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followed by rapid profile adjustment (PA) or moderate to high erosion (ME to
HE).



Table 10 .

St. Joseph Harbor, Lake Michigan, Summary of Profile Data (Beach Fills, Profile

Change, and Wave Energy)



Fia


profile influeneed by beach fill


LE


kM erosion


LD


kwdepostion




firet profile sufv«v


ME


medium erosion


MD


medium deposition


NC


no change between profiles


HE


high erosion


HD


high deposrtion


PA


pfT3file adjustment (net cfiange is zero)











Sumy
Date


Rg


R9 RSA


RIO


RIOA


Proni€
Rll


R12


RU


RI7


R20


R22


R23


Wivc
Entrsy


W.U Above
aCLOtS)


Volume

Fin


Unflh
FlU

(■)


34>l«y-91


H:-'^'r-; i






46


S22








0.6






1*Jin-91














ME - . - -


-


0.7






14.Aug'91














NC




mHD






XHD


PA












0.7






27-^19-91














HE




ME






ME


NC








ME




0.55






3IMii9«1












ta«).91


1^^^^^^^^^^^^^^^^^^^^^






74


822




NC


FILL PA




Fia
















323


0.35






ISOcl-91














FILL - - - .




0.3






15-0*91














HO


ME xHE


FILL


LO


mHE


NC













3269


03






190K-91














NC



HE





PA


NC


LE













12176


0.5






IS.Mv-92














ME


L£ X>HE


MD


NC


FILL


NC


nHO








IHD


,1762


0.55






U-M«»-92












22-M<y-92


i' 1






31


SZ2




LE


Ra FILL


PA


UD


HE


MD


UE








^^


794


0.55






1»>luv92


















PA




NC












-




0.6






1&0UV9:
















XXXHE XXSHE






NC


WOHO




xxHD


NC


lOcHO


^E


S18


0.5






ZmiH-92
















IHE mHE


xnHE


PA LD


WHE


OHE


MD


PA


XXHE




PA


6124


07






t-Urt-33












la-jiD-gs


1 1






2


807




PA


LE


LE




NC




MO


MD


xHD


WXHE


NC


110


0.S5






n-Ajg-gs












7-S«()-93


^S^






1527


30



Note: Wave energy (m^s) is H^ * T (wave height squared x wave period) provides indication of relative wave energy.



Chapter 5 Interpretation of Results - A Descriptive Model of Coastal Morphodynamics



85



86



The transition area of Sector E from the Waterworks revetment to south of
Line R12 is distinguished by an ephemeral beach feature (i.e., a beach subject
to significant fluctuation in size). Table 10 indicates that in two of the three
years of the monitoring program, this sector experienced deposition towards
early fall (as a result of the beachfiU moving south) and erosion in late fall as
the deposit was eroded by subsequent storms. Results of the model tests
indicate that this sector is subject to the highest alongshore transport rates for
the study area shoreline. Numerical model results also indicate that this area is
subject to ongoing downcutting, particularly offshore of the beach deposit. As
noted in the section entitled "1945/6 to 1964/5," the Waterworks revetment
probably helps to impound sediment and maintain the beach immediately south
of the revetment. Numerical model tests also revealed that the coarse-grained
beachfill derived from upland sources is much more effective at protecting the
glacial till under the beach in this sector.

Although downcutting of the nearshore profile in Sectors E and F may
eventually diminish owing to the deeper water that has developed offshore of
the shore protection, the numerical model results suggest it is still ongoing, as
did the 1991 to 1995 lake bed comparison (see Figure 32). Model results also
indicate that there may be ongoing deposition of sand in this sector, since only
about 50 percent of the coarse sediment transported into this sector from the
north is predicted to be transported southwards beyond Line R23. It was seen
that during the 1965 to 1991 period with higher annual beach nourishment
volumes, the rates of nearshore profile lowering in this sector were signifi-
cantly reduced (see Table 7). Table 10 shows that this sector typically
receives sediment sometime in mid to late fall. Based on the predicted reduc-
tion in potential transport rates of coarse sediment between Line R12 and Line
R23, we estimate that about half of the 600,000 m^ of coarse fill that has been
placed since the beginning of the Section 1 1 1 nourishment program has been
deposited in this sector. With this assumption, and assuming the deposition
occurs over a 500-m-wide band of the shore extending out to the 6-m contour,
the average gain in thickness of sand cover would be 0.067 m since 1976.
Based on the findings of lake bed surface comparisons and the results of the
numerical model tests, this annual deposition rate of 0.0035 m/year derived
from the beach nourishment is at least balanced, and probably outpaced by the
ongoing downcutting of the underlying glacial till. This was certainly the case
during the 1991 to 1995 period, with lower annual beach nourishment
volumes.

