This treatment method resembles the clay soil shelf and the underwater stone berm in that a shallow water planting zone was created. However, this technique utilizes sheet pile to hold the planting shelf in place rather than compacted clay or a stone berm. The use of this technique at the Garden was limited to shoreline areas where steep grades and/or flowthrough between the various lakes limited the ability to construct a compacted clay slope or stone berm. The submerged sheet pile was installed 6 inches below the water surface to create a 10- to 15-foot-wide planting bed behind it.
This method provides some of the shoreline stabilization and aquatic habitat creation benefits of the clay soil shelf and underwater stone berm, and it allows creation of a planting shelf even in shorelines with steep underwater grades. This method also provides the long-term stability inherent to conventional exposed sheet pile. From an ecological perspective, the primary disadvantage is that wave energy is partially "bounced" back from the sheet pile edge, thereby creating a scour zone on the lake side of the sheet piling where diminished aquatic habitat conditions will result. Although this reflection of energy is mitigated somewhat by placing the top of the sheet piling six inches below the normal water level, these adverse impacts will persist to at least a modest degree. In addition, the biologically rich transition zone in water depths between 6 inches and 2 feet is essentially eliminated with this treatment, since the water depth increases substantially and immediately (usually to 3 or more feet) on the lake side of the sheet piling.
|Treatment 3: Cross-sectional view||Treatment 3: Sheet pile installation|
|Treatment 3: Before shoreline restoration||Treatment 3: After shoreline restoration|