HYDROLOGY OF THE LEEWARD AQUIFERS, 

SOUTHEAST GAHU, HAWAII

By Paul Eyre, Charles Ewart, and Patricia Shade

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 85-4270

Honolu1u, hawa i i 

1986
UNITED STATES DEPARTMENT OF THE INTERIOR

DONALD PAUL MODEL, Secretary

GEOLOGICAL SURVEY 

Dallas L. Peck, Director

For additional information 

write to:

Copies of this report 

can be purchased from:

Distr ict Chief 

U.S. Geological Survey, WRD 

Rm. 6110, 300 Ala Moana Blvd. 

Honolulu, Hawaii 96850

Open-File Services Section 

Western Distribution Branch 

U.S. Geological Survey 

Box 25^25, Federal Center 

Denver, Colorado 80225 

(Telephone: [303] 236-7^76)
CONTENTS

Page

Abstract 1

Introducti on ----------------------------------------------------------- 2

Purpose and scope ------------------------------------------------- 4

Acknowledgment -_-----------------------_------_--_-------------- 4

Location and cultural setting ------------------------------------------ 5

Populat ion -------------------------------------------------------- 5

D ev e1opmen t ----------------------------------------------------- 7

Physical setting --- ------ -------------------- ------------------ 7

Climate ---- ------------------------ -------- ________-__--_--- 7

Topography --------_---------_--------------------------__-_----- 8

Geology --------------------------------------------------------- 11

Water-bearing rocks ---------------------------- ----- ---- - - 14

Surface water ------------------------- _____________________________ 17

Surface-water data ---------------------------------------------- 17

Surface-water development --------------------------------------- 19

Occurrence of ground water --------- -------__------------_--_-_-_----- 20

Dike-impounded water ---------------------------- _____--_------ 20

Perched water ------ - ------ __ 22

Basal water ---- ------- --- - 22

Calculation of ground-water flow rate through the Waialae

and Wai1upe-Hawaii Kai areas ------------------------------------ 26

Calculation of ground-water flow rate by Darcy's law ------------ 26

Water budget -- ------ ._.-._..__. .__ _ 30

Calculation of water budget parameters -------------------------- 32

Rainfall 32

Runoff -------- ------ -.- __ 34

Potential evapotranspirat ion --------------------------------- 36

Soil characteristics ----------------------------------------- 39

Calculation of recharge ------------------------------ _.-_ 4g

i i i
CONTENTS

Ground-water simulation ------------------

Conceptual model --------------------

Mathematical model ------------------

Model application and calibration -- 

Effects of pumping on the pre-pumping head distribution

Model predictions -------------------

Water quality -----------------------

Summary ----------------------------------

References -------------------------------

Supplemental data ------------------------

Page 

42

42

43

45

51

58

58

63

65

68

IV
ILLUSTRATIONS

Figure Page

1. Hydrologic study areas on the island of Oahu ----------------- 3

2. Leeward southeast Oahu study area ---------------------------- £

3. Oahu mean annual rainfall -------------------------------------- 9

4. Dominant landscape features of leeward southeast Oahu -------- 10

5. Rift zones and calderas of Koolau and Waianae volcanoes

on the island of Oahu ------------------------------------- 12

6. Generalized geologic map of leeward southeast Oahu ------------- 13

7. Dikes associated with the dike complex, marginal dike zone,

Kaau rift, Koko rift and other minor rifts in southern Oahu 15

8. Streams in leeward southeast Oahu ------------------------------ 18

9. Diagram showing perched water, water confined between dikes,

basal water, and perched and basal springs ---------- -- 21

10. Part of leeward southeast Oahu showing location of selected 

wells and distinctive basal-water reservoirs of 

different heads ------------------------------------------- 23

11. Section (A-A 1 ) across volcanic spurs at the 400-foot

contour showing thickness of basal-water reservoirs ----- 24

12. Section (B-B 1 ) across volcanic spurs at the 1,000-foot

contour showing thickness of basal-water reservoirs ------- 25

13. Water-level contour map of the Waialae area -------------------- 27

14. Finite-element mesh for leeward southeast Oahu ----------------- 33

15. Rainfal 1 -runoff relationship for leeward southeast Oahu -------- 35

16. Mean annual global radiation over Oahu ------------------------- 38

17. Finite-element mesh for leeward southeast Oahu showing

the thickness of the confining layer -------------------- 47

18. Simulated pre-pumping ground-water head

distribution in leeward southeast Oahu -- ---------------- 50

19. Simulated ground-water head distribution in 1971 as a

result of Waialae shaft and golf course well pumpage ------ 52

20. Simulated versus observed heads from 1935 to 1975 at

the Waialae shaft ---- - ------------------------------ 53
LLUSTRAT ION'S

Figure

21. Differences between observed and mean annual ra i nfal1,

and between simulated and observed heads

22. Simulated water levels using annually

and specific yields of 0.10, 0.05, and 0.02 

23. Simulated head versus time -------

2k. Steady-state head contours resulting from projected

pumpage in leeward southeast Oahu 

25. Maximum-minimum chloride concentration and pumpage at Waialae

adjusted recharge

shaft and rainfall at Wilhelmina Rise gage no. 721

Page 

54

56

59

60

61

Table 

1,

TABLES

occurrence of

Oahu

Water-bearing properties of rocks and

ground-water in leeward southeast 

Waialae shaft (1747-02) pumping test cjata for calculation of

aquifer hydraulic conductivity -----------------------

Water balance for leeward southeast Oc

Distribution of heads in leeward southeast Oahu

Cross reference of node numbers and we

hu

11 identification

16

29

41

49

49

VI
CONVERSION TABLE

The following table may be used to convert measurements in the inch-pound 

system to the International System of Units (SI).

Multip1y By To obtain

Length 

inch (in.) --------------------- 25.** ---- millimeter (mm)

foot (ft) 0.3048 meter (m) 

mile, statute (mi) ---- --- 1.609 ---- kilometer (km)

Area

2 2 

square foot (ft ) -- ---- 0.0929 ---- square meter (m )

2 2 

square mile (mi ) - -- --- 2.590 ---- square kilometer (km )

Volume

cubic foot (ft 3 ) 0.02832 cubic meter (m3 ) 

gallon (gal) 3.785 liter (L) 

mi 11 ion gal Ions (10 gal

o

or Mgal) ------- ----------- 3,7^5 ---- cubic meters (m )

Volume Per Unit Time (includes Flow)

 3 > 

cubic foot per second (ft /s) 0.02832 ---- cubic meter per second (m /s)

cubic foot per second-day

(ft 3 /s-d) 2,447 cubic meter (m3 ) 

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

million gallons per day

(10 gal/d or Mgal/d) 0.04381 cubic meter per second (mVs)

Niscellaneous 

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

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

2 2 foot squared per day (ft /d) 0.0929 ---- meter squared per day (m /d)

micromho per centimeter at 1.000 ---- microsiemens per centimeter at 

25° Celsius (ymho/cm at 25°C). 25° Celsius (pS/cm at 25°C).

VI I
HYDROLOGY OF THE LEEWARD AQUIFERS OF SOUTHEAST OAHU, HAWAII

By Paul Eyre, Charles Ewart, and Patricia Shade

ABSTRACT

The leeward southeast Oahu ground-water area includes the Waialae and 

Wai1upe-Hawaii Kai aquifers. The Waialae aquifer is separated from the ground 

water of Kaimuki to the west by Palolo valley fill and the Kaau rift zone, and 

from the Wai1upe-Hawaii Kai aquifer to the east by a line of northeast-trending 

volcanic dikes. The distinct ground-water head changes across these boundaries 

indicate that the aquifers are separate, with little or no leakage between them.

A water budget of leeward southeast Oahu determined the quantity and spatial 

distribution of ground-water recharge. These estimates of recharge, 6 million 

gallons per day over the Waialae area and 9.1 million gallons per day over the 

Wai1upe-Hawaii Kai area, were used as input to a finite-element two-dimensional 

ground-water flow model. Ground-water heads were simulated in the modeled 

aquifer for several pumping scenarios. Projected pumpage from the recently 

drilled wells in the area is predicted to draw the water table down about one 

foot from its present mean position.

The existing ground-water development of 1.4 million gallons per day is 

small compared to the quantity of ground-water that flows through the area and 

discharges to the sea. Because the Waialae and Wai1upe-Hawaii Kai aquifers are 

isolated from adjacent ground-water bodies, they can be fully developed without 

affecting ground-water resources outside the area.
NTRODUCTION

Many areas of the United States are dependent on ground water for a large 

part of their total water needs or for a ready reserve supply during droughts. 

As part of the national response to the severe drought of 1976-77 in the continental United States, the 95th Congress introduced a national program for the 

analysis of regional aquifer systems. The U.S. Geological Survey is conducting 

these studies.

Approximately 30 regional aquifer systems have been identified nationwide 

including the island of Oahu, Hawaii. The Regional Aquifer System Analysis 

(RASA) study for Oahu has two principal objectives: (1) to provide a firm 

understanding of the complex hydrology and hydraulics of Oahu's ground-water 

system, and (2) to provide a framework for future hydrologic studies and data 

gather!ng.

Oahu's regional aquifer system can be div

are enclosed by topographic divides (fig. 1). Tor the determination of recharge 

to the underlying ground-water bodies, topographic divides serve well as study 

area boundaries even though surface- and grounc-water divides may not coincide. 

Discrepancies between the location of topographic divides and ground-water 

boundaries, and the consequent adjustments in ground-water recharge, will be

ided into five study areas which

addressed in specific reports for each study

affect the flow of ground water within study areas will also be addressed in the 

individual reports.

area. Geologic boundaries that
158° 15' 158°00' 

21° 

301

'° *

HAWAIIAN 

ISLANDS

£>

0

OAHU

5 

NORTH - CENTRAL OAHU 

STUDY AREA WINDWARD

OAHU 

^STUDY

VAREA

SOUTHERN OAHU 

STUDY AREA

'L

/ S

Figure I. Hydrologic study areas on the island of Oahu.
Purpose and Scope

To define the hydraulics and hydrology of Oahu's ground-water system, the 

study areas need to be analyzed individually and their relationship to each other 

defined.

This report describes the aquifers in the 

It presents a conceptual model of the aquifer 

steady-state and transient flow conditions

eeward southeast Oahu study area, 

flow system, and simulations of 

obtained from a finite-element

aquifer model.

The report is the first of a series of reports defining Oahu's regional 

aquifer system.

Acknowledgment^

The authors thank Clifford Voss of the U.S. Geological Survey, Northeastern 

Regional office, for introducing them to the AQUIFEM-SALT model (Voss, 1984a), 

developing the finite-element mesh, and guiding their efforts in applying the 

mod e1.
LOCATION AND CULTURAL SETTING

Leeward southeast Oahu has an area of 23.4 square miles (fig. 2). The area 

is bounded on the north by the crest of the Koolau Range, on the south and east by 

the Pacific Ocean, and on the west by the Kaau rift zone, represented by a 

southwest-trending line from Kaau Crater at the crest to Diamond Head Crater at 

the coast.

It is unlikely that the Palolo valley fill, thought by Wentworth (1938) to 

be the western boundary of the study area, could be the cause of the 10-foot head 

difference that marks the separation of the ground water in the study area, from 

the ground water in the Kaimuki area to the west. At low elevations, the 

relatively impermeable valley fill is deep enough to affect the flow of ground 

water. However, at high elevations, the fill is not deep enough to intersect the 

water table and ground-water levels would be nearly the same in the two areas if 

not for the boundary created by the Kaau rift.

For this study, leeward southeast Oahu can be further divided into two 

areas; the Waialae area bounded on the west by the Kaau rift zone and on the east 

by a northeast-trending line of dikes, and the Wai lupe-Hawa i i Kai area which 

comprises the remainder of the study area.

Population

In 1980, the State population was 963,617 of whom 760,926 or almost 80 

percent resided on the island of Oahu (State of Hawaii, 1980). This 80 percent 

of the population live on about nine percent of the total land area yielding an 

average density on Oahu of about 1,300 persons per square mile. The study area 

has a population of about 50,000 most of whom reside in the heavily developed 

valley floors and narrow coastal plain from Diamond Head to Koko Head.
Figure 2. Leeward southeast Oa^u study area,
Development

The island of Oahu is the hub of commerce, industry, and government in the 

State of Hawaii. Most of these activities are located west of the study area 

between Diamond Head and Pearl Harbor. The leeward southeast Oahu study area 

lies east of the center of activities and serves as a major residential and 

recreational area. From the eastern flank of Diamond Head to Makapuu Point 

virtually every valley floor and several interval ley ridges are developed for 

residential use.

Prior to statehood in 1959, the principal residential area was near WaialaeKahala in the southern part of the Waialae area. Elsewhere, most of the 

population was involved in small-scale farming, raising pigs, vegetables, and 

flowers. Marsh areas and brackish-water springs, resulting from the near-shore 

discharge of groundwater, occurred across the area, but these have since been 

destroyed by urban development. Presently, scenic areas, surfing beaches, and 

two golf courses offer recreational opportunities to both residents and 

visi tors.

PHYSICAL SETTING

C1imate

Hawaii has a subtropical climate characterized by mild and equable temperature year round, persistent northeasterly tradewinds, moderate humidity, and 

extreme differences in rainfall within short distances. In most areas of the 

State including the study area, there are two seasons; summer between May and 

October, with warm, dry weather, and winter between November and April, with 

cooler temperatures, more cloudy rainy conditions, and a less dominant tradewind 

pattern.

Blumenstock and Price (1967) recognized seven climatic subregions in Hawaii 

based on major physiographic features and orientation to windward or leeward 

exposure. The southeast Oahu study area consists of two climatic subregions; the 

leeward lowlands, and the leeward mountain slopes.
The leeward lowlands have slightly higher daytime temperatures and slightly 

lower nighttime temperatures than in the windward lowland locations. Dry weather 

predominates, interrupted infrequently by light tradewind showers or major 

storms. The leeward mountain slopes have greater rainfall than the leeward 

lowlands, but generally significantly less rainfall than at the same elevation on 

the windward slopes. Temperature extremes and cloud cover are less on leeward 

slopes than on windward slopes. The mean annual temperature of the study area is 

about 75 F« The warmest and coolest months differ on the average by only 6.5 F.

Rainfall on the study area averages 50 inches annually or 56.8 Mgal/d

(million gallons per day) (fig. 3). The isohyel:s indicate a decrease in rainfall 

west to east across the study area, from about 118 inches near Kaau Crater to 

about 30 inches at Makapuu Point. The rainfall gradient from north to south is 

quite steep, especially at the western end of the study area (Kaau Crater to

Diamond Head). Most of the residential areas receive between 30 and 35 inches

annually.

Topography

Most of the leeward southeast Oahu study area consists of the eroded 

southeastern flank of the Koolau Volcano. The Koolau crest is highest at Puu 

Lanipo, 2,621 ft above sea level, and decreases eastward to about ^00 ft at 

Makapuu Point. The shape of valleys in southeast Oahu results from the combined

effects of stream erosion, and deposition from recent volcanic eruptions and 

higher stands of the sea. Thus, the valleys are U-shaped to box-shaped in their

lower reaches, where deposition was dominant and V-shaped with amphitheater

heads in the upper reaches. The steep, corrugated inter-valley ridges extend 

almost to the shore. i

The valleys tend to broaden below about the 200-ft altitude and join a 

narrow coastal plain. Near Diamond Head and Koko Head Craters, the coastal plain 

is significantly enlarged by the ash deposits resulting from the eruptions at

these craters. li |

I 

In addition to the Koolau crest and the deeply incised narrow valleys, the

dominant landscape features are the craters) and vents associated with the 

Quaternary Honolulu Group. Diamond Head, Kaau', and Kaimuki Craters are located 

at the western boundary of the study area, >and Koko Head, Koko Crater, and

Hanauma Bay Crater are at the eastern boundary (fig.

,8
5 MILES 

J

6 KILOMETERS

N

KAAU CRATER

0 1

1 1 1

*> 012 

>w

<? A

O ,$ 

<& $ 

 *? &££

f PUD LANIPO/^AS^" 

^ , / Q

234 MILES 

i i i

I i i

345 KILOMETERS

Outside of 

study 

area /O

\

Figure 3. Oahu mean annual rainfall in inches (Schroeder and Meisner, 1980)
Area

EXPLANATION

Former shoreline prior to 

eruption of Honolulu Group

of study

0

h

0

i

1

1 

i

i

2

2 

i

I

3

I

4

3 

i

1

5

4 MILES

i

KILOMETERS

KAAU CRATER

Outsld* of 

study 

area

Figure k. Dominant landscape features

10

of leeward southeast Oahu,
Geology

The following discussion of the volcanic history and description of the 

rocks of southeast Oahu are based on the investigations of Stearns and Vaksvik 

(1935), Palmer (1921 and 1955), Wentworth (1938), Wentworth and Jones (19^0), and 

Takasaki and Mink (1982).

