Flood of April 2007 in New Hampshire 

By Robert H. Flynn 

Prepared in cooperation with the Federal Emergency Management Agency 

Scientific Investigations Report 2008–5120 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia: 2008 

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reproduce any copyrighted materials contained within this report. 

Suggested citation: 

Flynn, R.H., 2008, Flood of April 2007 in New Hampshire: U.S. Geological Survey Scientific Investigations 

Report 2008–5120, 53 p. 
iii 

Acknowledgments 

The author would like to thank Stephen Doyon from the New Hampshire Department of 

Environmental Services (NHDES) for providing peak-stage and peak-discharge data from 

the streamgages that NHDES operates, and David Knowles from the Federal Emergency 

Management Agency for providing review comments on this report. The author would like to 

express appreciation to U.S. Geological Survey staff—Kenneth Toppin, Scott Olson, 

Chandlee Keirstead, Richard Kiah, Sanborn Ward, Heather Sirotnak and Glenn Berwick— 

who assisted with collection and analysis of the data in this report; and to Scott Olson and 

Gene Parker, who provided technical reviews of this report. 

v

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Description of Study Area ...................................................................................................................3

Storm Characteristics ..........................................................................................................................3

Peak-Stage Data............................................................................................................................................6

Peak-Discharge Data..................................................................................................................................17

Flow-Frequency Analyses of the April 2007 Flooding............................................................................18

Determination of the April 2007 Flood Discharge by Indirect Methods at Ungaged Sites..............24

Comparison of the April 2007 Flood Data to Flood-Insurance Studies ...............................................26

Summary........................................................................................................................................................30

Selected References...................................................................................................................................30

Appendix 1. HEC-RAS Model Calibrations to Estimate the April 2007 Flood-Peak Discharge from 

High-Water-Mark Data Collected for the Lamprey, Souhegan, and Suncook Rivers.........39

Figures

1. Map showing counties included in the Presidential Disaster Declarations of 

April 27 and May 10, 2007 ............................................................................................................2

2A–3. Screenshots showing—

2A. The 1-day observed precipitation totals ending on April 16, 2007, New Hampshire 

and Vermont..........................................................................................................................4

2B. The 1-day observed precipitation totals ending on April 17, 2007, New Hampshire 

and Vermont..........................................................................................................................4

2C. The 1-day observed precipitation totals ending on April 18, 2007, New Hampshire 

and Vermont..........................................................................................................................5

3. The April 2007 monthly observed precipitation, New Hampshire and Vermont........5

4A–5. Maps showing—

4A. Location of U.S. Geological Survey streamgage sites and indirect dischargemeasurement sites having peak stage and discharge data for the April 2007 

flood in Hillsborough County, New Hampshire.............................................................10

4B. Location of U.S. Geological Survey streamgage sites and indirect dischargemeasurement sites having peak stage and discharge data for the April 2007 

flood in Rockingham County, New Hampshire..............................................................11

4C. Location of U.S. Geological Survey streamgage sites and indirect dischargemeasurement sites having peak stage and discharge data for the April 2007 

flood in Merrimack County, New Hampshire................................................................12

4D. Location of U.S. Geological Survey streamgage sites having peak stage and 

discharge data for the April 2007 flood in Belknap County, New Hampshire..........13

4E. Location of U.S. Geological Survey streamgage sites having peak stage and 

discharge data for the April 2007 flood in Strafford County, New Hampshire ........14

4F. Location of U.S. Geological Survey streamgage sites having peak stage and 

discharge data for the April 2007 flood in Grafton County, New Hampshire...........15

4G. Location of U.S. Geological Survey streamgage sites having peak stage and 

discharge data for the April 2007 flood in Carroll County, New Hampshire ............16
vi

Conversion Factors and Datum

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2

) 2.590 square kilometer (km2) 

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29) and North American Vertical Datum of 1988 (NAVD 88).

Tables

1. Description of streamgages used in the April 2007 flood investigation, central and 

southern New Hampshire .........................................................................................................33

2. Peak-stage data and peak-discharge data during the April 2007 flood at 

57 streamgage sites in central and southern New Hampshire.............................................7

3. Flow-frequency data and recurrence-interval estimates for 57 streamgages 

during the April 2007 flood in central and southern New Hampshire................................19

4. Flow-frequency data and recurrence-interval estimates by indirect methods for four 

ungaged sites during the April 2007 flood in central and southern New Hampshire......25

5. Flood-insurance study data for selected streamgage sites in central and 

southern New Hampshire .........................................................................................................27

6. High-water-mark data used in the determination of April 2007 flood discharge by 

indirect methods for four ungaged sites in central and southern New Hampshire........29

5. Recurrence intervals for the April 2007 flood at streamgages in Hillsborough, 

Rockingham, Merrimack, Belknap, Strafford, Grafton, and Carroll Counties 

in New Hampshire .............................................................................................................23
Abstract

During April 16–18, 2007, central and southeastern 

New Hampshire experienced severe flooding as a result of 

up to 7 inches of rainfall from a storm that stalled off the 

New England coast. As a result of the flooding, a Presidential 

Disaster Declaration was issued on April 27, 2007. On that 

day, disaster declarations were announced for Grafton, 

Hillsborough, Merrimack, Rockingham, and Strafford 

Counties. On May 10, 2007, Belknap County was added to 

the disaster declaration.

Following the flooding, the U.S. Geological Survey, 

in a cooperative investigation with the Federal Emergency 

Management Agency, determined the peak stages, peak 

discharges, and recurrence-interval estimates of the April 2007 

flood at 57 streamgages and 4 ungaged sites in and adjacent 

to the counties named in the disaster declaration. Data from 

flood-insurance studies published by the Federal Emergency 

Management Agency also were compiled for each streamgage 

site for comparison purposes. 

The peak discharges during the April 2007 flood were 

the highest ever recorded at five long-term (more than 

10 years of record) streamgage sites on the New HampshireSalmon Falls River at Milton, Cocheco River near Rochester, 

Oyster River near Durham, Contoocook River at Peterborough, and South Branch Piscataquog River near Goffstown. 

In addition, peak discharges equaled or exceeded a 100-year 

recurrence interval at 10 streamgages and a 50-year recurrence interval at 16 streamgages. The most severe flooding 

occurred in Rockingham, Strafford, Merrimack, and 

Hillsborough Counties.

Introduction

Major flooding in central and southern New Hampshire 

(fig. 1) from April 16 to 18, 2007, resulted in substantial 

damage to public and personal property. Homes and roads 

were damaged, and numerous residential areas were evacuated 

for several days. As a result of the widespread damage 

caused by the flooding, President George W. Bush issued a 

Presidential Disaster Declaration on April 27, 2007, for the 

counties of Grafton, Hillsborough, Merrimack, Rockingham, 

and Strafford in New Hampshire (fig. 1; Federal Emergency 

Management Agency, 2007). Belknap County in New 

Hampshire was added to the disaster declaration on 

May 10, 2007 (Federal Emergency Management Agency, 

2007). In response to the disaster declaration, the U.S. 

Geological Survey (USGS), in cooperation with the Federal 

Emergency Management Agency (FEMA), measured or 

computed flood characteristics at 57 streamgages and 4 

ungaged locations within and adjacent to the disaster areas. 

The April 2007 flood is documented in this report 

through the presentation of flood data collected at 46 active 

and 11 discontinued streamgages and 4 ungaged locations in 

central and southern New Hampshire. The flood data include 

peak-stage data, peak-discharge data, flow-frequency curves, 

and estimates of flood-recurrence intervals at each streamgage. 

In addition, data were compiled from 20 town/city-wide and 

3 county-wide FEMA flood-insurance studies for comparison purposes. The active streamgages include 37 operated 

by the USGS, 7 operated by the New Hampshire Department 

of Environmental Services (NHDES), and 2 operated by the 

U.S. Army Corps of Engineers (USACE). All 11 discontinued 

streamgages previously had been operated by the USGS. A 

description of each streamgage site included in this investigation is provided in table 1 (in back of report). 

Although the April 16–18, 2007, storm produced less 

precipitation than either the October 1996 or May 2006 storm 

events, some streams in New Hampshire had higher discharges 

in the 2007 event. For example, on April 16, 2007, a peak 

discharge of 1,320 ft3

/s occurred at the Oyster River streamgage near Durham, N.H. Prior to this peak, the peak discharge 

of record at that station was 1,160 ft3

/s on October 21, 1996. 

The April 16–18, 2007, precipitation resulted in discharges 

that were the maximum for the period of record at 5 long-term 

(more than 10 years of record) streamgage sites in central and 

southern New Hampshire.

The primary difference between the flooding events of 

May 2006 and October 1996 was the antecedent ground conditions in May 2006 (National Oceanic and Atmospheric Administration, 2006b) that resulted in greater discharges during the 

May 2006 event at many streamgages. The primary difference 

between the April 2007 flooding event and the May 2006 and 

October 1996 events was the precipitation on top of snowpack 

that resulted in greater discharges during the April 2007 event 

at many streamgages. 

Flood of April 2007 in New Hampshire

By Robert H. Flynn
2 Flood of April 2007 in New Hampshire

Figure 1. Counties included in the Presidential Disaster Declarations of April 27 and May 10, 2007. (FEMA-1695-DR, 

Federal Emergency Management Agency, 2007)

EXPLANATION

Designated counties

Public assistance

Disaster area

COOS

GRAFTON

MERRIMACK

CARROLL

BELKNAP

CHESHIRE

SULLIVAN

HILLSBOROUGH ROCKINGHAM

STRAFFORD

0 5 10 20 MILES

0 5 10 20 KILOMETERS

72°

71°

43°

44°

45°

Base from U.S. Geological Survey Digital Line Graphs, 1:24,000, 1990−94 and 

National Hydrography Dataset, 1:24,000, 1999

Lake

Winnipesaukee

Atlantic

Ocean

NEW

HAMPSHIRE

MASSACHUSETTS

MAINE

VERMONT

NEW

YORK

CANADA

0 50 MILES

0 50 KILOMETERS

Mt. Washington

Durham

Epping

Concord

Greenville
Introduction 3

The higher than normal precipitation from the April 

2007 storm, which included precipitation on top of snowpack 

at higher elevations, downed trees, and wood debris in 

some rivers all contributed to the high flows and flooding 

in southern and central New Hampshire. In addition, an 

abnormally high spring tide along with a storm surge of 

nearly 3 ft caused tidal flooding along portions of the seacoast 

(National Oceanic and Atmospheric Administration, 2007b), 

and the prolonged period of strong northeast winds caused a 

prolonged storm surge along the coastline (National Climate 

Data Center, 2007). 

Description of Study Area

The six New Hampshire counties included in the 

disaster declaration (fig. 1) compose a land area of 

5,245 mi2

 in the northeastern United States. Land elevations 

range from zero feet above the North American Vertical 

Datum of 1988 (NAVD 88) at Mean Lower Low Water 

(MLLW) at the seacoast to greater than 4,000 ft above the 

NAVD 88 in the north-central part of New Hampshire. 

The climate of New Hampshire is humid. Precipitation is 

distributed fairly evenly across the state and averages about 

43 in. per year except in regions that can receive additional 

precipitation due to elevation and snowfall. From 1971 to 

2000, Mount Washington received an average of 101.9 in. of 

precipitation per year, while Concord received an average of 

37.6 in. of precipitation (National Climate Data Center, 2008). 

The average (1971–2000) precipitation for April in Concord, 

N.H., was approximately 3.07 in. (National Climate Data 

Center, 2008).

Storm Characteristics

The precipitation that occurred from April 15 to 19, 

2007, produced 6.54 in. of rainfall in the southeastern New 

Hampshire towns of Durham and Epping and 7.25 in. of 

rainfall in Greenville, N.H.—a town in the south-central 

part of the state (National Oceanic and Atmospheric 

Administration, 2007a). Because April 16, 2007, was the 

Patriot’s Day holiday, the storm has since been referred to as 

the Patriot’s Day storm. The rainfall began on Sunday, 

April 15, 2007; snow accumulated in many areas and 

changed to rain, at first along the coast then eventually 

inland and northward. In Concord, snow accumulated to a 

total melted precipitation of 1.26 in. (National Oceanic and 

Atmospheric Administration, 2007b) on April 15. The rainfall 

became heavy on Sunday, April 15, during the afternoon and 

overnight. By the morning of Monday, April 16, 3 to 5 in. of 

rain had fallen over much of southeastern New Hampshire 

(fig. 2A; Northeast River Forecast Center, 2007a), and 1 to 

3 in. had fallen across much of the remainder of the state. In 

the mountains of New Hampshire, 3 to 11 in. of snow had 

fallen. Although the heaviest precipitation fell from Sunday 

afternoon into Monday afternoon, precipitation persisted 

through Tuesday, April 17 (fig. 2B; Northeast River Forecast 

Center, 2007a) and into Wednesday, April 18 (fig. 2C; 

Northeast River Forecast Center, 2007a). The heaviest rain 

fell on Monday, April 16 with 5.46 in. of rain recorded in 

Durham (National Oceanic and Atmospheric Administration, 

2007a). The heavy rain combined with snow melt caused 

small rivers and streams in much of New Hampshire to flood. 

As with the May 2006 flood in New Hampshire (Olson, 2007), 

the most severe flooding occurred in Rockingham, Strafford, 

Merrimack, and Hillsborough Counties, although the smaller 

rivers in Rockingham County were the most severely affected 

(National Climate Data Center, 2007).

In addition to the rainfall, downed trees exacerbated 

flooding conditions in many rivers and streams. A barometricpressure gradient associated with the storm brought high 

winds to the region with a peak wind of 45 mph recorded 

in Concord on April 16, 2007 (National Oceanic and Atmospheric Administration, 2007b). The damage observed in the 

hardest-hit areas was typical for wind gusts of 60 to 80 mph 

(National Climate Data Center, 2007). Strong winds late on 

Sunday, April 15, and through most of Monday, April 16, were 

reported to have downed many trees, branches, and power 

lines. Damage from the wind was magnified because of the 

heavy rain that accompanied the wind and the soft, wet ground 

caused by the spring thaw. Due to high winds and antecedent 

wet-ground conditions, many trees were reported to have had 

their entire root systems lifted out of the ground (National 

Oceanic and Atmospheric Administration, 2007b). 

As a result of the Patriot’s Day storm of April 16–18, 

2007, the month of April 2007 is the second wettest April 

(fig. 3) ever recorded in Concord, N.H. (National Oceanic 

and Atmospheric Administration, 2007b). A total of 

7.22 in. of precipitation was recorded for Concord, which 

is just shy of the April record precipitation of 7.44 in. set in 

1904. Snowfall also was abundant in April 2007 with 

12 in. measured in Concord. This measurement tied the 1876 

and 1879 levels as the 9th-snowiest April for Concord in the 

past 140 years of snowfall records (National Oceanic and 

Atmospheric Administration, 2007b). The largest snowfall in 

April 2007 for Concord totaled nearly 7.7 in. and fell during 

April 4–5 (National Oceanic and Atmospheric Administration, 

2007b). All of the April snow for Concord fell over the first 

15 days of the month (National Oceanic and Atmospheric 

Administration, 2007b). In March and April 2007, Concord 

received 29.2 in. of rainfall.

The total precipitation that occurred during April 15–19, 

2007, in southeastern New Hampshire (6.54 in. in Durham) 

was approximately one-half of the 13 in. of precipitation that 

fell during October 20–22, 1996, across southeastern New 

Hampshire (National Oceanic and Atmospheric Administration, 1996). The total April 15–19, 2007, precipitation 

in southeastern New Hampshire was less than one-half of 

the up to 14 in. of precipitation that fell during May 11–15, 

2006, across the coastal regions of New Hampshire (National 

Oceanic and Atmospheric Administration, 2006a) and approximately 60 percent of the up to 11 in. of precipitation that fell 
4 Flood of April 2007 in New Hampshire

Figure 2A. The 1-day observed precipitation totals ending on April 16, 2007, New Hampshire and Vermont. 

(From Northeast River Forecast Center, 2007a)

Figure 2B. The 1-day observed precipitation totals ending on April 17, 2007, New Hampshire and Vermont. 

(From Northeast River Forecast Center, 2007a)

New York Vermont

Massachusetts

New Hampshire

Maine

0.01

6.0

4.0

2.5

1.5

0.75

0.25

10

5.0

3.0

2.0

1.0

0.50

0.10

8.0

Missing

Inches

New Hampshire & Vermont

1-Day Observed Precipitation - Valid 4/16/2007 1200 UTC

New York Vermont

Massachusetts

New Hampshire

Maine

0.01

6.0

4.0

2.5

1.5

0.75

0.25

10

5.0

3.0

2.0

1.0

0.50

0.10

8.0

Missing

Inches

New Hampshire & Vermont

1-Day Observed Precipitation - Valid 4/17/2007 1200 UTC
Introduction 5

Figure 2C. The 1-day observed precipitation totals ending on April 18, 2007, New Hampshire and Vermont. 

(From Northeast River Forecast Center, 2007a)

Figure 3. The April 2007 monthly observed precipitation, New Hampshire and Vermont. (From Northeast River 

Forecast Center, 2007b)

New York Vermont

Massachusetts

New Hampshire

Maine

0.01

6.0

4.0

2.5

1.5

0.75

0.25

10

5.0

3.0

2.0

1.0

0.50

0.10

8.0

Missing

Inches

New Hampshire & Vermont

1-Day Observed Precipitation - Valid 4/18/2007 1200 UTC

New York Vermont

Massachusetts

New Hampshire

Maine

0.01

10

6.0

4.0

2.0

1.0

0.25

20

8.0

5.0

3.0

1.5

0.50

0.10

15

Missing

Inches

New Hampshire & Vermont

April 2007 Monthly Observed Precipitation
6 Flood of April 2007 in New Hampshire

during May 11–15, 2006, in the south-central part of the 

state (National Oceanic and Atmospheric Administration, 

2006b). The October 20–22, 1996, May 11–15, 2006, and 

April 15–19, 2007, precipitation events all resulted in streamflow discharges that were the maximum for the periods of 

record at several streamgages in southern and southeastern 

New Hampshire. 

Peak-Stage Data

Peak-stage data at active streamgages operated by the 

USGS were retrieved directly from the stage data recorded at 

the streamgages, along with the precise date and time of the 

peak stage. At active streamgages not operated by the USGS, 

the peak stage with date and time was provided by the station 

operators. All peak-stage data from active streamgages were 

rated excellent, which means that measurements are considered to be within 0.05 ft of the actual water surface.

For discontinued streamgages, USGS personnel 

identified and flagged the April 2007 high-water marks near 

the streamgage. The high-water marks typically consisted 

of debris lines, wash lines, or mud lines left behind by the 

peak water elevation during the flood. The flagged highwater marks were rated for accuracy. This accuracy rating is 

subjective and is based on the type of high-water mark and 

the abundance of other confirming marks in the immediate 

vicinity (Benson and Dalrymple, 1967). The accuracies of the 

marks are defined as follows. A high-water mark with (1) an 

excellent rating is thought to be within 0.05 ft of the actual 

water surface; (2) a good rating, within 0.1 ft; (3) a fair rating, 

within 0.2 ft; and (4) a poor rating, greater than 0.2 ft from the 

true water surface.

The flagged high-water marks at the discontinued 

streamgages were referenced to the datum of the streamgage 

by using closed level-loop surveying techniques (elevations 

were determined at the high-water marks by differential 

leveling from a known elevation datum). The streamgage 

datum is the local base elevation that was used in developing 

the stage-discharge relationship when the streamgage was 

active. Because the high-water marks were referenced to the 

streamgage datum, the marks represented the peak stages of 

the flooding at the discontinued streamgage. The date of the 

peak stages at discontinued streamgages was estimated from 

peak-stage hydrographs for active streamgages in the same or 

adjacent watersheds.

