Coping with Sea Rise:
How Much and How Fast will Global Sea Level Rise?
By Dana Nuccitelli | May 4, 2018
The basic physics of how global warming contributes to sea-level rise has long been understood, but new research gives us a clearer picture of what to expect. Prior to the 1990s, most sea-level rise was attributed to melting glaciers and the thermal expansion of warming ocean waters. However, ice sheets such as those covering Greenland and Antarctica have also begun to melt and play a significant role in raising ocean levels. The author reviews the results of a number of recent studies. Two of them conclude that the seas could rise by 3 or more feet by the year 2100, and one argued that 5 feet or more by 2100 is a possibility. Exactly what happens, and when, will be influenced by the degree to which humans reduce carbon emissions, and the uncertain dynamics of the Antarctic ice sheet. Considerable sea-level rise will occur as a consequence of the global warming humans have already caused.
All Sea Level is Local:
By J. X. Mitrovica, C. Hay, R. Kopp, M. Lickley| May 4, 2018
When people read about climate change and sea level rise in the average mass-market, general-interest publication, they nearly always see references to “average global sea level rise” – for instance, that the worldwide average sea level rise will be about three feet (or six feet) by the end of this century. But what does that term really mean? And how useful is it for architects, city planners, businesses and local governments planning the latest bridge, highway, airport, seawall, or other infrastructure near the coast? Just how uniformly do the seas rise or fall? What geophysical processes come into play? And what are the consequences?
Smart City:
“A smart city has to have a comprehensive, holistic vision beyond levees and gates,” as Arnoud Molenaar, the city’s climate chief, put it. “The challenge of climate adaptation is to include safety, sewers, housing, roads, emergency services. You need public awareness. You also need cyber-resilience, because the next challenge in climate safety is cybersafety. You can’t have vulnerable systems that control your sea gates and bridges and sewers. And you need good policies, big and small.
A levee dike, dyke, embankment, floodbank or stopbank is an elongated naturally occurring ridge or artificially constructed fill or wall that regulates water levels. It is usually earthen and often parallel to the course of a river in its floodplain or along low-lying coastlines.
Some of the earliest levees were constructed by the Indus Valley Civilization (in Pakistan from 2600 CE) on which the agrarian life of the Harappan peoples depended.
Coastal Flood Prevention:
Levees are very common on the marshlands bordering the Bay of Fundy in New Brunswick and Nova Scotia, Canada. The Acadians who settled the area can be credited with the original construction of many of the levees in the area, created for the purpose of farming the fertile tidal marshlands. These levees are referred to as dykes. They are constructed with hinged sluice gates that open on the falling tide to drain freshwater from the agricultural marshlands, and close on the rising tide to prevent seawater from entering behind the dyke. These sluice gates are called "aboiteaux". In the Lower Mainland around the city of Vancouver, British Columbia, there are levees (known locally as dikes, and also referred to as "the sea wall") to protect low-lying land in the Fraser River delta, particularly the city of Richmond on Lulu Island. There are also dikes to protect other locations which have flooded in the past, such as the Pitt Polder, land adjacent to the Pitt River and other tributary rivers.
Coastal flood prevention levees are also common along the inland coastline behind the Wadden Sea, an area devastated by many historic floods. Thus the peoples and governments have erected increasingly large and complex flood protection levee systems to stop the sea even during storm floods. The biggest of these are of course the huge levees in the Netherlands, which have gone beyond just defending against floods, as they have aggressively taken back land that is below mean sea level.
Spur Dykes or Groynes:
These typically man-made hydraulic structures are situated to protect against erosion. They are typically placed in alluvial rivers perpendicular, or at an angle, to the bank of the channel or the revetment, and are used widely along coastlines. There are two common types of spur dyke, permeable and impermeable, depending on the materials used to construct them.
Super Levee:
Important cities in Japan (Tokyo and Osaka) developed a new flood protection known as Super levee. Super levees are thicker levees that will not fail even in the most extreme events.
A dike is a barrier used to regulate or hold back water from a river, lake, or even the ocean. In geology, a dike is a large slab of rock that cuts through another type of rock.
Dikes, which can be hundreds of miles long, are usually used to create farmland or residential space from a lakebed or even the ocean. The nation of the Netherlands has reclaimed more than a thousand hectares of land from the North Sea by constructing dikes along many tidal basins. The Dutch, people from the Netherlands, use the reclaimed land, called polders, for agriculture, residential, and industrial use. The first dikes in the Netherlands were constructed in the 1200s, and the country continues to maintain and expand the dike system today. In fact, dike is a Dutch word that originally meant the bank of a body of water.
Credit: shutterstock.com/GLF Media.
The Netherlands has, for centuries, dealt with flooding and high waters by developing innovative water management techniques and technologies, and in recent years, other countries have been tapping this Dutch expertise. Here, the Maeslantkering, a massive moveable storm surge barrier that can be engaged to protect the city and port of Rotterdam from flooding, sits open, with its two swinging gates resting on dikes on either side of the Nieuwe Waterweg channel. The barrier, completed in 1997, was part of the last phase of the Netherlands’ decades-long Delta Works project.