Oahu was formed by the building and coalescing of the Koolau and Waianae 

shield volcanoes. Each volcano has a collapsed caldera at or near its summit 

with two principal rift zones and one minor rift zone extending outward from the 

caldera area (fig. 5). The shield volcanoes are built primarily of thin basaltic 

lava flows which form slopes of 3 to 10 degrees. The leeward southeast Oahu 

study area includes parts of the southeast and southwest rift zones. The Kaau 

rift and a line of northeast trending dikes about 1.5 miles to its east are 

features of the southwest rift zone. The southeast rift zone, along the Koolau 

crest, is one of the two main fissure zones from which Koolau lavas emanated. 

Extensive erosion occurred during a long period of quiescence following the 

initial mountain-building phase of volcanic activity. This erosion resulted in 

the deposition of sediments in coastal areas which helped to form a narrow 

coastal plain. The coastal plain was further developed as coral reefs grew and 

eroded during sea-level fluctuations that accompanied Pleistocene glaciation in 

North America and Europe. Thus, fossil coral reefs and marine and terrestrial 

sediments make up the bulk of the coastal-plain deposits which form a caprock of 

low permeability over the highly permeable Koolau lavas. The long period of 

volcanic quiescence was followed by a renewal of volcanic activity in 

southeastern Oahu which produced the volcanic rocks of the Honolulu Group.

In the study area, the Honolulu Group (fig. 6) is represented by Diamond 

Head, Kaimuki Crater, Mauumae Crater, Kaau Crater along the Kaau rift, which is a 

reactivated rift of the Koolau volcano, and by Kcko Head and Koko Crater along 

the Koko rift, a rift of only the Honolulu Group. The rocks of the Koko rift 

consist almost entirely of ejecta, and some lava flows, of the post-erosional 

Honolulu Group. In general, lava flows of the Honolulu Group are thicker and 

more massive than the older Koolau lavas. A generalized geologic map (fig. 6) 

shows the distribution of the principal rock types.

11
N

Figure 5. Rift zones and calderas of Koolau and Waianae volcanoes on 

the Island of Oahu (modified from Macdonald, 1972).

12
N

2 MILES

Kaau 

Crater

Mauumae, and * 

Kaimuki

Craters

2 KILOMETERS

EXPLANATION

Calcareous sediments 

Talus and alluvium 

Ejecta I

-QUATERNARY

r Honolulu Group

Koolau Volcanics r TERTIARY (?)

Diamond 

Head

Figure 6. Generalized geologic map of leeward southeast Oahu (geology modified from Stearns, 1939).
The southeast rift zone separates ground water on the leeward side of the 

crest from that on the windward side. Where exposed by erosion, the rift zone is 

marked by numerous dikes, (fig. 7) which are vertical sheets of dense rock that, 

in their molten state, rose from deep within t^e island to feed the lava flows 

that erupted from the rift zone. The number of dikes is greatest in the central 

part of the zone, the "dike complex11 (Stearns and Vaksvik, 1935)> averaging more 

than 100 dikes per mile of horizontal distance (Macdonald, 1956), and usually 

composing more than 10 percent of the total 

decreases to between 10 and 100 dikes per m

rock volume. Dike occurrence 

le in the "marginal dike zone"

adjacent to the dike complex, and this number declines abruptly at the edges of 

the rift zone (Macdonald and Abbott, 1970). The dikes in the marginal dike zone

make up less than 5 percent of the total rock vc lume. Generally, the strike and

alignment of dikes is the same in each zone.

Dikes number much fewer than 100 dikes per mile in the Kaau rift and even 

less in the Koko rift and in the line of northeast trending dikes (Takasaki and 

Mink, 1982). The strike and alignment of dikes in the study area are nearly 

parallel to the lava flows and the direction of ground-water flow. This 

alignment does not impound water to high elevations as effectively as in other 

areas of Oahu where dikes are perpendicular to tie direction of ground-water flow 

(Takasaki and Mink, 1982). However, dikes in 

northeast trending dikes act as barriers to the lateral flow of ground water

between the ground water of Kaimuki (to the west 

Wailupe-Hawa ii Kai.

of the study area), Waialae, and

Water-Bear ing Rocks

The rocks of leeward southeast Oahu include dike-free and dike-intruded 

lava flows, breccia, tuff, cinders, and sedimentary material of volcanic origin. 

Coastal-plain deposits contain sedimentary rofcks of volcanic origin, clays,

coral, calcareous beach sand, and dunes. Permeability and the nature of groundI 

water occurrence for each of these rock types are presented in table 1.
157°50' 

21°30

157°40'

0123 4 KILOMETERS

^ ' rill 5 i,s.

> !_V i- j

Base from U.S. Geoloaical Survey 1:62,500 Island of Oahu, 1954

Figure J 0 Dikes associated with the dike complex, marginal dike zone, Kaau 

rift, Koko rift and other minor rifts in southern Oahu (modified 

from Takasaki and Mink, 1981).

15
Table 1. Water-bearing properties of the rocks and occurrence 

of ground water in leeward southeast Oahu

I 

(Modified from Takasaki and Mink, 1982)

Rock type PermeabiIi ty

Hydrauli c 

conductivity (K) 

(ft/d)

Ground-water 

occurrence

Principal Secondary

Sedimentary material 

Coral

In situ Moderate to high 100 to! 1000 Basal* Perched. 

Reworked - - - Low to moderate 1 to 500 do. Oo. 

Consolidated Low 1 to 100 do. Do. 

Unconsoli dated Moderate to high 100 to 1000 do. Do. 

Dunes

In situ -- - - - Low to moderate 1 to 500 Perched Basal. 

Reworked do. 1 to 500 Basal Perched. 

Consolidated Low 1 tO| 100 Perched Basal. 

Unconsolidated ~ - Low to moderate 1 to i 500 Basal Perched. 

Sand |

Consolidated - Low to moderate 1 to 500 Basal 

Unconsolidated Moderate to high 100 to 1000 do. 

Lagoonal

Sands || 

In situ

Consolidated Low 1 to 100 Basal 

Unconsolidated - Low to moderate 1 to 500 do. 

Muds

In situ

Consolidated - Very low less than 1 Perched 

Unconsolidated - Very low ! do> do. 

Alluv ium 

Younger

In situ -- - Low to moderate 1 to 500 Perched Perched. 

UnconsoIidated - do. 1 to 500 do. Do. 

Older I

In situ - - - Very low less than 1 Perched 

Reworked - do. do. do. 

Consolidated -- do. do. do. 

Unconsoli da ted Low 1 to 100 do. Basal. 

Volcanic

Honolulu Group 

Insi de caldera

Lava flows ~ - - Low to moderate 1 to 500 Perched 

Cinders Low 1 to 100 do. 

Tuff - Low 1 to 100 do. 

Outside caldera 

Lava flows

Dike complex -- Low to moderate I to 500 do. 

Marginal dike zone - do. 1 to 500 do. 

Dike-free High to very high 500 to 1000 Basal Perched. 

Cinders -- - - Low to moderate 1 to 500 Perched 

Tuff Low 1 to 100 Basal Perched. 

Saprolite -- - Very low | less than 1 Perched 

Koolau Volcanics 

Inside caldera

Lava flows - - Low 1 to 100 Dikeimpounded Perched.

Breccia do. 1 to[ 100 Perched 

Outside caldera '

Dike complex Low to moderate 1 to' 500 Dikeimpounded Perched.

Marginal dike zone Moderate to high 100 to 1000 do. Basal. 

Dike-free Very high greater than 1000 Basal 

Breccia Low 1 toj 100 Perched 

Saprolite (highly I 

weathered rock) - Very low less than 1 do.

Basal refers to the lens of freshwater floating on

16

seawater.
SURFACE WATER

Sixteen streams drain the study area and flow in the same southerly 

direction from the Koolau crest (fig. 8). These streams are intermittent except 

for short stretches near the head of some streams where perennial flow is low.

The streams are short, have steep gradients, and generally flow in narrow 

rectangular channels that are roughly normal to the crest of the Koolau Range. 

Of the 16 streams, 10 have no well-defined tributaries and 6 streams have one or 

more. In general, the drainage basins are shorter and wider in the eastern part 

of leeward southeast Oahu (Wailupe to Makapuu) than in the western part. No 

perennial streamflow reaches the ocean in the study area.

Surface-Water Data

With the exception of Waiomao Stream in the northwest corner of the study 

area, very little surface-water data exist. The U.S. Geological Survey operated 

a recording gage station (no. 2^60) on Waiomao Stream from June 1926 through 

September 1971 (fig. 8). The drainage area above the gage is 1.0^ square miles 

and the stream has a mean daily discharge of 1.86 ft /s (cubic feet per second)

based on ^5 years of record. The maximum discharge during this period occurred 3 

on April 11, 1930 when a peak of 1,550 ft /s was recorded. There were frequent

periods of no flow during dry weather.

Crest-stage partial-record stations in Wailupe Gulch (no. 2^75) and 

Kuliouou Valley (no. 2^79) are designed to record peak stages throughout the year 

from which the annual peak discharge is determined. Since 1958, annual peak 

flows have been recorded for Wailupe Gulch. The highest measured flow was 3,600 

ft /s which occurred on Dec. 18, 1967. In Kuliouou Valley, records of annual 

peak flows are available for 1958-59, and from 1970 to present. The highest flow

 3

during the period was 1,290 ft /s on Jan. 6, 1982.

17
Area of study

4 MILES 

j

5 KILOMETERS

KAAU CRATER

Outside of

Figure 8. Streams in leeward

18

southeast Oahu,
Flow to the sea occurs only during and after heavy rainfall. Streams in the 

Waialae area are perennial only at their headwaters near the Koolau crest. Data 

are insufficient to quantify the perennial flow, but a qualitative assessment can 

be made. Generally, the magnitude of perennial flow in a stream cut into dikeintruded rocks depends on the orientation of the dikes to the ground-water flow 

direction, size of the dike-impounded ground-water reservoir, quantity and 

frequency of recharge to the reservoir, and how deeply the stream has eroded into 

the reservoir. This general statement can also be made about perched water in a 

drainage basin.

In the Waialae area, the major perennial flow is from the headwaters of 

Waiomao Stream. Wentworth (1938) noted persistent seepage and what he termed 

"nearly perennial pools" in Waialaenui and Kapakahi Valleys. However, Takasaki 

and Mink (1982) did not find this to be true during their investigation. The 

only perennial flow they observed was in Wailupe Gulch where a small flow of 0.1 

to 0.2 Mgal/d originated in a small amphitheater-1 ike valley above an altitude of 

1,120 feet. In summary, the amount of perennial flow in this part of the study 

area is quite small when compared to the mean annual rainfall. Streams in the 

eastern part (Hawaii Kai) of the study area have no perennial flow even in their 

headwaters and quickly go dry after rain storms.

The estimated mean annual surface runoff for each basin in the study area 

was determined from a multiple regression equation developed by Matsuoka 

(written commun., 1981), which uses mean annual basin runoff as the dependent 

variable, and mean annual basin rainfall, drainage area, stream slope, and 

percent forest cover as the independent variables. The mean annual runoff from 

the study area is 6.^ Mgal/d. The estimated mean annual runoff for the 

individual basins ranges from 0.9 Mgal/d for the Waiomao basin to .05 Mgal/d for 

the Hawaii Kai golf course basin, northeast of Koko crater.

Surface-Water Development

Surface-water resources in the study area have not been developed. Because 

of the flashy nature of the streams and a lack of suitable sites capable of 

storing significant quantities of runoff, the development and utilization of 

streamflow is not feasible.

19
OCCURRENCE OF GROUND WATER

Dike-impounded water, perched water, and basal water are the three 

principal modes of ground-water occurrence on Oahu (fig. 9). Each of these will 

be discussed in relationship to the study area.

Dike-Impounded Water

Dike-impounded water refers to ground water impounded by volcanic dikes 

usually at high altitude in the interior of the island. Because of the vertical 

structure of the dikes this ground water does not come in contact with seawater.

In the study area, reservoirs of dike-impounded water are located in the Kaau and

i 

southeast rift zones near the crest of the KoolaU Range. Elsewhere in the study

area, dikes are less common and trend nearly parallel to the direction of groundwater flow. Therefore, ground water is not impounded in these areas.

Around 1910, two tunnels were driven into the east wall of Kaea Valley on

the southwest side of Kaau Crater. One tunnel, located at an altitude of about

1,130 feet was 100 feet in length. The tunnel iwas driven through dense Koolau 

lava which was broken by numerous joints. The maximum reported yield was about 

100,000 gallons per day. The tunnel was in service until 1920 when the portal 

was clogged with debris and the yield had dropped to a trickle. The second 

tunnel, driven at an altitude of about 870 feet was 120 feet long and in dense 

Koolau Volcanics. No water was developed from this tunnel, and both tunnels were 

abandoned (Stearns and Vaksvik, 1935).

Palolo tunnel, located at the site of th e former Waiomao Springs at an

altitude of 990 feet on the west bank of Waiomab Stream, was dug in 1920. The 

tunnel is 180 feet long and penetrates the permeable clinker zone of an aa lava 

flow and one 4-foot-thick dike. This dike, like many others in the area, trends 

slightly east of north. Discharge from the tunnel is variable and appears to 

fluctuate with rainfall. Initial tunnel discharge was about 1.5 Mgal/d and

lasted only a few months (Stearns and Vaksvik, 1935). The mean discharge in 1982 [

was 290,000 gallons per day (Honolulu Board of Water Supply, 1982). Water from 

the tunnel is used for domestic supply.

20
IZ

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to Q. 

to

3 

Q.
The small perennial flow observed near the heads of some valleys may be fed 

by the leakage of ground water through dikes, but no evidence of dike-impounded 

water in the middle and lower reaches of streams was found during field 

inspection by Takasaki and Mink, (1982). \

Perched Water

Perched water refers to water held up by a formation of low permeability,

which in Hawaii is usually a layer of weathered volcanic ash or alluvium. On 

Oahu the occurrence and importance of perched witer is small compared to dikeimpounded and basal water reservoirs and is important only locally. No evidence 

of significant discharges of perched water exists in the study area (Takasaki and 

Mink, 1S82), although some of the flow in upper Waiomao Stream may result from 

ground water perched on sills or low angle dikes.

Basal Water

Basal water is a lens of fresh ground water 

sea level and is in dynamic equilibrium with the

that is stored near and below 

underlying saline ground water.

Basal water can be confined or unconfined. Basal water occurs in all rocks that i

extend below sea level except in the rift zones. I Fresh to brackish water occurs

row coastal plain. The Ghyben- 3 

with density 1.000 g/cm (gram

in coralline limestone and dune sands of the nar

Herzberg relation states that a freshwater lens,

per cubic centimeter), floating on saltwater, with density 1.025 g/cm , will have

a thickness equal to 41 times the head of freshwater above sea level.

The basal water lens of the study area .is divided into two distinct 

reservoirs (Takasaki and Mink, 1982) (fig. 10). Figures 11 and 12 are crosssections showing the relative thickness of the lenses and the geologic features 

that separate them. Water levels shown on the two cross-sections were 

constructed primarily from data obtained from test-hole drilling by the Honolulu

Board of Water Supply in 1936. The sections we 

spurs of the Koolau Range at altitudes of 400 and

re located across the volcanic 

1,000 feet (Takasaki and Mink,

1982). The Kaau rift is an effective barrier between the Palolo reservoir and

the Waialae reservoir. Between the Waialae area and the Wai 1upe-Hawaii Kai area

the northeast trending dikes appear to be an effective barrier.

22
157° 49'30 157° 46*30' 157° 40'00' lOf <»O OU

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1646-03

/ ^v^-^ 

Approximate position of 

former Koolau shoreline

Head 2 MILES

2 KILOMETERS

"^* ^ ^»<upI K,p 1 K«P,

Base from U.S. Geological Survey 1:24.000 HONOLULU and.KOKO HEAD. 1969

Flniirf^ in Parf nf TooiA/nr/H cr«i i f hone f- Dahii chowlnn loration n

EXPLANATION

1745-01

Well and number

0BWS 37

HONOLULU

BOARD OF WATER SUPPLY 

Test boring and number

Line of section

Figure 10. Part of leeward southeast Oahu showing location of selected wells and distinctive basalwater reservoirs of different heads (modified from Takasaki and Mink, 1982).
IDC

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Heights Louis St. 

