Traditional Approaches
Traditional solutions to lakeshore erosion problems involve placement of man-made structures or hard materials along the shoreline. These approaches have included piles of broken concrete or large stone ("riprap"), sheet piling, and walls constructed from concrete or railroad ties. While these "hardscape" solutions offer some protection to shoreline soils, they usually provide little if any stability or enhancement of shoreline habitat.
Sheet pile is
perhaps the most easily recognized traditional measure to control shoreline erosion. The metal sheeting is
available in a wide range of thicknesses, depending on the severity of the upslope grades and the desired
longevity of the product's resistance to corrosion. In recent years, sheet pile fabricated from vinyl and
fiberglass have been introduced that are more resistant to corrosion, and these may offer cost-savings due to
the lighter weights involved with the installation process (as well as the increasing costs of steel.) The
length of sheet pile needed for a particular shoreline can be calculated by an engineer and considers physical
factors such as soil type, soil moisture, and wave action. A general rule of thumb is that the length of sheet
pile needed is about 2 to 2.5 times the final height of the sheet pile above the lakebed elevation; for example,
if the final desired sheet pile height is 4 feet above the lakebed, a length of sheet pile approximately 8 to 10
feet long may be appropriate. Sheet pile offers moderate- to long-lasting protection of shoreline soils against
wave-induced erosion, and it can be particularly effective along lakeshores that are battered by strong wave
action. However, a significant disadvantage of sheet pile is that its surface reflects the wave energy back into
the waterway as well as down the front face of the sheet pile, leading to "scour zones" in front of
the sheet pile that can be nearly devoid of plant or animal life. Typical costs for installing sheet pile range
from $150 to $400 per linear foot of shoreline. This cost includes the sheet pile product, installation,
securing the sheet pile to upslope areas via tiebacks (as needed), and backfilling with soil behind the sheet
pile.
Riprap with rock,
stone, or broken concrete is the other most commonly used traditional shoreline erosion control technique. To
varying degrees, it breaks up the energy of incoming waves and minimizes the direct contact of moving water
against shoreline soils. While some aquatic insects may find useful habitat within the voids between the stone,
the riprap usually forms a barrier to plant growth, and hence, provides minimal habitat for aquatic plants or
the wildlife that depends on those plants. Riprap stone material costs approximately $30 to $50 per cubic yard,
with an additional $10 to $15 per cubic yard in labor costs for a contractor to spread the material with a small
excavator. For a modest riprap installation that provides a 2-foot thick layer of stone over a 7-foot wide
shoreline zone, the resultant costs are approximately $20 to $35 per linear foot of shoreline.
