AN

ELECTRICAL RESISTIVITY PROFILE

FROM MAHUKONA TO KAWAIHAE, HAWAII

William M. Adams

Technical Report No. 23

HIG Series, HIG-WRRC - 1

November 1968

The work on which this report is based was funded by the Division of Waterand Land Development of the Department of Land and Natural Resources of theState of Hawaii and is a cooperative effort of the Water Resources ResearchCenter and the Hawaii Institute of Geophysics.

ABSTRACT

In order to Locate the reLativeLy optimum sites for driLLing

expLoratory hoLes for fresh water~ an eLectricaL resistivity survey was

conducted aLong the new Mahukona-Rawaihae Road on the west fLank of the

Rohal.a Mountain. Two resistivity soundings were run using the Sohl.um-

berger spread configuration to detenmine a satisfactory spacing for a

Wenner profiLe spread. Using an "a" spacing of 275 feet~ a profiLe of

209 stations was run using the Wenner spread configuration. The data

were correLated with eLevation at 0.41~ so a procedure for removing the

eLevation effect from observed apparent resistivity was deveLoped. The

procedUre is probabLy uniqueLy appLicabLe to insuLar environments. Based

on the reduced resistivity profiLe~ four reLativeLy optimum sites for

addi.trional: eeploratrion, such as by driLUng~ are specified. There is noi.,

however~ any interpretation of the data that can definiteLy indicate the

occurrence anywhere on the profiLe of Large underground reservoirs of

fresh water. This is because the interpretation of profiLe data is

essentiaLLy reLative~ not absoLute.

iii

CONTENTS

LIST OF FIGURES " v

LIST OF TABLES vi

INTRODUCTION 1

METHOD OF FI ELD OPERATIONS 3

DATA FOR ELECTRICAL RESISTIVITY SOUNDINGS 9

DATA FOR THE ELECTRICAL RESISTIVITY PROFILE 9

A PROCEDURE FOR REMOVING ELEVATION EFFECTS FROM APPARENTRESISTIVITY OBSERVATIONS 17

Correction to Apparent Resistivity at a Standard EleYation 17Correction to Resistivity of Upper Layer 18Profile Data Reduced for Elevation Effect 18

DISCUSSION 23

ACKNOWLEDGEMENTS 24

REFERENCES 24

APPEND ICES 25Appendix A: Flowchart 27Appendix B: IBM Printout 32

LIST OF FIGURES

Figure1

2

3

4

5

6

7

8

9

Location of Mahukona - Kawaihae Road and Station No. 39 2Circuitry of Specially Constructed Electrical ResistivityEqu i pment 'I-Power Supply and Heath Chart Recorder Mounted in Trunkof Renta1 Automobile 5Breakouts at Center of Cable and Two Pairs of Connectors 6Field Procedure at Recording Site 7Profile Recordings for Stations 109, 110, and 111 8Deep Sounding at Station No.1 Taken in June, 1968 10Deep Sounding at Station 1 Taken on August 22,1968 12Station Elevation and Apparent ~esistivlty versus StationNumber 15

v

10 Correction Factors for Removal of the Elevation EffectFrom Apparent Resistivity Observations 19

11 Station Elevation and Resistivity of Upper Layer versusStation Number 21

LIST OF TABLES

Table1 Electrical Resistivity Sounding Data for Station 39

Taken June 1968 Using Schlumberger Spread ll2 Electrical Resistivity Sounding Data for Station 39

Taken 22 August 1968 Using Schlumberger Spread 133 Electrical Resistivity Profile Data for 208 Stations

Taken June 1968 Using Wenner Spread 144 Correction Factor for Removing Elevation Effect From

Apparent Resistivity Observations 185 Profile Data Corrected for Elevation Effect to Resistivity

of the Upper Layer and 3-Point Moving Average 20

vi

INTRODUCTION

For more than one hundred years the population on parts of the

rugged western coast of North and South Kohala on the island of Hawaii

has been limited by the availability of fresh water. Any unknown

fresh-water resources should be located and developed to permit additional

population and economic development of the area. Intensive efforts

have recently been made to improve conventional geophysical techniques

for locating fresh water resources in volcanic terrain such as on the

southwest flank of Kohala Mountain.

A new highway has recently been completed from Kawaihae to Mahu-

kona, allowing easy access to about 12 miles of coastline that could

previously only be reached by 4-wheel drive vehicles. It is probable

that the pleasant climate, clear ocean waters, and easy accessibility

will stimulate development of the areas adjacent to the new highway.

Consequently, the Department of Land and Natural Resources, Water and

Land Development Division has requested geophysical work on the new

highway. The highway lies approximately north-south. Its location with

respect to Kohala Mountain is shown in Figure 1. The Kohala Mountain

orographically affects trade winds, hence, the volcanic slope on which

the road lies is on the leeward side. This leeward position, together

with the particular geological structure of the Kohala Volcano, causes

the shore region to be very dry. Indeed, part of this region has the

lowest rainfall anywhere in Hawaii.

