Heading 1 1

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

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2008– 5236

Ground-Water Availability in the Wailuku Area, 

Maui, Hawai‘i
COVER:

Aerial view, looking west, of the Wailuku area, Maui, Hawai‘i. (Photograph © by Douglas Peebles. Used with permission.)
Prepared in cooperation with the County of Maui Department of Water Supply

By Stephen B. Gingerich

Scientific Investigations Report 2008–5236

U.S. Department of the Interior

U.S. Geological Survey

Ground-Water Availability in the Wailuku Area, 

Maui, Hawai‘i

U S S G 
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

Produced in the Western Region, Menlo Park, California

Manuscript approved for publication September 9, 2008

Text edited by Peter Stauffer

Layout and design by Judy Weathers

U.S. Geological Survey, Reston, Virginia: 2008

This report and any updates to it are available online at:

http://pubs.usgs.gov/sir/2008/5236/

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

Suggested citation: 

Gingerich, S.B., 2008, Ground-water availability in the Wailuku area, Maui, Hawai‘i: 

U.S. Geological Survey Scientific Investigations Report 2008–5236, 95 p.
iii

Executive Summary

Most of the public water supply in Maui, Hawai‘i is from a freshwater lens in the Wailuku 

area of the island. Because of population increase, ground-water withdrawals from wells in this 

area increased from less than 10 Mgal/d during 1970 to about 23 Mgal/d during 2006. In response 

to increased withdrawals from the freshwater-lens system, water levels declined, the transition 

zone between freshwater and saltwater became shallower, and the chloride concentrations of water 

pumped from wells increased. To aid in management of ground-water resources and to plan for 

sustainable growth on the island, the Maui County Department of Water Supply (DWS) entered 

into a cooperative agreement in 2003 with the U.S Geological Survey (USGS) to study the groundwater availability in central and west Maui. The objectives of this 4.5-year study were to (1) obtain 

a better understanding of the ground-water flow system in the study area, (2) estimate ground-water 

recharge in the study area, and (3) simulate ground-water flow and transport using a numerical 

model to estimate the effects of selected withdrawal and recharge scenarios on water levels and the 

transition zone between freshwater and saltwater in the Wailuku Aquifer Sector. For management 

purposes, the State of Hawai‘i Commission on Water Resource Management (CWRM) divided 

central and west Maui into three aquifer-management sectors: Central, Wailuku, and Lahaina Sectors. Although the main area of interest for this study is the Wailuku Aquifer Sector, which includes 

the ÿÏao and Waiheÿe Aquifer Systems, the study area includes all of west Maui, the central isthmus, 

and about a third of east Maui in order to provide an understanding of the regional flow system. 

The most developed ground-water system in these areas comprises a lens-shaped freshwater body, 

an intermediate brackish water transition zone, and underlying saltwater.

Recharge and Discharge

Recharge was estimated for six periods on the basis of land use and precipitation: 

1926–79, 1980–84, 1985–89, 1990–94, 1995–99, and 2000–04. Estimated recharge to central 

and west Maui declined 44 percent from 1979 to 2000. The period 1926–79 had the highest 

estimated recharge; recharge from irrigation during this period was at least 50 percent higher 

than in any other period considered. The period 2000–04 had the lowest estimated recharge. 

Recharge from irrigation during this period was 46 percent of the recharge from irrigation during 1926–79, and rainfall was the lowest of any period considered in this study. 

Discharge from the aquifer in the study area is in the form of ground-water withdrawals 

from pumped wells, discharge to streams as base flow, and diffuse seepage to the ocean. Average withdrawals in 2000–06 were 21.4 Mgal/d in the Wailuku Aquifer Sector, about 4 Mgal/d 

in the Lahaina Aquifer Sector, and about 68 Mgal/d in the Central Aquifer Sector. Base flow 

represents ground-water discharge to streams. Most streams on West Maui Volcano receive 

ground-water discharge from dike-impounded ground water. Total average base flow at gaging 

stations operated on the 14 largest gaged streams in west Maui is about 101 Mgal/d.

Numerical Ground-Water Model

A three-dimensional numerical ground-water model capable of simulating density-dependent 

solute transport was developed as part of this study. Simulated water levels and salinity profiles 

generally were in agreement with measured water levels and salinity profiles from representative wells in the modeled area during the period 1926–2006. Within the Wailuku Aquifer Sector, 

simulated water levels relative to measured water levels are 1–3 ft lower north of Waiheÿe River, 

1–2 ft higher between the Waiheÿe River and ÿÏao Stream, and are reasonably similar south of 

ÿÏao Stream. Measured salinity profiles in the Waiehu deep monitor well indicate a shallowing 

of the brackish-water transition zone over time, and the simulated salinity profiles are consistent 

with this trend. The simulated trend of the depth where ground-water salinity is 50-percent that of 

seawater fits the measured values best for the more recent data (1995–2006). 
iv 

Future Recharge and Withdrawal Scenarios

The numerical ground-water model was used to simulate changes in ground-water level 

and salinity with ground-water withdrawal under various possible future withdrawal and 

recharge scenarios. Simulated salinities at selected DWS well fields after 30 years (a reasonable 

planning horizon) and 150 years (representing long-term sustainability) of withdrawal are classified as acceptable in this study if they are below 1-percent seawater salinity, cautionary if they 

are between 1- and 2.5-percent seawater salinity, and threatened if they are over 2.5-percent seawater salinity. This classification was developed cooperatively with the DWS to provide a basis 

for comparing the various scenarios investigated in this study. Scenarios included ground-water 

withdrawal at 2006 (most recent) and 1996 (least widespread) rates and locations assuming 

average recharge, and withdrawal at redistributed rates and locations assuming several different 

recharge scenarios.

 Simulation results from the 2006 and 1996 withdrawal distributions indicate the following for the Wailuku Aquifer Sector: (1) average recharge rates and the 2006 withdrawal distribution (21.4 Mgal/d from 6 well fields) cause average water levels in wells to decrease 2–3 ft 

and the transition zone to become more than 200 ft shallower after 150 years, and (2) average 

recharge rates and the 1996 withdrawal distribution (20.1 Mgal/d from 4 well fields) cause average water levels in wells to decrease by more than 3 ft and the transition zone to become more 

than 300 ft shallower after 150 years. With the 2006 distribution, two of the six well fields have 

simulated salinity values that increase into the cautionary or threatened range after long-term 

withdrawal, but these two well fields are already known to be vulnerable so their degradation 

was deemed less critical. With the 1996 distribution, three of the four well fields have simulated 

salinity values that increase into the threatened range after long-term withdrawal, indicating that 

the 1996 withdrawal distribution was not desirable. This pair of simulations demonstrates that 

the amount of water that can be pumped from an aquifer system depends on the distribution of 

wells and pumping rates. Namely, a pumping distribution that is more spread out can provide 

more water with less undesirable consequences than a distribution of fewer, higher rate wells.

An idealized scenario in which ground-water withdrawal was redistributed to maximize 

withdrawal and minimize salinities in the withdrawn water was determined using the numerical model. The redistributed withdrawal scenario was obtained by reducing rates at existing 

wells and adding withdrawal from potential new well sites that, in consultation with the DWS, 

were determined reasonable locations for future water-system expansion. The redistribution 

simulates 27.1 Mgal/d of withdrawal from 14 wells or well fields in the Wailuku Aquifer Sector, 

with 3.5 Mgal/d from the Waiheÿe Aquifer System, 19.14 Mgal/d from the ÿÏao Aquifer System, 

and 4.5 Mgal/d from the Waikapü Aquifer System. The proposed rate of 4.5 Mgal/d from the 

Waikapü Aquifer System is higher than the current State of Hawai‘i sustainable yield estimate 

of 2 Mgal/d. Simulation results from the five scenarios that include the redistributed withdrawal 

conditions indicate the following for the Wailuku Aquifer Sector: (1) withdrawal during times 

of average recharge rates causes average water levels to decrease 2–3 ft and the transition zone 

to become more than 200 ft shallower after 150 years; (2) a 5-yr drought condition similar 

to the 1998–2002 drought results in additional salinity increases after 30 years (12.5 years of 

normal recharge after drought conditions) but only one well has salinity increases of concern; 

(3) additional recharge from restored streamflow significantly increases water levels, thickens 

the freshwater body, and decreases salinity at withdrawal sites in the Waiheÿe and ‘Ïao Aquifer 

Systems; and (4) a complete removal of irrigation recharge decreases water levels and increases 

salinity in the central isthmus where irrigation is reduced, but recharge through restored 

streams still significantly increases water levels, thickens the freshwater body, and decreases 

salinity at withdrawal sites in the Waiheÿe and ‘Ïao Aquifer Systems.
 v

Contents

Executive Summary......................................................................................................................................iii

Recharge and Discharge....................................................................................................................iii

Numerical Ground-Water Model ......................................................................................................iii

Future Recharge and Withdrawal Scenarios .................................................................................iv

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

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

Acknowledgements..............................................................................................................................3

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

Land Use.................................................................................................................................................4

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

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

Hydraulic Properties of the Rocks ...................................................................................................10

Hydraulic Conductivity..............................................................................................................10

Dike-Free Volcanic Rocks ...............................................................................................10

Dikes ................................................................................................................................14

Weathering ........................................................................................................................14

Sedimentary Rocks...........................................................................................................14

Specific Storage and Effective Porosity ................................................................................14

Dispersion Characteristics.......................................................................................................15

Ground-Water Flow System.......................................................................................................................15

Freshwater Lens..................................................................................................................................15

Dike-Impounded System ...................................................................................................................17

Recharge..............................................................................................................................................17

Recharge from Streams............................................................................................................18

Discharge.............................................................................................................................................18

Withdrawals from Wells ...........................................................................................................18

Base Flow to Streams ...............................................................................................................23

Water Levels........................................................................................................................................27

Salinity ..................................................................................................................................................33

Simulation of Ground-Water Flow.............................................................................................................33

Model Construction............................................................................................................................35

Model Mesh................................................................................................................................35

Boundary Conditions.................................................................................................................35

Specified Pressures and No-Flow Boundaries ...........................................................35

Recharge............................................................................................................................35

Withdrawal ........................................................................................................................39

Initial Conditions ........................................................................................................................40

Representation of Hydrologic Features .................................................................................40

Water Properties........................................................................................................................40

Aquifer Properties .....................................................................................................................40

Simulated Historical Conditions 1926–2006....................................................................................41

Water Levels...............................................................................................................................41
vi 

Salinity Profiles...........................................................................................................................44

Simulated Future Scenarios..............................................................................................................48

Scenario 1—2006 Withdrawal Rates and Locations with 2000–04 Land Use and 

1926–2006 Rainfall ........................................................................................................51

Scenario 2—1996 Withdrawal Rates and Locations with 2000–04 Land Use and 

1926–2006 Rainfall ........................................................................................................53

Scenario 3—Redistributed Withdrawals with 2000–04 

Land Use and 1926–2006 Rainfall...............................................................................59

Scenario 4—Effects of Drought on Redistributed Withdrawals........................................61

Scenarios 5 and 6—Effects of Restoring Streamflow on 

Redistributed Withdrawals.........................................................................................63

Scenario 7—Effects of No Agricultural Irrigation or Stream Diversions.........................66

Additional withdrawal locations .............................................................................................68

Model Limitations.........................................................................................................................................72

Summary........................................................................................................................................................75

References Cited..........................................................................................................................................76

Appendix A. Wells in the central Maui study area with stratigraphic information, Hawai‘i...........80

Appendix B. Monthly ground-water withdrawals during 1900–2006 

from wells in central and west Maui, Hawai‘i...........................................................................83

Appendix C. Properties of pumped wells in the central and west Maui study area, Hawai‘i.........93

Figures

1. Location of study area and State of Hawai‘i Commission on Water Resource Management 

aquifer-management sectors and systems, Maui, Hawai‘i.......................................................2

2. Land use during 1926–2004 in central and west Maui, Hawai‘i (modified from Engott and 

Vana, 2007).........................................................................................................................................5

3. Mean annual rainfall and fog zone in central and west Maui, Hawai‘i. ....................................6

4. Generalized surficial geology in central and west Maui, Hawai‘i ..............................................8

5. Geologic cross sections of the ÿÏao aquifer area, Maui, Hawai‘i................................................9

6. Structural contours on the top of the Wailuku Basalt and locations of wells with stratigraphic information on that unit in central and west Maui, Hawai‘i. ....................................11

7. Structural contours on the top of the Kula Volcanics/ Honomanü Basalt and wells with 

stratigraphic information on those units in central and west Maui, Hawai‘i.......................12

8. Distribution of aquifer hydraulic conductivity in central and west Maui, Hawai‘i.................13

9. Geologic cross section of the ÿÏao aquifer area, showing ground-water occurrence and 

movement, Maui, Hawai‘i .............................................................................................................16

10. Estimated ground-water recharge for various periods during 1926–2004, central and west 

Maui, Hawai‘i. .................................................................................................................................19

11. Streamflow loss in Wailuku area streams, Maui, Hawai‘i.........................................................21

12. Ground-water withdrawals from the Central Aquifer Sector, 

1900–2006, Maui, Hawai‘i..............................................................................................................22

13. Ground-water withdrawals from the Wailuku Aquifer Sector, 1900–2006, 

Maui, Hawai‘i. .................................................................................................................................23
 vii

14. Ground-water withdrawals from the Lahaina Aquifer Sector, 1900–2006, 

Maui, Hawai‘i. ................................................................................................................................24

15. Average monthly ground-water withdrawal for public supply and sugarcane 

production in the Wailuku and Central Aquifer Sectors, 

1995–2006, Maui, Hawai‘i..............................................................................................................25

16. Water-level surveys of (A) December 5, 1970 and February 1979, and

 (B) May 17, 2005, Maui, Hawai‘i..................................................................................................28

17. Measured water levels in selected wells in theCentral Aquifer Sector, 

Maui, Hawai‘i. .................................................................................................................................30

18. Measured water levels in selected wells in the 

Wailuku Aquifer Sector, Maui, Hawai‘i.......................................................................................31

19. Measured water levels in selected wells in the Lahaina Aquifer Sector, 

Maui, Hawai‘i. .................................................................................................................................32

20. Measured salinity profiles in selected wells in the study area, Maui, Hawai‘i. . .....................34

21. Model discretization and features for the numerical model mesh 

of central and west Maui, Hawai‘i. .............................................................................................36

22. Vertical cross section of model mesh of central and west Maui, Hawai‘i................................37

23. Monthly ocean level during 1970–2006 at Kahului Harbor, Maui, Hawai‘i ................................37

24. Selected withdrawal wells used in construction of the numerical 

model of central and west Maui, Hawai‘i. .................................................................................39

25. Measured (black and green lines) and simulated (red lines) water levels 

in selected wells in central and west Maui, Hawai‘i. 

Well number shown in parentheses after well name. .............................................................42

26. Measured water levels on (A) December 5, 1970, and 

(B) May 17, 2005, compared with simulated water levels in

central and west Maui, Hawai‘i...................................................................................................45

27. Simulated water-level changes between 1926 and 2006 

in central and west Maui, Hawai‘i...............................................................................................47

28. Measured and simulated altitude of the top (2-percent seawater) 

and middle (50-percent seawater) of the transition zone in the 

Waiehu Deep Monitor well (5430-05), Maui, Hawai‘i. ..............................................................48

29. Measured and simulated salinity profiles in selected wells 

in central and west Maui, Hawai‘i...............................................................................................49

30. Simulated depth of 50-percent seawater salinity at end of historical 

simulation (2006) and locations of wells penetrating deeper than 1⁄4 

of the simulated depth to 50-percent seawater salinity in 

central and west Maui, Hawai‘i...................................................................................................50

31. Measured (black and green lines) and simulated water-level (red lines) and 

simulated salinity data (blue lines) for Scenario 1 using monthly and yearly 

pumping rates at selected wells in the Wailuku Aquifer Sector, 2000–2157, 

Maui, Hawai‘i. .................................................................................................................................52

32. Measured and simulated positions of the bottom of freshwater (2-percent seawater salinity) and middle of the transition zone (50-percent seawater salinity) for Scenario 1 at the 

Waiehu Deep Monitor well (5430-05), 2000–2157, Maui, Hawai‘i...........................................53

33. Simulated change (relative to end of historical simulation) in water level, 50-percent seawater salinity depth, and 2-percent seawater salinity depth after 150 years of withdrawal at 

2006 rates with long-term average recharge (1926–2006) [scenario 1], 

central Maui, Hawai‘i.....................................................................................................................54
viii 

34. Predicted salinities in wells included in scenarios 1–7, central Maui, Hawai‘i. ......................55

35. Simulated water-level (red lines) and salinity (blue lines) data for Scenario 2 (dark lines) 

compared with Scenario 1 (light lines) at selected wells in the 

Wailuku Aquifer Sector, 2000–2157, Maui, Hawai‘i. . ...............................................................58

36. Simulated positions of the bottom of freshwater (2-percent seawater salinity) 

and middle of the transition zone (50-percent seawater salinity) for Scenario 2 at the 

Waiehu Deep Monitor well (5430-05), 2000–2157, Maui, Hawai‘i...........................................59

37. Simulated change (relative to end of historical simulation) in water level, 50-percent sea 

water salinity depth, and 2-percent seawater salinity depth after 150 years of 

withdrawal at 1996 rates with long-term average recharge (1926–2006) [scenario 2], 

central Maui, Hawai‘i.....................................................................................................................60

38. Simulated water-level (red lines) and salinity (blue lines) data for Scenario 3 (dark lines) 

compared with Scenario 1 (light lines) at selected wells in the Wailuku Aquifer Sector, 

2000–2157, Maui, Hawai‘i..............................................................................................................62

39. Simulated positions of the bottom of freshwater (2-percent seawater salinity)

 and middle of the transition zone (50-percent seawater salinity) for Scenario 3 

compared with Scenario 1 at the Waiehu Deep Monitor well (5430-05), 2000–2157,

 Maui, Hawai‘i. ................................................................................................................................63

40. Simulated change (relative to scenario 1) in water level, 50-percent 

seawater salinity depth, and 2-percent seawater salinity depth after 

150 years of withdrawal at redistributed rates with long-term average recharge

 (1926–2006) [scenario 3], Maui, Hawai‘i. ...................................................................................64

41. Simulated water-level (red lines) and salinity (blue lines) data for Scenario 4 (dark lines) 

compared with Scenario 3 (light lines) at selected wells in the Wailuku Aquifer Sector, 

2000–35, Maui, Hawai‘i. ................................................................................................................65

42. Simulated positions of the bottom of freshwater (2-percent seawater salinity) 

and middle of the transition zone (50-percent seawater salinity) for Scenario 4 

compared with Scenario 3 at the Waiehu Deep Monitor well (5430-05), 

2000–35, Maui, Hawai‘i..................................................................................................................66

43. Simulated water-level (red lines) and salinity (blue lines) data for Scenarios 5 and 6 

compared with Scenario 3 at selected wells in the Wailuku Aquifer Sector,

 2000–2157, Maui, Hawai‘i.............................................................................................................67

44. Simulated positions of the bottom of freshwater (2-percent seawater salinity) 

and middle of the transition zone (50-percent seawater salinity) for 

Scenarios 5 and 6 compared with Scenario 3 at the Waiehu Deep Monitor 

well (5430-05), 2000–2157, Maui, Hawai‘i....................................................................................68

45. Simulated change (relative to scenario 3) in water level, 50-percent seawater 

salinity depth, and 2-percent seawater salinity depth after 150 years of withdrawal at 

redistributed rates with 12.3 Mgal/d of additional stream recharge [scenario 5], 

Maui, Hawai‘i. .................................................................................................................................69

46. Simulated change (relative to scenario 3) in water level, 50-percent seawater salinity depth, 

and 2-percent seawater salinity depth after 150 years of withdrawal at redistributed 

rates with 4.1 Mgal/d of additional stream recharge [scenario 6], Maui, Hawai‘i..............70

47. Simulated water-level (red lines) and salinity (blue lines) data for Scenario 7 

compared with Scenario 3 at selected wells in the Wailuku Aquifer Sector, 

2000–2157, Maui, Hawai‘i. ............................................................................................................71

48. Simulated positions of the bottom of freshwater (2-percent seawater salinity) and middle of 

the transition zone (50-percent seawater salinity) for Scenario 7 compared with 

Scenario 3 at the Waiehu Deep Monitor well (5430-05), 2000–2157, Maui, Hawai‘i. ..........72

49. Simulated change (relative to scenario 3) in water level, 50-percent seawater salinity depth, 

and 2-percent seawater salinity depth after 150 years of withdrawal at 

redistributed rates with no recharge from agriculture irrigation [scenario 7], 

Maui, Hawai‘i. .................................................................................................................................73
 ix

50. Simulated water-level (red lines) and salinity (blue lines) data for potential additional 

withdrawal sites in the Wailuku Aquifer Sector, 2000–2035, Maui, Hawai‘i.........................74

B1. Monthly ground-water withdrawals during 1900–2006 from wells in central and 

west Maui, Hawai‘i.........................................................................................................................83

Tables

1. Streamflow loss measurements and estimates in Waikapü, ÿÏao, and Waiehu Streams and 

Waihe‘e River, Maui, Hawai‘i. ......................................................................................................20

2. Base flow in selected study area streams, Maui, Hawai‘i. ...........................................................26

3. Estimated base flow and base flow simulated with MODFLOW-2000 model for 

selected study area streams, Maui, Hawai‘i. ............................................................................38

4. Recharge for historical simulation, 1926–2006, central and west Maui, Hawai‘i. .....................38

5. Aquifer-property values used in the construction of the numerical ground-water model of 

central and west Maui, Hawai‘i...................................................................................................41

6. Withdrawal and recharge used in various simulation scenarios, central and

 west Maui, Hawai‘i........................................................................................................................51

7. Classification of withdrawal for simulated scenarios, Wailuku Aquifer Sector, 

Maui, Hawai‘i. .................................................................................................................................57

8. Selected wells and rates used in redistributed withdrawal scenarios, central and 

west Maui, Hawai‘i.........................................................................................................................61

A1. Information for wells with stratigraphic information in the central Maui study area, 

Hawai‘i..............................................................................................................................................80

C1. Properties of pumped wells in the central and west Maui study area, Hawai‘i........................93
x 

Conversion Factors

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

square foot (ft2

) 0.09290 square meter (m2)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

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

cubic foot (ft3) 0.02832 cubic meter (m3) 

Flow rate

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

foot per year (ft/yr) 0.3048 meter per year (m/yr)

cubic foot per second (ft3

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

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

/s)

inch per hour (in./h) 0 .0254 meter per hour (m/h)

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

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

Pressure

atmosphere, standard (atm) 101.3 kilopascal (kPa)

bar 100 kilopascal (kPa) 

pound per square foot (lb/ft2) 0.04788 kilopascal (kPa) 

pound per square inch (lb/in.2

) 6.895 kilopascal (kPa) 

Density

pound per cubic foot (lb/ft3) 16.02 kilogram per cubic meter (kg/m3)

Hydraulic conductivity

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

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Dynamic viscosity

Slug per foot per second (slug/ft/s) 47.88 Pascal-sec (Pa-s)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

Vertical coordinate information is referenced to local mean sea level

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

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

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 25 °C).
Ground-Water Availability in the Wailuku Area, 

Maui, Hawai‘i

By Stephen B. Gingerich

Abstract

Most of the public water supply in Maui, Hawaiÿi, is from 

a freshwater lens in the Wailuku area of the island. Because 

of population growth, ground-water withdrawals from wells 

in this area increased from less than 10 Mgal/d during 1970 to 

about 23 Mgal/d during 2006. In response to increased withdrawals from the freshwater lens in the Wailuku area, water 

levels declined, the transition zone between freshwater and 

saltwater became shallower, and the chloride concentrations 

of water pumped from wells increased. These responses led to 

concern over the long-term sustainability of withdrawals from 

existing and proposed wells. 

A three-dimensional numerical ground-water flow and 

transport model was developed to simulate the effects of 

selected withdrawal and recharge scenarios on water levels, on 

the transition zone between freshwater and saltwater, and on 

surface-water/ground-water interactions. The model was constructed using time-varying recharge, withdrawals, and ocean 

levels. Hydraulic characteristics used to construct the model 

were initially based on published estimates but ultimately 

were varied to obtain better agreement between simulated and 

measured water levels and salinity profiles in the modeled area 

during the period 1926–2006. Scenarios included groundwater withdrawal at 2006 and 1996 rates and locations with 

average recharge (based on 2000–04 land use and 1926–2004 

rainfall) and withdrawal at redistributed rates and locations 

with several different recharge scenarios. Simulation results 

indicate that continuing 1996 and 2006 withdrawal distributions into the future results in decreased water levels, a thinner 

freshwater lens, increased salinity from pumped wells, and 

higher salinity at several current withdrawal sites.

A redistributed withdrawal condition in which groundwater withdrawal was redistributed to maximize withdrawal 

and minimize salinities in the withdrawn water was determined. The redistributed withdrawal simulates 27.1 Mgal/d 

of withdrawal from 14 wells or well fields in the Wailuku 

area. Simulation results from the five scenarios that include 

redistributed withdrawal conditions indicate the following for 

the Wailuku Aquifer Sector: (1) withdrawal during times of 

average recharge rates cause average water levels to decrease 

2–3 ft and the transition zone to become more than 200 ft shallower after 150 years; (2) a 5-yr drought condition similar to 

the 1998–2002 drought results in additional salinity increases 

after 30 years (12.5 years of normal recharge after drought 

conditions) but only one well has salinity increases of concern; 

(3) additional recharge from restored streamflow significantly increases water levels, thickens the freshwater body, 

and decreases salinity at withdrawal sites in the Waihe‘e and 

‘Ïao Aquifer Systems; and (4) a complete removal of irrigation recharge decreases water levels and increases salinity in 

the central isthmus where irrigation is reduced, but recharge 

through restored streams still significantly increases water 

levels, thickens the freshwater body, and decreases salinity at 

withdrawal sites in the Waihe‘e and ‘Ïao Aquifer Systems.

Introduction

The resident population on the island of Maui, Hawaiÿi, 

increased from 38,691 in 1970 to 117,644 in 2000, which 

represents an increase of more than 200 percent (State of 

Hawaiÿi, 2000). The total population (including visitors) on 

Maui in 2000 was 156,170 (State of Hawaiÿi, 2000). Because 

of the increase in population, the demand for ground water 

also increased. For example, ground-water withdrawals from 

wells in the Wailuku area increased from less than 10 million 

gallons per day (Mgal/d) during 1970 to about 23 Mgal/d during 2006. Ground-water withdrawals in nearby areas also have 

increased, and likely will continue increasing to meet future 

water demands. However, the amount of ground water that is 

available to meet future water demands is uncertain.

For management purposes, the State of Hawaiÿi Commission on Water Resource Management (CWRM) divided 

central and west Maui into three aquifer-management sectors: 

Central, Wailuku, and Lahaina Sectors. Further subdivisions of 

the sectors are hydrologically connected systems; Kamaÿole, 

Makawao, Päÿia, and Kahului Aquifer Systems in the Central sector; Kahakuloa, Waiheÿe, ÿÏao, and Waikapü Aquifer 

Systems in the Wailuku sector; and Honoköhau, Honolua, 

Honoköwai, Launiupoko, Olowalu, and Ukumehame Aquifer 

Systems in the Lahaina sector (fig. 1).
2 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 1. Location of study area and State of Hawai‘i Commission on Water Resource Management aquifer-management sectors and 

systems, Maui, Hawai‘i.

0 5.2 5 10 seliM

0 2.5 5 10 Kilometers

SCALE

156°�40’

21°�00’

20°�50’

20°�40’

156°�30’

156°�20’

22°

20°

158° 156° 160°

Kaua‘i

Ni‘ihau

O‘ahu Maui

Moloka‘i

Läna‘i

Kaho‘olawe

Hawai‘i

HAWAI‘I

Pacific Ocean

156°�40’

21°�00’

20°�50’

20°�40’

156°�30’ 156°�20’ 156°�10’ 156°�00’

study

area

MAUI

West Maui

Volcano

Haleakalä

Wailuku

Kahului

Makawao

Pukalani

Mäkena

Kïhei

Lahaina

Kä‘anapali

Pä‘ia

!

!

!

!

!

!

!

!

!

a

a

Pu‘u ‘Ula‘ula

(Red Hill)

10,023 ft

Pu‘u Kukui

5,788 ft

KAMA‘OLE

MAKAWAO

PÄ‘IA KAHULUI

‘ÏAO

WAIKAPÜ

UKUMEHAME

OLOWALU

LAUNIUPOKO

HONOKÖWAI

HONOLUA

HONOKÖHAU

KAHAKULOA

WAIHE‘E

CENTRAL

AQUIFER

SECTOR

WAILUKU

AQUIFER

SECTOR

LAHAINA

AQUIFER

SECTOR

study-area boundary

study-area boundary
Setting 3

In a freshwater-lens system, increased withdrawals will, 

in the long term, result in a decline in water levels, a shallowing of the transition zone between freshwater and saltwater, 

and a reduction of natural ground-water discharge to streams 

or the ocean. The extent to which water levels decline and 

the transition zone rises is dependent on factors including 

the distribution and rates of withdrawals and the hydraulic 

characteristics of the aquifer system. In some cases, pumping 

from a well also may induce brackish water to enter the well 

if the withdrawal rate is too high or the well is too deep.

In response to increased withdrawals from the freshwaterlens system of the ÿÏao aquifer, water levels declined, the 

transition zone between freshwater and saltwater became shallower, and the chloride concentrations of water pumped from 

wells increased (Meyer and Presley, 2001). Chloride concentrations in water pumped from Waiehu Heights pump 1 (State 

well number 5430-01) and Mokuhau pump 2 (5330-09) have 

exceeded 250 mg/L, which represents the U.S. Environmental 

Protection Agency’s recommended secondary standard for 

drinking water. Chloride concentrations of water pumped from 

other wells in the ‘Ïao and Waiheÿe aquifers increased over 

time, although concentrations generally remained below 200 

mg/L. The decline in water levels, shallowing of the transition zone between freshwater and saltwater, and increase in 

chloride concentrations in pumped water have led to concern 

over the long-term sustainability of withdrawals from existing 

wells in the ÿÏao aquifer. In 2003, CWRM designated the ÿÏao 

Aquifer System as a Ground-Water Management Area, triggered by ground-water withdrawals averaging more than 18 

Mgal/d (State of Hawaii, 2003). To manage the ground-water 

resources and to plan for sustainable growth on the island, an 

improved understanding of the ground-water flow system in 

central and west Maui was needed.

The Maui County Department of Water Supply (DWS) 

entered into a cooperative agreement in 2003 with the U.S. 

Geological Survey (USGS) to conduct a study of the groundwater availability in central and west Maui. The objectives 

of this 4.5-year study are to (1) obtain a better understanding of the regional ground-water flow system in the study 

area, (2) estimate ground-water recharge in the study area, 

and (3) to simulate the effects of selected withdrawal and 

recharge scenarios on water levels and the transition zone 

between freshwater and saltwater in the Wailuku Aquifer 

Sector. Although the main area of interest for this study is the 

Wailuku area of Maui, which includes the ÿÏao and Waiheÿe 

Aquifer Systems, the study area includes all of west Maui, 

the central isthmus, and about a third of east Maui in order to 

provide an understanding of the regional flow system (fig. 1). 

This report describes (1) information related to the regional 

hydrologic system of central and west Maui, (2) development 

of a numerical ground-water flow and transport model, and 

(3) results of model simulations assessing the hydrologic 

effects of various recharge and withdrawal conditions on the 

hydrologic system. 

