mum storage capacity, the excess recharges ground-wa- Table 4. Soil characteristics, island of Kauai

ter (eq. 3). Evapotranspiration is subtracted from soil- Avaliable Rooting Sexe
i: i i i salle neh mnch depth ture stora
some lesser actual rate, depending on the amount of wa- = = a ne ul
rin wailable to meet the demand (eq. 4). Am Aleka 0.20 32 6.40
water remaining in soil storage is carried over to the Hanalei 0.17 B 2.21
next month. Hanamaulu 0.14 36 5.04
SSyan +P, - Ryan = xX, (2) Hihimanu 0.12 45 5.40
Hulua 0.13 16 2.08
where: Toleau 0.13 15 1.95
SSjan = beginning January soil-moisture storage, panes hod 3 oe
aena
Pyan = January rainfall, Kalapa 0.13 20 2.60
Ryan = January runoff, and Kalihi 0.13 46 5.98
= first interim soil-moisture storage. Kaloko 0.13 20 2.60
Kapaa 0.14 14 1.96
Kekah 04 4 3.36
Kok 0.16 32 5.12
Tf X, > SSmraxs OR -IfX,;<SS_ 4G) Koln on m0 30
loa . .
then X1 — SSmnax = G then G = 0 and Xj = Xp. Kolokolo 0.13 28 3.64
and X; — G=X). Koolau 0.13 7 0.91
Kunuweia 0.08 12 0.96
wher 2 L " OAS. 26 3.90
X, = first interim soil storage in the month, Lihue 0.14 27 3.78
ii i i 30 3.60
my : Mahana 0.12 20 2.40
Ge ground. -water techarge, and “

Makapili 0. 13 28 3.64

Mamala 0.17 19 3.23

Mokulei 010 2 2.20
If X) 2 PE, OR IX, <PE, (4) Nin 012 36 432
then AE = PE then AE = X> Nohili 0.13 120 15.60

Nonopahu 0.11 31 341

and X5—PE = X.nq- and =0.
2 end Xend Ol 21 273
where: Paaiki 9 1.62
r — Pakala : QF 2.97
AE= actual evapotranspiration, _ Pamoa 010 62 6.20
PE= potential (maximum) evapotranspiration, and —_pohakupu 0.13 38 4.94
Xen = Soil-moisture storage at the end of the month. pooky 0.10 2B 430
Puhi 0.11 33 3.63

~The water-budget model accounts for soil-mois- Pau Opae 0.132989

ture storage through the months by calculating a begin- —Waialeale 0.21 4 0.84
Waiawa 0.16 14 2.24
where the ending value becomes the beginning value Waikomo 0.10 20 2.00
inni il-moi Badland (BL) 19.07 130 2.10
a rT 1
uary was determined to be 92 percent of capacity by Badland (BM) 0.09 40 3.60
A sae with initial coil-moi: Beaches 19.05 1g 0
100 percent, 50 percent, and 0 percent of capacity. End- Dune land 0.05 0 o
i il-moi i identi r Fill 10.15 17 2.55
i values were input Marshes 0.27 60 16.20
for January initial soil moisture. Riverwash 0.03 0
Rough broken land 10.12 130 3.60
TValue provided by [U.S.] Natural Resources Conservation Service,
Honolulu

416 Water Budget for the Island of Kauai, Hawail



wot LY

tof Mt Waialeale (==

\
an’
a,
“a
y & Stream
ry .

ic) 5 KILOMETERS.

‘Base moditied from U.S, Geological Survey
‘igtal data, 1:24,000, 1983, Abers equal area
projection, standard parallels 21°58" and 22°11",

‘central meridian 157°32'30"

EXPLANATION

DRAINAGE DIVIDE

ISLAND CREST AND DRAINAGE DIVIDE

40525

STREAMFLOW-GAGING STATION AND
ABBREVIATED NUMBER--Complete
number is preceeded by 16 and ends

in 00.

Figure 6. Gaged drainage basins used in the water-budget analysis, island of Kauai.

10 Water Budget for the Island of Kauai, Hawaii



22° 00"

0 5 MILES

oO 5 KILOMETERS

‘Base modfied from U.S. Geological Survey
digital data, 1:24,000, 1963, Albers equal area
projection, standard parallels 21°58 and 22°11,
‘central meridian 157°32'30"

EXPLANATION

MEAN ANNUAL GROUND-WATER RECHARGE, IN INCHES

HEE Greater than or equal to 150 Greater than or equal to 25 and

less than 50
E32) Greater than or equal to 100 and
less than 150 [] __ Greater than or equal to 10 and
less than 25
Greater than or equal to 50 and
less than 100 [-} Less than 10
----- ISLAND CREST

Figure 10. Mean annual ground-water recharge, island of Kauai.

20 Water Budget for the Island of Kauai, Hawaii


Water Budget for the Island of Kauai, Hawaii

By Patricia J- Shade

Abstract

dent population in 1990 was about 51,000 (State of Ha-

waii.

A geographic information system model was

the coast in centers including Kekaha, Lihue, Kapaa,

t for tt and Wailua. Resort developments also are located near
created to calculate a monthly water budget for .

island of Kauai. Ground-water recharge is the re-
sidual component of a monthly water budget calcu-
lated using long-term average rainfall, streamflow,
and pan-evaporation data, applied irrigation-water
estimates, and soil characteristics. The water-bud-
get components are defined seasonally, through the
use of the monthly water budget, and spatially by
aquifer-system areas, through the use of the geo-
graphic information system model.

The mean annual islandwide water-budget to-

the coast and with the growth and development has
come an increased demand for water. To meet the de-
mand, the Kauai County Department of Water, in coop-
eration with the U.S. Geological Survey (USGS), is
investigating ground-water availability on the island.
The project includes water-use data compilation, water-
budget calculation, ground-water modeling, and a pro-
gram of test drilling for aquifer analysis. This report de-
scribes the water- r-budget analysis and calculation of

water * modeling,

tals are 2,720 Mgal/d for rainfall plus irrigation;
1,157 Mgal/d for direct runoff; 911 Mgal/d for ac-
tual evapotranspiration; and 652 Mgal/d for

round-water recharge. Direct runoff is 43 percent,
actual evapotranspiration is 33 percent, and
ground-water recharge is 24 percent of rainfall plus
irrigation. Ground-water recharge in the natural
land-use areas is spatially distributed in a pattern
similar to the rainfall distribution.

Distinct seasonal variations in the water-bud-
get components are apparent from the monthly wa-
ter- pudget cs inet Rainfal! and nd ground water

embe ed by
Recharge is lowest in June (454 Meal/d) and No
vember (461 Mgal/d).