At active streamgages as well as at discontinued streamgages where high-water marks had been flagged, the peak 

stage was referenced to the National Geodetic Vertical Datum 

of 1929 (NGVD 29) and the NAVD 88 by using closed 

level-loop surveying techniques from either a known reference datum or from a reference datum established using Leica 

System 1200 Global Positioning System (GPS) with 3-mm 

(0.01-ft) horizontal accuracy and 10-mm (0.03-ft) vertical 

accuracy in static mode (Leica Geosystems, 2008). Referencing the peak stage to NGVD 29 and NAVD 88 allows the 

high-water mark to be compared to the existing FEMA FloodInsurance Study data for the streamgage location. 

The peak-stage data for all sites included in this investigation are shown in table 2. The location of each streamgage 

is shown, by county, in figures 4A–G. Although a disaster 

declaration was not made in Carroll County (fig. 4G), flows at 

four streamgages in that county were investigated because of 

their close proximity to Belknap and Grafton Counties, which 

were declared disaster areas (table 1, in back of report). 
Peak-Stage Data 

7

Table 2. Peak-stage data and peak-discharge data during the April 2007 flood at 57 streamgage sites in central and southern New Hampshire.—Continued[Location of streamgages in figure 4. USGS, U.S. Geological Survey; SR, State Route; ft, feet; NAVD 88, North American Vertical Datum of 1988; NGVD 29, National Geodetic Vertical Datum of 1929; ft3/s, cubic feet per second; na, not available. Periods of record without an end date are active streamgages]

USGS 

streamgage 

number

Streamgage name

April 2007 flood

Period of record

Maximum previously 

recorded flood

Peak 

stage, 

local 

datum 

(ft)

Peak 

stage, 

NGVD 29 

(ft)

Peak 

stage, 

NAVD 88 

(ft)

Quality 

ranking 

of stage

Peak 

discharge 

(ft3/s)

Day Time

Peak 

discharge 

(ft3/s)

Date

01064500 Saco River near Conway 8.30 426.49 426.05 Excellent 9,750n April 24 1:30 am 1904–10, 1929– 47,200 3-27-1953

01064801 Bearcamp River at South Tamworth 8.12 501.49 501.03 Excellent 3,720n April 17 12:30 am 1993– 6,150 6-14-199801065000 Ossipee River at Effingham Falls 9.25a na na Excellent 5,370a April 19 na 1942–90, 1998– 11,700 3-28-1953

01072100 Salmon Falls River at Milton 7.32a 404.46 403.90 Excellent 5,500a,b,c April 17 9:30 am 1968– 5,450 5-14-2006

01072800 Cocheco River near Rochester 20.82 140.20 139.59 Excellent 7,240c April 16 11:15 pm 1995– 5,550 5-14-200601072870 Isinglass River at Rochester Neck 

Road, near Dover

21.81 na na Excellent 6,160 April 17 12:30 pm 2003– 4,370 5-14-2006

01073000 Oyster River near Durham 10.20 75.49 74.78 Excellent 1,320c April 16 5:45 pm 1934– 1,160 10-21-199601073500 Lamprey River near Newmarket 17.49 55.77 55.04 Excellent 8,450 April 18 2:00 pm 1934– 8,970 5-14-200601073587 Exeter River at Haigh Road, 

near Brentwood

11.19 71.46 70.71 Excellent 2,840 April 17 5:30 am 1996– 3,520 5-15-2006

01073600 Dudley Brook near Exeter 8.35 94.40 93.65 Fair 470b,o April 17 na 1962–85 660 5-14-2006

01073750 Mill Brook near SR 108, at Stratham 11.06 496.19 495.44 Excellent 325b,o April 18 na 1973–79, 2003–04 390 4-2-1973

01073785 Winnicut River at Greenland, 

near Portsmouth

5.93 14.19 13.44 Excellent 1,030 April 16 8:15 am 2002– 1,450 5-14-2006

01073810 Berrys Brook at Sagamore Road, 

near Portsmouth

4.95 22.07 21.30 Excellent 278b,o April 17 na 2003–04 505 5-14-2006

01073838 Taylor River at Old Stage Road 

near Hampton

6.84 18.92 18.14 Fair 436o April 17 na 2004 na na

01074520 East Branch Pemigewasset River 

at Lincoln

8.86 829.89 829.58 Excellent 2,730n April 24 9:45 am 1993– 16,900 4-14-2002

01075000 Pemigewasset River at Woodstock 6.83 623.27 622.93 Excellent 4,460n April 23 10:30 pm 1939–77, 2002– 47,000 10-24-195901076000 Baker River near Rumney 5.65 502.99 502.59 Excellent 3,040n April 16 7:00 pm 1929–77, 2001– 21,400 6-15-194201076500 Pemigewasset River at Plymouth 10.71 467.78 467.37 Excellent 13,900n April 17 12:15 am 1904– 65,400 3-19-193601077000 Squam River at Ashland 12.06a na na Excellent 543a April 18 5:15 pm 1939– 1,090 7-4-197301077510 Newfound River below Newfound 

Lake near Bristol

8.81a na na Excellent 1,690a April 19 4:15 am 1994– 3,500 5-16-2006

01078000 Smith River near Bristol 8.65 458.45 458.07 Excellent 2,770 April 17 10:00 pm 1918– 8,100 3-19-193601079602 Poorfarm Brook near Gilford 5.74e 512.30e 511.86e Good 505o April 17 na 1998–2004 1,050 5-14-200601079900 Shannon Brook near Moultonborough 8.37 na na Excellent 570b,o April 17 na 1999–2004 565 5-14-2006

01080000 Lake Winnipesaukee at Weirs Beach 5.00a 505.00 504.57 Excellent na April 22 11:00 pm 1934– 505.86 6-4-1984

01080500 Lake Winnipesaukee Outlet 

at Lakeport

na na na Excellent 2,430a April 25 8:00 am 1933–83, 1988– 2,890f 3-31-1936
8 Flood of April 2007 in New Hampshire Table 2. Peak-stage data and peak-discharge data during the April 2007 flood at 57 streamgage sites in central and southern New Hampshire.—Continued [Location of streamgages in figure 4. USGS, U.S. Geological Survey; SR, State Route; ft, feet; NAVD 88, North American Vertical Datum of 1988; NGVD 29, National Geodetic Vertical Datum of 1929; ft3/s, cubic feet per second; na, not available. Periods of record without an end date are active streamgages] USGS stream- gage number Streamgage name April 2007 flood Period of record Maximum previously recorded flood Peak stage, local datum (ft) Peak stage, NGVD 29 (ft) Peak stage, NAVD 88 (ft) Quality ranking of stage Peak dis- charge (ft3/s) Day Time Peak discharge (ft3/s) Date 01081000 Winnipesaukee River at Tilton 7.61 449.48 449.01 Excellent 3,550 April 17 1:30 am 1937– 4,580 3-31-1984 01081500 Merrimack River at Franklin Junction 13.62 264.70 264.20 Excellent 17,300 April 17 5:15 am 1905–78, 1983– 83,000 3-19-1936 01082000 Contoocook River at Peterborough 7.21 739.18 738.46 Excellent 4,110c April 16 1:00 pm 1946– 3210 4-2-2004 01083000 Nubanusit Brook below MacDowell 

Dam near Peterborough

5.71 936.74 936.07 Excellent 637g April 24 4:00 pm 1921–31, 1946– 1,130 4-11-1931

01084500 Beards Brook near Hillsborough 8.69 602.33 601.72 Good 3,550b,o April 17 na 1946–76 4,800b,h 10-9-2005

01085000 Contoocook River near Henniker 14.49 484.81 484.19 Excellent 13,000 April 17 6:00 pm 1938, 1940–77, 

1989–

22,200 9-21-1938

01085500 Contoocook River below Hopkinton 

Dam at West Hopkinton

8.51 364.34 363.66 Excellent 5,370 April 30 5:45 pm 1964– 7,530 4-8-1987

01086000 Warner River at Davisville 11.87i 391.90 391.31 Excellent 7,730 April 16 10:45 pm 1940–78, 1999– 8,640 5-15-2006

01087000 Blackwater River near Webster 6.87 438.60 438.04 Excellent 1,950 April 25 12:30 pm 1919–20, 1927– 11,000j 3-19-1936

01087850 Contoocook River at River Hill, 

near Penacook

15.90g 347.87 347.27 Excellent 7,780g,o April 17 4:15 am na na na

01088400 Merrimack River at Concord 14.35 231.52 230.91 Excellent 32,800o April 21 2:00 pm na na na01089000 Soucook River near Concord na 305.79 305.21 Excellent 3,500k,o April 17 na 1952–1987 4,790k 5-14-2006

01089100 Soucook River at Pembroke Road, 

near Concord

13.37 269.26 268.66 Excellent 3,730 April 17 4:15 pm 1989– 5,110b 5-14-2006

01089500 Suncook River at North Chichester 15.97a 345.32 344.75 Excellent 10,600l April 17 na 1919–20, 1922–27, 

1929–70, 2007–

12,900 3-19-1936

01090800 Piscataquog River below Everett 

Dam, near East Weare

8.71 328.37 327.71 Excellent 1,600 April 25 3:00 am 1963– 1,770 6-12-1984

01091000 South Branch Piscataquog River 

near Goffstown

na 322.97 322.28 Good 8,880c,o,p April 16 na 1941–78 7,180 5-14-2006

01091500 Piscataquog River near Goffstown 13.05 187.70 187.03 Excellent 11,200 April 16 5:00 pm 1936, 1938, 

1940–78, 1983–

21,900 9-21-1938

01092000 Merrimack River near Goffs Falls, 

below Manchester

16.79 126.06 125.37 Excellent 59,700 April 17 12:45 pm 1936– 150,000j 3-20-1936

01093000 Sucker Brook at Auburn 4.12 256.84 256.14 Excellent nad,o April 17 na 1938–70 602m 9-12-1954

01094000 Souhegan River at Merrimack 12.71 173.29 172.59 Excellent 10,500 April 17 5:45 am 1910–76, 1980, 

1982–

16,900 3-19-1936

010965817 Beaver Brook at Fordway Extension 

at Derry

6.00 na na Excellent 1,100 April 16 7:00 pm 2006– na na
Peak-Stage Data 

9

Table 2. Peak-stage data and peak-discharge data during the April 2007 flood at 57 streamgage sites in central and southern New Hampshire.—Continued[Location of streamgages in figure 4. USGS, U.S. Geological Survey; SR, State Route; ft, feet; NAVD 88, North American Vertical Datum of 1988; NGVD 29, National Geodetic Vertical Datum of 1929; ft3/s, cubic feet per second; na, not available. Periods of record without an end date are active streamgages]

USGS 

streamgage 

number

Streamgage name

April 2007 flood

Period of record

Maximum previously 

recorded flood

Peak 

stage, 

local 

datum 

(ft)

Peak 

stage, 

NGVD 29 

(ft)

Peak 

stage, 

NAVD 88 

(ft)

Quality 

ranking 

of stage

Peak 

discharge 

(ft3/s)

Day Time

Peak 

discharge 

(ft3/s)

Date

010965844 Beaver Brook at South Road, 

near Derry

5.69 219.45 218.76 Excellent 1,470 April 16 7:15 pm 2006– 2,230 5-15-2006

010965852 Beaver Brook at North Pelham 13.52 162.78 162.07 Excellent 1,900 April 16 10:45 pm 1987– 2,940 5-15-200601096587 Tributary to Cobbetts Pond at I-93 

south exit ramp near Windham

3.67 na na Excellent 59 April 16 7:00 am 2006– 72 5-14-2006

01100505 Spicket River at North Salem 6.04 na na Excellent 434 April 18 3:45 am 2001– 801 5-15-200601100549 Policy Brook at Rockingham Park 

Boulevard at Salem

3.17 na na Excellent 95 April 16 6:45 pm 2006– na na

011005605 Policy Brook at I-93 north rest stop 

entrance ramp, near Salem

6.10 111.80 111.04 Excellent 338 April 16 9:30 pm 2006– 515 5-15-2006

01100561 Spicket River near Methuen, Mass. 9.01 109.91 109.14 Excellent 1,130 April 18 1:45 pm 2001– 2,480 5-15-2006

01137500 Ammonoosuc River at 

Bethlehem Junction

7.15 1,187.89 1,187.63 Excellent 3,370 April 16 4:45 pm 1940– 11,300 11-12-1995

01138500 Connecticut River at Wells River, Vt. 9.25 409.00 408.62 Excellent 27,300 April 24 5:00 pm 1950– 57,100 7-1-1973

01144500 Connecticut River at West Lebanon 16.41 337.93 337.52 Excellent 38,800 April 24 11:30 am 1912–76, 1979– 136,000 11-4-1927

01150500 Mascoma River at Mascoma 8.33a 749.01 748.71 Excellent 2,990a April 18 7:00 am 1924– 5,090 3-19-1936

a Data provided by New Hampshire Department of Environmental Services.b Discharge estimated by graphically extending stage-discharge relationship.c Discharge is maximum for the period of record which is greater than 10 years.d Backwater from downstream conditions invalidated the stage-discharge relationship.e Peak stages determined at upstream and downstream control locations as control for the streamgage was moved during period of record. Reported elevations are at a point approximately 100 ft downstream 

from the streamgage house.

f Maximum daily mean discharge.g Streamgage data obtained from the U.S. Army Corps of Engineer’s Web site (U.S. Army Corps of Engineers, 2007).h Discharge estimate from flagged high-water marks following the October 8 and 9, 2005, flood (Olson, 2007).i Stage of September 1938 flood was 12.80 ft.j Prior to construction of flood-control structures.k Discharge estimated by adjusting the peak discharge determined at the downstream streamgage 01089100 by using the ratio of the drainage areas.l Measurement of peak discharge at width contraction by indirect methods at locations upstream and downstream from the streamgage (Matthai, 1967; U.S. Army Corps of Engineers, 2005).m Maximum stage on May 14, 2006, was 4.36 ft, and on September 12, 1954, it was 2.55 ft.n Not the peak discharge for 2007 water year.o Not known if listed value is peak for 2007 water year because gage is inactive.p Discharge estimated by adjusting the peak discharge determined at the downstream streamgage 01091500 by using the ratio of the drainage areas. The drainage area of streamgage 01091500 was adjusted 

to 139 mi2 to account for negligible flow (20–50 ft3/s) below upstream gage 01090800 during the April 16, 2007, peak flow at downstream gage 01091500.
10 Flood of April 2007 in New Hampshire

Figure 4A. Location of U.S. Geological Survey (USGS) streamgage sites and indirect discharge-measurement sites having peak 

stage and discharge data for the April 2007 flood in Hillsborough County, New Hampshire.

Beards Brook

Souhegan River

at Merrimack

Beaver Brook

at North Pelham

Beards Brook

near Hillsborough

Piscataquog River

near Goffstown

Contoocook River

at Peterborough

South Branch

Piscataquog River

near Goffstown

Merrimack 

River

near Goffs Falls,

below Manchester

Piscataquog River

below Everett Dam,

near East Weare

Nubanusit Brook

below MacDowell Dam

near Peterborough

Souhegan River

at Wilton Road bridge, near

Wilton/Milford town line

HILLSBOROUGH

COUNTY

NEW HAMPSHIRE

MASSACHUSETTS

Souhegan River

Warner River

Contoocook River

Piscataquog River

North Branch

Suncook

River

Soucook

River

Merrimack

River

Beaver Brook

Blackwater River

Merrimack River

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

EXPLANATION

Active or discontinued 

USGS streamgage site (see table 1)

County boundary

72° 71°30'

42°45'

43°

43°15'

Base from U.S. Geological Survey Digital Line Graphs, 1:24,000, 1990−94 and 

 National Hydrography Dataset, 1:24,000, 1999

71°45' 71°15'

Indirect discharge-measurement site (see table 4)
Peak-Stage Data 11

Figure 4B. Location of U.S. Geological Survey (USGS) streamgage sites and indirect discharge-measurement sites having 

peak stage and discharge data for the April 2007 flood in Rockingham County, New Hampshire.

Policy Brook

at Rockingham Park 

Boulevard at Salem

Winnicut River

at Greenland,

near Portsmouth

Berrys Brook

at Sagamore Road,

near Portsmouth

NEW HAMPSHIRE

Sucker Brook

at Auburn

Dudley Brook

near Exeter

Spicket River

at North Salem

Spicket River

near Methuen, Mass.

Mill Brook

near State

Route 108,

at Stratham

Beaver Brook

at South Road,

near Derry

Policy Brook

at I-93 rest stop,

near Salem

Exeter River

at Haigh Road,

near Brentwood Taylor River

at Old Stage Road,

near Hampton

Tributary to

Cobbetts Pond

at I-93 exit ramp,

near Windham Beaver Brook

at Fordway Extension,

at Derry

Lamprey River

at Epping Road

railroad bridge,

Raymond

Atlantic Ocean

Salmon Falls River

ROCKINGHAM

COUNTY

NEW HAMPSHIRE

MAINE

Suncook River

Lamprey River

North River

Exeter River

Isinglass River

Merrimack River

MASSACHUSETTS

Beaver Brook

Spicket River

Soucook River

Oyster

River

Cocheco River

71°30' 71°

42°45'

43°

43°15'

EXPLANATION

Base from U.S. Geological Survey Digital Line Graphs, 1:24,000, 1990−94 and 

 National Hydrography Dataset, 1:24,000, 1999

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

Great Bay

71°15' 70°45'

Active or discontinued 

USGS streamgage site (see table 1)

County boundary

Indirect discharge-measurement site (see table 4)
12 Flood of April 2007 in New Hampshire

Figure 4C. Location of U.S. Geological Survey (USGS) streamgage sites and indirect discharge-measurement sites having 

peak stage and discharge data for the April 2007 flood in Merrimack County, New Hampshire.

Winnipesaukee River

Winnipesaukee

Lake

Smith River

near Bristol

Merrimack River

at Concord

Warner River

at Davisville

Soucook

River near

Concord

Blackwater

River near

Webster

Contoocook

River near

Henniker

Suncook

River at North

Chichester

Merrimack River

at Franklin Junction

Soucook 

River at

Pembroke 

Road,

near Concord

Contoocook River

at River Hill,

near Penacook

Contoocook River

below Hopkinton Dam

at West Hopkinton

Suncook River at

Websters Mill Road,

Chichester/Pittsfield

Suncook

River at Short Falls Road, 

Epsom

MERRIMACK COUNTY

Warner River

Merrimack River

Blackwater River

Smith River

North Branch

Contoocook River

Pemigewasset River

Soucook River

Piscataquog River

Suncook River

72° 71°30'

43°

43°30'

EXPLANATION

Base from U.S. Geological Survey Digital Line Graphs, 1:24,000, 1990−94 and 

 National Hydrography Dataset, 1:24,000, 1999

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

71°45' 71°15'

43°15'

Active or discontinued 

USGS streamgage site (see table 1)

County boundary

Indirect discharge-measurement site (see table 4)
Peak-Stage Data 13

Figure 4D. Location of U.S. Geological Survey (USGS) streamgage sites having peak stage and discharge data for the 

April 2007 flood in Belknap County, New Hampshire.

Ossipee River Ossipee

Lake

Winnipesaukee River Winnipesaukee

Lake

Winnipesaukee

River at Tilton

Pemigewasset River

Cocheco River

Salmon

Falls River

MAINE

NEW HAMPSHIRE

Squam

Lake

Poorfarm

Brook near

Gilford

Lake

Winnipesaukee

at Weirs Beach

Lake Winnipesaukee

Outlet at Lakeport

Active or discontinued 

USGS streamgage site (see table 1)

BELKNAP COUNTY

Soucook River

71°30' 71°

43°30'

43°45'

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

EXPLANATION

County boundary

Suncook River

Bearcamp River

Merrimack River

Base from U.S. Geological Survey Digital Line Graphs, 1:24,000, 1990−94 and 

 National Hydrography Dataset, 1:24,000, 1999

71°15'
14 Flood of April 2007 in New Hampshire

Figure 4E. Location of U.S. Geological Survey (USGS) streamgage sites having peak stage and discharge data for 

the April 2007 flood in Strafford County, New Hampshire.