Credit: Henk Monster, CC BY 3.0.
Water-pumping windmills were an early technology used by the Dutch to drain swampy areas — which often lay below sea level — and create polders, dryland plots surrounded by dikes.
In the aftermath of the flood, the Dutch redoubled their efforts to battle the sea, creating an enormous flood-control system known as the Delta Works. A modern engineering marvel, the Delta Works — built between the late 1950s and the 1990s — consists of nine dams and four storm barriers that have closed off estuaries and substantially reduced the Dutch coastline by about 700 kilometers. Delta Works has served the Dutch well for decades, but extreme flooding in the ‘90s caused mass evacuations and fueled rising concerns about climate change and sea-level rise. Dutch water managers saw limitations to “hard engineering” approaches like dikes and barriers in a rapidly changing and increasingly unpredictable climate, so they took a vigorous new approach.
Credit: Snempaa, CC BY-SA 4.0.
The 30-kilometer-long Houtribdijk between the towns of Enkhuizen and Lelystad was completed in 1975 as part of the Zuiderzee Works, a project begun in about 1920 to dam and reclaim land from the shallow Zuiderzee Inlet.
Credit: Bert Kaufmann, CC BY 2.0.
The 9-kilometer-long Oosterscheldekering, completed in 1986 as part of the Delta Works, is the largest storm surge barrier in the Netherlands and features sluice gates that can be opened or shut to allow water to pass through or to block it.
One experimental project in the Netherlands that is starting to catch on elsewhere is the Zandmotor, or Sand Engine — a 1-kilometer-long, hook-shaped sand peninsula that was built in 2011 along a stretch of coastline at Ter Heijde in South Holland. In a single operation 10 kilometers offshore, dredgers collected 21.5 million cubic meters of sand, which was then deposited in the designated area. Over time and by design, waves and tides slowly disperse the sand and naturally replenish nearby beaches. This conceptually simple experiment, also known as sandscaping, has performed as designed, preventing beach erosion. It has also been more efficient and economical, as well as less disruptive to the beach and to wildlife ecology, than a traditional approach such as regular sand replenishment. Its success has not gone unnoticed; another sand engine is now, with Dutch help, being constructed along the North Sea coast in Norfolk, England, an area where severe beach erosion threatens coastal towns and industry.
From Delhi, India, to Wuhan, China, to São Paulo, Brazil, cities around the world have begun to turn to the Dutch for help with water management strategies. The Dutch, in turn, have been eager to export their technology and expertise; in the Netherlands, water management is a $5.5 billion industry annually.
A seawall (or sea wall) is a form of coastal defence constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a sea wall is to protect areas of human habitation, conservation and leisure activities from the action of tides, waves, or tsunamis. As a seawall is a static feature it will conflict with the dynamic nature of the coast and impede the exchange of sediment between land and sea. The shoreline is part of the coastal interface which is exposed to a wide range of erosional processes arising from fluvial, aeolian and terrestrial sources, meaning that a combination of denudational processes will work against a seawall.
Raising roads above sea level can help drain water and reduce tidal flooding. In order to make sure that higher roads don’t channel flood waters to homes and stores at lower elevations, cities often use stormwater pumps to remove this excess water.
Coast Protection:
Vertical:Vertical seawalls are built in particularly exposed situations. These reflect wave energy. Under storm conditions a non-breaking standing wave pattern can form, resulting in a stationary clapotic wave which moves up and down but does not travel horizontally. These waves promote erosion at the toe of the wall and can cause severe damage to the sea wall. In some cases, piles are placed in front of the wall to lessen wave energy slightly.
Advantages:
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Disadvantages:
These can suffer a lot of expensive damage in a short period of time.
Vertical design can be undercut by high-wave energy environments over a long period of time.
Curved:
Curved or stepped seawalls are designed to enable waves to break to dissipate wave energy and to repel waves back to the sea. The curve can also prevent the wave overtopping the wall and provides additional protection for the toe of the wall.
Concave structure introduces a dissipative element.
The curve can prevent waves from overtopping the wall and provides extra protection for the toe of the wall
Curved seawalls aim to re-direct most of the incident energy, resulting in low reflected waves and much reduced turbulence.
Disadvantages:
More complex engineering and design process.
The deflected waves can scour material at the base of the wall causing them to become undermined.
Mound:
Current designs use porous designs of rock, concrete armour.
Slope and loose material ensure maximum dissipation of wave energy.
Lower cost option.
Disadvantages:
Less durable.
Shorter life expectancy.
Cannot withstand or protect from high-energy conditions effectively.
A sleeper dike (in Dutch slaperdijk) is a dike which does not normally face water, but serves as a backup if a "front-line" dike in front of it breaks.
The sleeper dikes are usually located at places where there is a high risk of dike breakthrough or where there used to be such a risk. The dike is only potentially safeguarding the land from the sea/river, and is "sleeping", hence the name. Sometimes there is even a secondary sleeper dike, which can be called a "dreamer dike".
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