The geology and hydrology of the Kohala and the Kawaihae area have

recently been reviewed by Lao and Adams (1968) and Cox and others (1968).

Gross geophysical studies for the island of Hawaii have been published

for gravity by Kinoshita~ et aZ.~ (1963), and for total magnetic field

by Malahoff and Woollard (1966), however, these are not sufficiently

detailed to permit estimation of information relevant to potential wa~er

resource development.

The easy accessibility along the highway and its relatively even

elevation suggested that an electrical resistivity profile would be appro-

priate. Under these conditions, a relatively high apparent resistivity

anomaly would indicate a better site for drilling; that is, drilling at

the site of such an electrical resistivity high anomaly should have a

better chance for locating either fresher water or more water, or both.

2

6-39

FIGURE I. LOCATION OF MAHUKONA - KAWAIHAE ROAD ANDSTATION NUMBER 39.

3

Consequently, the exploration essentially determined average electrical

resistivity background and high apparent resistivity anomalies.

METHOD OF FIELD OPERATIONS

The procedure planned was to run 1 or 2 soundings . Interpretation

of these soundings would provide an estimate of an appropriate spacing

for a profiling spread. A continuous profile, using the appropriate

spacing, could then be run from Mahukona to Kawaihae.

The circuitry of the equipment, especially built for this work, is

given in Figure 2. An inverter powered by the battery of the vehicle

supplied 110 volts. All the equipment was mounted in the trunk of a

4-door sedan (Figure 3). The power source for the electrodes was dry

batteries and the data were recorded on a Heath chart recorder which oper-

ated on 110 volts.

The cable consisted of an 825-foot twisted pair with plastic sheath.

Takeouts were positioned at 275-foot intervals with instrument leads for

power and recording in the middle of the cable. The cable was dragged

from setup to setup. A view of the connectors at the middle of the cable

is shown in Figure 4. The heavy cables are the power source and the light

cables are the voltage sensors. The survey required two weeks, during

which time the cables stretched about 6 feet. As the actual locations

of the stations have been used in plotting the data on the profile, the

stretching is considered.

The field procedure is shown in Figure 5, with the operator connect-

ing the cables from the recording vehicle to the cable. Rubber gloves

were worn by all personnel to minimize the hazard of electrical shock

from the lethal voltages used.

A typical recording is given in Figure 6 for stations 109, 110, and

111 (Field numbering: corresponding analysis numbers are 203, 204, and

205). Time runs from bottom to top, at a rate of about 10 inches per

minute. The battery voltage being used at this time was 225 volts: the

full scale on the Heath recorder is 250 millivolts. The baseline is quite

straight, indicating only small telluric currents . Four readings are

taken from each station and averaged . The deflections are first to the

right, and then to the left. The number written in marker pen beside each

,p.

BATTERY BANKS WITH FOURPHOTOFLASH BATTERIES INEACH BANK WITH 45 VI 120 VIAND 225 V OUTPUT FROMEACH BATTERY.

-=- 24 V

DPDT SPRING SWITCHI • TO OFF TOGGLE

SWITCHeIIII 'L...----,.III

I ... 1

DPDTVACUUMRELAY

--C

......cL

L e+L

......cL

FIGURE 2. CIRCUITRY OF SPECIALLY CONSTRUCTED ELECTRICALRESISTIVITY EQUIPMENT.

FIGURE 3. POWER SUPPLY AND HEATH CHART RECORDER MOUNTEDIN TRUNK OF RENTAL AUTOMOBILE: OPERATORS AREF. CAMPBELL AND P. MILNER.

5

6

.(f)

~u

~ouu,oVI~1-/

~

UJ...Jco5u,o

ffi~UJU

!;{(f)I-::>

~~co

...:t

UJ

~t!).....u,

-;.....~~ ""

.... "'.; ~'"'(;~

""',. ", ,' ,

8

, :

l ,I,11,---W- -_:- L! _jI 'i ! . ; ~I , . ' i ! ' : !: .~-1-~- _ . ~-_ _ :-~-oI ; I !

I ,

!

,!

;i- I

; I, I i I ! ;. ; :--:- +---~~ L...;..J.-:-- -:-f-1._.!.

: : :. ; Ij i ~ 1 i ; I! I I 1 I I i

-

...orlrl

...CTlorl

I, I !I ! I

r;; III I II ", ,

I I:-.I ~ I':. I

I.... I ~ i

~ ' I ~:~;II>. fr - . !!~ ~ .1

9

deflection is the current in milliamperes. The notable decay seen on

the left hand deflections of station 110 is typical of that due to polar-

ization; however, this is not acceptable as the cause because the decay

is not seen on the right hand deflections. Station 109 does not show

such decay to the left, nor does station Ill, hence, it is attributed

to instrumentation. Furthermore, induced polarization is not expected

in this terrain as the particle size is orders of magnitude too large.

The absence of power lines for other sources of electrical noise

along the Mahukona-Kawaihae Road simplified the instrumentation and did

not require extensive time for hum-bucking.

DATA FOR ELECTRICAL RESISTIVITY SOUNDINGS

A sounding was conducted at the location labeled S-39 in Figure 1.