In order to raise the profiles to the historic lake bed levels (i.e., to allow
unimpeded sediment transport to the south), and assuming about half of the
traditional coarse beach nourishment volume (i.e., about 20,000 m^/year since
1986) is deposited in this sector and that downcutting can be arrested in the
near future, almost 8 million m^ of sediment would be required over the next
400 years at the current rate of nourishment. The numerical model tests indi-
cated that the 2-mm grain size sediment was no more effective than the
0.2-mm sediment in protecting the underlying till from exposure and down-
cutting in this sector.

Chapter 5 Interpretation of Results - A Descriptive Model of Coastal Morphodynamics



The most southerly sector, Sector G, and the unprotected shoreUne further
to the south received about half of the historic net alongshore sediment supply
rate of coarse sediment. This is because the deep water offshore of Sector D
acts as a sink for about 50 percent of the coarse beachfill sediment. Therefore,
it is likely that the shoreline of Sector G, and particularly the shore to the
south of this sector, are suffering due to a depletion of the historic sand cover
with the associated increased exposure of the underlying till and increased
downcutting and shoreline recession rates. The loss of the coarse fraction
results in greater erosion close to shore (i.e., where slopes are steeper and only
the coarse-grain-size fractions remain relatively stable under most conditions).
The most recent lake bed comparison (1991 to 1995) revealed that the lower-
ing had in fact increased dramatically in Sector G compared to earlier periods.



Comments on the Effectiveness of the Beach
Nourishment Program



The fillet beach of Sector C would probably remain stable without beach
nourishment from the Section 111 program. At present, perhaps as much as
50 percent of the sand placed in the feeder beach area (particularly for the
dredged finer sediment) ends up back in the navigation channel from where it
was originally removed (and will be removed again).

There must be a more cost-effective approach to maintaining the position of
the shoreline in Sector D than beach renourishment. An alternative approach
may also be more environmentally acceptable and less disruptive to the local
community (i.e., not requiring the annual trucking operation for the placement
of coarse sand and gravel).

The primary local beneficiary of the ongoing nourishment is the transitional
part of Sector E. Here, too, there may be more cost-effective means of pro-
tecting this section of shoreline. The coarse sediment is much more effective
than the fine in protecting the till underneath the beach in this sector. The
coarse sediment fulfills a role (which would have been present historically) in
protecting the underlying till from downcutting that the fine sediment cannot
(i.e., over the steeper nearshore slopes).

Sector E has been a sink, possibly for up to 50 percent of the coarse sedi-
ment placed in the feeder beach area. However, the effectiveness of this
sediment (whether the coarse grain or fine grain type) in counteracting the
ongoing downcutting (either presently or in the future) is questionable. There
may be more cost-effective means of protecting the toe of the existing struc-
tures. It is unlikely that the placement of the 8 million m^ of beach nourish-
ment required to completely fill the depression that has developed over time is
justifiable.



Chapter 5 Interpretation of Results - A Descriptive Model of Coastal Morphodynamics



87



During the period from 1986 to 1995, Sector G and the area to the south
received perhaps 50 percent of the coarse sediment eroded from the feeder
beach. Therefore, this sector and the shoreline to the south experience a
deficit compared to the historic sediment supply. This situation, combined
with the depleted supply during the years prior to 1976, must have resulted in
decreased sediment cover in this area and may have caused an increase in
downcutting and shoreline recession. Comparison of the 1991 and 1995 lake
bed bathymetries indicates the problem of accelerated offshore lowering and
the related shoreline recession has extended south of Sector G.

It would be much more effective to place the entire annual allotment of
beach nourishment (or at least the trucked coarse sediment) south of Lines R22
or R23 where it would be 100 percent effective in supplying the downdrift
shores. The erosion problems in the study area could be addressed with site-
specific solutions. With this action, the implementation of further shoreline
structures to the south of Line 22, to counteract the increased erosion, may be
avoided.



