According to the US Geological Survey, the flooding that we went thru last weekend was officially a 100 year flood.
Flows during the flood peak for the Lamprey, Exeter, Warner, Soucook, Merrimack and Spicket rivers generally were at or exceeded those peaks that would be expected an average of once in a 100-year period, termed the 100-year return interval,” said Kenneth Toppin, a USGS hydrologist.
Examples of recorded peak flood flows highlight the magnitude of the flooding, Toppin said. For example, the peak flow in the Lamprey River at Newmarket was 9,100 cubic feet per second on May 16; normal flow for this date is 366 cubic feet per second. The Piscataquog River near Goffstown had a peak flow of 10,100 cubic feet per second on May 14; normal flow for this date is 426 cubic feet per second.
Some dams have had to be torn down or breached to relieve pressure. The retaining wall of one dam has developed cracks that are worrisome.
The local news station, WMUR, has a webpage up with links to several videos, stories and pictures of the flooding.
Atlantic Ave has lots of pics, links to videos with soundtracks that she made (Floodchasers and Watery New Hampton - patience with the loading time) and posts on the flooding of the seacoast region.
Here is a hand-drawn map of rainfall totals from observation data points around New England. Link from the Mount Washington Observatory. And here is a radar estimation (also from MWO).
The picture at right shows the radar estimates for rainfall totals for the past week's storm from the NWS radar in Gray, ME. The widespread 8 to 12 inch totals across the state are incredible to see, but I'm more drawn to the aberrations around, and specifically to the West of Mount Washington. The wedge of low totals west of Mount Washington have two causes, one real, one a figment of the technology used in the estimate.
The first and most apparent reason for the low precip wedge west of the peak is a phenomenon called beam blockage. The radar beam leaves Gray, ME, and performs numerous scans of the horizon at different angles to get its radar imagery. However, when the scan is performed on its lowest tilt, the beam actually hits our mountain somewhere just above treeline. Therefore the radar beam is actually blocked from recording low precipitation west of the mountain.
The second reason for the wedge, and more specifically the reduced rainfall totals west of the mountains, is down sloping. The rain that fell from this storm formed in very low clouds that were moving from east to west. As the storm clouds trekked from the ocean to the mountains, they lost much of their moisture as rainfall. Therefore, once the air rose over the peak, and descended the other side of the White Mountains, there was very little moisture left to fall as rain. The observers during the storm even observed a lot of clear air on the western slopes during the event, while the rest of the mountain was socked in!
The result of these two phenomena is the wedge of low precip and beam blockage extending from Mount Washington in today’s picture.
Comments from 07:54 AM Thur May 18th - Jim Salge - Observer
In other New Hampshire news:
Before I left for class Tuesday night, WS asked if I needed to get gas. I had filled up on the way home so didn't. He said that was a good thing becuase I wouldn't be able to get to the gas station - and it had nothing to do with flooding.
If it's not one thing closing the streets, it's another.
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