Acknowledgements

This study was funded through a cooperative agreement 

between the Maui DWS and the USGS. The author is grateful to Maui DWS Director Jeffrey Eng (and former Director George Tengan) and the staff of the Maui DWS for their 

cooperation and assistance, especially in discussing potential 

withdrawal and recharge scenarios. Carl Freedman of Haiku 

Design and Analysis also provided valuable assistance in 

developing the withdrawal scenarios. Randall Moore and 

the staff at Hawaiian Commercial and Sugar, Inc. (HC&S) 

provided pumping data and arranged access and cooperation for collecting water-level data in their wells. Other well 

owners who kindly provided access to their wells include the 

County of Maui Department of Public Works and Environmental Management; the County of Maui Department of Parks 

and Recreation; Maui Pineapple Company, Ltd.; The Dunes 

at Maui Lani Golf Course; Consolidated Baseyards, LLC; and 

Maui Electric Company, Ltd. Glenn Bauer, Kevin Gooding, 

and Mitch Ohye of the CWRM assisted with water-level data 

collection during the synoptic water-level survey. Toby Vana, 

Todd Presley, and Greg Berman of the USGS provided support in resurveying measuring points, and collecting valuable 

water-level data during the study. Ed Carlson of the National 

Geodetic Survey led the effort to resurvey benchmarks and 

measuring points for wells throughout central Maui.

For the recharge part of the study, the author thanks 

the Maui Land and Pineapple Co. (ML&P) for permitting 

us to install climate stations on their property and Nobriga’s 

Ranch, Inc. for providing access to a climate-station site. 

Randy Bartlett, ML&P Watershed Manager, and his staff, 

Greg Hansen and Hank Oppenheimer, provided crucial 

assistance in accessing, constructing, and maintaining these 

sites. Matt Wong and Phil Teeters of the USGS also provided support in maintaining the climate network. Specialuse permits for climate stations were granted through the 

Hawaiÿi Department of Land and Natural Resources’ Office 

of Conservation and Coastal Lands and the Natural Area 

Reserve System Commission. Wes Nohara (ML&P), Randall Moore and Lee Ingamells (HC&S), and Clayton Suzuki 

(Wailuku Water Co., Inc.) provided important agricultural 

data and assistance. Kevin Kodama of the National Weather 

Service provided rainfall data.

Finally, the author thanks the concerned citizens of Maui 

who continued to ask questions and provide feedback and 

encouragement at our presentations throughout the study. 

Especially notable participants include John Duey, Lucienne 

deNaie, David Snow, and the late Glenn Shepherd.

Setting

Maui is the second largest of the Hawaiian Islands and 

is located between longitudes 155o57’W and 156o47’W and 
4 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

between latitudes 20o32’N and 21o03’N (fig. 1). The island 

comprises two shield volcanoes, the older West Maui Volcano 

that reaches an altitude of 5,788 ft and the younger Haleakalä 

Volcano that reaches an altitude of 10,025 ft. The two volcanoes are separated by an isthmus, generally at altitudes 

less than 300 ft, which is covered with terrestrial and marine 

sedimentary deposits that are as much as 5 miles wide (Stearns 

and Macdonald, 1942). Although the main area of interest for 

this study is the Wailuku Aquifer Sector, the regional study area 

(fig. 1) includes all of west Maui, the central isthmus, and about 

a third of east Maui in order to provide an understanding of the 

regional flow system. West Maui Volcano is deeply dissected 

by numerous streams, which originate from near the summit 

of West Maui Volcano. No perennial streams are on the part of 

Haleakalä that is in the study area. Topography within the study 

area ranges from a broad flat plain to steep interior mountains.

Land Use

Gently sloping areas around west Maui and on the 

isthmus between west and east Maui have been used for 

agriculture for over a century. The urban areas spread over 

the northern part of the isthmus at Wailuku and Kahului and 

in resort areas along the coasts. The interior of west Maui is 

mostly forested conservation land. The principal agricultural 

crops (fig. 2) have been sugarcane, pineapple, macadamia 

nuts, and diversified agriculture. The historical changes in 

agricultural land use within the study area were estimated 

by Engott and Vana (2007) in order to estimate the historical 

application of irrigation water, and the following sections on 

land use are summarized from their work. During the early 

1900s until about 1979, land use was mostly unchanged except 

for some minor urbanization along the coasts. However, as 

large-scale plantation agriculture declined after 1979, land-use 

changes were more significant. During the period 1979–2004, 

agricultural land use declined about 21 percent, mainly from 

decreases in sugarcane acreage. 

On the west side of West Maui Mountain, the Pioneer 

Mill Co. was a major sugarcane cultivator during the late 

1800s until 1999, when it ceased sugarcane production 

and the land was subsequently bought by ML&P and other 

private investors. ML&P currently grows pineapple on the 

northwest slope of West Maui Mountain, where pineapple 

has a long history of cultivation, and in a small area of former Pioneer Mill Co. sugarcane lands. However, the extent 

of pineapple cultivation in west Maui has decreased considerably since the late 1990s. 

On the east slope of West Maui Mountain, the Wailuku 

Sugar Co. (currently the Wailuku Water Co.) first began 

growing sugarcane in 1856. By the mid-1980s, sugarcane was 

replaced by macadamia trees on the northern extent of the 

plantation. Additional sugarcane lands were replaced by pineapple by the end of the 1980s. In the 1990s, Wailuku Agribusiness, as the company was then named, continued diversifying 

away from sugarcane and agriculture altogether. By 2005, the 

company had leased the southern extent of the plantation to 

HC&S, halted macadamia operations, and sold much of its 

land for residential development.

On the central Maui isthmus, sugarcane has been grown 

continuously from the late 1800s until the present by HC&S 

and predecessor plantations. ML&P and several smaller companies currently cultivate pineapple on the lower northwest 

slope of Haleakalä. Pineapple has been grown in this area for 

more than a century.

Climate

The topography of Maui and the location of the north 

Pacific anticyclone relative to the island affect its climate, 

which is characterized by mild and uniform temperatures, 

seasonal variation in rainfall, and great geographic variation in 

rainfall (Blumenstock and Price, 1967). Average temperature 

in Wailuku, near the coast, is 75o F, whereas the average at 

Haleakalä summit is 47o F (Western Region Climate Center, 

2007). During the warmer dry season (May–September), the 

stability of the north Pacific anticyclone produces persistent 

northeasterly winds, known locally as trade winds, which blow 

80–95 percent of the time. During the cooler rainy season 

(October–April), migratory weather systems often travel past 

the Hawaiian Islands, resulting in less persistent trade winds 

that blow 50–80 percent of the time. Low-pressure systems 

and associated southerly winds can bring heavy rains to the 

island, and the dry coastal areas can receive most of their rainfall from these systems. 

The variation in mean annual rainfall with altitude is 

extreme on Maui, with differences of more than 130 in. within 

one mile of Puÿu Kukui (fig. 3) where average annual rainfall 

exceeds 355 inches per year (Giambelluca and others, 1986). 

Mean annual rainfall at the coast in the dry leeward areas is 

less than 15 in. At higher altitudes, precipitation is a combination of rainfall and fog drip where the montane forest canopy 

intercepts cloud water. Giambelluca and Nullet (1991) defined 

the fog zone on the leeward slopes of Haleakalä as extending from altitudes of about 3,900 to 5,900 ft and estimated a 

thicker fog zone, at altitudes of 2,000 to 6,560 ft, along windward slopes. Precipitation is supplemented by an unknown 

amount of fog drip, which is fog and precipitation (not measured by rain gages) that is intercepted by vegetation and that 

subsequently drips to the ground surface.

Geology

The geology of Maui was described in detail by Stearns 

and Macdonald (1942), and some of the geologic units were 

subsequently reclassified by Langenheim and Clague (1987). 

Cox (1951), Yamanaga and Huxel (1970), and Meyer and Presley (2001) presented stratigraphic information for the basalts 

and overlying sediments in the Wailuku area based on drilling 

information. 

West Maui Volcano has a central caldera and two main rift 

zones that trend in northwesterly and southeasterly directions 
Setting 5

Figure 2. Land use during 1926–2004 in central and west Maui, Hawai‘i (modified from Engott and Vana, 2007).

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

study-area boundary

study-area boundary

156 ̊40’

21 ̊00’

20 ̊50’

20 ̊40’

156 ̊30’

156 ̊20’ 156 ̊30’

 URBAN 

 PASTURE AND OTHER AGRICULTURE

 RANGELAND

 FOREST LAND

 WATER

 WETLAND

 BARREN LAND

 AGRICULTURAL 

Sugarcane

Pineapple

Macadamia nuts

Diversified Agriculture

Golf (formerly agriculture)

EXPLANATION

2000-04

1985-89 1990-94 and 1995-99

1926-79 1980-84
6 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 3. Mean annual rainfall and fog zone in central and west Maui, Hawai‘i (modified from Giambelluca and others, 1986; 

Giambelluca and Nullet, 1991).

0 5.2 5 10 seliM

0 2.5 5 10 Kilometers

SCALE

156°�40 ́

�21 00 ́

20°�50 ́

20°�40 ́

156°�30 ́

156°�20 ́

FOG ZONE 

LINE OF EQUAL RAINFALLNUMBER IS MEAN ANNUAL RAINFALL,

IN INCHES--interval is variable

20

30 20

15

40

60

80 100

120

160

200

240

280

320

350

30

40

50

60

80

100

120

20

30 20

15

40

60

80 100

120

160

200

240

280

320

350

30

40

50

60

80

100

120

EXPLANATION

Wailuku

Kahului

Makawao

Pukalani

Mäkena

Kïhei

Lahaina

Pä‘ia

!

!

!

!

!

!

!

!

!

Käÿanapali

study-area boundary

study-area boundary

°
Setting 7

from the caldera (fig. 4). Thousands of dikes exist within the 

rift zones, with the number of dikes increasing toward the caldera and with depth. Additional dikes exist outside the trends 

of the rift zones, creating a radial pattern of dikes emanating 

from the caldera (Macdonald and others, 1983). Thousands of 

lava flows emanated from vents in and near the caldera and rift 

zones. 

The rocks of West Maui Volcano consist of the mostly 

shield-stage Wailuku Basalt, which is overlain by the 

postshield-stage Honolua Volcanics and rejuvenated-stage 

Lahaina Volcanics. The Wailuku Basalt consists of tholeiitic, 

olivine-tholeiitic, and picritic tholeiitic basalt and postshieldstage caldera-filling lava of alkalic basalt, and it includes 

lava flows with associated intrusive rocks and pyroclastic 

and sedimentary deposits (Langenheim and Clague, 1987, 

p. 79). Individual lava flows range between 1 and 100 ft in 

thickness and dip between 5 and 20-degrees away from their 

sources (Stearns and Macdonald, 1942, p. 161). The Honolua 

Volcanics comprises mugearite, trachyte, and hawaiite, 

and it includes lava flows and associated domes, dikes, and 

pyroclastic deposits (Langenheim and Clague, 1987, p. 79). 

Individual flows range between 25 and 300 ft in thickness 

and may reach 500 ft thick near vents (Stearns and Macdonald, 1942, p. 173). These flows average about 75 ft thick and 

generally form a veneer on the older Wailuku Basalt. Isotopic 

age determinations indicate a Pleistocene age for the Wailuku 

Basalt and Honolua Volcanics (McDougal, 1964; Naughton and others, 1980). The Lahaina Volcanics comprises 

Pleistocene-age basanite and picritic basanite, and it includes 

lava flows and associated pyroclastic deposits (Langenheim 

and Clague, 1987, p. 79). These rock types are not very 

widespread and all lie on the west side of West Maui Volcano 

(Stearns and Macdonald, 1942, p. 180).

Haleakalä has three rift zones that trend in northerly, 

southwesterly, and easterly directions. Two of these rift 

zones form the eastern boundary of the study area. The rocks 

of Haleakalä Volcano consist of the shield-stage Honomanü 

Basalt, which is overlain by the postshield-stage Kula Volcanics and younger Häna Volcanics. The Honomanü Basalt 

comprises tholeiitic, olivine tholeiitic, and picritic tholeiitic 

basalt, and it includes lava flows and associated intrusive 

rocks and rare pyroclastic deposits (Langenheim and Clague, 

1987, p. 78). The end of the shield-building stage of the volcano is estimated to be between 0.97 and 0.93 million years 

ago on the basis of potassium-argon dating (Chen and others, 

1991). The lavas of the Honomanü Basalt have typical dips 

of 2–22 degrees, with the flatter dips near the isthmus where 

lava flows approached the West Maui Volcano. The basalts 

were laid down as vesicular pähoehoe and ÿaÿä flows averaging about 15 ft thick (Stearns and Macdonald, 1942, p. 70).

The Kula Volcanics, which overlies the Honomanü 

Basalt, comprises post-shield-stage lava flows of hawaiite 

with some ankaramite and alkalic basalt and associated intrusive rocks and pyroclastic and sedimentary deposits (Langenheim and Clague, 1987, p. 78). The Kula Volcanics is 

estimated to be 0.93–0.36 million years old, with many of the 

oldest rocks having chemical compositions transitional from 

the shield- to post-shield-stage lava (Chen and others, 1991). 

Exposures of this transitional phase are 50–100 ft thick and 

are commonly difficult to characterize as belonging to either 

the Honomanü Basalt or the Kula Volcanics. In some places, 

the two units are separated by a thin red soil layer that was 

altered by the weight and heat of the overlying flows. The 

Kula Volcanics almost completely covers the underlying 

Honomanü Basalt and exposures range between 2,500 ft in 

thickness near the summit and 50–200 ft in thickness near 

the coast. The thickness of individual lava flows averages 

about 20 ft near the summit and 50 ft near the periphery, 

but flows as much as 200 ft thick are not rare (Stearns and 

Macdonald, 1942, p. 75). The usual dip of the flows is about 

10 degrees.

The Häna Volcanics comprises alkalic basalt and basanite, and it includes lava flows and associated intrusive rocks 

and pyroclastic and sedimentary deposits (Langenheim and 

Clague, 1987, p. 78). The Häna Volcanics is mostly ÿaÿä and 

ranges between a few feet and several hundred feet in thickness where it was confined by valley walls during emplacement (Stearns and Macdonald, 1942, p. 96). The Kula 

Volcanics and the Häna Volcanics are the most widespread 

geologic units exposed at the land surface on Maui. Sherrod 

and others (2003) presented age-dating, geochemical, and 

geological evidence for Haleakalä lavas showing that the 

volcano has not yet begun a classically defined rejuvenated 

stage of growth, and therefore the Kula (Pleistocene) and 

Häna Volcanics (Pleistocene and Holocene) are products of 

the same stage of island formation.

The central isthmus is formed by nearly flat-lying lava 

flows of the Honomanü Basalt, which are interbedded with 

consolidated and unconsolidated sedimentary deposits (fig. 

5). Beneath the isthmus, Honomanü Basalt of Haleakalä 

overlies older Wailuku Basalt of West Maui Volcano with 

a wedge of sedimentary deposits between the two units. 

Sedimentary deposits throughout Maui have been divided 

into consolidated earthy deposits, calcareous sand dunes, and 

unconsolidated deposits (Stearns and Macdonald, 1942). The 

consolidated earthy deposits are primarily older alluvium, 

which forms the bulk of the alluvial plains stretching from 

the mountains of West Maui Volcano to the coast. The older 

alluvium primarily consists of poorly sorted conglomerates. 

Within these deposits, a thin layer of Lahaina Volcanics was 

found while drilling Test Hole E (5430-03); this lava flow 

is not exposed on the surface (fig. 4). The older alluvium 

has been partly eroded by Waikapü and ÿÏao Streams and 

Waiheÿe River. Calcareous sand dunes are found seaward 

of the exposed older alluvium. Unconsolidated deposits are 

found in streambeds and in the coastal areas, and primarily 

consist of younger, poorly sorted alluvium.

Burnham and others (1977, p. 6) describe four principal 

units of the sedimentary wedge beneath the Kahului area. The 

base of the sediments contains a westward-thickening wedge of 

alluvial clay, sand, and gravel that may reach 30–50 ft in thickness within the area. Overlying the alluvium and extending 
8 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 4. Generalized surficial geology in central and west Maui, Hawai‘i (modified from Stearns and Macdonald, 1942; 

Sherrod and others, 2003).

a

aa

a

a

5128-01

5130-02

5130-01

5430-03

5330-04

a

5330-05

EXPLANATION

SEDIMENTARY DEPOSITS

 UNCONSOLIDATED

 CONSOLIDATED

WEST MAUI VOLCANO

 LAHAINA VOLCANICS

 HONOLUA VOLCANICS

 WAILUKU BASALT

HALEAKALÄ VOLCANO

 HÄNA VOLCANICS

 KULA VOLCANICS

 HONOMANÜ BASALT

AXIS OF RIFT ZONE--Approximately located

BOUNDARY OF CALDERA--Approximately located

INFERRED BOUNDARY AND TRANSITIONAL AREA

 (DIAGONAL PATTERN) BETWEEN DIKE-IMPOUNDED 

 GROUND WATER AND FRESHWATER-LENS SYSTEM 

 (modified from Yamanaga and Huxel, 1969; 1970)

LINE OF SECTION

WELL MENTIONED IN TEXT

A'

B'B

A

B B'

a

5128-01

0 5.2 5 10 seliM

0 2.5 5 10 Kilometers

SCALE

156°����40 ́

21°�00 ́

20°50 ́

20°�40 ́

156°�30 ́

156°�20 ́

Waikapü Stream

ÿÏao Stream

Waiheÿe River

study-area boundary

study-area boundary
Figure 5. Geologic cross sections of the ÿÏao aquifer area, Maui, Hawaiÿi (modified from Meyer and Presley, 2001).

A 

FEET

4,0003,0002,0001,000

0

-1,000-2,000-3,000

B 

FEET

4,0003,0002,0001,000

0

-1,000-2,000-3,000

NO VERTICAL EXAGGERATION

00

1 MILE

0.5

0.5

1 KILOMETER

BEND IN SECTION

BEND IN SECTION

BEND IN SECTION

sea level

BEND IN SECTION

BEND IN SECTION

sea level

EXPLANATION

SEDIMENTARY DEPOSITS UNCONSOLIDATED CONSOLIDATED

WEST MAUI VOLCANO WAILUKU BASALTHALEAKALÄ VOLCANO KULA VOLCANICS / HONOMANÜ BASALT

DIKES
10 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

farther southeastward over residual clay on the lava is a buried 

coral reef complex, which appears to be the landward continuation of the present offshore reef. This reef material is dominantly coral mixed with coral debris and medium to fine sand. 

The reef complex is overlain by sand, which grades landward 

from coarse to fine and reaches thicknesses of 20–30 ft. The 

sedimentary materials are capped beneath the land areas by the 

windblown sand and soils of the present land surface (Burnham and others, 1977, p. 6). A similar sedimentary sequence 

would be expected across the isthmus; Stearns and Macdonald 

(1942, p. 109) report marine sediments 40 ft above sea level 

near the center of the isthmus in the Waikapü Shaft Test Hole 

(5128-01) (fig. 4).

Following a period of extensive erosion, during which 

stream valleys were deeply incised, some of the valleys were 

filled in by alluvial deposits during a period when sea level 

was higher than it is today. The deposits formed alluvial fans 

that extended up the stream valleys and were influenced by 

the growth of the Haleakalä slope to the east (Cox, 1951, 

p. 4). These valley-fill deposits extend below sea level, but 

a series of test holes drilled in the 1940’s did not provide 

evidence of how deeply these deposits extend. Estimates of 

similar valley-fills in Oÿahu suggest that these sediments may 

extend as much as 200 ft below sea level (Oki, 2005b, p. 17).

Because the sedimentary deposits are hydrologically significant owing to their relatively lower permeability compared 

to the volcanic rocks, the subsurface extent of these deposits 

was mapped using lithologic information from wells. Cox 

(1951, plate 2) presented an initial map of the pre-Honolua 

surface (top of the Wailuku Basalt) based on data from six 

wells in the ÿÏao area, and Burnham and others (1977, fig. 2) 

presented a map for the Kahului area showing the depth of 

the top of the lava rock aquifer (Kula Volcanics or Honomanü 

Basalt) using data from 28 wells. Lithologic information from 

an additional 60 wells (appendix A) was combined with these 

existing maps to construct maps of the top of the Wailuku 

Basalt and the top of the Kula Volcanics/ Honomanü Basalt 

for the entire study area and extending offshore (figs. 6 and 7). 

Where no lithologic information was available, the approximate position of the buried surface beneath Haleakalä and 

offshore was determined by extrapolating the broad topographic slope of the West Maui Volcano. The subsurface extent 

of valley-filling deposits was estimated from borehole data and 

from extrapolation below sea level of the slope of the stream 

valley walls.

Hydraulic Properties of the Rocks

The hydraulic properties of the various rock types control 

the occurrence and movement of ground water in the study 

area. Ground-water withdrawals are primarily from a freshwater lens system that occurs in the dike-free volcanic rocks 

outside of the dike-intruded rift zones. Some rocks effectively 

impede ground-water flow, creating barriers to flow and areas 

of steep hydraulic gradient.

Hydraulic Conductivity

Hydraulic conductivity is a quantitative measure of the 

capacity of a rock to transmit water. Hydraulic conductivity is 

the constant of proportionality in Darcy’s law, which relates 

specific discharge (discharge per unit area) to the hydraulic 

gradient: 

v =K( dh/dl ) , (1)

where 

v = specific discharge [LT–1], 

K = hydraulic conductivity [LT–1], and 

dh/dl = hydraulic gradient [LL–1].

Darcy’s law generally is assumed applicable to regional 

ground-water flow analyses in Hawaiÿi (Souza and Voss, 1987; 

Gingerich and Voss, 2005; Oki, 2005b). 

Rock hydraulic conductivity can be qualitatively 

described by permeability. Permeability describes the ease 

with which fluid can move through rock. The permeability 

of volcanic rocks is variable and depends on many factors, 

including the mode of emplacement and amount of weathering. Lava viscosity and topography also can affect permeability. Thicker flows generally are less permeable and form 

from highly viscous lava or on flat topography (Gingerich and 

Oki, 2000).

Dike-Free Volcanic Rocks

The permeability of the subaerial, shield-building, 

dike-free lava flows in the study area generally is high. The 

main elements of lava flows contributing to the permeability 

are (1) clinker zones associated with ÿaÿä flows, (2) voids 

along the contacts between flows, (3) cooling joints normal 

to flow surfaces, and (4) lava tubes associated with pähoehoe 

flows. The regional horizontal hydraulic conductivity of the 

dike-free volcanic rocks generally ranges between hundreds 

and thousands of feet per day (Burnham and others, 1977; 

Oki, 2005b; Rotzoll and others, 2007; Hunt, 2007) (fig. 8). 

Because of the high permeability of the dike-free volcanic 

rocks, horizontal water-table gradients in these rocks are 

small (about 1 ft/mi). Horizontal hydraulic conductivity in 

the lava flows may be anisotropic—several times greater 

parallel to the lava flows than perpendicular to the flows 

(Nichols and others, 1996, p. A14). 

In general, the vertical hydraulic conductivity of the dikefree lava flows may be tens to hundreds of times less than the 

horizontal hydraulic conductivity. In the Kahului area, Bowles 

(1970) suggested that horizontal permeability might be as great 

as ten times vertical permeability on the basis of aquifer tests 

on stormwater disposal wells. Burnham and others (1977) 

obtained acceptable results with their numerical model using 

horizontal hydraulic conductivity 10–100 times the vertical 

hydraulic conductivity near Kahului. Hunt (2007) used a ratio 

of horizontal to vertical hydraulic conductivity of 200 to 1 for a 

numerical modeling study of the Kïhei, Maui, area. Souza and 

Voss (1987) also estimated the ratio of horizontal to vertical 
Setting 11

Figure 6. Structural contours on the top of the Wailuku Basalt and locations of wells with stratigraphic information on that unit in 

central and west Maui, Hawaiÿi.

0 5.2 5 10 seliM

0 2.5 5 10 Kilometers

SCALE

156°�40 ́

20°�50 ́

20°�40 ́

156°�30 ́

156°�20 ́

EXPLANATION

-4,000

-6,000

0 LINE OF EQUAL ELEVATION OF

THE TOP OF THE WAILUKU 

BASALT, IN FEET RELATIVE TO 

MEAN SEA LEVEL, DASHED 

WHERE APPROXIMATE--interval

is 1,000 ft 

WELL WITH STRATIGRAPHIC

INFORMATION ABOUT THE

WAILUKU BASALT

-5,000

-4,000

-3,000

-2,000

-2,000

-1,000

-1,000

1,000

1,000

2,000

5,000

4,000

3,000

0

0

-6,000

@

@

@

@

@@

@@@@

@

@

@@

@@@

@

@

@

@

@

@

@

@

@

@

0

study-area boundary

study-area boundary

21°00 ́
12 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 7. Structural contours on the top of the Kula Volcanics/ Honomanü Basalt and wells with stratigraphic information on those 

units in central and west Maui, Hawaiÿi.

0 5.2 5 10 seliM

0 2.5 5 10 Kilometers

SCALE

156°�40 ́

21°�00 ́

20°�50 ́

20�40 ́

156°�30 ́

156°�20 ́

EXPLANATION

@

LINE OF EQUAL ELEVATION OF

THE TOP OF THE KULA VOLCANICS/

HONOMANÜ BASALT, IN FEET 

RELATIVE TO MEAN SEA LEVEL--

interval is variable

WELL WITH STRATIGRAPHIC

INFORMATION ABOUT KULA

VOLCANICS/HONOMANÜ 

BASALT 

0

40

0

-80

-40

-120

-160

-400

-200

120

200

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

40

0

-80

-40

-120

-160

-200

@@@

@

@@@

@@

@

@

@

@@@

@ @ @ @

@

@

@

@ @@@ @@@ @@@@@@@@@@@@@@@@@@@

@@

@@

@ @

@@ @@@

@@@

study-area boundary

study-area boundary
Setting 13

Figure 8. Distribution of aquifer hydraulic conductivity in central and west Maui, Hawaiÿi (modified from Rotzoll and others, 2007).

ESTIMATED HYDRAULIC CONDUCTIVITY, 

IN FEET PER DAY

 250 - 800

 800 - 1,600

 1,600 - 2,400

 2,400 - 3,200

 3,200 - 4,100

Wailuku

Basalt

Honomanü Basalt/

Kula Volcanics

Sediment

101

102

103

104

HYDRAULIC CONDUCTIVITY, IN FEET PER DAY

Median

Minimum

Maximum

Upper

quartile

Lower

quartile

WELL

Wailuku Basalt

Honomanü Basalt/

 Kula Volcanics

Sediment

0 5.2 5 10 seliM

0 2.5 5 10 Kilometers

SCALE

156°�40 ́

21°�00 ́

20°�50 ́

20°�40 ́

156°�30 ́

156°�20 ́

study-area boundary

study-area boundary

n=46

n=51

n=5
14 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

hydraulic conductivity to be 200 to 1 in their modeling study 

on Oÿahu. 

Dikes

Intrusive volcanic rocks include those rocks, such as dikes, 

sills, and stocks, which formed by magma that cooled below the 

ground surface. Dikes associated with the rift zones of the West 

Maui and Haleakalä Volcanoes are the dominant intrusive rocks 

on Maui, and they are most abundant within the central area 

of the rift zones and the caldera complex. Although the thickness of individual dikes generally is less than 10 ft, dikes are 

hydrologically significant because of their low permeability and 

their impounding effect on ground water. Ground-water levels in 

the interior of the West Maui Volcano may be as high as 3,000 ft 

above sea level as evidenced by tunnels tapping dike compartments (Stearns and Macdonald, 1942, p. 195).

In general, the average hydraulic conductivity of a rift 

zone decreases as the number of dike intrusions within the rift 

zone increases. In addition, hydraulic conductivity is expected 

to be higher in a direction along the strike of the dikes rather 

than perpendicular to the strike. Rotzoll and others (2007) 

report a hydraulic conductivity of about 20 ft/d from an analysis of an aquifer test made on a well in ÿÏao Valley in the dike 

complex. On the basis of a numerical model analysis, Meyer 

and Souza (1995) suggested that the average effective hydraulic conductivity of a dike complex ranges between about 0.01 

and 0.1 ft/d. These values reflect the influence of the intrusive 

dikes as well as the lava flows between dikes. The hydraulic 

conductivity of the intrusive dike material was estimated to 

range between 10–5 and 10–2 ft/d (Meyer and Souza, 1995). 

Weathering

Weathering reduces the permeability of all types of volcanic 

rocks. The reduction of permeability may be attributed to secondary mineralization that clogs the primary and secondary porosity, 

or to clays and colloids that precipitate from percolating water 

(Mink and Lau, 1980). Burnham and others (1977, p. 6) report that 

the buried lava surface beneath the Kahului area contains a residual clay, indicating a long period of exposure, soil formation, and 

erosion before burial. On the basis of laboratory permeameter tests 

on core samples, Wentworth (1938) estimated the hydraulic conductivity of weathered basalt to be between 0.083 and 0.128 ft/d. 

An injection test conducted in weathered basalt beneath Waiawa 

Stream valley on Oÿahu yielded a hydraulic conductivity of 0.058 

ft/d (R.M. Towill Corporation, 1978). Miller (1987) used the 

water-retention characteristics of core samples collected beneath 

central Oÿahu pineapple fields to estimate the saturated hydraulic 

conductivity of saprolite and found values ranging between 0.0028 

and 283 ft/d. The wide range of hydraulic-conductivity values 

estimated by Miller was attributed to the variability in secondary 

porosity among samples.

Sedimentary Rocks

The sediments of greatest hydrologic significance, 

because of their relatively low permeability, are the older 

consolidated alluvial deposits, which were created during the 

period of extensive erosion that carved deep valleys in the original volcanoes. These deposits are in deeply incised valleys and 

beneath the isthmus of Maui. The low permeability of consolidated alluvial deposits is caused by a reduction of pore space 

from the volume increase associated with weathering as well as 

from mechanical compaction (Wentworth, 1951). Wentworth 

(1938) estimated the hydraulic conductivity of three weathered 

alluvium samples from Oÿahu with the use of a laboratory 

permeameter. Two of the samples had a hydraulic conductivity of less than 0.013 ft/d, and the third sample had a hydraulic 

conductivity of 1.08 ft/d. Eight samples classified as alluvium, 

without reference to weathering, produced a range of hydraulic 

conductivity between 0.019 and 0.37 ft/d (Wentworth, 1938). 

The sedimentary deposits and underlying weathered volcanic rocks of the stream valleys, isthmus, and coastal plains 

form a low-permeability confining unit, called caprock, which 

overlies high-permeability volcanic rocks and impedes the 

seaward discharge of freshwater and the movement of water 

between the West Maui Volcano and Haleakalä volcanic-rock 

aquifers. Although the permeability of the various components 

of the caprock may vary widely, from low permeability in 

older alluvium and saprolite to high permeability in buried 

coral reef deposits and sand dunes, overall the caprock has 

lower regional permeability than the volcanic-rock aquifers. 

Rotzoll and others (2007) show a range of about 30–650 ft/d 

in hydraulic conductivity estimates from five aquifer tests in 

sediments of central Maui. Souza and Voss (1987) modeled a 

vertical cross section of the Pearl Harbor ground-water area on 

Oÿahu and estimated a caprock hydraulic conductivity of 0.15 

ft/d. In their analysis, Souza and Voss treated the caprock as a 

homogeneous and isotropic unit, although significant heterogeneity may exist (Oki and others, 1998). Little information 

about the anisotropy or vertical hydraulic conductivity of the 

caprock is available. Burnham and others (1977) modeled a 

clay layer overlying the volcanic-rock aquifer beneath Kahului 

using a range of vertical hydraulic conductivities between 

about 1 and 10 ft/d. Valley-fill deposits on Oÿahu were modeled with horizontal and vertical hydraulic conductivities ranging from 0.058 to 30 ft/d (Oki, 1998; 2005b).

Specific Storage and Effective Porosity

The effective porosity and specific storage of the rocks 

forming an aquifer affect the timing and amount of the waterlevel response to natural or human-induced changes. The 

effective porosity represents that part of the total rock porosity 

that contributes to flow, and specific storage is a measure of 

the compressive storage of the rocks and fluid. Small values of 

effective porosity or specific storage result in rapid and relatively 

large water-level changes in response to changes in pumping or 

recharge, whereas large values of effective porosity or specific 

storage result in slower and smaller water-level changes.

