Monitoring cruise at the Cornfield Shoals Disposal Site, August 1992

ARMY ,UE DAMOS

Monitoring Cruise at the
- Cornfield Shoals Disposal Site
August 1992

Disposal Area
Monitoring System
DAMOS

D A|M O §S

‘DISPOSAL AREA MONITORING SYSTEM

Contribution 106
January 1996

US Army Corps
of Engineers
___ New England Division

Te

REPORT DOCUMENTATION PAGE
OMB No. 0704-0188

Public reporting concern for the collection of information Is estimated to average 1 hour per response including the time for reviewing Instructions, searching existing
data sources, gathering and measuring the data needed and correcting and reviewing the collection of information. Send comments regarding this burden estimate or
any other aspect of this collection of Information Including suggestions for reducing this burden to Washington Headquarters Services, Directorate for information
Observations and Records, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302 and to the Office of Management and Support, Paperwork Reduction
Project (0704-0188), Washington, D.C. 20503.

1. AGENCY USE ONLY (LEAVE BLANK) 2. REPORT DATE 8. REPORT TYPE AND DATES COVERED
January 1996 Final report

4. TITLE AND SUBTITLE 6. FUNDING NUMBERS
Monitoring Cruise at the Comfield Shoals Disposal Site, August 1992

6. AUTHOR(S)
M. Baker Wiley

8. PERFORMING ORGANIZATION REPORT
NUMBER

SAIC- C112

}7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
Science Applications International Corporation
221 Thrid Street

Newport, RI 02840

0. SPONSORING/ MONITORING AGENCY
REPORT NUMBER

DAMOS Contribution
Number 106

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)
US Army Corps of Engineers-New England Division
424 Trapelo Road

Waltham, MA 02254-9149

11. SUPPLEMENTARY NOTES
Available from DAMOS Program Manager, Regulatory Division
USACE-NED, 424 Trapelo Road, Waltham, MA 02254-9149

12a. DISTRIBUTION/AVAILABILITY STATEMENT
Approved for public release; distribution unlimited

2b. DISTRIBUTION CODE

13. ABSTRACT

After fine-grained dredged material was released at the Cornfield Shoals Disposal Site (CSDS) between October 1991 and May
1992, there was evidence that ambient sand was being transported over the fine-grained dredged material deposit. The presence of
ambient sand over fine-grained dredged material in REMOTS sediment-profile photographs, current meter studies, and transmissometer
and backscatter data all supported active bedload transport in a study conducted at CSDS in 1991/1992. However, the areal extent of the
ine-grained dredged material under the sand and the thickness of the sand over the unknown.

The present study, conducted at the Cornfield Shoals Disposal Site in August 1992, attempted to delineate the extent of the fine
grained dredged material under the sand and to measure the sand thickness. Part of the May 1992 REMOTS survey was repeated in
August. All but two stations that were formerly fine-grained dredged material had been covered with sand by August. The new REMOTS
stations in August were concentrated south of the mapped fine-grained deposit . Dredged material was detected under sand at two
tations south of this area, extending the dredged material boundary to the south.

An acoustic sediment density study was conducted at CSDS to define the surface sediment density and locate the fine-grained
dredged material. It was also conducted to gather the subsurface sediment density information and map the thickness of the sand over
the mud. The surface density values, calculated every 50m along the survey track, did not delineate the fine-grained material that was at
REMOTS stations G8 and G9. Subsurface densities were measured at 15 cm_ intervals below the sediment water interface. These
subsurface densities did not detect any decrease in sediment density with depth, suggesting that the depth to the base of the mud was
ess than 15cm or that the acoustic survey was unable to detect the density changes.

The transformation from fine-grained dredged material at the center of the mound to sand over mud or sand at all but two
REMOTS stations (G8 and G9) continues to support the theory that sand is being transported over the fine-grained dredged material at
the Cornfield Shoals Disposal Site. This is not unexpected in that the site is dispersive and material is normally transported across and
Itimately out of the area.

The acoustic sediment density study was not successful in locating the fine-grained dredged material either at the center of the
isposal mound or under the sand on the flanks of the deposit. The lack of success with the 24 kHz acoustic survey may have been due
n part to the resolution of the system, but attention to and adjustment to varying system parameters in future surveys may result in more
Successful distinction between subbottom layers.

4. SUBJECT TERMS
Hacoustic sediment density studies REMOTS CSDS DAMOS fine-grained dredged material

15. NUMBER OF PAGES
16. PRICE CODE

7. SECURITY CLASSIFICATION OF REPORT _‘/18. SECURITY CLASSIFICATION OF THIS 9. SECURITY CLASSIFICATION OF 20. LIMITATION OF ABSTRACT
Unclassified PAGE ABSTRACT

¥ 5 ied : "i
i is i. J vA.
Do A n Ps , fe) ae
ae : : bal

on - :
7 Ae iy

“ie + yin
i oe ie ma -, J
Wie ad Ay rah Sy
ae eta iin

ss
a 2 : -

7“ mh ach if

sag
Wi

on

me |

et p40 a ad At e Anta oe? ‘7 af “ rn Recs ee
. ie oy TA, ey ag 2 ie: ‘eax
q - | if as
i 4h ; : a

MONITORING CRUISE
AT THE CORNFIELD SHOALS
DISPOSAL SITE
AUGUST 1992

CONTRIBUTION #106

January 1996

Report No.
SAIC C112

Submitted to:

Regulatory Division
New England Division
U.S. Army Corps of Engineers
424 Trapelo Road
Waltham, MA 02254-9149

Prepared by:
M. Baker Wiley

Submitted by;
Science Applications International Corporation
Admiral's Gate
221 Third Street
Newport, RI 02840

(401) 847-4210

US Army Corps
of Engineers
New England Division

a au co Vee US is

as a: = — —"

Pres ma)

Bearts

hy apr Moe

AL 7.

