Prepared in cooperation with the New Hampshire Department of Transportation

U.S. Department of the Interior

U.S. Geological Survey

Flood Study of Warren Brook in Alstead and Cold River in 

Alstead, Langdon, and Walpole, New Hampshire, 2005

Open-File Report 2006–1313 
Cover.  Photograph shows the confluence of Warren Brook (right) and Cold River (left) during the October 8–9, 2005 flood.

(Photograph courtesy of the New Hampshire State Police Aviation Unit)
Flood Study of Warren Brook in Alstead 

and Cold River in Alstead, Langdon, and 

Walpole, New Hampshire, 2005

By Robert H. Flynn

Prepared in cooperation with the New Hampshire Department of Transportation

Open-File Report 2006–1313

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2006

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Flynn, R.H., 2006, Flood study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, 

New Hampshire, 2005: U.S. Geological Survey Open-File Report 2006-1313, 48 p.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................1

Authority and Background ..................................................................................................................1

Coordination...........................................................................................................................................2

Previous Studies ...................................................................................................................................2

Flood Recovery Study Methods .........................................................................................................2

Description of the Study Area ............................................................................................................2

Principal Flood Problems Along Warren Brook and Cold River.............................................................4

Flood-Protection Measures Affecting Warren Brook and Cold River ..................................................4

Engineering Methods Used to Determine Flood Data .............................................................................4

Hydrologic Analyses.............................................................................................................................5

Hydraulic Analyses...............................................................................................................................6

Flood-Plain Management Applications......................................................................................................6

Summary........................................................................................................................................................11

References Cited..........................................................................................................................................11

Appendix 1: Cold River Flood Profiles......................................................................................................17

Appendix 2: Warren Brook Flood Profiles...............................................................................................27

Appendix 3: Elevation Reference Marks.................................................................................................47

Figures

1–5. Maps showing—

1. Extent of the flood insurance study of Cold River and Warren Brook in 

Alstead, Langdon, and Walpole, New Hampshire .........................................................3

2. Location of cross sections along Cold River in Walpole and Langdon, 

New Hampshire .................................................................................................................12

3. Location of cross sections along Cold River in Alstead and Langdon, 

New Hampshire .................................................................................................................13

4. Location of cross sections along Warren Brook in Alstead, New Hampshire........14

5. Location of cross sections along Warren Brook in Alstead, New Hampshire........15

Tables

1. Summary of the drainage area-peak relations for streams in New Hampshire, 

studied by detailed methods.......................................................................................................5

2. Manning’s “n” values for Cold River and Warren Brook .......................................................6

3. Cross sections and flood data for Cold River in Alstead, Langdon, and 

Walpole, New Hampshire............................................................................................................7

4. Cross sections and flood data for Warren Brook in Alstead, New Hampshire..................9
iv

OTHER ABBREVIATIONS USED IN REPORT

CCO Consultation Coordination Officer

FEMA Federal Emergency Management Agency

FIA Federal Insurance Administration

FIRM Flood Insurance Rate Map

FIS Flood Insurance Study

GIS Geographical Information System

HEC-RAS Hydrologic Engineering Center–River Analysis System

NH New Hampshire

NHDOT New Hampshire Department of Transportation

NFIP National Flood Insurance Program

NOAA National Oceanic and Atmospheric Administration

SFHA Special Flood Hazard Area

USACE U.S. Army Corps of Engineers

USGS U.S. Geological Survey

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.589 square kilometer (km2) 

square mile (mi2) 0.929 square meter (m2)

Volume

cubic foot (ft3) 0.02832 cubic meter (m3) 

Flow rate

foot per second (ft/s) 0.3048 meter per second (m/s)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Conversion Factors, Abbreviations, and Datum
Abstract

This report presents water-surface elevations and profiles 

as determined using the U.S. Army Corps of Engineers 

(USACE) one-dimensional Hydrologic Engineering Center 

River Analysis System, also known as HEC-RAS. Steady flow 

water-surface profiles were developed for two stream reaches: 

the Cold River from its confluence with the Connecticut River 

in Walpole, through Alstead to the McDermott Bridge in 

Langdon, NH, and Warren Brook from its confluence with the 

Cold River to Warren Lake in Alstead, NH. Flood events of a 

magnitude, which are expected to be equaled or exceeded once 

on the average during any 10-, 50-, 100-, or 500-year period 

(recurrence interval), were modeled using HEC-RAS as these 

flood events are recognized as being significant for floodplain management, determination of flood insurance rates, and 

design of structures such as bridges and culverts. These flood 

events are referred to as the 10-, 50-, 100-, and 500-year floods 

and have a 10-, 2-, 1-, and 0.2-percent chance, respectively, 

of being equaled or exceeded during any year. The recurrence 

intervals represent the long-term average between floods of 

a specific magnitude. The risk of experiencing rare floods 

at short intervals or within the same year increases when 

periods greater than one year are considered. The analyses in 

this study reflect the flooding potentials based on conditions 

existing in the communities of Walpole, Alstead and Langdon 

at the time of completion of this study.

Introduction

On October 8 and 9, 2005, significant flooding occurred 

in southwestern New Hampshire (NH) as a result of rainfall in 

excess of 7 in. within a 24-hour period. Unverified accounts 

stated that as much as 11 in. of rain fell in the Alstead, NH, 

area. The National Oceanic and Atmospheric Administration 

(NOAA) recorded 7.68 in. of rain during October 8–9, 

2005, at the precipitation station in Keene, NH (National 

Weather Service, 2005). Upstream from Alstead, on Warren 

Brook, the failure of a culvert and a road embankment 

that was impounding a significant amount of floodwater 

also contributed to severe flooding along Warren Brook 

and downstream on the Cold River in Alstead, Langdon, 

and Walpole. The current effective Federal Emergency 

Management Agency (FEMA) Flood Insurance Rate Maps 

(FIRM) (Alstead, 1986; Langdon, 1975; and Walpole, 2000) 

contain both detailed and approximately determined 100-

year (Zone A) special-flood-hazard areas that are no longer 

considered valid. In order to guide redevelopment and the 

replacement of damaged infrastructure and the allocation 

of appropriate State and Federal recovery resources, and to 

ensure that effective mitigation measures are in place to avoid 

future flood losses, it is essential that reliable and timely 

information on flood elevations be established for these rivers.

Purpose and Scope

This recovery study report provides flood elevations for 

the Cold River and Warren Brook to aid in the redevelopment 

and the replacement of infrastructure damaged in the October 

2005 flood and the allocation of appropriate State and Federal 

recovery resources, and to ensure that effective mitigation 

measures are in place to avoid future flood losses. The 

results of this study can also be used to update the previous 

flood insurance studies (FISs) and FIRMs for the towns of 

Alstead and Walpole, NH, and flood hazard boundary map 

for Langdon (Federal Emergency Management Agency, 1986, 

2000, 1975, respectively). This information can be used to 

update existing flood-plain regulations as part of the National 

Flood Insurance Program (NFIP). The minimum flood-plain 

management requirements for participation in the NFIP are set 

forth in the Code of Federal Regulations at 44 CFR, 60.3. The 

information also can be used by local and regional planners to 

further promote sound land-use and flood-plain development.

Authority and Background

The sources of authority for a flood insurance study 

are the National Flood Insurance Act of 1968 and the Flood 

Disaster Protection Act of 1973. On October 26, 2005, 

President George W. Bush declared five counties in New 

Hampshire to be a major disaster area as a result of the 

flooding that occurred on October 8–9, 2005. For the 2005 

FIS, the hydrologic and hydraulic analyses for the Cold River 

Flood Study of Warren Brook in Alstead and Cold River in 

Alstead, Langdon, and Walpole, New Hampshire, 2005

By Robert H. Flynn
and Warren Brook were conducted by the U.S. Geological 

Survey (USGS) in cooperation with the New Hampshire 

Department of Transportation (NHDOT) under agreement 

number 06E4NH24500017. This work was completed in 

April 2006.