Cocheco River

Oyster River

near Durham

Cocheco River

near Rochester

Lamprey River

near Newmarket

Salmon Falls River

at Milton

Isinglass River

at Rochester Neck Road,

near Dover

STRAFFORD

COUNTY NEW HAMPSHIRE

MAINE

Suncook River

Lamprey River

North River

Isinglass River

Oyster

River

Sa ml on Falls River

Soucook River

Lake Winnipesaukee

Great

Bay

71°15' 71° 70°45'

43°15'

43°30'

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

EXPLANATION

County boundary

Base from U.S. Geological Survey Digital Line Graphs, 1:24,000, 1990−94 and 

 National Hydrography Dataset, 1:24,000, 1999

Active or discontinued 

USGS streamgage site (see table 1)
Peak-Stage Data 15

Figure 4F. Location of U.S. Geological Survey (USGS) streamgage sites having peak stage and discharge data for the 

April 2007 flood in Grafton County, New Hampshire.

Connecticut River

at West Lebanon

Squam Lake

NEW HAMPSHIRE

VERMONT

Squam River 

at Ashland

Baker River near Rumney

Mascoma River

at Mascoma

Pemigewasset River

at Plymouth

Pemigewasset River at Woodstock

Connecticut River at Wells River

Ammonoosuc River

at Bethlehem Junction

East Branch Pemigewasset River

at Lincoln

Newfound River

below Newfound Lake

near Bristol

GRAFTON COUNTY

Connecticut River

Pemigewasset River

Ammonoosuc River

Mascoma River

Lake

Winnipesaukee

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

Smith River

EXPLANATION

County boundary

Baker River

72° 71°30'

43°45'

44°

44°15'

Base from U.S. Geological Survey Digital Line Graphs, 1:24,000, 1990−94 and 

National Hydrography Dataset, 1:24,000, 1999

Active or discontinued 

USGS streamgage site (see table 1)

71°15'
16 Flood of April 2007 in New Hampshire

Figure 4G. Location of U.S. Geological Survey (USGS) streamgage sites having peak stage and discharge data for the April 2007 flood 

in Carroll County, New Hampshire.

Winnipesaukee

Lake 

Pemigewasset River

Ammonoosuc River

Squam

Lake

Saco River

near Conway

Bearcamp River

at South Tamworth

Ossipee River

at Effingham Falls Shannon Brook

near Moultonborough

CARROLL COUNTY

MAINE

NEW HAMPSHIRE

Saco River

Ossipee River

71°30' 71°

43°30'

44°

Bearcamp River

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

EXPLANATION

County boundary

Base from U.S. Geological Survey Digital Line Graphs, 1:24,000, 1990−94 and 

 National Hydrography Dataset, 1:24,000, 1999

Active or discontinued 

USGS streamgage site (see table 1)

Ossipee

Lake
Peak-Discharge Data 17

Peak-Discharge Data

Peak discharges for most streamgages were determined by applying the peak stage to the most current stagedischarge relation developed for that streamgage (table 2). 

At discontinued streamgages, there is the possibility that the 

stage-discharge relation has changed during the years that the 

site has been inactive. Each of the discontinued streamgages, 

however, is at a site having a stable channel or control, and the 

most recent stage-discharge relationship available for the site 

provides reasonable results.

There were four exceptions to using the stagedischarge relation for determining the peak-discharge of the 

April 2007 flood:

1. At six streamgages (01072100, 01073600, 01073750, 

01073810, 01079900, and 01084500; table 2, footnote b), 

the current stage-discharge relation was undeveloped for 

the unusually large peak stage. In such cases, the stagedischarge relation was graphically extended to the peak 

stage by using the trend of the upper end of the stagedischarge relation. The error introduced to the peak-discharge value is unknown when the stage-discharge relation is extended without manually measured discharges. 

2. At discontinued streamgage 01093000, Sucker Brook 

at Auburn (fig. 4B; table 2, footnote d), Rockingham 

County, backwater resulting from hydraulic conditions in 

the channel downstream from the streamgage prevented 

the use of the stage-discharge relation to determine the 

peak discharge from the peak stage. The peak discharge at 

this streamgage is therefore unknown. 

3. At discontinued streamgage 01091000 (drainage 

area of 104 mi2

), South Branch Piscataquog River 

near Goffstown, N.H. (fig. 4A; table 2, footnote p), 

Hillsborough County, the USGS streamgage house was 

removed and datum reference marks were destroyed 

during the construction of a new bridge in 2003. Because 

the reference marks were destroyed, it was not possible 

to tie the surveyed high-water marks at this site to the 

streamgage datum. Without this information, the stagedischarge relation for the streamgage could not be used. 

Although enough high-water marks were available 

upstream and downstream from the bridge to allow a 

discharge estimate to be made at the bridge by using 

indirect techniques (Matthai, 1967), the area upstream 

from the bridge experienced backwater effects during 

the April 2007 flood. This invalidated the use of indirect 

techniques to determine the April 2007 flood discharge at 

this location. 

High-water-mark elevation data were collected upstream 

and downstream from discontinued streamgage 01091000 

at the Route 13 (Mount Vernon Road) bridge (drainage 

area of 54 mi2

) over the South Branch Piscataquog River 

in New Boston. These data were collected to determine 

the peak flow for the April 2007 flood at the Route 13 

bridge as well as at discontinued streamgage 01091000 

by using the ratio of the drainage areas between the 

Route 13 bridge and the discontinued streamgage. 

Although the bridge provides sufficient river constriction to allow a discharge estimate to be made by using 

indirect methods (Matthai, 1967), subsequent information 

provided by two residents living near the Route 13 bridge 

indicated that the main channel of the South Branch 

Piscataquog River overtopped the banks upstream from 

the Route 13 bridge, and water flowed down a road 500 ft 

south of the bridge, along the downstream side of 

Route 13, and back into the South Branch Piscataquog 

River downstream from the Route 13 bridge. This road 

overflow invalidated a discharge determination made by 

indirect methods at the Route 13 bridge in New Boston.

Peak discharge at discontinued streamgage 01091000, 

South Branch Piscataquog River near Goffstown, N.H., 

could not be determined by indirect methods due to 

backwater effects, nor could it be determined at the 

Route 13 bridge over the South Branch Piscataquog 

River in New Boston due to flow on the upstream 

right overbank. It was decided, however, that the April 

2007 peak discharge at streamgage 01091000, could be 

determined by using the ratio of the drainage area for 

this streamgage to the area for streamgage 01091500 

(drainage area of 202 mi2

), Piscataquog River near 

Goffstown (fig. 4A), downstream from discontinued 

streamgage 01091000. The South Branch Piscataquog 

River flows into the Piscataquog River downstream 

from streamgage 01090800 (drainage area of 63 mi2

) 

at Piscataquog River below Everett Dam, near East 

Weare and upstream from streamgage 01091500 at 

Piscataquog River near Goffstown. Determination of 

the April 2007 peak discharge by ratio of drainage 

areas between the South Branch Piscataquog River 

near Goffstown and Piscataquog River near Goffstown 

streamgages was deemed acceptable because there was 

negligible contribution to flow downstream from the 

Hopkinton-Everett Lake Dam (as recorded at streamgage 

01090800, Piscataquog River below Everett Dam, near 

East Weare) to the peak flood flow at the Piscataquog 

River near Goffstown, N.H. streamgage. The 202-mi2

drainage area of the Piscataquog River near Goffstown, 

N.H. streamgage was adjusted to 139 mi2

 to reflect the 

negligible contribution of 20–50 ft3

/s (U.S. Army Corps 

of Engineers, 2007) for April 16–17, 2007, below the 

Hopkinton-Everett Lake Dam in Contoocook as measured 

at the Piscataquog River below Everett Dam, near East 

Weare. The peak discharge at streamgage 01091000, 

South Branch Piscataquog River near Goffstown, was 

11,200 ft3

/s on April 16 at 5 pm. The flood-peak discharge 

for the April 2007 flood at the discontinued South 

Branch Piscataquog River near Goffstown streamgage 

was estimated to be 8,880 ft3

/s by adjusting the peak 
18 Flood of April 2007 in New Hampshire

discharge (using equation 1—explained in the section 

“Determination of the April 2007 Flood Discharge by 

Indirect Methods at Ungaged Sites”) determined for 

the downstream Piscataquog River near Goffstown 

streamgage by the ratio of the drainage areas for 

streamgages at South Branch Piscataquog River near 

Goffstown and Piscataquog River near Goffstown.

4. USGS streamgage 01089500 (drainage area of 155 mi2

), 

Suncook River at Depot Road in North Chichester 

(fig. 4C; table 2, footnote l), Merrimack County, was 

active during 1919 to 1920, 1922 to 1927, and 1929 

to 1970. In November of 2007, it was again activated. 

After the April 16–18, 2007, flood, high-water mark 

information was collected at the former streamgage site. 

By using the streamgage rating (stage/discharge relation) 

established for the period of record prior to 1970, a peak 

discharge of 15,000 ft3

/s was determined for the former 

location of the Suncook River at Depot Road in North 

Chichester streamgage for the April 16–18, 2007, flood. 

Subsequently, indirect discharge determinations were 

made at locations upstream and downstream from the 

discontinued streamgage. These locations are at the 

Websters Mill Road bridge in Chichester/Pittsfield and 

Short Falls Road bridge in Epsom, with drainage areas 

of 137 and 210 mi2

, respectively. The high-water marks 

upstream and downstream from each bridge, the bridgeopening geometry, and channel and floodplain cross 

sections upstream and downstream from the bridge 

were surveyed and the values were input to the USACE 

Hydrologic Engineering Center River Analysis System 

(HEC-RAS) program (2005). Discharges were selected 

iteratively and input to the HEC-RAS program so that the 

resulting water-surface-elevation output from the program 

matched the high-water marks surveyed upstream from 

the bridge. A flood-peak discharge of 10,600 ft3

/s was 

determined for the former Suncook River at Depot 

Road in North Chichester streamgage site on the basis 

of the discharge/drainage-area relation between the two 

indirectly determined (Matthai, 1967; U.S. Army Corps 

of Engineers, 2005) April 2007 flood-peak discharges 

at the Short Falls and Websters Mill Road bridges on 

the Suncook River. The upper end of the rating (stage/

discharge relation) at the former streamgage has shifted 

since it was determined from the March 19, 1936, flood 

data, when a discharge of 12,900 ft3

/s at a gage height of 

15.27 ft was ascertained by slope-area and contractedopening methods. The shift in the upper end of the rating 

likely is due to a greater amount of vegetation on the 

right overbank in 2007 than in 1936 (as seen in USGS 

photographs on file at the New Hampshire-Vermont 

Water Science Center) and the construction of a weir 

control along with the removal of a channel island below 

the streamgage in the summer of 1937. For this reason, 

the discharge of 10,600 ft3

/s was determined to be the 

peak discharge for the April 16–18, 2007, flood at the 

former streamgage.

The peak-discharge data for all of the sites included in 

this investigation are shown in table 2. At five long-term 

(more than 10 years of record) streamgages, the peak 

discharge from the April 2007 flood was the maximum 

discharge for the period of record. The discharges for 

these five streamgages are listed in table 2 in footnote 

c. Four of these streamgages have very long periods of 

record: streamgage 01091000, South Branch Piscataquog 

River near Goffstown, 1941–78; streamgage 01082000, 

Contoocook River at Peterborough, 1946–present (2007); 

streamgage 01073000, Oyster River near Durham, 

1934–present (2007); and streamgage 01072100, Salmon 

Falls River at Milton, 1968–present (2007).

Flow-Frequency Analyses of the 

April 2007 Flooding

Flow-frequency curves were determined for all 57 

streamgages included in this investigation. For 39 of the 57 

streamgages, the guidelines in Bulletin 17B (U.S. Interagency 

Advisory Committee on Water Data, 1982) were used to 

determine flow-frequency curves. Bulletin 17B recommends 

the use of a log-Pearson Type III distribution for estimating 

flow frequency and provides procedures for weighting station skews, determining historical peaks, and detecting and 

treating outliers and trends. Bulletin 17B also recommends 

at least 10 years of streamgage record for a flow-frequency 

analysis. Software developed by the USGS to analyze peakflow frequency (PeakFQ) was used for these computations 

(U.S. Geological Survey, 2007a). The peak-flow data used as 

input to the PeakFQ program were retrieved from the National 

Water Information System (NWIS) (U.S. Geological Survey, 

2007b). When the flow-frequency curves were computed, if 

peak discharges at a streamgage were affected by regulation, 

the station skew—without weighting from the generalized 

skew as described in Bulletin 17B—was used for computing 

the frequency curve. If the April 2007 peak discharge was the 

annual peak for the 2007 water year, it was added to the peakflow data prior to computing the frequency curves.

For 11 of the 57 streamgages, flood-control structures 

operated by the USACE are in the basin. Flow-frequency data 

for 3 of these 11 streamgages were obtained from frequency 

curves developed by the USACE and published in FEMA 

Flood-Insurance Studies (table 3, footnote a). At 8 of the 11 

streamgages, the flow-frequency curve published in the FEMA 

Flood-Insurance Study was not developed by the USACE and 

was recomputed for this study by following the Bulletin 17B 

guidelines and incorporating peak-flow data collected since 

the flood-control structures were built.

At 10 of the 57 streamgages in this investigation, a record 

length of 10 or fewer years was considered insufficient for a 
Flow-Frequency Analyses of the April 2007 Flooding 19

Table 3. Flow-frequency data and recurrence-interval estimates for 57 streamgages during the April 2007 flood in central and southern New Hampshire.—Continued[Location of streamgages in figure 4. USGS, U.S. Geological Survey; ft3/s, cubic feet per second; yr, year; <, less than; >, greater than; na, not available. Frequency curve determination method: LeBlanc, 

frequency curve estimated with regression equation (LeBlanc, 1978); LP3, log-Pearson type-3 frequency analysis; FIS, flow-frequency curve from Federal Emergency Management Agency flood-insurance study; Ratio, frequency curve based on a downstream streamgage with frequency curve adjusted by the ratio of drainage areas of the streamgages]

USGS 

streamgage 

number

Streamgage name

Peak 

discharge of 

April (16–18) 

2007 flood 

(ft3/s)

Estimated discharges for selected recurrence intervals 

(ft3/s)

Frequency curve 

determination 

method

Recurrence 

interval of 

April 2007 

flood 

(yr)

2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr

01064500 Saco River near Conway 9,750 17,000 26,200 32,700 41,200 47,700 54,400 70,700 LP3 <2

01064801 Bearcamp River at South Tamworth 3,720 3,640 5,070 6,000 7,140 7,970 8,790 10,650 LP3 2–5

01065000 Ossipee River at Effingham Falls 5,370 3,550 4,970 5,930 7,190 8,160 9,140 11,500 LP3 5–10

01072100 Salmon Falls River at Milton 5,500 1,440 2,380 3,190 4,450 5,590 6,920 10,900 LP3 25–50

01072800 Cocheco River near Rochester 7,240 2,140 3,850 5,350 7,740 9,920 12,500 20,300 LP3 10–25

01072800 Cocheco River near Rochester—record 

extension with Lamprey River streamgage 01073500

7,240 1,640 2,650 3,460 4,660 5,680 6,820 10,000 LP3c 100–500

01072870 Isinglass River at Rochester Neck Road, 

near Dover

6,160 1,560 2,380 2,920 3,940 4,680 5,620 8,230 LeBlancb 100–500

01073000 Oyster River near Durham 1,320 304 488 633 843 1,020 1,220 1,750 LP3 100–500

01073500 Lamprey River near Newmarket 8,450 2,190 3,550 4,660 6,320 7,760 9,400 14,100 LP3 50–100

01073587 Exeter River at Haigh Road, near Brentwood 2,840 1,250 2,410 3,450 5,140 6,690 8,530 14,100 LP3 5–10

01073587 Exeter River at Haigh Road, near 

Brentwood—record extension with Lamprey River streamgage 01073500

2,840 882 1,420 1,840 2,450 2,960 3,530 5,060 LP3c 25–50

01073600 Dudley Brook near Exeter 470 164 242 300 378 440 506 675 LP3 50–100

01073750 Mill Brook near NH108, at Stratham 325 157 312 450 667 863 1,089 1,755 LP3 5–10

01073785 Winnicut River at Greenland, 

near Portsmouth

1,030 227 334 406 542 637 758 1,100 LeBlancb 100–500

01073810 Berrys Brook at Sagamore Road, 

near Portsmouth

278 77.4 112 136 182 213 253 368 LeBlancb 100–500

01073838 Taylor River at Old Stage Road 

near Hampton

436 102 143 172 222 257 302 424 LeBlancb >500

01074520 East Branch Pemigewasset River at Lincoln 2,730 10,700 14,300 16,600 19,400 21,400 23,400 27,900 LP3 <2

01075000 Pemigewasset River at Woodstock 4,460 11,800 19,000 24,600 32,300 38,700 45,500 63,600 LP3 <201076000 Baker River near Rumney 3,040 5,130 8,620 11,600 16,300 20,500 25,500 40,500 LP3 <2

01076500 Pemigewasset River at Plymouth 13,900 21,200 30,100 36,400 44,700 51,200 58,000 74,900 LP3 <2

01077000 Squam River at Ashland 543 244 445 616 877 1,110 1,370 2,130 LP3 5–10

01077510 Newfound River below Newfound Lake 

near Bristol

1,690 1,590 2,300 2,720 3,190 3,500 3,780 4,350 LP3 2–5
20 Flood of April 2007 in New Hampshire Table 3. Flow-frequency data and recurrence-interval estimates for 57 streamgages during the April 2007 flood in central and southern New Hampshire.—Continued [Location of streamgages in figure 4. USGS, U.S. Geological Survey; ft3/s, cubic feet per second; yr, year; <, less than; >, greater than; na, not available. Frequency curve determination method: LeBlanc, frequency curve estimated with regression equation (LeBlanc, 1978); LP3, log-Pearson type-3 frequency analysis; FIS, flow-frequency curve from Federal Emergency Management Agency flood-insurance study; Ratio, frequency curve based on a downstream streamgage with frequency curve adjusted by the ratio of drainage areas of the streamgages] USGS stream- gage number Streamgage name Peak discharge of April (16–18) 2007 flood (ft3/s) Estimated discharges for selected recurrence intervals (ft3/s) Frequen- cy curve determi- nation method Recurrence interval of April 2007 flood (yr) 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr 01078000 Smith River near Bristol 2,770 1,750 2,610 3,270 4,220 5,020 5,900 8,300 LP3 5–10 01079602 Poorfarm Brook near Gilford 505 220 374 472 722 882 1,090 1,780 LeBlancb 10–25 01079900 Shannon Brook near Moultonborough 570 325 592 770 1,240 1,560 1,970 3,420 LeBlancb 2–5 01080000 Lake Winnipesaukee at Weirs Beach na na na 505.4 ft na 505.9 ft 506.2 ft 506.7 ft FIS <10

