FLOOD INSURANCE STUDY - GRANIT

FLOOD INSURANCE STUDY

VOLUME 1 OF 2 COOS COUNTY, NEW HAMPSHIRE (ALL JURISDICTIONS) COMMUNITY COMMUNITY NAME NUMBER BERLIN, CITY OF 330029 CARROLL, TOWN OF 330030 CLARKSVILLE, TOWN OF 330184 COLEBROOK, TOWN OF 330031 COLUMBIA, TOWN OF 330185 COOS COUNTY (UNINCORPORATED AREAS) 330171 DALTON, TOWN OF 330198 DUMMER, TOWN OF 330201 ERROL, TOWN OF 330206 GORHAM, TOWN OF 330032 JEFFERSON, TOWN OF 330033 LANCASTER, TOWN OF 335277 MILAN, TOWN OF 330035 NORTHUMBERLAND, TOWN OF 330036 PITTSBURG, TOWN OF 330186 RANDOLPH, TOWN OF 330187 SHELBURNE, TOWN OF 330037 STARK, TOWN OF 330038 STEWARTSTOWN, TOWN OF 330194 STRATFORD, TOWN OF 330039 WHITEFIELD, TOWN OF 330040

Effective Date: February 20, 2013

Federal Emergency Management Agency FLOOD INSURANCE STUDY NUMBER

33007CV001A

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NOTICE TO FLOOD INSURANCE STUDY USERS

Communities participating in the National Flood Insurance Program have established repositories of flood hazard data for floodplain management and flood insurance purposes. This Flood Insurance Study (FIS) report may not contain all data available within the Community Map Repository. Please contact the Community Map Repository for any additional data.

The Federal Emergency Management Agency (FEMA) may revise and republish part or all of this FIS report at any time. In addition, FEMA may revise part of this FIS report by the Letter of Map Revision process, which does not involve republication or redistribution of the FIS report. Therefore, users should consult with community officials and check the Community Map Repository to obtain the most current FIS report components.

Selected Flood Insurance Rate Map panels for this community contain information that was previously shown separately on the corresponding Flood Boundary and Floodway Map panels (e.g., floodways, cross-sections). In addition, former flood hazard zone designations have been changed as follows:

Old Zone(s) New Zone

A1 through A30

B

C

AE

X (shaded)

X

Initial Countywide Effective Date: February 20, 2013

Revised Countywide Effective Date(s):

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VOLUME 1

TABLE OF CONTENTS

Page 1.0 INTRODUCTION .............................................................................................................. 1

1.1 Purpose of Study ................................................................................................................ 1

1.2 Authority and Acknowledgements ..................................................................................... 2

1.3 Coordination ....................................................................................................................... 4

2.0 AREA STUDIED ............................................................................................................... 4

2.1 Scope of Study.................................................................................................................... 4

2.2 Community Description ..................................................................................................... 6

2.3 Principal Flood Problems ................................................................................................. 11

2.4 Flood Protection Measures ............................................................................................... 13

3.0 ENGINEERING METHODS ........................................................................................... 16

3.1 Hydrologic Analyses ........................................................................................................ 16

3.2 Hydraulic Analyses .......................................................................................................... 23

3.3 Vertical Datum ................................................................................................................. 28

4.0 FLOODPLAIN MANAGEMENT APPLICATIONS ...................................................... 30

4.1 Floodplain Boundaries ..................................................................................................... 30

4.2 Floodways ........................................................................................................................ 31

5.0 INSURANCE APPLICATION ........................................................................................ 48

6.0 FLOOD INSURANCE RATE MAP (FIRM) ................................................................... 48

7.0 OTHER STUDIES ............................................................................................................ 49

8.0 LOCATION OF DATA .................................................................................................... 49

9.0 BIBLIOGRAPHY AND REFERENCES ......................................................................... 51

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TABLE OF CONTENTS (Continued)

VOLUME 1 (Continued)

LIST OF FIGURES Page Figure 1. Floodway Schematic ...................................................................................................... 32

LIST OF TABLES

Page Table 1. CCO Meeting Dates for Prior FISs ................................................................................... 4

Table 2. New Detailed Studies ........................................................................................................ 5

Table 3. Detailed Studies (from Prior Studies)................................................................................ 5

Table 4. Summary of Stillwater Elevations ................................................................................... 17

Table 5. Summary of Ice Jam Discharges ..................................................................................... 18

Table 6. Hydrologic Method Used ................................................................................................ 19

Table 7. Summary of Discharges .................................................................................................. 20

Table 8: Manning’s “n” Values ..................................................................................................... 27

Table 9: Vertical Datum Conversions Single Conversion Factor (countywide) Method ............... 28

Table 10. Floodway Data .............................................................................................................. 33

Table 11. Community Map History ............................................................................................... 50

LIST OF EXHIBITS

Exhibit 1 – Flood Profiles

Androscoggin River Panels 001P-012P Bog Brook Panels 013P-016P Burnside Brook Panel 017P Caleb Brook Panels 018P-033P Clear Stream Panel 034P-035P Clement Brook Panel 036P-038P

VOLUME 2 Connecticut River Panels 039P-071P Dead River Panel 072P-079P Dead River and Jericho Brook Panel 080P Greenough Brook Panel 081P Indian Brook Panels 082P-096P Israel River Panels 097P-106P

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TABLE OF CONTENTS (Continued) VOLUME 2 (Continued)

LIST OF EXHIBITS (Continued) Moose Brook Panel 107P-113P Moose Brook Split Panel 114P Moose River Panel 115P-116P Otter Brook Panels 117P-118P Peabody River Panel 119P-122P Redman Brook Panels 123P-126P Tinker Brook Panel 127P-129P Whipple Brook Panel 130P-131P

Exhibit 2 –

Flood Insurance Rate Map Index Flood Insurance Rate Map

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FLOOD INSURANCE STUDY

COOS COUNTY, NEW HAPSHIRE ALL JURISDICTIONS

1.0

1.1 Purpose of Study

INTRODUCTION

This countywide Flood Insurance Study (FIS) revises and supersedes the previous FIS reports and/or Flood Insurance Rate Maps (FIRMs) for the geographic area of Coos County, New Hampshire, including the Towns of Carroll, Clarksville, Colebrook, Columbia, Dalton, Dummer, Errol, Gorham, Jefferson, Lancaster, Milan, Northumberland, Pittsburg, Randolph, Shelburne, Stark, Stewartstown, Stratford, and Whitefield; the City of Berlin; and Coos County (unincorporated areas), including Atkinson and Gilmanton Academy Grant, Bean’s Grant, Bean’s Purchase, Chandler’s Purchase, Crawford’s Purchase, Cutt’s Grant, Dix’s Grant, Dixville, Erving’s Location, Green’s Grant, Hadley’s Purchase, Kilkenny, Low &Burbank Grant, Martin’s Location, Millsfield, Odell, Pinkham’s Grant, Sargent’s Purchase, Second College Grant, Success, Thompson & Meserve’s Purchase, and Wentworth Location (hereinafter referred to collectively as Coos County).

No prior FIS reports were available for the Unincorporated Areas of Coos County, New Hampshire, or for the towns of Carroll, Clarksville, Columbia, Dalton, Dummer, Jefferson, Pittsburg, Randolph, Shelburne, Stark, Stewartstown or Whitefield.

The Digital Flood Insurance Rate Map (DFIRM) and FIS Report for this countywide study have been produced in digital format. Flood hazard information was converted to meet Federal Emergency Management Agency (FEMA) DFIRM database Specifications and Geographic Information System (GIS) format requirements. The flood hazard information was created and is provided in digital format so that it can be incorporated into a local GIS and be accessed more easily by the community.

This FIS aids in the administration of the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. This study has developed flood risk data for various areas of the community that will be used to establish actuarial flood insurance rates. This information will also be used by Coos County to update existing floodplain regulations as part of the Regular Phase of the National Flood Insurance Program (NFIP), and by local and regional planners to further promote sound land use and floodplain development. Minimum floodplain management requirements for participation in the NFIP are set forth in the Code of Federal Regulations at 44 CFR, 60.3.

In some states or communities, floodplain management criteria or regulations may exist that are more restrictive or comprehensive than the minimum federal requirements. In such cases, the more restrictive criteria take precedence and the state (or other jurisdictional agency) will be able to explain them.

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1.2 Authority and Acknowledgements

The source of authority for this FIS is the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973.

Information on the authority and acknowledgments for each of the previously printed FISs and FIRMs for communities within Coos County was compiled, and is shown below.

City of B erlin. For the December 15, 1981 FIS report (Reference 1), the hydrologic and hydraulic analyses were performed by the U.S. Geological Survey (USGS) for the Federal Emergency Management Agency (FEMA), under Inter-Agency Agreement No. IAA-H-9-77, Project Order No.30. This study was completed in June 1979.

Pre-Countywide

Town of C olebrook. For the May 17, 1989 FIS report (Reference 2), the hydrologic and hydraulic analyses were prepared by the USGS for FEMA, under Inter-Agency Agreement No. EMW-85-E-1823, Project Order No. 20. This work was completed in July 1987.

Town of Errol. For the April 16, 2003 revision to the FIS report (Reference 3), the hydraulic and hydrologic analyses for Akers Pond was prepared by the USGS for FEMA under Inter-Agency Agreement No. EMW-98-IA-0163. This work was completed in March 2000.

Town of G orham. For the October 1, 1980 FIS report (Reference 4), the hydraulic and hydrologic analyses were prepared by the USGS for the Federal Insurance Administration (FIA), under Inter-Agency Agreement No. IAA-H-9-77, Project Order No. 30. That work was completed in February 1979.

For the May 2, 1994 revision, the hydrologic and hydraulic analyses for the Peabody River were prepared by Roald Haestad, Inc., for FEMA, under Contract No. EMW-90-C-3126. This work was completed in March 1993.

Town o f L ancaster. For the October 1, 1981 FIS report (Reference 5), the hydraulic and hydrologic analyses represent a revision of the original analyses by the Soil Conservation Service (SCS) for FEMA under Contract No. H-4589. The updated version was prepared by Anderson-Nichols and Company, Inc., under agreement with FEMA. This study, which was completed in March 1979, covered all significant flooding sources in the Town of Lancaster.

Town of Milan. For the July 17, 2006 FIS report (Reference 6), the hydraulic and hydrologic analyses were performed by the USGS for FEMA, under Interagency Agreement No. EMW-2001-IA-0196. This study was completed in June 2003.

Town of Northumberland. For the May 4, 1989 FIS report (Reference 7), the hydraulic and hydrologic analyses for this study were performed by the USGS for FEMA, under Inter-Agency Agreement No. EMW-85-E-1823. This study was completed in July 1987.

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Town o f St ratford. For the October 18, 1982 FIS report (Reference 8), the hydraulic and hydrologic analyses were performed by Hamilton Engineering Associates, Inc., for FEMA under Contract No. EMW-C-0334. This study was completed in October 1981.

For this Countywide update new hydrologic and hydraulic analysis for the Androscoggin River, and portions of Clear Stream, Clement Brook, Dead River, Greenough Brook, Moose Brook, Moose River, Peabody River, and Tinker Brook was performed.

Countywide

A study from the June 3, 1991 FIS report (Reference 9) of the Town of Bloomfield, Vermont was incorporated along the Connecticut River in the Town of Columbia. The hydrologic and hydraulic analysis for this study was prepared by the USGS for FEMA, under Inter-Agency Agreement No. EMW-85-E-1823, Project Order No. 6. This work was completed in December 1988.

A study from the March, 1980 FIS report (Reference 10) of the Town of Canaan, Vermont was incorporated along the Connecticut River in the Towns of Columbia and Stewartstown. The hydrologic and hydraulic analysis for this study was prepared by DuBois & King, Inc., for the Federal Insurance Administration, under Contract No. H-4577. This study was completed in March 1977.

Redelineation of previously-effective flood hazard information for Akers Pond and portions of Dead River, Jericho Brook, and Moose River for this FIS report and accompanying FIRMs as well as conversion of the unincorporated and incorporated areas of Coos County into countywide format was performed by the Strategic Alliance for Risk Reduction (STARR) for FEMA under Contract No. HSFEHQ-09-D-0370, Task Order No. 3. This work was completed in April 2011.

The digital base mapping information was provided by New Hampshire GRANIT. Further information about the base mapping is available by contacting GRANIT. These files were complied by photogrammetric methods and meet or exceed National Map Accuracy Standards. Orthophotography was provided as a part of the US Department of Agriculture (USDA) National Agriculture Imagery Program (NAIP) at a 1 meter pixel resolution. Topographic information for areas of new study within the Androscoggin River basin was provided in Light Detection and Ranging (LiDAR) mass points and breaklines based on a fall of 2009 flight. The LiDAR data has sufficient vertical accuracy to support the generation of 2 foot contours. Topographic data for the rest of the county consists 20 ft contours taken from USGS orthoquads.

The projection used for the production of this FIRM is New Hampshire State Plane Zone 4676 (FIPSZONE 2800). The horizontal datum was NAD83. Differences in the datum, spheroid, projection or state plane zones used in the production of FIRMs in adjacent jurisdictions may result in slight positional

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differences in map features across jurisdiction boundaries. These differences do not affect the accuracy of the FIRM.

1.3 Coordination

The purpose of an initial Consultation Coordination Officer’s (CCO) meeting is to discuss the scope of the FIS. A final CCO meeting is held to review the results of the study. The dates of the initial and final CCO meetings held for prior FISs for the incorporated communities within Coos County are shown in Table 1.

Table 1. CCO Meeting Dates for Prior FISs

Community Name Initial CCO Date Final CCO Date Berlin, City of January, 1976 March 10, 1981 Colebrook, Town of February 12, 1985 December 11, 1987 Errol, Town of August 25, 1999 September 21, 2001 Gorham, Town of January, 1976 November 24, 1993 Lancaster, Town of February 5, 1980 April 10, 1979 Milan, Town of June 26, 2001 ** Northumberland, Town of February 12, 1985 December 11, 1987 Stratford, Town of June, 1979 March 15, 1982 *Not available

Initial scoping meeting call for Coos County was conducted by the USGS on September 1, 2005. Five groups including the USGS, New Hampshire Office of Energy Management (NHOEM), FEMA and Watershed Concepts participated in the call. Part of the scoping effort conducted by the USGS included phone interviews with affected communities. These phone interviews were carried out between August 2005 and September 2006.

For this study, an initial CCO meeting was held on June 2, 2010 and was attended by representatives from the Town’s of Colebrook, Dalton, Gorham, Lancaster, Milan, Stewartstown, the City of Berlin, the North Country Council, the New Hampshire Department of Energy and Planning, FEMA, the University of New Hampshire and STARR. The results of the study were reviewed at the final CCO meeting held on July 21, 2011, and attended by representatives from the Town’s of Carroll, Colebrook, Gorham, Jefferson, Lancaster, Milan, Shelburne, the City of Berlin, the North Country Council, the New Hampshire Department of Energy and Planning, FEMA, the University of New Hampshire and STARR. All problems raised at that meeting have been addressed.