The hydrologic and hydraulic analyses from the 1980 

FIS for the Cold River conducted by Environmental Engineers, 

Inc., for the Federal Insurance Administration (FIA) under 

contract number H-4590, were used for the May 4, 2000, 

FIS and FIRM for Walpole, NH. The 1980 FIS work was 

completed in October 1978. The FIS report was dated 

October 15, 1980, and the FIRM was dated April 15, 1981. 

The extent of the 1978 study along Cold River was limited to 

an approximately 1-mi reach above its confluence with the 

Connecticut River.

There are no FIS reports for the towns of Alstead and 

Langdon. For the original April 2, 1986, FIRM in Alstead, 

Zone A flood insurance rate zones were determined along 

Warren Brook and Cold River. Zone A is the flood insurance 

rate zone that corresponds to the 100-year flood-plain and 

is determined in a FIS by approximate methods. Because 

detailed hydraulic analyses are not performed for such areas, 

no base flood elevations or depths are shown within this zone. 

Langdon, NH, is not in FEMA’s NFIP, but special flood hazard 

areas (SFHA) were identified along the Cold River in the 

FIRM dated January 3, 1975.

Coordination

At an initial Consultation Coordination Officer’s (CCO) 

meeting on January 11, 2006, representatives of the NHDOT 

and the USGS discussed the scope of the FIS. Several 

meetings were held subsequently with the town of Alstead 

and representatives of various state agencies—on January 26, 

2006 (at the Alstead town offices) and on February 1, 2006 

(at the site of the former Kmiec’s Garage, which is located at 

the intersection of Route 123 and Route 123A). On March 23, 

2006, a New Hampshire Interagency Mitigation Meeting was 

held at the town library in Alstead.

Previous Studies

A FIS and FIRM was prepared for the town of Walpole 

in May 2000 (Federal Emergency Management Agency, 

2000). At that time, there were no FIS reports for the towns of 

Alstead or Langdon. For the original April 2, 1986, FIRM in 

Alstead, Zone A flood insurance rate zones were determined 

along Warren Brook. Langdon is not included in the FEMA’s 

NFIP, but SFHAs were identified along the Cold River in the 

FIRM dated January 3, 1975.

Because it is based on more up-to-date analyses, this 

FIS supersedes the previously printed flood study data for 

the towns of Walpole, Alstead, and Langdon on the Cold 

River and Warren Brook. This FIS also supersedes the 

flood boundary map for Cold River in the town of Walpole 

(published as part of the previously printed FIS), the Zone A 

flood insurance rate zones along Warren Brook and Cold River 

in Alstead and the SFHAs identified along the Cold River in 

Langdon, NH.

Flood Recovery Study Methods

This flood recovery study includes the Cold River and 

Warren Brook in the incorporated area of the towns of Alstead 

and Walpole in Cheshire County, and the town of Langdon in 

Sullivan County, NH (fig. 1). The Cold River was studied by 

detailed methods from the confluence with the Connecticut 

River to the McDermott covered bridge in Langdon. Warren 

Brook was studied by detailed methods from the confluence 

with Cold River to Warren Lake. Limits of detailed study 

are indicated on the flood profiles (appendixes 1 and 2). The 

areas studied by detailed methods were selected with priority 

given to all known flood hazard areas as well as to areas of 

projected development and proposed construction. The scope 

and methods of study were proposed to, and agreed upon by 

the NHDOT, USGS, and the town of Alstead.

Description of the Study Area

The towns of Walpole and Alstead are located in 

northwestern Cheshire County, which is in southwestern 

New Hampshire (fig. 1). The town of Langdon is in 

southwestern Sullivan County, which also is in southwestern 

New Hampshire. State Route 123 connects the towns of 

Walpole, Langdon, and Alstead.

Walpole is on a mountain-bordered plateau that slopes 

to the south and west. Alstead and Langdon are located in the 

foothills and mountains to the east and northeast of Walpole 

and its plateau. Here, the Cold River bisects the remnants of 

a delta, which extends back to Cock Hat Hill (just south of 

Vilas Pool) east of the Alstead town center, and was formed 

in glacial Lake Hitchcock 10,000 years ago. Terraces on 

either side of the river reveal that the elevation of the top 

of the delta was at an elevation of 492 ft (Cold River Local 

Advisory Committee, 2006). Most of the area is covered by 

glacial till, about two-thirds of which is derived principally 

from granitic rock and one-third from schistose rock. Soils 

developed on this till are naturally stony and, thus, most of 

the area is not suitable for large-scale agricultural activities, 

except in the broad floodplains of streams (Federal Emergency 

Management Agency, 2000).

The population of Alstead in 2004 was 2,019 residents 

(New Hampshire Employment Security, 2005a). Alstead 

contains 39.0 mi2 of land area and 0.4 mi2 of inland water 

area. There are 51.8 persons/mi2 of land area in Alstead. The 

villages of Alstead Center, East Alstead, and Mill Hollow are 

all within the town of Alstead (New Hampshire Employment 

Security, 2005a).

   Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005
Figure 1. Extent of the flood insurance study of Cold River and Warren Brook in Alstead, Langdon, and Walpole, 

New Hampshire.

Introduction 

EXPLANATION

 Study area

 Tributary streams

 State boundary

 Town boundary

 State route

 Approximate area of figures 2-5

 USGS streamgaging station

Walpole

Alstead

Charlestown

Acworth

0 1 2 MILES

0 1 2 KILOMETERS

New

Hampshire

71°

44°

43°

45°

Concord

Manchester

Maine

Massachusetts

Vermont

CANADA

72°

91

123A

12A

12

12A

123

123

Warren Brook

Warren

Lake

McDermott 

 bridge

Connecticut River

72o25' 72o20'

43o10'

43o06'

Cheshire County

Figure 2

Figure 3

Langdon

Sullivan County Cold River

Figure 4

Figure 5

Vilas Pool

Cock Hat

 Hill

Drewsville

Cheshire County

Sullivan County

Mill Hollow

01155000
The 2004 population of Langdon was 637 residents (New 

Hampshire Employment Security, 2005b). Langdon contains 

16.3 mi2 of land area and 0 mi2 of inland water area. There 

are 39.1 persons/mi2 of land area in Langdon. The villages of 

Cold River District and Condon Corner are within the town of 

Langdon (New Hampshire Employment Security, 2005b).

The 2004 population for Walpole was 3,704 residents 

(New Hampshire Employment Security, 2005c). Walpole 

contains 35.7 mi2 of land area and 1.0 mi2 of inland water 

area. There are 103.8 persons/mi2 of land area in Walpole. The 

villages of Drewsville and North Walpole are within the Town 

of Walpole (New Hampshire Employment Security, 2005c).

Principal Flood Problems Along 

Warren Brook and Cold River

Major floods can occur on Warren Brook and Cold River 

during the spring, fall, and winter. Some of the most severe 

flooding occurs in early spring as a result of snow melt and 

heavy rains in conjunction with ice jams. Fall is another 

critical season for flood danger because of typically heavy 

rainfall and the possibility of tropical storms. Flooding can 

occur, however, at any time of the year. Large thunderstorms 

can result in rapid runoff and flooding in the downstream 

portions of small streams (Federal Emergency Management 

Agency, 2000).

Most flooding in the town of Walpole has been from the 

Connecticut River and damaging floods along the Connecticut 

River have been recorded since the 1700s. Principal damaging 

floods of the 20th century occurred in March 1913, November 

1927, March 1936, September 1938, and July 1973.

On October 8 and 9, 2005, significant flooding occurred 

in southwestern New Hampshire as a result of rainfall in 

excess of 7 in. within a 24-hour period. On Warren Brook, 

upstream from the village of Alstead, failure of a culvert 

and a road embankment that was impounding a substantial 

amount of water also contributed to severe flooding along 

Warren Brook and downstream on the Cold River in Alstead, 

Langdon, and Walpole.

Flooding along Warren Brook and the Cold River was 

the worst ever documented in the area. On November 16, 

2005, FEMA authorized the USGS to document the October 

2005 flood event and establish new flood-discharge-frequency 

estimates for the Cold River and Warren Brook (Olson, 2006).

