Flooding in the Northeastern United States, 2011

Professional Paper 1821

U.S. Department of the Interior U.S. Geological Survey Outside cover. U.S. Geological Survey (USGS) streamgage 01388000 Ramapo River at Pompton Lakes, New Jersey, showing flood damages along Paterson-Hamburg Turnpike in Pompton Lakes on August 29, 2011, after major flooding associated with rainfall from the remnants of Hurricane Irene. Photograph by John Trainor, USGS.

Inside cover. Ice jam flooding on the Pemigewasset River at Plymouth, New Hampshire, March 2011. Photograph by Richard Kiah, USGS. Flooding in the Northeastern United States, 2011

By Thomas P. Suro, Mark A. Roland, and Richard G. Kiah

Professional Paper 1821

U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior SALLY JEWELL, Secretary U.S. Geological Survey Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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Suggested citation: Suro, T.P., Roland, M.A., and Kiah, R.G., 2015, Flooding in the Northeastern United States, 2011: U.S. Geological Sur- vey Professional Paper 1821, 32 p., http://dx.doi.org/10.3133/pp1821.

ISSN 2330-7102 (online) iii

Contents

Abstract...... 1 Introduction...... 1 Purpose and Scope...... 3 Collection and Application of Streamflow Data during Floods...... 4 2011 Flooding—Causes, Chronology, and Magnitude...... 5 Antecedent Conditions for the 2011 Eastern United States Flooding...... 6 Chronology and Magnitude of Flooding during 2011...... 8 2011 Flooding—Comparison with Historic Floods...... 17 Annual Exceedance Probability Analysis for 2011...... 23 Annual Exceedance Probability using Expected Moments Algorithm...... 25 Summary...... 28 Acknowledgments...... 28 References Cited...... 28 Glossary...... 31

Figures

1. Map showing the Northeastern United States and drainage area studied of flooding during 2011 ...... 2 2. Photograph showing U.S. Geological Survey hydrographer determining the outside stage at the Passumpsic River at Passumpsic, Vt., USGS streamgage, May 27, 2011...... 4 3. Photograph showing U.S. Geological Survey hydrographer making a streamflow measurement using an acoustic Doppler current profiler at the Mohawk River at Freeman’s Bridge at Schenectady, N.Y., USGS streamgage...... 5 4. Map showing monthly-average streamflow conditions across the United States for February 2011...... 6 5. Graphs showing cumulative precipitation totals from October 1, 2010, to September 30, 2011, in relation to historic average cumulative precipitation for selected sites in the Northeastern United States...... 7 6. Map showing cumulative precipitation totals for February 28, 2011, and locations of U.S. Geological Survey streamgages in Ohio with peak streamflows that had an annual exceedance probability of less than 4 percent and cumulative precipitation totals for March 6–7, 2011 and locations of U.S. Geological Survey streamgages in Connecticut and Massachusetts with peak streamflows that had an annual exceedance probability of less than 4 percent...... 9 7. Map showing cumulative precipitation totals for April 26–27, 2011 and locations of U.S. Geological Survey streamgages in New Hampshire, New York, and Vermont with peak streamflows that had an annual exceedance probability of less than 4 percent...... 11 8. Map showing streamflow conditions at U.S. Geological Survey streamgages on May 25, 2011...... 12 Flooding on the Sleepers River 9. Map showing cumulative precipitation totals for May 26–27, 2011 and locations near St. Johnsbury, Vermont, of U.S. Geological Survey streamgages in Vermont with peak streamflows that May 27, 2011. Photograph by had an annual exceedance probability of less than 4 percent...... 13 Richard Kiah, U.S. Geological Survey. iv

10. Geostationary Operational Environmental Satellite east image of Hurricane Irene making landfall near New York City on August 28, 2011...... 14 11. Map showing cumulative precipitation totals for August 27–29, 2011 and locations of U.S. Geological Survey streamgages in Delaware, Maine, Massachusetts, Maryland, New Hampshire, New Jersey, New York, and Vermont with peak streamflows that had an annual exceedance probability of less than 4 percent...... 15 12. Map showing cumulative precipitation totals for September 6–9, 2011 and locations of U.S. Geological Survey streamgages in Maryland, New Jersey, New York, and Pennsylvania with peak streamflows that had an annual exceedance probability of less than 4 percent...... 16 13. Graphs showing annual peak streamflows through 2011 and the 4-, 2-, 1-, and 0.2-percent annual exceedance probability streamflows for selected U.S. Geological Survey streamgages in the Northeast...... 18 14. Graphs showing streamflow for selected U.S. Geological Survey streamgages in the northeast for the 2011 flood period and selected previous major floods...... 20 15. Photograph showing rescuers use a boat to navigate the flooded streets of Pompton Lakes, N.J., as the Ramapo River overflows its banks because of the heavy rain on August 29, 2011...... 22 16. Map showing annual exceedance probabilities computed for peak streamflows during 2011 at selected USGS streamgages in the Northeastern United States and major drainage basins studied during 2011 flooding...... 26 17. Map showing selected U.S. Geological Survey streamgages in the Northeastern United States with annual exceedance probabilities computed using the expected moments algorithm method...... 27

Tables

1. Peak streamflows and flood probability estimates at selected streamgages in the Northeastern United States during the 2011 floods available at http://dx.doi.org/10.3133/pp1821 2. Peak streamflows and flood probability estimates computed using the expected moments algorithm at selected streamgages in the Northeastern United States during the 2011 floods available at http://dx.doi.org/10.3133/pp1821 v

Conversion Factors

Inch/Pound to International System of Units

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) mile, nautical (nmi) 1.852 kilometer (km) Area square mile (mi2) 259.0 hectare (ha) square mile (mi2) 2.590 square kilometer (km2) Flow rate cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s) cubic foot per second per square 0.01093 cubic meter per second per mile ([ft3/s]/mi2) square kilometer ([m3/s]/km2)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as °F = (1.8 × °C) + 32. Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as °C = (°F – 32) / 1.8.

Datums

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88). Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). U.S. Geological Survey (USGS) hydrographer flagging a high-water mark in a tree after the flooding associated with Tropical Storm Lee in September 2011, near Bloomsburg, Pennsylvania. Photograph taken by Clinton D. Hittle, USGS. Flooding in the Northeastern United States, 2011

By Thomas P. Suro, Mark A. Roland, and Richard G. Kiah

Abstract and are included in this report. The 2011 peak streamflow for 129 of those streamgages was estimated to have an AEP of less than or equal to 1 percent. Almost 100 of these peak Flooding in the Northeastern United States during 2011 streamflows were a result of the flooding associated with was widespread and record setting. This report summarizes Hurricane Irene in late August 2011. More extreme than the peak streamflows that were recorded by the U.S. Geological 1-percent AEP, is the 0.2-percent AEP. The USGS recorded Survey (USGS) during separate flooding events in February, peak streamflows at 31 streamgages that equaled or exceeded March, April, May, July, August, and September. The flooding the estimated 0.2-percent AEP during 2011. Collectively, of late April, which combined snowmelt and heavy rain and the the USGS recorded peak streamflows having estimated floods associated with the tropical storms of late August and AEPs of less than 1 percent in Connecticut, Delaware, September, were the most severe and widespread. Precipitation Maine, Maryland, Massachusetts, Ohio, Pennsylvania, New totals from March to May for Pennsylvania, New York, and Hampshire, New Jersey, New York, and Vermont and new Vermont were documented as being the highest totals in 117 period-of-record peak streamflows were recorded at more than years of record. In late August, the heavy rains associated with 180 streamgages resulting from the floods of 2011. Hurricane Irene produced widespread flooding in many parts of the Northeastern United States, which resulted in damage estimates in excess of $7 billion and approximately 45 deaths. In September, Tropical Storm Lee produced 6–12 inches of Introduction rain in parts of the Northeastern United States adding to the growing total of record peak streamflows set in 2011. Flooding in the Northeastern United States (hereafter The annual exceedance probability (AEP) for referred to as the Northeast) was documented on numerous 327 streamgages in the Northeastern United States were rivers during the general time frame of February to September computed using annual peak streamflow data through 2011 2011 (fig. 1). The most severe flooding was associated with

Flooding associated with Tropical Storm Lee in September 2011. The Susquehanna River overflowing the right (west) bank looking north (upstream) near the intersection of Pine Street and Front Street in the Borough of Wormleysburg, Pennsylvania. Photograph taken by Scott A. Hoffman (U.S. Geological Survey). 2 Flooding in the Northeastern United States, 2011 65° Study area NEW NEW BRUNSWICK precipitation site National Weather Service National Weather Drainage area studied EXPLANATION MAINE NEW HAMPSHIRE NEW 70° Boston RHODE ISLAND

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P 100 ONTARIO Washington VIRGINIA 0 0 80° PENNSYLVANIA Lake Erie Lake Huron WEST VIRGINIA WEST OHIO 85° MICHIGAN KENTUCKY INDIANA Lake Michigan he Northeastern United States and drainage area studied of flooding during 2011 T

TENNESSEE WISCONSIN ILLINOIS Base from U.S. Geological Survey digital data, 1:2,000,000 Mercator projection, zone 18 Universal Transverse North American Datum of 1983 90° 44° 42° 40° 38° 36° 46° Figure 1. Purpose and Scope 3