The data are presented in Figure 7 and given in Table 1. The unexpected

low dip at the 20-foot spacing is attributed to rainfall infiltration.

A Kona storm precipated 7 inches in 6 hours at Kamuela shortly before

field experiments were conducted. The sounding was repeated in August

to see if the position of this low changed. The data are presented in

Figure 8 and given in Table 2. No significant change occurred. Based

on these sounding data, an "a" spacing of 275 feet was selected for the

Wenner-spread technique of profiling.

DATA FOR THE ELECTRICAL RESISTIVITY PROFILE

The profile data taken with the Wenner spread configuration at

209 stations are listed in Table 3 as apparent resistivity versus sta-

tion number and elevation. These data and station elevations are plotted

in Figure 9. Possible correlation between the apparent resistivity and

the elevation above sea level is immediately apparent.

A cross correlation of apparent resistivity and elevation was run

at the Statistical and Computing Center at the University of Hawaii

using the pre-programmed MULREG code. This gave a correlation of 0.41.

Because of this high correlation of the apparent resistivity with eleva-

tion, a method for partially correcting the apparent resistivity for the

effects of elevation was developed.

103

-~I

q 102-~a:

I10 100 101 102 103

I-'o

AB/2" FEET

FIGURE 7. DEEP SOUNDING AT STATION NO. I (FIELD NUMBERINGSYSTEM: NO. 39 ON THE ANALYSIS NUMBERING SYSTEM)TAKEN IN JUNE, 1968. SCHLUMBERGER SPREAD USED.

TABLE 1. ELECTRICAL RESISTIVITY SOUNDING DATA FOR STATION 39TAKEN JUNE 1968 USING SCHLUMBERGER SPREAD

11

(foN/2): (AB/2)SPACl~ (FT.)

1:5

1:6

1:7

1:8

1:10

2:10

2:12

2:14

2:16

2:20

4:20

4:25

4:30

4:40

4:50

4:60

4:70

4:80

4:80

4: 100

20: 100

20:120

20:140

20:160

20:200

40:200

40:250

40:300

40:400

40:500

IIV

19.0

100.0

29.0

80.6

23.5

53.0

63.3

12.7

17 . 5

12.3

24.7

2.7

12.0

52.0

20.0

2.3

15.0

2.0

4.3

3.0

21.0

15.1

3.61.4

1.8

4.9

2.3

4.0

2.3

1.0

ma

3.1

22.4

9.4

31.713.5

15.5

29.0

8.7

19.022.8

24.1

4.9

38.6

236.7110.0

16.0

118.7

17.0

43.0

38.5

46.0

50.0

12.0

7.0

12.0

12.5

10.0

36.0

54.0

60.0

Ra(ohm-meter)

73

76

70

7581

78

75

65

54

51

48

39

33

42

5462

73

81

76

93

105

101

138

120

142

179

167

117

81

50

I- 50ZWa:~Q.4:

-~200W

~~I

~ 150Io-)0-I--~ 100I-WCDwa:

60 100 200SPREAD LENGTH (AB/2) IN FEET

FIGURE 8. DEEP SOUNDING AT STATION I (FIELD NUMBERING SYSTEM.:. NO. 39 ON THE ANALYSIS NUMBERING SYSTEM) TAKEN ON

AUGUST 22, 1968. SCHLUMBERGER SPREAD USED.

- - --

......N

TABLE 2. ELECTRICAL RESISTIVITY SOUNDING ·DATA FOR STATION 39TAKEN 22 AUGUST 1968 USING SCHLUMBERGER SPREAD :~

AB/2 FT. /of'l/2 FT. KO-m

ma mv V p

2 ~ 100 1 1. ~8 ~7.92~ 100

17 67 16 .75 63.617 62

19 62 .5 22 .9 7 75 . 519 62 .5

12 J3 JO . I~ 78 . JIJ J3

10 J~ 60 12 ~7 .37 83 .33~ 60

10 35 110 22 . 97 72 . ~36 110

12 28 68 J3 . ~9 80.730 72

I~ 50 85 ~5 .9~ 77 . 250 83

16 56 66 60 . 29 70. 757 63

20 69 58 9~ .7~ 79 .070 58

20 69 100 ~5.9~ 62.770 90

25 3\ 30 72 . 85 67.2J3 29

JO 23 IS 105.75 6~ . 726 I S

~O 170 7~ ~5 189 . ~9 80 .2170 70

50 125 39 297 .1 93 . J120 38

50 10 120 90 11~ .8 83 .0125 87

60 10 88 50 167 .5 ~ .288 ~9

70 10 87 ~I 229 . 7 108 .287 ~I

80 10 99 39 J 0 1. ~ 119 .6100 ~O

100 10 125 35 ~73.7 1J5 .0120 35

100 20 120 6 5 229 . 7 121.7125 65

120 20 200 85 J3~.9 1~2 . J200 85

I~O 20 200 63 ~59 . ~ 1~6 .5195 63

160 20 198 52 602 . 9 158.J198 52

200 20 190 3~ 9~ 7 . ~ 168 .3187 J3

200 ~o 310 120 90 ~59 .~ 1783\ 0 120

250 ~O 190 ~7 728 . 5 180190 ~7

300 ~O 230 30 1057 .5 135.8230 29

~OO ~o 3~0 IS 189~.9 8J .6J~D IS

500 ~O 187 J .2 2971.0 50187 3. 1

600 ~o ~1 5 3. ~ ~287 . 0 3~ .1~OO J .2

"AT CENTER POINT OF STATIO'< J9 IS A MJI>U1ENT PAINTED RED. fo£TAL STAKES

WERE USED AS ELECTRODES.