Total porosity of a rock is the ratio of the volume of 

void spaces to the total rock volume. Pore spaces in a layered 

sequence of lava flows may result from (1) vesicles (small 
Ground-Water Flow System 15

spaces formed by the expansion of gas bubbles during the 

solidification of cooling lava), (2) joints and cracks, (3) separations between lava flows, (4) void spaces between fragmented 

rock, including ÿaÿä clinker, and (5) lava tubes. Total porosity of the volcanic rocks on Oÿahu was measured at different 

spatial scales using rock samples (Wentworth, 1938; Ishizaki 

and others, 1967), borehole photographic logging (Peterson 

and Sehgal, 1974), and density logs from gravity surveys in 

underground tunnels (Huber and Adams, 1971). Total porosity estimates for volcanic rocks of Oÿahu range from less than 

0.05 to more than 0.5. Low porosity values may be associated 

with massive features, including dense flows, ÿaÿä cores, dikes, 

and thick lava flows, and high values may be associated with 

ÿaÿä clinker zones. Effective porosity, which includes only 

the hydraulically interconnected pore spaces, may be up to 

an order of magnitude less than total porosity. Estimates of 

effective porosity from modeling studies range between 0.04 

and 0.10 for volcanic-rock aquifers (Gingerich and Voss, 2005; 

Oki, 2005b; Hunt, 2007). Rotzoll and others (2007) analyzed 

aquifer-test data from wells in central Maui and estimated 

specific storage and specific yield from one test to be 2.0x10-6

ft-1 and 0.07, respectively.

Dispersion Characteristics

Freshwater mixing with underlying saltwater in an 

aquifer creates a transition zone of brackish water. The extent 

of mixing in an aquifer depends on several factors, including 

the ground-water velocity and the aquifer dispersivity. High 

values of dispersivity, all other factors being equal, result in 

greater mixing. Dispersivity values generally are larger in the 

(longitudinal) direction of flow relative to directions transverse 

to flow and may be controlled by aquifer anisotropy. Few 

reported dispersivity values are available for volcanic-rock 

aquifers. Meyer and others (1974) estimated the dispersivity to 

be about 200 ft for the volcanic-rock aquifer in the Honolulu, 

Oÿahu, area, and this value likely represents a longitudinal 

dispersivity. Using a cross-sectional numerical model, Souza 

and Voss (1987) estimated the longitudinal and transverse 

dispersivities of the Pearl Harbor area, Oÿahu, to be 250 and 

0.82 ft, respectively. Liu (2005) estimated vertical dispersivity 

values ranging between 0.4 and 2.1 ft from salinity profiles 

measured in deep monitor wells throughout the Pearl Harbor 

area, Oÿahu.

Ground-Water Flow System

Fresh ground water moves mainly from inland recharge 

areas to coastal discharge areas, where springs and seeps exist 

above and below sea level. Eastward flowing water from West 

Maui Volcano converges with westward flowing water from 

Haleakalä in the central isthmus, and the water then flows to 

discharge areas near the northern and southern coasts (Tenorio 

and others, 1970; Takasaki, 1972). Fresh ground water in the 

Wailuku area is mainly in freshwater-lens systems and dikeimpounded systems (Yamanaga and Huxel, 1970; Takasaki, 

1972; Meyer and Presley, 2001). 

Freshwater Lens

Currently, one of the most important sources of fresh 

ground water on Maui is from the freshwater lens in dikefree volcanic rocks in the ÿÏao aquifer area (fig. 9). The main 

ground-water system in this area consists of a lens-shaped 

freshwater body, an intermediate transition zone of brackish 

water, and underlying saltwater. Several geologic features 

form boundaries of the freshwater-lens system or impede 

ground-water flow within the system. Features that form 

boundaries of the freshwater-lens system include dikes in the 

interior of West Maui Volcano; features that may impede flow 

within the system include valley-fill barriers and the coastal 

sedimentary caprock that thickens in a seaward direction.

The freshwater lens in the study area forms because of 

the density difference between freshwater and underlying 

saltwater. The thickness of the lens can be estimated using the 

Ghyben-Herzberg relation (for example, Freeze and Cherry, 

1979). The relation assumes that freshwater and saltwater 

do not flow or mix. Although freshwater and saltwater do 

flow and mix in actual freshwater-lens systems, the Ghyben 

Herzberg relation can be used where the flow is primarily 

horizontal to estimate the depth at which salinity is about 50 

percent that of sea water. For these conditions, the freshwaterlens thickness below sea level is directly proportional to the 

height of the top of the freshwater above sea level. In principle, at a place where the water table stands 1 foot above sea 

level, for example, 40 feet of freshwater will be below sea 

level, and the freshwater lens will thus be 41 feet thick. This 

relation exists because the ratio of the density of salt water 

to fresh water is 41:40. In the dike-free volcanic rocks of the 

Wailuku area, freshwater mixing with underlying saltwater 

creates a brackish-water transition zone that may be hundreds 

of feet thick. (For the purposes of this report, brackish water 

has salinity that ranges between greater than 2-percent and less 

than 100-percent seawater salinity.) 

The water table in the dike-free volcanic rocks is less 

than a few tens of feet above sea level. In general, the watertable altitude in the dike-free volcanic rocks is lowest near 

the coast and increases landward at a rate of about 1 ft/mi, 

although local variations may exist near areas of converging 

flow caused by pumping from wells. Although freshwater 

flow is predominantly horizontal in the dike-free volcanic 

rocks, the flow may have an upward or downward component 

in some areas.

The lower permeability sedimentary caprock between West 

Maui Volcano and Haleakalä is a confining unit that impedes the 

flow of fresh ground water between the Wailuku area and the 

Haleakalä lavas in the isthmus and also ground-water discharge 

to the coast. The caprock extends offshore, beyond the seaward 

extent of the freshwater lens. The freshwater-lens system in the 
Figure 9. Geologic cross section of the ÿÏao aquifer area, showing ground-water occurrence and movement, Maui, Hawaiÿi (from Meyer an

0 2,0

4x VERTICA

4,000

FEET

EAST 

3,5003,0002,5002,0001,5001,000

500

SEA

LEVEL

-500

-1,000-1,500

DIKE COMPLEX

DIKE-IMPOUNDED GROUND WATEFRESHWATER LENS Unconfined ground water in Wailuk Confined ground water in Wailuku  Unconfined ground water in sedimPERCHED GROUND WATER IN SED DEPOSITS CONTINUOUS WITH  LENSWAILUKU BASALTSEDIMENTARY DEPOSITSGENERALIZED DIRECTION OF GRO FLOWWATER TABLEWATER TABLE OF PERCHED GROU BODY

Ocean

saltwater altwater

freshwater

transition zone transition zone

EXPLANATION

Dike-impounded

ground water

Unconfined fresh ground water in 

dike-free Wailuku Basalt

Confined fresh ground water in 

the Wailuku Basalt

Inferred boundary between dike-impounded 

ground water and freshwater lens

Boundary between unconfined and confined

ground water in the Wailuku Basalt

Approximate seaward extent of freshwater in

Wailuku Basalt for predevelopment conditions

3

2C

2B

2A

1

1

2A

2B

2C

3

High-leveltunnel
Ground-Water Flow System 17

dike-free volcanic rocks is mainly unconfined inland from the 

caprock. Within the caprock, the freshwater lens is unconfined. 

The lower permeability valley-filling sediments likely 

impede the flow of ground water to the north and south. Water 

levels often are an indicator of a low-permeability barrier to 

flow if abrupt differences in ground-water levels are found 

on either side of the suspected hydrologic barrier. The presence of valley-fill barriers in the ÿÏao area was first postulated 

by Cox (1951, p. 6), who cited a 3-ft difference between 

the head north and south of ÿÏao Valley and a much greater 

head drop (18 ft) from just south of ÿÏao Valley to south of 

Waikapü Valley. Later, drilling on the north side of Waikapü 

Stream revealed a head difference of about 4 feet between 

the Waikapü 1 (5130-01) and Waikapü 2 (5130-02) wells 

located about 1,600 ft apart but not near any known hydrologic feature. Mink and Lau (1990) subsequently located the 

boundary separating the ÿÏao and Waikapü Aquifer Systems 

between these two wells rather than along Waikapü Valley. 

Water-level differences between these wells and wells closer 

to ÿÏao Stream were 4 to 7 ft, also indicating that some type of 

hydrologic barrier is located in this area but not one necessarily corresponding to the surface expression of the current 

Waikapü Valley. Water levels drop more than 5 ft from south 

to north across Waiheÿe Valley, indicating that the valley-filling 

sediments here also are a partial barrier to flow.

A saltwater-circulation system exists beneath the freshwater lens. Saltwater flows landward in the deeper parts of the 

aquifer, flows upward, and then mixes with seaward-flowing 

fresher water (fig. 9). This mixing creates the brackish-water 

transition zone. When water is pumped from the freshwater 

lens system, water levels will decrease and the transition zone 

will rise until a new equilibrium is reached between the amount 

of recharge to the system and the amount of discharge to wells 

and the coast. In the ÿÏao/Waiheÿe Aquifer Systems, the coastal 

caprock that impedes the discharge of freshwater also impedes 

the flow of ocean water into the aquifer. This causes the balance 

between fresh and salt water to be out of equilibrium for tens of 

years as ocean water moves slowly into the aquifer to balance 

the freshwater that has been removed. Hence, the midpoint of 

the freshwater lens is deeper than would be expected by assuming the Ghyben-Herzberg principle. Only after a new equilibrium is reached will the depth of the midpoint of the transition 

zone be about 40 times the head at the water table. 

Dike-Impounded System

Dike-impounded systems are found near the caldera and 

rift zones of the volcanoes, where low-permeability dikes have 

intruded other rocks. Near-vertical dikes tend to compartmentalize areas of permeable volcanic rocks. Dikes impound water 

to heights as much as 3,000 ft above sea level in the interior 

of West Maui Volcano, as evidenced by tunnels tapping dike 

compartments (Stearns and Macdonald, 1942, p. 195). In 

some stream valleys, where extensive erosion exposed dike 

compartments, ground water discharges directly to streams. 

Nevertheless, the evidence supplied from gaining streams, 

ground-water tunnels, and wells indicate that ground water is 

impounded to high levels. The extent of the dike-impounded 

water body is inferred from the dikes exposed in valley walls, 

tunnels, and water levels in wells (Yamanaga and Huxel, 

1969, fig. 6; 1970, fig. 7). No data from wells are available 

for determining the depth to which freshwater extends below 

sea level within the dike-impounded system. Where erosion or 

tunneling extends to below the water level in the stream valleys, ground water discharges directly to the streams as base 

flow. Fresh ground water that does not discharge to streams or 

tunnels or is not withdrawn from wells in the dike-impounded 

system flows to downgradient areas in the freshwater-lens 

system. Although preferential flow to downgradient areas in 

some parts of the West Maui Volcano is likely, no evidence is 

available indicating where these areas might be.

Recharge

Ground-water recharge generally is greatest in the 

inland mountainous regions, where rainfall is highest, but the 

plantation-scale sugarcane cultivation (and, to lesser degrees, 

pineapple and macadamia nuts) have profoundly affected the 

amount and location of recharge to the ground-water system 

in agricultural areas (Engott and Vana, 2007). Since the early 

20th century, about 100 billion gallons of surface water has 

been diverted each year from island streams for crop irrigation 

within the study area. More than half of this diverted water, 

about 59 billion gallons per year, originates outside the study 

area, in east Maui. Under natural conditions, most stream 

water would flow to the ocean; instead, stream water diverted 

for irrigation is applied to the plant-soil system, creating an 

artificial increase in ground-water recharge. 

Irrigation rates in the study area have been steadily 

decreasing since the 1970s, when large-scale sugarcane plantations began a conversion from furrow to more-efficient drip 

irrigation methods and began reducing the acreage dedicated 

to sugarcane production. However, stream diversions were 

not reduced during this period. During 1979–2004, agricultural land use decreased about 21 percent, mainly because 

of decreased sugarcane acreage. During the same period, on 

the leeward (west) side of West Maui Mountain, sugarcane 

cultivation ceased altogether. Decreasing irrigation coincided 

recently with periods of below-average rainfall, leading to 

substantially reduced recharge rates in many areas. 

Engott and Vana (2007) used a daily water-budget method 

to estimate ground-water recharge during six periods as part of 

this study. Their mass-balance procedure accounted for water 

entering (rainfall, irrigation, and fog drip), leaving (runoff, 

evapotranspiration, and ground-water recharge), and being 

stored within the plant-soil system. Estimated recharge for 

central and west Maui declined 44 percent during the period 

1926–2004. The period 1926–79 had the highest estimated 

recharge. Recharge from irrigation during this period was at 

least 50 percent higher than in any other period considered. The 
18 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

period 2000–04 had the lowest estimated recharge. Recharge 

from irrigation during this period was 54 percent of recharge 

from irrigation during 1926–79, and rainfall was the lowest of 

any period.

The spatial recharge distributions over the period 1926–

2004 (fig. 10) indicate several patterns: (1) changes in agricultural land use resulted in corresponding changes in recharge 

distribution; (2) the reduction in sugarcane irrigation rates 

resulted in less pronounced differences between the recharge 

rates of adjacent sugarcane and non-sugarcane lands; (3) in 

nonagricultural areas, the spatial recharge distributions varied 

according to the amount and spatial distribution of rainfall; 

and (4) in agricultural areas, the spatial recharge distribution 

varied with the rainfall and irrigation distribution. 

Recharge from Streams

Downstream from the area of dike-impounded water, 

where the water table of the freshwater-lens system is below 

the streambed, potential exists for streamflow infiltration to 

recharge the freshwater-lens system. The only water flowing 

in these diverted streams is runoff immediately after rainfall, 

because at other times all low flow is captured by the diversion 

ditches for irrigation. The water budget estimates (Engott and 

Vana, 2007) calculated for this study did not account for historical recharge through streambed seepage, because streams 

were dry most of the time. In the future, some streams may be 

fully or partially restored to natural flow conditions, potentially changing future recharge. The report by Engott and Vana 

(2007) did include an estimate of recharge assuming no irrigation, but did not include the effects on recharge of restoring all 

streamflow. For this report, the effects of restored streamflow 

on recharge were investigated for only the Wailuku Aquifer 

Sector, because data were unavailable elsewhere. 

Most water diverted from Waikapü, ÿÏao, and Waiehu 

Streams and Waiheÿe River is transported to the isthmus and 

used for irrigation outside the area contributing recharge to the 

Wailuku Aquifer Sector. This causes a net decrease in recharge 

to the Wailuku Aquifer Sector because of a lack of seepage 

through the streambeds of these four streams. The potential 

amount of water that is lost recharge from streambeds of these 

four streams can be estimated using gaging station and flow 

measurement data (table 1). Seepage-loss measurements were 

made in losing sections of the four streams during periods 

when streamflow was being returned to the stream or was 

overtopping the diversion. The flow measurements and the 

length of stream channel between measurements were used 

to calculate stream loss, in gallons per day per foot of stream 

channel (fig. 11). Estimates of loss rate for the same stream 

reach on different days were averaged, and these average rates 

were extrapolated to nearby reaches on the same stream where 

flow measurements were not available. The estimate of total 

streamflow loss at undiverted streamflow conditions, which 

becomes recharge to the underlying ground-water system, is 

about 12.3 Mgal/d (table 1). Streamflow-loss estimates for the 

individual streams are: Waiheÿe River, 1.3 Mgal/d; Waiehu 

Stream, 2.7 Mgal/d; ÿÏao Stream, 5.5 Mgal/d; Waikapü Stream, 

2.8 Mgal/d. Waikapü Stream has the potential to lose more 

than 7 Mgal/d at high flows, but the average diverted flow is 

only about 2.8 Mgal/d; therefore 2.8 Mgal/d is the maximum 

flow that could infiltrate on an average basis.

Discharge

Discharge from the study area is in the form of groundwater withdrawals from pumped wells, discharge to streams as 

base flow, and diffuse seepage to the ocean. Withdrawals from 

pumped wells and base flow in streams have been measured 

in most locations, although records are incomplete for some 

periods and locations. Diffuse seepage to the ocean has not 

been measured.

Withdrawals from Wells

Withdrawals from dug wells in the study area began after 

1894 and increased substantially after the first Maui-type 

skimming shaft was constructed in 1900 (Stearns and Macdonald, 1942). Reported withdrawals were compiled from published records (Stearns and Macdonald, 1942; Yamanaga and 

Huxel, 1969, 1970; Takasaki, 1972; Meyer and Presley, 2001), 

information contained in USGS files (unpub. data, USGS 

Pacific Islands Water Science Center data files), and a CWRM 

digital database (unpub. data, 2007). Stearns and Macdonald 

(1942) present withdrawal records from individual wells starting in 1902. Earlier withdrawal records are not available. During the early period of ground-water development, most of the 

water used was for sugarcane cultivation in the central isthmus 

and the Lahaina area. 

Ground-water withdrawals from the Central Aquifer Sector 

increased steadily and peaked in the 1960s and 1970s before 

declining in the 1980s (fig. 12). During 1902–49, withdrawals 

averaged about 70 Mgal/d, all from the Päÿia and Kahului Aquifer Systems. During 1950–79, average withdrawals increased to 

about 168 Mgal/d. After the 1970s, average withdrawals began 

declining and spreading out into the Makawao and Kamaÿole 

Aquifer Systems. During 1980–1999, average ground-water 

withdrawal from the Central Aquifer Sector was 107 Mgal/d. 

During 2000–06, average withdrawals decreased to about 68 

Mgal/d. The CWRM sustainable yield estimate for the Central 

Aquifer Sector is 27 Mgal/d (State of Hawaii, 1990)

Ground-water withdrawals (fig. 13) from the freshwater 

lens in the Wailuku Aquifer Sector did not begin until 1948, 

when Shaft 33 (5330-05) (fig 4.) was built above Wailuku. 

During 1948–69, most of the average withdrawal of 5 Mgal/d, 

exclusively in the ÿÏao Aquifer System, was for sugarcane irrigation. Pumping increased during the 1970s through the 1990s 

and peaked in the 2000s with all of the water pumped after 1984 

for public supply (Meyer and Presley, 2001, table 4). Average 

withdrawals from the ÿÏao Aquifer System during these decades 

were as follows: 1970–79, 13.5 Mgal/d; 1980–89, 12.7 Mgal/d; 

1990–99, 19.3 Mgal/d; and 2000–06, 21.4 Mgal/d. Withdrawal 
Ground-Water Flow System 19

Figure 10. Estimated ground-water recharge for various periods during 1926–2004, central and west Maui, Hawai‘i (modified from 

Engott and Vana, 2007).

1995-99 2000-04

1985-89 1990-94

156 ̊40’ 1980-84

21 ̊00’

20 ̊50’

20 ̊40’

156 ̊30’

156 ̊20’

study-area boundary

1926-79

0

10

20

30

40

50

100

150

200

350

MEAN ANNUAL

GROUND-WATER

RECHARGE,

IN INCHES

EXPLANATION

0 5 10 miles

0 5 10 kilometers
20 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Table 1. Streamflow loss measurements and estimates in Waikapü, ‘Ïao, and Waiehu Streams and 

Waihe‘e River, Maui, Hawai‘i

[Mgal/d, million gallons per day; ft, feet; gal/d, gallons per day; USGS PIWSC, U.S. Geological Survey Pacific Islands Water 

Science Center; Waikapü-lower total estimated loss rate is the average flow of the stream at the diversion minus the total 

estimated loss rate of the Waikapü-upper reach]

Stream Date

Flow at measurement site

(Mgal/d) Streamflow loss

(Mgal/d)

Distance 

between 

measurements

(ft)

Loss per ft of 

channel length

Upstream Downstream (gal/d/ft)

Waihe‘e 12/12/2006 1.61 1.44 0.17 908 187

Waiehu

 North 3/7/2007 2.21 1.57 .64 3,036 211

 North 3/6/2007 1.68 1.31 .37 2,376 155

 North 3/7/2007 1.57 1.30 .27 2,376 114

 North 3/6/2007 1.31 0.96 .36 3,415 104

 North 3/7/2007 1.30 0.94 .36 3,415 104

 South 7/26/2006 1.60a 1.45 .16 1,060 146

 South 7/27/2006 1.80 1.45 .35 2,642 132

 Lower 3/6/2007 1.23 0.85 .39 5,007 78

 Lower 3/7/2007 1.45 1.03 .42 5,007 84

‘Ïao

 Upper 2/11/2008 29.08 26.82 2.26 5,015 451

 Upper 2/12/2008 26.11 23.33 2.78 5,015 554

 Upper 2/13/2008 23.20 21.72 1.49 5,015 296

 Upper 2/14/2008 22.43 19.84 2.59 5,015 516

 Upper 2/15/2008 20.71 19.52 1.20 5,015 238

 Lower 2/13/2008 8.40 6.79 1.61 7,154 226

 Lower 2/14/2008 6.22 4.21 2.01 7,154 281

Waikapü

 Upper 9/6/2006 1.54 1.33 0.21 4,171 50

 Upper 5/3/2007 2.48 2.33 0.15 4,171 36

 Lower 4/2/2007 4.78 3.64 1.14 7,665 149

 Lower 3/18/2004 10.53 4.59 5.95 15,837 375

 Lower 3/18/2004 4.59 3.71 0.88 3,068 286

a

combined flow from stream and diversion

Stream

Length of 

losing reach

(ft)

Average 

loss per ft of 

channel

(gal/d/ft)

Estimated loss 

rate

(Mgal/d)

Waihe‘e 7,000 187 1.31

Waiehu-north 7,070 138 0.94

Waiehu-south 7,360 139 1.02

Waiehu-lower 9,390 81 0.76

‘Ïao-upper 8,730 411 3.59

‘Ïao-lower 7,400 253 1.87

Waikapü-upper 10,790 43 0.46

Waikapü-lower 26,570 270 2.38

Total 12.34
Ground-Water Flow System 21

Figure 11. Streamflow loss in Wailuku area streams, Maui, Hawai‘i.

began in the Waiheÿe Aquifer System in 1997. Presently (2007), 

no significant withdrawals are reported from the Waikapü and 

Kahakuloa Aquifer Systems. The CWRM sustainable yield 

estimate for the Wailuku Aquifer Sector is 38 Mgal/d (State of 

Hawaii, 1990).

In the Lahaina Aquifer Sector, wells were constructed as 

early as 1897 but withdrawal records are only available after 

1918 (Stearns and Macdonald, 1942, p. 218). Ground-water 

withdrawals increased steadily during the 1920s and averaged 33 Mgal/d during 1918–29 (fig. 14). During 1930–79, 

average withdrawals were about 44 Mgal/d, mostly from the 

Honoköwai and Launiupoko Aquifer Systems. After 1979, 

sugarcane irrigation decreased and domestic withdrawals 

began increasing and spreading into the Honolua Aquifer 

System. Average withdrawals during 1980–2000 were about 

21 Mgal/d. During 2000–06, average withdrawals decreased to 

about 4 Mgal/d. The CWRM sustainable yield estimate for the 

Lahaina Aquifer Sector is 40 Mgal/d (State of Hawaii, 1990).

Ground-water withdrawals generally follow a seasonal pattern controlled by the amount of rainfall available for irrigation. 

During 1995–2006, the withdrawals for domestic uses in the 

Wailuku Aquifer Sector were highest in July and August and the 

withdrawals for sugarcane irrigation in the Central Aquifer Sector were highest in September and October (fig. 15).

Kahului

Bay

0.17

0.27-

0.64 0.37 0.36

0.35

1.62-2.01

0.16

1.20-2.78

0.15-0.21

1.14

5.95

0.88

0.39-0.42

Kahului

Bay

1.3

1.0

0.94

1.9

concrete

concrete

3.6

0.46

2.4

0.76

Area with dike-impounded ground water

Area underlain

by sediments

at sea level

EXPLANATION

STREAM REACH AND

MEASURED INFILTRATION

RATE, IN MILLION GALLONS

PER DAY

Area with dike-impounded ground water

Area underlain

by sediments

at sea level

EXPLANATION

STREAM REACH AND

ESTIMATED INFILTRATION

RATE, IN MILLION GALLONS

PER DAY

Waikapü Stream

‘Ïao Stream

Waihe‘e River

Waiehu

Stream

Waikapü Stream

‘Ïao Stream

Waihe‘e River

Waiehu

Stream

SCALE

2.5 MILES

0 2.5 KILOMETERS

0

SCALE

2.5 MILES

0 2.5 KILOMETERS

0
22 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 12. Ground-water withdrawals from the Central Aquifer Sector, 1900–2006, Maui, Hawai‘i. Sustainable-yield values 

(dashed lines; of 2007) are from the State of Hawai‘i Commission on Water Resource Management.

0

20

40

60

80

100

ANNUAL MEAN PUMPAGE, IN MILLION GALLONS PER DAY

0

50

100

150

200

250

300 Central Aquifer Sector management area (Kahului, Kama‘ole, Makawao, and Pä‘ia Aquifer Systems)

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

20

40

60

80

100

120

140

Kahului Aquifer System

Pä‘ia Aquifer System

0

2

4

6

8 Makawao Aquifer System

0

2

4

6

8

10

12 Kama‘ole Aquifer System

Sustainable-yield estimate
Ground-Water Flow System 23

Figure 13. Ground-water withdrawals from the Wailuku Aquifer Sector, 1900–2006, Maui, Hawai‘i. Sustainable-yield values 

(dashed lines; as of 2007) are from the State of Hawai‘i Commission on Water Resource Management. No pumpage reported in 

Waikapü and Kahakuloa Aquifer systems. Pumpage for public supply shown in dark gray.

Ground-water withdrawals from the sedimentary caprock 

in Kahului are mainly for landscape irrigation or industry. 

These withdrawals may total a few Mgal/d, but records of 

these withdrawals are limited.

Base Flow to Streams

Base flow represents ground-water discharge to streams. 

Nearly all perennial streams on West Maui Volcano depend on 

ground-water discharge from the dike-impounded water body 

for their supply (Stearns and Macdonald, 1942, p. 195). No 

perennial streams are in the study area on Haleakalä. The baseflow component of streamflow can be estimated from daily 

streamflow records. Daily streamflow records are available 

from gaging stations operated on the 14 largest streams on 

West Maui Volcano by the U.S. Geological Survey (table 2). 

Some streamflow records are from gaging stations that measured streamflow upstream of any diversion, and others were 

reconstructed from records collected on ditches and tunnels 

diverting the streams of interest. Streamflow from ungaged 

streams was considered a minor part of the total streamflow 

and was not included.

The base-flow component of streamflow was estimated 

using a computerized base-flow separation method described 

by Wahl and Wahl (1995). Two variables, N (number of days) 

and f (turning-point test factor) must be assigned values in the 

method. The method divides the daily streamflow record into 

nonoverlapping N-day periods and determines the minimum 

flow within each N-day window. If the minimum flow within a 

given N-day window is less than f times the adjacent minimums, then the central window minimum is made a turning 

point on the base-flow hydrograph. Wahl and Wahl (1995) 

recommend a value of 0.9 for the turning-point test factor for 

most applications. The value of N, determined independently 

for each stream, was 4 for all streams in this study.

Because the gaging stations were established at different 

dates and over varying time lengths, the streamflow records 

ANNUAL MEAN PUMPAGE, IN MILLION GALLONS PER DAY 0

10

20

30

40 Wailuku Aquifer Sector management system (Waikapü, ‘Ïao, Waihe‘e, and Kahakuloa Aquifer Systems)

0

5

10

15

20

25 ‘Ïao Aquifer System

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

2

4

6

8

10 Waihe‘e Aquifer System

Sustainable-yield estimate
24 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 14. Ground-water withdrawals from the Lahaina Aquifer Sector, 1900–2006, Maui, Hawai‘i. Sustainable-yield values (dashed 

lines; as of 2007) are from the State of Hawai‘i Commission on Water Resource Management. No pumpage reported in Honokohau 

Aquifer system. Pumpage for public supply show in dark gray. ANNUAL MEAN PUMPAGE, IN MILLION GALLONS PER DAY

0

10

20

30

40

50

60

Lahaina Aquifer Sector management system (Honoköhau, Honolua, Honoköwai, Launiupoko, Olowalu, and Ukumehame

 Aquifer Systems)

0

2

4

6

8

10

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 

0

1

2

3

4

5

6

Honoköwai Aquifer System

Olowalu Aquifer System

0

5

10

15

20

25

30

35 Launiupoko Aquifer System

0

5

10

15

20

25

Honolua Aquifer System

Sustainable-yield estimate
Ground-Water Flow System 25

Figure 15. Average monthly ground-water withdrawal for public supply and sugarcane production in the Wailuku and Central Aquifer 

Sectors, 1995–2006, Maui, Hawai‘i.

Figure 14.—Continued.

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 

0

1

2

3

4 Ukumehame Aquifer System

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

AVERAGE MONTHLY WITHDRAWAL, IN MILLION GALLONS PER DAY

0

50

100

150

200

250

Hawaiian Commercial & Sugar Co., Inc.

 maximum, average,

and minimum withdrawal

Maui Department of Water Supply maximum, average

and minimum withdrawal
Table 2. Base flow in selected study area streams, Maui, Hawai‘i.[Mgal/d, million gallons per day; index station shown in bold; number of days (N) in base-flow separation method window is 4 for all streams (Wahl and Wah

calculated by dividing the average base flow of Honoköhau Stream during 1913–2005 by the average base flow of Honoköhau Stream during the concurrent p

Stream name USGS gaging station numbers Concurrent period of record

Average base 

flow during 

concurrent

period

(Mgal/d)

Adjustment 

factor

Average base 

flow adjusted 

to index 

station

(Mgal/d)

Co

Waikapü 16648000, 

 16649000

1913-17 6.9 0.63 4.3 Combined flow in S

Ditch and Pälolo D

ÿÏao 16604500 1983-2005 19. 1.05 20. Flow upstream of MWaiehu 16610000 1913-17 4.8 0.63 3.1 Flow in South WaieWaihe‘e 16614000 1983-2005 30. 1.05 32. Flow upstream of WKahakuloa 16618000 1939-43, 

 1947-70, 

 1974-2005

4.5 1.03 4.6

Honoköhau 16620000 1913-2005 12.3 1.00 12.3 Flow upstream of H

Honolua 16623000 1913-17 1.5 0.64 1.0 Flow upstream of HHonoköwai 16629000 1913-67 3.7 .96 3.6 Flow in HonoköwaKahoma 16633000, 

 16634000

1913-17 5.3 .64 3.4 Combined flow fro

tunnel

Kanahä 16636000 1916-32 2.9 .92 2.7 Flow upstream of pKaua‘ula 16641000 1914-17 6.8 .61 4.1 Flow upstream of KLauniupoko 16644000 1913-17 1.1 .63 0.7 Flow upstream of dOlowalu 16645000 1913-67 3.7 .96 3.6 Flow in Olowalu D

Ukumehame 16647000 1913-19 5.2 .74 3.9

Total average base flow 101.
Ground-Water Flow System 27

were adjusted to a concurrent period using gaging station 

16620000 (Honoköhau Stream near Honoköhau, Maui) as an 

index station that operated throughout the period of record 

(1913–2005). The average base flow from the index station 

streamflow record determined over the entire period that the 

index station was operated was divided by the average base 

flow from the index station streamflow record, determined for 

the concurrent period for the gaging station to be adjusted. 

This adjustment factor ranges between 0.61 and 1.05 for the 

selected gaging stations (table 2). The base flow from the 

selected gaging station was multiplied by the appropriate 

adjustment factor, determining the base flow adjusted to the 

concurrent period for the selected gaging station. Adjusted 

base flow values range from 0.67 Mgal/d in Launiupoko 

Stream to 32 Mgal/d in Waiheÿe River (table 2). Total average 

base flow during 1913–2005 from the 14 gaged streams was 

about 101 Mgal/d.