Valley Palolo 

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21 Hole BWS 

section) in (Bend 

Drive Paula 

Gulch Waialaenui 

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1746-01 Well 

CD> ^ 

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03

1746-02 Well 

section) in (Bend 

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Gulch Wailupe 

Ridge Loa Hawaii 

> ^ 

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Valley Niu 

1744-01 Well 

1744-02 Well 
Outside

of 

study area

Wailupe-Hawaii Kai 

Area

1200- 

1000 

800 600 400 

200-

SEA LEVEL

200-400-

600-800-

1000-

1200 1400

1600-

Head 24 feet

Freshwater

Saline 

water

rPerched water Freshwater

Saline water 

-Kaau rift zone

/Head 

3.5 feet

Saline water

Northeast 

^trendinq dikes

0 4000 FEET I H H0 1000 METERS

Horizontal scale 

Vertical exaggeration 5x

Figure 12. Section (B-B 1 ) across volcanic spurs at the 1,000-foot contour showing 

thickness of basal-water reservoirs (from Takasaki and Mink, 1982).
CALCULATION OF GROUND-WATER FLOW RATE THROUGH THE 

WAIALAE AND WAILUPE-HAWAII KAI AREAS

Knowledge of the quantity of water that flows through the aquifers of 

leeward southeast Oahu is vital to the descriptions and predictions of the 

behavior of these water resources. Because of the errors and assumptions 

inherent in any calculation of ground-water flow, two independent approaches 

were used in its determination. In the first approach, Darcy's law is used to 

determine ground-water flow rates using water-level data, knowledge of the 

aquifer's physical boundaries, and an estimate of hydraulic conductivity. In the 

second approach, a water budget, estimates of runoff and evapotranspirat ion are

subtracted from rainfall, yielding rates of gro 

flow calculated by Darcy's law.

jnd-water recharge, the source of

Calculation of Ground-Water Flow Rate by Darcy's Law

(D

Darcy's law states that:

Q = KAdh/dl 

where:

Q = ground-water flow through the study area (L /t)

K = hydraulic conductivity (L/t) '

i 2 

A = the cross sectional area through which flow occurs (L )

dh/dl = the slope of the water table or pilezometric surface

In 1935 and 1936, the Honolulu Board of Water Supply (BWS) collected waterlevel data from several test wells in the Waialae area. A water-level- contour 

map constructed from these data (fig. 13) showed a hydraulic gradient of about k 

ft/mi (feet per mile) and, at the 10 foot water-level contour, a distance of

9,^00 feet between the Kaau rift boundary 

boundary on the east.

26

nd the northeast-trending dike
 15 Water level contour,

dashed where uncertain. Contour interval is 1 foot.

EXPLANATION

Number and location of 

test hole with 

water level in 1936.

H well drilled since 1936 

 - Drainage divide

Figure 13. Water-level contour map of the Waialae area (modified from Wentworth, 1938).
Drill hole 27, (fig. 13), whose head of 15 A feet provided the data for the 

hydraulic gradient of k ft/mi, is probably in the margin of the Kaau rift zone 

and not representative of the Waialae area. Well 17^7-03 drilled in Waialae Nui 

in 1983, had a head of 11.6 feet indicating that the head gradient in the Waialae 

area is probably closer to 2.5 ft/mi than 4 ft/mi. The simulation of groundwater flow presented later gives a representative head near drill hole 27 of

about 13 feet.

In June 1936, a pumping test at Waialae shaft produced data needed to

calculate the hydraulic conductivity (K) of the aquifer in the Waialae area 

(Wentworth, 1938). Wentworth corrected his data without explanation, assumed a 

flow thickness of 200 feet, and calculated K ti be 2,000 ft/d (feet per day). 

Takasaki and Mink (1S82), used Wentworth's corrected data with the Theis 

nonsteady radial flow formula and also calculated a K value of about 2,000 ft/d, 

assuming a 200-foot thickness of flow. Thi^ value is unreasonably large 

considering that the rate of flow implied by K,' coupled with a gradient of 2.5 

ft/mi, is greater than the rate of rainfall over the recharge area. Hydraulic 

gradients in other Koolau basalt aquifers where no dikes are observed and where 

rainfall is relatively high are 1 ft/mi. [The steep hydraulic gradient, 

relatively low rainfall, and presence of dikes imply that the hydraulic

conductivity of this area is lower than the usuc 1 values of 1,000 to 2,000 ft/d

calculated for dike-free Koolau lavas.

In addition, Wentworth observed significant upconing of saltwater at 

Waialae shaft prior to sealing of the pump sump floor. From this observation, an 

equation describing flow to a dug well through a hemispherical surface area 

(Bear, 1979, p. 3^5) seems preferable, to the Thiem equation employed by

Wentworth (1938) describing radial flow to a ve 

that both equations produced similar results 

penetrating well that tapped the flank flows

rtical well. Eyre (1983) found 

when applied to a partiallyof the Koolau mountain. When

drawdown, s, is substituted for Bear's head term, the following equation results:

'2 - S 1

where:

9

Q. = flow rate from the pumped well (L /t)

K = hydraulic conductivity of the aquifer (L/t)

s = the observed drawdown at radius = r, from the pumped well (L).

r = radial distance from pumped well (L).

28

(2)
The flow rate during the Waialae Shaft test was 4,000 gallons per minute. 

The locations of the shaft and observation wells are shown in figure 13 and the 

data obtained from observation wells and the calculated K values obtained by use 

of equation 2 are presented in table 2.

Table 2. Waialae shaft (1747-02) pumping test data for

calculation of aquifer hydraulic conductivity,

June 10-20, 1936

[Constant pumping rate of 4,000 gal/min for 10 days; 

data from Wentworth, 1938, p. 193]

Observation

wel I

W1

21

21

21

21

23

23

23

24

24

I pa i r

W2

23

24

22

27

24

22

27

22

27

Distance 

from pump

(ft)

r1

690

690

690

690

2320

2320

2320

2610

2610

r2

2320

2610

4650

5750

2610

4650

5750

4650

5750

Hydraul i c 

conductivity (K) 

Drawdown (ft/d)

(ft)

s1

0.93

.93

.93

.93

.80

.80

.80

.79

.79

s2

0.80

.79

.49

.54

.79

.49

.54

.49

.54

average K

(equation 2)

960

930

340

400

590

85

121

68

102

= 400 ft/d

If the aquifer was homogeneous, isotropic, and infinite in areal extent, all 

of the calculated K values presented in table 2 would be the same. The 

variability of K is an indication of heterogeneity of the aquifer as well as the 

effects of the Kaau rift and dike intrusions. In some parts of the Waialae area, 

water moves easily through the rocks and in other parts the rocks offer more 

resistance to flow. The observed hydraulic gradient of 2.5 ft/mi indicates that 

the effective K throughout the aquifer is relatively small compared to typical K 

values for dike-free Koolau lavas; therefore, K is assumed to be the average of 

the values presented in table 2, which is 400 ft/d.

29
The amount of water flowing through the Waialae area can be estimated from 

the information just presented. Again, 

Q = KAdh/dl

Q = ground-water flow rate 

K = 400 ft/d

A = (41)(10)(9,400) by the Ghyben-Herzbero 

width of flow at the ten-foot water 

dh/dl = 2.5/5,280 

and the ground-water flow through the Waialae ar

Q = (400)(410)(9,400)(2.5/5,280) = 7.3 x 10

relationship and the measured 

-level contour

:a is :

Yd = 5.5 Mgal/d

In the Wai1upe-Hawaii Kai area the only water level data available are from 

3 widely-spaced wells (elements 119? 152, and 216, fig. 14). These wells 

indicate a gradient of about 1.5 ft/mi and a wi^lth of flow of 22,000 ft at the 

3.5-foot water-level contour. Assuming a hydraulic conductivity of 1,000 to 

1,500 ft/d, as observed in many wells that tap dike-free Koolau lavas, the 

ground-water flux through the Wai1upe-Hawaii Kai area is:

Q = (1,000)(41)(3.5)(22,000)0-5/5,280) = 8^7,000 ft 3 /d or 6.7 Mgal/d.

If K = 1,500 ft/d the resulting flow rate is 10.1 Mgal/d.

Water Budget

The purpose of this water budget is to determine the rate and spatial 

distribution of ground-water recharge. This information will aid in the 

prediction of long-term head changes resulting from additional pumpage that is 

planned for the leeward southeast Oahu area.

Estimates of the recharge rate through the western part of the study area 

have been reported by Stearns and Vaksvik (1935, p. 327) and Wentworth (1938, p. 

257). Stearns and Vaksvik concluded that where annual rainfall was greater than 

30 inches, approximately one third of the rainfall recharged the aquifer, and 

where annual rainfall was less than 30 inches, no recharge occurred. Wentworth 

thought that one fifth of rainfall in excess of 30 inches was a more correct 

factor for the determination of recharge.

30
Rainfall over southeast Oahu averages 57 million gallons per day (Mgal/d), 

or 50 inches per year over the 23 square mile area, as calculated from the 

isohyetal map produced by Schroeder and Meisner (1980) (fig. 3). Applying the 

factors of Steam's and Vaksvik (1935) and Wentworth (1938), of one third and one 

fifth, recharge is 19 Mgal/d or 11 Mgal/d, respectively. A State Water 

Commission report (197S) estimated the sustainable yield of leeward southeast 

Oahu to be 5 Mgal/d, or about one fourth to one half of recharge. Sustainable 

yield is defined as the amount of water that can normally be withdrawn from an 

aquifer without producing undesirable effects.

The estimates of recharge obtained by Stearns and Vaksvik and Wentworth used 

mean annual data over large areas. Mather (1578) has shown that recharge is more 

accurately calculated by using observed daily data rather than monthly or annual 

averages. Using long-term mean data generally overestimates evapotranspiration 

and underestimates recharge because actual evapotranspirat ion is often much less 

than the potential evapotranspirat ion used in the budget. A computer watershed 

model using actual storm data and basin characteristics has accurately simulated 

the hydrologic process in Moanalua Valley, Oahu, Hawaii (Shade, 1984). The model 

shows that ground-water recharge in this wet valley, where mean annual rainfall 

is 100 in./yr (inches per year), is 43 percent of rainfall. The difficulty in 

obtaining the required short-term data over a broad area precluded such an 

approach for this study.

Giambelluca (1983) produced a water budget computed from observed monthly 

data from 1946 to 1975 for 258 water-balance zones that compose the Honolulu and 

Pearl Harbor basins, northwest of this study area. His results for the Pearl 

Harbor basin indicate that approximately 44 percent of rainfall becomes recharge 

to the aquifer, a smaller fraction recharging dry areas and a larger fraction 

recharging wet areas. An approach similar to Giambel1uca's, which addressed the 

spatial and temporal variations in recharge, was used in this study.

31
Recharge to the aquifers of leeward southeast Oahu was calculated using a 

water-budgeting approach introduced by Thornthwaite and Mather (1955). Their 

equation states that:

Rainfall - runoff - recharge - evapotranspirat ion - change in soil 

storage = 0.

The equation was solved using mean monthly data 

the southeast Oahu finite element mesh (fig. 

flow model presented in this report. Mean monthly 

seasonal fluctuations into the calculations, 

too coarse and daily data over the area do not ex

(3)

for each of the 284 elements of 

created for the ground-water 

data were used to incorporate 

Annual data were considered to be 

ist.

Calculation of Water Budget Parameters

Rainfal1

Mean monthly rainfall for each element was determined by first transferring 

mean annual rainfall from the isohyetal map (fig. 3) to the elements of the grid 

and then applying regression equations that calculate monthly values. The 12 

monthly regression equations, from Stidd and Leopold (1950), are based on the 

linear relationship between mean monthly and msan annual rainfall determined 

from many long-term rain gage records on Oahu.

Rainfall decreases from 120 in./yr in the mountainous northwest part to 30 

in./yr in the south and east parts of the study area. The mean annual rainfall

over the study area is 57 Mgal/d, of which 2k Mgal/d (62 in./yr) is over the 8.1-

2 2 mi Waialae area, and 33 Mgal/d (45 in./yr) is over the 15.3-mi Wailupe-Hawaii

Kai area.

32
EXPLANATION

Note: Elements 81-116 are within this area 

of NE trending dikes.

13 Finite element and number

c

\

Figure 14. Finite-element mesh for leeward southeast Oahu.
Runoff

To calculate mean monthly runoff from each element, first the mean annual 

runoff for each drainage basin in the study area was calculated. Using data from 

gaged leeward basins in Hawaii with 10 or more years of continuous record, 

Matsuoka (U.S. Geological Survey, written commun., 1583) derived a multiple 

regression equation that estimates mean annua

basin rainfall, drainage area, stream slope, 

equation is:

basin runoff from mean annual 

and percent forest cover. The

log Q = -5-30 + 1.84 (log P) + 0.669 (log p.A.) + 0.814 (log S) (4) 

- 0.331 (log F.C.)

where:

Q = mean annual runoff in cubic feet per second

P = mean annual precipitation in inches

D.A. = drainage area in square miles

S = stream channel slope in feet per mile

F.C. = percent forest cover

log = logarithm to the base 10

An annual rainfal1-runoff relationship 

established by fitting a power curve, of the form 

basin runoff versus mean basin rainfall (fig. 

procedure yielded the equation:

Runoff = 0.00173 x Rainfall 2 ' 06153

2 (the coefficient of determination, R = 0.77).

for southeastern Oahu was 

y = ax , through a plot of mean 

15). A least squares fitting

(5)

This equation was applied to the rainfall of each element of the grid, 

producing annual runoff in inches for each element.
DC 25 

<

LU

20

o: 

LU

0-

CO 

Lil

I 

o

15

u. 

u.

O

z

ID

o:

CO

<

CD

Z 

<

LU

10

Runoff = 0.00173 x Rainfall

2.06153

0

20

30 40 50 60 70 80 

MEAN BASIN RAINFALL, IN INCHES PER YEA

Figure 15. Rainfall-runoff relationship for leeward southeas
To check that the total basin runoff had not been altered by applying the 

power curve relationship to each element, the sum of runoff from elements in a 

basin was compared to the basin's runoff calculated from equation A. The 

difference in basin runoff calculated by the two methods ranged from + 1.5 to -1.6 

in./yr for 16 basins in the study area. The mean difference was .002 inches

which indicates that basin runoff calculated per

different from the runoff calculated for the whole basin. Monthly runoff per 

element was calculated by multiplying annual runoff by the ratio of the element's

monthly to annual rainfall. In this way seasons 

into the runoff component of the water budget ca

The mean annual runoff from the study area, calculated by equation 5» is 6.4 

Mgal/d; 3-5 Mgal/d (9 in./yr) from the Waialae eirea and 2.9 Mgal/d (4 in./yr) 

from the drier Wai1upe-Hawaii Kai area.

element was not significantly

1 fluctuations were introduced 

culat ions.

Potential Evapotranspirat ion

A large fraction of rainfall is evaporated and transpired back to the

atmosphere. Estimates of potential evapotranspirat ion, "water loss from a large

homogeneous, vegetation-covered area that never suffers from a lack of water"

(Mather, 1978), can be made by an energy budget of solar radiation data.

Under optimum soi1-moisture conditions, and if advected energy is 

negligible, potential evapotranspirat ion (PE) may equal net radiation. Net 

radiation is defined as the incoming long- and short-wave radiation from the sun, 

minus reflected radiation and outgoing long-wiwe radiation from the earth 

(Mather, 1978, p. 4). Therefore:

PE = net radiation = global radiation - (reflectance) (global radiation) 

+ actual net long-wave radiation (6)

36
where:

Global radiation = mean annual incoming long- and short-wave radiation

(fig. 16) 

Reflectance = the fraction of global radiation that is reflected by the

earth, approximately 10 percent for Oahu (Ekern, 1965) 

Actual net long-wave radiation = (clear-day net Iong-wave)(g1obal

radiation/clear-day global)

2 Clear-day net long-wave = approximately -150 cal/cm /d (calories per

2 centimeter per day) (Charnell, 1967)

Clear-day global = 0.8 Angot value for 20° north latitude (Yoshihara and

Ekern, 1978) 

Angot value = the amount of incoming solar radiation at the top of the

atmosphere 

Using these equations, equation 6 can be rewritten:

PE =

/1 niwiui j-4.- \_L -150 x global radiation (1 - 0.1)(global radiation) + - * 

0.8 x Angot value at 20°N

^-> (7)

2 Global radiation, from figure 16, was converted to units of cal/cm /d by dividing

2 watts/m (watts per square meter) by 2.06. Because there are about 30 days in a

2 month, and 1,485 cal/cm are required to evaporate an inch of water, the factor

2 30/1,485 converts units of cal/cm /d to inches of water per month.

Ekern (1983) has shown that PE can be calculated from the Priestley-Taylor 

relationship (1972), which for Hawaiian conditions indicates that PE is about 0.9 

times net radiation. Owing to the uncertainties in the data required to 

calculate both net radiation and the Priestley-Taylor factor, setting PE equal to 

net radiation, as in equation 6, is an acceptable approximation.

