Coastal Engineering Structures Research Articles

The performance of some coastal engineering structures for shoreline stabilization and coastal defence in Trinidad, West Indies

Abstract Coastal erosion in Trinidad has caused a loss of land and subsequent damage to many coastal engineering structures. Damage includes roadway failures, loss of agricultural land, coastal flooding and damage to property. In many areas, structural engineering measures have been implemented to prevent these from recurring. An example of erosion and structural measures used in a segment of rapidly eroding coastline along the east coast of the island is presented. The site is part of a coastal section of the largest wetland on the island, the Nariva Swamp, through which drains the largest river system, the Nariva River. Structural measures used include steel sheet piled revetment, steel-reinforced concrete retaining walls, gabion basket retaining structures, boulder splash aprons, a steel-reinforced concrete pile cluster, concrete columns and blocks and boulder riprap. All these an show signs of structural failure, and some have already collapsed. Failures include spelling and cracking of concrete; rebar corrosion; steel pile corrosion; foundation settlement under retaining walls and structures, with subsequent surfical cracking; basal foundation sediment scour and undermining; wave and fluvial induced removal of rip-rap and splash apron boulders, and seasonal burial and sedimentation of the splash apron and concrete pile cluster. Based on this study, it appears that construction-induced high energy conditions and oversight in design and construction were partly responsible for failures.

Coastal modification due to human influence in south-western Taiwan

The coastal zone of southwest Taiwan is characterised by muddy tidal flats, offshore bars, spits, lagoons and coastal sand dunes. These geomorphic features from an essential part of the natural defences against sea-level change and coastal erosion. Between 1955 and 1995 the area bounded by the Pei-Kang and Tseng-Wen rivers underwent considerable land use and topographic changes. Two examples were studied using time-series aerial photographs, remote sensing images and geomorphological field mapping. The result of this investigation demonstrates the influence of human activities and the importance of the natural coastal landscape in acting as a first-line of coastal defence and protection in Taiwan. Attention is drawn to: (1) inappropriately designed or misplaced coastal engineering structures which may destroy or reduce the effectiveness of neighbouring natural and engineered structures leading to storm damage, flooding and encroachment by the sea; (2) the need for a co-ordinated coastal management program to regulate on-shore activities, in particular the removal of ground water within the coastal zone. This research demonstrates that there is significant land subsidence and inland penetration of sea water into the ground water system in the coastal zone. Human activities also lead to considerable financial expenditure on the prevention of coastal erosion in Taiwan.

Coastal Erosion and Engineering Structures: The Oregon Experience

Seawalls and riprap revetments are used on the Oregon coast to protect properties threatened during erosion of seacliffs and sand spits. The erosion processes involve the combined effects of swash from storm waves and embayments cut through the berm by rip currents. Most shore protection structures on the Oregon coast have not been designed by engineers, and therefore commonly do not follow sound design practices. They often are grossly overbuilt and do not take into consideration the processes of erosion and beach morphology. Particularly difficult is the protection of high cliffs where the structures can defend only the toe of the slope. Questions have been raised as to whether the structures might contribute to erosion of the beach and adjacent unprotected properties. Although such adverse impacts have been demonstrated in our laboratory wave-basin experiments, the role of rip currents in Oregon-coast erosion produces significant longshore variability in property losses and tends to mask impacts by structures. We are presently monitoring beach-topography changes adjacent to seven structures, including both seawalls and riprap, with the objective of determining whether the structures do cause erosion.

OCEAN WAVE RECORD ANALYSIS BY TUCKER'S METHOD - AN EVALUATION

The planning and design of any Coastal Engineering structure requires adequate knowledge of the wave characteristics. It is desirable that this knowledge of waves is based on instrumentally recorded data over a number of years, so that reliable values could be used for the computation of the design wave. Analysis of instrumentally recorded data to yield the relevant wave characteristics like the significant wave height, though not complicated is too time consuming. A simple method of analysis has been proposed by Tucker (9, 10), wherein the relevant information is obtained with only a few measurements of the larger waves. This method is also recommended by Draper (6) in his plea for uniformity of the analysis and presentation of wave data. This paper deals with the application of the Tucker's method to analysis of waves recorded off the Mangalore Harbour on the West Coast of India.

COASTAL ENGINEERING RESEARCHES ON THE WESTERN COAST OF TAIWAN

Taiwan is an island located at the edge of the continental shelf of the East China Sea. Her eastern coast fronts precipitously on the Pacific Ocean, whereas the major part of the western coast is formed by very flat sandy beaches. Various engineering works such as the planning of newly building or extension of harbors, tidal land development, cooling water intake of steam power plants as well as shore protection works have been performed on this coast. However, owing to the geomorphological situation of this coast, monsoons of NNE or NE direction originated from high pressure atomosphere overlaying East Asia continent prevail from September to March, and in the summer months, the coast is assailed by typhoons. Waves caused by these meteorological phenomena are mainly being generated in shallow water region, besides, their fetch areas are limitted by the China mainland and Taiwan island. The forecast technics must be reconsidered in stead of utilizing traditional methods. Most coastal engineering structures are subjected to the waves after breaking since the beach slope is exceptionally flat. Many rivers of rapid stream bring tremendous amount of sediment from the high mountains down to the sea. In consequence, sand drift along this coast is so severe that small harbors will be silted up only a few months during monsoon season or after one strong typhoon assailing.

The measurement of wave heights by means of a float in an open‐end pipe

A series of experiments was performed to test the possibility of using OPEN‐end pipes with float‐type recorders for measuring wave heights, for the purpose of applying these data to the planning of coastal engineering structures. The main problem was one of resonance in the tubes. This was particularly pronounced in actual installation for wave periods of from one to six seconds. A mathematical analysis has been made for the case of a train of waves of constant period. It was shown that the hand of frequencies encountered in the ocean would make it quite difficult if not a practical impossibility to analyze data obtained by this method.

Colalloy armorplate

Coastal freshwater and tidal wetland habitats are being transformed as a result of increasing demand for commercial, residential and tourism activities. The consequence is a habitat seascape complex, comprising a mosaic of natural and engineered coastal features. This study used the freely available mapping tool (Google Earth) to define the extent of coastal engineering structures in the Great Barrier Reef World Heritage Area (GBR; Australia), a marine ecosystem of global biodiversity and cultural significance. Continuing threats to the heritage estate concomitant with expanding urban and industrial developments has raised concerns directed at the future conservation and resilience of the reef ecosystems, along with maintaining expected human lifestyles and livelihoods it provides. The data here shows that break walls and pontoons/jetties dominate development, contributing to approximately 10% (equivalent) of the coastline linear length. Most (60%) development occurs along the coastline or within the first few kilometres upstream along estuaries. While conservation and protection of natural coastal habitats is still preferred for the objective of fisheries production and biodiversity, managers must consider seascape implication/benefits more broadly when approving new marine infrastructure rather than a case-by-case approach which further contributes to an ad hoc mosaic seascape of natural and engineered habitats. Not only within the GBR heritage estate, but more broadly, coastal managers need to regard wider seascape connectivity processes during the assessment of any new development. There is an urgent need for policy and planning instrument reform that is inclusive of accumulative impacts of urban and industrial development in this heritage estate. Opportunities to include eco-friendly (green engineering) solutions, in the repair and revitalisation of existing artificial structures, is necessary in any new proposed urban and industrial development and expansion.