northern portions of this region, the dominant plants are forbs such as the Sea Fig (Carpobrotus edulis
and C. aequilaterus). These are effective for sand stabilization but are not good dune builders.
Great Lakes Region. Dune development is mostly confined to the Michigan and Indiana shores
of Lake Michigan; however, the discussion, which follows, is applicable to all the shores of the Great
Lakes. American beachgrass is the dominant species. Native species, especially prairie sandreed, will
often invade naturally. Once the dunes have been stabilized, volunteer or planted species of upland
vegetation can be established. Species of grasses suggested would include reed canarygrass, big
bluestem, little bluestem, and switchgrass, all native to the area. These grasses may be planted from
early May to the middle of June at a rate of about 0.5 pounds of seed per 1000 square feet. All require
full sun and may be mowed occasionally. Reed canarygrass is especially useful in wet spots.
Various ground covers may also be planted. The species which may be utilized are best suggested
by local agricultural experts. The same holds true for shrubs and trees.
An additional problem which landowners in the Great Lakes region have is the stabilization of
bluffs. Often, structural corrections are required in concert with vegetation. Once the structural
stabilization is accomplished, vegetative cover will aid in preventing erosion, reducing seepage, and
slowing runoff.
The type of vegetation which can be established on bluff slopes is dependent upon the slope angle.
Slopes steeper than 1 on 1 generally preclude successful vegetation; slopes flatter than 1 on 3 can be
planted as a lawn and maintained in the usual manner. Slopes between 1 on 3 and 1 on 1 can be planted
with grasses which will not be mowed, ground covers, trees and shrubs, or combinations of these three.
As mentioned before, local expertise (e.g., agricultural extension agents) can aid the landowner in
selecting suitable species, and in describing the most practical methods of establishment and
maintenance.
INFILTRATION AND DRAINAGE CONTROLS
Infiltration and drainage controls are often needed for stability along high bluff shorelines.
Although many factors lead to slope stability problems, groundwater is one of the most important. The
majority of slope failures and landslides occur during or after periods of heavy rainfall or increased
groundwater elevations. Infiltration controls prevent water from entering the ground, while drainage
controls remove water already present in the soil or on the surface.
Since water entering surface cracks can lead to further instability, these should be filled with
compacted soil (preferably clay) as they develop. Surface runoff should also be diverted from critical
areas of the bluff by either drainage ditches or swales.
The treatment of subsurface drainage problems is complex.
Where such problems exist, a
geotechnical engineer should be consulted.
SLOPE FLATTENING
A bluff slope may be flattened to enhance its stability when adequate room exists at the top, and it
does not interfere with the desired land use. Freshly excavated slopes should be planted to prevent
erosion due to surface runoff. It may also be necessary to build a revetment or bulkhead at the toe of the
slope to protect against wave action.
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