0 ‘cama

‘oi toa Nag vee 7 it
Ci EAR, yt

Sent

“9) bec inderlit?

a)

iz

7, eae. f ‘
Filey & Fin ye nial : ’ : i : re te
moran] dani peat wail a "
edie ie utio? (A 20 . La

ih 7 a) : (4
bank clown T MM? . «i

5 )
5 URyO Se EEY AM. coresitn $i f - at n.
.

bid an bade

-

vr SUS ie

wee . “J | ius a

¢¢ beaiowure , a ae

q
wo : , ie y
/ 4 , i
o . =) . ‘> y 1 Sf piosy A arr Mt! A 4 o a
7, = hernc? Gcdieamual sat lela epee > ee
‘ : : vt
¢ ‘ "Ft vet DB Wi a y 7
1 ith) Sati a) ) :
j ‘ ‘ :
ake. F, yr f
Sorite, Tenth .¥ ern

»
iw 2 ' 7 ot
i Ihe 04 iM ; Rhy ee ’ A i
H i. igese A f via iy '
a os oe \ MC10 ne i 1
} - i

. ‘ bh is Gene ei, ue -
i ‘. ‘ — Se ee eee ie ieee :

TABLE OF CONTENTS

LELSIMORSEIG URE SM as Pika featene rere oh AIG Ges, oe x Jaane un huge sees Uae meee
OE © WAIVE TS WIMINEAR YY aay sees crete ee ee eh Be, ove ler eae eat 7s pe aes Sen
OPIN TROD WGCMION Mr eric e BR eo eis, ce esate ys eth va ee ees See eee eee Ropes Se
ZO ure VUES TE OD) Si2 fe reer Ree NN et 0 Als BE nes BOR PMnes, © 0 ee
Di ilie @ Bath yIMetiyy. eee oak chen ce Mies te em 'ey woe cies onthe ae klein eae cena Te NN eon ie.
De PRE NI OMS Sap, masenste cet eles fay es yar vase tet ck oem Ie Ae stb ay pero Nae a Rem ee
DBS Eers SCCUMEMEIDEMSIL VA co feccck cs keme: Fah Aes bac PRN OA SE RM NR cuck tect apeepae 9 IM fat ci vale
EO emma S WGI Soa rcrea es ys d ti een Mee eR ei hve! eens Sree RO ene Lat ame ana
Smt ot eBathymetivien anaes shed, ick cee hohe deraaeeeh ARO AD sae UMN SoU ce katie boot
Be2 tay SREMO US Sag Sie TWO ee cca aichaop guy etucbnate sphcon sc e aeemareyen ewes
Bo ee SeGimentyDensityaur Wee es cea) once ann i nt ae
AAO EDISCUSSI Gite, Sera wan te eS PRE ie 242 24 w Riascanece Ghee aul eouohs ouereon areca earls
SHOR CON CIEW STON RO aes INEM NT RN HR OS Aa ah EES SPN os see scene
Gr O Re R BRE NG EG yay Aye ae Gitte eek ca eines Se cats ous eee Lek a ee
INDEX

23

4

ae

G eek ams

eee

pera

ee

LIST OF FIGURES

Figure 1-1.

Figure 1-2.

Figure 2-1.

Figure 2-2.

Figure 3-1.

Figure 3-2.

Figure 3-3.

- Figure 3-4.

Figure 3-5.

Figure 3-6.

Figure 3-7.

Figure 3-8.

Figure 3-9.

Figure 3-10.

Page
Location of Cornfield Shoals Disposal Site .................... 2
Location of disposal buoy and current meters at the Cornfield
Shoals Disposal Sites 1991-1992 vn cess fe ae es eee le ga ee 3
REMOTSS station locations at the Cornfield Shoals Disposal Site,
VE y SO DE renner eon TNs, us unc aes Siac iat ol ER Sed OS a gn eee eu, Se 6
REMOTS® station locations at the Cornfield Shoals Disposal Site,
AUG USE MOO 2 red tatenee ce ete, MeN ainsi ooh eee eM ons Tee ee ee Ee 8
Bathymetric contour plot at the Cornfield Shoals Disposal Site,
Mayall S2i(Gepthsinsmeters)in cs 2 ue as ee ee 10
Bathymetric contour plot at the Cornfield Shoals Disposal Site,
Aupustol9927(depthtinemeters) 2. | a een eee eee 11
Negative depth difference contour plot between May 1992 and
August 1992) (contours iat 0:2 Mm)". 2) eee 12
Positive depth difference contour plot between May 1992 and
AMI SUSt 992i (Contoursyae Oe2yand!Or4 smi) eee ee 13
Map of sediment type at the Cornfield Shoals Disposal Site,
AU SUSE LOO 2 BR ey OE so athe ee eNom ee tee ey 2 14
Station E3 showing sand/mud in May 1992 (A) and sand in
PAUIOUISESDOOON (BO Re SR Pe WR Oe a) Noe ee ee cto Cel ae ee 15
Station F9 in May 1992 (A) and August 1992 (B), showing change
from ambient sandy sediment to sand over mud ................ 16

Sand and dredged material distribution at the Cornfield Shoals Disposal Site,

May andwAupustil O92 sie Sith) Os Tei Re Oe BORD RG ccc hace 17
Smooth sheet of surface sediment density (g-cc") at the Cornfield
ShoalsyDisposalySite; Augusel992 2) si eng) eee nena 19
Contour plot of surface sediment density (g-cc") at the Cornfield
Shoals#Disposal§Sites-August 9992 arenas ene eee 20

ul

LIST OF FIGURES (cont.)

