U.S. Department of the Interior

Numerical Simulation of Ground-Water Withdrawals in the 

Southern Lihue Basin, Kauai, Hawaii

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 01-4200

Prepared in cooperation with the

COUNTY OF KAUAI DEPARTMENT OF WATER
Numerical Simulation of Ground-Water Withdrawals in the 

Southern Lihue Basin, Kauai, Hawaii

By Scot K. Izuka and Delwyn S. Oki

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 01-4200

Prepared in cooperation with the

COUNTY OF KAUAI DEPARTMENT OF WATER

Honolulu, Hawaii

2002
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes 

only and does not constitute endorsement by the U.S. Geological Survey.

For additional information write to: Copies of this report can be purchased 

from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

677 Ala Moana Blvd., Suite 415 Box 25286

Honolulu, HI 96813 Denver, CO 80225-0286

U. S. DEPARTMENT OF THE INTERIO

R

MARCH 3, 1849
Contents iii

CONTENTS

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

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

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

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

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

Geology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Hydraulic Properties of the Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

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

Effects Of Ground-Water Withdrawals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Numerical Model Simulation of the Effects of Ground-Water Withdrawals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Original Numerical Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Uncertainties in Recharge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Model Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Steady-State Simulations of Proposed Withdrawals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Effects of the 2000 (0.42 Mgal/d) Projection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Effects of the 2010 (0.83 Mgal/d) Projection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Effects of the 2020 (1.16 Mgal/d) Projection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Implications of the Steady-State Simulations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Rate of Development of the Effects of the Proposed Ground-Water Withdrawals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Transient Simulations of the 2000 (0.42 Mgal/d) Projection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Transient Simulations of the 2010 (0.83 Mgal/d, Alternative Distribution) Projection . . . . . . . . . . . . . . . . . . . . . . 37

Transient Simulations of the 2020 (1.16 Mgal/d, Alternative Distribution) Projection . . . . . . . . . . . . . . . . . . . . . . 37

Implications of the Transient Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

FIGURES

1–3. Maps showing:

1. The southern Lihue Basin, Kauai, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2. Distribution of rainfall in the Lihue Basin, Kauai, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3. Geology of the Lihue Basin, Kauai, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4. Block diagram showing the structure and stratigraphy of the southern Lihue Basin, Kauai, Hawaii . . . . . . . . 8

5. Diagrammatic representation of ground-water flow in the southern Lihue Basin, Kauai, Hawaii . . . . . . . . . . 9

6. Generalized water-table map and profile for the southern Lihue Basin, Kauai, Hawaii . . . . . . . . . . . . . . . . . . 11

7. Generalized section showing the effects of ground-water withdrawals in the southern 

Lihue Basin, Kauai, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

8–15. Maps showing:

8. Model grid, boundaries, streams, pumped wells, and monitoring points used in the numerical 

ground-water flow model of the southern Lihue Basin, Kauai, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . 14
iv Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

9. Distribution of geology used in the numerical ground-water flow model of the southern 

Lihue Basin, Kauai, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

10. Simulated streams, wells, and monitoring points used in the steady-state simulations 

of projected increases in ground-water withdrawal in the southern Lihue Basin, Kauai, Hawaii . . . . . 22

11. Simulated steady-state changes in water levels resulting from the 0.42-million-gallon-per-day

increase in ground-water withdrawal projected for 2000 in the southern Lihue Basin, 

Kauai, Hawaii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

12. Simulated steady-state changes in water levels resulting from the 0.83-million-gallon-per-day

increase in ground-water withdrawal projected for 2010 in the southern Lihue Basin, 

Kauai, Hawaii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

13. Simulated steady-state changes in water levels resulting from the alternative distribution of the 

0.83-million-gallon-per-day increase in ground-water withdrawal projected for 2010 in the 

southern Lihue Basin, Kauai, Hawaii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

14. Simulated steady-state changes in water levels resulting from the 1.16-million-gallon-per-day 

increase in ground-water withdrawal projected for 2020 in the southern Lihue Basin, 

Kauai, Hawaii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

15. Simulated steady-state changes in water levels resulting from the alternative distribution of 

the 1.16-million-gallon-per-day increase in ground-water withdrawal projected for 2020

in the southern Lihue Basin, Kauai, Hawaii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

16–21. Graphs showing:

16. Simulated water-level changes with time since start of withdrawal of the 0.42 million gallons 

per day projected for the southern Lihue Basin, Kauai, Hawaii, in 2000 . . . . . . . . . . . . . . . . . . . . . . . 38

17. Simulated stream base-flow changes with time since start of withdrawal of the 0.42 million gallons

per day projected for the southern Lihue Basin, Kauai, Hawaii, in 2000 . . . . . . . . . . . . . . . . . . . . . . . 38

18. Simulated water-level changes with time since start of withdrawal of the 0.83 million gallons per day 

(alternative distribution) projected for the southern Lihue Basin, Kauai, Hawaii, in 2010 . . . . . . . . . . 39

19. Simulated stream base-flow changes with time since start of withdrawal of the 0.83 million gallons

per day (alternative distribution) projected for the southern Lihue Basin, Kauai, Hawaii, in 2010 . . . 39

20. Simulated water-level changes with time since start of withdrawal of the 1.16 million gallons per day

(alternative distribution) projected for the southern Lihue Basin, Kauai, Hawaii, in 2020 . . . . . . . . . . 40

21. Simulated stream base-flow changes with time since start of withdrawal of the 1.16 million gallons 

per day (alternative distribution) projected for the southern Lihue Basin, Kauai, Hawaii, in 2020 . . . 40

TABLES

1. Kauai Department of Water projections for increases in water demand for Lihue, Kauai, Hawaii . . . . . . . . . . . . . . 3

2. Kauai Department of Water ground-water development projects in the Lihue area, Kauai, Hawaii . . . . . . . . . . . . . 3

3. Simulated steady-state water levels in the southern Lihue Basin, Kauai, Hawaii, for various estimates 

of recharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4. Simulated steady-state base flows of streams and rivers in the vicinity of the southern Lihue Basin, Kauai, 

Hawaii, for various estimates of recharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

5. Conditions before, and simulated steady-state changes resulting from, the additional ground-water 

withdrawal of 0.42 million gallons per day projected for 2000 in the southern Lihue Basin, Kauai, Hawaii . . . . 24

6. Simulated steady-state stream base flow and changes resulting from the additional ground-water withdrawal 

of 0.42 million gallons per day projected for 2000 in the southern Lihue Basin, Kauai, Hawaii . . . . . . . . . . . . . 24

7. Conditions before, and simulated steady-state changes resulting from, the additional ground-water withdrawal 

of 0.83 million gallons per day projected for 2010 in the southern Lihue Basin, Kauai, Hawaii . . . . . . . . . . . . . 26
Contents v

8. Simulated steady-state stream base flow and changes resulting from the additional ground-water withdrawal 

of 0.83 million gallons per day projected for 2010 in the southern Lihue Basin, Kauai, Hawaii . . . . . . . . . . . . . 26

9. Conditions before, and simulated steady-state changes resulting from, an alternative distribution of the additional 

ground-water withdrawal of 0.83 million gallons per day projected for 2010 in the southern Lihue Basin,

Kauai, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

10. Simulated steady-state stream base flow and changes resulting from an alternative distribution of the additional 

ground-water withdrawal of 0.83 million gallons per day projected for 2010 in the southern Lihue Basin, 

Kauai, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

11. Conditions before, and simulated steady-state changes resulting from, the additional ground-water withdrawal

of 1.16 Mgal/d projected for 2020 in the southern Lihue Basin, Kauai, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . 31

12. Simulated steady-state stream base flow and changes resulting from the additional ground-water withdrawal

of 1.16 million gallons per day projected for 2020 in the southern Lihue Basin, Kauai, Hawaii . . . . . . . . . . . . . 31

13. Conditions before, and simulated steady-state changes resulting from, an alternative distribution of the additional 

ground-water withdrawal of 1.16 million gallons per day projected for 2020 in the southern Lihue Basin, 

Kauai, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

14. Simulated steady-state stream base flow and changes resulting from an alternative distribution of the 

additional ground-water withdrawal of 1.16 million gallons per day projected for 2020 in the southern 

Lihue Basin, Kauai, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

15. Storage coefficients and specific-storage values from aquifer tests in the Lihue Basin, Kauai, Hawaii . . . . . . . . . . 36
vi Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii
Introduction 1

Abstract

Numerical simulations indicate that groundwater withdrawals from the Hanamaulu and Puhi 

areas of the southern Lihue Basin will result in a 

decline in water levels and reductions in base flows 

of streams near proposed new water-supply wells. 

Most of the changes will be attained within 10 to 20 

years of the start of pumping. Except for areas such 

as Puhi and Kilohana, the freshwater lens in most 

inland areas of the southern Lihue Basin is thick 

and model simulations indicate that changes in 

water level and the position of the freshwatersaltwater interface in response to pumping will be 

small relative to the present thickness of the freshwater lens. Effects of the proposed withdrawals on 

streamflow depend on withdrawal rate and proximity of the wells to streams. Placing pumped wells 

away from streams with low base flow and toward 

streams with high base flow can reduce the relative 

effect on individual streams. 

Simulation of the 0.42-million-gallon-per-day 

increase in withdrawal projected for 2000 indicates 

that the resulting changes in water levels and interface position, relative to conditions prior to the 

withdrawal increase, will be small, and that stream 

base flow will be reduced by less than 10 percent. 

Simulation of the 0.83-million-gallon-per-day 

withdrawal projected for 2010 indicates further 

thinning of the freshwater lens in the Puhi area, 

where the lens already may be thin, as well as baseflow reduction in Nawiliwili Stream. Simulation of 

an alternative distribution of the 0.83-

million-gallon-per-day withdrawal indicates that 

the effects can be reduced by shifting most of the 

new withdrawal to the Hanamaulu area where the 

freshwater lens is thicker and stream base flows are 

greater. 

Simulation of the 1.16-million-gallon-per-day 

increase in withdrawal projected for 2020 indicates 

that if withdrawal is distributed only among Hanamaulu wells 1, 3, and 4, and Puhi well 5A, further 

thinning of the already-thin freshwater lens in the 

Puhi area would occur. Such a distribution would 

also exceed the maximum draft recommended by 

the water-systems standards used in Hawaii. 

Another simulation in which part of the 1.16 million gallons per day was distributed among three 

additional hypothetical wells in the Hanamaulu 

area showed that the pumping effects could be 

shifted from the Puhi area to the Hanamaulu area, 

where the freshwater lens is thicker, but that base 

flow in Hanamaulu Stream may decrease by as 

much as 16 percent. 

INTRODUCTION

Projected increases in demand have compelled the 

Kauai County Department of Water (Kauai DOW) to 

explore for additional ground-water sources in the 

Lihue Basin, which includes the most populated areas 

on Kauai, Hawaii (fig. 1). The projected increases will 

come from and serve the southern Lihue Basin which, 

for the purposes of this study, is defined as the area of 

the Lihue Basin south of South Fork Wailua River (fig. 

1). In 1990, Kauai’s population was about 51,000, of 

which about 20 percent resided in the Lihue District 

(State of Hawaii, 1991). Total ground-water withdrawal 

from wells near Lihue in 1990 was estimated to be about 

Numerical Simulation of Ground-Water Withdrawals in 

the Southern Lihue Basin, Kauai, Hawaii

By Scot K. Izuka and Delwyn S. Oki
2 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Figure 1. The southern Lihue Basin, Kauai, Hawaii.

Nawiliwili

Bay

Hanamaulu

Bay

Waita

Reservoir

Kapaa Stream

North Fork Wailua River

South

Fork Wailua River

Hanamaulu Stream

Huleia Stream

Lawai Stream

Makaleha

Stream

Konohiki

Stream

Opaekaa Stream

Nawiliwili Stream

0 1 2 MILES

0 1 2 KILOMETERS

Lihue

Puhi

Omao

Lawai

Wailua

Kapaa

Kealia

PA

CIFIC

O

CEAN

159 ̊30' 159 ̊25' 159 ̊20'

22 ̊

21 ̊55'

22 ̊05'

EXPLANATION

BOUNDARY OF THE SOUTHERN 

 LIHUE BASIN

IRRIGATION DITCH OR TUNNEL

WELL

ELEVATION, IN FEET ABOVE MEAN

 SEA LEVEL

Waialeale (5148)

Kawaikini

(5243)

Kilohana

Volcano

(1149)

Kalepa Ridge

Nonou Ridge

Haupu Ridge

Makaleha

Mountains

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

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

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

159 ̊32'30". Relief from U.S. Geological Survey 

digital elevation models, 1:250,000

(2297)

(2297)

(709)

(3089)

(707)

(1241)

Alakai

Swamp

Area of

map

KAUAI

PACIFIC

OCEAN

22 ̊

20 ̊

160 ̊ 158 ̊ 156 ̊

PACIFIC OCEAN

Kauai

Niihau

Oahu Maui

Molokai

Lanai

Kahoolawe

Hawaii

HAWAII

LOCATION MAP

Puhi wells 

5A and 5B

Northeast Kilohana and

Hanamaulu wells 

3 and 4

Northwest 

Kilohana 

well

Hanamaulu

well 1

Hanamaulu

well

Puakukui Springs 

well

Pukaki and Pukaki Reservoir 

wells
Introduction 3

5 Mgal/d (Shade, 1995a). Since then, however, the 

Lihue Basin has undergone changes in land use accompanied by changes in water use. Since the mid-19th century, sugarcane cultivation grew to become the 

dominant land use in the Lihue Basin, but in the 1970’s 

the sugarcane industry began a decline that ultimately 

led to the closure of the last plantation in 2000. Some 

former sugarcane lands have been converted to residential use or diversified agriculture. 

The Kauai DOW recently projected water-demand 

increases of 1.16 Mgal/d by 2020 in the Lihue Basin 

(table 1). The Kauai DOW plans to meet the projected 

increases in water demand by constructing four new 

wells in the Hanamaulu area and two wells in the Puhi 

area during 2000 and 2001 (Kauai DOW, written commun., 2000) (table 2). Only the four wells in Hanamaulu 

and one well in Puhi (well 5A) will be pumped; the 

other well in Puhi (well 5B) will be a standby well for 

infrequent use (G. Fujikawa, Kauai DOW, oral commun., 2000). In this report, the term “pre-development,” 

when applied to ground-water development, refers to 

the conditions (including existing pumped wells) prior 

to the addition of the proposed wells listed in table 2. 

The Kauai DOW is concerned about the potential 

effects of the additional withdrawal, and whether the 

potential effects will limit well yields in the southern 

Lihue Basin. Increased ground-water withdrawal in a 

coastal area such as the southern Lihue Basin may lower 

the water table, raise the underlying saltwater, and 

reduce streamflow and discharge to the ocean. With a 

few exceptions, wells developing water in the southern 

Lihue Basin cause substantial depression of nearby 

water levels in the aquifer because of the low regional 

permeabilities of the basin’s aquifers, but the effect of 

pumping on saltwater rise in Lihue is not known. 

Ground-water discharge to streams in the southern 

Lihue Basin is substantial (Izuka and Gingerich, 

1998a). Because of this ground-water/surface-water 

connection, ground-water withdrawals may reduce 

streamflows. State laws governing the reduction of flow 

in streams thus emerge as a potential limiting factor for 

ground-water development projects. However, the 

Hawaii State Water Code (Chapter 174C, Hawaii 

Revised Statutes) allows for streamflow reduction, provided the reduction does not cause flows to diminish 

below an “instream flow standard,” which is defined as 

“the quantity or flow of water or depth of water which 

1 All values for additional withdrawal are relative to existing withdrawals prior to 2000

Table 1. Kauai Department of Water projections for increases in 

water demand for Lihue, Kauai, Hawaii (Kauai County Department

of Water, written commun., 2000)

Year Projected additional ground-water withdrawal1

(million gallons per day)

2000 0.42

2010 0.83

2020 1.16

1

Puhi well 5B will be used as standby only, and therefore pumped infrequently (Gregg Fujikawa, Kauai County Department of Water, oral 

commun., 2000)

Table 2. Kauai Department of Water ground-water development projects in the Lihue area, Kauai, Hawaii (Kauai 

County Department of Water, written commun., 2000)

[gal/min, gallons per minute; Mgal/d, million gallons per day]

Well Project Capacity

(gal/min)

Capacity

(Mgal/d)

Estimated 

completion date Location

Hanamaulu well 1 50 0.07 2000 Hanamaulu

Hanamaulu well 3 160 0.23 2000 Hanamaulu

Hanamaulu well 4 300 0.43 2000 Hanamaulu

Pukaki well 120 0.17 2000 Hanamaulu

Puhi well 5A 400 0.58 2001 Puhi

Puhi well 5B1 700 1.01 2001 Puhi
4 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

is required . . . to protect fishery, wildlife, recreational, 

aesthetic, scenic, and other beneficial instream uses.” 

Although final instream flow standards were not yet 

established for the streams in the southern Lihue Basin 

at the time of this study, their eventual implementation 

will consider “existing and potential water developments including the economic impact of restriction of 

such use.” Assessment of ground-water-development 

effects relative to instream flow standards requires 

quantitative estimates of streamflow reduction. 

Purpose and Scope

To quantify the effects that may result from proposed ground-water development in the southern Lihue 

Basin, the U. S. Geological Survey (USGS), in cooperation with the Kauai DOW, undertook a study in which 

several proposed ground-water development scenarios 

were simulated using an existing numerical groundwater-flow model (Izuka and Gingerich, 1998a) of the 

southern Lihue Basin. This report summarizes the 

results of these simulations and their implications for 

ground-water development in the southern Lihue Basin.

Acknowledgments

The authors are grateful to the Kauai DOW Manager and Chief Engineer Ernest Lau, and the staff of the 

Kauai DOW for their cooperation and assistance. 

SETTING

The Lihue Basin is a large semicircular depression 

in southeastern Kauai, the fourth-largest island (553 

mi2

) in the tropical, north-Pacific archipelago of Hawaii 

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

central mountains of Kauai, on the north by the 

Makaleha Mountains, on the south by Haupu Ridge, and 

on the east by the Pacific Ocean. In the southcentral part of the basin lies the broad dome of Kilohana 

Volcano. Numerous streams and rivers drain from the 

Lihue Basin, but in the southern half of the basin where 

the town of Lihue is located, the smaller streams 

coalesce so that nearly all of the surface drainage empties into the ocean by three principal channels: the 

Wailua River, Hanamaulu Stream, and Huleia Stream. 

