Causes of Coastal Flooding
Several factors contribute to coastal floods.
- Severe weather events create meteorological conditions that drive up the water level, creating a storm surge. These conditions include strong winds and low atmospheric pressure that can be caused by tropical cyclones (such as hurricanes), by mid-latitude extratropical storms (such as Nor'easters), or by any severe weather conditions.
- Large waves, whether driven by local winds or swell from distant storms, raise average coastal water levels and can cause large and damaging waves to reach land.
- High tide levels are caused by normal variations in the astronomical tide cycle. When a severe storm hits during high tide, the risk of flooding increases significantly.
- Depending on the storm event, flooding from storm surge may be combined with river flooding from rain in the upland watershed, thus increasing the flood severity. It is important to note that coastal flooding is different from river flooding, which is generally caused by severe precipitation.
- Other larger scale regional and ocean scale variations, caused by seasonal heating and cooling and ocean dynamics, can contribute to high water levels.
Coastal floods are extremely dangerous, and the combination of storm surge, tides, river inflow, and waves can cause severe damage.
Total Water Level = Storm Surge + Tide + Waves + Rivers + Other Additional Factors
Storm surge is the term used to describe an abnormal rise of water generated by a storm, over and above the predicted astronomical tides or wave conditions. Storm tide describes the water level rise due to the combination of storm surge and the astronomical tide. The total water level from a storm is caused by all contributing factors, including surge, tide, waves, and rivers. This rise in total water level can cause extreme flooding in coastal areas, particularly when storm surge coincides with high tide. This occurrence makes the storm surge even more devastating.
Storm Surge vs. Storm Tide