212

1981 irrigation, with drought 131

1998 irrigation, with drought 114

No irrigation, with drought 84

12 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
Effects of Irrigation, Drought, and 

Ground-Water Withdrawal on 

Ground-Water Levels

Assessing the link between the observed decline in 

ground-water levels and historical drought and changes in 

irrigation and ground-water withdrawals in the Lihue Basin 

requires simultaneous consideration of the variation of these 

factors in space and time together with the hydraulic properties of the rocks. Numerical ground-water-flow modeling 

is currently the most comprehensive method available for 

studying the complex, interrelated factors governing groundwater systems. Ground-water levels computed by the model 

simulate those in the real aquifer. Stresses such as drought 

and changes in ground-water withdrawals or irrigation can be 

simulated in the model, and simulated ground-water levels 

can be tracked to assess how ground-water levels in the real 

aquifer will be affected. 

By incorporating recently revised recharge estimates and 

using updated information to compute historical changes in 

ground-water withdrawals, the numerical ground-water-flow 

model of the southern Lihue Basin created by Izuka and Gingerich (1998) can be adapted to determine which factors, or 

combination of factors, are likely to have caused the observed 

decline in ground-water levels in the Lihue Basin. Although 

the model covers only half the basin, it includes the KilohanaPuhi well field (fig. 1), which is both an important source of 

drinking water and an area where declining water levels have 

threatened the productivity of wells (fig. 9).

Original Southern Lihue Basin Model 

For discussion purposes, the numerical ground-waterflow model of the southern Lihue Basin constructed by Izuka 

and Gingerich (1998) is referred to as the original southern 

Lihue Basin model (or simply “original model”) in this report. 

A detailed description of this model is given in the report by 

Izuka and Gingerich; a review of model features relevant to 

this study is given here. The original southern Lihue Basin 

model was created using a modified version of the finite-difference modeling program SHARP (Essaid, 1990), which 

allows quasi-three-dimensional simulation of the freshwater/

saltwater systems in island and coastal aquifers. Freshwater 

and saltwater are treated as immiscible fluids separated by a 

sharp interface. Ground-water flow is governed by user-specified aquifer properties and distribution of model-calculated 

freshwater and saltwater heads. Streams and offshore areas 

were simulated using leaky confined cells. Ground-water 

seepage to streams and the ocean is governed by user-specified streambed and ocean-floor hydraulic properties and by the 

difference between model-calculated heads in the uppermost 

layer of the model and user-specified heads in the streams and 

at the ocean bottom. Head above a stream cell was set equal 

to the elevation of the stream cell as determined from topographic maps; head above an ocean-floor cell was set at sealevel equivalent freshwater head (head adjusted for the density 

difference between freshwater and saltwater and the depth of 

the cell below sea level, also determined from topographic 

maps).

Although the area of interest of the original southern 

Lihue Basin model lies entirely within the Lihue Basin, the 

model includes areas of southeastern Kauai that lie outside 

the basin (fig. 9). The model was extended beyond the limits 

of the basin so that model boundaries would not substantially 

affect ground-water flow within the basin (Izuka and Gingerich, 1998). Because areas outside the basin are not within 

the area of interest, it was not necessary to model them in as 

much detail as areas within the basin. The modeled area was 

divided into two layers, each layer having 2,475 cells, and 

each cell representing an area 2,000 ft by 2,000 ft. The upper 

layer extended to an elevation of -500 ft, which corresponds 

to the depth of the contact between the Koloa Volcanics and 

the underlying Waimea Canyon Basalt as shown on the geologic map by Macdonald and others (1960). The lower layer 

extended from -500 ft to -6,000 ft elevation. 

Recharge in the original model was 191 Mgal/d distributed over the modeled area according to the average annual 

recharge estimated by Shade (1995) on the basis of conditions that existed in 1990. Ground water in the Lihue Basin 

is developed from conventional vertical wells and from water 

Table 2. Comparison of recharge estimates from previous water-budget studies. 

[From Izuka and others (2005)]

Study Conditions

Percent of total input (precipitation plus irrigation)

Runoff Actual 

evapotranspiration Recharge

Izuka and others (2005) 1998 irrigation, normal rainfall 30 36 34

Shade (1995) 1990 conditions 48 34 19

Effects of Irrigation, Drought, and Ground-Water Withdrawal on Ground-Water Levels 13
Hanapepe River

Nawiliwili Stream

Huleia Stream

Hanamaulu Stream

South Fork Wailua River North Fork Wailua River

0

0

5 MILES

5 KILOMETERS

22o 00’

159o 20’

159o 20’

159o 30’

159o 40’

22o 00’

22o 10’ 22o

 10’

159o 40’

159o 30’

Kilohana-Puhi well field

No-flow boundary of model

Model grid lines

Boundary of the southern Lihue Basin

EXPLANATION

Figure 9. 

Figure 9. Boundaries of the numerical ground-water-flow model of the southern Lihue Basin, Kauai, Hawaii. (Modified from 

Izuka and Gingerich, 1998.) 

14 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
tunnels (infiltration galleries that are driven parallel to the 

water table near streams). In the original model, withdrawals from conventional wells were based on water-use statistics obtained in 1993 from CWRM. Three water tunnels are 

within the active area of the original southern Lihue Basin 

model. Because these tunnels essentially intercept ground 

water that would normally have discharged to nearby streams, 

the tunnels were simulated using leaky confined aquifer cells. 

Three hydrogeologic groups with contrasting hydraulic 

conductivities were included in the original model: (1) the 

Koloa Volcanics, with Kh of 0.275 ft/d and Kv of 5.5 × 10-4 ft/d; 

(2) the dike-free Waimea Canyon Basalt, with Kh of 200 ft/d 

and Kv of 1.0 ft/d; and (3) the dike-intruded Waimea Canyon 

Basalt with Kh of 1.11 ft/d and Kv of 1.1 × 10-2 ft/d. 

Adjusting the Model to Revised Recharge 

Estimates

In any steady-state ground-water-flow model, a balance 

exists between simulated parameters such as hydraulic properties, water levels, and discharge. In constructing a model 

that is representative of an area of interest, values of model 

parameters that are known with the least certainty are adjusted 

until the values of other model parameters match known or 

measured values in the area of interest (a procedure commonly 

referred to as calibration). In the original southern Lihue 

Basin model, aquifer hydraulic properties were considered a 

parameter of greater uncertainty than ground-water recharge, 

water levels, or withdrawals, or stream base flow. Therefore, 

once a reliable estimate of ground-water recharge and well 

withdrawals was entered into the model, hydraulic properties 

were adjusted until (1) simulated water levels matched water 

levels measured in wells and (2) simulated ground-water discharge to streams matched base flows computed from streamgage records. Ground-water recharge in the original southern 

Lihue Basin model was based on the recharge estimates of 

Shade (1995). Because the recharge estimates are probably 

low, it was necessary for the purposes of this study to update 

the model using the revised recharge estimates of Izuka and 

others (2005). In this report, the model adjusted to the revised 

recharge estimates is referred to as the adjusted southern Lihue 

Basin model (or simply, “adjusted model”). 

After the revised recharge estimates were incorporated 

into the model, two aspects of the model — namely, the 

representation of streams and the distribution of hydraulic 

conductivity — were adjusted until simulated ground-water 

levels matched measured ground-water levels and simulated 

ground-water discharge to streams matched computed stream 

base flows. Ground-water levels used for matching purposes 

were the same as those used in the original model; pumping 

conditions were also kept the same as those simulated in the 

original model during the matching procedure. Ground-water 

recharge computed by Izuka and others (2005) for 1998 irrigation and normal rainfall conditions (table 1) was used in the 

adjustment because these conditions are similar to those on 

which the original model was based. 

Izuka and others (2005) computed recharge only for areas 

within the Lihue Basin. The original southern Lihue Basin 

model, however, includes areas that are outside the basin (fig. 

9). To estimate recharge for areas outside the basin, regression equations relating ground-water recharge to mean annual 

soil infiltration (precipitation minus runoff) were developed 

from the results of Izuka and others (see Appendix). Mean 

annual soil infiltration for areas outside the basin was entered 

into the regression equations to compute ground-water 

recharge. Mean annual soil infiltration was determined using 

an approach similar to that used by Izuka and others for areas 

within the basin. Using a geographic information system 

(GIS), mean annual precipitation was determined from the 

mean-annual rainfall map of Kauai by Giambelluca and others 

(1986). Fog contribution of 0.18 times mean annual rainfall 

was added to precipitation in areas above 2,000 ft elevation. A 

runoff-to-rainfall ratio of 0.28 was computed for the drainage area of stream gage 16049000 on the Hanapepe River and 

applied to the mean annual rainfall map of Giambelluca and 

others to determine the distribution of mean annual runoff. 