2.0 AREA STUDIED

2.1 Scope of Study

This FIS covers the geographic area of Coos County, New Hampshire, including the incorporated communities listed in Section 1.1 and unincorporated areas.

Approximate methods of analysis were used to study those areas having a low development potential or minimal flood hazards as identified at the initiation of the study. The scope and methods of study were proposed to and agreed upon by FEMA, the State of New Hampshire, and Coos County officials.

The following streams were studied by detailed methods in this FIS report:

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Table 2. New Detailed Studies

Flooding Source Study Limits

Androscoggin River From the Oxford Maine County Boundary to just downstream of the Lake Umbagog Dam

Clear Stream From its confluence with Androscoggin River to its confluence with Greenough Brook

Clement Brook From its confluence with Androscoggin River to approximately 3,600 feet upstream of State Highway 2

Dead River From its confluence with Androscoggin River to approximately 5,000 feet upstream of Hillside Avenue

Greenough Brook From its confluence with Clear Stream to the downstream face of Akers Pond Dam.

Moose Brook From its confluence with Androscoggin River to approximately 1,000 feet upstream of Jimtown Road

Moose Brook Split From its confluence with Moose Brook to its Divergence from Moose Brook

Moose River From its confluence with Androscoggin River to approximately 2,500 feet upstream of Main Street

Peabody River From its confluence with Androscoggin River to approximately 10,000 feet upstream of Glen Road

Tinker Brook From its confluence with Androscoggin River to approximately 5,000 feet upstream of Main Street

Those streams studied previously by detailed methods are shown in Table 3. Limits of Detailed Studies are indicated on the Flood Profiles (Exhibit 1) and on the FIRM (published separately).

Table 3. Detailed Studies (from Prior Studies) Flooding Source Study Limits

Bog Brook From its confluence with Connecticut River to Egan Road

Burnside Brook From its confluence with Caleb Brook to its confluence with Whipple Brook

Caleb Brook From its Confluence with Otter Brook to Pleasant Valley Road

Connecticut River From approximately 4.5 miles upstream of Bridge Hill Road to approximately 3.0 miles upstream of Vermont Avenue.

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Table 3. Detailed Studies (from Prior Studies) (Cont.)Flooding Source Study Limits

Dead River From approximately 5,000 feet upstream of Hillside Avenue to its confluence with Jericho Brook

Indian Brook From its confluence with Connecticut River to approximately 5,000 feet upstream of the Railroad

Israel River From its confluence with Connecticut River to approximately 4700 feet upstream of its confluence with Otter Brook

Jericho Brook From its confluence with Dead River to approximately 800 feet upstream of Canadian National Railroad

Moose River From 2,500 feet upstream of Main Street to 1,700 feet upstream of private drive.

Otter Brook From it confluence with Israel River to its confluence with Burnside and Caleb Brook

Redman Brook From its confluence with Caleb Brook to Pleasant Valley Road

Whipple Brook From its confluence with Burnside Brook to approximately 6000 feet upstream

The areas studied by detailed methods in previous FIS reports were selected with priority given to all known flood hazard areas and areas of projected development and proposed construction.

No Letters of Map Revisions (LOMRs) or Letters of Map Amendments (LOMAs) were incorporated into this countywide FIS. A Summary of Map Amendments (SOMA), which lists the status of the Letters of Map Changes (LOMCs) associated with Coos County, is included in the Technical Support Data Notebook (TSDN) associated with this FIS update. Copies of the TSDN may be obtained from the Community Map Repository.

2.2 Community Description

Coos C ounty is located on the northern panhandle of New Hampshire, and is bordered by Grafton and Carroll Counties on the south, by Quebec, Canada on the north, by Essex County, Vermont on the west, and by Oxford County, Maine on the east. The major transportation arteries of Coos County include U.S. Routes 2, 3 and 302; State Routes 16 and 26; and the Androscoggin River. The county seat is the Village of Lancaster. According to the U.S. Census Bureau, the 2009 estimated population for Coos County is 31,487 (Reference 11).

City of Berlin is located in the southeastern portion of Coos County in northern New Hampshire. It is approximately 100 miles north of Concord and 50 miles west of the Town of Rumsford, New Hampshire. Berlin is bordered by the Town of Milan to the north, by the unincorporated Township of Success to the east, by the Town of Randolf and the Town of Gorham to the south, and by the unincorporated Township of Killkenny to the west. According to the U.S.

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Census Bureau figures, the estimated population of the Town in 2009 was 9,351 (Reference 11).

Berlin is situated in the midst of the White Mountains. The lowest elevations of approximately 1,000 feet are found near the center of the community, while the highest elevation of 3,890 feet in the city is found on Round Mountain. The land area of Berlin is 57.1 square miles, of which only six percent is urbanized. The remainder of the land area is undeveloped or wooded, with 58 percent of the community within White Mountain National Forest.

The climate of the study area is variable. The average annual precipitation is 38 inches, including an average snowfall of 101 inches. Average monthly temperature range from a low of 16 degrees Fahrenheit in January to a high of 66.5 degrees Fahrenheit in July. Temperature extremes during 80 years of record have reached a low of -44 degrees Fahrenheit and a high of 100 degrees Fahrenheit.

Town of C arroll is located in south western Coos County in northern New Hampshire approximately 90 miles north of Manchester. Crooksville is bordered by the Town of Jefferson to the northeast, by Grafton County to the southwest, and by the unincorporated areas of Coos County on all other sides. The estimated population of the Town in 2009 was 726 (Reference 11).

Town of Clarksville is located in northeastern Coos County in Northern New Hampshire, and is approximately 140 miles north of Manchester, New Hampshire. Clarksville is bordered by the Town of Pittsburg to the north and to the west, by the Town of Stewartstown to the south, and by the unincorporated areas of Coos County to the east. The estimated population of the Town in 2009 was 276 (Reference 11).

Town of Colebrook is located in the western part of Coos County in northern New Hampshire. It is bordered by the Town of Stewartstown to the north, by the Town of Dixville to the east, by the Town of Columbia to the south, and by the Towns of Canaan and Lemington, Vermont, to the west. According to U.S. Census Bureau figures, the population estimate for the Town of Colebrook was 2,305 in 2009 (Reference 11).

The climate of Colebrook is moderate and is characterized by the even distribution of an average of approximately 40 inches of precipitation during the year. The town experiences large ranges of temperature both on a daily and an annual basis and a considerable variety of weather in short periods of time. The topography of the town ranges from gently rolling terrain in the valleys to steep, hilly terrain in several upland areas. The land area of Colebrook consists mainly of well-drained, glacial, stratified drift in the valleys and glacial till and bedrock in the uplands.

Town of Columbia is located in eastern Coos County in Northern New Hampshire approximately 105 miles north of Concord. Columbia is bordered by Vermont to the west, by the Town of Colebrook to the north, by the Town of Stratford to the south, and by the unincorporated areas of Coos County to the east. According to U.S. Census Bureau figures, the population estimate for the Town of Columbia was 798 in 2009 (Reference 11).

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Town of Dalton is located in southwestern Coos County in northern New Hampshire. Dalton is bordered by Vermont to the northwest, by Grafton County, New Hampshire to the southwest, by the Town of Lancaster to the northeast, and by the unincorporated areas of Coos County to the east. Dalton is located approximately 80 miles north of Concord, New Hampshire. According to U.S. Census Bureau figures, the population estimate for the Town of Dalton was 866 in 2009 (Reference 11).

Town of Dummer is located in central Coos County in northern New Hampshire approximately 95 miles north-northeast of Concord, New Hampshire. Dummer is bordered by the Town of Milan to the south, by the Town of Errol to the northeast, by the Town of Stark to the west, and by the unincorporated areas of Coos County to the east and to the north. According to U.S. Census Bureau figures, the population estimate of the Town in 2009 was 296 (Reference 11).

Town of Errol, Coos County, in northern New Hampshire has a land area of approximately 68.9 square miles and is bounded on the north by the Town of Wentsworth Location, on the east by the Towns of Upton and Lincoln Plantation, Maine, on the south by the Towns of Dummer and Cambridge, and on the west of the Town of Millsfield. According to U.S. Census Bureau figures, the population estimate of the Town in 2009 was 276 (Reference 11).

The Errol area is mountainous and forested. The average annual precipitation over the watershed is approximately 49 inches and is distributed rather uniformly throughout the year (Reference 12).

Town of Gorham is located in the southeastern portion of Coos County, in northern New Hampshire. Gorham is bordered by the City of Berlin to the north, by the unincorporated Township of Success to the northeast, by the Towns of Shelburne and Randolph to the east and west, respectively, and by the unincorporated Townships of Beans Purchase, Martins Location, and Thompson and Meserves Purchase to the southeast, south and southwest, respectively. The Town of Gorham is situated approximately 100 miles north of the City of Concord, New Hampshire and 50 miles west of the Town of Rumsford, Maine. The total land area of Gorham is 35.3 square miles. According to U.S. Census Bureau figures, the population estimate of the Town in 2009 was 2,795 (Reference 11).

The climate of northern New Hampshire is variable. The average annual precipitation for the Town of Gorham is 38 inches, including 101 inches of snowfall. Average monthly temperatures range from a low of 16 degrees Fahrenheit in January to a high of 66.5 degrees Fahrenheit in July. Temperature extremes during 80 years of record ranged from a low of -44 degrees Fahrenheit to a high of 100 degrees Fahrenheit.

Town of Jefferson is located in southwestern Coos County in northern New Hampshire approximately 80 miles north of Concord, New Hampshire. Jefferson is bordered by the Town of Randolph to the east, by the Town of Lancaster to the north, by the Town of Carroll to the southwest, and by the unincorporated areas of Coos County to the west, south and northeast. According to U.S. Census Bureau figures, the population estimate of the Town in 2009 was 1,032 (Reference 11).

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Town of Lancaster occupies 51.6 square miles of Coos County in northwestern New Hampshire. It is located on the Connecticut River approximately 90 miles north of Concord and 160 miles southeast of Montreal, Quebec. Lancaster is bordered by the communities of Northumberland to the north, Kilkenny to the east, Jefferson, Whitefield, and Dalton to the south, and Lunenburg and Guildhall, Vermont, to the west. According to U.S. Census Bureau figures, the population estimate of the Town in 2009 was 3,219 (Reference 11).

The surficial geology, soils, land use, and vegetative cover of a watershed reflect its response to precipitation and thus its flood peaks. Geologically, Lancaster lies in the margin of the White Mountain section of the New England Physiographic Province. Glaciation has modified the area by erosion and deposition, leaving a blanket of till over the higher elevations and outwash sand and gravel deposits in the valleys. Flooding since glaciation has covered the Connecticut River flood plain and portions of the flood plains of other streams with alluvial deposits of sand and silt (Reference 13, 14).

The soils of the Connecticut River flood plain are primarily moderately well to excessively drained, fine to very fine sandy loams. Numerous deposits of peat and mucky peat may be found, some with depths of 30 feet. Soils along the Israel River flood plain are similar to those of the of the Connecticut River flood plain in its lower reaches. In its upper reaches, near the mouth of Otter Brook, soils are excessive to moderately well drained fine sandy loams and loamy sands formed from glacial outwash deposits. Theses soil types also extend up Otter Brook and the lower reaches of Burnside, Whipple, and Caleb Brooks. The upper reaches of Burnside, Whipple, and Caleb Brooks and all of Redman Brook are founded on poor to moderately well drained stony to very stony loams formed from compact glacial till. The swampy area along Burnside Brook and part of the swampy area along Indian Brook is composed of pooly drained fine sandy loam which occupies depressions on glacial outwash plains. Peat and mucky peat comprise the remainder of the Indian Brook swamp area (Reference 14). Upland soils are typically shallow to bedrock loams and very stony loams formed from glacial till. Theses soils are moderately well drained and many have numerous bedrock outcrops (Reference 14).

The vegetative cover of the Town of Lancaster consists of forest in the uplands with pastures and agricultural land in the flood plains and adjacent outwash plains.

Town of Milan is located in central Coos County and has a land area of 61.7 square miles. The Town of Milan is bordered on the north by the Towns of Dummer and Cambridge, on the east by the Town of Success, and on the south by the City of Berlin. Elevation varies from the Androscoggin River at about 1,100 feet to 2,800 feet in the mountains in the southwestern corner of the town. According to U.S. Census Bureau figures, the population estimate of the Town in 2009 was 1,333 (Reference 11).

The Androscoggin River flows to the south through the Town of Milan. The flow of the Androscoggin through the Town of Milan is regulated by Rangley, Mooselookmeguntic, Richardson, Aziscohos and Umbagog Lakes. These reservoirs have a combined usable capacity of about 28.1 billion cubic feet.

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Town of Northumberland is located in the western part of Coos County. It is bordered by the Town of Stratford to the north, by the Town of Stark to the east, by the Town of Lancaster to the south, and by the Towns of Guildhall, Vermont, and Maidstone, Vermont, to the west. According to U.S. Census Bureau figures, the population estimate of the Town in 2009 was 2,290 (Reference 11).

Town of P ittsburg is located in the northern part of Coos County in northern New Hampshire. Pittsburg is bordered by the Town of Clarksville to the south and on all other sides by the unincorporated areas of Coos County. According to U.S. Census Bureau figures, the population estimate of the Town in 2009 was 808 (Reference 11).

Town o f R andolph is located in the south central part of Coos County in northern New Hampshire. Randolph is bordered by the Town of Jefferson to the west, by the Town of Gorham to the east, and by the unincorporated areas Coos County to the north and south. According to U.S. Census Bureau figures, the population estimate of the Town in 2009 was 327 (Reference 11).

Town of Shelburne is located in the western part of Coos County in northern New Hampshire. Shelburne is bordered by the Town of Gorham to the west, by the unincorporated areas of Coos County to the north and south, and by the State of Maine to the east. According to U.S. Census Bureau figures, the population estimate of the Town in 2009 was 367 (Reference 8).

Town of S tark is located in central Coos County in northern New Hampshire. Stark is bordered by the Town of Dummer to the east, by the Town of Northumberland to the west, and by the unincorporated areas of Coos County to the north and south. According to U.S. Census Bureau figures, the population estimate of the Town in 2009 was 474 (Reference 11).

Town of Stewartstown is located in northwestern Coos County in northern New Hampshire. Stewartstown is bordered by the Town of Colebrook to the south, by the Town of Clarksville to the north, by the unincorporated areas of Coos County to the east, and by the State of Vermont to the west. According to U.S. Census Bureau figures, the population estimate of the Town in 2009 was 964 (Reference 11).