01080500 Lake Winnipesaukee Outlet at Lakeport 2,430 1,650 2,140 2,350 2,520 2,610 2,670 2,750 LP3 10–25

01081000 Winnipesaukee River at Tilton 3,550 2,260 3,000 3,440 3,940 4,290 4,610 5,280 LP3 10–25

01081500 Merrimack River at Franklin Junction 17,300 17,700 20,000 20,900 21,600 21,900 22,100 22,300 LP3 <2

01082000 Contoocook River at Peterborough 4,110 1,310 1,920 2,370 2,990 3,480 3,990 5,330 LP3 100–500

01083000 Nubanusit Brook below MacDowell Dam 

near Peterborough

637 na na 650 na 700 800 900 FISa <10

01084500 Beards Brook near Hillsborough 3,550 1,200 1,640 1,930 2,300 2,580 2,850 3,510 LP3 >500

01085000 Contoocook River near Henniker 13,000 4,960 7,360 9,240 12,000 14,300 16,800 23,900 LP3 25–50

01085500 Contoocook River below Hopkinton Dam 

at West Hopkinton

5,370 4,580 5,570 6,070 6,570 6,880 7,150 7,630 LP3 2–5

01086000 Warner River at Davisville 7,730 2,200 3,390 4,310 5,630 6,730 7,930 11,200 LP3 50–100

01087000 Blackwater River near Webster 1,950 1,790 2,100 2,200 2,270 2,300 2,320 2,340 LP3 2–5

01087850 Contoocook River at River Hill, 

near Penacook

7,780 na na 8,000 na 15,000 23,300 33,000 FISa <10

01088400 Merrimack River at Concord 32,800 na na 19,300 na 33,750 44,000 86,250 FISa 10–50

01089000 Soucook River near Concord 3,500 1,270 2,000 2,560 3,370 4,030 4,760 6,750 Ratio 25–50

01089100 Soucook River at Pembroke Road, 

near Concord

3,730 1,360 2,130 2,730 3,590 4,300 5,080 7,200 LP3 25–50

01089500 Suncook River at North Chichester 10,600 2,230 3,550 4,680 6,430 7,990 9,820 15,300 LP3 100–500

01090800 Piscataquog River below Everett Dam, 

near East Weare

1,600 1,030 1,380 1,580 1,780 1,910 2,010 2,220 LP3 10–25

01091000 South Branch Piscataquog River 

near Goffstown

8,880 2,040 3,000 3,650 4,460 5,070 5,680 7,110 LP3 >500

01091500 Piscataquog River near Goffstown 11,200 3,200 5,100 6,500 8,420 9,950 11,600 15,700 LP3 50–100

01092000 Merrimack River near Goffs Falls, 

below Manchester

59,700 30,200 39,200 45,000 52,400 57,800 63,200 75,900 LP3 50–100
Flow-Frequency Analyses of the April 2007 Flooding 21

Table 3. Flow-frequency data and recurrence-interval estimates for 57 streamgages during the April 2007 flood in central and southern New Hampshire.—Continued[Location of streamgages in figure 4. USGS, U.S. Geological Survey; ft3/s, cubic feet per second; yr, year; <, less than; >, greater than; na, not available. Frequency curve determination method: LeBlanc, 

frequency curve estimated with regression equation (LeBlanc, 1978); LP3, log-Pearson type-3 frequency analysis; FIS, flow-frequency curve from Federal Emergency Management Agency flood-insurance study; Ratio, frequency curve based on a downstream streamgage with frequency curve adjusted by the ratio of drainage areas of the streamgages]

USGS 

streamgage 

number

Streamgage name

Peak 

discharge of 

April (16–18) 

2007 flood 

(ft3/s)

Estimated discharges for selected recurrence intervals 

(ft3/s)

Frequency curve 

determination 

method

Recurrence 

interval of 

April 2007 

flood 

(yr)

2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr

01093000 Sucker Brook at Auburn na 256 379 459 556 626 693 843 LP3 na

01094000 Souhegan River at Merrimack 10,500 3,170 4,930 6,370 8,530 10,400 12,600 18,800 LP3 50–100

010965817 Beaver Brook at Fordway Extension at Derry 1,100 463 811 1,110 1,590 2,020 2,520 4,060 Ratio 5–10010965844 Beaver Brook at South Road, near Derry 1,470 618 1,080 1,490 2,120 2,700 3,370 5,430 Ratio 5–10

010965852 Beaver Brook at North Pelham 1,900 799 1,400 1,920 2,740 3,490 4,360 7,020 LP3 5–10

01096587 Tributary to Cobbetts Pond at I-93 south exit 

ramp near Windham

59 20.8 37.5 48.3 79.3 98.7 124 218 LeBlancb 10–25

01100505 Spicket River at North Salem 434 338 519 639 884 1,050 1,270 1,900 LeBlancb 2–501100549 Policy Brook at Rockingham Park Boulevard 

at Salem

95 57.3 88.3 109 151 180 217 326 Ratio 5–10

011005605 Policy Brook at I-93 north rest stop entrance 

ramp, near Salem

338 204 314 387 538 640 772 1,160 LeBlancb 5–10

01100561 Spicket River near Methuen, Mass. 1,130 854 1,200 1,440 1,820 2,110 2,470 3,410 LeBlancb 2–501137500 Ammonoosuc River at Bethlehem Junction 3,370 4,360 6,290 7,700 9,620 11,100 12,800 16,930 LP3 <2

01138500 Connecticut River at Wells River, Vt. 27,300 32,700 41,100 46,000 51,500 55,100 58,500 65,600 LP3 <2

01144500 Connecticut River at West Lebanon 38,800 47,100 62,800 73,900 88,900 101,000 113,000 145,000 LP3 <2

01150500 Mascoma River at Mascoma 2,990 2,020 2,980 3,580 4,290 4,780 5,250 6,230 LP3 5–10

a Computed by the U.S. Army Corps of Engineers for the flood-insurance study.b Results from the LeBlanc (1978) regression equations may be unreliable in basins with urbanization or regulation.c Bulletin 17B “two-station comparison” technique applied to extend the streamgage record by using long-term streamgage 01073500, Lamprey River near Newmarket.
22 Flood of April 2007 in New Hampshire

flow-frequency analysis. At these sites, the flow-frequency 

curves were computed by Olson (2007) by using the regression equations for estimating flow frequency developed by 

LeBlanc (1978). The resulting frequency curves were not 

adjusted for urbanization or regulation. 

At two streamgages, the flow record was sufficient for 

flow-frequency analysis; however, both of these sites have 

a short period of record, and within that short record period, 

these streamgage sites have experienced severe flooding. 

The streamgage Cocheco River near Rochester (01072800) 

(fig. 4E) has 13 years of record, and the streamgage Exeter 

River at Haigh Road near Brentwood (01073587) (fig. 4B) 

has 12 years of record. A log-Pearson Type III analysis was 

performed on the flow record at the streamgages and resulted 

in a recurrence interval for the April 2007 flood peak of 10 

to 25 years for the Cocheco River near the Rochester streamgage and 5–10 years for the Exeter River at Haigh Road near 

Brentwood streamgage. The two-station-comparison technique 

in Bulletin 17B was applied to extend the records of these 

streamgages (S.A. Olson, U.S. Geological Survey, written 

commun., 2008) by using the long-term streamgage Lamprey River near Newmarket (01073500) (fig. 4E), which has 

73 years of record. The records of the streamgages Cocheco 

River near Rochester and Exeter River at Haigh Road near 

Brentwood have correlation coefficients with the record of 

the streamgage at Lamprey River near Newmarket of 0.84 

and 0.97, respectively. The two-station comparison recordextension technique resulted in a recurrence interval for the 

April 2007 flood peak of 100 to 500 years for the streamgage 

Cocheco River near Rochester and 25 to 50 years for the 

streamgage Exeter River at Haigh Road near Brentwood. 

These data are listed in table 3 and shown in figure 5.

For the streamgage Lake Winnipesaukee at Weirs Beach 

(01080000), only stage data are available. The frequency data 

for this site were obtained from the Flood-Insurance Study for 

the city of Laconia (Federal Emergency Management Agency, 

1980a).

Results of the flow-frequency analyses are shown in 

table 3. The recurrence interval of the April 2007 peak flow 

at each streamgage was determined by using the results of 

frequency analysis. Peak discharge equaled or exceeded a 

50-year flood at 16 streamgages. Peak discharge equaled or 

exceeded a 100-year flood at the 10 streamgages listed below:

1. Cocheco River near Rochester (01072800—with 

streamgage-record extension);

2. Isinglass River at Rochester Neck Road, near Dover 

(01072870);

3. Oyster River near Durham (01073000);

4. Winnicut River at Greenland, near Portsmouth 

(01073785);

5. Berrys Brook at Sagamore Road, near Portsmouth 

(01073810);

6. Taylor River at Old Stage Road, near Hampton 

(01073838);

7. Contoocook River at Peterborough (01082000);

8. Beards Brook near Hillsborough (01084500);

9. Suncook River at North Chichester (01089500); and

10. South Branch Piscataquog River near Goffstown 

 (01091000).
Flow-Frequency Analyses of the April 2007 Flooding 23

Figure 5. Recurrence intervals for the April 2007 flood at streamgages in Hillsborough, Rockingham, Merrimack, Belknap, Strafford, 

Grafton, and Carroll Counties in New Hampshire.

COOS

GRAFTON

MERRIMACK

CARROLL

BELKNAP

CHESHIRE

SULLIVAN

HILLSBOROUGH ROCKINGHAM

STRAFFORD

0 5 10 20 MILES

0 5 10 20 KILOMETERS

EXPLANATION

Lake

County boundary

River

Recurrence interval of peak discharge

at streamgages, April 2007 (see table 3).

Less than 10-year flood

10- to less than 50-year flood

50- to less than 100-year flood

Equal to or greater than 100-year flood

Recurrence interval unknown

72°

71°

43°

44°

45°

Base from U.S. Geological Survey Digital Line Graphs, 1:24,000, 1990−94 and 

National Hydrography Dataset, 1:24,000, 1999
24 Flood of April 2007 in New Hampshire

Determination of the April 2007 Flood 

Discharge by Indirect Methods at 

Ungaged Sites

Four bridge sites were chosen for the determination of 

the April 2007 peak discharge by indirect methods (Matthai, 

1967; table 4):

1. Lamprey River at Epping Road railroad bridge in 

Raymond, N.H. (drainage area of 70 mi2

);

2. Souhegan River at Wilton Road (Elm Street) bridge 

in Milford, N.H., approximately 2,000 ft east of the 

Wilton/Milford, N.H. town line (drainage area of 

102 mi2

);

3. Suncook River at Short Falls Road bridge in 

Epsom, N.H. (drainage area of 210 mi2

); and

4. Suncook River at Websters Mill Road bridge at the 

Chichester/Pittsfield, N.H. town line (drainage area 

of 137 mi2

).

The four locations chosen for the indirect determination 

of the April 2007 peak-flood discharge have never been 

streamgage sites. High-water-mark information (table 6), the 

bridge-opening geometry, and channel and floodplain cross 

sections upstream and downstream from the bridge were 

surveyed at each of these sites and input into the USACE 

HEC-RAS program (2005). The discharges were iteratively 

selected and input into the HEC-RAS program to match the 

surface-elevation output and surveyed high-water marks 

(appendix 1, tables 1–1 to 1–4). 

All four of these sites are located on rivers that have 

streamgage records. On the basis of the indirectly determined 

April 2007 flood-peak discharge at the ungaged location 

(by using high-water-mark data and the USACE HEC-RAS 

program) and the April 2007 flood-peak discharge determined 

for the streamgage site, a flow-frequency curve was generated for each of the four ungaged sites (table 4). To determine 

the flow-frequency curve at the ungaged site, the relation 

between the April 2007 peaks and drainage areas at the gaged 

and ungaged sites was determined. After this relation was 

determined, it was applied to the log-Pearson Type III flowfrequency curve determined at the streamgage site to ascertain 

the flow-frequency curve at the ungaged site. For comparison 

purposes, flow-frequency curves at all four sites also were 

computed by using the regression equations for estimating 

flow frequency developed by LeBlanc (1978) (table 4). 

The coefficient n in the equation below was determined 

through a drainage-area relation between the April 2007 flood 

peak discharge at the streamgage site and the indirectly determined April 2007 peak discharge at the ungaged site on each 

of the rivers of interest by using the drainage-area relation:

Q Qg g A A n= ( ) , (1)

where

 Q is the discharge at the ungaged site, 

Qg is the discharge at the USGS streamgage site, 

 A is the drainage area at the ungaged site, 

 Ag is the drainage area at the USGS streamgage 

site, and

 n is the drainage-area adjustment value.

The drainage areas are shown in table 1 (in back of 

report) for the streamgages and in table 4 for the indirect discharge-measurement sites. April 2007 peak flood discharges 

are shown in table 2 for the streamgage sites and in table 4 

for the indirect discharge-measurement sites. The calculatedcoefficient n values for each indirect discharge-measurement 

location and related streamgage are shown below:

1. Lamprey River between Epping Road railroad 

bridge in Raymond, N.H., and streamgage 01073500 

near Newmarket (n = 0.79);

2. Souhegan River between Wilton Road bridge near 

the Wilton/Milford, N.H. town line and streamgage 

01094000 at Merrimack (n = 0.80);

3. Suncook River between Short Falls Road bridge in 

Epsom, N.H., and streamgage 01089500 at North 

Chichester (n = 0.94); and

4. Suncook River between Websters Mill Road bridge 

in Chichester/Pittsfield, N.H., and streamgage 

01089500 at North Chichester (n = 0.94).
Determination of the April 2007 Flood Discharge by Indirect Methods at Ungaged Sites 25

Table 4. Flow-frequency data and recurrence-interval estimates by indirect methods for four ungaged sites during the April 2007 flood in central and southern New Hampshire.[Location of indirect discharge-determination sites in figures 4A–C. ft3/s, cubic feet per second; yr, year; >, greater than. Frequency curve determination method: LeBlanc, frequency curve estimated with 

regression equation (LeBlanc, 1978); LP3, log-Pearson type-3 frequency analysis; Ratio, frequency curve based on a downstream streamgage with frequency curve adjusted by the ratio of drainage areas of the streamgages]

Indirect dischargedetermination location

Indirect peak 

discharge of 

April (16–18) 

2007 flood 

(ft3/s)

Estimated discharges for selected recurrence intervals 

(ft3/s) Frequency-curve 

determination 

method

Recurrence 

interval of 

April 2007 

flood 

(yr)

2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr

1a) Lamprey River at Epping Road railroad 

 bridge in Raymond, N.H.  (drainage area = 70 mi2

)

3,990 891 1,230 1,470 1,830 2,110 2,470 3,350 LeBlanca >500

1b) Lamprey River at Epping Road railroad 

 bridge in Raymond, N.H.  (drainage area = 70 mi2

)

3,990 1,030 1,660 2,180 2,960 3,630 4,400 6,600 Ratio with LP3 

at streamgage 01073500

50–100

2a) Souhegan River at Wilton Road bridge 

 near the Wilton/Milford, N.H. town line  (drainage area = 102 mi2

)

6,950 1,910 2,830 3,450 4,540 5,340 6,370 9,090 LeBlanca 100–500

2b) Souhegan River at Wilton Road bridge 

 near the Wilton/Milford, N.H. town line  (drainage area = 102 mi2

)

6,950 2,100 3,260 4,210 5,640 6,880 8,330 12,400 Ratio with LP3 

at streamgage 01094000

50–100

3a) Suncook River at Short Falls Road 

 in Epsom, N.H.  (drainage area = 210 mi2

)

14,100 2,140 2,790 3,280 3,850 4,380 5,040 6,480 LeBlanca >500

3b) Suncook River at Short Falls Road 

 in Epsom, N.H.  (drainage area = 210 mi2

)

14,100 2,980 4,740 6,250 8,590 10,700 13,100 20,400 Ratio with LP3 

at streamgage 01089500

100–500

4a) Suncook River at Websters Mill Road 

 in Chichester/Pittsfield, N.H.  (drainage area = 137 mi2

)

9,400 3,260 5,030 6,200 8,430 10,100 12,100 17,900 LeBlanca 25–50

4b) Suncook River at Websters Mill Road 

 in Chichester/Pittsfield, N.H.  (drainage area = 137 mi2

)

9,400 1,990 3,160 4,170 5,730 7,120 8,750 13,600 Ratio with LP3 

at streamgage 01089500

100–500

a Results from the LeBlanc (1978) regression equations may be unreliable in basins with urbanization or regulation.
26 Flood of April 2007 in New Hampshire

Comparison of the April 2007 Flood 

Data to Flood-Insurance Studies

FEMA Flood-Insurance Studies provide communities with information on the severity of flood hazards. This 

information includes estimated discharges and water-surfaceelevation profiles for the 10-, 50-, 100-, and 500-year floods 

for selected potential surface-water bodies around which 

development has occurred or is expected to occur. The 10-, 

50-, 100-, and 500-year floods have a 10-, 2-, 1-, and 0.2-percent chance, respectively, of being equaled or exceeded in any 

given year. These data are used for planning purposes and for 

setting flood-insurance rates for structures within communities 

participating in the National Flood-Insurance Program. 

For the streamgage and indirect-discharge sites in 

this study that were included in a Flood-Insurance Study, 

discharges and peak water-surface elevations (stage) were 

compiled from the appropriate study and are given in 

table 5. Flood-Insurance Study recurrence-interval discharges 

were obtained from the “Summary of Discharges” table for 

the reach that incorporated the streamgage site, and the peak 

water-surface elevations were extracted from the watersurface-elevation profiles. In cases where the streamgage site 

was not identified on the water-surface-elevation profiles, 

interpretation of the streamgage location was required to 

obtain the water-surface-elevation for the corresponding 

recurrence interval.

The compiled Flood-Insurance Study data are shown in 

table 5 along with the peak-stage and peak-discharge data for 

the April 2007 flood. The flow-frequency data obtained from 

the Flood-Insurance Studies (table 5) often differ from the 

flow-frequency data determined for this investigation 

(table 3) because the methods used for determining the 

frequency curves may be different, and (or) more data are currently available for the development of the frequency curves.

The data contained in this report may aid in the updating of future Flood-Insurance Study water-surface-elevation 

profiles for some communities through FEMA’s Map Modernization program. For instance, at the Piscataquog River 

near Goffstown streamgage (01091500), the peak discharge 

in April 2007 was 11,200 ft3

/s. The recurrence interval for 

this discharge, as reported in the Goffstown Flood-Insurance 

Study (Federal Emergency Management Agency, 1978b), 

is 50 to 100 years. It would be expected that the peak stage 

in April 2007 also would fall between the 50- and 100-year 

water-surface-elevation profiles at this location. However, the 

peak stage for the April 2007 flood was 187.70 ft (NGVD 29), 

which is greater than the 100-year water-surface elevation 

reported in the Goffstown Flood-Insurance Study. There are 

16 streamgage sites and 1 indirect discharge site for which the 

observed peak discharge of the April 2007 flood is bracketed 

by a recurrence interval different than the Flood-Insurance 

Study recurrence interval that brackets the observed peak 

April 2007 flood stage or water-surface elevation (table 5). 

