Hawaiian Beaches
Abstract:
Sandy beaches are some of the most well-liked and popular recreational destinations for tourism. Coastal properties are also some of the most precious real estates in the country. Beaches are transitory environments that are located between land and water, with distinctive innate ecosystems. Beachfront lands are large sites for commercial development and residential places even though they are extremely vulnerable to numerous amounts of natural dangers such as sea-level rise, flooding, drainage problems, marine inundation, and coastal erosion. Erosion is the wearing away of land surface by ice, wind, water, or other geological factors. Geological erosion refers to the natural loss of land that is caused by geological processes acting over long periods of time. Many people are moving to the coasts as they want to live there, which makes the beaches more susceptible to erosion. The US Geological Survey (USGS) is carrying out a national evaluation of coastal change. An example of them performing this effort is by “the National Assessment of Shoreline Change,” which uses shoreline position as a representation of coastal change due to shoreline positioning is one of the most ordinary monitored gauges of environmental change. The purpose of the USGS shoreline change research is to grow a familiar methodology so any shoreline changes that occur in the US, whether it being in Hawaii, Alaska, California, or North Carolina, can be updated regularly in a structured and consistent manner. The main objectives of this study were to develop and execute better methods of monitoring and observing shoreline movement and improve the present-day understanding of the operations that control shoreline movement. Achieving these objectives requires that research examines the initial sources of shoreline research.
Body:
Conducting a national assessment of shoreline change is needed due to there not being a nationally standardized method of analyzing the change. Each state has its own coastal-zone management duties and data, which in turn influences its standards and techniques when calculating rates of shoreline movement. In consequence, projected rates of shoreline erosion and their calculated rates of change can’t be directly compared. The US Army Corps of Engineers (1971) performed the first national evaluation of coastal erosion. However, the rates of shoreline movement weren’t calculated by it, so Dolan and others 1985 performed a thorough analysis of shoreline change for the US (mainland only). Their analysis was constructed by the compilation of rates of shoreline change from other investigators and their own studies. The first study of Hawaii was conducted by Moberly in (1963) who explored the dynamic nature of its beach. In 1981, Hwang constructed a methodology that included aerial photographs that were used to determine vegetation-line position changes on the island of Oahu since 1928. That methodology was then used by Makai Ocean Engineering and Sea Engineering who then expanded it to neighboring islands, updating the previous database.
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The Hawaii hotspot is located just south of the “Big Island.” It feeds magma to three active volcanoes, two subaerial and one submarine. The main Islands are built on shield volcanoes. Valley floors between coastal plains and volcanoes neighboring them consist of sediments that were eroded from carbonate deposits around the shoreline and interior. The geology of beaches and coastlines in Hawaii is characterized by carbonate deposits (reef and beach rock, unconsolidated carbonate sand, etc), volcanic bedrock, etc. Unconsolidation occurs from the erosion of offshore reefs or sources from land. It also can occur directly from what marine organisms produce as it is collected along the shore which can form narrow beaches respective to our normal continental siliciclastic beaches. Hawaii’s beaches (white sand) come from fringing reefs. Beach history and origin are attached to the geologic framework of reefs.
Effective sustainable administration of Hawaiian beach structures needs an understanding of sediment production. The reason being is that many beaches are eroding or losing sediment over time. Hawaiian beach sands primarily come from calcareous (containing calcium carbonate) debris that is eroded reef shelves. It is then deformed into sand-sized grains by waves that crash upon the shoreline and reef shelf. The average size of the sand particles on Hawaiian beaches is medium when compared both to small and large. However, the actual sediment grain size varies around the Hawaiian Islands as the grain size is generally related to current and wave energy. This also relates to Hawaii’s shoreline aspect. The sediments on these islands are mainly finest on the northeastern-facing coasts due to the persistence of the wind with the waves that work on the sediments. On the other hand, the sediment on the south shore of beaches tends to be mainly coarse and badly sorted, as the southerly storms wash coastal plain sediments back into the coastal system. Commonly, the grain-size diameter of sand on all the coastal beaches of Hawaii tends to be coarser in the winter months (November to March) and finer in the summer months (June to September). Reef morphology and beaches tend to also be similarly dependent upon the shoreline aspect. Beaches that are located on the north and west-facing coastlines tend to be the widest and longest, while the reefs tend to be more narrow and deep. However, in the winter, the north and west-facing beaches transition from gently sloping and wide to narrow and steep as the sand is moved seaward. The color of most Hawaiian beaches is fairly light as it is a consequence of grains from “fragmented marine invertebrate animals and algae” (Salazar 17). After performing numerous tests on the sand grains of the island of Oahu, it was found that more than 90 percent of the sand grains located there were biogenic carbonate, meaning they were from skeletal fragments of different types of algae and coral/mollusk fragments. The results of this work showed that age and sand composition can vary tremendously across the sea floor. By using the radiocarbon age of carbonate sands, one can find the longevity, production rate, and conveyance of coastal sediments. By using the dates that are measured for Hawaiian skeletal and coral fragments, one is able to find that sediment is transported, produced, and lost from the shore on a millennial scale.
Hawaiian beach systems store sediment by two processes, either nearshore bodies of sediment or beach reservoirs. Beach reservoirs in the Hawaiian islands aren’t very common compared to continental settings. However, nearshore sediment reservoirs are very common on the Hawaiian islands as they contain sands that are most likely part of the “active sand exchange system” (Salazar 18), which in turn has gained many researchers' attention. On the reef surface, sediment trapping keeps sand available for circulation rather than letting it stray to offshore sites. The majority of sediment that is located in reef systems is produced on the shallow part of the nearshore platform where erosion and carbonate productivity are elevated.