Hurricane Irene and the remnants of Tropical Storm Lee, The flooding of 2011 was spread throughout the year which were back-to-back storms in late August and early and the region and resulted in about 300 USGS streamgages September. Persistent spring precipitation combined with documenting peak streamflows that exceeded the 4-percent snowmelt produced earlier major flooding in parts of New AEP streamflow, and of those, 129 streamgages documented Hampshire, New York, and Vermont (fig.1). Localized peak streamflows that were less than or equal to the 1-percent intense precipitation of short duration caused varying levels AEP streamflow. The USGS recorded new period-of-record of flooding in parts of the Northeast in the early summer peak streamflows at more than 180 streamgages as a result months, whereas excessive precipitation on saturated soils of the floods of 2011. The National Weather Service (NWS) associated with two tropical cyclones produced record Flood Loss Report for the United States during 2011 indicated setting flooding during August and September in parts of that direct freshwater damages from Hurricane Irene and Connecticut, Delaware, Maine, Maryland, Massachusetts, Tropical Storm Lee totaled at least $3.9 billion from Virginia New Hampshire, New Jersey, New York, Pennsylvania, and to Vermont (National Weather Service, 2014b). Vermont. Precipitation totals from March to May for much The USGS is a national science agency and within of Pennsylvania, New York, and Vermont ranged from about its mission areas is charged with documenting the water 16 inches to almost 20 inches, and the totals were documented resources and assessing natural hazards of the United as being the highest totals in 117 years of record (National States. Documenting flood peaks, along with the antecedent Climate Data Center, 2012a). Record flood levels on Lake conditions, flood chronology, and AEP, will help to put Champlain during April and May of 2011 exceeded the the floods of 2011 into historic perspective and facilitate previous maximum known elevation since 1827 (Lumia and public and private awareness of the flooding potential and others, 2014). considerations of land use and flood-insurance regulations In late August, Hurricane Irene tracked up the east by local and regional citizens and elected officials. The coast of the United States and weakened from a category 1 data collected by the USGS to document these major floods hurricane (or cyclone) to a strong tropical storm as it made will also assist other Federal, State, and local agencies with landfall in New Jersey. The heavy rains associated with emergency management planning for future floods, hazard this storm produced widespread flooding in many parts of mitigation plans, and resiliency planning. the Northeast resulting in damage estimates in excess of $7 billion and approximately 45 deaths. In New Jersey, about 1 million people were evacuated (NBC News, 2014) and initial damage estimates were approximately $1 billion Purpose and Scope (Watson and others, 2014). In New York, 31 counties were declared disaster areas and damage estimates were more The purpose of this report is to provide a broad overview than $1.3 billion (Lumia and others, 2014) because of the of the flood magnitudes and frequencies in the Northeast flooding associated with rains from Hurricane Irene. As during 2011. The USGS maintains a national database of a result of this storm, nearly 100 U.S. Geological Survey water information and has flood documentation dating (USGS) streamgages recorded a peak streamflow exceeding back to the 1800s. Documenting the magnitude, extent, and the 1-percent annual exceedance probability (AEP) and frequency of major floods preserves this important information more than 70 USGS streamgages recorded a new period- that is necessary in protecting human life, property, and of-record peak streamflow. The AEP is the probability, or infrastructure. The streamgages included in this report chance, that a peak streamflow will be equaled or exceeded were selected on the general basis of documenting a peak in any given year. In September 2011, another storm, the streamflow having an AEP of about 4 percent or less. The remnants of Tropical Storm Lee, tracked northward toward AEPs for all 327 streamgages presented in this report were the still recovering Northeast delivering more heavy rains computed using the log-Pearson type III (LPIII) method, and and widespread flooding. Rainfall totals were 6–12 inches AEPs for 122 of these 327 streamgages also were computed throughout the Susquehanna River Basin and upwards of by the Expected Moments Algorithm method. Other USGS 12 inches in parts of southern New York. flood reports providing more detailed analysis of the flooding The floods of 2011 in the Northeast stand out with respect in the Northeastern United States during 2011 are available at to the cost of human life, property damage, and environmental the USGS publications warehouse (http://pubs.er.usgs.gov/). effect but also stand out with respect to the persistence of This report consolidates and summarizes the flooding the 2011 floods. The documentation of the severity and information and documents the flood peaks (stage and stream- unusual repetitiveness of the flooding in the Northeast is flow) for many States in the Northeast that were affected by important for the future protection of life and property. Other the floods of 2011. In this report, the 8-digit number listed in recently published USGS reports provide additional details parentheses after a streamgage name is the USGS station num- and analyses of the 2011 flooding in New Jersey (Watson ber for that streamgage. Additionally, each USGS streamgage and others, 2014), New York (Lumia and others, 2014), listed in table 1 (available at http://dx.doi.org/10.3133/pp1821) Massachusetts (Olson and Bent, 2013; Bent and others, 2013), contains a map number that allows cross reference from the and Vermont (Medalie and Olson, 2013). table to the respective map figure for that flood period. 4 Flooding in the Northeastern United States, 2011 Collection and Application of 2014a). The U.S. Army Corps of Engineers, the Federal Emergency Management Agency, and many other state and Streamflow Data during Floods local agencies and organizations rely on streamflow data to assist in their respective operational duties such as water The organizational structure of the USGS is based on control, emergency management, and mitigation during times the following seven science mission areas: Climate and Land of flooding. Use Change, Core Science Systems, Ecosystems, Energy and Digital flood-inundation maps, which can be accessed Minerals, Environmental Health, Natural Hazards, and Water. through the USGS Flood Inundation Mapping Science Web Specific to the Water Mission Area, one of the objectives site at http://water.usgs.gov/osw/flood_inundation/, depict is to provide tools that managers and policymakers can the estimated areal extent and depth of flooding correspond- use for understanding, predicting, and mitigating water- ing to stages at select USGS streamgages. These maps, in related hazards such as floods (Evenson and others, 2013). conjunction with the near real-time stage data from USGS To help accomplish this objective, the USGS collects and streamgages and National Weather Service flood-stage disseminates reliable, impartial, and timely information forecasts, can help guide the general public in taking indi- about the Nation’s rivers and streams. The following are vidual safety precautions and provide local officials with a several examples from Holmes and others (2010) that tool to efficiently manage emergency flood operations. The include data collection and scientific interpretation of documentation of high-water marks as a result of flooding is streamflow data as the data relate to flooding: the operation also an important piece of information that can be useful for of a nationwide network of streamgages, the development validating the accuracy of data being recorded at streamgages of flood-inundation maps, the documentation of high-water and for developing water-surface profiles through a reach. mark elevations, and the determination of annual exceedance Water-surface profiles may be used to assist in the calibration flood probabilities. of mathematical models for flood simulation and many associ- The USGS operates and maintains a network of more ated applications such as flood insurance studies, development than 9,000 streamgages across the Nation that provides of flood-mapping products, and (or) estimating flow quanti- valuable streamflow information over the internet on a near ties. Estimates of the frequency and magnitude of floods are real-time basis (http://waterdata.usgs.gov/usa/nwis/rt). This essential for flood insurance studies, flood-plain management, information may be related to water quality (such as pH, and the design of bridges and flood-control structures (Roland temperature, or turbidity); water level (commonly referred and Stuckey, 2008). The estimation of flood frequencies and to as stage); or water quantity (typically reported as a rate magnitudes is based on an analysis using annual peak stream- of streamflow or discharge). Stage and streamflow data are flow data. The reliability of these data is contingent upon the of particular interest during times of flooding, or predicted accuracy of the data collected at a streamgage. flooding, to a variety of agencies, organizations, and munici- A primary function of a streamgage is to record the palities, as well as the general public. The USGS streamgage stage of the river, or stream, at the established location of network is continuously maintained and relations between the streamgage on a preset interval (for example, every river stage and streamflow are regularly checked to define 15 minutes) and transmit that data to a central USGS database constantly changing conditions to ensure quality data are available at all times. A photograph of a USGS hydrographer deter- mining the outside stage at the Passump- sic River at Passumpsic, Vt. (01135500) streamgage on May 27, 2011, is shown in figure 2. The stage is determined by reading the staff gage on the outside of the streamgage shelter as an independent check on the hydrologic recording equipment Staff gage inside of the streamgage shelter. The NWS uses information such as precipitation and historical streamflow data to forecast flood stages at select streamgages (also known as flood forecast sites) using mathemati- cal models that simulate the movement of floodwater as it flows downstream. Flood forecast information typically is available 3–5 days in advance of events in many Figure 2. U.S. Geological Survey (USGS) hydrographer determining the outside locations, with typical reporting intervals stage at the Passumpsic River at Passumpsic, Vt. (01135500) USGS streamgage, of 6 hours (National Weather Service, May 27, 2011. Photograph by Richard Kiah, USGS.

rol15-HWCR00-0022_fig 02 2011 Flooding—Causes, Chronology, and Magnitude 5

on a near real-time basis where the data are processed and emphasis typically is placed on maintaining streamgage made available online to the public. Continuous real-time operations to ensure uninterrupted data delivery and on data are extremely valuable because the data allow for remote obtaining sufficient high-flow measurements for defining and monitoring of stage at many rivers and streams across the adjusting rating curves. United States. Stage data can be related to streamflow, or Rating curves that have been well defined generally discharge (typically reported in units of cubic feet per second translate to increased confidence in the forecasted stages, [ft3/s]) by establishing a stage-discharge relation typically resulting in improved reliability of stage and streamflow referred to as a rating curve. A rating curve is unique to each data during flood events. Reliable streamflow data provide streamgage and is established by making a series of discrete emergency management agencies, first responders, and the streamflow measurements over a range of stages. These general public with critical information about river conditions; streamflow measurements and associated stages are plotted thus, allowing better informed operational and response and used to define a relation (or curve) between stage and decisions for the protection of life and property. The ability streamflow. Changes to channel geometry and drainage basin of USGS field personnel to respond rapidly allows for the characteristics require continuous monitoring and adjustment collection and dissemination of accurate and timely data of rating curves to accurately represent stage-discharge to those who rely on the data. The USGS made more than relationships. Defining a rating curve at extreme high stages 2,000 discrete measurements of streamflow to verify or define can be challenging because of the relative infrequency of rating curves at many streamgages throughout the Northeast extreme flood events and, in some cases, not being able to during the floods of August and September 2011. physically access or measure a river or stream that is flooding. A photograph of a USGS hydrographer making a streamflow measurement at the Mohawk River at Freeman’s Bridge at 2011 Flooding—Causes, Chronology, Schenectady, N.Y. (01354500) streamgage during the flooding associated with Hurricane Irene in August 2011 is shown in and Magnitude figure 3. The hydrographer is using an acoustic doppler current profiler (ADCP) mounted in a small boat and tethered by a Floods are caused when meteorological processes deliver rope to collect water depth and velocity data. The data are more precipitation or runoff to a region than can be retained continuously transmitted by radio link to a nearby laptop, not or stored in a watershed. Climate, geology, topography, shown in the photograph. During times of flooding, additional and antecedent conditions all play a role in the delivery and retention of precipitation in a watershed. In a region as diverse as the Northeast, flood-causing processes can range from orographic lifting and thermal convection, to lake-effect precipitation along the Great Lakes, to extra tropical or tropical cyclones. Typically, localized flooding is caused by severe, convective storms; whereas, widespread flooding is caused by frontal systems that move into the region from the south and west or by tropical storms that can include cyclones (Paulson and others, 1991). The 2011 flooding in the Northeast was on small streams and large rivers. Much of the flooding was widespread and included parts of Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, and Vermont. During February to September of Figure 3. U.S. Geological Survey (USGS) hydrographer making a streamflow measurement 2011, each month recorded at least using an acoustic Doppler current profiler (ADCP) at the Mohawk River at Freeman’s Bridge one separate flood event somewhere at Schenectady, N.Y. (01354500) USGS streamgage. Photograph by Alicia Gearwar, USGS. in the Northeast.

rol15-HWCR-0022_fig 03 6 Flooding in the Northeastern United States, 2011

Antecedent Conditions for the 2011 Eastern seventh largest in the last 46 years (National Climatic Data United States Flooding Center, 2012b). In mountainous regions of New York and New England, the snowpack in some locations contained As noted by Holmes and others (2010) the genesis of the equivalent of 18–20 inches of water (National Weather most major widespread flooding is not just one particular Service, 2012a), of which the melting contributed to flooding storm but the result of frequent and consistently abundant by saturating the soils and filling the streams to near bankfull precipitation­ over the same geographic area for an extended conditions in numerous locations. period. As soils become saturated, infiltration capacities A dichotomy of conditions existed in the northeast decrease and stream levels can rise to bankfull conditions or during 2011 as evidenced when comparing October 2010 beyond. Additional precipitation and associated runoff will through September 2011 (The 12-month period from result in progressively severe flooding. In the Northeast, the October 1, 2010 to September 30, 2011 is referred to as water presence of frozen soils or accumulated snow cover may be year 2011) cumulative­ precipitation with historic average factors of great importance in determining the nature and cumulative precipitation­ (1981–2010) for four selected extent of flooding. Flooding in 2011 began in late winter with precipitation gages (National Climatic Data Center, 2012a; February monthly streamflows ranging from 25 to 75 percent fig. 5A–D). The October 2010 through September 2011 of normal for most of the Northeast (fig. 4). During the cumulative precipitation and the historic average cumulative winter of 2010–11, above-average snowfall was reported precipitation at four selected sites in the northeast are shown in the northern States. The March 2011 snowpack was the in figure A5 –D. Water year 2011 was the wettest on record

