The St. Clair River Delta A Unique Lake Delta

ABSTRACT
The St. Clair River Delta
A Unique Lake Delta*
C. Nicholas Raphael and Eugene
Jaworski
Because of long-term and shortterm lake level changes, the geomorphology and vegetation patterns
of the St. Clair River delta are unique.
Marine delta studies and Late Quaternary chronology in the Great Lakes
have progressed significantly in the
past decade and the delta is investigated from the viewpoint of these
developments. Although this delta
has a shape similar to the Mississippi River delta, several forms and
processes are different.
INTRODUCTION
Department of Geography and Geology
Eastern M ichigan University
Ypsilanti, Michigan 48197
* Th is
investigation was in part sponsored
by the Office of Water Research and
Technology, U.S. Department of the Interior.
Since the classical study of Lake
Bonneville by Gilbert,' deltas in lakes,
with only a few exceptions, have
been largely ignored by geomorphologists. The major deltas of the
world are located on continental
shelves and have held the interest
of geologists and geographers because of petroleum resources, agricultural production, and waterborne
activities. Altough lake deltas are of
smaller size, they share most of the
processes characteristic of marine
deltas. However, an unique aspect
of lake deltas is their dynamic response to relatively rapid changes
of base level that not only produce
special landforms, but distinctive
vegetation zonation as well.
During the past decade the study
of marine deltas has progressed significantly. Also, Late Quaternary
events in the Great Lakes have been
repeatedly reexamined and refined.
The St. Clair River delta was investigated from the viewpoint of these
more recent developments . The
vegetation was the first clue which
led us to conclude that this delta
7
had landforms or surfaces not found
on active marine deltas. Furthermore, our comparative aerial photograph studies and vegetation traverses over time revealed that plant
communities do not occupy similar
delta landforms through time but respond to changing lake levels. In
th is investigation the geomorphology of the lake delta, including landform-vegetation relationships, is examined and compared to that of
marine deltas.
Located on the internat i onal
boundary between Ontario and
Michigan, the St. Clair delta is the
largest delta in the Great Lakes Basin (Figure 1). Considering its recreational significance and commercial importance with regard to
Seaway navigation, geographic literature on the area has not been
abundant. The first significant investigation was done several decades
ago by Cole who determined that
the delta was being deposited atop
deepwater, proglacial lake clays. 2
More recently, Wightman attempted
to establish a Late Quaternary chronology for the delta formation. 3 Detailed investigations by geologists
have partially documented the sedimentological composition of the
delta's surface, particularly in Muscamoot and Goose Bays. 4 During
the 1950's, engineering studies by
the U.S. Army Corps of Engineers
preceeded construction of the 27-foot
Seaway channel through the delta.
Although not published, much of
these data, in the form of bore records, are on file at the Detroit District Office. Recent environmental
studies associated with flooding
problems on the shores of Lake St.
8
Clair and dredged spoil disposal site
locations have also contributed some
useful data for this study.5
LAKE LEVELS, FLOW REGIME,
AND SEDIMENT SOURCES
With the retreat of the Late Wisconsin ice some 13,000 years ago,
a series of moraines and lake plains
were deposited in the Great Lakes
Basin. The outlets of the Great Lakes
were changing or even blocked ,
causing the lake levels to oscillate
several tens of feet. 6 Lake Erie established its present level some
4,000 years ago and Lake Huron
shortly thereafter. The St. Clair River
and its delta came into existence
during these changing lake levels.
At present Lake St. Clair has an
established elevation of 573 feet
above mean sea level at Father Point,
Quebec . Hydrographic records,
however, reveal that since 1898 the
lake level has varied as much as 5.9
feet. Since 1965, the level of Lake St.
Clair has fluctuated four feet. 7 These
noncyclic short-term oscillations,
which are principally related to water
budgets in the Great Lakes Basin,
are important determinants of delta
landforms and vegetation zonation
as well.
.
A second factor determining the
delta morphology is the flow regime
of the St. Clair River. The river is a
strait connecting Lake St. Clair with
Lake Huron, not a fluvial system with
tributary streams . Therefore, the
discharge is relatively constant and
averages about 177,000 cubic feet
per second. s With flow velocities up
to two miles per hour, the system
is capable of transporting coarse
sand. 9 Instead of a spring flood typ-
overbank flow is not an annual event
and its occurrence is dependent, in
part, upon seasonal lake level conditions.
ical of most rivers, discharge into
Lake St. Cla ir is slightly increased in
midsummer when lake levels in Lake
Hu ron are highest (Figure 2) . Thus,
~
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I
10
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20 30
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I
MIL ES
40
I
On tari o
Michigan
Er ie.·:·:::
LAKE
o
2
3
ST.OLAIR
"
MIL ES
Figure 1. The St. Clair River Delta .
9
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Figure 2. Average Monthly Discharge of the St. Clair River at Port Huron,
Michigan. Period of Record, 1957-1971. Source: Great Lakes Basin Commission, Framework Study, Appendix 11, Levels and Flows, 1975, p. 374.
Based on flow distri~ution, it is
clear that the most active portion of
the delta is presently confined to the
western side of Lake St. Clair. Much
of the flow of the St. Clair River is
carried by the large distributaries on
the American side of the delta. North,
Middle and South Channels account
for approximately 95 percent of the
flow volume whereas the principal
Canadian distributary, Chenal Ecarts,
accou nts for five percent.'o Although North Channel appears to
have been the main channel a century ago, construction and continual
d redg i ng of the St. CI air Cutoff
channel has increased the flow of
South Channel.