INTRODUCTION

Growth and change are occurring on the island of
Kauai. Kauai is a relatively rural island where the resi-

The water supply for the population of the island of
Kauai is obtained primarily from ground-water sources.

well as for commercial, industrial, and some agricultur-

charged by the infiltration of rainfall and irrigation
water. An estimate of ground-water recharge is needed
for management of the resource.

Purpose and Scope

The purpose of this report is to describe the calcu-
lation of a mean n monthly w water er budget f for the island of

support “calculations on this time scale, Calculations as-
sume natural land-use conditions except for the areas of
irrigated agriculture on plantations. The monthly spatial
distribution of the water-budget components islandwide
and by State of Hawaii aquifer-system areas is dis-
played and tabulated.

Introduction 1



— {
Mt Waidieale
eS.

5 MILES

0 5 KILOMETERS

‘Base modified from U.S. Geological Survey
‘gia! data, 1:24,000, 1983, Abbers equal area
projection, standard parallels 21°55" and 22°11",
central meridian 157°3230"

EXPLANATION
MAXIMUM SOIL-MOISTURE STORAGE, IN INCHES

Less than or equal to 2
Greater than 2 and less than or equal to 4

Greater than 4 and less than or equal to 6.5

Greater than 6.5

Figure 9. Maximum soil-moisture storage, island of Kauai.

Water-Budget Model 17


159° 30" s

ak Princbille
U7 KALIL

20201

% KILAUEA
; / 20105 “A

159° 40°

22° 10°

y WAINIHA

NA PALI 20203

ANAHOLA
20104

ay .
° SWAILUAY om
{ 20103 ny us

;

( (HANAPEPE J
22° 00" : / 1 /20304

% HANAMAULU Lihue
x, 20102 .

7 (Ve

J” MAKAWELI
20303

0 5 MILES

oO 5 KILOMETERS

Base modified from U.S. Log eathonl ll
itl data, 1:24 00,1983, bers

prfcton, Sanda pres 2°58 and 20°11
ceria mein 15793230"

EXPLANATION

—-—  AQUIFER-SYSTEM BOUNDARY

KOLOA AQUIFER-SYSTEM NAME AND
20101 NUMBER

Figure 13. Aquifer-system areas, island of Kauai (from George A. L. Yuen and Assoc., 1990).

Application of Water-Budget Results to Water-Management Areas 23


the summer months of July and August, to 690 Mgal/d
and 727 Mgal/d, respectively, relative to June (461
Mgal/d) and September (541 Mgal/d). This slight peak
in recharge is a direct result of increased orographic
rainfall from the more persistent trade winds in July and
August (Giambelluca and others, 1986). Annual aver-
age recharge is 652 Mgal/d for the island.

Annual recharge distribution and monthly re-
charge distribution over the island for a wet (January)
and a dry (June) month are shown in figures 10, 11, and
12. The annual distribution of ground-water recharge
(fig. 10) is similar to annual rainfall distribution (fig. 2).
Departure from this pattern is due primarily to the effect
of ground-water recharge from irrigation, noticeable
particularly in the low rainfall areas along the southwest
coast near Kekaha and Waimea, and near Kapaa and
Anahoia on the northeast coast. By comparing figures 9
and 10 the effect on recharge of differences in the soil
characteristic of maximum soil-moisture storage capac-
ity can also be seen. Ground-water recharge is highest
at the highest altitudes at the center of the island and oc-
curs over the largest area in the rainy winter months
(fig. 11) when the soil moisture is high and AE is low,
and decreases significantly at these altitudes in drier
months (fig. 12).

Islandwide rainfall is highest during the winter
months but increases slightly in mid-summer, relative
to the other dry months, because of increased orograph-
ic rainfall generated from strong northeast trade winds.
The runoff component has a similar monthly distribu-
tion showing a slight peak in the summer months of July
and August. The magnitude of AE variability is less
through the months, ranging from 790 Mgal/d to 1,024
Mgal/d on an islandwide basis. AE values decrease as
moisture becomes more limited during the drier sum-
mer months. Because ground-water recharge is the re-
sult of the interaction of the other water-budget
components there is no direct correlation between re-
charge variability and the other components through the
year. Soil-moisture storage begins to decrease from
February through July as shown by the negative change
in soil storage values, and increases in August, continu-
ing through January. The mass balance result of -1
Mgal/d is the result of round-off error in the calcula-
tions. The monthly results totaled and divided by 12 in-
dicate the annual average obtained from the monthly
calculations. Expressed as a percentage of rainfall, run-
off is 43 percent, AE is 33 percent, and recharge is 24
percent on an islandwide basis.

APPLICATION OF WATER-BUDGET
RESULTS TO WATER-MANAGEMENT
AREAS

Water-budget results can be applied to the areas
used by water managers for resource management.
Aquifer-system areas on Kauai, as defined by the State
of Hawaii for regulatory purposes (George A.L. Yuen
and Associates, Inc., 1990), are shown in figure 13. The
system boundaries generally coincide with topographic
drainage divides. Water-budget results for each of the
areas are shown in table 7. Ground-water pumpage from
each of these areas in 1990 is also included (Shade,
1995). Two systems have relatively high ground-water
withdrawal to ground-water recharge ratios, as com-
pared with the other systems. In the Kekaha system,
where several thousand acres of sugarcane are irrigated,
water-budget results indicate a ground-water recharge
rate of 12 Mgal/d, yet water-use data indicate a ground-
water withdrawal rate of almost 23 Mgal/d. Ground-wa-
ter from outside the Kekaha system is flowing into the
system from the upgradient Waimea system. Another
noteworthy area is the Koloa system where substantial
agricultural and resort developments are located. This
system shows ground-water withdrawals of about one-
third the ground-water recharge rate. In all other sys-
tems ground-water recharge rates substantially surpass
ground-water pumping rates.

Another point to note is the high proportion of AE
in comparison with rainfall and applied irrigation water
in the systems that have large agricultural areas. These
ratios are 53 percent, 45 percent, 42 percent, 72 percent,
and 47 percent in the Koloa, Hanamaulu, Anahola, Ke-
kaha, and Makaweli systems, respectively. Because
these agricultural areas are presently dominated by sug-
arcane, which has a high water demand, the continuing
diversification of agricultural crops to lower-water-de-
mand crops and development of agricultural land for
housing and resorts will distinctly shift the balance of
the water-budget components. The AE proportion of the
balance in these areas will decrease as will ground-wa-
ter recharge from a decrease in applied irrigation water.

Application of Water-Budget Results to Water-Management Areas 19


Oo 5 KILOMETERS

Base modified from U.S. Geological Survey
‘gal data, 1:24,000, 1983, Abbers equal area
projection, standard parallels 21°55' and 22°11",

‘central meigian 157°32'30"

EXPLANATION

—60—

LINE OF EQUAL MEAN ANNUAL PAN
EVAPORATION--Interval 10 inches.