Recommendations for Future Monitoring



The following monitoring activities should be continued to assess the effective-
ness of modifications to the beach nourishment program.



Aerial photos should be continued to monitor the level of shoreline pro-
tection in and south of Sectors F and G.



Aerial photos should be regularly analyzed to monitor recession rates in
and south of Sections F and G to update the MDNR data.

Lines R12 to R23 and new lines further to the south should be moni-
tored regularly to improve understanding of the lake bed changes in
these areas.

A complete survey of the lake bed, both north and south of the harbor
jetties, should be completed 5 to 10 years after the 1995 SHOALS
survey, or after significant modification to the beach nourishment
program.



88



Chapter 5 Interpretation of Results - A Descriptive Model of Coastal Morphodynamics



6 Beach Nourishment Design
Guidelines



Based on the findings of this investigation and the knowledge of cohesive
shores that has developed since the early 1980's, some general design
guidelines are presented for the specific circumstances of SL Joseph, and for
some general categories of cohesive shore situations.



Recommendations for St. Joseph

Lowering of the lake bed offshore of the MDOT and C&O revetment (i.e.,
Sector E in Figure 34) is a result of both the interruption of alongshore
transport (particularly prior to the initiation of the Section 1 1 1 program) and
the stabilization of the shoreline position related to the construction of the
revetment.

The present beach nourishment program does not appear to provide any
significant benefit to the stability of the revetment along the Sector E shoreline
or to the lake bed offshore of the revetment. This is despite the fact that
perhaps 50 percent of the beachfiU sediment is deposited permanently on the
lake bed in this sector, and volume losses dropped to less than one fifth their
former 20-year average during the 30 years after nourishment was initiated.

Beach nourishment is definitely effective at maintaining a stable shoreline
position in Sector D. The coarse grain sediment is an essential component
which protects the tiU under the upper beach from downcutting during storms.
Fine-grain nourishment on its own (i.e., from dredging alone) is, however,
insufficient to protect the underlying till from exposure and downcutting.

Placement of unrestricted beachfdl (i.e., without any substantial retaining
structures such as headlands) is probably not a cost-effective means of main-
taining an average stable shoreline position. A solution to retaining a
permanent beach at this location should be sought through the use of rock
headlands or breakwaters. It may be argued that this is not the intention of the
Section 1 1 1 program; however, it must be recognized that this has been the



Chapter 6 Beach Nourishment Design Guidelines



89



90



result of and would continue to be the result of an unmodified nourishment
program.

The greatest flaw in the current nourishment program is that the area where
a supply of sediment is most urgently required is only receiving 50 percent or
less of the historic supply rate of coarse sediment This seems to have
accelerated recession rates for the shoreline south of the study area (i.e.,
Sectors G and southward 1991 - 1995). These erosion pressures result in
construction of more shoreline protection by property owners. In the long
term, these actions only further aggravate the problem by further reducing the
supply rate (by eliminating the input of sediment from shoreline erosion and
by impeding alongshore transport as deep water develops offshore of the struc-
tures).

The authors recommend that beach nourishment be placed downdrift of
Line R22 so that 100 percent of the fill reaches the area where it is required
(i.e., versus the current situation where perhaps 50 percent or less of the coarse
beach nourishment is deposited in Sector E without any apparent benefits).
The nourishment should consist of both fine (dredged) and coarse grain
components. By moving the feeder beach to the south, the sedimentation rate
experienced in the navigation channel should be significantly reduced. As a
result, maintenance dredging costs may be reduced if less ft-equent channel
dredging is needed.



General Recommendation for Beach Nourishment
on Cohesive Shores Downdrift of Harbor
Structures

It must be recognized that cohesive shores have very different erosion
characteristics from sandy shores and this has a significant impact on the
downdrift nourishment requirements. In addition, there are varying degrees of
cohesive shores (related to the extent and role of the overiying sand cover),
which also have an important influence on the nourishment requirements.

Furthermore, effective downdrift nourishment requirements must be
determined in light of changes to the lake bed that may have occurred as a
result of the presence of the harbor structures prior to the initiation of a
nourishment program. This is not necessarily the case for sandy shores down-
drift of harbor structiu"es.

