Antecedent Hydrologic Conditions 

and Storm Characteristics

Areas of northern Maine received 

between 150 and 200 inches of snow 

during the winter of 2007–08, an aboveaverage amount for the region. From 40 

to 70 inches of this snowpack (equivalent 

to 10 to 15 inches of water from snow) 

remained on the ground in mid-April 

(River Flow Advisory Commission, State 

of Maine, 2008). High air temperatures 

caused the water content of the snowpack 

to drop more than 8 inches between 

April 15 and 29, filling rivers and streams 

to capacity. In the week preceding the 

heavy rain, streamflows in the Fish and 

St. John Rivers were elevated, with 

annual exceedance probabilities between 

50 and 10 percent (recurrence intervals 

between 2 and 10 years). 

A low-pressure system developed 

in Pennsylvania on Monday, April 27, 

and the resulting storm moved into 

southern Maine by April 29. Rain 

continued through April 30, and rainfall 

totals ranged from 2 to 4 inches in 

northern Maine.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2010–3003

March 2010

Introduction

Severe flooding occurred in 

Aroostook and Penobscot Counties in 

northern Maine between April 28 and 

May 1, 2008, and damage was extensive 

in the town of Fort Kent. Aroostook 

County was declared a Federal disaster 

area on May 9, and the declaration was 

expanded to include Penobscot County 

on May 16—qualifying the entire region 

for federal assistance. 

Water in the St. John River peaked 

at 30.17 feet in Fort Kent (5 feet above 

flood stage), hit the low steel of the 

International Bridge connecting Fort 

Kent to New Brunswick, caused closure 

of international bridges in Fort Kent, 

Van Buren, and Hamlin and came within 

inches of the top of a 30-foot-high 

earthen dike constructed to protect the 

downtown area of Fort Kent. Longterm streamgages with 25 to 84 years 

of record on the Big Black, St. John, 

Allagash, Fish, and Aroostook Rivers 

recorded maximum streamflows for their 

respective periods of record.

Northern Maine experienced major 

floods in 1923, 1973, 1974, 1979, and 

1983 (Maloney and Bartlett, 1991). 

Flood debris line along St. John River dike in Fort 

Kent, Maine, on May 3, 2008. (Photograph by 

Laura Flight, U.S. Geological Survey)

Printed on recycled paper

All of these floods were in late April or 

early May when heavy rain combined 

with snowmelt runoff. 

Prepared in cooperation with the Federal Emergency Management Agency

Flood of April and May 2008 in Northern Maine

Fort Kent, Maine, on May 1, 2008. (Photograph courtesy of the Maine 

Department of Public Safety)

The U.S. Geological Survey (USGS) Maine Water 

Science Center has worked with the Federal 

Emergency Management Agency (FEMA) for 

decades to document the magnitude and extent 

of major floods in Maine. A report describing 

the April/May 2008 flood in northern Maine is 

an example of this cooperative relationship 

(Lombard, 2010). The documentation of peak stream 

elevations, peak streamflow magnitudes, and 

annual exceedance probabilities provides essential 

information for the delineation of flood plains and 

for flood-mitigation decisions by local, State, and 

Federal emergency management officials.
Peak Stream Elevations 

Seventy-five peak stream elevations 

were determined in Aroostook and 

Penobscot Counties following the April/

May 2008 flood. Peak stream elevations 

were determined using data from 

streamgages and by surveying highwater marks.

Peak Streamflow Magnitudes and 

Exceedance Probabilities

Peak streamflow magnitudes and 

exceedance probabilities were calculated 

for the April/May 2008 flood at 20 

locations (fig. 1). Peak streamflows were 

determined from a rating curve (relation 

between streamflow and stream elevation 

at a streamgage) at 14 sites and by use 

of hydraulic models that were based on 

relations between streamflow and streamchannel geometry at 6 sites.

Streamflows observed during the 

spring 2008 flood had the lowest exceedance probabilities along Maine’s northern 

border with Canada (fig. 1). The Allagash 

River near Allagash (USGS streamgage 

01011000), the St. John River in Fort 

Kent (USGS streamgage 01014000), 

and Fish River at Fort Kent (USGS 

streamgage 01013500) all had flows 

with annual exceedance probabilities of 

less than 1 percent (recurrence intervals 

greater than 100 years). 

Selected References

Lombard, P.J., 2010, Flood of April and May 2008 

in northern Maine: U.S. Geological Survey 

Scientific Investigations Report 2010–5003, 17 p.

Maloney, T.J., and Bartlett, W.P., 1991, 

Maine floods and droughts, in Paulson, 

R.W., Roberts, R.S., and Moody, D.W., comps., 

National water summary 1988–89—Hydrologic 

events and floods and droughts: U.S. Geological 

Survey Water-Supply Paper 2375, p. 311–318.

National Weather Service, 2008, Climate data—Past 

weather and normals: Gray, Maine, National 

Weather Service Forecast Office, accessed May 

21, 2008, at http://www.erh.noaa.gov/er/gyx/

climate_f6.shtml#daily_hi_lo_precip_annual.

River Flow Advisory Commission, State of Maine, 

2008, Maine cooperative snow survey: accessed 

August 1, 2008, at http://www.maine.gov/rfac/

rfac_snow.shtml.

By Pamela J. Lombard

For more information, please contact:

Robert Lent, Director

USGS Maine Water Science Center

196 Whitten Road

Augusta, Maine 04330

Telephone: (207) 622-8201

E-mail: dc_me@usgs.gov

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

EXPLANATION

Base from USGS digital data, 1:24,000

Universal Transverse Mercator projection, zone 19

Penobscot River

Piscataquis River

River

Roads

Annual

exceedance

probability,

in percentage

East Branch Penobscot River

MAINE

QÚEBEC,

CANADA

NEW BRUNSWICK,

CANADA

Fish River

Allagash River

Big Black River

West Branch Mattawamkeag River

St. John River

Meduxnekeag

River

Mattawamkeag River

Aroostook River

St. John River

20 MILES

0 10

0

 20 KILOMETERS

10

AROOSTOOK COUNTY

PISCATAQUIS COUNTY SOMERSET COUNTY

PENOBSCOT

COUNTY

WASHINGTON COUNTY HANCOCK

COUNTY

70° 69° 68°

48°

47°

46°

1

1

>10

>10

>10

>10

2–1

>10

2–1

>10

>10

2–1

>10

10–2

10–2

10–2

1–0.2

1–0.2

1–0.2

1–0.2

10−2 Hamlin

Van Buren

Houlton

Allagash

Fort Kent

Presque Isle

Study area

Maine

New

Hampshire

Vermont

Atlantic

Ocean

Qúebec,

Canada

Massachusetts

Figure 1. Peak streamflow exceedance probabilities associated with the spring 2008 flood 

in northern Maine. 

FLOOD-FREQUENCY TERMINOLOGY 

In past flood reports, flood frequencies were expressed as recurrence 

intervals for selected flood quantiles such as the “100-year flood.” The use of 

recurrence-interval terminology is now discouraged by the U.S. Geological 

Survey because it sometimes causes confusion for the general public. 

Recurrence-interval terminology is sometimes interpreted to imply there is a 

set time interval between floods of a particular magnitude; however, floods are 

random processes that are best understood using probabilistic terms. The use 

of annual exceedance probability is now recommended because it conveys the 

probability, or odds, of a flood of a given magnitude being equaled or exceeded 

in any given year. The exceedance probability is equivalent to the reciprocal of 

the recurrence interval and is expressed as a percent. For example, a flood with 

an annual exceedance probability of 1 percent corresponds to a 100-year flood.