Shore Protection Methods Research Articles

Investigation on innovative pile head breakwater for coastal protection

Coastal erosion is a global concern that has been augmenting due to the natural evolution of beaches, human activities and sea-level rise. One of the eco-friendly shore protection methods is to dissipate the wave energy by constructing offshore breakwaters. Conical pile head breakwater (CPHB) is one of the eco-friendly innovative offshore structures consisting of closely spaced piles with an enlarged cross-sectional area (conical pile head) in the vicinity of the free surface. In the present study, perforations are incorporated over the conical pile head to achieve higher efficiency by promoting energy dissipation. The influence of the perforations on the performance characteristics, namely wave transmission (Kt), wave reflection (Kr) and energy dissipation (Kd) of the perforated CPHB is comprehensively investigated through physical model studies. The effect of perforations and their distribution around the pile head (Pa), percentage of perforation (P) and size of perforations (S/D) on the wave attenuation characteristics are evaluated to arrive at an optimum configuration. The study is carried out under monochromatic waves of varying wave height (0.06–0.16 m) and wave period (1.4–2 s) at different depths of water (0.35, 0.40 and 0.45 m). A minimum Kt of 0.58 associated with Kr of 0.26 and Kd of 0.78 is obtained with an optimum configuration of Pa = 50%, P = 19.2% and S/D = 0.25. The Kt of the proposed CPHB is about 19 to 35% lesser than that of the perforated hollow pile breakwater under matching test conditions. Overall, providing the perforations is found to be effective in enhancing the wave attenuation capability by up to 12.4%. Further, empirical equations are formulated and validated with the experimental data. The empirical equations estimate the Kt and Kr values accurately with a high coefficient of determination ( R2 ≥ 0.90).

A century of U.S. beach nourishment

This study analyzed decadal and regional trends in one type of shore protection method: beach nourishment, since its beginning in the U.S. nearly 100 years ago. While strategies such as managed retreat may be more feasible in the long-term, beach nourishment is a dominant method of shore protection in the U.S. today. During the last century, the beaches of over 475 U.S. communities have been restored with over 1.5 billion cubic yards (cy) (1.2 billion cubic meters (m3) of sand. Over 3200 individual nourishment events have occurred with many communities renourishing multiple times. Six states account for over 83% of the total volume of sand placed on beaches: California, Florida, New Jersey, North Carolina, New York, and Louisiana. New Jersey has been the most productive state in terms of sand volume per linear foot (meter) of shoreline, but has placed less than 3 cy along each foot (7 m3/m) of its oceanfront coasts annually. Growth in sand volume placed has been exponential over the last century, with the total annual volume of sand placed on U.S. beaches increasing to 37 million cy (28 million m3) per year in the last decade. Regionally, long-term beach management programs in California, Florida, and Louisiana reveal that despite significant differences in motivation, timelines and funding mechanisms, similarities are long-term beach management plans and dedicated funding sources at local, state, and/or federal levels.

Monitoring of the collapse of the shores of reservoirs and the technology of their surface and deep fixing

Due to the unique water regime of the Astrakhan region, characterized by an uneven distribution of runoff that is directly dependent on the discharge from the Volgograd hydroelectric power station, coastal zones of water bodies are subject to intense negative effects. It is established that, despite the existing variety of ways to protect coasts from erosion, the search for new technical solutions at the moment continues to be an urgent task in hydraulic construction. The purpose of this work was to evaluate the application of a new methodology for studying the destruction of coastal zones and the method of shore protection. The article discusses the features of work on shore protection of territories subject to slope processes. The role of studies of the leading processes of destruction of coastal zones in the course of engineering and geological surveys, to predict and prevent risk, as well as to ensure the information content of further work on the construction of reliable shore protection, is emphasized. The result of the study was a new method for identifying the destroyed coastal zones, technologies for surface and deep fixing of the Bank slopes, and a method for preventing the collapse of steep river banks. In this paper, a positive assessment of the investigated method of Bank protection was given. Research has shown that prevention of emergency situations, especially in urbanized areas subject to intense anthropogenic impact, is possible only with the construction of engineering protection structures that have a positive effect in both protective and environmental aspects.

