U.S. Department of the Interior

U.S. Geological Survey

Pamphlet to accompany

Scientific Investigations Map 3216

Prepared in cooperation with the Village of Delhi, New York; 

the Delaware County Soil and Water Conservation District; 

and the Delaware County Planning Department

Flood-Inundation Maps for the West Branch Delaware River, 

Delhi, New York, 2012
Cover. Photographs of Delhi, New York, showing flooding along the main stem of the West Branch Delaware River and road overflow 

from a tributary, Steele Brook (photos by Graydon Dutcher, Delaware County Soil and Water Conservation District).
Flood-Inundation Maps for the West Branch 

Delaware River, Delhi, New York, 2012

By William F. Coon and Brian K. Breaker

Prepared in cooperation with the Village of Delhi, New York; 

the Delaware County Soil and Water Conservation District; 

and the Delaware County Planning Department

Pamphlet to accompany

Scientific Investigations Map 3216

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

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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:

Coon, W.F., and Breaker, B.K., 2012, Flood-inundation maps for the West Branch Delaware River, Delhi, New York, 

2012: U.S. Geological Survey Scientific Investigations Map 3216, 9 p. pamphlet, 10 sheets, scale 1:20,000. 

Available online at http://pubs.usgs.gov/sim/3216.
iii

Acknowledgments

The authors wish to thank the New York City Department of Environmental Protection 

and the Delaware County Department of Public Works for funding the operation and maintenance of the Delhi streamgage, data from which were used for this study. Special thanks are 

given to Michael Jastremski and Shelly Johnson of the Delaware County Planning Department 

for promoting communication among the local government agencies and to Graydon Dutcher 

of the Delaware County Soil and Water Conservation District for facilitating the application 

process by the Village of Delhi for funding of this study through the Stream Corridor Management Program. Thanks also go to Richard Maxey, the Mayor of Delhi, and to the Village Board, 

the lead agency in securing funding for this study. Finally, thanks go to the National Weather 

Service for continued support of the USGS flood-inundation mapping initiative. 
iv

Contents

Acknowledgments........................................................................................................................................iii

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

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

Purpose and Scope ..............................................................................................................................3

Study Area Description........................................................................................................................4

Previous Studies ...................................................................................................................................4

Approach.........................................................................................................................................................4

Computation of Water-Surface Profiles............................................................................................4

Topographic Data.........................................................................................................................4

Hydrologic and Steady-State Flow Data..................................................................................5

Model Calibration and Performance ........................................................................................5

Development of Water-Surface Profiles..................................................................................6

Development of Inundation Maps......................................................................................................6

Flood-Inundation Maps on the Internet ...................................................................................8

Disclaimer for Flood-Inundation Maps ....................................................................................8

Uncertainty Associated with Inundation Maps......................................................................8

Summary..........................................................................................................................................................9

References Cited............................................................................................................................................9

Figures

1. Map showing location of study reach of the West Branch Delaware River in Delhi, 

New York, and locations of U.S. Geological Survey streamgages.......................................2

2. Map showing flood-inundation map for West Branch Delaware River, Delhi, 

New York, with high-water marks from the Hurricane Irene flood of August 28, 2011.....7

Tables

1. U.S. Geological Survey streamgage information for sites on the West Branch

Delaware River, Delhi, New York................................................................................................3

2. Simulated water-surface profiles, with corresponding estimated discharges, 

used in the HEC–RAS model for the West Branch Delaware River, Delhi, 

New York ........................................................................................................................................5

3. Occurrence of roadway flooding at selected stages of the West Branch 

Delaware River, Delhi, New York................................................................................................6
v

Sheets

[Separate documents available online with this report at the U.S. Geological Survey 

Publications Warehouse (http://pubs.usgs.gov/sim/3216/)]