At two discontinued streamgaging stations, Cold River at 

Drewsville and Ashuelot River at Gilsum, high-water marks 

exceeded all previously recorded peak stages by several feet. 

The previously recorded maximum stage and discharge for 

the period of record at the Cold River station (1940–74) were 

12.30 ft and 6,700 ft3/s, respectively. The stage at the Cold 

River station for the October 2005 flood was 23.7 ft, with an 

estimated discharge of 21,800 ft3/s, which greatly exceeded the 

500-year recurrence-interval discharge (12,700 ft3/s) for the 

Cold River (Olson, 2006).

Flood-Protection Measures Affecting 

Warren Brook and Cold River

There are no major flood control structures along the 

streams studied. The Connecticut River, however, is regulated 

by powerplant dams and flood-control reservoirs located on 

the river and its tributaries. These control measures contribute 

a combined usable storage capacity of 24.8 billion ft3 (Federal 

Emergency Management Agency, 2000) for the Connecticut 

River. A small, unregulated dam is located on Cold Brook at 

Vilas Pool upstream from the confluence with Warren Brook. 

Three small, unregulated dams are located on Warren Brook—

at Warren Lake, at an old mill along State Route 123 in Mill 

Hollow, and between State Route 123 and Prentice Hill Road. 

These dams do little to attenuate major flood peaks.

Engineering Methods Used to 

Determine Flood Data

For the flooding sources studied in detail in the FIS 

communities, hydrologic and hydraulic analyses were used 

to determine the flood data required for this FIS. Flood 

events 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 flood-plain management and for flood 

insurance rates. These events, commonly termed the 10-, 50-, 

100-, and 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 

average period between floods of a specific magnitude, floods 

can recur at short intervals and within the same year. The risk 

of experiencing a flood increases when periods greater than 

1 year are considered. For example, the risk of a flood that 

equals or exceeds the 100-year flood (1-percent chance of 

annual exceedence) 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. Maps and flood elevations will need to be amended 

periodically to reflect future changes.

All FISs 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. All flood elevations given in this flood 

recovery study report are referenced to the National Geodetic 

Vertical Datum of 1929 (NGVD 29), unless otherwise noted. 

All structure, flood, and ground elevations in the FIS communities are referenced to NGVD 29 in the FIS profiles.

It is important to note that adjacent communities may 

be referenced to the North American Vertical Datum of 

1988 (NAVD 88), which may result in differences in base 

 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005
flood elevations across the corporate limits between the 

communities.

For more information on NAVD 88, see Converting the 

National Flood Insurance Program to the North American 

Vertical Datum of 1988, FEMA Publication FIA-20/June 

1992, or contact the Vertical Network Branch, National 

Geodetic Survey, Coast and Geodetic Survey, National 

Oceanic and Atmospheric Administration, Rockville, 

Maryland 20910 (Internet address http://www.ngs.noaa.gov).

A description of the reference marks used in this study 

is presented in Elevation Reference Marks (appendix 3). 

Elevation reference marks are referenced to NGVD 29.

Hydrologic Analyses

Hydrologic analyses were used to establish the peak 

discharge-frequency relations for the Cold River and Warren 

Brook. For the May 2000 revision of the flood study for 

Walpole, NH, the USACE performed an analysis of ice jams 

along the Connecticut River. The analysis of ice-jam flooding 

required the development of elevation-frequency curves for 

ice-jam events and free-flow events. The data were plotted 

using Weibull plotting positions (rank/(n+1)) to develop the 

ice-jam elevation-frequency curve for two locations along the 

Connecticut River: a trailer park in Charleston and near the 

Cheshire Bridge. The elevation-frequency analysis for freeflowing events was taken from the FIS communities’ flood 

profiles for the Connecticut River. The composite elevationfrequency curve (ice-jam and free-flow) was developed by 

plotting the points on probability paper. For the Cold River 

in Walpole, the 1980 FIS for Walpole developed flood-flow 

frequency data by using a log-Pearson Type III analysis of 

stream frequency-discharge values determined at the USGS 

streamgaging station on the Cold River (streamgaging station 

No. 01155000) in Drewsville, NH (Federal Emergency 

Management Agency, 2000).

For the 2006 revision, peak-flow frequency estimates 

for Warren Brook were estimated by Olson (2006) by using 

peak-flow regression equations published in LeBlanc (1978). 

Basin characteristics used in the regression equations include 

drainage area, mean channel slope, and the 2-year, 24-hour 

rainfall for the basin. Drainage area and mean channel slope 

were determined using a geographic information system 

(GIS), electronic copies of USGS 1:24,000 topographic maps 

(U.S. Geological Survey, 1998a–d), and the National Elevation 

Dataset (U.S. Geological Survey, 2001). The 2-year, 24-hour 

rainfall was determined from Hershfield (1961). Peak-flow 

frequency estimates for the Cold River were estimated by 

Olson (2006) by using a log-Pearson Type III analysis as 

described in “Guidelines for Determining Flood Flow Frequency” (Interagency Advisory Committee on Water Data, 

1982). Data from USGS streamgaging station 01155000 on 

the Cold River at Drewsville, NH, were used for computing 

the frequency curve. A “natural” peak for the October 2005 

event (without the effect of an embankment breach on 

Warren Brook) was determined at the Cold River streamgaging station in Drewsville and added to the dataset before 

analysis (Olson, 2006).

A summary of the drainage area-peak discharge 

relations for the streams studied by detailed methods in this 

FIS revision is given in table 1 (Olson, 2006).

Table 1. Summary of the drainage area-peak relations for streams in New Hampshire, studied by detailed methods.

[mi2, square mile; ft3/s, cubic foot per second]

Flooding source and location Drainage area 

(mi2)

Peak discharges 

(ft3/s)

10-year 50-year 100-year 500-year

Cold River

McDermott Bridge, Langdon 59.2 2,930 4,910 5,980 9,090

Vilas Pool Dam, Alstead 61.3 3,030 5,080 6,190 9,410

Route 123 bridge, village of Alstead 74.6 3,690 6,190 7,530 11,500

USGS streamgaging station 01155000, Drewsville 82.7 4,090 6,860 8,350 12,700

Confluence with Connecticut River 102 5,040 8,460 10,300 15,700

Warren Brook

Mill Hollow 5.21 289 508 615 958

Route 123 temporary bridge 6.21 361 640 776 1,210

Cooper Hill Road 9.24 629 1,140 1,380 2,190

Confluence with Cold River 12.5 805 1,430 1,740 2,710

Engineering Methods Used to Determine Flood Data   
Hydraulic Analyses

Analyses of the hydraulic characteristics of flooding from 

the sources studied were carried out to provide estimates of the 

elevations of floods at the selected recurrence intervals. Cross 

sections for the flooding sources studied by detailed methods 

were obtained from field surveys. Valley and below-water 

portions of the cross-section data obtained for the Cold River 

and Warren Brook for this revision were obtained from field 

measurements. Additional valley portions of cross-section 

data on Warren Brook were obtained from 2-ft contour data 

created by Eastern Topographic in the fall of 2005 (Eastern 

Topographic, 2006) and provided by the NHDOT. All bridges, 

dams, and culverts were field surveyed to obtain elevation 

data and structural geometry. Bridge, dam, and culvert crosssection data collection sites were located at close intervals 

above and below bridges and dams in order to compute the 

significant backwater effects of these structures. Locations 

of selected cross sections used in the hydraulic analyses are 

shown in the flood profiles (appendixes 1 and 2, and in 

figs. 2–5 (in back of report)).

For this FIS revision, water-surface elevations of floods 

for the selected recurrence intervals for the Cold River 

and Warren Brook were computed by using the USACE 

HEC-RAS (U.S. Army Corps of Engineers, 2005). Starting 

water-surface elevations for the Cold River were based on 

normal depth analysis, which is the depth at which flow is 

steady and hydraulic characteristics are uniform. The model 

computational procedure is based on the solution of the onedimensional energy equation (U.S. Army Corps of Engineers, 

2006). Energy losses are evaluated by friction and contraction 

and expansion. The momentum equation is used in situations 

where the water surface is rapidly varied.