From U.S. Geological Survey WaterWatch, accessed December 12, 2012 (http://waterwatch.usgs.gov)

EXPLANATION Streamflow conditions, in percentile classes

High 10 to 24, below normal

Greater than 90, much above normal Less than 10, much below normal

76 to 90, above normal Low

25 to 75, normal

Figure 4. Monthly-average streamflow conditions across the United States for February 2011 (U.S. Geological Survey, 2012a).

rol15-HWCR00-0022_fig 04 2011 Flooding—Causes, Chronology, and Magnitude 7 ept. S A ug. uly J for selected une J (1981–2010) M ay 2011 A pr. M ar. Water year Water eb. F an. J D ec. ov. N 2010 O ct. B. Burlington, Vermont D. Norfolk, Virginia EXPLANATION ept. S A ug. uly October 2010 through September 2011 cumulative precipitation Historic cumulative precipitation (1981 – 2010) J une J 2011 M ay A pr. M ar. Water year Water (National Climatic Data Center, 2012b). (National Climatic Data Center, eb. F an. J D ec. ov. N 2010 umulative precipitation totals from October 1, 2010, to September 30, 2011, in relation historic average cumulative precipit ation C O ct.

A. Williamsport, Pennsylvania Trenton, New Jersey C. Trenton,

0 0

7 0 6 0 5 0 4 0 3 0 2 0 1 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0 Cumulative precipitation, in inches in precipitation, Cumulative Figure 5. sites in the Northeastern United States rol15-HWCR-0022_fig 05 rol15-HWCR-0022_fig 8 Flooding in the Northeastern United States, 2011 for hydrologic units in New England, New Jersey, New York, In Ohio, more than 4 inches of snow-water equivalent Ohio, and Pennsylvania (U.S. Geological Survey, 2012) as was present on February 27, 2011, and was reduced to trace precipitation was consistently above normal. In contrast, amounts by March 1, 2011 (National Weather Service, some hydrologic units in Delaware, Maryland, and Virginia 2012d). Peak-of-record streamflow was recorded at the USGS reported below normal to much-below normal runoff in water streamgages Ottawa River at Lima, Ohio (04187100); Honey year 2011 as precipitation was normal to below normal during Creek at Melmore, Ohio (04197100); and Old Woman Creek much of the year. at Berlin Road near Huron, Ohio (04199155). In this report, the 8-digit number listed in parentheses after a streamgage name is the USGS station number for that streamgage. In Chronology and Magnitude of Flooding during Southern New England upwards of 10 inches of snow-water 2011 equivalent was present on March 5, 2011, and was reduced to trace amounts by March 8, 2011 (National Weather Service, The 2011 Northeast floods recorded from February 2012d). Peak-of-record streamflow was recorded at the USGS through September were caused by persistent spring streamgage Saugatuck River near Redding, Conn. (01208990; precipitation combined with snowmelt, localized intense table 1). Rain and rapidly melting snow combined to mobilize precipitation of short duration, and excessive precipitation the ice cover on some northern rivers causing ice jams and amounts on saturated soils resulting from tropical cyclones. localized flooding in some locations. The late February and Well-above average precipitation amounts were observed early March events did not result in severe flooding outside in many areas of the Northeast. Parts of Pennsylvania, New of Ohio and southern New England; however, the widespread England, New Jersey, and New York received precipitation rainfall and snowmelt contributed­ to increased soil-moisture from 4–20 inches above average (National Weather Service, levels and streamflows in other areas. 2012b). The 12-month total precipitation was composed of Precipitation and snowmelt contributed to flooding in numerous discrete storm sequences that induced multiple late April and early May of 2011. During April 26–29, 2011, flooding events in different geographic locations. above normal temperatures, snowmelt in the mountains, and Peak streamflows for 327 streamgages in the northeast bands of rainfall and thunderstorms (fig. 7) caused flooding in that had estimated AEPs of about 4 percent or less were northern areas of New Hampshire, New York, and Vermont. included in table 1. Of these 327 streamgages, 183 recorded The snow-water equivalent in the mountains of New York peak-of-record streamflows during the 2011 floods. A few and Vermont held upwards of 10 inches of water on April 26, selected streamgages that reported peak streamflows with 2011(National Weather Service, 2012e). Substantial flooding estimated AEPs greater than 4 percent were also included in occurred along the Hudson River in New York as peak-of- table 1 to indicate the extent of major flooding. Approaches record streamflows were recorded at the USGS streamgages used in computing AEPs are described in the “Annual in North Creek (01315500), Hadley (01318500), Fort Edward Exceedance Probability Analysis, 2011” section of this (01327750), and Stillwater (01331095). The peak streamflow report. To minimize figure clutter, only the major rivers (for recorded at the USGS streamgage Hudson River at Newcomb, example, Connecticut, Hudson, Susquehanna Rivers) and NY (01312000), was the second highest peak on record and selected small rivers mentioned in the report text for that was only exceeded by the peak of January 1998 (table 1). particular flood period are shown on the figures. The 2011 Other peak-of-record streamflows were recorded at USGS peak-stage and streamflow data, previous peak-of-record streamgages in New Hampshire and Vermont (table 1). flood data, estimated AEP for the 2011 peak streamflow, and In the winter and spring of 2011, record rainfall estimates of the magnitude of the streamflow corresponding to and snowmelt for much of the Northeast contributed to the 4-percent, 2-percent, 1-percent, and 0.2-percent AEP are streamflows that were above normal at numerous USGS listed in table 1. For each figure corresponding to a particu­ streamgages in New England, New York, New Jersey, lar flood period, the size of the symbol for each streamgage Delaware, and Maryland (fig. 8). Precipitation totals for March represents the estimated AEP that corresponds to the magni­ through May in New York (16.68 inches), Pennsylvania tude of the computed peak streamflow—the less probable (less (19.13 inches), and Vermont (17.14 inches) were the highest frequent) the peak streamflow, the larger the symbol. Daily in 117 years of record (National Climate Data Center, 2012a). NWS rainfall observations for the United States were used to Record rainfall contributed to record flooding on Lake represent cumulative precipitation totals for individual storm Champlain during the spring of 2011. Lake Champlain was events (National Weather Service, 2012c). above the National Weather Service flood stage of 100 feet (ft) The first flood-inducing precipitation events began on for 68 days from April 13 to June 19, 2011. The peak water- February 28, 2011 (fig. 6A) and March 6, 2011 (fig. 6B). These surface elevation of Lake Champlain, 103.27 ft, was recorded snowmelt-enhanced events caused major flooding in parts on May 6, 2011, at the Lake Champlain at Burlington of Ohio, Connecticut, and Massachusetts. Flooding resulted (04294500) lake gage (Kiah and others, 2013). This elevation from increased streamflow as well as localized ice jamming surpassed the maximum known elevation since at least 1827 (U.S. Geological Survey, 2013). of 102.1 ft on May 4, 1869. 2011 Flooding—Causes, Chronology, and Magnitude 9 " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " "

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" " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " EXPLANATION " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " Flood annual exceedance probability (AEP), in percent —Number " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " 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precipitation totals for March 6–7, 2011 " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " , " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " 2 to 3 " " " " " " 3 to 5 " " " " " " " " " " " B " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " -85°13' " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " 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"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" """"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" """""""""""""""""""""""""""""""""""""""""""""50""""""""""""""""""""""""""""""""" """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" """"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" ""41°40'"""""""""""" """""""""""""""""""""""" """""""""""" """"""""""""""""""""""""""""""""""""""""""""""""51""""""""""""""""""""""""""""""""""""""" """"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" """"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" """"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" """"PENNSYLVANIA""""""""""""""""""""""""""""""""""""""""""""" """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" """B"as"e "fro"m" U".S." G"eo"log"ic"al" Surv"ey" digital""" data"", 1"99"8, "1:"5,0"00",0"00"""""""""""""""""""""""""""0 """"" 30 60 MILES Albers Equal-Area Conic projection Standard parallels 29°50’N and 45°50’N 0 30 60 KILOMETERS Central meridan 96°00’W North American Datum of 1983 EXPLANATION

Precipitation, in inches—Interval Flood annual exceedance probability (AEP), in percent—Number 1 inch is map number (table 1)

" 0 to 1 " 3 to 4 Greater than 4 " 1 to 2 " 4 to 5 2 to 4 " 2 to 3 " 5 to 6 1 to 2

Figure 6. Cumulative precipitation totals for A, February 28, 2011, and locations of U.S. Geological Survey streamgages in Ohio with peak streamflows that had an annual exceedance probability of less than 4 percent and B, cumulative precipitation totals for March 6–7, 2011 (National Weather Service, 2012c) and locations of U.S. Geological Survey streamgages in Connecticut and Massachusetts with peak streamflows that had an annual exceedance probability of less than 4 percent.—Continued

rol15-HWCR-0022_fig 06b 2011 Flooding—Causes, Chronology, and Magnitude 11

75°50' 73°45' 71°40'

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Base from U.S. Geological Survey digital data, 1998, 1:5,000,000 0 30 60 MILES Albers Equal-Area Conic projection Standard parallels 29°50’N and 45°50’N 0 30 60 KILOMETERS Central meridan 96°00’W North American Datum of 1983 EXPLANATION

Precipitation, in inches—Interval Flood annual exceedance probability (AEP), in percent—Number 1 inch is map number (table 1)

" 0 to 1 " 3 to 4 Greater than 4 0.2 to 1 " 1 to 2 " 4 to 5 2 to 4 " 2 to 3 " 5 to 6 1 to 2 Less than 0.2

Figure 7. Cumulative precipitation totals for April 26–27, 2011 (National Weather Service, 2012c) and locations of U.S. Geological Survey streamgages in New Hampshire, New York, and Vermont with peak streamflows that had an annual exceedance probability of less than 4 percent. rol15-HWCR-0022_fig 07 12 Flooding in the Northeastern United States, 2011

From U.S. Geological Survey WaterWatch, accessed December 12, 2012 (http://waterwatch.usgs.gov)

EXPLANATION Streamflow conditions, in percentile classes

High 10 to 24, below normal Greater than 90, much above normal Less than 10, much below normal 76 to 90, above normal Low 25 to 75, normal

Figure 8. Streamflow conditions at U.S. Geological Survey streamgages on May 25, 2011 (U.S. Geological Survey, 2012).

