technical report s-69-4 - "geological investigation of the mississippi

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TECHNICAL REPORT S-69-4 .
GEOLOGICAL INVESTIGATION OF THE
MISSISSIPPI RIVER AREA
ARTONISH TO DONALDSONVILLE, LA.
by
R. T. Saucier
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April 1969
Sponsored by
The President, Mississippi River Commission
Conducted by
U. S. Army Engineer Waterways Experiment Station
CORPS OF ENGINEERS
Vicksburg, Mississippi
ARMY-MRC VICKSBURG, MISS.
I
1D
GEOLOGICAL INVESTIGATION OF
THE MISSISSIPPI RIVER AREA, ARTONISH TO DONALDSONVILLE, LA.
GEOGRAPHIC SETTING
moval of lar ge areas of backswamp deposits .
These deposits we re replace d la rgely with point bar
deposits and deposits that accumulated in abandoned channel environments.
1. The area under c onside r ation in this report encompasses some 2500 square miles that
12. Several smalL _t;l.i s t r ibutaries such a s B ayou Latenache , Bayou For doche - B ayou G rosse
flank the Mississippi River between a point about 4 miles north of Artonish, Louisiana, and a point
Tete , and Bayou Plaquemine (see plates for locations) are apparent in th e a r ea because of their well -
about 15 miles east of Donaldsonville, Louisiana (fig . 1). It lies almost entirely within the New Orleans
developed natural levee r i dges.
District of the Corps of Engineers , ext ending from Mississippi River miles 152 to 327 above Head of
small volume of flow onl y at flood stages on the river , and ori ginated as crevasses. Bayou Lafourche
Passes. Baton Rouge, Louisiana , is by far the lar gest urban complex within the area.
is the only distributary in the study area that carried all or a significant portion of the Mississippi
The.se distributaries were apparently short- l ived , carried only a
River d ischarge (r efe rence 6).
2. Physiographically, the study area includes the extreme southeastern part of the Lower
Mississippi Valley or the Mississippi River floodplain p lus a smaller area of terracelands or blufflands of Pleistocene age lying east of the floodplain. Throughout the area , the Mississippi River flows
DATA PRESENTATION
close to the base of the bluffs, which decrease in height downstream until , at Donaldsonville, they ris e
onlyas a low terrace 10ft or less above floodplain level. The floodplain area west of the river is part
of the large Atchafalaya Basin of Louisiana.
13. The plates in this f olio show the distribution of alluvial deposits in plan and in profile.
Toward the south and southeast , the study area merges
On each of the base maps (plates designated "a" ), which are full - s c al e reproductio ns of the latest
with the Mississippi River Deltaic Plain.
standard 1: 62 ,500 -scale topographic quadrangles, four o f the six environments o f deposition of the
topstratum a re shown in color.
PURPOSES AND SCOPE
The other two environments , the alluvial apron and the natural levee
deposits, a re shown as a dashed and a dotted overprint, respectively, in order that the type s of deposit s
lying beneath these two essentially surficial deposits will n ot be masked .
Heavy black dashed lines
are u sed to show the locations of selected major s wales in point bar areas that illustrate the trends
3. The purposes of this investigation have been to (a) determine the areal distribution and
of the meanders .
phys ical characteristics of the various alluvial deposits, (b) analyze subsurface soils conditions of
14. A green line pattern is used to delineate that part of the backswamp environment where
various environments of deposition to aid in determining foundation and underseepage conditions ,
(c) d etermine the nature of and the depth to the Tertiary or Pleistocene deposits l ying beneath the
the deposits are unusually thin.
Recent alluvium , and (d) delineate the major geolo gic formations or basic lithologi c types in the
terpreted as being the location of the meander belt of the local valley drainage system that was situ-
uplands or blufflands.
a ted near the eastern valley wall whi l e the M iss issippi River was flowing near the we s te r n valley wall.