Rainfall distribution in the 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, forcing 

warm, moist air into the cool, higher elevations. Average annual rainfall ranges from about 50 in/yr at lowlying coastal areas to more than 400 in/yr near the crest 

of Kauai’s central mountains (Giambelluca and others, 

1986). 

Much of the land in the Lihue Basin has historically been used for sugarcane cultivation. From the late 

19th through the 20th century, ditches and reservoirs 

built by the sugar industry not only redistributed water 

within the Lihue Basin, but also transferred water to and 

from adjacent basins (Wilcox, 1996). Thus, the natural 

drainage pattern of the Lihue Basin has been modified 

into a network of natural stream channels crossed by 

irrigation ditches. Shade (1995a) estimated that in 1990, 

about 18.3 Mgal/d was diverted from surface-water 

sources within the combined drainage areas of Hanamaulu and Huleia Streams. Shade (1995a) also estimated that 30.56 Mgal/d was diverted from surfacewater sources in the Wailua River drainage basin in 

1990, but some of that water was used for hydroelectric 

power and returned back to the stream. A decline in 

Hawaii's sugar industry began in the 1970’s and by the 

mid-1990’s, Kauai was one of only two islands in the 

State that still had operational sugar plantations (Wilcox, 1996). Although some of the former sugarcane 

fields in the Lihue Basin had been taken out of sugar 

production, the largest of the sugar plantations in the 

Lihue Basin remained in operation through the remainder of the 20th century. That plantation, however, 

finally ceased operations in November 2000, leaving 

the future of the sugarcane fields and supporting irrigation infrastructure uncertain. 

Geology

The Lihue Basin has undergone complex structural 

evolution. Present understanding of Kauai’s geologic 

framework is the result of studies by numerous investigators, beginning with the early descriptions by Stearns 

(1946) and the comprehensive study of geology and 

water resources by Macdonald and others (1960), and 

later continuing with contributions by Krivoy and others (1965), Clague and Dalrymple (1988), Moore and 

others (1989), Holcomb and others (1997), and Reiners 

and others (1998). According to these studies, Kauai 

was formed during the Pliocene by mid-plate, hot-spot 

volcanism that created one or more large shield 
Setting 5

Figure 2. Distribution of rainfall in the Lihue Basin, Kauai, Hawaii (modified from Giambelluca and others, 1986).

Nawiliwili

Bay

Hanamaulu

Bay

Kapaia

Reservoir

Kapaa Stream

North Fork Wailu a River

South Fork Wailua

River

Hanamaulu

Str e am

Huleia Strea

Pu

m

akukui Stream

Lawai Stream

Makaleha

St ream

Konohiki

Stream

Opaekaa Stream

Iliiliula Stream

Nawiliwili

Stream

Kam ooloa Stream

Waita

Reservoir

0 1 2 MILES

0 1 2 KILOMETERS

Lihue

Puhi

Omao

Lawai

Nawiliwili

Wailua

Kapaa

Kealia

PA

CIFIC

O

CEAN

EXPLANATION

LINE OF EQUAL AVERAGE ANNUAL

 RAINFALL--Interval, in inches, is variable

BOUNDARY OF THE SOUTHERN 

 LIHUE BASIN

IRRIGATION DITCH OR TUNNEL

Waialeale

Kilohana

Volcano

crater

Kalepa Ridge

Nonou Ridge

Haupu Ridge

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

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

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

159 ̊32'30"

Makaleha

Mountains

159 ̊30' 159 ̊25' 159 ̊20'

22 ̊

21 ̊55'

22 ̊05'

80

60

60

80

80

120

120

160

160

200

235

275

355

315

375435
6 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

volcanoes. Beginning in the shield-building stage, and 

continuing into a subsequent 0.5- to 1-million-year 

period of relative volcanic quiescence, erosion and 

faulting created large valleys, canyons, and other 

depressions (including the Lihue Basin). These depressions were later partly filled with sediments as well as 

lava flows and other igneous rocks from scattered rejuvenated volcanism in the late Pliocene and Pleistocene 

(fig. 3). 

The origin of the circular Lihue Basin has been 

variously attributed to stream erosion (Stearns, 1946, 

1985) or collapse (Macdonald and others, 1960; Holcomb and others, 1997). The Lihue Basin was subsequently partially filled with marine and terrigenous 

sediments and lava flows from rejuvenated volcanism 

(including Kilohana Volcano). Geochemical and stratigraphic evidence indicates that the sediments and rocks 

from rejuvenated volcanism are more than 1,000 ft thick 

in some places, and that the basement below these rocks 

has hundreds of feet of relief (Reiners and others, 1998).

The rocks of the Lihue Basin are divided into two 

geologic formations that are separated by an erosional 

unconformity (Macdonald and others, 1960; Langenheim and Clague, 1987). The Pliocene-age Waimea 

Canyon Basalt, which formed during the shield-building stage and constitutes most of the bulk of Kauai, 

forms the basement on which younger sediments and 

volcanic rocks of the Lihue Basin lie (figs. 3 and 4). The 

Waimea Canyon Basalt in the Lihue Basin consists 

mostly of thin lava flows. Most of the Waimea Canyon 

Basalt is obscured by the younger rocks of the basin, 

except at outcrops in the ridges and mountains surrounding and within the basin. In the ridges, the lava 

flows of the Waimea Canyon Basalt are intruded by 

numerous, near-vertical, sheet-like, volcanic dikes 

(Macdonald and others, 1960). Dikes are probably also 

present in the Waimea Canyon Basalt below the floor of 

the basin. However, dikes are rare in outcrops of the 

Waimea Canyon Basalt south of Mt. Waialeale and 

west and south of Haupu Ridge (Macdonald and others, 

1960). At the northwest boundary of the basin near Mt. 

Waialeale is an outcrop of the thick-bedded lava flows 

that have been variously interpreted as caldera-filling 

lava (Macdonald and others, 1960) or lava that accumulated between multiple shield volcanoes (Holcomb and 

others, 1997). 

Resting unconformably on the Waimea Canyon 

Basalt are volcanic rocks and intercalated sediments of 

the Pliocene- and Pleistocene-age Koloa Volcanics 

(Macdonald and others, 1960; Langenheim and Clague, 

1987). The Koloa Volcanics is a heterogeneous unit that 

fills depressions in the Waimea Canyon Basalt. The volcanic rocks include variably weathered, thick, massive 

lava flows and pyroclastic deposits of highly alkalic 

mafic composition, erupted from edifices scattered over 

the old, eroded shield volcano during the rejuvenated 

stage of volcanism. Terrigenous and marine sediments 

are intercalated with the lava flows. 

Overlying the Koloa Volcanics in some places are 

sediments of Pleistocene and Holocene age that form 

coastal plains and fill valley bottoms, but these deposits 

are relatively small in volume (Macdonald and others, 

1960; Izuka and Gingerich, 1998a). 

Hydraulic Properties of the Rocks

Most wells in the Lihue Basin develop water from 

the Koloa Volcanics. The volcanic rocks and sediments 

of the Koloa Volcanics are considered one hydrogeologic unit in this report because individual lava flows 

and sedimentary layers are too numerous and finely 

intercalated to be distinguished, and wells in the Koloa 

Volcanics penetrate both sedimentary and volcanic 

rock. Specific capacities of production wells indicate 

that permeability of the Koloa Volcanics varies widely. 

However, the predominance of low-productivity wells 

in the basin indicates that the regional permeability of 

the Koloa Volcanics is low, and that areas of high permeability are localized. Although wells in the localized 

high-permeability areas may have high initial yields, 

their long-term yields will ultimately be limited by the 

low regional permeability. 

The permeability of an aquifer may be expressed in 

terms of its hydraulic conductivity. Whereas the ability 

of the aquifer to transmit a fluid depends on the properties of the fluid, hydraulic conductivity is a measure of 

the ability of an aquifer to transmit water under a 

hydraulic gradient. Analysis of aquifer-test data indicates that horizontal hydraulic conductivity (Kh) ranges 

from 0.042 ft/d to greater than 100 ft/d (Izuka and Gingerich, 1998a; Gingerich, 1999). Izuka and Gingerich 

(1998a) estimated that the regional Kh of the Koloa Volcanics is probably less than 1 ft/d and used a value of 

0.275 ft/d in a numerical ground-water flow model of 

the basin. This regional hydraulic conductivity is one to 

four orders of magnitude lower than the regional 
Setting 7

Figure 3. Geology of the Lihue Basin, Kauai, Hawaii (modified from Macdonald and others, 1960).

0 1 2 MILES

0 1 2 KILOMETERS

PA

CIFIC

O

CEAN

EXPLANATION

SEDIMENTARY DEPOSITS (Holocene and Pleistocene)

KOLOA VOLCANICS (Pleistocene and Pliocene)

WAIMEA CANYON BASALT (Pliocene

 and Miocene?)

 Olokele Member (Pliocene)

 Haupu Member (Pliocene)

 Napali Member (Pliocene and Miocene?)

GEOLOGIC CONTACT--Dashed 

 where approximate

BOUNDARY OF SOUTHERN 

 LIHUE BASIN

Lihue

Puhi

Omao

Lawai

Nawiliwili

Wailua

Kapaa

Kealia

Nawiliwili

Bay

Hanamaulu

Bay

Kalepa Ridge

Nonou

Ridge

Haupu Ridge

Makaleha

Mountains

Waialeale

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

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

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

159 ̊32'30"

Kilohana

Volcano

159 ̊30' 159 ̊25' 159 ̊20'

22 ̊

21 ̊55'

22 ̊05'
8 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

hydraulic conductivity of many other areas that have 

ground-water development in the Hawaiian Islands. 

Some wells in the Lihue Basin, and most wells 

near but outside the basin, develop water from the 

shield-building lava flows of the Waimea Canyon 

Basalt. Within the basin, the Waimea Canyon Basalt 

crops out only in ridges that were left uncovered by the 

younger Koloa Volcanics. These ridges are intruded by 

low-permeability, sheet-like volcanic dikes that cut vertically or near vertically across the thin shield-building 

lava flows. The dikes reduce the regional permeability 

of the shield-building lava flows (Takasaki and Mink, 

1985; Hunt, 1996). In some areas outside the basin, particularly on the southern flank of Haupu Ridge, dikes 

are apparently less numerous (Macdonald and others, 

1960). Little information exists on the hydraulic properties of the Waimea Canyon Basalt underlying the Koloa 

Volcanics in the Lihue Basin, but it is likely that the 

Waimea Canyon Basalt is intruded by dikes as are the 

ridges surrounding the basin. Using curve-matching 

methods to analyze aquifer-test data, Gingerich (1999) 

estimated Kh for the Waimea Canyon Basalt of the 

northern flank of Haupu Ridge to be 15.8 to 16.1 ft/d, 

however, these estimates are probably higher than the 

regional Kh of the dike-intruded ridge because only the 

earliest part of the time-drawdown data was analyzed, 

which may not reflect the dikes that are likely to be at 

some distance from the test wells. Izuka and Gingerich 

(1998a) used a Kh of 1.11 ft/d for the dike-intruded 

Waimea Canyon Basalt in their numerical ground-water 

flow model of the southern Lihue Basin.

Dike-free shield-building lava flows on Oahu have 

Kh ranging from hundreds to thousands of feet per day 

(Soroos, 1973). The hydraulic conductivity of dike-free 

shield-building lava flows on Kauai is probably in the 

lower part of this range because the lava flows on Kauai 

are older and more altered. Izuka and Gingerich (1998a) 

used a Kh of 200 ft/d for dike-free Waimea Canyon 

Basalt in their numerical ground-water flow model of 

the southern Lihue Basin. 

Figure 4. Block diagram showing the structure and stratigraphy of the southern Lihue Basin, Kauai, Hawaii (from Izuka and Gingerich, 

1998a).

EXPLANATION

SEDIMENTARY DEPOSITS

KOLOA VOLCANICS

WAIMEA CANYON BASALT

INFERRED FAULT -- Arrows indicate direction of relative movement

?

?

?

Kalepa Ridge

Ocean

Waialeale

Kalepa

Ridge

Hanam aulu

Stream

North Fork Wailua River

South Fork Wailua River

Volcano

Kilohana

Volcano

Kilohan

Dike a

Kapaia

Reservoir
Setting 9

Pleistocene and Holocene sediments in the basin 

are of small areal extent and have not been developed 

much for water or studied hydrologically, and therefore 

are not discussed as a separate hydrogeologic unit in 

this report. 

Vertical hydraulic conductivity.--The vertical 

hydraulic conductivity (Kv) of an aquifer composed of 

gently dipping lava flows is likely to be substantially 

less than Kh. Estimates of Kv/Kh for lava flows in 

Hawaii range from 1/3 to 1/200 (Hunt, 1996). Whereas 

dike-free lava flows of the Waimea Canyon Basalt may 

have hydraulic properties similar to other basalts in 

Hawaii, the Koloa Volcanics probably has a lower value 

of Kv/Kh because it has thicker lava flows that are intercalated with sediments and weathered zones. Intrusion 

of dikes into the lava flows of the Waimea Canyon 

Basalt probably increases the value of Kv/Kh because 

dikes are essentially planar vertical structures that 

reduce the horizontal hydraulic conductivity of the 

intruded lava flows. In a numerical ground-water flow 

model of the southern Lihue Basin, Izuka and Gingerich 

(1998a) used Kv/Kh values of 1/200 for the dike-free 

lava flows of the Waimea Canyon Basalt, 1/100 for the 

dike-intruded part of the Waimea Canyon Basalt, and 

1/500 for the Koloa Volcanics.

Ground-Water Occurrence and Movement

Fresh ground water in Kauai, as in other oceanic 

islands, forms a freshwater lens that is underlain by saltwater originating from the ocean (fig. 5). Freshwater in 

the lens moves downward in inland areas of recharge, 

horizontally toward the coast, and upward to be discharged to the ocean or at streams and springs on land. 

The freshwater lens is buoyed by the density difference between saltwater and freshwater (the density 

of the saltwater in the aquifer is about 1.025 times the 

density of the freshwater). The transition from freshwater to saltwater is a diffuse zone of mixing, but for 

simplicity, especially in aquifers where the freshwater 

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

Figure 5. Diagrammatic representation of ground-water flow in the southern Lihue Basin, Kauai, Hawaii (from Izuka and 

Gingerich, 1998a).

Not to scale

Ocean

Saltwater

Freshwater

Dike

Seepage to ocean

Seepage to streams

KOLOA VOLCANICS

WAIMEA CANYON BASALT

LINE OF EQUAL FRESHWATER HEAD

WATER TABLE

DIRECTION OF GROUND-WATER MOVEMENT

EXPLANATION
10 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

sharp interface (fig. 5). The Ghyben-Herzberg relation, 

which uses the density difference between freshwater 

and saltwater to estimate the thickness of the freshwater 

lens, indicates that the depth of the interface below sea 

level is about 40 times the elevation of the water table 

above sea level. The interface position computed by the 

Ghyben-Herzberg relation is commonly considered to 

be an approximation of the position of a 50-percent 

freshwater and 50-percent saltwater mixture in the transition zone, and the relation is commonly used to estimate freshwater-lens thickness in island and coastal 

aquifers. Because the Ghyben-Herzberg relation 

assumes hydrostatic conditions, however, the relation 

gives inaccurate freshwater-thickness estimates and 

does not accurately predict pumping-induced rises of 

the interface and saltwater intrusion in regions of the 

aquifer where ground-water flow has a substantial vertical component. 

Ground water in the southern Lihue Basin originates mostly as recharge from rainfall. Ground water 

flows downward in the western part of the basin where 

recharge is highest, then flows to the north, east, and 

south where it discharges in streams or the ocean (fig. 5) 

or flows to adjacent ground-water areas. The groundwater system in the southern Lihue Basin is characterized by flow through low-permeability rock, a thick 

freshwater lens with a water table that is within a few 

tens of feet of the ground surface, steep horizontal and 

vertical hydraulic-head gradients, and a relatively large 

proportion of ground-water discharge to streams compared with most other places in Hawaii. The highest 

ground-water levels are found in the mountains at the 

western rim of the southern Lihue Basin where rainfall 

is highest and low-permeability intrusive dikes in the 

Waimea Canyon Basalt impound water to high elevations (figs. 5 and 6). In the central part of the basin, 

ground water saturates the Koloa Volcanics to elevations as high as 850 ft above sea level. The high heads 

in the saturated ground-water system in the southern 

Lihue Basin result from the low permeabilities of the 

Koloa Volcanics and dike-intruded Waimea Canyon 

Basalt. Because of the large flux of ground water 

through the basin and the high resistance to flow provided by the low-permeability rock, steep gradients 

result and fresh ground water saturates nearly to the 

land surface. Streams incising the upper part of the aquifer maintain water levels just below the land surface in 

interstream areas. The streams thus play an important 

part in shaping the water table in the southern Lihue 

Basin. Ground water that does not discharge to streams 

or springs eventually discharges at or beyond the coast. 

Water-budget calculations for the southern Lihue Basin 

indicate that at least 64 percent of recharge is eventually 

discharged to the streams; the remainder is withdrawn 

by wells or discharges directly into the ocean (Izuka and 

Gingerich, 1998a). 

Effects Of Ground-Water Withdrawals

Prior to ground-water development, ground-water 

flow is in a state of long-term average dynamic equilibrium, commonly referred to as steady state. Seasonal 

variations may result in short-term imbalances, but in 

the long term, the average ground-water recharge rate is 

balanced by the average ground-water discharge rates to 

streams and the ocean. 

When the pre-development equilibrium is upset by 

artificial withdrawals, such as pumping a well, the 

shape and size of the freshwater lens changes (fig. 7). 

During this period of change, the freshwater lens adjusts 

to the new stress presented by the withdrawal and the 

associated lowering of hydraulic head, and is said to be 

in a transient state. Artificial withdrawals cause the 

freshwater lens to shrink by lowering the water level 

(which is a measure of hydraulic head in the freshwater 

lens) in the well and the surrounding aquifer to form a 

cone of depression, and by inducing the freshwater/saltwater interface to rise and encroach inland. Lowering of 

water levels and rising of the interface continue as long 

as the cone of depression spreads. 

