Flood Inundation Map Library, Fort Kent, Maine

Floods are the most widely occurring and costly natural hazard in the United States. Although maps of theoretical 

floods associated with given recurrence intervals or exceedance probabilities for a town are often available in the form 

of Flood Insurance Rate Maps (FIRMs), flood inundation maps show the inundated area for actual and forecast flood 

stages—filling the gap between maps made for regulatory purposes and maps delineating floods in real time. Flood inundation maps make current flood stages provided by the U.S. Geological Survey, and peak-forecast flood stages projected 

by the National Weather Service relevant to the public; assist emergency-management workers to evaluate risk, prioritize 

relief efforts for people and property in flood-prone areas, and are a powerful tool for use in response, mitigation, and 

damage assessments.

Introduction

Severe flooding occurred in northern 

Maine from April 28 to May 1, 2008, 

and damage was extensive in the town of 

Fort Kent (Lombard, 2010). Aroostook 

County was declared a Federal disaster 

area on May 9, 2008. The extent of flooding on both the Fish and St. John Rivers 

during this event showed that the current 

Federal Emergency Management Agency 

(FEMA) Flood Insurance Study (FIS) 

and Flood Insurance Rate Map (FIRM) 

(Federal Emergency Management 

Agency, 1979) were out of date. The U.S. 

Geological Survey (USGS) conducted a 

study to develop a flood inundation map 

library showing the areas and depths for a 

range of flood stages from bankfull to the 

flood of record for Fort Kent to complement an updated FIS (Federal Emergency 

Management Agency, in press).

Hydrologic analyses that support the 

maps include computer models with and 

without the levee and with various depths 

of backwater on the Fish River. This 

fact sheet describes the methods used to 

develop the maps and describes how the 

maps can be accessed.

Inputs Necessary for Flood 

Inundation Mapping

Flood surveying and documentation 

(Lombard, 2010) and the field work for 

a new FEMA FIS and FIRM provided 

many of the elements needed to develop 

flood inundation maps.

 Lidar Elevation Data

Light detection and ranging (lidar) 

technology supports the rapid collection 

of high-accuracy elevation data for large 

areas. Lidar uses an airplane equipped 

with laser range finders that pulse tens 

of thousands of times a second and a 

EXPLANATION

161

1

USGS streamgage

and number

Old USGS streamgage

(no longer in use)

Limits of study area

U.S. route marker

State route marker

National boundary

Flood-inundation area

Area protected by levee

Levee

Temporary levee

Flow arrow—Indicates

direction of water flow

01013500

MAINE

Study

area

River

Figure 1. Area of flood inundation, Fort Kent, Maine, when the Fish River 

streamgage 01013500 is at a flood stage of 14.3 feet.

Surveyed Elevation Data high-precision global positioning system 

(GPS). The result is topographic data 

with a vertical accuracy equivalent to 

2-foot contour intervals. Topographic 

maps with this level of detail provide 

elevation data for the banks and flood 

plains along a river for both hydraulic 

models and flood mapping.

High water marks were surveyed 

following the flood; the survey provided calibration points for updating the 

hydraulic models of these rivers. Additional field data included elevation data 

measured with a total-station theodolite 

and underwater depths measured with 

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3119

September 2012
Figure 2. Lidar data for Fort Kent, Maine, 

2009. (Lidar, light detection and ranging)

Figure 3. U.S. Geological Survey National Flood Inundation Mapper showing Fort Kent, 

Maine, and accessed at http://wim.usgs.gov/FIMI/.

an Acoustic Doppler Current Profiler 

(ADCP) referenced to the elevation of the 

water surface at the time of the survey. 

Underwater and channel-bank field-survey data were merged with lidar data to 

create a final base map of high-precision 

elevation data.

Hydraulic Model

A Hydrologic Engineering Centers 

River Analysis System ( HEC–RAS) 

step-backwater model (U.S.Army Corps 

of Engineers, 2001) calibrated with highwater marks from the 2008 flood provided the elevations used to create flood 

boundaries and flood-depth grids for the 

St. John and Fish Rivers.

Flood-Forecast Streamgages

The gages on the St. John River 

below the Fish River at Fort Kent (USGS 

streamgage 01014000, not shown on fig. 

1) and on the Fish River near Fort Kent 

(USGS streamgage 01013500) are both 

used as flood-forecast streamgages by the 

National Weather Service (National Oceanic and Atmospheric Administration, 

2010). The current and forecasted water 

levels are linked to the flood-inundation 

maps.

Interaction of St. John and Fish 

Rivers

Flood inundation maps for Fort Kent 

include flood inundation boundaries and 

depths for both the St. John and Fish Rivers. Backwater from the St. John River 

affects flood elevations on the Fish River, 

with the greatest interaction at the mouth. 

The flood inundation map library consists 

of a set of maps developed at 1-foot 

contour intervals for a total of nine stages 

(20.6 to 28.6 feet) at the St. John River 

streamgage in Fort Kent (01014000) and 

for a total of seven stages (8.3 to 14.3 

feet) at the Fish River streamgage at Fort 

Kent (01013500). The user can select the 

map that best matches current or forecast 

stages at the St. John and Fish River 

streamgages to see the areal extent of 

expected inundation.

Maps Available in Multiple 

Formats

The flood inundation map library for 

Fort Kent is available to water managers and the public in multiple formats: 

downloadable geographic information 

system (GIS) file format, keyhole markup 

language (KML) format, and portable 

document format (PDF). The Fort Kent 

flood inundation map library is also available through the USGS Flood Inundation 

Mapper at http://wim.usgs.gov/FIMI/ 

(fig. 3). This interactive tool allows the 

user to select maps according to flood 

stages at USGS streamgaging stations 

or NWS flood-warning forecasts. All 

maps and supporting documentation are 

available at: http://water.usgs.gov/osw/

flood_inundation/projects/fort-kent/.

References Cited

Federal Emergency Management Agency, 

1979, Flood insurance study, Town 

of Fort Kent, Aroostook County, 

Maine: Washington, D.C., December 

1979, 19 p. 

Lombard, P.J., 2010, Flood of 

April and May 2008 in northern 

Maine: U.S. Geological Survey 

Scientific Investigations Report 

2010–5003, 17 p. (Also available at 

http://pubs.usgs.gov/sir/2010/5003/.)

Lombard, P.J., 2011, Flood inundation 

maps for the St. John and Fish Rivers 

in Fort Kent, Maine: U.S. Geological Survey Scientific Investigations 

Map 3157, 8 p. 

National Oceanic and Atmospheric 

Administration, 2010, National 

Weather Service Advanced 

Hydrologic Prediction Service, 

accessed October 10, 2010 at 

http://water.weather.gov/ahps/.

U.S. Army Corps of Engineers, 2001, 

Hydrologic Engineering Center, 

River Analysis System (HEC–RAS), 

version 4.0.

—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