During the past decade , the U .S. Army Engineer Waterways Experiment Sta-
This situation occurs along a narrow, d i sconti nuous band that is in-
tion (WES) has been conducting continuin.g investigations of the Yazoo, St. Francis, and Boeuf- T ensas
The thin backswamp a nd natural levee deposits now overlying a nd obscuring all surface expr ession o f
Basins of the Lower Mississippi Valley with similar goals. In all cases, including the present study ,
the meander belt were deposited after the Mississippi R i ver adopted its present course near the
the basic data presentation form is a standard 1: 62 ,500- scale topog raphic quadrangle supplemented by
eastern valley wall.
one or more geologic eros s s-ecti-ons . The 10 quad rang l es included herein are thus part of what will
15 . A blue checkered pattern is u s ed to portray la rg e swalelik e a reas of v a r ious origins
ultimately be almost complete engineering-geologic quadrangle map coverage of the Lower Mississippi
(e . g. , crevasse scourings a nd a re a s of s lack-water deposition behind bars) whe re thick deposits o f
Va lley area. A loose-leaf f olde r format has be en adopted for the report series to fac ilitate addition
soft, fine- g rained materials (almost exclusively c lays) occur. Certain a r eas o f point bar environment
of supplemental data and/ or r e visions.
are delineated by a fi ne dotted red overprint. In these areas , the point bar deposits a r e consid erabl y
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finer grained than is t y pical for the environment .
This situation devel ops where the river is force d
to meander i n an anomalous manner due to its impingement against the highly erosion-r esistant
MAPPING PROCEDURE
Pleistocene or Tertiary uplands. Deposition of fine - gra i ned m a terials (mostly silts with clay laye rs)
4.
The areal distribution of the Recent environments of deposition was determine d l argely
actually r e s u lts from an eddy and/ or slack- water condition that develops in the bend .
from aerial photos and photo mosaics ranging in scale from 1:10,000 to 1: 63 , 360 and in date from the
1930's to the 196 0's.
Pertinent geological publications such as groundwater investigations and state
16 .
T he elevations of the surfaces of the entrenched Tertiary or Plei stocene formation s are
shown by red contours .
The borings used to contour the surfaces a re shown as small red dots .
geological survey bulletins , and unpublished data from manuscript reports and graduate theses (s ee
17. Where boring information is suffic i ent , one or more cross sections have been prepared
plates for references ) provided much of the data on the P leistocene and Tertiary fo rmations expo s ed
to acc ompany each map. Each p late containing cross sections bears the designati on " b ." Where in-
in the uplands and beneath the Recent alluvium.
formation is sufficiently detailed , principa lly where closely spaced engineering borings have been
5 . A lar ge volume of subsurface data was obtained from the files of agencies such as the U .S.
Army Engineer District, New Orleans, the U.S. Geological Surve y , the Louisiana Department of High-
made, t he soil types are shown in color .
Note that soil t ypes are shown only to the depths of the de-
tailed borings.
ways, several private founda tion engineering firms , and numerous private industries with p lants in
18. The classification of soil types used in the cross sections is based on the s y ste m used by
the area . The more detailed subsurface information, usually the logs of holes drilled b y the Corps of
the Lower Mississippi Valley Division, CE , prior t o 1950. This was unfort unately nece ssary bec ause
Engineers , was used to construct c ross sections through the v a rious quadrangle a r eas and to contour
o f the l arge number of borings used in the study tha t p re dat e 1 950 . For comparison with more recent
the surface of the entrenched v alley .
borings classified by the Unified Soil Classification System (USGS) , and in order that these borings
could be used in the study, probable equivalents of the older s y s tem and the
uses were
determine d
a nd are shown in the legend. It is emphasized, however, that the two s y stems cannot be equat ed pre-
GEOLOGIC SETTING
ci s ely; for exampl e , soils clas sified a s lean clay (C L ) according to t h e USCS may occasionally be in6 . Deposits of Tertiary age are exposed in the uplands only at a few small and scattered localities north of St. F rancisville, Louisiana (fig. 1).
These materials everywhere are fine-grained
cluded with the older syste m soil types shown in blue (clay sand, sandy clay, silt, s andy silt) as well
as w ith t hose shown i n green (clay, blue mud, silty clay, clay silt).
and a r e identifi e d as undifferentia t e d Pliocene-Miocene d e posits, probably b eing eithe r the Pascagoula or the Hattiesburg forma tion equivalents (see reference 1 for further information on Tertiary
stratigraphy).
MAPPING LIMITATIONS
Fluvial deposits of Pleistocene age , characteristically g raveliferous, form a nearly
continuous thin blanke t over the T er tiary formations north of Zachary, Louisiana (reference 2 conta ins
19. The maps and cross sections in this folio should be conside red as being of a r ec onnais -
detailed descriptions of the deposits ). South of this point (fig . 1), the fluvia l deposits are in the form
sance nature only.