With time, the cone of depression spreads to areas 

of natural ground-water discharge such as streams or the 

coast, where it causes a reduction in the rate of groundwater discharge. Ultimately, if pumping and recharge 

conditions remain the same for a sufficiently long time, 

the natural discharge to streams and the ocean will be 

reduced by an amount equal to the pumping rate, again 

establishing a new equilibrium and steady state. The 

ultimate magnitude of the water-level decrease and 

interface rise caused by the artificial withdrawals, the 

amount of time needed for a new steady state to become 

established, and where reductions in stream and coastal 

discharge will occur, depend on numerous factors 

including the withdrawal rate, distribution of wells, distance to areas of natural discharge, and the geometry 

and hydraulic properties of the aquifer. 
Setting 11

Figure 6. Generalized water-table map and profile for the southern Lihue Basin, Kauai, Hawaii (from Izuka and Gingerich, 1998a).

0 1 2 MILES

0 1 2 KILOMETERS

Lihue

Puhi

Omao

Lawai

Nawiliwili

Wailua

Kapaa

PA

CIFIC

O

CEAN

159 ̊30' 159 ̊25' 159 ̊20'

22 ̊

21 ̊55'

22 ̊05'

Waialeale

Kilohana

Volcano

crater

Kilohana

Volcano crater

Kalepa Ridge

Nonou Ridge

Haupu Ridge

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

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

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

159 ̊32'30"

EXPLANATION

WATER-TABLE CONTOUR--Shows 

 elevation of water table (1910-96). 

 Interval 100 feet. Datum is mean sea 

 level. Dashed where inferred

BOUNDARY OF THE SOUTHERN 

 LIHUE BASIN

LINE OF SECTION

IRRIGATION DITCH OR TUNNEL

Nawiliwili

Bay

Hanamaulu

Bay

Kapaia

Reservoir

North Fork Wailu a River

South Fork Wailua

River

Hanamaulu

Str e am

Huleia Strea

Pu

m

akukui Stream

Lawai Stream

Kono hiki Stream

Opaekaa Stream

Iliiliula Stream

Nawiliwili

Stream

Kam ooloa Stream

Waita

Reservoir

100

100

200

300

400

600

800

700

500

1000

900

2,000

FEET

Sea level

500

-500

1,000

1,500

A

A

A

A'

A'

A'

Vertical exaggeration x 7

Bend in section

Ocean

Water table
12 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Figure 7. Generalized section showing the effects of ground-water withdrawals in the southern Lihue Basin, Kauai, Hawaii (from Izuka and

Gingerich, 1998a).

Not to scale

Not to scale

Freshwater Freshwater

Freshwater Freshwater

Ocean

Ocean

Saltwater

Saltwater

BEFORE PUMPING

DURING PUMPING

Freshwater

Freshwater

Saltwater rises

in response to

pumping

Seepage to streams

and ocean is reduced

Seepage to ocean

Seepage to streams

Downward movement

of ground water

(Head decreases with

depth in aquifer)

KOLOA VOLCANICS

WAIMEA CANYON BASALT

LINE OF EQUAL FRESHWATER HEAD

WATER TABLE

DIRECTION OF GROUND-WATER MOVEMENT

EXPLANATION

Pumped well
 Numerical Model Simulation of the Effects of Ground-Water Withdrawals 13

NUMERICAL MODEL SIMULATION OF THE 

EFFECTS OF GROUND-WATER 

WITHDRAWALS

The factors governing the effects of ground-water 

withdrawals in an island aquifer such as the southern 

Lihue Basin, where substantial ground water discharges 

naturally to streams, include the spatial distribution of 

aquifer hydraulic properties, discharge boundaries, and 

recharge, and the flow of both saltwater and freshwater. 

Effects of ground-water withdrawal in such an environment include lowering of water levels, rise of the freshwater/saltwater interface, and reduction of groundwater discharge to streams and the ocean. Accurate 

assessment of the effects of ground-water withdrawals 

in the southern Lihue Basin requires simultaneous consideration of these factors and effects. Numerical 

ground-water-flow modeling is a comprehensive 

method for studying the factors governing the effects of 

ground-water withdrawal. 

Original Numerical Model

With some modifications, the model of the southern Lihue Basin developed by Izuka and Gingerich 

(1998a) was used to study the effects of the groundwater withdrawals proposed for Hanamaulu and Puhi. 

The model was created using a modified version of the 

finite-difference modeling program SHARP (Essaid, 

1990; Izuka and Gingerich, 1998a), which allows simulation of coupled freshwater and saltwater flow. A 

detailed description of the original southern Lihue 

Basin numerical model and its development is provided 

in Izuka and Gingerich (1998a); a synopsis of the 

aspects of the original model that are pertinent to the 

objectives of this study is provided here.

The SHARP program treats freshwater and saltwater as immiscible fluids separated by a sharp interface. Horizontal flow, vertical flow, and ground-water 

discharge to streams and the ocean are controlled by 

hydraulic-head gradients and hydraulic properties of the 

aquifer. Horizontal ground-water flow is computed 

from user-specified horizontal aquifer properties and 

the distribution of model-calculated freshwater and saltwater hydraulic heads. Vertical flow between layers is 

computed from user-specified vertical aquifer properties and differences between model-calculated heads in 

adjacent layers. Discharge of ground water to streams 

and the ocean is computed from user-specified streambed and ocean-floor hydraulic properties and 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. 

The southern Lihue Basin model encompasses not 

only the southern Lihue Basin, but a 17.0-mi by 20.8-mi 

area in the southeast corner of Kauai and adjacent offshore areas (fig. 8). The modeled area was extended 

beyond the margins of the southern Lihue Basin so that 

the no-flow boundaries required at the periphery of the 

model would not substantially affect, or be affected by 

changes in, ground-water flow in the southern Lihue 

Basin. This is particularly important for testing hypothetical ground-water development scenarios. However, data from outside the basin are sparse, therefore 

the model may not accurately simulate conditions outside the basin. Areas outside the basin served only as 

gross approximations of the hydrologic system between 

the study area and the no-flow boundaries. The western 

and northern no-flow boundaries roughly parallel either 

the regional ground-water flow lines or ground-water 

divides. Ground-water withdrawal from the southern 

Lihue Basin is not likely to affect the location of these 

flow lines and divides because the propagation of the 

cones of depression will probably be halted by the large 

amount of water available through reduced groundwater discharge at rivers, streams, and coastal areas 

within the model. The southern and eastern no-flow 

boundaries of the ground-water model were placed in 

the ocean at a minimum of 2.5 mi from the coast to 

allow sufficient space for the freshwater lens in the 

model to extend seaward without impinging on the noflow boundary (fig. 8). The no-flow boundary at the 

base of the model was set at an elevation of -6,000 ft, 

which is consistent with geophysical evidence from 

Kilauea Volcano, Hawaii, that indicates that porosity 

becomes nearly zero below 6,000 ft from the ground 

surface (Kauahikaua, 1993). 

The simulated area was divided into two layers, 

each having 2,475 cells, and each cell representing an 

area 2,000 ft by 2,000 ft (fig. 8). The upper layer extends 

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 of Macdonald and others (1960). The 

lower layer extends from -500 ft to -6,000 ft elevation. 
14 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Figure 8. Model grid, boundaries, streams, pumped wells, and monitoring points used in the numerical ground-water flow model of the 

southern Lihue Basin, Kauai, Hawaii (from Izuka and Gingerich, 1998a).

0 1 2 MILES

0 1 2 KILOMETERS

PA

CIFIC

OCEAN

22 ̊

21 ̊55'

22 ̊05'

21 ̊50'

159 ̊35' 159 ̊30' 159 ̊25' 159 ̊20' 159 ̊15'

5

5

10

15

20

25

30

35

40

45

10

15

20

25

30

35

40

45

50

55

COLUMN

ROW

BOUNDARY OF SOUTHERN

 LIHUE BASIN

MONITORING POINT

PUMPED WELL

TUNNEL

UNCONFINED (WATER TABLE)

OCEAN

STREAM OR RIVER

NO-FLOW BOUNDARY

MODEL CELLS

EXPLANATION

VERTICAL SECTION THROUGH ROW 18 OF MODEL GRID

Offshore

6,000

StreamStreamStream

FEET

Sea level

-6,000
 Numerical Model Simulation of the Effects of Ground-Water Withdrawals 15

In the model, the rocks of the southern Lihue Basin 

are divided into three hydrogeologic regions: (1) the 

Koloa Volcanics, (2) the dike-free lava flows of the 

Waimea Canyon Basalt, and (3) the dike-intruded lava 

flows of the Waimea Canyon Basalt (fig. 9). In the 

model, the Koloa Volcanics was assigned a Kh of 0.275 

ft/d and a Kz of 5.5×10-4 ft/d, the dike-free lava flows of 

the Waimea Canyon Basalt were assigned a Kh of 200 

ft/d and a Kz of 1.00 ft/d, and the dike-intruded lava 

flows of the Waimea Canyon Basalt were assigned a Kh

of 1.11 ft/d and a Kz of 0.0111 ft/d. Recharge to the 

model was 191 Mgal/d distributed over the onshore area 

according to the average annual recharge estimated by 

Shade (1995b). Existing ground-water withdrawals in 

the model were based on water-use data obtained in 

1993 from the Hawaii State Commission on Water 

Resource Management.

Uncertainties in Recharge

The original numerical ground-water model of the 

southern Lihue Basin used recharge estimates from a 

water budget computed by Shade (1995b). Izuka and 

Gingerich (1998a) concluded that the southern Lihue 

Basin model was sensitive to uncertainties in recharge, 

but did not quantify the uncertainties. Shade’s (1995b) 

method of accounting for evapotranspiration has the 

potential to overestimate recharge, which could lead to 

overestimation of ground-water availability. To assess 

the degree of uncertainty in the recharge estimates used 

in the southern Lihue Basin model, aspects of Shade's 

(1995b) water budget were investigated. The physical 

basis and computational procedures used for the uncertainty analysis are discussed in detail in the appendix; a 

synopsis is presented here. 

Recharge in the original southern Lihue Basin 

model.--The water-budget approach to recharge estimation is based on the concept that part of the water that 

falls as precipitation runs off the land directly to the 

ocean; the remainder infiltrates the soil where the water 

is stored temporarily and is subject to evapotranspiration. Recharge to the aquifer occurs only when the soil's 

water-storing capacity is exceeded and the excess infiltrated water is passed to the underlying aquifer (Thornthwaite and Mather, 1955). 

During a given precipitation event, how much 

water ultimately goes to recharge depends on the intensity of the precipitation and the amount of water already 

stored in the soil. If the soil moisture was nearly 

depleted by evapotranspiration prior to precipitation, 

much of the infiltrated water may remain in the soil, and 

little water passes to recharge. If the soil is nearly saturated prior to precipitation, more of the infiltrated water 

would become recharge. The water-budget method 

mimics this process by computing a water budget for 

short consecutive periods (such as days or months) 

using the amount of soil moisture at the end of one 

period as the input soil moisture for the next period. 

Accuracy of the recharge estimates is affected by the 

length of the individual consecutive periods in the 

water-budget computation. In general, daily water budgets more accurately estimate recharge than do monthly 

budgets. 

The order in which evapotranspiration is assigned 

relative to recharge in the water-budget computation 

also affects the recharge estimate. Evapotranspiration 

may be subtracted from the infiltrated water initially, 

then if the remaining water exceeds soil-moisture storage capacity, the excess is assigned to recharge. Alternatively, infiltration in excess of soil-moisture storage 

capacity may be assigned first to recharge, then evapotranspiration acts only on the water remaining in the 

soil. Water budgets that assign evapotranspiration 

before recharge tend to underestimate recharge (Giambelluca and Oki, 1987; Rushton and Ward, 1979; 

Howard and Lloyd, 1979; Alley, 1984), whereas water 

budgets that account for recharge before evapotranspiration tend to overestimate recharge. The degree of 

overestimation or underestimation may be substantial 

for water budgets that are computed on a monthly or 

longer basis. For example, Shade (1997) computed 

monthly water budgets for the island of Molokai, 

Hawaii, and estimated a range for island-wide recharge 

of 140 Mgal/d (accounting for evapotranspiration 

before recharge) to 237 Mgal/d (accounting for 

recharge before evapotranspiration).

Recharge in the original southern Lihue Basin 

model totals 191 Mgal/d (Izuka and Gingerich, 1998a). 

The recharge for the model is based on a monthly calculation in which recharge was accounted for before 

evapotranspiration (Shade, 1995b), thus the estimate is 

expected to be high. The recharge estimate can be 

improved by computing a daily budget and accounting 

for evapotranspiration before recharge. In addition, the 

original water budget and recharge estimates could be 

improved by (1) using hydrograph-separation techniques to compute the runoff-to-rainfall ratio,
16 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Figure 9. Distribution of geology used in the numerical ground-water flow model of the southern Lihue Basin, Kauai, Hawaii (from Izuka 

and Gingerich, 1998a).

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 Koloa Volcanics

 Dike-intruded Waimea Canyon Basalt

 Dike-free lava flows of the Waimea Canyon Basalt

 Ocean

 No-flow boundary

BOUNDARY OF SOUTHERN LIHUE BASIN

EXPLANATION

UPPER LAYER
 Numerical Model Simulation of the Effects of Ground-Water Withdrawals 17

Figure 9. Distribution of geology used in the numerical ground-water flow model of the southern Lihue Basin, Kauai, Hawaii (from Izuka and 

Gingerich, 1998a)--Continued.

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18 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

(2) accounting for fog drip, and (3) correcting for an 

apparent overestimation of evapotranspiration in irrigated areas. 

Assessing the range of recharge uncertainty.--

Recomputation of an entirely new water budget is 

beyond the scope of this report. Instead, daily water 

budgets were computed for selected sites with adequate 

data and compared with water budgets computed from 

the same data using the monthly techniques described 

by Shade (1995b). In the daily water budgets, the conservative approach of accounting for evapotranspiration 

before recharge was taken, and base-flow estimates 

from hydrograph-separation techniques (Izuka and Gingerich, 1998a) were used to compute the runoff-torainfall ratios. Regression equations were developed to 

describe the relation between average annual recharge 

estimated from a daily water budget and average annual 

recharge estimated from a monthly water budget. The 

regression equations were used to adjust recharge in 

each cell of the model. Adjustments to appropriate 

model cells for fog drip and for Shade's (1995b) apparent overestimation of evapotranspiration in irrigated 

areas were then made over a range of values, thus yielding a range of uncertainty in the recharge. These adjustments changed the magnitude and distribution of 

recharge in the model.

After the adjustments made in this study, the 

resulting estimated total recharge for the area of the 

southern Lihue Basin model ranged from a low of 167 

Mgal/d to a high of 194 Mgal/d. The original 191 

Mgal/d estimate is within the range of the adjusted estimates, but is near the high end of the range. The lower 

estimate in the range is 13 percent lower than the original 191 Mgal/d estimate for the modeled area, whereas 

the higher estimate is 2 percent higher. However, the 

actual recharge is unlikely to be as high or as low as 

either end members of the range. The original 191 

Mgal/d estimate is only about 6 percent higher than the 

mean of the high and low estimates. Thus, although the 

analysis indicates that the original 191 Mgal/d may be 

high, it is probably high by only a few percent.

Although recomputed recharge estimates were a 

product of this analysis, the intent of the analysis was 

not to ultimately revise the recharge estimate. Thorough 

estimation of recharge requires extensive data collection, monitoring, and analyses that are not within the 

scope of this study. The analysis used in this study is 

tied to the original recharge estimate, and is therefore 

valid only for assessing uncertainty of the original estimate so that the southern Lihue Basin model could be 

tested over a range of recharge commensurate with the 

range of uncertainty.

Sensitivity of the model within the range.--The 

sensitivity of the southern Lihue Basin model to the 

recharge estimates was tested by substituting the high 

and low estimates of the recharge range into the model 

and running the simulations to steady state. Other 

parameters of the model were kept the same as the original model of Izuka and Gingerich (1998a). The water 

levels resulting from the simulations are shown in table 

3. The absolute values of the differences between the 

observed and simulated water levels using the original 

recharge estimate of Shade (1995b) averaged 45 ft. 

Similarly, the absolute values of the differences 

between the observed and simulated water levels using 

the low recharge estimate also averaged 45 ft, as did the 

absolute values of the differences between the observed 

and simulated water levels using the high recharge estimate. As will be discussed in the “Model Limitations” 

section, the differences between simulated and 

observed heads can be partly attributed to averaging as 

a result of the coarseness of horizontal and vertical discretization (Izuka and Gingerich, 1998a). 

Table 4 shows that when the original recharge estimate is used in the southern Lihue Basin model, the 

simulated base flow of Hanamaulu Stream is within the 

range of expected base flow determined by hydrograph 

separation (Izuka and Gingerich, 1998a), the simulated 

base flow of Huleia Stream is lower than expected by 

about 45 percent, and the simulated base flow of South 

Fork Wailua River is about 3 percent lower than the 

lowest expected base flow. When the high recharge estimate is used, the simulated base flow of Hanamaulu 

Stream is again within the range of expected base flow, 

the simulated base flow of Huleia Stream is lower by 

about 56 percent, and the simulated base flow of South 

Fork Wailua River is about 14 percent lower than the 

lowest expected base flow. The high recharge estimate, 

despite being slightly higher in total than the original 

recharge, results in lower simulated water levels in 

monitor wells (table 3) and lower base flows for Huleia 

Stream and South Fork Wailua River (table 4) because 

the high and original estimates differ in the way the 

recharge is distributed (see appendix).

When the low recharge estimate is used, all three 

streams had simulated base flows that were lower than 
 Numerical Model Simulation of the Effects of Ground-Water Withdrawals 19

expected: simulated base flow of Hanamaulu Stream is 

37 percent lower than the lowest value in the expected 

range, simulated base flow of Huleia Stream is 64 percent lower, and simulated base flow of South Fork 

Wailua River is about 20 percent lower than the lowest 

value in the expected range. 

Recharge used for this study.--The foregoing 

analysis indicates that the original recharge used in the 

southern Lihue Basin model may be high, and therefore 

non-conservative. Simulated water levels and base 

flows in the southern Lihue Basin model are sensitive to 

recharge within the range of estimated uncertainty. 