13

14

TABLE 3. ELECTR ICAL RESISTIVITY PROFILE DATA FOR 208 STATIONSTAKEN JUNE 1968 USING WENNER SPREAD

"'. Alll nnE. R.ESISTIVITY 'll. ALTITWE RESISTIVITY 'll . AL11TLCf: RESi STIV ITYI~ FRY IN oh_·_ten IN FEET IN ohlt· .. ters IN F!H IN oh. -..t erlI I I ". ~ I,)O ltt f). lJOu 11 2 4 0 . ) 1)0 2 1t . d OO "1 Ill. 000 ~J1. ':100, 1 1 3 . UO\) JII ... 000 " ] 1 t. 0 0 0 17b . OOO h ' 1 74 . !lOC l 'i lh QOQ, l Cq . J uO h l . ODD IJ 1 1 A . OOO 231. 0 0 0 h) 1 r r . 0 1')0 1)2. 0 00, Il l oll l) (\ lH.OOO " N1. s ao 16 8.00 0 10 . 20 1 .000 )98. 000 ". 16 2. ~OO 1 0 ... . 0 00

" 1't 6 .'hJO Ib2 . 00 0 10120 I .000 283.000 111 15 1.~OO 111.000

J. 14 r . 0 0 0 13" . 0 0 0 10 . 2 1 1.~OO 3J ~ .ooo ". 132.000 12 2.000,. 1 48. 000 1 22 . ADO 10 ' 226. 000 16".001) 11 ' I l lt . OOO 1 38 . 0 00' 0 h 8 . 0 0 l) IH . OOO 110 U9 . 000 280 . 000 180 I 11. SOD

9 0 . 0 0 0

. 1 14 ~ . O O O 10!>. OOO III 22 1. SOC 224. 000 18 ' I 18. ~ 00 122.000

" I S 1 . 0 0 0 lJO. 0 0 0li Z 1 2 1 . 000 2V . IlOO I8 Z 121 . 0 00 88. 000

" U O. VOO I b 7 . 00 011 ) 2 H .OO O 2 73 .0 00 I.) 12". 000 100; . 0 0 0., 151 . 0 0 u I ~4. 0 00 I I' 2 0 1.S 0 0 2 CH.000 ..' 114 . 0 0 0 I b 1.000., 14 r . 000 14 5 . 0 0 0 11 , 20 1. 1)0 0 2 50 . 00ll 18' 1 2 0 . 0 tl O 220 .000,. 14 1. 0 lJO 2 .. 0 . uOO 11 ' 1'014 . 000 2 :lt t . 0 0 0 ,.. 11 1. ')0 0 I bb .000

.7 IH . Ct or 16 0 . 0 0 0 111 18 ! .~ OO 1 "9 . 000 181 l a b. 000 2 21.000,. 1 ll . OOO 20d .000 'I. 111 . 000 18 0.1,)00 lO. l (,b. OOO 23b .000•• I 1 I . ')00 18 7. 0 0 0 II' 111 . 0 0 0 "31. 0 0 0 ,.. "l') .OOO 1 0 .~ O O' 0 l" b . OI,)O H Z. OOO 1' 0 ltd .OUO

201. 000 1.0 9 2 . sao Il J . OOO.. I S" . 000 1 6 7 . 000 I ZI U..!t.I,)O O l lU . n o o 191 91.000 50.000" I ')'J . "> OC I H. OOO " ' I b l . HOll

Ib'9.00 0 ,.z "14 . 0 0 0 5 .2 10" 16 l. ';0 0 21 1 . 0 00 I II 1 !t9 .'> OU

2 ~0 . 0 OIl I" 95.1l 00 4 ). 0 0 0.. Ibh . UUO Z41 . 0 0 0 I" I 51h ')00 l b ') . OOO I" 'U. OOO I tI. ~ OO.- I h "l . u OO 1 7 0. 0 0 0 1" 1 ~ It . 0 0 0 21J . (lOIl 1.' e s , 0 0 0 ] 8.4 0 0.. 1 71 . 0 0 l1 JO~ . OOC' I'. 1"' 1 . 000 1t>l. OO() 1" 70. 000 119 .000" I r r , "'0 0 311 . 000 III 14 Y. OU(·