The a e rial photo interpretat ion coul d be fi eld checked to only a limited deg ree,
of well-defined terraces that lack near- surface graveliferous units and that thicken rapidly southward
and borings were not available as substantiating data in many are a s.
to thicknesses of at l east several hundred feet (r efe rence 3 ). The youngest t e rr ace , designated as the
technique allows for little quality control, i. e . featur e s of doubtful origin and/ or areal extent nece s -
Prairie formation (Qtp) according to Fisk (r eferenc e 4 ), is widespread and easily identifiable .
sarily are portrayed in the same manner as ar e well-defined one s of une quivocal origin .
Al-
Fur the r more , the mappi ng
Also, it
though a ll of the olde r Pleistocene deposits north of Zach a ry have a lso been differ entiated by Fisk
should be kept in mind that the a ccuracy of individual contacts, contours, and other designa tions is
into t e rr ace formation s , r ecent inves tigations by Parsons (r eference 2) a nd others have indicated
affected b y the scale of the map , limitations in the source data , and progress i ve er r o rs that m ay de -
that alternat e interpretations are t e n abl e but not definitive .
velop during the seve r a l stages of drafting a nd p rint ing .
Such deposits a r e identified only as un-
more than ±2 00 ft be expected f or the position of a contact , contour , or other designatio n .
differentiated Pleistoc ene deposits (Qtu) in this r eport .
7.
In no case should an a ccuracy in plan of
The b ase of the Recent alluvium is an e ntr e nched surface displaying a dendritic drainag e
pattern. The a v erage e l e vation of the surface is well over 100 ft below floodplain l e v e l, and m aximum
depths of as much as 350 ft b e low floodplain level occur in th e deepest trench.
LITERATURE CITED
The entrenched sur-
face w as c r eat ed during l a t e Pleis toc e n e times as a r esult of the Mississippi River and various
tributar i es adjusting their gradi ents to lowe r - th a n - present sea l evel s during p e riods of c ontinental
1. Sauci er , R . T ., "Geol ogical Investigation ·o f the Boeuf-Tensas B a sin, Lowe r Mississippi Valley ,"
Technical Report No . 3-757 , Feb 1 967 , U . S. Army E n g ine er Waterways Exper iment Station, CE,
Vicksburg, Miss .
g lac i ation. North o f the l atitude of Zachary , Louisiana, the e ntrenchment affected Terti ary fo r mation s ,
while south of this latitude , P l e istoc e n e formations a r e pr esent a nd fo rm the entrenched surface . T he
conta ct between the two is inte rpr e t e d to b e a long a m a jor f a ult zone known a s the Bancroft Fault Zone
(reference 5 ).
T his f a ult z one (shown in plates Fordoc he (a ) and New R oads (a )) is one of several i n
2. Pars o ns, B . E ., Geol ogical Factors I nflue n c i ng R echarge to the Baton Rouge Grou nd- W ate r Sys tem, with Empha sis on the Citr onelle Formation, unpublishe d M a ste r's thesis , Louisia na State
University ,· B a ton Rouge , La., Au g 1967 .
the study a r ea tha t trend roughly eas t - west and that a r e composed of parallel normal faults with near -
3 . Meyer , R . R . and Turcan, A . N. , J r ., "Geology and Ground- W ate r R e sources of the Baton Rouge
Area , Louisiana ," W ate r Supply Paper 1 296 , 1955 , U .S. Ge ol o gica l Survey, Washington, D . C .
surface displacements of sev eral tens of f ee t.
4.
8.
The oldest Recent deposits filling the e ntr enched valley are included in th e thick wedge of
fluvia l sub s tr a tum sands and g r a v els .
This unit is by fa r the thickest and most continuous body of
sediments of essentia lly one type that occur s i n the study area or in the entire Mississippi Alluvial
Valley. At occasional points above the de epe r entr enchments , substratum d e posits a ttain a thickness
F isk, H . N ., " Geological Investigation of the Alluvial Valley o f the Lower M is sissippi R iv er ,"
Dec 1 944 , Loui s i a n a State University, Baton Roug e , La . ; prepared for Depar tme n t of the Army ,
Mississippi R i ver Commi ssion, C E , Vicksbur g , Miss.
