Flood of May 2006 in New Hampshire
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Prepared in cooperation with the Federal Emergency Management Agency Flood of May 2006 in New Hampshire Open-File Report 2007–1122 U.S. Department of the Interior U.S. Geological Survey Cover. Photograph showing Cocheco River near Rochester, New Hampshire streamgage during the flood of May 2006. Flood of May 2006 in New Hampshire By Scott A. Olson Prepared in cooperation with the Federal Emergency Management Agency Open-File Report 2007–1122 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DIRK KEMPTHORNE, Secretary U.S. Geological Survey Mark D. Myers, Director U.S. Geological Survey, Reston, Virginia: 2007 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Olson, S.A., 2007, Flood of May 2006 in New Hampshire: U.S. Geological Survey Open-File Report 2007–1122, 32 p. iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Description of Study Area ...................................................................................................................1 Storm Characteristics ..........................................................................................................................1 Peak-Stage Data ............................................................................................................................................2 Peak-Discharge Data ....................................................................................................................................3 Flow-Frequency Analyses of the May 2006 Flooding ..............................................................................3 Comparison of the May 2006 Flood Data to Flood-Insurance Studies ..................................................4 Summary..........................................................................................................................................................6 Acknowledgments .........................................................................................................................................6 Selected References .....................................................................................................................................6 Figures 1. Screenshot showing the 7-day precipitation totals ending on May 18, 2006, northeastern United States ..........................................................................................................2 2–3. Maps showing: 2A. Location of streamgages having peak stage and discharge data for the May 2006 flooding in Hillsborough County, New Hampshire........................................8 2B. Location of streamgages having peak stage and discharge data for the May 2006 flooding in Rockingham County, New Hampshire ........................................9 2C. Location of streamgages having peak stage and discharge data for the May 2006 flooding in Merrimack County, New Hampshire.........................................10 2D. Location of streamgages having peak stage and discharge data for the May 2006 flooding in Belknap County, New Hampshire..............................................11 2E. Location of streamgages having peak stage and discharge data for the May 2006 flooding in Strafford County, New Hampshire ............................................12 2F. Location of streamgages having peak stage and discharge data for the May 2006 flooding in Grafton County, New Hampshire ...............................................13 2G. Location of streamgages having peak stage and discharge data for the May 2006 flooding in Carroll County, New Hampshire ................................................14 3. Recurrence intervals of the May 2006 flood at streamgages in Hillsborough, Rockingham, Merrimack, Belknap, Strafford, Grafton, and Carroll Counties in central and southern New Hampshire .............................................................................5 iv Tables 1. Description of streamgages used to characterize the floods of May 2006 in central and southern New Hampshire ....................................................................................16 2. Peak-stage data and peak-discharge data for the flooding in May 2006 at 65 streamgages in central and southern New Hampshire ..................................................22 3. Flow-frequency data and recurrence interval estimates of the May 2006 flood for 65 streamgages in central and southern New Hampshire ............................................26 4. Relation of computed May 2006 flood discharge and stage data to flood-insurance study data for selected streamgages in central and southern New Hampshire .............30 Conversion Factors and Datums Multiply By To obtain Length inch (in.) 2.54 centimeter (cm) inch (in.) 25.4 millimeter (mm) foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) Area square mile (mi2) 2.590 square kilometer (km2) Flow rate cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s) Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27). Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29) and North American Vertical Datum of 1988 (NAVD 88). Flood of May 2006 in New Hampshire By Scott A. Olson Abstract intervals at each streamgage. In addition, data were compiled from FEMA flood-insurance studies for comparison purposes. From May 13–17, 2006, central and southern New The active streamgages included 37 operated by the USGS, 8 Hampshire experienced severe flooding caused by as much operated by the New Hampshire Department of Environmental as 14 inches of rainfall in the region. As a result of the flood Services (NHDES), 2 operated by the U.S. Army Corps of damage, a presidential disaster declaration was made on Engineers (USACE), and 1 operated privately. All 17 discon- May 25, 2006, for seven counties—Rockingham, Hillsbor- tinued streamgages were those that had been operated by the ough, Strafford, Merrimack, Belknap, Carroll, and Grafton. USGS. A description of each streamgage location included Following the flooding, the U.S. Geological Survey, in a in this investigation is listed in table 1 (in back of report). All cooperative investigation with the Federal Emergency Man- data contained in this report should be considered provisional agement Agency, determined the peak stages, peak discharges, and, therefore, subject to revision. and recurrence-interval estimates of the May 2006 flood at 65 streamgages in the counties where the disaster declaration Description of Study Area was made. Data from flood-insurance studies published by the Federal Emergency Management Agency also were compiled The New Hampshire counties declared in the disaster for each streamgage location for comparison purposes. comprise a land area of 5,923 mi2 in the northeastern United The peak discharges during the May 2006 flood were States. Land altitudes range from sea level along the coast the largest ever recorded at 14 long-term (more than 10 years to greater than 4,000 ft NAVD 88 in the north-central part of of record) streamgages in New Hampshire. In addition, peak New Hampshire. The climate of New Hampshire is humid. discharges equaled or exceeded a 100-year recurrence interval Precipitation is distributed fairly evenly across the state and at 14 streamgages and equaled or exceeded a 50-year recur- averages about 43 in. per year except in regions of high eleva- rence interval at 22 streamgages. The most severe flooding tion, which can receive an additional 10 to 15 in. of precipi- occurred in Rockingham, Strafford, Merrimack, and eastern tation annually. The statewide average precipitation for the and northern Hillsborough Counties. month of May is approximately 3.75 in. (Northeast Regional Climate Center, 2006). Introduction Storm Characteristics Major flooding in central and southern New Hampshire from May 13–17, 2006, resulted in significant damage to The storms of May 11–15, 2006, produced nearly 14 in. public and personal property. Roads were damaged and of rainfall in the coastal regions of New Hampshire (National numerous residential areas were evacuated for several days. Oceanic and Atmospheric Administration, 2006a) and up to As a result of the widespread damage caused by the flooding, 11 in. in the south-central part of the state (National Oceanic President George W. Bush declared a disaster area in seven and Atmospheric Administration, 2006b). The rainfall began counties in New Hampshire on May 25, 2006. In response on May 11, 2006. As an on-shore flow developed, copious to this declaration, the U.S. Geological Survey (USGS), in amounts of moisture were drawn in from the Atlantic cooperation