How high's the water mama?

October 29, 2012 11:56 AM

[sandyfilter] Can someone explain storm surge and sea levels?

My parent live near the upper Narragansett Bay, supposedly at nearly 800 feet above sea level. Nearby Save the Bay Drive which is right on the water is 780 ft.

Addresses on the actual Atlantic show altitudes in the teens and twenties as I'd expect.

So, how is there that much drop in Narragansett Bay? I could understand if there was a constriction before it emptied into the sea like Lake Pontchartrain.

Altitudes are vs. mean sea level, right? Sandy is moving slowly enough that there's concern that storm surge might last through three high tides. What does this mean for people not right on the water, but up a hill and across several acres from it?

Besides wind, there are two risks from water, right? Rain not being able to flow to the sea fast enough & finding alternate routes (flash flooding) and storm surge. What's the bigger risk in that area?

posted by morganw to science & nature (5 answers total)

Using your link, the elevation for Bristol, RI, is 49'. But the elevation for Hope Street, Bristol, RI, is 823'. Therefore I think the altitude algorithm is a bit broken, and probably Save the Bay Drive does not actually have an altitude of 780'.
posted by Lebannen at 12:23 PM on October 29, 2012

That veloroutes site is wrong. Google Earth shows elevations in that area around 20 to 50 feet above sea level. Wikipedia gives the elevation of downtown Providence as 75 ft.
posted by theodolite at 12:24 PM on October 29, 2012

I live on the southern coast of Massachusetts....very close to the southern opening of Narragansett Bay. The wind is really howling now.....gusting to 81 mph at a weather buoy just off the coast.....and power is intermittent. Anyway.... If they live on the Bay near sea-level then there is a HIGH probability off storm surge flooding at the next high tide (this evening at about 8 PM). If they live on a hill, then they will be OK. The storm surge occurs when wind piles water into narrow bays and inlets. The wind prevents the water from moving out. Normal high tides are always higher during a full moon...and today the moon is full so the storm surge is higher than it would have been if this same storm occurred during a half-moon. There will not be any significant flooding from rain in this area so your parents should not have to worry about that either. Again, the main concern from this Hurricane in RI and SE Mass is storm surge flooding. Only folks living on or very close to the beach will be affected. I know that Newport RI, Westerly RI, and other locations along the southern RI coast are experiencing storm surge flooding.

And that elevation of 797 ft on Narragansett Blvd in Providence is WRONG. Bad data. The topography in that area is, of course, sea-level right along the bay with the land rising variably to small hills that are no more than 100 ft above sea level away from the coast. But again, as long as they live away from the water at an elevation of 20 or more feet, they will be totally OK.
posted by Seymour Zamboni at 12:25 PM on October 29, 2012

NOAA has a good explanation of storm surge.
Wikipedia has a good explanation of sea level.
posted by gyusan at 12:26 PM on October 29, 2012 [1 favorite]

Thanks all! Turns out the biggest risk is probably the nearby, lower fuel depot being inundated and catching fire/spewing airborne toxins at my parents. Google Earth: duh! I don't know why I didn't think of that for checking altitudes in the first place, so thanks.

They've reported in that they are very boring: didn't even lose power.
posted by morganw at 12:21 PM on October 30, 2012