5 . Winne r, M.D ., Jr. , Forb e s, M. J., J r., and Broussa r d , W. L ., " Wat er Resour ces of Pointe Coupee
Parish, Louisia n a ," W a t e r Resourc es Bulleti n No . 11, Ma r 196 8, Louisiana Geological Survey ,
Baton Rouge, L a .
of 3 00ft. The typic a l substratum seque nce i s fine sands g r adin g downward into prog res s ively coarser
sands . T h e fir s t g r ave l s a ppear a t d e pths of 75 to 1 5 0ft a nd become mor e a bundant a nd l a rger in size
with inc r easin g depth .
9.
6 . Kolb, C . R . and Van Lopik, J. R. , " Geology of th e Mississippi R iver Deltaic P l ain , Southeastern
Louisiana ," Techni cal R eport No . 3 -483 (2 v ols ), Jul y 1 958 , tJ . S. Army Engin ee r W aterwa ys .Experiment Station, CE , Vicks burg , Mi ss .
Substr atum d e posits b e low a d e pth of 80 to 100 £t were d e posited by shallow , swiftly flowing ,
br aided c ours es of the Mississippi Rive r whe n it w as ca rr y ing l a r ge volumes of coarse gl acial d e bri s .
SELECTED BIBLIOGRAPHY
Those subs tr a tum deposits a bove this d e pth , largely limited to the a re a of the pre s e nt Mississippi
Rive r m eande r b e lt, wer e d ep osite d by the river since it c hanged f rom a br aid e d to a meandering
r egime n , po ss ibly a bout 12,000 years ag o.
Cardwell, G . T ., Roll o, J. R ., a nd L ong , R. A., " Basic Ground- Water D ata for t h e Miss iss ippi
Rive r Parishes South o f Baton Rouge , Louisia n a ," June 1 963 , L oui s i a na De p artme n t o f P ublic
Work s , B a ton R ouge , La .
10. Depo s it s l a id down since that time a re a ll rel a t ively fine - g r a ined a nd a r e s ubdivide d according to e nvironme nt of deposition .
F i gur e 2 summa ri ze s the c h a r acte ristics of the six m ajor e n-
vironme nts r ecogni zed i n th e s tudy are a t h a t collective ly a r e r efe rre d to as topstr a tum d e po s it s .
11. Sediments depo sit ed in the b ackswamp e nvironme nt a r e by far the thickes t a nd a r eally
most ext ensiv e in the s tudy a r ea . Initial d e position b egan a bout 1 2 ,000 years ago when the Mississippi
Rive r fo llowe d a c our se a l ong the w es t e rn side of its a lluvia l valley a nd continued uniformly a cross
the study area until a bout 4,000 year s ag o , a t whi c h time the r iver s hifte d to
a c ours e a long
F isk , H. N. et a l., " Geolog i cal Investi gati on of the Atchafalaya Basin and th e Problem of Mississippi R ive r Dive r sio n ," Apr 1 9 52 , U . S . Army Engi nee r Waterways Expe r iment S t ation , C E ,
V icksbur g , M iss . ; prepared f or D epartment o f the Army , Miss issippi R iver Commission, CE,
Vicksbur g , M i ss.
Kolb, C . R ., " Distr ibution of Soils Bordering the Mississippi Rive r from Donal dsonville to Head
of Passes ," T echnical R eport No . 3 - 6 01, June 1 962 , U . S. Army Eng~m!e r W ate r ways Expe riment
S tation, CE , Vicks bur g , Miss.
the eastern
s ide of the v a lley. Backswa mp deposits continued to accumulate a l ong the flank of the new me a nder
b e lt; howeve r, mea nd e ring of the r iver within the n e w m eande r b e lt resulted in the er osion a ndr e-
Mor gan , C . 0., " Ground - W ater R esour ces of Eas t Felic i a n a and West Feliciana Parishes,
L ouisia n a ,'' Oct 1963 , Louisia n a Departme nt of Public Works, B aton Rou ge , La .
TYPE OF
TOP STRATUM
DEPOSITS
DIAGRAMMATIC ILLUSTRATION
APPEARANCE ON AERIAL PHOTOGRAPHS
METHOD OF DEPOSITION
OCCURRENCE AND CHARACTERISTICS
Natural levees are low ridges which flank b oth
sides of streams that periodically o verflow their
banks . Since the coarsest and gr e atest quanti ties of sediment are deposited closest to t he
s tream channels , the natural levees are h ighes t
and thickest in t hese areas and gradually thin
away from the channels. In general, the greater
the distance from the stream, the greater the
percentage of the finer grained sediments . Mi nute drainage channels trending at right angles
to the parent stream (down the backslope of the
l evees) are rather common; major crevas ses
are indicated w hen these channels are large and
pronounced. Abandoned c revasse channels are
often filled with sediment s that are di s tinctly
c oarser than the remainde r o f the natur a l levee .