However, the original recharge lies within the range 

estimated in the uncertainty analysis. Inasmuch as the 

original recharge is within the range of estimated uncertainty, and no recharge estimates of clearly better accuracy presently exist, the original recharge was used for 

simulating the effects of proposed ground-water withdrawals. 

a

 From Izuka and Gingerich (1998a)

b

 Except for recharge, all parameters are the same as in the original model from Izuka and Gingerich (1998a). All simulated water 

levels are from upper layer of model.

c From Izuka and Gingerich (1998a), based on recharge calculated by Shade (1995b)

d

 Water level inferred from a marsh in the summit crater of Kilohana Volcano 

a

 Estimated by hydrograph separation from Izuka and Gingerich (1998a)

b

 Except for recharge, all parameters are the same as in the original model from Izuka and Gingerich (1998a)

c Based on recharge calculated by Shade (1995b)

Table 3. Simulated steady-state water levels in the southern Lihue Basin, Kauai, Hawaii, for various estimates of 

recharge

[Mgal/d, million gallons per day; all water levels in feet above sea level]

Well name

(and State well number)

Observed 

water levela

Location in 

model grid 

(row, column)

Simulated water levels from the numerical ground-water 

flow model of the Lihue Basinb

Using original 

recharge estimate

(191Mgal/d)c

Using high 

recharge estimate

(194 Mgal/d)

Using low 

recharge estimate

(167 Mgal/d)

Puakukui Springs (2-5626-01) 173 26, 27 162 162 159

Northwest Kilohana (2-0126-01) 576 12, 25 686 634 634

Northeast Kilohana (2-0124-01) 428 9, 31 423 409 405

Hanamaulu (2-5923-08) 243 14, 34 296 289 279

Kilohana Crater d 820 14, 27 790 730 729

Pukaki Reservoir (2-0023-01) 252 12, 34 312 299 297

Table 4. Simulated steady-state base flows of streams and rivers in the vicinity of the southern Lihue Basin, Kauai, 

Hawaii, for various estimates of recharge

[all base-flow values in million gallons per day (Mgal/d); n.d., not determined]

Stream or river

Expected base flow 

from analysis of 

gage recordsa

Simulated base flow from the numerical ground-water flow 

model of the Lihue Basinb

Using original 

recharge estimate

(191 Mgal/d) c

Using high 

recharge estimate

(194 Mgal/d)

Using low 

recharge estimate

(167 Mgal/d)

North Fork Wailua River n.d 21.60 24.6 22.8

South Fork Wailua River 57 to 74 55.34 49.3 45.6

Hanamaulu Stream 3 to 5 3.82 4.7 1.9

Nawiliwili Stream n.d 1.09 1.5 0.3

Huleia Stream 22 12.10 9.6 8.0

Hanapepe Stream 46 44.95 42.5 37.7
20 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Model Limitations

The resolution of any numerical model is limited 

by the level of discretization used to create the model. 

The level of discretization used in the southern Lihue 

Basin model may be too coarse for studying effects at a 

local scale, but the discretization is adequate for studying ground-water withdrawal effects at the regional 

scale. For example, the model can only simulate major 

streams and rivers (fig. 8) and cannot indicate precisely 

which reaches of a stream or river will be most affected. 

However, the model can be used to study the overall 

effects on the major streams. The model also cannot 

predict precisely what the water-level decline in a particular well will be but can simulate the regional waterlevel decline in the aquifer. Actual water levels in individual pumped wells are likely to be lower than indicated by the model, depending on local aquifer 

properties, well construction, and well location. 

In the southern Lihue Basin, the limitations of discretization also become apparent when the simulated 

head in a model cell is compared to actual water-level 

measurements from a well located within the area represented by the cell (table 3). The simulated head in a 

cell is an average head in the area of the aquifer represented by the cell, whereas an actual water-level measurement from a well only represents the head over a 

small part of the area. Also, a water level in a well represents a vertically averaged head over the distance into 

the saturated aquifer the well penetrates, whereas the 

head in a cell is averaged over the entire saturated thickness of the cell. Because ground-water gradients in the 

southern Lihue Basin are steep in both the horizontal 

and vertical directions, the head within the volume of 

aquifer represented by the cell could vary by several 

tens of feet from place to place; likewise, an observed 

water level in a well may differ by several tens of feet 

from the head in the model cell. Although the model 

may not be able to resolve some local details in water 

levels or predict what the water levels in wells will be 

when the proposed withdrawal increases are implemented, the model can incorporate regional hydraulic 

conditions and boundaries to estimate regional-scale 

water-level declines. 

Discretization also affects the simulated freshwater-saltwater interface position, which is a function of 

freshwater and saltwater head. In areas where local 

hydraulic complexities are too small to be resolved with 

the model’s degree of discretization, the model can only 

simulate the regional interface position, which may 

differ from the true interface position. Furthermore, the 

model cannot simulate pumping-induced movement of 

the interface beneath areas where the freshwater saturates to the no-flow boundary at the bottom of the model 

(that is, where the interface elevation is below -6,000 

ft). In some areas (near Puhi well 5A, for example) 

where local hydrologic complexities are known to exist 

but are not incorporated in the model, the possibility of 

saltwater intrusion cannot be assessed from the model 

simulations alone and consideration of other criteria 

may be warranted. Despite the limitations of the southern Lihue Basin model, the simulated interface is 

regionally consistent with the hydrologic data, although 

the actual depth of the interface throughout most of the 

southern Lihue Basin is unknown. 

The southern Lihue Basin ground-water model 

used in this study incorporated land-use conditions that 

existed in the 1990's. Thus, the model simulations show 

the effects of the proposed ground-water withdrawal 

increases relative to conditions that existed when much 

of the sugar industry in the southern Lihue Basin was 

still active. The recent demise of the sugar industry constitutes a substantial change in land use in the southern 

Lihue Basin, but the future of the former sugarcane 

lands, and how the land-use changes will affect ground 

water, is uncertain. Assessment of the potential effects 

resulting from land-use changes is beyond the scope of 

this study. 

Uncertainties in recharge can result in uncertainties in hydraulic conductivities used in the model, the 

model-calculated water levels, and the modelcalculated discharges. Underestimation of recharge will 

result in an underestimation of hydraulic conductivity 

and an overestimation of water-level declines caused by 

artificial ground-water withdrawals. Overestimation of 

recharge will result in an overestimation of hydraulic 

conductivity and an underestimation of water-level 

declines caused by artificial ground-water withdrawals. 

Uncertainties in the spatial distribution of estimated 

recharge can also affect model results. Although it is 

recognized that uncertainty in recharge exists, the 

southern Lihue Basin model is nevertheless the best tool 

currently available for assessing the effects of additional ground-water withdrawals on water levels and 

stream discharge. 
Steady-State Simulations of Proposed Withdrawals 21

STEADY-STATE SIMULATIONS OF 

PROPOSED WITHDRAWALS 

Steady-state simulations were used to study the 

ultimate effects of the proposed withdrawals. The 

results of these simulations represent the new equilibrium (steady-state) conditions that would persist under 

the proposed ground-water withdrawal conditions, so 

long as those withdrawal conditions and recharge 

remain the same. The steady-state simulations do not 

address how long steady state would take to be achieved 

or how far the effects would have advanced at any time 

before steady state is achieved. Analysis of time-dependent ground-water withdrawal effects requires transient 

simulations, which are described in a later section. 

Three ground-water development projections for 

the southern Lihue Basin were simulated with the 

numerical model: (1) 0.42 Mgal/d in 2000, (2) 0.83 

Mgal/d in 2010, and (3) 1.16 Mgal/d in 2020. These 

withdrawals are projected increases over the groundwater withdrawals already in existence prior to 2000. 

Wells used in the simulations were based on the wells 

listed in the schedule of the Kauai DOW ground-water 

development projects (table 2). Simulated withdrawal 

for the 2000 projection was distributed among the four 

wells in the Hanamaulu area; simulated withdrawals for 

the 2010 and 2020 projections were distributed among 

the four wells in Hanamaulu (Hanamaulu wells 1, 3, and 

4 and the Pukaki well) and one well in Puhi (well 5A). 

Puhi 5B was not simulated because it is intended as an 

infrequently used standby well (G. Fujikawa, Kauai 

Department of Water, oral commun., October 2000). 

Withdrawals were assigned to the cells in the model 

most closely representing the location and hydrologic 

conditions of the wells (fig. 10). Because Hanamaulu 

wells 3 and 4 will be located close to each other, their 

combined withdrawal was assigned to one cell in the 

model. 

The effects of ground-water withdrawal on freshwater head were monitored at pumping locations as well 

as at a location representing the Lihue Town well field 

(fig. 10). Most of the wells in the Lihue Town well field 

lie within 2 mi of the coast, and therefore may be 

affected by saltwater intrusion resulting from upgradient ground-water development. Effects of ground-water 

withdrawals on the interface position were monitored 

beneath Hanamaulu well 1 and the Lihue Town well 

field, but could not be monitored at the other well sites 

because saltwater does not exist beneath these locations 

in the model. 

Effects of the 2000 (0.42 Mgal/d) Projection

The future long-term average withdrawal of each 

new well in table 2 is not known. To simulate the 0.42 

Mgal/d ground-water-withdrawal increase projected for 

2000, an approximation of the future withdrawal distribution was obtained by setting withdrawal at an individual well on the basis of the proportion of the total pump 

capacity the well constituted:

(1)

where: Qw = simulated withdrawal for an individual 

well [L3

/T],

Qt = total projected new withdrawal [L3/T], 

Cw = capacity of pump in the well [L3/T], and

Ct = total capacity of all new wells among 

which the projected withdrawal will be 

distributed [L3

/T].

The combined withdrawal at Hanamaulu wells 3 

and 4 constitutes 74 percent of the projected 0.42 

Mgal/d increased withdrawal for 2000. Simulated 

water-level decrease in this location was 53 ft (fig. 11, 

table 5). Other wells had much smaller withdrawals and 

correspondingly smaller effects. Simulated water level 

in the vicinity of the Pukaki well declined by 15 ft. Simulated water level in the vicinity of Hanamaulu well 1 

declined by 7 ft and the interface rose 1 ft. The ratio of 

the simulated interface rise to the simulated water-level 

decline differs from the 40:1 ratio implied by the Ghyben-Herzberg relation because the Ghyben-Herzberg 

relation ignores vertical hydraulic head gradients and 

therefore is not an accurate predictor of pumpinginduced interface rise. The simulated withdrawal distribution for the 2000 projection did not result in any perceptible change in water-level or interface position in 

the Lihue Town well field. 

The simulated changes in the water table and interface represent the regional effect of the proposed 

ground-water withdrawals. In reality, water levels in 

individual pumped wells are likely to be lower, depending on local aquifer properties, well construction, and 

well location. The measured water level is about 243 ft 

Qw Qt

Cw

Ct

= × ------
22 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Figure 10. Simulated streams, wells, and monitoring points used in the steady-state simulations of projected increases in ground-water 

withdrawal in the southern Lihue Basin, Kauai, Hawaii.

Hanamaulu 

well 1

Nawiliwili Str.

Huleia Str.

 Fork Wailua R.

South

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 Unconfined (water table)

 Ocean

 Stream or river

 No-flow boundary

BOUNDARY OF SOUTHERN LIHUE BASIN

MONITORING POINT

SIMULATED PROPOSED WELL

EXPLANATION

Hanamaulu 

wells 3 and 4

Pukaki well

Puhi well 5A

Lihue Town 

well field

hypothetical wells

(for 2020 simulation)

Hanamaulu

Str.
Steady-State Simulations of Proposed Withdrawals 23

Figure 11. Simulated steady-state changes in water levels resulting from the 0.42-million-gallon-per-day increase in ground-water withdrawal 

projected for 2000 in the southern Lihue Basin, Kauai, Hawaii.

-10

-10

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 No-flow boundary

EXPLANATION

LINE OF EQUAL CHANGE IN WATER LEVEL IN UPPER LAYER 

 OF MODEL --Interval is 10 feet

BOUNDARY OF SOUTHERN LIHUE BASIN

MONITORING POINT

SIMULATED PROPOSED WELL

0
24 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

above sea level in the vicinity of Hanamaulu wells 3 and 

4 and 252 ft above sea level in the vicinity of the Pukaki 

well (Izuka and Gingerich, 1998a), and water levels 

near Hanamaulu well 1 are about 249 ft above sea level 

(data in ground-water files at the USGS, Honolulu). 

Model simulations indicate that the freshwater extends 

several thousand feet below sea level at all three of these 

locations. By comparison, the simulated water-level 

changes and interface rise that would result from withdrawing 0.42 Mgal/d of ground water from the Hanamaulu area are small. 

With the distribution of the 0.42 Mgal/d withdrawal as shown in table 5, the stream that is most 

affected is Hanamaulu Stream (table 6), which is closest 

to the wells. Simulated base flow in Hanamaulu Stream 

was reduced by 0.27 Mgal/d, which is 64 percent of the 

total effect of the proposed withdrawal on natural 

ground-water discharge. Although Hanamaulu Stream 

has the largest simulated change, the reduction in the 

base flow is only 5 to 9 percent of the estimated predevelopment base flow or 7 percent of the simulated 

pre-development base flow of the stream (compare 

tables 4 and 6). Simulated base flow in South Fork 

Wailua River was reduced by 0.14 Mgal/d, and simulated base flow at Nawiliwili Stream was reduced by 

0.01 Mgal/d. The simulated base-flow reduction in 

these streams accounts for all of the 0.42 Mgal/d withdrawn from the wells; the effects of ground-water withdrawal apparently do not extend beyond these streams 

or to coastal areas (fig. 11). This is consistent with the 

a All wells are in upper layer of model

b For monitoring purposes only; no part of the 0.42 Mgal/d is pumped at this site

c Measured on 10/1/98. Data from well files at the U.S. Geological Survey, Honolulu

d From Izuka and Gingerich (1998a)

e Measured on 4/12/97. Data from well files at the U.S. Geological Survey, Honolulu

f Computed from interface elevations in lower layer of model

g Computed from freshwater heads in upper layer of model 

h Cannot be determined because the pre-development interface is deeper than the bottom of the model

Table 5. Conditions before, and simulated steady-state changes resulting from, the additional ground-water withdrawal 

of 0.42 million gallons per day projected for 2000 in the southern Lihue Basin, Kauai, Hawaii

[Mgal/d, million gallons per day; n.a., not applicable; n.d., not determined; <, less than; water-level and elevation datum is mean sea level]

Well and location 

(row, column) 

in model grid a

Pre-development Steady-state condition with simulated

0.42 Mgal/d additional withdrawal

 Measured 

water level

(feet)

Simulated 

interface 

elevation f

(feet)

Withdrawal 

(Mgal/d)

 Water-level 

decrease g

(feet)

 Interface rise f

(feet)

Hanamaulu 1 (13, 36) 249 c -5,430 0.03 7 1

Hanamaulu 3 and 4 (9, 31) 243 d < -6,000 0.31 53 n.d.h

Pukaki (12, 34) 252 d < -6,000 0.08 15 n.d.h

Puhi b (17, 30) 65 e < -6,000 n.a. 0 n.d.h

Lihue Town well field b (17, 41) n.a. -3,171 n.a. 0 0

Table 6. Simulated steady-state stream base flow and changes resulting from the additional ground-water withdrawal 

of 0.42 million gallons per day projected for 2000 in the southern Lihue Basin, Kauai, Hawaii

[Mgal/d, million gallons per day]

Stream or river

Simulated pre-development

base flow

(Mgal/d)

Steady-state base flow with 

simulated withdrawal

(Mgal/d)

Base-flow decrease

(Mgal/d)

South Fork Wailua 55.34 55.20 0.14

Hanamaulu 3.82 3.55 0.27

Nawiliwili 1.09 1.08 0.01

Huleia 12.10 12.10 0
Steady-State Simulations of Proposed Withdrawals 25

lack of change in simulated head and interface position 

in the Lihue Town well field. 

Effects of the 2010 (0.83 Mgal/d) Projection

Initial simulation of the 0.83 Mgal/d withdrawal 

projected for 2010 used the withdrawal distribution 

among the four wells in Hanamaulu and Puhi well 5A 

determined by equation 1; withdrawal values for each 

well are shown in table 7. The largest withdrawals in 

this simulation were the combined withdrawal at Hanamaulu wells 3 and 4 (45 percent) and the withdrawal at 

Puhi well 5A (39 percent). Simulated water-level 

decline was 65 ft in the vicinity of Hanamaulu wells 3 

and 4, and 58 ft in the vicinity of Puhi well 5A (fig. 12, 

table 7). Other wells had smaller simulated withdrawals 

and water-level decreases. Simulated water-level 

decrease near Hanamaulu well 1 was 8 ft and the interface rose 2 ft. The effect of the 0.83-Mgal/d withdrawal 

on water levels in the Lihue Town well field was imperceptible in the model, but resulted in a 1-ft rise of the 

simulated interface. 

When compared to the pre-development measured 

water level, the simulation results indicate that the distribution of ground-water withdrawals shown in table 7 

will lower the water-level in the vicinity of Puhi well 5A 

to within 7 ft of sea level, which raises the possibility of 

saltwater intrusion. Although the modelsimulated interface does not extend beneath Puhi well 

5A, a high degree of uncertainty is associated with the 

simulated interface position. Puhi well 5A lies in an 

anomalous area where water-level declines during drilling indicate a steep vertical head gradient complicated 

by intercalated low- and high-permeability horizons 

(Izuka and Gingerich, 1998a). When the well was shallow, measured water-level elevations were about 375 ft, 

which is comparable to the simulated water-level elevation (483 ft) prior to the proposed ground-water withdrawal, but the water-level elevation measured when 

the well was completed was only 65 ft. This anomaly 

cannot be resolved with the level of vertical discretization in the southern Lihue Basin model, but the anomaly 

is of small areal extent (Izuka and Gingerich, 1998a) 

and its omission from the model does not affect the 

model’s ability to assess regional effects of the proposed ground-water withdrawal increases in most areas. 

However, the model’s ability to simulate interface rise 

directly beneath Puhi well 5A is limited. The GhybenHerzberg relation indicates a water level of 65 ft above 

sea level would have a pre-development interface elevation of -2,600 ft, but the relation ignores vertical head 

gradients. Extrapolating the vertical gradient measured 

in Puhi well 5A during drilling indicates a pre-pumping 

interface elevation of about -1,700 ft (Izuka and Gingerich, 1998b), but this estimate assumes that the head gradient in the well persists to the interface. Neither the 

Ghyben-Herzberg relation nor the method of Izuka and 

Gingerich (1998b) can determine pumping-induced 

interface rise. Because the location and pumpinginduced interface rise is uncertain, and because Puhi 

well 5A extends hundreds of feet below sea level, saltwater intrusion remains a possibility. 