Sixteen tunnels were constructed during 1900–26 to 

increase streamflow by developing water from the dikeimpounded water body in West Maui Volcano (Stearns and 

Macdonald, 1942, p 195). Little evidence is available to determine whether these tunnels increased streamflow by capturing 

additional water not discharging to any stream or if they just 

redistributed streamflow by capturing water that would eventually discharge into the streambed farther downstream.

Water Levels

Ground-water flow directions commonly are inferred 

from ground-water levels measured in wells. Ground-water 

levels also are an indicator of changes in recharge or withdrawals from the ground-water system, and can be an indicator of freshwater-lens thickness. In the study area, groundwater levels vary spatially (horizontally and vertically) and 

temporally. 

In general, measured water levels in the study area are 

lowest near the coast. Water levels increase inland toward 

the recharge areas of West Maui and Haleakalä Volcanoes 

(Yamanaga and Huxel, 1969, 1970; Takasaki, 1972; Souza, 

1981; Meyer and Presley, 2001). On December 5, 1970, a 

ground-water-level survey was made in the central Maui 

isthmus area after wells were shut off for 10 days (Takasaki, 

1972, fig. 12). Water levels measured in the 1970 survey 

ranged between 3.2 and 17.7 ft above mean sea level (fig. 

16). An additional synoptic water-level survey was completed on May 17, 2005, on 38 wells as part of this study by 

the USGS with the assistance of staff from the County of 

Maui DWS, Hawaiian Commercial and Sugar Co., and the 

State of Hawaiÿi CWRM (U.S. Geological Survey, 2006a). 

Water levels measured on May 17, 2005, ranged from 0.84 

feet above sea level near the coast to about 637 feet above 

mean sea level in the dike-impounded aquifer. Before these 

measurements, wells were pumping on their regular pumping 

schedules. In general, measured water levels in the freshwater lens were lowest in the central isthmus and were highest 

where sediments impede flow in the ÿÏao aquifer area (fig. 

16). In the Lahaina area, simultaneous water levels were 

reported for 10 wells during February 1979 and 1980 and 

ranged between 2.0 and 6.5 ft above mean sea level (Souza, 

1981, sheet 1).

Water levels were not corrected for tidal fluctuations in 

any of the water-level surveys, nor for the effects of nearby 

actively pumping wells, and thus the water levels represent the 

configuration of the water-table surface at only a specific point 

in time. Nevertheless, the water-table configuration throughout 

the year is probably represented by the measured water levels.

Measuring points for each of the wells measured in 

the synoptic survey were resurveyed to tie all wells in to a 

common, updated sea-level datum (U.S. Geological Survey, 

2006b). Existing measuring-point elevations changed as much 

as 1.88 ft as a result of the resurvey. Owing to the measuringpoint changes, the accuracy of the historical water-level 

records became questionable, because the timing of the change 

in measuring-point elevations is unknown. The original measuring-point elevations could have been wrong initially, they 

could have changed over time owing to settling or land-surface 

change, or they could have changed abruptly due to damage, 

earthquake, or other causes. Because the timing of the measuring-point changes is unknown, water levels measured before 

October 1, 2003 (to coincide with the beginning of the USGS 

water year), were unadjusted and subsequent water levels were 

adjusted using the new measuring-point elevations.

The magnitude of the horizontal hydraulic gradient varies 

spatially and is about 0.00004–0.0002 ft/ft (about 0.2–1 ft/

mi) in the central isthmus area and about 0.0005 ft/ft (about 

2.6 ft/mi) in the Lahaina area. Burnham and others (1977, p. 

28) estimated a hydraulic gradient of about 1.6 ft/mi in the 

volcanic rocks in the isthmus near Kahului. In the Wailuku 

area, where valley-filling and caprock sediments are assumed 

to impede flow, gradients are much higher. Water-level information is not available for determining vertical gradients, but 

it is likely that near inland recharge areas, heads in the aquifer 

may decrease with depth, whereas near coastal discharge areas 

heads in the aquifer may increase with depth. 

The first successful well drilled on Maui was in the 

Lahaina area and was completed in 1883 (McCandless, 1936), 

and the first shaft or skimming tunnel (tunnel and sump constructed at or near sea level to collect water from the top of the 

freshwater lens) was constructed in 1900 in the central isthmus 

(Stearns and Macdonald, 1942, p. 126). However, published 

water levels from wells are not available earlier than 1935. 

Water levels in the central isthmus and Lahaina areas ranged 

between 2 and 7 ft above mean sea level at the time of these 

first recorded measurements (figs. 17–19). Water levels before 

development from the basaltic aquifer of the ÿÏao Aquifer 

System were first measured in 1940 in the ÿÏao Valley Test 

hole (5331-01) and ranged between about 31 and 37 ft above 

sea level during 1940–42 (fig. 18). Water levels in the Waiheÿe 

Aquifer System were first measured in 1988 and were about 

11 ft above sea level in North Waiheÿe 1 (5631-02).
28 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 16. Water-level surveys of (A) December 5, 1970 and February 1979, and (B) May 17, 2005, Maui, Hawai‘i (historical water levels 

from Takasaki, 1972, and Souza, 1981).

Kahului

Bay

Mä‘alaea 

Bay

3.6 3.5

3.6

4.0

4.3

4.9

5.7

4.2

17.7

3.8

3.7

4.0 4.4

3.9

3.4

3.3

3.5

4.3

3.9

6.2

4.0

4.0

4.0

0 5.2 5 01 seliM

0 5.2 5 10 sretemoliK

156°�40' SCALE

21°00'

20°�50'

20°�40'

156°�30'

156°�20'

EXPLANATION

AREA WITH DIKE-IMPOUNDED GROUND WATER

AREA WITH SEDIMENTS AT SEA LEVEL

WITHDRAWAL WELL

WATER-LEVEL WELL--water level next to well

symbol is in feet above mean sea level on 

December 5, 1970 (rounded to nearest tenth of a foot) 

WATER-LEVEL WELL--water level next to well

symbol is in feet above mean sea level in 

February, 1979 (rounded to nearest tenth of a foot)

@

a

3.8

@

@

@

@

@ @ @

@ @

@

@

@ @

@ @ @ @

@ @

@ @ @ @

@

@

@@ @

@ @

@ @

@ @

@ @

@@

@

@

@

@

@

@

a

a

a

a

a

a

a

a

a

a a a

a

a

a

a

a

a

a

a a

a

a

a

a

a

a

a

a

a aa

a

a

3.3

3.3

3.3

2.9

3.3

2.0

2.9 5.8

6.5

2.3

3.2

A
Ground-Water Flow System 29

Figure 16.—Continued.

Kahului

Bay

Mä‘alaea 

Bay

5.7

2.6

0.8

4.0

9.7

2.9

2.8 3.4

1.0

3.8

3.7 2.1

2.7

2.5

3.8

3.2

3.4

3.8

3.9 4.4

2.3

3.7

3.4

11.2

10.2

637

10.3

11.6

4.2

4.3

6.7

5.1

3.5 3.3

11.5

10.7

12.8

B

0 5.2 5 01 seliM

0 5.2 5 10 sretemoliK

156°�40' SCALE

21°�00'

20°�50'

20o�40'

156o�30'

156°�20'

EXPLANATION

AREA WITH DIKE-IMPOUNDED GROUND WATER

AREA WITH SEDIMENTS AT SEA LEVEL

WITHDRAWAL WELL

WATER-LEVEL WELL--water level next to well

symbol is in feet above mean sea level on 

May 17, 2005 (rounded to nearest tenth of a foot) 

@

a

3.8

@

@

@

@@@@@

@

@

@

@

@

@

@

@@@

@ @

@

@ @ @ @ @ @

@

@

@

@ @

@ @ @ @

@ @

@ @

@ @ @ @@

@ @ @@

@

@

@@@ @

@@@

@ @

@ @

@

@ @ @

@ @

@@ @@

@

@ @ @

@@ @

@

@

@ @

@ @ @

@

@

@@@@

@

a

a a

a a

a

a a

a a a

a

a

a a

a a a a

a

a

a

a

a

a

a

a

a a

a

a

a

aa

aaa
30 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 17. Measured water levels in selected wells in the 

Central Aquifer Sector, Maui, Hawai‘i.

0 2.5 Mi

0 2.5 Km

SCALE

156 ̊40’

21 ̊00’

20 ̊40’

156 ̊20’ 156 ̊00’

MAUI

area

of map

Aquifer system

boundary

@

@

@

@

@

@

@

@@

@

@

@

@

@

5331-01

5130-01

5631-01 5520-01

5431-01

5430-03

Kahului

Bay

Kula

Maliko

Kulanihakoi

Gl

Ditch

SprecklesDitch

Makawao

Pukalani

Kihei !

!

!

MAKAWAO

PÄ‘IA

KAHULUI

@ @ @

@

@ @

@ @

@ @

@

2

3

4

5

6

7

Pump 7 (5128-02)

1930 1940 1950 1960 1970 1980 1990 2000

2

3

4

5

6

7

Pu‘unënë (4928-02)

1930 1940 1950 1960 1970 1980 1990 2000 

2

3

4

5

6

7

Pump 3 (4825-01)

1930 1940 1950 1960 1970 1980 1990 2000 

2

3

4

5

6

7

Kïhei Exploratory (4824-01)

1

2

3

4

5

6

Pump 6 (5226-02)

1

2

3

4

5

6

Central Power Plant (5327-07)

1930 1940 1950 1960 1970 1980 1990 2000 

1

2

3

4

5

6

Pump 4 (5424-01)

2

3

4

5

6

7

Pump 9 (5224-02)

2

3

4

5

6

7

Pump 18 (5321-01)

1

2

3

4

5

6

Pump 17 (5422-02)

2

3

4

5

6

7

Pump 12 (5522-01)

WATER LEVEL, IN FEET ABOVE MEAN SEA LEVEL 0

1

2

3

4

5

6

Pump 8 (5227-04)

Pump 19 (5227-05)

Measuring-point

resurvey
Ground-Water Flow System 31

Figure 18. Measured water levels in selected wells in the 

Wailuku Aquifer Sector, Maui, Hawai‘i.

0 2.5 Mi

0 2.5 Km

SCALE

156 ̊40’

21 ̊00’

20 ̊40’

156 ̊20’ 156 ̊00’

MAUI

area

of map

Aquifer syste

m

boundary

@

@

@

@

@

@

@

@

@

@@

4937-01

4835-01

156 ̊30’

Waihe‘e

River

‘Ïao

Str

Honokohau

Str Kahakuloa

Str

Honolua Str

Kanaha Str

Olowalu

Str

Waikapü

Str

Ukumeham

e

Kahului

Kihei

KAHULUI

‘ÏAO

WAIKAPÜ

WAIHE‘E

KAHAKULOA

WAIHEE

1930 1940 1950 1960 1970 1980 1990 2000

2

3

4

5

6

7

Mä‘alaea 272 (4831-01)

1930 1940 1950 1960 1970 1980 1990 2000 

10

12

14

16

18

20

Waikapü 1 (5130-01)

10

12

14

16

18

20

Waikapü 2 (5130-02)

600

620

640

660

680

700

Kepaniwai Observation (5332-04)

10

5

15

20

25

Test Hole E (5430-03)

5

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Measuring-point

resurvey
32 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 19. Measured water levels in selected wells in the Lahaina Aquifer Sector, Maui, Hawai‘i.

0 2.5 Mi

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Simulation of Ground-Water Flow 33

The history of water-level decline in wells in the ÿÏao 

and Waiheÿe Aquifer Systems was documented by Meyer and 

Presley (2001). Water levels in these areas indicate seasonal 

variations and a long-term downward trend during the early 

1980s to the early 2000s (fig. 18). Water levels in several wells 

declined 7–10 feet during 1980–2000. However, water-level 

data during 2001–present show no downward trend in water 

levels. The 20-yr water-level decline (1980–2000) was caused 

by a combination of increased ground-water withdrawals 

from the aquifer over time and variations in rainfall (Meyer 

and Presley, 2001). Oki (2005a) documented a statewide 

downward trend in rainfall during 1913–2001 that may have 

contributed to the overall water-level decline. Water levels 

in the ÿÏao and Waiheÿe Aquifer Systems also are strongly 

affected by the seasonal pattern of recharge and ground-water 

withdrawals for public supply. This effect is evident at Test 

Hole E (5430-03) where measured water levels vary by about 

2–3 ft from highs in January–March, after the months when 

withdrawal is lowest, to lows in September–November, after 

the summer when withdrawal is highest (fig. 18).

Salinity

Salinity is one of the main factors controlling groundwater availability in the study area. Generally, with few exceptions, the salinity of water withdrawn from wells in the area 

increases with depth, proximity to the coast, and withdrawal 

rate. Public supply wells in the ÿÏao and Waiheÿe Aquifer Systems mostly produce water with 1 percent or less of seawater 

salinity (Meyer and Presley, 2001), but occasionally as high 

as 2.5 percent of seawater salinity (U.S. Geological Survey, 

2006c). Before the addition of irrigation water from east 

Maui surface-water sources, ground water beneath the central 

isthmus was believed to be naturally brackish (Stearns and 

Macdonald, 1942, p. 129). Many of the older, high-capacity 

irrigation wells and shafts operated by sugarcane plantations 

in central Maui produce water exceeding 4 percent of seawater salinity; some reported values are as high as 20 percent 

of seawater salinity (Stearns and Macdonald, 1942, p. 220). 

Saltwater intrusion is a problem at these wells because of the 

high withdrawal rates and low water levels.

Measuring the salinity profiles in deep open boreholes 

that fully penetrate the freshwater lens is a common method 

used in Hawaiÿi to monitor the distribution of salinity with 

depth in freshwater-lens systems. Salinity profiles are usually measured in terms of chloride concentration or of fluid 

specific conductance. For this study, seawater was assumed 

to have a chloride concentration of 19,600 mg/L and a fluid 

specific conductance of 50,000 μS/cm, values that are near 

the maximum values measured in deep boreholes (Meyer and 

Presley, 2001, p. 48). Measured values of concentration or 

fluid specific conductance were divided by 19,600 mg/L or 

50,000 μS/cm as appropriate and multiplied by 100 to obtain 

salinity in terms of percent of seawater salinity. 

Measured salinity profiles provide an indication of the 

freshwater volume in the aquifer. Collection of salinity profiles 

over time provides an indication of the changes in freshwater volume. In the ÿÏao Aquifer System, two deep wells have 

been drilled for monitoring salinity profiles. The Waiehu 

Deep Monitor well (5430-05) has been sampled for chloride 

concentration at discrete depths by the U.S. Geological Survey 

since 1985 and additionally for specific electrical conductance by the CWRM since 1999. The ÿÏao Deep Monitor well 

(5230-02) was monitored for specific electrical conductance 

by the CWRM since 2006. Salinity profiles collected from 

the Waiehu deep monitor well indicate a shallowing of the 

brackish-water transition zone and a reduction of freshwater 

thickness over time (fig. 20). Based on measurements from the 

Waiehu Deep Monitor well (U.S. Geological Survey, 2006c), 

the middle of the transition zone (depth of 50-percent seawater 

salinity) rose by about 154 ft during 1985–2006. Trends are 

not discernible from measurements in the ÿÏao Deep Monitor 

well because of limited temporal data.

Transition-zone information from the Central Aquifer 

Sector is limited to a few measurements indicating that the 

freshwater lens is relatively thin in this area. Data from two 

wells (5328-24, -43) in Kahului collected during 1936–70 

show that the middle of the transition zone was about 80–160 

ft below sea level (fig. 20) (Burnham and others, 1977, fig. 

7). Burnham and others (1977, p. 18) concluded that even 

though these data were widely spaced in time, the configuration of the transition zone in the area probably remained the 

same. Since 2002, fluid specific conductance measurements 

in the Lahaina Aquifer Sector made in the Mähinahina Deep 

Monitor well (well 5739-03) by the CWRM indicate that the 

middle of the transition zone is around 140 ft below sea level 

(fig. 20).

Salinity profiles from deep open boreholes may be 

affected by flow within the borehole (Paillet and others, 2002). 

Borehole flow can be caused by natural and withdrawalinduced vertical-head differences in the aquifer. Head may 

increase with depth in the aquifer near coastal discharge areas 

and near partially penetrating pumped wells, and increasing head in the aquifer with depth may lead to upward flow 

within an open borehole that is in hydraulic communication 

with zones of contrasting head in the aquifer. Upward borehole flow may cause saltwater to flow upward in the borehole, 

which in turn may lead to an underestimate of the freshwaterlens thickness based on the recorded salinity profile. In areas 

where head decreases with depth, downward borehole flow 

may lead to an overestimate of the freshwater-lens thickness 

based on the recorded salinity profile. 

Simulation of Ground-Water Flow

The numerical model developed for this study is a threedimensional model that simulates the transition from fresh water 

to ocean water and incorporates hydrogeologic features such as 

the sediments forming the less-permeable caprock, valley fill, 

and layer between the lavas of West Maui and Haleakalä Volcanoes. The model code used for this study was SUTRA (version 
Figure 20. Measured salinity profiles in selected wells in the study area, Maui, Hawai‘i. Salinity profiles from Burnham and others (1977) [5328-24, 

Survey data [5430-05]; and the Commission on Water Resource Management [5430-05, 5230-02, and 5739-03].

Waiehu Deep Monitor Well (5430-05)

SALINITY, IN PERCENT SEAWATER SALINITY

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Mähinahina Deep Monitor Well (5739-03) Fairgrounds 

Kahu

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08/22/1985

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Simulation of Ground-Water Flow 35

2D3D.1) (Voss and Provost, 2003), modified to account for 

water-table storage (Gingerich and Voss, 2005) using the aquifer 

specific yield. SUTRA is a finite-element code that simulates 

fluid movement and the transport of dissolved substances in a 

ground-water system. SUTRA (version 2D3D.1) is capable of 

simulating three-dimensional, variable-density ground-water 

flow and solute transport in heterogeneous anisotropic aquifers. 

Model construction was facilitated using a graphical user interface (SutraGUI) (Winston and Voss, 2003) capable of reading 

geographic information system (GIS) spatial data and writing 

files used by SUTRA (version 2D3D.1). 

Model Construction

The numerical model of ground-water flow and transport 

was developed to simulate ground-water levels and salinity 

movement within the freshwater-lens system during 1926–

2006, and it incorporates time-varying recharge, withdrawals, 

and ocean level. Model construction includes designation of 

spatial and temporal discretization, assignment of boundary 

conditions and initial conditions, and delineation of fluid and 

aquifer properties. 

Model Mesh

The model finite-element mesh used for this study 

comprises 346,256 nodes and 330,924 elements, covers the 

entire freshwater-lens system in central and west Maui, and 

extends 1–2 miles offshore to include the zone where fresh 

ground water discharges to the ocean (fig. 21). The model 

mesh excludes dike-intruded areas as described by Yamanaga 

and Huxel (1969, 1970) in the West Maui Volcano interior, 

although flow from these excluded areas to the freshwater-lens 

system is included in the model. 

The top of the onshore model domain is assumed equal 

to sea level. Although the top water-table boundary in onshore 

areas is truncated at sea level, the aquifer transmissivity is 

underestimated by less than 1 percent using this assumption. 

The top of the offshore model domain is defined by oceanbottom bathymetry (National Geophysical Data Center, 2004). 

The modeled domain extends to 5,906 ft below mean sea 

level, coinciding with an assumed aquifer bottom similar to 

that used for a Pearl Harbor model on Oÿahu (Souza and Voss, 

1987; Oki, 2005b). Node spacing is variable in the vertical 

and horizontal directions and is finest in the upper part of the 

aquifer and near areas of increased ground-water withdrawal 

and discharge. Horizontal spacing is variable but identical at 

all depths in the aquifer. Onshore, the vertical spacing between 

nodes varies from 33 ft within the top 1,312 ft of the aquifer 

to 328 ft within the bottom 1,640 ft of the modeled domain; 

offshore, the vertical spacing between nodes is dependent on 

the bathymetry within the top 1,312 ft of the aquifer, but it is 

the same as the onshore spacing within the bottom 4,594 ft of 

the modeled domain (fig. 22). 

Boundary Conditions

The model domain extent is defined by vertical boundaries that are either specified-pressure, no-flow, or recharge 

boundaries.

Specified Pressures and No-Flow Boundaries

The offshore, vertical boundaries of the model domain 

are a specified-pressure (hydrostatic ocean water) boundary 

condition. Pressure at each node along the offshore boundary 

is equal to the pressure of a column of ocean water extending 

from the node to sea level. For simulations before 1970, when 

ocean level data are not available, specified pressures were 

held constant in time. During 1970–2006, the pressures were 

varied to match the observed ocean levels at the Kahului Harbor (fig. 23). For simulations of future conditions, pressures 

also were held constant in time. Water may either enter or exit 

the flow system across the offshore vertical boundary of the 

model. Water entering along this boundary has salinity equal 

to that of ocean water, and water exiting along the boundary 

has salinity equal to that of water in the adjacent aquifer.

The top of the offshore model domain is defined by the 

ocean-bottom bathymetry (National Geophysical Data Center, 

2004) and is a specified-pressure (hydrostatic ocean water) 

boundary condition. These pressures were also held constant 

for simulations before 1970, varied to match observed ocean 

levels during 1970–2006, and held constant for simulations of 

future conditions. Ocean water may enter the model domain at 

the top of the boundary in offshore areas, and water from the 

aquifer may exit at the top boundary in offshore areas.

The eastern boundaries are formed by the northern and 

southern rift zones of Haleakalä Volcano and are treated as 

no-flow boundaries in the model. The interior model boundary 

in west Maui represents the contact between the dike-intruded 

areas and the lavas of West Maui Volcano. Flow from the dikeintruded area recharges the model along this boundary, and the 

determination of the amount and distribution of inflow to the 

model from the dike-intruded area is described below. Below 

altitudes of -98 ft, this boundary is a no-flow boundary. The 

model bottom is assumed to be a no-flow boundary.

Recharge

Recharge was added to the model for the periods 1926–

79, 1980–84, 1985–89, 1990–94, 1995–99, and 2000–04 

based on the distributions (fig. 10) estimated by Engott and 

Vana (2007). Recharge enters the model at the top, water-table 

boundary in onshore areas. Because the modeled area did 

not include the West Maui Volcano interior, recharge around 

the interior model boundary was distributed with the aid of 

a simple ground-water flow model constructed using MODFLOW-2000 (Harbaugh and others, 2000). Recharge from the 

interior boundary enters the model between altitudes of –20 ft 

and –98 ft relative to mean sea level. This interval was chosen 

because it is below the top layer of nodes, avoiding assigning two sets of recharge (lateral and areal) at the same node 
36 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 21. Model discretization and features for the numerical model mesh of central and west Maui, Hawai‘i.

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VOLCANIC-ROCK AQUIFER, UNCONFINED

WAILUKU BASALT, ‘ÏAO

WAILUKU BASALT, KÄNOA

WAILUKU BASALT, LAHAINA

WAILUKU BASALT, MÄ‘ALAEA

HONOMANÜ/KULA BASALT

HONOLUA VOLCANICS

SEDIMENTARY DEPOSITS

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RECHARGE BOUNDARY NODE (AT ALTITUDES OF -20 TO -98 FEET)-

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Simulation of Ground-Water Flow 37

Figure 22. Vertical cross section of model mesh of central and west Maui, Hawai‘i.

Figure 23. Monthly ocean level during 1970–2006 at Kahului Harbor, Maui, Hawai‘i (data from National Oceanic and Atmospheric 

Administration, 2007). 

in SUTRA, and shallow enough to avoid adding fresh water 

to a node of simulated saltwater. All recharge was assigned 

a salinity concentration of 0.000036 kg/kg, about equal to a 

chloride concentration of 20 mg/L, the average concentration 

measured in flow from a water-supply tunnel tapping the dikeimpounded water body (U.S. Geological Survey, 2006c). The 

water is assumed to be representative of recharge reaching the 

freshwater-lens system.

The MODFLOW model was constructed to represent 

the ground-water flow system of West Maui Volcano, including the low-permeability caldera and dike complexes of the 

volcano interior and the deeply incised stream valleys that 

drain much of the interior. This model, which simulates only 

freshwater flow, is applicable because the ground-water flow 

system in the dike complex is tens to thousands of feet above 

sea level and contains only freshwater. Aquifer hydraulic 

conductivity (assumed homogenous because of the lack of 

hydraulic conductivity data) and streambed leakage values 

were adjusted in the model until simulated discharge from 

the aquifer to the stream valleys for the 1926–79 recharge 

period roughly matched estimated base flow flowing from the 

volcano’s interior during the same period as determined from 

the historic records of West Maui’s stream gaging stations 

(table 3). For subsequent recharge periods, the best-fit adjusted 

values of hydraulic conductivity and streambed leakage were 

used in the MODFLOW model to calculate base flow based on 

the specified recharge for the period.

The program ZONEBUDGET (Harbaugh, 1990) was 

used to calculate the flow amount from 11 regions (roughly 

the space between adjacent streams) of the dike-impounded 

water body (fig. 21) into adjacent parts of the freshwater-lens 

system. Because no data exist to determine areas of preferential flow to the adjacent freshwater-lens system, the flow was 

distributed uniformly on the basis of the length of the boundary 

of each of the 11 regions. The amount of flow through each 

of the 11 regions as a percentage of the total flow from the 

vertical exaggeration x 10

offshore

bathymetry

0

-1,312

-1,640

-4,265

-5,906

ALTITUDE, IN FEET RELATIVE TO MEAN SEA LEVEL

Perspective view looking north of southern edge of numerical model mesh.

 0791 0891 0991 0002 6002

-1.0

-0.5

0.0

0.5

1.0

MONTHLY OCEAN LEVEL,

IN FEET RELATIVE

TO MEAN SEA LEVEL
38 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Stream name

Estimated 

average base 

flow during 

1926-79a

(Mgal/d)

Simulated 

base flow using 1926–79 

recharge

(Mgal/d)

Difference between simulated 

and estimated average base flow

Mgal/d Percent

Waikapü 4.19 5.47 1.28 31

ÿÏao 19.09 20.66 1.57 8

Waiehu 2.98 2.99 0.01 0

Waihe‘e 30.93 33.02 2.09 7

Kahakuloa 4.45 4.62 0.17 4

Honoköhau 11.91 11.12 -0.79 -7

Honolua 0.93 0.68 -0.25 -27

Honoköwai 3.50 3.88 0.38 11

Kahoma 3.31 5.47 2.16 65

Kanahä 2.59 3.12 0.53 20

Kaua‘ula 4.01 4.76 0.74 18

Launiupoko 0.65 0.00 -0.65 -100

Olowalu 3.50 3.75 0.25 7

Ukumehame 3.74 2.69 -1.05 -28

Total 95.79 102.22 6.43 7

a

Estimated from daily streamflow records

Table 3. Estimated base flow and base flow simulated with MODFLOW-2000 model 

for selected study area streams, Maui, Hawai‘i. 

[Mgal/d, million gallons per day]

Model period

Estimated recharge Estimated base 

flow to streams 

from dike 

complex

Estimated 

flow from dike 

complex to 

surrounding 

aquifers

Total recharge used 

Modeled area Dike complex in SUTRA simulation

1926–79 481 202 96 106 587

1980–84 314 218 107 111 425

1985–89 342 276 151 125 467

1990–94 241 229 113 116 357

1995–99 229 181 86 95 324

2000–04 214 163 70 93 307

Future average 

conditions

244 206 98 108 352

1998–2002 

drought 167 162 78 84 251

Table 4. Recharge for historical simulation, 1926–2006, central and west Maui, Hawai‘i. 

[All values in million gallons per day; estimated recharge from Engott and Vana (2007); total recharge used in simulation is the sum of the estimated recharge to the modeled area and the estimated flow from the dike complex; estimated base flow to streams estimated using MODFLOW simulations; estimated flow from dike complex to surrounding aquifers divided into zones based on the following percentages: zone 1–7.1%, zone 2–5.8%, zone 3–5.8%, zone 

4–5.3%, zone 5–7.0%, zone 6–5.8%, zone 7–9.3%, zone 8–12.8%, zone 9–15.1%, zone 10–13.9%, zone 11–12.1%]
Simulation of Ground-Water Flow 39

Figure 24. Selected withdrawal wells used in construction of the numerical model of central and west Maui, Hawai‘i.

dike-impounded system to the freshwater-lens system ranges 

from 5.3 percent in recharge boundary zone 4 to 13.9 percent 

in recharge boundary zone 10 (table 4). These flow percentages 

were used for each recharge period to determine the amount 

of water added to the SUTRA model along the interior boundary for the entire modeled period. Recharge across the interior 

boundary ranged between a high of 125 Mgal/d during 1985–89 

and a low of 93 Mgal/d during 2000–04 (table 4). Total recharge 

to the SUTRA model was highest during 1926–79 at 587 

Mgal/d and lowest during 2000–04 at 307 Mgal/d.

Withdrawal

Reported monthly withdrawals from wells during 

1926–2006 were simulated in the numerical model (appendix B). Reported withdrawals were compiled from published 

records (Stearns and Macdonald, 1942; Yamanaga and Huxel, 

1969, 1970; Takasaki, 1972; Meyer and Presley, 2001), information contained in USGS files (unpub. data, USGS Pacific 

Islands Water Science Center data files), and a CWRM digital 

database (unpub. data, 2007).

model boundary

model boundary

Kahului

Bay

Mä alaea 

Bay

0 5.2 5 01 seliM

0 5.2 5 10 sretemoliK

156°40’ SCALE

21°00 ́

20°50’

20°40’

156°30’

156°20’

4727-01

4426-03 4427-03

3826-01

3826-02

3826-03

4426-13

4426-14

4226-12

4126-02

4126-03

4026-04

4026-05

4026-06

3926-03 3926-02, -05 3926-04, -06 3926-09 3926-08

4727-01

4426-16

4928-02

5128-02

5228-20

5129-01

5228-17

5228-18 5230-01

5229-03

5229-02

5330-05

5330-09, -10, -11

5938-03 5938-02 5838-03 5938-01

5838-01

5838-02

5739-02 5738-01

5739-01

5638-03

5539-02

5539-01

5640-01

5641-02

5641-01

5540-03

5540-02

5540-01

5541-01

5339-03

5838-02

5340-01

5240-03

5140-01

4937-01

5138-01

4835-01 4837-01

5240-01

5341-01

5838-04

5430-01, -02 5431-02, -03, -04

5731-02 5631-02, -03

4825-01 4822-01

5021-01

5320-01

5420-02

5321-01

5422-02

5522-01

5422-01 5423-02 5423-01

5323-01

5224-02

5424-01 5525-01

5226-02 5226-045

5226-04

5326-01

5226-01

5327-01 5328-02

5328-51

5328-48

5328-01

5328-28

@

@

@

@@@@@

@

@

@

@

@

@

@

@@@

@ @

@

@ @ @ @ @ @

@

@

@

@ @

@ @ @ @ @

@ @

@ @

@ @ @ @@

@ @ @@

@

@

@@@ @

@@@

@ @

@ @

@

@ @ @4

@ @

@@ @@@@@

@

@ @ @

@@ @

@

@@

@

@ @

@ @

@

@

@

@@@@

@

EXPLANATION

AREA WITH DIKE-IMPOUNDED GROUND WATER

AREA WITH SEDIMENTS AT SEA LEVEL

WITHDRAWAL WELL AND WELL NUMBER

10

@

4426-13
40 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Withdrawal wells (fig. 24) were represented in the model 

by the nearest vertical column of nodes to the withdrawal well. 

Within the nearest vertical column of nodes from a withdrawal 

well, only those nodes corresponding to the well interval open 

to the aquifer (appendix C) were used to simulate withdrawal. 