An isolated weather system in late May contributed Report (Avila and Cangialosi, 2011). The NWS rainfall precipitation amounts as much as 7 inches as a band of observations for the Northeast from August 27–29, 2011, storms tracked across northern Vermont on May 26–27, 2011 document cumulative precipitation of more than 6 inches over (fig. 9). Localized thunderstorms, hail, and heavy rainfall were an area of about 20,000 mi2, with some areas receiving two to associated with several miniature supercells (National Weather three times as much precipitation (fig. 11). The intense rainfall Service, 2012f). Substantial flooding was limited mostly to associated with Hurricane Irene contributed to new August streams with drainage areas less than 100 square miles (mi2), total precipitation records for New Hampshire, New Jersey, such as Sleepers River near St. Johnsbury, Vt. (01135300), New York, and Vermont (National Climatic Data Center, where a peak-of-record streamflow was recorded on May 27, 2012b). The record precipitation produced streamflows with 2011 (table 1). estimated AEPs less than 4 percent at 186 USGS streamgages, Hurricane Irene made landfall in New Jersey on of which 119 were period-of-record peaks. Particularly hard hit August 28, 2011, as a category 1 hurricane, according to initial were New York (46 peak-of-record streamflows), New Jersey reports, weakened to a tropical storm as it moved towards (32 peak-of-record streamflows), and Vermont (12 peak-of- New York and to an extra tropical cyclone over Vermont. record streamflows). Peak-of-record streamflows were recorded Winds and widespread flooding resulted in damage estimates at 31 additional USGS streamgages in Delaware, Maine, in excess of $7 billion and approximately 45 deaths (National Maryland, Massachusetts, New Hampshire, and Pennsylvania. Oceanic and Atmospheric Administration, 2012). 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G"eo"log"ica"l Su"rv"ey digital"" data"", 19"98", 1:5",00"0,0"00 """"""""" ""0"""""15 30 60 MILES " Alb"ers Equal-Area" Conic projection" " " " " " " " " Standard parallels 29°50’N and 45°50’N Central meridan 96°00’W 0 15 30 60 KILOMETERS North American Datum of 1927 EXPLANATION

Precipitation, in inches—Interval Flood annual exceedance probability (AEP), in percent—Number 1 inch is map number (table 1). Not all ranges are represented on map

" 0 to 1 " 3 to 4 Greater than 4 0.2 to 1 " 1 to 2 " 4 to 5 2 to 4 " 2 to 3 " 5 to 6 1 to 2 Less than 0.2

Figure 9. Cumulative precipitation totals for May 26–27, 2011 (National Weather Service, 2012c) and locations of U.S. Geological Survey streamgages in Vermont with peak streamflows that had an annual exceedance probability of less than 4 percent.

rol15-HWCR-0022_fig 09 14 Flooding in the Northeastern United States, 2011

Figure 10. Geostationary Operational Environmental Satellite (GOES) east image of Hurricane Irene making landfall near New York City on August 28, 2011. Image is courtesy of the National Oceanic and Atmospheric Administration, 2011. highways (Vermont Emergency Management, 2014). Runoff peaks (table 1). In the upper reaches of the Susquehanna greater than 700 cubic feet per second per square mile was River, near peak-of-record streamflows were recorded at the computed in high-elevation, small drainage tributaries in streamgages Susquehanna River at Unadilla, N.Y. (01500500) the Green Mountains (USGS streamgages Whetstone Brook and Susquehanna River at Conklin, N.Y. (01503000). Farther Tributary near Marlboro, Vt. [01156300] and Kent Brook near downstream along the Susquehanna River in New York, peak- Killington, Vt. [01150800]). The USGS streamgage at Saxtons of-record streamflows were recorded at the USGS streamgages River at Saxtons River, Vt. (01154000), recorded a peak in the communities of Vestal (01513500), Owego (01513831), streamflow of 21,600 ft3/s on August 28 that was 155 percent and Waverly (01515000). In Binghamton, N.Y., about 20,000 greater than the previous peak-of-record streamflow residents were evacuated (Associated Press, 2011) as the (8,460 ft3/s) set in 1976 (table 1), and the peak stage of 19.58 ft streamgage Susquehanna River at Vestal, N.Y. (01513500) was the maximum stage since at least 1869. reached a peak-of-record stage of 35.26 ft with an associated Recovery efforts for Hurricane Irene were still underway peak streamflow of 129,000 ft3/s on September 8. The peak when remnants of Tropical Storm Lee tracked across the stage of 35.26 ft was 1.6 ft higher than the previous peak-of- Northeast drenching already saturated areas of Maryland, New record stage of 33.66 ft set in 2006. Farther downstream at the Jersey, New York, and Pennsylvania. During September 8–9, streamgage Susquehanna River at Waverly, N.Y. (01515000), substantial precipitation and subsequent flooding took place located 1 mi. downstream from the New York-Pennsylvania as 6–12 inches were reported throughout the Susquehanna State line, a peak-of-record stage of 26.67 ft and discharge of River Basin and upwards of 12 inches of rain was reported 167,000 ft3/s were recorded. The 2011 peak stage exceeded in parts of southern New York, and greater than 20 inches the previous peak-of-record stage set during the flood of was reported in parts of Virginia (fig. 12). Peak streamflows June 2006 by more than 4 ft and exceeded the historic peak having an estimated AEP of less than 4 percent were recorded stage set back in March of 1936 by more than 5 ft (Suro and at 59 USGS streamgages, of which 31 were period-of-record others, 2009). rol15-HWCR-0022_fig 10 2011 Flooding—Causes, Chronology, and Magnitude 15

75° 74° 73° 72° 71° 70°

326 325 8

r

e

v i 1 R

t u c VERMONT ti MAINE ec 45° nn 322 Co

311 2 312 320 13 313 3 319 14 4 310 318 15 314 NEW 16 18 17 HAMPSHIRE

315 19 317 44° 316 21 20 23 22

61

24 68 67 65 74 88 69 66 30 64 27 31 75 89 63 26 87 29 MASSACHUSETTS 90 28

43° H 46 u d 32 s

o

NEW YORK 86 n

R 36

84 C i

85 91 v 48 o

82 e n r 37 83 n 80 76 41 e c r 81 39 t e i v 162 77 c i 165 45 u R 79 78 t a 92 40 163 R nn 97 a i h 93 94 v e 164 e u 42 r q 95 43 s 169 u 167 166 S 96 44 99 49 170 171 168 98 101 102 RHODE 172 103 CONNECTICUT ISLAND 42° 173 105 106 104 174

100 107 175 122 112 108 121 110 119 123 111 NEW 52 120 124 JERSEY 53 176 126 125 113 115 130 109 116 129 131 PENNSYLVANIA 118 127 179 117 133 180 139 147 114 132 136 134 41° 182 148 135 141 146 149 137 142 150 138 144 145 151 143 152 153 EXPLANATION 183 184 195 154 Precipitation, in inches—Intervals of 1, 2, 197 187 155 196 188 and 4 inches 189 186 201 185 " 0 to 1 " 5 to 6 " 14 to 16 190 S " " " u 1 to 2 6 to 8 16 to 20 s qu " " " eh 156 2 to 3 8 to 10 20 to 24 a 206 202 157 40° nn 159 " " a 204 207 158 3 to 4 10 to 12 Ri ve 208 r 203 " " 205 160 4 to 5 12 to 14

209 Figure 11. Cumulative Flood annual exceedance probability (AEP), 210 in percent—Number is map number (table 1) precipitation totals for 216 215 Greater than 4.0 or not estimated August 27–29, 2011

268 212 2.0 to 4.0 (National Weather Service, 214 211 MARYLAND 213 1.0 to 2.0 2012c) and locations of 0.2 to 1.0 39° DISTRICT OF DELAWARE U.S. Geological Survey COLUMBIA Less than 0.2 streamgages in Delaware, Maine, Massachusetts, Maryland, New Hampshire, 275 276 New Jersey, New York, and Vermont with peak Base from U.S. Geological Survey digital data, 1998, 1:5,000,000 0 30 60 120 MILES streamflows that had Albers Equal-Area Conic projection Standard parallels 29°50’N and 45°50’N an annual exceedance Central meridan 96°00’W 0 30 60 120 KILOMETERS probability of less than North American Datum of 1983 4 percent. rol15-HWCR-0022_fig 11 16 Flooding in the Northeastern United States, 2011

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Figure 12. Cumulative precipitation totals for September 6–9, 2011 (National Weather Service, 2012c) and locations of U.S. Geological Survey streamgages in Maryland, New Jersey, New York, and Pennsylvania with peak streamflows that had an annual exceedance probability of less than 4 percent.