Although the southern Lihue Basin model cannot 

predict whether saltwater will actually be pumped at 

Puhi well 5A, the model can be used to examine the 

effects of shifting the stress of the ground-water withdrawals away from the Puhi area and toward parts of the 

aquifer where the freshwater lens is thicker. An alternative withdrawal distribution is discussed in a later section of this report. 

With the initial distribution of withdrawal (as 

shown in table 7), 0.79 Mgal/d of the 0.83-Mgal/d withdrawal was accounted for by reductions in base flows of 

South Fork Wailua River and Hanamaulu, Nawiliwili, 

and Huleia Streams (table 8). The largest effect is on 

Hanamaulu Stream, where base flow was reduced by 

0.34 Mgal/d or 41 percent of the total effect of the 

ground-water withdrawals on natural ground-water 

discharge. Base flow in South Fork Wailua River was 

reduced by 0.17 Mgal/d, base flow at Nawiliwili Stream 

was reduced by 0.19 Mgal/d, and base flow at Huleia 

Stream was reduced by 0.09 Mgal/d. With the exception 

of Nawiliwili Stream, reductions of base flows caused 

by the 2010 projected withdrawals are less than 10 percent of the simulated pre-development base flows of the 

streams. The relative base-flow reduction in Nawiliwili 

Stream is higher (17 percent) because the stream has a 

small pre-development base flow and projected withdrawal at nearby Puhi well 5A is high. The alternative 

withdrawal distribution discussed below will examine 

whether shifting withdrawal toward Hanamaulu can 

reduce the base-flow reduction in Nawiliwili Stream. 
26 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Table 7. Conditions before, and simulated steady-state changes resulting from, the additional ground-water withdrawal 

of 0.83 million gallons per day projected for 2010 in the southern Lihue Basin, Kauai, Hawaii

[Mgal/d, million gallons per day; n.a., not applicable; n.d., not determined; <, less than; water-level and elevation datum is mean sea level]

Well and location

(row, column)

in model grid a

Pre-development Steady-state condition with simulated 0.83 Mgal/d 

additional withdrawal

 Measured 

water level

(feet)

Simulated

interface

elevationf

(feet)

Withdrawal

(Mgal/d)

 Water-level 

decreaseg

(feet)

 Interface rise f

(feet)

Hanamaulu 1 (13, 36) 249 c -5,430 0.04 8 2

Hanamaulu 3 and 4 (9, 31) 243 d < -6,000 0.37 65 n.d.h

Pukaki (12, 34) 252 d < -6,000 0.10 18 n.d.h

Puhi 5A (17, 30) 65 e < -6,000 0.32 58 n.d.h

Lihue Town well field b (17, 41) n.a. -3,171 n.a. 0 1

a All wells are in upper layer of model

b For monitoring purposes only; no part of the 0.83 Mgal/d is pumped at this site

c Measured on 10/1/98. Data from well files at the U.S. Geological Survey, Honolulu

d From Izuka and Gingerich (1998a)

e Measured on 4/12/97. Data from well files at the U.S. Geological Survey, Honolulu

f Computed from interface elevations in lower layer of model

g Computed from freshwater heads in upper layer of model

h Cannot be determined because the pre-development interface is deeper than the bottom of the model

Table 8. Simulated steady-state stream base flow and changes resulting from the additional ground-water withdrawal 

of 0.83 million gallons per day projected for 2010 in the southern Lihue Basin, Kauai, Hawaii

[Mgal/d, million gallons per day]

Stream or river

Simulated pre-development 

base flow

(Mgal/d)

Steady-state base flow 

with simulated withdrawal

(Mgal/d)

Base-flow decrease

(Mgal/d)

South Fork Wailua 55.34 55.17 0.17

Hanamaulu 3.82 3.48 0.34

Nawiliwili 1.09 0.90 0.19

Huleia 12.10 12.01 0.09
Steady-State Simulations of Proposed Withdrawals 27

Figure 12. Simulated steady-state changes in water levels resulting from the 0.83-million-gallon-per-day increase in ground-water 

withdrawal projected for 2010 in the southern Lihue Basin, Kauai, Hawaii.

-10

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OCEAN

22 ̊

21 ̊55'

22 ̊05'

21 ̊50'

159 ̊35' 159 ̊30' 159 ̊25' 159 ̊20' 159 ̊15'

5

5

10

15

20

25

30

35

40

45

10

15

20

25

30

35

40

45

50

55

COLUMN

ROW

MODEL CELL

 Unconfined (water table)

 Ocean

 Stream or river

 No-flow boundary

EXPLANATION

LINE OF EQUAL CHANGE IN WATER LEVEL IN UPPER LAYER

 OF MODEL --Interval is 10 feet

BOUNDARY OF SOUTHERN LIHUE BASIN

MONITORING POINT

SIMULATED PROPOSED WELL

-10

-10

0

0

0
28 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

An alternative distribution of the 0.83 Mgal/d 

ground-water withdrawal.--Because Puhi well 5A penetrates deep into a part of the freshwater lens that is thin 

relative to elsewhere in the Lihue Basin, and because 

proximity of the well to Nawiliwili Stream can cause 

significant reduction in the stream’s base flow if withdrawal at the well is high, an alternative distribution of 

ground-water withdrawal wherein withdrawals were 

moved away from the Puhi area and toward Hanamaulu 

was simulated in the southern Lihue Basin model. Table 

9 and figure 13 summarize the results of a simulation in 

which withdrawal at each of the Hanamaulu area wells 

was increased to 67 percent of the pump capacity. This 

represents the maximum withdrawal from the Hanamaulu wells for the given pump capacity according to 

the State of Hawaii Water System Standards (County 

Departments of Water Supply, State of Hawaii, 1985), 

which recommend that wells have pumps large enough 

to meet the maximum daily demand by pumping not 

more than 16 hours per day. Maximizing the withdrawal 

in the Hanamaulu wells allowed withdrawal at Puhi 

well 5A to be reduced to 69 percent of the withdrawal 

assigned to this well in the initial withdrawal distribution. 

The resulting water-level decrease in the vicinity 

of Puhi well 5A is 40 ft, which is 18 ft less than in the 

initial distribution (compare tables 7 and 9). The alternative distribution of ground-water withdrawal caused 

water levels to decrease by an additional 13 ft in the 

vicinity of Hanamaulu wells 3 and 4, by an additional 3 

ft in the vicinity of Pukaki well, and by an additional 1 

ft in the vicinity of Hanamaulu well 1 relative to the 

water-level decreases in the initial withdrawal distribution. However, the pre-development water table is hundreds of feet above sea level in the vicinity of these 

wells. Relative to the initial distribution of groundwater withdrawal, the simulated interface position in the 

alternative distribution was 7 ft higher at Hana-maulu 

well 1 and 3 ft higher at the Lihue Town well field, but 

the simulated interface positions in these areas are still 

thousands of feet below sea level. 

The alternative withdrawal distribution resulted in 

a base-flow reduction of 0.14 Mgal/d at Nawiliwili 

Stream; this effect is 0.05 Mgal/d less than with the initial 0.83-Mgal/d-withdrawal distribution (table 10). The 

effect of the alternative withdrawal distribution on base 

flow in Huleia Stream was also less than the effect of the 

initial 0.83-Mgal/d-withdrawal distribution. Effects on 

Hanamaulu Stream and South Fork Wailua River were 

larger with the alternative withdrawal

distribution, but the effects on these streams relative to 

their larger base flows are relatively small. The simulation indicates that base flow will decrease by 13 percent 

in Nawiliwili Stream, 10 percent in Hanamaulu Stream, 

and less than 1 percent each at Huleia Stream and South 

Fork Wailua River. 

Effects of the 2020 (1.16 Mgal/d) Projection

The simulations for the 2010 projection showed 

that by distributing most of the proposed pumping stress 

on the Hanamaulu wells, the potential of saltwater 

entering Puhi well 5A is reduced. Therefore, the first of 

two simulations of the 1.16 Mgal/d withdrawal projected for 2020 used a distribution that is proportionally 

similar to the alternative distribution of the 2010 scenario, wherein most (73 percent) of the proposed withdrawal comes from the Hanamaulu wells (table 11). The 

simulation indicates that water levels in the vicinity of 

Hanamaulu wells 3 and 4 would decrease by 110 ft, and 

water levels in the vicinity of the Pukaki well and Hanamaulu well 1 would decrease by 30 and 13 ft, respectively (table 11, fig. 14). The simulated interface 

beneath Hanamaulu well 1 rose 11 ft as a result of the 

proposed ground-water withdrawal and the simulated 

interface at the Lihue Town well field rose 5 ft. The simulated water-level declines and interface rises in the 

Hanamaulu area are small relative to the simulated 

thickness of fresh-water below sea level. However, the 

simulation indicates that water levels in the vicinity of 

Puhi well 5A would decrease by 56 ft; because the lens 

is thinner in this area and the well is deep, the potential 

for saltwater to rise into the well exists. The simulation 

indicates that most of the changes to stream base flow 

resulting from the 1.16 Mgal/d withdrawal proposed for 

2020 would occur at Hanamaulu Stream and South Fork 

Wailua River (table 12), which is consistent with the 

greater withdrawal in the Hanamaulu area compared to 

the Puhi area. 

To maintain the distribution of ground-water withdrawal projected for 2020, pumps in the proposed 

Hanamaulu wells would be operating at 94 to 100 percent of the proposed pump capacities (compare tables 

11 and 2). Such high pumping exceeds the maximum 

draft of 16 hours of pumping per well per day 
Steady-State Simulations of Proposed Withdrawals 29

Table 9. Conditions before, and simulated steady-state changes resulting from, an alternative distribution of the 

additional ground-water withdrawal of 0.83 million gallons per day projected for 2010 in the southern Lihue Basin, 

Kauai, Hawaii

[Mgal/d, million gallons per day; n.a., not applicable; n.d., not determined; <, less than; water-level and elevation datum is mean sea level]

Well and location 

(row, column) 

in model grid a

Pre-development Steady-state condition with simulated

0.83 Mgal/d additional withdrawal

 Measured 

water level

(feet)

Simulated 

interface 

elevation f

(feet)

Withdrawal 

(Mgal/d)

 Water-level 

decrease g

(feet)

 Interface rise f

(feet)

Hanamaulu 1 (13, 36) 249 c -5,430 0.05 9 9

Hanamaulu 3 and 4 (9, 31) 243 d < -6,000 0.44 78 n.d.h

Pukaki (12, 34) 252 d < -6,000 0.12 21 n.d.h

Puhi 5A (17, 30) 65 e < -6,000 0.22 40 n.d.h

Lihue Town well field b (17, 41) n.a. -3,171 n.a. 0 4

a All wells are in upper layer of model

b For monitoring purposes only; no part of the 0.83 Mgal/d is pumped at this site

c Measured on 10/1/98. Data from well files at the U.S. Geological Survey, Honolulu

d From Izuka and Gingerich (1998a)

e Measured on 4/12/97. Data from well files at the U.S. Geological Survey, Honolulu

f Computed from interface elevations in lower layer of model

g

 Computed from freshwater heads in upper layer of model

h

 Cannot be determined because the pre-development interface is deeper than the bottom of the model

Table 10. Simulated steady-state stream base flow and changes resulting from an alternative distribution of the 

additional ground-water withdrawal of 0.83 million gallons per day projected for 2010 in the southern Lihue Basin, 

Kauai, Hawaii

[Mgal/d, million gallons per day]

Stream or river

Simulated pre-development 

base flow

(Mgal/d)

Steady-state base flow 

with simulated 

withdrawal

(Mgal/d)

Base-flow decrease

(Mgal/d)

South Fork Wailua 55.34 55.14 0.20

Hanamaulu 3.82 3.42 0.40

Nawiliwili 1.09 0.95 0.14

Huleia 12.10 12.04 0.06
30 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Figure 13. Simulated steady-state changes in water levels resulting from the alternative distribution of the 0.83-million-gallon-per-day 

increase in ground-water withdrawal projected for 2010 in the southern Lihue Basin, Kauai, Hawaii.

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0 1 2 KILOMETERS

PA

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OCEAN

22 ̊

21 ̊55'

22 ̊05'

21 ̊50'

159 ̊35' 159 ̊30' 159 ̊25' 159 ̊20' 159 ̊15'

5

5

10

15

20

25

30

35

40

45

10

15

20

25

30

35

40

45

50

55

COLUMN

ROW

MODEL CELL

 Unconfined (water table)

 Ocean

 Stream or river

 No-flow boundary

EXPLANATION

LINE OF EQUAL CHANGE IN WATER LEVEL IN UPPER LAYER

 OF MODEL --Interval is 10 feet

BOUNDARY OF SOUTHERN LIHUE BASIN

MONITORING POINT

SIMULATED PROPOSED WELL

0

0

-10

-10

0 -10
Steady-State Simulations of Proposed Withdrawals 31

Table 11. Conditions before, and simulated steady-state changes resulting from, the additional ground-water 

withdrawal of 1.16 Mgal/d projected for 2020 in the southern Lihue Basin, Kauai, Hawaii

[Mgal/d, million gallons per day; n.a., not applicable; n.d., not determined; <, less than; water-level and elevation datum is mean sea level]

Well and location 

(row, column) 

in model grid a

Pre-development Steady-state condition with simulated

1.16 Mgal/d additional withdrawal

 Measured

water level

(feet)

Simulated 

interface 

elevation f

(feet)

Withdrawal 

(Mgal/d)

 Water-level 

decrease g

(feet)

 Interface rise f

(feet)

Hanamaulu 1 (13, 36) 249 c -5,430 0.07 13 11

Hanamaulu 3 and 4 (9, 31) 243 d < -6,000 0.62 110 n.d.h

Pukaki (12, 34) 252 d < -6,000 0.16 30 n.d.h

Puhi 5A (17, 30) 65 e < -6,000 0.31 56 n.d.h

Lihue Town well field b (17, 41) n.a. -3,171 n.a. 0 5

a All wells are in upper layer of model

b For monitoring purposes only; no part of the 1.16 Mgal/d is pumped at this site

c Measured on 10/1/98. Data from well files at the U.S. Geological Survey, Honolulu

d From Izuka and Gingerich (1998a)

e Measured on 4/12/97. Data from well files at the U.S. Geological Survey, Honolulu

f Computed from interface elevations in lower layer of model

g Computed from freshwater heads in upper layer of model

h Cannot be determined because the pre-development interface is deeper than the bottom of the model

Table 12. Simulated steady-state stream base flow and changes resulting from the additional ground-water withdrawal 

of 1.16 million gallons per day projected for 2020 in the southern Lihue Basin, Kauai, Hawaii

[Mgal/d, million gallons per day]

Stream or river

Simulated pre-development 

base flow

(Mgal/d)

Steady-state base flow with 

simulated withdrawal

(Mgal/d)

Base-flow decrease

(Mgal/d)

South Fork Wailua 55.34 55.05 0.29

Hanamaulu 3.82 3.26 0.56

Nawiliwili 1.09 0.89 0.20

Huleia 12.10 12.01 0.09
32 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Figure 14. Simulated steady-state changes in water levels resulting from the 1.16-million-gallon-per-day increase in ground-water 

withdrawal projected for 2020 in the southern Lihue Basin, Kauai, Hawaii.

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0 1 2 KILOMETERS

PA

CIFIC

OCEAN

22 ̊

21 ̊55'

22 ̊05'

21 ̊50'

159 ̊35' 159 ̊30' 159 ̊25' 159 ̊20' 159 ̊15'

5

5

10

15

20

25

30

35

40

45

10

15

20

25

30

35

40

45

50

55

COLUMN

ROW

MODEL CELL

 Unconfined (water table)

 Ocean

 Stream or river

 No-flow boundary

EXPLANATION

LINE OF EQUAL CHANGE IN WATER LEVEL IN UPPER LAYER

 OF MODEL --Interval is 10 feet

BOUNDARY OF SOUTHERN LIHUE BASIN

MONITORING POINT

SIMULATED PROPOSED WELL

0

0

0

-10

-10

-10
Steady-State Simulations of Proposed Withdrawals 33

recommended by the State of Hawaii Water Systems 

Standards (County Departments of Water Supply, State 

of Hawaii, 1985). Indeed, if all of the 1.16 Mgal/d projected for 2020 were withdrawn only from the Pukaki 

well, Hanamaulu wells 1, 3, and 4, and Puhi well 5A 

with the pump sizes given in table 2, the maximum recommended draft would be exceeded regardless of distribution. The total pump capacity for these wells is 1.48 

Mgal/d; if each well is limited to an average 16 hours of 

withdrawal per day, the maximum average withdrawal 

would be only 0.99 Mgal/d. To maintain withdrawal at 

each well below the recommended maximum and to 

lower withdrawal at Puhi well 5A to reduce the risk of 

saltwater intrusion, either the size of the pumps in the 

Hanamaulu wells would have to be increased or new 

wells would be needed. 

An alternative distribution of the 1.16 Mgal/d 

ground-water withdrawal.--To simulate the 1.16 

Mgal/d additional withdrawal projected for 2020 without exceeding the maximum-withdrawal guidelines, 

three wells (wells A, B, and C in table 13 and fig. 10) 

were added to the Hanamaulu area of the model. The 

pump capacity of these hypothetical wells was assumed 

to be 120 gal/min (0.17 Mgal/d), which is equal to the 

pump capacity of the nearby Pukaki well. 

In this simulation, 80 percent of the total proposed 

withdrawal came from wells in the Hanamaulu area, 

thus placing most of the stress of the proposed withdrawal where the freshwater lens is thick. Simulated 

water-level decreases in this area ranged from 82 ft in 

the vicinity of Hanamaulu wells 3 and 4 to 10 ft in the 

vicinity of Hanamaulu well 1, whereas pre-development measured water levels in these areas are more than 

200 ft above sea level (table 13, fig. 15). Simulated 

withdrawal at Puhi well 5A, where the freshwater lens 

is thinner, accounted for 20 percent of the total proposed 

withdrawal, and simulated water-level decrease in the 

vicinity of this well was 41 ft. The simulated interface 

beneath Hanamaulu well 1 rose 10 ft as a result of the 

proposed ground-water withdrawal and the simulated 

interface beneath the Lihue Town well field rose 5 ft. 