Page

Figure 3-11. Surface sediment density values >1.6 gcc! .................. 21
Figure 3-12. Sediment density (g-cc’') at the Cornfield Shoals Disposal Site,

22

approximately 15 cm below the sediment surface ...............

EXECUTIVE SUMMARY

After fine-grained dredged material was released at the Cornfield Shoals Disposal Site
(CSDS) between October 1991 and May 1992, there was evidence that ambient sand was being
transported over the fine-grained dredged material deposit. The presence of ambient sand over
fine-grained dredged material in REMOTS® sediment-profile photographs, current meter studies,
and transmissometer and backscatter data all supported active bedload transport in a study
conducted at CSDS in 1991/1992. However, the areal extent of the fine-grained dredged material
under the sand and the thickness of the sand cover were unknown.

The present study, conducted at the Cornfield Shoals Disposal Site in August 1992,
attempted to delineate the extent of the fine-grained dredged material under the sand and to
measure the sand thickness. Part of the May 1992 REMOTS® survey was repeated in August.
All but two stations that were formerly fine-grained dredged material had been covered with sand
by August. The new REMOTS® stations in August were concentrated south of the mapped fine-
grained deposit. Dredged material was detected under sand at two stations south of this area,
extending the dredged material boundary to the south.

An acoustic sediment density study was conducted at CSDS to define the surface sediment
density and locate the fine-grained dredged material. It was also conducted to gather subsurface
sediment density information and map the thickness of the sand over the mud. The surface
density values, calculated every 50 m along the survey track, did not delineate the fine-grained
material that was at REMOTS® stations G8 and G9. Subsurface densities were measured at 15
cm intervals below the sediment water interface. These subsurface densities did not detect any
decrease in sediment density with depth, suggesting that the depth to the base of the mud was less
than 15 cm or that the acoustic survey was unable to detect the density changes.

The transformation from fine-grained dredged material at the center of the mound to sand
over mud or sand at all but two REMOTS® stations (G8 and G9) continues to support the theory
that sand is being transported over the fine-grained dredged material at the Cornfield Shoals
Disposal Site. This is not unexpected in that the site is a dispersive site and material is normally
transported across and ultimately out of the area.

The acoustic sediment density study was not successful in locating the fine-grained
dredged material either at the center of the disposal mound or under the sand on the flanks of the
deposit. The lack of success with the 24 kHz acoustic survey may have been due in part to the
resolution of the system, but attention to and adjustment to varying system parameters in future
surveys may result in more successful distinction between subbottom layers.

pts
ee

ry] =e wens I~ ai Frege ey Pren

- Teas baka ed ober siibestartl peed erta yea
dupiid, 1 Sm see yorum *ETOMSE ROE ein enh
bwtn tow banat. sod St eae Jawan heatiang qoait Vb
eal hegre) tb to (lane iar, ee ieeg A Be
| pag a ta Hunay 3 es a wel ahag scfiaaeh jibe 2

i
a ies

ya me i s TI we VRE vile FI ib om Ye ae ay ui gil ne Ge civ reverie

Fs
) 2
Lin

wilt ig

lyre atl aopics of LIT? is twa Hid Bann te ania

ied DO weycilt Te Laisa, Pawir Tia rierae Ory pear
waa he 435 7 bg > f ry ' alt apni wy dined dewihende pe a,

fag ueni) WA is 1 pa Daginh beain pet ee SO lg Wage bet
ie aL tie @ erated? 2g db OMG ed EO) oe pa int ea

Gigi Wiaeg | Vie a ' elty wa US.)%S pratt Ne ey ac) and

Mave om bis year

we} hi TLD io ) '‘ chee f er tN “Degperily tops

heme ait as bine " 1a eons 7 eatt-cpanis ON at unig

ina Palit & dj warn. Cr tame DEY. acredlety: FP TO bi
eel Laks a Sh en a, aden Gat f: ae wat sie B10 nemiben an
Mg weed 206 ae Binet ade 207 goign git Ppt y Aiw. cleanly sesanfeagal

aah s view nat 3790 ot Spiele seu Yaris Tanti eRe

nr phi ne easing a a

gone G&S unokoal wf tifeehoque: ieee ehatd. Veli outa alah
T - ite wa Oe avn Lagour { jAj ” 2x00 wt) i ile ii 1 nit i
‘le
a} vers) cash rove enlods SAS AD eas west da WHE aya

seek Pe }
Moos Tpit ae ae le mm Ga ‘amen (nbn

—

NN

1.0 INTRODUCTION

The Cornfield Shoals Disposal Site (CSDS) is located 3.3 nmi south of Cornfield
Point in Old Saybrook, Connecticut (Figure 1-1). It is the only dredged material disposal
site managed as a dispersive site by the US Army Corps of Engineers, New England
Division (NED), as part of the Disposal Area Monitoring System (DAMOS) Program. At a
dispersive disposal site, unlike a containment site, it is expected that dredged material
disposed at the site will be transported out of the area.

The Cornfield Shoals Disposal Site has been under study by the NED as part of the
DAMOS Program since 1978. From 1978 to 1991, the site received low volumes of mostly
hydraulically dredged sands (29,000 m3 annually) although some mechanically dredged fine-
grained material (5,500 yds? from North Cove) was released at the site in January 1988.
The material was released at LORAN-C coordinates, usually at the center of the disposal
site. Bathymetric surveys conducted before 1991 did not detect any well-defined dredged
material disposal mounds (SAIC 1988, Germano et al. 1994).