2I Q.O OO ' 97 ll . OOO l 5.lt OO,. 1ft r , s o c 2eft . onn Il . 1"6. '>0 0 'Jb . 40 0 ,.. It7 , SOO 29 .200.. lYIt . ll o r, 2 1t1. 0 00 I l V 14/ . ') (\0 ) ) 0 . 000 19 ' " 7 . 0 0 0 6 .0 20.0 2( " .000 I ~U . o (l O 1'0 l .. ..,. ·)\ )O 2 31 . 0 0 0 200 .. . . 50 0 11. 0 0 0

'1 1l 1. !tOO 1'>1. u OO I II I ~1 . O llOHtt . OOO 201 s o . 00 0 7 . 2>0

.Z I1 l . ,>I) t,} 1 H . UOO III I '> L~ (lO l lh . l",Jl ' 202 , 1. ' 00 lZ .6 00., UtI . OOO 16 b. DOO IIJ a... ,. . !to

350

f-a300

W...,0n::11.

u,

250 0

f-0z

W wWu, 200

~

ZZ 0'Y0 ::>~

I150 ~

~~

W •-IW

100

50

(j)WZ...J

n::w~o11.

• RAW DATA

• ELEVATION

•• 44

4 •4 •

wzoN

Zoi=a::>n::~zoaz(5wm

IIISO17517016516 015515014514 0510152025303540O '----'-----'-----....L------'-----'-------'-------'-----'--------'---'-~~_=_---'-------'----..1.---_ _ --'-- --''-- ....1..- --'-- --''-- ....1..- _

STATION NUMBER

FIGURE 9:

•. ,.Ai

•• i••

••••• • • •••• •••

••• • •••• •• •••••••• ••

wzoNZof=o:Ja:I-

~o••• 0

• •• 0

•••••• ..Q•• •••• • ••• •• ••• •• • •••

190 195 200 205 45 50 55 60 65 70 75 80 85 90 95 100 105

LEVATION AND RAW DATASTATION NUMBER

110 115 120

wC)oa:m~

125 130 135

700

600

ItW~

500 W~I

~I

400~

>-~

300 >l=CJ)

CJ)

200 WIt

100

o

17

A PROCEDURE FOR REMOVING ELEVATION EFFECTS

FROM APPARENT RESISTIVITY OBSERVATIONS

Elevation effects on apparent resistivity profiling data are

severe (Grant and West, 1965). However, no successful effort for their

removal is reported in the literature. In applying resistivity to pro-

filing in the dryer regions of the island of Hawaii, it may be reasonably

assumed, at least at elevations of less than 300 feet,as on the Mahukona-

Kawaihae Road, that an interface exists at sea level. Furthermore, the

resistivity of the material below sea level is approximately zero. Based

on these two assumptions, an approximate procedure for removing elevation

effects from the resistivity profile can be developed.

The distribution of resistivity may be considered to be a two-

layered model, with the upper layer having a thickness equal to the

elevation and a resistivity equal to the resistivity observed at the

smallest spacing used in the sounding. The lower layer is a half-space

with zero apparent resistivity.

For the above assumptions, the corresponding two-layer curve for

the Wenner spread can be found in Figure 33 of Van Nostrand and Cook

(1966). The appropriate curve is that for a perfect conductor (k equals

-1) in the lower half of their figure.

Correction to Apparent Resistivity at a Standard Elevation

The apparent resistivity value observed at a given elevation may

be corrected to the apparent resistivity which would have been observed

if the same station were at an elevation of 275 feet. Enter Van Nostrand

and Cook's Figure 33 on the bottom scale at the value equal to the ratio

of 275 feet divided by the elevation in feet. At the intersection of

the perfect conductor curve, determine the corresponding value of the

normalized apparent resistivity . Call this p • The ratio of 0.68 (thee

normalized apparent resistivity for a spacing value of 275 feet) to Pe

is the desired correction factor, K275. These values are listed in

column three of Table 4 and are plotted in Figure 10 (bottom curve).

Multiplying the apparent resistivity observed at a given elevation by

the appropriate correction factor, K275, will give the apparent resis-

tivity which would have been observed if the elevation had been

18

275 feet.

TABLE 4. CORRECTION FACTOR FOR REMOVING ELEVATION EFFECTFROM APPARENT RESISTiVITY OBSERVATIONS

(11) (:a) K275 Kt rue0.3 0.98 0.69 1.020.4 0.96 0.71 1.040.5 0.92 0.74 1.090.6 0.89 0.76 1.12

0.7 0.84 0.81 1.190.8 0.80 0.85 1.25

0.9 0.73 0.93 1.371.0 0.68 1.00 1.47

1.2 0.56 1.21 1.781.4 0.47 1.44 2.12

1.6 0.37 1.84 2.70

1.8 0.29 2.34 3.45

2.0 0.23 2.96 4.35

Correction to Resistivity of Upper Layer

An alternate procedure for correcting for the elevation of the

spread is to correct to the true resistivity of the upper layer. This

can be done by the following procedure.