Because the St. Clair River has
10
few tributary streams, the source
area for delta sediments are not
solely of fluvial origin . Rather, the
principal source appears to be the
shorelines of Lake Huron, not incoming streams or river bank erosion . It has been determined that
21,700 cubic yards of sediment, primarily sand size, is transported by
littoral currents from the southeastern shore of Lake Huron annually."
An undetermined amount of sediment is also derived from moraines
and ancient beaches along the western shore of Lake Huron. Size and
mineral composition of Muscamoot
Bay sediments are similar to the glacial sediment of the southern Lake
Huron coastal zone.'2
The unusual transparency of the
river water suggests that most of
the material is being carried as bed
load, not in suspension. It has been
estimated that the total sediment
load of the St. Clair River is about
20,000 cubic yards annually.13 Not
only is the sediment load very low,
but much of it may be transported
through the delta into Lake St. Clair,
thus accounting for the lack of present subaerial delta extension. In addition, over the past 55 years maintenance dredging by the Corps of
Engineers in the St. Clair River has
averaged 80,000 cubic yards annually.1 4 Private dredgers have also
been extracting sand and gravel for
many years, particularly from North
Channel. Because dredging removes
much of the bed load and since little
material is carried in suspension , lit-
D
tie subaerial delta growth is occurring .
DELTAIC LANDFORMS
As a lake delta, the St. Clair exhibits several of the landform characteristics of marine deltas, such as
active and inactive distributaries, interdistributary bays, and crevasses
which lead into interdistributary bays
(Figure 3) . However, although the
St. Clair River delta has a classical
bird-foot morphology, as does the
Mississippi River delta, significant
landform differences are also apparent. Atypical landforms include a
premodern surface located at the
apex of the delta and unusually wide
distributary channels.
The active distributaries, North,
Middle, and South Channels, average some 1,500 feet in width and 35
NOlural
lev •••
~ Modern
~Oelto
Figure 3. Landforms of the St. Clair River Delta.
11
feet in depth. However, widths of
2,000 feet and depths of 80 feet are
not uncommon. At the mouths of
the distributaries, channel depths
decrease abruptly indicating the
presence of river mouth bars six to
twelve feet below mean lake level.
As a depositional basin , Lake St.
Clai r is relatively small with a maximum depth of 21 feet and a length
of 25 miles.
North, Middle and South Chan nels exhibit shoulder-like features
along both the cutbank and pointbar sides (Figure 4) . A similar morphology has been attributed to periodic cut and fill associated with
slight base level oscillations.15 Borings obtained from the Corps of Engineers reveal that the distributary
channels of the St. Clair River delt a
are entrenched in lacustrine clays
which lie · beneath a 10 to 15-foot
veneer of coarser deltaic sediment.
On the cut-bank side, where flow
velocities may be relatively high
during high water conditions, an
erosional berm usually less than
eight feet below the water surface
slopes gently from the cutbank towards the channel center. These
features may be caused by lateral
erosion of the fine, sandy deltaic
sediments which overlie the lacustrine clays. On the inside bank, especially along Middle Channel, point
bar deposits characterized by ridge
and swale topography are conspicuous. Here the distributary shoulde rs probably represent a fill de-
Figure 4. During the Lower Water Conditions of 1949, the Distributary
Shoulders were Evident. The Docks on the North Side of the Channel Delimit
the Extent of this Feature.
12
Figure 5. Well-Developed Crevasse Deposits Adjacent to Middle Channel
Which is Flowing to the Southwest. Many of These Crevasses have been
Intermittently Active for Over a Century.
posit which are colonized by
emergent vegetation during lowwater periods.
Because the water level fluctuates
only 1.5 to two feet seasonally, spring
floods are not a normal occurrence
within the delta, hence natural levees are scarcely discernible adjacent
to modern distributaries. Even
though levees are poorly developed,
averaging a few inches to 1.5 feet in
elevation, flooding and subsequent
overbank flow does occur. Overbank
flow is associated with breaching of
levees in abnormally low areas along
a levee. As a levee is breached, crevasse deposits are introduced into
the interdistributary bays at right
angles to the channels (Figure 5) .
With continued deposition, the openwater bay will be filled with cre-
vasse deposits and colonized by
sedges and emergent aquatics.
Crevasse channels, locally known
as "highways", are operative for
several years. However, deposition
into the bays is not rapid. A comparison of navigation maps reveals
that such features may be part of
the delta landscape for over a century. This suggests that crevasse
channels are active intermittently and
transport little sediment into the interdistributary bays.
During the winter and early spring
when Lake St. Clair is frozen, pack
ice accumulates at the mouths of
distributaries forming ice jams.
Channel flow is then diverted into
crevasses and some overbank flow
may occur. However, because the
dominant grain size is sand, little
13
tt
suspended sediment is transported
from the deep distributaries into the
interdistributary bays. Thus, in the
St. Clair delta the filling of interdistributary bays and delta growth is a
slow process.