Flood profiles were drawn using computed water-surface 

elevations of floods at the selected recurrence intervals. In 

those areas where the analysis indicated supercritical flow 

conditions, critical depth was assumed for the flood elevation 

because of the inherent instability of supercritical flow.

Manning’s “n” roughness factors (Barnes, 1967) used 

in the hydraulic computations were assigned on the basis of 

engineering judgment and field observations of the stream and 

flood-plain areas. Table 2 lists the channel and overbank “n” 

values for the streams studied by detailed methods.

Table 2. Manning’s “n” values for Cold River and Warren Brook.

Stream Channel “n” Overbank “n”

Cold River 0.040–0.070 0.035–0.100

Warren Brook 0.045–0.080 0.030–0.110

The hydraulic analyses for this study were based on an 

assumption of unobstructed flow. Thus, the flood elevations 

shown in the profiles are considered valid if hydraulic 

structures remain unobstructed, operate properly, and do not 

fail. The resulting flood elevations of the HEC-RAS (U.S. 

Army Corps of Engineers, 2005) flood analyses for Cold River 

are shown in table 3, and the results for Warren Brook are 

shown in table 4.

Flood-Plain Management Applications

State and local governments are encouraged by the 

NFIP to adopt sound flood-plain management programs. To 

provide a national standard without regional discrimination, 

the 1-percent annual chance (100-year) flood has been adopted 

by FEMA as the base flood for flood-plain management 

purposes. The 0.2-percent annual chance (500-year) flood 

is used to indicate additional areas of flood risk in the FIS 

communities. Each FIS typically provides 100-year floodplain data, which may include a combination of the following: 

10-, 50-, 100-, and 500-year flood elevations; 100- and 

500-year flood-plain delineations; and 100-year floodway 

delineation. In addition to the data presented in the FIS, it is 

recommended that users reference any additional information 

that may be available before making flood elevation and/or 

floodplain boundary determinations.

 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005
Table 3. Cross sections and flood data for Cold River in Alstead, Langdon, and Walpole, New Hampshire.

[Location of cross sections A–AG are in fig. 2, AH–BL are in fig. 3, where scale permits, and in appendix 1; ft, foot; NGVD 29, National Geodetic 

Vertical Datum of 1929]

Cold River 

cross section

Cumulative 

distance 

upstream

(ft)

Channel 

elevation 

(ft, NGVD 29)

Annual chance flood elevation 

(ft, NGVD 29)

10 percent 

(10-year)

2 percent

(50-year)

1 percent

(100-year)

0.2 percent

(500-year)

A 290.0 226.6 1244.6 1250.2 1252.8 1260.0

B 408.0 219.5 1244.6 1250.2 1252.8 1260.0

C 466.5 219.5 1244.6 1250.2 1252.8 1260.0

D 751.5 226.0 1244.6 1250.2 1252.8 1260.0

E 1,499.5 230.1 1244.6 1250.2 1252.8 1260.0

F 1,582.5 230.7 1244.6 1250.2 1252.8 1260.0

G 1,654.5 230.3 1244.6 1250.2 1252.8 1260.0

H 1,708.5 230.5 1244.6 1250.2 1252.8 1260.0 

I 1,791.5 231.0 1244.6 1250.2 1252.8 1260.0

J 1,871.5 230.5 1244.6 1250.2 1252.8 1260.0

K 2,369.5 234.1 1244.6 1250.2 1252.8 1260.0

L 3,251.5 235.9 245.0 1250.2 1252.8 1260.0

M 5,223.5 247.0 253.2 255.1 255.5 1260.0

N 6,527.5 254.5 263.2 265.4 266.6 268.9

O 7,287.5 258.7 266.4 268.7 269.7 272.1

P 9,382.5 279.4 285.4 287.3 288.2 290.6

Q 10,815.5 285.3 295.9 298.7 299.9 302.8

R 11,955.5 291.2 300.4 303.5 304.8 307.8

S 13,643.5 302.1 310.3 312.3 312.9 314.4

T 15,013.5 310.1 318.2 320.6 321.6 323.6

U 15,968.5 311.9 319.9 322.2 323.2 325.5

V 18,123.5 342.1 346.1 347.7 348.5 350.5

W 18,301.5 353.9 362.1 365.4 367.0 371.2

X 18,349.5 374.2 381.3 383.4 384.4 386.9

Y 18,379.5 374.2 383.6 387.2 388.9 394.4

Z 18,520.5 377.7 384.8 388.6 390.4 395.2

AA 18,565.5 379.9 385.1 388.8 390.6 395.4

AB 19,453.5 383.6 390.4 391.1 392.0 395.8

AC 21,358.5 392.8 398.5 399.9 400.4 401.6

AD 21,893.5 394.3 402.1 403.5 404.0 405.1

AE 22,482.5 397.7 404.7 406.0 406.5 407.7

AF 23,118.5 400.9 408.6 409.4 409.7 410.5

AG 23,923.5 404.6 411.7 412.9 413.4 414.5

AH 25,713.5 417.0 423.0 423.9 424.3 425.3

AI 26,444.5 426.6 431.0 431.9 432.3 433.2

Flood-Plain Management Applications 
Table 3. Cross sections and flood data for Cold River in Alstead, Langdon, and Walpole, New Hampshire.—Continued

[Location of cross sections A–AG are in fig. 2, AH–BL are in fig. 3, where scale permits, and in appendix 1; ft, foot; NGVD 29, National Geodetic 

Vertical Datum of 1929]

Cold River 

cross section

Cumulative 

distance 

upstream

(ft)

Channel 

elevation 

(ft, NGVD 29)

Annual chance flood elevation 

(ft, NGVD 29)

10 percent 

(10-year)

2 percent

(50-year)

1 percent

(100-year)

0.2 percent

(500-year)

AJ 27,831.5 433.6 441.2 442.4 442.9 444.1

AK 28,921.5 442.9 448.9 450.3 450.7 452.3

AL 30,419.5 452.6 461.3 463.7 464.8 467.0

AM 30,591.5 450.5 461.9 464.3 465.3 467.3

AN 30,642.0 450.2 462.1 464.6 465.7 468.0

AO 30,850.0 454.7 464.8 467.6 468.9 472.2

AP 31,588.0 468.1 473.2 474.6 475.4 477.6

AQ 32,609.0 478.5 486.3 487.7 488.3 489.8

AR 33,510.0 490.4 500.1 502.6 504.0 506.6

AS 33,714.0 499.4 506.5 509.3 510.3 513.2

AT 33,965.0 497.8 508.7 511.0 512.1 514.8

AU 34,084.0 503.2 510.3 512.5 513.6 516.5

AV 34,290.0 508.9 514.2 515.7 516.6 518.5

AW 34,925.0 513.0 519.5 520.8 521.1 523.3

AX 35,070.0 515.5 521.9 524.2 525.6 528.4

AY 35,125.0 523.5 539.9 542.4 543.6 545.9

AZ 35,195.0 523.5 539.9 542.4 543.6 545.9

BA 36,205.0 537.0 539.7 542.6 543.8 546.2

BB 36,305.0 537.0 541.7 542.4 543.6 546.1

BC 38,045.0 549.0 556.3 558.3 558.4 558.7

BD 40,530.0 572.9 577.6 578.8 580.3 582.3

BE 42,238.0 589.2 595.1 596.3 596.5 596.8

BF 42,373.0 588.5 595.8 596.8 597.1 597.7

BG 42,407.0 589.8 595.9 597.0 599.4 602.2

BH 42,420.0 589.8 595.9 597.0 599.1 602.1

BI 42,445.0 589.8 596.1 597.5 599.4 602.3

BJ 42,455.0 589.8 596.2 597.6 599.5 602.3

BK 42,465.0 589.8 596.3 597.7 599.6 602.3

BL 42,530.0 590.3 596.6 598.8 600.5 602.8

1

Backwater elevation from the Connecticut River.

 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005
Table 4. Cross sections and flood data for Warren Brook in Alstead, New Hampshire.

