Synthesis of monitoring surveys at the Cornfield Shoals Disposal Site, July 1991 to May 1992

66 Pages·1996·1.9 MB·English

by  Wiley, Mary Baker

Synthesis of Monitoring at the
Cornfield Shoals Disposal Site
July 1991 to May 1992
Disposal Area
Monitoring System
DAMOS
4fe^-
D A M O S
DISPOSALAREAMONITORINGSYSTEM
Contribution 105
January 1996
US Army Corps
of Engineers
New England Division

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1.AGENCYUSEONLY (LEAVEBLANK) 2.REPORTDATE 3.REPORTTYPEANDDATESCOVERED
January1996 Finalreport
4.TITLEANDSUBTITLE 5.FUNDINGNUMBERS
SynthesisofMonitoringSurveysattheCornfieldShoalsDisposalSite, July1991 to
May1992
6.AUTHORS)
M. BakerWiley
7.PERFORMINGORGANIZATIONNAMEfS)ANDADDRESSES) B.PERFORMINGORGANIZATION REPORT
ScienceApplicationsInternationalCorporation NUMBER
221 ThridStreet SAIC-C106
Newport, Rl 02840
9.SPONSORING/MONITORINGAGENCYNAME(S)ANDADDRESS(ES) 10.SPONSORING/MONITORINGAGENCY
USArmyCorpsofEngineers-NewEngland Division REPORTNUMBER
424TrapeloRoad DAMOSContribution
Waltham, MA 02254-9149 Number105
11.SUPPLEMENTARYNOTES
AvailablefromDAMOSProgramManager, RegulatoryDivision
USACE-NED,424 TrapeloRoad, Waltham, MA02254-9149
12a.DISTRIBUTION/AVAILABILITYSTATEMENT 12b.DISTRIBUTIONCODE
Approvedforpublicrelease; distributionunlimited
13.ABSTRACT
Preliminary evidence of active bed transport at the Cornfield Shoals Disposal Site (CSDS) prompted the National Marine
Fisheries Service and Connecticut Department of Environmental Protection to express concern about possible sediment transport
towards, and impact on, shellfish beds located north ofthe site, north ofLong Sand Shoal. This preliminary study was designed to
determine ifthe field-observed transport atthe disposal site is consistentwith the predicted east-westtransport pattern found in the
historicalrecord.
This investigation atCSDS betweenJuly 1991 and May 1992 provided strong circumstantial evidenceforactivebedtransport.
Thisstudyincludedaseriesofbathymetricsurveys, currentmetersuspendedsedimentdatacollection, and REMOTSphotographyofthe
sediment-water interface. The circumstantial evidence for active bed transport included shifts in areas ofsediment accumulation and
erosion, increased suspended sedimentdeposits atthesediment-waterinterface. In general, active bedtransportappearstofollowthe
historicaleast-westcurrentdirection,andtheextentofthetransportdependsonthetypeofmaterial. Theactualdirectionandmagnitude
ofactivebed transportapparentlydependonlocaltopographyandthenatureofmaterialsbeingtransported.
Sedimentaccumulated overa broad area nearthedisposal points ofsand hydraulicallydredged fromtheConnecticutRiverin
September 1991. Subsequent bathymetric surveys showed apparentmovement ofthis materialtothewest. Aclearly defined deposit
formed atthedisposal pointforfine-grained material mechanicallydredged from North Cove, Connecticut. This depositoffine-grained
dredgedmaterialapparentlydidnotmove, butwaspartiallycoveredbybedloadtransportofadjacentcoarse-grainedsediments.
Thepresentstudyconcludedthat:
Thepredominanttransportdirectionatthesiteappearstobeeast-west. Thisissupportedbycurrentmeterdeploymentsand
observederosionanddepositionpatterns.
Sedimentdisposedatthesidewasnotimmediatelydispersedandwasdefinedwithindiscretedeposits. Thiswasobservedfor
bothfine-grainedandsandysediments.
Thedispersionprocessappearstooccuroveraperiodofweekstomonths. Thedispersionrateforfine-grainedmaterialsmay
bemarkedlyslowedbysandarmorthatmigratesoverthemorecohesive, lesserosivesilt-clay.
Theabovefindings,takenovertheten monthtimeperiod, reduceconcernsaboutfarfieldtransportofmaterialoveroysterbeds
to the north. The dispersion of material over a time scale of years, and the effectiveness ofthe sand armor overthe silt-clays are
unknown.
14.SUBJECTTERMS 15.NUMBEROFPAGES
bathymetricsurveys REMOTS CSDS DAMOS 30
16.PRICECODE
17.SECURITYCLASSIFICATIONOFREPORT 18.SECURITYCLASSIFICATIONOFTHIS 19.SECURITYCLASSIFICATIONOF 20.LIMITATIONOFABSTRACT
Unclassified PAGE ABSTRACT

SYNTHESIS OFMONITORING SURVEYS
AT THE CORNFIELD SHOALS
DISPOSAL SITE
JULY 1991 TO MAY 1992
CONTRIBUTION #105
January 1996
ReportNo.
SAIC-C106
Submittedto:
Regulatory Division
New EnglandDivision
U.S.Army Corps ofEngineers
424TrapeloRoad
MA
Waltham, 02254-9149
Preparedby:
M. BakerWiley
Submittedby:
ScienceApplications InternationalCorporation
Admiral's Gate
221 ThirdStreet
Newport, RI02840
[phone]
USArmyCorps
ofEngineers
NewEnglandDivision

TABLE OF CONTENTS
Page
LIST OF TABLES iii
LIST OF FIGURES iv
LIST OF PLATES vi
EXECUTIVE SUMMARY
vii
1.0 INTRODUCTION 1
METHODS
2.0 5
2.1 Bathymetry 5
2.2 Current and Suspended Sediment Measurements 8
2.3 REMOTS® 9
3.0 RESULTS 10
3.1 Bathymetry 10
3.2 Current Meter Data 18
3.3 Suspended Sediment Concentrations 22
3.4 REMOTS® 22
4.0 DISCUSSION 27
5.0 CONCLUSIONS 29
6.0 REFERENCES 30
PLATES

LIST OF TABLES
Page
Table 2-1. Summary ofDisposal and Monitoring Activities at CSDS, June 1991
to May 1992 7