Town o f St ratford is located in western Coos County in northern New Hampshire. Stratford is bordered by the Town of Columbia to the north, by the Town of Northumberland to the south, by the State of Vermont to the west, and by the unincorporated areas of Coos County to the east. According to U.S. Census Bureau figures, the population estimate of the Town in 2009 was 872 (Reference 11).

Town of Whitefield is located in south western Coos County in northern New Hampshire. Whitefield is bordered by the Town of Dalton to the west, by the Town of Carroll to the southeast, by the Town of Jefferson to the east, by the Town of Lancaster to the north, and by Grafton County to the southwest. According to U.S. Census Bureau figures, the population estimate of the Town in 2009 was 1,933 (Reference 11).

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2.3 Principal Flood Problems

There is no information relating to flooding problems in the Towns of Carroll, Clarksville, Columbia, Dalton, Dummer, Dixville, Jefferson, Millsfield, Northumberland, Pittsburg, Randolph, Shelburne, Stark, Stewartstown or Whitefield, or in the Unincorporated Areas of Coos County.

Flooding in Coos County has occurred in every season of the year. Spring floods are common and are caused by rainfall in combination with snowmelt. Floods in late summer and fall are usually the result of above normal precipitation. Winter floods result from the occasional thaws, particularly in years of heavy snow cover.

Major floods that have occurred on the Connecticut River in this region have taken place in March 1913, November 1927, March 1936, September 1938, June 1943, April 1954, May 1972, and March 1979. The worst of these floods occurring in 1936 and 1943. In 1936, gage No. 01131500 recorded a discharge of 48,300 cubic feet per second (cfs) which was the highest peak for that gage on record.

For the Androscoggin River, major flood occurrences have taken place in 1826, 1869, 1896, 1927, 1936, and 1953, 1969 and 1998. The worst flood took place in 1869 when two people were killed in a flood that was called the “pumpkin freshet”.

City of Berlin

Severe floods occurred on the Androscoggin River in the City of Berlin in 1869, 1917, 1923, 1936, and 1953. During the flood of October 1869, two men in the area were killed when a mill was swept away (Reference 15). Discharges of 20,000 cfs occurred on June 18, 1917, and April 30, 1923. These flows were mean daily discharges by computations of flow over a dam and through wheels and gates at the Brown Paper Company's Riverside Plant located three-quarters of a mile upstream from the confluence of the Dead River with the Androscoggin River (Reference 16).

In 1928, the USGS established a gaging station at Pulsifer Rips in the Town of Gorham two miles downstream from the mouth of the Dead River. The highest flood recorded at this station was 19,900 cfs during the flood of March 1936 (Reference 15). This flood caused about $175,000 in damages in the New Hampshire portion of the Androscoggin River basin. The paper and textile mills along the river downstream from Berlin were seriously affected. In Berlin, 75 business properties near the mouth of the Dead River were flooded, with damage estimates placed at $500,000 (Reference 17). This study has determined that the 1936 flood discharge had a recurrence interval of 65 years. The recurrence intervals for the 1917 and 1923 floods were nearly the same.

On March 27, 1953, the USGS gaging station at the Town of Gorham recorded a discharge of 17,900 cfs on the Androscoggin River. Streets were flooded and stores damaged in the business section of the city by the overflow of the Dead River (Reference 15). The recurrence interval of this flood was approximately 35 years.

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Town of Colebrook

Floods in Colebrook have occurred in every season of the year. Spring floods are common and are caused by rainfall in combination with snowmelt. Floods in late summer and fall are usually the result of above-normal precipitation. Winter floods result from the occasional thaws, particularly in years of heavy snow cover.

Major Colebrook floods in the 20th century occurred in March 1913, November 1927, March 1936, September 1938, and June 1943. Of these floods, two floods (March 1936 and June 1943) were most severe. Long-term stream flow records (1930 to present) at USGS gaging station No. 01129500 on the Connecticut River at North Stratford indicate that the March 1936 and June 1943 floods were 1-percent-annual-chance floods.

Town of Errol

Flooding may occur during all seasons of the year. The watershed is mountainous and predominately forested. According to a letter dated November 19, 1997 from the Town of Errol, flooding due to spring runoff has occurred only one time in the past 20 years, and this was limited to one area.

Town of Gorham

Severe flooding occurred on the Androscoggin River within the Town of Gorham in 1826, 1869, 1896, 1927, and 1936. During the flood of October 1869 (known as "the pumpkin freshet"), two men were killed when a mill was swept away. The November 1927 flood on the Androscoggin River caused damage in the Town of Gorham and Town of Berlin area (Reference 18). The highest flood recorded since 1929 at the Gorham gaging station was 19,900 cfs, recorded during the flood of March 1936 (Reference 15). A flood of that magnitude is a 2-percent-annual-chance flood event, however, under present hydraulic conditions, the WSEL of a 2-percent-annual-chance flood event in Gorham would be lower than that of the 1936 flood. Discharges of 20,000 cfs (determined by computations of flow over dams and through wheels and gates located approximately 3 miles above the Gorham gage) occurred on June 18, 1917, and April 30, 1923.

Town of Lancaster

Lancaster has experienced damaging floods from the Connecticut River in 1927, 1936, 1954, and 1972. The largest recorded discharge is 48,300 cfs in 1936 at the Dalton, New Hampshire gage, 10 miles downstream of Lancaster (Reference 19). A discharge of this magnitude has a one percent chance of occurring in any year.

The Israel River has experienced 25 significant floods since 1870. Sixteen of these floods have been caused by ice jams (Reference 13). The most recent occurred in 1974. The greatest discharge not associated with an ice jam was estimated to be 8,840 cfs (elevation 863.2 feet) at the Main Street Bridge in November 1927. The most severe ice jam flood occurred in March 1968 (elevation 866.3 feet) at the Main Street Bridge. The USACE has assigned

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recurrence intervals of approximately 40 years and 33 years respectively to these two floods.

The flat watershed of Indian Brook between Depot Street and Summer Street has also been subject to repeated high water. This is due to the backwater effect of the railroad culvert just downstream of Depot Street.

Significant floods have also occurred along Otter, Burnside, and Caleb Brooks.

Town of Milan

Floods of significant magnitude have occurred in the Town of Milan in 1785, 1826, 1869, 1917, 1923, 1936, 1969, and 1998. The recurrence interval of the 1998 flood at the gage, at the Androscoggin River near the Town of Gorham, New Hampshire, which is 7.2 miles downstream from the Town of Milan corporate limit, was approximately 40 years.

Town of Stratford

Floods on the Connecticut River in excess of the 10-percent-annual-chance flood flow have occurred several times within the 79 years of records at the USGS gaging station at North Stratford. Major floods occurred in June 1943, April 1954, May 1972, and March 1979. Many floods occur during the spring and most of these are caused by heavy rain or heavy rain combined with snowmelt.

The the largest flood occurred March 7, 1979. After days of steady rain and warm weather, snow and ice floated down the Connecticut River. The ice backed up behind the Stratford Road Bridge, causing the Connecticut River to overflow its banks. When the ice jam gave way and went through the bridge, water moved south closing State Route 3 and doing considerable damage to housing on River Street. North Stratford was declared a Federal Disaster Area, and the community "relocated" 29 families whose homes were flooded.

2.4 Flood Protection Measures

There are no flood protection measures identified in the Towns of Carroll, Clarksville, Columbia, Dalton, Dummer, Jefferson, Northumberland, Pittsburg, Randolph, Shelburne, Stark, Stewartstown or Whitefield, or in the Unincorporated Areas of Coos County.

City of Berlin

A number of dams and lakes in the Androscoggin River headwater can store significant amounts of runoff, thereby reducing floods peaks. During the flood of March 1936, the six lakes upstream of the Town of Gorham, with a storage area of 1,045 square miles at Errol Dam, stored more than 16 billion cubic feet of floodwater. This is equivalent to 75 percent of the total possible flood runoff for this flood (Reference 17).

The Jericho Pond Dam, built on the Jericho Brook in 1969 by the Soil Conservation Service (SCS), is very effective in controlling flooding on the Dead River. Jericho Pond was created by the dam and has a large storage capacity (67.0 million cubic feet) in relation to its drainage area (6.5 square miles).

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Because the Dead River has caused considerable flood damage in the business section of the City of Berlin, the city has channelized the river here as part of its urban renewal project.

In order to utilize available water power, four hydroelectric power stations have been constructed. However, these dams do not store large volumes of water and they operate on the water released by regulation dams upstream at the Towns of Errol and Pantacook. At two of the dams in Berlin, maximum river stages occur just before the flash boards are raised.

The dam farthest upstream on the Androscoggin River is the Sawmill Station Dam located near 7th street. This is a concrete dam with a 530-foot spillway, operates with a 17.5 foot head, and is privately owned. The Riverside Dam, also privately owned, has a spillway 802 feet long and operates on a 20.75 foot head. A third dam is owned by a public utility company and is a part of the J. Brody Smith Power Station Complex. The power station is located near the mouth of the Dead River; the dam is upstream of the power station and although it has a height of only 20 feet, it provides an operating head of 88 feet on the generators by means of a penstock. The spillway of this dam is 426 feet long. A fourth dam is owned by a paper manufacturing company and is called the Cross Power Station Dam. It is located approximately 0.5 miles downstream of City Hall and has a normal operating head of 25.3 feet with a 437-foot spillway (Reference 1).

Town of Colebrook

Storage capabilities within the First and Second Connecticut Lakes and Lake Francis exert a major effect on the Connecticut River in Colebrook (Reference 2

Town of Errol

No flood protection measures are currently known to exist in the Town of Errol (Reference 3).

Town of Gorham

A number of dams and lakes located on the headwaters of the Androscoggin River can store significant amounts of runoff, thereby reducing peak flow intensity. For example, during the flood of March 1936, six lakes about 35 miles upstream from the Town of Gorham stored more than 16 billion cubic feet of floodwater, equivalent to 75 percent of the total possible flood runoff from the drainage area of 1,095 square miles (Reference 20). None of the dams used to generate electric power within Gorham provide protection from the 1-percent-annual-chance flood.

Non-structural measures of flood protection are also being utilized to aid in the prevention of future flood damage. These are in the form of land-use regulations which control building within the areas that have a high risk of flooding (Reference 4).

Town of Lancaster

Flood hazard determinations for the October 1, 1981 FIS for the Town of Lancaster were based on hydrologic and hydraulic conditions that existed at the

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time the report was prepared (1981). Two flood control structures affecting the Town of Lancaster had been proposed at the time the 1981 FIS was written, but their indefinite status precluded the consideration of their hydraulic effect into the 1981 study. One project was an upstream dam and downstream drop inlet structure designed for Indian Brook by the SCS under Public Law 566 (Reference 5).

These structures, accompanied by land treatment practices, were designed to relieve the persistent flooding problem between Depot Street and Summer Street. The effect that this project would have on the 1-percent-annual-chance flood profile of Indian Brook is shown in the 1972 Flood Hazard Analysis Report (Reference 19). For the 1981 FIS, both the SCS and Town officials were contacted regarding the status of this project, but both were unable to provide a proposed date for completion.

The second proposed structure is a USACE ice control structure to be located on the Israel River in order to prevent ice jam flooding of the center of Lancaster. The USACE has been studying the Israel River ice jam problem since 1965 and has published several reports dealing with its details and proposed solution (References 13 and 21). The view of the USACE in 1981 was that a low dam should be constructed 0.5 mile upstream of the center of Lancaster at the site of a former Twin State Gas and Electric Company hydropower dam. At the time of the 1981 FIS report, USACE plans were incomplete, thus the effect of the proposed structure could not be considered in this study. The USACE has indicated that plans should soon be complete and construction is imminent but no timetable has been set. The USACE project should soon relieve the Israel River ice jam flooding problem, thus it was deemed unnecessary to include an ice jam flood analysis in the 1981 FIS report. For details of previous analyses, refer to the USACE reports and the SCS Flood Hazard Analysis Report (References, 13, 19, 21).

The only existing flood control structure affecting streams in Lancaster is an emergency dike on the Israel River just upstream of Otter Brook. This dike was constructed by the USACE in 1970 as a temporary measure to relieve ice jam flooding until a permanent structure could be built. The ice jam flood of 1974 showed the dike to be relatively ineffective (Reference 21).

Town of Milan

There are no physical flood protection measures currently known to exist in the Town of Milan. There are large reservoirs that regulate flow, but the reservoirs, primarily used for power generation, are not designed for flood control (Reference 6).

Town of Stratford

The Lake Francis Dam on the Connecticut River at Pittsburg is a flood control upstream of the Town of Stratford. North of Lake Francis, the First Connecticut and Second Connecticut Lakes are present, which have a combined storage capacity of greater than 3.8 billion cubic feet (Reference 8).

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3.0

For the flooding sources studied by detailed methods within the County, standard hydrologic and hydraulic study methods were used to determine the flood hazard data required for this study. Flood events of a magnitude that are expected to be equaled or exceeded once on the average during any 10-, 50-, 100- or 500-year period (recurrence interval) have been selected as having special significance for floodplain management and for flood insurance rates. These events, commonly termed the 10-, 50-, 100- or 500-year floods, have a 10-, 2-, 1- and 0.2-percent chance, respectively, of being equaled or exceeded during any year. Although the recurrence interval represents the long-term

ENGINEERING METHODS

average

3.1 Hydrologic Analyses

period between floods of a specific magnitude, rare floods could occur at short intervals or even within the same year. The risk of experiencing a rare flood increases when periods greater than 1 year are considered. For example, the risk of having a flood that equals or exceeds the 1-percent-annual-chance flood in any 50-year period is approximately 40 percent (4 in 10), and for any 90-year period, the risk increases to approximately 60 percent (6 in 10). The analyses reported herein reflect flooding potentials based on conditions existing in the community at the time of completion of this study.

Hydrologic analyses were carried out to establish the peak discharge-frequency relationships for each flooding source studied by detailed methods affecting the county.

This FIS report includes information from previously published FIS reports where streams were studied in detail. It also includes new information for streams studied in detail during this study.

Detailed Studies

Peak discharges for the 10-, 2-, 1-, and 0.2-percent-annual-chance floods of each flooding source studied in detail in previous FIS reports and in the current study are shown in Table 4.


Pre-Countywide Analyses

City of Berlin

Discharge values for the Dead River upstream of approximately 4,700 feet upstream of Hillside Avenue and for Jericho Brook for the 10-, 2-, and 1-percent-annual-chance flood events were obtained by using formulas developed by the USGS for estimating flood-frequencies on rural unregulated streams in New Hampshire (Reference 22). This method relates flood flows to basin characteristics such as drainage area, main channel slope, and precipitation. This method was adapted to calculate the flow for the 0.2-percent-annual-chance event. The area of the drainage basin upstream of the Jericho Pond Dam was

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excluded from this study because the dam can completely shut off flow for long periods of time, especially during flood hazard periods.

