Many solutions exist to combat and repair shoreline erosion. These solutions range in price, material and classification. Landshore® broadly defines projects into three primary categories: structural, bio-technical and non-structural.
The choice of methodology depends on proper research and investigation of the problem by professional engineers. Depending on the complexity of the problem, such tasks would involve a civil engineer, structural engineer, environmental engineer, geotechnical engineer, surveyor, attorney and other disciplines or specialties.
The selection of viable solutions can only be done based on scientific and practical design approach.
Basic Information on Various Popular Applications
Many solid concrete sea walls observed by our company are slowly deteriorating – usually within 20 – 30 years due to corrosion of steel reinforcement and cracking under hydrostatic pressure behind the wall. Sea wall applications can destroy the waterfront property and becomes a safety issue if the railing and fencing are not properly installed.
Landshore® strongly suggests preventative replacement before any failure may occur. The dewatering and sheet piling process becomes very complicated and expensive when challenged with removing collapsed structures and rebuilding properties. We use a variety of methods to stabilize existing retaining walls showing signs of backfill erosion, unstable foundation, buckling or rotation. Those methods include tie-backs with the highest quality American-made Magnum Helix Anchors and cement or resin injection pressure grouting.
Sheet piling is another structural solution to prevent erosion. Sheet pile design requires a geotechnical engineer to determine soil properties and calculate stability and deflection properties. Without proper backfill and drainage, sheet piles runs the risk of cracking or failure under hydrostatic pressure – which can even be caused by seismic activity of a home too close to the vicinity of the sheet piling.
Gabions, Sand-Cement Bags, Concrete or Rock Blocks
While the use of cement bags is an alternative to costly sea walls (because it may be installed directly without special equipment), It is important to notice that mechanical properties of soil may not support the weight of cement bags. This can lead to settlement, inward rotation, outward rotation and failure.
Without a geo-synthetic liner, rocks are only creating turbulence around them and accelerating erosion by sinking deeper into the shoreline each time when a wave washes against the shore. It could have an unsightly appearance and become a major safety hazard, since the material becomes extremely slippery due to micro-organisms growth.
Polyamide sandbags were first used by Dutch government as far back as 1957. Due to relatively inexpensive price point, geo-synthetic containers or tubes became very popular in United States. Thoroughly tested by the US Army Corps of Engineers, this method is widely deployed by many specialists such as Landshore®. Proper geotechnical investigation and bathymetric survey are needed to determine the correct sizes and quantities when selected as a solution.
Often the main reason for geo-tube failure is improper installation. Installation appears easy when properly designed by our engineering department. But it is tedious work by specially trained employees and divers after doing proper research, surveying and design to establish soil criteria, slope stability calculation, study of site hydrology and wave action.
Coir logs may be used along a shoreline where the erosion does not exceed one-foot vertical height and the velocity of water is not sufficient to wash it out. We do not recommend this method when the drop-off is one foot or higher or when shear stress caused by movement of water exceeds our defined thresholds.
Burlap is typically used in combination with other stabilization methods to protect any lake or pond shelf from erosion during low water events. Landshore® does not recommend this option when drop-off is 6-inches or higher or when shear stress caused by movement of water exceeds our defined thresholds.
Aquatic planting works well in combination with other stabilization methods and where lake or pond shelf is already established. Littoral plantings may protect the lake bank form erosion when wave action is very mild, and velocity of water is very low. However, by itself, aquatic plans are unable to solve stability or seepage problems.
Matting in general proves to be an excellent liner for establishing and promoting ground vegetation cover on steep slopes in many situations. Beware of any mat being stapled to an underwater slope and then having material pumped beneath the mat to fill the eroded portion on the slope to bring it into conformance with a typical section. This approach is problematic because it makes it impossible for material particles suspended in the water to consolidate. Unless the water body is pumped down significantly below the problem area and suitable material is imported and properly compacted, the risk exists for structural failure.
Various matting are wonderful aids in erosion protection of steep slopes for two main reasons:
– Extensive root systems improve the physical parameters of top and underlying soils.
– Dense vegetative cover prevents infiltration.
Both play major roles in slope stability analysis by structural or geotechnical engineers.
Concrete Blocks and Fabric Formed Concrete Revetments
Cabled concrete blocks with geotextile filters provide flexible and stable protection in high flow, high-scour applications. Concrete blankets provide excellent cover for geotextile in such places where vegetation covers have low survival rates due to restricted access, shadow or the absence of irrigation.
Because of the weight of concrete blankets, due diligence must be exercised by the engineer of record in slope stability calculations and hydrogeological research in order to prevent possible failure.