As part of a joint study Letween the University of Connecticut and the ivewnort, RI,
office of Science Applications International Corporation (SAIC), a taut-wire moore:! buoy
was deployed at two locations within CSDS in 1991. Between 12 September and 9 (ctober
1991, 50,803 m* of sandy dredged material was released at buoy location A2 (Figure 1-2).
Between November 13, 1991 and April 14, 1992, 105,479 m’ of fine-grained dredged
material from North Cove was released at buoy location B. Coincident with these aisposal
operations, a near-bottom current meter was deployed at BTM-A (near A2) on August 8,
prior to disposal, and moved to BTM-B (near B) on October 21. A midwater current meter
(MWM) was deployed southwest of BTM-A on August 1 (Figure 1-2). A series of studies at
CSDS from July 1991 (predisposal) to May 1992 (postdisposal) documented the accumulation
of dredged material at these buoy locations and provided circumstantial evidence for active
bed transport in the area (Wiley 1994). The current meter data showed the east-west tidal
component as the dominant current direction. Maximum velocities for the midwater meter
were 120 cm:s” on the spring tide and 60 cm-s' on the neap. For the nearbottom meter,
maximum velocities were 80 cm-s" on the spring and 40 cm:s" on the neap. All of these
current velocities are sufficient to erode medium to fine sands (Bohlen et al. 1992)

The accumulation of dredged material at CSDS from 1991 to 1992 was detected both
with bathymetry and with REMOTS® sediment-profile photography. The bathymetric
surveys from August 1991 to May 1992 documented the formation of the disposal mounds
and illustrated the shifts in sediment accumulation patterns over time. These shifts in
accumulation patterns may have been due to the addition of dredged material to the site
and/or to the natural sediment transport patterns within the area.

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

Cornfield Shoals Disposal Site, Connecticut

Nott {sland

OLD SAYBROOK

Long Island Sound

Cornfield Shoals
Disposal Site

Figure 1-1. Location of Cornfield Shoals Disposal Site

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

~

7661-1661
‘QS [esodsiq, s[eoys pjaljusoD oy) ye sio}oU JUALIN pue Aonq jesodsip Jo uoNes0T = °7-T sans

Co00r/5 :eLes5 .
evel MO'OE te e240 MOS te cZ0 MO°0O ce 240

NO'Sb ect bb NO'’GSb cl bev

dp)
=
Pe)
<
Mm
<
@
O
S
Zz
O
>
po)
<

NOOO EF tr

MO°OO te 240 MOST te 240 MO°OE te e240 MO'Sb te e240 MO°0O ce 240

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

Because the ambient sediment at CSDS is sand, the fine-grained dredged material that
formed the disposal mound at buoy location B was seen very clearly in the May 1992
REMOTS® photographs. On the flanks of the fine-grained disposal mound, the REMOTS®
photographs showed a thin layer of sand (<10 cm) covering the mud. At further distances
from the center of the mound, ripples on the surface of the sand appeared in the REMOTS®
photographs. The apparent movement of sand over the mud contributed to the evidence for
active bed transport at CSDS. Additional evidence for active bed transport included optical
backscatter and transmissometer data.

The present investigation, conducted 5-10 August 1992, was designed to assess any
further sediment transport, particularly the movement of sand over mud. It was expected
that the two disposal mounds detected by earlier surveys would have remained stable and that
the extent and thickness of the sand veneer over the fine-grained dredged material would be
detectable using subbottom profiling.

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

2.0 METHODS

The August 1992 CSDS survey team used bathymetry, REMOTS® sediment-profile
photography, and a 24 kHz acoustic survey to determine the stability of the disposal mounds
and investigate any further sediment transport at the disposal site. The bathymetric and
REMOTS® sediment-profile surveys have been used in numerous studies to monitor benthic
conditions (Parker and Revelas 1989, Germano et al. 1994). The 24 kHz acoustic survey has
been used at other disposal sites to determine both surface (Wiley 1993) and subsurface
sediment densities (SAIC 1991). Together these technologies should provide an accurate
assessment of the sedimentology at the site.

2.1 Bathymetry

The SAIC Integrated Navigation and Data Acquisition System (INDAS) provided the
precision navigation required for all field operations. This system uses a Hewlett-Packard
9920® series computer to collect position, depth, and time data for later analysis, and to
provide real-time navigation. A Del Norte Trisponder® System provided positioning to an
accuracy of +3 m. Shore stations weze established in Connecticut at known benchmarks at
Cornfield Point (41°15.79’ N, 72°23.04’ W) and Lynde Point Light (41°16.29’ N,
72°20.59’ W) in Old Saybrook, Connecticut. DAMOS Contribution No. 60 (Parker and
Revelas 1989) contains a detailed description of INDAS and its operation.

An ODOM DF3200 Echotrac® Survey Recorder with a narrow-beam 208 kHz
transducer recorded depth to a resolution of 3.0 cm (0.1 ft) as described in DAMOS
Contribution No. 48 (SAIC 1985). Depth values transmitted to the computer were adjusted
for speed of sound and transducer depth. Before starting the bathymetry survey, a SeaBird
Instruments, Inc. SEACAT SBE 19-01 conductivity-temperature-depth profiler (CTD) was
used to calculate a sound velocity profile. During analysis, all depth values were converted |
to. Mean Low Water (MLW) after compensating for vessel draft and tidal fluctuations that
occurred while surveying. Position and depth data were also checked to identify and
eliminate any outlying values before producing an accurate contour plot. Analysis of the
bathymetric data was conducted using the Hydrographic Data Analysis System (HDAS).

The August 5, 1992 bathymetric survey at CSDS was set up over the same grid used
in the 1991 and May 1992 surveys (Wiley 1994). The 1200 x 1200 m survey consisted of
49 lanes oriented east and west with 25 m lane spacing.