Annual global radiation per element was obtained by transferring values 

from figure 16 to each element. Monthly global radiation was calculated by 

multiplying mean annual global radiation by the 12 ratios of mean monthly to mean 

annual radiation determined at Makiki Agriculture Station No. 707, 1.5 miles 

northwest of the study area (How, 1978). Monthly Angot values were obtained from 

Chang (1971).

37
21° _ 

30'

CO

158° 15

I

158°00' 157°45'

OAH

01 234

0246 

175-

 G

_ 

15'

Figure 16. Mean annual global radiation over Oahu in watts per squ

(from Ramage, 1979)«
Equation 7 provided the values of potential evapotranspirat ion for 

equation 3. Estimates of actual evapotranspirat ion, one of the results from the 

use of equation 3> may be less than potential evapotranspirat ion. This occurs 

because the rainfall for a given month may not be sufficient to supply the full 

amount of potential evapotranspirat ion.

Mean annual evapotranspi rat i on in this relatively dry and sunny area of Oahu 

was 35-5 Mgal/d; 1^.5 Mgal/d (38 in./yr) from the Waialae area and 21 Mgal/d (29 

in./yr) from the Wailupe-Hawaii Ka i area. Even though solar radiation is 

greater, the actual rate of evapotranspirat ion (in units of in./yr) is less in 

the drier Wai1upe-Hawaii Kai area than in the Waialae area because low rainfall 

limits the amount of water available for evapotranspirat ion.

Soil Characteristics

To calculate the term "change in soil storage" in the water budget equation, 

the amount of water the soil can store must be known. This amount, called 

maximum soil storage in this report, is equal to the available water in the soil 

(field capacity minus wilting point) multiplied by the depth of the vegetation 

root zone. Water content in excess of field capacity will drain from the soil 

and recharge the aquifer. Water content less than wilting point will be held in 

the soil unavailable for evapotranspirat ion.

Because much of southeast Oahu has received only a reconnaissance soil 

survey, available water and plant root depth were estimated. These estimates 

were based on data from Foote and others (1972), field trips to the area, and 

discussions with soil-survey personnel. Values of available water ranged from 

0.1 to 0.15 inch per inch of soil. Plant root depth ranged from 4 to 10 inches in 

mountainous areas where bedrock is near or at the surface and from 2 to 4 feet in 

alluvial areas where vegetation is more dense.

Based on the soil survey, approximately 10 different soil types were 

assigned to the 284 elements of the finite-element mesh. Although the values of 

soil storage are approximate, the relatively fine discretization of soil types 

across the area enabled the effects of variable soil properties to be 

incorporated into the calculation of recharge.

39
Calculation of Recharge

Having quantified the components of the w^ter budget equation, equation 3 

is solved for monthly values of recharge for each element of the mesh in the 

following way:

1) Runoff is subtracted from rainfall and

2)

storage. 

If the resulting soil storage is greater than the maximum soil storage,

the excess is set equal to recharge

maximum soil storage. If the resulting soil storage is less than 

maximum soil storage, no recharge occurs. 

3) Potential evapotranspirat ion (PE) is subtracted from soil storage. If

PE is greater than soil storage, PE i

the difference is added to soil

and soil storage is set equal to

s set equal to soil storage, and

soil storage goes to zero. In this way, actual evapotranspirat ion is 

estimated. An annual water budget would not be able to correct for 

the difference between potential and actual evapotranspiration. 

4) Repeat the process for the next month.

Commonly, steps 2 and 3 of the preceding calculation are reversed, 

allocating water to evapotranspirat ion before recharge occurs. Allowing 

recharge to occur first, as was done for this report, seems more correct in this 

case, for two reasons. First, recharge occurs mainly during storms, when 

rainfall intensity is high and evapotranspirat ion is low. Second, the saturated 

infiltration rate through these soils is on the: order of feet per day, whereas

the rate of evapotranspi rat ion is on the orde r of feet per year. Therefore,

during and after storms, much of the soil water infiltrates past the root zone 

before it can evaporate back to the atmosphere.

Mean annual recharge was calculated by suiTiming monthly recharge. Monthly 

and annual recharge by element are pre-sented at the end of the report. The 

foregoing process yielded 15.1 Mgal/d of recharge through the study area 

(table 3). This value is 26 percent of the total rainfall of 57 Mgal/d 

(51 in./yr). Of the 15.1 Mgal/d, 6 Mgal/d (16 in./yr) recharges the Waialae area 

and 9.1 Mgal/d (12 in./yr) recharges the Wai1upe-Hawaii Ka i area. Present 

pumpage from the Waialae and Wai1upe-Hawaii Kai areas is 1.2 and 0.2 Mgal/d, 

respectively.
The calculation of ground-water flow through the Waialae area, using 

Darcy's law, yielded a value of 5»5 Mgal/d. Values of 6.7 and 10.1 Mgal/d were 

calculated for the Wailupe-Hawaii Kai area depending on whether hydraulic 

conductivities of 1,000 or 1,500 ft/d were used.

Table 3. Water balance for leeward southeast Oahu

EvapotransRainfal1 Runoff pi rat ion Recharge 

Area Mgal/d in./yr Mgal/d in./yr Mgal/d in./yr Mgal/d in./yr

Waialae (8.1 mi 2 ) 24 62 3-5 9 14.5 38 6.0 16 

Wa ilupe-Hawa i i Ka i

(15.3 mi 2 ) 33 45 2.9 4 21.0 29 9.1 12

41
GROUND-WATER SIMULATION

Conceptual Model

The western part of the study area, the Wsialae area, is bounded on the

north, east, and west by dike intrusions and on the south by coastal sediments

(caprock) that are significantly less permeable than basalts. Ground-water 

recharges the aquifer principally in the highlands where rainfall is greatest. 

The low permeability of the dikes provides a barrier to lateral movement of 

ground water which causes most of the ground water to discharge through the 

caprock as diffuse leakage along the coast. Water-level records confirm that 

ground water flows principally from north to south, and show that the caprock 

inhibits free discharge of ground water to the sea s creating 8- to 10-foot heads 

near the caprock-basalt contact.

Though there may be some leakage of ground water from Waialae to WailupeHawaii Kai, the abrupt head drop between the two areas indicate that the dike

boundary is poorly permeable and leakage is probably small. The total ground2 water flow through the 8.1-mi Waialae area is about 6 Mgal/d, or about 4 Mgal/d

per mile width of aquifer.

The hydrologic boundaries of the Wa i lupe-Hawa i i Kai area, east of the 

Waialae area, are the dikes of the Koolau rift zone to the north, the northeasttrending dike divide on the west (Takasaki and Mink, 1S82) and the caprock 

discharge boundary on the south and east. A thin lens of freshwater has formed 

as a result of the combined effects of lower rainfall and more permeable coastal 

sediments than in the Waialae area. Wells drilled near the coast produce 

brackish water. Two wells drilled more than a mile inland tap a freshwater lens 

having 3" to 4-foot heads. Heads in this area decline to the east as rainfall

declines, and to the south as the lens discharges to the sea. Ground-water flow

2 through the 15.3-mi Wai1upe-Hawaii Kai area is about 9 Mgal/d, or about 1 Mgal/d

per mile width of aquifer.
The Ghyben-Herzberg relation states that a static freshwater lens (with

 3 0 t

density = 1.0 grams/cm ), floating on seawater (with density = 1.025 grams/cnr), 

will have a thickness equal to about 41 times the head of freshwater above sea 

level. Several deep monitor wells in Hawaii show that the thickness of a lens 

may be closely predicted by the relation, or in error up to plus or minus 20 

percent. The 10 foot heads in the Waialae area indicate that the thickness of 

the freshwater lens is about 400 feet. Three-foot heads in the western part of 

the Wai 1 upe-Hawa i i Kai area suggest that the thickness is about 120 feet, 

becoming thinner so that brackish water predominates in the southern and eastern 

parts.

Mathematical Model

Computer programs that simulate the flow of groundwater solve the groundwater flow equation for the specific conditions of the user's problem. The 

ground-water flow equation, Eq. 8, represents the combination of the conservation of mass equation with Darcy's law. The conservation of mass states that 

the change of storage that occurs within a certain control volume equals the 

amount of water that flows into the volume minus the amount that flows out. 

Given a flow rate that satisfies the conservation of mass, then the water table 

must have a slope that is consistent with Darcy's law. When the equation of the 

conservation of mass and Darcy's law are coupled for a water-table problem in 

two-dimensions, the ground-water flow equation is (Voss, 1984a):

c ^h _ ^ n ^ n \ _L <* n 9l"h , n , ft /o\ s at - ^ (X JZ} + a7 (X 97} + Q + \ (8)

where:

h = h(x, y, t) is the hydraulic head in the freshwater body (L)

S = S(x, y) storage coefficient of the aquifer (dimensionless)

2 X = is transmissivity T(x, y) for portions of the (L /T)

aquifer confined both above and below, or 

= product of hydraulic conductivity and aquifer thickness, 

Kb (x, y, t), for aquifer portions unconfined either 

above or below.
K = K(x, y) is the hydraulic conductivity of the aquifer (L/T) 

b = b(x, y, t) is the saturated freshwater thickness of

the aquifer (L) 

Q = Q(*> y) is the strength of a source furction, that is:

volume of the freshwater per time adced per horizontal (L/T)

 2 2 

area of the aquifer (L^/T)/(L aquifer)

Q. = Q, (x, y, t) is the strength of leakage into the

freshwater body that is: volume of freshwater (L/T)

leakage into the aquifer per time and per horizontal

 D 2 

area of aquifer (L P /T)/(L aquifer)

x, y = coordinate directions

t = time * (T)

Q. is a steady leakage through a semi-confi

n - ( ' >

^1 ~" ~ \i D I

ning bed, and is defined as:

(8a)

where:

Og ) is called the leakance of the confining bed

K. = the hydraulic conductivity of the confining bed 

B = the thickness of the confining bed

h = the hydraulic head on the side of the semi-confin ing bed opposite

the aquifer 

For flow out of an aquifer, through a semi-

(L/T) 

(L)

:onfining bed like the caprock,

Q. is negat ive,

This study used the finite-element program, AQUIFEM-SALT (Voss, 1984a), 

developed as a modification to the program AQUIFEM (Finder and Voss, 1979). Voss 

modified the aquifer-thickness and storage terms in AQUIFEM to incorporate the 

Ghyben-Herzberg ratio into the model so that it could be used for situations 

where a freshwater lens floats on seawater. Essentially, thickness was set equal 

to 41 times the head, and changes in storage were calculated as 41 times the

change in head times the specific yield. Also,

truncated above or below to a thickness of lesji than 41 times the head by a 

confining unit such as the caprock.

the free-floating lens may be

44
The relationship of 41 to 1 between the lens thickness and head is true only 

when the lens is at equilibrium. In reality, the water table continually 

fluctuates in response to changes in rainfall and pumping conditions, but the 

motion of the bottom of the lens is more sluggish and responds to the flow fields 

of both the freshwater and the underlying saltwater. The location of the lens 

bottom is more accurately predicted by the water-table elevation averaged over a 

time span of several years rather than by any instantaneous measurement of the 

water-table elevation. Such a deficiency does not affect the value of the model 

when used to describe the equilibrium freshwater flow system and distribution of 

heads. However, head values resulting from short-term transient simulations may 

contain some error.

Model Application and Calibration

Using input data of aquifer characteristics and recharge rates, the 

computer model calculates ground-water heads at each node of the finite elementmesh presented in figure 14. Nodes are located at the intersection of element 

boundary-lines. Ground-water flow in the Koko Volcanics was not simulated 

because those volcanics form a brackish-water aquifer separate from the Koolau 

basalt aquifer (Takasaki and Mink, 1982). The western and northern perimeters 

are modeled as no-flow boundaries simulating the dikes of the Kaau rift zone and 

the Koolau Range. Along the eastern and southern boundaries, the caprock is 

treated as a leaky confining layer through which water discharges upward to the 

sea at a rate proportional to the head in the underlying basalt aquifer. The 

northeast-trending dikes, which act as a barrier between the Waialae and WailupeHawaii Kai areas, are simulated by narrow elements with a low hydraulic 

conductivity of 0.1 ft/d.

Soroos (1973) analyzed many pumping tests and obtained hydraulic 

conductivities of flank flows of Koolau basalts that ranged from 300 to 2,000 

ft/d and averaged 1,100 ft/d. After several trial simulations the hydraulic 

conductivity (K) of the Waialae area was selected to be 500 ft/d. This value 

corresponds well to the value of 400 ft/d obtained from the Waialae shaft pumping 

test, is reasonable for flank flows of Hawaiian volcanoes that are sparsely 

intruded by dikes, and produced simulations that were in closest agreement with 

the observed ground-water gradient. A hydraulic conductivity of 800 ft/d for the

Wailupe-Hawaii Kai area provided the best simulation results for that area.

45
Other model input data were chosen as follows: Thornthwaite and Mather's 

(1955) water-budget approach was used to calculate recharge for each element of

the mesh. Withdrawal at a pumping node was set

rate of the well at that node. Mink (1980) shows that the specific yield for 

Koolau basalt aquifers is between 0.02 and O.lA. A value of 0.1 was used in the 

long term simulations presented in this report. Assigned caprock leakance 

(hydraulic conductivity of the caprock/thicknesis of caprock) ranged from a low of

O.OOOA per day in the coastal Waialae area to

at the long-term-average-pumping

a high of 0.02 per day in the

coastal Hawaii Kai area.

The leakance assigned to the confining elements determined the ease with 

which water could escape from the aquifer to the sea. A low value of leakance

caused heads to build up in the aquifer. A hi gh value allowed water to escape

more easily, creating lower heads in the aquifer. The spatial variation in 

leakance simulates the decrease in caprock effectiveness between the western and 

eastern parts of the study area. The changing of leakance values was the 

principal adjustment used to obtain good Agreement between observed and 

simulated heads.

The leakance of O.OOOA per day corresponds to a section of caprock about 800 

feet thick, with hydraulic conductivity of 0.3 fi:/d. These are reasonable values

for the area around Diamond Head. The leakance of 0.02 per day corresponds to a

section of caprock about 50 feet thick, with hydraulic conductivity of 1 ft/d. 

These are reasonable values for the coastal sediments of the Wai1upe-Hawaii Kai 

area.

The model only accepts 1 value of hydraulic conductivity for the leaky 

confining elements. To achieve the desired leakances, a hydraulic conductivity 

of 0.3 ft/d was used and the thickness of eacfh confining element was set as 

presented in figure 17.
N 

Boundary between confined seaward elements

C

\

and unconfined inland elements 

400 Thickness of confining layer o '

Figure 17. Finite-element mesh for leeward southeast Oahu showing the thickness of the 
Because leakance is the least known variabl e in the model, it is appropriate

that significant adjustments be made to obtain close agreement between observed

and simulated heads. Hydraulic conductivity is

was adjusted only within a narrow range. Recharge was not adjusted at all from 

the values obtained from the water budget, except for short term simulations that

investigated fluctuations in head that result f

a better known variable and It

"om wet or dry years.

Data from several wells provide a distribution of heads across the study 

area that can be compared to the simulated results (tables 4 and 5, and 

figure 18). The close agreement between simulated and observed heads shows that

the model has been adequately calibrated. Most of the historic head data were

obtained after the initiation of pumping from tqe Waialae golf course well (node 

76) and Waialae shaft (node kl). The observed head data reflect area-wide 

drawdown, and therefore simulations for head calibration included pumpage from 

those two sources.

An equally good fit between simulated and observed heads, as presented in 

table 4, was achieved by increasing hydraulic conductivity of the northeasttrending dike zone from 0.1 to 1 ft/d, thus cil lowing about 2 Mgal/d to leak

eastward across the barrier. The drop in Waiala 

of water was compensated for by decreasing the

e area heads caused by this loss 

caprock leakance in the Waialae

area.