Beach nourishment guidelines for the two extremes of cohesive shore
conditions (with respect to extent of historic, predevelopment sand cover) are
discussed here. A final special condition is also considered.

In some cases, sections of cohesive shore on the Great Lakes (and else-
where) will feature only a "limited" sand cover. As a possible defining
variable, the sand cover between the 4-m depth contour and the bluff would

Chapter 6 Beach Nourishment Design Guidelines



•7

have a volume of less than 100 m /m in these cases. Under these conditions,
the underlying glacial till is either only thinly covered (i.e., with beach and bar
thickness of less than 1 m) or entirely exposed. In other words, the tiU is
frequently exposed over the entire profile to conditions of active downcutting.
In these situations, it is not clear that the impoundment of sand in an updrift
fdlet beach, and the deprivation of this sand from the downdrift beaches and
lake bed wiU have any measurable impact on the rate of lake bed downcutting
and the associated rate of shoreline recession. This hypothesis was
successfully applied in the Port Burwell (north central shore of Lake Erie)
litigation case where the Government of Canada successfully defended against
a $30-miUion claim which held that the harbor structures at Port Burwell had
caused accelerated recession for 40 km of downdrift cohesive shore (see
Philpott (1986)).

The opposite extreme consists of a situation where the glacial tiU under-
neath the sand cover is rarely, if ever, exposed in the natural condition (prior
to the construction of harbor jetties). This situation has been documented for
the niinois shoreline north of Chicago by Shabica and Pransclike (1994). In
this case, the interception and impoundment of alongshore sediment by large
shore-perpendicular structures has resulted in a reduction of sand cover from
over 500 m^/m to less than 200 rn^/rn in places. In this case, the reduced sand
cover resulting from the impoundment at the shore-perpendicular structures
results in accelerated shoreline recession along the downdrift shore. Beach
nourishment is required in these cases, not only to reinstate the historic
sediment supply rate, but also to replenish the sand cover to its historic level.
The latter requirement may be achieved through augmenting the sand cover
volume to its natural level (this may not be practical or realistic owing to the
large volumes required). Otherwise, the requirement may be relaxed if the
effectiveness of the protective characteristics of the overlying sand cover can
be augmented. The protectiveness of the sand cover could be improved
through the provision of sediment which is coarser than the natural or native
sediment Specific grain size requirements should be determined based on the
profUe shape, properties of the underlying till, wave exposure, and sediment
transport characteristics (both alongshore and crossshore).

A special condition of cohesive shore which may be relatively common
relates to cases where the natural profile shape is convex instead of concave
(see Stewart and Pope (1993)). Gray and Wilkinson (1979) document the
existence of this type of cohesive shore at locations on the east shoreline of
Lake Michigan north of St. Joseph. This condition is a result of the presence
of a more erosion-resistant surface in the nearshore. The protected nearshore
shelf may consist of some form of bedrock or glacial till that is armored by a
boulder and cobble lag deposit. Shoreline (or bluff) recession on this type of
cohesive shore is particularly sensitive to changes in lake level. While
downdrift nourishment requirements for this type of cohesive shore may be
less in volume (i.e., less than what might be determined based on potential
transport rates), the timing and grain size characteristic requirements should be
careftilly considered.



Chapter 6 Beach Nourishment Design Guidelines



91



In summary, the nourishment requirements for cohesive shores downdrift of
harbor structures (or other impediments to alongshore transport) are more
complicated than the requirements for similar situations on sandy shores. The
requirements must be established on a site-specific basis. They may vary from
cases where no beach nourishment is required to others where the natural
supply must be completely replaced and/or augmented with coarse grain
sediment.



92 Chapter 6 Beach Nourishment Design Guidelines



References



Foster, D. S., Brill, A. L., Folger, D. W., Andrensen, C, Carroll, D. G.,
Fromm, G. L., and Seidel, D. R. (1992). "Preliminary results of a pilot
study conducted between St. Joseph, Michigan and Michigan City,
Indiana," U.S. Geological Survey Open File Report 92-348, Woods Hole,
MA.

Gray, D. H., and Wilkinson, B. H. (1979). "Influence of nearshore till lithol-
ogy on lateral variations in coastal recession rate along southeastern Lake
Miclugan," J. of Great Lakes Res. 5(1), 78-83.