T he larg e st and most widespread n a tural l ev ees in the area occu r along t he present cou rs e
and m a jor abandone d distributari e s of the M i s sis sip pi River . T h ey a ttain c r e s t heights of 15 to
2 0 ft above the adja cent backs w amp areas, and
may be 3 mil e s o r mo r e in width. Natu ral levees
a l s o occu r along smaller streams in the area;
h owever , they are apprecia bly nar r owe r and
steeper t h an tho s e along the Mississippi River .
Typical natural l evee deposits consist of stiff
tovery stiff, brown to gray ish - brown silts , s ilty
clays , and clay s tha t exhibi t moderate to h igh
degrees of oxid a tion. Na tural w a te r contents of
the de p o s its are t y pically l ow , and organic matte r
is seldom p resent except i n the fo r m o f r oots.
ALLUVIAL
APRON
Alluvial aprons are combination s of allu vial
and colluvial deposits which ove r l ie the flood p l ain deposits along the valley w a ll s and along
the sides of upland remna nts w ithin t h e valley .
Typically, symmet rical a lluvi a l fans are pres ent at the mouths of streams that drain the up land s. When these s tr eams are rather clo sely
spaced , the fans coalesce to fo r m the alluvial
aprons . When the s tr eams are more widely
spac ed, the fans are s e p a r ated, and the inter vening portions of the aprons are composed
main ly of sediments t h a t have wa s he d down from
the upl a nds or tha t h ave moved d owns l o pe by
soil creep (colluvial deposits) .
Alluvial apron depo s it s are not wide s p r e ad
in t his area: they occur int e r mittentl y along
the e ast ern v a lley wall north of St. Francis v ille ,
La . T hey ar e best d eveloped near the mouths of
t he s m all s t reams that enter from th e uplands
and parti cula rly where they overlie backswamp
depo sits and thus h ave not been a ffe·c ted by r i ver
migration.
Reflecting the compos ition of the mater ials in
the u plands (loe ss and terra ce depo s it s primar ily) , t he alluvial ap r on deposits cons ist of clayey
silts, silts, and fine sands . Coarser sand and
p os s ibly even s mall quantities of g ra vel ma y be
pres ent near the m ouths of t h e more active u pland
st ream s . Becaus e th e y are well drained, th e y
ar e oxidize d and generally sim ilar to natu r al
levee deposits .
POINT BAR
Point ba r deposits consist of sediment s l aid
down on the inside s of river b ends as a r esult
of meandering of the stream . Although the de p o sits extend to a depth e qual to the d eepest portion or thalweg o f the p arent str e am, only t he
uppermo st , fi n e - g r a i ned portion is included as
p art of the topstratum . Within the point bar top stratum, there are two types of depo sits : silty
and sandy, e longat e ba r deposits o r "ridges"
which are laid down during high s tage s . on t he
stream, and silty and clayey deposits i n arcuate
d epr e ssio ns o r " swales " whi c h are laid d own
during f alling river stages. C h a r acter is t i cally ,
the ridges and swales for m an a lternat ing se ri e s, the configur ati on of whic]::l conforms t o the
curvatu re of t he mig r ating c hannel a nd indi cates
the direction a nd e xtent of meandering.
P o int bar depos its are w i de spread o n ly along
the present cour s e of the Mis siss i ppi Rive r,
partic ularly north of Baton Rouge , La. The
topstratum deposits cons i s t of tan to gray clays ,
clayey silts, silts , and fine sands in t he ridges ,
and so ft g ra y clays and s i lty clay s in the swales .
Typically, the point bar topstratum (excluding
majo r swal e s) average s a b out 20 to 40 ft thi ck.
However , in certain areas whe r e the river h as
mean de r e d anomalously d u e to impingement
aga i nst the valley wall , the tops t r a t um may b e as
much as 8 0 to 100 ft t h ick. Both w ater and organic
contents are hig h in swale s and in t he anomal ously
thi ck tops t rat um areas , whereas they are both
commonly l ow in the ridge depos i t s .