2.2 REMOTS®
A REMOTS® survey was conducted at CSDS on August 6, 1992 to define the limits

of dredged material distribution. In May 1992, a 45-station orthogonal REMOTS® grid had
been surveyed to define the dredged material boundary (Figure 2-1). In August 1992,

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

7661 ABW ‘AIS [esodsiq sjeoug pjayws0D ay; 3 suoHedO] UOHEIS gSLOWAU “T-Z e1ns1q

N.0S°ZLolvP

SIB}EW

123)
Vv

oO
>
4
=a
=<
=
m
4
2
9)
wn
Cc
a
<
m
<
wo
fe)
Cc
2
ie)
>
es]
<

M.0S°LZoeZ

N.OO'ELolY

SNOILVOO1 oSLOWAY
c66L AVIN SdGSD

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

N

15 stations were resurveyed. Ten additional stations along the southern boundary of the
dredged material deposit were surveyed at this time to map further the extent of the fine-
grained dredged material documented in the May survey (Figure 2-2). Three replicates were
taken at all stations. Analysis of the REMOTS® sediment-profile photographs was limited to
grain size measurement, average penetration, and documentation of the presence of dredged
material.

2.3. Sediment Density

REMOTS ® photographs from the May 1992 survey at CSDS showed the presence of
two sediment types with sharply different densities: sand and fine-grained mud (Wiley 1994).
The 24 kHz acoustic survey conducted at CSDS on August 10, 1992 was designed to
determine if the system could identify the different sediment densities that were observed in
the REMOTS® photographs. The sediment density survey interfaced the 24 kHz sound
source with the Acoustic Core System® (model CE-IB-100; Caulfield Engineering Group,
Oyama, BC, Canada). The Acoustic Core System® is a combination hardware/software
package designed to provide quality control during shallow seismic data acquisition. It
provided acoustic impedance and density predictions based on signal amplitude in the shallow
seismic field. The system calculated impedance values relative to seawater and generated
density estimates based on the work of Hamilton (1970, 1971). The survey covered the same
area as the first 25 lanes of the bathymetric survey and collected data every 50 m along the
survey track. Subsurface density information was collected every 15 cm below the seafloor.

Data output from the Acoustic Core System® included amplitude and acoustic
impedance values. Acoustic impedances have been reliably assigned to different sediment
types; therefore, they can be used to detect changes between sediments with dissimilar
impedance characteristics (Hamilton 1970, 1971). Impedance values were converted to
density values and mapped to quantify changes in sediment type. The densities of surface
sediment samples taken from the site were used to verify the densities calculated from the
impedance values. For a more detailed discussion of the analysis procedure, see Caulfield
and Yim (1983) and Caulfield (1984).

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

Z661 IsNBny ‘oNg Jesodsiq sjeoys pfalyus0D ay} ye sUOTEDO] UOHEIS eBSLOWAU °Z-Z 21N31q

S190

N.SZZlolt

MSZ LZ07L
M.00°C2ocL

Ajuo ysnBny u! peAerins suoneis S N O ILVO O71 SLO TAN | Y
isnBny pue Aew ul peAeains suonelg ow "A 6 6 L LS NM C) a) V : S qd S 0)

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

3.0 RESULTS
3.1 Bathymetry

The bathymetry at CSDS changed very little between May 1992 (Figure 3-1) and August
1992 (Figure 3-2). At approximately 72°21.75’ W and 41°12.85’ N, the mound formed by the
disposal of fine-grained sediment from North Cove caused the contour lines to bend to the south
in both surveys. South of 41°12.50’ N, the contours in the August survey were slightly deeper
and more convoluted than in May. This is the area where sand waves were recorded in the
fathometer trace in May (Wiley 1994). Comparing depths in the two bathymetric surveys showed
very little loss from May to August (Figure 3-3). Five areas of -20 cm depth difference exist,
each a maximum of 75 m in diameter. Up to 40 cm of material had accumulated at 16 locations
in the southern portion of the survey area from May to August (Figure 3-4). Each of these areas
was less than 100 m in diameter.

3.2 REMOTS®

Of the 25 REMOTS® stations surveyed at CSDS in August 1992, two were fine-grained
dredged material, and four were sand over mud. The remaining stations were sand (Figure 3-5).
The two stations with fine-grained dredged material (G8 and G9) were located closest to the
specified disposal point. Of the REMOTS® stations that were surveyed both in May and August
1992, E3, F6, F7, G5, G10, D3, F8, and E9 were sand over mud in May, but only sand was
visible in August (Figure 3-6). Station F9 was ambient sandy sediment in May, but in August it
was sand over dredged material (Figures 3-7 and 3-8). Stations G6, G8, and G9 remained
unchanged. Sand is very difficult for the REMOTS® camera to penetrate; as a result, REMOTS®
photographs taken at a sandy station usually have very low penetration and often do not show the
subbottom structure. Ten new stations were surveyed in August to determine if there was any
other fine-grained material at the site that had not been detected in May. Eight of these stations
detected only sand, but D6 and D7 showed sand over fine-grained dredged material.

In addition to documenting the presence of ambient sand or fine-grained dredged material,
the REMOTS® sediment-profile photographs showed variations in the sand grain size between
Stations and mapped the locations of sand waves or lag deposits. In both May and August,
coarser grained sand with lag deposits of pebbles or shells was found north of 41°12.75’ N, and
finer grained sand with bed forms was found to the south (Figure 3-8).