In the Mississippi delta, in contrast, crevasse deposits rapidly convert open interdistributary bays into
mud flats which are subsequently
colonized with marsh grasses. During flood stage, the crevasse channels are scoured deep enough to be
maintained and rapid deposition will
occur. In the past 135 years, crevasse deposits have transformed the
open interdistributary bays of the
modern delta of the Mississippi River
into a complex of marshy subdeltas. 16
Beaches on the present delta
shoreline are poorly developed and
appear transgressive in origin . On
the Canadian side, where the
beaches are somewhat better developed, the berms may reach three to
four feet in height and are colonized
with sumac and small trees. Our
borings reveal that the principal
constituents of these beaches are
coarse sand or fine gravel (- 1.5 phi)
separated by layers of sand and organic materials including rafted logs,
bulrush stems and other debris .
Coarse sands and fine gravels are
not evident, and storm berms seldom exceed two feet in elevation.
Characteristic vegetation of these
shoreline features are either sedge
marsh or a complex community of
grasses, thistles and other nonwoody species.
Within the interdistributary
marshes, especially on lower Dickinson and Harsens Islands, are ar-
14
cuate-shaped features resembling
beach ridges . Our borings through
one of these ridges revealed up to
10 feet of fine sand . The absence of
wash over deposits and organic sediments indicate that these features
may be regressive beaches and represent shorelines as delta accretion
took place.
A comparison between the eastern and western portions of the St.
Clair delta illustrates two other dis-
Figure 6. Chematogan Channel,
Cutting Through the Premodern
Surface, is Almost Abandoned. In
this Area, the Snow-Covered Natural Levees are Well Defined and Cultivated.
tinct differences. On the Canadian
side, Chenel Ecarte and Johnson
Channel are narrow, shallow distributaries which do not carry a significant portion of the volume of the
St. Clair River. Moreover, open interdistributary bays are few and are
colonized by marsh vegetation. Delta
extension has ceased and maximum
delta accretion is now occurring to
the west as evidenced by the active
digital distributaries of North, Middle and South Channels and Chenal
a bout Rond . In the past, Chematogan and Bassett channels were approximately 1500 feet in width, comparable to the modern distributaries,
but have been alluviated and colonized with aquatic plants as abandonment occurred (Figure 6).
In most deltas with large fluvial
systems, lateral migration of the delta
occurs because of the changes in
the course of the river upvalley. The
premodern lateral displacements of
the Mississippi River delta originated within the alluvial valley, several miles from the Gulf Coast. Such
a diversion process is evident in
some lake deltas as well. Several
older deltas of the Omo River, for
example, have been identified which
are related to the former position of
the river within its alluvial valley.17
However, the St. Clair delta has
no comparable alluvial valley and
delta migration has occurred from
east to west at the shoreline of Lake
St. Clair. As the Canadian distributaries degenerated, new distributar-
Premoder n De lta
Mod orn De lta
Bassett
H arsens
1,land
1,land
Walpole
1,land
- 20 -- ---9
10
11
12
Mile,
De lt aic Sed i ments
[J
COARSE SAND
~ ORG ANIC
EJ SILTY S AND
o
SAN DY CL AY
Figure 7. A Cross Section of the St. Clair Basin. Source: Bore Data Furnished
in Part by the U.S. Army Corps of Engineers.
15
ies were created on the western side
of the delta.
DELTA STRATIGRAPHY AND
GEOMORPHIC CHRONOLOGY
A series of borings, cores, and
exposures indicate that in cross section the St. Clair delta is a thin and
sandy deposit. An east-west cross
section reveals that above the shale
bedrock, lacustrine clays have been
deposited over a th in deposit of glacial till (Figure 7). The coarse delt aic deposits, having a maximum
thickness of 20 feet rest upon blue
lake clays.
The north-south cross section from
the apex of the delta into Lake St.
Clair illustrates the near-surface
stratigraphy (Figure 8). Topographi cally however, this cross section reveals two distinct levels, a modern
West
0
Clinton R.
Mich .
Son y
Si II
Harsens
Island
Sandy
Sill
and the equally obvious premodern
surface. The premodern surface,
standing about five feet above Lake
St. Clair, consists of coarse, oxidized
sand and is confined to the apex of
the delta complex. It has been dissected by long , sinuous channels
which have been alluviated . Occasionally during high lake levels these
channels have been reoccupied ,
particularly in areas such as Dickinson Island, where human interference has been minima l. As this
higher surface is topographically and
sedimentologically distinct, it is a
surface which was deposited during
a pre-existing higher lake level. The
modern delta with its finer sediment
(2 to 3.35 phi) is located at present
mean lake level and is represented
by the active crevasses and interdistributary marsh deposits.' 8
Dover Centre,
Island
Onto
Sandy
Sand
Si II ___________
East
Harsens
25
Sofl
Cloy
C loy
Se d imen ts
DELTAIC
LA CUSTRINE
DEPOS ITS
50
Salt
Cloy
I-
Soft
Cloy
GLACIA L TILL
75
w
100
Clayey
Grovel
BEDROCK
125
"-
150
"-
....
"-
Shale
.7Mi .
Figure 8. Stratigraphy of the St. Clair River Delta . Source : Data from t he U.S.
Army Corps of Engineers, W ightman, op. cit. , Footnote 3, p. 77, and Field
Borings.
16
750
600
300
150
12000
9000
Years Before
6000
3000
0
the Present
\
ALGONQUI N STAN LEY
EARLY
ERIE
EARL Y
ERIE
NIPISSING
ERIE
HURON
LAKE
STAGE
ERIE
Figure 9. Lake Levels and Lake Stages in the Huron and Erie Basins. Source:
Dorr and Eschman 1970 (Footnote 21).