Withdrawal from the aquifer was assumed uniform within 

the well interval open to the aquifer. Withdrawals from shafts 

with large-capacity infiltration tunnels were represented in 

the model by several nodes along the reported orientation of 

the tunnels (Takasaki, 1972). In several cases where wells 

are closely spaced, a model node represented more than one 

well. In the model, withdrawals were not simulated from the 

top layer of nodes, thus avoiding assigning areal recharge and 

pumpage at the same node in the model. 

Initial Conditions

Initial conditions for the historical simulation during 

1926–2006 were estimated from a steady-state simulation 

using average (1926–79) recharge and average withdrawals 

for the period 1902–26. Average total recharge of 587 Mgal/d 

was used in the steady-state model, and simulated withdrawal, 

mainly from sugar irrigation wells, was about 39 Mgal/d. 

A two-step iterative process was used to determine model 

adjusted hydrologic properties and initial conditions. Firstly, 

selected hydrologic properties were adjusted to improve the 

match between simulated heads and salinities, and historically 

measured values during the simulation of 1926–2006 conditions; and secondly, the steady-state simulation was repeated 

with the adjusted properties to compute new initial conditions. 

The process was repeated until the change in model adjusted 

hydrologic properties was small.

Representation of Hydrologic Features

Several hydrogeologic features of low permeability 

were represented in the numerical model. Valley-fill barriers 

associated with Waikapü and ÿÏao Valleys were represented as 

partially penetrating, vertical, low-permeability zones continuing inland from the low permeability sedimentary wedge (fig. 

21). The penetration depth of the valley-fill barriers is uncertain because of a paucity of available information. The final 

location of the valley-fill barrier representing Waikapü Valley 

was determined through trial and error by matching the head 

differences measured on either side of the presumed feature. A 

simulated valley-fill barrier was not required beneath Waiheÿe 

Valley to match the drop in head across the valley. 

A uniform thickness of about 800 ft was specified for the 

sedimentary layer between West Maui Volcano and Haleakalä 

on the basis of stratigraphic information from one well and the 

assumed slope of the top of the Wailuku Basalt. The Wailuku 

Mill Test Hole (5330-04) (fig. 4) likely penetrated lavas from 

Haleakalä between altitudes of -16 and -191 ft and sediments 

below the lavas to -524 ft (Meyer and Presley, 2001, fig. 9). 

The slope of the top of the Wailuku Basalt beneath the location 

of this test hole projects to an altitude of -1,000 ft, indicating 

that the total thickness of the sedimentary wedge is at least 

800 ft (from about -200 to about -1,000 ft altitude).

Water Properties

Water was assigned a fluid compressibility of 2.14x10-8

ft2 lb-1 (4.47x10-10 Pa-1) and a dynamic viscosity of 2.1x10-5

slug ft-1 s-1)[1.00x10-3 kg m-1 s-1)]. Solute concentrations in the 

model are expressed as a mass fraction: mass of total dissolved solids (TDS) per unit mass of fluid. Freshest water was 

assigned a TDS concentration of zero and 100 percent ocean 

water was assigned a TDS concentration of 3.57x10-2 kg/kg. 

The density of water was assumed to increase linearly with 

salinity from 62.42 lb ft-3 (1,000 kg m-3) for freshwater to 

63.98 lb ft-3 (1,024.99 kg m-3) for ocean water.

Molecular diffusion (Fickian) of a solute is driven by 

concentration gradients in the fluid and may take place in the 

absence of ground-water flow. Molecular diffusion of a solute in 

a fluid is characterized by the molecular diffusivity, which was 

assigned a value of 1.1x10-8 ft2

/s (1.0 x10-9 m2/s) in the model.

Aquifer Properties

For the numerical model, aquifer properties were 

assigned values based on published estimates. Matrix compressibility was assigned a value of 1.2x10-7 ft2

 lb-1 (2.5x10-9

Pa-1) (Souza and Voss, 1987). For all aquifers, the values of 

effective porosity (and of specific yield for the top onshore 

nodes of the mesh) used in the model were 0.15 (table 5). 

The effective porosity values used in the model are within the 

range of previously estimated values for basaltic-rock aquifers 

on Oÿahu (Souza and Voss, 1987) but greater than values used 

in the simulation of the Pearl Harbor aquifer (Oki, 2005b). 

The larger values improved the match between measured and 

simulated salinity profiles and the historical shallowing of the 

transition zone. Smaller values of effective porosity caused 

the simulated transition zone to rise much faster than was 

measured in the Waiehu Deep Monitor Well (5430-05). One 

possible explanation for a higher effective porosity of basaltic rocks on Maui than on Oÿahu is that the rocks on Maui 

are younger (< 1.5 Ma for Maui compared to 2.6-1.8 Ma for 

Oÿahu) and therefore less exposed to weathering which typically reduces the rock porosity.

For all basalt units the transverse dispersivity was assigned 

a value of 0.66 ft (0.20 m), and for sedimentary and valley-fill 

deposits the value was 3.3 ft (1.0 m) (Souza and Voss, 1987) 

(table 5). Longitudinal dispersivity was assigned a value of 

250 ft (76 m) in the horizontal direction (corresponding to the 

major and semi-major axes of the permeability tensor) (Souza 

and Voss, 1987) and 25 ft (7.6 m) in the vertical direction (corresponding to the minor axis of the permeability tensor). 

The hydraulic-conductivity values for the different 

geologic features initially were estimated on the basis of 

published information (Rotzoll and others, 2007) and were 

adjusted in the numerical model to provide a better match 
Simulation of Ground-Water Flow 41

Parameter Estimated value

Hydraulic conductivity (ft/d) Vertical Horizontal, transverse Horizontal, longitudinal

Wailuku Basalt, ‘Ïao 0.38 200 300

Wailuku Basalt, Känoa 2.62 699 2,097

Wailuku Basalt, Lahaina 10.49 699 2,097

Wailuku Basalt, Mä‘alaea 9.72 2,593 7,778

Honolua Volcanics 0.08 0.08 0.08

Honomanü/Kula Basalt 13.85 3,694 11,083

Sedimentary deposits 0.38 17 17

Valley-fill barriers 0.69 6.9 6.9

Dispersivity (ft) Transverse Longitudinal, 

minimum

Longitudinal, 

middle and maximum

All volcanic units 0.66 25 250

Sedimentary and valley-fill deposits 3.30 25 250

Porosity (and specific yield) 0.15

Solid-matrix compressibility (ft2

/lb) 1.2x10-7

[ft, feet; ft/d, feet per day; ft2/lb, feet squared per pound]

Table 5. Aquifer-property values used in the construction of the numerical ground-water model of central and 

west Maui, Hawai‘i. 

to measured water levels and salinity profiles from selected 

wells in the study area. Horizontal hydraulic-conductivity 

values used in the model ranged between 0.08 ft/d for Honolua 

Volcanics and 11,083 ft/d for the volcanic-rock aquifers of 

Haleakalä (table 5). Horizontal hydraulic-conductivity values 

for the volcanic-rock aquifers in the model were highest 

along the assumed longitudinal axis of the surficial lava flows 

(approximately perpendicular to the existing topographic contours) and generally one-third as much along the transverse 

axis. Vertical hydraulic conductivity of the volcanic-rock 

aquifers in the model was 0.00125 to 1 times lower than the 

longitudinal hydraulic conductivity. Horizontal hydraulic 

conductivity of the sedimentary caprock is 17 ft/d and vertical hydraulic conductivity is 0.69 ft/d. The valley-fill barriers 

were modeled using a horizontal hydraulic conductivity of 6.9 

ft/d and a vertical hydraulic conductivity 10 times lower.

Simulated Historical Conditions 1926–2006

Transient historical conditions were simulated using 

15-day time steps during 1926–2006 and initial conditions 

derived from the steady-state simulation. Withdrawal rates 

varied monthly, recharge rates were steady for each of the 

six recharge periods, and specified pressures representing the 

ocean varied monthly after 1970. Hydraulic properties used in 

the model were initially based mainly on previous estimates 

but were adjusted in the model to obtain better agreement 

between simulated and measured water levels and measured 

salinity profiles. The main hydrologic parameters controlling 

flow in the Wailuku Aquifer Sector are the hydraulic conductivity of the valley-filling deposits and the sedimentary 

caprock and the effective porosity of the basalt aquifer. The 

high initial water levels (greater than 30 ft) could only be 

simulated by creating barriers to the eastward flow of ground 

water toward the isthmus and the north/south flow of ground 

water toward the coast at Waiheÿe and Mäÿalaea. 

The final distribution of hydrologic parameters was determined through an extensive trial and error process to determine the most likely values. The trial and error fitting process 

included matching long-term water level changes throughout 

the system over tens of years, matching short-term changes 

over a few months at individual wells, matching hydrologic 

gradients from well to well and from wells to the coast, matching salinity profile changes over tens of years, and matching 

salinities at individual pumped wells. Aquifer properties were 

adjusted in a wide range of reasonable values and a suitable 

combination of property values was found that produced a 

reasonable match between simulated heads, gradients, and 

salinities to the historic hydrologic data.

Water Levels

Simulated water levels generally are in agreement with 

measured water levels from representative wells in the modeled 

area (fig. 25). Measured and simulated water levels in the Wailuku Aquifer Sector decline beginning about 1950 after pumping in this area began. Although measured water levels in the 

Central and Lahaina Aquifer Sectors are scarce, the simulated 

water levels match their relatively smaller declines throughout 

the simulated period near areas of higher withdrawal. Where 
42 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 25. Measured (black and green lines) and simulated (red lines) water levels in selected wells in central and west Maui, 

Hawai‘i. Well number shown in parentheses after well name.

5

10

15

20

25

30

WATER LEVEL, IN FEET ABOVE SEA LEVEL

0

2

4

6

8

10

0

2

4

6

8

1930 1940 1950 1960 1970 1980 1990 2000 

5

10

15

20

25

30

35

1930 1940 1950 1960 1970 1980 1990 2000 

-10

-5

0

5

10

15

20

25

30

35

-2

0

2

4

6

8

0

2

4

6

8

5

10

15

20

25

30

0

5

10

15

0

5

10

15

Pump 17 (5422-02) Pump 8 (5227-04)

Kïhei exploratory (4824-01) Waiohuli Exploratory (4422-01)

Känoa Test Hole (5731-05) North Waihe‘e 1 (5631-02)

Test Hole A (5631-01)

Test Hole E (5430-03)

Waiehu Deep Monitor (5430-05)

Test Hole T-112 (5330-03) Shaft 33 (5330-05)

Wailuku Aquifer Sector

Central Aquifer Sector

Pump 19 (5227-05)
Simulation of Ground-Water Flow 43

Figure 25.—Continued.

0

2

4

6

8

10

0

2

4

6

8

10

1930 1940 1950 1960 1970 1980 1990 2000 

0

2

4

6

8

10

1930 1940 1950 1960 1970 1980 1990 2000

-2

0

2

4

6

8

0

2

4

6

8

10

5

10

15

20

25

30

Waikapü 1, 2 (5130-01, -02)

‘Alaeloa (5840-01)

Pump M (5340-01) Pump N (4937-01)

Näpili A (5838-01)

Mä‘alaea 272 (4831-01)

Lahaina Aquifer Sector

EXPLANATION

MEASURED WATER LEVEL

 BASED ON ORIGINAL MEASURING 

 POINT

 BASED ON REVISED MEASURING POINT 

 AFTER 2003 RESURVEY (U.S. Geological

 Survey, 2006)

SIMULATED WATER LEVEL
44 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

original and revised measuring points are available, the historic 

water levels are plotted using both measuring points, because 

the timing of the measuring-point changes is unknown.

Because recharge in the historical model was based 

on average estimates over 53 years during 1926–79 and for 

5-yr periods afterward, interannual variations in water levels 

caused by interannual variations in recharge were not simulated. Some interannual variability in water levels was simulated, however, because of withdrawal variations. The match 

of simulated and measured water levels improves after 1979, 

when the recharge periods are reduced to 5-yr increments.

The effects of including ocean-level variations in the 

historical simulation are most apparent at wells near the coast 

and away from areas of relatively lower permeability sedimentary deposits. Simulated water levels at the Kïhei Exploratory 

well (4824-01), Mäÿalaea 272 (4831-01), and ÿAlaeloa well 

(5840-01) reasonably match short- and long-period observed 

water-level variations. For example, the increase in ocean 

level of about 0.5 ft during 2000–04 (fig. 25) is reflected by 

the increase in water levels in these three wells during a time 

when recharge rates were relatively lower and withdrawal near 

these wells was not decreasing.

Within the Wailuku Aquifer Sector, simulated water 

levels generally match measured water levels, especially after 

2000 (fig. 26). Within the Central and Lahaina Aquifer Sectors, simulated water levels are slightly higher than measured 

water levels in some areas and slightly lower in others, with no 

apparent bias to a particular area.

Some of the discrepancy between measured and simulated water levels can be attributed to uncertainties in the 

estimated distribution of hydraulic properties in the numerical 

model. Some discrepancy also may be related to other factors including: (1) few reported predevelopment water levels 

are available in the ÿÏao area and none are available north of 

Waiheÿe River, (2) temporally coarse 5-yr recharge estimates 

may not reflect conditions antecedent to the day when water 

levels were measured, (3) reported ground-water withdrawal 

information may be inaccurate, (4) some of the measured 

water levels are from pumping wells and therefore may reflect 

only local aquifer conditions near the well, (5) model spatial 

discretization may be too coarse in some areas to accurately 

simulate local water level changes.

During 1926–2006, simulated ground-water levels 

decline the most in the Wailuku Aquifer Sector because 

of increased withdrawal and decreased recharge (fig. 27). 

Simulated water levels have declined more than 25 ft near the 

Waiheÿe (5431-02, -03, -04) and Waiehu Heights (5430-01, 

-02) wells. Beneath the isthmus in the Central Aquifer Sector, 

simulated water levels declined 1–4 ft, mainly because of 

decreased recharge. Simulated water levels declined 1–2 ft in 

parts of the Lahaina Aquifer Sector.

Salinity Profiles

Before about 1985, useful salinity profiles from deep 

monitor wells in the study area were limited to only one well, 

the Fairground well (5328-24), where a single profile is available from 1936 (fig. 20). Salinity profiles have been collected 

quarterly in the Waiehu Deep Monitor well (5430-05) since 

1985 and the Mähinahina Deep Monitor well (5739-03) since 

2002. A few profiles from the new ÿÏao Deep Monitor well 

(5230-02) between ÿÏao and Waikapü Streams are available, 

but only since 2005, and so they are not compared with results 

from the historical simulation. Measured salinity profiles in 

the Waiehu Deep Monitor well indicate a shallowing of the 

brackish-water transition zone over time, and simulated salinity profiles are consistent with this trend (fig. 28). The simulated trend of the depth where the water is 50-percent seawater 

fits the measured values best for the more recent data, rising a 

little more than about 6 ft/yr during 1995–2006. The simulated 

trend of the depth where the water is 2-percent seawater shows 

a more rapid shallowing than was measured in the Waiehu 

Deep Monitor well. The shapes of the simulated salinity profiles also generally are consistent with the measured profiles. 

At the Waiehu Deep Monitor well, simulated and measured 

depths where salinity is 50 percent that of seawater are within 

about 16 feet of each other at the end of the historical simulation. At the Mähinahina Deep Monitor well (5739-03), the 

simulated depth where salinity is 50 percent that of seawater is 

about 80 ft deeper than the measured depth at the end of 2006 

(fig. 29). At the Fairgrounds Test Hole (5328-24), the simulated 50- percent depth is about 150 ft lower than the measured 

depth. These wells are in areas where water-level data are 

scarce; therefore, the modeled water levels and thickness of 

the freshwater lens may be too high and too large, respectively. 

The scarce data and the lower priority interest of these areas in 

this study, little effort was spent adjusting aquifer properties in 

the model to improve the agreement between these simulated 

and measured profiles. 

Some of the discrepancy between measured and simulated salinity profiles can be attributed to (1) uncertainties 

in the estimated distribution of hydraulic properties in the 

model, (2) possible borehole flow in the deep monitor wells 

(Paillet and others, 2002), (3) insufficient vertical discretization in the numerical model mesh, and (4) additional factors 

described above for simulated water levels. Borehole flow in 

the deep monitor wells can cause a lack of agreement between 

the simulated and measured profiles. The simulated profile is 

computed using the freshwater head near the transition zone, 

whereas the measured profile is influenced by the water level 

in the open well or borehole, which (because of the vertical 

hydraulic communication created by the open borehole and 

the accompanying intra-borehole flow) represents a composite 

head in the interval of aquifer penetrated by the well. Near the 

coast, the head at depth tends to be greater than at the water 

table, so the water level in an open well near the coast that 

penetrates a large interval of the aquifer will tend to be lower 

than that of the surrounding aquifer at the water table. Hence, 

the midpoint of the measured salinity profile in the well will 

tend to be shallower than in the aquifer.

The simulated depth where water in the aquifer has 

50-percent seawater salinity is deeper than 700 ft below sea 
Simulation of Ground-Water Flow 45

Figure 26. Measured water levels on (A) December 5, 1970, and (B) May 17, 2005, compared with simulated water levels in central and 

west Maui, Hawai‘i.

Kahului

Bay

Mä‘alaea 

Bay 5

5

5

4

3

2

1

6

6

7

10

15

30

35

25

20

9

8

7

4 6

5

6

7

8

3

2

1

6

7

4

3

2

1

3.6 3.5

3.6

4.0

4.3

4.9

5.7

4.2

17.7

3.8

3.7

4.0 4.4

3.9

3.4

3.3

3.5

4.3

3.9

6.2

4.0

4.0

4.0

0 5.2 5 01 seliM

0 5.2 5 10 sretemoliK

156°�40' SCALE

21°00'

20°�50'

20°�40'

156°�30'

156°�20'

EXPLANATION

AREA WITH DIKE-IMPOUNDED GROUND WATER

AREA WITH SEDIMENTARY DEPOSITS AT SEA LEVEL

WITHDRAWAL WELL

WATER-LEVEL WELL--water level next to well

symbol is in feet above mean sea level (rounded to

nearest tenth of a foot) December 5,1970 

LINE OF EQUAL SIMULATED WATER LEVEL,

 IN FEET--Interval is variable

@

10

a

model boundary

model boundary

@

@

@

@

@ @ @

@ @

@

@

@ @

@ @ @ @

@ @

@ @ @ @

@

@

@@ @

@ @

@ @

@ @

@ @

@@

@

@

@

@

@

@

a

a

a

a

a

a

a

a

a

a a a

a

a

a

a

a

a

a

a a

a

a

A
46 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 26.—Continued.

Kahului

Bay

Mä‘alaea 

Bay

6

5

4

10

25

3

1

2

3

4 5

6

7

8

9

10

20

4

3

2

1

3

4

1

2

5

7

6

5

4

3

2

1

15

5

6

5.7

2.6

0.8

4.0

9.7

2.9

2.8 3.4

1.0

3.8

3.7 2.1

2.7

2.5

3.8

3.2

3.4

3.8

3.9 4.4

2.3

3.7

3.4

11.2

10.2

637

10.3

11.6

4.2

4.3

6.7

5.1

3.5 3.3

11.5

10.7

12.8

B

0 5.2 5 01 seliM

0 5.2 5 10 sretemoliK

156°�40' SCALE

21°00'

20°�50'

20°�40'

156°�30'

156°�20'

EXPLANATION

AREA WITH DIKE-IMPOUNDED GROUND WATER

AREA WITH SEDIMENTARY DEPOSITS AT SEA LEVEL

WITHDRAWAL WELL

WATER-LEVEL WELL--water level next to well

symbol is in feet above mean sea level (rounded to

nearest tenth of a foot) May 17, 2005 

LINE OF EQUAL SIMULATED WATER LEVEL,

 IN FEET--Interval is variable

@

10

a

model boundary

model boundary

@

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@@@

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@ @

@

@ @ @

@ @

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@

@ @ @

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@

@

@ @

@ @ @

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@

a

a a

a a

a

a a

a a a

a

a

a a

a a a a

a

a

a

a

a

a

a

a

a a

a

a

a

aa

aaa
Simulation of Ground-Water Flow 47

Figure 27. Simulated water-level changes between 1926 and 2006 in central and west Maui, Hawai‘i.

Kahului

Bay

Mä‘alaea 

Bay

1

2

2

2

3

3 4

20

10

5

1

1

0 5.2 5 01 seliM

0 5.2 5 10 sretemoliK

156°�40’ SCALE

21° �00’

20°�50’

20°�40’

156°�30’

156°�20’ @

@

@

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@

@

@

@

@

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@ @

@

@ @ @ @ @ @

@

@

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@

EXPLANATION

AREA WITH DIKE-IMPOUNDED GROUND WATER

WITHDRAWAL WELL @

WATER-LEVEL DECLINE, IN FEET

 1 to 5

 5 to 10

 10 to 15

 15 to 20

 20 to 25

model boundary

model boundary
48 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 28. Measured and simulated altitude of the top (2-percent seawater) and middle (50-percent 

seawater) of the transition zone in the Waiehu Deep Monitor well (5430-05), Maui, Hawai‘i.

level in part of the Wailuku Aquifer Sector (fig 30). The 

50-percent salinity contours generally follow the pattern of the 

simulated water-level map (fig. 26), being deeper inland where 

water levels are higher. Withdrawal wells that are drilled 

deeper than the CWRM’s recommended well depth guidelines 

compared to simulated salinity are shown in red in figure 26. 

The CWRM recommends that new wells be drilled no deeper 

than 1⁄4 of the depth to 50-percent seawater salinity (State of 

Hawaiÿi, 2004).

Simulated Future Scenarios

The numerical model constructed for this study was used 

to quantify changes in ground-water level and salinity with 

continued ground-water withdrawal under various withdrawal 

and recharge scenarios (table 6). Scenarios included groundwater withdrawal at 2006 rates and locations with 2000–04 

land use and 1926–2006 rainfall (scenario 1), withdrawal at 

1996 rates and locations with 2000–04 land use and 1926–

2006 rainfall (scenario 2), and withdrawal at redistributed rates 

and locations using various recharge scenarios (scenarios 3–7). 

Scenarios 1–3 and 5–7 were simulated for 2007–2157 and 

scenario 4 for 2007–2037. Most of the scenarios were continued for 150 years to reach equilibrated hydrologic conditions, 

when no significant water-level or salinity changes are apparent. Scenario 2, with 1996 withdrawal rates and locations, 

represents the historical condition with the highest withdrawal 

rates from the fewest wells in the ÿÏao Aquifer System. In this 

scenario, withdrawal after 1996 was maintained at the 1996 

rates through the end of the 150-yr scenario. The simulated 

initial conditions for all other scenarios were the final conditions from the 1926–2006 historical simulation. 

For each simulation, the simulated salinity at selected 

pumping wells is classified as: (1) acceptable, salinity less 

than 1.0 percent seawater; (2) cautionary, salinity between 1.0 

and 2.5 percent seawater; and (3) threatened, salinity greater 

than 2.5 percent seawater. Wells with simulated salinity in the 

cautionary class have the potential to produce water with salinity higher than is acceptable for drinking. Wells with simulated 

salinity in the threatened class are likely to produce water 

unacceptable for drinking. This classification was developed 

cooperatively with the DWS to provide a basis for comparing the various scenarios investigated in this study. At several 

sites, the simulated water levels and salinities are shown for the 

location in the model representing the deepest well (or representative well if depths are similar) in the group of closely spaced 

wells (referred to hereafter as a well field). The Känoa Test Hole 

DATE

1930 1940 1950 1960 1970 1980 1990 2000 

ALTITUDE, IN FEET

-1,000

-800

-600

-400

-200

0

Measured 50-percent seawater concentration

Measured 2-percent seawater concentration

Simulated 2-percent seawater concentration

Simulated 50-percent seawater concentration

2006
Figure 29. Measured and simulated salinity profiles in selected wells in central and west Maui, Hawai‘i.

Waiehu Deep Monitor Well (5430-05)

SALINITY, IN PERCENT SEAWATER SALINITY

0 20 40 60 80 100

-1000

-800-600-400-200

0

12/2006 (simulated)

9/1995 (simulated)9/1985 (simulated)

1/7/2007

8/31/1995

8/22/1985

Fairgrounds Test Hole (5328-24)

0 20 40 60 80 100

ALTITUDE, IN FEET BELOW SEA LEVEL

-1000

-800-600-400-200

0

5/22/1936

1936 (simulated)

Mähinahina Deep 

0 20 40 

-1000

-800-600-400-200

0

2005 (sim

2002 (sim

1/20/20052/6/2002
50 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 30. Simulated depth of 50-percent seawater salinity at end of historical simulation (2006) and locations of wells penetrating 

deeper than 1⁄4 of the simulated depth to 50-percent seawater salinity in central and west Maui, Hawai‘i.

Kahului

Bay

Mä‘alaea 

Bay

-100

-100

-100

-200

-200

-200

-200

-200

-300

-300

-400

-400

-500

-600

-700

0 5.2 5 01 seliM

0 5.2 5 10 sretemoliK

156°�40’ SCALE

21°�00’

20°�50’

20°�40’

156°�30’

156°�20’

EXPLANATION

AREA WITH DIKE-IMPOUNDED GROUND WATER

WITHDRAWAL WELL--well shown in red when

bottom of well is deeper than 1/4 of the depth to

50-percent seawater salinity

LINE OF EQUAL DEPTH OF 50-PERCENT

SALINITY, IN FEET--Interval is 100 feet

-200
Simulation of Ground-Water Flow 51

Scenario Recharge condition Pumping condition in Wailuku Aquifer Sector 

Management Area

1 350 Mgal/d: 2000–04 land use with 1926–2004 rainfall 21.4 Mgal/d: 2006 withdrawal rates

2 350 Mgal/d: 2000–04 land use with 1926–2004 rainfall 20.1 Mgal/d: 1996 withdrawal rates

3 350 Mgal/d: 2000–04 land use with 1926–2004 rainfall 27.1 Mgal/d: Redistributed withdrawal

4 251 Mgal/d during drought: 2000–04 land use with1926–2004 

rainfall with worst historic drought (1998–2002 rainfall) 

during 2017–2022

27.1 Mgal/d: Redistributed withdrawal

5 362.3 Mgal/d: 2000–04 land use with 1926–2004 rainfall plus 

12.3 Mgal/d of recharge from four ÿÏao/Waiheÿe area streams

27.1 Mgal/d: Redistributed withdrawal

6 354.1 Mgal/d: 2000–04 land use with 1926–2004 rainfall plus 

4.1 Mgal/d of recharge from four ÿÏao/Waiheÿe area streams

27.1 Mgal/d: Redistributed withdrawal

7 274 Mgal/d: Natural land use with 1926–2004 rainfall plus 

12.3 Mgal/d of recharge from four ÿÏao/Waiheÿe area 

streams

27.1 Mgal/d: Redistributed withdrawal

Table 6. Withdrawal and recharge used in various simulation scenarios, central and west Maui, Hawai‘i. 

[All simulations are from 2007–2157, except scenario 4 from 2007–2037; Mgal/d, million gallons per day]

(5731-05) represents the Känoa well field of Känoa 1 (5731-

02) and Känoa 2 (5731-04); North Waiheÿe well field includes 

North Waiheÿe 1 (5631-02 [deepest]) and North Waiheÿe 2 

(5631-03) wells; Waiheÿe well field includes Waiheÿe 1 (5431-

02 [deepest]), Waiheÿe 2 (5431-03), and Waiheÿe 3 (5431-04); 

Waiehu Heights well field includes Waiehu Heights 1 (5430-01 

[deepest]) and Waiehu Heights 2 (5430-02); Mokuhau well field 

includes Mokuhau pump 2 (5330-09), Mokuhau pump 1 (5330-

10), and Mokuhau pump 3 (5330-11).

Scenario 1—2006 Withdrawal Rates and Locations 

with 2000–04 Land Use and 1926–2006 Rainfall

In scenario 1, the most likely future average recharge and 

most recent withdrawal estimates were used to simulate the 

effects of continuing the current conditions over the next 150 

years. Assigned total recharge over the model domain was 350 

Mgal/d, based on 2000–04 land use and 1926–2006 rainfall 

(table 6). Total withdrawal was simulated in two ways on the 

basis of reported 2006 withdrawal rates using (1) monthly 

rates and (2) average annual rates. This approach was used to 

determine whether using average annual rates, which provide 

faster and slightly more stable model solutions versus using 

monthly rates, was acceptable. Total withdrawal averaged 69 

Mgal/d throughout the modeled area, with about 21.4 Mgal/d 

from the Wailuku Aquifer Sector (16.8 Mgal/d from ÿÏao and 

4.6 Mgal/d from Waiheÿe Aquifer Systems). 

Model results indicate that for most wells, average annual 

withdrawal rates provide the same long-term trends computed 

using monthly withdrawal rates (fig. 31). For each well shown, 

the simulated water level is the average of the water levels of 

the nodes representing the well and the simulated salinity is for 

the deepest node representing the well. The exception to this is 

the Waiehu Deep Monitor well (5430-05), where the simulated 

water level is determined nearer the top of the well’s open 

interval at -138 ft. The depths of the nodes used are shown 

under each well name and number. Simulated seasonal waterlevel fluctuations, caused as pumping varies throughout the 

year, are centered about the water levels at annual average rates 

for all of the wells pictured. The largest seasonal fluctuations, 

about 4 ft/yr, are near the Waiheÿe and Mokuhau well fields (as 

indicated by Waiheÿe 1 (5431-02) and Mokuhau 2 (5330-09) 

wells, respectively). Long-term average water-level differences 

are 2–3 ft lower than the starting water levels after 150 years in 

many of the wells. Simulated salinity values are the same for 

both withdrawal methods in the wells with the freshest water 

but slightly higher for the simulated monthly withdrawals in the 

wells where salinity is increasing over time. This result is consistent with the understanding that cyclical withdrawal from a 

freshwater-lens system tends to increase mixing of water in the 

aquifer. The largest long-term simulated salinity increases are 

at the Küpaÿa well (5731-03) and Känoa well field (as indicated 

by Känoa Test Hole (5731-05)), where the salinity increases 

by about 1-percent seawater salinity over 150 years. The largest seasonal fluctuations, at the Känoa well field, are about 

0.5-percent seawater salinity. Near the Waiehu Heights well 

field, the model develops a numerical instability, when monthly 

pumping rates are used, most likely because of numerical 

dispersion near the top of the transition zone enhanced by the 

monthly change in withdrawal rates in the well. This instability 

goes away when yearly pumping rates are used.

The simulated depths of the bottom of freshwater and the 

middle of the transition zone at the Waiehu deep monitor well 

continue to shallow and are about 250 ft shallower after 150 

years (fig. 32). These results are identical for both simulated 

withdrawal methods. Regional changes of average water levels 

in the aquifer after 150 years, presented relative to conditions 

at the end of the 1926–2006 historical simulation, are greatest 
52 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 31. Measured (black and green lines) and simulated water-level (red lines) and simulated salinity data (blue lines) for Scenario 1 

using monthly and yearly pumping rates at selected wells in the Wailuku Aquifer Sector, 2000–2157, Maui, Hawai‘i. For each well shown, the 

simulated water level is the average of the water levels of the nodes representing the well and the simulated salinity is for the deepest node 

representing the well. The exception to this is the Waiehu Deep Monitor well (5430-05), where the simulated water is determined nearer the 

top of the well’s open interval at -138 ft. The depths of the nodes used are shown under each well name and number.