The reasons for these discrepancies are beyond the scope of 

this study. 
Comparison of the April 2007 Flood Data to Flood-Insurance Studies 27

Table 5. Flood-insurance study data for selected streamgage sites in central and southern New Hampshire.—Continued[Location of streamgages in figure 4. na, not available; ft3/s, cubic feet per second; yr, year; NAVD 88, North American Datum of 1988; NGVD 29, National Geodetic Vertical Datum of 1929]

USGS 

streamgage 

number

Streamgage name and 

ungaged site location

Peak discharge of 

April 2007 

flood (ft3/s)

Magnitude of discharge for X-yr recurrence interval at streamgage location 

from flood-insurance study (ft3/s)

Peak stage 

of April 2007 

flood, 

NGVD 29 (ft)

Water-surface elevation for X-yr 

recurrence interval at streamgage 

location from flood-insurance study, 

NGVD 29 (ft)

Value to 

subtract 

from 

NGVD 29 

elevation to 

obtain 

NAVD 88 (ft)

10-yr 50-yr 100-yr 500-yr 10-yr 50-yr 100-yr 500-yr

01064500 Saco River near Conway 9,750 29,750 45,840 53,640 72,180 426.49 431.9 435.4 437.1 440.5 0.44

01064801 Bearcamp River at South Tamworth 3,720 na na 14,900 na 501.49 na na 510 na 0.46

01072100 Salmon Falls River at Miltona 5,500 2,930 4,500 5,290 7,490 404.46 408.1 409.2 409.8 411.0 0.56

01072800 Cocheco River near Rochestera 7,240 3,160 5,100 6,120 9,580 140.20 135.0 136.6 137.5 139.8 0.6101073500 Lamprey River near Newmarket 8,450 4,120 6,270 7,300 10,000 55.77 48.1 52.0 53.5 58.0 0.73

01073587 Exeter River at Haigh Road, 

near Brentwooda

2,840 1,810 2,640 3,010 3,900 71.46 69.0 70.1 70.4 71.2 0.75

01073600 Dudley Brook near Exetera 470 na na 506 na 94.40 na na 94.1 na 0.7501074520 East Branch Pemigewasset River 

at Lincoln

2,730 13,000 24,000 30,300 50,000 829.89 834.0 836.5 838.0 842.0 0.31

01075000 Pemigewasset River at Woodstock 4,460 na na 47,700 na 623.27 na na 632.0 na 0.34

01076000 Baker River near Rumney 3,040 8,200 12,800 14,400 19,000 502.99 506.4 509.1 509.7 511.4 0.40

01076500 Pemigewasset River at Plymouth 13,900 35,000 53,500 62,000 82,700 467.78 482.0 482.5 483.4 494.0 0.41

01080000 Lake Winnipesaukee at Weirs Beach na na na na na 505.00 505.4 505.9 506.2 506.7 0.43

01080500 Lake Winnipesaukee Outlet at Lakeport 2,430 2,600 2,600 3,500 4,300 na 504.0 504.3 504.3 504.3 0.44

01081000 Winnipesaukee River at Tiltona 3,550 3,465 4,965 5,715 7,670 449.48 449.8 451.4 452.2 454.1 0.47

01081500 Merrimack River at Franklin Junction 17,300 14,800 25,000 30,000 62,000 264.70 263.1 268.4 270.4 281.1 0.50

01082000 Contoocook River at Peterborough 4,110 2,300 4,310 5,700 9,890 739.18 736.7 739.4 740.5 742.6 0.72

01083000 Nubanusit Brook below MacDowell 

Dam near Peterborough

637 650 700 800 900 936.74 na na na na 0.67

01084500 Beards Brook near Hillsborougha 3,550 2,300 3,900 4,800 7,100 602.33 598.4 601.8 603.7 610.0 0.61

01085000 Contoocook River near Henniker 13,000 9,100 17,000 21,600 34,000 484.81 484.4 489.2 491.6 496.0 0.62

01085500 Contoocook River below Hopkinton 

Dam at West Hopkinton

5,370 7,200 7,300 9,500 13,000 364.34 365.7 365.8 367.5 370.0 0.68

01086000 Warner River at Davisvillea 7,730 4,600 7,800 9,500 14,550 391.90 386.0 388.0 389.0 391.5 0.59

01087000 Blackwater River near Webster 1,950 na na 2,600 na 438.60 na na 440.0 na 0.56

01087850 Contoocook River at River Hill, 

near Penacook

7,780 8,000 15,000 23,300 33,000 347.87 348.2 352.3 356.1 359.5 0.60

01088400 Merrimack River at Concorda 32,800 19,300 33,750 44,000 86,250 231.52 226.4 230.1 232.4 238.8 0.61

01089000 Soucook River near Concorda 3,500 2,410 4,100 5,045 7,605 305.79 301.4 304.0 305.2 307.0 0.58
28 Flood of April 2007 in New Hampshire Table 5. Flood-insurance study data for selected streamgage sites in central and southern New Hampshire.—Continued [Location of streamgages in figure 4. na, not available; ft3/s, cubic feet per second; yr, year; NAVD 88, North American Datum of 1988; NGVD 29, National Geodetic Vertical Datum of 1929] USGS stream- gage number Streamgage name and ungaged site location Peak dis- charge of April 2007 flood (ft3/s) Magnitude of discharge for X-yr recur- rence interval at streamgage location from flood-insurance study (ft3/s) Peak stage of April 2007 flood, NGVD 29 (ft) Water-surface elevation for X-yr recurrence interval at streamgage location from flood-insurance study, NGVD 29 (ft) Value to subtract from NGVD 29 elevation to obtain NAVD 88 (ft) 10-yr 50-yr 100-yr 500-yr 10-yr 50-yr 100-yr 500-yr 01089100 Soucook River at Pembroke Road, near Concorda 3,730 2,620 4,450 5,475 8,255 296.26 268.0 271.2 272.0 274.0 0.60 01089500 Suncook River at North Chichester 10,600 4,775 8,335 10,330 15,970 345.32 341.3 344.0 345.2 347.9 0.57 Ungaged location Suncook River at Short Falls Road bridge in Epsom 14,100 6,040 10,540 13,065 20,195 308.57 302.5 306.8 308.2 312.0 0.59

Ungaged 

location

Suncook River at Websters Mill Road 

bridge in Chichester/Pittsfield

9,400 4,510 7,870 9,750 15,070 393.21 391.0 392.5 393.5 395.0 0.56

01090800 Piscataquog River below Everett Dam, 

near East Weare

1,600 na na 2,200 na 328.37 na na 329.6 na 0.66

01091000 South Branch Piscataquog River 

near Goffstown

8,880 3,690 5,910 6,990 10,220 322.97 317.8 320.0 321.0 323.8 0.67

01091500 Piscataquog River near Goffstowna 11,200 5,300 9,700 12,500 21,000 187.70 182.9 185.8 186.9 189.4 0.67

01092000 Merrimack River near Goffs Falls, 

below Manchestera

59,700 44,000 56,000 69,000 127,000 126.06 122.1 126.0 128.0 140.0 0.69

01094000 Souhegan River at Merrimack 10,500 6,920 11,900 12,500 22,000 173.29 171.1 174.2 174.7 179.0 0.70

Ungaged 

location

Souhegan River at Wilton Road bridge 

in Milforda

6,950 3,740 6,360 7,550 11,000 297.88 297.2 299.5 300.2 302.8 0.68

010965817 Beaver Brook at Fordway Extension 

at Derry

1,100 750 1,520 1,860 3,300 na 239.5 240.6 241.0 242.6 0.69

010965844 Beaver Brook at South Road, near Derrya 1,470 860 1,760 2,160 3,600 219.45 217.5 218.8 219.2 220.4 0.69

010965852 Beaver Brook at North Pelhama 1,900 1,450 2,470 3,070 4,750 162.78 161.3 162.9 163.5 165.3 0.7101100561 Spicket River near Methuen, Mass. 1,130 900 1,600 1,900 2,900 109.91 109.0 111.3 111.6 114.3 0.77

01138500 Connecticut River at Wells River, Vt. 27,300 na na 80,300 na 409.00 na na 420.0 na 0.38

01144500 Connecticut River at West Lebanon 38,800 72,000 108,000 125,000 157,000 337.93 345.4 351.0 353.9 358.0 0.41

01150500 Mascoma River at Mascomaa 2,990 3,500 5,750 7,000 10,000 749.01 748.8 750.8 752.8 754.0 0.30

a The FIS recurrence interval that brackets the observed peak discharge of the April 2007 flood differs from the FIS recurrence interval that brackets the observed peak April 2007 flood stage or watersurface elevation.
Comparison of the April 2007 Flood Data to Flood-Insurance Studies 29

Table 6. High-water-mark data used in the determination of April 2007 flood discharge by indirect methods for four ungaged sites in central and southern New Hampshire.[ft, feet; NAVD 88, North American Vertical Datum of 1988; NGVD 29, National Geodetic Vertical Datum of 1929]

High-watermark name Elevation NAVD 88 (ft) Elevation NGVD 29 (ft) Latitude (decimal degree) Longitude (decimal degree) River name Location/road Town Mark rating Mark type Mark description

Ray10 187.9 188.625 43.03811 -71.17194 Lamprey Abandoned railroad bridge behind I.C. Reed 

and Son’s (Epping Street)

Raymond Good Seed line Nail in 1.5-ft-diameter 

pine tree

Ray11 187.79 188.515 43.03801 -71.17255 Lamprey Upstream from abandoned railroad bridge 

behind I.C. Reed and Son’s (Epping Street)

Raymond Good Seed line Nail in 1.0-ft-diameter 

hardwood

Ray12 187.685 188.41 43.03798 -71.17266 Lamprey 30 ft upstream from Ray11 behind I.C. Reed 

and Son’s (Epping Street)

Raymond Good Seed line Nail in 2.0-ft-diameter 

dead pine tree

Ray13 186.675 187.4 43.03761 -71.17160 Lamprey Downstream from abandoned railroad bridge 

behind I.C. Reed and Son’s (Epping Street)

Raymond Good Seed line Nail in 2.0-ft-diameter 

pine tree

Ray14 186.67 187.395 43.03738 -71.17309 Lamprey 55 ft downstream from monitoring well 

behind I.C. Reed and Son’s (Epping Street)

Raymond Good Seed line Nail in 0.5-ft-diameter 

pine tree

Sunhwm33 308.055 308.645 43.20207 -71.38300 Suncook 100 ft downstream and 80 ft bankward at 

Short Falls Road bridge

Epsom Good Seed line Nail in base of 

pine tree

Sunhwm34 308.905 309.495 43.20224 -71.38233 Suncook Top downstream corner of old abutment at 

Short Falls Road bridge

Epsom Fair Wash line Stake with line

Sunhwm35 309.225 309.815 43.20235 -71.38183 Suncook Top of left bank at Short Falls Road bridge Epsom Good Weed line Nail in pine tree

Souh8 294.76 295.44 42.84212 -71.71996 Souhegan 

River

200 ft downstream of Wilton Road bridge Milford Fair Wash line Nail in tree

Souh9 298.77 299.45 42.84086 -71.72031 Souhegan 

River

100 ft upstream of Wilton Road bridge Milford Good Wash line Nail in tree

Souh10 296.075 296.755 42.84185 -71.72022 Souhegan 

River

20 ft downstream from mill and 150 ft 

downstream from Wilton Road bridge

Milford Fair Sash line Nail in tree

SuncookWMB1 394.445 395.005 43.27838 -71.34515 Suncook 100 ft upstream from Websters Mill bridge 

on left bank

Pittsfield Poor Sash line Stake with mark

SuncookWMB2 389.045 389.605 43.27888 -71.34735 Suncook 300 ft downstream from bridge on right bank 

and 15 ft streamward from mailbox #186

Pittsfield Poor Sash line Stake with mark

SuncookWMB3 395.295 395.855 43.27916 -71.34491 Suncook 300 ft upstream from last house on upstream 

right bank and 400 ft upstream from bridge on right bank

Pittsfield Poor Sash line Stake with mark

SuncookWMB4 395.49 396.05 43.27890 -71.34451 Suncook 600 ft upstream from bridge on right bank Pittsfield Fair Debris line Nail in base of 1.0-ftdiameter maple tree

SuncookWMB6 383.365 383.925 43.27773 -71.34895 Suncook Left edge of water at Websters Mill Pittsfield Fair Seed line Nail in base of 

spruce tree
30 Flood of April 2007 in New Hampshire

Summary

During April 16–18, 2007, central and southern 

New Hampshire experienced severe flooding caused by 

as much as 7 in. of rainfall in the region. A Presidential 

Disaster Declaration was issued on April 27, 2007, for five 

counties (Grafton, Hillsborough, Merrimack, Rockingham, 

and Strafford) in New Hampshire. On May 10, 2007, a sixth 

county (Belknap) was added to the disaster declaration. 

The U.S. Geological Survey, in a cooperative investigation 

with the Federal Emergency Management Agency (FEMA), 

measured or computed flood data at 57 streamgages and 4 

ungaged sites in and adjacent to the counties declared disaster 

areas. These data include peak stages, peak discharges, and 

recurrence-interval estimates for the April 2007 flooding, 

and data compiled from FEMA Flood-Insurance Studies for 

comparison purposes.

The total precipitation that occurred during April 15–19, 

2007, in southeastern New Hampshire (6.54 in. in Durham) is 

approximately one-half of the 13 in. of precipitation that fell 

during October 20–22, 1996, in the same area (National 

Oceanic and Atmospheric Administration, 1996). The total 

April 15–19, 2007, precipitation in southeastern New 

Hampshire is less than one-half of the up to 14 in. of precipitation that fell during May 11–15, 2006, across the coastal 

regions of New Hampshire (National Oceanic and Atmospheric Administration, 2006a) and approximately 60 percent 

of the up to 11 in. of precipitation that fell during May 11–15, 

2006, in the south-central part of the state (National Oceanic 

and Atmospheric Administration, 2006b). Although the 

April 2007 storm produced less precipitation than either the 

October 1996 or May 2006 storm events, some streams in 

New Hampshire had higher discharges in the 2007 event. The 

higher than normal precipitation from the April 2007 storm, 

including precipitation on top of snowpack at higher elevations, downed trees, and wood debris in some rivers contributed to the high flows and flooding in southern and central 

New Hampshire. In addition, an abnormally high spring tide 

along with a storm surge of nearly 3 ft caused tidal flooding 

along portions of the seacoast (National Oceanic and Atmospheric Administration, 2007b), and the prolonged period of 

strong northeast winds caused a prolonged storm surge along 

the coastline (National Climate Data Center, 2007).

At 5 long-term (more than 10 years of record) streamgage sites, the peak discharge in April 2007 was the maximum 

discharge for the period of record. These streamgages include 

South Branch Piscataquog River near Goffstown (1941–78), 

Contoocook River at Peterborough, 1946–present (2008); 

Oyster River near Durham, 1934–present (2008); Cocheco 

River near Rochester, 1995–present (2008); and Salmon Falls 

River at Milton, 1968–present (2008).

Peak discharges equaled or exceeded a 100-year recurrence interval at 10 streamgages and equaled or exceeded 

a 50-year recurrence interval at 16 streamgages. The most 

severe flooding was in Rockingham, Strafford, Merrimack, 

and Hillsborough Counties.

Peak-flood discharge and stage data from the April 2007 

flood event at streamgage and indirect-discharge sites were 

compared to recurrence-interval discharges and peak watersurface elevations (stage) determined by Flood-Insurance 

Studies, where available. Flood-Insurance Study recurrenceinterval discharges were obtained from the “Summary 

of Discharges” table for the reach that incorporated the 

streamgage site, and the peak water-surface elevations were 

extracted from the water-surface-elevation profiles. In cases 

where the streamgage site was not identified on the watersurface-elevation profiles, interpretation of the streamgage 

location was required to obtain the water-surface-elevation for 

the corresponding recurrence interval.

Selected References

Benson, M.A., and Dalrymple, Tate, 1967, General field and 

office procedures for indirect discharge measurements: 

U.S. Geological Survey Techniques of Water-Resources 

Investigations, book 3, chap. A1, 30 p.

Federal Emergency Management Agency, 1977, Floodinsurance study, Town of Henniker, Merrimack County, 

New Hampshire: Washington, D.C., 15 p.

Federal Emergency Management Agency, 1978a, Floodinsurance study, Town of Chichester, Merrimack County, 

New Hampshire: Washington, D.C., 15 p.

Federal Emergency Management Agency, 1978b, Floodinsurance study, Town of Goffstown, Hillsborough County, 

New Hampshire: Washington, D.C., 18 p.

Federal Emergency Management Agency, 1978c, Floodinsurance study, Town of Hillsborough, Hillsborough 

County, New Hampshire: Washington, D.C., 20 p.

Federal Emergency Management Agency, 1979a, Floodinsurance study, City of Franklin, Merrimack County, 

New Hampshire: Washington, D.C., 20 p.

Federal Emergency Management Agency, 1979b, Floodinsurance study, Town of Merrimack, Hillsborough County, 

New Hampshire: Washington, D.C., 27 p.

Federal Emergency Management Agency, 1979c, Floodinsurance study, Town of Pelham, Hillsborough County, 

New Hampshire: Washington, D.C., 22 p.

Federal Emergency Management Agency, 1979d, Floodinsurance study, Town of Peterborough, Hillsborough 

County, New Hampshire: Washington, D.C., 21 p.
Selected References 31

Federal Emergency Management Agency, 1979e, Floodinsurance study, Town of Milford, Hillsborough County, 

New Hampshire: Washington, D.C., 22 p.

Federal Emergency Management Agency, 1980a, Floodinsurance study, City of Laconia, Belknap County, 

New Hampshire: Washington, D.C., 24 p.

Federal Emergency Management Agency, 1980b, Floodinsurance study, City of Manchester, Hillsborough County, 

New Hampshire: Washington, D.C., 24 p.

Federal Emergency Management Agency, 1987, Floodinsurance study, Town of Warner, Merrimack County, 

New Hampshire: Washington, D.C., 18 p.

Federal Emergency Management Agency, 1988, Floodinsurance study, Town of Hopkinton, Merrimack County, 

New Hampshire: Washington, D.C., 16 p.

Federal Emergency Management Agency, 1991, Floodinsurance study, Town of Tamworth, Carroll County, 

New Hampshire: Washington, D.C., 12 p.

Federal Emergency Management Agency, 1993a, Floodinsurance study, Town of Weare, Hillsborough County, New 

Hampshire: Washington, D.C., 16 p.

Federal Emergency Management Agency, 1993b, Floodinsurance study, Town of Webster, Merrimack County, 

New Hampshire: Washington, D.C., 10 p.

Federal Emergency Management Agency, 1997, Floodinsurance study, Town of Tilton, Belknap County, 

New Hampshire: Washington, D.C., 20 p.

Federal Emergency Management Agency, 1999, Floodinsurance study, City of Concord, Merrimack County, 

New Hampshire: Washington, D.C., 20 p.

Federal Emergency Management Agency, 2001, Floodinsurance study, Town of New Boston, Hillsborough 

County, New Hampshire: Washington, D.C., 18 p.

Federal Emergency Management Agency, 2002, Floodinsurance study, Town of Conway, Carroll County, 

New Hampshire: Washington, D.C., 21 p.

Federal Emergency Management Agency, 2005a, FloodInsurance Study, Rockingham County, New Hampshire, 

all jurisdictions: Washington, D.C., 87 p.

Federal Emergency Management Agency, 2005b, Floodinsurance study, Strafford County, New Hampshire, all 

jurisdictions: Washington, D.C., 41 p.

Federal Emergency Management Agency, 2007, Initial notices 

and amendments, New Hampshire severe storms and flooding: Initial Notice and Amendments No. 1 and 2, accessed 

December 27, 2007, at http://www.fema.gov/news/eventdfrns.fema?id=7906

Federal Emergency Management Agency, 2008, Floodinsurance study, Grafton County, New Hampshire, all 

jurisdictions: Washington, D.C., 79 p.

LeBlanc, D.R., 1978, Progress report on hydrologic investigations of small drainage areas in New Hampshire—

Preliminary relations for estimating peak discharge on rural, 

unregulated streams: U.S. Geological Survey WaterResources Investigations Report 78–47, 9 p.

Leica Geosystems, 2008, Leica GPS1200, GPS1200 surveying systems, accessed November 9, 2007, at http://www.

leica-geosystems.com/corporate/en/products/total_stations/

lgs_4521.htm

Matthai, H.F., 1967, Measurement of peak discharge at width 

contractions by indirect methods: Techniques of WaterResources Investigations, book 3, chap. A4, 44 p.