Mean annual runoff was subtracted from mean annual precipitation to determine mean annual soil infiltration, which was, 

in turn, used in the regression equation to determine mean 

annual ground-water recharge. The resulting total recharge 

within the active model area for 1998 irrigation and normal 

rainfall conditions was 304 Mgal/d (table 3), which is about 54 

percent higher than in the original model. 

Table 3. Recharge rates used in model simulations of various 

drought and irrigation scenarios in the ground-water-flow model 

of the southern Lihue Basin, Kauai, Hawaii.

Scenario Recharge in model

(million gallons per day)

1981 irrigation, normal rainfall 315

1998 irrigation, normal rainfall 304

No irrigation, normal rainfall 274

1998 irrigation, with drought 144

No irrigation, with drought 118

Result of Model Adjustment

To a large extent, the representation of streams in the 

adjusted model is the same as that in the original model. 

Some simulated streams were lengthened or shortened (fig. 

10) to more accurately represent streams in the southern 

Lihue Basin, and the heads overlying some stream cells were 

adjusted to more precisely represent stream-channel elevations 

shown on topographic maps. A single value of 2.3×10-5 day-1

was used for both stream-bed and ocean-floor leakance (Kv of 

a stream cell divided by one-half the vertical thickness of the 

cell), which is equal to the value used by Izuka and Gingerich 

(1998) in the original model. 

Effects of Irrigation, Drought, and Ground-Water Withdrawal on Ground-Water Levels 15
10

20

30

40

10 20 30 40 50

0

0 5 KILOMETERS

5 MILES

N

Stream cell

Offshore cell

Unconfined cell

No-flow cell

Stream

Coastline

Boundary of the southern 

Lihue Basin

Well

Water tunnel

Cell monitored for Kilohana-Puhi

ground-water levels 

Cell used for matching simulated 

and measured ground-water levels

Location of stream gage used for 

matching simulated and observed 

base flows 

EXPLANATION

Kilohana

Well I

Figure 10. Cells used to simulate streams, submarine areas, wells, and water tunnels in the adjusted model of the 

southern Lihue Basin, Kauai, Hawaii. 

16 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
The distribution of hydraulic conductivities in the 

adjusted model is also similar to those in the original model, 

except that some detail was added to improve consistency 

with the geologic map by Macdonald and others (1960), and 

to more accurately represent the relative positions of rock 

types and streams. In the original model, the Waimea Canyon 

Basalt was divided into dike-intruded and dike-free units with 

different hydraulic properties, but the Koloa Volcanics was 

modeled as a single hydrogeologic unit with uniform hydraulic 

properties. In the adjusted model, both the Koloa Volcanics 

and the Waimea Canyon Basalt are divided into dike-intruded 

and dike-free units (fig. 11). In the adjusted model, distribution of dike-intruded and dike-free Waimea Canyon Basalt is 

based on dikes shown on the geologic map by Macdonald and 

others. The distribution of dike-intruded and dike-free Koloa 

Volcanics in the adjusted model is based on the locations of 

lineaments and associated volcanic vents depicted by Macdonald and others, and the premise that dikes probably intrude 

the Koloa Volcanics along fissures marked by lineaments and 

reduce the bulk hydraulic conductivity of the region. The 

lineaments and associated volcanic vents are limited to the 

western two-thirds of the Lihue Basin; thus, in the adjusted 

model, the Koloa Volcanics in the western two-thirds of the 

basin was presumed to be intruded by dikes and given a lower 

hydraulic conductivity than the Koloa Volcanics in the eastern 

part of the basin (fig. 11). 

The values of hydraulic conductivity in the adjusted 

model are, in most areas, equal to or higher than those in the 

original model; this is expected because the recharge in the 

adjusted model is higher than the recharge in the original 

model. Values of hydraulic conductivity for the dike-intruded 

Koloa Volcanics in the adjusted model are equal to or slightly 

lower than the values for the Koloa Volcanics in the original model, whereas the values of hydraulic conductivity for 

the dike-free Koloa Volcanics are higher than in the original 

model. Hydraulic conductivities of all parts of the Koloa 

Volcanics in the adjusted model are, however, within the range 

determined by Gingerich (1999) from aquifer-test analyses. 

Values of hydraulic conductivity for the dike-intruded Waimea 

Canyon Basalt are higher in the adjusted model than in the 

original model. Values of hydraulic conductivity for the 

dike-free Waimea Canyon Basalt are the same in the adjusted 

model and the original model. 

The overall distribution of simulated ground-water levels 

in the adjusted model matched measured water levels at monitor points more closely than did the simulated water levels 

in the original model (fig. 12). The distribution of simulated 

ground-water levels in the upper layer of the adjusted model 

(fig. 13) is consistent with the distribution of measured water 

levels in the southern Lihue Basin (fig. 7) and similar to the 

distribution of ground-water levels in the original model. 

The agreement between total simulated ground-water 

discharge (table 4) and total simulated ground-water recharge 

(equal to ground-water recharge for 1998 irrigation, normal 

rainfall conditions in table 3) confirms that the adjusted model 

represents steady-state conditions. As a whole, simulated 

stream base flows in the adjusted model match observed base 

flows of streams in the modeled area more closely than did 

simulated base flows in the original model (fig 12). As in the 

original model, a larger fraction of ground-water flow discharges at streams than at the coast. Of the 304 Mgal/d total 

ground-water discharge in the adjusted model, 181 Mgal/d (60 

percent) discharges at streams, 108 Mgal/d (35 percent) discharges to the ocean, and 15 Mgal/d (5 percent) is withdrawn 

from wells. 

Model-simulated ground-water discharges at the Hanapepe Pump 3, Kokolau, and Garlinghouse tunnels differ substantially from average recorded withdrawals (table 5), but the 

discrepancies do not affect the results of the adjusted model as 

they relate to the objectives of this study. The discrepancies 

result because tunnels are so close to streams that the model 

cells representing the tunnels incorporate some seepage to 

and from nearby streams. In some cases (Hanapepe Pump 3, 

for example), simulated tunnel discharge is less than recorded 

draft because the tunnel develops both ground water and 

surface water from the nearby stream (Izuka and Gingerich, 

1998). In other cases (Kokolau, for example), simulated tunnel discharge is greater than recorded draft because the model 

cell representing the tunnel probably incorporates some seepage from the nearby stream. 

The level of discretization in both the original and 

adjusted models precludes closer matching of simulated to 

observed ground-water levels and stream base flows, especially where horizontal hydraulic gradients are steep, as in 

most areas of the basin. Whereas a measured ground-water 

level is characteristic of the water level at a single point on a 

Table 4. Simulated ground-water discharge in the adjusted 

model of the southern Lihue Basin, Kauai, Hawaii.

[Actual values from Izuka and Gingerich (1988). NA, not applicable]

Discharge location

Ground-water discharge

(million gallons per day)

Model Actual

Hanapepe Stream 46 46

Huleia Stream 16 22

Hanamaulu Stream 5 5

South Fork Wailua River 59 57

Other streams 55 NA

Total for streams 181 NA

Ocean 108 NA

Wells 15 15

Total ground-water discharge 304 NA

Effects of Irrigation, Drought, and Ground-Water Withdrawal on Ground-Water Levels 17 
Figure 11. Distribution of hydraulic conductivities in the adjusted numerical model of the southern Lihue Basin, 

Kauai, Hawaii. Lineaments tracing vents of the Koloa Volcanics are shown for comparison. Kh is horizontal hydraulic 

conductivity, and Kv is vertical hydraulic conductivity.

DIKE-INTRUDED KOLOA VOLCANICS --

Kh = 0.220 to 0.275 feet per day, 

Kv = 0.0009 to 0.0011 feet per day

DIKE-FREE KOLOA VOLCANICS --

Kh = 1.10 feet per day, 

Kv = 0.0022 feet per day.

DIKE-INTRUDED WAIMEA CANYON 

BASALT -- Kh = 3.89 feet per day, 

Kv = 0.0389 feet per day.

DIKE-FREE WAIMEA CANYON BASALT --

Kh = 200 feet per day, 

Kv = 1.00 foot per day.

No-flow cell

Coastline

Boundary of the southern Lihue Basin

EXPLANATION

UPPER LAYER

10

20

30

40

10 20 30 40 50

N

0

0 5 kilometers

5 miles

Figure 11. 

LINEAMENTS MARKING TRENDS IN 

 LOCATION OF VENTS OF THE KOLOA

 VOLCANICS -- Dashed where approximate. 

 Modified from Macdonald and others (1960)

18 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
DIKE-INTRUDED WAIMEA CANYON

 BASALT, INNER BASIN -- includes dikes from

 Waimea Canyon Basalt and Koloa Volcanics

Kh = 0.220 to 0.275 feet per day, 

Kv = 0.0009 to 0.0011 feet per day.

DIKE-INTRUDED WAIMEA CANYON 

BASALT -- Kh = 3.89 feet per day, 

Kv = 0.0389 feet per day.

