LOAN COPY OrllfHAIAU- T-70-002 C2

SEAGRANT 70-2

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HAWAII INSTITUTE OF GEOPHYSICS

UNIVERSITY OF HAWAII

HIG-70-16

RECONNP1SSANCKl SAND 1ÃVFlVIOBY,: PF I>ZWARD OAIDJ

J ~ P ~ CBItlpbp ll p Wa Tr Coujbol1rny R ~ Moberly Jr ~ p

I3. R. Ro eM.ahl

June 1'!'IO

Pr eparer.i. un~'!er theNational Science F~oun<lation

SEA GRANT PROGRAM

Gran<; No. GH-PO!

Apprwe~! by Direct, or

Date' P4 June 1'!'I'0

6 IP> TRP.CT

'1'hi. -out,h<rrn ar«i we:",i.em coa.;t,n of Oahu have been nurveye6 for

:;1<<rilnv-vaf;< r iranri bo<lie:",, uaint~ a o"ei"mic reflect,ion technique.

l'inn<i b<~ti<.' di;:<.Uvered an<3 mappe<k in vat,<rr <1<.pth of b< tween 6<l and

1«.. 1, c<~nta.in ab<>u't, g' t! mii..l.ion cubic yaK.-, of nant. Gar«pie.", f r<»<r

a fi<w locat,iorr vere of fine-grain<.d < alcareou.", «arr<l t.trat, va..;::ir«ilar

t,o, but, fin«r 3,han, mo" t ltavaiian beech,,an<i:>. The T< r onnainnanc<;

;urvey poise f;o:-><.venal los alit.ie:; where detaile<l eampling anil mappir<LT,

aro var r at < t.ed.

TABLE OF CONT~~S

ABSTRACT ~ ~ ~ ~ ~ ~ ~ ii 1~ ~ ~ ~ ~ ~ ~

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 4 ~

~ 4 ~ ~ ~ ~ I ~ ~ ~

Locat i on

Method.s ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ f ~ ~ ~ ~

~ ~ 3~ ~ ~ ~ ~ t ~ ~

~ ~ 4~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Summary ~ ~ ~ l3

References Cited. l4~ ~ ~

TART& OF CONTENTS

ILLUSTRATIONS

Analysis

Results

~ ~ ~ ~ ~ ~ ~ 0 t ~ ~ ~ ~ ~

II>1>U.>7i < ATIOI!,

'>>R .

'B.

2I! ~

3B.

3C ~

~ ~ P

Map»>f Oats>, i awa t:i . show i nt» sect,»>rs ofrecor>na:issance s»rvevn

."->1>iI> t,racks t>et,ween Nakua andKcpuhi Point, l eewar<l Oahu

,>hi p t,racks and sampl» locat.iona hetw< enKcpuhi P»:i nt ar«X Maili Point;, leeward Oahu

Dt>ip t,racks an»i sami>le lL>< at,i<>ns hetween MailiPo:int. and E3arbr r Point, Leeward oat>u

Ht>ip tra» ks het.ween i<art>erv, Poi nt,and Keahi Point, leeward Oat>u

Ship t,racks between Keatti Point. andEtonolulu EIart>or, leeward] Oahu

Areas»>f sandy bott,om, and se ismicreflect,iot> traverses, sect, or R

Areas of sandy bot:tom, and se:ism:tireflect. ii>n traver 'es, sect«r Jt

>areas of sandy bottom, and seismic ref'lectiont.raverses s tor C.

3D. Areas of sandy bot;tom, and seismicret'lect, ion t,raverses, s>ector ]>

3F,. Areas of s>andy bottom, and seismicref! ect.ion traverses, sector F,

4. ">grker-type> seismi» reflect,ion system used

qA. Tracings of ei mic. reflection records,sector R. Travcrscs 1-3 sh»>wn on Fig. 3A

qB. Tracing oi' seismic reflection records,sector R, Traverses 4-9 shown on Fig. 3A

yC. Tracing~ of seismic reflect, i or> records,sect;or A. Traverse- 10-l4 shown in Fig.

