Coastal erosion in California
It is established that coastlines were not made along with the beaches. There was a drop in the sea levels during the ice ages. The various continental shelves contained exposed sediments, which were constantly eroded by rainfall and wind. When the ice started to melt, there was a rise in the sea levels, causing the waves to scatter the loose sediments cutting the bedrock, which is a firm rock layer beneath the surface of the soil. Sand beaches are mainly built at times when we have huge sea-stands just like our present state. However, there have been cases of erosion along the southern Californian beaches causing a lot of stir among environmentalists. Waves, sedimentation, deposition and erosion are all affected by climate changes and rise in the sea level. The beaches in The Golden State of California are temporary streams of loose sand, which are constantly in motion due to the processes of deposition and erosion. These processes are completely natural but there are others resulting entirely from human interference. In order to preserve these beaches, we need to understand the sediment and energy structure of the coastal regions. (Gunn, 2001)
For California, its beaches act as an important financial advantage as it helps to attract tourists improving the tourism industry. They also provide a rich habitat for the marine animals, the shorebirds and the invertebrates. Beaches mainly contain coarse products of erosion from the land, which are pebble and sand particles, and from sea, which are coral and shell remains. The currents in the wave pick up the sediments and drag them along the shore, forming a stream of sand particles, and deposit them along the coast of California. Materials, which are coarser, stick to the coast and below the surface of the moving sediments bedrock, which slopes towards the sea, functions as the basis for the formation of the beaches. (Till, 2007)
For the beaches to maintain equilibrium, a firm wave force is required in the seasonal rotation. In the summer, the low waves move the sand particles on top of the beach, widening it. However, the high and stormy waves in winter shift the sand particles offshore, narrowing the beach. Thus in wintertime, the beaches are bared of sand, as they are sometimes eternally lost to seawater, although the cobbles, being heavier, stay on the shore. If a stormy weather is experienced for a long time, the beaches will be continuously eroded. This would expose the bedrock and cobblestones, and sand will be deposited in the deep seawater, creating an imbalance in the beaches. The landforms of the beaches are dynamic by nature and are continuously altered by the waves and winds. This is a continuous seasonal process where sand is deposited and lost depending on the season. While they are slightly sloping and very gentle in the summers, they become narrow and very steep during the winters. Thus, we need to maintain a balance between the winter season when the sand is removed from the beaches and the summer, when the sand is returned to the bare shores. (Ehlen, 2005)
The seawater near the shore gathers most of its energy from the tidal currents and waves yielded by the winds. Scattering of nutrients, pollutants, sediments and water and also the creation and erosion of the beaches are a result of this near-shore energy dissolution. The waves generate tidal currents, which are responsible for the transportation and deposition of the sediments on the coasts. They move the materials towards the bottom of the ocean and wait for the milder currents for their transfer. The history of wave climate in southern California bay shows that some waves have reached a massive height of 10 m in recent times, while others have been less than 4m. The action of the waves alongside the Californian coastal area is seasonal and is effected by the changes in the pattern of the wind, which blows over the great Pacific Ocean. Some of the waves are produced in the southern ocean. These ultimately end up on the beaches of California. The period and height attained by the waves rely on the duration and the speed of the winds, generating them. Wave refraction is responsible for making the wave fronts cause a parallel shape of the coast when they hit the shore. When the waves fall on the beaches making an angle, their momentum produces onshore currents, which travels in the same direction as the wave. When water is piled up on the shore, long-shore currents are formed, and they travel in a parallel manner along the beach. The tides generate coastal and shelf currents, which are responsible for the transfer of fine sediments. The elevation of a wave attacking a shoreline is determined by the tidal range and if the tides have a greater influence, it can even cause flooding and are enlarged due to changes in the sea level because of the El Niño. (Till, 2007)
In southern California, sea cliffs support the beaches. The east coast of America is a broad shelf having coastal plains (trailing-edge coasts) and the west coast contains rocky watersheds and a narrow shelf (collision coasts). The Gulf of California has a marginal seacoast. This means that it has a fine shelf and slightly rocky coast. It is surrounded by island arcs and landmasses. The border of the southern California bay is extraordinarily large and consists of narrow shelves and basins. Vertical fault planes have broken it into a number of blocks. While the elevated blocks are responsible for creating the offshore islands, like the Santa Rosa and San Clemente, the lower blocks form the basins, like the Santa Barbara and San Diego. The coasts are all divided into small natural components known as the littoral cells. Each of the cells has a total sedimentation cycle, which includes the sources, transportation paths and the sinks of the cells. This transportation of sand within a cell is responsible for the existence of sand on any beach. Thus, when constructions like harbors and dams obstruct the transportation of sand, beaches start to erode. Buffland erosion, gully, streams and sea cliff erosions are common sources of sediments. The currents and waves transport sand along the coastline and nourish the beaches. (Trenhaile, 2006)