ISLAND CREST

PAN-EVAPORATION STATION
AND NUMBER

Figure 8. Mean annual pan evaporation, island of Kauai (modified from Ekern and Chang, 1985).

14 Water Budget for the Island of Kauai, Hawaii



High-level-water is impounded _at altitudes above
the basal-water level by relatively impermeable rock
(Macdonald and others, 1960). In the absence of the rel-
atively impermeable rock this water would descend to
basal levels. High-level water is recharged by rainfall
and discharges to springs and seeps scattered through-
out the island and to streams as base runoff. The Alakai

Data Requirements.

A geographic information system (GIS) model was
created to calculate the monthly water budget by linking
the spatial and quantitative characteristics of the vari-
ables in equation 1. The data requirements for the GIS
water-budget model include rainfall, stream discharge

Swamp is in such an area where moderately to poorly
permeable rock underlies an area that receives more

(runoff) and associated drainage areas, pan evaporation,
soil properties, and irrigated-agriculture land-use distri-

than 200 in/yr of rainfall. The swamp covers more than
10 mi? and is underlain mostly by the Olokele Member

swamp ris underlain by Koloa Volcanics (Macdonald.
and-others,1960).Fhe major hydrologic characteristics
of the swamp are discussed by van't Woudt and Nelson
(1963) who concluded that:

Tomore than half the swamp area is dissected by
stream channels,

2. less than 30 percent of the area is flat to moderately
sloping where permeability is low and peat has

3. the area is constantly saturated and is essentially a

bution.

Mean monthly rainfall data and spatial distribu-
tions were obtained by digitizing the monthly rain!
maps for the island of Kauai by Giambelluca and others
(1986). The value assigned to the area between the lines
of equal rainfall was the average value of the bounding
lines.

Eight drainage basins around the island, digitized
from USGS 1:24,000-scale topographic maps compiled
in 1983, had USGS streamflow-gaging stations located
near the shore. These basins were selected because they

———fomed, SCS... ad Fong term streamflow records averaging about 30

years, coincident with the period of record of the rain-

fall dat:
falt

collecting and overflow basin, and

swamp area), derived from subsurface storage be-
low the swamp, supplies the base-flow discharge in
the Waimea and Makaweli Rivers.

WATER-BUDGET MODEL

Ground-water recharge can-be estimated by using
a -water-budget model. The method for calculating the
water budget is similar to that developed by Thomth-
waite (1948) and Thomihwaite ane Mather (1955) and

that balances moisture inputs of rainfall, and moisture
outputs of streamflow, evapotranspiration, and ground-
water recharge. The relation is expressed by:

C= P+IER
I—R

The mean annual pan-evaporation data were ob-

. ined by digitizing the pan-evaporatior p for is-

land of Kauai (Ekem and Chang, 1985). The average of

tion -was assigned to the area between the two lines.

Digital soil maps were provided by the [U.S.] Nat-
ural Resources Conservation Service (formerly, the Soil
Conservation Service). Forty-nine soil types are delin-
eated and representative values for the soil properties of
rooting depth, available soil moisture (the difference
between the amount of water held in the soil-at field-ca-
Pacity and é at wilting point), and maximum soil-mois-

(1972). Maximum soi moisture storage is s the key soil

1; thus a digital map of
this soil-property distribution was created from the orig-
inal soil maps to use in the GIS model.

G=Pr+

where: G is ground-water recharge,
P is rainfall,
Tis irrigation,
Ris direct runoff,
AE is actual evapotranspiration, and

ASS is change in soil-moisture storage.

Land-use information was obtained from the five
large plantations on the island that, combined, irrigate
more than 33,000 acres. The principal crop is sugar-
cane, with smaller areas planted in coffee and macad-
amia nuts. Maps of the fields were digitized and data
regarding methods of irrigation and crop types were
coded. The remainder of the island area was modeled as
natural cover.

6 Water Budget for the Island of Kaual, Hawail



5 MILES

5 KILOMETERS

Irrigated plantation
agricultural fields

Base modified from U.S. Geological Survey
digital data, 1:24,000, 1983, Atbers equal area
projection, standard parallels 21°58" and 22°11",
ccenral meridian 157°32'30"

Figure 1. Hawaiian islands and island of Kauai.

Geology and Ground-Water Occurrence 3


Acknowledgments

The author acknowledges the cooperation and _as-
sistance of personnel from the Kauai County Depart-
ment of Water and the Natural Resources Conservation
Service (U.S. Department of Agriculture) for providing
data and aiding in making estimates when no data were

The island of Kauai is essentially a broad volcanic
dome formed by the eruption of many thin layers of lava
rock sloping away from the summit which was located
near Mt. Waialeale (fig. 3). The island comprises two
volcanic formations: the Waimea Canyon Basalt and
the younger Koloa Volcanics. The Pliocene and Mi-
ocene(?) Waimea Canyon Basalt built the broad volca-

available. The field maps provided by the major planta-
tions were much appreciated and helpful in the analysis.

nic dome and includes lavas of the Napali, Haupu,
Olokele, and Makaweli Members. These are all thick

The study area encompasses the entire island of
Kauai, 553 mi2 (fig. 1). Population centers and more
than 33,000 acres of irrigated agricultural land are locat-
ed near the coast from west of Kekaha to Anahola on the
east coast of the island. The interior of the island is un-
developed and rugged in the areas of Waimea Canyon,
the Alakai Swamp, and in the uplands on the north and
east sides of the island, as well as from the headwaters

Rainfall variability over the island is extreme (fig.

accumulations of individual lava flows with alternating
massive flow cores and rubbly or fragmented interflow
whereas the others are thicker-bedded. The interflow
zones of all members are highly permeable. Macdonald
and others (1960) have characterized the Haupu,
Olokele, and Makaweli Members as moderately to.
poorly permeable, and the Napali Member as mostly
highly permeable.
Lavas of the Koloa Volcanics (Pleistocene and.

Pliocene) erupted after a long period of volcanic quies-

ni ion during which time large parts of the
eastem slope of the volcanic dome collapsed. Lavas of
the Koloa Volcanics are found mostly on the east side

2), from less than 30 in/yr along the leeward (westem)
coast near Kekaha to more than 400 in/yr at Mt. Waiale-

places on earth, at an altitude of over 5,100 ft. This

in/mi. A striking variability in vegetation accompanies
this rainfall regime from dryland, xerophytic plants in
the Kekaha coastal areas to rain forests on the upper
slopes of Mt. Waialeale and in the Alakai Swamp.