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

10

(sxoj0u ul ydap) 7661 ARI ‘SUS [eso 7SIG sIBOLES pjoljuIO_D sy} 38 Jojd InojuO0S aneuAweg “[-¢ wns

Co0or/5 :ereos
vem MO'OE te e240 MOS? te e240 MO°0O ce e400

NO'Sb 2F ty + apd ; NO'Sb 25 tb

NO‘OO EF tr -|- aL NOOO EF FP

MO°OO te e240 MO'ST te 240 MO°OE te 240 MO'Sb te 240 MO°00 ce 240

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

11

(S19}9Ul
ul yidap) Z66T isnsny ‘ag jesodsiq sjeoug P[eljuIOD sy? 18 jojd inojwos oIneWIAIeg = °7-¢ aINSIY

—

MO'OE fe 240 MO'Sb te 2240 MO°OO ee 2240

=o

NO'OE cl tr —

NO'Gp ch te —

— NO'Sr eb bv -|-

Ho OO Et te -|- NO 00 EE te

MO OO te 2240 MO GE te 240 MO OE fe 240 MO Spy te 240 MO OO ee 240

=

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

(Ww 70
y@ SINOJUOS) ZG] IsNSNY puK ZG] Ae UIEMIEq i0Jd InOJUOD soUaIAZJIp ydap sANVSAN “€-€ dINnshy

QOOOOt/t -81829S

OTT] MO°OE te &40 MO’ Gb te 2240 MO°0O ce cZL0
cos == -00F = O0E——CESCCO o

eed
2665 Ae 03 asntne
@2uaJasstD Uadep
S{e0uS Diet yudoD

NO'OE ct tr

NO'Sb cr Tey -|- NO'Sp cl bP

NOOO EF te -|- NO'OO EF ter

MO°OO te 240 MOST te 220 MC°OE te 240 MO'’Sb te 220 MO°OO ce e240

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

(WI 0 pue

Z'(Q) 8 SINOJUOD) 766] ISNENY pue 766" Ae UIaMIOq JO[d INoJUOD sdUaIAIJIP dap aaNIsog *p-E GANTT

OOOOF/ 5 :8te2S
8181
cos oor Ooe 008 oor 0

coor Aew 09 3enBne
BousJes)¢p UyWdep
Steous pretsusoy

NO'Gp et tr

NOOO EF tr -|-

MO'0O te 2240

MO'OE te 220 MO'GSb te 240 MO°OO ee 240

ces ° Dg. ( Moe
PP

4
b= 4
oy we

+ + + mae

a Aona &

NOOO EF tr

MO'GT te e240 MO'OE te 2240 MO Gb te 240 MO°O0O ee 220

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

14

7661 Isnsny

PNW 48AQ pues
|eueieyy pebpesg peuiesB-ouly

6

aug [esodsiq steoyg pjalyuioD oy 2% adA} JUoUMIpas Jo dey = *S-¢ BANS

s19}0;y

NGL ZLolY

NM.SLLZ0o7L
M.00°%20eL

C66EL LSNONV ‘SGSOD

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

Station E3 showing sand/mud in May 1992 (A) and sand in August 1992 (B)

Figure 3-6.

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

“Sp, nega af Les bh 1+ eel angb
| - |

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

Station F9 in May 1992 (A) and August 1992 (B), showing change from ambient

sandy sediment to sand over mud

Figure 3-7.

° 7
,
i
e
>
i
ve

oc abe

- | a

ae
i an. i

a
.

a

= A

End 7 RTRs hear 4 GP ae, wr RG bat! ;

v4

Ll

pete

‘Chel,

ass

me
Watri > @

: _
— ee

—— tel
Ae kai arn anil
of _— @ :

na

ts

ats

ae

ry

17

7661 Isnsny

pue Arey ‘aig jesodsiq sjeoyg pjalyusog oy) ye UONNINsIp jelioyeul pospolp pue pues ‘g-¢ oNSIq

N.SZ Cb ob?

M .00 22 cL

jelayeyy pebpeig isniny — |
fevayeyy pebpaiq Aey | 74

uoneis @SLOWSH VW

VN NNN NINN
‘

DS

?
47
4s
Pe.
4s
PP
47
47
Oo
4s
oe
47
Oo
22

S SSO BSS DS GS GS
SS SSS NOS SS

Kad

Za
7
7
7

7
7

ysodap He] yy juswIpes poures6 Jasue0g

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

18

3.3. Sediment Density

Surface density data ranged from 1.3 g-cc' to 2.3 g-cc!. The surface sediment
density data show high variability between data points (Figure 3-9). At REMOTS® stations
G8 and G9, where the median grain size mode was greater than 4 phi (silt/clay), the density
values range from 1.5 to 1.8 g:cc'. The remaining REMOTS® stations surveyed in August
all had grain sizes of one to two phi (medium to fine sand) which should correspond to
densities of more than 1.9 g-cc'. The density data show values of 1.3 g-cc’ and greater at
all the REMOTS® locations. The contour plot of the density data (Figure 3-10) shows areas
of relatively uniform density between 1.3 and 1.6 g-cc. Values greater than 1.6 g-cc!
(Figure 3-11) are concentrated north of 41°12.75’ N.

Subsurface sediment density at CSDS was collected at 15 cm intervals below the
surface. Data was collected for multiple intervals although attenuation and data degradation
prevented any realistic analysis on all but the initial layer. The contour plot of the density
values of the first layer (15 cm below the sediment water interface) shows an increase in
density at all points of the survey (Figure 3-12). .

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

072 21 15.0W

=
[o}
(oe)
m
~~“
9]
au
DS
o

072 21 45.0W

vite wt
“7 0°2z-
yet fat

st OLEH,

19

41 12 45.0N

ace Densit

25x25m cells

072 214 30.0W

072 21 45.0W

Smooth sheet of surface sediment density (g-cc™') at the Cornfield Shoals Disposal Site,

August 1992

ec

ies ni

G wo
44 410° 45-0N

Figure 3-9.