0

5

10

15

20

0.0

0.5

1.0

1.5

2.0

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2000 2025 2050 2075 2100 2125 2150 

5

7

9

11

13

15

17

0.0

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0.4

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0.8

1.0

WATER LEVEL, IN FEET ABOVE SEA LEVEL

2000 2025 2050 2075 2100 2125 2150 

5

7

9

11

13

15

0.0

0.5

1.0

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2.0

SALINITY, IN PERCENT RELATIVE TO SEAWATER

beginning of scenario

simulated water level (monthly rates)

simulated water level (yearly rates)

simulated salinity (monthly rates)

simulated salinity (yearly rates)

measured water level

Shaft 33 (5330-05)

0 to -164 ft

Mokuhau 2 (5330-09)

-197 ft

North Waiheÿe 1 (5631-02)

-33 to -99 ft

Känoa Test Hole (5731-05)

0 to -33 ft

Küpaÿa (5731-03)

0 to -66 ft

Waiheÿe 1 (5431-02)

-197 ft

Waikapü 1 & 2 (5130-01, -02)

-33 ft

Test Hole A (5631-01)

-33 ft

Waiehu Deep Monitor Well (5430-05)

-164 ft

0

1

2

4

3

5

10

15

20

Waiehu Heights 1 (5430-01)

-328 ft

numerical instability

in model
Simulation of Ground-Water Flow 53

Figure 32. Measured 

and simulated positions of 

the bottom of freshwater 

(2-percent seawater 

salinity) and middle 

of the transition zone 

(50-percent seawater 

salinity) for Scenario 1 at 

the Waiehu Deep Monitor 

well (5430-05), 2000–2157, 

Maui, Hawai‘i.

inland of the four main well fields in the ÿÏao Aquifer System, where average water-level differences are 1–3 ft lower 

(fig. 33). Near the well fields in the Waiheÿe Aquifer System, 

average water-level differences are higher by less than a foot. 

However, this apparent rise results because water levels at the 

end of the historical simulation are available only at the time 

in the yearly pumping pattern when withdrawal is highest, 

whereas the water levels at the end of the 150 years are from 

a time when the withdrawal is lowest. Even though average 

water levels are about 1 ft lower, the monthly low water level 

at the beginning of the simulation is lower than the monthly 

high water level at the end of the simulation, giving an apparent rise of the water table in figure 33. The freshwater body 

has thinned, mainly in the ÿÏao Aquifer System, as the depths 

of the bottom of the freshwater and the middle of the transition 

zone are higher in a broad area by more than 200 ft. 

As the freshwater body thins, the simulated salinity at the 

Waiehu Heights well field moves into the cautionary salinity class (1.0–2.5 percent seawater) after 30 years (fig. 34). 

After 150 years, the simulated salinity at the Waiehu Heights 

well field is in the threatened class (greater than 2.5 percent 

seawater salinity) and the simulated salinity at the Känoa well 

field is in the cautionary class. The Waiehu Heights wells are 

more vulnerable to increased salinities because they penetrate 

deeper below sea level than other withdrawal wells; Waiehu 

Heights 1 (5430-01) is open to the aquifer down to 338 ft 

below sea level. The Känoa wells are more vulnerable to 

increased salinities because they are near the northern limit of 

the sedimentary caprock where the freshwater lens is thinner 

and less isolated from the ocean.

For this scenario, withdrawal of 4.6 Mgal/d from Waiheÿe 

Aquifer System results in 2.83 Mgal/d of cautionary yield after 

150 years (table 7). Withdrawal of 16.8 Mgal/d from ÿÏao Aquifer System results in 1.51 Mgal/d of cautionary yield after 30 

years and 1.51 Mgal/d of threatened yield after 150 years. No 

withdrawal was simulated from the Waikapü aquifer system.

Scenario 2—1996 Withdrawal Rates and 

Locations with 2000–04 Land Use and 1926–2006 

Rainfall

In 1996, 20.1 Mgal/d were withdrawn from four well 

fields in the ÿÏao Aquifer System, before withdrawal was 

spread north into the Waiheÿe Aquifer System (fig. 13). By 

simulating this withdrawal condition during 1996–2006 and 

then 150 years into the future, the long-term effects of groundwater withdrawal near the CWRM’s sustainable yield estimate 

from four well fields in the ÿÏao Aquifer System can be investigated. Assigned total recharge over the model domain was 350 

Mgal/d based on 2000–04 land use and 1926–2006 rainfall 

(table 6). Total withdrawal averaged 77 Mgal/d throughout the 

modeled area, with 20.1 Mgal/d from the ÿÏao Aquifer System, 

and was simulated using monthly rates.

Several well fields show significant water-level declines 

and salinity increases when the 1996 rates are maintained for 

150 years (fig. 35). Average water levels decline as much as 

5 ft at the Mokuhau well field and simulated salinity values 

increase to 2-3 percent seawater salinity (as indicated by 

Mokuhau 2 (5330-09). Salinities at Waiehu Heights well field 

increase to about 15-percent seawater salinity, and salinities 

increase to about 1.5-percent seawater salinity at Waiheÿe well 

field. These results indicate that the 1996 pumping distribution 

would cause several well fields to produce nonpotable water in 

the future. Water levels at wells in the Waiheÿe Aquifer System 

increase and salinity decreases because these wells were not 

pumped in this simulation. The simulated depths of the bottom of freshwater and the middle of the transition zone at the 

Waiehu deep monitor well are about 300 ft shallower after 150 

years (fig. 36). Regional changes of water levels and freshwater depths in the aquifer after 150 years, presented relative to 

conditions at the end of the historical simulation, are greatest 

inland of the Waiehu Heights and Mokuhau well fields. Water 

levels decrease more than 3 ft and the depths of the bottom of 

DATE

2000 2025 2050 2075 2100 2125 2150 

ALTITUDE, IN FEET

-700

-600

-500

-400

-300

-200

Simulated 2-percent seawater salinity depth

Simulated 50-percent seawater salinity depth

Measured 2-percent seawater salinity depth

Measured 50-percent seawater salinity depth

beginning of scenario
Figure 33. Simulated change (relative to end of historical simulation) in water level, 50-percent seawater salinity depth, and 2-percent seawater sa

of withdrawal at 2006 rates with long-term average recharge (1926–2006) [scenario 1], central Maui, Hawai‘i.

iuluhaK

Bay

Mä‘alaea 

Bay

Mä‘alaea 

Bay

iuluhaK

Bay

20°�50’

156°�30’

2.5 Miles

2.5 Kilometers

SCALE

20°�50’

156°�30’

20°�50’

1

@

@

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Area with dike-impounded ground water

Area with dike-impounded ground water

Area with dike-impounded ground water

htiw aerA

stnemides

level aes ta

htiw aerA

stnemides

level aes ta

WATER-LEVEL DIFFERENCE, 

IN FEET

More than -5-5 to -3-3 to -1-1 to -0.5-0.5 to -0.10.1 to 0.50.5 to 1More than 1

EXPLANATION

50-PERCENT SEAWATER

DEPTH DIFFERENCE, IN FEET

EXPLANATION

Lower Higher

More than -200 -200 to -160 -160 to -120 -120 to -80 -80 to -40

Shallower

@ WITHDRAWAL WELL

@ WITHDRAWAL WELL 

@@

@@

@@

@@

@@

@@
Simulation of Ground-Water Flow 55

Figure 34. Predicted salinities in wells included in scenarios 1–7, central Maui, Hawai‘i.

Kahului

Bay

Mä‘alaea 

Bay

Mä‘alaea 

Bay

Kahului

Bay

Mä‘alaea 

Bay

Kahului

Bay

Mä‘alaea 

Bay

Kahului

Bay

Mä‘alaea 

Bay

Kahului

Bay

Mä‘alaea 

Bay

Kahului

Bay

Mä‘alaea 

Bay

Kahului

Bay

20o50’

156o30’

20o50’

156o30’

20o50’

156o30’

20o50’

156o30’

20o50’

156o30’

20o50’

156o30’

20o50’

156o30’

@

@

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Area with dike-impounded ground waterArea with dike-impounded ground water

Area with

sediments

at sea level

Area with

sediments

at sea level

Area with dike-impounded ground water

Area with

sediments

at sea level

Area with dike-impounded ground water

Area with

sediments

at sea level

Area with dike-impounded ground water

Area with

sediments

at sea level

Area with dike-impounded ground water

Area with

sediments

at sea level

Area with dike-impounded ground water

Area with

sediments

at sea level

@

@

@

@@

@

@@

@ @ @@

@@ @

@

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@

@

Scenario 4

Waihe‘e - 3.50

‘Ïao - 19.14

Waikapü - 4.5

30 years

Scenario 4

Waihe‘e - 3.50

‘Ïao - 19.14

Waikapü - 4.5

30 years

@

@

@

@@@ @

@

@

@

@ @@ @

@

Mä‘alaea 

Bay

Kahului

@@ Bay

@

20o50’

156o30’

@@

Area with

sediments se

at sea level t 

Küpaÿa

Känoa

North Waihe‘e

Kälepa

Waihe‘e

Waiehu Heights

Pu‘uohala

Mokuhau ‘Ïao

Tank Shaft 33

Maui Lani

Waikapü Tank

Kehalani

Waikapü South

Pohakea

Scenario 3

Waihe‘e - 3.50

‘Ïao - 19.14

Waikapü - 4.5

30 years

Scenario 3

Waihe‘e - 3.50

‘Ïao - 19.14

Waikapü - 4.5

150 years

Scenario 2

‘Ïao - 20.1

30 years

Scenario 2

‘Ïao - 20.1

150 years

Scenario 1

Waihe‘e - 4.62

‘Ïao - 16.82

30 years

Scenario 1

Waihe‘e - 4.62

‘Ïao - 16.82

150 years

Well names
56 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Kahului

Bay

Mä‘alaea 

Bay

Mä‘alaea 

Bay

Kahului

Bay

Mä‘alaea 

Bay

Kahului

Bay

Mä‘alaea 

Bay

Kahului

Bay

Mä‘alaea 

Bay

Kahului

Bay

Mä‘alaea 

Bay

Kahului

Bay

Ma‘alaea 

Bay

Kahului

Bay

20o50’

156o30’

20o50’

156o30’

20o50’

156o30’

20o50’

156o30’

20o50’

156o30’

20o50’

156o30’

20�50’

156�30’

@

@

@

@

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@

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Area with dike-impounded ground waterArea with dike-impounded ground water

Area with

sediments

at sea level

Area with

sediments

at sea level

Area with dike-impounded ground water

Area with

sediments

at sea level

Area with dike-impounded ground water

Area with

sediments

at sea level

Area with dike-impounded ground water

Area with

sediments

at sea level

Area with dike-impounded ground water

Area with

sediments

at sea level

Area with dike-impounded ground water

Area with

sediments

at sea level

Scenario 7

Waihe‘e - 3.50

‘Ïao - 19.14

Waikapü - 4.5

30 years

Scenario 7

Waihe‘e - 3.50

‘Ïao - 19.14

Waikapü - 4.5

150 years

WELL LOCATION INDICATING

LOCATION OF WELL WITH

WITHDRAWAL RATE NOT

CHANGING IN THESE SCENARIOS

WITHDRAWAL RATE (top) AND

MODELED SALINITY (bottom)--

size proportional to rate in Mgal/d

and color indicating percent seawater

salinity

1.5 4.0 6.4

< 1 > 2.5

2.5 Miles

2.5 Kilometers

SCALE

Scenario 6

Waihe‘e - 3.50

‘Ïao - 19.14

Waikapü - 4.5

30 years

Scenario 6

Waihe‘e - 3.50

‘Ïao - 19.14

Waikapü - 4.5

150 years

Scenario 5

Waihe‘e - 3.50

‘Ïao - 19.14

Waikapü - 4.5

30 years

Scenario 5

Waihe‘e - 3.50

‘Ïao - 19.14

Waikapü - 4.5

150 years

EXPLANATION

Figure 34.—Continued.
Simulation of Ground-Water Flow 57

Table 7. Classification of withdrawal for simulated scenarios, Wailuku Aquifer Sector, Maui, Hawai‘i. 

Aquifer system CWRM 

sustainable yield

Total simulated 

withdrawal

After 30 years After 150 years

Cautionary 

withdrawal

Threatened 

withdrawal

Cautionary 

withdrawal

Threatened 

withdrawal

Scenario 1—2006 withdrawal

Waiheÿe 8 4.6 0.0 0.0 2.83 0.0

ÿÏao 20 16.8 1.51 0.0 0.0 1.51

Waikapü 2 0.0 0.0 0.0 0.0 0.0

Scenario 2—1996 withdrawal

Waiheÿe 8 0.0 0.0 0.0 0.0 0.0

ÿÏao 20 20.1 8.23 1.56 0.0 14.94

Waikapü 2 0.0 0.0 0.0 0.0 0.0

Scenario 3—redistributed withdrawal

Waiheÿe 8 3.5 0.5 0.0 0.0 0.5

ÿÏao 20 19.14 2.1 0.0 1.5 0.6

Waikapü 2 4.5 0.0 0.5 0.0 0.5

Scenario 4—5-yr drought

Waiheÿe 8 3.5 0.5 0.0 na na

ÿÏao 20 19.14 1.5 0.6 na na

Waikapü 2 4.5 0.0 0.5 na na

Scenario 5—restored streamflow (12.3 Mgal/d)

Waiheÿe 8 3.5 0.0 0.0 0.0 0.0

ÿÏao 20 19.14 0.0 0.0 0.0 0.0

Waikapü 2 4.5 0.0 0.5 0.0 0.5

Scenario 6—restored streamflow (4.1 Mgal/d)

Waiheÿe 8 3.5 0.0 0.0 0.0 0.0

ÿÏao 20 19.14 1.5 0.0 2.1 0.0

Waikapü 2 4.5 0.0 0.5 0.0 0.5

Scenario 7—no irrigation

Waiheÿe 8 3.5 0.0 0.0 0.0 0.0

ÿÏao 20 19.14 1.5 0.0 1.5 0.0

Waikapü 2 4.5 0.0 0.5 0.0 0.5

[All results in million gallons per day; CWRM, State of Hawaiÿi Commission on Water Resource Management; na, not applicable]
58 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 35. Simulated water-level (red lines) and salinity (blue lines) data for Scenario 2 (dark lines) compared with Scenario 1 

(light lines) at selected wells in the Wailuku Aquifer Sector, 2000–2157, Maui, Hawai‘i. For each well shown, the simulated water 

level is the average of the water levels of the nodes representing the well and the simulated salinity is for the deepest node 

representing the well. The exception to this is the Waiehu Deep Monitor well (5430-05), where the simulated water is determined 

nearer the top of the well’s open interval at -138 ft. The depths of the nodes used are shown under each well name and number.

-5

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WATER LEVEL, IN FEET ABOVE SEA LEVEL

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SALINITY, IN PERCENT RELATIVE TO SEAWATER

beginning of scenario

simulated water level

Scenario 1

Scenario 1

Scenario 2

Scenario 2

simulated salinity

Shaft 33 (5330-05)

0 to -164 ft

Mokuhau 2 (5330-09)

-197 ft

North Waiheÿe 1 (5631-02)

-33 to -99 ft

Känoa Test Hole (5731-05)

0 to -33 ft

Küpaÿa (5731-03)

0 to -66 ft

Waiheÿe 1 (5431-02)

-197 ft

Waikapü 1 & 2 (5130-01, -02)

-33 ft

Test Hole A (5631-01)

-33 ft

Waiehu Deep Monitor Well (5430-05)

-164 ft

Waiehu Heights 1 (5430-01)

-328 ft
Simulation of Ground-Water Flow 59

Figure 36. Simulated 

positions of the bottom 

of freshwater (2-percent 

seawater salinity) and 

middle of the transition 

zone (50-percent seawater 

salinity) for Scenario 2 at 

the Waiehu Deep Monitor 

well (5430-05), 2000–2157, 

Maui, Hawai‘i.

the freshwater are shallower by more than 200 ft over a large 

area near the Waiheÿe and Waiehu Heights well fields (fig. 37). 

As the freshwater body thins the simulated salinity at the 

Waiehu Heights well field increases into the threatened range 

after 30 years (fig. 34). The simulated salinity at the Waiheÿe 

well field becomes cautionary after 30 years and threatened 

after 150 years. Also after 150 years, the simulated salinity 

at the Mokuhau well field is in the threatened class. For this 

scenario, withdrawal of 20.1 Mgal/d from ÿÏao Aquifer System 

results in 9.79 Mgal/d of cautionary and threatened yield after 

30 years and 14.94 Mgal/d of threatened yield after 150 years. 

No withdrawal was simulated from the Waiheÿe or Waikapü 

Aquifer systems (table 7).

Scenario 3—Redistributed Withdrawals with 

2000–04 Land Use and 1926–2006 Rainfall

In scenario 3, ground-water withdrawal was redistributed 

to maximize withdrawal and minimize salinities in the pumped 

water. Reduced rates at existing wells were combined with 

withdrawal from potential new well sites that, in consultation 

with the Maui DWS, were determined reasonable locations 

for future water-system expansion. Rates and locations were 

adjusted in an iterative process, and the results of the various realizations were evaluated for acceptable conditions. A 

formal optimization procedure was not feasible because of the 

complexities and length of time required in simulating variable density ground-water flow. Assigned total recharge over 

the model domain was 350 Mgal/d, based on 2000–04 land 

use and 1926–2006 rainfall (table 6). Total withdrawal was 

simulated using annual rates, and the wells not included in the 

adjustment process were maintained at 2006 withdrawal rates. 

In the final redistributed condition, withdrawal was 75 Mgal/d 

throughout the modeled area, with about 27.1 Mgal/d from the 

Wailuku Aquifer Sector (table 7). Potential new withdrawal 

locations in the Wailuku Aquifer Sector include existing but 

currently unused DWS wells at Küpaÿa (5731-03), ÿÏao Tank 

(5230-03), and Waikapü Tank (5131-01), a set of private 

Pöhäkea wells (4930-01 to -03), and new locations at Kälepa, 

Puÿuohala, Kehalani (2 wells), and Waikapü South (2 wells) 

(fig. 34; table 8). The Shaft 33 replacement well represents 

a vertical well drilled at the same location as the shaft. Also 

included is planned withdrawal from the Maui Lani wells 

(5229-04 to -06) in the Kahului Aquifer System.

Most wells have water-level declines and salinity 

increases after 150 years when compared to the end of the 

historical simulation when the redistributed rates and locations 

are maintained for 150 years, but the changes are less than 

observed after 150 years at the withdrawal wells in scenario 

1 (fig. 38). Maximum water-level declines are 3–6 ft near the 

new wells. After 150 years, the simulated depths of the bottom of freshwater and the middle of the transition zone at the 

Waiehu Deep Monitor well are about 240–250 ft shallower 

than the end of the historical simulation but very similar to the 

depths at the end of scenario 1 (fig. 39). Regional differences 

of water levels and freshwater depths in the aquifer after 150 

years, relative to conditions at the end of scenario 1, are largest 

around the new well fields, where water levels are more than 

5 ft lower (fig. 40). Where withdrawal was reduced at some of 

the existing wells, water levels are as much as 1 ft higher relative to the end of scenario 1. 

As the freshwater body thins, the simulated salinities 

at the Waiehu Heights well field, Waikapü Tank (5131-01), 

and Küpaÿa wells (5731-03) increase to cautionary after 30 

years and the salinity at the Pöhäkea wells (4930-01) becomes 

threatened (fig. 34). After 150 years, the simulated salinities 

at the Waiehu Heights well field and Küpaÿa well (5731-03) 

increase to threatened. The Waiehu Heights wells are more 

vulnerable to increased salinities because they penetrate 

deeper below sea level than other withdrawal wells; Waiehu 

Heights 1 (5430-01) is open to the aquifer down to 338 ft 

DATE

2000 2025 2050 2075 2100 2125 2150 

ALTITUDE, IN FEET

-700

-600

-500

-400

-300

-200

Simulated 2-percent seawater salinity depth

Simulated 50-percent seawater salinity depth

beginning of scenario Scenario 2

Scenario 2

Scenario 1

Scenario 1
Figure 37. Simulated change (relative to end of historical simulation) in water level, 50-percent seawater salinity depth, and 2-percent seawater sal

of withdrawal at 1996 rates with long-term average recharge (1926–2006) [scenario 2], central Maui, Hawai‘i.

iuluhaK

Bay

Mä‘alaea 

Bay

Mä‘alaea 

Bay

iuluhaK

Bay

20°�50’

156°�30’

2.5 Miles

2.5 Kilometers

SCALE

20°�50’

156°�30’

20°�50’

 

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Area with dike-impounded ground water

Area with dike-impounded ground water

htiw aerA

stnemides

level aes ta

htiw aerA

stnemides

level aes ta

WATER-LEVEL DIFFERENCE, 

IN FEET

More than -5-5 to -3-3 to -1-1 to -0.5-0.5 to -0.10.1 to 0.50.5 to 1More than 1

EXPLANATION

50-PERCENT SEAWATER

DEPTH DIFFERENCE, IN FEET

More than -160-160 to -120-120 to -80-80 to -4040 to 8080 to 120120 to 160

EXPLANATION

50-PERCENT SEAWATER

DEPTH DIFFERENCE, IN FEET

More than -160-160 to -120-120 to -80-80 to -4040 to 8080 to 120120 to 160

EXPLANATION

Lower Higher

ShallowerDeeper

@ 

WITHDRAWAL WELL @ WITHDRAWAL WELL 
Simulation of Ground-Water Flow 61

Table 8. Selected wells and rates used in redistributed withdrawal scenarios, central and 

west Maui, Hawai‘i. 

Well name Well number Withdrawal rate

(million gallons per day)

Waiheÿe aquifer system

North Waiheÿe 5631-02,-03 1.57

Känoa 5731-01,-02 1.43

Küpa‘a 5731-03 0.5

Total 3.5

ÿÏao aquifer system

Kälepa new 1.0

Waiehu Heights 5430-01,-02 0.6

Waiheÿe 5431-02,-03,-04 6.39

Puÿuohala new 1.0

Mokuhau 5330-09,10,11 3.15

ÿÏao Tank 5230-03 1.0

Shaft 33 replacement 

well new 1.5

Waikapü Tank 5131-01 1.5

Kehalani 2 new 1.5

Kehalani 3 new 1.5

Total 19.14

Waikapü aquifer system

Waikapü South new 4.0

Pöhäkea 4930-01,-02,-03 0.5

Total 4.5

Total Wailuku aquifer management area 27.14

Kahului aquifer system

Maui Lani 5229-04,-05,-06 0.96

[All other wells remain at 2006 withdrawal rates]

below sea level. The Känoa wells are more vulnerable to 

increased salinities because they are near the northern limit of 

the sedimentary caprock and where the freshwater lens is thinner and less isolated from the ocean. Therefore, in the process 

of determining the desired redistributed withdrawal conditions, the simulated salinities at these well sites received less 

importance as, because of their depth and location, there was 

less concern whether the salinities increased. For this scenario, 

withdrawal of 3.5 Mgal/d from the Waiheÿe Aquifer system 

results in 0.5 Mgal/d of cautionary yield after 30 years and 0.5 

Mgal/d of threatened yield after 150 years (table 7). Withdrawal of 19.14 Mgal/d from ÿÏao Aquifer System results in 

2.10 Mgal/d of cautionary yield after 30 years and 2.10 Mgal/d 

of threatened and cautionary yield after 150 years. Withdrawal 

of 4.50 Mgal/d from Waikapü Aquifer System results in 0.5 

Mgal/d of threatened yield after 30 and after 150 years.

Scenario 4—Effects of Drought on Redistributed 

Withdrawals

The effects of drought and the redistributed withdrawal 

were investigated in scenario 4. Assigned total recharge over 

the model domain was 350 Mgal/d, based on 2000–04 land 

use and 1926–2006 rainfall during simulation periods 2007–16 

and 2022–37. A 5-yr drought in the middle of the 30-yr 

simulation was represented during simulation period 2017–21 

using historical recharge conditions estimated with 2000–04 

land use and 1998–2002 rainfall (Engott and Vana, 2007, table 

11). The recharge during this period was 251 Mgal/d. In the 

redistributed withdrawal condition, withdrawal was 75 Mgal/d 

throughout the modeled area, with about 27.1 Mgal/d from the 

Wailuku Aquifer Sector. This scenario is considered a worstcase scenario, because the 5-yr drought is not balanced by 
62 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 38. Simulated water-level (red lines) and salinity (blue lines) data for Scenario 3 (dark lines) compared with Scenario 1 (light 

lines) at selected wells in the Wailuku Aquifer Sector, 2000–2157, Maui, Hawai‘i. For each well shown, the simulated water level is the 

average of the water levels of the nodes representing the well and the simulated salinity is for the deepest node representing the well. 

The depths of the nodes used are shown under each well name and number.

0

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2000 2025 2050 2075 2100 2125 2150 

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2000 2025 2050 2075 2100 2125 2150 

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SALINITY, IN PERCENT RELATIVE TO SEAWATER

beginning of scenario

simulated water level (scenario 3)

simulated salinity (scenario 3)

scenario 1

Känoa Test Hole (5731-05)

0 to -33 ft

Küpaÿa (5731-03)

0 to -66 ft

North Waiheÿe 1 (5631-02)

-33 to -99 ft

Waiheÿe 1 (5431-02)

-197 ft

Mokuhau 2 (5330-09)

-197 ft

Waiehu Heights 1 (5430-01)

-328 ft

Shaft 33 (5330-05)

0 to -164 ft

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Waikapü South

-33 ft

Waikapü Tank (5131-01)

0 to -131 ft

ÿÏao Tank (5230-03)

 -33 to -131 ft
Simulation of Ground-Water Flow 63

Figure 39. Simulated 

positions of the bottom 

of freshwater (2-percent 

seawater salinity) and 

middle of the transition 

zone (50-percent 

seawater salinity) for 

Scenario 3 compared 

with Scenario 1 at the 

Waiehu Deep Monitor 

well (5430-05), 2000–2157, 

Maui, Hawai‘i.

some compensating wet years that would typically occur to 

balance out the long-term average during a 30-yr period.

Differences in water levels between the drought and the 

nondrought scenario are insignificant after 30 years (fig. 41). 

Water levels are 2–5 ft lower by the end of the 5-yr drought 

but recover relatively quickly to the same water levels as 

the non-drought conditions by the end of the 30-yr simulation. Simulated salinities increase in several wells during the 

drought and do not return to the same salinities as during the 

prior nondrought conditions after 30 years. The most significant salinity increases are at the Waiehu Heights well field and 

Küpaÿa well (5731-03), where the salinities are about 2 and 

1 percent higher, respectively, relative to the nondrought scenario after 30 years. This demonstrates that movement of the 

transition zone can commonly lag behind head changes at the 

water table, because it takes longer for the stresses to propagate downward through the aquifer. The simulated depths of 

the bottom of freshwater and the middle of the transition zone 

at the Waiehu Deep Monitor well are shallower relative to the 

nondrought scenario after 30 years (fig. 42). The middle of 

the transition zone is about 10 ft shallower and the bottom of 

the freshwater is about 50 ft shallower at the end of the 30-yr 

simulation.

Because of the drought, the simulated salinities at the 

Waiehu Heights wells (5430-01) increase to threatened after 

30 years (fig. 34). In scenario 3, the simulated salinities in 

this well were lower, in the cautionary class. For this scenario, 

withdrawal of 3.5 Mgal/d from the Waiheÿe Aquifer system 

results in 0.5 Mgal/d of cautionary yield after 30 years (table 

7). Withdrawal of 19.14 Mgal/d from ÿÏao Aquifer System 

results in 2.10 Mgal/d of cautionary and threatened yield after 

30 years. Withdrawal of 4.50 Mgal/d from Waikapü Aquifer 

System results in 0.5 Mgal/d of threatened yield after 30 years.

Scenarios 5 and 6—Effects of Restoring 

Streamflow on Redistributed Withdrawals

The effects of restoring all or a portion of currently 

diverted streamflow to four streams overlying the Wailuku 

Aquifer Sector were investigated in scenarios 5 and 6. 

Assigned total recharge over the model domain was based on 

2000–04 land use, 1926–2006 rainfall, and an additional 12.3 

Mgal/d (scenario 5) or 4.1 Mgal/d (scenario 6) of recharge 

distributed along Waikapü, ÿÏao, and Waiehu Streams and 

Waiheÿe River (table 6). The additional recharge for scenario 

5 was estimated assuming no stream diversions and that all 

seepage loss measured in these streams (table 1) recharges the 

aquifer at sea level. Scenario 6 represents a case where onethird of the diverted streamflow is restored to the streams and 

seepage losses are proportionally lower. Neither scenario 5 nor 

6 was simulated ideally, because no recharge distribution is 

available that includes removal of just the irrigation provided 

by these four streams. However, between Waiheÿe River and 

Waikapü Stream, there is very little land use in the 2000–04 

period that includes irrigation (fig. 2), so the change between 

the available recharge distribution used for these scenarios 

and a recharge distribution with irrigation water from these 

four streams removed would be insignificant. Therefore, these 

scenarios provide an adequate representation of conditions for 

the area of interest. Scenarios 5 and 6 represent possible future 

conditions but are not posed as recommendations or suggestions for future stream management. Ground-water withdrawal 

in scenario 5 and 6 was the same as in scenario 3, in which 

withdrawal was 75 Mgal/d throughout the modeled area, with 

about 27.1 Mgal/d from the Wailuku Aquifer Sector. 

All Wailuku Aquifer Sector well fields show significant 

water-level increases and salinity decreases relative to scenario 3 

DATE

2000 2025 2050 2075 2100 2125 2150 

ALTITUDE, IN FEET

-700

-600

-500

-400

-300

-200

Simulated 2-percent seawater salinity depth

scenario 1

scenario 3

Simulated 50-percent seawater salinity depth

beginning of scenario
Figure 40. Simulated change (relative to scenario 1) in water level, 50-percent seawater salinity depth, and 2-percent seawater salinity depth after 

at redistributed rates with long-term average recharge (1926–2006) [scenario 3], Maui, Hawai‘i.

iuluhaK

Bay

Mä‘alaea 

Bay

Mä‘alaea 

Bay

iuluhaK

Bay

20°�50’

156°�30’

2.5 Miles

2.5 Kilometers

SCALE

20°�50’

156°�30’

20°�50’

1

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htiw aerA

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stnemides

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WATER-LEVEL DIFFERENCE, 

IN FEET

EXPLANATION

50-PERCENT SEAWATER

DEPTH DIFFERENCE, IN FEET

EXPLANATION

Higher Lower 

More than -80 -80 to -40 40 to 80 more than 80

Shallower

@

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WITHDRAWAL WELL existing proposed

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WITHDRAWAL WELL existing proposed

More than -5-5 to -3-3 to -1-1 to -0.5-0.5 to -0.10.1 to 0.50.5 to 1More than 1

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Simulation of Ground-Water Flow 65

Figure 41. Simulated water-level (red lines) and salinity (blue lines) data for Scenario 4 (dark lines) compared with Scenario 3 (light 

lines) at selected wells in the Wailuku Aquifer Sector, 2000–35, Maui, Hawai‘i. The gray band represents the drought period. For each 

well shown, the simulated water level is the average of the water levels of the nodes representing the well and the simulated salinity 

is for the deepest node representing the well. The depths of the nodes used are shown under each well name and number.

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SALINITY, IN PERCENT RELATIVE TO SEAWATER

beginning of scenario

drought drought

simulated water level

simulated salinity

scenario 3

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2000 2005 2010 2015 2020 2025 2030 2035 2000 2005 2010 2015 2020 2025 2030 2035 

Känoa Test Hole (5731-05)

0 to -33 ft

Küpaÿa (5731-03)

0 to -66 ft

North Waiheÿe 1 (5631-02)

-33 to -99 ft

Waiheÿe 1 (5431-02)

-197 ft

Mokuhau 2 (5330-09)

-197 ft Waiehu Heights 1 (5430-01)

-328 ft

Shaft 33 (5330-05)

0 to -164 ft

Waikapü South

-33 ft

Waikapü Tank (5131-01)

0 to -131 ft

ÿÏao Tank (5230-03)

-33 to -131 ft
66 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 42. Simulated 

positions of the bottom 

of freshwater (2-percent 

seawater salinity) and 

middle of the transition 

zone (50-percent 

seawater salinity) for 

Scenario 4 compared 

with Scenario 3 at the 

Waiehu Deep Monitor 

well (5430-05), 2000–35, 

Maui, Hawai‘i.

after 150 years when the additional recharge is added beneath 

the streams (fig. 43). Average water levels are 1–5 ft higher for 

scenario 5 relative to the water levels at the end of scenario 3, 

with the largest differences at Waiheÿe, Waiehu Heights, and 

Mokuhau well fields. Average water levels are 0.5–2 ft higher 

for scenario 6 relative to the water levels at the end of scenario 

3. Simulated salinity values are lower at all of the well fields, 

with the largest differences at Waiehu Heights well field and 

Küpaÿa well (5731-03) (fig. 43). The simulated depths of the 

bottom of freshwater and the middle of the transition zone 

at the Waiehu Deep Monitor well from scenario 5 are about 

160–170 ft deeper relative to scenario 3 after 150 years (fig. 