BACKSWAMP
Backswamp deposits c onsist of fine -grained
sediments laid down i n broad, shallow basins d u ring periods of stream flooding . T h e s ediment carrying floodwafer m ay be ponde d b etween the
natural levee ridges on sepa rate m eander belts ,
o r be tw een natur a l levee r idge s and the u pla nds
or upland remnan t s w i thin the a lluvial valley .
Backswamp areas typi cally have ve ry low r elief
and a distinc tive , complicated drainage pattern
in which the chann e l s a lte rna t ely s e rv e as trib utaries a nd distrib u taries at different times of
t he annual flood c ycle.
Backswampdeposits ar e by f ar the most char a c teristic materials in t h e ar e a , be ing p r e s ent
a n d virt ually uninterrupted by other deposit s ove r
thousands of squar e miles . A ver ag e d epos it
thi ckness e s vary from about 75 t o 80 ft in the
n or t hern p ar t of the ar e a t o abo ut 11 0 ft in t he
southe rn p ar t , Total t hicknesses of fi n e - grain ed
mate r i als (topstratum d eposits) may r eac h 130 ft
wher e natural l evee d eposits overlie b ackswamp
d eposits .
So ft to stiff, gray to dark gray - brown clays and
silty clays are the typical backswamp depo s its .
Occasio nal thin layers of silt or sand may be
found , andorganic matt er i n th e for m o fdiss emi n ated particle s , peat l ayers , and lar ge wood
fragments i s numerous . Ave r age water contents
o f t h e deposits are m oderate ly hi gh but less t h a n
tho se o f channel and swale fillin g s.
ABANDONED
CH ANN EL
Abandone d cha nne ls, or • •clay p lu gs '' as t hey
a r e commonly calle d, a re partially or wholly
filled segment s of stream c h annel s f ormed whe n
the st r eam short e n s i ts c ours e . Soon after fo r mation, t h ey ar e u s u ally c haracte ri ze d by ope n
water or oxbow l akes . Sub seque ntly , they may
becom e essentia lly fi lled a n d occasionally com pletely obs cured by variou s meander belt de posits . T h e abandone d segment may r ep r esent
a n e ntir e meand e r l oop formed by the stream
c utting directl y ac r oss a narrow neck of two
conve r g i ng a rms o f a l oop (a n eck cutoff). or i t
m a y repres e nt a po r t i on of a loop f o rmed w hen
a stream occupi es a l a r ge p oint bar swale d u ring flood s t age and abandons the out er po rti o n
of the l oop (a chute c utoff).
A b andoned channels of the Miss is s ippi River
are not n ume rous in this area and occur only
north of Baton Rouge , La. Indi vidu al aba ndone d
c hanne ls vary in leng t h f r om a few m iles t o
20 m il es o r mo r e , have widths of 3000 to 5 0 00 ft
or more , and usually exceed 100 ft i n depth .
The u ppe r po r tions o f the arms o f the looptl of
neck c u toffs a r e normally fi lled w ith a short
wedge of fin e sand a nd silty sand . The soft, g ra y
or blue-gr ay clays wi t h h igh wate r conten t s that
occu r around the loop b etwe e n t h e sand wedges
c omp rise the " clay p lug " portion of the abandon ed cha n n el. Homogeneous , s oft, fat clays""'1. 0 0
to 120 ft thick have been e n c o u nte r e d in Miss i s s i p pi Rive r clay p lug s.
ABANDON ED
COURSE
AND
DI STR IBUTARY
Abandon e d courses are l e n g thy s egm ents of a
rive r abando n e d wh e n the s tr ea m fo rms a new
c o u rs e a cros s the floodpl ain. The aban doned
cou rse , varyi n g from a few miles u p t o h undred s
of mil es in l e n gth , g r a dua lly fill s w ith sediment
and is often occu pied by a smalle r or underfit
strea m. In man y case s , th e smaller s tream mea nde r s w ithin the confines o f t he l a r ge r m ean der
b e l t a n d destroys segm·en t s of the abandoned
co u rse . In other cases , the smalle r st r eam delineates the ext e n t of the a b a ndone d co u rse when
the re are n o other indica tion s of its presenc e .