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

7661 Isnsny
‘aug esodsiq s[eoys plaiyusoD oy) 3 (,.99-3) Ajsuap JUOWIpas sdeJINS Jo Jojd InoWWOD “OT-¢ 2aNnsIy

oooor/t s1e35
5u21an MO OE Ie eZ40 MO Gb Ie e420 MO OO ce eZ0

‘l

Aytsuag asejsns MN

ce6/01/B UIOI NO O€ el Iv

5

vw
oY if

BOC Ma

NO Gp el tv -|-

NO Gb et tb

AYVGNNOG ASAYN

Wa Ni
SOG

NO OO EF tr -|-

NO OO Et Ir

MO'0O fe 220 MOSH Te e200 MO°OE te e240 MO’ Gb te 220 MO’ 00 ce eZ0

| pal IL ¢ Pe MLA waza | IL ss

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

Bian

ou oor voc coe oor o
——— i

T3578) ATISN30 39¥3unS
= 266 iSnonv
ae SWOHS Gai sNuOD

— NO Sp ct tv -|-

NO 0O EF tp +

MO Sb Oc cZO MO'00O te e240

109-8 O°] < Sonjea AjIsuap JUSUTIpas soRJING “[]-¢ 9INSIy

MO OO ce cZO0

@ Aona -B

NO OE cr tt

MO OE te &cZ4O MO GY Ie cZ40

MO SE te cZO

op)
e Hh
30
<
m
~< NO Ge el Iv
oy
2)
eH
Zz
s)
>
Se)
<
NOOO EF Iv

MO'°SE te e240 MO°OE fe 240 MO'Gb Itc cZO MO'0O ee eZL0

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

NO Gb ch te -+-

NO 00 EF tr -{.

ee ee, (eS | | |

JOvJINS JUSUIIPas ot}
MOA WD GT Ajayeuttxoidde ‘ayig jesodsiq sjeoys pyaljuso|_ ou) ye (,.99-3) Asuap JUOWIPSS *Z{-¢ ainsi

oooot/t -3(e82s

Cer MO OE te 240 MO Gb te e240 MO'0O ee ¢cZ0

@ Aona - a

on -|- + NO OE ch tb —-

NO'GP ect tb

AYVGNNOG AAAYNS

NOOO EF Tr

)

MO'OO fe e240 MO'SI Fe 220 MO’ OE te 220 MO'GP Ie eZ0 MO’OO ce eZ0

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

23

4.0 DISCUSSION

The absence of any large areas of gain or loss at CSDS between May and August
1992 and the transformation from sand over mud to all sand at seven of the stations surveyed
by REMOTS® support the active bed transport processes deduced from the May 1992 survey
at CSDS (Wiley 1994). Although there is a predominant east-west transport direction at the
site, the dispersion rate for fine-grained materials was suspected to be markedly retarded by
sand armor that migrates over the more cohesive, less erosive fine-grained dredged material.

Comparing the May to August bathymetric surveys showed a clustering of positive
depth differences in the southern portion of the survey area. This coincides with the known
location of a sand wave field. Migration of sand waves (part of the east-west transport
supported by previous studies [Wiley 1994]) could have caused the accumulations noted
between May and August 1992. The north-south alignment of the areas of accumulation are
also parallel to the wave crests.

At the North Cove buoy location, up to 50 cm of dredged material had accumulated
between December 1991 and May 1992 (Wiley 1994). The two areas of 20 cm loss in
August were to the east and west of this area of accumulation. Based on the bathymetric
measurements, there was no change in the water depth at the center of the disposal mound
between May and August, again supporting the relative stability of the fine-grained deposit.

In May, the REMOTS® photographs on the mound showed fine-grained material at
the center surrounded by sand over mud on the flanks. By August fine-grained dredged
material was visible only at the two stations closest to the center of the mound. Sand over
mud was found at two stations on the flanks and at two stations almost 300 m to the
southwest. Where there was dredged material or sand over mud in May but sand in August,
it is likely that the fine-grained material remains buried under an accumulation of sand.
When the photographs showed sand over mud in May, the sand may have been acting as a
barrier to the erosion of the mud. How thick the layer of sand could be over the mud is
unknown.

The absence of any detectable accumulations where the sand had moved over the mud
may be a result of compaction of the mud under the sand. The change at F9 from sand in
May to sand over mud in August 1992 may have been due to a loss of sand, allowing the
REMOTS® camera to penetrate through to the dredged material. The new stations surveyed
in August detected mud under the sand at stations D6 and D7. This extended the previous
estimation of the location of the fine-grained dredged material boundary to the south.

Because sand deposits limit REMOTS® camera penetration, the absolute boundary of
the fine-grained dredged material deposit remained unknown after the sediment profile

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

24

survey. The size of the fine-grained deposit, its thickness and area, would help determine
how much of the original material remained on site and was buried under the sand.

The 24 kHz acoustic survey at CSDS on August 10 was conducted to try to provide
answers to this question. The subbottom profiler system gathered both surface and
subsurface sediment density values. Changes in subsurface densities (from sand to mud)
should become apparent as the acoustic signal passes from surface sand to the underlying
mud. On the surface, density values should decrease as the signal passes over the center of
the fine-grained deposit. The results of the surface density analysis did show a predominance
_ of values greater than 1.6 g-cc’' concentrated north of 41°12.75' N. These values do
correspond to the location of coarser grained material and shell lag identified in the
REMOTS® photographs. An exact correlation between the REMOTS® photographs and the
measured surface density values is not clear. As the survey passed over the fine-grained
material at REMOTS® locations G8 and G9, the surface density values ranged from 1.5 to
1.8 g-cc’, higher than expected for the fine-grained material that was documented in the
REMOTS® photographs.

Subsurface density values were collected by the 24 kHz acoustic survey at 15 cm
intervals below the seafloor. If the fine-grained material had been detected by this system
(i.e., the mud was located at 15 or 30 cm below the surface), there would have been a
corresponding drop in density values. The density results around the mound (at 15 cm below
the seafloor) all exceed 2.0 g-cc!. In the REMOTS® photographs, the top of the fine-grained
deposit was detected within 8 cm from the seafloor. Only if the deposit exceeded 7 cm thick
would it have been discernible by the subbottom system. Based on depth differences before
and after the deposit of the North Cove material, the mound formed was 50 cm high at its
apex. This is reason to believe that there should have been fine-grained material detected in
the 24 kHz acoustic survey.