Based on the chronology of the
proglacial Great Lakes, field data,
and available C14 data, the relative
geomorphological events of the St.
Clair delta may be determined (Figure 9). Since the retreat of the Late
Wisconsin ice, the outlets of the
Great Lakes, and hence lake levels
in the St. Clair basin, have oscillated
sufficiently to construct two deltas.
Compared to other proglacial Great
Lakes, Lake St. Clair was a less permanent feature as the lake bottom
was exposed to subaerial modification due to the fluctuating ice sheet
which determined the outlets to the
north and east.
One C14 date retrieved from the
upper portion of the lake clays, but
beneath the premodern delta, indi-
cates that both deltas are less than
7,300 ± 80 years old .19 Based upon
older proglacial Great Lakes chronology, the premodern delta may
have been deposited during the latter stage of Algonquin time .20 With
the subsequent retreat of ice during
the Lake Stanley low-water stage,
an outlet for the Lake Huron basin
to the St. Lawrence was created via
North Bay, Ontario. Quite possibly
during this stage the premodern
sands of the St. Clair delta may have
been exposed, oxidized, and dissected. Following the Lake Stanley
low-water stage, Lake Huron once
again rose to the Nipissing stage
and drained into the lower Great
Lakes via the St. Clair River.
As determined by the more re17
cent chronology, the premodern delta
may have been deposited during
Nipissing time some 3,500 to 5,000
years before the present and not
during Algonquin time. 21 The premodern delta was deposited during
a higher than present lake level and
the subsurface sediments range in
age from 7,300 to 9,300 years before
the present. It is suggested that following the Lake Stanley stage (i.e.,
Nipissing stage), the St. Clair River
once again flowed south into Lake
St. Clair and the premodern delta
was deposited at an elevation slightly
higher than the modern delta (Table
1).
On many coasts, evidence for
lower than present sea levels is determined by depositional surfaces
which dip beneath younger sediments. 22 Had the premodern delta
been deposited during the Algonquin stage and the subsequent early
Lake Stanley stage, evidence of that
event as a depositional surface be-
neath the modern delta or a paleosol should be apparent. Numerous
borings by us and others suggest
that the premodern delta does not
plunge beneath the modern sediment. Since the stratigraphy implies
that lake levels were lower than
present only once, a Nipissing stage
is favored for the deposition of the
premodern delta. Organic deposits,
commonly composed of large wood
fragments (probably red ash) lie beneath both deltas. Assuming that
the peat accumulated from organic
growth above the water table, it
probably was deposited during a
low-water period prior to the Nipissing stage (Lake Stanley?).
Following the Lake Nipissing high
level, Lakes St. Clair and Huron fell
to their present levels. The premodern channels were sl ig htly entrenched and the premodern surface
oxidized during the last 3,500 years.
Towards the apex of the premodern
delta, beyond the areas of flooding,
TABLE 1
Interpretation of the Events Related to the Origin of the St. Clair
River Delta
Approximate
Dates B.P.
lake Stage
3,500 to Present
Modern Lake St.
Clair and Algoma
Phase
3,500 to 5,000
Lake Nipissing
5,000 to 10,500
Lake Stanley
10,500 to 12,500
18
Lake Algonqu in and
Post-Algonquin
Phases
Event
Flow of Lake Huron continues southward .
Deposition of modern St. Clair River
delta and dissection of premodern
surface.
Deposition of premodern delta
approximately 5 feet above present
mean lake level.
Lake St. Clair basin exposed ; outlet for
upper Great Lakes via North Bay,
Ontario.
Valders Maximum .
a mix of hardwoods has colonized
the oxidized soils and evidence of
drowning of a pre-Lake Stanley delta
by Nipissing high water levels is
lacking. With the fall to the approximate present lake level, the modern
delta was deposited in Lake St. Clair.
COMPARISON WITH MARINE
DELTAS
A unique aspect of a delta's geomorphology is related to its changing base levels. The base level of all
marine deltas appears to have been
eustatically stable over the past
5,000 years. In the Mississippi delta,
because of the stable sea level, the
ancestral streams deposited a series
of delta lobes along the Louisiana
coast. In the St. Clair changing base
levels have produced two distinct
deltas at different levels, the premodern and the modern. Examples
of this base level change are apparently rare. 23
Marine deltas are often characterized by subsidence due to sediment
loading. Geosynclinal downwarping
and sediment compaction in response to sediment accumulation in
the Mississippi River delta has allowed up to 400 feet of deltaic deposits to accumulate since the termination of the Lake Wisconsin
glacial age. 24 With continued sedimentation and subsidence, the shifting delta lobes overlapped, burying
older deltaic environments. Therefore, the traditional sedimentological units, top-set, fore-set, and bottom-set beds, identified on the
margins of Lake Bonneville by Gilbert, do not occur in the Mississippi
River delta complex. 25
The bore data reveal that the St.
Clair River delta is stable. Sediments
accumulating in the delta are not of
sufficient thickness to allow any significant downwarping to occur. Our
.borings on several beaches suggest
that the base of these depositional
features is at approximately low
water datum. Apparently the beaches
have not subsided like the cheniers
have on the flanks of the Mississippi
River delta.