‘Dramatic landscapes have evolved because of the
abundance of water on Kauai. The combined erosional
forces of rainfall and-runoff fromthe wet summit area
have formed Waimea Canyon and the Spectacular scen-

of the island. They fill large depressions in the lavas of
the Waimea Canyon Basalt, which they overlie except
where erosional remnants protrude. The lavas o!
Koloa Volcanics are generally massive and heteroge-
neous. The layering evident in the lavas of the Waime
Basalt is typically not evident in the Koloa lavas and
Macdonald and others (1960) have characterized the
Koloa lavas as poorly to moderately permeable. High
rainfall on the windward (eastem) side of the island has
weathered the surface of the Koloa lavas to.a-clay-rich
mantle over the less weathered rock at depth.

Sedimentary rocks occupy a-small fraction of
Kauai. i, They are of marine and ‘errigenous origin and

others = (1960) characterized ‘the sedimentary rocks a as

GEOLOGY AND =

OCCURRENCE

Ground water on the island is either basal water or

The following description of the geology and
ground water of Kauai is based on the comprehensive
geologic mapping and description of Macdonald and
others (1960), which includes discussion of the water-
bearing properties of the rocks and the ground-water re-
sources of the island. Updated geologic names are from
Langenheim-and-Clague (1987).

water floating on the underlying saltwater in approxi-
mate accordance with the Ghyben-Herzberg relation:
for every foot that freshwater stands above sea level,
about 40 ft of freshwater extend below sea level. Basal
water moves generally from the mountain recharge ar-
eas to the near-shore discharge areas and is found in all
the geologic units, but the Napali Member is considered
the most easily developed as an aquifer.

2 Water Budget for the Island of Kaual, Hawail



Table 2. Mean monthly and annual pan-evaporation, island of Kauai (modified from Ekern and Chang, 1985)
{Station is pan evaporation station; values are in inches]

Station No. Mean

925 12 5465.59 7:17-—*72-66——*8.26 8879-63-91 BG 754 6485.55 91.12

941 22 5.14 5.65 693 743 782 805 910 937 8.23 7.33 6.17 5.40 86.58

944 21 454 498 631 667 7.07 7.29 759 755 682 5.96 489 4.15 73.53
962 10 5.22 5.30 7.03, 7.77 8.96 940 9.68 9.50 8.24 77 6.16 5.50 92.94
981 il 436 410 612 645 7.09 7.82 870 9.15 7.75 670 498 443 78.31
986.1 21 497 5.03 634 664 7.70 7.80 839 809 7.23 6.38 5.14 4.66 78.46
993 20 443 493 5.79 5.95 649 655 7.09 7.15 6.36 5.89 474 439 66.74
1004 20 3.63 4.03 437 4.78 543 5.84 615 5.72 5.07 4.55 3.75 3.29 57.84
1005 20-483 4.98 5.58 5.81 5.97 5.90 6.19 653 6.21 5.77 4.75 444 66.04 0
1006 19 3.57 3.66 4.23. 490 556 585 618 621 5.30 4.69 3.71 __ 3,32 __ 55.49

1061.3 16 4.39 4.07 4.24 4.27 5.00 5.30 6.07 5.93 5.61 4.80 3.90 3.74 58.16
1062.1 16 453 455 5.78 617 646 651 7.07 687 6.22 5.57 452 4.46 68.24
1064.3 12 486 5.04 630 663 7.28 748 827 810 7.47 6.72 5.16 5.06 78.64
1092 12 3.57 3.56 425 4.18 4.16 5.01 5.33 544 4.78 4.48 3.57 3.45 53.05
1101.1 12 486 485 610 661 7.24 689 7.28 7.55 6.72 6.14 5.02. 5.05 74.17
1104.2 10 5.01 5.44 646 678 749 7.21 7.68 7.76 6.97 6.50 5.43 5.40 78.16
1114 13 481 5.06 6.08 _ 6.70 __7.78 __ 7.76 __7.72__7.82__7.03 6.29 5.04. 4.91 77.50

Table 3. Mean monthly to annual pan-evaporation ratios, iskand of Kauai
[Stations are pan-evaporation stations; values are in percent]

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

Leeward stations (7 stations)

6.29 6.29 8.29 8.29 9.57 9.71 10.29 10.14 9.14 8.14 7.00 6.14

Windward stations (18 stations)

6.44 6.94 8.06 8.67 9.39 9.67 10.39 10.11 9.28 8.17 6.94 6.39
Applied ratio

6:40 6-16, 8A2 8.56 9.44 9.68 10.36 10.12 9.24 8.16 6.96. 6.32

Water-Budget Model 15



22° 00"

5 MILES

0 5 KILOMETERS

Base mogllied from U.S. Geological Survey
‘gal data, 1:24,000, 1989, Abbers equal area
projection, standard parallels 21°55" and 22°11",
central meridian 157°32'30"

EXPLANATION

SEDIMENTARY DEPOSITS (Holocene) WAIMEA CANYON BASALT (Pliocene
and Miocene?)

KOLOA VOLCANICS (Pleistocene and
Pliocene)

Makaweli Member (Pliocene)

Olokele Member (Pliocene)
in Palikea Breccia Member (Pleistocene?

and Pliocene?) Haupu Member (Pliocene)

meillia

Napali Member (Pliocene and Miocene?)

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

Geology and Ground-Water Occurrence 5


5 MILES

0 5 KILOMETERS

Base modltied from U.S. Geological Survey
gia data 1:24,000, 1983, Albers equal area
projection, standard parallels 21°55' and 22°11,
central meridian 157°32'30"

EXPLANATION

MEAN JANUARY GROUND-WATER RECHARGE, IN INCHES

Greater than or equal to 15 a Greater than or equal to 1
and less than 5
Greater than or equal to 10
and less than 15 | | Less than 1
Greater than or equal to 5
andlessthan1000 0 ISLAND CREST

Figure 11. Mean ground-water recharge for January, island of Kauai.

Application of Water-Budget Results to Water-Management Areas 21


___WATER BUDGET FOR THE ISLAND OF KAUAI, HAWAII]

By Patricia J. Shade

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 95-4128

KAUAI COUNTY DEPARTMENT OF WATER

Honolulu, Hawaii
1995



i Ns =~ ne Ip /

—
—_

-_ cs
° 5 KILOMETERS fata ur Ll”

‘Base modified from U.S, Geological Survey SY

‘igtal data, 1:24,000, 1983, Aers equal area
projection, standard parallels 21°55 and 22°11",

‘central meridian 157°32'30"

EXPLANATION

— 4—— LINE OF EQUAL MEAN JANUARY RAINFALL
Interval, in inches, is variable

sat ISLAND CREST

Figure 4. Mean rainfall for January, island of Kauai (modified from Giambelluca and others, 1986).