DIKE-FREE WAIMEA CANYON BASALT --

Kh = 200 feet per day, 

Kv = 1.00 foot per day.

No-flow cell

Coastline

Boundary of the southern Lihue Basin

EXPLANATION

LOWER LAYER

10

20

30

40

10 20 30 40 50

N

0

0 5 KILOMETERS

5 MILES

Figure 11. Continued

LINEAMENT MARKING TREND 

 IN LOCATION OF VENTS OF THE

 KOLOA VOLCANICS -- Dashed

 where approximate. Modified from 

 Macdonald and others (1960)

Figure 11.—Continued.

Effects of Irrigation, Drought, and Ground-Water Withdrawal on Ground-Water Levels 19
0

100

200

300

400

500

600

700

800

900

0 100 200 300 400 500 600 700 800 900

MEASURED GROUND-WATER LEVEL, IN FEET

SIMULATED GROUND-WATER LEVEL IN FEET

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100

SIMULATED BASE FLOW, IN CUBIC FEET PER SECOND

OBSERVED BASE FLOW, IN CUBIC FEET PER SECOND

Adjusted model

Original model

Slope = 1

Figure 12. 

Figure 12. Observed ground-water levels and stream base flows compared with simulated ground-water levels and stream 

base flows in the adjusted numerical ground-water model of the southern Lihue Basin, Kauai, Hawaii.

steep gradient, a simulated ground-water level represents an 

average ground-water level in a 4-million-square-foot area 

near the observation point in the model. Similarly, the aquifer 

properties, aquifer water level, and stream elevation simulated in a stream cell are each an average of these properties 

within the area represented by the cell. Actual stream properties, especially stream elevation, can vary greatly within the 

2,000-ft by 2,000-ft area of a model cell. 

Simulation of the Effects of Irrigation, Drought, 

and Ground-Water Withdrawal

The adjusted southern Lihue Basin model was used for 

steady-state and transient simulations to study the relations 

between the observed decline in ground-water levels and 

historical irrigation, drought, and ground-water withdrawals. 

Various conditions of rainfall and irrigation were simulated 

in the model by incorporating the recharge estimates of Izuka 

and others (2005). Recharge for areas outside the basin was 

estimated using the regression method described previously. 

Changes in ground-water withdrawal from conventional 

wells (water tunnels were simulated as leaky confined-aquifer cells, as discussed earlier) for the periods represented by 

the recharge scenarios of Izuka and others (2005) were also 

computed and incorporated into the adjusted model. Groundwater withdrawals representative of 1981 and 1998 were 

computed from records at the CWRM. The records consist of 

withdrawal rates reported periodically (about monthly). Most 

wells have some records, but these records are not always 

complete for the entire period the well was in use (K. Gooding, CWRM, oral commun., 2005), especially before adoption of the Hawaii State Water Code in 1987. For this study, 

estimates of the average ground-water-withdrawal rates in the 

southern Lihue Basin for 1981 and 1998 were computed on 

the basis of reported pumping rates and dates indicating when 

Table 5. Water tunnels in the area simulated by the ground-water model of the southern Lihue Basin, Kauai, Hawaii.

[Data on reported draft from K. Gooding, Hawaii State Commission on Water Resource Management, written commun., 2005; Mgal/d, million gallons per day]

Well number Tunnel Year built Location

Average reported draft Simulated discharge in

adjusted model 

(Mgal/d)

Rate 

(Mgal/d)

Period of 

record

5534-01 Hanapepe Pump 3 1899 Outside basin 10.505 1983-2001 1.071

5725-01 Kokolau 1928 In basin 0.288 1987-2005 0.602

5823-01 Garlinghouse 1935 In basin 0.715 1987-2005 0.474

20 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
Figure 13. Distribution of simulated ground-water levels in the upper layer of the adjusted model of the southern 

Lihue Basin, Kauai, Hawaii.

100

Kilohana-Puhi well field

Line of equal simulated head, in feet relative

 to sea level

Stream

Boundary of the southern Lihue Basin

EXPLANATION

100

200

300

400

500

600

800

1,000

1,200

1,400

1,600

1,800

2000

10

20

30

40

10 20 30 40 50

N

0

0 5 KILOMETERS

5 MILES

Figure 13.

Effects of Irrigation, Drought, and Ground-Water Withdrawal on Ground-Water Levels 21
the well was in use, such as (1) the date of the first and last 

reported withdrawal; (2) the date of well construction; (3) the 

date of pump installation; (4) the “draft” date, which is the 

date an approximate average withdrawal from the well was 

reported; and (5) the “use” date, which is the date the use of 

well’s water was reported. For example, if the date of the first 

reported draft, pump-installation date, or the “use” or “draft” 

date for a given well is earlier than 1981, and the last reported 

draft is after 1981, the well was presumed to have been in use 

in 1981, whether or not any draft was reported for 1981. If 

the date of the first reported draft is after 1981 and no pumpinstallation date or “draft” date is listed, then the date of well 

construction was considered. If the well was completed more 

than 4 years before 1981 and there is a record of the well 

having been in use after 1981, then the well was assumed to 

have been in use in 1981. A similar procedure was used to 

determine which wells were in use in 1998. Once a well was 

determined to have been in use in 1981 or 1998, a withdrawal 

rate equivalent to the average of the reported draft rates was 

simulated in the ground-water model (tables 6, 7). 

Table 7. Production wells and estimated draft used in the 

numerical-model simulation of 1998 conditions in the southern 

Lihue Basin, Kauai, Hawaii.

[Data from K. Gooding, Hawaii State Commission on Water Resource Management, written commun., 2005; Mgal/d, million gallons per day] 

Well 

number Name Year built

Simulated draft 

(Mgal/d)

In basin

5820-01 Westin 3 1987 0.065

5821-03 Westin 1 1987 0.032

5821-04 Westin 2 1987 0.107

5821-05 Westin 4 1987 0.107

5821-06 Westin 5 1987 0.098

5822-02 Grammar school 1961 0.083

5824-01 Puhi 1 1975 0.158

5824-03 Puhi 2 1980 0.033

5824-05 Puhi 3 1990 0.213

5824-06 Puhi 4 1993 0.096

5923-01 Kilohana A 1974 0.248

5923-02 Kilohana B 1977 0.280

5923-03 Kilohana C 1978 0.057

5923-04 Kilohana F 1980 0.031

5923-05 Kilohana G 1981 0.150

5923-07 Kilohana I 1982 0.652

Total 2.410

Outside basin

5426-04 Koloa C 1977 0.575

5426-05 Koloa D 1981 0.770

5427-01 Koloa A 1953 0.177

5427-02 Koloa B 1964 0.311

5529-01 Huinawai Reservoir 1950 1.690

5530-03 Lawai 1 1962 0.193

5530-04 Lawai 2 1986 0.162

5533-01 Hanapepe Valley A 1974 0.552

5533-02 Hanapepe Valley B 1980 0.287

5534-03 Hanapepe Town 1966 0.029

5631-01 Kalaheo A-Diesel 1974 0.403

5631-02 Kalaheo B 1985 0.067

5635-01 Domestic Water 1947 1.373

5635-02 500 H.P. Irrigation 1969 0.806

Total 7.395

Table 6. Production wells and estimated draft used in the 

numerical-model simulation of 1981 conditions in the southern 

Lihue Basin, Kauai, Hawaii.

[Data from K. Gooding, Hawaii State Commission on Water Resource Management, written commun., 2005; Mgal/d, million gallons per day] 

Well 

number Name Year built Simulated draft (Mgal/d)

In basin

5822-01 Sugar mill 1965 0.032

5822-02 Grammar school 1961 0.083

5824-01 Puhi 1 1975 0.158

5923-01 Kilohana A 1974 0.248

Total 0.521

Outside basin

5427-01 Koloa A 1953 0.177

5425-11 Mahaulepu 11 1927 0.924

5426-03 Koloa 1953 2.263

5523-01 Kipu Kai 1950 0.011

5523-02 Kipu Kai 1960 0.209

5526-01 Kaluahonu 1966 0.118

5527-01 Kahoano 1966 0.444

5427-02 Koloa B 1964 0.311

5529-01 Huinawai Reservoir 1950 1.690

5530-03 Lawai 1 1962 0.193

5533-01 Hanapepe Valley A 1974 0.552

5534-03 Hanapepe Town 1966 0.029

5631-01 Kalaheo A-Diesel 1974 0.403

5635-01 Domestic Water 1947 1.373

5635-02 500 H.P. Irrigation 1969 0.806

Total 9.503

22 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
Steady-State Simulations

Steady-state simulations represent the ground-water 

levels that would ultimately develop under a given set of 

conditions (rainfall, irrigation, and ground-water withdrawal), 

assuming enough time is allowed to achieve equilibrium. 