National Climate Data Center, 2007, Storm events data base, 

accessed December 27, 2007, at http://www4.ncdc.noaa.

gov/cgi-win/wwcgi.dll?wwEvent~Storms

National Climate Data Center, 2008, Normal precipitation, 

inches, accessed February 19, 2008, at http://www.ncdc.

noaa.gov/oa/climate/online/ccd/nrmpcp.txt

National Oceanic and Atmospheric Administration, 1996, 

Climatological data—New England, October 1996: Climatological Data, v. 108, no. 10, 46 p.

National Oceanic and Atmospheric Administration, 2006a, 

Record of climatological observations (COOP), accessed 

November 17, 2006, at http://www7.ncdc.noaa.gov/IPS/

coopgetpublications.html

National Oceanic and Atmospheric Administration, 2006b, 

Public information statement, accessed November 17, 2006, 

at http://www.ncdc.noaa.gov/oa/climate/research/2006/may/

boxpns.txt

National Oceanic and Atmospheric Administration, 2007a, 

Record of climatological observations (COOP), accessed 

December 27, 2007, at http://www1.ncdc.noaa.gov/pub/

orders/7A7D76FF-CE3F-4DDD-0A85-6A86CFEDA9E8.

PDF

National Oceanic and Atmospheric Administration, 

2007b, Public information statement, accessed December 27, 2007, at http://www.srh.noaa.gov/productview.

php?pil=CLMCON&version=7&max=61

Northeast River Forecast Center, 2007a, 1-day observed 

precipitation—Valid April 16–18, 2006, 1200 UTC, 

accessed December 27, 2007, at http://www.erh.noaa.gov/

nerfc/obsprecip.shtml
32 Flood of April 2007 in New Hampshire

Northeast River Forecast Center, 2007b, New Hampshire: 

April 2007 monthly observed precipitation, accessed 

December 27, 2007, at http://www.srh.noaa.gov/rfcshare/

precip_analysis_new.php?location=tar&overlay=1100101

Olson, S.A., 2007, Flood of May 2006 in New Hampshire: 

U.S. Geological Survey Open-File Report 2007–1122, 32 p.

U.S. Army Corps of Engineers, May 2005, HEC-RAS river 

analysis system, Version 3.1.3: Hydrologic Engineering 

Center, accessed September 2, 2007, at http://www.hec.

usace.army.mil

U.S. Army Corps of Engineers, 2007, New England District 

Corp of Engineers reservoir regulation team, accessed 

September 8, 2007, at https://rsgis.crrel.usace.army.mil/nae/

pls/nae/nae_web.nae_webmenu.displaymenu?menu=hydro

U.S. Geological Survey, 2007a, Water resources application 

software, PeakFQ, accessed October 12, 2007, at 

http://water.usgs.gov/software/peakfq.html

U.S. Geological Survey, 2007b, Peak streamflow for 

New Hampshire: National Water Information System, 

accessed October 12, 2007, at http://nwis.waterdata.usgs.

gov/nh/nwis/peak

U.S. Interagency Advisory Committee on Water Data, 

1982, Guidelines for determining flood flow frequency, 

Bulletin 17-B of the Hydrology Subcommittee: Reston, 

Va., U.S. Geological Survey, Office of Water Data Coordination, 183 p.
Table 1 33

Table 1. Description of streamgages used in the April 2007 flood investigation, central and southern New Hampshire.—Continued[Location of streamgages in figure 4. USGS, U.S. Geological Survey; SR, State Route, mi2, square miles; lat, latitude; long, longitude; NHDES, New Hampshire Department of Environmental Services; 

ft, feet; USACE, U.S. Army Corps of Engineers]

USGS 

streamgage 

number

Streamgage name Status Operator

Drainage 

area 

(mi2)

Streamgage location

01064500 Saco River near Conway Active USGS 385 Lat 43°59'27", long 71°05'29", Carroll County, on left bank, at Odell Falls, 0.4 mi upstream from 

US 302, 1.5 mi northeast of the intersection of SR 16 and 113 in Conway, and 1.8 mi downstream from mouth of Swift River.

01064801 Bearcamp River at 

South Tamworth

Active USGS 67.6 Lat 43°49'48", long 71°17'18", Carroll County, on right bank, at downstream side of abandoned stone 

abutments, 0.7 mi upstream from Sanger Brook, 0.8 mi east of Bemis Mountain Road and SR 25 intersection at South Tamworth, 1.0 mi downstream from Cold Brook, and 1.1 mi west of SR 25 and SR 113 intersection at Whittier.

01065000 Ossipee River at 

Effingham Falls

Active NHDESa 330 Lat 43°47'42", long 71°03'35", Carroll County, on left bank, 850 ft upstream from SR 153 bridge, 

1,400 ft downstream from dam at outlet of Ossipee Lake, and 0.2 mi west of the intersection of SR 153 and 25 at Effingham Falls.

01072100 Salmon Falls River at 

Milton

Active NHDESa 108 Lat 43°24'48", long 70°59'15", Strafford County, on right bank, just downstream from Milton Pond 

Dam and 300 ft southeast of SR 125 and Prospect Hill Road intersection in Milton.

01072800 Cocheco River near 

Rochester

Active USGS 85.7 Lat 43°16'06", long 70°58'27", Strafford County, on right bank, directly behind Rochester Country 

Club, 2,200 ft upstream from treatment lagoons, and 0.5 mi southeast of Main Street and Church Street intersection in Gonic.

01072870 Isinglass River at Rochester 

Neck Road, near Dover

Active USGS 73.6 Lat 43°14'05", long 70°57'25", Strafford County, 600 ft upstream from Rochester Neck Road bridge, 

and 0.7 mi upstream from mouth on Cocheco River.

01073000 Oyster River near Durham Active USGS 12.1 Lat 43°08'55", long 70°57'56", Strafford County, on left bank, 50 ft upstream from Old Concord Road 

bridge, and 0.6 mi east of US 4 and SR 155 intersection.

01073500 Lamprey River near 

Newmarket

Active USGS 183 Lat 43°06'09", long 70°57'11", Strafford County, on right bank, 200 ft upstream from Packers Falls and 

Packers Falls Road bridge.

01073587 Exeter River at Haigh 

Road, near Brentwood

Active USGS 63.5 Lat 42°59'04", long 71°02'20", Rockingham County, on right bank, 10 ft downstream from Haigh 

Road bridge.

01073600 Dudley Brook near Exeter Discontinued USGS 4.97 Lat 42°59'35", long 71°01'20", Rockingham County, on right bank, upstream side of breached dam, 100 ft upstream from SR 111A culvert, and 180 ft west of SR 111A and Deer Hill Road intersection.

01073750 Mill Brook near SR 108, 

at Stratham

Discontinued USGS 2.3 Lat 43°01'24", long 70°55'04", Rockingham County, on right bank, at most downstream culvert of the Stratham traffic circle at the intersection of SR 108 and 33 in Stratham.

01073785 Winnicut River at Greenland, near Portsmouth Active USGS 14.1 Lat 43°02'12", long 70°50'55", Rockingham County, on left bank, 20 ft upstream from State Fish and Game Department Dam, 150 ft downstream from SR 33 bridge, and 1.1 mi west of the intersection 

of SR 33 and 151 in Greenland.

01073810 Berrys Brook at Sagamore 

Road, near Portsmouth

Discontinued USGS 5.38 Lat 43°02'10", long 70°44'59", Rockingham County, on right bank, at upstream side of Sagamore Road, and 0.7 mi south of SR 1A and Sagamore Road intersection at Foyers Corner in Rye.

01073838 Taylor River at Old Stage 

Road near Hampton

Discontinued USGS 8.41 Lat 42°56'33", long 70°52'40", Rockingham County, on left bank, at upstream side of dam, 100 ft upstream from Old Stage Road bridge, and 650 ft southwest of Old Stage Road and Timber Swamp 

Road intersection at Coffins Mill in Hampton.
34 Flood of April 2007 in New Hampshire Table 1. Description of streamgages used in the April 2007 flood investigation, central and southern New Hampshire.—Continued [Location of streamgages in figure 4. USGS, U.S. Geological Survey; SR, State Route, mi2, square miles; lat, latitude; long, longitude; NHDES, New Hampshire Department of Environmental Services; ft, feet; USACE, U.S. Army Corps of Engineers] USGS stream- gage number Streamgage name Status Operator Drainage area (mi2) Streamgage location 01074520 East Branch Pemigewasset River at Lincoln Active USGS 115 Lat 44°02'51", long 71°39'37", Grafton County, on right bank, at upstream side of Old Crib Dam, locally known as “the old hole,” 800 ft upstream from Cooper Memorial Drive bridge, 1,900 ft downstream from Pollard Brook, 1.8 mi above mouth, and 0.8 mi east of Connector Road and SR 112 intersection in Lincoln. 01075000 Pemigewasset River at Woodstock Active USGS 193 Lat 43°58'34", long 71°40'48", Grafton County, on right bank at downstream side of abandoned bridge abutments, immediately east of Woodstock Fire Station, 300 ft upstream from southernmost SR 175 bridge, and 300 ft east of North Station Road and SR 175 intersection in Woodstock.

01076000 Baker River near Rumney Active USGS 143 Lat 43°47'44", long 71°50'45", Grafton County, on right bank, 200 ft upstream from small right bank 

tributary, 1,900 ft upstream from mouth of Halls Brook, 1,400 ft west of Halls Brook Road and SR 25 intersection, and 1.7 mi southeast of Sand Hill Road and SR 25 intersection in West Rumney.

01076500 Pemigewasset River at 

Plymouth

Active USGS 622 Lat 43°45'33", long 71°41'10", Grafton County, on right bank, 150 ft downstream from Holderness 

Road bridge in Plymouth, 1,700 ft downstream from Baker River, and 0.8 mi south of SR 3A and US 3 intersection.

01077000 Squam River at Ashland Active NHDESa 57.6 Lat 43°42'19", long 71°37'49", Grafton County, on right bank, 250 ft downstream from the Little 

Squam Lake Dam, 300 ft upstream from River Street bridge, and 300 ft north of River Street and US 3 intersection.

01077510 Newfound River below 

Newfound Lake near Bristol

Active NHDES 98 Lat 43°37'02", long 71°44'28", Grafton County, at outlet of Newfound Lake, 75 ft downstream from 

Newfound Lake Dam, 500 ft downstream from West Shore Road, and 800 ft west of West Shore Road and SR 3A intersection in Bristol.

01078000 Smith River near Bristol Active USGS 85.8 Lat 43°33'59", long 71°44'54", Merrimack County, on right bank, 2,200 ft north of Borough Road and 

Axtell Road intersection, and 4,700 ft upstream from Borough Road bridge in Bristol. 

01079602 Poorfarm Brook near 

Gilford

Discontinued USGS 6.38 Lat 43°34'22", long 71°21'20", Belknap County, on right bank, at downstream side of Scenic Drive bridge, 250 ft downstream from SR 11, 500 ft west of Scenic Drive and SR 11 intersection, 950 ft 

upstream from mouth on Lake Winnipesaukee.

01079900 Shannon Brook near 

Moultonborough

Discontinued USGS 6.99 Lat 43°43'49", long 71°21'28", Carroll County, on left bank, immediately upstream from SR 109 bridge (gage house is 20 ft downstream from bridge), 3,800 ft south of the intersection of SR 109 and 171 in 

Moultonborough, and 1.4 mi upstream from mouth on Lake Winnipesaukee.

01080000 Lake Winnipesaukee at 

Weirs Beach

Active NHDESa 363 Lat 43°36'27", long 71°27'34", Belknap County, 600 ft east of Weirs Beach Post Office, and 0.3 mi 

northwest of US 3 bridge across Paugus Bay at Weirs Beach.

01080500 Lake Winnipesaukee Outlet 

at Lakeport

Active NHDESa 363 Lat 43°32'57", long 71°27'54", Belknap County, 100 ft upstream from Elm Street bridge across Paugus 

Bay, 150 ft upstream from dam across Paugus Bay, and 0.2 mi northwest of Elm Street and Union Avenue intersection in Lakeport.

01081000 Winnipesaukee River at 

Tilton

Active USGS 471 Lat 43°26'30", long 71°35'17", Belknap County, on right bank, 150 ft upstream from Bridge/School 

Street bridge, 300 ft south of Town Hall in Tilton, and 0.3 mi southeast of US 3 and SR 132 intersection in Tilton.
Table 1 35

Table 1. Description of streamgages used in the April 2007 flood investigation, central and southern New Hampshire.—Continued[Location of streamgages in figure 4. USGS, U.S. Geological Survey; SR, State Route, mi2, square miles; lat, latitude; long, longitude; NHDES, New Hampshire Department of Environmental Services; 

ft, feet; USACE, U.S. Army Corps of Engineers]

USGS 

streamgage 

number

Streamgage name Status Operator

Drainage 

area 

(mi2)

Streamgage location

01081500 Merrimack River at 

Franklin Junction

Active USGS 1,507 Lat 43°25'22", long 71°39'12", Merrimack County, on right bank, at Franklin Junction, 4,000 ft south of 

SR 127 and US 3 intersection, 5,300 ft downstream from confluence of Pemigewasset and Winnipesaukee Rivers, and 1.5 mi south of US 3 and Church Street intersection in Franklin.

01082000 Contoocook River at 

Peterborough

Active USGS 68.1 Lat 42°51'45", long 71°57'35", Hillsborough County, on left bank, 750 ft upstream from Morrison Road 

bridge, 1,300 ft downstream from mill dam in Noone, and 0.6 mi southwest of US 202 and SR 101 intersection in Peterborough.

01083000 Nubanusit Brook below 

MacDowell Dam near Peterborough

Active USGS 44 Lat 42°53'34", long 71°59'14", Hillsborough County, on left bank, 300 ft downstream from Edward 

MacDowell Dam, 600 ft upstream from abandoned mill dam, and 0.4 mi north of Wilder Street and Union Street in West Peterborough.

01084500 Beards Brook near 

Hillsborough

Discontinued USGS 55.4 Lat 43°06'51", long 71°55'36", Hillsborough County, on right bank, 300 ft upstream from West Main Street bridge, 560 ft upstream from mouth on North Branch, and 1,800 ft west of US 202 and West 

Main Street intersection in Hillsborough.

01085000 Contoocook River near 

Henniker

Active USGS 368 Lat 43°09'07", long 71°51'28", Merrimack County, on right bank, 900 ft west of Western Avenue and 

Cote Hill Road intersection, 1.6 mi downstream from Sand Brook, and 1.7 mi upstream from Western Avenue bridge in Henniker.

01085500 Contoocook River below 

Hopkinton Dam at West Hopkinton

Active USGS 427 Lat 43°11'33", long 71°44'43", Merrimack County, on right bank 750 ft downstream from covered 

bridge at West Hopkinton, 2,200 ft downstream from Hopkinton Dam, and 1.2 mi north of the intersection of SR 127 and 9 in Hopkinton.

01086000 Warner River at Davisville Active USGS 146 Lat 43°15'03", long 71°43'58", Merrimack County, on left bank, 60 ft downstream from SR 127 bridge 

at Davisville, and 0.9 mi east of I-89 and SR 103 interchange in Warner.

01087000 Blackwater River near 

Webster

Active USGS 129 Lat 43°17'49", long 71°41'42", Merrimack County, on left bank, 1,200 ft west of Clothespin Bridge 

Road and Pleasant Street intersection at Dingit Corner, 2,300 ft downstream from Clothespin Bridge Road bridge, and 2.4 mi downstream from Blackwater Dam.

01087850 Contoocook River at River 

Hill, near Penacook

Active USACE 760 Lat 43°14'59", long 71°37'12", Merrimack County, at Horse Hill Road bridge, 200 ft west of River 

Road, Horse Hill Road, and Bog Road intersection at River Hill, and 2.4 mi southwest of US 3 and Washington Street intersection in Penacook.

01088400 Merrimack River at 

Concord

Active USACE 2,300 Lat 43°12'32", long 71°31'51", Merrimack County, at downstream side of Bridge Street (SR 9) bridge 

over the Merrimack River, and 1,600 ft east of Bridge Street (SR 9) and Main Street (US 3) intersection in Concord.

01089000 Soucook River near 

Concord

Discontinued USGS 76.8 Lat 43°14'19", long 71°27'45", Merrimack County, on left bank, 500 ft upstream from SR 9 bridge, 4,300 ft upstream from Cemetery Brook, and 0.4 mi northeast of the intersection of SR 106 and 9.

01089100 Soucook River at Pembroke 

Road, near Concord

Active USGS 81.9 Lat 43°12'49", long 71°28'51", Merrimack County, on left bank, 100 ft upstream from Pembroke Road 

bridge, 550 ft upstream from Frenchs Brook, and 770 ft east of SR 106 and Pembroke Road intersection in Concord.

01089500 Suncook River at 

North Chichester

Discontinuedb USGS 155 Lat 43°15'24", long 71°22'12", Merrimack County, on left bank, 100 ft downstream from Depot Road, 800 ft east of Depot Road and SR 28 intersection, and 2,000 ft upstream from Sanders Brook. 
36 Flood of April 2007 in New Hampshire Table 1. Description of streamgages used in the April 2007 flood investigation, central and southern New Hampshire.—Continued [Location of streamgages in figure 4. USGS, U.S. Geological Survey; SR, State Route, mi2, square miles; lat, latitude; long, longitude; NHDES, New Hampshire Department of Environmental Services; ft, feet; USACE, U.S. Army Corps of Engineers] USGS stream- gage number Streamgage name Status Operator Drainage area (mi2) Streamgage location 01090800 Piscataquog River below Everett Dam, near East Weare Active USGS 63.1 Lat 43°05'29", long 71°39'36", Hillsborough County, on right bank, 500 ft downstream from Everett Dam, 2,700 ft upstream from Clough Park Road bridge, and 1.7 mi north of Clough Park Road and River Road intersection in Weare. 01091000 South Branch Piscataquog River near Goffstown Discon- tinued USGS 103 Lat 43°00'53", long 71°38'31", Hillsborough County, on right bank, 20 ft upstream from Breed Brook Road bridge, 50 ft northwest of Breed Brook Road and SR 13 intersection, 2.3 mi west of the inter- section of SR 13 and 114 and Mountain Road in Goffstown. 01091500 Piscataquog River near 

Goffstown

Active USGS 202 Lat 43°01'00", long 71°33'04", Hillsborough County, on left bank, 300 ft upstream from Henry Bridge 

Road bridge, 1,400 ft upstream from Harry Brook, and 0.6 mi northwest of Henry Bridge Road and SR 114 intersection in Goffstown.

01092000 Merrimack River near 

Goffs Falls, below Manchester

Active USGS 3,092 Lat 42°56'53", long 71°27'50", Hillsborough County, on right bank, 600 ft upstream from I-293 bridge, 

and 3,300 ft downstream from Bowman Brook in Manchester.

01093000 Sucker Brook at Auburn Discontinued USGS 27.8 Lat 43°00'21", long 71°20'57", Rockingham County, on left bank, 600 ft upstream from SR 121, and 600 ft north of SR 121 and Hooksett Road intersection in Auburn.

01094000 Souhegan River at 

Merrimack

Active USGS 171 Lat 42°51'27", long 71°30'24", Hillsborough County, on left bank, at head of Wildcat Falls, 2,850 ft 

upstream from southbound bridge on Everett Turnpike, 0.9 mi southwest of Baboosic Lake Road and US 3 intersection in Merrimack.