These simulated interface rises are small relative to the 

simulated thickness of freshwater below sea level at 

these sites. 

Most of the changes to stream base flow resulting 

from the simulated 1.16 Mgal/d withdrawal for 2020 

occurred at Hanamaulu Stream and South Fork Wailua 

River (table 14), which is consistent with the greater 

withdrawal in the Hanamaulu area compared to the Puhi 

area. Change in base flow at Hanamaulu Stream alone 

accounted for more than half of the proposed additional 

withdrawal. Hanamaulu Stream also ranked highest in 

terms of relative change, with a simulated base flow 

decrease of 16 percent relative to simulated predevelopment base flows. Nawiliwili Stream decreased 

by 14 percent, and Huleia Stream and South Fork 

Wailua River decreased by less than 1 percent relative 

to pre-development base flows.

Implications of the Steady-State Simulations

The steady-state simulations indicate that with 

respect to stream base flow, the effects of the projected 

withdrawal increases will be greatest on streams nearest 

the location of the proposed wells. Redistributing withdrawal can change the effect on individual streams, but 

because streams are so numerous in the southern Lihue 

Basin, it is difficult to shift the net effect away from 

streams as a whole. Although the net effect on streams 

cannot be substantially reduced, the proportional effects 

can be partially mitigated by shifting ground-water 

withdrawal away from streams with low base flow and 

toward streams with high base flow. 

Estimates of streamflow reductions provided by 

the model simulations will allow quantitative comparisons when final instream flow standards are established 

and implemented as mandated by the Hawaii Water 

Code. Quantitative effects estimated by the simulations 

in this study or by additional simulations can be used to 

help identify pumping distributions that meet both the 

need to provide drinking water as well as the need to 

maintain instream flow standards. 

The steady-state simulations indicate that in most 

inland areas of the southern Lihue Basin, with the 

exception of the Puhi area, the depression of the water 

table and rise of the interface caused by the proposed 

ground-water withdrawal will be small relative to the 

pre-development thickness of freshwater above and 

below sea level. In the Puhi area, the model simulations 

cannot assess with certainty the rise of the interface 

because layered heterogeneities that exist in the area are 

too small to be resolved given the level of vertical discretization of the model. The heterogeneities in this area 

appear to be anomalous, however, and limited to the 

Puhi and Kilohana areas (Izuka and Gingerich, 1998a). 

Throughout most inland areas of the southern Lihue 
34 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Table 13. Conditions before, and simulated steady-state changes resulting from, an alternative distribution of the 

additional ground-water withdrawal of 1.16 million gallons per day projected for 2020 in the southern Lihue Basin, 

Kauai, Hawaii

[Mgal/d, million gallons per day; n.a., not applicable; n.d., not determined; <, less than; water-level and elevation datum is mean sea level]

Well and location 

(row, column) 

in model grid a

Pre-development Steady-state condition with simulated

1.16 Mgal/d additional withdrawal

 Measured 

water level

(feet)

Simulated 

interface 

elevation f

(feet)

Withdrawal 

(Mgal/d)

 Water-level 

decrease g

(feet)

 Interface rise f

(feet)

Hanamaulu 1 (13, 36) 249 c -5,430 0.05 10 10

Hanamaulu 3 and 4 (9, 31) 243 d < -6,000 0.45 82 n.d.h

Pukaki (12, 34) 252 d < -6,000 0.12 22 n.d.h

Puhi 5A (17, 30) 65 e < -6,000 0.23 41 n.d.h

Well A (9, 33) n.a. < -6,000 0.10 45 n.d.h

Well B (10, 33) n.a. < -6,000 0.11 35 n.d.h

Well C (10, 34) n.a. < -6,000 0.10 35 n.d.h

Lihue Town well field b (17, 41) n.a. -3,171 n.a. 0 5

a All wells are in upper layer of model

bFor monitoring purposes only; no part of the 1.16 Mgal/d is pumped at this site

c Measured on 10/1/98. Data from well files at the U.S. Geological Survey, Honolulu

dFrom Izuka and Gingerich (1998a)

e Measured on 4/12/97. Data from well files at the U.S. Geological Survey, Honolulu

f Computed from interface elevations in lower layer of model

gComputed from freshwater heads in upper layer of model 

hCannot be determined because the pre-development interface is deeper than the bottom of the model

Table 14. Simulated steady-state stream base flow and changes resulting from an alternative distribution of the 

additional ground-water withdrawal of 1.16 million gallons per day projected for 2020 in the southern Lihue Basin, 

Kauai, Hawaii

[Mgal/d, million gallons per day]

Stream or river

Simulated pre-development 

base flow

(Mgal/d)

Steady-state base flow with 

simulated withdrawal

(Mgal/d)

Base-flow decrease

(Mgal/d)

South Fork Wailua 55.34 55.06 0.29

Hanamaulu 3.82 3.19 0.63

Nawiliwili 1.09 0.94 0.15

Huleia 12.10 12.04 0.06
Steady-State Simulations of Proposed Withdrawals 35

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0 1 2 MILES

0 1 2 KILOMETERS

PA

CIFIC

OCEAN

22 ̊

21 ̊55'

22 ̊05'

21 ̊50'

159 ̊35' 159 ̊30' 159 ̊25' 159 ̊20' 159 ̊15'

5

5

10

15

20

25

30

35

40

45

10

15

20

25

30

35

40

45

50

55

COLUMN

ROW

MODEL CELL

 Unconfined (water table)

 Ocean

 Stream or river

 No-flow boundary

EXPLANATION

LINE OF EQUAL CHANGE IN WATER LEVEL IN UPPER LAYER

 OF MODEL --Interval is 10 feet

BOUNDARY OF SOUTHERN LIHUE BASIN

MONITORING POINT

SIMULATED PROPOSED WELL

0

-10

0

0

-10

-10

Figure 15. Simulated steady-state changes in water levels resulting from the alternative distribution of the 1.16-milliongallon-per-day increase in ground-water withdrawal projected for 2020 in the southern Lihue Basin, Kauai, Hawaii.
36 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Basin, where the freshwater lens is thick and hydraulic 

conductivities are low, the rise of the interface in 

response to ground-water withdrawal is relatively 

small. 

RATE OF DEVELOPMENT OF THE 

EFFECTS OF THE PROPOSED 

GROUND-WATER WITHDRAWALS

Whereas the steady-state simulations indicate the 

full effects of constant ground-water withdrawal that 

will ultimately be attained given enough time, transient 

simulations can show how the effects develop over 

time. To study the rate at which the effects caused by the 

proposed ground-water withdrawal will develop, the 

southern Lihue Basin model was modified to allow transient simulations. The rate at which an aquifer responds 

to withdrawal is a function of aquifer storage. Other 

parameters being equal, the lower the storage, the faster 

the response to withdrawal will be. The transient simulations thus require estimates of aquifer storage. 

Because aquifer storage is not precisely known, the proposed withdrawals were tested using a range of storage 

values. 

The storage of an aquifer is the volume of water the 

aquifer will yield per unit area as a result of a unit 

decline in head in the aquifer. The amount of water 

released depends on the effective porosity and compressibility of the aquifer, the expandability of water, 

and whether the aquifer is confined or unconfined. In an 

unconfined aquifer, the amount of water released comes 

mainly from draining of pore spaces. Water released as 

a result of aquifer compression or water expansion is 

relatively small. Porosity in the lava-flow aquifers in 

Hawaii, as determined from laboratory procedures or 

photo analysis, ranges from about 5 to 50 percent, but 

these values represent total porosity; effective porosity 

may be lower by a factor of 10 (Hunt, 1996). Massive 

lava flows, such as those in the southern Lihue Basin, 

are likely to have even lower porosities. For the transient simulations in this report, porosities of 1 and 10 

percent were used, which is consistent with the lower 

total porosities measured for dense basalt in Hawaii 

(Hunt, 1996) and recognizes that effective porosity will 

be lower than total porosity.

In a confined aquifer, where the pore space is not 

drained, the aquifer yields water as the rock compresses 

and water expands. The storage in a confined aquifer is 

thus a function of aquifer elasticity and water compressibility, and is expressed in terms of specific storage. 

Aquifer-test analyses yield storage in terms of storage 

coefficient, which is related to specific storage by

, (2)

where: Ss = specific storage (L-1),

S = storage coefficient (dimensionless), and 

b = aquifer thickness (L). 

Gingerich (1999) analyzed aquifer-test data from 

several wells in the southern Lihue Basin and determined storage coefficients ranging from 8.2 × 10-2 to 

8.5 × 10-4 (table 15). To derive specific storage, which 

is the parameter needed for the transient simulations, 

the storage coefficients in Gingerich (1999) were 

divided by the assumed aquifer thicknesses. The resulting specific-storage values ranged from 8.4 × 10-5 ft-1 to 

9.3 × 10-7 ft-1. The transient simulations were tested 

over a similar range of specific storage (rounded to the 

nearest whole power of 10) of 10-4 ft-1 to 10-6 ft-1.

The rate of response of stream base flow also 

depends on how the withdrawal is distributed relative to 

the streams. The transient simulations used the same 

withdrawal distributions as in the steady-state simulations. Different combinations of Ss, porosity, and 

S

s

S

b = --

Table 15. Storage coefficients and specific-storage values from aquifer tests in the Lihue Basin, Kauai, Hawaii

Well number Well name Storage 

coefficienta

Assumed aquifer 

thicknessa

(feet)

Specific storage

(feet-1)

2-0023-01 Pukaki Reservoir 8.2×10−2 975 8.4×10−5

2-0124-01 Northeast Kilohana 1.6×10−2 924 1.7×10−5

2-0126-01 Northwest Kilohana 8.5×10−4 916 9.3×10−7

a

 From Gingerich, 1999
 Rate of Development of the Effects of the Proposed Ground-Water Withdrawals 37

withdrawal distribution used in the transient simulations yielded a range of rates for water-level decreases 

and base-flow reductions.

Transient Simulations of the 2000 (0.42 Mgal/d) 

Projection

Graphs of the simulated effects of the 0.42 Mgal/d 

ground-water withdrawal projected for 2000 (using the 

distribution of ground-water withdrawal described in 

table 5) on water levels and stream base flows (figs. 16 

and 17) show how the rate at which the effects will 

develop depends on Ss and porosity. The combination of 

low Ss (10-6 ft-1) and low porosity (1 percent) in one 

simulation resulted in such rapid declines in water levels and base flows that the full effects (as indicated by 

the steady-state simulation of the same withdrawal distribution) were attained within the first 20 years of the 

start of withdrawal. Simulated changes using the higher 

values of Ss (10-4 ft-1) and porosity (10 percent) were 

more gradual. Still, the simulation indicates that 95 percent of the full effects on water levels in the vicinity of 

Hanamaulu wells 3 and 4 (31 ft), and 80 to 87 percent 

of the full effect on base flow in the nearest streams 

(Hanamaulu Stream and South Fork Wailua River) 

would be attained within 20 years. 

Transient simulations combining the higher Ss

value (10-4 ft-1) with the lower porosity value (1 percent), gave virtually the same results as simulations 

combining the lower Ss value (10-6 ft-1) with the higher 

porosity value (10 percent). These simulations indicate 

intermediate rates of change: within 20 years, 99 percent of the full water-level effects in the vicinity of 

Hanamaulu wells 3 and 4, and 92 to 94 percent of the 

full base-flow effects in Hanamaulu Stream and South 

Fork Wailua River, were attained (figs. 16 and 17). 

Transient Simulations of the 2010 (0.83 Mgal/d, 

Alternative Distribution) Projection

Transient simulation of the 0.83 Mgal/d groundwater withdrawal projected for 2010 (table 9) using the 

lower values of Ss and porosity, indicates that the full 

effects on water levels at these sites would be attained 

within 5 years from the start of withdrawal (fig. 18). 

Even if the higher values of Ss and porosity are used, the 

transient simulations indicate that 96 percent of the ultimate water-level decrease in the vicinity of Hanamaulu

wells 3 and 4, and 90 percent of the full effect on water 

levels in the vicinity of Puhi well 5A would be attained 

within 20 years. Transient simulations combining the 

higher Ss value with the lower porosity and combining 

the lower Ss value with higher porosity indicate that 

within 20 years, 99 percent of the full effects on water 

levels in the vicinity of Hanamaulu wells 3 and 4, and 

about 95 percent of the full effect on water levels in the 

vicinity of Puhi well 5A, would be attained. 

The transient simulations also indicate that within 

the first 20 years of the start of ground-water withdrawal, streams near the pumped wells (in this case 

Nawiliwili Stream, which is near Puhi well 5A, and 

Hanamaulu Stream and South Fork Wailua River, 

which are near the Hanamaulu wells) nearly attain the 

full base-flow reductions indicated by the steady-state 

simulations (fig. 19). In the simulation showing the fastest response to ground-water withdrawal, the full effects 

on base flows at these streams were attained within 11 

years from the start of withdrawal. In the simulation 

showing the slowest response to ground-water withdrawal, 74 to 86 percent of the full effects on base flows 

were attained within 20 years. In the simulations showing intermediate rates of response, 84 to 93 percent of 

the full effects on base flows were attained within 20 

years. 

Transient Simulations of the 2020 (1.16 Mgal/d, 

Alternative Distribution) Projection

In the transient simulations of the alternative distribution of the 1.16 Mgal/d additional withdrawal projected for 2020 (table 13) the fastest response to groundwater withdrawal indicates that the full effects on water 

levels would be attained in about 2 years at Hanamaulu 

wells 3 and 4, and about 4 years at Puhi well 5A (fig. 

20). The simulation showing the slowest response indicates that in 20 years, more than 90 percent of the full 

effects on water levels at these locations would be 

attained. In the simulations showing intermediate rates 

of response, 96 to 99 percent of the full effects on water 

levels at these sites was attained within 20 years. 

In the simulation showing the fastest response to 

ground-water withdrawal, the full effects on base flows 

were attained in about 6 to 7 years in Hanamaulu and 

Nawiliwili Streams, and South Fork Wailua River (fig. 

21). In the simulation showing the slowest response to 

ground-water withdrawal, 84 percent of the full 
38 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Figure 16. Simulated water-level changes with time since start of 

withdrawal of the 0.42 million gallons per day projected for the 

southern Lihue Basin, Kauai, Hawaii, in 2000 (n, porosity; Ss, specific 

storage).

0 20 40 60 80 100

Hanamaulu wells 3 and 4

YEARS SINCE START OF WITHDRAWAL

CHANGE IN WATER LEVEL, IN FEET

-60

-50

-40

-30

-20

-10

0

n = 1 percent,Ss = 10−4 feet−1

n = 10 percent,Ss = 10−4 feet−1

n = 1 percent,Ss = 10−6 feet−1

n = 10 percent,Ss = 10−6 feet−1

Figure 17. Simulated stream base-flow changes with time since 

start of withdrawal of the 0.42 million gallons per day projected 

for the southern Lihue Basin, Kauai, Hawaii, in 2000 (n, porosity; 

Ss, specific storage).

Hanamaulu Stream

CHANGE IN BASE FLOW, IN MILLION GALLONS PER DAY

South Fork Wailua River

YEARS SINCE START OF WITHDRAWAL

n = 1 percent,Ss = 10−4 feet−1

n = 10 percent,Ss = 10−4 feet−1

n = 1 percent,Ss = 10−6 feet−1

n = 10 percent,Ss = 10−6 feet−1

-0.30

-0.25

-0.20

-0.15

-0.10

-0.05

0.00

0 20 40 60 80 100

-0.16

-0.14

-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

0.00
 Rate of Development of the Effects of the Proposed Ground-Water Withdrawals 39

Figure 18. Simulated water-level changes with time since start of 

withdrawal of the 0.83 million gallons per day (alternative 

distribution) projected for the southern Lihue Basin, Kauai, Hawaii, 

in 2010 (n, porosity; Ss, specific storage).

Hanamaulu wells 3 and 4

CHANGE IN WATER LEVEL, IN FEET

Puhi well 5A

YEARS SINCE START OF WITHDRAWAL

n = 1 percent,Ss = 10−4 feet−1

n = 10 percent,Ss = 10−4 feet−1

n = 1 percent,Ss = 10−6 feet−1

n = 10 percent,Ss = 10−6 feet−1

-100

-80

-60

-40

-20

0

0 20 40 60 80 100

-50

-40

-30

-20

-10

0

Figure 19. Simulated stream base-flow changes with time since 

start of withdrawal of the 0.83 million gallons per day (alternative 

distribution) projected for the southern Lihue Basin, Kauai, Hawaii, 

in 2010 (n, porosity; Ss, specific storage).

Hanamaulu Stream

CHANGE IN BASE FLOW, IN MILLION GALLONS PER DAY

South Fork Wailua River

Nawiliwili Stream

YEARS SINCE START OF WITHDRAWAL

n = 1 percent,Ss = 10−4 feet−1

n = 10 percent,Ss = 10−4 feet−1

n = 1 percent,Ss = 10−6 feet−1

n = 10 percent,Ss = 10−6 feet−1

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

-0.25

-0.20

-0.15

-0.10

-0.05

0.00

0 20 40 60 80 100 120

-0.16

-0.14

-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

0.00
40 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Figure 20. Simulated water-level changes with time since start of 

withdrawal of the 1.16 million gallons per day (alternative 

distribution) projected for the southern Lihue Basin, Kauai, Hawaii, in 

2020 (n, porosity; Ss, specific storage).

Hanamaulu wells 3 and 4

CHANGE IN WATER LEVEL, IN FEET

Puhi well 5A

YEARS SINCE START OF WITHDRAWAL

n = 1 percent,Ss = 10−4 feet−1

n = 10 percent,Ss = 10−4 feet−1

n = 1 percent,Ss = 10−6 feet−1

n = 10 percent,Ss = 10−6 feet−1

-100

-80

-60

-40

-20

0

0 20 40 60 80 100

-50

-40

-30

-20

-10

0

Figure 21. Simulated stream base-flow changes with time since 

start of withdrawal of the 1.16 million gallons per day (alternative 

distribution) projected for the southern Lihue Basin, Kauai, Hawaii, 

in 2020 (n, porosity; Ss, specific storage).