'~D. Tracings of eismic rr fleet,ior> records,sector B. Travcrses 1-y shown on Fig. 38

~qH. Tracing" of s» ismic rr fleet,ion records,-ector B. Traverse 6-9 shown on Fig. 3B

yF. I'racin ;- «f seismic reflection rec»>rd.,ector B. Traverses 10-L hown <>n Fig. 3V

J'o l l.oVs!~Pa c

sr',USTamloNS C<~tinu< d!

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Tracirrgs of seismic ref I ection r«!or<is,e<!t,or 11. Trav< r;>.; 13-lIr:;I!carr <rn Fig. 38

Tracings <f seismic ref lecti on rec ords,se<!t,or C. Traverses 1-6 hewn on Fig. 3C

Tracings of .>ei mic ref l.ection records,..actor C. Travexsc" 7-lO shown on Fig. 3C

TracinGs oi' -< ismic reflect,ion r< c<!rds,se<.t<!r C. Trav" r..<..s 11-14 . Irovn on Fig. jC

Tracing. of sci mic reflection records,s< et or C. Traverses I g-16 shovn on Fig. 3C

yL. Tracings of se ismic x'cf lection records,sector D. Traverses I -j shovn on Fig. '<D

yM. Tracing- of sei. mic reflection record.s,sector U. Traverse>s 6-o shovn on Fig. 3D

'!N. Trac I ngs of s<!ismic reflection re< ord.sect,<rr D. Iraverscs I.o-13 shown on Fig. 3D

'>0. Tracings of seismi< reflection recoxdsect;<!x E. Traverses 1-4 shown on Fig. 3R

5P. Tracings of seismic reflection recoxd,sector K. Traverse. p "7, hown on Fig ~ 3E

,!Q. Tracing of eismic reflect ion records,sector E. Traverses 8" 10 shavn on Fig. 3E

jB. Tracings of s< ismic reflection recordsector E. Traverse= 11-1" shown on Fig. 3E

Table l. Texture of sediment, dr<>dgod near Pokai Bay, Oahu

Col.or vf sediment dredged near Pokai Bay, Oahu

Sand indicated on continuous reflection profiles,leeward Oahu, by coastal sector and by depthinterval. Correct;ed f or direct,ion of traverses

Fo i l ops !

~Pa e

Tjocat i on

The leeward coast, of Oahu from Makua to the entrance to Honolulu

llarbor has been surveyed. This section of coastli.ne, approximately 30

miles long, has been divided into five sector- for the purpose of this

rcport Fig. 1!. The..e sectors are. Makua to Kepuhi Point, Kcpuhi

Point, to Maili Point, Naili Point to Harbors Point, 3arbers Point to

Keahi Point and. Keahi Point to the main, or eastern, entrance to Honolulu

Harbor. Figures ..A-PE show the individual sectors with the location of

the ship tracks. The ship generally moved. In a zig-zag pattern, cro sing

in and out of shallow water. Altogether 6~/ crossings resulted. in useful

seismic profiles of the area inclo ed by the 60- and. 300-foot contours.

Methods

Prior to surveyi,ng the area, aerial photographs and available sampling

charts vere analyzed. to determine areas af sand. Submarine sand. bodies

are commonly visible on aerial photographs to depths of 20 or 30 feet.

Outlines of sandy areas were transferred to a common scale and plotted.

on a chart of the waters near t.he island, of Oahu. These bodies, generally

large sand-bottomed channels, arc located off some of the larger beaches

in the area and are believed to fill channels that were cut through the

reefs during late Pleistocene times when sea level wa lower than at

present Moberly, 1968!. Hand moving through these channels to deeper

water is completely lo" t t;o the beach system and is therefore of prime

interest for any offshore sand mining operat,ion. Hand channel' located

by thi method are indicated. on Figures 3A-3H.

The U. S. Coast and Geodetic Survey boat sheets shoving their

..ample locations around Oahu and. the type of bottom, e.g., sand., rock,

etc ~, were examined. and areas of sandy bottom were marked. off and.

transferred. to the same chart as the air photo results. The area

covered by sand. bottom was then measured. and. a minimum figure for the

island of Oahu obtained. This was 10 square yards. Xn the area7

covered by this report the area of sandy bottom amounted. to 1 ~ 7 x 106

square yards.