[Location of cross sections A–AA are in fig. 4, AB–BD are in fig. 5, where scale permits, and in appendix 2; ft, foot; NGVD 29, National Geodetic 

Vertical Datum of 1929]

Warren Brook 

cross section

Cumulative 

distance 

upstream

(ft)

Channel 

elevation 

(ft, NGVD 29)

Annual chance flood elevation 

(ft, NGVD 29)

10 percent 

(10-year)

2 percent

(50-year)

1 percent

(100-year)

0.2 percent

(500-year)

A 0.0 500.1 509.9 512.4 513.6 516.6

B 89.0 504.2 509.6 512.3 513.5 516.6

C 96.0 504.3 510.3 512.9 514.0 516.6

D 185.5 507.3 511.1 513.2 514.2 516.3

E 222.5 508.2 512.8 514.6 515.4 518.1

F 248.5 508.2 513.4 515.3 516.3 519.9

G 301.5 511.3 515.4 517.6 517.9 520.0

H 846.5 521.2 525.4 526.3 526.7 527.0

I 2,366.5 582.9 586.4 587.2 587.6 588.6

J 2,516.5 588.2 592.9 594.1 594.7 596.1

K 2,664.5 587.2 595.6 597.5 598.2 599.9

L 3,261.5 604.7 608.8 610.6 611.1 611.9

M 4,160.5 629.5 633.6 635.1 635.8 637.3

N 4,578.5 639.7 642.9 644.0 644.5 645.8

O 4,862.5 646.3 649.9 650.7 651.1 651.9

P 4,948.5 649.3 652.0 653.3 653.8 656.8

Q 4,974.5 647.8 653.3 654.9 656.0 658.6

R 5,061.5 650.5 654.4 656.0 656.9 658.7

S 5,851.5 663.8 665.9 666.3 666.5 667.1

T 5,903.5 663.7 667.2 668.5 669.1 671.0

U 5,962.5 663.8 670.3 673.0 673.4 673.8

V 5,994.5 665.0 671.7 673.2 673.5 674.0

W 7,076.5 689.2 691.6 692.2 692.4 693.0

X 8,082.5 708.3 712.4 713.6 714.0 715.1

Y 8,769.5 718.8 721.4 722.6 723.1 724.5

Z 10,221.5 750.9 754.5 755.3 755.8 756.9

AA 11,036.5 775.9 779.5 780.9 781.4 783.4

AB 12,058.5 798.0 800.7 801.8 802.2 803.2

AC 12,208.5 795.5 801.7 803.0 803.5 804.9

AD 12,221.5 796.4 801.4 802.6 803.0 804.1

AE 12,283.5 797.4 802.1 803.6 804.2 805.8

AF 12,386.5 799.8 803.3 804.8 805.3 807.0

AG 13,156.5 804.8 807.9 809.0 809.5 810.9

AH 15,160.5 823.3 826.0 826.4 826.5 826.9

AI 16,741.5 845.6 850.1 851.6 852.1 853.8

Flood-Plain Management Applications   
Table 4. Cross sections and flood data for Warren Brook in Alstead, New Hampshire.—Continued

[Location of cross sections A–AA are in fig. 4, AB–BD are in fig. 5, where scale permits, and in appendix 2; ft, foot; NGVD 29, National Geodetic 

Vertical Datum of 1929]

Warren Brook 

cross section

Cumulative 

distance 

upstream

(ft)

Channel 

elevation 

(ft, NGVD 29)

Annual chance flood elevation 

(ft, NGVD 29)

10 percent 

(10-year)

2 percent

(50-year)

1 percent

(100-year)

0.2 percent

(500-year)

AJ 16,810.5 846.0 850.5 852.1 852.9 854.7

AK 16,902.5 845.8 853.1 853.9 854.2 854.9

AL 16,955.5 845.9 853.3 854.1 854.4 855.2

AM 18,324.5 900.5 902.3 903.0 903.3 904.1

AN 18,414.5 902.1 905.1 905.9 906.3 907.1

AO 18,456.5 902.7 905.5 906.3 906.7 907.4

AP 18,502.5 905.6 910.3 911.5 911.9 912.9

AQ 18,976.5 924.9 927.3 928.3 928.7 929.8

AR 19,342.5 950.4 952.3 953.1 953.4 954.4

AS 20,176.5 1,010.5 1,012.7 1,013.5 1,013.9 1,014.8

AT 21,346.5 1,067.0 1,069.7 1,070.2 1,070.4 1,070.9

AU 21,418.5 1,071.4 1,074.5 1,075.5 1,075.9 1,077.1

AV 21,555.5 1,081.9 1,090.2 1,097.9 1,103.3 1,103.4

AW 21,570.5 1,084.7 1,090.3 1,098.0 1,103.4 1,103.6

AX 22,872.5 1,164.1 1,166.5 1,167.4 1,167.8 1,168.9

AY 22,935.5 1,171.0 1,172.8 1,173.4 1173.7 1,174.4

AZ 22,975.5 1,170.5 1,174.3 1,175.1 1,175.5 1,176.4

BA 23,059.5 1,175.3 1,176.9 1,177.6 1,177.9 1,178.8

BB 23,065.5 1,180.8 1,191.5 1,192.8 1,193.3 1,193.9

BC 23,091.5 1,180.8 1,191.5 1,192.8 1,193.3 1,194.0

BD 23,136.5 1,185.2 1,192.8 1,195.4 1,195.7 1,196.3

BE 23,186.5 1,185.6 1,193.0 1,195.4 1,195.7 1,196.3

BF 23,244.5 1,186.6 1,193.0 1,195.4 1,195.7 1,196.4

BG 23,364.5 1,188.5 1,193.0 1,195.4 1,195.7 1,196.4

BH 23,494.5 1,190.9 1,192.9 1,195.4 1,195.7 1,196.4

BI 23,612.5 1,190.3 1,197.1 1,197.9 1,199.0 1,199.6

BJ 23,632.5 1,190.3 1,198.1 1,199.0 1,199.5 1,200.1

BK 23,667.5 1,192.3 1,198.8 1,199.6 1,199.9 1,200.5

BL 23,698.5 1,192.1 1,198.8 1,199.6 1,200.0 1,200.5

BM 23,732.5 1,192.7 1,199.7 1,200.6 1,200.8 1,201.2

BN 23,776.5 1,193.6 1,199.8 1,200.6 1,200.9 1,201.3

BO 23,791.5 1,193.6 1,201.9 1,202.8 1,203.1 1,203.5

10 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005
Summary

Rainfall in excess of 7 inches resulted in severe flooding 

on October 8 and 9, 2005, along Warren Brook in Alstead, 

NH, and Cold River in Walpole, Alstead, and Langdon, NH. 

This flood recovery study was undertaken to help guide 

redevelopment and the replacement of damaged infrastructure, 

allocate appropriate State and Federal recovery resources, and 

ensure that effective mitigation measures are in place to avoid 

future flood losses.

Water surface elevations and profiles as determined using 

the U.S. Army Corps of Engineers (USACE) one-dimensional 

Hydrologic Engineering Center River Analysis System, also 

known as HEC-RAS (U.S. Army Corps of Engineers, 2005) 

are presented in this report. 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) were modeled using HEC-RAS as these flood 

events have been selected as being significant for flood-plain 

management, determination of flood insurance rates, and 

design of structures such as bridges and culverts. The analyses 

in this study reflect the flooding potentials based on conditions 

existing in the communities of Walpole, Alstead, and Langdon 

at the time of completion of this study.

References Cited

Barnes, H.H., Jr., 1967, Roughness characteristics of natural 

channels: U.S. Geological Survey Water-Supply Paper 

1849, 213 p.

Cold River Local Advisory Committee, 2006, A detailed geological history of the Cold River, accessed on October 23, 

2006, at http://www.coldriver.org/geology.htm.

Eastern Topographic, 2006, Alstead preliminary plan view 

with two-foot contours of combined SDR and aerial survey, 

January 12, 2006, scale 1:1,2000.

Federal Emergency Management Agency, 1975, Flood hazard 

boundary map, town of Langdon, Sullivan County, New 

Hampshire: Washington, D.C., January 3, 1975.

