Bristol's planning for the adverse flooding arising from the long-term relative sea level rise is very important and needs to be applauded. The disastrous Silver Creek bridge should not be repeated.

The solution lies in effective zoning and common sense dictated by nature. A proper understanding of the rise is the first step. The sea level along the coast has always been rising and falling; that is different from the changes seen out to sea.

The coastal level had many wild swings during glacial times, and the present rise was recognized by America’s early colonists. Measuring the change was perhaps the first “big” science project, with precise measurements at ports being made for over 200 years.

The chart of NOAA’s sea level measurements for Providence, that now extends to 2020, shows a steady rise of 0.79 feet per century, with no significant increase in rate indicated. Boston’s records, which go back about 200 years, show a slightly higher long-term trend from the most recent studies. These records ignore the daily tides, including the extra high King tide that flooded parts of Boston Harbor a few days ago.

However, there is a lesser known 18.6-year lunar tide that needs to be considered. It causes nine years of rising tide that appears to be an extra sea level rise in the record and nine years of falling tide noted as a drop in sea level. It takes a full cycle to show any increase in the relative sea level rise.

To make it more complicated, the sea level change seen along the coasts of North America is mainly due, not to sea level rise, but to the up and down movements of the land that varies from place to place. This is from a combination of many factors, such as the 23-foot drop and flooding resulting from pumping oil at Long Beach, California.

In some cases, the land movement and sea level rise match, resulting in shorelines that have remained the same for 1,000 years. The rise at Bristol is relatively high due to the tilting of the East Coast into the Atlantic Ocean. A group studying the problems of the sea level rise in Warren uses 1/8 of an inch per year. That is above the measured rate, but not bad. Bristol could simplify this to 1 foot per century, which is still high. The town could add this rate to that reached by the ’38 hurricane for extreme storms.

No higher rate is justified by today’s measurements.

Patrick Barosh, PhD, Geologist
Bristol