This sensitivity analysis shows that despite a good simulation of observed 

heads, all uncertainties in the flow system cannot be resolved. Because the 

western and eastern barriers of the Waialae area are similar in nature, outflow

across the eastern boundary, if any, will nearb

west. Therefore, flow across these boundaries was fixed near 0 Mgal/d.

f be equalled by inflow from the
Table 4. Distribution of heads in leeward southeast Oahu

Node number 

(shown on 

figure 18) 41 45 62 76 78 144 163 206 237 277 316 317

Observed head, (ft) 9.6 11.5 10.6 8.5 9.5 2.7 3-7 2.2 3.7 0.8 1.3 2.2 

Simulated head, (ft) 9-7 11.2 10.4 8.2 10.2 2.8 3.8 2.4 3.8 0.4 1.4 2.4

Table 5. Cross reference of node numbers

and well identification

Node

number

41

45

62

76

78

144

163

206

237

277

316

317

uses

number

1747-02

1747-03

none

1646-01, 02

1746-01

1746-02

1745-01

1744-01, 02

1843-01

1842-01

1840-01

1840-04

Name or

locat ion

Waialae shaft

Waialae nui

Drill hole 23

Waialae Golf Course

Aina Koa

Waialae Iki

Wa i 1 upe

N i u Va 1 1 ey

Kul i ouou valley

Kami lonui val ley

Kalama val ley

Kalama val ley

49
N

U1

o

Points o

and nod

Dike zon

Ground-

where 

is 1 fo

3000 METERS

Figure 18. Simulated pre-pumping ground-water head distribution in leeward 
Effects of Pumping on the Pre-pumping Head Distribution

Initial heads in the study area were simulated by eliminating pumpage in the 

calibrated data set and running the simulation until heads stopped rising and 

reached a steady state (fig. 18). The history of head changes was then simulated 

by running the model and adding pumpage at the proper time. The Waialae golf 

course well (node 76) began pumping at a rate of 0.35 Mgal/d in 1881, Waialae 

shaft (node 41) at 0.42 Mgal/d in 1937 and the Aina Koa well (node 78) at 0.42 

Mgal/d in 1971. Figure 19 shows the simulated head distribution in 1971. A 

graph of simulated and maximum annual observed heads from 1935 to 1975 at the 

Waialae shaft is presented in figure 20. Minimum annual heads track less than 

0.5 feet below maximum annual heads.

It was suspected that the fluctuations in observed water levels shown in 

figure 20 were caused by varying recharge rates from years of high and low 

rainfall. To test this idea, the difference between simulated annual heads 

resulting from constant recharge, and observed heads was analyzed by comparing 

their differences with the smoothed differences between observed and mean annual

rainfall in the area. This comparison is shown in figure 21. The best

2 correlation (R = 0.89) between the two sets of differences, obtained by a linear

least-squares method, was achieved with a centered three-year moving average of 

the rainfall differences, lagged one year with respect to the water-level 

differences. Figure 21 shows that where large seasonal pumping stresses do not 

occur, as in the study area, fluctuations in head can be explained by 

fluctuations in rainfall. The statistical correlation shows that about one year 

is required for the effects of recharge to be transmitted from the ground surface 

to the water table. This lag may be in error by several months, because lag times 

of about one year cannot be accurately determined using annual data.

Transient simulations of short term ground-water head fluctuations are 

desired because the improved understanding of lens behavior will allow pumping 

rates to be better managed. Also, to the extent that ground-water head reflects 

the position of the freshwater-saltwater interface, a more detailed knowledge of 

head fluctuations will allow the chloride distribution through the lens to be 

est imated.
N

237

3000 METERS

Points 

obse

Dike z

Groun

Conto

Figure 19* Simulated ground-water head distribution in 1971 as a result of W

(node 41) and golf course well (node 76) pumpage.
LU 

LU

LU

> 

LLI

_l

cc

LLI

11.0

10.8

10.6

10.4-

TT n I I I I I I I I I I I I I I I I I I I I I I 

EXPLANATION

Observed annual maximum water 

level

Simulated water level using 

constant recharge

Simulated water level using 

annually adjusted recharge

i i i i I i i i i I i i 

9.2-

9.0 i i i i l i i

1935 1940 1945 1950 1955 1960 1965 

TIME, IN YEARS

Figure 20. Simulated versus observed heads from 1935 to 1975 at the Waialae 

Specific yield = O.IO.
VJ1

-CQ 

LJJ

rr

LJJ 

CO 

CQ

LJJ 

UJ

LJJ

m 

LJJ

S

CO 

LJJ

o

< 

cr

O 

CO

35

30

25

20

15

10

5

0

-5 

10 

15

-20

P"

EXPLANATION

Smooth difference between 

observed and mean annual rainfall

Difference between simulated and 

observed water levels

I 

I 

I 

I

1935 1940 1945 1950 1955 1960

1965 19

TIME, IN YEARS

Figure 21. Differences between observed and mean annual rainfall, an

simulated and observed heads.
In an attempt to simulate the annual fluctuations of the water table, new 

recharge data sets were recalculated annually from fluctuations in rainfall. 

However, simulated head values are consistently low by a few tenths of a foot. 

The model was calibrated using long term mean recharge, and therefore, during the 

dry years, 1935 to 19&2, annual simulations produce low heads. During the wet 

years, 1963 to 1975, simulated heads rise and become greater than observed heads.

Also, the simulated fluctuations shown in figure 20 do not match the 

observed fluctuations particularly well, especially the higher frequency 

fluctuations. A possible source of this error is the inherent limitation of a 

two-dimensional plan-view model which assumes hydrostatic equilibrium of fresh 

and salt water. The problem of simulating high-frequency water-level fluctuations revolves around the relationship between changes in water volume in the 

aquifer and associated changes in head. This relationship is dependent on the 

storage of the aquifer.

The model uses a storage coefficient that is 41 times greater than the 

specific yield of the aquifer because, at equilibrium, a one-foot rise in the 

water table will cause the bottom of the lens to move down 40 feet. The volume of 

water associated with these changes will be distributed accordingly. Initially, 

after the water table rises from a slug of recharge, the bottom of the lens has 

not had time to fully readjust. Therefore, the lens is not in equilibrium, the 

storage coefficient of 41 times the specific yield is too large, and simulated 

head changes are smaller than observed. This may be occuring in the present 

simulat ions.

Better simulations can be obtained by decreasing the storage coefficient by 

reducing the specific yield (fig. 22). The amount of adjustment in specific 

yield required to obtain a good simulation may, in view of the equilibrium 

assumption, reflect the amount of disequilibrium in the lens. The required 

adjustment would change depending on the time scale of the fluctuations.

55
12

LLJ 

LLJ 

LL

11

EXPLANATION

i^^m Observed annual maximum water level

 Simulated head using specific yield 0.02

/

 Simulated head using specific yield 0.05 /

Simulated head using specific yield 0.10 /

8

1935 1940

Figure 22.

1945 1950 1955 1960 1965 1970 

TIME, IN YEARS

Simulated water levels using annually adjusted recharge 

and specific yields of 0.10, 0.05, and 0.02.
The variation in response resulting from different specific yield values, 

c , is shown in figure 22. As is expected, the lower values of e allow better 

simulation of the higher frequency components of head change. The lower values 

of specific yield, e = 0.02 and £ = 0.05, are, in fact, reasonable values and are 

within the present range of uncertainty for Koolau basalts. Thus, another 

uncertainty in model calibration arises because it is not possible to determine 

from available data how much model error is due to the equilibrium assumption and 

how much is due to the particular choice of a specific yield value. Of course 

unavoidable error in recharge data also limit the accuracy of short term 

s imulat ions.

In one sense the "equilibrium-specific yield dilemma" is not a serious 

problem. The model is able to predict a new 'steady-state' head distribution 

across the aquifer given a new set of pumping or recharge conditions no matter 

what specific yield is used because the 'steady-state' heads do not depend on 

specific yield. However, both the time it takes to achieve 'steady-state' and 

the magnitude of water-table fluctuations are dependent on the specific yield. 

With a low specific yield, 'steady-state 1 will occur sooner and fluctuations will 

be greater than with a larger specific yield.

The unfortunate consequence of the "equilibrium-specific yield dilemma" is 

that the location of the freshwater-saltwater interface cannot be predicted with 

much accuracy. Inaccuracy in the location of the interface, where chloride 

concentration is about 10,000 mg/L (milligrams per liter), makes estimation of 

the chloride distribution through the ground-water lens subject to excessive 

error.

57
Model Predictions

Recent ly-dri 1 led wel 1 s at nodes 45, 163, and 237 wi 11 be put into product ion 

within the next two years. The effect on ground-water heads was predicted by 

adding pumpage of 0.2 and 0.4 Hgal/d from ecich of these new sources to the 

simulations previously discussed. Figure 23 shows the simulated history of heads 

at the Waialae golf course well and Waialae shaft, including the projected 

effects of new pumping. Water levels in the Wcialae area will drop about a foot 

from their present mean position as a result of continued drawdown from present 

pumpage as well as additional drawdown from projected pumpage. These curves

result from using a specific yield of 0.10. As

be steeper and level off sooner if a smaller specific yield had been used.

However, the equilibrium head which occurs when

stated earlier, the curves would

the curve stops declining, would

be the same as those shown in figure 23. Figure 24 shows the projected head 

distribution over the study area resulting from a pumping rate of 0.2 Mgal/d at 

the new sources. A rate of 0.4 Mgal/d lowers the head an additional 0.2 foot. 

Water levels in the Wai1upe-Hawaii Kai area will drop about 0.5 foot in the 

eastern part and essentially no change will occur in the western part.

Water Quality

Contamination by saltwater upconing is the major water-quality concern in 

southeast Oahu. The computer simulation done for this study addressed long-term

water-level changes resulting from present and future pumping, from which waterquality changes can only be inferred. Figure 2f> shows the dependence of chloride

concentration on rainfall and pumpage. Figure 20 shows corresponding

fluctuations in water levels. From 1955 through 1959 rainfall declined and 

pumpage was reduced slightly, and the chloride concentration of water pumped from

Waialae shaft was relatively constant, ranging from 130 to 160 mg/L. In 1960, as

rainfall increased, pumpage was increased to 246 Mgal for the year. This large 

volume of pumpage, combined with the probability that the ground-water lens had 

not recovered from the previous period of lo/v rainfall, caused the chloride

concentration to rise to 200 mg/L in late 1960 and early 1961.

58
YEAR

oo

00

o

O)

CM 

O) O)

CO 

O)

00 

O)

O 

O 

CM

CM 

O 

CM

O 

CM

CD 

O 

CM

 WAIALAE SHAFT OBSERVATION WELL 1747-1

--- WAIALAE GOLF COURSE WELL 1646-2

1881 Start pumping at Waialae golf course well

1937 Start pumping at Waialae shaft

1971 Start pumping at Aina Koa well

1986 Start'pumping at new wells

at 0.02 million gallons per day each

00 

O 

CMT~

OT 

CM

CMTCM CM

Existing pumpage

Projected pumpage

Existing pumpage

«O-O Projected 

pumpage

40 60 80 100 120 140 160 180 200 220 240260 

ELAPSED TIME, IN YEARS

Figure 23. Simulated head versus time 

(Spec!fie yield = 0.10).
N

4 ^^\»*' > -" 4 ** V v ^r.'^^v,*^.--

3000 METERS

Figure 2k. Steady-state head contours resulting from projected pumpage in l
19

Q0)

n 11 

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5' CU 

cu ,T' 

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MILLION IN PUMPAGE, 

DAY PER GALLONS 

MILLION IN CHLORIDE, 

DAY PER GALLONS 

INCHES IN RAINFALL, 

01

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In 1961, the pump at Waialae shaft was shut off for one month, and when

pumping was resumed at a relatively low rate of 10 Mgal/mo (million gallons per

month), the chloride concentration stabilized at about 150 mg/L.

As rainfall increased through the early- dnd mid-1960's, pumpage increased 

slightly with no adverse effect on chloride concentration. The chloride peak of 

190 mg/L in 1969 resulted from one month of hic|h pumpage, 22 Mgal/mo. At more 

moderate rates (12 Mgal/mo) the chloride concentration again stabilized around 

150 mg/L, showing seawater upconing as a potential problem that could be avoided 

with proper management of pumpage.

The computer simulation predicts that with 

future heads will decrease about 1 foot from the

decrease will make wells in the area somewhat more susceptible to upconing as the 

lens thickness will decrease to about 85 percent of its 1985 thickness. 

Available data indicate that chloride concent|-ation at pumped wells probably 

will not rise more than 100 to 200 mg/L as a result of these new conditions.

projected pumping rates average 

r present mean position. Such a

62
SUMMARY

The leeward aquifers of southeast Oahu are bounded by dikes near the crest 

of the Koolau range to the north, the Kaau rift zone to the west, and the Pacific 

Ocean to the south and east. Internally, a set of dikes divide the area into the

western Waialae area and the eastern Wai 1upe-Hawaii Kai area. The ground-water

2 flow rate is 6 Mgal/d through the 8.1-mi Waialae area and 9 Mgal/d through the

2 15.3-mi Wai1upe-Hawaii Kai area. Coastal sediments impound the ground water of

the Waialae area to an altitude of 10 feet above sea level. This environment is 

much more advantageous for ground-water development than the Wai1upe-Hawaii Kai 

area, where the head is about three feet and saltwater encroachment is of 

constant concern. Present pumpage is only 1.2 Mgal/d from the Waialae area and 

0.2 Mgal/d from the Wai1upe-Hawaii Kai area. Because of the geologic boundaries, 

increased water development in the study area will not affect the water resources 

of adjacent aquifers.

The ground-water system was simulated using AQUIFEM-SALT, a two-dimensional 

finite-element model of ground-water flow for aquifers containing a freshwatersaltwater interface. The model accurately simulates observed heads averaged 

over several years and predicts an area-wide head decline of about 1 foot when 

three recently completed wells are put into production.

This drop in head is not enough to cause chloride concentration at pumped 

wells to rise significantly. However, as in the past, rises in chloride 

concentration will occur during years of low rainfall or when pumping rates are 

unusually h igh.

The magnitude of simulated water table fluctuations, obtained by using 

annually adjusted recharge data in the AQUIFEM-SALT data set, are in error by a 

few tenths of a foot relative to observed annual water table fluctuations. This 

error is caused by inaccuracy in the lens thickness calculated by the GhybenHerzberg principle, inaccuracy in the chosen value of specific yield, and by 

unavoidable inaccuracy in the recharge data. Errors in simulated short term 

water levels decrease confidence in estimates of the chloride concentration of 

pumped water.

63
SUTRA, a solute transport and density dependent flow model developed by Voss

(1984b) should be able to produce more detailed

lens as well as the distribution of the chloride concentration. Results from

this model can be used to improve future AQUIF 

A deep monitor well would provide direct

simulations of the motion of the

EM-SALT simulations, 

data regarding the location and

movement of the interface. Such data would eliminate some ambiguities of the

present model, enable changes in pumped wate 

would also improve the ability of a solute t 

chloride distributions in the lens.

< quality to be anticipated, and 

ransport model to predict future
REFERENCES

Bear, Jacob, 1979, Hydraulics of groundwater: New York, McGraw Hill, 345 p. 

Blumenstock, D. I., and Price, Saul, 196?, Climate of Hawaii in climates of the

states: U.S. Department of Commerce, no. 60-51, 20 p. 

Chang, J. H., 1971, Problems and methods in agricultural climatology: Taipei,

Taiwan, Oriental Publishing Company, 96 p. 

Charnell, R. T., 1967, Long-wave radiation near the Hawaiian Islands: Journal of

Geophysical Research, v. 72, no. 2, 494 p. 

Ekern, P. C., 1965, The fraction of sunlight retained as net radiation in Hawaii:

Journal of Geophysical Research, v. 70, no. 4, p. 7SO.

 --- 1978, Variation in sunlight induced by topography under the trade wind 

regime on Oahu, Hawaii: American Meteorological Society, Conference on 

climate and energy, Cl imatological aspects and industrial operations, 

p. 60.

 _ 1983, Measured evaporation in high rainfall areas, leeward Koolau Range, 

Oahu, Hawaii: Water Resources Research Center, University of Hawaii, 

Technical Report No. 156, Honolulu, 60 p.

Eyre, P. R., 1983, Investigation of Waikele well no. 2401-01, Oahu, Hawaii: 

Pumping test, well logs and water quality, U.S. Geological Survey WaterResources Investigations Report 83-4089, 38 p.

Foote, D. E., Hill, E. L., Nakamura, Sakuichi, and Stephens, Floyd, 1972, Soil 

survey of islands of Kauai, Oahu, Maui, Molokai, and Lanai, State of Hawaii: 

U.S. Department of Agriculture, Soil Conservation Service, 232 p.

Giambelluca, T. W., 1983, Water balance of the Pearl Harbor - Honolulu basin 

1946-1975: Ph. D. dissertation, University of Hawaii, Honolulu, 308 p.

Honolulu Board of Water Supply, 1982, Annual report and statistical summary: 

City and County of Honolulu, 112 p.

How, K. T. S., 1978, Solar radiation in Hawaii 1932-1975: Division of Water and 

Land Development, Department of Land and Natural Resources, State of 

Hawaii, Report R57, 99 p.

Macdonald, G. A., 1956, The structure of Hawaiian volcanoes: Koninklijk 

Nederlandsch Geologisch--Mijnbouwkundig Genootschap, Verhandelingen, 

v. 16, p. 274-295.

65
Macdonald, G. A., 1972, Volcanoes: Englewood Cliffs, New Jersey, Prentice-Hall,

Inc., 510 p. 