rol15-HWCR-0022_fig 12 2011 Flooding—Comparison with Historic Floods 17 2011 Flooding—Comparison with at Danville, Pa. (01540500; fig. 14B), which have drainage areas of approximately 4,770 and 11,200 mi2 respectively, Historic Floods can have a daily mean streamflow that is of relatively similar magnitude as the instantaneous peak; whereas, streamgages In 2011, record-breaking rainfall events produced monitoring streamflow on relatively smaller rivers, such as the widespread flooding across the Northeast resulting in peak streamgages Saco River at Conway, N.H. (01064500; fig. 14C) streamflows being recorded at 327 streamgages that generally or North River at Shattuckville, Mass. (01169000; fig. 14D), equaled or exceeded the estimated 4-percent AEP streamflow which have drainage areas of approximately 385 and 90 mi2, (table 1), of which 263 were recorded during the months of respectively, may have daily mean streamflows significantly August and September. As previously discussed, some of the less than the instantaneous peak. Several factors and basin storm events in 2011 tended to be more isolated in nature characteristics may contribute to the ratio of peak streamflow leading to more localized flooding; however, the storms that to daily mean streamflow, such as rainfall duration and had the most effect on a regional basis were two tropical intensity, percentage of impervious surfaces within a basin, systems, Tropical Storm Irene and the remnants of Tropical and channel slope; however, for larger drainage basins the Storm Lee. Arriving only a week apart from each other time required for precipitation to drain through the basin is in late August and early September, tropical storms Irene probably a large part of the reason why the ratio is lower. and Lee caused catastrophic flooding. The NWS reported At many USGS streamgages, the 2011 peak streamflows 37 fatalities directly related to freshwater flooding and direct were the largest peaks in many decades. Major flooding freshwater flood damages of $3.9 billion from Virginia to because of a combination of rain with significant snowmelt Vermont (National Weather Service, 2014a). Other reports during April 26–May 4, 2011, resulted in new peak-of-record summarize 45 fatalities and more than $7 billion in total streamflows being recorded at Hudson River at Hadley, damages (National Oceanic and Atmospheric Administration, N.Y. (01318500, fig. 1); at Raquette River at Raymondville, 2012). Tropical Storm Irene made landfall at Little Egg Inlet, N.Y. (04268000, fig. 1) and at 10 additional streamgages in N.J., (fig. 1) on August 28, 2011, depositing 6–7 inches of the Hudson and St. Lawrence River Basins in northeastern precipitation across most of the State causing record-breaking New York. In western New York, streamgages on Flint floods at many streams. In New Jersey alone, about 1 million Creek and North Branch Salmon River, tributaries to Lake people across the State were evacuated, and every county was Ontario, also recorded new period-of-record streamflows declared a Federal disaster area (Watson and others, 2014). during April 26– May 4, 2011. A new period-of-record peak As stated by Holmes and others (2010, 2013) in streamflow of 34,900 ft3/s was recorded on April 28, 2011, discussing 2008 flooding in the Midwest United States and at the streamgage Hudson River at North Creek, N.Y. 2011 floods in the central United States, when significant (01315500; table 1), which has been in operation since rainfall events produce flooding, it is important to document 1907 (fig. 13), exceeding the previous peak streamflow of the magnitude of a flood so it can be put into context for 28,900 ft3/s on December 31, 1948. Other select streamgages comparison with previous floods (table 1). Eight USGS within the Hudson River Basin experiencing new peaks-of- streamgages in the Northeast were selected to illustrate record were the streamgages Indian River near Indian Lake, the comparison of historic flood peaks to the flood peaks N.Y. (01315000; table 1); West Canada Creek at Kast Bridge, recorded during the 2011 floods. A timeline of annual peak N.Y. (01346000; table 1); and Hudson River at Hadley, N.Y. streamflows for each of these eightstreamgages was plotted (01318500; table 1), which have periods of record dating back to show a comparison of the magnitude of 2011 flood to 1913, 1921, and 1922, respectively. In the St. Lawrence peaks with previous annual peak streamflows (fig. 13). The River Basin, the streamgage Raquette River at Piercefield, estimated values of the 4-, 2-, 1-, and 0.2-percent AEP flood N.Y. (04266500; table 1) has peak streamflow records dating quantiles are also included for each streamgage to provide back to 1909, and a new period-of-record peak streamflow of perspective among recorded annual peaks. Additionally, 10,400 ft3/s was set on May 1, 2011. New period-of-record hydrographs for a subset of these selected USGS streamgages peak streamflows also were recorded farther downstream at in the Northeast are presented in figure 14A–D that depict the Raquette River at South Colton, N.Y. (04267500; table 1) daily mean streamflow over time (represented by a solid and Raquette River at Raymondville, N.Y. (04268000; table 1; line) as well as the annual peak streamflows for select years Suro, 2011) streamgages. (represented by an independent marker), thus allowing In 1955, the mid-Atlantic and Northeast United States comparison of the 2011 flood events to previous major floods. experienced massive amounts of rainfall from hurricanes The annual peak streamflows are associated with a peak stage Connie and Diane, which were within about a week of each at a specific time (or instant) when a river crested; therefore, other. The hurricanes caused severe flooding across the region the values will be equal to, or higher than the daily mean resulting in an estimated 180 deaths and $680 million dollars streamflows. Comparatively, the hydrographspresented in in property damage (National Weather Service, 2014d). figure 14A–D show that streamgages monitoring streamflow The USGS streamgages recorded record flood peaks across on a larger river, such as the streamgages Susquehanna River the Northeast as a result of precipitation associated with at Waverly, N.Y. (01515000; fig. 14A) and Susquehanna River hurricanes Connie and Diane. Flood peaks from the 1955 18 Flooding in the Northeastern United States, 2011

Hudson River at North Creek, New York, USGS streamgage 01315500 d

n 40,000 c o e s

35,000 r e p

t

e 30,000 e f c i

b 25,000 c u

n

, i 20,000 w o l f

m 15,000 a e

r Mad River near Moretown, Vermont, USGS streamgage 04288000 t d s

n 30,000 10,000 k c o a e e s p

r l 5,000 e a 25,000 p u

t n e n

0 e A f

1900 1920 1940 1960 1980 2000 c

i 20,000 Water year b c u

n

, i 15,000 w o l f m

a 10,000 e r

78° 75° 72° 69° t s

k a

e 5,000 p

l a u

45° n n 0 MAINE A CANADA VERMONT 1900 1920 1940 1960 1980 2000 Water year

LAKE ONTARIO NEW HAMPSHIRE Saco River near Conway, New Hampshire, USGS streamgage 01064500 d

n 80,000

NEW YORK c o e s

70,000 r e

MASSACHUSETTS p

42° t e 60,000 e f c

CONNECTICUT i

b 50,000 c u

PENNSYLVANIA RHODE n ISLAND , i 40,000 w o l f

m 30,000 a e r t s 20,000 k a e p

l 10,000 a

NEW JERSEY u n n 0 MARYLAND A WEST ATLANTIC OCEAN 1900 1920 1940 1960 1980 2000 VIRGINIA 39° Water year D.C. DELAWARE 0 50 100 MILES VIRGINIA

North River at Shattuckville, Massachusetts, USGS streamgage 01169000 d 0 50 100 KILOMETERS n 40,000 c o e s

35,000 r e p

State boundaries from National Atlas, 2014 t e 30,000 e Streams from EPA River Reach Files, Level 1, 2004 f c i

Universal Transverse Mercator projection, Zone 18 b 25,000 c u

North American Datum of 1983 n

, i 20,000 w o l f

m 15,000 a e r t s 10,000 EXPLANATION k a e p

Estimated annual exceedance probability l 5,000 a u

streamflow (graphs)—In percent n n 0 0.2 A 1900 1920 1940 1960 1980 2000 1 Water year 2 4 U.S. Geological Survey (USGS) streamgage (map)

Figure 13. Annual peak streamflows through 2011 and the 4-, 2-, 1-, and 0.2-percent annual exceedance probability streamflows for selected U.S. Geological Survey streamgages in the Northeast.

rol15-HWCR00-0022_fig 13a 2011 Flooding—Comparison with Historic Floods 19

Susquehanna River near Waverly, New York, USGS streamgage 01515000 d

n 200,000 c o

e 180,000 s

r e p

160,000 t e e f 140,000 c i b 120,000 c u

n

, i 100,000 w o l f 80,000 m a e

r Susquehanna River at Danville, Pennsylvania, USGS streamgage 01540500

60,000 d t s n 400,000

k c o a 40,000 e e s p

350,000 r l e a 20,000 p u

t n e n 300,000

0 e A f

1900 1920 1940 1960 1980 2000 c i

b 250,000 Water year c u

n

, i 200,000 w o l f

m 150,000 a e r

78° 75° 72° 69° t s 100,000 k a e p

l 50,000 a u

45° n n 0 MAINE A CANADA VERMONT 1900 1920 1940 1960 1980 2000 Water year

LAKE ONTARIO NEW HAMPSHIRE Ramapo River near Mahwah, New Jersey, USGS streamgage 01387500 d

n 24,000

NEW YORK c o e s

r

e 20,000 p

MASSACHUSETTS t

42° e e f c CONNECTICUT i 16,000 b c u

PENNSYLVANIA n , i 12,000

RHODE w o l ISLAND f m

a 8,000 e r t s

k a

e 4,000 p

l a

NEW JERSEY u n

n 0 MARYLAND A WEST ATLANTIC OCEAN 1900 1920 1940 1960 1980 2000 VIRGINIA Water year 39° D.C. DELAWARE

0 50 100 MILES VIRGINIA Christina River at Coochs Bridge, Delaware, USGS streamgage 01478000 d

n 12,000 0 50 100 KILOMETERS c o e s

r

e 10,000 p

State boundaries from National Atlas, 2014 t e e Streams from EPA River Reach Files, Level 1, 2004 f c

i 8,000

Universal Transverse Mercator projection, Zone 18 b c u

North American Datum of 1983 n

, i 6,000 w o l f m

a 4,000 e r t s

EXPLANATION k a

e 2,000 p

Estimated annual exceedance probability l a u

streamflow (graphs)—In percent n n 0 0.2 A 1900 1920 1940 1960 1980 2000 1 Water year 2 4 U.S. Geological Survey (USGS) streamgage (map)

Figure 13. Annual peak streamflows through 2011 and the 4-, 2-, 1-, and 0.2-percent annual exceedance probability streamflows for selected U.S. Geological Survey streamgages in the Northeast.—Continued

rol15-HWCR00-0022_fig 13b 20 Flooding in the Northeastern United States, 2011

A. Susquehanna River at Waverly, New York, U.S. Geological Survey streamgage 01515000 180,000

EXPLANATION

d 160,000 2011 Peak n

c o 2011 Daily mean e s

r 2006 Peak

e 140,000 p

2006 Daily mean t e

e 1972 Peak f c i 1972 Daily mean

b 120,000 c u

n , i w

o 100,000 l f m a e r t s

80,000 k a e p

l a

u 60,000 n

40,000

20,000 Daily mean and a n

0 March April May June July August September October Month

B. Susquehanna River at Danville, Pennsylvania, U.S. Geological Survey streamgage 01540500 400,000

EXPLANATION

d 2011 Peak n 350,000

c o 2011 Daily mean e s

r 2006 Peak e p

2006 Daily mean t 300,000 e

e 1972 Peak f c i 1972 Daily mean b c u 250,000 n , i w o l f m

a 200,000 e r t s

k a e p

l 150,000 a u n

100,000

50,000 Daily mean and a n

0 March April May June July August September October Month

Figure 14. Streamflow for selected U.S. Geological Survey streamgages in the northeast for the 2011 flood period and selected previous major floods. 2011 Flooding—Comparison with Historic Floods 21