For the sandy beaches to exist a balance must be maintained between the influence of the currents and waves and the amount of sediments present for transportation. This sediment budget or balance is obtained from contributions made by sediment flux and losses of the cells. The deposits are the sediment flux obtained from streams, losses occur mainly in the submarine canyons and shelves. This sediment budget is balanced within the area defined by the littoral cells. If the beaches seize to exist, the wave energy will cause the bedrock to erode forming sea cliffs and platforms. The former is a landward feature, which is formed when the wave cuts the rocky coasts and the latter is a flat and slightly sloping surface, which extends towards the sea from the cliffs. It has been found that when the sea cliffs retreat, they release sediments, cobbles and sand, contributing to the beaches about 20% of the sand, under normal conditions. The rest comes from buffland and stream erosion. The process of retreat of the sea cliffs is not reversible through natural processes. The rate of erosion of the sea cliffs mainly depends on the contact it has had with the wave attacks, the energy and height of the waves in that area and the physical attributes and the potency of the materials of the sea cliff. Its degree of hardness and existence of interior weaknesses, like faults and fractures, affects its resistance to the force implied by the waves and weathering of the cliff rocks due to chemicals and seawater. This erosion of the cliffs can occur through several procedures. One of the most important processes is hydraulic impact, which is the impact of a wave breaking on a cliff. (VanLaningham, 2006)
The coastal erosion in California may take various forms. Although every season the beach continuously erodes, it is a reversible procedure. The sand, which is lost during the winters, is again replenished in the summers. However, the creation of huge engineering structures on the coasts and man made dams have been causing the supply of sand to diminish over the years due to which the beaches are becoming narrow and are continuously eroding. As the sand supply is being reduced, the Californian beaches are eroding day after day. This can only be rebuilt if the sand supply is restored to its original value. Most of the seacoasts in San Mateo, Santa Cruz, Santa Barbara and San Diego have low cliffs or bluffs. They have been cut into the elevated marine terrace, which contains younger and less seasoned sedimentary rocks. The presence of these almost horizontal and flat beaches beside the coastline of California provides the basis for its widespread coastal expansion. Convenient and user friendly constructions have made life easy for the communities based on the ocean edge. However, the sedimentary rocks, although well bedded, are comparatively weak and often fall prey to wave erosion. Due to rises in the sea level, these cliffs are continuously breaking down and retreating away from the coastlines. However, the breaking and retreating of the sea cliffs are not just because of the rising sea levels. It also depends on the amount of resistance, which is showed by the materials making up the cliffs, and natural physical forces, which impose a continuous wear and tear action on the cliffs. As said earlier the degree of consolidation or hardness of the sea cliff rocks, the spacing between the rocks, their existence, stability, occurrence of groundwater and presence of internal weak points are all responsible for making the materials in the cliff resistant to the various actions of the waves. If a protective beach is absent then the sea cliffs will erode more. (Ferrier, 2005)
The building and erosion of the beaches is a natural process, which has been distorted by the extended development being done along the coast of California. Before the beginning of these developments, the sand particles, which were naturally lost from the beaches mainly due to the canyons and dunes, were replenished by a supply of natural sand by the nearby streams and rivers. However, after dams were created on the rivers, almost half of the natural sand, which used to be supplied to the beaches, has been cut down. Thus, the natural balance, which existed on the beaches, has been thoroughly altered due to the construction of the various jetties and breakwaters along the shores. They have changed the slope of the beaches by diverting the location of the sand from one place to another. A number of major projects to nourish the beach have been formed at certain locations and they have helped to create wider beaches. Nevertheless, unfortunately they have all eroded away since most of the coastal regions are not suitable for bearing such projects. Even in those places where the projects have had success, the methods of solving the problems of sand erosion are quite expensive and not permanent. (Stephenson, 2004)
The powerful and severe winter storms which are related with the El Niño also causes the erosion of the sea cliffs, formation and destruction of the beaches and harms the coastal regions of California. The El Niño is a disturbance in the marine atmospheric transmission patterns, which occurs in the seawaters at unequal intervals. It generally causes the trade winds to grow weaker and the surface water becomes warm in eastern Pacific Ocean. This affects the weather conditions in places, which are situated away from the tropical regions. A number of researchers and scientists have found that the destructive and violent coastal storms, which occur in the winter months of the El Niño, are three times more damaging then in normal conditions. Normally in a year if a big storm occurs, the beaches can absorb most of the force produced by them. Nevertheless, in the year of the El Niño, most of the protective beaches are lost and thus, they hit the coast much harder than usual. The high waves not only attack the beaches but also various structures built on them. As a lot of rainfall accompanies the storms, it saturates and makes the coastal areas weak. The sea levels rise and huge waves break on the shore, causing more erosion of the beaches. Because of global warming the sea levels are rising causing more and more damages to the coastal regions. A reasonable part of the population of California lives along its coasts and are in danger due to the frequent storms and rising sea levels. Although the storms caused by the El Niño are to a certain extent responsible for erosion of the beaches, they also refill the beaches as a large amount of fresh and new sediments are deposited from streams and rivers in to the seawaters during storms. Nevertheless, if the intensity of the El Niño increases, it creates an exponential raise in the various elements, which lead to erosion of the coastal areas. (Ehlen, 2005)