Isostatic rebound in the St. Clair
basin, due to the waning of Wisconsin ice following the Valders maximum some 10,500 to 12,500 years
ago, has been minimal. Pertinent
zero isobases since the Valders
maximum are the Algonquin and
Nipissing hinge lines which are oriented east-west and located in the
central portion of Lake Huron.
Therefore, crustal displacement due
to regional glacial rebound or localized sedimentation does not appear
to have directly influenced the vertical and horizontal morphology of
the St. Clair River delta. The St. Clair
River delta has, in fact, extended itself across an essentially rigid platform.
Although structural stability and
minimum subsidence characterize
the St. Clair delta, significant changes
in the level of Lake St. Clair in the
past few millenia have contributed
to the morphology of the delta.
Based upon a structural framework,
deltas may be deposited in one of
three geologic environments: a subsiding area, a stable area, or an elevating area. 26 The Mississippi River
delta with its thick accumulation of
recent sediments, is a classic example of a subsiding delta. Although the Lake St. Clair basin is
19
geologically stable, the effect of a
lower lake level on the delta complex is similar to elevating the land.
Since base level in Lake St. Clair has
dropped in the last 4,000 years, the
focus of deposition has shifted lakeward creating the modern St. Clair
River delta.
The configuration of deltas is related to offshore slope, relative wave
power in the nearshore zone, and
riverine influence.27 A delta such as
the Mississippi with its digital distributaries and marshy embayments,
is dominated by its river since its
offshore slope is flat to convex and
the nearshore wave power is low.
Although long-term wave data have
not been recorded for Lake St. Clair,
wave energy must be considered to
be low since the maximum fetch for
wave generation for the delta is only
22 miles. The subaqueous delta front
is shallow and concave, causing
waves generated in the shallow lake
to attenuate lakeward of the delta. 2B
Also, marshes have become established on exposed offshore areas
between Johnson Bay and the minus six-foot contour, suggesting that
low wave energy conditions prevail.
Although there may be an occasional dominance of marine processes as evidenced by the presence of transgressive beaches, it
must be concluded that the geometry of the St. Clair delta, like that of
the Mississippi, is principally dictated by its river.
LANDFORM-VEGETATION
RELATIONSHIPS
In deltas, vegetation zonation is
conspicuous, reflecting subtle variations in relief and edaphic condi-
20
tions. Elements such as substrate
composition, salinity, water depth,
and protection from wave action are
important variables determining plant
distributions. 29 The vegetation patterns, in turn, can be used to identify deltaic landforms or depositional environments. 3D In the St. Clair
delta, where wave energies are low
and calcareous soils prevail, water
depth or depth to the groundwater
table appears to be the most significant variable. Unlike plant communities in marine deltas, the vegetation associations periodically shift
landward or lakeward depending
upon short-term lake-level conditions.
The vegetation of the St. Clair
delta occurs, in broad, arcuate zones
which extend from the apex near
Algonac south into Lake St. Clair
(Figure 10). Five major plant associations have been identified using
aerial photography and verified in
the field . Although significant cultural modifications such as residential development and clearing of land
for cultivation have occurred on the
delta, sufficient plant communities
do remain and may be used to reconstruct the natural vegetation
cover.
Landform-vegetation relationships observed in the delta are indicated in Table 2. The vegetation
type on high ground consists of
stands of oak-ash hardwoods distributed over premodern deltaic
remnants of Dickinson, Harsens,
Walpole, Squirrel and Ste. Anne Islands which range in elevation between three and ten feet. Once extensive, these hardwood stands are
now discontinuous as a result of
jNCHOR
Bj Y
o,
2,
Mile s
+
~
OAK- ASH HARDWOOD
~
DOGWOOD MEADOW
8
SEDGE MARSH
~
0.......
CATTAIL MARSH
D
0
~
BULRUSH MARSH
DREDGED DISPOSAL
CULTIVATED LAND
. 2° 30'
LAKE
URBAN
Figure 10_ Natural Vegetation and Land Cover of the St Clair River Delta
Based on 1972 Data_
21
TABLE 2
Landform-Vegetation Relationships in the St. Clair River Delta
Landform
Associated Vegetation Type
Premodern Delta
Transition Zone
Modern Deltaic Surface
Inactive Beaches
Actively Eroding Shorelines
Natural Levees
Interdistributary Bays
Abandoned Channels
Oak-Ash Hardwoods
Dogwood Meadow and Aspen Stands
clearing for agricultural use in the
late 1800's and early 1900'S.31 Based
on the size and abundance, the major species are swamp white oak
(Quercus bie%r) , red ash (Fraxinus
pennsy/vanica), and shagbark hickory (Carya ovata) . Except where
abandoned channels have dissected
the premodern surface, the soils are
Sedge Marsh and Dogwood Meadow
Sedge Marsh
Sedge Marsh
Cattail and Bu lrush Marshes
Bulrush and Aquatic Communities
comprised of oxidized, well-drained
sands with pH values ranging between 7.0 and 8.0. 32
Lakeward of the hardwoods is a
complex of communities referred to
as the dogwood meadow (Figure
11). Geomorphologically, this zone
occupies the broad contact between
the premodern and modern delta
Figure 11. Well-Defined Contact Between the Dogwood Meadow in the Foreground and the Transition Zone now Colonized by Aspens and Hardwoods.
Because of Recent Cultivation, Few Dogwood are Present in this Meadow.