1. Flood-inundation maps for the West Branch Delaware River, Delhi, New York, 

referenced to the U.S. Geological Survey streamgage, West Branch Delaware 

River upstream from Delhi (station number 01421900), and corresponding 

to a stream stage of 7.0 feet

2. Flood-inundation maps for the West Branch Delaware River, Delhi, New York, 

referenced to the U.S. Geological Survey streamgage, West Branch Delaware 

River upstream from Delhi (station number 01421900), and corresponding 

to a stream stage of 8.0 feet

3. Flood-inundation maps for the West Branch Delaware River, Delhi, New York, 

referenced to the U.S. Geological Survey streamgage, West Branch Delaware 

River upstream from Delhi (station number 01421900), and corresponding 

to a stream stage of 9.0 feet

4. Flood-inundation maps for the West Branch Delaware River, Delhi, New York, 

referenced to the U.S. Geological Survey streamgage, West Branch Delaware 

River upstream from Delhi (station number 01421900), and corresponding 

to a stream stage of 10.0 feet

5. Flood-inundation maps for the West Branch Delaware River, Delhi, New York, 

referenced to the U.S. Geological Survey streamgage, West Branch Delaware 

River upstream from Delhi (station number 01421900), and corresponding 

to a stream stage of 11.0 feet

6. Flood-inundation maps for the West Branch Delaware River, Delhi, New York, 

referenced to the U.S. Geological Survey streamgage, West Branch Delaware 

River upstream from Delhi (station number 01421900), and corresponding 

to a stream stage of 12.0 feet

7. Flood-inundation maps for the West Branch Delaware River, Delhi, New York, 

referenced to the U.S. Geological Survey streamgage, West Branch Delaware 

River upstream from Delhi (station number 01421900), and corresponding 

to a stream stage of 13.0 feet

8. Flood-inundation maps for the West Branch Delaware River, Delhi, New York, 

referenced to the U.S. Geological Survey streamgage, West Branch Delaware 

River upstream from Delhi (station number 01421900), and corresponding 

to a stream stage of 14.0 feet

9. Flood-inundation maps for the West Branch Delaware River, Delhi, New York, 

referenced to the U.S. Geological Survey streamgage, West Branch Delaware 

River upstream from Delhi (station number 01421900), and corresponding 

to a stream stage of 15.0 feet

10. Flood-inundation maps for the West Branch Delaware River, Delhi, New York, 

referenced to the U.S. Geological Survey streamgage, West Branch Delaware 

River upstream from Delhi (station number 01421900), and corresponding 

to a stream stage of 16.0 feet
vi

Conversion Factors and Datums

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 30.48 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

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

Vertical coordinate information is referenced to either (1) stage, the height above an arbitrary 

datum established at a streamgage, or (2) elevation, the height above the North American 

Vertical Datum of 1988 (NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).
Flood-Inundation Maps for the West Branch Delaware 

River, Delhi, New York, 2012

By William F. Coon and Brian K. Breaker

and residents with information that is critical for floodresponse activities, such as evacuations and road closures, as 

well as for post-flood recovery efforts.

Introduction

The Village of Delhi is a small rural community in the 

Town of Delhi, Delaware County, New York (fig. 1), with a 

population of 3,087 (Richard Maxey, Mayor, Village of Delhi, 

N.Y., oral commun., 2012). Delhi has experienced severe 

flooding numerous times along the West Branch Delaware 

River, most notably during January 1996, June 2006, October 

2010, and August 2011. Most of the flood plain in the village 

on the northwestern side of the West Branch Delaware River is 

used for residential and commercial purposes; therefore, when 

flooding occurs, the damages and costs can be great. 

Prior to this study, emergency responders in Delhi 

have relied on several information sources (all of which are 

available on the Internet) to make decisions on how to best 

alert the public and minimize the dangers associated with 

flooding. One source is the Federal Emergency Management 

Agency (FEMA) Flood Insurance Study (FIS) for the Town 

and Village of Delhi dated August 1, 2009 (Federal Emergency Management Agency, 2009a and 2009b). A second 

source of information is the U.S. Geological Survey (USGS) 

streamgage, West Branch Delaware River upstream from 

Delhi, N.Y. (station number 01421900; table 1), from which 

current (U.S. Geological Survey, 2011a) and recent (U.S. 