Federal Emergency Management Agency, 1986, Flood Insurance Rate Map, town of Alstead, Cheshire County, New 

Hampshire: Washington, D.C., April 2, 1986.

Federal Emergency Management Agency, 2000, Flood Insurance Rate Map and Flood Insurance Study, town of Walpole, Cheshire County, New Hampshire: Washington, D.C., 

May 4, 2000.

Hershfield, D.M., 1961, Rainfall frequency atlas of the United 

States for durations from 30 minutes to 24 hours and return 

periods from 1 to 100 years: U.S. Department of Commerce Weather Bureau Technical Paper No. 40, 61 p.

Interagency Advisory Committee on Water Data, 1982, Guidelines for determining flood flow frequency, Bulletin 17-B of 

the hydrology subcommittee: Reston, VA, U.S. Geological 

Survey, Office of Water Data Coordination, 183 p.

LeBlanc, D.R., 1978, Progress report on hydrologic investigations of small drainage areas in New Hampshire—preliminary relations for estimating peak discharges on rural, 

unregulated streams: U.S. Geological Survey WaterResources Investigations Report 78–47, 10 p.

National Weather Service, 2005, Daily climate data, 

accessed May 4, 2006, at http://www.erh.noaa.gov/er/box/

dailystns.shtml.

New Hampshire Employment Security, Economic and Labor 

Market Information Bureau, 2005a, Community profiles 

(Alstead), accessed March 27, 2006, at http://www.nhes.

state.nh.us/elmi/htmlprofiles/alstead.html.

New Hampshire Employment Security, Economic and Labor 

Market Information Bureau, 2005b, Community profiles 

(Langdon), accessed March 27, 2006, at http://www.nhes.

state.nh.us/elmi/htmlprofiles/langdon.html.

New Hampshire Employment Security, Economic and Labor 

Market Information Bureau, 2005c, Community profiles 

(Walpole), accessed March 27, 2006, at http://www.nhes.

state.nh.us/elmi/htmlprofiles/walpole.html.

Olson, S.A., 2006, Flood of October 8–10, 2005, on Warren 

Brook in Alstead and the Cold River in Alstead, Langdon 

and Walpole, New Hampshire: U.S. Geological Survey 

Open-File Report 2006–1221.

U.S. Army Corps of Engineers, 2005, Hydrologic Engineering 

Center-River Analysis System (HEC-RAS), Davis, CA, 

v. 3.1.3, May 2005.

U.S. Army Corps of Engineers, 2006, Hydrologic Engineering Center-River Analysis System (HEC-RAS), HEC-RAS 

Philosophy, accessed March 29, 2006, at http://www.hec.

usace.army.mil/software/hec-ras/.

U.S. Geological Survey, 1998a, Alstead, New Hampshire 

7.5-minute series quadrangle map: U.S. Geological Survey 

Topographic Map, scale 1:24,000.

U.S. Geological Survey, 1998b, Bellows Falls, VermontNew Hampshire 7.5 minute series quadrangle map: U.S. 

Geological Survey Topographic Map, scale 1:24,000.

U.S. Geological Survey, 1998c, Gilsum, New Hampshire 

7.5-minute series quadrangle map: U.S. Geological Survey 

Topographic Map, scale 1:24,000.

U.S. Geological Survey, 1998d, Walpole, New HampshireVermont 7.5-minute series quadrangle map: U.S. Geological Survey Topographic Map, scale 1:24,000.

U.S. Geological Survey, 2001, National Elevation Dataset, 

accessed February 16, 2006, at http://edcnts12.cr.usgs.

gov/ned/.

Summary 11
Figure 2. Location of cross sections along Cold River in Walpole and Langdon, New Hampshire. Cross section locations, in relation 

to streambed and flood profiles, are shown in appendix 1. Cross sections X and Y are not shown on figure 2, but are shown in 

appendix 1-6. Approximate location of figure 2 is shown in figure 1.

12 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

12

123

123

A-C

D

E-I

J

Connectic

ut River

K

L

M

N O

Q

P

R

S

T U

V-Z

AA

AB AC

AD

AE

AF

AG

Great Brook

EXPLANATION

 Cross section

 USGS streamgaging station

 01155000 at Drewsville

X Elevation benchmark 

 4611-0100 at Drewsville

72°26' 72°25'

43°07'

72°24' 72°23'

43°08'

43°09'

E

E’

F

F’

G

G’

H

H’

I

I’

J

J’

V

V’

W

W’

Z

Z’

AB

AB’

0

0

1,000 2,000 FEET

250 500 METERS

AA’

AA

Langdon

Walpole

VT NH

Drewsville

X

Drewsville

X

01155000

01155000

Cold River
Figure 3. Location of cross sections along Cold River in Alstead and Langdon, New Hampshire. Cross section locations, in 

relation to streambed and flood profiles, are shown in appendix 1. Cross sections AM, AN, AX, AY, and BB, BF, and BK, are 

not shown on figure 3, but are shown in appendixes 1-6, 1-7, and 1-9. Approximate location of figure 3 is shown in figure 1.

Figures 13

0

0

1,000 2,000 FEET

250 500 METERS

72°23' 72°22' 72°21'

43°09'

43°10'

AH

AI

AJ

AK

AL AO

AP AQ AR

Cold River

Warren Brook

Cold River

AW

BA

AZ

BC

BD

BE BL

AS

AT’

AS’

AU’

AV’

AT

AU

AV

AT’-AV’

AS

123

123

123A

123

EXPLANATION

 Cross section

X Elevation benchmark 

 C 22 USGS 1926 

 at Alstead Center

Langdon

Alstead

Vilas

Pool

Cock Hat

Hill

12A

Alstead Center

Hill Road

Crane Brook Road

Dam

X

Sullivan County

Cheshire County

Darby Brook
Figure 4. Location of cross sections along Warren Brook in Alstead, New Hampshire. Cross section locations, in 

relation to streambed and flood profiles, are shown in appendix 2. Cross sections D, E, F, and P and Q are not shown on 

figure 4, but are shown in appendixes 2-1 and 1-4. Approximate location of figure 4 is shown in figure 1.

14  Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

72°21' 72°20'

43°09'

43°08'30"

A-C H

Warren Brook

AA

0

0

1,000 2,000 FEET

250 500 METERS

I J K

L

M

N O

R

W

X

Y

Z

S-V

A G B

C

G’

A’ B’

C’

12A

123

S

S’

T

U T’

U’ V

V’

G

Cold River

EXPLANATION

 Cross section

Griffen Road
Figure 5. Location of cross sections along Warren Brook in Alstead, New Hampshire. Cross section locations, in relation to 

streambed and flood profiles, are shown in appendix 2. Cross sections AC, BA, BC, BD, BI, BJ, BL, BM, BN, and BO are not 

shown in figure 5, but in appendixes 2-11, 2-18, and 2-19. Approximate location of figure 5 is shown in figure 1.

Figures 15

AL

72°19' 72°18'

43°08'

43°07'30"

AB

AD

AE AF’

AG

AH

AI

AJ

AK

AM-AP AQ

AR

AS

AT

AU

AV AW

AX

AY-BB

BK

BE-BH

AB

AD

AE

AF AF’

AE’

AD’

AB’

AL

AI AJ

AK

AL’

AI’

AJ’

AK’

AP

AO

AN

AM AP’

AO’

AN’

AM’

AV AW

AT

AU AW’

AV’

AT’

AU’

AX

BK

AY

BH

AZ

BB

BB’

BE

BF

BG

BE’ AX’

AZ’ AY’

BF’ BG’

BH’

BK’

0

0

1,000 2,000 FEET

250 500 METERS

Warren

Lake

Warren Brook

123

123

Cooper Hill

Road

Allen Brook

Camp Brook

Water impounded by Cooper

Hill Road embankment

EXPLANATION

 Cross section

X Elevation benchmark 

 C 24 USGS 1926 

 near Warren Lake

X

Pine Cliff

Road Prentice Hill Rd. Dam

X

Dam

Appendix 1: Cold River Flood Profiles

Appendix 1 17
Figure 1-1.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Cold River in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown in

figure 2.