22
and is referred to as the "Transition
Zone." Abundant species, in terms
of area covered , are bluejoint grass
(Calamagrostis canadensis), red
dogwood (Comus stolonifera) , and
gray dogwood (C. racemosa) . Areas
within this vegetation type which
were previously cultivated or mowed
for hay are now being invaded by
quaking aspen (Populus tremu la ides) or reverting to dogwood
meadow . In Ontario, because of
continued expansion of commercial
cultivation, the dogwood meadow is
sporadically distributed.
A linear vegetation zone located
between the dogwood meadow and
the cattail marsh is the sedge marsh.
This community is dominated by the
sedge Carex stricta var. strictior
wh ich forms tussocks in response to
a fluctuating surface water table .
Bluejoint grass grows commensally
in the tussocks with the sedge. The
sedge marsh is distributed along
river channels on low natural levees, on actively eroding shorelines,
as well as on relict shorelines now
stranded in the cattail marsh . The
preferred substrate appears to be
calcareous sands and silts rather than
peats and clays. Because natural
levees of the defunct distributary
channels , such as Chematogan
Channel, are barely discernible, they
can be read ily identified on the basis of parallel strips of sedge marsh.
Similarly, relict beaches identified in
the cattail marsh can be mapped
because of their association with
sedges.
Where permanent inundation occurs and water depths exceed 10 to
12 inches, the sedges are replaced
by a cattail marsh (mostly Typha
glauca) . An ecotone of mixed sedge
and cattail occurs along the edges
where water depths range from six
to ten inches. Growing seven to ten
feet in height, the hybrid cattail (T.
glauca) thrives in dense colonies and
shades out the tussock sedges. The
lower portions of Dickinson, Harsens and Walpole Islands, which
represent the modern deltaic surface, are colonized by cattail marsh.
Water depths within this marsh average 0.5 to 3.0 feet and the preferred substrate consists of peats
and organic-rich clays. Scattered
shallow-water openings and muskrat lodges are common in this
marsh and are useful for aerial photo
interpretation of cattail colonies.
Where water depths exceed one
to two feet and the substrate sediments are more sandy, the cattails
appear to be less competitive and
may be replaced by hard-stem bulrush (Scirpus acutus). Although only
small colonies of hard-stem bulrush
occur in the delta, they are fairly
widespread in St. Johns Marsh, in
the partially silted, abandoned channels, and in open-water areas on
Dickinson Island. On exposed sand
shoals in Muscamoot Bay and Anchor Bay colonies of this bulrush are
also common.
Several other plant communities
are conspicuous, though of insufficient density to map in detail. Thick
colonies of reed grass (Phragmites
australis), usually less than an acre
in extent, occupy the distributary
shoulders along South, Middle, and
North Channels. In the abandoned
river channels, which appear as partially-filled , elongate lakes, emergents such as yellow pond lily (Nu-
23
phar sp.), hard stem bulrush, and
water smartweed (Polygonum amphibium) are prevalent.
The landform-vegetation relationships provide important clues to the
geomorphic history of the delta. In
general, the premodern surface can
be identified and mapped by the
presence of upland hardwood vegetation and numerous old channels.
In contrast, the extent of the modern
surf ace is indicated by the cattail
marsh.
Both the upland hardwood vegetation and ancient channels are clues
to base level change. With the exception of natural levee areas, upland vegetation normally does not
occur in deltaic environments. The
abandoned channels, clearly visible
on aerial photographs, are en-
trenched into the premodern surface and disappear in the marshlands of the modern surface (Figure
12). One abandoned channel, north
of Goose Lake, trends westward
across the premodern surface of the
Canadian side of the delta. Such a
feature suggests that in the past the
base level of the St. Clair River
dropped as much as 10 feet, causing
entrenchment of the distributaries.
At the same time, the delta shifted
westward as flow ceased on the Canadian side allowing the ancestral
channel to cross the upland surface
without capture.
This interpret:ation is corroborated by the shoreline features isolated in the cattail marsh, especially
on Dickinson and Harsens Islands.
As these features are regressive
Figure 12. An Abandoned Channel on the Premodern Surface of Harsens
Island Colonized by a Variety of Emergent Aquatics. Paralleling the Channel
Margins is a Sedge Marsh.
24
NE.
SW.
July 1972
Hart_"1 hland
Mut •• ool Sa,
ASPEN
.,
THREE
SEDGE
SQUARE
-,
BULRUSH
-,
'00
' 00
600
800
1000
3100
'600
. 000
fEET
October 197"
.,
~
ASPf.N
BULRUSH
CAnAll
°
-,
-,
'00
'00
600
000
1000
'600
3100
' 000
fEET
\I(
.10
Veo e 'el;..._,,.u.l.
Figure 13. A Comparison of Vegetation Changes on Lower Harsens Island
East of Middle Channel. Although July, 1972, Lake Level was only 0.3 Feet
Higher than the October, 1974, Level Significant Changes are Evident.
beaches, they may represent shorelines as the base level dropped
slightly and the western portion of
the delta underwent accretion. Partial oxidation of the fine sands, which
lie beneath the cattail marsh, to a
depth of two to three feet indicate
the maximum extent of base level
lowering .