0 20 40 60 80 100

Hanamaulu Stream

CHANGE IN BASE FLOW, IN MILLION GALLONS PER DAY

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

South Fork Wailua River

YEARS SINCE START OF WITHDRAWAL

-0.35

-0.30

-0.25

-0.20

-0.15

-0.10

-0.05

0.00

Nawiliwili Stream

-0.16

-0.14

-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

n = 1 percent,Ss = 10−4 feet−1

n = 10 percent,Ss = 10−4 feet−1

n = 1 percent,Ss = 10−6 feet−1

n = 10 percent,Ss = 10−6 feet−1
Summary and Conclusions 41

base-flow effect on Hanamaulu Stream, 75 percent of 

the full base-flow effect on South Fork Wailua River, 

and 77 percent of the full base-flow effect on Nawiliwili 

Stream were attained in 20 years. In the simulations 

showing intermediate rates of response, 87 to 93 percent 

of the full effects on base flows of these streams was 

attained within 20 years.

Implications of the Transient Simulations

The transient simulations indicate that most of the 

changes resulting from the projected increase in 

ground-water withdrawal from the Hanamaulu and Puhi 

areas of the southern Lihue Basin will develop within 

10 to 20 years of the start of ground-water withdrawal. 

Even assuming the slowest expected aquifer response, 

90 percent or more of the water-level declines at 

pumped wells will be attained within 20 years, and 75 

percent or more of the ultimate base-flow reductions 

will be attained in streams nearest the ground-water 

withdrawals, and these streams will ultimately undergo 

the greatest changes. This relatively quick response of 

streamflow to ground-water withdrawal is consistent 

with the proximity of the wells to streams. Because the 

southern Lihue Basin has so many streams, it is difficult 

to construct a well that is not near a stream.

SUMMARY AND CONCLUSIONS

Numerical simulations indicate that ground-water 

withdrawals from the Hanamaulu and Puhi areas of the 

southern Lihue Basin will result in depression of water 

levels and reductions in stream base flows in and near 

proposed new water-supply wells. Except for areas such 

as Puhi and Kilohana, which have unique hydraulic 

characteristics that are of limited extent, the freshwater 

lens in most inland areas of the southern Lihue Basin is 

thick and hydraulic conductivities are low. Model simulations indicate that the rise of the interface in response 

to ground-water withdrawal in most areas of the southern Lihue Basin will be small relative to the pre-development thickness of freshwater. Effects of the projected 

withdrawals on streams depend on the withdrawal rate 

and proximity of the pumped wells to streams. Because 

the southern Lihue Basin has so many streams, it is difficult to construct a well that is not near a stream. However, shifting ground-water withdrawals away from 

streams with small base flow and toward streams with 

large base flow can reduce the relative effect on individual streams. 

Quantitative streamflow-reduction estimates, such 

as those provided by the model simulations, are needed 

to assess the effects of ground-water development relative to final instream flow standards mandated by the 

Hawaii State Water Code. Model simulations can help 

identify pumping distributions that meet both the need 

to provide drinking water as well as the need to maintain 

the environmental, aesthetic, and recreational qualities 

of streams. 

Simulation of the projected 0.42 Mgal/d increased 

withdrawal for 2000 included withdrawals from proposed new water-supply wells in Hanamaulu. The simulation indicates that the resulting depression of water 

levels and rise of the interface will be small in comparison to the pre-development freshwater thickness. Virtually all of the 0.42 Mgal/d pumped from the wells will 

ultimately come from base-flow reductions in Hanamaulu Stream, South Fork Wailua River, and Nawiliwili Stream. The largest proportional change in the simulation occurred at Hanamaulu Stream, where base flow 

was reduced by about 7 percent. 

Simulation of the 0.83 Mgal/d withdrawal projected for 2010 included withdrawal from wells in 

Hanamaulu as well as from Puhi well 5A. Because Puhi 

well 5A penetrates deep into a relatively thin freshwater 

lens, the potential exists that saltwater will enter the 

well. The model simulation cannot assess with certainty 

the rise of the interface beneath the Puhi area because of 

vertical heterogeneities that are apparently limited to 

the Puhi and Kilohana areas, but simulations indicate 

that thinning of the already-thin freshwater lens in the 

Puhi area can be reduced by shifting most of the new 

withdrawal to the Hanamaulu area where the freshwater 

lens is thicker. The shift of withdrawal to the Hanamaulu area will also reduce the effect on Nawiliwili 

Stream, which already has small base flow, and increase 

the effect on the larger streams and rivers in the Hanamaulu area. 

The increased withdrawal of 1.16 Mgal/d projected 

for 2020 cannot be obtained from the combination of 

Hanamaulu wells 1, 3, and 4, the Pukaki well, and Puhi 

well 5A without exceeding the recommended maximum rates for the pumps planned for these wells. Therefore, simulation of the 2020 projection included three 

additional hypothetical wells in the Hanamaulu area, 

such that 80 percent of the total proposed 
42 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

withdrawal came from wells in the Hanamaulu area. 

Resulting water-level decline and interface rise were 

small relative to the simulated thickness of freshwater 

below sea level at these sites. The simulation indicates 

that base flow will decrease by 16 percent in Hanamaulu Stream, 13 percent in Nawiliwili Stream, and 1 

percent in South Fork Wailua River.

Most of the changes in water level and streamflow 

will develop within 10 to 20 years of the start of groundwater withdrawals. Even assuming the slowest expected 

aquifer response, 75 percent or more of the ultimate 

base-flow reductions in streams nearest the new 

ground-water withdrawals, and 90 percent or more of 

the water-level declines at pumped wells will be 

attained within 20 years. This relatively quick response 

of streams to ground-water withdrawals is consistent 

with the proximity of the wells to streams. 

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Appendix 44

APPENDIX

RECHARGE UNCERTAINTY IN THE LIHUE BASIN 

AREA, KAUAI

Ground-water recharge used in the original numerical model of the southern Lihue Basin by Izuka and 

Gingerich (1998a) was estimated by Shade (1995b) 

using a water-budget approach. The water-budget 

approach to recharge estimation is based on the concept 

that part of the water that falls as precipitation runs off 

the land directly to the ocean; the remainder infiltrates 

the soil where the water is stored temporarily and is subject to evapotranspiration. Recharge to the aquifer 

occurs only when the soil's water-storing capacity is 

exceeded and the excess infiltrated water is passed to 

the underlying aquifer (Thornthwaite and Mather, 

1955). How much water ultimately goes to recharge 

depends on the intensity of the precipitation and the 

amount of water already stored in the soil. If the soil 

moisture was nearly depleted by evapotranspiration 

prior to precipitation, much of the infiltrated water may 

remain in the soil, and little water passes to recharge. If 

the soil is nearly saturated prior to precipitation, a 

greater part of the infiltrated water would become 

recharge. The water-budget method mimics this process 

by computing a water budget for short consecutive periods (such as days or months) using the amount of soil 

moisture at the end of one period as the input soil moisture for the next period. Accuracy of the recharge estimates is affected by the length of the individual 

consecutive periods in the water-budget computation. 

Daily water budgets can account for intra-month variability in rainfall and evapotranspiration and therefore 

provide more accurate recharge estimates than monthly 

water budgets.

The order in which evapotranspiration is assigned 

relative to recharge in the water-budget computation 

also affects the recharge estimate. Evapotranspiration 

may be subtracted from the infiltrated water initially, 

then if the remaining water exceeds soil-moisture storage capacity, the excess is assigned to recharge. Alternatively, infiltration in excess of soil-moisture storage 

capacity may be assigned first to recharge, then evapotranspiration acts only on the water left in the soil. 

Water budgets that assign evapotranspiration before 

recharge tend to underestimate recharge (Giambelluca 

and Oki, 1987; Rushton and Ward, 1979; Howard and 

Lloyd, 1979; Alley, 1984), whereas water budgets that 

account for recharge before evapotranspiration tend to 

overestimate recharge. The degree of overestimation or 

underestimation may be substantial for water budgets 

that are computed on a monthly or longer basis. For 

example, Shade (1997) computed monthly water budgets for the island of Molokai, Hawaii, and estimated a 

range for island-wide recharge of 140 Mgal/d (assigning evapotranspiration before recharge) to 237 Mgal/d 

(assigning recharge before evapotranspiration). 

Ground-water recharge used in the numerical model of 

the southern Lihue Basin was estimated from a monthly 

water budget that accounts for recharge before evapotranspiration (Shade, 1995b), and is thus expected to be 

higher and less accurate than recharge estimated from a 

daily water budget. 

This study assesses the potential inaccuracy of the 

recharge used in the original model of the southern 

Lihue Basin by comparing average annual recharge 

estimated using a daily water-budget approach versus 

recharge estimated using a monthly water-budget 

approach. Both the daily and monthly water budgets 

were computed using the same data from the same 

selected sites in and near the Lihue Basin. The monthly 

water-budget computation assigned recharge before 

evapotranspiration, which is the method used by Shade 

(1995b). In contrast, the daily water-budget computation accounted for evapotranspiration before recharge, 

which is a more conservative approach, and used base 

flows computed from hydrograph-separation techniques in the computation of the runoff-to-rainfall 

ratios. Regression equations relating average annual 

recharge estimates from the two methods were developed and used to adjust the original recharge in each cell 

of the southern Lihue Basin ground-water model so that 

a daily-water-budget-based recharge distribution could 

be obtained for the model. This distribution was further 

refined by including fog drip, and correcting for an 

apparent overestimation of evapotranspiration in irrigated areas of the original Lihue Basin water budget. 

Adjustments for fog and the apparent overestimation of 

evapotranspiration in irrigated areas were then made 

over a range of values, thus yielding a range of uncertainty in the recharge estimate. 

Data

To develop equations relating average annual 

recharge estimated from a daily water budget and average annual recharge estimated from a monthly water 

budget, available pan-evaporation (Ekern and Chang, 
45 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

1985) and daily rainfall data (Hydrosphere, 1996) from 

stations in and near the Lihue Basin (fig. A1, table A1) 

were used. The same rainfall and pan-evaporation data 

were used in a daily water budget and a monthly water 

budget. For the monthly water budget, daily rainfall and 

pan-evaporation values were aggregated into monthly 

totals. Pan evaporation was used as an estimate of 

potential evapotranspiration (Shade, 1995b) in the 

water budgets.

 Only stations with at least 1 year of daily rainfall 

data were considered for the analysis, and all but two of 

these stations had daily or monthly pan-evaporation 

data. Only annual pan-evaporation data were available 

for stations 1045 and 1047, but these two stations were 

included in the analysis because (1) these were the only 

two stations meeting the other selection criteria that had 

an average annual rainfall value greater than 100 in., (2) 

the annual pan-evaporation rates are probably adequate 

because persistent orographic clouds reduce seasonal 

variations in pan-evaporation rates (Ekern and Chang, 

1985), and (3) the estimated annual pan-evaporation 

rate at these two sites is less than 20 percent of the 

annual rainfall and therefore evapotranspiration is a less 

important component of the water budget than at drier 

sites. For these stations, the annual pan-evaporation 

total was uniformly distributed throughout the year. At 

station 1020.1, concurrent daily rainfall and panevaporation data were used. For all stations other than 

1020.1, 1045, and 1047, the available daily rainfall and 

monthly pan-evaporation data were not from concurrent 

periods. At these sites, monthly pan evaporation was 

estimated from mean monthly pan evaporation adjusted 

by an annual solar radiation factor (Ekern and Chang, 

1985, p. 11), and the monthly pan-evaporation total was 

uniformly distributed throughout the month. 

Daily Water Budget

The water-budget method that was used in this 

study is a variant of the Thornthwaite and Mather 

(1955) bookkeeping procedure. For a given area, daily 

runoff was assumed to be a constant fraction of daily 

rainfall for a given month (table A2). Daily runoff was 

subtracted from daily rainfall, and the remaining volume was added to the beginning soil-moisture storage 

for the day to determine interim soil-moisture storage:

Xi = Pi − Ri + Si-1, (A1)

where: Xi = interim soil-moisture storage for current 

day [L],

Si-1 = ending available soil-moisture storage 

from previous day (i−1), equal to the 

beginning available soil-moisture storage 

for current day (i) [L], 

Pi = precipitation for current day [L],

Ri = runoff for current day [L], and

i = subscript designating current day number.

All volumes of water are expressed as an equivalent 

depth of water over an area by dividing by the total area. 

Available soil-moisture storage, expressed as a depth of 

water, is equal to the root depth multiplied by the 

difference between the existing volumetric soilmoisture content within the root zone and the 

volumetric wilting-point moisture content. 

Si-1 = D × (θi-1 − θwp), (A2)

where: D = plant root depth [L],

θi-1 = ending volumetric soil-moisture content 

from previous day (i−1), equal to the 

beginning volumetric soil-moisture 

content for current day (i) [L3

/L3], and

θwp = volumetric wilting-point moisture content 

[L3

/L3].

The maximum soil-moisture storage, expressed as a 

depth of water, is equal to the root depth multiplied by 

the available water capacity, which is the difference 

between the volumetric field-capacity moisture content 

and the volumetric wilting-point moisture content. 

Sm = D φ,

φ = θfc − θwp, (A3)

where: Sm = maximum soil-moisture storage [L],

φ = available water capacity [L3/L3], and 

θfc = volumetric field-capacity moisture content 

[L3

/L3].

For a given day, evapotranspiration was subtracted 

from the interim soil-moisture storage, and any soil 

moisture remaining above the maximum soil-moisture 

storage was assumed to be recharge. Evapotranspiration
Appendix 46

Figure A1. Areas with different runoff-to-rainfall ratios in the southern Lihue Basin, Kauai, Hawaii.

BOUNDARY OF AREA WITH UNIFORM RUNOFF-TO-RAINFALL RATIOS

STREAM-GAGING STATION AND NUMBER

RAIN-GAGING STATION AND STATE NUMBER

MAP DESIGNATION OF AREA USED IN WATER-BUDGET

 COMPUTATION--see table A2

EXPLANATION

1020.1

0 1 2 MILES

0 1 2 KILOMETERS

PA

CIFIC

OCEAN

22 ̊

21 ̊55'

22 ̊05'

21 ̊50'

159 ̊35' 159 ̊30' 159 ̊25' 159 ̊20' 159 ̊15'

16049000

16060000

16052500

16052500

Haupu Ridge

5

7

3

2

4

1

1

6

927

931

935

940

936

994

1005

1006

1047

1045

1004

1011

1020.1

941

Hanapepe

Lihue

Wailua

Kapaa

Mt Waialeale
47 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

a

 Averages for period computed from data in Hydrosphere (1996)

b Monthly and annual data from Ekern and Chang (1985); daily data from Hydrosphere (1996)

Table A1. Rainfall and pan-evaporation stations used in the water-budget analysis, Lihue Basin area, Kauai

Station 

number

Period of daily rainfall 

record used

Average annual 

rainfalla

(inches)

Pan evaporationb

Type of data 

available

Average annual

(inches)

927 3/1/1951-6/30/1956 35 monthly 104

931 10/1/1949-9/30/1955 43 monthly 90

935 4/1/1950-8/31/1953 37 monthly 88

936 2/1/1955-1/31/1956 82 monthly 53

940 10/1/1949-11/30/1954 37 monthly 93

941 11/1/1950-4/30/1953 62 monthly 92

994 10/1/1949-2/29/1952 91 monthly 66

1004 12/1/1951-9/30/1953 75 monthly 63

1005 2/1/1954-6/30/1956 97 monthly 75

1006 10/1/1949-8/31/1952 78 monthly 61

1011 3/1/1954-6/30/1956 81 monthly 70

1020.1 1/1/1979-11/30/1991 41 daily 99

1045 7/1/1995-9/30/1999 160 annual 30

1047 4/1/1997-9/30/1999 349 annual 30

a

 area 3 corresponds to the drainage basin for station 16060000

b area 4 corresponds to the drainage basin for station 16049000

c area 6 corresponds to the drainage basin for station 16052500

d runoff-to-rainfall ratios from area 4

e runoff-to-rainfall ratios from area 6

f for area 1, runoff-to-rainfall ratios from areas 4 and 6 were used to compute recharge with a daily water budget, and the average recharge value 

was used

Table A2. Runoff-to-rainfall ratios used in the monthly and daily water budgets

[nc, not computed]

Area

(fig. A1)

Ratio of runoff-to-rainfall

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Annual

Monthly water budget

1 0.330 0.373 0.398 0.313 0.213 0.175 0.215 0.228 0.135 0.203 0.398 0.393 nc

2 0.714 0.621 0.689 0.675 0.612 0.404 0.469 0.447 0.323 0.486 0.791 0.705 nc

3a 0.639 0.457 0.550 0.444 0.369 0.251 0.280 0.303 0.307 0.338 0.545 0.547 0.43

4b 0.376 0.485 0.505 0.383 0.320 0.284 0.343 0.350 0.247 0.266 0.406 0.420 0.37

5 0.595 0.518 0.638 0.635 0.580 0.403 0.383 0.360 0.358 0.440 0.698 0.613 nc

6c 0.251 0.241 0.185 0.274 0.123 0.070 0.057 0.059 0.070 0.056 0.283 0.311 0.18

7 0.595 0.518 0.638 0.635 0.580 0.403 0.383 0.360 0.358 0.440 0.698 0.613 nc

Daily water budget

1d,f 0.315 0.406 0.423 0.321 0.268 0.238 0.287 0.293 0.207 0.223 0.340 0.352 nc

1e,f 0.167 0.161 0.123 0.183 0.082 0.047 0.038 0.039 0.047 0.037 0.189 0.207 nc

2 0.654 0.468 0.563 0.454 0.378 0.257 0.287 0.310 0.314 0.346 0.558 0.560 nc

3 0.654 0.468 0.563 0.454 0.378 0.257 0.287 0.310 0.314 0.346 0.558 0.560 0.44

4 0.315 0.406 0.423 0.321 0.268 0.238 0.287 0.293 0.207 0.223 0.340 0.352 0.31

5 0.654 0.468 0.563 0.454 0.378 0.257 0.287 0.310 0.314 0.346 0.558 0.560 nc

6 0.167 0.161 0.123 0.183 0.082 0.047 0.038 0.039 0.047 0.037 0.189 0.207 0.12

7 0.167 0.161 0.123 0.183 0.082 0.047 0.038 0.039 0.047 0.037 0.189 0.207 nc
Appendix 48

was determined as a function of potential evapotranspiration and soil moisture. At all sites, potential evapotranspiration was assumed to be equal to pan evaporation. For soil-moisture contents greater than or equal to 

a threshold value, Ci

, the rate of evapotranspiration was 

assumed to be equal to the potential evapotranspiration 

rate. For soil-moisture contents below Ci

, the rate of 

evapotranspiration was assumed to occur at a reduced 

rate that declines linearly with soil-moisture content:

for S ≥ Ci,

E = PEi,

and for S < Ci,

E = S×PEi/Ci, (A4)

where: E = instantaneous rate of evapotranspiration 

[L/T],

PEi = potential evapotranspiration rate for 

current day [L/T],

S = instantaneous soil moisture [L], and

Ci = threshold soil-moisture content below 

which evapotranspiration is reduced 

below the potential evapotranspiration 

rate [L].