Restoring the beaches in California has become utmost important to the people in recent times. A huge amount of money is being spent to determine the beaches that need the help of these beach nourishment projects. The reasons for erosion and the beaches facing them are being evaluated and the places the sand is going to be taken from are still being determined. Also, as sand does not stay at same place and moves along with the wind, we also need to determine whether sea nourishment projects are effective or not. Although El Niño refills most of the sediments that it washes away, the situation is not same in the southern Californian beaches. Here the dams situated on the coastal rivers interfere with the transportation of the nutrients and sediments onto the seacoasts. The dams can be removed once its use is over. Humans build seawalls, which cuts off the sand obtained from the erosion of the sea cliffs. In southern California, along its coastal basins, a huge amount of sand has been trapped behind the dams. This is a valuable and completely unexploited source of sand, which can be brought back to the coasts. (Constantine, 2003)
The various coastal lagoons also store huge amounts of sand. We need to develop new methods to restore the habitat of the wetlands and its tidal circulation, while bringing out the sand required for the beaches. The drowned river valleys and terraces also contain huge amounts of sand and can be used as an alternative source for the sand required for the nourishment projects. The main sink of the valuable sediments for the littoral cells of southern Californian beaches are the submarine canyons. When the sand reaches the submarine canyons, it is lost forever. Thus, we should take proper environmental steps to stop this from happening and get back the sand, which has been lost. As the climate of southern California has reached a dry phase, the intensity of the storms have lessened allowing the littoral cells to retain the sand particles for more time. Therefore, it is being said that this is the right time to nourish the beaches. Properly nourished beaches not only provide greater protection to the beaches, but also help to sustain a rich habitat and build resistance against any climate changes. However, if we let the beaches remain the way they are without proper amount of sand, they will loose their resistance. This would ultimately result in more erosion. Lastly, they would be eroded more by the storms. (Constantine, 2003)
More than 900 miles of the coastline in southern California is being eroded day by day. This poses a huge threat to the coastal development plans, which seem to be crumbling. Seawalls and ripraps are being constructed to protect the structures on the coasts and lessen the impacts of the strong waves. The Californian government is also trying to restore the lost balance of the littoral cells by working on the issue regarding lost sediment. Structures like gunite bluff stabilization acts as a natural sea cliff and acts as a means of protection for the beaches. We can also devise armoring plans, which can predict places of erosions and build structures in cases of emergencies. Most of the structures, which are under threat, can also be relocated if it is viable economically. As the sand beaches help to protect us from the storms and protect the sea cliffs and coastal areas, we need to have a wide, long, sandy and nourished beach. (Till, 2007)
References:
Constantine, José A. Gregory B. Pasternack, Michael L. Johnson; 2003; Floodplain evolution in a small, tectonically active basin of northern California; Earth Surface Processes and Landforms; 28, 8, 869-888; Department of Land, Air and Water Resources, University of California, Davis, CA 95616, USA; John Muir Institute of the Environment, University of California, Davis, CA 95616, USA
Ehlen, Judy, William C. Haneberg, Robert A. Larson; 2005; Humans as Geologic Agents; Geological Society of America
Ferrier, Ken L. James W. Kirchner, Robert C. Finkel; 2005; Erosion rates over millennial and decadal timescales at Caspar Creek and Redwood Creek, Northern California Coast Ranges; Earth Surface Processes and Landforms; 30, 8, 1025-1037; Department of Earth and Planetary Science, University of California, Berkeley, California 94720-4767, USA; Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California 94550, USA
Gunn, Angus Macleod; 2001; The Impact of Geology on the United States: A Reference Guide to Benefits and Hazards; Greenwood Publishing Group
Till, Alison B. Sarah M. Roeske, James C. Sample, David A. Foster; 2007; Exhumation Associated With Continental Strike-slip Fault Systems; Geological Society of America
Trenhaile, A. S; 2006; Modelling the effect of waves, weathering and beach development on shore platform development; Earth Surface Processes and Landforms, 30, 5, 613-634; Department of Earth Sciences, University of Windsor
Stephenson, Wayne J. Anna J. Taylor, Maree A. Hemmingsen, Hidekazu Tsujimoto, Robert M. Kirk; 2004; Short-term microscale topographic changes of coastal bedrock on shore platforms; Earth Surface Processes and Landforms; 29, 13, 1663-1673; School of Anthropology, Geography and Environmental Studies, University of Melbourne, Victoria 3010, Australia
VanLaningham, Sam A. Andrew Meigs, Chris Goldfinger; 2006; The effects of rock uplift and rock resistance on river morphology in a subduction zone forearc, USA; Earth Surface Processes and Landforms; 31, 10, 1257-1279; College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA; Department of Geosciences, Oregon State University, Corvallis, Oregon 97331, USA