Macdonald, G. A., and Abbott, A. T., 1970, Volcanoes in the sea: University of

Hawaii Press, Honolulu, Hawaii, 441 p. 

Mather, J. R., 1978, The climatic water budget in environmental analysis: D.C.,

Heath and Company, 239 p.

Mercer, J. W., Larson, S. P. and Faust, C. R.,

simulate areal flow of saltwater and freshwater separated by an interface:

U.S. Geological Survey Open File Report 80-407, 58 p. 

Mink, J. F., 1980, State of the groundwater resources of southern Oahu: Board of

Water Supply, City and County of Honolulu,, p. 74. 

Pinder, G. F. and Voss, C., 1979, AQUIFEM, A finite element model for aquifer

evaluation (documentation): Department of Water Resources Engineering,

Royal Institute of Technology, Stockholm, 

3806. (Code prepared by G. Pinder, E. Fr

1980, Finite-difference model to

Sweden, Report 7911; TRITA-VATnd, P. Trescott and C. Voss).

Priestley, C. H. B., and Taylor, R. S., 1972, On the assessment of surface heat

parameter flux and evaporation using large-scale parameters: Monthly

Weather Review, v. 100, p. 81-92. 

Ramage, C. S., 1979, Prospecting for meteorological energy in Hawaii: Bulletin

of the American Meteorological Society, v; 60, p. 430-438. 

Schroeder, Thomas and Meizner, Bernard, 1980, Revised rainfall maps of the

Hawaiian Islands: Department of Meteorology, University of Hawaii,

Honolu1u. 

Shade, P. J., 1984, Hydrology and sediment transport, Moanalua Valley, Oahu,

Hawaii: U.S. Geological Survey Water- Resources Investigations Report

84-4156, 54 p. 

State of Hawaii Department of Planning and Economic Development, 1980, State of

Hawaii data book; a statistical abstract: City and County of Honolulu,

580 p. 

State Water Commission, 1979, Hawaii's water resources, directions for the

future: A report to the Governor of the Si:ate of Hawaii, 40 p.

Stearns, H. T., 1939, Geologic map and guide of

Hydrography Bulletin 2, 75 p.? 6 pi. 

Stearns, H. T. and Macdonald, G. A., 1946, Geol

Oahu, Hawaii: Hawaii Division of

ogy and ground-water resources of

the island of Hawaii: Hawaii Division of Hydrography Bulletin 9, 222 p.

66
Stearns, H. T., and Vaksvik, K. N., 1935, Geology and ground-water resources of 

the island of Oahu, Hawaii: Hawaii Division of Hydrography Bulletin 1, 

479 p.

Stidd, C. K., and Leopold, L. B., 1950, The geographic distribution of average 

monthly rainfall, Hawaii: Meteorological Monographs, v. 1, no. 3, p. 24-33.

Takasaki, K. J., and Mink, J. F., 1982, Water resources of southeast Oahu: U.S. 

Geological Survey Water-Resources Investigations Report 82-628, 89 p.

Thornthwa ite, C. W., and Mather, J. R., 1955, The water balance: Publications in 

climatology, Laboratory of climatology, v. 8, no. 1, 104 p.

Voss, C. I., 1984a, AQUIFEM-SALT, A finite-element model for aquifers containing 

a seawater interface: U.S. Geological Survey Water-Resources Investigations Report 84-4263, 37 p.

 1984b, SUTRA, A finite element simulation model for saturated-unsaturated, 

fluid density dependent ground-water flow with energy transport or 

chemically reactive single species solute transport: U.S. Geological 

Survey Water-Resources Investigations Report 84-4369, 409 p.

Wentworth, C. K., 1938, Geology and ground-water resources of the Palolo-Waialae 

District Oahu, Hawaii: Honolulu Board of Water Supply, City and County of 

Honolulu, 274 p.

Yoshihara, Takeshi, and Ekern, P. C., 1978, Assessment of the potential of solar 

energy in Hawaii - final report: The Hawaii Natural Energy Institute, 

University of Hawaii, Honolulu, 74 p.

67
SUPPLEMENTAL DAlU

68
Monthly and Annual Average Recharge, by Elements, for Southeast Oahu

Element

no.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

Jan

0

0

0

0

0

0

0

0

0

0

0

0

1

3

1

5

6

8

8

8,

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

3.

3.

4.

5.

6.

8.

8.

7,

0.

0.

0.

0.

.0

.0

.0

.8

.8

.9

.0

.0

.8

.8

.9

.9

.0

.9

.2

.2

.5

.4

.4

.1

.0

.0

.0

,0

,8

.8

,9

.9

.0

.8

.8

.9

.9

.9

.4

,2

.5

.3

.1

.9

.0

,0

.0

.8

Feb

0.0

0.0

0.0

0.9

0.9

0.9

0.0

0.0

0.9

0.9

0.9

0.9

1.0

3.0

1.1

1.9

3.6

4.7

4.7

4.9

0.0

0.0

0.0

0.0

0.9

0.9

0.9

0.9

0.0

0.9

0.9

0.9

1.6

1.6

3.4

2.0

3.3

4.5

4.4

4.8

0.0

0.0

0.0

0.9

Mar

0.0

0.0

0.0

0.6

0.6

0.7

0.0

0.0

0.6

0.6

0.7

0.7

0.8

2.1

0.9

0.5

3.0

3.9

3.9

3.8

0.0

0.0

0.0

0.0

0.6

0.6

0.7

0.7

0.0

0.6

0.6

0.7

0.7

0.7

2.6

1.2

2.3

3.5

3.6

3.6

0.0

0.0

0.0

0.6

Apr

0.0

0.0

0.0

0.6

0.6

0.6

0.0

0.0

0.6

0.6

0.6

0.6

0.7

1.9

0.9

0.5

3.2

4.3

4.3

4.0

0.0

0.0

0.0

0.0

0.6

0.6

0.6

0.6

0.0

0.6

0.6

0.6

0.5

0.5

2.4

1.2

2.5

4.0

4.0

3.8

0.0

0.0

0.0

0.6

Recharge in inches

May

0.0

0.0

0.0

0.2

0.2

0.3

0.0

0.0

0.2

0.2

0.3

0.3

0.3

0.4

0.5

0.0

1.5

2.6

2.6

2.3

0.0

0.0

0.0

0.0

0.2

0.2

0.3

0.3

0.0

0.2

0.2

0.3

0.0

0.0

0.9

0.0

0.8

2.2

2.3

2.1

0.0

0.0

0.0

0.2

June

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

1

2

2

2

0,

0,

0,

0,

0.

0.

0.

0.

0,

0,

0,

0.

0.

0.

0.

0,

0,

2,

2

1.

0

0.

0

0.

.0

.0

.0

.1

.1

.2

.0

.0

.1

.1

.2

.2

.3

.1

.5

.0

.2

.4

.4

.1

.0

.0

,0

,0

.1

,1

,2

,2

,0

,1

,1

.2

.0

.0

.6

.0

.5

.0

.1

.9

.0

.0

.0

.1

July

0.0

0.0

0.0

0.1

0.1

0.2

0.0

0.0

0.1

0.1

0.2

0.2

0.3

0.0

0.4

0.0

1.2

2.3

2.3

2.0

0.0

0.0

0.0

0.0

0.1

0.1

0.2

0.2

0.0

0.1

0.1

0.2

0.0

0.0

0.5

0.0

0.5

2.0

2.0

1.8

0.0

0.0

0.0

0.1

Aug

0.0

0.0

0.0

0.2

0.2

0.2

0.0

0.0

0.2

0.2

0.2

0.2

0.3

0.3

0.5

0.0

1.6

2.9

2.9

2.5

0.0

0.0

0.0

0.0

0.2

0.2

0.2

0.2

0.0

0.2

0.2

0.2

0.0

0.0

0.9

0.0

0.9

2.5

2.5

2.3

0.0

0.0

0.0

0.2

Sept

0.0

0.0

0.0

0.2

0.2

0.3

0.0

0.0

0.2

0.2

0.3

0.3

0.4

0.6

0.6

0.0

1.7

2.8

2.8

2.4

0.0

0.0

0.0

0.0

0.2

0.2

0.3

0.3

0.0

0.2

0.2

0.3

0.0

0.0

1.1

0.0

1.0

2.4

2.4

2.3

0.0

0.0

0.0

0.2

Oct

0.0

0.0

0.0

0.3

0.3

0.4

0.0

0.0

0.3

0.3

0.4

0.4

0.4

0.8

0.6

0.0

1.6

2.5

2.5

2.2

0.0

0.0

0.0

0.0

0.3

0.3

0.4

0.4

0.0

0.3

0.3

0.4

0.0

0.0

1.2

0.0

0.9

2.2

2.2

2.1

0.0

0.0

0.0

0.3

Nov

0.0

0.0

0.0

0.7

0.7

0.8

0.0

0.0

0.7

0.7

0.8

0.8

0.8

2.4

1.0

1.0

3.6

4.8

4.8

4.4

0.0

0.0

0.0

0.0

0.7

0.7

0.8

0.8

0.0

0.7

0.7

0.8

1.0

1.0

2.9

1.7

2.9

4.4

4.4

4.3

0.0

0.0

0.0

0.7

Dec

0

0

0

0

0

1

0

0

0

0

1

1

1

3

1

2

4.

5.

5,

5,

0.

0.

0.

0.

0.

0.

1.

1.

0.

0.

0.

1.

1.

1.

3.

2.

3.

5.

5.

5.

0,

0.

0.

0.

.0

.0

.0

.9

.9

.0

.0

.0

.9

.9

.0

.0

.1

.2

.2

.0

.3

.4

.4

.6

.0

.0

.0

,0

,9

,9

,0

.0

.0

.9

.9

.0

.8

.8

.7

.4

.7

.3

.1

.4

,0

.0

.0

,9

Annual 

recharge

0

0

0

5

5

6

0

0

5

5

6

6

7

18

9,

11.

32.

47.

47

44,

0,

0.

0.

0,

5.

5.

6.

6.

0.

5,

5.

6.

9,

9.

24,

13,

25,

43.

43.

42,

0.

0,

0,

5,

.0

.0

.0

.7

.7

.5

.0

.0

.7

.7

.5

.5

.4

.8

.6

.2

.8

.0

.0

.3

.0

.0

,0

,0

,7

,7

,5

,5

.0

,7

.7

.5

.6

.6

.6

.8

.6

.3

.1

,4

.0

.0

.0

.7

Annual 

recharge 

as 

fraction 

of 

annual 

rainfall

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0,

0,

0,

0,

0.

0.

0.

0.

0.

0,

0,

0,

0

0

0

0

0,

0,

0,

0,

0,

0,

0,

.00

.00

.00

.18

.18

.18

.00

.00

.18

.18

.18

.18

.19

.48

.19

.19

.42

.40

.40

.40

.00

.00

.00

.00

.18

.18

.18

.18

.00

.18

.18

.18

.24

.24

.52

.23

.33

.38

.39

.40

.00

.00

.00

.18

Area 

in 

thousands

of 

2

feet

9,

8,

1,

1,

1,

1,

1,

2,

3,

4,

4,

4,

4,

4,

3,

8,

9,

1,

1,

1,

1,

1,

1,

1,

1,

2,

3,

4,

4,

5,

5,

5,

3,

4,

4,

1,

1,

305

360

370

900

995

725

040

750

825

865

200

855

785

310

880

795

820

180

190

225

370

985

400

065

020

865

020

770

410

000

995

840

800

085

260

460

145

130

055

320

800

350

585

185

Annual 

recharge 

in 

Mgal/d

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0,

0,

0,

0,

0,

0,

0,

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0,

0,

0,

0.

0.

0.

0.

0.

0.

0.

.000

.000

.000

.009

.010

.019

.000

.000

.008

.008

.013

.021

.035

.106

.080

.092

.270

.335

.336

.244

.000

.000

,000

,000

,010

,008

,011

,020

,000

,010

,010

.020

.046

,051

,179

,105

,225

,379

.372

.240

.000

,000

.000

.012
Monthly and Annual Average Recharge, by El«

Element

no .

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

Jan

0.8

3.5

3.7

3.9

3.9

5.2

6.5

7.7

7.6

7.4

0.0

0.0

0.0

0.8

0.8

3.3

3.5

3.9

3.9

5.2

6.5

7.1

6.9

0.0

0.0

0.0

3.3

0.8

3.5

3.5

3.9

3.9

5.0

6.2

6.5

6.5

0.0

0.0

0.0

3.3

3.3

3.5

3.5

3.9

Feb

0.9

2.7

1.9

2.0

1.0

2.0

3.3

4.2

4.1

4.4

0.0

0.0

0.0

0.9

0.9

1.5

1.7

3.0

3.0

2.1

3.3

3.7

3.6

0.0

0.0

0.0

2.5

0.9

2.7

2.7

3.0

3.0

2.1

3.1

3.3

3.3

0.0

0.0

0.0

2.5

2.5

1.7

1.7

2.0

Mar

0.6

1.8

1.0

1.1

0.1

1.2

2.3

3.3

3.2

3.2

0.0

0.0

0.0

0.6

0.6

0.6

0.8

2.1

2.1

1.2

2.3

2.8

2.6

0.0

0.0

0.0

1.6

0.6

1.8

1.8

2.1

2.1

1.0

2.0

2.3

2.3

0.0

0.0

0.0

1.6

1.6

0.8

0.8

1.1

Apr

0.6

1.6

0.7

0.9

0.0

1.2

2.5

3.7

3.5

3.3

0.0

0.0

0.0

0.6

0.6

0.3

0.6

1.9

1.9

1.2

2.5

3.1

2.9

0.0

0.0

0.0

1.3

0.6

1.6

1.6

1.9

1.9

1.0

2.2

2.5

2.5

0.0

0.0

0.0

1.3

1.3

0.6

0.6

0.9

Recharge in inches

May

0.2

0.1

0.0

0.0

0.0

0.0

0.8

1.9

1.8

1.6

0.0

0.0

0.0

0.2

0.2

0.0

0.0

0.4

0.4

0.0

0.8

1.4

1.2

0.0

0.0

0.0

0.0

0.2

0.1

0.1

0.4

0.4

0.0

0.5

0.8

0.8

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

June

0.1

0.0

0.0

0.0

0.0

0.0

0.5

1.7

1.5

1.4

0.0

0.0

0.0

0.1

0.1

0.0

0.0

0.1

0.1

0.0

0.5

1.1

1.0

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.1

0.1

0.0

0.3

0.5

0.5

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

July

0.1

0.0

0.0

0.0

0.0

0.0

0.5

1.6

1.5

1.3

0.0

0.0

0.0

0.1

0.1

0.0

0.0

0.0

0.0

0.0

0.5

1.1

0.9

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.0

0.0

0.0

0.2

0.5

0.5

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Aug

0.2

0.0

0.0

0.0

0.0

0.0

0.9

2.1

2.0

1.8

0.0

0.0

0.0

0.2

0.2

0.0

0.0

0.3

0.3

0.0

0.9

1.5

1.3

0.0

0.0

0.0

0.0

0.2

0.0

0.0

0.3

0.3

0.0

0.6

0.9

0.9

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Sept

0.2

0.3

0.0

0.0

0.0

0.0

1.0

2.1

1.9

1.8

0.0

0.0

0.0

0.2

0.2

0.0

0.0

0.6

0.6

0.0

1.0

1.5

1.4

0.0

0.0

0.0

0.0

0.2

0.3

0.3

0.6

0.6

0.0

0.7

1.0

1.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Oct

0.3

0.5

0.0

0.0

0.0

0.0

0.9

2.0

1.8

1.7

0.0

0.0

0.0

0.3

0.3

0.0

0.0

0.8

0.8

0.0

0.9

1.4

1.3

0.0

0.0

0.0

0.3

0.3

0.5

0.5

0.8

0.8

0.0

0.7

0.9

0.9

0.0

0.0

0.0

0.3

0.3

0.0

0.0

0.0

^

c

ments , for

ov

.7

2.0

1

l

C

.2

.4

.4

1.7

2

i

'.

;

C

C

C

(

C

.9

.1

.9

.8

.0

.0

.0

.7

.7

0.8

j.o

2-4

t

1

^

c

c

c

c

c

]

.4

.7

.9

.5

.3

.0

.0

.0

..8

6.7

4.

1

A

A

4.

4

4.