8 Water Budget for the Island of Kauai, Hawaii



Rainfall

Rainfall on Kauai is notable for its extremes (fig.
2). The island lies in the path of the persistent northeast
tradewinds that gather substantial moisture as they pass
over the Pacific Ocean. Rainfall along the windward
(eastem) side of the island is orographically induced as

flow, monthly direct runoff was calculated as the differ-
ence between mean monthly streamflow and mean
monthly base runoff. Base runoff was calculated in this
study from monthly flow-duration analyses as the dis-
charge maintained at least 90 percent of the time during
the chosen month, a conservative estimate of the
ground-water component.

the air is forced to rise over Mt. Waialeale, where the
measured mean annual rainfall is 449 in/yr (Giambellu-

(westem) side of the island, rainfall diminishes drasti-

rainfall is about it in, This range represents a 1 rainfall
gradient of more than-25 in/mi.

Twelve maps showing lines of equal mean month-
ly rainfall for the island of Kauai were compiled from
data collected at a network of 12 base stations that had
complete records for the base period from 1916 through
1983, Data from_an additional 9 stations that had long
periods of record were used in the statistical analyses

Giambelluca and others, 1986). These monthly ma
were digitized and compose the rainfall data set for the
GIS model. These data were used to calculate mean
monthly rainfall values for the island that range from a
low in June of about 1,550 Mgal/d to almost 3,500
Mgal/d in January.

Direct runoff was calculated from data from eight
streamflow-gaging stations located near the shore
around the island (fig. 6). These sites were selected be-
cause they had long-term records averaging about 30
years, coincident with the period of record of the rain-
fall data. These gaged drainage basins, as with all the
major drainage basins on the island, are characterized
by large ranges of elevation and rainfall from the head-
waters to the shore.

The gaged drainage basins were digitized and rela-
tions between average direct runoff, measured at the
eight stations, and average rainfall over the drainage ba-
sins were calculated by overlaying rainfall data and

rainfall relations are considered representative o of the Te-

tion ‘of the g gage relative t toa a topo: veraphic divide that sep-

The spatial distribution of rainfall varies from arates the windward and leeward sides of the island.

month to month, and most significantly from winter to
summer months (figs. 4 and 5). In general, rainfall sea-
sonality is more pronounced in dry leeward areas, such
as near Kekaha, than in wet areas such as Mt. Waialeale.
Figures 4 and 5 show that June rainfall near Kekaha is
about 25 percent of January rainfall, but near Mt. Wa-
ialeale, June rainfall is about 80 percent of January rain-
fall.

Runoff

Streamflow comprises direct runoff, the water that
flows into stream channels promptly after rainfall, and

The average of these runoff to rainfall ratios shows a
distinct spatial distribution. Basins on the windward
side of the topographic divide, at stations 0600, 0710,
0932, and 1030, have runoff to rainfall ratios about
twice those of basins on the leeward side of the divide,
stations 0310, 0360, 0490, and 0525. (Station numbers
used in this report are abbreviated, complete numbers
are preceded by 16 and end in 00.) The poorly perme-
able Koloa Volcanics that predominates on the wind-

weathering and id resulting decreased permeability of the

off to rainfall ratios in the windward basins,

base runoff, the part of streamflow that is sustained
through periods of dry weather from discharge of
ground water (Langbein and Iseri, 1960). Generally, hy-
drographs from measured perennial streams on Kauai
have storm-generated peaks of short duration. Usually
within a few days the flow decreases to the level sus-
tained between storms by ground-water discharge. To
avoid including the ground-water component of stream-

In the water-budget model, direct runoff for gaged
drainage basins was calculated by multiplying average
monthly rainfall over the basi by the monthly runoff to
rainfall ratio for that basin. On the basis of the data in
table-t, direct runoff to-rainfall ratios were regionalized.
for ungaged areas of the island by applying the average
of the windward or leeward basins runoff to rainfall ra-
tios (table 1) to the mean monthly rainfall in the area,

Water-Budget Model 7



159° 40"

22° 00°

i) 5 MILES

i) 5 KILOMETERS

Base madified from U.S. Geological Survey
‘igtal data, 1:24,000, 1983, Abbers equal area
projection, standard parallels 21°55' and 22°11,
‘central meridian 157°3230"

EXPLANATION

— 40— LINE OF EQUAL MEAN ANNUAL RAINFALL
Interval, in inches, is variable

TTT ISLAND CREST

Figure 2. Mean annual rainfall, island of Kauai (modified from Giambelluca and others, 1986).

4 Water Budget for the Island of Kauai, Hawaii


Irrigation

In irrigated agricultural areas, significant AE (ac-
tual evapotranspiration) and ground-water recharge re-
sult from applied irrigation water. In 1990 more than
33,000 acres were planted principally in drip-irrigated
sugarcane, with additional acreage in coffee and macad-
amia nuts. To simulate the effects of irrigation on the
water budget, a sub-routine was added to the GIS mod-
el. The agricultural fields were digitized from the plan-
tation's field maps, and furrow- or drip-irrigation and
crop type were coded. Irrigation water was estimated
from 1990 data supplied by the major plantations on the
island and discussed by Shade (1995). For each planta-
tion in the GIS model, the irrigation water was applied
homogeneously over the fields and equally for each
month.

Crop AE demand was calculated as a factor of pan
evaporation (table 5). Irrigation recharge was calculated
as the difference between applied irrigation water and
crop AE requirements. The irrigation recharge was su-
perposed on the ground-water recharge calculated from
rainfall in these areas. Islandwide, applied irrigation
water was about 218 Mgal/d and AE was 187 Mgal/d,

Table 5. Irrigated plantation crops, island of Kauai

86 percent of the applied water. Ground-water recharge
from the infiltration of agricultural irrigation water was
31 Mgal/d, which is 14 percent of the applied irrigation
water. Fourteen percent is about one-third the irrigation
recharge rate from sugarcane fields calculated by Dale
(1967). However, Dale's (1967) agricultural field data
were from 1931 through 1965, when all fields were fur-
row-irrigated indicating that application rates were a
factor of pan evaporation equal to 1.6.

Ground-Water Recharge and Water-Budget
Results

Ground-water is recharged during months when
soil-moisture storage exceeds the maximum soil-stor-
age capacity. In an average year on an islandwide basis,
ground-water is recharged every month, although more
recharge occurs in the wet months, and none occurs in
the dry months in the driest areas. Average monthly val-
ues for the components of the water budget for Kauai
are shown in table 6. January is the wettest month with
almost 3,700 Mgal/d of rainfall and irrigation, and more
than 980 Mgal/d of recharge. Recharge increases during

Crop actual
evapotranspiration
Crop Acres Irrigation method (factor of pan evaporation)
Sugarcane 18,600 dip 10
Sugarcane 9,400 furrow 10
Coffee 225 drip 05
Macadamia nuts 5,000 drip 06

Note: Plantation estimates the evaporative demand of macadamia nut trees to be 50 inches per year. This value, on average, converts to 0.6 x pan

evaporation in the area of irrigated macadamia nut fields.