Three steady-state conditions were simulated in this study: (1) 

pre-development conditions, when no irrigation was applied in 

the study area and no ground water was being withdrawn from 

wells; (2) 1981 irrigation and ground-water-withdrawal conditions; and (3) 1998 irrigation and ground-water-withdrawal 

conditions. Normal rainfall was used in all three steady-state 

simulations. As discussed earlier, the level of discretization, 

together with the steep hydraulic gradients characteristic of the 

study area, limits the precision to which model ground-water 

levels can be made to match actual ground-water levels. The 

adjusted model simulates ground-water-level differences, however, with sufficient accuracy for the purposes of this study. 

Figure 14 shows the difference in simulated steady-state 

ground-water levels between pre-development and 1981 

conditions. Ground-water levels in the lowland areas between 

major streams are substantially higher in the simulation of 

1981 conditions as a result of the recharge-enhancing effects 

of furrow irrigation (fig. 3). Steady-state ground-water levels 

beneath some irrigated areas are as much as 200 ft higher in 

the 1981 simulation than in the pre-development simulation. 

In some parts of the Kilohana-Puhi well field (fig. 1), irrigation raised simulated water levels by more than 50 ft. In areas 

of the southern Lihue Basin unaffected by furrow irrigation, 

ground-water levels in the 1981 simulation are slightly lower 

(as indicated by values less than zero in fig. 14) as a result of 

ground-water withdrawal. The effect of irrigation on simulated ground-water levels is, however, overwhelmingly greater 

than the effect of ground-water withdrawal. 

Figure 15 shows the difference in simulated steady-state 

ground-water levels between 1981 and 1998 conditions. The 

largest difference is in the area between Huelia and Nawiliwili 

Streams, where water levels in the 1998 steady-state simulation are as much as 100 ft lower than in the 1981 steady-state 

simulation. This area corresponds to a part of the aquifer 

underlying fields that were taken out of sugarcane production between 1981 and 1998. The area is also downgradient 

from fields that were converted from furrow to drip irrigation 

between 1981 and 1998, and the Kilohana-Puhi wells, most of 

which were built from the 1970s to 1990s (fig. 3). In the area 

south of Huleia Stream, ground-water levels in the 1998 simulation are slightly higher than in the 1981 simulation. The 

higher water levels result from the decrease in ground-water 

withdrawal after pumping from an irrigation well south of the 

Lihue Basin was halted. 

The steady-state simulations indicate that irrigation 

changes from pre-development to 1981 and from 1981 to 

1998 had an overwhelming effect on ground-water levels in 

the southern Lihue Basin. In contrast, the changes in groundwater withdrawals during those periods had a much smaller 

effect on regional ground-water levels. The steady-state 

simulations represent the ground-water levels that would 

ultimately result if enough time is available for steady state to 

be achieved, but in reality, the ground-water system may not 

fully adjust to changes that occur quickly, or to stresses (such 

as droughts) that are of short duration. For example, it is 

possible that the difference in simulated ground-water levels 

between 1981 and 1998 shown in figure 15 did not, in reality, 

develop fully before conditions again changed with the onset 

of drought in 1998 and the end of sugarcane irrigation in 2000. 

Effects of this relatively rapid succession of changes are more 

effectively studied using transient simulations. 

Transient Simulations

Transient simulations show how effects on groundwater levels develop over time. The rate at which an aquifer 

responds to irrigation, drought, and ground-water withdrawal 

is a function of aquifer porosity and storage — lower porosity and storage values correspond to faster aquifer response. 

Because aquifer porosity and storage are not precisely known, 

the effects were tested using a range of values. Laboratory 

testing and photograph analysis indicate that total porosity in 

the lava-flow aquifers in Hawaii ranges from about 5 to 50 

percent, but effective porosity (n) may be lower by a factor 

of 10 (Hunt, 1996). Massive lava flows, such as those of the 

Koloa Volcanics and dike-intruded Waimea Canyon Basalt 

in the Lihue Basin, are likely to have even lower n. For the 

transient simulations in this report, n values of 1 and 10 percent were used. Specific storage (Ss

) was varied between 10-6

ft-1 and 10-4 ft-1, which is consistent with aquifer-test analyses 

by Gingerich (1999) and similar to the values used by Izuka 

and Oki (2002) in their transient simulations of ground-water 

withdrawals in the Lihue Basin.

Three sets of transient simulations, each representing a 

given combination of drought, irrigation, and ground-waterwithdrawal conditions, were tested in this study. Within each 

set, values of n and Ss were varied. In all cases, the results of 

the steady-state simulation of 1981 conditions with normal 

rainfall were used as initial conditions, and various combinations of drought, irrigation, and ground-water withdrawal were 

applied as stresses. Changes in water level in an upper-layer 

cell (row 16, column 33) of the model were monitored to 

represent water-level changes in the Kilohana-Puhi well field. 

Changes in this water level were tracked through model-simulated time to study the rate of aquifer response to simulated 

stresses. 

Independent effects of irrigation reduction and changes 

in ground-water withdrawal.—In the first set of transient 

simulations, the effect of irrigation reduction from 1981 to 

1998 was isolated from the effects of drought and changes in 

ground-water withdrawal. Beginning with the results from 

the simulation of steady-state 1981 conditions with normal 

rainfall, recharge distribution was changed to that of 1998 

irrigation and normal rainfall. Ground-water withdrawal 

was kept at 1981 rates, which is the same as that of the initial 

conditions. The simulation results indicate that the change 

Effects of Irrigation, Drought, and Ground-Water Withdrawal on Ground-Water Levels 23
100

Kilohana-Puhi well field

Line of equal difference in simulated head,

 in feet

Stream

Boundary of the southern Lihue Basin

EXPLANATION

50

0

50

50

50

100

150

150 100

0

10

20

30

40

10 20 30 40 50

N

0

0 5 KILOMETERS

5 MILES

Figure 14. 

Figure 14. Difference in simulated steady-state ground-water levels between pre-development and 1981 

conditions in the adjusted model of the southern Lihue Basin, Kauai, Hawaii. Positive values indicate that 1981 

steady-state ground-water levels are higher than pre-development steady-state ground-water levels.

24 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
0

0

0

0

0

0

0

0

0

0

0

-50

-100

100

Kilohana-Puhi well field

Line of equal difference in simulated head, 

 in feet

Stream

Boundary of the southern Lihue Basin

EXPLANATION

10

20

30

40

10 20 30 40 50

N

0

0 5 KILOMETERS

5 MILES

Nawiliwili Stream

Huleia Stream

Figure 15. 

Figure 15. Difference in simulated steady-state ground-water levels between 1981 and 1998 conditions in the 

adjusted model of the southern Lihue Basin, Kauai, Hawaii. Negative values indicate that 1998 steady-state 

ground-water levels are lower than 1981 steady-state ground-water levels.

Effects of Irrigation, Drought, and Ground-Water Withdrawal on Ground-Water Levels 25
from 1981 to 1998 irrigation rates would cause water levels 

in the Kilohana-Puhi well field to decline by about 17 ft (fig. 

16). With a simulated n of 1 percent and simulated Ss of 10-6

ft-1, the decline would take about 2 years. With a simulated 

n of 10 percent and simulated Ss of 10-4 ft-1, the water level 

would decline more gradually, achieving a decrease of 12 ft in 

5 years and 16 ft in 10 years. Other combinations of n and Ss

correspond to intermediate rates of decline. 

In the second set of transient simulations, the effect 

of changing from 1981 to 1998 ground-water withdrawal 

rates was isolated from other effects (fig. 16). Recharge was 

maintained at the 1981 rate, which is the same as in the initial 

conditions. The simulations indicate that the change from 

1981 to 1998 ground-water withdrawal rates would cause 

water levels in the Kilohana-Puhi well field to decline by 

less than 3 ft if this rate persisted for 20 years. These results 

indicate that the change in ground-water withdrawal between 

1981 and 1998 had a smaller effect on ground-water levels 

in the Kilohana-Puhi well field than did the change in irrigation during the same period. These results are consistent with 

those of the steady-state simulations, which show that the 

recharge-enhancing effect of irrigation overwhelms the effect 

of changes in ground-water withdrawal. 

Combined effects of drought, irrigation reduction, 

and changes in ground-water withdrawal.—The third set 

of transient simulations combined the effects of irrigation 

reduction, ground-water withdrawal changes, and drought 

in the sequence in which they occurred in history (table 8). 