In addition to long-term base level
changes, modern or short-term lake
level changes are a significant cause
of vegetation shifting in the delta as
well as on other Great Lakes' shoreIines.33 Over the years the level of
Lake St. Clair rises and falls sufficiently enough to cause a displacement of the vegetative zones. Traverses taken in 1972 and 1974 reveal
the vegetation shifts which have
taken place as communities adjusted to higher water levels (Figure
13). As expected, the most extensive
changes are evident in the modern
delta. Nearly continuous during lowwater periods, large tracts of cattail
marsh in St. Johns Marsh, and along
lower Dickinson, Harsens, and Walpole Islands have reverted to open
water. Also, in response to increased water depths, a landward
shift of the sedge marsh has occurred. The cattail marsh invaded
the sedge marsh which, in turn colonized the dogwood.
A DELTA PERSPECTIVE
Because of its bird-foot shape, it
may be assumed that the processes
governing the formation of the St.
Clair delta are similar to marine deltas of like morphology. A study of
the morphology of marine deltas reveals that river regime, coastal processes, structural behavior, and climatic factors including vegetation,
25
control delta formation. 34 A morphological comparison of the St. Clair
and Mississippi River deltas has revealed that factors such as flow regime and structural behavior of the
depositional basin are indeed different. 35 The only similarity between
the two deltas is the offshore profile
which partially controls the marine
wave energy (Table 3) . Delta morphology is basically a function of
the relative influence of river depositional processes versus coastal
processes and submarine topography.36 Because of the short fetch,
wave energies of many lake environments are low, resulting in prograding deltas with a digital shape.
Low wave energy combined with
depositional basin stability and base
level changes characterize lake del-
tas such as the St. Clair delta. However, even as a lake delta, the St.
Clair is atypical in that its river is not
a true fluvial system. As such, the
delta lacks the seasonal flow variation, an alluvial valley and other
common deltaic landforms such as
well-developed natural levees. The
wide distributaries and distributary
shoulders created as channels attempt to meander while eroding into
proglacial clays are also unusual.
Because dredging operations remove much of the sediment the St.
Clair River is transporting, little delta
accretion has occurred during the
past century. Thus the delta appears
to be in quasi equilibrium, with neither depositional nor erosional processes dominating. Since the St. Clair
delta comprises the largest wetland
TABLE 3
Factors Influencing Lake and Marine Delta Morphology
Factors
Geomorphic :
Characteristics
Base level
Flow Reg ime
Channel Diversion
Structural Behavior of
Basin of Deposition
Dom inant Sed iment
Size
Relative Rate of
Sed imentation
St. Clair Delta
Long-and-short-term
variations
Seasonally constant
Downstream (spring ice
jams)
Stable
Mississippi Delta
Stable
Fine to coarse sand
Seasonally variable
Within alluvial valley
(spring floods)
Sediment compaction
and significant
subsidence
Clay to silt
Slow
Rapid
Marine:
Relative Wave Energy
Offshore Profile
Low
Flat and gently sloping
Low
Flat and gently sloping
Vegetative :
Vegetation
Morphology
Deciduous trees to
freshwater marsh
Control of Vegetation
Distribution
Short-term lake level
changes
Predominantly fresh to
brackish to salt
ma rsh
Salinity, substrate
composition and
tidal range
26
environm ent in t he Great Lakes and
is pa rt of an important navigat ional
link, these geomo rph ic considera tions may provide useful input for
a management strategy. Clea rl y
many of the process-response concepts applicab le to marine deltas
can not be app lied to t he St. Cla ir
delta.
Although the St. Cla ir delta does
not ill ust rate dynamic Lat e-Recent
changes in geomorphology as do
ma ri ne deltas, its vegetation does.
Shifts in vegetation zonation every
few years of other lake deltas has
not been documented in detail and
therefore cannot be evaluated in a
broader setting as t he geomorphology can. Significant losses in coastal
marshland due to flood ing and severe erosion problems in the Great
Lakes do suggest there is an urgent
need for such studies. Only then can
current problems such as wetland
management, be clearly identified
and placed in proper perspective.
REFERENCES AND NOTES
1. G. K. Gllben, (1890). Lake Bonneville, (U .S. Geological
Survey Monograph, No. I, 1890). 438 pp.
2. L. J. Cole. (1903), "The Delta of the St. Clair River." Geological Survey of Michigan, 19: 1- 28.
3. R. W. Wightman, (1961), The St. Clair Delta, Unpublished
M.A. Thesis (London : University of Western Ontario,
Depanment of Geography), 140 pp.
4. J. M. Pezzetta, (1968), The St. Clair River Delta, Unpublished Ph.D. Dissenation (Ann Arbor, University of Michigan, Depanment of Geology), 193 pp; H. Mandelbaum,
1969, " Analysis of Sediment Cores from Big Muscamoot
and Goose Bay in the St. Clair River Delta," Proceedings
of the International Association of Great Lakes Research,
12th Conference, 271-299.
5, See for example U.S. Army Corps of Engineers, (1973).
Proposed Diked Disposal Area on Dickinson Island, St.
Clair County, Michigan (Detroit : District Engineers). 235
pp.
6. J. L. Hough, (1958), Geology of the Great Lakes, (Urbana: University of Illinois Press), 313 pp.
7. National Oceanic and Atmospheric Administration, (1975),
Hydrograph of Monthly Mean Levels of the Great Lakes
(Lak9 Survey Center, Detroit).
8. I. M. Korkigian, (1963). " Channel Changes in the SI. Clair
River Since 1933," Journal of the Waterways and Harbor
Division, American Society of Civil Engineers, 89 : 1-14.