Town of Colebrook

For the May 17, 1989 FIS for the Town of Colebrook, New Hampshire, the 1-percent-annual-chance flood discharge for the Connecticut River in Colebrook was based on analyses of records of 54 annual peak discharges from the long-term USGS Gaging Station No. 011295000 on the Connecticut River at North Stratford, New Hampshire (Reference 23). The analyses followed the standard log-Pearson Type III method as outlined in Bulletin 17B (Reference 23).

Town of Errol

For the April 16, 2003 FIS for the Town of Errol, New Hampshire, the inflow 1-percent-annual-chance flood discharge value for Akers Pond was determined based on the regional peak discharge and frequency formulas developed by the USGS (Reference 24).

The stillwater elevations for flooding sources studied by detailed methods were determined and are summarized in Table 4.

Table 4. Summary of Stillwater Elevations

Flooding Source and Location

Elevation (Feet NAVD88) 10-percent-

annual-chance

2-percent-annual-chance


0.2-percent-annual-chance

Akers Pond Entire shoreline within the Town of Errol

* * 1,230.3 *

* Data not available

Town of Gorham

A regional analysis was made to establish the discharges as selected recurrence intervals for Moose River from 2,500 feet upstream of Main Street. Values of the 10-, 2-, 1-, and 0.2-percent-annual-chance peak discharges for these streams were based on the relationship between slope and runoff, expressed in cubic feet per square mile. This relationship was established for selected floods at 20 USGS gaging sites in the area. The discharges obtained agree with those determined using a method developed by the USGS for estimating flood frequencies in Maine (Reference 25). This method was utilized because the topography and stream characteristics of this section of New Hampshire are similar to those of western Maine.

Town of Lancaster

For the October 1, 1981 FIS for the Town of Lancaster, New Hampshire, discharges for the Connecticut River were developed from a log-Pearson Type III distribution analysis of flood records from 1927 to 1972 for the USGS gage at

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Dalton, New Hampshire. Addition of records from the years of 1973 to 1977 and use of the most recently adopted technique for analyzing flood records did not produce significantly different results from the previous analysis (Reference 26). Thus, the results from the previous analysis were retained for use in the study.

The peak discharge values for Indian Brook and the Israel River and its tributaries were determined by standard SCS methods as described in the SCS National Engineering Handbook (Reference 27). The SCS methodology uses precipitation, runoff curve numbers, time of concentration and time of travel as parameters for developing sub-area discharges, and then combines and routes these discharges through a drainage basin system. Study watersheds were divided into 22 sub-areas and 24 routing reaches to be used in the TR-20 Project Formulation Program, which determines the discharge for each reach for each desired recurrence interval (Reference 19).

Town of Northumberland

For the May 4, 1989 FIS for the Town of Northumberland, New Hampshire, the 1-percent-annual-chance discharge for the Connecticut River in Northumberland was based on analysis of records of 54 annual peak discharges from the long-term USGS gaging station (No. 01129500) on the Connecticut River at North Stratford, New Hampshire (Reference 28). The analyses followed the standard log-Pearson Type III method as outlined in Bulletin 17B (Reference 23).

Town of Stratford

For the October 18, 1982 FIS for the Town of Stratford, New Hampshire, the free-flowing discharges for the Connecticut River were determined using log-Pearson Type III statistical analyses (Reference 3) of peak discharges at the stream gage located on the Connecticut River at North Stratford. The gage has been in operation since 1931. Winter discharges (used for ice jam analyses) for flows on the Connecticut River were determined using log-Pearson Type III statistical analyses (Reference 29) for USGS estimated peak discharges at the gage in North Stratford. The free-flowing discharges for Bog Brook were determined using the USGS regional equations which were based on multiple-regression analyses of gaged data in New Hampshire (Reference 22). A summary of drainage area-peak discharge relationships for the Connecticut River ice jam analyses is shown in Table 5, “Summary of Ice Jam Discharges”.

Table 5. Summary of Ice Jam Discharges


Drainage Area

(square miles)

Peak Discharges (cfs)





Connecticut River Maidstone-Stratford Hollow

Bridge 898.0 11,820 19,460 23,280 33,610 Canadian National Railroad 627.7 9,030 14,880 17,800 25,700

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Peak discharges for the 10-percent-annual-chance (10-year), 2-percent-annual-chance (50-year), 1-percent-annual-chance (100-year) and 0.2-percent-annual-chance (500-year) storm events were determined for each of the new detailed study reaches in Coos County. The discharge values for unregulated watersheds were determined using regression equations found in Scientific Investigations Report (SIR) 2008-5206 (Reference 30).

Countywide Analyses

For the Androscoggin River a flood frequency analysis was performed using the PeakFQ Flood Frequency Analysis software developed by the USGS. PeakFQ automates flood frequency analyses and is based on methods described in Guidelines for Determining Flood Flow Frequencies, Bulletin 17B (Reference 23).

HEC-HMS software package (version 3.4.0) developed by the U.S. Army Corps of Engineers was used to model several regulated watersheds where gage data was unavailable. Table 6 outlines the method used for each study.

Table 6. Hydrologic Method Used Stream Name Method Used Androscoggin River Gage analysis Clear Stream HEC-HMS Clement Brook Regression Dead River Regression Greenbough Brook HEC-HMS Moose Brook Regression Moose River Regression Peabody River Regression Tinker Brook Regression

For the June 3, 1991 FIS for the Town of Bloomfield, Vermont that was incorporated in the Town of Columbia, New Hampshire, the 1-percent-annual-chance flood discharge for the Connecticut River in Bloomfield was based on analyses of records of 54 annual peak discharges from the long-term USGS Gaging Station No. 011295000 on the Connecticut River at North Stratford, New Hampshire (Reference 8). The analyses followed the standard log-Pearson Type III method as outlined in Bulletin 17B (Reference 23).

For the March 1980 FIS for the Town of Canaan, Vermont that was incorporated in the Towns of Clarksville and Stewartstown, New Hampshire the flood discharges for the Connecticut River were determined by a log-Pearson Type III analysis outlined by the U.S. Water Resouces Council (Reference 29). The USGS gages used in this study include the gage (no. 01129200) on the Connecticut River below Indian Stream, with a period of record of 20 years and the gage (no. 01129500) on the Connecticut River at North Stratford, New Hampshire, with a period of record of 46 years.

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A summary of the drainage area-peak discharge relationships for all the streams studied by detailed methods is shown in Table 7.

Table 7. Summary of Discharges


Drainage Area

(square miles)






Akers Pond At Akers Pond Dam (routed) 9.5 * * 1,160 *

* Data not available Androscoggin River

At County Boundary with Oxford, ME 1,500 20,900 26,100 28,200 32,700

Approximately 1.0 Miles Upstream of North Road 1,466 19,800 22,300 23,900 27,400

Approximately 1.8 Miles Downstream of Unity Street 1,365 16,700 20,600 22,100 25,300

Approximately 2.3 Miles Downstream of Bridge Street 1,274 15,400 19,200 20,700 23,900

Approximately 1.2 Miles Upstream of Upton Road 1,044 12,000 15,700 17,100 20,100

Bog Brook U.S. Rout 3 26.2 2,763 5,370 6,755 12,000 Christie Road 17.9 1,783 3,480 4,377 7,620

Burnside Brook At confluence with Otter Brook 7.3 1,160 2,200 2,740 4,300

Caleb Brook At confluence with Otter Brook 5.5 700 1,300 1,600 2,320 Upstream of second Pleasant

Valley Road crossing 3.8 575 1,080 1,330 2,090 Upstream of confluence of

Redman Brook 2.4 370 700 860 1,350 Clear Stream

At Confluence with the Androscoggin River 64.1 5,200 8,910 11,100 13,600

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Table 7. Summary of Discharges (Cont.)


Drainage Area

(square miles)






Connecticut River At Dalton corporate limits 1,400 33,500 44,000 48,300 59,000 Upstream of the confluence of

Israel River 1,250 30,800 40,300 44,300 54,300 At USGS Gaging Station No.

01129500 799 * * 29,300 * Approximately 1.2 miles

upstream of State Route 26 488 10,700 14,900 17,250 22,500 Just upstream of Leach Creek 377 7,300 10,600 12,400 17,000 Just upstream of Halls Stream 285 5,050 7,500 8,900 12,400

* Data not available Clement Brook

At Confluence with the Androscoggin River 5.5 615 975 1,160 1,610

Approximately 0.4 miles upstream of the confluence with the Androscoggin River 1.5 215 350 423 600

Dead River At Confluence with the

Androscoggin River 16.2 563 874 1,040 1,430 At Marsh Road 7.491 406 707 854 1,280

1 Does not include drainage area of Jericho Pond (5.52 square miles) Greenough Brook

At Confluence with Clear Stream 9.78 391 1,080 1,160 1,210 Indian Brook

At confluence with the Connecticut River 2.2 75 110 120 160

Upstream of Depot Street 2.0 70 100 115 150 Approximately 4,600 feet

upstream of Summer Street 1.4 1101 2101 2601 4101 1 Larger upstream discharges are due to substantial storage in swampy area above Depot Street. Israel River

At the confluence with the Connecticut River 135 10,140 18,720 22,970 35,000

Upstream of the confluence of Otter Brook 109 6,570 12,300 15,140 23,800

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Table 7. Summary of Discharges (Cont.)


Drainage Area

(square miles)






Jericho Brook At State Route 110 3.131 197 358 436 675

1 Does not include drainage area of Jericho Pond (5.52 square miles) Moose Brook


Approximately 1.8 miles upstream of the confluence with the Androscoggin River 5.88 800 1,280 1,540 2,140

Approximately 2.6 miles upstream of the confluence with the Androscoggin River 4.54 720 1,170 1,410 1,980

Approximately 2.7 miles upstream of the confluence with the Androscoggin River 1.53 300 500 610 870

Moose Brook Split At Confluence with Moose Brook NA 738 920 1,030 1,420

Moose River At Confluence with the

Androscoggin River 23.8 2,400 3,780 4,530 6,270 Peabody River


Otter Brook At the confluence with Israel

River 25 1,910 3,560 4,380 6,800 Upstream of Garland Road 23 1,740 3,280 4,050 6,400

Redman Brook At confluence with Caleb Brook 1.3 270 510 630 1,130

Tinker Brook At Confluence with the

Androscoggin River 2.99 310 500 600 850 Whipple Brook

At the confluence with Burnside Brook 8.7 1,290 2,560 3,180 5,200

4,000 feet upstream of mouth 6.8 1,030 2,050 2,560 4,100

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3.2 Hydraulic Analyses

Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the elevations of floods of the selected recurrence intervals. Users should be aware that flood elevations shown on the FIRM represent rounded whole-foot elevations and may not exactly reflect the elevations shown on the Flood Profiles or in the Floodway Data table in the FIS report. Flood elevations on the FIRM are primarily intended for flood insurance rating purposes. For construction and/or floodplain management purposes, users are cautioned to use the flood elevation data presented in this FIS report in conjunction with the data shown on the FIRM.

The hydraulic analyses for this study were based only on unobstructed flow. The flood elevations shown on the profiles are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. Changes in existing bridge dimensions and elevations could also affect the given water surface elevations (WSELs).

This section includes information from previously published FIS reports where streams were studied by detailed and approximate methods. It also includes new information for streams studied by detailed methods.

Detailed Studies


Pre-Countywide Analyses

City of Berlin

For the December 15, 1981 FIS for the City of Berlin, cross-section data for the backwater analyses of the Dead River from approximately 5,000 feet upstream of Hillside Road were obtained by ground survey. All bridges, culverts, and dams were field-surveyed to obtain elevation data and structural geometry. The survey data obtained for this portion of Dead River was supplemented by data collected by the Soil Conservation Service (SCS) for their study of the watershed in 1968 (Reference 31).

Water-surface elevations of floods of the selected recurrent intervals were computed through the use of the USGS E431 step-backwater computer program (Reference 32).

For the streams studied by approximately methods within the City of Berlin, the 1-percent-annual-chance flood elevations were established using the method developed by USGS hydrologists at the Augusta, Maine office (Reference 33). This method was utilized because of the similarity between the study area and the mountainous areas of western Maine. The method uses a regional stage-frequency relationship and then estimates a 10-foot rise over the mapped stream elevation as the inundation limits of the 1-percent-annual-chance flood.

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Town of Colebrook

For the May 17, 1989 FIS for the Town of Colebrook, New Hampshire, the 1-percent-annual-chance flood elevations for the Connecticut River were based on elevations of high-water marks of notable past floods located along the Connecticut River in Colebrook. The high-water marks have been published as flood-crest data in USGS Water-Supply Paper 798 (Reference 15).

Flood profiles were drawn showing computed water-surface elevations for the 1-percent-annual-chance flood. The water-surface elevations determined were then used along with USGS topographic maps to determine the extent of flooding (Reference 34).

Streambed elevations plotted on the flood profiles were determined from contours crossing the stream channel on the topographic maps at a scale of 1:62,500 with a contour interval of 20 feet (Reference 34).

Town of Errol

For the April 16, 2003 FIS for the Town of Errol, New Hampshire, hydraulic analyses, considering storm characteristics and the shoreline and bathymetric characteristics of the flooding sources studied, were carried out to provide estimates of the elevations of floods of the selected recurrence intervals along each of the shorelines.

All bridges, dams, and culverts were field-surveyed to obtain elevation data and structural geometry. Bridge, dam, and culvert cross-section data were located at close intervals above and below bridges and dams in order to compute the significant backwater effects of these structures.

Water-surface elevations of floods of the selected recurrence intervals were computed through an analysis of the Akers Dam using weir and orifice equations.

Town of Gorham

For the May 2, 1994 FIS for the Town of Gorham, New Hampshire, cross-sections for the flooding sources studied by detailed methods were obtained from field surveys. All bridges, dams, and culverts were field-surveyed to obtain elevation data and structural geometry.

For the Moose River from 2,500 feet upstream of Main Street, water-surface elevations for floods of the selected recurrence intervals were computed through use of the USGS E431 step-backwater computer program (Reference 32).

Approximate flood elevations for the original study were determined using a regional stage-frequency relationship developed by the Augusta, Maine Sub district Office of the USGS (Reference 35). In this method, a 10-foot rise over the mapped stream elevation is estimated and used as the inundation limit of the 1-percent-annual-chance flood.

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Town of Lancaster

For the October 1, 1981 FIS for the Town of Lancaster, New Hampshire, analyses of the hydraulic characteristics of the flooding sources studied in detail were carried out to provide estimates of the elevations of floods of the selected recurrence intervals along each of these flooding sources.

