O'Fallon, Missouri
Client:Monticello Lake Association
Terra Technologies was retained by the Monticello Lake Association to author a technical opinion on the causes of shoreline recession attributed to erosion and to make formal recommendations for suitable, cost-appropriate solutions to address the lakeshore erosion concern.
The subject of the evaluation was an approximate 3.7-acre lake, located on approximately 7 acres of common ground, adjoined by residential homes along portions of the west, north, and east sides and by wetland setback areas and common ground to the south and east. The hard-surface walkway roughly parallels the shoreline along the eastern boundary of the lake and provides access to the lake for nature watching and fishing.
The geomorphology and soils of the site were examined. Additionally, the existing shoreline erosion was documented and the severity was determined to be moderate within most reaches of shoreline. Shoreline erosion was being caused by the combination of rapid water level fluctuations, bank slope geometry deficiencies, moderately cohesive soils and lack of appropriate vegetation (non-turf grasses) to provide a matrix to stabilize soil within areas of saturation. The results were evident with occurrences of soil slumping along large reaches of the shoreline, particularly along the portions of residential lawns where encroachment upon the shoreline corridor by adjoining homeowners is occurring and banks slope geometry is deficient. To a lesser degree, wind-driven wave transmission and ice movement contribute to the erosion potential where shorelines are deficient of a means to stabilize saturated soils.
Terra Technologies offered several solutions, detailing the benefits and drawbacks of each, along with the approximate costs. The options included 1) relaxing the slopes and establishing a healthy native wetland plant community appropriate to shorelines, 2) placing riprap stones and turf reinforced mats along the lake edge, and 3) a grouted geocellular confinement wall that would provide the highest amount of armoring, but would preclude any vegetation. |
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