18 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

A

B

C

D E

F

G

H

I

J

K L

STATE ROUTE 12

STATE ROUTE 123

BACKWATER FROM CONNECTICUT RIVER

CONFLUENCE WITH

CONNECTICUT RIVER

 290 280 270 260 250 240 230 220 210 200 0 400 800 1,200 1,600 2,000 2,400 2,800 3,200 3,600 4,000 4,400 4,800 5,200

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH CONNECTICUT RIVER

ELEVATION, IN FEET (NGVD 29)

COLD RIVER

U.S. GEOLOGICAL SURVEY

01

WALPOLE, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

C

Annual chance flood, in percent

Bridge deckLow chord
Figure 1-2.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Cold River in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown in

figure 2.

Appendix 1 19

COLD RIVER

U.S. GEOLOGICAL SURVEY

02

WALPOLE, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

o

Annual chance flood, in percent

 320 310 300 290 280 270 260 250 240 230

5,200 5,600 6,000 6,400 6,800 7,200 7,600 8,000 8,400 8,800 9,200 9,600 10,000 10,400

M N O

P

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH CONNECTICUT RIVER

ELEVATION, IN FEET (NGVD 29)
Figure 1-3.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Cold River in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown in

figure 2.

20 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

COLD RIVER

U.S. GEOLOGICAL SURVEY

03

WALPOLE AND LANGDON, NH

CHESHIRE AND SULLIVAN COUNTIES

FLOOD PROFILES

350340330320310300290280270260

10,400 10,800 11,200 11,600 12,000 12,400 12,800 13,200 13,600 14,000 14,400 14,800 15,200 15,600

Q R S

T

GREAT BROOK

WALPOLE

LANGDON

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH CONNECTICUT RIVER

ELEVATION, IN FEET (NGVD 29)

CHESHIRE COUNTY

SULLIVAN COUNTY

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

T

Annual chance flood, in percent
Figure 1-4.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Cold River in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown in

figure 2.

Appendix 1 21

COLD RIVER

U.S. GEOLOGICAL SURVEY

04

WALPOLE AND LANGDON, NH

CHESHIRE AND SULLIVAN COUNTIES

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

U

Annual chance flood, in percent

Bridge deckLow chord

 400 390 380 370 360 350 340 330 320 310

15,600 16,000 16,400 16,800 17,200 17,600 18,000 18,400 18,800 19,200 19,600 20,000 20,400 20,800

U V W

X

Y

Z

AA

AB

STATE ROUTE 123 (DREWSVILLE)

USGS STREAMGAGING

STATION 01155000

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH CONNECTICUT RIVER

ELEVATION, IN FEET (NGVD 29)

CHESHIRE COUNTY

SULLIVAN COUNTY

WALPOLE

LANGDON
Figure 1-5.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Cold River in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown in

figures 2 and 3.

22 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

COLD RIVER

U.S. GEOLOGICAL SURVEY

05

WALPOLE, LANGDON, AND ALSTEAD, NH

CHESHIRE AND SULLIVAN COUNTIES

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

AC

Annual chance flood, in percent

WALPOLE

LANGDON

CHESHIRE COUNTY

SULLIVAN COUNTY

SULLIVAN COUNTY LANGDON

CHESHIRE COUNTY ALSTEAD

 460 450 440 430 420 410 400 390 380 370

20,800 21,200 21,600 22,000 22,400 22,800 23,200 23,600 24,000 24,400 24,800 25,200 25,600 26,000

AC AD AE AF AG

AH

DARBY BROOK

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH CONNECTICUT RIVER

ELEVATION, IN FEET (NGVD 29)
Figure 1-6.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Cold River in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown in

figure 3.

Appendix 1 23

COLD RIVER

U.S. GEOLOGICAL SURVEY

06

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

AI

Annual chance flood, in percent

Bridge deckLow chord

 490 480 470 460 450 440 430 420 410 400

26,000 26,400 26,800 27,200 27,600 28,000 28,400 28,800 29,200 29,600 30,000 30,400 30,800 31,200

AI AJ AK

AL A

A

M

N

AO

STATE ROUTE 123 (MAIN ST.)

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH CONNECTICUT RIVER

ELEVATION, IN FEET (NGVD 29)
Figure 1-7.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Cold River in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown in

figure 3.

24 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

COLD RIVER

U.S. GEOLOGICAL SURVEY

07

LANGDON AND ALSTEAD, NH

SULLIVAN AND CHESHIRE COUNTIES

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

AP

Annual chance flood, in percent

TOP OF

DAM

ABUTMENTS

TOP OFDAM

 550 540 530 520 510 500 490 480 470 460

31,200 31,600 32,000 32,400 32,800 33,200 33,600 34,000 34,400 34,800 35,200 35,600 36,000 36,400

AP AQ AR AS AT

AU

AV AW A

A

X

Y

AZ

BA

BB

WARREN BROOK

VILAS POOL DAM

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH CONNECTICUT RIVER

ELEVATION, IN FEET (NGVD 29)

SULLIVAN COUNTY

CHESHIRE COUNTY

LANGDON

ALSTEAD
Figure 1-8.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Cold River in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown in

figure 3.

Appendix 1 25

COLD RIVER

U.S. GEOLOGICAL SURVEY

08

LANGDON, NH

SULLIVAN COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

BC

Annual chance flood, in percent

 620 610 600 590 580 570 560 550 540 530

36,400 36,800 37,200 37,600 38,000 38,400 38,800 39,200 39,600 40,000 40,400 40,800 41,200 41,600

BC

BD

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH CONNECTICUT RIVER

ELEVATION, IN FEET (NGVD 29)
Figure 1-9.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Cold River in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown in

figure 3.

26 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

COLD RIVER

U.S. GEOLOGICAL SURVEY

09

LANGDON, NH

SULLIVAN COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

BE

Annual chance flood, in percent

Bridge deckLow chord

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH CONNECTICUT RIVER

ELEVATION, IN FEET (NGVD 29)

650640630620610600590580570560

41,600 42,000 42,400 42,800 43,200 43,600 44,000 44,400 44,800 45,200 45,600 46,000 46,400 46,800

BE B

B

F

G

B

B

H

I

BJ

BK

BL

CRANE BROOK ROAD

MCDERMOTT COVERED BRIDGE
Appendix 2: Warren Brook Flood Profiles

Appendix 2 27
Figure 2-1.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 4.

28 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

WARREN BROOK

U.S. GEOLOGICAL SURVEY

01

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

C

Annual chance flood, in percent

Bridge deckLow chord

570560550540530520510500490480 0 100 200 300 400 500 600 700 800 900 1,000 1,100 1,200 1,300

A B

C

D E

F

G H

CONFLUENCE WITH COLD RIVER

STATE ROUTE 123A

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)
Figure 2-2.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 4.

Appendix 2 29

WARREN BROOK

U.S. GEOLOGICAL SURVEY

02

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

J

Annual chance flood, in percent

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

610600590580570560550540530520

1,300 1,400 1,500 1,600 1,700 1,800 1,900 2,000 2,100 2,200 2,300 2,400 2,500 2,600

I J
Figure 2-3.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 4.

30 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

WARREN BROOK

U.S. GEOLOGICAL SURVEY

03

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

L

Annual chance flood, in percent

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

650640630620610600590580570560

2,600 2,700 2,800 2,900 3,000 3,100 3,200 3,300 3,400 3,500 3,600 3,700 3,800 3,900

K L
Figure 2-4.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 4.

Appendix 2 31

WARREN BROOK

U.S. GEOLOGICAL SURVEY

04

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

O

Annual chance flood, in percent

Bridge deckLow chord

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

690680670660650640630620610600

3,900 4,000 4,100 4,200 4,300 4,400 4,500 4,600 4,700 4,800 4,900 5,000 5,100 5,200

M N O

P

Q

R

GRIFFEN ROAD
Figure 2-5.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 4.

