Tidal flooding
Tidal flooding, also known as sunny day flooding[1] or nuisance flooding,[2] is the temporary inundation of low-lying areas, especially streets, during exceptionally high tide events, such as at full and new moons. The highest tides of the year may be known as the king tide, with the month varying by location. These kinds of floods tend not to be a high risk to property or human safety, but further stress coastal infrastructure in low lying areas.[3]
This kind of flooding is becoming more common in cities and other human-occupied coastal areas as sea level rise associated with climate change and other human-related environmental impacts such as coastal erosion and land subsidence increase the vulnerability of infrastructure.[4] Geographies faced with these issues can utilize coastal management practices to mitigate the effects in some areas, but increasingly these kinds of floods may develop into coastal flooding that requires managed retreat or other more extensive climate change adaptation practices are needed for vulnerable areas.
Effects on infrastructure[edit]
Tidal flooding is capable of greatly inhibiting natural gravity-based drainage systems in low-lying areas when it reaches levels that are below visible inundation of the surface, but which are high enough to incapacitate the lower drainage or sewer system. Thus, even normal rainfall or storm surge events can cause greatly amplified flooding effects. One passive solution to intrusion through drainage systems are one way back-flow valves in drainage ways. However, while this may prevent a majority of the tidal intrusion, it also inhibits drainage during exceptionally high tides that shut the valves. In Miami Beach, where resilience work is underway, the pump systems replace insufficient gravity-based systems.[5]
Relation to climate change[edit]
Sunny day flooding is often associated with coastal regions, where sea level rise attributed to global warming can send water into the streets on days with elevated high tides.[6] Further, regions with glaciers also experience sunny day flooding as climate change alters the dynamics of glacier meltwater.[6] Abnormally hot temperatures not only swell rivers and creeks directly through accelerated snowmelt, but can burst ice dams and cause water from glacial lakes to swell waterways less predictably.[6]
A warming climate causes physical changes to the types of ice on a glacier.[6] As glaciers retreat, there is less firn (water-retaining snow) so that more meltwater runs directly into the watershed over deeper, impervious glacial ice.[6]