010965817 Beaver Brook at Fordway 

Extension at Derry

Active USGS 23.9 Lat 42°52'21", long 71°19'47", Rockingham County, on left bank, 30 ft upstream from culverts on 

Fordway Extension, 75 ft east of Fordway Street, Fordway Extension and Bridge Street intersection, 0.4 mi south of Fordway Street and West Broadway (SR 102) intersection, 0.6 mi east of I-93 and Nashua Road (SR 102) interchange, and 0.7 mi southwest of West Broadway (SR 102), Birch Street (SR 28), Storer Street (SR 102), and Crystal Avenue (SR 28) intersection.

010965844 Beaver Brook at 

South Road, near Derry

Active USGS 30.3 Lat 42°50'22", long 71°21'00", Rockingham County, on left bank, upstream side of South Road, at Kendall Pond outlet, 100 ft east of Kendall Pond Road and South Road intersection, 0.8 mi southeast of 

the intersection of SR 128 and 102 in Londonderry.

010965852 Beaver Brook at 

North Pelham

Active USGS 47.8 Lat 42°46'58", long 71°21'15", Hillsborough County, on right bank, 10 ft downstream from SR 128 

bridge at the Windham-Pelham town line, 0.7 mi north of SR 128 and Castle Hill Road intersection in North Pelham, and 1.4 mi south of the intersection of SR 111 and 128.

01096587 Tributary to Cobbetts Pond 

at I-93 south exit ramp near Windham

Active USGS 0.54 Lat 42°48'24", long 71°16'27", Rockingham County, on right bank, upstream from I-93 south exit 

ramp, 675 ft upstream from mouth at Cobbetts Pond, 675 ft south of SR 111 and I-93 south exit ramp intersection, and 1.7 mi east of Lowell Road and SR 111 intersection at Windham.

01100505 Spicket River at 

North Salem

Active USGS 16.5 Lat 42°50'57", long 71°12'56", Rockingham County, on right bank, 70 ft downstream from Haverhill 

Road bridge, 100 ft southeast of North Main Street, Haverhill Road, and Island Pond Road intersection in Cowbell Corners, and 1,200 ft south of Island Pond Road and SR 111 intersection in Derry.
Table 1 37

Table 1. Description of streamgages used in the April 2007 flood investigation, central and southern New Hampshire.—Continued[Location of streamgages in figure 4. USGS, U.S. Geological Survey; SR, State Route, mi2, square miles; lat, latitude; long, longitude; NHDES, New Hampshire Department of Environmental Services; 

ft, feet; USACE, U.S. Army Corps of Engineers]

USGS 

streamgage 

number

Streamgage name Status Operator

Drainage 

area 

(mi2)

Streamgage location

01100549 Policy Brook at Rockingham Park Boulevard 

at Salem

Active USGS 5.1 Lat 42°46'04", long 71°13'23", Rockingham County, on left bank, 300 ft downstream from Rockingham Park Boulevard, 0.2 mi southwest of Rockingham Park Boulevard and South Broadway (SR 28) 

intersection, 0.2 mi upstream from mouth of Porcupine Brook, 1.0 mi south of Broadway (SR 28) and Main Street (SR 97) intersection in Salem Depot, and 1.8 mi southwest of Main Street (SR 97), Bridge Street, and School Street intersection in Salem.

011005605 Policy Brook at I-93 north 

rest stop entrance ramp, near Salem

Active USGS 10.2 Lat 42°45'13", long 71°13'15", Rockingham County, on left bank, upstream from I-93 northbound reststop entrance ramp, and 2,100 ft southeast of the Cross Street bridge over I-93 in Salem.

01100561 Spicket River near 

Methuen, Mass.

Active USGS 62.1 Lat 42°44'35", long 71°12'32", Rockingham County, on left bank, at upstream side of Hampshire Road 

bridge at the New Hampshire-Massachusetts border, 800 ft downstream from mouth of Policy Brook, and 0.5 mi west of SR 28 and Lawrence Road intersection.

01137500 Ammonoosuc River at 

Bethlehem Junction

Active USGS 87.6 Lat 44°16'07", long 71°37'51", Grafton County, on left bank, 1,200 ft upstream from US 302 bridge at 

Pierce Bridge, 1,300 ft south of US 302 and Muchmore Road intersection and 3.0 mi east of US 302 and SR 142 intersection in Bethlehem.

01138500 Connecticut River at 

Wells River, Vt.

Active USGS 2,644 Lat 44°09'12", long 72°02'32", Orange County, on right bank, at village of Wells River, 200 ft downstream from US 302 bridge, 400 ft upstream from Wells River, 1,200 ft downstream from Ammonoosuc River, and 0.2 mi west of US 302 and SR 135 in Woodsville, N.H.

01144500 Connecticut River at 

West Lebanon

Active USGS 4,092 Lat 43°38'46", long 72°18'46", Grafton County, on left bank, 50 ft downstream from Boston & Maine 

railroad bridge, 500 ft downstream from White River, and 1,100 ft northwest of US 4 and SR 12A intersection in West Lebanon.

01150500 Mascoma River at 

Mascoma

Active NHDESa 153 Lat 43°38'56", long 72°10'57", Grafton County, on left bank, 100 ft upstream from Payne Road bridge, 

100 ft downstream from Mascoma Lake Dam, and 0.2 mi south of US 4 and Payne Road intersection in Mascoma.

a Streamgage formerly operated by the U.S. Geological Survey.b Streamgage 01089500 active as of November 14, 2007.

Appendix 1. HEC-RAS Model Calibrations to 

Estimate the April 2007 Flood-Peak Discharge 

from High-Water-Mark Data Collected for the 

Lamprey, Souhegan, and Suncook Rivers

Tables

1-1. HEC-RAS model calibration to estimate the April 2007 Lamprey River flood-peak 

discharge from high-water-mark data collected at the railroad bridge upstream of 

Epping Road in Raymond, New Hampshire............................................................................40

1-2. HEC-RAS model calibration to estimate the April 2007 Souhegan River flood-peak 

discharge from high-water-mark data collected at the Wilton Road (Elm Street) 

bridge in Milford, New Hampshire...........................................................................................42

1-3. HEC-RAS model calibration to estimate the April 2007 Suncook River flood-peak 

discharge from high-water-mark data collected at the Short Falls Road bridge in 

Epsom, New Hampshire ............................................................................................................44

1-4. HEC-RAS model calibration to estimate the April 2007 Suncook River flood-peak 

discharge from high-water-mark data collected at the Websters Mill Road bridge 

in Chichester/Pittsfield, New Hampshire................................................................................47
40 Flood of April 2007 in New Hampshire

Table 1-1. HEC-RAS model calibration to estimate the April 2007 Lamprey River flood-peak discharge from high-water-mark data 

collected at the railroad bridge upstream of Epping Road in Raymond, New Hampshire.—Continued

[River station locations are indicated by an arbitrary cross-section numbering system and are not shown on any figure. ft, feet; ft3/s, cubic feet per second]

River station

Q, total

discharge

(ft3

/s)

Minimum 

channel 

elevation

(ft)

Water-surface 

elevation 

(ft)

Energy grade 

slope 

(ft/ft)

Flow area 

(ft2

)

Top width 

(ft)

Channel 

Froude

number

4 4,000 169.90 187.79 0.00011 2,728.74 233.30 0.08

4 3,990 169.90 187.79 0.00011 2,727.37 233.27 0.08

4 3,980 169.90 187.78 0.00011 2,726.00 233.25 0.08

4 3,970 169.90 187.77 0.00011 2,724.63 233.22 0.08

4 3,960 169.90 187.77 0.00010 2,723.26 233.20 0.08

4 3,950 169.90 187.76 0.00010 2,721.90 233.17 0.08

4 3,940 169.90 187.76 0.00010 2,720.54 233.15 0.08

4 3,930 169.90 187.75 0.00010 2,719.19 233.12 0.08

4 3,920 169.90 187.74 0.00010 2,717.84 233.10 0.08

4 3,910 169.90 187.74 0.00010 2,716.49 233.08 0.08

4 3,900 169.90 187.73 0.00010 2,715.16 233.05 0.08

3 4,000 168.91 187.58 0.00061 1,148.02 134.55 0.18

3 3,990 168.91 187.58 0.00061 1,147.33 134.53 0.18

3 3,980 168.91 187.57 0.00061 1,146.66 134.52 0.18

3 3,970 168.91 187.57 0.00061 1,145.98 134.50 0.18

3 3,960 168.91 187.56 0.00060 1,145.30 134.48 0.18

3 3,950 168.91 187.56 0.00060 1,144.63 134.47 0.18

3 3,940 168.91 187.55 0.00060 1,143.96 134.45 0.18

3 3,930 168.91 187.55 0.00060 1,143.29 134.44 0.18

3 3,920 168.91 187.54 0.00059 1,142.63 134.42 0.18

3 3,910 168.91 187.54 0.00059 1,141.96 134.41 0.18

3 3,900 168.91 187.53 0.00059 1,141.30 134.39 0.18

2.7 4,000 169.20 186.80 0.00186 571.85 38.79 0.32

2.7 3,990 169.20 186.80 0.00185 571.80 38.79 0.32

2.7 3,980 169.20 186.80 0.00184 571.76 38.79 0.32

2.7 3,970 169.20 186.80 0.00183 571.72 38.79 0.32

2.7 3,960 169.20 186.80 0.00183 571.68 38.79 0.32

2.7 3,950 169.20 186.80 0.00182 571.63 38.79 0.32

2.7 3,940 169.20 186.79 0.00181 571.59 38.79 0.32

2.7 3,930 169.20 186.79 0.00180 571.55 38.79 0.32

2.7 3,920 169.20 186.79 0.00179 571.51 38.79 0.31

2.7 3,910 169.20 186.79 0.00178 571.47 38.79 0.31

2.7 3,900 169.20 186.79 0.00177 571.43 38.79 0.31

2.5 Bridge

2.3 4,000 169.78 186.22 0.00270 502.80 37.90 0.38

2.3 3,990 169.78 186.23 0.00268 502.89 37.90 0.38

2.3 3,980 169.78 186.23 0.00267 502.98 37.90 0.38

2.3 3,970 169.78 186.23 0.00266 503.07 37.90 0.38

2.3 3,960 169.78 186.23 0.00264 503.16 37.90 0.38

2.3 3,950 169.78 186.24 0.00263 503.24 37.90 0.38

2.3 3,940 169.78 186.24 0.00261 503.33 37.90 0.38

2.3 3,930 169.78 186.24 0.00260 503.42 37.90 0.38

2.3 3,920 169.78 186.24 0.00258 503.50 37.91 0.38

2.3 3,910 169.78 186.25 0.00257 503.59 37.91 0.38

2.3 3,900 169.78 186.25 0.00255 503.68 37.91 0.37
Appendix 1 41

Table 1-1. HEC-RAS model calibration to estimate the April 2007 Lamprey River flood-peak discharge from high-water-mark data 

collected at the railroad bridge upstream of Epping Road in Raymond, New Hampshire.—Continued

[River station locations are indicated by an arbitrary cross-section numbering system and are not shown on any figure. ft, feet; ft3/s, cubic feet per second]

River station

Q, total

discharge

(ft3

/s)

Minimum 

channel 

elevation

(ft)

Water-surface 

elevation 

(ft)

Energy grade 

slope 

(ft/ft)

Flow area 

(ft2

)

Top width 

(ft)

Channel 

Froude

number

2 4,000 165.71 186.67 0.00006 3,064.42 280.06 0.08

2 3,990 165.71 186.67 0.00006 3,064.41 280.06 0.08

2 3,980 165.71 186.67 0.00006 3,064.40 280.06 0.08

2 3,970 165.71 186.67 0.00006 3,064.39 280.06 0.08

2 3,960 165.71 186.67 0.00006 3,064.38 280.06 0.08

2 3,950 165.71 186.67 0.00006 3,064.37 280.06 0.08

2 3,940 165.71 186.67 0.00006 3,064.36 280.06 0.08

2 3,930 165.71 186.67 0.00006 3,064.35 280.06 0.08

2 3,920 165.71 186.67 0.00006 3,064.34 280.05 0.08

2 3,910 165.71 186.67 0.00006 3,064.33 280.05 0.08

2 3,900 165.71 186.67 0.00006 3,064.32 280.05 0.07

1 4,000 171.11 186.66 0.00029 3,115.09 362.46 0.10

1 3,990 171.11 186.66 0.00028 3,115.09 362.46 0.10

1 3,980 171.11 186.66 0.00028 3,115.09 362.46 0.10

1 3,970 171.11 186.66 0.00028 3,115.09 362.46 0.10

1 3,960 171.11 186.66 0.00028 3,115.09 362.46 0.10

1 3,950 171.11 186.66 0.00028 3,115.09 362.46 0.10

1 3,940 171.11 186.66 0.00028 3,115.09 362.46 0.10

1 3,930 171.11 186.66 0.00028 3,115.09 362.46 0.10

1 3,920 171.11 186.66 0.00027 3,115.09 362.46 0.10

1 3,910 171.11 186.66 0.00027 3,115.09 362.46 0.10

1 3,900 171.11 186.66 0.00027 3,115.09 362.46 0.10
42 Flood of April 2007 in New Hampshire

Table 1-2. HEC-RAS model calibration to estimate the April 2007 Souhegan River flood-peak discharge from high-water-mark data 

collected at the Wilton Road (Elm Street) bridge in Milford, New Hampshire.—Continued

[River station locations are indicated by an arbitrary cross-section numbering system and are not shown on any figure. ft, feet; ft3/s, cubic feet per second]

River station

Q, total

discharge

(ft3

/s)

Minimum 

channel 

elevation

(ft)

Water-surface 

elevation 

(ft)

Energy grade 

slope 

(ft/ft)

Flow area 

(ft2

)

Top width 

(ft)

Channel 

Froude

number

6 7,000 288.52 299.45 0.00463 1,093.40 135.79 0.42

6 6,990 288.52 299.44 0.00463 1,092.31 135.77 0.42

6 6,980 288.52 299.43 0.00462 1,091.41 135.75 0.42

6 6,970 288.52 299.42 0.00462 1,090.33 135.72 0.42

6 6,960 288.52 299.42 0.00462 1,089.42 135.70 0.42

6 6,950 288.52 299.41 0.00462 1,088.33 135.68 0.42

6 6,940 288.52 299.40 0.00462 1,087.24 135.66 0.42

6 6,930 288.52 299.40 0.00462 1,086.35 135.64 0.42

6 6,920 288.52 299.39 0.00462 1,085.26 135.61 0.42

6 6,910 288.52 299.38 0.00462 1,084.36 135.59 0.42

6 6,900 288.52 299.37 0.00462 1,083.28 135.57 0.42

5 7,000 288.28 298.81 0.00839 1,119.23 136.23 0.38

5 6,990 288.28 298.81 0.00839 1,118.11 136.21 0.38

5 6,980 288.28 298.80 0.00838 1,117.22 136.20 0.38

5 6,970 288.28 298.79 0.00838 1,116.10 136.18 0.38

5 6,960 288.28 298.78 0.00838 1,115.22 136.16 0.38

5 6,950 288.28 298.78 0.00838 1,114.10 136.14 0.38

5 6,940 288.28 298.77 0.00838 1,112.98 136.12 0.38

5 6,930 288.28 298.76 0.00838 1,112.10 136.11 0.38

5 6,920 288.28 298.75 0.00838 1,110.98 136.09 0.38

5 6,910 288.28 298.75 0.00837 1,110.10 136.07 0.38

5 6,900 288.28 298.74 0.00837 1,108.98 136.05 0.38

4.7 7,000 284.76 297.21 0.00564 968.32 104.05 0.42

4.7 6,990 284.76 297.20 0.00563 967.54 104.03 0.42

4.7 6,980 284.76 297.19 0.00563 967.09 104.02 0.42

4.7 6,970 284.76 297.19 0.00562 966.31 104.00 0.42

4.7 6,960 284.76 297.18 0.00562 965.87 103.99 0.42

4.7 6,950 284.76 297.17 0.00561 965.09 103.98 0.42

4.7 6,940 284.76 297.17 0.00561 964.31 103.96 0.42

4.7 6,930 284.76 297.16 0.00560 963.88 103.95 0.42

4.7 6,920 284.76 297.16 0.00560 963.10 103.93 0.42

4.7 6,910 284.76 297.15 0.00559 962.67 103.92 0.42

4.7 6,900 284.76 297.14 0.00559 961.90 103.91 0.42

4.5 Bridge

4.3 7,000 283.70 297.03 0.00484 1,025.16 119.93 0.41

4.3 6,990 283.70 297.02 0.00484 1,024.29 119.92 0.41

4.3 6,980 283.70 297.02 0.00483 1,023.81 119.91 0.41

4.3 6,970 283.70 297.01 0.00483 1,022.94 119.89 0.41

4.3 6,960 283.70 297.01 0.00482 1,022.48 119.88 0.41

4.3 6,950 283.70 297.00 0.00482 1,021.60 119.86 0.41

4.3 6,940 283.70 296.99 0.00482 1,020.72 119.84 0.41

4.3 6,930 283.70 296.99 0.00481 1,020.26 119.84 0.41

4.3 6,920 283.70 296.98 0.00481 1,019.39 119.82 0.41

4.3 6,910 283.70 296.98 0.00481 1,018.94 119.81 0.41

4.3 6,900 283.70 296.97 0.00480 1,018.07 119.79 0.41
Appendix 1 43

Table 1-2. HEC-RAS model calibration to estimate the April 2007 Souhegan River flood-peak discharge from high-water-mark data 

collected at the Wilton Road (Elm Street) bridge in Milford, New Hampshire.—Continued

[River station locations are indicated by an arbitrary cross-section numbering system and are not shown on any figure. ft, feet; ft3/s, cubic feet per second]

River station

Q, total

discharge

(ft3

/s)

Minimum 

channel 

elevation

(ft)

Water-surface 

elevation 

(ft)

Energy grade 

slope 

(ft/ft)

Flow area 

(ft2

)

Top width 

(ft)

Channel 

Froude

number

4 7,000 282.64 296.09 0.00642 950.43 94.97 0.41

4 6,990 282.64 296.09 0.00641 949.86 94.96 0.41

4 6,980 282.64 296.09 0.00640 949.71 94.95 0.41

4 6,970 282.64 296.08 0.00639 949.14 94.93 0.41

4 6,960 282.64 296.08 0.00637 948.99 94.93 0.41

4 6,950 282.64 296.07 0.00636 948.42 94.91 0.41

4 6,940 282.64 296.07 0.00635 947.85 94.89 0.41

4 6,930 282.64 296.06 0.00634 947.71 94.89 0.41

4 6,920 282.64 296.06 0.00633 947.14 94.87 0.41

4 6,910 282.64 296.06 0.00631 947.01 94.86 0.41

4 6,900 282.64 296.05 0.00630 946.45 94.84 0.41

3 7,000 282.21 294.36 0.01649 673.14 74.79 0.61

3 6,980 282.21 294.37 0.01641 673.66 74.81 0.61

3 6,970 282.21 294.37 0.01637 673.55 74.80 0.61

3 6,960 282.21 294.37 0.01629 674.07 74.82 0.61

3 6,950 282.21 294.37 0.01625 673.97 74.82 0.61

3 6,940 282.21 294.37 0.01621 673.86 74.81 0.60

3 6,930 282.21 294.38 0.01613 674.38 74.83 0.60

3 6,920 282.21 294.38 0.01609 674.28 74.83 0.60

3 6,910 282.21 294.38 0.01601 674.80 74.84 0.60

3 6,900 282.21 294.38 0.01597 674.70 74.84 0.60

2 7,000 278.67 294.76 0.00400 1,043.55 103.02 0.36

2 6,990 278.67 294.76 0.00400 1,043.29 103.01 0.36

2 6,980 278.67 294.76 0.00398 1,043.79 103.03 0.36

2 6,970 278.67 294.76 0.00397 1,043.53 103.02 0.36

2 6,960 278.67 294.76 0.00395 1,044.04 103.04 0.36

2 6,950 278.67 294.76 0.00395 1,043.78 103.03 0.36

2 6,940 278.67 294.76 0.00394 1,043.51 103.02 0.36

2 6,930 278.67 294.76 0.00392 1,044.02 103.04 0.36

2 6,920 278.67 294.76 0.00391 1,043.77 103.03 0.36

2 6,910 278.67 294.76 0.00390 1,044.28 103.05 0.36

2 6,900 278.67 294.76 0.00389 1,044.02 103.04 0.36

1 7,000 280.46 293.83 0.00442 1,104.17 113.64 0.36

1 6,990 280.46 293.83 0.00441 1,104.17 113.64 0.36

1 6,980 280.46 293.84 0.00438 1,105.31 113.65 0.36

1 6,970 280.46 293.84 0.00437 1,105.31 113.65 0.36

1 6,960 280.46 293.85 0.00434 1,106.45 113.66 0.36

1 6,950 280.46 293.85 0.00433 1,106.45 113.66 0.35

1 6,940 280.46 293.85 0.00432 1,106.45 113.66 0.35

1 6,930 280.46 293.86 0.00429 1,107.58 113.68 0.35

1 6,920 280.46 293.86 0.00428 1,107.58 113.68 0.35

1 6,910 280.46 293.87 0.00426 1,108.72 113.69 0.35

1 6,900 280.46 293.87 0.00424 1,108.72 113.69 0.35
44 Flood of April 2007 in New Hampshire