44). For scenario 6, the simulated depths of the bottom of 

freshwater and the middle of the transition zone are about 100 

ft deeper relative to scenario 3.

Regional changes of water levels and freshwater depths in 

the aquifer after 150 years, relative to conditions at the end of 

scenario 3, are greatest around ÿÏao and Waiehu Streams where 

most of the additional recharge is located. In scenario 5, water 

levels are more than 5 ft higher and the depths of the bottom 

of the freshwater are deeper by more than 200 ft (fig. 45). In 

scenario 6, water levels are 1–3 ft higher and the depths of the 

bottom of the freshwater are deeper by 40–80 ft (fig. 46).

The additional recharge causes the freshwater body to 

thicken; therefore, some of the wells that were potentially or 

likely to produce water unacceptable for drinking in scenario 

3 have lower simulated salinities in scenarios 5 and 6 (fig. 34). 

For scenario 5, the simulated salinities in all of the selected 

wells, with the exception of the Pöhäkea wells in the Waikapü aquifer system, are in the acceptable class, even after 

150 years. For scenario 6, the simulated salinity at Waikapü 

Tank well (5131-01) increases to cautionary after 30 years and 

remains cautionary after 150 years. For scenario 5, withdrawal 

of 3.5 Mgal/d from the Waiheÿe Aquifer system results in no 

cautionary or threatened yield after 150 years (table 7). Withdrawal of 19.14 Mgal/d from ÿÏao Aquifer System results in 

no cautionary or threatened yield after 150 years. Withdrawal 

of 4.50 Mgal/d from Waikapü Aquifer System results in 0.5 

Mgal/d of threatened yield after 30 and 150 years. For scenario 

6, withdrawal of 3.5 Mgal/d from the Waiheÿe Aquifer system 

results in no cautionary or threatened yield after 150 years 

(table 7). Withdrawal of 19.14 Mgal/d from ÿÏao Aquifer System results in 1.50 Mgal/d of cautionary yield after 30 years 

and 2.10 Mgal/d of cautionary yield after 150 years. Withdrawal of 4.50 Mgal/d from Waikapü Aquifer System results 

in 0.5 Mgal/d of threatened yield after 30 and after 150 years.

Scenario 7—Effects of No Agricultural Irrigation 

or Stream Diversions

The effects of removing agricultural irrigation in the 

study area were investigated in scenario 7. Recharge was 

based on the hypothetical Land Use III condition of Engott 

and Vana (2007, table 11) which represented 2000–04 land 

use, 1926–2004 rainfall, and no agricultural irrigation. 

Assigned recharge was 274 Mgal/d, which included 12.3 

Mgal/d of additional recharge assuming no stream diversions 

for agricultural irrigation. Scenario 7 represents a hypothetical 

condition, the results of which can be informative about the 

hydrologic system, and it is not posed as a recommendation 

or suggestion for future land use. Ground-water withdrawal in 

scenario 7 was the same as in scenario 3, in which withdrawal 

was 75 Mgal/d throughout the modeled area, with about 27.1 

Mgal/d from the Wailuku Aquifer Sector.

Most Wailuku Aquifer Sector well fields show significant 

water-level increases and salinity decreases relative to scenario 

3 after 150 years (fig. 47). Near these withdrawal wells, the 

effect of the additional recharge beneath the streams is greater 

than the effects from the loss of recharge beneath the central 

-700

-600

-500

-400

-300

-200

DATE

2000 2005 2010 2015 2020 2025 2030 2035 

ALTITUDE, IN FEET

Simulated 2-percent seawater salinity depth

Simulated 50-percent seawater salinity depth

Scenario 3

Beginning of scenario drought

Scenario 3

Scenario 4

Scenario 4
Simulation of Ground-Water Flow 67

Figure 43. Simulated water-level (red lines) and salinity (blue lines) data for Scenarios 5 and 6 compared with Scenario 3 at 

selected wells in the Wailuku Aquifer Sector, 2000–2157, Maui, Hawai‘i. For each well shown, the simulated water level is the 

average of the water levels of the nodes representing the well and the simulated salinity is for the deepest node representing the 

well. The depths of the nodes used are shown under each well name and number.

5

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Waikapü Tank (5131-01)

0 to -131 ft

ÿÏao Tank (5230-03)

-33 to -131 ft

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SALINITY, IN PERCENT RELATIVE TO SEAWATER

beginning of scenario

simulated water level

scenario 6

scenario 3

scenario 3

scenario 6

scenario 5

scenario 5

simulated salinity

Känoa Test Hole (5731-05)

0 to -33 ft

Küpaÿa (5731-03)

0 to -66 ft

North Waiheÿe 1 (5631-02)

-33 to -99 ft

Waiheÿe 1 (5431-02)

-197 ft

Mokuhau 2 (5330-09)

-197 ft

Waiehu Heights 1 (5430-01)

-328 ft

Shaft 33 (5330-05)

0 to -164 ft
68 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 44. Simulated 

positions of the bottom 

of freshwater (2-percent 

seawater salinity) and 

middle of the transition 

zone (50-percent 

seawater salinity) for 

Scenarios 5 and 6 

compared with Scenario 

3 at the Waiehu Deep 

Monitor well (5430-05), 

2000–2157, Maui, Hawai‘i.

isthmus. Average water levels are 1–5 ft higher for scenario 7 

relative to the water levels at the end of scenario 3, with the 

largest differences at Waiheÿe, Waiehu Heights, and Mokuhau well fields. At wells near and south of Waikapü Stream, 

the water level differences are smaller relative to scenario 5, 

because this area has reduced irrigation recharge that balances 

the gains from the additional stream recharge (compare figs. 45 

and 49). Simulated salinity values are lower compared to scenario 3 at most of the well fields, with the largest differences at 

Waiehu Heights well field and Küpaÿa well (5731-03) (fig. 47). 

Salinity is slightly higher at Waikapü South because of some 

reduced irrigation recharge. The simulated depths of the bottom of freshwater and the middle of the transition zone at the 

Waiehu Deep Monitor well from scenario 7 are about 150–160 

ft deeper relative to scenario 3 after 150 years (fig. 48). 

Regional changes of water levels and freshwater depths 

in the aquifer after 150 years, relative to conditions at the end 

of scenario 3, are greatest around ÿÏao and Waiehu Streams, 

where most of the additional recharge occurs. In scenario 7, 

water levels are more than 5 ft higher and the depths of the 

bottom of the freshwater are deeper by more than 160 ft (fig. 

49). Reduced irrigation in the isthmus leads to water levels 

that are more than 1 ft lower and broad areas where the depths 

of the bottom of the freshwater and the middle of the lens are 

more than 40 ft shallower.

As in scenario 5, for the selected wells in the Wailuku 

Aquifer Sector, only the simulated salinity in the Waikapü 

Tank well (5131-01) increases to cautionary after 30 years 

(fig. 34). For scenario 7, withdrawal of 3.5 Mgal/d from the 

Waiheÿe Aquifer system results in no cautionary or threatened yield after 150 years at the DWS wells or well fields 

(table 7). Withdrawal of 19.14 Mgal/d from ÿÏao Aquifer System results in 1.50 Mgal/d of cautionary yield after 30 and 

after 150 years. Withdrawal of 4.50 Mgal/d from Waikapü 

Aquifer System results in 0.5 Mgal/d of threatened yield 

after 30 and after 150 years.

Additional withdrawal locations

As part of the iterative process used in developing the 

redistributed pumping distribution used in scenarios 3–7, 

additional withdrawal sites were considered around the 

northern and southern coasts of west Maui (fig. 50). Six sites 

were tested in the Waiheÿe Aquifer System north of the Küpaÿa 

well, each with a withdrawal rate of 0.5 Mgal/d for 30 years 

using 2000–04 land use, 1926–2004 rainfall, and the redistributed pumping distribution of scenario 3. Four of the six sites 

(Waiokila, Wailena, Waipili, and Waihali) had final simulated 

salinity values ranging between 3 and 4-percent of seawater 

salinity and another (Kahakuloa) was more than 1-percent 

seawater. Only the Poÿelua site, farthest to the north, had a 

simulated salinity below 1 percent of seawater salinity. Salinity at this well was higher at the end of the historical simulation mainly because of lower recharge during 2000–2004 than 

in the future scenario with average conditions. The model 

mesh in this northern area was not constructed with fine discretization, nor were there any measured water-level or salinity values for comparison, so the results are considered less 

reliable. However, the results are sufficient to indicate that it is 

less likely that a series of wells, each withdrawing 0.5 Mgal/d 

of potable water, could be developed in this area. Although 

this area receives ample recharge under average conditions, 

the relatively high aquifer permeability coupled with the lack 

of a low-permeability capping layer at the coast lead to the 

development of a relatively thin freshwater lens that is more 

susceptible to seawater intrusion. 

Two potential well sites in the southern part of the 

Waikapü Aquifer System were considered because of their 

DATE

2000 2025 2050 2075 2100 2125 2150 

ALTITUDE, IN FEET

-700

-600

-500

-400

-300

-200

Simulated 2-percent seawater salinity depth

Simulated 50-percent seawater salinity depth

beginning of scenario

scenario 5

scenario 5

scenario 6

scenario 3

scenario 6

scenario 3
Figure 45. Simulated change (relative to scenario 3) in water level, 50-percent seawater salinity depth, and 2-percent seawater salinity depth after 

at redistributed rates with 12.3 Mgal/d of additional stream recharge [scenario 5], Maui, Hawai‘i.

iuluhaK

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WATER-LEVEL DIFFERENCE, 

IN FEET

0.1 to 0.50.5 to 11 to 33 to 5more than 3

EXPLANATION

50-PERCENT SEAWATER

DEPTH DIFFERENCE, IN FEET

40 to 8080 to 120120 to 160160 to 200more than 200

EXPLANATION

50-PERCENT SEAWATER

DEPTH DIFFERENCE, IN FEET

40 to 8080 to 120120 to 160160 to 200more than 200

EXPLANATION

Higher

Deeper

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WITHDRAWAL WELL existing proposed

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ÿÏao Stream

Waiehu Stream

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Figure 46. Simulated change (relative to scenario 3) in water level, 50-percent seawater salinity depth, and 2-percent seawater salinity depth after 

at redistributed rates with 4.1 Mgal/d of additional stream recharge [scenario 6], Maui, Hawai‘i.

iuluhaK

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htiw aerA

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WATER-LEVEL DIFFERENCE, 

IN FEET

0.1 to 0.50.5 to 11 to 33 to 5more than 3

EXPLANATION

50-PERCENT SEAWATER

DEPTH DIFFERENCE, IN FEET

40 to 8080 to 120120 to 160160 to 200more than 200

EXPLANATION

50-PERCENT SEAWATER

DEPTH DIFFERENCE, IN FEET

40 to 8080 to 120120 to 160160 to 200more than 200

EXPLANATION

Higher

Deeper

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WITHDRAWAL WELL existing proposed

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Simulation of Ground-Water Flow 71

  Simulated water-level (red lines) and salinity (blue lines) data for Scenario 7 compared with Scenario 3 at selected 

wells in the Wailuku Aquifer Sector, 2000–2157, Maui, Hawai‘i. For each well shown, the simulated water level is the average of 

the water levels of the nodes representing the well and the simulated salinity is for the deepest node representing the well. The 

depths of the nodes used are shown under each well name and number.

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Waikapü South

-33 ft

Waikapü Tank (5131-01)

0 to -131 ft

ÿÏao Tank (5230-03)

-33 to -131 ft

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WATER LEVEL, IN FEET ABOVE SEA LEVEL

2000 2025 2050 2075 2100 2125 2150 

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SALINITY, IN PERCENT RELATIVE TO SEAWATER

beginning of scenario

simulated water level

scenario 7

scenario 3

scenario 3

scenario 7

simulated salinity

Känoa Test Hole (5731-05)

0 to -33 ft

Küpaÿa (5731-03)

0 to -66 ft

North Waiheÿe 1 (5631-02)

-33 to -99 ft

Waiheÿe 1 (5431-02)

-197 ft

Mokuhau 2 (5330-09)

-197 ft

Waiehu Heights 1 (5430-01)

-328 ft

Shaft 33 (5330-05)

0 to -164 ft

0

1

2

3

4
72 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 48. Simulated 

positions of the bottom 

of freshwater (2-percent 

seawater salinity) and 

middle of the transition 

zone (50-percent seawater 

salinity) for Scenario 7 

compared with Scenario 

3 at the Waiehu Deep 

Monitor well (5430-05), 

2000–2157, Maui, Hawai‘i.

proximity to existing water-supply infrastructure, but even 

without ground-water withdrawal at these sites, simulated 

salinities increased to nonpotable levels as a result of withdrawal elsewhere in the aquifer (fig. 50). The simulated salinity at the Puÿu Hona site increased from about 1-percent to 

nearly 2.5-percent seawater salinity after 30 years. Measured 

salinity data during 1939–60 from monitoring well 4931-01 at 

the Puÿu Hona site ranged between 112 and 316 mg/L chloride 

(about 0.6–1.6-percent seawater salinity), indicating that the 

simulated salinity values are a reasonable approximation of 

field conditions (unpublished chloride data in files of USGS 

Pacific Island Water Science Center). Simulated salinities 

at the Mäÿalaea Tank site increased from about 8-percent to 

nearly 15-percent seawater salinity, indicating a lack of freshwater resource in this area.

Model Limitations

The numerical model developed for this study simulates 

water levels and salinity on a regional scale and may not accurately predict either the pumping water level at an individual 

well or the salinity of water pumped from that well. Salinity of 

water pumped from a well may be controlled by local heterogeneities in the aquifer that are not represented in the model, 

and the level of model discretization affects the numerical 

accuracy with which transport mechanisms are simulated. The 

model has several other limitations for predictive purposes 

because of the various assumptions used and possible uncertainties in input data. These limitations are discussed below.

Differences between measured and simulated water levels 

and salinity profiles are greater in some areas than others, 

which may reflect uncertainties in the recharge or withdrawal 

estimates, boundary conditions, assigned parameter values in 

the model, or representations of the different hydrogeological 

features in the model. Recharge estimates are based on waterbudget computations that could be improved with a better 

understanding of the spatial distributions of rainfall, evapotranspiration, runoff, and land-cover characteristics. Improved 

recharge estimates in the study area will lead to improved 

estimates for parameter values in the numerical ground-water 

model and greater confidence in model results. Withdrawals 

represented in the model were based on available information. 

Unreported withdrawals and uncertainties in reported withdrawals that cannot be quantified also affect the accuracy of 

model results. 

For this study, no-flow boundaries were assigned in the 

east at the rift zones of Haleakalä, which precludes groundwater movement across these boundaries. Although some 

flow likely takes place across these boundaries, the amount is 

probably small and cannot be quantified without expanding 

the modeled area. 

The distributions of parameter values assigned in the 

model were kept simple to avoid creating an overly complex 

model that could not be justified on the basis of existing information. Heterogeneity in the ground-water system likely exists 

but is poorly understood. Values assigned to model parameters 

initially were based on existing estimates and subsequently 

adjusted to simulate historical head and salinity observations. 

However, some of these parameter values, particularly dispersion coefficients, may be poorly known. 

Most of the modeling effort focused on matching the 

hydrologic response in the Wailuku Aquifer Sector. Although 

simulated water levels generally match measured data in the 

Central and Lahaina Aquifer Sectors, more effort is needed 

to refine these areas, especially if concerns about these areas 

need to be addressed further.

The geometrical representation of the valley-fill barriers, caprock, and contact between West Maui Volcano and 

DATE

2000 2025 2050 2075 2100 2125 2150 

ALTITUDE, IN FEET

-700

-600

-500

-400

-300

-200

Simulated 2-percent seawater salinity depth

Simulated 50-percent seawater salinity depth

beginning of scenario

scenario 7

scenario 3

scenario 7

scenario 3
Figure 49. Simulated change (relative to scenario 3) in water level, 50-percent seawater salinity depth, and 2-percent seawater salinity depth after 

at redistributed rates with no recharge from agriculture irrigation [scenario 7], Maui, Hawai‘i.

iuluhaK

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Mä‘alaea 

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DEPTH DIFFERENCE, IN FEET

EXPLANATION

Area with dike-impounded ground water

Area with dike-impounded ground water

Area with dike-impounded ground water

htiw aerA

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WATER-LEVEL DIFFERENCE, 

IN FEET

more than 3-3 to -1-1 to -0.5-0.5 to -0.1

EXPLANATION

more than -80-80 to -40

Lower Higher

Deeper

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74 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure 50. Simulated water-level (red lines) and salinity (blue lines) data for potential additional withdrawal sites in the Wailuku 

Aquifer Sector, 2000–2035, Maui, Hawai‘i.

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SALINITY, IN PERCENT RELATIVE TO SEAWATER

aneliaW alikoiaW

Puÿu Hona Mäÿalaea Tank

2000 2005 2010 2015 2020 2025 2030 2035 2000 2005 2010 2015 2020 2025 2030 2035 

0

1

2

3

4

5

0

2

4

6

8

10

0

1

2

3

4

5

0

1

2

3

4

aolukahaK ilipiaW

beginning of scenario

simulated water level

simulated salinity

0

1

2

3

4

5

0

1

2

3

4

Poÿelua

0

1

2

3

4

5

0

1

2

3

4

5

6

Waihali

@

@

@ @

@

@

@

@

Küpa‘a

Waiokila

Wailena

Waipili

Kahakuloa

Waihali

Po‘elua @

156 ̊30’

@

@

@@

Mä‘alaea Tank

Pu‘u Hona

Pöhäkea

MAUI

Withdrawal wells

area of maps

Existing

Potential

@

@
Summary 75

Haleakalä also were simplified for the model. The geometric 

definition of the valley-fill barriers can be improved using 

surface geophysical techniques in conjunction with drilling 

additional monitor wells within the valleys. For this study, the 

coastal caprock was represented as a homogeneous zone of 

relatively low permeability. High-permeability zones likely 

exist in the caprock, but they are poorly understood and were 

not represented in the model. Confidence in model results can 

be improved by addressing the limitations described in this 

section. In particular, improved estimates of the distribution of 

model parameters likely will lead to better model reliability. 

Despite these limitations, the model presented here does an 

adequate job for the purposes of this study. 

Summary

Most of the public water supply in Maui, Hawaiÿi, is from 

a freshwater lens in the Wailuku area of the island. Because 

of population increase, ground-water withdrawals from wells 

in this area increased from less than 10 Mgal/d during 1970 

to about 23 Mgal/d during 2006. In response to increased 

withdrawals from the freshwater-lens system, water levels 

declined, the transition zone between freshwater and saltwater 

became shallower, and the chloride concentrations of water 

pumped from wells increased. 

To aid in prudent management of ground-water 

resources and plan for sustainable growth on the island, the 

Maui County Department of Water Supply (DWS) entered 

into a cooperative agreement in 2003 with the U.S Geological Survey (USGS) to conduct a study of the ground-water 

availability in central and west Maui. The objectives of this 

4.5-year study are to (1) obtain a better understanding of the 

regional ground-water flow system in the study area, (2) estimate ground-water recharge in the study area, and (3) use a 

numerical ground-water flow and transport model to estimate 

the effects of selected withdrawal and recharge scenarios on 

water levels and on the transition zone between fresh water 

and ocean water. 

Irrigation rates in the study area have been steadily 

decreasing since the 1970s. Decreasing irrigation coincided 

recently with periods of below-average rainfall, leading to 

substantially reduced recharge rates in many areas. Recharge 

was determined for six periods (Engott and Vana, 2007). 

The period 1926–79 had the highest estimated recharge. 

Recharge from irrigation during this period was at least 50 

percent higher than in any other period considered. Estimated 

recharge for central and west Maui declined 44 percent during 

1979–2000. The period 2000–04 had the lowest estimated 

recharge. Recharge from irrigation during this period was 46 

percent lower than during 1926–79, and rainfall was the lowest of any period. 

Average withdrawals in 2000–06 were 21.4 Mgal/d in the 

Wailuku Aquifer Sector. Average withdrawals from the Central 

Aquifer Sector were about 68 Mgal/d and average withdrawals 

from the Lahaina Aquifer Sector during 2000–06 were about 4 

Mgal/d. Most streams on West Maui Volcano receive groundwater discharge from the dike-impounded water body. Total 

average base flow at gaging stations operated on the largest 14 

gaged streams on West Maui Volcano is about 101 Mgal/d.

A three-dimensional numerical ground-water model 

capable of simulating density-dependent solute transport 

was developed as part of this study. The model used published estimates for most of the permeability, storage, and 

dispersivity values. Simulated water levels and salinity profiles 

generally were in agreement with measured water levels and 

salinity profiles from representative wells in the modeled area 

during the period 1926–2006. Measured salinity profiles in 

the Waiehu deep monitor well indicate a shallowing of the 

brackish-water transition zone over time, and simulated salinity profiles are consistent with this trend.

The numerical model constructed for this study was 

used to quantify changes in ground-water level and salinity 

with ground-water withdrawal under various withdrawal and 

recharge scenarios. Scenarios included ground-water withdrawal at 2006 and 1996 rates and locations with average 

recharge, and withdrawal at redistributed rates and locations 

with several different recharge scenarios. Simulation results 

from the two scenarios that include the former withdrawal 

distributions indicate the following for the Wailuku Aquifer 

Sector: (1) average recharge rates and the 2006 withdrawal 

distribution (21.4 Mgal/d from 6 well fields) cause average 

water levels at wells to decrease 2–3 ft and the transition zone 

to become more than 200 ft shallower after 150 years, and (2) 

average recharge rates and the 1996 withdrawal distribution 

(20.1 Mgal/d from 4 well fields) cause average water levels at 

wells to decrease by more than 3 ft and the transition zone to 

become more than 300 ft shallower after 150 years. With the 

2006 distribution, two of the six well fields have simulated 

salinity values that increase into the range of concern after 

long-term withdrawal. With the 1996 distribution, three of the 

four well fields have simulated salinity values that increase 

into the range of concern after long-term withdrawal. 

A condition in which ground-water withdrawal was redistributed to maximize withdrawal and minimize salinities was 

determined using the numerical model in an iterative manner. 

Reduced rates at existing wells were combined with withdrawal 

from potential new well sites that, in consultation with the Maui 

DWS, were determined reasonable locations for future watersystem expansion. The redistribution simulates 27.1 Mgal/d of 

withdrawal from 14 wells or well fields in the Wailuku Aquifer 

Sector. Simulation results from the five scenarios that include 

redistributed withdrawal conditions indicate the following for 

the Wailuku Aquifer Sector: (1) average recharge rates cause 

average water levels to decrease 2–3 ft and the transition zone 

to become more than 200 ft shallower after 150 years; (2) 

a 5-yr drought condition similar to the 1998–2002 drought 

causes additional salinity increases after 30 years but only one 

well has salinity increases of concern; (3) additional recharge 

from restored streamflow significantly increases water levels, 

thickens the freshwater body, and decreases salinity at withdrawal sites; and (4) a complete removal of irrigation recharge 
76 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

decreases water levels and increases salinity in the central isthmus, but recharge through streams still significantly increases 

water levels, thickens the freshwater body, and decreases salinity at withdrawal sites in the Wailuku Aquifer Sector.

The numerical model developed for this study simulates 

water levels and salinity on a regional scale and may not accurately predict either the pumping water level at an individual 

well or the salinity of water pumped from that well. Salinity of 

water pumped from a well may be controlled by local heterogeneities in the aquifer that are not represented in the model. 

The model has several other limitations for predictive purposes, because of the various assumptions used and possible 

uncertainties in input data. Model reliability can be improved 

as understanding of ground-water recharge, the distribution of 

model parameter values, and the geometry of the sedimentary 

layers and valley-fill barriers improves. 

References Cited

Blumenstock, D.I., and Price, Saul, 1967, Climates of the 

States-Hawaii: U.S. Department of Commerce, Climatography of the United States, no 60-51, 27 p.

Bowles, S.P., 1970, Storm runoff disposal wells at Kahului, 

Maui: A report for Kahului Development Co., July 1970.

Burnham, W.L., Larson, S.P., and Cooper, H.H., Jr., 1977, Distribution of injected wastewater in the saline lava aquifer, 

Wailuku-Kahului wastewater treatment facility, Kahului, 

Maui, Hawaii: U.S. Geological Survey Open-File Report 

no. 77-469, 58 p.

C. Takumi Engineering Inc., 1999, Preliminary engineering 

report for new potable water source Kanoa Well No. 1 (State 

Well No. 5731-02), Waihee, Maui, Hawaii: Prepared for 

Department of Water Supply, County of Maui.

Chen, C.-Y., Frey, F.A., Garcia, M.O., Dalrymple, G.B., and 

Hart, S.R., 1991, The tholeiite to alkalic basalt transition at 

Haleakala Volcano, Maui, Hawaii: Contributions to Mineralogy and Petrology, v. 106, p. 183–200.

Cox, D.C., 1951, Lowland ground-water development prospects in and north of Iao Valley, Wailuku, Maui: Honolulu, 

Hawaii, Hawaii Sugar Planter’s Association, 12 p.

Engott, J.A., and Vana, T.T., 2007, Effects of agricultural landuse changes and rainfall on ground-water recharge in central 

and west Maui, Hawaiÿi, 1926–2004: U.S. Geological Survey Scientific Investigations Report 2007-5103, 56 p.

Freeze, R.A., and Cherry, J.A., 1979, Groundwater: Englewood Cliffs, N.J., Prentice-Hall, Inc., 604 p.

Giambelluca, T.W., and Nullet, Dennis, 1991, Influence of the 

trade-wind inversion on the climate of a leeward mountain 

slope in Hawaii: Climate Research, v. 1, p. 207–216.

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

Rainfall atlas of Hawaii: State of Hawaii, Department of 

Land and Natural Resources, Division of Water and Land 

Development, Report R76, 267 p.

Gingerich, S.B., and Oki, D.S., 2000, Ground water in Hawaii: 

U.S. Geological Survey Fact Sheet FS126-00, 6 p. 

Gingerich, S.B., and Voss, C.I., 2005, Three-dimensional variabledensity flow simulation of a coastal aquifer in southern Oahu, 

Hawaii, USA: Hydrogeology Journal, v. 13, p. 436-450.

Harbaugh, A.W., 1990, A computer program for calculating subregional water budgets using results from the U.S. 

Geological Survey modular three-dimensional ground-water 

flow model: U.S. Geological Survey Open-File Report 

90-392, 46 p. 

Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, 

M.G., 2000, MODFLOW-2000, the U.S. Geological Survey 

modular ground-water model—user guide to modularization 

concepts and the ground-water flow process: U.S. Geological Survey Open-File Report 00-92, 121 p.

Huber, R.D., and Adams, W.M., 1971, Density logs from 

underground gravity surveys in Hawaii: University of 

Hawaii Water Resources Research Center Technical Report 

no. 45, 39 p.

 Hunt, C.D., Jr., 2007, Ground-water nutrient flux to coastal 

waters and numerical simulation of wastewater injection 

at Kihei, Maui, Hawaii: U.S. Geological Survey Scientific 

Investigations Report 2006–5283, 69 p. 

Ishizaki Kenneth, Burbank, N.C., Jr., and Lau, L.S., 1967, 

Effects of soluble organics on flow through thin cracks 

of basaltic lava: University of Hawaii Water Resources 

Research Center Technical Report no. 16, 56 p.

Langenheim, V.A.M., and Clague, D.A., 1987, The HawaiianEmperor volcanic chain, part II, stratigraphic framework of 

volcanic rocks of the Hawaiian Islands, chap. 1 of Decker, 

R.W., Wright, T.L., and Stauffer, P.H., eds., Volcanism in 

Hawaii: U.S. Geological Survey Professional Paper 1350, v. 

1, p. 55-84. 

Liu, C.C.K., 2005, Completion report of a research project on 

analytical groundwater flow and transport modeling for the 

estimation of the sustainable yield of Pearl Harbor Aquifer 

for Hawaii Department of Land and Natural Resources State 

Commission on Water Resource Management (unedited 

manuscript), 58 p.

Macdonald, G.A., Abbott, A.T., and Peterson, F.L., 1983, Volcanoes in the sea, the geology of Hawaii (2d ed.): Honolulu, 

Hawaii, University of Hawaiÿi Press, 517 p.

McCandless, J.S., 1936, Development of artesian well water in 
References Cited 77

the Hawaiian Islands, 1880–1936: Honolulu, Hawaii, 79 p.

McDougall, Ian, 1964, Potassium-argon ages from lavas of the 

Hawaiian Islands: Geological Society of America Bulletin, 

v. 75, p. 107–128.

Meyer, C.F., Kleinecke, D.C., Todd, D.K., and Ewing, L.E., 

1974, Mathematical modeling of freshwater aquifers having saltwater bottoms: Final technical completion report 

GE74TMP-43, General Electric Co., TEMPO, Center for 

Advanced Studies, Santa Barbara, California, 176 p. + app.

Meyer, William, and Presley, T.K., 2001, The response of 

the Iao aquifer to ground-water development, rainfall, and 

land-use practices between 1940 and 1998, island of Maui, 

Hawaii: U.S. Geological Survey Water-Resources Investigations Report 00-4223, 60 p.

Meyer, William, and Souza, W.R., 1995, Factors that control the 

amount of water that can be diverted to wells in a high-level 

aquifer, in Hermann, Raymond, Back, William, Sidle, R.C., 

and Johnson, A.I., eds., Water resources and environmental 

hazards: emphasis on hydrologic and cultural insight in the 

Pacific Rim: Proceedings of the American Water Resources 

Association Annual Summer Symposium, Honolulu, Hawaii, 

June 25-28, 1995, p. 207-216.

Miller, M.E., 1987, Hydrogeologic characteristics of central 

Oahu subsoil and saprolite; implications for solute transport: University of Hawaii at Manoa M.S. thesis, 231 p.

Mink, J.F., and Lau, L.S., 1980, Hawaiian groundwater geology and hydrology, and early mathematical models: University of Hawaii Water Resources Research Center Technical 

Memorandum Report no. 62, 74 p.

Mink, J.F., and Lau, L.S., 1990, Aquifer identification and 

classification for Maui: groundwater protection strategy 

for Hawaii: Honolulu, Hawaii, University of Hawaii Water 

Resources Research Center, Technical Report no. 185, 47 p. 

National Geophysical Data Center, 2004, NGDC Coastal 

Relief Model: National Oceanic and Atmospheric Administration Web page Carla J. Moore, webmaster [http://www.

ngdc.noaa.gov/mgg/coastal/coastal.html. last accessed 

July 28, 2006]

National Oceanic and Atmospheric Administration, 2007, 

Historic tide data: [http://tidesandcurrents.noaa.gov/

data_menu.shtml?stn=1615680%20Kahului,%20

HI&type=Historic+Tide+Data. Last accessed June 16, 2007].

Naughton, J.J., Macdonald, G.A., and Greenberg, V.A., 1980, 

Some additional potassium-argon ages of Hawaiian rocks; 

the Maui Volcanic Complex of Molokai, Maui, Lanai, 

and Kahoolawe: Journal of Volcanology and Geothermal 

Research, v. 7, p. 339–355.