Table 6. Water-budget results, island of Kauai
[Values are in million gallons per day]

Rainfall and Actual Change In soi-
Month Irrigation Runoff evapotranspiration Recharge _ moisture storage
January 3,698 1,689 1024 981 +4
February 3,081 1,323 1,009 756 -7
March 3,220 1,716 928 594 -18
April 3,123 1,507 905 718 -7
May 2,425 1,019 832 583 9
June 1,764 517 790 461 4
July 2,246 700 857 690 -1
August 2,302 7 877 721 +1
September 1,914 502 870 541 41
October 2,401 807 973 610 +11
November 3,079 1,727 894 454 +4
December 3,386 1,683 969 710 424
Mean annual 2,720 1,157 O11 652 -1

‘Note: Annual average values are the average of the monthly values.

18 Water Budget for the Island of Kaual, Hawail


Table 7. Water-budget results by aquifer system, island of Kauai

[Aquifer-system names and numbers are from George A.L. Yuen and Associates, Inc., 1990; values are in million gallons per day]

Actual evapo-
Aquifer-system  Aquifer-system —_ Rainfall and trans-
name number Irrigation Runoff plration Recharge Pumpage
Koloa 20101 198 66 104 28 9.64
Hanamaulu 20102 249 112 ill 26 5.24
Wailua 20103 338 169 3 OL 0.74
Anahola 20104 217 101 91 25 2.97
Kilauea 20105 83 45 30 8 0.42
Kalihiwai 20201 96 52 27 17 1.22
Hanalei 20202 274 162 49 63 0.12
Wainiha 20203 352 190 Ss it 0.10
Na Pali 20204 102 33 41 28 0.00
Kekaha 20301 149 29 108 12 22.68
Waimea 20302 248 73 60 5 0.82
Makaweli 20303 273 715 127 71 2.16
Hanapepe 20304 141 50 34 57 0.17
TOTAL. .......0. 00. e cece ee eee 2,720 1,157 911 652 46.28

SUMMARY AND CONCLUSIONS

Ground water is the main source of public water
supply for the island of Kauai. Aquifers on the 553
square mile island are replenished by ground-water re-
charge from rainfall and agricultural irrigation water
that percolates through and beyond the root zone in the
soil to the subsurface rock. Rainfall ranges from less
than 20 inches per year near sea level along the south-
west coast to more than 400 inches annually at the sum-
mit of the island at an altitude of over 5,100 feet. Most
of the agricultural irrigation water used on the five large
plantations is diverted from streams, and almost 220
Mgal/d (million gallons per day) is applied to the fields.

Ground-water recharge is the residual component
of a monthly water budget calculated using long-term
average rainfall, streamflow, and pan-evaporation data,
and applied irrigation-water estimates and soil charac-
teristics. The water-budget components are defined sea-
sonally, through the use of the monthly water budget,
and spatially by aquifer-system areas, through the use of
a geographic information system model.

Islandwide rainfall is highest during the winter
months, November through April, with a slight increase
in July and August owing to increased orographic rain-
fall generated from persistent summer trade winds.
Monthly direct runoff has a similar distribution through
the year. The least monthly variability is in the actual
evapotranspiration, which ranges from 790 to 1,024
Mgal/d islandwide. Monthly ground-water recharge

24 Water Budget for the Island of Kaual, Hawaii

ranges from a low of 461 Mgal/d in June and 454
Mgal/d in November to a high of 981 Mgal/d in Janu-
ary. The annual average ground-water recharge for
Kauai is 652 Mgal/d, 24 percent of the total of the annu-
al average rainfall and applied irrigation water. The
ground-water recharge in the natural land-use areas is
spatially distributed in a pattern similar to the rainfall
distribution. Islandwide average annual direct runoff
and evapotranspiration are 1,157 Mgal/d and 911
Mgal/d, 43 and 33 percent of the total average rainfall
and irrigation water, respectively.

The water-budget components are also tabulated
for the 13 aquifer systems used by the State of Hawaii
for water management. In all but one of the aquifer sys-
tems, ground-water pumpage is less than ground-water
recharge. In the Kekaha system, pumpage exceeds re-
charge by almost 11 Mgal/d indicating that ground wa-
ter likely flows into this system from an adjacent
upgradient aquifer system.


CONVERSION FACTORS

Multiply By To obtain
acre 4,047 square meter
foot (ft) 03048 meter
million gallons per day (Mgal/d) 0.04381 cubic meter per second
inch (im) 25:4 millimeter
inch per year (in/yr) 2.54 centimeter per year
mile (mi) 1.609 kilometer
square mile (mi2) 2.590 square kilometer

Ww

Contents



Table_1._Mean-monthly direct_runoff_and rainfall, and _runoffto-rainfall ratios, island of Kauai
[Years shown are period of record; Q, direct runoff, in inches; R, rainfall, in inches; %, runoff to rainfall ratio, in percent}
Jan.___ Feb. Mar. Apr. May June _July__ Aug. Sept. Oct. Nov. Dec.
Windward streamflow-gaging stations

Station 0600 (1959-87)

Q 8.66 5.51 748 6.30 4.72 2.36 3.54 3.94 3.15 4.33 7.87 787

% 63.9 45.7 55.0 444 36.9 25.1 28.0 30.3 30.7 33.8 54.5 54.7

Station 0710 (1953-87)
Q 9.45 748 9.45 9.45 7.48 3.54 5.51 5.51 3.15 5.91 11.02 10.24
R 13.23 12.04 13.72 14.0 12.22 8.76 = 11.74 12.33 9.74 12.17 13.93 14.53

% 714 62.1 68.9 67.5 61.2 40.4 46.9 44.7 32.3 48.6 79.1 70.5
Station 0932 (1966-82)

Q 4.72 3.94 4.72 5.91 4.72 1.97 1.97 1.57 1.18 2.76 5.91 5.12

R 9.91 8.89 10.01 8.64 7.09 4.08 6.41 6.20 4.43 7.22 9.49 9.55

Yo. 47.6 44.3 47.2 68.4 66.6 48.3 30.7 25.3 26.6 38.2 62.3 53.6
Station 10304196487)

Q 10.63 9.45 16.54 14.96 11.02 5.91 8.27 787 7.09 8.66 15.35 12.60

% 55.3 55.1 83.6 BI 66.7 483 46.6 44.5 53.3 54.8 84.1 65.6
Windward average monthly runoff to rainfall ratio, in percent:
59.5 518 63.8 635 580 403 383 36.0 35.8 44.0 69.8 613
Leeward streamflow-gaging stations