The simulation results can be compared to actual measured 

water levels in the Kilohana-Puhi well field to assess whether 

the general trends and the timing of changes in trends were 

consistent. More than 20 years of water-level measurements 

are available from Kilohana well I, but water levels in the well 

show high-frequency fluctuations because the well is actively 

being pumped and is affected by pumping from nearby wells 

(Taogoshi and others, 2002). The measured water levels 

in Kilohana well I represent a single point in the well field, 

whereas the simulated ground-water levels represent an average of water levels within the area of a cell near Kilohana well 

I (fig. 10). To compare measured with simulated groundwater levels, the data from Kilohana well I were transformed 

by subtracting the average water level of Kilohana well I for 

the period of record from the individual water-level measurements, and smoothing the results using a moving average of 

the preceding 12 records (the average interval between records 

is 58 days). The simulated ground-water levels were also 

transformed by subtracting the average, but the results were 

not smoothed. 

Figure 17 compares the transformed simulated groundwater levels with the curve of the transformed and smoothed 

water-level data from Kilohana well I. The discretization of 

recharge and ground-water withdrawal into blocks of time 

(table 8) contributes to the discrepancy between simulated 

and measured ground-water levels. Even so, the trends and 

timing of changes in trends shown in the model agree with 

those shown in the data from Kilohana well I. Both show a 

declining trend before 1998 that corresponds with reductions 

in irrigation resulting from removing nearby sugarcane fields 

from production and conversion of some fields from furrow 

to drip irrigation (fig. 3), and with increasing ground-water 

withdrawals from the Kilohana-Puhi well field. Near 1998, 

the downward trend of both the Kilohana well I and simulated 

water-level curves becomes steeper with the onset of drought. 

At the end of 2000, the downward trend of the simulated and 

measured ground-water levels becomes even steeper when 

irrigation was completely halted while the drought was still in 

effect. The combined effects of the drought and loss of irrigation, however, had only a brief effect on ground-water levels. 

After the end of the drought, both the measured and modelsimulated water levels show a rise. 

The transient simulations can also be used to assess 

how ground-water levels in the southern Lihue Basin will 

be affected in the future. Projecting the model simulations 

beyond the present shows that simulated water levels in the 

Kilohana-Puhi area continue to recover from the 1998-2002 

drought and eventually attain a level that is within about 4 ft of 

Table 8. Periods of irrigation, ground-water withdrawal, and rainfall in transient simulations of the adjusted ground-water model of the 

southern Lihue Basin, Kauai, Hawaii. 

[NA, not applicable]

Conditions during simulated period Duration 

(years) Dates represented

Starting conditions (normal rainfall, 1981 irrigation rates, 1981 ground-water withdrawal rates) NA Pre-1982

Normal rainfall1 1998 irrigation rates, 1998 ground-water withdrawal rates 16 1982-1997

Drought, 1998 irrigation rates, 1998 ground-water withdrawal rates 3 1998-2000

Drought, no irrigation, 1998 ground-water withdrawal rates 2 2001-2002

Normal rainfall, no irrigation, 1998 ground-water withdrawal rates 38 2003-2040

1

 Rainfall in 1982-1987 at the Lihue Airport (National Climatic Data Center, 2006) averaged 41.11 inches per year, which is comparable to the long-term 

average for this gage (41.25 inches per year). 

26 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
ELAPSED TIME, IN YEARS

0 2 4 6 8 10 12 14 16 18 20

-3

-2

-1

0

EFFECT OF CHANGING GROUND-WATER WITHDRAWAL CONDITIONS

-20

-10

0

EFFECT OF CHANGING IRRIGATION CONDITIONS

CHAN

G

E IN SIMULATED HEAD, IN FEET

Figure 16.

n = 10 %, Ss = 10-4 feet -1

n = 10 %, Ss = 10-6 feet -1

n = 1 %, Ss = 10-4 feet -1

n = 1 %, Ss = 10-6 feet -1

Figure 16. Simulated changes in water level in the Kilohana-Puhi well field resulting from 

reductions in irrigation and changes in ground-water withdrawals that occurred between 1981 

and 1998. n is effective aquifer porosity, % is percent, and Ss is aquifer specific storage.

Effects of Irrigation, Drought, and Ground-Water Withdrawal on Ground-Water Levels 27
the pre-drought conditions (fig. 18). The water levels do not 

recover fully to the pre-drought conditions, however, because 

of the loss of sugarcane irrigation. These projections assume 

that the last set of conditions simulated in the transient model 

(1998 ground-water withdrawal rates, normal rainfall, and no 

irrigation) persist for a long time. It is likely, however, that at 

least rainfall will vary on a cyclic basis, and droughts as well 

as high-rainfall periods will recur with corresponding fluctuations in ground-water levels. 

Study Implications and Limitations

The steady-state and transient simulations both indicate 

that of the three factors examined in this study (drought, 

irrigation, and ground-water withdrawal), irrigation changes 

resulted in the largest effects on water levels in the area near 

the Kilohana-Puhi well field, when both magnitude and duration are considered. The drought of 1998-2002 contributed to 

the decline in simulated ground-water levels, but the effect was 

of limited duration; the simulations show (and recent measurements indicate) that ground-water levels in the area have risen 

with the return of normal and higher-than-normal rainfall. 

Ground-water withdrawal, despite increasing over the decades, 

had a much smaller effect on average water levels in the Kilohana-Puhi well field. These findings are consistent with the 

large effect irrigation had on ground-water recharge compared 

to the relatively small historical ground-water withdrawal 

in the Lihue Basin. Estimated ground-water recharge in the 

Lihue Basin under 1981 irrigation conditions was 52 Mgal/d 

greater than under pre-development conditions (table 1), 

whereas ground-water withdrawal from the entire Lihue Basin 

is currently only about 7 Mgal/d (Izuka and others, 2005). 

These results indicate that the primary cause of the 

observed decline in water levels, at least in the Kilohana-Puhi 

wells, was the reduction and ultimate cessation of sugarcane 

irrigation in the late 20th century. Inasmuch as irrigation in 

the future will probably not return to the same levels as during 

the period of sugarcane agriculture, the decline in groundwater levels resulting from the reduction and loss of sugarcane 

irrigation can be considered permanent.

The possibility exists that long-term trends in climate 

will affect ground-water recharge, water levels, and availability of ground water in the future. Recent statistical analyses 

indicate that ground-water discharge to streams has decreased 

Figure 17.

n=1%, Ss=10-4 feet-1

n=1%, Ss=10-6 feet-1

n=10%, Ss=10-4 feet-1

n=10%, Ss=10-6 feet-1

Kilohana well I 

(moving average of preceding 

12 records)

-20

-15

-10

-5

0

5

10

15

YEAR

1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 

GROUND-WATER LEVEL MINUS AVERAGE GROUND-WATER

LEVEL, IN FEET

Simulated 1998 irrigation and ground-water 

withdrawal, normal rainfall

Start of drought

End of 

drought

End of 

irrigation

Figure 17. Comparison of measured water levels in Kilohana well I and model-simulated 

changes in water level at the Kilohana-Puhi well field, Kauai, Hawaii. n is effective aquifer 

porosity, % is percent, and Ss is aquifer specific storage.

28 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
from 1913 to 2002; the decrease is coincident with a downward trend in rainfall, and may indicate a long-term decline in 

ground-water storage and recharge (Oki, 2004). This potential 

downward trend was not simulated in the model. 

The effect of increasing ground-water withdrawals 

beyond 1998 levels also was not simulated in this study. An 

increase in ground-water withdrawals would affect groundwater levels in the immediate vicinity of pumped wells, 

especially in the low-permeability rocks of the Lihue Basin. 

Whether or not regional ground-water levels will be substantially affected depends on the magnitude and location of the 

increases. The Kauai DOW and private landowners have 

worked cooperatively to develop surface-water resources in 

the Lihue Basin, which will reduce reliance on ground water 

as the source of drinking water. 

Summary and Conclusions

Updated ground-water-withdrawal data and recharge estimates for various historical conditions were incorporated into 

a numerical ground-water-flow model of the southern Lihue 

Basin to determine whether the decline in ground-water levels 

observed in the 1990s to early 2000s is related to drought, 

decreases in sugarcane irrigation, and changes in ground-water 

withdrawal. Steady-state model simulations indicate that, 

given enough time, the recharge-enhancing effect of furrowirrigation methods used in 1981 could have raised groundwater levels in some areas of the southern Lihue Basin by as 

much as 200 ft over pre-development levels. The increase 

in ground-water withdrawals during that same period would 

tend to lower ground-water levels, but the model simulations 

indicate that the effect is small relative to the overwhelming 

effect of irrigation. The steady-state simulations also indicate that, given enough time, the decrease in irrigation that 

occurred between 1981 and 1998 could theoretically lower 

ground-water levels in parts of the southern Lihue Basin by as 

much as 100 ft.

n = 10 %, Ss = 10-4 feet -1

n = 10 %, Ss = 10-6 feet -1

n = 1 %, Ss = 10-4 feet -1

n = 1 %, Ss = 10-6 feet -1

End of 

simulated

drought

End of simulated

irrigation

Figure 18. 1990

1995

2000

2005

2010

20152020

20252030

2035

-40

-20

-10

-30

SIMULATED CHANGE IN GROUND-WATER LEVEL

 RELATIVE TO 1981, IN FEET 

YEAR

Figure 18. Projected future changes in water level in the Kilohana-Puhi well field, Kauai, 

Hawaii, assuming conditions that existed in 2003 remain unchanged. Changes are relative 

to 1981 water levels. n is effective aquifer porosity, % is percent, and Ss is aquifer specific 

storage.