C. Saco River near Conway, New Hampshire, U.S. Geological Survey streamgage 01064500 60,000 d

n EXPLANATION c o

e 50,000 2011 Peak s

r

e 2011 Daily mean p

t 1987 Peak e e f 1987 Daily mean c i

b 40,000 1953 Peak c u 1953 Daily mean n , i w o l f m

a 30,000 e r t s

k a e p

l a u

n 20,000

10,000 Daily mean and a n

0 March April May June July August September October Month

D. North River at Shattuckville, Massachussetts, U.S. Geological Survey streamgage 01169000 35,000

EXPLANATION d

n 2011 Peak 30,000 c o

e 2011 Daily mean s

r

e 2005 Peak p

t 2005 Daily mean e e f 25,000 1987 Peak c i

b 1987 Daily mean c u

n , i w

o 20,000 l f m a e r t s

k

a 15,000 e p

l a u n

10,000

5,000 Daily mean and a n

0 March April May June July August September October Month

Figure 14. Streamflow for selected U.S. Geological Survey streamgages in the northeast for the 2011 flood period and selected previous major floods.—Continued 22 Flooding in the Northeastern United States, 2011 storms are still the highest recorded peaks for streamgages did surpass the 1999 flood peaks, establishing new period-of- such as West Branch Farmington River near New Boston, record flood peaks (table 1). Mass. (01185500); Rutgers Creek at Gardnerville, N.Y. In the New England region, flooding associated with (01368500); and Delaware River at Trenton, N.J. (01463500). Tropical Storm Irene in late August 2011 resulted in new For other streamgages that were in operation during 1955 and period-of-record peak streamflows being recorded at 2011, such as Mill River at Northampton, Mass. (01171500); 37 streamgages across Vermont, western Massachusetts, Roundout Creek at Rosendale, N.Y. (01367500); and Flat northern New Hampshire, and parts of eastern New York Brook near Flatbrookville, N.J. (01440000); flooding from (Olson and Bent, 2013). The 2011 peak-of-record streamflow Tropical Storm Irene produced comparatively higher peaks at the streamgage North River at Shattuckville, Mass. (table 1). In the Passaic and Hackensack River Basins in (01169000) was 30,300 ft3/s, which exceeded the previously New Jersey (fig. 1), the streamgages Whippany River at known maximum streamflow of 18,800 ft3/s, which was Morristown, N.J. (01381500); Wanaque River at Awosting, recorded in 2005 (figs. 13, 14D, table 1). Peak-of-record N.J. (01383500); Ramapo River near Mahwah, N.J. streamflows were also recorded at the streamgages Saco River (01387500; fig. 13); and Ramapo River at Pompton Lakes, near Conway, N.H. (01064500; figs. 13, 14C, table 1) and N.J. (01388000) recorded the highest flood peaks in more Mad River near Moretown, Vt. (04288000; fig. 13, table 1), than 90 years of record (table 1; Watson and others, 2014). A which have periods of record dating back to 1904 and 1928, photograph of rescuers using a boat to navigate the flooded respectively. streets of Pompton Lakes, N.J., after the Ramapo River In September 2011, the Susquehanna River main overflowed its banks because of the heavy rain associated stem experienced record-setting (or near record-setting) with Tropical Storm Irene on August 29, 2011, is shown in streamflows at USGS streamgages in New York and figure 15. Pennsylvania where water levels topped levees along Heavy rainfall from Hurricane Floyd in September 1999 the river, which inundated several cities in New York resulted in record flooding in parts of Maryland, Delaware, including Waverly, Owego, Vestal, Endicott, Johnson City, New Jersey, Pennsylvania and New York. The flood peaks and downtown Binghamton (National Weather Service, from September 1999 at several streamgages in the northeast 2014a). The streamgage Susquehanna River at Waverly, such as Wissahickon Creek at Mouth, Philadelphia, Pa. N.Y. (01515000; figs. 13, 14A, table 1), situated near the (01474000), White Clay Creek near Newark, Del. (01479000), New York-Pennsylvania border, has been in operation since and the Raritan River at Manville, N.J. (01400500), which 1936, and the September 2011 flood peak is the largest has 100 years of streamflow record, were not surpassed by the streamflow recorded at this site and exceeds the previous flood peaks of 2011. However, for other streamgages such as peak-of-record stage set in 2006 by more than 4 ft. The peak Sawmill Creek at Glen Burnie, Md. (01589500); Hackensack streamflows associated with the September 2011 event at River at West Nyack, N.Y. (01376800); and Christina River at the streamgages along the Susquehanna River at Towanda Coochs Bridge, Del. (01478000; fig. 13), all of which were in (01531500; table 1); at Wilkes-Barre (01536500; table 1); operation in 1999, flooding from Tropical Storm Irene in 2011 and at Danville, Pa. (01540500; figs. 13, 14B, table 1); were second only to the peak-of-record streamflows associated with Hurricane Agnes in 1972. In Harrisburg, Pennsylvania, where the forecast of flooding led to the evacuation of about 100,000 people, including 10,000 people and the Governor’s residence in the downtown area (National Weather Service, 2014a), the September 2011 recorded peak streamflow at the streamgage Susquehanna River at Harrisburg, Pa. (01570500; table 1) was 590,000 ft3/s, well below the 1972 peak-of-record streamflow of 1,020,000 ft3/s. Conversely, on Swatara Creek (a tributary joining the Susquehanna River approximately 10 miles downstream from the Susquehanna River at Harrisburg streamgage), the September 2011 peak streamflow recorded at the streamgage Swatara Creek at Harper Tavern, Pa. (01573000; table 1) exceeded the 1972 peak by approximately 12 percent. The difference in annual peak streamflow relations between the Susquehanna River at Harrisburg streamgage and the Swatara Creek at Harper Tavern streamgage for the 1972 and 2011 storm events may Figure 15. Rescuers use a boat to navigate the flooded streets be attributed to relative size of basins at the gaged locations 2 of Pompton Lakes, N.J., as the Ramapo River overflows its banks (24,100 and 337 mi , respectively) and the geographic and because of the heavy rain on August 29, 2011. Photograph by temporal distribution of the rainfall associated with each Robert Atkinson, U.S. Geological Survey. storm event. Annual Exceedance Probability Analysis for 2011 23

The 1972 flooding was a result of heavy and persistent probability distribution. The probability distribution relates rainfall associated with the remnants of Hurricane Agnes and the probability to the magnitude of a specific peak streamflow resulted in major flooding on many of the tributaries and much being equaled or exceeded in any given year. of the main stem of the Susquehanna River in Pennsylvania The selection of the probability distribution and the and the southern tier of New York. Nationwide, 122 deaths process of fitting the parameters of the distribution can vary were attributed to Agnes, of which 50 were in the State of depending on the underlying characteristics of the data. The Pennsylvania, and total damages from the storm reached more Interagency Advisory Committee on Water Data produced than $3 billion dollars nationwide, with more than $2 billion standard guidelines adopted by many Federal agencies for dollars in losses in the Susquehanna River Basin (National consistent computations of these probabilities known as Bul- Weather Service, 2014c). letin 17B (Interagency Advisory Committee on Water Data, 1982). These guidelines recommend the use of the LPIII distribution and the “method of moments” for estimating the Annual Exceedance Probability distribution parameters (mean, standard deviation, and skew- ness of the data). The analysis is based on annual peak stream- Analysis for 2011 flow data at USGS streamgages, which are available online from the USGS National Water Information System (NWIS) This report provides the results of exceedance prob- at http://waterdata.usgs.gov/nwis (U.S. Geological Survey, ability analyses of annual peak streamflow for 327 selected 2013). In many previously published USGS reports flood streamgages in the Northeast that experienced moderate to probabilities have been expressed as flood frequencies using major flooding during 2011. The probability analyses were a T-year recurrence interval for a particular flood quantile (for computed using annual peak streamflow data through 2011. example, the “100-year flood”). Use of the T-year recurrence Current methods outlined in Bulletin 17B (Interagency interval to describe flood probability is now discouraged by Advisory Committee on Water Data, 1982) were used for the many agencies (including USGS) because it tends to confuse analysis, but the results of newer experimental methods of the general public. A T-year recurrence interval is sometimes flood frequency analysis are presented in table 2 (available at interpreted to imply that there is a set time interval between http://dx.doi.org/10.3133/pp1821) for comparison. An expla- floods of a specific magnitude when, in fact, floods are random nation of these newer experimental methods is provided in the processes that are best understood using probabilistic terms. section titled Annual Exceedance Probability using Expected The use of an AEP percentage to describe the estimated prob- Moments Algorithm. ability of selected flood magnitudes is recommended as a way The evaluation of future flood risk is an integral part to better communicate the annual chance of occurrence. The of why the probability of annual maximum streamflow reader can convert from the AEP to the previously used T-year is analyzed. Knowing the flood ranking at a streamgage recurrence interval by simply taking the reciprocal of the AEP. or the maximum elevation at selected locations helps in For example, the 1-percent AEP flood corresponds to a stream- understanding local flooding conditions, but an analysis of the flow magnitude that has a 1-percent chance of being equaled exceedance probability of an annual peak streamflow allows or exceeded in any given year. A 1-percent chance relates to a for a better evaluation of the flood risk and provides data probability of 0.01 when expressed as a decimal. The recipro- for better infrastructure design and flood damage mitigation cal of 0.01 is 100; thus, the T-year recurrence interval for the planning. Annual peak streamflows are used to estimate a 1-percent AEP flood is referred to as the 100-year flood.

Aerial views of damage in West Bridgewater, Vermont, as a result of floodwaters during Tropical Storm Irene in August 2011. Photograph courtesy of Lars Gange, Mansfield Heliflight. 24 Flooding in the Northeastern United States, 2011