Enter the graph on the bottom scale at the value equal to the ratio

of 275 feet divided by the elevation in feet. At the intersection on

the perfect conductor curve, determine the corresponding value of the

normalized apparent resistivity. Call this p. The inverse of p ise ethe desired correction factor, Kt . These values are listed in columnruefour of Table 4 and are also plotted in Figure 10 (upper curve). Multi-

plying the apparent resistivity observed at a given elevation by the

appropriate correction factor, Kt ' will give the true resistivity ofruethe upper layer.

Profile Data Reduced for Elevation Effect

Using the procedure described in the foregoing section for the

reduction of the elevation effects, the field profiling data have been

corrected to the resistivity of the upper layer and are presented in

Table 5 and graphed with the elevation in Figure 11. Compare these to

19

4 .5

3.5

K 2.5

1.5

CORRECTION TOFIRST LAYERRESISTIVITYK T R U E

CORRECTIONTO SPREADRESISTIVITYK::Z7 15

2.01.0

0.5 '-- ~ ___J

oA/Z.

FIGURE 10. CORRECTION FACTORS FOR RE-MovAL OF THE ELEVATION EFFECTFROM APPARENT RESISTIVITY OB-SERVATIONS.

20

TABLE 5. PROFILE DATA CORRECTED FOR ELEVATION EFFECT TO RESISTIVI TYOF THE UPPER LAYER AND 3-POINT MOVING AVERAGE

RESISTI VITY3-POINT

RESISTIVITY 3-POINT .RESISTiVI TY 3- POINTI'IJ .

I N ohm-met ersKl'I II'(; AVEAAGE I'IJ . IN cha -eeeers Kl'III'(; AVERAGE I'IJ . IN ohm-me t e rs Kl'I I I'(; AVERAGEIN ohm·mete rs I N ohm-meters IN ohm-met ers

1 G.O •• 1$ • •• • • 66 44l . 0 43 3 8 2. M 3 13 1 tl t.Jl:I . 0 ') .0 ~ 1

6 l -W O. OO\J . ll .bhl 11 349. 9 n 32 6 . 01 2 13 6 't tHJ. 14 5 ~ 12 .0H1 b lJ l) . Q ~O b .,O . Oq 1 12 30 0 . 160 3 54 • .12 1 131 ~ 1 0. J4q 54 l .8 748 l~S . ! 7 J 411 . 4 05 1l 4 1l . 8 11 4 l 4 .4 0 t.J 1 38 56 4 .121 ~:d J .94 'J9 l O 1 . ~ 4 2 25 8 .4 , R 14 560 .25 B 4 25. 2 td 139 40 1 .360 4 Q t .. 71 '}

10 2 1 8 .1 6 l 41J . 3b B 15 302. 120 4 l3. S n 140 4 6't. H51 1t ,l.. net

11 IIC.OOO 4 32 .8R I 1 6 4 0 1.603 36 6 .1 32 141 I b 6 . t"l J 4 "i Rb . '1 H12 .i u D. ~O O .B 3 . ~00 11 .188. 0 13 38 6 .4H2 14l '> 2 ~ . '1'17 341 .1 ')113 ) ~ / C . O OJ 10 41 . 8 11 18 363 . 1 11 4 0 8. 4 37 14 3 J5 1. 3b O 55 9 . B Tl14 1 19 5 . 0 0 0 I l 9 8 .31] 19 413 .454 336 .015 144 19 l • .Ill 50 2 .U9IS 1 13 0. 0('11) I ll B ol 33 80 111 . 0 0 0 353 . 55 1 14 5 35 I . 0 0 0 8 1 8.30 1

16 I D O. OOO 980.0 44 ' 8 1 4 16 . l18 l ll .339 146 1.\ 0 5. 1h .I c» I . 15111 4 8 0. 132 7 It 2. 'lZb 8 2 22b . BOO 30 9. 84 8 141 4 1 b . 1 r,Q 11 2. 18 118 4 1 1. 4 4 1 4 91. 'tvq 83 28 6 .52 1 21 4 .335 14 8 59 4 .0 1l 444 . ~ b q19 ~ 16.64 9 l Qij . H 9 B4 309. 6B O 31 9 .344 149 12.3 . H2 5 'l .I .36 S20 lOI . 0 42 3 BI . 50 0 8 5 36 1 .B 25 348.0 5 I ISO ,·5l .1Q6 ,.,Oti.

I I I I71.00 76.00 81.00 86.00

STRTI~N NUMBEA(RNRLYSIS)66.0061. 0056.0051 .0046.0041. 0036 .00

'.

31 .0026.0021. 0016.0011.006.00

00

a00J

0aaco ,~-00

a

91.00 96 .00 101. 00 106.00 111. 00 116.00 121.00 126.00 131. 00 136. 00 141. 00 146.00 151. 00 156.00 161. 00 166.00 171. 0'

3SERVED APPARENT RESISTIVITY FOR ELEVATION EFFECT) VERSUS STATION NUMBER. ATHREE-POINT MOVING AVERAGE IS ALSO GIVEN,

166 .00 171. 00 176.00 181 .00 186. CO 191. 00 196 .00

23

the data presented in Table 3 and Figure 9. The correlation with the

elevation has again been computed by multiple regression and is now found

to be only 0.23.