Next a reconnaissance survey using a sparker-type seismic reflection

system of the Haw'aii Institute of Geophysics Kroenke and, Woollard, 1966!

was made. Basically the syste~ consists of an EOkG sparker, an Alpine

wet-paper recorder, a 25-foot toved hydrophone array, tvo Hewlett-

packard differential amplifiers, and. two Khronhite filters. Figure 4

shows a schematic arrangement of the equipment . For this survey the

sparker was operated. at half-pow'er, 500 joules, with a repetition rate

of 0.5 second.. A windov betveen 200 and. 500 Hz was set with the filters.

The length of the outgoing pulse was about 20 msec. Working in water

depths shallow'er than 60 feet vas therefore a problem~ because the

reflection of the bottom vas masked. by the outgoing pulse and. so could.

not be seen on the record.. This difficulty with the outgoing pulse-

length also limited our ability to interpret the minimum thickness of'

sand shovn on the profiles. Xf the sub-bottom reflector is parallel to

the bottom, a thickness of greater than 60 feet is needed. to delineate

clear1y the sub-bottom surface. However, vhere the sub-bottom surface

is at sane angle to the bottom, the bottom and. sub-bottom reflections

can be traced with sufficient confidence that sediment as thin as 5 feet

can be mapped.

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THOUSANDS OF VAR DS

A

2A. Ship track- between Nakua and Keyuhi Point, leeward C>ahu.

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THOUSANDS OF YARDS

2B. Ship tracks and sample location= between Keg@hi Point and. Maili

Point, leeward Oahu.

:'C ..'~!ihip t,ra<.k" arr~l -ariq>lc. Ivr at,i »i bet.w~.< rr >taiEi Puitrt, arr ~ t!arE>~.r .

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THOUSANDS OF YARDS

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gA. Areas of sary bottom, anG seismic reflection traverses, sector A.

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THOUSANDS OF YARDS

8

3B. Areas of .".andy battatn, and "ei -mic ref'j ection traver" es, sector B.

0 I 2 5 4 5

THOUSANDS OF YA RDS

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3 ',. Area:, of' @andy»vt;tora, anil ~r.i.;mi.i. ro! .~ < i f,:i i in t,"avi r'.'o:.,

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During th~ survey of 10 to 1'3 November 1~$6'3, the,".parker electrode

and the hydrophone array vore toved. Off the stern af the H/V TEiITU.

Thc hip cruised at a speed of about 4 knots to minimize noise and.

maximize the horizontal scale on the records. At each turning point

the ship's position vas determined. by the ship's personnel using the

ship's radar. The scientific party also obtained fixes at each turning

pcint as well as at intermediate points where necessary, by horizontal

sext,ant angles.

Tracings vere made of the bottom and sub-bottom reflection" of all

parts af the records showing seismic penetration of sediment Figs.

58!. Our interpretation of sediment thickness and location was trans-

ferred back to the track plots and correlated. fram track to track, using

a additional control the bathymetry and data obtained from the aerial

photo and sample location studies. The areal extent of the sediment

bodies is shown on Figures 3A-3E.

To det,ermine cross-sectional area of sand. along the tracks, the

penetrat,ion time vas measured. along a set grid. pattern across the

profiles and. an average penetrat,ion time used to calculate the thickness.

To convert penetratian time to sediment thickness~ a velocity of 5,400

feet/sec was used. for the sand. This velocity vas determined. fram

seismic refraction lines shat in Kaneohe Bay where the grain size of

the sand. is similar to that sampled. fram some of these sand bod.ies

Moberly and Campbell, 1969!. Horizontal distances vere determined by

calculating the ship'- speed from the track plots. A speed had to be

determined for each crossing because the effect of currents and. winds

on the ship's movements varied. with different headings and. geographic

location . The time elapsed in crossing each of the sand. bodies was

picked off the tracing and. multiplied by the ship's speed, to get

horizontal distance.

Cross-sectional areas in square yard" per track were calculated for

all crossings. The calculations were made separately for different

depths of water: 60-120, 1.0-180, and. 180-300 feet ~ The three separate

compilations wore made so that intere ted parties, knowing the depth

capabilities of their own recovery equipment, can better calculate what

they may be able t,o exploit. Calculations were al o made of the average

number of square yards per yard. of coastline, by rotating the lines of

sections into a plane perpendicular to the trend of the coastline or

the sand. body.