Summary and Conclusions 29
Transient simulations in which irrigation effects are 

examined independently from other effects indicate that the 

reduction in irrigation from 1981 to 1998 would have caused 

water levels in the Kilohana-Puhi well field to decline by 

about 17 ft; this decline would take from 2 to more than 20 

years, depending on aquifer properties. Transient simulations in which ground-water-withdrawal effects are examined 

independently indicate that the changes in ground-water withdrawal between 1981 and 1998 would cause water levels in 

the Kilohana-Puhi well field to decline by less than 3 ft, even 

if this rate persisted for 20 years. These results are consistent 

with the overwhelming irrigation effect shown by the steadystate simulations. 

Transient simulations combining historical irrigation 

reduction, ground-water withdrawal changes, and drought 

show trends in ground-water levels that correspond with trends 

in measured water levels in the Kilohana-Puhi well field. 

In both the measured and simulated ground-water levels, a 

declining trend between 1981 and 1998 corresponds to reductions in irrigation and increases in ground-water withdrawals. The downward trend becomes steeper at the onset of 

drought in 1998, and even steeper when sugarcane irrigation 

was halted in 2000. Measured and simulated ground-water 

levels both show a rise corresponding to the end of the drought 

in 2002. If the final conditions in the transient simulations 

(1998 ground-water withdrawal rates, normal rainfall, and no 

irrigation) persist, model projections indicate that water levels 

in the Kilohana-Puhi area will continue to recover from the 

drought and eventually attain a level that is within about 4 ft 

of the pre-drought conditions. Water levels on average will 

remain below pre-drought conditions, however, because of the 

loss of sugarcane irrigation.

The ground-water model simulations indicate that when 

both magnitude and duration are considered, the loss of irrigation had a larger effect on ground-water levels than either 

drought or increases in ground-water withdrawal, especially 

in the area near the Kilohana-Puhi well field in the southern 

Lihue Basin. Ground-water withdrawal effects are long in 

duration but small in magnitude, whereas drought effects 

are high in magnitude and widespread but of short duration. 

These results indicate that the primary cause of the observed 

decline in ground-water levels, at least in the Kilohana-Puhi 

wells, was irrigation reduction. Inasmuch as irrigation in the 

future will probably not return to the high levels prevalent during the 20th century, the decline in ground-water levels resulting from the reduction and loss of sugarcane irrigation can be 

considered permanent. 

The possibility exists that long-term trends in climate will 

affect ground-water recharge, levels, and availability in the 

future. A possibility also exists that ground-water withdrawals will increase in the future. The effects of these changes 

on ground-water levels in the southern Lihue Basin were not 

addressed in this study.

References Cited

Clague, D.A., and Dalrymple, G.B., 1988, Age and petrology of alkalic post-shield and rejuvenated stage lava from 

Kauai, Hawaii: Contributions to Mineralogy and Petrology, 

v. 99, p. 202–218.

Essaid, H.I., 1990, The computer model SHARP, a quasithree-dimensional finite-difference model to simulate freshwater and saltwater flow in layered coastal aquifer systems: 

U.S. Geological Survey Water-Resources Investigations 

Report 90-4130, 181 p.

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

Rainfall atlas of Hawai‘i: State of Hawaii, Department of 

Land and Natural Resources, Division of Water and Land 

Development Report R76, 267 p.

Gingerich, S.B., 1999, Estimating transmissivity and storage 

properties from aquifer tests in the southern Lihue Basin, 

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

Investigations Report 99-4066, 33 p.

Gingerich, S.B., and Izuka, S.K., 1997, Construction, geologic 

log, and aquifer test of the Northwest Kilohana Monitor 

Well (State well 2-0126-01), Lihue, Kauai, Hawaii: U.S. 

Geological Survey Open-File Report 97-40, 20 p.

Holcomb, R.T., Reiners, P.W., Nelson, B.K., and Sawyer, N.E., 

1997, Evidence for two shield volcanoes exposed on the 

Island of Kauai, Hawaii: Geology, v. 25, no. 9, p. 811–814.

Hunt, C.D., Jr., 1996, Geohydrology of the island of Oahu, 

Hawaii: U.S. Geological Survey Professional Paper 1412-B, 

54 p.

Izuka, S.K., and Gingerich, S.B., 1997a, Construction, geologic log, and aquifer tests of the Hanamaulu Monitor Well 

(State well 2-5923-08), Lihue, Kauai, Hawaii: U.S. Geological Survey Open-File Report 97-36, 23 p.

Izuka, S.K., and Gingerich, S.B., 1997b, Construction, geologic log, and aquifer tests of the Northeast Kilohana Monitor Well (State well 2-0124-01), Lihue, Kauai, Hawaii: U.S. 

Geological Survey Open-File Report 97-37, 23 p.

Izuka, S.K., and Gingerich, S.B., 1997c, Construction, geologic log, and aquifer tests of the Pukaki Reservoir Monitor 

Well (State well 2-0023-01), Lihue, Kauai, Hawaii: U.S. 

Geological Survey Open-File Report 97-41, 22 p.

Izuka, S.K., and Gingerich, S.B., 1997d, Construction and 

geologic log of the South Wailua Monitor Well (State well 

2-0121-08), Lihue, Kauai, Hawaii: U.S. Geological Survey 

Open-File Report 97-38, 14 p.

30 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
Izuka, S.K., and Gingerich, S.B., 1998, Ground water in the 

southern Lihue Basin, Kauai, Hawaii: U.S. Geological Survey Water-Resources Investigations Report 98-4031, 71 p.

Izuka, S.K., and Gingerich, S.B., 2003, A thick lens of fresh 

groundwater in the southern Lihue Basin, Kauai, Hawaii, 

USA: Hydrogeology Journal, v. 11, p. 240-248.

Izuka, S.K., and Oki, D.S., 2002, Numerical simulation of 

ground-water withdrawals in the southern Lihue Basin, 

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

Investigations Report 01-4200, 54 p.

Izuka, S.K., Oki, D.S., and Chen, Chien-Hwa, 2005, Effects of 

irrigation and rainfall reduction on ground-water recharge 

in the Lihue Basin, Kauai, Hawaii: U.S. Geological Survey 

Scientific Investigations Report 2005-5146, 48 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, in Decker, R.W., 

Wright, T.L., and Stauffer, P.H., eds., Volcanism in Hawaii: 

U.S. Geological Survey Professional Paper 1350, v. 1, p. 

55-84.

Macdonald, G.A., Davis, D.A., and Cox, D.C., 1960, Geology 

and ground-water resources of the island of Kauai, Hawaii: 

Hawaii Division of Hydrography Bulletin 13, 212 p.

National Climatic Data Center, 2006, Local climate data, 

annual summary with comparative data: URL http://www7.

ncdc.noaa.gov/IPS/LCDPubs?action=getstate

[accessed April 5, 2006].

Oki, D.S., 2004, Trends in streamflow characteristics at 

long-term gaging stations, Hawaii: U.S. Geological Survey 

Scientific Investigations Report 2004-5080, 120 p.

Reiners, P.W., Nelson, B.K., and Izuka, S.K., 1998, Structural 

and petrologic evolution of the Lihue Basin and eastern 

Kauai, Hawaii: Geological Society of America Bulletin, v. 

111, p. 674-685. 

Shade, P.J., 1995, Water budget for the island of Kauai, 

Hawaii: U.S. Geological Survey Water-Resources Investigations Report 95-4128, 25 p. 

Soroos, R.L., 1973, Determination of hydraulic conductivity 

of some Oahu aquifers with step-drawdown test data: Honolulu, University of Hawaii, M.S. thesis, 239 p. 

Stearns, H.T., 1946, Geology of the Hawaiian Islands: Hawaii 

Division of Hydrography Bulletin 8, 112 p. 

Stearns, H.T., 1985, Geology of the State of Hawaii (2d ed.): 

Palo Alto, Calif., Pacific Books, 335 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. 

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.

Taogoshi, R.I, Wong, M.F., Nishimoto, D.C., and Teeters, 

P.C., 2002, Water resources data, Hawaii and other Pacific 

areas, water year 2001; volume 1, Hawaii: U.S. Geological 

Survey Water-Data Report HI-01-1, 369 p. 

U.S. Census Bureau, 2006, American Factfinder, DP1. Profile 

of general demographic characteristics: 2000: URL http://

factfinder.census.gov/ [accessed March 23, 2006].

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

Honolulu, University of Hawai’i Press, 191 p.