For the reaches of the Connecticut River, the Israel River, Otter Brook, Burnside Brook, Whipple Brook, and Indian Brook studied by detail in previous studies, existing surveyed cross-sections were checked and in most cases used without modification (References 4, 8, and 9). For detailed study reaches and streams completed for the 1981 FIS, channel and overbank cross-sectional information was obtained by field survey by the study contractor in May 1978. Cross-sections for the backwater analyses of the detailed study streams were located at close intervals above and below bridges in order to compute the significant backwater effects of those structures in the developed areas. In long reaches between structures, appropriate valley cross-sections were also surveyed.

Water-surface elevations of floods of selected recurrence intervals were computed for the streams in the study area through the use of the SCS WSP-2 step-backwater computer program (Reference 36).

Starting water-surface elevations for the Connecticut River were taken from the Flood Hazard Analysis Profiles (Reference 19). Starting water-surface elevations for the Israel River, Otter Brook, Redman Brook, and Indian Brook were determined by the slope/area method. Starting water-surface elevations for Burnside and Caleb Brook were taken from the upstream water surface of Otter Brook as peaks will be coincident on these streams. The elevations on Burnside Brook at the mouth of Whipple Brook were used as Whipple Brook starting water-surface elevations as the peaks of these streams will also be coincident.

Town of Northumberland

For the May 4, 1989 FIS for the Town of Northumberland, New Hampshire, analyses of the hydraulic characteristics of flooding from the source studied were carried out to provide estimates of the elevations of floods of the selected recurrence intervals.

The 1-percent-annual-chance flood elevations for the Connecticut River were based upon elevations of high-water marks of notable past floods located along the Connecticut River in Northumberland. The high-water marks have been published as flood-crest data in USGS Water-Supply Paper 798 (Reference 15). Flood profiles were drawn showing computed WSELs for the 1-percent-annual-chance flood. The WSELs determined were then used along with USGS topographic maps to determine the extent of flooding (Reference 37). Streambed elevations plotted on the flood profiles were determined from contours crossing the stream channel on the topographic maps at a scale of 1:62,500 with a contour interval of 20 feet (Reference 37).

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Town of Stratford

For the October 18, 1982 FIS for the Town of Stratford, New Hampshire, analyses of the hydraulic characteristics of the flooding sources studied in detail were carried out to provide estimates of the elevations of floods of the selected recurrence intervals along each of these flooding sources.

For both free-flowing and ice jam analyses, WSELs of floods of the selected recurrence intervals were computed through use of the USACE’s HEC-2 step-backwater computer program (Reference 38). Starting WSELs for the Connecticut River free-flowing analyses were calculated using the slope/area method. Known starting WSELs, based on preliminary critical depth calculations, were used for the Connecticut River ice jam analyses. Starting WSELs for Bog Brook were calculated using critical depth.

Cross-sections for the backwater analyses of the Connecticut River and Bog Brook were obtained from aerial photographs flown in May 1980 at a scale of 1.0 inch equals 800 feet (Reference 39). The below-water sections were obtained by field measurements. All bridges, dams, and culverts were field-checked to obtain elevation data and structural geometry.

Cross sections and hydraulic structures for the analysis of the Androscoggin River, Clear Stream, Clement Brook, Dead River from its confluence with Androscoggin River to approximately 5,000 feet upstream of Hillside Avenue, Greenough Brook, Moose Brook, Moose Brook split, Moose River from its confluence with Androscoggin River to approximately 2,500 feet upstream of Main Street, Peabody River, and Tinker Brook were obtained by field survey. The survey data obtained for these streams was supplemented with mass points, breaklines and 2 foot contours obtained through LiDAR in the fall of 2009.

Countywide Analyses

Water surface elevations of floods of the selected recurrence intervals for Androscoggin River, Clear Stream, Clement Brook, Dead River from its confluence with Androscoggin River to approximately 5,000 feet upstream of Hillside Avenue, Greenough Brook, Moose Brook, Moose Brook split, Moose River from its confluence with Androscoggin River to approximately 2,500 feet upstream of Main Street, Peabody River, and Tinker Brook were computed through the use of the USACE HEC-RAS computer program (Version 4.0.0).

Starting water-surface elevations for Androscoggin River, Clear Stream, Clement Brook, Dead River from its confluence with Androscoggin River to approximately 5,000 feet upstream of Hillside Avenue, Greenough Brook, Moose Brook, Moose Brook split, Moose River from its confluence with Androscoggin River to approximately 2,500 feet upstream of Main Street, Peabody River, and Tinker Brook were calculated using normal depth.

For the June 3, 1991 FIS for the Town of Bloomfield, Vermont, the 1-percent-annual-chance flood elevations for the Connecticut River were based on elevations of high-water marks of notable past floods located along the Connecticut River in Colebrook. The high-water marks have been published as flood-crest data in USGS Water-Supply Paper 798 (Reference 15).

27

For the June 3, 1991 FIS for the Town of Canaan, Vermont, cross sections and dimensions of structures were obtained from field survey. The WSELs of floods of the selected recurrence intervals for the Connecticut River were computed through use of the USACE’s HEC-2 step-backwater computer program (Reference 38). Starting water surface elevation for the lower reaches of the Connecticut River was determined by normal depth. The upper reach of the Connecticut River were determined using critical depth over the dam above the Village of Canaan.

Roughness factors (Manning’s “n”) used in the hydraulic computations were estimated from photographs and field reconnaissance of the study area. Roughness factors used in the detailed studies are summarized in Table 8.

Table 8: Manning’s “n” Values

Flooding Source Channel “n” Values Overbank “n” Values Androscoggin River 0.031 to 0.10 0.030 to 0.10

Bog Brook 0.03 to 0.04 0.07 to 0.20 Burnside Brook 0.060 to 0.082 0.08 to 0.18

Caleb Brook 0.030 to 0.063 0.06 to 0.17 Clear Stream 0.038 to 0.039 0.039 to 0.10

Clement Brook 0.04 to 0.041 0.04 to 0.10 Connecticut River 0.020 to 0.030 0.05 to 0.17

Dead River 0.02 to 0.045 0.04 to 0.10 Greenough Brook 0.038 to 0.039 0.038 to 0.10

Indian Brook 0.027 to 0.057 0.05 to 0.17 Israel River 0.022 to 0.060 0.04 to 0.17

Jericho Brook 0.02 to 0.045 0.04 to 0.095 Moose Brook 0.04 to 0.05 0.03 to 0.10

Moose Brook Split 0.04 to 0.05 0.03 to 0.10 Moose River 0.038 to 0.04 0.04 to 0.10 Otter Brook 0.030 to 0.063 0.06 to 0.17

Peabody River 0.035 to 0.050 0.040 to 0.20 Redman Brook 0.030 to 0.063 0.07 to 0.17 Tinker Brook 0.035 0.04 to 0.10

Whipple Brook 0.050 to 0.078 0.06 to 0.15

Detail-studied streams include a “profile base line” on the maps. This “profile base line” provides a link to the flood profiles included in the FIS report. For streams that were not re-studied as part of this map update, the detail-studied stream centerline may have been digitized or redelineated as part of this revision.

28

The “profile base lines” for these streams were based on the best available data at the time of their study and are depicted as they were on the previous FIRMs. In some cases where improved topographic data was used to redelineate floodplain boundaries, the “profile base line” may deviate significantly from the channel centerline or may be outside the SFHA.

Flood profiles were drawn showing computed water-surface elevations for floods of the selected recurrence intervals.

3.3 Vertical Datum

All FIS reports and FIRMs are referenced to a specific vertical datum. The vertical datum provides a starting point against which flood, ground and structure elevations can be referenced and compared. Until recently, the standard vertical datum in use for newly created or revised FIS reports and FIRMs was the National Geodetic Vertical Datum of 1929 (NGVD29). With the finalization of the NAVD88, many FIS reports and FIRMs are being prepared using NAVD88 as the referenced vertical datum.

All flood elevations shown in this FIS report and on the FIRM are referenced to NAVD88. Structure and ground elevations in the community must, therefore, be referenced to NAVD88. It is important to note that adjacent communities may be referenced to NGVD29. This may result in differences in Base Flood Elevations (BFEs) across the corporate limits between communities. Effective information for this FIS was converted from NGVD29 to NAVD88. An average conversion of -0.301 feet (NGVD29 - 0.301 = NAVD88) was applied uniformly across the county to convert all effective BFEs and other profile elevations. The conversion factor was calculated using Corpscon (Reference 40) to obtain the conversion at the south east corner of each USGS 7.5 minute orthoquad within 2.5 miles of the county boundary, and an average conversion factor was determined. Table 9 contains the conversion factors for the orthoquads around Coos County.

Table 9: Vertical Datum Conversions Single Conversion Factor (countywide) Method

Quadrangle Name Corner

NAD83 Latitude

(dec. deg.)

NAD83 Longitude (dec. deg.)

NGVD29 to NAVD88 Elevation Change

Carter Dome SE 44.25 -71.125 -0.187 ft Mount Washington SE 44.25 -71.25 -0.187 ft Mount Dartmouth SE 44.25 -71.375 -0.098 ft

Berlin SE 44.375 -71.125 -0.338 ft Mount Crescent SE 44.375 -71.25 -0.325 ft Mount Crescent SW 44.375 -71.375 -0.266 ft

Lancaster SE 44.375 -71.5 -0.341 ft Gilman SE 44.375 -71.625 -0.358 ft

Success Pond SW 44.5 -71.125 -0.404 ft West Milan SE 44.5 -71.25 -0.377 ft

Stark SE 44.5 -71.375 -0.302 ft Groveton SE 44.5 -71.5 -0.420 ft

Teakettle Ridge SE 44.625 -71.125 -0.344 ft Dummer Ponds SE 44.625 -71.25 -0.361 ft

29

Table 9: Vertical Datum Conversions Single Conversion Factor (countywide) Method (Cont.)

Quadrangle Name Corner

NAD83 Latitude

(dec. deg.)

NAD83 Longitude (dec. deg.)

NGVD29 to NAVD88 Elevation Change

Percy Peaks SE 44.625 -71.375 -0.377 ft Stratford SE 44.625 -71.5 -0.410 ft

Errol SE 44.75 -71.125 -0.259 ft Errol SW 44.75 -71.25 -0.256 ft

Blue Mountain SE 44.75 -71.375 -0.236 ft Blue Mountain SW 44.75 -71.5 -0.367 ft

Bloomfield SE 44.75 -71.625 -0.292 ft Wilsons Mills SW 44.875 -71.125 -0.276 ft

Diamond Pond SE 44.875 -71.25 -0.256 ft Lovering Mountain SE 44.875 -71.375 -0.197 ft

Monadnock Mountain SE 44.875 -71.5 -0.292 ft Magalloway Mountain SE 45 -71.125 -0.200 ft

Lake Francis SE 45 -71.25 -0.236 ft Pittsburg SE 45 -71.375 -0.308 ft

Pittsburg OE E SE 45 -71.5 -0.331 ft Second Connecticut

Lake SE 45.125 -71.125 -0.194 ft Cowen Hill SE 45.125 -71.25 -0.240 ft

Metallak Mountain SE 45.125 -71.375 -0.354 ft Prospect Hill SE 45.25 -71.125 -0.354 ft

Greeley Brook SE 45.25 -71.25 -0.358 ft Crawford Notch SE 44.125 -71.375 -0.197 ft

Wild River SE 44.25 -71 -0.246 ft Twin Mountain SE 44.25 -71.5 -0.184 ft Twin Mountain SW 44.25 -71.625 -0.243 ft

Shelburne SE 44.375 -71 -0.472 ft Miles Pond SE 44.375 -71.75 -0.328 ft

Success Pond SE 44.5 -71 -0.322 ft Stone Mountain SE 44.5 -71.625 -0.436 ft

B Pond SW 44.625 -71 -0.367 ft Umbagog Lake North SE 44.75 -71 -0.364 ft

Wilsons Mills SE 44.875 -71 -0.262 ft Greeley Brook SW 45.25 -71.375 -0.341 ft

Range of Conversion Values -0.472 through -0.098 Average Conversion Values -0.301 Max Offset from the average conversion value 0.203

For more information on NAVD88, see the FEMA publication entitled Converting the National Flood Insurance Program to the North American Vertical Datum of 1988 (FEMA, June 1992), or contact the Vertical Network Branch, National Geodetic Survey, Coast and Geodetic Survey, National Oceanic and Atmospheric Administration, Silver Spring, Maryland 20910. (Internet address http://www.ngs.noaa.gov.)

Temporary vertical monuments are often established during the preparation of a flood hazard analysis for the purpose of establishing local vertical control.

http://www.ngs.noaa.gov/�

30

Although these monuments are not shown on the FIRM, they may be found in the Technical Support Data Notebook associated with this FIS and FIRM. Interested individuals may contact FEMA to access this data.

4.0

The NFIP encourages the State and local governments to adopt sound floodplain management programs. Therefore, each FIS provides 1-percent-annual-chance flood elevations and delineations of the 1- and 0.2-percent-annual-chance floodplain boundaries and 1-percent-annual-chance floodway to assist communities in developing floodplain management measures. This information is presented on the FIRM and in many components of the FIS report, including Flood Profiles and Floodway Data Tables. Users should reference the data presented in the FIS report as well as additional information that may be available at the local map repository before making flood elevation and/or floodplain boundary determinations.

FLOODPLAIN MANAGEMENT APPLICATIONS

4.1 Floodplain Boundaries

In order to provide a national standard without regional discrimination, the 1-percent-annual-chance flood has been adopted by FEMA as the base for floodplain management purposes. The 0.2-percent-annual-chance floods are employed to indicate additional areas of flood risk in the community. For each stream studied by detailed methods, the 1- and 0.2-percent-annual-chance floodplain boundaries have been delineated using the flood elevations determined at each cross-section.

Between cross-sections for Androscoggin River, Clear Stream, Clement Brook, Dead River from its confluence with Androscoggin River to approximately 5,000 feet upstream of Hillside Avenue, Greenough Brook, Moose Brook, Moose Brook split, Moose River, Peabody River, and Tinker Brook the 1- and 0.2-percent-annual-chance floodplain boundaries were delineated using a Triangulated Irregular Network (TIN) created from topographic information developed from LiDAR flown in the fall of 2009 that supports the generation of 2 foot contours.

All other study streams were not updated for this countywide update. Between cross-sections for all other studied streams the 1-percent-annual-chance floodplain boundaries were delineated using USGS orthquauds with a twenty foot contour interval.

The 1- and 0.2-percent-annual-chance floodplain boundaries are shown on the FIRM (published separately). On this map, the 1-percent-annual-chance floodplain boundary corresponds to the boundary of the areas of special flood hazards (Zones A and AE); and the 0.2-percent-annual-chance floodplain boundaries correspond to the boundary of the areas of moderate flood hazards (Zone X). In cases where the 1- and 0.2-percent-annual-chance floodplain boundaries are close together, only the 1-percent-annual-chance floodplain boundary has been shown on the Exhibit 2 (published separately). Small areas within the floodplain boundaries may lie above the flood elevations but cannot be shown due to limitations of the map scale and/or lack of detailed topographic data.