Defense of beach by active coast-protecting structures

The results of physical modeling of recreational beach protection by active protection methods are presented. The experiments were carried out in the wave pool on models of intermittent breakwaters with T-shaped and V-shaped traverses and dike dam systems. The use of active shore protection methods makes it possible to preserve natural and artificial beaches with the formation of a stable coastline. The geometrical parameters and hydrodynamic characteristics of the shore protection structures are established and recommendations for their operation are developed. Based on the research results, the dike dam system has been put into practice to protect the coastal strip of the “Urzuf” recreation complex on the shore of the Sea of Azov.

Biorock Electric Reefs Grow Back Severely Eroded Beaches in Months

Severely eroded beaches on low lying islands in Indonesia were grown back in a few months—believed to be a record—using an innovative method of shore protection, Biorock electric reef technology. Biorock shore protection reefs are growing limestone structures that get stronger with age and repair themselves, are cheaper than concrete or rock sea walls and breakwaters, and are much more effective at shore protection and beach growth. Biorock reefs are permeable, porous, growing, self-repairing structures of any size or shape, which dissipate wave energy by internal refraction, diffraction, and frictional dissipation. They do not cause reflection of waves like hard sea walls and breakwaters, which erodes the sand in front of, and then underneath, such structures, until they collapse. Biorock reefs stimulate settlement, growth, survival, and resistance to the environmental stress of all forms of marine life, restoring coral reefs, sea grasses, biological sand production, and fisheries habitat. Biorock reefs can grow back eroded beaches and islands faster than the rate of sea level rise, and are the most cost-effective method of shore protection and adaptation to global sea level rise for low lying islands and coasts.

Soft shore protection methods: The use of advanced numerical models in the evaluation of beach nourishment

Beach nourishment is one of the worldwide most common soft shore protection methods. However, the design of these projects is usually based on empirical equations and rules, leaving large margins of error regarding their expected efficiency. In the present work, an advanced wave and sediment transport numerical model is developed and tested in the evaluation of beach nourishment. Non-linear wave transformation in the surf and swash zone is computed by a non-linear breaking wave model based on the higher order Boussinesq equations, for breaking and non-breaking waves. The new Camenen and Larson (2007), transport rate formula for non-cohesive sediments (involving unsteady aspects of the sand transport phenomenon) is adopted for estimating the sheet flow sediment transport rates, as well as the bed load and suspended load over ripples. Suspended sediment transport rate is incorporated by solving the 2DH depth-integrated transport equation. Model results are compared with experimental data of both profile (cross-shore) and planform morphology evolution; the agreement between the two is considered to be quite satisfactory.

Increasing the dynamism of coastal landforms by modifying shore protection methods: examples from the eastern German Baltic Sea Coast

Redesign of shore protection projects in Mecklenburg-Vorpommern (Germany) is allowing landforms to become more dynamic after centuries of employing structures to increase stability. Current policies are designed to maintain sediment transfers, re-establish wetlands, ensure zero net loss of coastal habitat and apply the user-pays principle for restoring damaged habitat. Projects that achieve new nature-oriented goals include (1) relocating dykes landward or allowing dykes or protective dunes to erode to expose more land to episodic inundation by the sea; (2) reinstating sediment transfers from bluffs to adjacent low-lying shores; (3) increasing sediment transport rates through groyne fields; and (4) removing exotic vegetation from dunes. These actions create new habitat, add portions of the coast to the public domain, and provide a wider buffer against accelerated sea-level rise for developed lands further inland. The management actions have been relatively small in scale, applied where there has been little threat to human facilities and done to achieve specific environmental goals, but they provide examples of workable options to increase the dynamism of stabilized landforms on other exposed coasts. The need to restore natural functions while providing some stability places emphasis on a strategy of controlling dynamism rather than preventing it.