AEP flood quantiles can be computed in many different Holmes and others (2010) provided detailed discussions­ ways, including the above referenced Bulletin 17B methods about how to express the accuracy of RREs in terms of equiv- that were used for this report. The reliability of the flood alent years of record and suggested that weighting by variance quantiles computed using Bulletin 17B methods may be provides a more natural characterization of the underlying expressed as a “variance of prediction” that is computed uncertainty of the various peak streamflow estimates. At a by using the asymptotic formula given by Cohn and others gaged location, the optimal estimate of the AEP flood quantile (2001), with the addition of the mean-squared error of is determined by weighting the AEP flood-quantile estimate generalized skew (Griffis and others, 2004). The variance­ determined from the Bulletin 17B methods with the AEP flood of prediction varies as a function of record length, the fitted quantile estimate determined from the RRE. The weights are flood-probability distribution parameters (mean, standard­ inversely proportional to the variances of prediction (equa- deviation, and weighted skew), and the accuracy of the tion 1), yielding the weighted estimator: method used to determine the regional skew component of the weighted skew. ()Var[]RRE ×+LogLQVar[]LPIII × ogQ LogQ = PL ,, PIII P RRE (1) An additional method is the use of regional regression PO, PT ()VarR[ RRE][+VarLPIII] techniques to develop regional regression equations (RRE) to estimate the AEP flood quantiles. These techniques are used where to develop a relation between flood-probability data at many QP,OPT is the optimal estimate of AEP flood quantile streamgages throughout a region and basin characteristics of for a particular probability of flooding p( ; those streams (Jennings and others, 1994). Once developed, Interagency Advisory Committee on Water the RRE can be used to estimate various streamflow Data, 1982, appendix 8), characteristics, such as the 1-percent AEP flood quantile, Var[RRE] is the variance of the RRE estimate of for almost any location along a stream (gaged or ungagged) the AEP flood quantile for a particular within the reliable boundaries of the RREs. The variance­ of probability of flooding p( ), prediction from the regional regression is a function of the QP,LPIII is the Bulletin 17B method estimate of RRE and values of independent variables used to develop the the AEP flood quantile for a particular streamflow estimate from the RRE. The variance generally probability of flooding p( ), increases with departure of actual values from mean values of Var[LPIII] is the variance of the Bulletin 17B estimate the independent variables. of the AEP flood quantile for a particular The USGS National Streamflow Statistics (NSS) Pro- probability of flooding p( ), and gram has software (http://water.usgs.gov/ software/nss.html) QP,RRE is the RRE estimate of the AEP flood quantile that can be used to apply the RRE by allowing the user to for a particular probability of flooding p( ). enter basin and land-use characteristics­ (drainage area, basin Previous USGS reports have expressed the accuracy slope, area of wetlands, surficial geology, and so on) that are of RREs in terms of equivalent years of record and used used in the equations as independent (explanatory) variables these estimates with the length of record at the streamgage into RRE and compute various streamflow characteristics.­ The to combine RRE and LPIII AEP flood quantile estimates (for USGS StreamStats Program has developed a more compre- example, Hodge and Tasker, 1995; Ries and Dillow, 2006). hensive online tool called “StreamStats”, which allows the Although this method was presented in the Bulletin 17B user to work in an interactive map environment to select a guideline, the length of record can fail to account for the true site of interest and have basin and streamflow characteristics variance of LPIII flood-probability estimates. For all records computed and displayed in a report format (http://water.usgs. of the same length, the accuracy is assumed to be of the same gov/osw/streamstats). reliability, which may not be accurate. The flood-probability distributions computed from two different streamgage records of the same length may not be of equal reliability because of differences in underlying variances of the streamflow records for each site. For example, one streamgage may have less stable control conditions and more highly varied records making it more difficult to accurately measure the streamflow than another. The LPIII distributions at the first streamgage, therefore, could have larger variances than the second streamgage in the example. More importantly, the equivalent years-of-record concept, although relatively easy to understand, misrepresents the relation between the AEP flood quantile estimates and the variances. Using estimated variances Debris catches on snowmobile bridge near Waterbury, Vermont, as a result provides a more natural characterization of the underlying of floodwaters from the Winooski River during Tropical Storm Irene, in August uncertainty of the various streamflow estimates. The weighted 2011. Photograph courtesy of Lars Gange, Mansfield Heliflight. estimates of the AEP flood quantiles corresponding to the Annual Exceedance Probability using Expected Moments Algorithm 25 4-, 2-, 1-, and 0.2-percent AEP, along with their respective Annual Exceedance Probability using 95-percent confidence limits, for selected streamgages in the Northeast, are listed in table 1. Streamgages that generally Expected Moments Algorithm recorded an annual peak streamflow that exceeded the 4-percent AEP during 2011 were included in table 1, with a few The Hydrology Subcommittee of the Interagency exceptions to help define the extent of major flooding. Advisory Committee on Water Data (1982) developed the Another statistic included in table 1 that was typically not Bulletin 17B guidelines for determining flood frequency included in previous USGS reports is the “typical range” for studies in the United States. These guidelines include methods the 66.7-percent confidence level for the computed AEPs for for improving skew estimates and testing for outliers, but the 2011 flood peaks. In table 1, the values under the column the authors of Bulletin 17B also identified the need for heading of “AEP for observed 2011 flood” are the estimated methodological improvements and recommended further AEPs for each 2011 flood peak and the corresponding typical study. The Hydrologic Frequency Analysis Work Group is range of the AEP. The AEPs of the 2011 floods were calculated considering modest changes to Bulletin 17B guidelines to using the methods outline in USGS Office of Surface Water address those recommendations for improved methods. The Technical Memorandum 2013.01 (U.S. Geological Survey, work group is proposing the adoption of the expected moments 2012b). As previously stated, the AEP is estimated from algorithm (EMA; Cohn and others, 1997) with Multiple a LPIII statistical model fit to the at-site peak streamflow Grubbs-Beck low outlier screening (Cohn and others, 2013). data. The typical range is presented to report the lower and AEPs using the EMA method for 122 of the upper bounds on 66.7-percent confidence level for the true 327 streamgages included in table 1 are listed in table 2 AEP. These bounds, unlike the AEP estimate, are based on (available at http://dx.doi.org/10.3133/pp1821). The peak order statistics and do not assume a model. The distinction streamflows that are reported in table 1 are also included in is important because the model-based AEP estimates may table 2 as a reference. The 122 streamgages included in table 2 occasionally lie outside the nonparametric confidence bounds, that have AEP estimates using the EMA method are also which intuitively may not make sense to the reader. The shown in figure 17 as an additional geographic reference. confidence bounds, or typical range of the true AEP, are intended to communicate the magnitude of the uncertainty in estimates of the AEP by providing the likely range of the AEP corresponding to the k-th largest event in a sample of size N. For example, if the exceedance probability corresponding to a particular flood at 2 percent is estimated, the understanding is that the uncertainty in this statistic is large, and, in general, a 66.7-percent confidence level for the true exceedance probability of the 2-percent flood extends from 0.4 to 4 percent. The Streamflow of 2011—Water Year Summary shows that statewide streamflow in the northeast was above average to wet using a statistical period from 1930 to 2011(Jian and others, 2012). During 2011, the USGS recorded peak streamflows that were generally equal to or less than a 4-percent AEP at 327 streamgages in the northeast. These 327 streamgages that generally recorded moderate to major flooding during 2011 in the northeast are listed in table 1 and shown in figure 16. More than 180 of the 327 streamgages listed recorded a new period-of-record peak streamflow in 2011. Peak streamflows greater than or equal to the 1-percent AEP discharge were recorded at 129 streamgages across Connecticut, Delaware, Maine, Maryland, Massachusetts, Ohio, Pennsylvania, New Hampshire, New Jersey, New York, and Vermont. Additionally, nearly 100 of the 129 peaks with an AEP of 1 percent or less were a result of the flooding associated with Hurricane Irene in late August 2011, and at 24 of these streamgages the recorded peak was extreme enough to exceed the 0.2-percent AEP during the August storm. A total of 31 of the streamgages listed in table 1 recorded peak streamflows that equaled or exceeded the 0.2-percent AEP Aerial view of damage along U.S. Route 4 near Killington, Vermont, as a result of floodwaters during Tropical Storm Irene in August 2011. Photograph during 2011. courtesy of Lars Gange, Mansfield Heliflight. 26 Flooding in the Northeastern United States, 2011 # * # * # * # * 109 # * # * # * 110 113 # * # * # * 131 # * 108 112 150 # * # * # * # * 128 # * 132 123 129 127 # * # * 134 # * # * # * # * # * 130 # * 149 Study area # * # * # * 118 133 # * # * 148 145 121 125 146 124 122 # * # * # * # * # * 126 # * 114 # * 120 142 # * 147 # * 143 # * # * 117 116 # * 100 119 # # * * 144 139 141 # * 115 # * # * 140 # * # * 137 # * 178 # * 135 138 # * MAINE # * 176 136 # * 179 177 # * # * # * # * 182 70° 180 1 # * EXPLANATION 2 # * annual exceedence probability (AEP) —Labeled with map number ISLAND RHODE 6 4 percent to less than 2 2 percent to less than 1 1 percent to less than 0.5 0.5 percent to less than 0.2 Not applicable 7 5 4 # * Drainage area studied U.S. Geological Survey streamgages with 3 # * # * # * 35 # * 9 8 25 NEW NEW # * # * # * 11 13 # * 33 327 34 # * 10 # * # * 17 # # # * # * # * * * # * # * 23 # * 12 14 326 # * 21 200 # * 16 HAMPSHIRE 31 325 # * # * MASSACHUSETTS # * # * 30 38 # * 32 # # * * 37 # * 45 24 15 19 320 # * 29 323 # * # * 43 # * # * 27 # * # * 22 # * # * 20 # * # * 18 # * 44 # * 36 321 # * 28 41 # * # * # * # * # * # * 26 # * # * 319 # * # * 46 65 324 # * # * 39 322 50

317 42 # * 316 # *

67 # * CONNECTICUT 51 66 40 # * # * # * # * # OCEAN ATLANTIC * 318 # * 68 63 # * 61 64 # * # * # * # * # * # * 47 107 # * # * VERMONT 49 60 105 # * 89 62 48 312 315 # * # * # * 103 # * # * 313 # * # * # * # * 106 # * 90 # * 314 # * # * 97 59 # * # * # * 151 153 # * 69 # 102 * 154 # * # * 99 155 # * 57 88 311 # * Lake # * # * # * 55 104 # * # * # * 91 # * # * 58 # * # * # * # * # * # * # * 310 # * # * # * # # * * 87 # * # * # * 101 # * # * # * # * # * # * # * # * # # * * # * 100 # * 98 # * 186 # * 152 # * # * # * # * 157 # * 54 # * # # * * # Champlain * # * # # * * # * # * # 86 * 173 # * # * # * # * # * 74 56 # * 307 # * # * 187 143 # * # * # * # * 184 # * # * # * # * # * # * 85 # * # * # * # * # * # * # * # * # * # * # * 158 # * # * # * # * # * # * # * 156 70 # * 185 # * # * 308 # * # * 174 73 75 # * # * 309 # * # * # * # * # * 160 # * 183 159 190 # * # * NEW JERSEY NEW # * 217 # # * * 200 # * # * # * 71 304 # * 175 # * 75° # * 165 # * # * # * # * 72 # * # * # * 218 # * # * 161 # * 198 # * 305 199 # * 220 219 # * 224 188 # * 211 202 # * 191 189 # * 208 # * 221 # * # * 223 # * 302 # * 181 210 195 # * # * # * # * # * # * # * 212 225 303 # * # * 215 197 # * 201 # * 209 196 # * # * DELAWARE 235 306 # * # * # * 222 194 # * 192 # * # * # * 236 227 234 213 # * # * 226 # * 301 214 # * # * # * # * 193 # * # * # * 230 255 256 228 # * # * 216 232 266 # * # * 249 237 MILES # * 242 296 # * 238 # * # * 229 # * # * 252 # * # * 265 # * # * # * # * 258 # * 244 264 250 CANADA # * # * 100 # * 231 # * # * 233 # * # * # * 254 241 # * # * 300 # * 299 # * # * # * 251 267 # * # * # * # * # * 274 # * # * # * 257 # * # * 270 253 # * # * 264 # * # * # * NEW YORK NEW 268 KILOMETERS 269 243 245 246 248 262 # * 239 276 # * 240 273 247 # 271 * 275 298 # * 100 261 # * 272 297 50 50 ONTARIO Lake Ontario 0 0 95 # * MARYLAND # * # * 94 VIRGINIA 96 78 # * # * 76 # * # * 77 # * # * # * 166 # * 93 # * # * 167 278 # * PENNSYLVANIA 82 98 92 # * 80 168 # * 79 # * # * # * # * # * 80° # # * * # * 81 169 162 84 83 171 85 170 # * 172 # * 295 # * 163 # * 164 # * 294 279 280 # * # * # * 292 293 # * # * # * # * 278 WEST VIRGINIA WEST Lake Erie 291 . (Data are listed in table 1). # * 290 289 # * Lake Huron # * 288 281 # * 285 287 OHIO # * # * # * 286 KENTUCKY 284 283 # * # * 85° 282 # * MICHIGAN 207 206 # * nnual exceedance probabilities computed for peak streamflows during 2011 at selected USGS streamgages in the Northeastern Unit ed States and major # * 203 # * A # * 205 # *

204

Michigan Lake Lake INDIANA Base from U.S. Geological Survey digital data, 1983, 1:6,000,000 Mercator projection Universal Transverse North American Datum of 1983 Figure 16. drainage basins studied during 2011 flooding 44° 42° 40° 38° Annual Exceedance Probability using Expected Moments Algorithm 27