Sand was dredged from six of the seven sites ~here sampling was

attempted Fig. 2B and. 2C! ~ The sampl.es were analyzed for grain-size

and color Tables 1 and. 2!.

Results

Table 3 summarizes the cross-sectional areas of sand. found on each

profile, corrected for direction of the traverses by rotation of the

profiles. The sand in the 60- to 120-foot depth range is concentrated

primarily in areas off the sand. channels that were mapped fram the air

photos. fn the 220- to 180-foot depth range, sand. was found on 52 of

the 69 crossings, indicating that sand. bodies are fairly widespread at

that depth. The profiles that do not show sand. are off areas where

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Table 1. Texture of sediment dredged near Pokai Hay, Oahu

Median Grain Size SortingSample Ho.

Phi mm Wentworth Class Phi Deviation FrleQman Class

2-35

2. 00

1.37

l. 02

Mod.erately sorted

Poor ly s ort ed

1.25

i.480.20 Fine sand.

0.3 0.8 Coarse sand

-1.4 2.6 Granules

2.5 0.18 Fine sand

.3 0.2. Fine sand.

Coral gravel!

2.05 0.24 Fine sand.

Very poorIy sorted.

Poorly sorted.

Moderately sorted.

Mod.crate+ s aWed.

Table ". Color of sediment dredged near Fokai Bay, Oahu

Color and Munsell Code!

Sample No. After Exposure to Sun, in DaysAs Dredged

Ye11owish gray Yellowish gray Grayish yellow Very pale orange

5Y 7/2 ! 5Y 8/2 ! �OYR 8/4 ! 1OYR 8/2 !

Yel1owf,sh gray Yellowish gray Yellowish gray Very pale orange

�Y 7/2! �Y 8/2! �Y 7/2! �OYR 8/2!

Lt. grayMed.. dk. gray Med.. lt. gray Lt. gray

N6! N4! N7!

Very lt. grayLt. grayLt. gray

N8! N7!

Coral gravel !

Med.. lt . grayLt. olive gray Dk. yellowish Med.. graybrown

�Y 5/2! �0YR 4/2! N5! N6!

Olive gray

�Y 4/1!

Olive gray

�Y 4/1!

Lt. olive gray Lt. olive gray Lt ~ gray

�Y 6/1! �Y 6/1! N7!

Area on Hccord. sq. yds. corrected!Hect or Traverse

60-120 ft. 120-180 it. 180-300 i' t. Total

2470269 2201

41921947756

50941646311 3137

2378 ? 962584

2609

42473265

1857

982

2268

53671544 3823

3180 573 o2550

2623241"10

934259653224

�862444 5242

Table 3. Sand indicat;ed. on continuums

ref1ection prafiles, leevard Oahu, by coastal sector

and by depth interva1. Corrected i'or direction of traversed

Table 3 ccntinued!

Sector Traverse

60-120 ft. 120-180 ft. 180-300 ft. Total

71943664 3530

276114

1694 3203

46� sq. yds.

i.e., sector A averages 4654 yd per yd. of coast. !3

Le~h of sector A: 8400 yds.

Volume, sect, or A; 39,100,000 cu. yds.

198945881160 �37

47643531j �3

74145379

9181�84

37505Q1

609l452l1 5 � Q

3 88160. 053133

3!I.P5161!179o

18l184 0' 922 5

394310

Mean, profiles w/sand: 372

Mean, all profiles:

Area, on Record sq. yds. corrected!

2035

r!Q97

Table 3 '.ontinued!

Sector Traverse

60-120 ft. 120-180 ft. 180-300 ft. Total

1760 183070

145362 500 5925

5514g714 1 522813

393 o

, 804 3810

7408 sq. yd.s.Mean, all profiles'.

Length,h of sector D: 10,300 yd.s.

Volume, sector 3: 76,300,000 cu. yd.s.

40004000

3 563556 3 007

1480768755B442088

lg85 3954330

2222

147314 �

2389 1733

81103274'=' 7 82108

!�7'3!�72

Mean, profiles w/sand; 3542

Area on Record. sq. yds. corrected.!

-1 0-

Tat>le 3 Continued!