The failure of the correction procedure to completely remove the

dependence of the observed apparent resistivity on the elevation is

attributed to failure of the assumptions to be exactly true, e.g., there

are actually many layers so that the two-layer model is only an appro-

ximation. Hence, the interface may be tens of feet below sea level.

Further, the layer below the interface is very conductive but not per-

fectly conductive.

A 3-point moving average of the reduced data is also shown in

Figure 11. The 3-point moving average has been used to eliminate any

erratic high due to one reading.

DISCUSSION

The purpose of this electrical work was to suggest

for drilling for water along the Mahukona-Kawaihae road.

of the fresh-brackish interface due to an increased head

optimum sites

A depression

would be

associated with an increase in apparent resistivity, thus, the objective

was to find resistivity highs. An alternate condition that would also

be desirable, would be a more highly permeable basalt. In this case,

there might not be an increase in the head, but the water might be

fresher at a given distance from the shoreline, also producing an anoma-

lous resistivity high. Both s ituations would result in the desirable

electrical anomaly being a high apparent resistivity.

From the data given in Figure 11, it appears that there are notable

apparent resistivity highs at two locations near the north end of the

road and at two, possibly three, locations near the end of the road.

The optimum locations for test wells appear to be at stations 14, 154,

and 187.

Note that the large anomaly at the south end, at station 187, is

strongly dependent upon the removal of the elevation effect. This

anomaly is considered to be real because the average is reached again

before the Honokoa Gulch Bridge. No elevation correcti~n has been made

for the data obtained south of the Honokoa Gulch Bridge (station 195)

because the non-linear correction factor exceeds a reasonably prudent

24

mUltiplicative factor.These locations are specified on the basis of relative resistivity

highs. Consequently, there is little possibility of estimating the

variation in head or salinity required to provide the anomaly. Additional

exploration such as electrical resistivity soundings, audiomagnetotelluric

soundings, or drill holes would be appropriate to obtain such estimates.

ACKNOWLEDGEMENTS

This study had been funded by the Division of Water and Land

Development of the Department of Land and Natural Resources of the State

of Hawaii. The success of this field effort was due primarily to the

hard-working members of the field crew : F. Campbell, P. Milner, D. Loomis,

L. Groves, E. Nakagawa, and R. Loomis. Access to the area was graciously

permitted by the J. M. Tanaka Construction Company. State engineers

S. Nambu and S. Kurnakahi were also very helpful in arranging for entry.

Computing facilities were provided by the University of Hawaii

Statistical and Computing Center and the programming was done by Edith

Fujikawa.

REFERENCES

Cox, D. C., F. Peterson, W. M. Adams, C. Lao and J. Campbell. Coastalevidences of ground water conditions in the vicinity of Anaehoomaluand Lalamilo, South Kohala, Hawaii. Technical Report 24, WaterResources Research Center, University of Hawaii. In preparation.

Grant, F. S. and G. F. West. 1965. Interpretation theory in appliedgeophysics. McGraw Hill Book Co. 583 p . See section 14-16.

Kinoshita, W. P., H. L. Krivoy, B. R. Maybe and R. R. MacDonald. 1963.Gravity survey of the Island of Hawaii. U. S. Geological SurveyProfessional Paper 475-C:1l4-ll6.

Lao, C. and W. M. Adams. 1968. Potential water development of the Kahuaarea, Kohala, Hawaii. Technical Report 19, Water Resources ResearchCenter, University of Hawaii . 16 p.

Ma1ahoff, A. and G. P. Woollard. 1966. "Magnetic measurements over theHawaiian ridge and the volcanological implications." BulletinVolcanologique. Tome XXIX, pp. 735-760.

Van Nostrand, R. G. and K. L. Cook. Interpretation of resistivity data.Geological Survey Professional Paper 499.

APPENDICES

Flowchart and Listing of Computer Program for Removing the ElevationEffect from Apparent Resistivity Observations and an IBM Printout.

by Edith M. Fujikawa

27

APPENDIX A

fLOW CHART

PURPOSE Of PROGRAM: TO CALCULATE THE AVERAGE AND 3-POINT RUNNING AVERAGEOf THE RESISTIVITY PROFILE

DIMENSION ALT (400), RAD (400), CORREC (400), RATIO (400),AMULT (400), AVCORR (400), RATE (400)

START Of DO LOOP

N =1, L TIMES RATIO (N) =ALT (N)/275.0

IRATIO # RATIO (N) * 10

IRATIO = IRATIO - 2

3 .- 3 =6 60

4 =4 = 7 7

= 5 = 850 8

= 9 9

28

CD -I AMULT(N) = 5.0 I -@ 7 BIGR = .80 10SMR = .70BIGM = 1.8SM = 2.2

0 ~( AMULT(N) = 5.0 f -@ (0 - BIGR = . 90 10SMR = .80BIGM = 1.6SM = 1.8

501----' BIGR = .60SMR = . 50BIGM = 3.1SM =4.4

J----'10 ®--1 AMULT(N) = 1.2 I--~@

60 BIGR.= .70SMR = .60BIGM = 2.2SM = 3.1

1----.f10

NOTE: THE FOLLOWING PORTION CALCULATES THE MULTIPLIER BY INTERPOLATING .

