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Scientific Investigations Report 2009–5102

Prepared in cooperation with the Federal Emergency Management Agency

Flood of April 2007 in Southern Maine

By Pamela J. Lombard


Thumbnail of and link to report PDF (9.05 MB)

Up to 8.5 inches of rain fell from April 15 through 18, 2007, in southern Maine. The rain—in combination with up to an inch of water from snowmelt—resulted in extensive flooding. York County, Maine, was declared a presidential disaster area following the event.

The U.S. Geological Survey, in cooperation with the Federal Emergency Management Agency (FEMA), determined peak streamflows and recurrence intervals at 24 locations and peak water-surface elevations at 63 sites following the April 2007 flood. Peak streamflows were determined with data from continuous-record streamflow-gaging stations where available and through hydraulic models where station data were not available. The flood resulted in peak streamflows with recurrence intervals greater than 100 years throughout most of York County, and recurrence intervals up to 50 years in Cumberland County. Peak flows for selected recurrence intervals varied from less than 10 percent to greater than 100 percent different than those in the current FEMA flood-insurance studies due to additional data or newer regression equations. Water-surface elevations observed during the April 2007 flood were bracketed by elevation profiles in FEMA flood-insurance studies with the same recurrence intervals as the recurrence intervals bracketing the observed peak streamflows at seven sites, with higher elevation-profile recurrence intervals than streamflow recurrence intervals at six sites, and with lower elevation-profile recurrence intervals than streamflow recurrence intervals at one site.

The April 2007 flood resulted in higher peak flows and water-surface elevations than the flood of May 2006 in coastal locations in York County, and lower peak flows and water-surface elevations than the May 2006 flood further from the coast and in Cumberland County. The Mousam River watershed with over 13 dams and reservoirs was severely impacted by both events. Analyses indicate that the April 2007 peak streamflows in the Mousam River watershed occurred despite the fact that up to 287 million ft3 of runoff was stored by 13 dams and reservoirs.

For additional information contact:
U.S. Geological Survey,
Maine Water Science Center
196 Whitten Road
Augusta, Maine 04330

Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.

Suggested citation:

Lombard, P.J., 2009, Flood of April 2007 in southern Maine: U.S. Geological Survey Scientific Investigations Report 2009–5102, 34 p., available only online at




Antecedent Hydrologic Conditions

Soil Moisture



Storm Characteristics

Precipitation Amounts

Rainfall Frequency

Peak Stream Elevations and Flows

Peak Water-Surface Elevations

Peak Streamflows

Determination of Peak Streamflows through Stage/Discharge Rating Curves

Determination of Peak Streamflows through Hydraulic Modeling using

Indirect Methods

Flow-Frequency Analyses

Characteristics of the Flood in the Mousam River Watershed

Square Pond

Mousam Lake

Estes Lake

Combined Impact of Dams

Historical Floods in Southern Maine

Comparison of the April 2007 Flood Data to Flood Insurance Studies

Summary and Conclusions


References Cited

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