Table 1-3. HEC-RAS model calibration to estimate the April 2007 Suncook River flood-peak discharge from high-water-mark data 

collected at the Short Falls Road bridge in Epsom, New Hampshire.—Continued

[River station locations are indicated by an arbitrary cross-section numbering system and are not shown on any figure. ft, feet; ft3/s, cubic feet per second]

River station

Q, total

discharge

(ft3

/s)

Minimum 

channel 

elevation

(ft)

Water-surface 

elevation 

(ft)

Energy grade 

slope 

(ft/ft)

Flow area 

(ft2

)

Top width 

(ft)

Channel 

Froude

number

6 14,500 289.88 309.33 0.00163 2,016.51 158.58 0.35

6 14,400 289.88 309.30 0.00161 2,012.63 158.37 0.35

6 14,300 289.88 309.28 0.00160 2,008.81 158.17 0.35

6 14,200 289.88 309.25 0.00159 2,005.08 157.97 0.35

6 14,100 289.88 309.23 0.00157 2,001.38 157.77 0.35

6 14,000 289.88 309.21 0.00156 1,997.76 157.58 0.35

6 13,900 289.88 309.19 0.00154 1,994.20 157.39 0.34

6 13,800 289.88 309.16 0.00153 1,990.69 157.20 0.34

6 13,700 289.88 309.14 0.00152 1,987.22 157.02 0.34

6 13,600 289.88 309.12 0.00150 1,983.84 156.84 0.34

6 13,500 289.88 309.10 0.00149 1,980.50 156.66 0.34

5.5 14,500 288.33 309.11 0.00295 1,906.97 145.14 0.37

5.5 14,400 288.33 309.09 0.00292 1,903.78 145.04 0.37

5.5 14,300 288.33 309.07 0.00290 1,900.64 144.94 0.37

5.5 14,200 288.33 309.05 0.00287 1,897.57 144.84 0.36

5.5 14,100 288.33 309.03 0.00284 1,894.53 144.74 0.36

5.5 14,000 288.33 309.01 0.00281 1,891.57 144.64 0.36

5.5 13,900 288.33 308.99 0.00278 1,888.65 144.55 0.36

5.5 13,800 288.33 308.97 0.00275 1,885.79 144.46 0.36

5.5 13,700 288.33 308.95 0.00272 1,882.96 144.36 0.36

5.5 13,600 288.33 308.93 0.00269 1,880.21 144.27 0.35

5.5 13,500 288.33 308.91 0.00266 1,877.49 144.19 0.35

5 14,500 288.33 308.43 0.00252 1,505.33 111.13 0.43

5 14,400 288.33 308.42 0.00249 1,504.00 110.93 0.43

5 14,300 288.33 308.41 0.00246 1,502.71 110.74 0.42

5 14,200 288.33 308.40 0.00243 1,501.45 110.56 0.42

5 14,100 288.33 308.39 0.00241 1,500.23 110.38 0.42

5 14,000 288.33 308.38 0.00238 1,499.04 110.20 0.42

5 13,900 288.33 308.36 0.00235 1,497.89 110.03 0.41

5 13,800 288.33 308.35 0.00232 1,496.77 109.87 0.41

5 13,700 288.33 308.34 0.00229 1,495.67 109.70 0.41

5 13,600 288.33 308.33 0.00226 1,494.61 109.55 0.41

5 13,500 288.33 308.33 0.00223 1,493.58 109.39 0.40

4.7 14,500 287.48 308.49 0.00172 1,725.49 124.84 0.40

4.7 14,400 287.48 308.48 0.00170 1,723.86 124.79 0.40

4.7 14,300 287.48 308.47 0.00168 1,722.27 124.75 0.39

4.7 14,200 287.48 308.45 0.00166 1,720.73 124.71 0.39

4.7 14,100 287.48 308.44 0.00165 1,719.23 124.67 0.39

4.7 14,000 287.48 308.43 0.00163 1,717.77 124.63 0.39

4.7 13,900 287.48 308.42 0.00161 1,716.34 124.59 0.38

4.7 13,800 287.48 308.41 0.00159 1,714.95 124.56 0.38

4.7 13,700 287.48 308.40 0.00157 1,713.59 124.52 0.38

4.7 13,600 287.48 308.39 0.00155 1,712.27 124.48 0.38

4.7 13,500 287.48 308.37 0.00153 1,710.98 124.45 0.38

4.5 Bridge
Appendix 1 45

Table 1-3. HEC-RAS model calibration to estimate the April 2007 Suncook River flood-peak discharge from high-water-mark data 

collected at the Short Falls Road bridge in Epsom, New Hampshire.—Continued

[River station locations are indicated by an arbitrary cross-section numbering system and are not shown on any figure. ft, feet; ft3/s, cubic feet per second]

River station

Q, total

discharge

(ft3

/s)

Minimum 

channel 

elevation

(ft)

Water-surface 

elevation 

(ft)

Energy grade 

slope 

(ft/ft)

Flow area 

(ft2

)

Top width 

(ft)

Channel 

Froude

number

4.3 14,500 287.48 307.48 0.00210 1,601.24 120.77 0.44

4.3 14,400 287.48 307.49 0.00207 1,602.19 120.82 0.43

4.3 14,300 287.48 307.50 0.00204 1,603.12 120.86 0.43

4.3 14,200 287.48 307.50 0.00201 1,604.05 120.91 0.43

4.3 14,100 287.48 307.51 0.00198 1,604.97 120.96 0.43

4.3 14,000 287.48 307.52 0.00195 1,605.89 121.00 0.42

4.3 13,900 287.48 307.53 0.00192 1,606.79 121.05 0.42

4.3 13,800 287.48 307.53 0.00189 1,607.69 121.09 0.42

4.3 13,700 287.48 307.54 0.00186 1,608.57 121.14 0.41

4.3 13,600 287.48 307.55 0.00183 1,609.45 121.18 0.41

4.3 13,500 287.48 307.56 0.00180 1,610.32 121.22 0.41

4 14,500 286.73 307.99 0.00032 4,897.13 385.23 0.16

4 14,400 286.73 307.99 0.00031 4,897.21 385.23 0.16

4 14,300 286.73 307.99 0.00031 4,897.29 385.23 0.16

4 14,200 286.73 307.99 0.00031 4,897.37 385.24 0.16

4 14,100 286.73 307.99 0.00030 4,897.45 385.24 0.15

4 14,000 286.73 307.99 0.00030 4,897.53 385.24 0.15

4 13,900 286.73 307.99 0.00029 4,897.60 385.24 0.15

4 13,800 286.73 307.99 0.00029 4,897.69 385.25 0.15

4 13,700 286.73 307.99 0.00028 4,897.76 385.25 0.15

4 13,600 286.73 307.99 0.00028 4,897.84 385.25 0.15

4 13,500 286.73 307.99 0.00028 4,897.91 385.26 0.15

3 14,500 276.83 308.05 0.000063 9,822.06 631.09 0.09

3 14,400 276.83 308.05 0.000063 9,821.64 631.08 0.09

3 14,300 276.83 308.05 0.000062 9,821.20 631.06 0.09

3 14,200 276.83 308.05 0.000061 9,820.77 631.05 0.09

3 14,100 276.83 308.05 0.000060 9,820.37 631.04 0.09

3 14,000 276.83 308.05 0.000059 9,819.94 631.03 0.09

3 13,900 276.83 308.05 0.000058 9,819.52 631.02 0.09

3 13,800 276.83 308.04 0.000057 9,819.11 631.01 0.09

3 13,700 276.83 308.04 0.000057 9,818.71 631.00 0.08

3 13,600 276.83 308.04 0.000057 9,818.31 630.99 0.08

3 13,500 276.83 308.04 0.000057 9,817.90 630.97 0.08

2 14,500 270.77 308.08 0.00002 15,316.79 937.35 0.05

2 14,400 270.77 308.08 0.00002 15,315.73 937.34 0.05

2 14,300 270.77 308.08 0.00002 15,314.65 937.33 0.05

2 14,200 270.77 308.08 0.00002 15,313.59 937.32 0.05

2 14,100 270.77 308.08 0.00002 15,312.56 937.31 0.05

2 14,000 270.77 308.08 0.00002 15,311.50 937.31 0.05

2 13,900 270.77 308.08 0.00002 15,310.47 937.30 0.05

2 13,800 270.77 308.08 0.00002 15,309.44 937.29 0.05

2 13,700 270.77 308.07 0.00002 15,308.44 937.28 0.05

2 13,600 270.77 308.07 0.00002 15,307.41 937.27 0.05

2 13,500 270.77 308.07 0.00002 15,306.41 937.26 0.05
46 Flood of April 2007 in New Hampshire

Table 1-3. HEC-RAS model calibration to estimate the April 2007 Suncook River flood-peak discharge from high-water-mark data 

collected at the Short Falls Road bridge in Epsom, New Hampshire.—Continued

[River station locations are indicated by an arbitrary cross-section numbering system and are not shown on any figure. ft, feet; ft3/s, cubic feet per second]

River station

Q, total

discharge

(ft3

/s)

Minimum 

channel 

elevation

(ft)

Water-surface 

elevation 

(ft)

Energy grade 

slope 

(ft/ft)

Flow area 

(ft2

)

Top width 

(ft)

Channel 

Froude

number

1 14,500 286.21 308.00 0.00014 9,571.49 943.03 0.12

1 14,400 286.21 308.00 0.00014 9,571.49 943.03 0.12

1 14,300 286.21 308.00 0.00014 9,571.49 943.03 0.12

1 14,200 286.21 308.00 0.00013 9,571.49 943.03 0.12

1 14,100 286.21 308.00 0.00013 9,571.49 943.03 0.12

1 14,000 286.21 308.00 0.00013 9,571.49 943.03 0.12

1 13,900 286.21 308.00 0.00013 9,571.49 943.03 0.12

1 13,800 286.21 308.00 0.00013 9,571.49 943.03 0.12

1 13,700 286.21 308.00 0.00012 9,571.49 943.03 0.12

1 13,600 286.21 308.00 0.00012 9,571.49 943.03 0.12

1 13,500 286.21 308.00 0.00012 9,571.49 943.03 0.11
Appendix 1 47

Table 1-4. HEC-RAS model calibration to estimate the April 2007 Suncook River flood-peak discharge from high-water-mark data 

collected at the Websters Mill Road bridge in Chichester/Pittsfield, New Hampshire.—Continued

[River station locations are indicated by an arbitrary cross-section numbering system and are not shown on any figure. ft, feet; ft3/s, cubic feet per second]

River station

Q, total

discharge

(ft3

/s)

Minimum 

channel 

elevation

(ft)

Water-surface 

elevation 

(ft)

Energy grade 

slope 

(ft/ft)

Flow area 

(ft2

)

Top width 

(ft)

Channel 

Froude

number

6 9,500 387.95 395.76 0.00631 988.50 224.12 0.94

6 9,400 387.95 395.72 0.00632 980.41 223.67 0.94

6 9,300 387.95 395.68 0.00632 972.32 223.22 0.94

6 9,200 387.95 395.64 0.00633 964.23 222.78 0.94

6 9,100 387.95 395.61 0.00633 956.06 222.33 0.94

6 9,000 387.95 395.58 0.00628 951.44 222.07 0.94

6 8,900 387.95 395.55 0.00627 944.01 221.66 0.94

6 8,800 387.95 395.51 0.00626 936.47 221.25 0.93

6 8,700 387.95 395.48 0.00625 928.87 220.83 0.93

6 8,600 387.95 395.44 0.00625 921.21 220.40 0.93

6 8,500 387.95 395.40 0.00624 913.45 219.97 0.93

5 9,500 387.63 395.39 0.00496 1,133.44 246.66 0.84

5 9,400 387.63 395.34 0.00501 1,119.73 246.29 0.85

5 9,300 387.63 395.28 0.00506 1,105.85 245.91 0.85

5 9,200 387.63 395.23 0.00511 1,091.88 245.52 0.85

5 9,100 387.63 395.17 0.00517 1,077.81 245.14 0.86

5 9,000 387.63 395.12 0.00518 1,066.95 244.84 0.86

5 8,900 387.63 395.06 0.00526 1,051.18 244.41 0.86

5 8,800 387.63 394.95 0.00548 1,025.07 243.69 0.88

5 8,700 387.63 394.88 0.00559 1,007.50 243.20 0.89

5 8,600 387.63 394.80 0.00574 987.66 242.65 0.90

5 8,500 387.63 394.73 0.00583 971.71 242.21 0.90

4 9,500 385.45 394.46 0.00739 942.93 184.20 1.01

4 9,400 385.45 394.42 0.00740 935.53 184.01 1.01

4 9,300 385.45 394.38 0.00742 928.15 183.83 1.01

4 9,200 385.45 394.34 0.00743 920.77 183.64 1.01

4 9,100 385.45 394.30 0.00745 913.34 183.46 1.01

4 9,000 385.45 394.25 0.00752 903.55 183.21 1.01

4 8,900 385.45 394.21 0.00751 897.17 183.05 1.01

4 8,800 385.45 394.17 0.00752 889.61 182.86 1.01

4 8,700 385.45 394.13 0.00753 882.58 182.69 1.01

4 8,600 385.45 394.10 0.00751 876.09 182.52 1.01

4 8,500 385.45 394.05 0.00755 867.84 182.32 1.01

3.7 9,500 384.07 393.47 0.00264 964.61 137.62 0.62

3.7 9,400 384.07 393.42 0.00265 957.86 136.96 0.62

3.7 9,300 384.07 393.36 0.00265 951.29 136.33 0.62

3.7 9,200 384.07 393.31 0.00266 944.49 135.67 0.62

3.7 9,100 384.07 393.25 0.00267 937.62 135.01 0.62

3.7 9,000 384.07 393.20 0.00267 930.79 134.35 0.62

3.7 8,900 384.07 393.14 0.00268 923.96 133.69 0.62

3.7 8,800 384.07 393.09 0.00268 917.05 133.02 0.62

3.7 8,700 384.07 393.03 0.00269 910.18 132.35 0.62

3.7 8,600 384.07 392.98 0.00270 903.20 131.68 0.62

3.7 8,500 384.07 392.92 0.00270 896.23 131.00 0.62
48 Flood of April 2007 in New Hampshire

Table 1-4. HEC-RAS model calibration to estimate the April 2007 Suncook River flood-peak discharge from high-water-mark data 

collected at the Websters Mill Road bridge in Chichester/Pittsfield, New Hampshire.—Continued

[River station locations are indicated by an arbitrary cross-section numbering system and are not shown on any figure. ft, feet; ft3/s, cubic feet per second]

River station

Q, total

discharge

(ft3

/s)

Minimum 

channel 

elevation

(ft)

Water-surface 

elevation 

(ft)

Energy grade 

slope 

(ft/ft)

Flow area 

(ft2

)

Top width 

(ft)

Channel 

Froude

number

3.5 Bridge

3.2 9,500 384.07 391.82 0.00558 767.08 127.89 0.87

3.2 9,400 384.07 391.78 0.00559 761.65 127.79 0.87

3.2 9,300 384.07 391.73 0.00562 755.17 127.66 0.88

3.2 9,200 384.07 391.67 0.00565 748.92 127.53 0.88

3.2 9,100 384.07 391.63 0.00567 743.12 127.41 0.88

3.2 9,000 384.07 391.58 0.00570 736.80 127.29 0.88

3.2 8,900 384.07 391.56 0.00562 734.79 127.25 0.87

3.2 8,800 384.07 391.51 0.00566 728.28 127.12 0.87

3.2 8,700 384.07 391.45 0.00570 721.64 126.98 0.88

3.2 8,600 384.07 391.40 0.00573 715.00 126.85 0.88

3.2 8,500 384.07 391.35 0.00576 708.66 126.72 0.88

3 9,400 381.86 391.91 0.00210 1,112.27 151.73 0.55

3 9,300 381.86 391.86 0.00211 1,103.75 151.49 0.55

3 9,200 381.86 391.80 0.00211 1,095.52 151.26 0.55

3 9,100 381.86 391.75 0.00211 1,087.83 151.05 0.55

3 9,000 381.86 391.70 0.00211 1,079.53 150.82 0.55

3 8,900 381.86 391.68 0.00208 1,076.52 150.74 0.55

3 8,800 381.86 391.62 0.00208 1,067.98 150.50 0.55

3 8,700 381.86 391.56 0.00209 1,059.29 150.26 0.55

3 8,600 381.86 391.50 0.00209 1,050.62 150.02 0.55

3 8,500 381.86 391.45 0.00209 1,042.31 149.79 0.54

2 9,500 381.20 389.07 0.01078 858.68 220.06 0.93

2 9,400 381.20 389.01 0.01088 849.29 219.86 0.94

2 9,300 381.20 388.98 0.01082 844.65 219.76 0.93

2 9,200 381.20 388.94 0.01079 838.84 219.64 0.93

2 9,100 381.20 388.89 0.01084 830.78 219.46 0.93

2 9,000 381.20 388.86 0.01081 825.01 219.34 0.93

2 8,900 381.20 388.67 0.01165 795.84 215.51 0.96

2 8,800 381.20 388.63 0.01167 788.71 214.23 0.96

2 8,700 381.20 388.58 0.01167 782.00 213.02 0.96

2 8,600 381.20 388.54 0.01168 775.15 211.77 0.96

2 8,500 381.20 388.49 0.01175 766.75 210.25 0.96

1 9,500 376.99 383.37 0.00598 1,089.92 241.65 0.67

1 9,400 376.99 383.37 0.00585 1,089.92 241.65 0.66

1 9,300 376.99 383.37 0.00573 1,089.92 241.65 0.65

1 9,200 376.99 383.37 0.00561 1,089.92 241.65 0.65

1 9,100 376.99 383.37 0.00549 1,089.92 241.65 0.64

1 9,000 376.99 383.37 0.00537 1,089.92 241.65 0.63

1 8,900 376.99 383.37 0.00525 1,089.92 241.65 0.63

1 8,800 376.99 383.37 0.00513 1,089.92 241.65 0.62

1 8,700 376.99 383.37 0.00501 1,089.92 241.65 0.61

1 8,600 376.99 383.37 0.00490 1,089.92 241.65 0.60

1 8,500 376.99 383.37 0.00479 1,089.92 241.65 0.60