When the neighborhoods along Wellington Avenue and Bridge Street were first developed hundreds of years ago, their locations close to Newport Harbor were seen as a benefit. As time progressed more homes and businesses were established and the City installed storm drainage infrastructure in these neighborhoods and throughout the City. The investments in storm drainage infrastructure have served the City well for decades, and in many areas still provide adequate storm drainage even during the largest and most intense precipitation events. Recently, the Wellington Avenue and Bridge Street neighborhoods have experienced what is perceived to be more frequent and more severe street flooding events. The City is conducting a drainage investigation and flood analysis for these two locations to identify the causes and to develop short- and long-term mitigation measures. The investigation will consider observations made during recent street flooding events and trends in sea level, tidal cycles, and extreme precipitation events. In order to identify mitigation measures that will best address the concerns of residents in these neighborhoods, the City requests your input and support. You can also view maps of the study areas by accessing these links.
Do you know your Datum?
When discussing the depth of water, whether it be flood depths or tide heights, it is important to understand the datum (reference point used in measuring elevations) from which the water depths are being measured. For the purpose of this study, all elevations are presented in North American Vertical Datum of 1988 (NAVD88) datum reference. The NAVD88 datum was selected for this study because it is the datum also used by FEMA Flood Insurance Rate Maps (FIRM) that show calculated flood elevations for coastal storms. Water level data from the National Oceanic and Atmospheric Association (NOAA) references either a local tide gage station datum or a mean lower low water (MLLW) datum. The graphic below shows the different datums relative to one another.
Climate Change Information
How’s this for heavy rainfall:
Heavy Rainfall is Getting Worse in the Northeast:
Street flooding and other drainage problems are the worst during short, heavy rainstorms, which seem to be happening more often in recent memory. The latest National Climate Assessment in 2014 described how the heaviest rainfall events have become heavier and more frequent across the United States. The following figure published in 2014 by the U.S. Global Change Research Program shows that since 1991, the amount of rain falling in very heavy precipitation events (the heaviest 1% of all daily events) has risen 74% in the northeast above the 1901-1960 average.
More frequent Higher High Water Tides:
Sea levels are rising and that affects how often high tides back up into storm sewers under Newport’s streets. The City analyzed tide gage data since records were started in 1930 at the Newport tide gage on Coasters Harbor Island. The number of days that high tide exceeded the current Mean Higher High Water (MHHW) level was counted for each year (MHHW is the current average of the highest tide recorded each day). The figure shows that the number of times MHHW is exceeded in a year has increased linearly since the beginning of the record. During the first 10 years of record (1931 through 1940), MHHW was exceeded on average 68.5 times, but during the last 10 years of record (2003 through 2012), MHHW was exceeded, on average, 208.4 times. The frequency of higher high tides may rise at an even faster rate with the latest sea level rise forecasts of three to five feet in the next 100 years.