Peak river stages and streamflows for 20 long-term streamgaging stations located across New Hampshire and Vermont are presented in the map to the right and table below. New record peak stages and streamflows were recorded at 11 of the 20 sites and are estimated as having peak flows with an annual exceedance probability (AEP) of 1% or less, or in other words, flows with 1 percent chance of being equaled or exceeded in any one year. Nine of the sites recorded lesser flows but still ranked amongst the highest 4 peaks ever recorded at those sites and having AEP ranging from 10% (1 in 10 chance of being equaled or exceeded in any one year) to 2% (1 in 50 chance of being equaled or exceeded in any one year).

The USGS has also provided these and other record streamflows along the east coast of the U.S. on the Hurricane Irene Activities website.

The New Hampshire-Vermont Water Science Center has field personnel collecting additional high water mark information from a network of streamgages across the two states at sites where indirect determinations of flow need to be made for estimating peak flows. In addition, field personnel will be collecting high water mark data at a network of crest and discontinued streamgage sites across the affected area for use in documenting the historical flood event and in determination of peak flows at a network of smaller, sometimes higher elevation, and flashier watersheds across the area. These data are expected to be updated as new data are available.

PROVISIONAL PEAK STREAMFLOW DATA FOR AUGUST 28-29, 2011