32 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

WARREN BROOK

U.S. GEOLOGICAL SURVEY

05

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

S

Annual chance flood, in percent

Bridge deckLow chord

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

720710700690680670660650640630

5,200 5,300 5,400 5,500 5,600 5,700 5,800 5,900 6,000 6,100 6,200 6,300 6,400 6,500

S T U V

STATE ROUTE 123
Figure 2-6.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 4.

Appendix 2 33

WARREN BROOK

U.S. GEOLOGICAL SURVEY

06

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

W

Annual chance flood, in percent

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

740730720710700690680670660650

6,500 6,600 6,700 6,800 6,900 7,000 7,100 7,200 7,300 7,400 7,500 7,600 7,700 7,800

W
Figure 2-7.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 4.

34 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

WARREN BROOK

U.S. GEOLOGICAL SURVEY

07

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

X

Annual chance flood, in percent

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

770760750740730720710700690680

7,800 7,900 8,000 8,100 8,200 8,300 8,400 8,500 8,600 8,700 8,800 8,900 9,000 9,100

X Y
Figure 2-8.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 4.

Appendix 2 35

WARREN BROOK

U.S. GEOLOGICAL SURVEY

08

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

Z

Annual chance flood, in percent

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

790780770760750740730720710700

9,100 9,200 9,300 9,400 9,500 9,600 9,700 9,800 9,900 10,000 10,100 10,200 10,300 10,400

Z
Figure 2-9.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figures 4 and 5.

36 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

WARREN BROOK

U.S. GEOLOGICAL SURVEY

09

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

AA

Annual chance flood, in percent

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

820810800790780770760750740730

10,400 10,500 10,600 10,700 10,800 10,900 11,000 11,100 11,200 11,300 11,400 11,500 11,600 11,700

AA
Figure 2-10.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 5.

Appendix 2 37

WARREN BROOK

U.S. GEOLOGICAL SURVEY

10

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

AC

Annual chance flood, in percent

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

860850840830820810800790780770

11,700 11,800 11,900 12,000 12,100 12,200 12,300 12,400 12,500 12,600 12,700 12,800 12,900 13,000

AB A

A

C

D

AE AF

ALLEN BROOK

COOPER HILL ROAD (BREACHED)
Figure 2-11.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 5.

38 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

WARREN BROOK

U.S. GEOLOGICAL SURVEY

11

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

AG

Annual chance flood, in percent

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

870860850840830820810800790780

13,000 13,100 13,200 13,300 13,400 13,500 13,600 13,700 13,800 13,900 14,000 14,100 14,200 14,300

AG
Figure 2-12.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 5.

Appendix 2 39

WARREN BROOK

U.S. GEOLOGICAL SURVEY

12

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

AH

Annual chance flood, in percent

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

880870860850840830820810800790

14,300 14,400 14,500 14,600 14,700 14,800 14,900 15,000 15,100 15,200 15,300 15,400 15,500 15,600

AH

CAMP BROOK
Figure 2-13.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 5.

40 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

WARREN BROOK

U.S. GEOLOGICAL SURVEY

13

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

AI

Annual chance flood, in percent

CULVERT

DECK

LOW

CHORD

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

890880870860850840830820810800

15,600 15,700 15,800 15,900 16,000 16,100 16,200 16,300 16,400 16,500 16,600 16,700 16,800 16,900

AI AJ

STATE ROUTE 123
Figure 2-14.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 5.

Appendix 2 41

WARREN BROOK

U.S. GEOLOGICAL SURVEY

14

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

AL

Annual chance flood, in percent

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

910900890880870860850840830820

16,900 17,000 17,100 17,200 17,300 17,400 17,500 17,600 17,700 17,800 17,900 18,000 18,100 18,200

AK AL
Figure 2-15.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 5.

42 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

WARREN BROOK

U.S. GEOLOGICAL SURVEY

15

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

AO

Annual chance flood, in percent

Bridge deckLow chord

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

970960950940930920910900890880

18,200 18,300 18,400 18,500 18,600 18,700 18,800 18,900 19,000 19,100 19,200 19,300 19,400 19,500

AM AN AO AP AQ

AR

STATE ROUTE 123 (TEMPORARY BRIDGE)
Figure 2-16.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 5.

Appendix 2 43

WARREN BROOK

U.S. GEOLOGICAL SURVEY

16

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

AS

Annual chance flood, in percent

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

990980970960

1,0501,0401,0301,0201,0101,000

19,500 19,600 19,700 19,800 19,900 20,000 20,100 20,200 20,300 20,400 20,500 20,600 20,700 20,800

AS
Figure 2-17.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 5.

44 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

WARREN BROOK

U.S. GEOLOGICAL SURVEY

17

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

AT

Annual chance flood, in percent

CULVERT DECKLOW CHORD

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

1,1301,1201,1101,1001,0901,0801,0701,0601,0501,040

20,800 20,900 21,000 21,100 21,200 21,300 21,400 21,500 21,600 21,700 21,800 21,900 22,000 22,100

AT AU A

A

V

W

STATE ROUTE 123
Figure 2-18.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 5.

Appendix 2 45

WARREN BROOK

U.S. GEOLOGICAL SURVEY

18

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

AX

Annual chance flood, in percent

CULVERT DECKLOW CHORD

TOP OF DAM

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

1,2001,1901,1801,1701,1601,1501,1401,1301,1201,110

22,100 22,200 22,300 22,400 22,500 22,600 22,700 22,800 22,900 23,000 23,100 23,200 23,300 23,400

AX AY AZ B

B

A

B

BC

BD BE BF BG

OLD MILL

STATE ROUTE 123
Figure 2-19.  Annual chance flood profiles (0.2, 1, 2, and 10 percent) for Warren Brook in Walpole, Langdon, and Alstead, New Hampshire. Locations of cross sections are shown

in figure 5.

46 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005

WARREN BROOK

U.S. GEOLOGICAL SURVEY

19

ALSTEAD, NH

CHESHIRE COUNTY

FLOOD PROFILES

EXPLANATION

0.212

10

Streambed

Cross-sectionlocation andidentifier

BH

Annual chance flood, in percent

Bridge deckLow chord

STREAM DISTANCE, IN FEET ABOVE CONFLUENCE WITH COLD RIVER

ELEVATION, IN FEET (NGVD 29)

 1,250 1,240 1,230 1,220 1,210 1,200 1,190 1,180 1,170 1,160

23,400 23,500 23,600 23,700 23,800 23,900 24,000 24,100 24,200 24,300 24,400 24,500 24,600 24,700

BH BI

BJ

BK BL BM BN

BO

PRENTICE HILL ROAD

PINE CLIFF ROAD

WARREN LAKE DAM

TOP OF ABUTMENTTOP OF DAM
Appendix 3: Elevation Reference Marks

Appendix 3 47
Information that may be available at the local community map repository before making flood elevation and(or) flood-plain 

boundary determinations.

Appendix 3.  Elevation reference marks.

[ft, foot; NGVD 29, National Geodetic Vertical Datum of 1929; USGS, U.S. Geological Survey]

Reference mark Elevation

(ft, NGVD 29) Description of location

4611-0100 392.21 Standard tablet stamped “461-0100” set in the top of the upstream end of the north abutment of the 

Route 123 bridge over the Cold River in Drewsville, NH. (See fig. 2)

C 22 USGS 1926 477.77 Standard USGS disk stamped “C 22 1926” and set in the north concrete curb of the grass triangle 

formed by the road junction of State Routes 12A and 123 and Hill Road in Alstead. (See fig. 3)

C 24 USGS 1926 1,190.78 Standard USGS disk stamped “C 24 1926” and set in a concrete dam and foundation to an old 

(1767) grist mill, 40 ft north of the center of State Route 123 and 525 ft northwest of the outlet of 

Warren Lake. (See fig. 5)

48 Flood Study of Warren Brook in Alstead and Cold River in Alstead, Langdon, and Walpole, New Hampshire, 2005
For more information concerning the research in this report, contact:

Keith W. Robinson, Director

U.S. Geological Survey

New Hampshire-Vermont Water Science Center

361 Commerce Way

Pembroke, NH 03275

or visit our Web site at:

http://nh.water.usgs.gov