31

For the streams studied by approximate methods, only the 1-percent-annual-chance floodplain boundary is shown on Exhibit 2 (published separately).

4.2 Floodways

Encroachment on floodplains, such as structures and fill, reduces flood-carrying capacity, increases flood heights and velocities, and increases flood hazards in areas beyond the encroachment itself. One aspect of floodplain management involves balancing the economic gain from floodplain development against the resulting increase in flood hazard. For purposes of the NFIP, a floodway is used as a tool to assist local communities in this aspect of floodplain management. Under this concept, the area of the 1-percent-annual-chance floodplain is divided into a floodway and a floodway fringe. The floodway is the channel of a stream, plus any adjacent floodplain areas, that must be kept free of encroachment so that the 1-percent-annual-chance flood can be carried without substantial increases in flood heights. Minimum standards of FEMA limit such increases in flood heights to 1.0 foot, provided that hazardous velocities are not produced. The floodways in this study are presented to local agencies as minimum standards that can be adopted directly or used as a basis for additional floodway studies.

The floodways presented in this FIS and on the FIRMs were directly obtained from the previous FIS reports in the Floodway Data Tables or for new detailed study reaches were calculated as part of this Countywide Update. They were computed for certain stream segments on the basis of equal conveyance reduction from each side of the floodplain. Floodway widths were computed at cross-sections. Between cross-sections, the floodway boundaries were interpolated. The results of the floodway computations were tabulated at selected cross-sections in Table 10. In cases where the floodway and 1-percent-annual-chance floodplain boundaries are either close together or collinear, only the floodway boundary has been shown.

No floodway was computed for portions of the Connecticut River and for Moose River from 2,500 feet upstream of Main Street to 1,700 feet upstream of private drive; therefore, no floodways are shown in the study for those streams.

The area between the floodway and the 1-percent-annual-chance floodplain boundaries is termed the floodway fringe. The floodway fringe encompasses the portion of the floodplain that could be completely obstructed without increasing the water surface elevation of the 1-percent-annual-chance flood more than 1.0 foot at any point. Typical relationships between the floodway and the floodway fringe and their significance to floodplain development are shown inFigure 1.

The floodways in this report are recommended to local agencies as minimum standards that can be adopted or used as a basis for additional studies.

32

Figure 1. Floodway Schematic

MEANSECTION VELOCITY

WIDTH AREA (FEET PER WITHOUT WITH INCREASEDISTANCE 1 (FEET) (SQ. FEET) SECOND) REGULATORY FLOODWAY FLOODWAY (FEET)

833 280 4,406 6.4 691.6 691.6 692.0 0.48,052 731 7,346 3.8 695.5 695.5 696.5 1.0

11,551 1091 9,527 3.0 696.6 696.6 697.5 0.913,879 379 4,852 5.8 697.8 697.8 698.8 1.018,015 348 5,349 5.3 701.0 701.0 702.0 1.018,566 252 3,462 8.1 701.4 701.4 702.3 0.920,690 658 6,110 4.6 703.7 703.7 704.6 0.926,064 764 5,221 5.4 709.9 709.9 710.8 0.930,720 1504 6,900 4.1 716.1 716.1 717.1 1.033,049 247 2,756 10.2 720.8 720.8 721.6 0.834,087 415 3,464 8.1 724.1 724.1 724.5 0.437,984 1476 18,350 1.5 746.1 746.1 746.5 0.442,730 807 8,384 2.9 746.3 746.3 746.7 0.444,233 785 7,134 3.4 746.7 746.7 747.2 0.548,960 366 2,019 11.8 763.4 763.4 764.2 0.849,672 502 3,196 7.5 774.2 774.2 774.7 0.555,752 283 2,813 8.5 785.0 785.0 785.7 0.760,611 184 2,365 10.1 795.0 795.0 795.4 0.461,062 242 2,748 8.7 795.9 795.9 796.6 0.763,869 721 3,298 7.3 817.4 817.4 817.4 0.069,883 288 2,784 8.6 826.1 826.1 826.1 0.076,858 216 1,971 11.2 851.5 851.5 851.7 0.278,934 435 2,133 10.4 912.2 912.2 912.2 0.081,915 341 5,053 4.4 916.0 916.0 916.2 0.2

COOS COUNTY, NH(ALL JURISDICTIONS) Androscoggin River

RSTUVW

GH

P

IJKLMN

CROSS SECTIONAndroscoggin River

AB

O

CDEF

FLOODING SOURCE FLOODWAY1-PERCENT-ANNUAL-CHANCE FLOOD

WATER SURFACE ELEVATION(FEET NAVD)

Q

1 Stream distance in feet above Oxford Maine County Boundary

TAB

LE 10

FEDERAL EMERGENCY MANAGEMENT AGENCYFLOODWAY DATA

X



83,147 361 3,222 6.9 930.8 930.8 930.9 0.183,498 370 2,690 8.2 932.1 932.1 932.2 0.187,208 259 1,567 14.1 991.7 991.7 991.7 0.087,607 640 12,528 1.8 1010.6 1010.6 1010.6 0.090,406 82 1,065 20.8 1045.9 1045.9 1045.9 0.091,615 155 1,730 12.8 1081.4 1081.4 1081.4 0.092,579 670 7,415 3.0 1087.8 1087.8 1088.5 0.793,099 813 3,330 6.6 1098.3 1098.3 1098.3 0.094,623 700 4,443 5.0 1102.2 1102.2 1102.6 0.496,949 301 3,819 5.8 1103.6 1103.6 1103.9 0.399,493 446 5,439 4.1 1104.8 1104.8 1105.1 0.3

105,192 286 4,591 4.8 1106.1 1106.1 1106.6 0.5113,112 799 8,795 2.5 1108.2 1108.2 1108.7 0.5121,144 334 6,492 3.2 1109.2 1109.2 1109.9 0.7129,019 763 8,473 2.4 1110.1 1110.1 1110.7 0.6131,621 306 6,240 3.3 1110.3 1110.3 1111.0 0.7136,340 381 7,688 2.7 1111.0 1111.0 1111.6 0.6145,621 352 7,251 2.9 1111.7 1111.7 1112.3 0.6152,252 255 2,906 7.1 1112.5 1112.5 1113.2 0.7156,792 389 2,339 8.9 1132.4 1132.4 1132.5 0.1160,210 196 1,688 12.3 1143.4 1143.4 1143.5 0.1163,260 122 1,958 10.6 1155.0 1155.0 1155.4 0.4163,387 540 4,349 4.8 1169.9 1169.9 1169.9 0.0170,280 1876 14,656 1.4 1170.7 1170.7 1171.1 0.4173,094 972 9,449 2.2 1170.9 1170.9 1171.4 0.5

TAB

LE 10

(Continued)

Androscoggin River

1 Stream distance in feet above Oxford Maine County Boundary

FEDERAL EMERGENCY MANAGEMENT AGENCYFLOODWAY DATACOOS COUNTY, NH

(ALL JURISDICTIONS)

AGAHAIAJ

AMAN

AT


Y

AOAP

AEAF

FLOODWAY

AAABACAD

Z

1-PERCENT-ANNUAL-CHANCE FLOODWATER SURFACE ELEVATION

(FEET NAVD)

AUAV

AKAL

FLOODING SOURCE

AW

AQARAS


WIDTH AREA (FEET PER WITHOUT WITH INCREASEDISTANCE (FEET) (SQ. FEET) SECOND) REGULATORY FLOODWAY FLOODWAY (FEET)

180,270 1 560 6,238 3.3 1173.4 1173.4 1174.4 1.0186,380 1 1074 6,355 3.3 1174.1 1174.1 1175.0 0.9194,379 1 258 3,914 5.3 1178.6 1178.6 1179.2 0.6200,604 1 194 3,258 6.4 1181.1 1181.1 1181.5 0.4208,816 1 313 5,642 3.7 1184.1 1184.1 1184.6 0.5212,540 1 180 2,068 10.0 1184.5 1184.5 1185.2 0.7212,564 1 180 2,568 8.1 1187.4 1187.4 1188.0 0.6220,066 1 204 2,451 8.4 1193.6 1193.6 1193.9 0.3226,094 1 285 4,787 4.3 1197.2 1197.2 1197.5 0.3232,144 1 317 3,078 6.7 1201.7 1201.7 1201.9 0.2239,818 1 246 2,358 8.8 1210.8 1210.8 1211.1 0.3244,819 1 205 2,850 7.3 1216.8 1216.8 1216.9 0.1252,866 1 293 4,842 4.3 1221.9 1221.9 1222.1 0.2254,796 1 300 4,669 4.4 1222.1 1222.1 1222.5 0.4255,485 1 177 1,739 11.9 1226.7 1226.7 1226.7 0.0258,349 1 571 10,997 1.9 1230.5 1230.5 1230.5 0.0

850 2 45 398 17.0 864.4 860.4 3 860.4 3 0.0900 2 260 3,249 2.1 866.6 866.6 866.6 0.0

1,483 2 26 331 20.4 866.6 866.6 866.6 0.01,550 2 300 4,079 1.7 873.2 873.2 873.2 0.02,630 2 227 1,463 4.6 873.3 873.3 873.4 0.12,700 2 267 1,829 3.7 874.1 874.1 874.1 0.0

TAB

LE 10


Androscoggin River, Bog Brook

F

COOS COUNTY, NH(ALL JURISDICTIONS)

DE

1 Feet above Oxford Maine County Boundary 2 Feet above confluence with Connecticut River 3 Elevation computed without consideration of backwater effects from the Connecticut River

AX

BK

BIBJ

Bog BrookABC

AYAZBABBBCBDBEBFBGBH

BLBM


(Continued)





4,728 1 320 976 6.9 902.0 902.0 902.0 0.04,800 1 355 3,667 1.8 904.8 904.8 904.8 0.05,900 1 185 845 8.0 904.8 904.8 904.8 0.08,900 1 240 1,243 5.4 928.1 928.1 928.7 0.6

11,150 1 230 713 6.1 951.0 951.0 951.0 0.013,380 1 206 711 6.2 978.0 978.0 978.6 0.613,450 1 140 672 6.5 979.1 979.1 979.3 0.216,276 1 280 727 6.0 1032.4 1032.4 1032.5 0.116,350 1 220 754 5.8 1034.1 1034.1 1034.1 0.017,485 1 262 811 5.4 1062.5 1062.5 1062.5 0.017,550 1 325 854 5.1 1064.5 1064.5 1064.6 0.1

530 2 109 489 5.6 976.1 976.1 976.5 0.42,050 2 350 1,370 2.0 978.6 978.6 979.6 1.03,320 2 127 806 3.4 984.0 984.0 984.9 0.9

620 3 115 410 3.9 977.6 977.6 978.4 0.82,040 3 70 229 7.0 982.9 982.9 983.6 0.73,300 3 135 229 7.0 994.2 994.2 994.8 0.64,895 3 72 182 8.8 1009.0 1009.0 1009.5 0.55,730 3 130 281 5.7 1016.1 1016.1 1016.8 0.76,810 3 18 88 15.1 1036.6 1036.6 1036.8 0.2

COOS COUNTY, NH

Bog Brook, Burnside Brook, Caleb Brook

OPQ

Burnside Brook

(ALL JURISDICTIONS)

1 Feet above confluence with Connecticut River 2 Feet above confluence with Caleb Brook 3 Feet above confluence with Otter Brook

TAB

LE 10


LM

E

N

D

Bog Brook (Continued)

JK



GH

CBA

CROSS SECTION

CCaleb Brook

I

F

AB



7,540 1 35 180 7.4 1052.1 1052.1 1052.1 0.08,430 1 70 155 8.6 1059.2 1059.2 1059.6 0.49,350 1 36 87 9.9 1073.7 1073.7 1074.0 0.3

10,200 1 38 77 11.2 1088.9 1088.9 1089.2 0.312,800 1 45 83 10.4 1132.0 1132.0 1132.3 0.313,760 1 45 83 10.4 1151.1 1151.1 1151.4 0.314,730 1 31 148 5.8 1179.3 1179.3 1179.3 0.015,570 1 25 63 13.6 1203.2 1203.2 1203.2 0.016,570 1 38 96 9.0 1240.1 1240.1 1240.1 0.0

1,506 2 128 1,196 9.3 1222.1 1218.4 3 1219.3 3 0.91,661 2 220 1,416 7.8 1222.1 1220.6 3 1220.9 3 0.32,838 2 949 4,699 2.4 1223.3 1223.3 1224.0 0.72,862 2 935 5,234 2.1 1223.6 1223.6 1224.2 0.63,845 2 605 3,930 2.8 1224.3 1224.3 1224.7 0.44,875 2 623 4,489 2.5 1225.5 1225.5 1226.3 0.84,890 2 622 4,379 2.5 1225.5 1225.5 1226.4 0.95,740 2 779 4,881 2.3 1226.0 1226.0 1226.8 0.87,640 2 643 3,814 2.9 1226.6 1226.6 1227.5 0.9

I

Clear StreamABC

TAB

LE 10

FEDERAL EMERGENCY MANAGEMENT AGENCY

ML

G

FLOODWAY DATACOOS COUNTY, NH(ALL JURISDICTIONS) Caleb Brook, Clear Stream


(FEET NAVD)

NO

Caleb Brook

K

HI

CROSS SECTION

FLOODING SOURCE FLOODWAY

F

GH

J

E

1 Feet above confluence with Otter Brook 2 Feet above confluence with the Androscoggin River 3 Elevation computed without considering backwater effects from Androscoggin River

D



1,829 1 43 261 4.4 700.5 699.0 3 700.0 3 1.01,959 1 35 200 5.8 700.5 699.6 3 700.1 3 0.53,104 1 48 250 4.6 702.0 702.0 702.7 0.73,240 1 58 297 3.9 703.0 703.0 703.7 0.73,826 1 50 190 6.1 704.6 704.6 704.9 0.34,813 1 47 148 7.9 709.6 709.6 709.9 0.36,104 1 39 72 5.9 726.4 726.4 726.6 0.2

23,952 2 1,500 / 770 4 12,684 3.8 847.2 847.2 848.2 1.027,952 2 400 / 330 4 8,764 5.5 847.7 847.7 848.6 0.931,152 2 290 / 210 4 6,260 7.7 848.4 848.4 849.3 0.931,492 2 560 / 520 4 9,451 5.1 849.7 849.7 850.5 0.834,282 2 2,000 / 264 4 12,684 3.8 850.0 850.0 850.8 0.841,702 2 2,560 / 2,480 4 15,063 3.2 850.3 850.3 851.2 0.949,592 2 2,176 / 913 4 10,711 4.5 850.7 850.7 851.5 0.855,432 2 2,185 / 1,670 4 12,684 3.8 851.2 851.2 852.0 0.859,332 2 730 / 550 4 9,094 5.3 851.5 851.5 852.2 0.762,332 2 1,574 / 1,499 4 9,426 4.7 852.0 852.0 852.8 0.867,822 2 3,064 / 1,852 4 19,261 2.3 852.5 852.5 853.2 0.774,262 2 2,550 / 1,520 4 15,276 2.9 852.6 852.6 853.4 0.8