Station 0310 (1945-89)
Q 5.12 3.54 433 2.76 1.18 0.39 0.79 1.18 0.39 1.18 3.54 4.33
R 15.23 10.53 10.25 10.31 6.17 3.65 5.1 5.59 4.42 5.71 8.47 11.61
Yo 33.6 33.6 42.2 26.6 19.1 10.7 15.5 21.1 8.8 20.7 ALB 37.3
Station 0360 (1944-87)
Q 51 4.33 5.51 3.94 1,97. 118 1.97. 1.97 0.79. 1.97 4.72 5.51
R 15.60 10.23 1119 11.86 OAL 4.91 6.44 6.82 5.91 7.31 9.76 11.77
Station 0490 (1928-87)
Q 6.30 5.12 6.69 5.12 3.54 2.36 3.54 3.94 36 76 5.5 6.30
R 16.75 10.55 13.26 13.37 11.05 831 10.31 11.26 9.57 10.36 13.57 14.99

% 376 45 505 383 320 284 %¥43 350 247 266 406 420
Station 0525 (1964-72)
Q 236 157 157 197 0.79 039 039 039 039 039 236 2.76
R 940 651 850 7.19 6.41 5.55 6.82657 5.55 69S 8338.87
% 251 AL 85 TA 12.3 105.7 59 70 56 283 31.
______Leeward average monthly runoff to rainfall ratio, in percent:

33.0. 373 398 313 213 175 15 22.8 13.5 20.3 39.8 39.3

Water-Budget Model 11



depending on the location of the area relative to the to-
pographic divide.

Istandwide monthly direct runoff ranges from a
low of about 500 Mgal/d in June and September to
highs of about 1,700 Mgal/d in January, March, No-
vember, and December. The islandwide monthly runoff

budget model range from a low of 30 percent in Sep-
tember to a high of 60 percent in November.

were calculated by multiplying the annual pan-evapora-
tion value (the average of the values of the bounding
contours is assigned to the area between contour lines)
shown in figure 8 by the monthly to annual pan-evapo-
ration ratios shown in table 3. Data from 7 leeward sta-
tions and 18 windward stations were averaged
separately, and variability in the ratios showed no spa-
tial tendencies. Thus, the average of the ratios from all
stations was applied in the areas where there are season-

al variations in PE, where the pan-evaporation value is
more than or equal to 30 ine Within the 30-in. con-

‘Accounting

Actual evapotranspiration (AE) is the quantity of
water evaporated from water and soil surfaces and tran-
spired by plants. Islandwide AE data from direct mea-
surements from field experiments do not exist. It is
possible to estimate AE, however, from pan-evapora-
tion and soil data through the application of the water-
budget model.

one-twelfth of the annual value, simulating the lack of
summer increases in pan-evaporation values.

If the PE demand in a particular month is not met
by the amount of water in soil storage, then AE is less
than PE. To estimate AE the maximumr soit moisture-
storage capacity was calculated for each of the soil se-
ries on Kauai. The soils and their characteristics have
been mapped and tabulated by the Natural Resources
Conservation Service (Foote and others, 1972) and

Pan-evaporation data from class A evaporating
i i f ntial (m:
evapotranspiration (PE) on the island. For this study pan
evaporation is assumed to equal PE on the basis of the

were digitized by the Natural Resources Conservation
ervice. Estimates of the available water and rootin;

depth for each soil series on the island are from Foote

and others (1972) and are shown in table 4. The avail-

results of lysimeter studies in sugarcane fields (Chang,
1968; Campbell and others, 1959) where the average ra-

able water value for each soil series in table 4 is the av-
erage of the range reported by Foote and others (1972).

tio between PE and pan evaporation was about 1.0. The
map of mean annual pan evaporation for Kauai (Ekem
and Chang, 1985) is shown in figure 8 and was digitized
for the GIS water-budget model. Where sugarcane is
grown, pan evaporation is well-defined by data from 25
stations with from 10 to almost 30 years of record (table
2). The mean annual pan evaporation in these areas
ranges from about 50 in/yr at high altitudes where tem-
peratures are low and rainfall and cloud cover are high

The rooting depth was assumed to be at the depth where
the profile description changed from "abundant roots"
to “few roots.” For the few soil types where Foote and
others (1972) did not provide values for available water
or rooting depth, estimates were provided by the Natu-
tal Resources Conservation Service in Honolulu (C.
Smith and S. Nakamura, oral commun., 1992). The
maximum soil-moisture storage capacity of a particular
soil s¢ series is the Product « of its available water and root-

Other pan-evaporation stations with few data allow

pacity was generated (fig. 9) and used with the monthly
rainfall and pan-evaporation maps in the GIS model to

the contours to be extended inland in the centrat uplands
to a value of 30 in/yr. Pan evaporation probably de-

cause of decreasing temperatures and persistent cloud
cover (Ekem_and Chang, 1985), Ekem and Chang
(1985) note that in this area, seasonal fluctuations in PE
are insignificant because there is no seasonal advection
of heat energy as there is at low altitudes near the lee-
ward coast.

The islandwide mean monthly PE distributions

calculate monthly values of AE and ground-water re-
charge.

The month-to-month bookkeeping procedure cal-
culates changes in the amount of water (moisture) in
soil storage. This volume changes month by month, and
it is from this reservoir that actual evapotranspiration
(AE) is withdrawn. In the water-budget model, the dif-
ference between the month's rainfall and direct runoff is
the volume of water added to soil storage (eq. 2). If the
new amount of water in soil storage exceeds the maxi-

Water-Budget Model 13



CONTENTS

ADSUACE oe cee ee nee eee eee e ee eee eee ee ees ee esse esteeeeeseeeeenees 1
Introduction wl
Purpose and Scope . 1
Acknowledgments ... 2
Description of the Study Area .............. 2
Geology and Ground-Water Occurrence ..........+++ 22
Water-Budget Model ..... 0.6.0 ccc c cece eee e eee nee renee eee n eee n ene ene tener eens ene 6
Data Requirements 6

13

Actual Evapotranspiration and Soil-Moisture Accounting. . .

Irrigation . 218

Ground-' Water Recharge and Water Budget Results. . 218
Application of Water-Budget Results to Water-Management Areas . .19
Summary and Conclusions. 24
References Cited .............45 25
FIGURES

1-13. Maps showing:
1. Hawaiian islands and island of Kauai .

. Mean annual rainfall, island of Kauai -

. cele of the island of Kauai

= Mean rainfall for Tune, island of Kauai
sins used in the water-budget analysis, island of Kauai
Rock permeability characteristics, island of Kauai . .
Mean annual pan evaporation, island of Kauai ... ..