Reduction of sand demand for shore protection

Beach nourishment is an environmentally preferred method of shore protection, but the annual sand requirement may lead to substantial maintenance costs. The shoreline processes, involving the surf zone, beach and dune, are reviewed with the aim of reducing the annual sand requirement of eroding shorelines. It is shown that surf zones with equilibrium profiles, on which the wave energy conversion is evenly distributed across the surf zone, from experience for given conditions indicate least loss of sand. On steep, eroding shorelines it may be difficult to establish an equilibrium profile. For such cases, the use of perched surf zones is recommended, which are supported at the seaward limit by an underwater sill. For reduction of littoral transport, the use of pervious pile groynes is recommended. These are arguably more efficient than impervious groynes. The sand loss from a usually dry beach by raised water levels is shown to be a function of the beach slope and is least when the storm waves at raised water levels do not cut an erosion escarpment. The loss of sand from a dune by infrequent severe storm tides can be prevented with the aid of a built-in membrane. These sand losses are usually large and constitute an uneconomic use of this sand resource. The proposed concepts and measures are linked to existing knowledge, augmented by data from the large wave flume (LWF) in Germany and field data from the North and Baltic Sea coasts.

Offshore sand sources for beach replenishment: Potential borrows on the continental shelf of the Eastern Gulf of Mexico

Erosion of sandy beaches is a worldwide problem that elicits innovative geoengineer‐ing techniques to reduce adverse impacts of shoreline retreat. Beach replenishment has emerged as the “soft”; shore‐stabilization technique of choice for mitigating beach erosion. This method of shore protection involves the addition of sand to the littoral sediment budget for sacrificial purposes. Because inland sand sources are often uneconomical or impractical to use, and known nearshore sources are limited, finding adequate quantities of suitable sand on the inner continental shelf is often vital to beach replenishment projects. The technical studies of survey and materials analysis that identify and delineate usable sand sources are sometimes almost as expensive as small‐project dredging, pumping, and placing the sand on the beach as fill. Inadequate quantity or substandard quality of shelf sand, as well as often‐prohibitive overhead expenses, thus compel shoreline managers to seek suitable sand sources offshore. In the study area off the central‐west coast of Florida, offshore potential borrow areas (PBAs) were identified on the basis of studies conducted in reconnoitory and detailed phases. Sophisticated state‐of‐the‐art equipment used in this investigation provided more detailed subbottom mapping information than is normally obtained with conventional seismic equipment. An example of sand exploration studies was incorporated in a 215‐km2 survey of offshore areas by conducting bathymetric surveys and subbottom seismic profiling, collecting jet probes, grab samples, and vibrocores, and analyzing sediment grading in subsamples from vibrocores. These combined analyses indicated that at least 8.8 ×106 m3 of sand is available in potential borrow areas from 7.0 to 12 km offshore in water depths of 8.0 to 11.5 m. In the PBAs, mean grain size of sand falls into the range 0.13–0.53 mm, sorting averages 0.65–1.31ø, and the overall silt content varies from 3.9–8.5%. High silt contents (13–19%) mapped in some areas make these sedimentary deposits unsuitable as fill for artificial beach renourishment.

LOW-COST SHORE PROTECTION ON THE GREAT LAKES: A DEMONSTRATION/RESEARCH PROGRAM

Shore erosion is currently causing millions of dollars of damage to shoreline property along the Great Lakes (1,2). Erosion is caused by the energy of waves and currents which are produced by large wind storms. The erosion process on the Great Lakes is most severe when lake levels are near the top of their 6-foot (1.8 meter) range'for several years as is currently being experienced. The severe erosion process continues even after lake levels fall, as the bluffs have become unstable and waves from intense storms can still attack them. In order to alleviate the erosion damages to beaches and bluffs, shoreline owners must rely on shore protection methods. Effective methods of shore protection are designed to slow or stop the erosion process by dissipating wave energy and/or preventing bluff attack. However, the most effective methods are very expensive, costing over $200 per foot ($656 per meter) of shoreline. (Costs are calculated, for the purposes of this study, as the length of shoreline which is expected to be protected by the shore protection methods. For sites utilizing revetments, artificial nourishment, and seawalls, the length is the stretch of shoreline actually covered by the method. For locations utilizing groin systems and breakwaters, the system was designed to protect the entire length of the sites; the costs have been calculated on that basis. Whether these systems actually protect that length of shoreline is to be determined by this study.) Shoreline homeowners are usually not able to meet such expenses, and often resort to less efficient and costly alternatives. Private shoreline owners need accurate, reliable information about effective low-cost shore protective methods in order to reduce or alleviate the severe erosion damages to their shoreline.