9. L. D. Kirshner and F. A . Blust, (1965), " Compensation for
Navigation Improvements in St. Clair-Detroit River System," Miscellaneous Paper 65-' (Depanment of the Army,
Detroit, Lake Survey District), p. 5.
10. U.S. Army Corps of Engineers (1968). 1968 Flow Distribution in the St. Clair River (Mimeographed. Detroit District), 20 pp.
11 . Korkigian, op. cit.. footnote 6, pp. 10-11 .
12. S. C. Sachdev and R. Furlong, (1973). " Sedimentation in
the SI. Clair River Delta, Muscamoot Bay Area, Michigan ," North -Central Section, (Geological Society of
America), 5: 346.
13. Pezzetta, op. cit., footnote 4, p. 1.
14. C. N. Raphael. E. Jaworski and others, (1974), Future
Dredg ing Quantities in the Great Lakes, (Corvallis, U.S.
Environmental Protection Agency). pp. 55-56; Because
of anificial sedimentation, dredging volumes can seldom be equated to natural stream volumes. See pp.
191-205 of this reference for funher discussion .
15. K. W. Butzer, (1971). " Recent History of an Ethiopian
Delta," Research Paper No. 136 (Chicago, University of
Chicago Press), pp. 44-49.
16. J. M. Coleman and S. M. Gagliano, (1964). " Cyclic Sedimentation in the M ississippi River Deltaic Plain," Transactions of the Gulf Coast Association , 4 : 67-80.
17. Butzer, op. cit. , footnote 15, pp. 69-71 .
18. Penetta, op. cit., footnote 4, p. 52 ; Mandelbaum, op. cit.,
footnote 4, p. 295.
19. Wightman, op. cit., footnote 3, Appendix. Addi tional C14
Dates have been obtained by Mandelbaum. op. cit.. footnote 4, p. 295. The dated materials range in age from
6100 ± 80 to 9300 ± 200 years. These organic materials
do not appear to be in situ and they have not been included in our interpretation. However. even if the laner
dates were used they would not detract from our argument. Pezzetta, op. cit., footnote 4, p. 2 also has ra·
diogenic data that reveal that the minimum age of the
delta sediments is 4,300 years before the present.
20. R. F. Flint, (1964), Glacial and Pleistocene Geology, Founh
Printing (New York : John Wiley and Sons), p. 347.
21 . J. A. Dorr and D. F. Eschman, Geology of Michigan (Ann
Arbor: University of Michigan Press, 1970), p. 167; R. F.
Flint, (1971). Glacial and Quaternary Geology (New York:
John Wiley and Sons), pp. 56&-567.
22. R. J. Russell. (1964), " Techniques in Eustasy Study,"
Zeitschrih fiir Geomorphologie, 8: 25-42 ; for a specific
study see R. J. Shelemon (1971). " The Quaternary Deltaic and Channel System in the Central Great Valley.
California," Annals of the Associa t ion of American
Geographers, 61 : 427-440.
23. J. P. Morgan, (1970), " Deltas-A Resume." Journal of
Geological Education, 18: p. 111 .
24. J. P. Morgan, (1970), " Depositional Processes and Products in the Deltaic Environment," in J . P. Morgan (Ed.),
Deltaic Sedimenta tion: Modern and Ancient (Tulsa: So-
27
ciely of Economic Paleontologists and Mineralogists), p.
35.
25. Gilben, op. cil., footnote 1, pp. 6&-70.
26. Morgan, op. cil., footnote 27, pp. 1"-113.
31 . W. l. Jenks, (1912), St. Clair County, Michigan (Lewis
Publishing Company, Chicago), 2 vols., 1389 pp.
32. G. R. Landtiser, (1974), Soil Survey of 51. Clair County,
Michigan (U.S. Depanment of Ag riculture, Soil Conser·
vation Service, Washington D.C.), Map Sheets 59-62.
27. l. D. Wright and J. M. Coleman, (1973), " Variations in
Morphology of Major River Deltas as Functions of Ocean
Wave and River Discharge Regimes." Bulletin of the
Am erican Association of Petroleum Geologists, 57:
37C>-398.
33. E. Jaworski and C. N. Rapha el, (1976), " Modification and
Management Alternatives of Coastal Wetlands in South·
eastern Michigan," Michigan Academican, 8 : 303-318.
28. U.S. Army Corps of Engineers, Lake St. Clair (1971) ,
(Detroit: Lake Survey District), Chan Number 42.
35. E. Jaworski and C. N. Raphael, (1973). " A Morphological
Comparison of the St. Clair and Mississippi River Del·
tas," Proceedings of the Association of American Geog·
raphers, 5: 121-126.
29. R. C. West, (1966), " The Natural Vegetation of the Ta·
bascan Lowland, Mexico ," Revist. Geografica, 64 :
108-122.
30. J. H. Vann , (1959), " Landform·Vegetation Relationships
in the Atrato Delta," Annals of the Association of Amer·
ican Geographers, 49: 34&-360.
28
34. Morgan, op. cit., footnote 28, pp. 31-35.
36. Wright and Coleman, op. cil. , footnote 32, pp. 37C>-398;
J. M. Coleman, (1976), Deltas : Processes of Deposition
and Models for Exploration (Conti nuing Education Pub·
lication Company, Inc., Champaign), 102 pp.