C

C

C

]

:

]

]

i

:.o

:.o

1.4

\ A

..4

i . 6

:.9

;.9

.0

.0

.0

.8

.8

.0

.0

.4

Dec

0.9

2.8

2.0

2.2

1.2

2.4

3.7

4.8

4.6

5.0

0.0

0.0

0.0

0.9

0.9

1.6

1.8

3.2

3.2

2.4

3.7

4.2

4.1

0.0

0.0

0.0

2.6

0.9

2.8

2.8

3.2

3.2

2.2

3.4

3.7

3.7

0.0

0.0

0.0

2.6

2.6

1.8

1.8

2.2

Southeast Oahu

Annual

recharge

5.7

15.3

10.5

11.6

6.7

13.8

25.6

39.3

37.3

36.5

0.0

0.0

0.0

5.7

5.7

8.1

9.5

18.8

18.8

13.9

25.6

32.4

30.5

0.0

0.0

0.0

13.4

5.7

15.3

15.3

18.8

18.8

12.6

22.7

25.6

25.6

0.0

0.0

0.0

13.4

13.4

9.5

9.5

11.6

Annual 

recharge 

as 

fraction 

of 

annual

rainfall

0.18

0.43

0.28

0.29

0.17

0.23

0.33

0.38

0.38

0.39

0.00

0.00

0.00

0.18

0.18

0.26

0.27

0.48

0.48

0.24

0.33

0.36

0.35

0.00

0.00

0.00

0.43

0.18

0.43

0.43

0.48

0.48

0.23

0.30

0.33

0.33

0.00

0.00

0.00

0.43

0.43

0.27

0.27

0.29

Area 

in 

thousands 

of

2

feet

1,085

2,540

1,520

1,650

2,300

2,520

2,625

2,755

3,065

1,015

4,850

5,740

1,745

1,950

1,300

2,425

1,705

1,800

2,400

2,520

2,965

2,395

2,185

5,380

4,950

930

2,630

2,790

5,820

3,900

4,140

5,385

5,355

6,160

4,270

1,505

410

585

135

160

120

240

150

160

Annual 

recharge 

in

Mgal/d

0.011

0.066

0.027

0.033

0.026

0.059

0.115

0.185

0.195

0.063

0.000

0.000

0.000

0.019

0.013

0.034

0.028

0.058

0.077

0.060

0.130

0.132

0.114

0.000

0.000

0.000

0.060

0.027

0.152

0.102

0.133

0.173

0.115

0.239

0.187

0.066

0.000

0.000

0.000

0.004

0.003

0.004

0.002

0.003

70
Monthly and Annual Average Recharge, by Elements, for Southeast Oahu

Element 

no.

89

90

91

92

93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

Recharge in inches

Jan

3.9

5.0

6.2

6.2

0.0

0.0

0.0

3.3

3.3

3.5

3.5

3.9

4.2

5.0

6.1

6.2

0.0

0.0

0.0

0.8

3.3

3.5

3.5

3.9

3.9

5.0

6.1

6.1

0.0

0.0

0.8

3.3

3.5

3.5

3.9

3.9

5.0

6.1

6.1

0.0

0.0

3.3

3.3

0.8

Feb

3.0

2.2

3.1

3.1

0.0

0.0

0.0

0.0

2.5

0.2

1.7

2.0

3.2

2.2

3.0

3.1

0.0

0.0

0.0

0.9

0.0

0.2

1.7

2.5

2.0

2.2

3.0

3.0

0.0

0.0

0.9

2.5

1.5

2.7

0.9

0.9

2.2

3.0

3.0

0.0

0.0

2.5

2.5

0.9

Mar

2.1

1.0

2.0

2.0

0.0

0.0

0.0

0.0

1.6

0.0

0.8

1.1

2.3

1.0

1.9

2.0

0.0

0.0

0.0

0.6

0.0

0.0

0.8

1.6

1.1

1.0

1.9

1.9

0.0

0.0

0.6

1.6

0.6

1.8

0.0

0.0

1.0

1.9

1.9

0.0

0.0

1.6

1.6

0.6

Apr

1.9

1.0

2.2

2.2

0.0

0.0

0.0

0.0

1.3

0.0

0.6

0.9

2.2

1.0

2.0

2.2

0.0

0.0

0.0

0.6

0.0

0.0

0.6

1.4

0.9

1.0

2.0

2.0

0.0

0.0

0.6

1.3

0.4

1.6

0.0

0.0

1.0

2.0

2.0

0.0

0.0

1.3

1.3

0.6

May

0.4

0.0

0.5

0.5

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.6

0.0

0.4

0.5

0.0

0.0

0.0

0.2

0.0

0.0

0.0

0.0

0.0

0.0

0.4

0.4

0.0

0.0

0.2

0.0

0.0

0.1

0.0

0.0

0.0

0.4

0.4

0.0

0.0

0.0

0.0

0.2

June

0.1

0.0

0.3

0.3

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.4

0.0

0.1

0.3

0.0

0.0

0.0

0.1

0.0

0.0

0.0

0.0

o.o0.0

0.1

0.1

0.0

0.0

0.1

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.1

0.0

0.0

0.0

0.0

0.1

July

0.0

0.0

0.2

0.2

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.3

0.0

0.0

0.2

0.0

0.0

0.0

0.1

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.1

Aug

0.3

0.0

0.6

0.6

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.6

0.0

0.4

0.6

0.0

0.0

0.0

0.2

0.0

0.0

0.0

0.0

0.0

0.0

0.4

0.4

0.0

0.0

0.2

0.0

0.0

0.0

0.0

0.0

0.0

0.4

0.4

0.0

0.0

0.0

0.0

0.2

Sept

0.6

0.0

0.7

0.7

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.8

0.0

0.5

0.7

0.0

0.0

0.0

0.2

0.0

0.0

0.0

0.1

0.0

0.0

0.5

0.5

0.0

0.0

0.2

0.0

0.0

0.3

0.0

0.0

0.0

0.5

0.5

0.0

0.0

0.0

0.0

0.2

Oct

0.8

0.0

0.7

0.7

0.0

0.0

0.0

0.0

0.3

0.0

0.0

0.0

1.0

0.0

0.6

0.7

0.0

0.0

0.0

0.3

0.0

0.0

0.0

0.3

0.0

0.0

0.6

0.6

0.0

0.0

0.3

0.3

0.0

0.5

0.0

0.0

0.0

0.6

0.6

0.0

0.0

0.3

0.3

0.3

Nov

2.4

1.4

2.6

2.6

0.0

0.0

0.0

0.0

1.8

0.0

1.0

1.4

2.7

1.4

2.5

2.6

0.0

0.0

0.0

0.7

0.0

0.0

1.0

1.9

1.4

1.4

2.5

2.5

0.0

0.0

0.7

1.8

0.8

2.0

0.0

0.0

1.4

2.5

2.5

0.0

0.0

1.8

1.8

0.7

Dec

3.2

2.3

3.4

3.4

0.0

0.0

0.0

0.0

2.6

0.0

1.8

2.2

3.4

2.3

3.3

3.4

0.0

0.0

0.0

0.9

0.0

0.0

1.8

2.7

2.2

2.3

3.3

3.3

0.0

0.0

0.9

2.6

1.6

2.8

0.4

0.4

2.3

3.3

3.3

0.0

0.0

2.6

2.6

0.9

Annual 

recharge

18

12,

22

22

0

0

0

3,

13,

3.

9.

11.

21.

12.

20.

22.

0.

0.

0.

5.

3.

3.

9.

14.

11.

12,

20.

20.

0.

0.

5.

13.

8.

15.

5.

5.

12.

20,

20.

0.

0.

13,

13.

5.

.8

.8

.7

.7

.0

.0

.0

,3

.4

,7

.5

,6

,7

.8

.8

7

,0

0

0

7

3

7

,5

4

6

,8

,8

,8

,0

,0

7

.4

,5

,3

.3

.3

,8

.8

,8

,0

,0

,4

,4

7

Annual 

recharge 

as 

fraction 

of 

annual 

rainfall

0

0

0

0

0

0

0

0

0,

0,

0,

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0,

0,

0,

0,

0,

0,

0,

0,

0,

0,

0.

0,

0,

0,

0,

0,

0.

0.

.48

.23

.30

.30

.00

.00

.00

.10

.43

.10

.27

.29

.50

.23

.29

,30

,00

,00

,00

,18

,10

,10

.27

.37

.29

.23

.29

.29

.00

.00

.18

.43

.24

.43

.13

.13

.23

.29

.29

.00

.00

.43

,43

,18

Area 

in 

thousands

of 

2 

feet

200

210

260

200

875

815

220

320

240

480

300

280

335

420

455

380

380

460

110

160

120

240

150

170

190

210

270

180

15,405

3,370

2,380

1,595

3,910

2,310

2,555

2,475

2,260

2,450

1,195

14,495

6,070

5,350

5,360

3,780

Annual 

recharge 

in 

Mgal/d

0,

0,

0

0,

0,

0,

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0,

0.

0.

0.

0,

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

.006

.005

.010

.008

.000

.000

.000

.002

.005

,003

,005

,006

012

,009

016

015

000

000

000

002

001

002

,002

,004

,004

,005

,010

,006

,000

,000

,023

,036

,057

.060

.023

.022

.049

.087

.042

,000

,000

,122

,123

037

71
Monthly and Annual Average Recharge, by Elements, for Southeast Oahu

Element 

no.

133

13A

135

136

137

138

139

1AO

1A1

1A2

1A3

1AA

145

1A6

147

1A8

1A9

150

151

152

153

ISA

155

156

157

158

159

160

161

162

163

16A

165

166

167

168

169

170

171

172

173

17A

175

176

Recharge

Jan

0.9

3.9

A. 2

5.0

5.5

5.8

0.0

0.0

0.8

0.8

0.9

0.0

0.0

0.8

0.8

0.0

0.0

3.3

3.3

0.9

3.5

3.9

A. 2

5.0

5.5

5.5

0.0

0.0

3.3

3.3

3.5

3.5

3.9

A. A

5.0

5.5

5.5

0.0

0.0

0.8

0.0

0.0

0.8

0.8

Feb

0.9

0.9

2.2

2.2

2.6

2.8

0.0

0.0

0.9

0.9

0.9

0.0

0.0

0.9

0.9

0.0

0.0

2.5

2.5

0.9

2.7

3. A

l.A

2.2

2.6

2.6

0.0

0.0

2.5

2.5

1.7

2. A

3.0

2.4

2.2

2.6

2.6

0.0

0.0

0.9

0.0

0.0

0.9

0.9

Mar

0.7

0.0

1.3

1.0

1.5

1.7

0.0

0.0

0.6

0.6

0.7

0.0

0.0

0.6

0.6

0.0

0.0

1.6

1.6

0.7

1.8

2.5

0.3

1.0

1.5

1.5

0.0

0.0

1.6

1.6

0.8

1.5

2.1

1.6

1.0

1.5

1.5

0.0

0.0

0.6

0.0

0.0

0.6

0.6

Apr

0.6

0.0

1.2

1.0

1.5

1.8

0.0

0.0

0.6

0.6

0.6

0.0

0.0

0.6

0.6

0.0

0.0

1.3

1.3

0.6

1.6

2.3

0.2

1.0

1.5

1.5

0.0

0.0

1.3

1.3

0.6

1.3

1.9

l.A

1.0

1.5

1.5

0.0

0.0

0.6

0.0

0.0

0.6

0.6

May

0.3

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.2

0.2

0.3

0.0

0.0

0.2

0.2

0.0

0.0

0.0

0.0

0.3

0.1

0.8

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

O.A

0.0

0.0

0.0

0.0

0.0

0.0

0.2

0.0

0.0

0.2

0.2

June

0.2

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.1

0.2

0.0

0.0

0.1

0.1

0.0

0.0

0.0

0.0

0.2

0.0

0.5

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.1

0.1

in inches

July

0.2

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.1

0.2

0.0

0.0

0.1

0.1

0.0

0.0

0.0

0.0

0.2

0.0

O.A

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.1

0.1

Aug

0.2

0.0

0.0

0.0

0.0

0.2

0.0

0.0

0.2

0.2

0.2

0.0

0.0

0.2

0.2

0.0

0.0

0.0

0.0

0.2

0.0

0.7

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.3

0.0

0.0

0.0

0.0

0.0

0.0

0.2

0.0

0.0

0.2

0.2

Sept

0.3

0.0

0.0

0.0

0.1

0.3

0.0

0.0

0.2

0.2

0.3

0.0

0.0

0.2

0.2

0.0

0.0

0.0

0.0

0.3

0.3

1.0

0.0

0.0

0.1

0.1

0.0

0.0

0.0

0.0

0.0

0.0

0.6

0.1

0.0

0.1

0.1

0.0

0.0

0.2

0.0

0.0

0.2

0.2

Oct

O.A

0.0

0.0

0.0

0.1

0.3

0.0

0.0

0.3

0.3

O.A

0.0

0.0

0.3

0.3

0.0

0.0

0.3

0.3

O.A

0.5

1.2

0.0

0.0

0.1

0.1

0.0

0.0

0.3

0.3

0.0

0.2

0.8

0.2

0.0

0.1

0.1

0.0

0.0

0.3

0.0

0.0

0.3

0.3

Nov Dec

0.8 1.0

0.0 O.A

1.7 2. A

l.A 2.3

1.9 2.8

2.2 3.0

0.0 0.0

0.0 0.0

0.7 0.9

0.7 0.9

0.8 1.0

0.0 0.0

0.0 0.0

0.7 0.9

0.7 0.9

0.0 0.0

0.0 0.0

1.8 2.6

1.8 2.6

0.8 1.0

2.0 2.8

2.8 3.6

0.7 l.A

l.A 2.3

1.9 2.8

1.9 2.8

0.0 0.0

0.0 0.0

1.8 2.6

1.8 2.6

1.0 1.8

1.7 2.5

2.4 3.2

1.9 2.7

l.A 2.3

1.9 2.8

1.9 2.8

0.0 0.0

0.0 0.0

0.7 0.9

0.0 0.0

0.0 0.0

0.7 0*9"

0.7 0.9

Annual 

recharge

6.5

5.3

13.0

12.8

15.9

18.2

0.0

0.0

5.7

5.7

6.5

0.0

0.0

5.7

5.7

0.0

0.0

13. A

13. A

6.5

15.3

23.2

8.2

12.8

15.9

15.9

0.0

0.0

13. A

13. A

9.5

13.2

18.8

1A.7

12.8

15.9

15.9

0.0

0.0

5.7

0.0

0.0

5;7

5.7

Annual 

recharge 

as 

fraction 

of 

annual 

rainfall

0.18

0.13

0.30

0.23

0.25

0.27

0.00

0.00

0.18

0.18

0.18

0.00

0.00

0.18

0.18

0.00

0.00

O.A3

O.A3

0.18

O.A3

0.59

0.19

0.23

0.25

0.25

0.00

0.00

O.A3

O.A3

0.27

0.37

O.A8

0.31

0.23

0.25

0.25

0.00

0.00

0.18

0.00

0.00

0.18

0.18

Area 

in 

thousands

of 

2 

feet

3,050

3,260

3,070

2,810

2.A75

825

5.5A5

4,100

1,325

2,665

3,240

4,790

3,930

1,605

1,730

1,850

975

1,215

2,260

4,720

2,400

2,640

2,240

2,265

1,875

435

1,310

950

1,380

2,270

5,590

3,800

3,645

2,595

2,270

1,585

180

2,945

2,205

990

2,440

1,900

1,210

1,300

Annual 

recharge 

in 

Mgal/d

0.034

0.029

0.068

0.061

0.067

0.026

0.000

0.000

0.013

0.026

0.036

0.000

0.000

0.016

0.017

0.000

0.000

0.028

0.052

0.052

0.063

0.105

0.031

0.049

0.051

0.012

0.000

0.000

0.032

0.052

0.091

0.086

0.117

0.065

0.050

0.043

0.005

0.000

0.000

0.010

0.000

0.000

0.012

0.013

72
Monthly and Annual Average Recharge, by Elements, for Southeast Oahu

Element 

no.

