U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2009–3049

June 2009

Floods of May 2006 and April 2007 in Southern Maine

The U.S. Geological Survey Maine Water Science Center has worked with the Federal Emergency 

Management Agency for decades to document the magnitude and extent of major floods in Maine. Reports 

describing the May 2006 and April 2007 floods in southern Maine are examples of this cooperative relationship. 

The documentation of peak stream elevations and peak streamflow magnitudes and recurrence intervals 

provides essential information for the delineation of flood plains and for flood-mitigation decisions by local, 

State, and Federal emergency management officials.

Introduction

Extreme floods occurred on streams 

in southern Maine in May 2006 and in 

April 2007 (fig.1). Floods with recurrence 

intervals greater than 100 years (having 

less than a 1-percent probability of 

exceedence each year) occurred during 

the Mother’s Day Storm of May 2006 and 

the Patriots’ Day Storm of April 2007. 

Although both storms were centered in 

York County, the 2006 storm resulted in 

higher streamflows near the coast, and 

the 2007 storm resulted in flooding over a 

wider geographical area—extending 

into Cumberland County and western 

York County. 

The documentation of peak stream 

elevations and peak streamflow magnitudes and recurrence intervals associated 

with extreme floods is important for the 

calibration of models used to delineate 

100- and 500-year flood plains in regulatory flood-insurance studies. Minimal 

historical peak-flow data are available for 

southern Maine; however, riverine floods 

occurred in 1936, 1953, 1987, and 1996. 

Storm Characteristics

The Mother’s Day Storm from 

May 10–17, 2006, was characterized by up 

to 16 inches (in.) of rain falling on saturated ground in locations centered around 

Ogunquit, Maine. The wettest month of 

May since 1871 (12.3 in.) was recorded in 

Portland, Maine, in 2006. Cape 

Neddick received 20.3 in. of rain in May 

2006 (National Weather Service, 2008). 

Rainfall received during the Mother’s Day 

Storm exceeded the 100-year recurrence 

interval for 2-, 4-, 7-, and 10-day rainfall 

totals at many locations in southern Maine. 

The Patriots’ Day Storm from 

April 15–18, 2007, dropped up to 8.5 in. of 

rain over much of southern Maine—from 

the western border with New Hampshire 

to the coast (National Weather Service, 

2008)—and was augmented with up to 

1 in. of water from snowmelt. The average 

rainfall for the Patriots’ Day Storm 

Figure 1. Josias River washout of culvert, York County, Maine, May 2006.

Figure 2. Identifying high water marks 

in southern Maine 2007.
was roughly equivalent to the 100-year 

recurrence interval for 2-day rainfall totals at 

selected locations in southern Maine.

Peak Stream Elevations

Peak stream elevations were 

determined for 80 points at 25 sites in 

York County following the May 2006 flood 

and 160 points at 63 sites in York and 

Cumberland Counties following the April 

2007 flood. Most peak stream elevations 

were determined through the identification 

and surveying of high-water marks 

immediately following the floods. 

Peak Streamflow Magnitudes and 

Recurrence Intervals

Peak streamflow magnitudes and recurrence intervals (such as the 100-year peak 

streamflow) were calculated for the May 

2006 flood at 9 locations and for the April 

2007 flood at 24 locations in southern Maine 

(fig. 3). Peak streamflows were higher in 

2006 at five of the nine locations for which 

peak streamflows were calculated for both 

years (table 1). 

The most reliable method for computing peak streamflows is from a rating 

(relation between streamflow and stream 

elevation at a streamflow-gaging station). 

If a rating is unavailable or unreliable for 

extremely high flows, peak streamflow 

can be calculated using a hydraulic model 

based on relations between streamflow and 

the geometry of the stream channel. Peak 

streamflow recurrence intervals were 

greater than 100 years for much of 

York County during both the May 

2006 and April 2007 floods—and were 

up to 50 years in Cumberland County 

during the April 2007 flood (fig. 3). 

It is possible to have storms 

with large recurrence intervals in 

consecutive years; however, recurrence 

intervals greater than 100 years have a 

large amount of uncertainty associated 

with them, especially when the period 

of recorded data at a streamflowgaging station is short. As the length 

of record at a gaging station increases, 

the computed recurrence intervals 

become more accurate. Stationarity (the absence of trends) in peak 

streamflows over time is an assumption of recurrence-interval computations. The validity of this assumption 

is currently being investigated for peak 

streamflows in Maine (G. Hodgkins, 

U.S. Geological Survey, oral commun., 

2008).

Selected References

Lombard, P.J., 2009, Flood of April 2007 

in southern Maine: U.S. Geological 

Survey Scientific Investigations Report 

2009–5102, 34 p.

National Weather Service, 2008, Daily 

high/low temperature and precipitation 

statistics: Gray, Maine, Gray Weather 

Forecast Office, accessed May 21, 

2008, at http://www.erh.noaa.gov/er/

gyx/climate_f6.shtml#daily_hi_lo_

precip_annual

Stewart, G.J., and Kempf, J.P., 2008, 

Flood of May 2006 in York County, 

Maine: U.S. Geological Survey Scientific Investigations Report 2008–5047, 

17 p., 1 pl.

By Pamela J. Lombard 

For more information, please contact:

Robert Lent, Director

U.S. Geological Survey 

Maine Water Science Center

196 Whitten Road

Augusta, ME 04330

Telephone: (207) 622-8201

E-mail: rmlent@usgs.gov

Web site: http://me.water.usgs.gov

Figure 3. Peak-streamflow recurrence intervals associated with the May 2006 flood 

and April 2007 flood at selected sites in southern Maine. 

Table 1. May 2006 and April 2007 peak 

streamflows for selected sites in southern 

Maine.

[ft3/s, cubic feet per second]

Stream and location

2006

Peak 

flow 

(ft3/s)

2007

Peak 

flow 

(ft3/s)

Mousam River near 

West Kennebunk

6,100 9,230

Little River, Berwick 3,390 4,640

Cape Neddick River, York 2,250 1,010

Ogunquit River, Ogunquit 3,110 2,230

Blacksmith Brook, Wells 473 260

Merriland River, Wells 2,240 1,860

Branch Brook near 

Kennebunk

1,500 1,330

Stony Brook at 

East Sebago

40 125

Saco River at Cornish 14,900 17,000

Portland Portland

Ogunquit

Cape Neddick

Ogunquit

Cape Neddick

ATLANTIC OCEAN

ATLANTIC OCEAN

N N YORK COUNTY

YORK COUNTY

CUMBERLAND COUNTY

CUMBERLAND 

COUNTY 

 OXFORD 

COUNTY

 OXFORD 

COUNTY

ANDROSCOGGIN 

COUNTY

ANDROSCOGGIN 

COUNTY

0 10 MILES

May 2006 Flood April 2007 Flood

Base from U.S. Geological Survey and 

Maine Office of Geographic Information System digital files, 

North American Datum 83, Universal Transverse Mercator grid, Zone 19

0 10 KILOMETERS

>500

>500

>500

>500

>500

>500

>500

>500

100-500

<5

<5

<5

25

5-10 10-25

10-25

25-50

10-25 10-25

50-100

100-500

100-500

500

500

>500

>500

>500

>500 >500

25-50

10-25

25-50

50-100

100-500

MAINE

CANADA

Area shown ATLANTIC OCEAN

EXPLANATION

500

>

<

Streamflow site and recurrence interval

less than

greater than