RATF(N) = (RATIO(N) - SMR) * (SM - BIGM)!CBIGR - SMR)

AMULT(N) = SM - RATF(N)

80J-----~ CORREC(N) = AMULT(N) * RAD(N)

AVCORR(N-1) = (CORREC(N) + CORREC(N-1) + CORREC(N-2)!3

END OF 00 LOOP

START OF 00

29

o

=0

=0

WRITE ALT~ RAD~ CORREC~ AVCORR

WRITE SKIPS A LINE

END OF 00

WRITE THE HEADING ON OUTPUTON TOP OF EACH PAGE

30

CORR PROGRAM - EXPLANATIONS

STATEMENT NUMBER

001

003

004

DIMENSION ALLOWS FOR 400 DATA SETS.

L =THE NUMBER OF DATA (CARDS) TO BE READ DURING THE RUN.

NOTE: (A) IN COUNTING THE NUMBER OF DATA CARDS DO NOT COUNT THE CAJTHE VALUE OF L IS PUNCHED ON. '1

(B) L IS IN REALITY THE NUMBER OF DATA TO BE USED.

(C) F(l)RMAT (13) :. CAN HAVE 999 DATA.

005{

ALT =ALTITUDERAD = RADIUS ONE ON EACH CARD

(A) F0RMAT 2F15.2

007 THIS WRITE PRINTS THE HEADINGS FOR THE OUTPUT.

010 CALCULATES THE RATIO.

011 THESE TWO STATEMENTS SET UP THE VALUE OF RATIO012 TO THE RANGE IT FALLS IN.

013 THIS "GO TO" STATEMENT SENDS THE PROGRAM TO DIFFERENTSTATEMENT NUMBERS DEPENDING ON THE VALUE OF lRATIO

IF:lRATIO = 1lRATIO =2lRATIO =3lRATIO =4lRATIO =5lRATIO =6lRATIO =7

GOES TO 3GOES TO 4GOES TO 50GOES TO 60GOES TO 7GOES TO 8GOES TO 9

AT EACH OF THE 7 STATEMENTS THE VALUES OF:BIGR (BIG RATIO),SMR (SMALL RATIO),BIGM (BIG MULTIPLIER),SM (SMALL MULTIPLIER),

ARE ASSIGNED

31

J46~ THIS PORTION OF THE PROGRAM CALCULATES THED50 MULTIPLIER BY INTERPOLATION.

)51- THIS DO LOOP ARRANGES TO HAVE A LINE SKIP)58 BETWEEN EVERY FIVE SETS OF DATA AND HAVE A

TITLE ACROSS THE TOP OF EACH PAGE.

NOTE: THE FUNCTION MOD IS OF THE FORM,MOD (aI' a2), AND IS DEFINED AS,al-(al/a2) .

DATA:

1) 1ST CARD:

COLUMNS 1""3

2) 2ND AND SUBSEQUENT CARD:

# OF CARDS TO BE READ IN

NOTE: DATA MUST END IN 3RD COLUMN

VALUES OF RADIUS AND ALTITUDESARE PUNCHED IN THE REST OF THE CARDS.

THE 1ST 15 COLUMNS ARE RESERVEDFOR ALTITUDE VALUES; COLUMNS16 .... 30 ARE RESERVED FOR RADIUS.

NOTE: THE VALUES OF EACH MAY BEPUNCHED ANYWHERE IN THERESPECTIVE COLUMNS.

NOTE: ONE SET OF DATA PER CARD WAS PUNCHED: THEREFORE, OTHERINFORMATION MAY BE ADDED FOR EACH STATION, IF DESIRED.

32

APPEPtI>IX 13: IBM PRINTOUT

0001

0002

000300040005000600070006

00090010

00110012001300140015001b001700111001900200021002200230,0240025002b0027002&0029OOJO003100320033003400350030003700360039

0040004100420043004'+

004~

0040OC470046004900500051005200530054

DIMENSIUN ALrI400I,RAOI4001,C URRECC400I,RAIIUI400I,hMULfI40 01 ,1 AVCURRI400l,RATfl4001

OATA RATIO/.4b,.43,195*C.I,AMULl/5.C,5.0,195.0.I,CORREC/0.,10b'J. b,l'J5.0.1REAOl5,111 L

71 FORMATI1 31REAOl5,101 IALTlII,RIIOIIl ,I =t,lI

70 FORMATl2Fl5.21WRI Tl::lo ,451

45 FORMA TllH I, T6, 'NUMBER' ,T 20,' All ITl/lJE' ,136,' I, 5t> I I ALT I"II, RAD INI, COKR t.c IN I ,AVC. URRI NI)

5b FUKMATIT 20,Fll.3,Tj5,FB.3,T51, f S.3,T 65,Fll.3112 FORr~AT I' 'I16 CONII NU E

STOPI:NO