References Cited 31
Introduction

The ground-water recharge estimates of Izuka and others 

(2005) were limited to areas within the Lihue Basin. The 

numerical ground-water model of the southern Lihue Basin 

(Izuka and Gingerich, 1998), however, extended to areas 

outside of the basin (see fig. 10 in main text). In this study, 

estimates of ground-water recharge for areas outside the 

basin were computed using a regression analysis that relates 

recharge to mean annual rainfall. Rainfall is the primary 

form of precipitation on Kauai; fog can contribute significant 

amounts, but only in areas of limited extent. As a result, 

recharge is strongly correlated with mean annual rainfall. The 

strong correlation suggests that mean annual rainfall can be 

used as a predictor of recharge outside the basin if appropriate regression models can be developed from the rechargerainfall relation of the water-budget analysis within the basin. 

The key premise of this approach is that regression equations 

developed from one area can be used to estimate recharge in 

another area. The transferability of equations from one area to 

another probably depends on the similarities in climate, land 

use, vegetation, and soil between the two areas. If these physical conditions differ from one area to another, the differences 

can be mitigated by adjustments or refinements to the regression equations. 

Shade and Nichols (1996) used a similar approach to 

estimate ground-water recharge in parts of southern Oahu, 

Hawaii. Their analysis developed regression equations from 

an existing detailed water-budget analysis for southern Oahu 

by Giambelluca (1983, 1986). Shade and Nichols developed 

separate rainfall-recharge regression equations for both natural 

conditions and for conditions where significant additional 

water was brought in by irrigation or where xerophytic pineapple plants were present. They could ignore the effects of 

other factors, such as basin runoff characteristics, soil type, 

or contributions from other forms of precipitation, because 

their use of the equations was limited to estimating recharge 

in areas that were in close proximity to the water-budget study 

area.

Development of Regression Equations

Bivariate plots and regression equations for estimating ground-water recharge were developed on the basis of a 

detailed water-budget computed by Izuka and others (2005) 

for the Lihue Basin. The water-budget analysis of Izuka and 

others (2005) used a geographic-information-system (GIS) 

procedure to divide the Lihue Basin into 77,000 subareas 

(commonly referred to as polygons) having homogeneous 

precipitation, agriculture, runoff, and evapotranspiration 

Appendix: Estimating Ground-Water Recharge for Areas Outside the Lihue Basin

characteristics. A daily water budget was computed for each 

subarea. These subareas were the basis for the regression 

analysis, one subarea constituting one data point in the regression. For the regression analysis, the number of subareas 

was reduced by eliminating subareas for which land use was 

unclassified or classified as bare land, unconsolidated shore, or 

water bodies. The number of subareas in the regression analysis was further reduced by eliminating multiple occurrences of 

identical X- and Y-value pairs. 

The results of the 1981-irrigation, normal-rainfall 

scenario of Izuka and others (2005) were used to generate a 

bivariate plot of recharge versus mean annual rainfall (fig. 

A1). Data points tended to cluster along five main trends 

defined principally by five land-use/climate conditions: (1) 

non-agricultural subareas outside the fog zone, (2) non-agricultural subareas within the fog zone, (3) furrow-irrigated 

subareas, (4) drip-irrigated subareas, and (5) subareas with two 

or more irrigation methods.

Within the five major trends, data points tend to group 

even further, probably in relation to discretized parameters 

such as runoff-to-rainfall ratios, soil-water capacity, root 

depths, and evapotranspiration. Although most water-budget 

parameters in nature vary continuously from one location to 

the next, in the water-budget analysis by Izuka and others 

(2005) the parameters were discretized into regions of uniform 

value. For example, the trend of data points representing subareas within the fog zone has a different slope than does the 

trend of data points for areas outside the fog zone. This difference is primarily an artifact resulting from determining fog as 

a percentage of rainfall. To remove the artifacts resulting from 

discretizing runoff-to-rainfall ratios and fog distribution, fog 

was added and runoff subtracted from rainfall to yield mean 

annual soil infiltration. A plot of recharge versus mean annual 

soil infiltration (fig. A2) shows fewer groups, tighter clustering 

of data points, and a stronger correlation than the bivariate plot 

of recharge versus simple mean annual rainfall. 

Figures A1 and A2 both show natural groupings of data 

points that reflect the presence or absence of irrigation, or differences in method of irrigation. Subareas of furrow-irrigated 

sugarcane plot along a trend that indicates significantly higher 

recharge than in other subareas, which is consistent with the 

known inefficiency of the furrow-irrigation method. On the 

other hand, data points representing drip-irrigated subareas 

plot in a cluster that is not much different from non-agricultural areas, which indicates that drip irrigation does not 

substantially enhance recharge. Subareas with mixed irrigation methods plot between the furrow-irrigation group and 

drip-irrigation group. 

A closer look at the low-infiltration end of the bivariate 

plot of recharge versus infiltration shows that for non-agricultural areas, the data trend above a mean annual soil infiltration of about 50 in/yr has a steeper slope than below 50 in/yr 

32 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
A

 50

100

 0

150

200

250

300

350

400

0 100 200 300 400 500

MEAN ANNUAL RAINFALL, IN INCHES

MEAN ANNU

AL G

R

OUND-WATER REC

AHR

GE, IN INCHES

 Unirrigated, no fog

 Unirrigated, with fog

 Mixed irrigation

 Drip irrigation

 Furrow irrigation

Figure A1. Bivariate scatter plot of ground-water recharge versus mean annual rainfall 

for subareas in the Lihue Basin, Kauai, Hawaii, from the water-budget analysis of Izuka and 

others (2005).

 50

100

 0

150

200

250

300

350

400

0 100 200 300 400 500

 Unirrigated, no fog

 Unirrigated, with fog

 Mixed irrigation

 Drip irrigation

 Furrow irrigation

MEAN ANNUAL INFILTRATION, IN INCHES

MEAN ANNUAL

G

R

OUNDW

ATER

REC

AHRGE, IN INCHES

Figure A2. Bivariate scatter plot of ground-water recharge versus mean annual soil 

infiltration (rainfall plus fog minus runoff), for subareas in the Lihue Basin, Kauai, Hawaii, 

from the water-budget analysis of Izuka and others (2005). 

Appendix 33
(fig. A3), indicating that more than one regression line may 

be needed to adequately describe the infiltration-recharge 

relation. Previous studies have used multi-segment regression 

lines to describe the relation between rainfall and recharge 

in other areas of Hawaii. Shade and Nichols (1996) used as 

many as four regression line segments to describe the rainfallrecharge relation for non-agricultural areas of southern Oahu. 

Their regression line segments were discontinuous at the 

endpoints, however, which can lead to additional uncertainties 

beyond those inherent in normal continuous-function linear 

regression.

For the purpose of estimating ground-water recharge for 

areas of the model outside the Lihue Basin, regression equations were developed using mean annual soil infiltration as the 

independent variable. Regression equations were computed 

separately for (1) furrow-irrigated subareas, (2) drip-irrigated 

subareas, and (3) non-agricultural subareas. For non-agricultural subareas, a two-segment linear regression equation was 

developed. The two segments of the relation share a common 

breakpoint, thus eliminating the added uncertainty associated 

with the discontinuous equation of Shade and Nichols (1996). 

The equations for each segment were determined by testing 

all combinations of values for the X-axis intercept (from 0 to 

100 in/yr, in increments of 1 in/yr) and X-value breakpoint 

separating the two linear segments (from X-axis intercept plus 

1 to 200 in/yr, in increments of 1 in/yr). Slopes for each line 

segment were determined by least-squared-error analysis. The 

values for the X-axis intercept and X-value breakpoint that 

produced the highest R2 value were selected. Coefficients for 

the three analyses developed in this study are summarized in 

table A1.

0

0 25 50 75 100 125 150

50

75

25

100

125

150

MEAN ANNUAL SOIL INFILTRATION, IN INCHES

MEAN ANNUAL G

R

OUNDWATER RECHAR

G

E, IN INCHES

Figure A3. Bivariate scatter plot of ground-water recharge versus low values of mean annual soil infiltration 

(rainfall plus fog minus runoff), for subareas in the Lihue Basin, Kauai, Hawaii, from the water-budget analysis of 

Izuka and others (2005).