A b andone d di stributaries , ch a r acteristic featur es of the d e ltaic p l ain , a r e a n alogou s in both
morphology and lithol ogy to a b a n doned cou rses
a lth ou gh a n y one di st r i buta ry may n ever have
c arr ie d all or even a s ubsta n t ia l part of the tot al
st r e am dis c harg e .
Bayo u Lafourche marks the position of the o nly
major M ississippi R ive r abandoned distributary
in t h e a r ea . There are no major abandoned
cou rse s i n t h e area mappe d a n d all o the r distrib utaries are s mall a n d were apparently quit e short
live d .
Onl y sparce data are a va i l abl e on th e n atu r e o f
the deposits filling the a b a n doned distributari es .
A l arge downstr e am-thinning sand w edge i s
k n own t o be presen t in the Lafou r che distributary;
h o wever , the smaller distr i butaries appear to be
fill e d a l most e ntir e l y with fine-grai ned sediment s. T h e physi c a l charac teristics of t h e fine g r a ined m a t erial s shoul d be es s enti a lly the same
as t h ose of abandoned ch annel deposits .
NATURAL
LEVEE
Fig . 2 .
Nature and occurr ence of Rec ent topstrat um depos i ts , Miss i ss i ppi River area, Artonish to Donaldsonville , La .
FOREWORD
LIST OF PLATES
Authorization for this study is contained in a letter from the Division Engineer,
U. S. Army Engineer Division,
Lower Mississippi Valley, to the Director,
U.S. Army Engineer Waterways Experiment Station (WES), dated 9 July 1965, subject,
"Status of Soils Division Projects for MRC and LMVD for FY 1965 and Request for
Funds for Projects for FY 1966."
The collection and interpretation of data for this study and the preparation of
the text and plates for this report were accomplished by Dr. R. T. Saucier, Geology
Branch, Soils Division, WES. All work was conducted under the direct supervision of
Dr. C. R. Kolb, Chief of the Geology Branch, and Mr. W. B. Steinriede, Jr., Chief of
the Civil Projects Section, Geology Branch, and under the general supervision of
Messrs. W. J. Turnbull and A. A. Maxwell, Chief and Assistant Chief, respectively,
of the Soils Division, WES.
Directors of the WES during the conduct of this study and the preparation of
this report were COL John R. Oswalt, Jr., CE, and COL Levi A. Brown, CE.
Tech-
nical Directors were Mr. J. B. Tiffany and Mr. F. R. Brown.
Artonish (a)
Artonish (b)
Distribution of Alluvial Deposits, Artonish, Miss.-La.
Sections A-A' and B-B', Artonish, Miss.-La.
Batchelor (a)
Batchelor (b)
Distribution of Alluvial Deposits, Batchelor, La.-Mis s.
Sections A-A' and B-B', Batchelor, La.-Miss.
Baton Rouge (a)
Baton Rouge (b)
Distribution of Alluvial Deposits, Baton Rouge, La.
Sections A-A', B-B', and C-C', Baton Rouge, La.
Donaldsonville (a)
Donaldsonville (b)
Distribution of Alluvial Deposits, Donaldsonville, La.
Sections A-A', B-B', and C-C', Donaldsonville, La.
Fordoche (a)
Fordoche (b)
Distribution of Alluvial Deposits, Fordoche, La.
Sections A-A' and B-B', Fordoche, La.
Grosse Tete (a)
Grosse Tete (b)
Distribution of Alluvial Deposits, Grosse Tete, La.
Sections A-A' and B-B', Grosse Tete, La.
New Roads (a)
New Roads (b)
Distribution of Alluvial Deposits, New Roads, La.
Sections A-A' and B-B', New Roads, La.
-st. Francisville (a)
St. Francisville (b)
Distribution of Alluvial Deposits, St. Francisville, La.-Miss.
Section A-A', St. Francisville, La.-Miss.
White Castle (a)
White Castle (b)
Distribution of Alluvial Deposits, White Castle, La.
Sections A-A' and B-B', White Castle, La.
Zachary (a)
Zachary (b)
Distribution of Alluvial Deposits, Zachary, La.
Section A-A' , Zachary, La.
~
~
- N-
MISS.
-----etC--
B~
Zachary
NEW
ROADS
FORDOCHE
:tlf
ZACHARY
GROSSE
TETE
WHITE
CASTLE
5
5
0
10
MILES
Fig. 1.
Quadrangle coverage of the Mississippi River area, Artonish to Donaldsonville, La.