177

178

179

180

181

182

183

ISA

185

186

187

188

189

190

191

192

193

19A

195

196

197

198

199

200

201

202

203

20A

205

206

207

208

209

210

211

212

213

21A

215

216

217

218

219

220

Recharge in inches

Jan

3.5

3.5

3.9

4.7

5.0

5.2

0.0

0.0

0.8

0.0

0.0

0.8

0.8

3.5

3.9

A. 2

A. 7

5.0

5.2

0.0

0.0

3.3

3.3

3.5

3.9

A. A

A. 7

5.0

0.0

0.0

0.8

0.5

0.0

0.0

0.8

0.0

0.0

3.5

3.5

3.9

A. 2

A. 7

5.0

5.0

Feb

0.3

0.8

1.6

2.1

2.2

2. A

0.0

0.0

0.9

0.0

0.0

0.9

0.9

2.7

1.6

3.2

2.0

2.2

2. A

0.0

0.0

2.5

2.0

1.3

3.0

3. A

2.0

2.2

0.0

0.0

0.9

0.6

0.0

0.0

0.9

0.0

0.0

2.0

0.6

3.0

3.2

2.6

2.2

2.2

Mar

0.0

0.0

0.7

1.3

1.0

1.2

0.0

0.0

0.6

0.0

0.0

0.6

0.6

1.8

0.7

2.3

0.8

1.0

1.2

0.0

0.0

1.6

1.1

O.A

2.1

2.6

0.8

1.0

0.0

0.0

0.6

O.A

0.0

0.0

0.6

0.0

0.0

1.1

0.0

2.1

2.3

1.8

1.0

1.0

Apr

0.0

0.0

0.5

1.2

1.0

1.2

0.0

0.0

0.6

0.0

0.0

0.6

0.6

1.6

0.5

2.2

0.7

1.0

1.2

0.0

0.0

1.3

0.8

0.2

1.9

2. A

0.7

1.0

0.0

0.0

0.6

0.2

0.0

0.0

0.6

0.0

0.0

0.9

0.0

1.9

2.2

1.7

1.0

1.0

May

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.2

0.0

0.0

0.2

0.2

0.1

0.0

0.6

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

O.A

0.9

0.0

0.0

0.0

0.0

0.2

0.0

0.0

0.0

0.2

0.0

0.0

0.0

0.0

O.A

0.6

0.1

0.0

0.0

June

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.1

0.1

0.0

0.0

O.A

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.6

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.0

0.1

0.0

0.0

0.0

0.0

0.1

O.A

0.0

0.0

0.0

July

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.1

0.1

0.0

0.0

0.3

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.5

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.0

0.1

0.0

0.0

0.0

0.0

0.0

0.3

0.0

0.0

0.0

Aug

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.2

0.0

0.0

0.2

0.2

0.0

0.0

0.6

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.3

0.9

0.0

0.0

0.0

0.0

0.2

0.0

0.0

0.0

0.2

0.0

0.0

0.0

0.0

0.3

0.6

0.1

0.0

0.0

Sept

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.2

0.0

0.0

0.2

0.2

0.3

0.0

0.8

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.6

1.1

0.0

0.0

0.0

0.0

0.2

0.0

0.0

0.0

0.2

0.0

0.0

0.0

0.0

0.6

0.8

0.3

0.0

0.0

Oct

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.3

0.0

0.0

0.3

0.3

0.5

0.0

1.0

0.0

0.0

0.0

0.0

0.0

0.3

0.0

0.0

0.8

1.2

0.0

0.0

0.0

0.0

0.3

0.0

0.0

0.0

0.3

0.0

0.0

0.0

0.0

0.8

1.0

0.5

0.0

0.0

Nov

0.0

0.1

1.0

1.7

l.A

1.7

0.0

0.0

0.7

0.0

0.0

0.7

0.7

2.0

1.0

2.7

1.2

l.A

1.7

0.0

0.0

1.8

1.3

0.6

2. A

2.9

1.2

l.A

0.0

0.0

0.7

O.A

0.0

0.0

0.7

0.0

0.0

1.3

0.0

2. A

2.7

2.2

l.A

l.A

Annual

Dec recharge

0.0

0.9

1.8

2. A

2.3

2.5

0.0

0.0

0.9

0.0

0.0

0.9

0.9

2.8

1.8

3. A

2.0

2.3

2.5

0.0

0.0

2.6

2.1

l.A

3.2

3.7

2.0

2.3

0.0

0.0

0.9

0.6

0.0

0.0

0.9

0.0

0.0

2.1

0.0

3.2

3. A

2.9

2.3

2.3

3.9

5. A

9.6

13. A

12.8

1A.3

0.0

0.0

5.7

0.0

0.0

5.7

5.7

15.3

9.6

21.7

11. A

12.8

1A.3

0.0

0.0

13. A

10.6

7.5

18.8

2A.6

11. A

12.8

0.0

0.0

5.7

2.7

0.0

0.0

5.7

0.0

0.0

11.0

A. 2

18.8

21.7

16.9

12.8

12.8

Annual 

recharge 

as 

fraction 

of 

annual 

rainfall

0.11

0.15

0.2A

0.26

0.23

0.2A

0.00

0.00

0.18

0.00

0.00

0.18

0.18

O.A3

0.2A

0.50

0.22

0.23

0.2A

0.00

0.00

O.A3

0.3A

0.21

O.A8

0.52

0.22

0.23

0.00

0.00

0.18

0.17

0.00

0.00

0.18

0.00

0.00

0.31

0.12

O.A8

0.50

0.33

0.23

0.23

Area 

in 

thousands

of 

2 

feet

3,705

A,OAO

3,465

2,355

2.A90

1.5A5

2,235

1,225

760

2.A20

1,180

1,050

875

A, 300

A, 275

3,915

2,665

2,650

750

5,280

2,730

3,595

2,810

5,520

2,775

2,365

2.1AO

2,330

3,925

2,560

1,175

1,125

A, 190

2,565

880

3,705

2,660

2,A80

A,A25

6,AOO

5,380

A, 130

5,070

1,215

Annual 

recharge 

in 

Mgal/d

0.025

0.037

0.057

0.05A

0.05A

0.038

0.000

0.000

0.007

0.000

0.000

0.010

0.009

0.112

0.070

0.1A5

0.052

0.058

0.018

0.000

0.000

0.082

0.051

0.071

0.089

0.099

O.OA2

0.051

0.000

0.000

0.011

0.005

0.000

0.000

0.009

0.000

0.000

O.OA7

0.032

0.205

0.199

0.119

0.111

0.027

73
Monthly and Annual Average Recharge, by Clements, for Southeast Oahu

Element

no.

221

222

223

22A

225

226

227

228

229

230

231

232

233

23A

235

236

237

238

239

2AO

2A1

242

2A3

2AA

2A5

2A6

2A7

2A8

2A9

250

251

252

253

25A

255

256

257

258

259

260

261

262

263

26A

Jan

0.0

0.0

0.9

3.5

3.9

4.7

A. 7

0.0

0.0

3.5

3.5

3.9

A. 7

0.0

0.0

0.9

1.0

3.9

A. 2

A. 4

0.0

0.0

0.9

0.0

0.0

3.5

3.9

A. 2

A. A

A. A

0.0

0.0

3.9

3.9

A. 2

A. A

0.0

0.0

1.0

3.9

A. 2

0.0

0.0

3.9

Feb

0.0

0.0

0.9

2.7

3.0

2.6

2.0

0.0

0.0

1.6

2.7

3.0

2.6

0.0

0.0

0.9

1.0

1.0

3.8

A.O

0.0

0.0

0.9

0.0

0.0

2.7

3.0

3.2

3. A

A.O

0.0

0.0

3.0

3.0

3.8

A.O

0.0

0.0

1.0

3.0

3.2

0.0

0.0

3.0

Mar

0.0

0.0

0.7

1.8

2.1

1.8

0.8

0.0

0.0

0.7

1.8

2.1

1.8

0.0

0.0

0.7

0.8

0.1

2.9

3.2

0.0

0.0

0.7

0.0

0.0

1.8

2.1

2.3

2.6

3.2

0.0

0.0

2.1

2.1

2.9

3.2

0.0

0.0

0.8

2.1

2.3

0.0

0.0

2.1

Apr

0.0

0.0

0.6

1.6

1.9

1.7

0.7

0.0

0.0

0.5

1.6

1.9

1.7

0.0

0.0

0.6

0.7

0.0

2.8

3.0

0.0

0.0

0.6

0.0

0.0

1.6

1.9

2.2

2.4

3.0

0.0

0.0

1.9

1.9

2.8

3.0

0.0

0.0

0.7

1.9

2.2

0.0

0.0

1.9

Recharge in inches

May

0.0

0.0

0.3

0.1

O.A

0.1

0.0

0.0

0.0

0.0

0.1

O.A

0.1

0.0

0.0

0.3

0.3

0.0

1.2

1.5

0.0

0.0

0.3

0.0

0.0

0.1

O.A

0.6

0.9

1.5

0.0

0.0

0.4

0.4

1.2

1.5

0.0

0.0

0.3

O.A

0.6

0.0

0.0

O.A

June

0.0

0.0

0.2

0.0

0.1

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.0

0.2

0.3

0.0

1.0

1.2

0.0

0.0

0.2

0.0

0.0

0.0

0.1

O.A

0.6

1.2

0.0

0.0

0.1

0.1

1.0

1.2

0.0

0.0

0.3

0.1

O.A

0.0

0.0

0.1

July

0.0

0.0

0.2

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.2

0.3

0.0

0.9

1.1

0.0

0.0

0.2

0.0

0.0

0.0

0.0

0.3

0.5

1.1

0.0

0.0

0.0

0.0

0.9

1.1

0.0

0.0

0.3

0.0

0.3

0.0

0.0

0.0

Aug

0.0

0.0

0.2

0.0

0.3

0.1

0.0

0.0

0.0

0.0

0.0

0.3

0.1

0.0

0.0

0.2

0.3

0.0

1.2

1.5

0.0

0.0

0.2

0.0

0.0

0.0

0.3

0.6

0.9

1.5

0.0

0.0

0.3

0.3

1.2

1.5

0.0

0.0

0.3

0.3

0.6

0.0

0.0

0.3

Sept

0.0

0.0

0.3

0.3

0.6

0.3

0.0

0.0

0.0

0.0

0.3

0.6

0.3

0.0

0.0

0.3

O.A

0.0

l.A

1.7

0.0

0.0

0.3

0.0

0.0

0.3

0.6

0.8

1.1

1.7

0.0

0.0

0.6

0.6

l.A

1.7

0.0

0.0

O.A

0.6

0.8

0.0

0.0

0.6

Oct

0.0

0.0

O.A

0.5

0.8

0.5

0.0

0.0

0.0

0.0

0.5

0.8

0.5

0.0

0.0

0.4

O.A

0.0

1.6

1.8

0.0

0.0

O.A

Nov

0.0

0.0

0.8

2.0

2. A

2.2

1.2

0.0

0.0

0.9

2.0

2. A

2.2

0.0

0.0

0.8

0.8

O.A

3.3

3.5

0.0

0.0

0.8

0.0 0.0

0.0

0.5

0.8

1.0

1.2

1.8

0.0.

0.0

0.8

0.8

0.0

2.0

2. A

2.7

2.9

3.5

0.0

0.0

2. A

2. A

1.6 3.3

1.8 3.5

0.0

0.0

O.A

0.8

1.0

0.0

0.0

0.8

0.0

0.0

0.8

2. A

2.7

0.0

0.0

2. A

Dec

0.0

0.0

1.0

2.8

3.2

2.9

2.0

0.0

0.0

1.7

2.8

3.2

2.9

0.0

0.0

1.0

1.1

1.2

A.O

A. 3

0.0

0.0

1.0

0.0

0.0

2.8

3.2

3. A

3.7

4.3

0.0

0.0

3.2

3.2

A.O

A. 3

0.0

0.0

1.1

3.2

3.4

0.0

0.0

3.2

Annual 

recharge

0.0

0.0

6.5

15.3

18.8

16.9

11. A

0.0

0.0

9.0

15.3

18.8

16.9

0.0

0.0

6.5

7. A

6.7

28.3

31.2

0.0

0.0

6.5

0.0

0.0

15.3

18.8

21.7

24.6

31.2

0.0

0.0

18.8

18.8

28.3

31.2

0.0

0.0

7. A

18.8

21.7

0.0

0.0

18.8

Annual 

recharge 

as 

fraction 

of 

annual 

rainfall

0.00

0.00

0.18

O.A3

O.A8

0.33

0.22

0.00

0.00

0.25

O.A3

O.A8

0.33

0.00

0.00

0.18

0.19

0.17

0.65

0.66

0.00

0.00

0.18

0.00

0.00

O.A3

0.48

0.50

0.52

0.66

0.00

0.00

O.A8

O.A8

0.65

0.66

0.00

0.00

0.19

O.A8

0.50

0.00

0.00

O.A8

Area 

in 

thousands

of 

2 

feet

5,320

2,160

875

1,A80

2,360

3,330

1,100

A, 700

1,775

2,710

2,650

3,180

2,615

A, 350

1,965

2,050

1,270

1,335

3,525

3,330

A, 055

2,275

1,895

2,300

1,625

6,105

3,3AO

3,6A5

3,995

1,600

2,525

3.A50

8,000

A.1AO

3,960

1,395

2,625

3,590

A,6A5

3.0A5

A, 260

1,190

1,935

6,730

Annual 

recharge 

in 

Mgal/d

0.000

0.000

0.010

0.039

0.076

0.096

0.021

0.000

0.000

0.042

0.069

0.102

0.075

0.000

0.000

0.023

0.016

0.015

0.170

0.177

0.000

0.000

0.021

0.000

0.000

0.159

0.107

0.135

0.168

0.085

0.000

0.000

0.257

0.133

0.191

0.07A

0.000

0.000

0.059

0.098

0.158

0.000

0.000

0.216
Monthly and Annual Average Recharge, by Elements, for Southeast Oahu

Element

no.

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

280

281

282

283

284

Recharge in inches

Jan

3.

4,

0,

0.

1.

3,

0

3,

3

0

0,

3,

0

3

3

0,

0

2

0,

0

.9

.2

.0

.0

.0

.9

.0

.9

.9

.0

.9

.9

.0

.3

.5

.0

.0

.9

.0

.0

Feb

3.

3.

0.

0.

1.

3.

0.

3.

3,

0.

0.

1.

0.

2.

2.

0.

0.

0.

0.

0.

,0

8

,0

.0

,0

.0

.0

.0

.0

.0

.9

.1

.0

.5

.7

.0

.0

.3

.0

.0

Mar

2.

2.

0.

0.

0.

2.

0.

2.

2.

0.

0.

0.

0.

1.

1.

0.

0.

0.

0.

0.

1

9

,0

,0

,8

1

,0

,1

.1

.0

.7

.2

.0

.6

,8

.0

,0

.0

0

,0

Apr

1.

2.

0.

0.

0.

1.

0.

1.

1.

0.

0.

0.

0.

1.

1.

0.

0.

0.

0.

0.

9

8

,0

,0

,7

9

.0

.9

.9

.0

.6

.0

.0

.3

.6

.0

,0

.0

.0

.0

May

0.

1.

0.

0.

0.

0.

0.

0,

0,

0.

0.

0,

0,

0.

0.

0,

0.

0.

0,

0.

,4

.2

,0

.0

.3

.4

.0

.4

.4

.0

.3

.0

.0

.0

.1

.0

.0

.0

.0

.0

June

0.

1.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

1

0

,0

0

3

1

,0

1

,1

,0

.2

,0

,0

.0

.0

,0

,0

,0

0

0

July

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0

9

.0

0

3

,0

,0

,0

0

.0

.2

.0

,0

.0

.0

.0

,0

.0

.0

0

Aug

0.

1.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

3

2

.0

.0

.3

,3

.0

.3

,3

.0

.2

.0

.0

.0

.0

.0

.0

.0

.0

.0

Sept

0.

1.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

6

4

,0

0

.4

6

.0

.6

,6

.0

.3

.0

.0

.0

.3

.0

.0

.0

.0

.0

Oct

0.

1.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

,8

6

.0

.0

,4

.8

.0

.8

.8

.0

.4

.0

.0

.3

.5

.0

.0

.0

.0

.0

Nov

2.

3.

0.

0.

0.

2.

0.

2.

2.

0.

0.

0.

0.

1.

2.

0.

0.

0.

0.

0.

,4

,3

.0

.0

.8

,4

.0

.4

.4

.0

.8

,5

.0

.8

.0

.0

.0

.0

.0

.0

Dec

3.

4.

0.

0.

1.

3.

0.

3.

3.

0.

1.

1,

0.

2.

2.

0.

0,

0.

0.

0.

.2

.0

.0

.0

.1

.2

.0

.2

,2

.0

.0

,3

.0

.6

.8

.0

,0

.4

.0

.0

Annual

recharge

18.

28.

0.

0.

7,

18.

0.

18.

18.

0,

6

7

0,

13,

15,

0

0

3,

0.

0.

.8

.3

.0

.0

.4

.8

.0

.8

.8

.0

.5

.1

.0

.4

.3

.0

.0

.6

.0

.0

Annual 

recharge 

as 

fraction 

of 

annual

rainfall

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

,48

65

.00

,00

,19

,48

.00

.48

.48

.00

.18

.18

.00

.43

.43

.00

.00

.13

.00

,00

Area 

in 

thousands 

of

2

feet

9,220

3,285

1,190

2,800

5,235

7,460

5,705

11,225

10,635

3,070

2,725

3,985

2,175

9,270

9,900

3,115

3,045

7,140

1,135

3,060

Annual 

recharge 

in

Mgal/d

0.

0,

0,

0,

0,

0

0,

0,

0,

0

0

0

0

0

0

0,

0

0,

0,

0

.296

.159

.000

.000

.066

.239

.000

.360

.341

.000

.030

.048

.000

.212

.258

.000

.000

.044

.000

.000

TOTALS 804,080 15.063

75