The US coastal regions are dynamic business environments and highly desirable places to live. Coasts support jobs in many industries and their seaports serve as business hubs for trade with global partners – New York City is a good example. In addition to the economic benefits of the coasts, they are also home to diverse ecosystems such as beaches, estuaries and deltas. These natural environments provide opportunities for recreation, sustainable fishing and water sports.
However, coastal regions are continually exposed to climate hazards. For example, events such as high tides, storms, strong waves and heavy precipitation can cause flooding. The impact of these events can range from mere inconveniences to serious material damage, combined with injuries and casualties.
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Rising Sea Levels: A Threat to Coastal Properties
The global average sea level is rising and affecting low-lying areas. This increases the magnitude, frequency and duration of coastal flooding. According to tide gauges on every continent and satellite, global average sea level has risen approximately 7 to 8 inches since 1900. Sea level changes in a specific area depend on a combination of global and regional factors. In the construction sector, building resilience will become more important year after year.
There are regions where the land is rising faster than sea level, mainly due to tectonic forces, and this gives the impression that sea level is falling. However, there are also regions where the land is shrinking and the effect of sea level rise is amplified. The following are some conditions that could produce localized sea level rise:
- Subsidence in river deltas, tectonic shifts and earth movements
- Thermal expansion of water as its temperature increases (shorter time frames)
- Changes in surface and deep ocean circulation
- Groundwater extraction
- Reservoir construction
- Changes in runoff
- Melting glaciers and ice sheets
Coastal erosion
As global sea levels rise, wave action at higher altitudes increases the risk of coastal erosion. This is the process by which rising sea levels, wave action and coastal flooding erode or carry rocks, soil and sand along the coast. It is common for coastlines to suffer various natural events that cause erosion, such as tropical storms. A very damaging scenario is the combination of high tide storms with the additional effects of strong waves, which is typical of tropical storms that make landfall.
In the past, a common method of protecting against coastal erosion was “shoreline hardening”. This method used structures such as dikes, groins, riprap and dikes to reinforce the shoreline. As understanding of coastlines has improved, it is suspected that structural solutions may have caused more problems than they solved. Local governments often prohibit these methods.
- They interfere with natural water currents
- They prevent sand from moving along the coast
- High initial and maintenance costs
Nature-based or “green” protective measures improve the natural ability of shorelines to dissipate storm energy without interfering with coastal processes. Beach nourishment is a common, non-structural shoreline stabilization technique. This technique involves placing additional sand on the beach, which acts as a buffer against erosion while also increasing the recreational value of the beach. Other methods include stabilizing dunes with fencing or natural vegetation, protecting and restoring wetlands, and relocating or removing structures.
Floods at high tide
A high tide flooding event occurs when the local sea level rises above a specified threshold, in the absence of storm surge or river flooding. Consequences of high tide flooding can include water pooling on low-lying roads or seawater entering stormwater systems. High tide flooding was initially called nuisance flooding since it causes public inconveniences such as road closures and saturated storm drainage. The impact can become more severe when high tides coincide with other conditions:
- Coastal storms
- Winds that blow inland push large volumes of water
- Heavy rains, which increase the volume of water
Extreme high tides usually occur a few times a year during a new or full moon. These are known as perigean spring tides or king tides and are astronomical in origin. When the Earth, Moon, and Sun are in a straight line, the combined gravitational pull of the Moon and Sun on Earth's ocean results in abnormally high tides. However, astronomical alignment is not the only factor that influences high tides; Large changes in climate and ocean circulation patterns, such as the El Niño Southern Oscillation, can affect high tide flooding frequencies.
Flooding caused by high tides is forcing certain cities, especially those on the East Coast, to install expensive pumping stations that clean floodwaters from streets. As global sea levels rise, flooding will become a more frequent and serious problem. Therefore, coastal cities must start taking measures to mitigate their impact.