Geological Survey, 2011b) water levels and discharges (starting in December 1996) can be obtained. A discontinued USGS 

streamgage (01422000) that was located within the village 

limits and 0.9 mile downstream from the current streamgage 

provided water-level (stage) data from 1937 to 1970. The 

streamflow record from this earlier streamgage is considered 

equivalent to the record collected at the current streamgage. 

Station 01422000 is shown in the figures in this report for 

informational purposes only. The combined peak-flow data 

from both stations are available through the USGS National 

Water Information System (U.S. Geological Survey, 2011b). 

A third source of flood-related information is the National 

Abstract

Digital flood-inundation maps for a 5-mile reach of the 

West Branch Delaware River through the Village and part 

of the Town of Delhi, New York, were created by the U.S. 

Geological Survey (USGS) in cooperation with the Village 

of Delhi, the Delaware County Soil and Water Conservation 

District, and the Delaware County Planning Department. 

The inundation maps, which can be accessed through the 

USGS Flood Inundation Mapping Science Web site at http://

water.usgs.gov/osw/flood_inundation/ and the Federal Flood 

Inundation Mapper Web site at http://wim.usgs.gov/FIMI/

FloodInundationMapper.html, depict estimates of the areal 

extent and depth of flooding corresponding to selected water 

levels (stages) referenced to the USGS streamgage at West 

Branch Delaware River upstream from Delhi, N.Y. (station 

number 01421900). 

In this study, flood profiles were computed for the stream 

reach by means of a one-dimensional step-backwater model 

that had been used to produce the flood insurance rate maps 

for the most recent flood insurance study for the Town and Village of Delhi. This hydraulic model was used to compute 10 

water-surface profiles for flood stages at 1-foot (ft) intervals 

referenced to the streamgage datum and ranging from 7 ft or 

near bankfull to 16 ft, which exceeds the stages that correspond to both the estimated 0.2-percent annual-exceedanceprobability flood (500-year recurrence interval flood) and the 

maximum recorded peak flow. The simulated water-surface 

profiles were then combined with a geographic information 

system (GIS) digital elevation model, which was derived 

from Light Detection and Ranging (LiDAR) data with a 1.2-ft 

(0.61-ft root mean squared error) vertical accuracy and 3.3-ft 

(1-meter) horizontal resolution, to delineate the area flooded at 

each water level. A map that was produced using this method 

to delineate the inundated area for the flood that occurred on 

August 28, 2011, agreed well with highwater marks that had 

been located in the field using a global positioning system. 

The availability of the 10 flood-inundation maps on the USGS 

Flood Inundation Mapping Science Web site, along with 

Internet information regarding current stage from the USGS 

streamgage, will provide emergency management personnel 
2 Flood-Inundation Maps for the West Branch Delaware River, Delhi, New York, 2012

Figure 1. Location of study reach of the West Branch Delaware River in Delhi, New York, and locations of U.S. 

Geological Survey streamgages.

01422000

01421900

DELHI

NEW YORK Schoharie County

Delaware County

Upper West Branch 

Delaware River Basin

DELAWARE COUNTY

SCHOHARIE COUNTY

Village of Delhi

Upper West Branch 

Delaware River Basin

Town of Delhi

Little Delaware River

West Branch Delaware River

Elk Creek

Falls Creek

Ste ele Brook

Little Delawar e River 0 0.25 0.5 1 MILE

0 0.25 0.5 1 KILOMETER

Current U.S. Geological Survey streamgage and identifier

Discontinued U.S. Geological Survey streamgage and identifier

Stream

Village boundary

Limit of study area

01421900

01422000

EXPLANATION

West Branc

h

D

elaware

River

New York State Plane Eastern Zone, units feet. North American Datum of 1983.