Hector Traverse

60-120 ft. mo-180 ft. 180-300 f t. Total

1y18 87872061

2148 49212773

4316 1908 7055

248413

1642 81635282

100471704

6627662I

3179

61" sq. yds.Mean, all profiles:

Length of' sector 0: 14,'='00 yds.

Volume, sector C: 86,900,000 cu. yds.

44164416

41564152

2787 2787

13031303

28872887

Iy52

Mean, profiles ~/sand.: 146!

Ax'ea on Record sq. yd.s. corrected.!

Table 3 Continued!

Area on Record. sq ~ yds. corrected!Sector Traverse

60-1'.0 ft. 120-180 ft. 180-300 ft. Total

3225 3225

3984820

410 1763594317794

1578 37o710 2 jl29

5422735 1379

1426 47351084

q45

3030

4473 sg, yds.Mean, all profiles:

Length of sector D: 17,$00 yd.s.

Volume, sector D: 80,lN!,000 cu. yd.s.

920

4784392

�8 94 7005

45802526c9 1458

765845991081

14414814362o

Mean, profiles w /sand: 934

4392

3243

Table 3 Continued.!

Area on Hecord sq. yells. corrected!

Sector Traverse

60-l"0 ft. L?0"180 n . 180-300 ft. Total

61 �3873 i'303

414~ 14'3'�

105!c'I,l0!

4g8,. 109011!9910

"39!

30;6

68 8 q. yes.Mean, s.ll profiles:

J.cinch ot "actor L' 13,300 y<Is.

Volume, sector Z: I�,800,000 cu. yd.

Total Voluble "ectors A-H: !'�, '00,000 cu. yds.

Mean, prof iles w'/sand: lip 1

3? 33

43'0

31i4

-13-

ridges on land approach the shore or where promentories break the shore-

line into littoral cells, for example off Kepuhi, Naili, and. Barbers

Points. The sand. In the 180- to 300-foot, depth range appears on all

but two of the profiles. One of these does not cross this depth zone

and. the other is at the very northern end of the surveyed area, where

Brock and. Chamberlain �.'368! observed only patchy sand in depths down

to and below the depths of present Interest.

Th<. sector betw'een Makua and. Kepuhi Point. contains about ~4o million

cubic yards of sand, the lowest sand. volume of the 5 coastal egment

About 2/3 of the sand Is found between the 180" an� 300-foot depths,and. very little is shallower than l20 feet,. This sector of coast would

probably receive a low priority for future offshore exploratory and.

exploitative work. Between Kepuhi and Maili points the survey indicated

about 7'j million cubic yards of sand.. That, coastal .egment is a prime

candidate for additional detailed. work, because major bodies of sand

were found. at depths sha13.ower than 60 feet ~ From Maili Point to Barbers

Point. there is about, 85 million cubic yard.s of sand., nearly half of which

is in the 1"-.0- to 180-foot, depth range. The .Last, two sectors, Barbers

Point to Keahi Point, and Keahi Point to Honolulu Harbor entrance, have

about 80 miU.Ion and 90 million cubic yards of sand., respectively, ancL

in each sector the sand is about evening split between the 1"0- to 180-

and. the 180- to 300-foot depth intervals; only modest amount" of sand

are in shallower depths than 1'0 feet.

The sand resource off the leeward coast of Oahu are on the order

-14-

oi 3.7 x 10 cubic yards. Their great volume irnlicates the need of8

detailed inventories vf- t,his resource.

References Cited

53rock, V. Z., and C5~ber.lain, T., 1'�8, A geologicaj anti ecologicalreconnaissance off western Oahu, Hawaii, principally by means ofthe research submarine Asherah: Pacific Hcience, v. 2'-', p. '3'�-384.

Kroenke, L. W., and Woollari5., G. P., 19K>G, eismic reflection investi-gations in the vicinity of the 55awaiian Ridge' .Hawaii Inst.

66

Moberly, B., Jr., 1'�8, Loss of 5 awaiian l.itt oral sand: Jour. Sedinmn-1.

Moberly, R., Jr., and Campbell, J. 5 ., 196'3, Hawaiian hall ow marinesan<2 inventory, Part 2, Ahu o Laka ~and. Deposit Ksneohe J3ay,Oahu' -Hawaii Inst. Geophys. Be ort 6'5-j 0, .'5ea Grant 69-1, '4 pp.