The threshold soil moisture, Ci, was estimated from a 

model having the form:

for [a + bD + cPEi]< 1,

Ci = [a + bD + cPEi] × Sm,

and for [a + bD + cPEi] ≥ 1,

Ci = Sm. (A5)

The calibration coefficients a, b, and c were determined 

by Giambelluca (1983) on the basis of lysimeter studies 

from Hawaii (Ekern, 1966). For D expressed in mm, 

and PEi expressed in mm per day, the calibration 

coefficients were determined to be:

for PEi ≤ 6 mm/d,

a = 1.25,

b = -1.87 × 10-3,

c = 5.20 × 10-2,

and for PEi > 6 mm/d,

a = 1.41,

b = -1.87 × 10-3,

c = 2.20 × 10-2.

By recognizing that E = −dS/dt, the total depth of 

water lost to evapotranspiration during a day, Ei, was 

determined as:

for Xi > Ci, ti <1,

Ei = PEiti + Ci{1-exp[−PEi(1-ti)/Ci]},

for Xi > Ci, ti ≥1,

Ei = PEi ,

and for Xi ≤ Ci,

Ei = Xi{1-exp[−PEi/Ci]}, (A6)

where: Ei = depth of water lost to evapotranspiration 

during the day [L], and

ti = (Xi – Ci)/PEi, which is the time during 

which soil moisture storage is above Ci

[T].

Recharge and soil-moisture storage at the end of a given 

day were assigned according to the following equations:

for Xi−Ei ≤ Sm, 

Qi = 0,

Si = Xi−Ei, (A7)

and for Xi−Ei > Sm, 

Qi = Xi−Ei−Sm,

Si = Sm, (A8)

where: Qi = ground-water recharge during the day [L], 

and

Si = soil-moisture storage [L] at the end of the 

current day, i.

Monthly Water Budget

The monthly water-budget method used for this 

study was identical to the method described by Shade 

(1995b). Daily rainfall data from the selected stations 

(table A1) were aggregated into monthly values, and 

these monthly values were used as input to the monthly 

water budget. Unlike the daily water budget, the 

monthly water budget was computed by assuming that 

recharge occurs before evapotranspiration. In addition, 

evapotranspiration was assumed to occur at the 
49 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

potential evapotranspiration rate for soil moisture above 

the wilting point, and was assumed to be zero for soil 

moisture below the wilting point. Monthly runoff, 

assumed to be a constant fraction of monthly rainfall 

(table A2), was subtracted from monthly rainfall, and 

this volume was added to the beginning soil-moisture 

storage for the month to determine interim soil-moisture 

storage:

Xj = Pj − Rj + Sj-1, (A9)

where: Xj = interim soil-moisture storage for current 

month [L],

Sj-1 = ending soil-moisture storage from previous 

month (j−1), equal to the beginning soilmoisture storage for current month (j) 

[L], 

Pj = precipitation for current month [L],

Rj = runoff for current month [L], and

j = subscript designating current month 

number.

All volumes of water are expressed as an equivalent 

depth of water over an area by dividing by the total area. 

Recharge was assumed to occur only for interim soilmoisture storage values in excess of the maximum soilmoisture storage, Sm:

for Xj ≤ Sm,

Qj = 0,

and for Xj > Sm,

Qj = Xj−Sm, (A10)

where: Qj = ground-water recharge during the month 

[L].

In the monthly water budget, evapotranspiration was 

assigned last and was determined as a function of 

potential evapotranspiration and available soil 

moisture:

for Xj – Qj < PEj, 

Ej = Xj – Qj, 

Sj = 0,

and for Xj – Qj ≥ PEj,

Ej = PEj,

Sj = Xj – Qj – PEj, (A11)

where: Ej = evapotranspiration during the current 

month [L],

PE j = potential evapotranspiration for the current 

month [L], and

Sj = ending soil-moisture storage for the current 

month (j) [L].

Runoff-to-Rainfall Ratios

Essential to the determination of direct runoff and 

runoff-to-rainfall ratios is the separation of base flow 

from total flow measured at a stream gage. A commonly 

used method of determining base flow is to conduct a 

flow-duration analysis and assume that base flow is 

equal to the discharge that is equaled or exceeded 90 

percent of the time (known as Q90). Shade (1995b) used 

this method to determine base flow for the water budget 

on which the recharge for the southern Lihue Basin 

model is based. However, the use of Q90 is arbitrary, 

and may not be appropriate for all drainage basins. 

Izuka and Gingerich (1998a) estimated base flow for 

selected streams in the Lihue Basin using a hydrographseparation computer program by Wahl and Wahl 

(1995). For U.S. Geological Survey gages 16049000 

(Hanapepe River), 16052500 (Lawai Stream), and 

16060000 (South Fork Wailua River), mean annual runoff-to-rainfall ratios computed using the base flows 

from Izuka and Gingerich (1998a) differ from the runoff-to-rainfall ratios computed by Shade (1995b). 

To relate the recharge estimates from Shade 

(1995b) to recharge estimates from a daily water budget, it was necessary to retain the runoff-to-rainfall 

ratios from Shade (1995b) (table A2) in the monthly 

water budget used in this analysis. However, for the 

daily water budget, the original runoff-to-rainfall ratios 

(Shade, 1995b) were adjusted to reflect more recent 

estimates of base flow (Izuka and Gingerich, 1998a). 

For the drainage basin of station 16049000, the annual 

runoff-to-rainfall ratio determined by Shade (1995b) is 

0.37, whereas the annual runoff-to-rainfall ratio using 

the base-flow estimate from Izuka and Gingerich 

(1998a) is 0.31. For the drainage basin of station 

16049000, the monthly ratios of runoff-to-rainfall from 

Shade (1995b) were multiplied by a factor of 31/37 to 

reflect the more recent base-flow estimates. Similarly, 

for the drainage basins of stations 16052500 and 
Appendix 50

16060000, the monthly ratios of runoff-to-rainfall from 

Shade (1995b) were multiplied respectively by factors 

of 12/18 and 44/43. In ungaged areas or areas where 

Izuka and Gingerich (1998a) did not estimate base flow, 

runoff-to-rainfall ratios were assumed to be the same as 

in adjacent gaged basins in similar climatologic settings 

(fig. A1, table A2). Thus, areas 2 and 5 (fig. A1) on the 

windward side of Kauai were assigned the same runoffto-rainfall ratios as the drainage basin for gage 

16060000 (area 3), which is also on the windward side. 

Area 7, which lies leeward of Haupu Ridge, was 

assigned the same runoff-to-rainfall ratio as the drainage basin for gage 16052500 (area 6). For area 1 in figure A1, runoff-to-rainfall ratios from areas 4 and 6 

(basins of gages 16049000 and 16052500, respectively) 

were used to compute two different recharge distributions, and the two distributions were averaged. 

Comparison of Recharge from Daily and 

Monthly Water Budgets

For each of the gaged and ungaged areas (fig. A1) 

in the vicinity of the Lihue Basin, daily and monthly 

water budgets were computed using all of the selected 

rainfall and pan-evaporation data (table A1) and the 

appropriate runoff-to-rainfall ratios for the area (table 

A2). Within the Lihue Basin area, maximum soil-moisture storage values are generally about 1 to 3 in. (Shade, 

1995b), thus, the daily and monthly water budgets were 

computed for maximum soil-moisture storage values of 

1, 2, and 3 in. Maximum soil-moisture storage in the 

daily budget is the product of available water capacity 

and root depth (equation A3). For each value of maximum soil-moisture storage tested, available-watercapacity values of 0.10, 0.13, and 0.16 were used in the 

daily water budget. The root depths were adjusted such 

that the desired maximum soil-moisture storage values 

of 1, 2, and 3 in. were obtained. 

 Estimated annual recharge from the daily and 

monthly water budgets were compared for each of the 

gaged and ungaged areas in the vicinity of the Lihue 

Basin (fig. A2). Using the water-budget methods 

described above, the total recharge from a daily water 

budget will be less than the total recharge from a 

monthly budget, given the same runoff-to-rainfall 

ratios. In some areas, the runoff-to-rainfall ratios used in 

the daily budget were less than the ratios used in the 

monthly budget. For this condition, total recharge from 

a daily budget could exceed the total recharge from a 

monthly budget. 

Each of the relations between annual recharge 

computed from a daily budget and annual recharge 

computed from a monthly budget were generalized by 

fitting (least-square error) a second-degree polynomial 

curve to the data (fig. A2). The appropriate seconddegree polynomial equation was used to adjust the original annual recharge estimates (computed from a 

monthly budget) in the Lihue model grid. For each 

model cell, given the annual recharge estimate from a 

monthly water budget, the corresponding annual 

recharge estimate from a daily water budget was determined by using the appropriate second-degree polynomial equation appropriate for the area in which the 

model cell was located. By applying the appropriate 

equations, total recharge over the modeled area was 

estimated to be 149 Mgal/d, which is 23 percent lower 

than the original estimate of 191 Mgal/d. 

Fog Drip

Cloud vapor that is intercepted by vegetation and 

drips to the ground, also known as fog drip, can be a significant component of the water budget in an area (see 

for example Ekern, 1964; Juvik and Ekern, 1978). 

Ekern (1983) collected fog on the leeward side of the 

Koolau Range on the island Oahu, and his data indicate 

a fog-to-rain ratio of 0.06. On the windward side of 

Mauna Loa on the island of Hawaii, the average annual 

fog-to-rain ratio at an altitude of about 5,000 ft was 0.30 

(Juvik and Ekern, 1978). However, average annual rainfall at the Mauna Loa site was about 100 in., which is 

considerably less than annual rainfall at comparable 

altitudes on Kauai. For wet months with rainfall exceeding 20 in., the fog-to-rain ratio at the Mauna Loa site 

ranged from 0.17 to 0.19, which is lower than the average annual value (Juvik and Ekern, 1978). 

No fog-collection studies are available for the 

island of Kauai. For this study, fog drip was assumed to 

occur above an altitude of 2,000 ft, which is consistent 

with data from Oahu (Ekern, 1983). The fog-to-rain 

ratio above an altitude of 2,000 ft was assumed to 

decrease from the windward to leeward side of the 

island crest (fig. A3). Because of the uncertainty in fogdrip estimates for Kauai, upper and lower estimates for 

the fog-to-rain ratio were tested. For the lower estimate, 

fog-to-rain ratios of 0.03 and 0.10 were used for 
51 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Figure A2. Relation between recharge from a monthly water budget and recharge from a daily water budget for the Lihue Basin area, Kauai, 

Hawaii using various runoff-to-rainfall ratios: (A) area 1 with runoff-to-rainfall ratios in the daily water budget from area 4; (B) area 1 with 

runoff-to-rainfall ratios in the daily water budget from area 6; (C) area 2; (D) area 3; (E) area 4; (F) area 5; (G) area 6; and (H) area 7. Areas 

1 to 7 are shown in figure A1, and runoff-to-rainfall ratios are given in table A2.

0 50 100 150 200 250 300 0 50 100 150 200 250 300

0

50

100

150

200

250

300

0

50

100

150

200

250

300

ANNUAL RECHARGE FROM A DAILY WATER BUDGET, 

Rd, IN INCHES

ANNUAL RECHARGE FROM A MONTHLY WATER BUDGET, Rm, IN INCHES

A B

C D

Best-fit second-degree polynomial curve:

Rd = 0.00108Rm

2

 + 0.691Rm – 6.25

Rd = 0.000947Rm

2

 + 1.01Rm – 6.49

Rd = 0.00168Rm

2 R + 0.646Rm – 5.07 d = 0.00174Rm2

 + 1.14Rm – 3.77
Appendix 52

Figure A2. Relation between recharge from a monthly water budget and recharge from a daily water budget for the Lihue Basin area, Kauai, 

Hawaii using various runoff-to-rainfall ratios: (A) area 1 with runoff-to-rainfall ratios in the daily water budget from area 4; (B) area 1 with 

runoff-to-rainfall ratios in the daily water budget from area 6; (C) area 2; (D) area 3; (E) area 4; (F) area 5; (G) area 6; and (H) area 7. Areas 

1 to 7 are shown in figure A1, and runoff-to-rainfall ratios are given in table A2--Continued. ANNUAL RECHARGE FROM A DAILY WATER BUDGET, 

Rd, IN INCHES

ANNUAL RECHARGE FROM A MONTHLY WATER BUDGET, Rm, IN INCHES

E F

G H

Rd = 0.00235Rm

2 R + 0.862Rm – 4.57 d = 0.00137Rm2

 + 0.805Rm – 5.62

Rd = 0.000769Rm

2 R + 1.77Rm – 1.72 d = 0.000873Rm2

 + 0.828Rm – 8.17

0 50 100 150 200 250 300 0 50 100 150 200 250 300

0

50

100

150

200

250

300

0

50

100

150

200

250

300
53 Numerical Simulation of Ground-Water Withdrawals in the Southern Lihue Basin, Kauai, Hawaii

Figure A3. Cells with fog drip and irrigation recharge added to recharge used in original ground-water flow model of the southern Lihue 

Basin, Kauai, Hawaii.

0 1 2 MILES

0 1 2 KILOMETERS

PA

CIFIC

OCEAN

22 ̊

21 ̊55'

22 ̊05'

21 ̊50'

159 ̊35' 159 ̊30' 159 ̊25' 159 ̊20' 159 ̊15'

5

5

10

15

20

25

30

35

40

45

10

15

20

25

30

35

40

45

50

55

COLUMN

ROW

MODEL CELL

 Fog drip

 Irrigated agriculture

 No fog drip or irrigation

 No-flow boundary

ISLAND CREST AND DRAINAGE DIVIDE

EXPLANATION
Appendix 54

leeward and windward areas, respectively. For the 

upper estimate, fog-to-rain ratios of 0.06 and 0.15 were 

used for leeward and windward areas, respectively. 

Fog drip was computed for each model cell above 

an altitude of 2,000 ft from the product of mean annual 

rainfall (Giambelluca and others, 1986) and the 

assumed fog-to-rain ratio. Because annual rainfall in the 

model cells above an altitude of 2,000 ft is generally 

more than twice the annual pan-evaporation rate, it was 

assumed that rainfall is sufficient to meet the evaporative demand and that all of the fog drip contributes to 

recharge. Estimated recharge from fog drip in the modeled area ranges from 11.8 to 19.2 Mgal/d. 

Evapotranspiration in Irrigated Areas

In the original monthly water budget for Kauai 

(Shade, 1995b), evapotranspiration and recharge in irrigated sugarcane areas were computed in two steps. 

First, a monthly water budget that accounted for rainfall 

but not irrigation was computed, and then additional 

recharge and evapotranspiration were estimated from 

the volume of applied irrigation water. The additional 

evapotranspiration associated with the applied irrigation water was set equal to potential evapotranspiration 

in irrigated sugarcane areas. The additional recharge 

associated with the applied irrigation water was then 

computed from the difference between applied irrigation water and potential evapotranspiration. This computational procedure can lead to overestimation of 

evapotranspiration in irrigated sugarcane for two reasons: (1) summing evapotranspiration associated with 

rainfall and potential evapotranspiration associated with 

irrigation in the same area applies the evapotranspiration effect twice on the water budget for that area, and 

(2) the assumption that evapotranspiration is equal to 

the potential rate is only valid if water is always available for crop use, which may not be true on a day-to-day 

basis. 

Because evapotranspiration appears to be overestimated in the irrigated areas, recharge should be 

increased by an amount equal to the overestimated 

evapotranspiration. The increase in recharge in the irrigated areas should be at least equal to the estimated 

evapotranspiration from the monthly water budget that 

accounts for rainfall and not irrigation. (An additional 

increase could be justified on the basis that evapotranspiration may not occur at the potential rate.) In the 

monthly water budget (Shade, 1995b), the maximum 

monthly evapotranspiration is equal to the maximum 

soil-moisture storage. Within the Lihue Basin area, the 

maximum soil-moisture storage in irrigated areas generally is 2 in. or more. For a maximum soil-moisture 

storage value of 2 in., the maximum annual evapotranspiration rate would be 24 in. For values of maximum 

soil-moisture storage greater than 2 in., the maximum 

annual evapotranspiration rate would be greater than 24 

in. In the monthly water budget without irrigation, the 

monthly evapotranspiration is probably less than the 

maximum soil-moisture storage value because low 

monthly rainfall may limit evapotranspiration. 

Because it was not possible to verify the original 

evapotranspiration estimates associated with rainfall in 

irrigated areas (Shade, 1995b), a lower and upper estimate was used for this study. For the irrigated areas, 

estimated lower and upper values for evapotranspiration were 6 and 24 in., respectively. Thus, annual 

recharge in model cells representing irrigated areas (fig. 

A3) was increased by either 6 or 24 in. The estimated 

increase in recharge in irrigated areas ranges from 6.4 to 

25.7 Mgal/d. 

Results and Discussion

A number of sources of uncertainty in the original 

recharge estimate of 191 Mgal/d for the modeled Lihue 

Basin area were identified in this study. Total recharge 

over the modeled area was estimated to range from 167 

to 194 Mgal/d after accounting for (1) differences 

between a daily water budget and a monthly water budget, (2) the most recent runoff-to-rainfall ratio estimates, (3) fog drip, and (4) overestimation of 

evapotranspiration in irrigated areas in the original 

water budget (Shade, 1995b). The adjusted recharge 

values range from 13 percent lower to 2 percent higher 

than the original 191 Mgal/d estimate for the modeled 

area (Izuka and Gingerich, 1998a). Although the 

adjusted recharge values should not be viewed as rigorously derived estimates, it does appear that the originally estimated recharge value of 191 Mgal/d is 

reasonable. A daily water budget computed over the 

Lihue Basin area would provide a refined estimate of 

recharge.