FLOODWAY DATACOOS COUNTY, NH(ALL JURISDICTIONS) Clement Brook, Connecticut River

TA

BLE

10


DEFGHI

CROSS SECTION

Connecticut RiverABC

A

G

CD

FLOODWAY1-PERCENT-ANNUAL-CHANCE FLOOD


FLOODING SOURCE

J

E

B

1 Feet above confluence with the Androscoggin River 2 Feet above Bridge Hill Road 3 Elevation computed without considering backwater effects from Androscoggin River 4 Width/Width Within Corporate (County) Limits

Clement Brook

KL

F


WIDTH 3 AREA (FEET PER WITHOUT WITH INCREASEDISTANCE 1 (FEET) (SQ. FEET) SECOND) REGULATORY FLOODWAY FLOODWAY (FEET)

78,642 2,025 / 1,985 10,302 4.3 852.7 852.7 853.6 0.985,052 672 / 188 8,686 5.1 853.3 853.3 854.1 0.886,122 672 / 193 8,686 5.1 853.3 853.3 854.1 0.889,972 527 / 527 8,686 5.1 854.1 854.1 854.9 0.8

177,458 1,010 / 215 5,919 5.1 864.6 2 861.8 862.6 0.8178,038 144 / 140 2,834 10.6 864.9 2 862.1 863.1 1.0178,108 761 / 175 5,796 5.2 865.3 2 863.5 864.4 0.9182,308 1,950 / 1,940 10,878 2.8 869.4 2 866.7 867.3 0.6188,908 2,754 / 2,620 17,981 1.7 871.8 2 868.9 869.3 0.4199,658 1,713 / 1,180 14,519 2.1 874.1 2 871.4 871.9 0.5206,153 618 / 610 6,503 4.6 875.6 2 872.5 873.1 0.6211,403 1,108 / 1,070 9,816 3.1 877.9 2 874.6 875.2 0.6216,983 200 / 195 3,793 7.5 880.7 2 877.3 878.1 0.8219,258 725 / 435 9,570 3.0 882.5 2 879.4 880.3 0.9227,418 1,591 / 1,575 13,886 2.0 887.8 2 883.3 883.9 0.6229,208 330 / 320 3,882 7.2 888.9 2 883.9 884.5 0.6231,178 852 / 840 7,220 3.9 892.3 2 887.2 887.8 0.6234,028 230 / 225 3,466 8.0 896.5 2 891.3 891.7 0.4236,288 250 / 245 3,284 7.0 900.6 2 895.3 895.9 0.6236,678 318 / 280 3,671 6.3 901.1 2 896.0 896.7 0.7

Connecticut River

W

AC

MNOPQ

CROSS SECTION

1 Feet above Bridge Hill Road 2 Water surface elevation affected by ice jam condition 3 Width/Width Within Corporate (County) Limits

TA

BLE 10


(ALL JURISDICTIONS) Connecticut River



AA

AE

Z

AB

AD

XY

UV

RST

AF



236,858 1 418 / 385 5 4,396 5.3 901.5 4 896.7 897.4 0.7236,943 1 465 / 460 5 5,087 4.6 901.5 4 896.9 897.6 0.7238,123 1 305 / 185 5 2,377 9.7 902.9 4 897.8 898.4 0.6241,923 1 455 / 155 5 3,534 6.6 910.1 4 907.2 907.9 0.7244,693 1 440 / 435 5 2,992 7.7 920.5 4 917.9 918.0 0.1247,693 1 550 / 126 5 4,340 5.3 930.8 4 928.4 928.6 0.2

NA NA NA NA NA NA NA NA

495 2 15 79 13.1 964.1 964.1 964.6 0.5714 2 20 105 10.0 967.5 967.5 968.5 1.0938 2 17 86 12.1 971.0 971.0 971.2 0.2953 2 32 234 4.4 973.3 973.3 974.2 0.9998 2 54 228 4.6 973.4 973.4 974.2 0.8

1,171 2 16 81 12.8 979.3 979.3 979.3 0.01,357 2 26 217 4.8 989.5 989.5 989.5 0.01,478 2 61 309 3.4 989.8 989.8 989.8 0.01,509 2 58 270 3.9 989.8 989.8 989.8 0.01,706 2 24 111 9.4 990.1 990.1 990.2 0.11,934 2 19 163 6.4 995.0 995.0 995.0 0.02,035 2 18 163 6.4 995.4 995.4 995.4 0.0

1 Feet above Bridge Hill Road 2 Feet above confluence with the Androscoggin River 3 No Floodway Computed for Cross Section AM-BO 4 Water Surface Elevation affected by Ice Jam condition5 Width/Width Within Corporate (County) Limits

TA

BLE

10


AI

CROSS SECTION

DE

HI

AM - BO 3

(ALL JURISDICTIONS) Connecticut River, Dead River

G

L

Dead River

AL

FLOODWAY DATACOOS COUNTY, NH

J

BC


(FEET NAVD)

AJAK

F

AGConnecticut River

K

A

AH




2,207 64 397 2.6 996.3 996.3 996.4 0.12,381 76 390 2.7 996.6 996.6 997.3 0.72,698 46 116 9.0 1013.2 1013.2 1013.2 0.02,715 53 217 4.8 1015.5 1015.5 1015.5 0.03,330 39 415 2.5 1034.1 1034.1 1035.1 1.04,982 38 207 5.0 1046.3 1046.3 1046.8 0.55,112 59 240 4.3 1048.8 1048.8 1048.8 0.05,617 54 241 4.3 1049.7 1049.7 1049.8 0.18,050 304 1,913 0.5 1050.0 1050.0 1050.7 0.79,040 310 1,338 0.7 1050.0 1050.0 1050.9 0.99,160 280 1,157 0.8 1050.0 1050.0 1050.8 0.8

10,570 190 951 0.9 1050.0 1050.0 1050.8 0.811,060 140 465 1.8 1050.1 1050.1 1050.9 0.811,090 80 385 2.2 1051.2 1051.2 1051.9 0.711,870 250 1,413 0.6 1051.6 1051.6 1052.3 0.712,950 380 1,940 0.4 1051.6 1051.6 1052.5 0.714,810 150 398 2.1 1051.7 1051.7 1052.7 0.916,580 300 550 1.6 1052.7 1052.7 1052.9 1.0

18,310 130 181 2.4 1056.0 1056.0 1056.4 0.219,510 80 153 2.8 1058.8 1058.8 1058.8 0.419,540 80 484 0.9 1062.2 1062.2 1062.2 0.020,300 191 126 3.4 1066.7 1066.7 1066.7 0.0

S

V

X

AD

N

R

U

OP

AC

W

YZ

AA

Q

AB

M

T

Dead River, Jericho Brook

1 Feet above confluence with the Androscoggin River

TAB

LE 10


(ALL JURISDICTIONS)

Jericho BrookAEAFAG



FLOODING SOURCE

CROSS SECTIONDead River

AH



507 1 150 513 2.3 1226.1 1222.5 3 1223.5 3 1.0641 1 50 230 5.1 1226.1 1222.6 3 1223.5 3 0.9750 1 24 174 6.7 1226.1 1223.3 3 1223.8 3 0.5776 1 24 149 7.8 1226.1 1224.4 3 1225.4 3 1.0809 1 56 412 2.8 1226.1 1225.9 3 1226.7 3 0.8

1,645 1 130 875 1.3 1226.1 1226.1 1227.0 0.93,268 1 45 239 4.8 1226.5 1226.6 1227.5 0.93,304 1 69 491 2.4 1229.4 1229.4 1230.4 1.0

300 2 24 19 6.2 852.3 837.1 4 837.1 4 0.0895 2 23 41 2.9 852.3 843.3 4 843.4 4 0.1

1,265 2 13 67 1.8 852.3 849.0 4 849.0 4 0.01,485 2 13 80 1.5 852.3 851.1 4 851.1 4 0.01,800 2 16 67 1.8 852.3 851.1 4 851.1 4 0.02,040 2 15 55 2.2 852.3 851.2 4 851.2 4 0.02,8102 15 82 1.4 858.1 858.1 858.1 0.02,8852 28 144 0.8 858.1 858.1 858.1 0.03,2602 18 88 1.3 858.1 858.1 858.1 0.03,3522 14 61 1.9 858.6 858.6 858.6 0.04,2202 13 50 2.3 858.6 858.6 859.2 0.6K

Indian Brook

IJ

1 Feet above confluence with Clear Stream 2 Feet above confluence with Connecticut River 3 Elevation computed without consideration of backwater effects from the Clear Stream 4 Elevation computed without consideration of backwater effects from the Connecticut River

TA

BLE

10


(ALL JURISDICTIONS) Greenough Brook, Indian Brook

H

BCDEFG

CROSS SECTION

A

HG



EF

Greenough BrookAB

DC



5,530 55 144 1.8 860.2 860.2 861.2 1.06,870 10 33 7.8 886.4 886.4 886.7 0.37,970 17 32 8.1 931.1 931.1 931.1 0.0

2,820 1,590 8,204 2.8 851.6 844.2 2 845.2 2 1.05,600 775 3,235 7.1 852.6 852.6 852.6 0.06,200 570 2,864 8.0 853.6 853.6 854.2 0.67,230 570 2,671 8.6 856.4 856.4 857.1 0.77,700 400 2,486 9.2 858.6 858.6 859.2 0.68,175 151 1,436 16.0 859.2 859.2 859.2 0.08,505 136 2,167 10.6 867.1 867.1 867.1 0.08,880 187 2,033 11.3 869.0 869.0 869.3 0.39,480 213 1,898 12.1 874.1 874.1 874.3 0.2

10,130 155 1,320 17.4 885.0 885.0 885.0 0.010,450 146 1,492 15.4 886.5 886.5 886.6 0.111,100 202 2,069 11.1 892.3 892.3 892.7 0.412,950 124 1,436 16.0 906.6 906.6 906.8 0.214,790 80 1,727 13.3 921.1 921.1 921.5 0.415,400 468 2,671 8.6 923.8 923.8 924.4 0.620,130 572 2,610 5.8 930.3 930.3 931.0 0.7

LM

TA

BLE 10


(ALL JURISDICTIONS) Indian Brook, Israel River

ABCD

L

E

P

CROSS SECTION

Israel River



N

Indian Brook

IJK

MN

H

1Feet above confluence with Connecticut River 2 Elevation computed without considering backwater effects from Connecticut River

G

O

F



653 68 349 7.4 798.4 798.4 798.4 0.0739 117 386 6.7 801.5 801.5 801.5 0.0

1,802 38 197 13.1 822.5 822.5 822.5 0.01,909 105 600 4.3 829.3 829.3 830.1 0.82,926 115 339 7.6 842.2 842.2 842.2 0.03,763 52 324 7.9 860.7 860.7 860.7 0.05,557 139 419 6.1 888.4 888.4 888.4 0.07,213 47 238 10.8 908.5 908.5 908.6 0.17,345 34 248 10.4 910.8 910.8 910.9 0.18,649 28 161 9.6 924.2 924.2 924.4 0.28,766 152 1,232 1.3 928.8 928.8 929.0 0.29,329 38 139 11.1 931.9 931.9 931.9 0.09,449 55 227 11.3 937.3 937.3 937.3 0.09,517 100 327 4.7 938.5 938.5 938.5 0.09,991 42 144 10.7 956.1 956.1 956.1 0.010,111 163 580 2.7 963.4 963.4 963.4 0.011,758 33 133 11.6 1013.9 1013.9 1013.9 0.012,206 47 148 10.4 1028.7 1028.7 1028.8 0.112,322 106 469 3.3 1037.0 1037.0 1037.6 0.612,839 48 175 8.8 1046.8 1046.8 1046.8 0.012,987 51 165 9.3 1050.5 1050.5 1050.6 0.113,524 95 195 7.9 1068.5 1068.5 1068.5 0.013,617 120 435 3.5 1072.2 1072.2 1072.2 0.014,757 50 94 6.5 1097.4 1097.4 1097.5 0.114,912 60 422 1.5 1111.5 1111.5 1112.4 0.915,657 17 58 10.4 1128.5 1128.5 1128.8 0.3

CROSS SECTION

TAB

LE 10


(ALL JURISDICTIONS) Moose Brook



1 Feet above confluence with the Androscoggin River

X

K

Y

N

CDEFG

W

H

V

LM

BA

IJ

Moose Brook

OPQ

Z

RSTU



172 1 20 142 7.3 928.2 928.2 928.9 0.7240 1 23 162 6.4 929.2 929.2 929.8 0.6667 1 20 113 9.2 933.9 933.9 934.6 0.7757 1 49 317 3.3 936.7 936.7 937.0 0.3

1135 2 58 408 11.1 794.1 794.1 794.7 0.61986 2 75 563 8.1 801.7 801.7 802.0 0.32399 2 84 518 8.8 806.5 806.5 806.5 0.04064 2 77 392 11.6 826.5 826.5 826.7 0.2

NA NA NA NA NA NA NA NA

6,930 3 135 826 5.3 933.0 933.0 933.0 0.09,180 3 150 973 4.5 936.0 936.0 936.9 0.9

10,700 3 65 274 16.0 954.4 954.4 954.7 0.311,540 3 205 876 5.0 958.8 958.8 959.3 0.513,010 3 65 569 7.7 963.2 963.2 963.5 0.313,685 3 55 289 14.0 964.0 964.0 964.6 0.614,220 3 185 810 5.0 967.4 967.4 968.1 0.715,650 3 365 1,446 2.8 969.7 969.7 970.7 1.0

TA

BLE

10


1 Feet above confluence with Moose Brook 2 Feet above confluence with the Androscoggin River 3 Feet above confluence with Israel River 4 No Floodway Computed for cross section E-G

FLOODWAY DATACOOS COUNTY, NH(ALL JURISDICTIONS) Moose Brook Split, Moose River, Otter Brook

BCDEFG

CROSS SECTION

Otter BrookA

E-G 4

BCD



Moose RiverABCD

Moose Brook SplitA

H



2,772 1 137 1,052 14.3 775.1 775.1 775.5 0.42,880 1 140 1,306 11.5 778.4 778.4 778.4 0.04,176 1 99 980 15.3 791.7 791.7 792.1 0.44,233 1 136 1,238 12.1 793.7 793.7 794.0 0.34,944 1 90 857 17.5 805.9 805.9 805.9 0.06,798 1 124 942 15.9 837.7 837.7 837.7 0.08,370 1 163 1,156 13.0 864.1 864.1 864.1 0.09,433 1 153 1,048 14.3 877.7 877.7 877.7 0.1