Maximum soil-moisture storage, island of Kauai .
40. Mean annual ground-water recharg , island of Kauai
ie Mean an grounds |-water er recharge for or January: island of Kaui

0 94

TABLES

Mean monthly direct runoff and rainfall, and runoff to rainfall ratio, island of Kauai .
Mean monthly and annual pan evaporation, island of Kauai
Mean monthly to annual pan-evaporation ratios, island of Kauai .
Soil characteristics, island of Kauai. .
Irrigated plantation crops, island of Kat
Water-budget results, island of Kauai .............--+
Water-budget results by aquifer system, island of Kauai. .

IID [IP |S oe

Contents lil



159° 40"

5 MILES

0 5 KILOMETERS

‘Base modtied from U.S, Geological Survey
gia data, 1:24,000, 1989, Abers equal area
projection, standard paralels 21°55' and 22°11
central meridian 157°32°30"

EXPLANATION

MEAN JANUARY GROUND-WATER RECHARGE, IN INCHES

Greater than or equal to 15 fa] Greater than or equal to 1
and less than 5

Greater than or equal to 10
and less than 15 CJ] Less than 1

Greater than or equal to 5
andlessthan1000 2 ISLAND CREST

Figure 12. Mean ground-water recharge for June, island of Kauai.

22 Water Budget for the Island of Kauai, Hawaii


U.S. DEPARTMENT OF THE INTERIOR
___________ BRUCE BABBITT, Secretary SSeS

~_U.S.GEOLOGICAL SURVEY —<“i‘“—‘“‘“‘“<_l
Gordon P. Eaton, Director

A trade. irm-names.in-this-publication
y product,-or fi this publicati

is for descriptive purposes only and does not imply
endorsement by the U.S. Government

For sale by the U.S. Geological Survey
Earth Science Information Center
Open-File Reports Section

Box 25286, MS 517

Denver Federal Center

Denver, CO 80225

District Chief

U.S. Geological Survey

677 Ala Moana Blvd., Suite 415
Honolulu, HI 96813



REFERENCES CITED

Campbell, R.B., Chang, J.H., Cox, D.C., 1959, Evapotranspi-
ration of sugar cane in Hawaii as measured by in-field
lysimeters in relation to climate, in Proceedings of the
10th congress of the International Society of Sugarcane
Technologists 1959: Amsterdam, Elsevier, p. 637-649.

Chang, J.H., 1968, Climate and agriculture: Chicago, Aldine,
304 p.

Dale, R.H., 1967, Land use and its effect on the basal water
supply Pearl Harbor area, Oahu, Hawaii, 1931-65: U.S.
Geological Survey Hydrologic Investigations Alas HA-
267, 2 sheets.

Ekern, P.C., 1983, Measured evaporation in high rainfall ar-
eas, leeward Koolau Range, Oahu, Hawaii, University of
Hawaii, Water Resources Research Center, Technical
Report No. 156, Honolulu, Hawaii, 60 p.

— and Chang, J.H., 1985, Pan evaporation: State of Hawaii,
1894-1983, State of Hawaii Department of Land and
Natural Resources, Report R74, 171 p.

Foote, D.E., Hill, E.L., Nakamura, Sakuichi, and Stephens,
Floyd, 1972, Soil survey of the islands of Kauai, Oahu,
Maui, Molokai, and Lanai, State of Hawaii: U.S. Depart-
ment of Agriculture, Soil Conservation Service, 232 p.

George A.L. Yuen and Associates, Inc., 1990, Water resourc-
es protection plan: Honolulu, Hawaii, prepared for State
of Hawaii, Department of Land and Natural Resources,
Commission of Water Resource Management, variously
paged.

Giambelluca, T.W., 1983, Water balance of the Pearl Harbor-
Honolulu basin, Hawaii, 1946-1975, University of Ha-
waii, Water Resources Research Center, Technical Re-
port No. 151, Honolulu, Hawaii, 151 p.

—, , Nullet, M.A., and Schroeder, T.A., 1986, Rainfall atlas
of Hawaii: State of Hawaii, Department of Land and Nat-
ural Resources, Report R76, 267 p.

Langbein, W.B. and Iseri, K.T., 1960, General introductions
and hydrologic definitions: U.S. Geological Survey Wa-
ter-Supply Paper 1541-A, 29 p.

Langenheim, V.A.M., and Clague, D.A., 1987, Stratigraphic
framework of volcanic rocks of the Hawaiian islands,
chap. 1 of Decker, R.W., Wright, T.L., and Stauffer,
P.H., eds., Volcanism in Hawaii: U.S. Geological Survey
Professional Paper 1350, v. 1, p. 55-84.

Macdonald, G.A., Davis, D.A., and Cox, D.C., 1960, Geolo-
gy and ground-water resources of the island of Kauai,
Hawaii: Hawaii Division of Hydrography Bulletin 13,
212 p.

Shade, Pa ., 1995, Estimated water use in 1990 for the island
of Kauai, Hawaii: U.S. Geological Survey Water Re-
sources Investigations Report 93-4180, 23 p.

State of Hawaii, 1991, The population of Hawaii, 1990: State
of Hawaii, Department of Business, Economic Develop-
ment and Tourism, Statistical Report 219, Honolulu, Ha-
wai, 28 p.

Thomthwaite, C.W., 1948, An approach toward a rational
classification of climate: Geographical Review, v. 38,
no. I, p. 55-94.

Thornthwaite, C.W., and Mather, J.R., 1955, The water bal-
ance: Publications in climatology v. 8, no. 1, p. 1-104.

van't Woudt, B.D. and Nelson, R.E., 1963, Hydrology of the
Alakai swamp Kauai, Hawaii: Hawaii Agricultural Ex-
periment Station, University of Hawaii, Bulletin 132, 30

Pp.

Wentworth, C.K., 1951, Geology and ground-water resourc-
es of the Honolulu-Pearl Harbor area, Oahu, Hawaii:
City and County of Honolulu Board of Water Supply,
111p.

References Cited 25


EXPLANATION

— 4— LINE OF EQUAL MEAN JUNE RAINFALL
in inches, is variable.

Interval, in in

ine ISLAND CREST

Figure 5. Mean rainfall for June, island of Kauai (modified from Giambelluca and others, 1986).

Water-Budget Model 9



5 MILES

0 5 KILOMETERS

Base modified from U.S. Geological Survey
‘gital data, 1:24,000, 1983, Abers equal area
projection, standard parallels 21°55" and 22°11",
central meridian 157°32'30"

EXPLANATION

ROCK PERMEABILITY
[==] Highly permeable
Moderately to poorly permeable

Poorly to moderately permeable

Ee Poorly permeable

Figure 7. Rock permeability characteristics, island of Kauai (from Macdonald and others, 1960).

12 Water Budget for the Island of Kauai, Hawaii