34 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
Testing the Regression Equations

Before using the regression equations to compute 

ground-water recharge for areas outside the Lihue Basin, the 

equations were tested to see how closely they could replicate 

the water-budget-based recharge results of Izuka and others 

(2005). Recharge was computed for the four scenarios shown 

in table A2 using the regression equations in table A1. Mean 

annual rainfall used as input to the regression analysis was 

based on maps by Giambelluca and others (1986). Mean 

annual infiltration was computed by adding fog drip to mean 

annual rainfall and subtracting runoff. Fog drip was computed 

as a fraction (0.18) of mean annual rainfall in areas higher 

than 2,000 m above sea level, which is the method Izuka and 

others (2005) used to estimate fog drip. Runoff was computed by multiplying mean annual rainfall by the average of 

the monthly runoff-to-rainfall ratios used by Izuka and others 

(2005); these ratios ranged from 0.29 to 0.35, depending on 

location in the basin. For drought scenarios, mean annual 

rainfall was reduced by multiplying by a factor of 0.64, which 

is equal to the factor Izuka and others (2005) used to simulate 

a moderate drought. To compute ground-water recharge for a 

given area, equations were selected depending on the presence 

or absence of irrigation, or the method of irrigation. If an area 

had more than one irrigation type, recharge was computed 

using the equations of all irrigation methods present in that 

area, and the results were averaged.

Table A2 summarizes results of the regression-based 

recharge analysis for the Lihue Basin and compares them with 

the results of the water-budget analysis of Izuka and others 

(2005). In two out of the four scenarios, the discrepancy 

between the regression-based and water-budget-based recharge 

estimates is less than 4 percent. Only in the scenarios representing drought conditions was the discrepancy greater than 

4 percent; even so, the discrepancy was not large. 

Using the Regression Equations to 

Estimate Ground-Water Recharge 

Outside the Lihue Basin

The area of the ground-water-flow model outside the 

Lihue Basin lies between Haupu Ridge and the Hanapepe 

River (see fig. 10 in text). This area was included in the 

model only so that the model boundaries would coincide with 

defensible hydrologic boundaries (Izuka and Gingerich, 1998). 

Because the area was coarsely discretized and the hydrologic 

parameters were broadly generalized, only a broadly generalized representation of the recharge distribution is required 

for this part of the model. The regression-based approach for 

estimating recharge is considered adequate for this purpose.

Table A1. Coefficients for regression equations to estimate ground-water recharge based on water-budget analysis by Izuka and 

others (2005) for the Lihue Basin, Kauai, Hawaii.

Regression equation

Regression

Slope Intercept 

(inches) R2

Drip-irrigated subareas 1.571 -41.84 0.86

Furrow-irrigated subareas 1.647 24.94 0.83

Non-agricultural subareas ---- ---- 0.99

Mean annual infiltration greater than 9 inches and less than or equal to 50 inches 0.154 -1.38 ----

Mean annual infiltration greater than 50 inches 1.095 -48.30 ----

Table A2. Comparison of regression-based and water-budget-based estimates of ground-water recharge for 1981 irrigation conditions 

in the Lihue Basin, Kauai, Hawaii.

Recharge scenario

Recharge (million gallons per day)

Water budget analysis of Izuka Percent difference

and others (2005) Regression

1981 irrigation, normal rainfall 264 261 -1.1

1981 irrigation with drought 131 125 -4.6

No irrigation, normal rainfall 212 211 -0.5

No irrigation with drought 84 88 4.8

Appendix 35
Furrow irrigation is not currently used in this area, and 

the irrigation of coffee in the area probably contributes only 

a minor amount to ground-water recharge. Therefore, the 

equation developed for non-agricultural subareas (table A1) 

is adequate for estimating the broadly generalized recharge 

distribution needed for this section of the ground-water-flow 

model. The distribution of soil infiltration required for the 

regression analysis was computed by adding fog drip and 

subtracting runoff from the mean annual rainfall distribution maps of Giambelluca and others (1986). Infiltration 

was computed for both normal rainfall and drought conditions. For normal rainfall conditions, the mean annual 

rainfall distribution of Giambelluca and others (1986) was 

left unchanged. For drought conditions, mean annual rainfall 

was multiplied by a factor of 0.64. Contribution from fog 

drip was estimated by multiplying rainfall by a factor of 0.18 

for all areas above 2,000-ft elevation. Runoff was estimated 

by applying a runoff-to-rainfall ratio (0.28), computed for 

the Hanapepe River using hydrograph-separation results for 

USGS stream gages 1604900 and 1604300 (Izuka and Gingerich, 1998), to rainfall within the drainage area estimated 

from the maps of Giambelluca and others (1986).

A GIS was used to merge the regression-based estimates with the water-budget-based estimates of Izuka and 

others (2005) for areas within the Lihue Basin. The GIS was 

also used to merge the recharge distribution with the grid of 

the ground-water-flow model and compute the recharge for 

each cell in the grid by taking the area-weighted average of 

all recharge subareas (polygons) within the cell. Resulting 

distributions of recharge used for simulating various combinations of irrigation and rainfall conditions in the adjusted 

southern Lihue Basin model are shown in figure A4 .

References Cited in Appendix

Giambelluca, T.W., 1983, Water budget of the Pearl HarborHonolulu basin, Hawaii, 1946-1975: Honolulu, University 

of Hawaii Water Resources Research Center Technical 

Report 151, 151 p.

Giambelluca, T.W., 1986, Land-use effects on the water balance of a tropical island: National Geographic Research, v. 

2, p. 125-151.

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

Rainfall atlas of Hawai‘i: State of Hawaii, Department of 

Land and Natural Resources, Division of Water and Land 

Development Report R76, 267 p.

Izuka, S.K., and Gingerich, S.B., 1998, Ground water in the 

southern Lihue Basin, Kauai, Hawaii: U.S. Geological Survey Water-Resources Investigations Report 98-4031, 71 p.

Izuka, S.K., Oki, D.S., and Chen, Chien-Hwa, 2005, Effects 

of irrigation and rainfall reduction on ground-water 

recharge in the Lihue Basin, Kauai, Hawaii: U.S. Geological Survey Scientific Investigations Report 2005-5146, 48 

p.

Shade, P.J., and Nichols, W.D., 1996, Water budget and the 

effects of land-use changes on ground-water recharge, 

Oahu, Hawaii: U.S. Geological Survey Professional Paper 

1412-C, p. C1-C38.

36 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
Figure A4. Distributions of ground-water recharge (in inches per year) in adjusted ground-water model of the 

southern Lihie Basin, Kauai, Hawaii, used to simulate conditions of normal rainfall with no irrigation (A), normal 

rainfall and 1981 irrigation (B), normal rainfall and 1988 irrigation (C), drought with no irrigation (D), drought and 1981 

irrigation (E), and drought and 1988 irrigation (F).

NORMAL RAINFALL, NO IRRIGATION

EXPLANATION

Coastline

Boundary of the 

southern Lihue Basin

200 to 300

Greater than 300

Offshore or no-flow cell

0 to 20

20 to 40

40 to 60

60 to 80

80 to 100

100 to 200

10

20

30

40

10 20 30 40 50

N

0

0 5 KILOMETERS

5 MILES

A

Appendix 37
Figure A4.—Continued.

NORMAL RAINFALL, 1981 IRRIGATION

EXPLANATION

Coastline

Boundary of the 

southern Lihue Basin

200 to 300

Greater than 300

Offshore or no-flow cell

0 to 20

20 to 40

40 to 60

60 to 80

80 to 100

100 to 200

10

20

30

40

10 20 30 40 50

N

0

0 5 KILOMETERS

5 MILES

B

38 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
Figure A4.—Continued.

NORMAL RAINFALL, 1998 IRRIGATION

EXPLANATION

Coastline

Boundary of the 

southern Lihue Basin

200 to 300

Greater than 300

Offshore or no-flow cell

0 to 20

20 to 40

40 to 60

60 to 80

80 to 100

100 to 200

10

20

30

40

10 20 30 40 50

N

0

0 5 KILOMETERS

5 MILES

C

Appendix 39
Figure A4.­—Continued.

DROUGHT, NO IRRIGATION

EXPLANATION

Coastline

Boundary of the 

southern Lihue Basin

200 to 300

Greater than 300

Offshore or no-flow cell

0 to 20

20 to 40

40 to 60

60 to 80

80 to 100

100 to 200

10

20

30

40

10 20 30 40 50

N

0

0 5 KILOMETERS

5 MILES

D

40 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin
Figure A4.­—Continued.

DROUGHT, 1981 IRRIGATION

EXPLANATION

Coastline

Boundary of the 

southern Lihue Basin

200 to 300

Greater than 300

Offshore or no-flow cell

0 to 20

20 to 40

40 to 60

60 to 80

80 to 100

100 to 200

10

20

30

40

10 20 30 40 50

N

0

0 5 KILOMETERS

5 MILES

E

Appendix 41
Figure A4.—Continued.

DROUGHT, 1998 IRRIGATION

EXPLANATION

Coastline

Boundary of the 

southern Lihue Basin

200 to 300

Greater than 300

Offshore or no-flow cell

0 to 20

20 to 40

40 to 60

60 to 80

80 to 100

100 to 200

10

20

30

40

10 20 30 40 50

N

0

0 5 KILOMETERS

5 MILES

F

42 Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin

Izuka—Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin, Kauai, Hawaii—SIR 2006–5291

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