Hands, E. B. (1970). "A geomorphic map of the Lake Michigan shoreline."
Proceedings of the 13th Conference on Great Lakes Research, Buffalo, NY.
American Society of CivU Engineers, NY, International Association for
Great Lakes Research, Ann Arbor, MI, 250-65.

. (1976). "Some data points of erosion and flooding for subsiding



coastal regions." Proceedings of the 2nd International Symposium on Land
Subsidence. Anaheim, CA, International Association of Hydrological Sci-
ences, Washington, DC, 629-45.

. (1979). "Changes in rates of shore retreat. Lake Michigan,



1967-76," Technical Paper No. 79-4, Coastal Engineering Research Center,
U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, 62-63.

Hubertz, J. M., Driver, D. B., and Reinhard, R. D. (1991). "Wave information
studies of the U.S. coastlines, hindcast wave information for the Great
Lakes," WIS Report 22, U.S. Army Engineer Waterways Experiment Sta-
tion, Vicksburg, MS.

Jolinson, C. N. (1992). "Mitigation of harbor caused shore erosion with beach
nourishment delayed mitigation." Coastal Engineering Practice '92, Amer-
ican Society of Civil Engineers, New Yoric, 137-53.

Nairn, R. B. (1993). "Quasi-3DH morphodynamic modelling: Development,
validation and testing." Proc. Canadian Coastal Conference. Canadian
Coastal Science and Engineering Association, Vancouver, Ottawa. Canada,
485-97.



References



93



Nairn, R. B., and Southgate, H. N. (1993). "Deterministic profile modelling
of nearshore processes; Part 2, Sediment transport and beach profile
development," Coastal Engineering 19, 57-96. Elsevier, Amsterdam.

Parson, L. E. (1992). "An example of coarse grained beach nourishment:
St. Joseph, Michigan - preliminary results." Proc. of the 5th Annual
National Conference on Beach Preservation Technology. St. Petersburg,
FL.

Parson, L. E., and Smith, J. B. (1995). "Assessment of native beach char-
acteristics for St. Joseph, Michigan, Southeastern Lake Michigan," Miscella-
neous Paper CERC-95-2, U.S. Army Engineer Waterways Experiment
Station, Vicksburg, MS.

Parson, L. E., Morang, A., and Nairn, R. B. (1996). "Geologic effects on
behavior of beach fill and shoreline stability for southeast Lake Michigan,"
Technical Report CERC-96-10, U.S. Army Engineer Waterways Experiment
Station, Vicksburg, MS.

Philpott, K. L. (1986). "Coastal engineering aspects of the Port Burwell shore
erosion damage litigation." Proc. of Cohesive Shores, National Research
Council, Ottawa, Canada. 309-38.

Shabica, C, and Pranschke, F. (1994). "Survey of littoral drift sand deposits
along the Illinois and Indiana shores of Lake Michigan." Journal of Great
Lakes Research 20(1), 61-72.

Southgate, H. N., and Nairn, R. B. (1993). "Deterministic profile modelling of
nearshore processes; Part 1, waves and currents," Coastal Engineering 19,

27-56.

Stewart, C. J., and Pope, J. (1993). "Erosion Processes Task Group Report."
Working Committee 2, Land Use and Management, International Joint
Commission, Great Lakes-St. Lawrence Water Levels Reference Study
Board.

U.S. Army Corps of Engineers. (1973). "Section 111 detailed project report
on shore damage at St. Joseph Harbor, Michigan," Detroit, MI.



94



References



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REPORT DATE

July 1997



3. REPORT TYPE AND DATES COVERED

Final report



4. TITLE AND SUBTITLE

Effectiveness of Beach Nourishment on Cohesive Shores, St. Joseph,
Lake Michigan



6. AUTHOR(S)

Robert B. Nairn, Peter Zuzek, Andrew Morang, Larry E. Parson



5. FUNDING NUMBERS



PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

W.F. Baird & Associates, Coastal Engineers, Ltd.

221 Lakeshore Road East, Suite 30, Oakville, Ontario, Canada L6J 1H7

U.S. Army Engineer Waterways Experiment Station

3909 HaUs Ferry Road, Vicksburg, MS 39180-6199



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REPORT NUMBER

Technical Report CHL-97-15



SPONSORING/MONITORING AGENCY NAME(S) AND ADORESS(ES)
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10. SPONSORING/MONITORING


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