10,195 1 170 1,270 11.8 888.3 888.3 889.3 1.012,496 1 164 1,215 12.4 919.2 919.2 920.2 1.012,592 1 151 1,363 11.0 923.1 923.1 923.1 0.014,220 1 123 952 15.8 948.3 948.3 948.7 0.416,142 1 100 928 16.2 975.6 975.6 976.6 1.018,156 1 163 1,541 9.7 1002.1 1002.1 1003.1 1.020,371 1 114 971 15.5 1038.9 1038.9 1039.0 0.121,872 1 114 971 15.5 1060.5 1060.5 1060.7 0.2

950 2 30 143 4.4 1072.3 1072.3 1073.1 0.81,540 2 26 55 11.4 1084.0 1084.0 1084.3 0.32,510 2 27 50 12.7 1115.6 1115.6 1115.9 0.33,620 2 30 217 2.9 1153.0 1153.0 1153.1 0.1

TA

BLE

10


(ALL JURISDICTIONS) Peabody River, Redman Brook

ABCD


CROSS SECTION

Redman Brook


(FEET NAVD)

OP

A

DE

1 Feet above confluence with the Androscoggin River 2 Feet above confluence with Caleb Brook

FG

Peabody River

B

N

HIJKLM

C



176 1 20 140 4.3 848.3 848.3 848.9 0.61,418 1 48 81 7.4 862.0 862.0 862.0 0.01,724 1 11 163 3.7 888.9 888.9 889.8 0.91,939 1 46 544 1.1 915.0 915.0 915.1 0.12,522 1 18 119 5.0 915.1 915.1 915.1 0.02,614 1 34 422 1.4 923.9 923.9 923.9 0.02,637 1 31 273 2.2 923.9 923.9 923.9 0.03,938 1 89 120 5.0 1060.5 1060.5 1060.5 0.05,141 1 47 79 7.6 1109.1 1109.1 1109.1 0.06,724 1 15 55 10.9 1206.5 1206.5 1207.1 0.6

1,550 2 275 859 3.7 993.6 993.6 994.5 0.92,820 2 155 612 5.2 1004.3 1004.3 1005.0 0.75,380 2 259 711 3.6 1014.3 1014.3 1015.2 0.96,090 2 70 301 8.5 1021.2 1021.2 1021.6 0.4

TA

BLE

10


(ALL JURISDICTIONS) Tinker Brook, Whipple Brook



Whipple BrookABCD

FLOODING SOURCE

CROSS SECTION

B

1 Feet above confluence with the Androscoggin River 2 Feet above confluence with Burnside Brook

IJ

Tinker Brook

CDEFGH

A

48

5.0

For flood insurance rating purposes, flood insurance zone designations are assigned to a community based on the results of the engineering analyses. These zones are as follows:

INSURANCE APPLICATION

Zone A The flood insurance risk zone that corresponds to the 1-percent-annual-chance floodplains that are determined in the FIS by approximate methods. Because detailed hydraulic analyses are not performed for such areas, no BFEs or base flood depths are shown within this zone.

Zone AE The flood insurance risk zone that corresponds to the 1-percent-annual-chance floodplains that are determined in the FIS by detailed methods. In most instances, whole-foot BFEs derived from the detailed hydraulic analyses are shown at selected intervals within this zone.

Zone X The flood insurance risk zone that corresponds to areas outside the 0.2-percent-annual-chance floodplain, areas within the 0.2-percent-annual-chance floodplain, areas of 1-percent-annual-chance flooding where average depths are less than 1 foot, areas of 1-percent-annual-chance flooding where the contributing drainage area is less than 1 square mile, and areas protected from the 1-percent-annual-chance flood by levees. No BFEs or base flood depths are shown within this zone.

6.0

The FIRM is designed for flood insurance and floodplain management applications.

FLOOD INSURANCE RATE MAP (FIRM)

The FIRM for Coos County is, for insurance purposes, the principal result of the FIS. Exhibit 2 (published separately) contains the official delineation of flood insurance zones and BFE lines. BFE lines show the locations of the expected whole-foot WSELs of the base flood. This map is developed in accordance with the latest flood insurance map preparation guidelines published by FEMA.

For flood insurance applications, the map designates flood insurance rate zones as described in Section 5.0 and, in the existing conditions 1-percent-annual-chance floodplains that were studied by detailed methods, shows selected whole-foot BFEs or average depths. Insurance agents use the zones and BFEs for existing conditions in conjunction with information on structures and their contents to assign premium rates for flood insurance policies.

For floodplain management applications, the map shows by tints, screens and symbols, the 1- and 0.2-percent-chance-annual floodplains. Floodways for the 1-percent-annual-chance flood extent and the locations of selected cross-sections used in the hydraulic analyses and floodway computations are shown where applicable.

49

The current FIRM presents flooding information for the entire geographic area of Coos County. Previously, separate FIRMs were prepared for each incorporated community and for the unincorporated areas of the county with identified special flood hazard areas. Historical data relating to the maps prepared for each community are presented in Table 11.

7.0

Since it is based on more up-to-date analyses, this FIS supersedes previously printed FIS reports for Coos County, New Hampshire. This FIS also supersedes the Flood Boundary and Floodway Maps for Coos County that were printed as part of previous FISs. The information on the Flood Boundary and Floodway Maps has been added to the FIRM accompanying this FIS. This report either supersedes or is compatible with all previous studies published on the streams studies in this report and should be considered authoritative for the purposes of the NFIP.

OTHER STUDIES

8.0

Information concerning the pertinent data used in preparation of this study can be obtained by contacting the FEMA Region I, Mitigation Division, 99 High Street, Sixth Floor, Boston, Massachusetts 02110.

LOCATION OF DATA

Future revisions may be made that do not result in the republishing of the FIS Report. To ensure that any user is aware of all revisions, it is advisable to contact the map repository of flood hazard data located in the community.

FLOOD HAZARDCOMMUNITY INITIAL BOUNDARY MAP FIRM FIRM

NAME IDENTIFICATION REVISION DATE(S) EFFECTIVE DATE REVISION DATE(S)

Berlin, City of July 19, 1974 August 27, 1976 June 15, 1982 NoneCarroll, Town of January 24, 1975 November 12, 1976 April 15, 1986 NoneClarksville, Town of January 3, 1975 None February 20, 2013 NoneColebrook, Town of May 20, 1977 None May 17, 1989 NoneColumbia, Town of January 3, 1975 None April 2, 1986 NoneCoos County (Unincorporated Areas) February 20, 2013 None February 20, 2013 NoneDalton, Town of December 4, 1985 None December 4, 1985 NoneDummer, Town of January 17, 1975 None March 1, 1995 NoneErrol, Town of January 17, 1975 None June 1, 1995 April 16, 2003Gorham, Town of March 1, 1974 July 30, 1976 April 1, 1981 May 2, 1994Jefferson, Town of June 28, 1974 February 21, 1975 April 15, 1986 None

September 10, 1976July 19, 1977

Lancaster, Town of April 13, 1973 None April 13, 1973 July 1, 1974December 12, 1975

April 1, 1982Milan, Town of June 28, 1974 None April 2, 1986 July 17, 2006Northumberland, Town of February 22, 1974 April 18, 1975 May 4, 1989 NonePittsburg, Town of January 31, 1975 January 7, 1977 February 20, 2013 NoneRandolph, Town of January 3, 1975 None February 20, 2013 NoneShelburne, Town of November 29, 1974 None April 2, 1986 NoneStark, Town of November 29, 1974 December 3, 1976 April 2, 1986 NoneStewartstown, Town of January 10, 1975 None March 1, 2000 NoneStratford, Town of July 26, 1974 October 3, 1975 April 18, 1983 NoneWhitefield, Town of July 26, 1974 November 26, 1976 April 2, 1986 None

September 21, 1979

TA

BL

E 11


COMMUNITY MAP HISTORYCOOS COUNTY, NH

(ALL JURISDICTIONS)

51

9.0

1. Flood Insurance Study, City of Berlin, Coos County, New Hampshire, December 15, 1981.

BIBLIOGRAPHY AND REFERENCES

2. Flood Insurance Study, Town of Colebrook, Coos County, New Hampshire, May 17, 1989.

3. Flood Insurance Study, Town of Errol, Coos County, New Hampshire, April 16, 2003.

4. Flood Insurance Study, Town of Gorham, Coos County, New Hampshire, May 2, 1994.

5. Flood Insurance Study, Town of Lancaster, Coos County, New Hampshire, October 1, 1981.

6. Flood Insurance Study, Town of Milan, Coos County, New Hampshire, July 17, 2006.

7. Flood Insurance Study, Town of Northumberland, Coos County, New Hampshire, May 4, 1989.

8. Flood Insurance Study, Town of Stratford, Coos County, New Hampshire, October 18, 1982.

9. Flood Insurance Study, Town of Bloomfield, Essex County, Vermont, June 3, 1991.

10. Flood Insurance Study, Town of Canaan, Essex County, Vermont, March, 1980.

11. U.S. Census Bureau’s 2008 and 2009 Population Estimates retrieved August 4, 2010, from http://factfinder.census.gov.

12. US Department of the Interior, Geological Survey. NH – Basin Characteristics, Gage 01052500 on the Diamond River near Wentworth Location

13. US Army Corps of Engineers, New England Division,

, New Hampshire, 1941 – 1995.

Local Protection Project Isreal River Lancaster, New Hampshire – Detailed Project Report

14. US Department of Agriculture, Soil Conservation Service,

, Waltham, Massachusetts, September 1973.

Soils and the Interpretations for Various Land Uses, Town of Lancaster, Coos County, New Hampshire

15. US Department of the Interior, Geological Survey, Water-Supply Paper 798,

, Washington, D.C., July 1977.

The Floods of March 1936, Part 1, New England

16. US Department of the Interior, Geological Survey, Water-Supply Paper 1301,

, Washington, D.C., 1937

Compilation of Records of Surface Waters through September 1950, Part 1-A, North Atlantic Slope Basins, Maine to Connecticut, Washington, D.C., 1954.

http://factfinder.census.gov/�

52

17. New England-New York Inter-Agency Committee, The Resources of the New England-New York Region, Androscoggin River Basin

18. Michael Hickey, North County Council, Franconia, New Hampshire, Personal Communication, 1978.

, New York, 1953.

19. US Department of Agriculture, Soil Conservation Service, Flood Hazard Analysis, Town of Lancaster, Coos County, New Hampshire

20. State of New Hampshire, Department of Resources and Economic Development,

, Washington, D.C., September 1973.

Public Water Supply, Phase 1 Report,

21. US Army Corps of Engineers, New England Division,

Concord, New Hampshire, 1969.

Local Ice-Jam Flood Control Project Isreal River – Revised Supplement to Detailed Project Report

22. US Department of the Interior, Geological Survey, Water Resources Investigations 78-47,

, Waltham, Massachusetts, February 1978.

Progress Report on Hydrologic Investigations of Small Drainage Areas in New Hampshire, Preliminary Relations for Estimating Peak Discharges of Rural, Unregulated Streams,

23. U.S. Department of the Interior, Geological Survey, Interagency Advisory Committee on Water Data, Office of Water Data Coordination, Hydrology Subcommittee, Bulletin No. 17B,

Washington, D.C., 1978.

Guidelines for Determining Flood Flow Frequency

24. US Department of the Interior, Geological Survey, Water Resources Investigations 99-4008,

, September 1981, revised March 1982.

Estimating the Magnitude of Peak Flows for Streams in Main for Selected Recurrence Intervals,

25. US Department of the Interior, Geological Survey, Open File Report, A

Augusta, Maine, G. Hodgkins (Author) 1999.

Technique for Estimating the Magnitude and Frequency of Floods in Maine

26. Water Resources Council,

, R.A. Morrill (Author), Washington, D.C., 1975.

Guidelines for Determining Flood Flow Frequency, Bulletin 17,

27. US Department of Agriculture, Soil Conservation Service,

Washington, D.C., March, 1976.

National Engineering Handbook, Section 4, Hydrology

28. US Department of the Interior, Geological Survey, National Water Data Storage and Retrieval System,

, Washington, D.C., August, 1972.

WATSTORE Peak Flow File

29. Water Resources Council,

, Reston, Virginia, September, 1984.

Guidelines for Determining Flood Flow Frequency, Bulletin 17A,

30. Olson, S.A., USGS,

June, 1977.

Estimation of Flood Discharges at Selected Recurrence Intervals for Streams in New Hampshire by 2009, Scientific Investigations Report (SIR) 2008-5206.). 2009.

53

31. US Department of Agriculture, Soil Conservation Service, Dead River Watershed Project, Berlin, Coos County, New Hampshire

32. US Department of the Interior, Geological Survey, Open File Report,

, Washington, D.C., 1968.

Computer Applications for the Step-Backwater and Floodway Analysis

33. US Department of the Interior, Geological Survey,

, James O Shearman (Author), Washington, D.C., 1976.

Methods of Determining limits of Inundation by 100-year Frequency Flood-Prone Areas Maps

34. US Department of the Interior, Geological Survey, 15-minute Series Topographic Maps, Scale 1:62,500, Contour interval 20 feet: Averill, Vermont, 1953; Dixville, Vermont, 1930.

, unpublished.

35. State of New Hampshire, Department of Public Works, Highway Design Division, Topographic Maps, Scale 1:2,400, Contour interval 5 fee: Town of Gorham, Coos County, New Hampshire, 1964, Town of Shelburne, Coos County, New Hampshire, 1964.

36. US Department of Agriculture, Soil Conservation Service, Technical Release No. 61, WSP-2 Computer Program

37. US Department of the Interior, Geological Survey, 15-minute Series Topographic Maps, Scale 1:62,500, Contour interval 20 feet: Guildhall, Vermont, 1956; Percy, Vermont, 1930.

, Washington, D.C., May, 1976.

38. US Army Corp of Engineers, Hydrologic Engineering Center, Computer Program 723-X6-1202A, HEC-2 Water Surface Profiles

39. Moore Survey and Mapping, of Maps compiled from Aerial photographs, Scale 1:9,600, Contour interval of 5 feet: Town of Startford, New Hampshire, May 1980.

, Davis California, December 1968, updated 1980 – experimental modification 99.4 for Ice Cover Analysis.

40. U.S. Army Corps of Engineers, Topographic Engineering Center, retrieved on March 20, 2009, from http://crunch.tec.army.mil/software/corpscon/corpscon.html.

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THE 2-PERCENT-ANNUAL-CHANCE FLOOD PROFILE IS

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FLOOD INSURANCE STUDY - GRANIT

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