The lack of success with the 24 kHz acoustic survey may have been due in part to the
resolution of the system, but attention to and adjustment to varying system parameters in
future surveys may result in more successful distinction between subbottom layers.

ee

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

25
5.0 CONCLUSIONS

The REMOTS® sediment-profile photographs at CSDS in August 1992 strongly
suggest that sand at the disposal site is continuing to be transported over, and accumulating
on, the fine-grained dredged material mound that was created at CSDS from sediments from
North Cove. Although there is no net accumulation between bathymetric surveys in May
1992 and August 1992, the resolution of that acoustic system (>20 cm) may be too large to
measure the combined sand accumulation and mud compaction. The surface sediment
density study at CSDS did not reveal well-defined areas of fine-grained sediment. Instead it
showed variability in the data with density values ranging from 1.3 up to 2.0 g-cc™ over
50 m. The denser sediments were concentrated north of 41°12.75’ N, which generally
corresponds to the location of sandy sediments with shell lag and pebbles. The subsurface
density data did not prove to be a reliable means of locating changes in sediment density.
Different sediment types observed in the REMOTS® sediment-profile photographs were, in
many cases, less than 15 cm thick, the resolution of the acoustic profiling system.

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

26

6.0 REFERENCES

Bohlen, W. F.; Cohen, D.; Strobel, K. H. 1992. An investigation of water column currents
and suspended sediment dispersion associated with dredged material disposal
operations, Cornfield Shoals Disposal Site, Eastern Long Island Sound. Submitted to
SAIC, Newport, RI.

Caulfield, D. D.; Yim, Y. C. 1983. Prediction of shallow sub-bottom sediment acoustic
impedance while estimating absorption and other losses. J. Can. Soc. Expl.
Geophys., Vol. 19(1):44-50.

Caulfield, D. D. 1984. Shallow seismic derived acoustic core logs. Offshore Technology
Conference, Houston, TX, 7-9 May.

Germano, J. D.; Parker, J.; Christiansen, C. 1994. Monitoring cruise at the Cornfield Shoals
Disposal Site, July 1990. DAMOS Contribution No. 90 (SAIC Report No. SAIC-
90/7597&C91). US Army Corps of Engineers, Waltham, MA.

Hamilton, E. L. 1970. Reflection coefficients and bottom losses at normal incidence
computed from Pacific sediment properties. Geophysics, Vol. 35:995-1004.

Hamilton, E. L. 1971. Elastic properties of marine sediments. J. Geophys. Res., Vol.
76:579-604. .

Parker, J. H.; Revelas, E. C. 1989. Monitoring cruise at the New London Disposal Site,
August 1985 - July 1986. DAMOS Contribution No. 60 (SAIC Report No. SAIC-
86/7540&C60). US Army Corps of Engineers, New England Division, Waltham,
MA.

SAIC. 1985. Standard operation procedure manual for DAMOS monitoring activities: volume
I and volume II. DAMOS Contribution No. 48 (SAIC Report No. SAIC-
85/7516&C48). US Army Corps of Engineers, New England Division, Waltham,
MA.

SAIC. 1988. Bathymetric survey at the Cornfield Shoals Disposal Site, July 1987. DAMOS
Contribution No. 70 (SAIC Report No. SAIC-88/7526&C70). US Army Corps of
Engineers, New England Division, Waltham, MA.

SAIC. 1991. Monitoring and reconnaissance cruise of the New York Mud Dump and Eastern
Adjacent Area, October 1990. SAIC Report No. SAIC-91/7607&255. Submitted to
Department of the Army, US Army Corps of Engineers, New York District, New
York, NY.

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

27

Wiley, M. B. 1993. Monitoring cruise at the Portland Disposal Site, July 1992. SAIC Report
No. C110. Final report submitted to US Army Corps of Engineers, New England
Division, Waltham, MA.

Wiley, M. B. 1994. Synthesis of monitoring surveys at the Cornfield Shoals Disposal Site,

July 1991 to May 1992. SAIC Report No. C106. Final report submitted to US
Army Corps of Engineers, New England Division, Waltham, MA.

Monitoring Cruise at the Cornfield Shoals Disposal Site, August 1992

INDEX

benthos 5 bathymetry iii, 1, 5, 7,
buoy iii, 1, 3, 4, 23 9-11, 23, 25, 26
disposal iii, 3 postdisposal 1
conductivity 5 predisposal 1
containment 1 REMOTS® v, 5
CTD meter 5 sub-bottom v, 4, 9, 26
currents 26 suspended sediment v, 4, 26
direction 1 temperature 5
meter iii, v, 1, 3 tide 1,5
speed 1 transmissivity
density iii, iv, v, 7, 18-25 transmissometer v, 4
dispersion v, 1, 23, 26 waves 9, 23

dispersive site v, 1
Cornfield Shoals 1, iii, iv,
v, 1-3, 6-11, 14, 17,
19520222.) 23%
25-27
disposal site
Cornfield Shoals 1, iii, iv,
v, 1-3, 6-11, 14, 17,
19, 20, 22, 23,
25-27
New London 26
Portland 26
erosion 23
grain size 7, 9, 18
REMOTS® iii, v, 1, 4-9, 18,
23-25
camera 9, 23
sandy iii, 1, 9, 16, 25

sediment
clay 18, 24
sand ili, v, 1, 4, 7, 9,
15-18, 23-25
silt 18

transport 1, 4, 5
sediment sampling
cores 7, 26
seismic 7, 26
shore station 5
species
dominance 1
survey