Local respective sea level around Hawaii isn’t just dependent upon the global average trend but is also affected by oceanographic patterns and the restricted flexure of the oceanic lithosphere, which in turn is caused by the weighty load of the volcanic rocks. The sea level has grown roughly around 1.5 mm/yr over the past 100 years. Although the rate may seem small, in the long term, sea level increasing can lead to persistent coastal erosion, drainage problems, and coastal flooding. This long-term drift also increases the influence of short-term variations such as erosion along the coast and episodic flooding which occur due to the extreme tides. Coastal erosion is a significant element in managing the complication of rising sea levels. As sea-level rise speeds up, the expansion of erosion also increases, possibly affecting beaches that were previously stable and secure. In spite of the fact that the rate of sea-level rise has roughly doubled since 1990, it has also decreased in other areas of the world. This is because the sea level is affected by ocean currents and winds, which are always constantly changing. Not only is the sea level changing gradually, but climate change is aiding in causing the sea-level rise to continue to speed up for many countries. Sea-level rise endangers Hawaiian beaches (ultimately causing erosion), quality of life, infrastructure, and tourism. Many communities will be affected whether it be infrastructure or their own homes. Not only this but the actual plants and crops of farmers will die due to them being drowned in water (suffocating plants) from the flooding. Waves can also affect Hawaii from a beach, agriculture, or plant life perspective. Storms, whether predictable or unpredictable can have major tolls as well. An (almost) unpredictable event such as El Niño influences the waves of Hawaii. With the increase in groundwater as it will rise and fall with the sea level, drainage will become considerably difficult, especially for coastal communities. Hawaii also receives a large number of extratropical storms as. Strong winds are associated with these storms and produce large swells, traveling thousands of miles. However, as one would expect the storms to increase in the summer months, that is not the case. In the summer, the Pacific storms move north. Based on this idea, the wave heights in the winter are generally much higher due to the storms. Without a storm, the average winter wave heights are around 3 meters or higher, while the summer waves are only 2 meters or less. Yet, waves can reach 5 to 10 meters in the winter due to storms.
All the processes talked about so far impact beach morphology in Hawaii. Some morphologic changes include chronic trends, seasonal beach profile changes, and extreme events. Seasonal beach-profile changes comes from the seasonal fluctuation of the wave cycle. In the summer months, the south-facing shorelines are left exposed to the wave activity from the southern swell while in the winter months the north-facing shorelines are exposed to more wave activity. This wave activity is related to an increased impact and run-up to the coastal dunes and beaches. Chronic erosion or beach changes in Hawaii can happen from sediment budget deficiency (related to human ventures) and long-term sea-level rise.
Conclusion:
The most used sources of historical shoreline data have normally been the National Ocean Service’s topographic sheets and perpendicular aerial photographs. Depending upon the location, scientific preference, and data source, and different methods are used to represent the location of the shoreline. They can use a wet-dry line, first line of vegetation, crest or toe of an abutting dune, low water line (toe of beach), etc. There are many current ways that Hawaii authorities use to help slow down beach erosion as it is inevitable. Sand dunes are one of the most common ways to avert erosion. Natural sand dunes are created when the wind blows across the beach, causing it to create a build-up due to an object. Anything from a bottle to a cluster of seaweed can cause a sand dune to be created. Typically, sea oat seeds are thrown around in the air and eventually create a pile which then begins to grow. If the sand dune that is forming is located far enough from water, it’ll continue to grow, creating a natural sand dune. Natural dunes aid in the growth of vegetation greater than man-made dunes. Man-made dunes lack characteristics of natural sand dunes as they consist of different types of sand, which is visible when the dune erodes. They also have no layers. Yet, the layers in natural dunes allow sea oats and other vegetation to grow into the sand. The roots of plants put into the sand aid in holding the sand in place, making the sand dunes steadier. However, the plants themselves need to be abnormally sturdy as they must survive the harsh conditions, therefore making the number of species of plants available to perform this exceedingly low. Regarding harsh conditions, they must be able to endure hot summers, be fine with an environment that has little nutrients along with being beaten and concealed by sand, from time to time be flooded by saltwater, and be fine with being sprayed by salt. Van Der Waal's forces also aid in strengthening natural dunes. The electrical bonds unite sand grains and water particles between the grains. On the other hand, man-made dunes are ineffective due to vegetation not being able to stabilize them and the Van Der Waal forces not being able to perform their function because of the irregular sizes of sand grains. Man-made sand dunes also disrupt the innate tendencies of beaches. Transporting sand from the anterior part of the beach to the posterior in order to build a dune actually causes the beach to erode. Food chains are destroyed by the unnatural dunes being created as they can destroy habitats. They are also more easily destroyed in storms and are often fairly expensive to rebuild and maintain. Seawalls, sand fences, and sandbags are some ways used to attempt to stop erosion. However, its impact is generally negative rather than positive as it impacts communities and beaches in a negative aspect. Seawalls, for instance, typically made of boulders, concrete, or steel, run along the water in a parallel fashion to the beach, however, when the waves hit the walls, it takes the sand back with them. This causes a sudden dropoff to form, which can never permanently be fixed. It also causes storm waves to have greater energy, in turn, causing erosion and the breakdown of the wall to occur faster. Sandbags typically have the same drawbacks as seawalls, but also make the beaches look less appealing. The most effective way out of the three is sand fences as they are extremely simple. They help the sand grains from dunes stay where they are by forming a “barrier” to trap the wind-blown sand. Typically, they’re only around two feet tall and run parallel to the ocean water. Sand dunes are able to form almost around six feet high. Unfortunately, the dunes that are created aren’t stable.
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