Nichols, W.D., Shade, P.J., and Hunt, C.D., 1996, Summary 

of the Oahu, Hawaii regional aquifer-system analysis: U.S. 

Geological Survey Professional Paper 1412-A, 61 p.

Oki, D.S., 1998, Geohydrology of the central Oahu, Hawaii, 

ground-water flow system and numerical simulation of 

the effects of additional pumping: U.S. Geological Survey 

Water-Resources Investigations Report 97-4276, 132 p.

Oki, D.S., 2005a, Trends in streamflow characteristics at 

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

Scientific Investigations Report 2004-5080, 120 p.

Oki, D.S., 2005b, Numerical simulation of the effects of lowpermeability valley-fill barriers and the redistribution of 

ground-water withdrawals in the Pearl Harbor Area, Oahu, 

Hawaii: U.S. Geological Survey Scientific Investigations 

Report 2005-5253, 111 p.

Oki, D.S, Souza, W.R., Bolke, E.L., and Bauer, G.R., 1998, 

Numerical analysis of the hydrogeologic controls in a layered coastal aquifer system, Oahu, Hawaii, USA: Hydrogeology Journal, v. 6, no. 2, p. 243-263.

Paillet, F.L., Williams, J.H., Oki, D.S., and Knutson, K.D., 

2002, Comparison of formation and fluid-column logs in a 

heterogeneous basalt aquifer: Ground Water, v. 40, no. 6, p. 

577-585.

Peterson, F.L., and Hargis, D.R., 1971, Effect of storm runoff 

disposal and other artificial recharge to Hawaiian GhybenHerzberg aquifers: University of Hawaii, Water Resources 

Research Center Technical Report no. 54, 51 p.

Peterson, F.L., and Sehgal, M.M., 1974, Determining porosity 

with neutron logs from Hawaiian basaltic aquifers: University of Hawaii Water Resources Research Center Technical 

Report no. 80, 37 p.

R.M. Towill Corporation, 1978, Feasibility study, surface 

water impoundment/recharge Pearl Harbor basin Oahu, 

Hawaii, variously paginated.

Rotzoll, K., El-Kadi, A.I., and Gingerich, S.B., 2007, Estimating hydraulic properties of volcanic aquifers using constantrate and variable-rate aquifer tests: Journal of the American 

Water Resources Association v. 43, no. 2, p. 334–345.

Sherrod, D.R., Nishimitsu, Yoshitomo, and Tagami, Takahiro, 

2003, New K-Ar ages and the geologic evidence against 

rejuvenated-stage volcanism at Haleakalä, East Maui, a 

postshield-stage volcano of the Hawaiian island chain: 

Geological Society of America Bulletin, v. 115, no. 6, p. 

683-694.

Soroos, R.L., 1979, Test monitoring of prototype injection 

well, Waiale, Maui, Hawaii: U.S. Geological Survey OpenFile Report no. 79-274, 31 p.
78 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Souza, W.R., 1981, Ground-water status report, Lahaina 

District, Maui, Hawaii: U.S. Geological Survey Open-File 

Report 81-549, 2 sheets.

Souza, W.R., and Voss, C.I., 1987, Analysis of an anisotropic coastal aquifer system using variable-density flow and 

solute transport simulation: Journal of Hydrology, v. 92, p. 

17-41.

State of Hawaii, 1961, Summary of drilling logs and pumping 

test for Exploratory Well No. 1, Waikapu, Maui, Hawaii: 

Department of Land and Natural Resources Division of 

Water and Land Development Circular C4.

State of Hawaii, 1965, Summary of drilling log and pumping 

test for Alaeloa Well 318, Alaeloa, Maui, Hawaii: Department of Land and Natural Resources Division of Water and 

Land Development Circular C35.

State of Hawaii, 1967, Summary of drilling log and pumping 

test for Maalaea Well 272, Maalaea, Maui, Hawaii: Department of Land and Natural Resources Division of Water and 

Land Development Circular C43.

State of Hawaii, 1990, Water resources protection plan, volumes I and II, June 1990: Commission on Water Resource 

Management, Department of Land and Natural Resources, 

variously paginated.

State of Hawaii, 2000, The State of Hawaii data book 2000, a 

statistical abstract: State of Hawaii, Department of Business, 

Economic Development, and Tourism [http://www.hawaii.

gov/dbedt/db00. accessed June 10, 2002].

State of Hawaii, 2003, Public Notice of Iao Ground-Water 

Management Area Designation, Island of Maui: State of 

Hawaii Department of Land and Natural Resources Commission on Water Resource Management [http://hawaii.

gov/dlnr/cwrm/current/iao/nt030721.pdf.]

State of Hawaii, 2004, Hawaii well construction and 

pump installation standards: State of Hawaii Department of Land and Natural Resources Commission on Water 

Resource Management 2nd edition, variously paginated.

Stearns, H.T., 1976, Second supplement to the central Maui 

water study of March 1974, unpublished report to Waiehu 

Heights Association in U.S. Geological Survey files.

Stearns, H.T., and Macdonald, G.A., 1942, Geology and 

ground-water resources of the island of Maui, Hawaii: 

Hawaii Division of Hydrography Bulletin 7, 344 p. 

Takasaki, K.J., 1972, Preliminary report on the water resources 

of Central Maui: State of Hawaii, Department of Land and 

Natural Resources, Division of Water and Land Development, Circular C62, 59 p. plus appendixes. 

Tenorio, P.A., Young, R.H.F., Burbank, N.C., Jr., and Lau, 

L.S., 1970, Identification of irrigation return water in the 

sub-surface, phase III Kahuku, Oahu and Kahului and 

Lahaina, Maui: University of Hawaii, Water Resources 

Research Center Technical Report no. 44, 53 p.

U.S. Geological Survey, 2006a, Synoptic water-level survey, 

Central Maui, Hawaii: [http://hi.water.usgs.gov/projects/cmaui_gw/synoptic_cmaui_data.htm. accessed 

June 16, 2006].

U.S. Geological Survey, 2006b, Revised measuring-point 

elevations for selected wells in the Waihee and Iao Aquifer 

areas on the Island of Maui: [http://hi.water.usgs.gov/

studies/cmaui_gw/project_cmaui_mp.html. , accessed 

June 16, 2006].

U.S. Geological Survey, 2006c, Recent hydrologic conditions, Iao and Waihee aquifer areas, Maui, Hawaii: [http://

hi.water.usgs.gov/iao/iao_summary.htm. accessed November 27, 2006].

Voss, C. I., and Provost, A.M., 2003, SUTRA, a model for 

saturated-unsaturated variable-density ground-water flow 

with solute or energy transport: U.S. Geological Survey 

Water-Resources Investigations Report 02-4231, 250 p. 

Wahl, K.L., and Wahl, T.L., 1995, Determining the flow of 

Comal Springs at New Braunfels, Texas: Proceedings of 

Texas Water ’95, A Component Conference of the First 

International Conference on Water Resources Engineering, 

American Society of Civil Engineers, August 16-17, 1995, 

San Antonio, Texas, p. 77-86.

Wentworth, C.K., 1938, Geology and ground water resources 

of the Palolo-Waialae District; Honolulu, Hawaii: Honolulu 

Board of Water Supply, 274 p.

Wentworth, C.K., 1951, Geology and ground-water resources 

of the Honolulu-Pearl Harbor area, Oahu, Hawaii: Honolulu 

Board of Water Supply, 111 p.

Western Region Climate Center, 2007, Climatological Data 

Summaries: [http://www.wrcc.dri.edu/summary/Climsmhi.

html. accessed July 24, 2007].

Winston, R.B., and Voss, C.I., 2003, SutraGUI, a graphicaluser interface for SUTRA, a model for ground-water flow 

with solute or energy transport: U.S. Geological Survey 

Open-File Report 03-285, 114 p., [http://water.usgs.gov/nrp/

gwsoftware/sutra.html].

Yamanaga, George, and Huxel, C.J., 1969, Preliminary report 

on the water resources of the Lahaina District, Maui: State of 

Hawaii, Department of Land and Natural Resources, Division 

of Water and Land Development, Circular C51, 47 p.

Yamanaga, George, and Huxel, C.J., 1970, Preliminary report 

on the water resources of the Wailuku area, Maui: State of 

Hawaii, Department of Land and Natural Resources, Division of Water and Land Development, Circular C61, 43 p.
Appendix A–C 79

Appendixes A–C
80 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Appendix A. Wells in the central Maui study area with stratigraphic 

information, Hawai‘i

Table A1. Information for wells with stratigraphic information in the central Maui study area, Hawai‘i. 

[Altitude relative to mean sea level; ft; feet; --, not applicable; CWRM, State of Hawai‘i Department of Land and Natural Resources 

Commission on Water Resource Management; USGS, U.S. Geological Survey Pacific Islands Water Science Center; TH, test hole]

Well 

number Local well name

Altitude of top 

of Wailuku 

Basalt

(ft)

Altitude of top of 

Honomanü Basalt / 

Kula Volcanics

(ft)

 Reference

4829-01 Keälia Pond -- -26 CWRM well completion report

4829-02 Mäÿalaea Power Plant -- -38 do

4829-03 Mäÿalaea Back-Up -- -15 do

4829-04 Mäÿalaea M-17 -- -53 do

4830-01 Mäÿalaea Triangle 16 -- do

4831-01 Mäÿalaea 272 130 -- State of Hawaii (1967)

4928-02 Puÿunënë Airport Shaft -- 45 Stearns and Macdonald (1942)

4929-01 Field 910 -- 24 do

4931-01 Near Puÿu Hele 264 -- do

4936-01 Olowalu ÿElua 135 -- CWRM well completion report

5028-01 Waikapü Shaft TH -- 61 Stearns and Macdonald (1942)

5028-02 Waikapü Shaft TH -- 25 do

5128-01 Waikapü Shaft TH -- -40 do

5130-01 Waikapü 1 383 -- State of Hawaii (1961)

5130-02 Waikapü 2 210 -- unpublished driller’s log in USGS files

5138-01 Launiupoko 1 566 -- do

5227-06 Tmk 3-8-09-24 -- 14 do

5228-08 Tmk 3-8-23-18 -- -6 do

5228-14 Tmk 3-8-19-29 -- 24 do

5228-15 Molokaÿi Street Disposal -- 9 Peterson and Hargis (1971)

5228-17 Luana II-1 -- 42 CWRM well completion report

5228-18 Luana III-2 -- 47 do

5228-19 Kahului -- 36 do

5228-20 ÿElima Irrigation -- 43 do

5229-01 Waiÿale Prototype -- 80 Soroos (1979)

5229-02 Maui Lani 1 -- 85 CWRM well completion report

5229-03 Maui Lani 2 -- 30 do

5230-01 Ka Hale A Ke Ola -- 141 do

5240-04 Lahaina -45 -- unpublished driller’s log in USGS files

5327-10 Kanahä Pond -- -35 do

5328-01 Cannery Shaft -- 15 do

5328-02 Cannery -- -50 Peterson and Hargis (1971)

5328-22 Kahiki Street -- -65 do
Appendix A 81

 Well number Local well name

Altitude of top 

of Wailuku 

Basalt

(ft)

Altitude of top of 

Honomanü Basalt / Kula 

Volcanics

(ft)

Reference

Table A1. Information for wells with stratigraphic information in the central Maui study area, Hawai‘i.—Continued

[Altitude relative to mean sea level; ft; feet; --, not applicable; CWRM, State of Hawai‘i Department of Land and Natural Resources 

Commission on Water Resource Management; USGS, U.S. Geological Survey Pacific Islands Water Science Center; TH, test hole]

5328-23 Kahiki Street -- -14 do

5328-24 Fair Grounds -- -52 Stearns and Macdonald (1942)

5328-26 Cannery -- -48 Peterson and Hargis (1971)

5328-27 Cannery -- -30 do

5328-28 Cannery -- -20 do

5328-30 Tmk 3-8-18-9 -- -8 unpublished driller’s log in USGS files

5328-31 -- -5 do

5328-32 Tmk 3-8-23-1 -- -14 do

5328-33 Tmk 3-8-19-14 -- -12 do

5328-34 Tmk 3-8-22-1 -- -9 do

5328-35 Tmk 3-8-15-1 -- -23 do

5328-36 Tmk 3-8-23-35 -- -21 do

5328-37 Tmk 3-8-23-45 -- 13 do

5328-38 Tmk 3-8-19-37 -- -1 do

5328-39 Tmk 3-8-12-60 -- -26 do

5328-40 Tmk 3-8-16-31 -- -19 do

5328-41 Tmk 3-8-19-51 -- 2 do

5328-42 Kauaÿi Street -- -16 Peterson and Hargis (1971)

5328-43 Kahului -- 2 unpublished driller’s log in USGS files

5328-45 Kahului -- 4 Soroos (1979)

5328-48 Hale Mahaolu II -- 4 CWRM well completion report

5328-49 Kahului Community Park -- 26 do

5329-01 Tmk 3-8-35-70 -- 43 unpublished driller’s log in USGS files

5329-06 Baldwin High TH -- 16 Stearns and Macdonald (1942)

5329-08 Tmk 3-8-40-5 -- 44 unpublished driller’s log in USGS files

5329-09 Tmk 3-8-30-39 -- 21 do

5329-10 Tmk 3-8-39-30 -- 33 do

5329-11 218 Hõlua Avenue -- 48 Peterson and Hargis (1971)

5329-12 Hõlua Avenue -- 88 do

5329-13 Kunu Place -- 40 do

5329-18 Waiÿale Observation -- 38 Soroos (1979)

5329-19 Maui Central Park 1 -- 10 CWRM well completion report

5329-20 Maui Central Park 2 -- 14 do

5329-21 Maui Central Park 3 -- 3 do

5330-03 TH-112 68 -- unpublished geologist log in USGS files

5330-04 Wailuku Mill TH -- -16 do
82 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

 Well number Local well name

Altitude of top 

of Wailuku 

Basalt

(ft)

Altitude of top of 

Honomanü Basalt / Kula 

Volcanics

(ft)

 Reference

[Altitude relative to mean sea level; ft; feet; --, not applicable; CWRM, State of Hawai‘i Department of Land and Natural Resources 

Commission on Water Resource Management; USGS, U.S. Geological Survey Pacific Islands Water Science Center; TH, test hole]

5330-05 Wailuku Shaft 33 68 -- do

5330-06 Mokuhau TH 1 -150 -- do

5330-07 Mokuhau TH 2 3 -- do

5330-08 Mokuhau TH 3 -25 -- do

5330-09 Mokuhau 1 -58 -- unpublished driller’s log in USGS files

5330-12 Puÿuohala TH-C -151 -- Stearns (1976)

5331-01 TH-102 303 -- Stearns and Macdonald (1942)

5427-01 Kahului PP A -- -88 unpublished driller’s log in USGS files

5427-08 Injection Test -- -58 do

5429-02 Päpöhaku Park -- -55 CWRM well completion report

5430-01 Waiehu Heights 1 187 -- Stearns (1976)

5430-03 TH-E -76 -- do

5430-04 TH-D 89 -- do

5430-05 Waiehu Deep Monitor well 99 -- unpublished driller’s log in USGS files

5431-01 TH-B 463 -- Stearns (1976)

5431-04 Waiheÿe 3 413 -- CWRM well completion report

5530-02 Waiehu TH -97 Stearns and Macdonald (1942)

5631-02 North Waiheÿe 1 250 -- CWRM well completion report

5731-02 Känoa 1 60 -- C. Takumi Engineering Inc. (1999)

5731-03 Küpaÿa 1 564 -- do

5731-05 Känoa TH 57 -- do

5840-01 ÿAlaeloa 175 -- State of Hawaii (1965)

5841-03 Shoemaker 4 -- CWRM well completion report

GS-5 -- -50 Burnham and others (1977)

GS-7 -- -5 do

GS-4 -- -65 do

Table A1. Information for wells with stratigraphic information in the central Maui study area, Hawai‘i.—Continued
Appendix B 83

Appendix B. Monthly ground-water withdrawals during 1900–2006 from 

wells in central and west Maui, Hawai‘i WITHDRAWAL, IN MILLION GALLONS

0

10

20

30

40

50

60

70

0

20

40

60

0

40

80

120

160

0

10

20

30

40

0

4

8

12

16

20

0

2

4

6

8

10

12

14

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

2

4

6

8

10

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

2

4

6

8

10

12

0

4

8

12

16

0

5

10

15

20

25

Seibu 2 (3826-01)

Seibu 4 (3826-03)

Wailea 8 (3926-03)

Seibu 6 (3926-05)

Seibu 10 (3926-08)

Seibu 3 (3826-02)

Seibu 1 (3926-02)

Seibu 5 (3926-04)

Seibu 8 (3926-06)

Seibu 11 (3926-09)

monthly monthly

monthly

monthly

monthly

monthly

monthly

monthly

monthly

monthly

yearly

yearly yearly

yearly

Figure B1. Monthly ground-water withdrawals during 1900–2006 from wells in central and west Maui, Hawai‘i.
84 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure B1.—Continued.

0

20

40

60

0

40

80

120

160

0

10

20

30

40

0

4

8

12

16

20

0

4

8

12

16

0

2

4

6

8

10

12

14

0

2

4

6

8

10

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

2

4

6

8

10

12

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

1

2

3

4

0.0

0.2

0.4

0.6

0.8

1.0

WITHDRAWAL, IN MILLION GALLONS

monthly

monthly

monthly

monthly

monthly

monthly

monthly

monthly

monthly

yearly

yearly yearly

monthly

Mäkena Surf (3926-11)

Wailea 6 (4026-05) Wailea 7 (4026-06)

Wailea 2 (4126-02)

Wailea 5 (4226-12)

Wailea 10 (4226-14) Maui Kama‘ole (4226-16)

Wailea 9 (4226-13)

Wailea 3 (4126-03)

Wailea 4 (4026-04)
Appendix B 85

Figure B1.—Continued.

0

5

10

15

20

25

30

35

0.02

0.04

0.06

0.08

0

500

1,000

1,500

2,000

2,500

3,000

3,500

0.0

0.00

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0

2,000

4,000

6,000

8,000

0

200

400

600

800

1,000

1,200

0

100

200

300

400

500

600

700

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

200

400

600

800

1,000

1,200

1,400

withdrawal x 1,000

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

100

200

300

400

500

600

WITHDRAWAL, IN MILLION GALLONS

Kïhei Maui R&T (4426-03)

Pump 1 (4727-01)

Kula Meadows (4822-01)

Pump P (4835-01)

Pu‘unënë (4928-02)

Pump O (4837-01)

Pump N (4937-01)

Pump 3 (4825-01)

Kïhei Community (4727-91)

Medo (4427-03)

monthly

monthly monthly

monthly

monthly

monthly

yearly

yearly

yearly

yearly

yearly

yearly

monthly monthly
86 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure B1.—Continued.

WITHDRAWAL, IN MILLION GALLONS

0

4

8

12

16

20

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

0

2

4

6

8

10

12

0

40

80

120

160

0

1

2

3

4

0

1

2

3

4

5

0

2,000

4,000

6,000

0

2,000

4,000

6,000

8,000

10,000

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

2,000

4,000

6,000

8,000

10,000

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

2,000

4,000

6,000

Pukalani Golf Course (5021-01)

Reynolds 1 (5129-01)

Puamana 1 (5140-01)

Pump 9 (5224-02)

Pump 6 (5226-02)

Pump 5 (5226-01)

Pump 8 (5227-04)

Puamana 2 (5140-02)

Pump 7 (5128-02)

Launiupoko 1 (5138-01)

monthly

monthly

monthly

monthly

monthly monthly

monthly

monthly

monthly

yearly

yearly

yearly

yearly yearly

yearly
Appendix B 87

Figure B1.—Continued. WITHDRAWAL, IN MILLION GALLONS

0

2,000

4,000

6,000

8,000

10,000

0.0

0.4

0.8

1.2

0.0

0.4

0.8

1.2

0.00

0.02

0.04

0.06

0.08

0

5

10

15

20

25

0

5

10

15

20

25

30

0.0

0.2

0.4

0.6

0

500

1,000

1,500

2,000

2,500

3,000

3,500

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

2,000

4,000

6,000

8,000

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

10

20

30

yearly

yearly

yearly

monthly

monthly

monthly

monthly

monthly monthly

monthly

monthly

monthly

monthly

Pump 19 (5227-05)

Luana III-2 (5228-18)

Maui Lani 1 (5229-02)

Ka Hale A Ke Ola (5230-01)

Pump B (5240-03)

Maui Lani 2 (5229-03)

Pump C (5240-01)

Hamakuapoko 2 (5320-01)

‘Elima Irrigation (5228-20)

Luana II-1 (5228-17)
88 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure B1.—Continued. WITHDRAWAL, IN MILLION GALLONS

10

20

30

40

1,000

2,000

3,000

4,000

500

1,000

1,500

2,000

2,500

3,000

3,500

20

40

60

0

1,000

2,000

3,000

4,000

5,000

0

1,000

2,000

3,000

4,000

5,000

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

2,000

4,000

6,000

8,000

10,000

0

10

20

30

40

50

0

20

40

60

80

100

120

140

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

0 0

0 0

400

800

1,200

monthly

monthly

monthly

monthly

monthly

monthly

monthly

monthly

yearly

yearly yearly

yearly

yearly

yearly

yearly

monthly

Kepaniwai (5332-05) Waipuka 1,2 (5339-01, -02)

Pump M (5340-01)

Hamakuapoko 1 (5420-02)

Kanahä 1, 2 (5339-03, -04)

Pump L (5341-01)

Pump 13 (5422-01)

Kailua Gulch (5423-01)

Pump 17 (5422-02)

Pump 16 (5423-02)
Appendix B 89

WITHDRAWAL, IN MILLION GALLONS

0

2,000

4,000

6,000

8,000

10,000

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

0

100

200

300

400

500

0

40

80

120

160

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

100

200

300

400

500

600

700

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

50

100

150

200

250

300

350

0

2,000

4,000

6,000

0

1,000

2,000

3,000

4,000

yearly

yearly

yearly

yearly

yearly

monthly

monthly

monthly

monthly monthly

monthly

monthly

monthly

Pump 18 (5321-01)

Old Pump 3 (5326-01)

Cannery Shaft (5328-01)

Brine Well 1 (5328-28)

Shaft 33 (5330-05) Mokuhau 1, 2, 3 (5330-10, -09, -11)

Hale Mahaolu II (5328-48)

Cannery (5328-02)

Central Power Plant (5327-07)

Pump 2 (5323-01)

Figure B1.—Continued.
90 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure B1.—Continued.

0

100

200

300

400

0

20

40

60

80

100

120

140

160

180

WITHDRAWAL, IN MILLION GALLONS

0

1,000

2,000

3,000

0

500

1,000

1,500

2,000

2,500

0

5

10

15

20

25

30

35

0

5

10

15

20

25

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

10

20

30

40

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

10

20

30

40

0

1,000

2,000

3,000

4,000

5,000

0

1,000

2,000

3,000

monthly

monthly

monthly

monthly

monthly

monthly

monthly

monthly

monthly

yearly

yearly

yearly

yearly

Pump 4 (5424-01)

Pump 11 (5520-01)

P-1 (5539-01)

Pu‘ukoli‘i (5540-01) Hähäkea 1 (5540-02)

P-2 (5539-02)

Pump 12 (5522-01)

Waiehu Heights 1, 2 (5430-01, -02) Waihe‘e 1, 2, 3 (5431-02, -03, -04)

Sprecklesville (5425-01)
Appendix B 91

Figure B1.—Continued. WITHDRAWAL, IN MILLION GALLONS

0

40

80

120

0

20

40

60

0

500

1,000

1,500

2,000

2,500

0

1,000

2,000

3,000

4,000

5,000

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

400

800

1,200

1,600

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

20

40

60

80

100

120

140

0.000

0.005

0.010

0.015

0.020

0.025

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0

10

20

30

0

400

800

1,200

1,600

monthly

monthly

monthly

monthly

yearly

yearly

yearly

yearly

monthly

monthly

monthly

monthly

monthly

monthly

Hähäkea 2 (5540-03)

Hokoana (5620-02)

North Waihe‘e 1, 2 (5631-02, -03)

Pump R (5640-01)

Pump F (5641-02)

Pump D (5641-01)

Känoa 1, 2 (5731-02, -04)

Honoköwai B (5638-03)

Pa‘uwela-Lewis 2 (5620-04)

Pump G (5541-01)
92 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Figure B1.—Continued. WITHDRAWAL, IN MILLION GALLONS

0

10

20

30

40

50

0

10

20

30

40

50

60

70

0

20

40

60

0

5

10

15

20

25

30

35

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

40

80

120

160

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

0

2

4

6

8

10

0

20

40

60

0

10

20

30

40

50

0

20

40

60

0

10

20

30

40

monthly

monthly

monthly

monthly

monthly

monthly

monthly

monthly

monthly

monthly

P-5 (5738-01)

P-6 (5739-02)

P-4 (5739-01)

Näpili A (5838-01)

Honokahua A (5838-03)

Honokahua B (5938-01)

Näpili B (5838-02)

Näpili C (5838-04)

Kapalua 1 (5938-02) Kapalua 2 (5938-03)
Appendix C 93

Appendix C. Properties of pumped wells in the central and west Maui 

study area, Hawai‘i.

Well no. Well name Year drilled

Altitude of top of 

open interval

(feet relative to sea 

level)

Altitude of bottom of 

open interval

(feet relative to sea 

level)

3826-01 Seibu 2 1978 6 -22

3826-02 Seibu 3 1978 7 -23

3826-03 Seibu 4 1978 7 -23

3926-02 Seibu 1 1977 9 -22

3926-03 Wailea 8 1976 -1 -29

3926-04 Seibu 5 1984 11 -19

3926-05 Seibu 6 1984 6 -24

3926-06 Seibu 8 1988 11 -19

3926-08 Seibu 10 1988 0 -24

3926-09 Seibu 11 1988 10 -20

3926-11 Mäkena Surf 2002 -4 -14

4026-04 Wailea 4 1972 0 -31

4026-05 Wailea 6 1975 8 -31

4026-06 Wailea 7 1975 5 -20

4126-02 Wailea 2 1969 3 -17

4126-03 Wailea 3 1969 0 -21

4226-12 Wailea 5 1972 0 -23

4226-13 Wailea 9 1989 0 -20

4226-14 Wailea 10 1990 6 -14

4226-16 Maui Kamaÿole 2001 4 -26

4426-03 Kïhei Maui R&T 1990 -3 -33

4427-03 Medo 1948 0 -14

4727-01 Pump 1 (shaft) 1900 0 -39

4822-01 Kula Meadows 2000 -6 -60

4825-01 Pump 3 (shaft) 1900 0 -47

4835-01 Pump P (shaft) 1934 0 -64

4837-01 Pump O (shaft) 1905 0 -40

4928-02 Puÿunënë (shaft) 1942 0 -3

4937-01 Pump N (shaft) 1933 0 -10

5021-01 Pukalani Golf Course 1972 -12 -52

5128-02 Pump 7 (shaft) 1926 0 -42

5129-01 Reynolds 1 1959 -32 -107

5131-01 Waikapü Tank 1999 -1 -101

5138-01 Launiupoko 1 1979 1 -44

5140-01 Puamana 1 1987 -3 -31

Table C1. Properties of pumped wells in the central and west Maui study area, Hawaiÿi.
94 Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i

Table C1. Properties of pumped wells in the central and west Maui study area, Hawaiÿi.—Continued

5140-02 Puamana 2 1987 -12 -45

5224-02 Pump 9 (shaft) 1938 0 -5

5226-01 Pump 5 (shaft) 1899 0 -45

5226-02 Pump 6 (shaft) 1934 0 -4

5227-04 Pump 8 (shaft) 1939 0 -4

5227-05 Pump 19 (shaft) 1952 0 -5

5228-17 Luana II-1 1986 -6 -38

5228-18 Luana III-2 1986 -5 -50

5228-20 ÿElima Irrigation 1997 3 -49

5229-02 Maui Lani 1 1980 -12 -52

5229-03 Maui Lani 2 1980 -5 -25

5230-01 Ka Hale A Ke Ola 1997 -21 -51

5230-03 ÿÏao Tank

5240-01 Pump C (shaft) 1897 0 -51

5240-03 Pump B (shaft) 1897 0 -20

5320-01 Hamakuapoko 2 1993 0 -32

5321-01 Pump 18 (shaft) 1938 0 -6

5323-01 Pump 2 (shaft) 1929 0 -42

5326-01 Old Pump 3 (shaft) 1898 0 -40

5327-07 Central Power Plant (shaft) 1894 0 -40

5328-01 Cannery Shaft (shaft) 1926 0 -4

5328-02 Cannery not available -120 -280

5328-28 Brine Well 1 1958 -278 -300

5328-48 Hale Mahaolu II 1979 9 -36

5328-51 ÿAkahi 1969 0 0

5330-05 Shaft 33 (shaft) 1946 30 -280

5330-09 Mokuhau 2 1953 -58 -247

5330-10 Mokuhau 1 1953 -69 -247

5330-11 Mokuhau 3 1967 not available -251

5339-01 Waipuka 1 1962 4 -57

5339-03 Kanahä 1 1977 1 -52

5340-01 Pump M (shaft) 1933 0 -1

5341-01 Pump L (shaft) 1897 0 -34

5420-02 Hamakuapoko I 1992 0 -63

5422-01 Pump 13 (shaft) 1923 0 -4

Well no. Well name Year drilled

Altitude of top of 

open interval

(feet relative to sea 

level)

Altitude of bottom of 

open interval

(feet relative to sea 

level)
Appendix C 95

5422-02 Pump 17 (shaft) 1932 0 -3

5423-01 Kailua Gulch (shaft) 1899 0 -5

5423-02 Pump 16 (shaft) 1899 0 -30

5424-01 Pump 4 (shaft) 1911 0 -35

5425-01 Sprecklesville (shaft) 1895 0 -50

5430-01 Waiehu Heights 1 1975 0 -338

5430-02 Waiehu Heights 2 1975 0 -206

5431-02 Waiheÿe 1 1976 -1 -182

5431-03 Waiheÿe 2 1976 -1 na

5431-04 Waiheÿe 3 1981 -1 -156

5522-01 Pump 12 (shaft) 1933 0 -5

5539-01 P-1 1990 -1 -61

5539-02 P-2 1991 0 -63

5540-01 Puÿukoliÿi 1968 0 -28

5540-02 Hähäkea 1 1971 0 -20

5540-03 Hähäkea 2 1971 0 -20

5541-01 Pump G (shaft) 1923 0 -2

5620-02 Hokoana 1969 0 -6

5631-02 North Waiheÿe 1 1981 -9 -106

5631-03 North Waiheÿe 2 1981 -19 -106

5638-03 Honoköwai B 1976 10 -43

5640-01 Pump R (shaft) 1952 0 -14

5641-01 Pump D (shaft) 1897 0 -23

5641-02 Pump F (shaft) 1921 0 -20

5731-02 Känoa 1 1999 3 -51

5731-03 Küpaÿa 1999 4 -49

5738-01 P-5 1982 4 -36

5739-01 P-4 1982 3 -54

5739-02 P-6 1982 1 -47

5838-01 Näpili A 1971 0 -33

5838-02 Näpili B 1972 1 -32

5838-03 Honokahua A 1978 0 -31

5838-04 Näpili C 1979 -1 -21

5938-01 Honokahua B 1987 0 -20

5938-02 Kapalua 1 1989 13 -54

5938-03 Kapalua 2 1991 -2 -42

Table C1. Properties of pumped wells in the central and west Maui study area, Hawaiÿi.—Continued

Well no. Well name Year drilled

Altitude of top of 

open interval

(feet relative to sea 

level)

Altitude of bottom of 

open interval

(feet relative to sea 

level)
128 A Volcano Rekindled: The Renewed Eruption of Mount St. Helens, 2004−2006

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2 A Volcano Rekindled: The Renewed Eruption of Mount St. Helens, 2004−2006

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Gingerich—Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i—Scientific Investigations Report 2008–5236