75° 70°

NEW YORK 123 119 ! 122 ! 6 ! ! 128 ! 120 124 ! 111 ! !! ! ! 328 176! 125!130 ! ! 112 CONNECTICUT 326 ! 129 178 115 113 ! 177 ! 126 ! 7 ! ! ! 131 327 ! ! 116 ! 127 325 117 118 ! 324 8 179 ! ! ! 180 ! ! 133 132 140 139 ! ! 10 ! ! !114 ! 323 ! 11 9 1 136 ! ! ! ! ! !! 147 148 322 182! ! 134 ! 12 ! MAINE 135 ! !!146 ! !321 137 141 142 ! ! ! 149 13 ! 145 ! ! 144 150 ! 138 319 320 ! !3 2 143 151 ! ! ! NEW ! 14 ! 44° 152 15 183 JERSEY !! ! 4 ! 153 184 ! VERMONT ! 154 PENNSYLVANIA 18 !16 ! ! ! 187 155 ! 318! ! 185 ! 17 190 ! 186 316 19 ! ! 20 NEW HAMPSHIRE ! 157 60 ! 200 ! 21 202! ! ! ! 156 !! 209 ! 22 23 ! 159 158 ! !67 24 DELAWARE MARYLAND ! 160 ! 161 65 !30 ATLANTIC OCEAN !! 26 64 ! ! !!27 !46 28 29 !32 MASSACHUSETTS 47 !36 !! 39 !37 48 ! !41 42° ! ! 40 ! 38 45 42! RHODE !43 ! ISLAND NEW YORK 44 PENNSYLVANIA ! 50 CONNECTICUT !51 !! ! ! !! ! ! ! ! ! ! !! !!! ! !! ! NEW YORK ! ! !! ! ! !!! ! ! ! !!! ! !! ! ! NEW ! ! JERSEY ! ! !! ! ATLANTIC OCEAN 40° ! EXPLANATION ! !! ! 1 ! U.S. Geological Survey streamgages ! ! and map number ! ! ! ! ! MARYLAND ! ! DELAWARE Base from U.S. Geological Survey digital data, 1983, 1:6,000,000 0 30 60 MILES Universal Transverse Mercator projection North American Datum of 1983 Study area 0 30 60 KILOMETERS

Figure 17. Selected U.S. Geological Survey streamgages in the Northeastern United States with annual exceedance probabilities computed using the expected moments algorithm method. (Data are listed in table 2). 28 Flooding in the Northeastern United States, 2011 Summary analyzed were estimated to have an AEP of 1 percent or less at 129 streamgages in Connecticut, Delaware, Maine, Mary- The combination of several major flooding events in 2011 land, Massachusetts, Ohio, Pennsylvania, New Hampshire, caused damages that were estimated to exceed $7 billion in the New Jersey, New York, and Vermont. Flooding associated Northeastern United States. The flooding in the Northeastern with Hurricane Irene contributed to 100 of the 129 stream- United States also resulted in approximately 45 deaths and flow peaks with an AEP of 1 percent or less and 24 of the more than 180 U.S. Geological Survey (USGS) streamgages peak streamflows with an AEP of 0.2 percent or less. In 2011, recorded new period-of-record maximum. The flooding events 31 streamgages recorded peak streamflows that equaled or began in late February and early March with snowmelt- exceeded the more extreme 0.2-percent AEP. enhanced peak streamflows in northern Ohio, western Connecticut, and central Massachusetts. In late April, parts of northern New Hampshire, New York, and Vermont were Acknowledgments flooded as a result of rainfall on heavy snowpack. Relatively wet conditions persisted throughout the year as a result of The authors would like to thank Robert Mason and numerous small scale rain events (summer thunderstorms) Robert Holmes for their support and contributions to this from late May through mid-August, until record-setting report and all of the U.S. Geological Survey hydrologists and precipitation associated with Hurricane Irene and the remnants hydrologic technicians that worked extremely hard during and of Tropical Storm Lee caused major flooding disasters after these floods to collect and analyze the data used in this throughout the Northeastern United States. report. The authors would also like to acknowledge and thank In the winter and spring of 2011, record rainfall and Elizabeth Ahern, Gardner Bent, Jonathan Dillow, Gary Firda, snowmelt throughout many areas of the Northeastern United Gregory Koltun, Rick Lumia, Scott Olson, Greg Stewart, and States contributed to streamflows that were above normal at Kara Watson for providing flood and flood frequency data numerous USGS streamgages in New England, New York, used in this report and Greg Sturgis and Kara Watson for New Jersey, Delaware, and Maryland. During the spring their support in developing the tables and figures used in this of 2011, the streamgage Lake Champlain at Burlington,Vt. report. (04294500) recorded record flooding as a result of the combined runoff from record rainfall and snowmelt. Lake Champlain was above the National Weather Service flood stage of 100 feet (ft) for 68 days from April 13 to June References Cited 19, 2011, and peaked at 103.27 ft on May 6, 2011, surpassing the maximum known elevation since at least 1827 of 102.1 Associated Press, 2011, Tropical Storm Lee drenches ft on May 4, 1869. The intense rainfall associated with northeast, prompting evacuations due to flooding, accessed Hurricane Irene contributed to new August total precipitation on December 20, 2012, at http://www.foxnews.com/ records for New Hampshire, New Jersey, New York, weather/2011/09/08/remnants-lee-fresh-flood-worries-to- and Vermont and resulted in new period-of-record peak east/. streamflows being recorded at 119 USGS streamgages. In the Green Mountains of Vermont, 13 communities were isolated Avila, L.A., and Cangialosi, J., 2011, Tropical cyclone report, for days as floodwaters damaged or destroyed bridges, hurricane Irene, 21–28 August 2011: National Hurricane culverts, and 500 miles of State highways. New York reported Center 14 December 2011, 45 p., accessed on March 22, similar damages to roads and bridges, and every county in 2015, at http://www.nhc.noaa.gov/data/tcr/AL092011_Irene. New Jersey was declared a Federal disaster area. Several pdf. streamgages in New York and New Jersey, with more than 90 years of data, recorded new peak-of-record maximums Bent, G.C., Medalie, Laura, and Nielsen, M.G., 2013, High- during the 2011 flood. In early September 2011, rainfall water marks from Tropical Storm Irene for selected river associated with the remnants of Tropical Storm Lee caused reaches in northwestern Massachusetts, August 2011: the main stem of the Susquehanna River and many tributaries U.S. Geological Survey Data Series 775, 13 p., also to rise to record setting levels in southern New York and available at http://pubs.usgs.gov/ds/775/. Pennsylvania. The peak streamflows associated with the early Cohn, T. A., Lane, W. L., Baier, W. G., 1997, An algorithm for September 2011 event at the streamgages Susquehanna River computing moments-based flood quantile estimates when at Towanda, Pa., Susquehanna River at Wilkes-Barre, Pa., and historical flood information is available: U.S. Geological Susquehanna River at Danville, Pa., were second only to the Survey, Water Resources Research, v. 33, p. 2089–2096. peak-of-record streamflows associated with Hurricane Agnes in 1972. Cohn, T.A., Lane, W.L., and Stedinger, J.R., 2001, Confi­dence Annual Exceedance Probabilities (AEPs) were esti- intervals for Expected Moments Algorithm flood quantile mated for 327 sites in the Northeastern United States using estimates: Water Resources Research, v. 37, no. 6, p. 1695– annual peak streamflows through 2011. The peak streamflows 1706. References Cited 29

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Glossary

Note: Glossary definitions are taken from Langbein and Iseri (1960) whenever possible.

A E annual exceedance probability (AEP) The expected moments algorithm is an alterna- probability, or chance, of a flood of a given tive to maximum likelihood estimation (MLE) streamflow magnitude being equaled or or the Bulletin 17 (Interagency Advisory exceeded in any given year. The probability Committee on Water Data, 1982) methods for can be expressed as a fraction, decimal, or incorporating historical information in flood percentage. frequency analysis or studies. annual exceedance probability flood quantile (AEP flood quantile) The value of the peak F streamflow that corresponds to a particular flood An overflow or inundation that comes annual exceedance probability (for example, from a river or other body of water, and 1-percent AEP flood quantile). causes or threatens damage. flood peak The highest value of the stage B or streamflow attained by a flood; generally Bulletin 17B Report by the Interagency designated as peak stage or peak streamflow, Advisory Committee on Water Data, pub- respectively. The annual flood peak is the lished in 1982, that identifies guidelines largest flood peak for a given year or water delineates the recommended method for year. flood-probability analysis. flood quantile See annual exceedance prob- ability flood quantile. C flood stage The stage at which overflow of confidence limits To gage the accuracy the natural banks of a stream begins to cause of an approximation based on a probability damage in the reach in which the water sur- distribution, upper and lower confidence face elevation is measured. limits can be estimated based on the prop­ erties of the probability distribution. This H report includes the 95-percent confidence limits of the estimate of the flood quantiles as hydrograph A graph showing stage, stream- computed by the methods outlined in Bulletin­ flow, velocity, or other property of water with 17B. respect to time. confidence interval is based on order statis- L tics and is intended to communicate the gen- eral magnitude of the uncertainty in estimates log-Pearson type III probability distribution of the AEP by providing the likely range of (LPIII) One of the family of probability dis- the AEP corresponding to the k-th largest tributions developed by Karl Pearson that is event in a sample of size N. AEP estimates commonly used in the United States as a best- may occasionally lie outside the nonparamet- fit for the distribution of annual peak flood ric confidence intervals. streamflows and is suggested in Bulletin 17B as “the base method” for analysis procedures D developed by the Interagency Advisory Com- mittee on Water Data (1982). discharge In its simplest concept discharge­ means outflow; therefore, the use of this term O is not restricted as to course or location, and it can be applied to describe the flow of water orographic lifting The change in air flow from a pipe or from a drainage basin. when the topography of the land forces the air up the side of a mountain. 32 Flooding in the Northeastern United States, 2011

P recurrence interval The average interval­ of peak-of-record streamflow The larg­est time within which the given flood is expected instantaneous streamflow value for the period to be equaled or exceeded once. that data have been collected. regional regression equation Equa­tion peak stage See flood peak. developed through use of regression tech- niques that relate the flood-probability data peak streamflow See flood peak. at many streamgages in a region to the basin precipitation As used in hydrology, precipi- characteristics of the streams monitored by tation is the discharge of water, in liquid or the streamgages. For any location along a solid state, out of the atmosphere, generally stream, a user can enter the basin characteris- upon a land or water surface. It is the common tics (for example, drainage area, basin slope) process by which atmospheric water becomes as independent variables­ into the equations surface or subsurface water. The term “precip- and compute various flow characteristics (for itation” is also commonly used to designate example, 1-percent AEP flood quantile, the quantity of water that is precipitated. 2-percent AEP flood quantile, and annual probability A means to express the likeli- mean streamflow). hood of something occurring, also known as chance. The probability can be expressed as a S fraction, decimal, or percentage. stage Height of a water surface above probability distribution Describes the range of an established datum, also known as gage possible values that a random variable­ can attain height. and the probability that the value of the random streamflow The discharge that occurs in a variable is within any subset of that range. natural channel. Although the term discharge can be applied to flow in a canal, the word R streamflow uniquely describes the discharge rating curve A graph showing the rela- in a surface stream course. The units of tion between the stage (gage height), usually measure­ment generally are reported in cubic 3 plotted as the ordinate, and amount of water feet per second (ft /s). flowing in the channel (streamflow) expressed streamgage A particular site on a stream as volume per unit time, plotted as abscissa. where a record of streamflow is obtained.

Debris catches on snowmobile bridge near Waterbury, Vermont, as a result of floodwaters from the Winooski River during Tropical Storm Irene, in August 2011. Photograph courtesy of Lars Gange, Mansfield Heliflight. Publishing support provided by: Rolla Publishing Service Centers

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Or visit the Office of Surface Water Web site at: http://water.usgs.gov/osw/ Suro and others—Flooding in the Northeastern United States, 2011—Professional Paper 1821 ISSN 2330-7102 (online) http://dx.doi.org/10.3133/pp1821