Orthoimagery from ESRI base-map download of Bing Maps Aerial Imagery (January 11, 2012).

74°56' 74°55' 74°54' 74°53'

42°17'

42°18'

42°16'
Introduction 3

Weather Service (NWS) Advanced Hydrologic Prediction Service (AHPS), which also displays the USGS stage data from 

the Delhi streamgage (National Weather Service, 2011). The 

NWS forecasts flood stages at many USGS streamgages but 

does not do so for headwater streamgages with relatively small 

drainage areas, such as West Branch Delaware River upstream 

from Delhi, because the time between a precipitation runoff 

event and peak streamflow at a streamgage is shorter than the 

6-hour time step used by the NWS for stage forecasts. 

Although the current stage at a USGS streamgage is 

particularly useful for residents in the immediate vicinity of a 

streamgage, it is of limited use to residents farther upstream 

or downstream because the water-surface elevation is not 

constant along the entire stream reach. Knowledge of a stage 

at a streamgage is difficult to translate into water levels—both 

their depth and aerial extent—at different locations along a 

stream. One way to address these informational gaps is to 

produce a library of flood-inundation maps that are referenced 

to the stages recorded at the USGS streamgage. By referring 

to the appropriate map, emergency responders can discern the 

severity of flooding (depth of water and aerial extent), identify 

roads that are or soon will be flooded, and make plans for notification or evacuation of residents in harm’s way for some distance upstream and downstream from the streamgage. In addition, the capability to visualize the potential extent of flooding 

has been shown to motivate residents to take precautions and 

heed warnings that they previously might have disregarded; 

therefore, in 2011, the USGS, in cooperation with the Village 

of Delhi, N.Y.; the Delaware County Soil and Water Conservation District; and the Delaware County Planning Department, 

conducted a study to produce a library of flood-inundation 

maps for the West Branch Delaware River near Delhi, N.Y.

Purpose and Scope

The purpose of this report is to describe the development 

of a series of flood-inundation maps for the West Branch Delaware River near Delhi, N.Y., and to present the maps, which 

are also available on the USGS Flood Inundation Mapping 

Science Web site (U.S. Geological Survey, 2012c). The floodinundation maps cover a reach about 5 miles (mi) long from 

about 2 mi upstream from the village’s northeastern boundary 

near the confluence of West Branch Delaware River and Elk 

Creek to about 0.5 mi downstream from the village’s southwestern boundary at the confluence of West Branch Delaware 

River and Little Delaware River (fig. 1). The maps were 

produced for flood levels, referenced to the stage recorded at 

the USGS streamgage on the West Branch Delaware River 

upstream from Delhi (01421900), that range from 7 feet (ft), 

Table 1. U.S. Geological Survey streamgage information for sites on the West Branch Delaware River, 

Delhi, New York.

[Station locations are shown in figure 1. ft, feet; ft3/s, cubic feet per second; NAVD 88, North American Vertical Datum of 1988]

Station name

West Branch Delaware River

at Delhi

West Branch Delaware River

upstream from Delhi

Station number 01422000 01421900

Drainage area (square miles) 142 134

Latitude 42°16ʹ16ʺ 42°16ʹ49ʺ

Longitude 74°55ʹ05ʺ 74°54ʹ27ʺ

Period of peak-flow record

(water years1) 1937–74, 1996 1997–2011

Maximum recorded stage, in ft, gage datum 

(elevation, in ft above NAVD 88) and date

9.8 (1,354.6)

January 19, 1996

12.53 (1,363.55)

August 28, 2011

Maximum discharge, in ft3/s, and date 2

13,000 

January 19, 1996

8,860

August 28, 2011

1

Water year is the 12-month period from October 1 of one year through September 30 of the following year and is designated 

by the calendar year in which it ends.

2

Estimated.
4 Flood-Inundation Maps for the West Branch Delaware River, Delhi, New York, 2012

gage datum, or approximately bankfull, to 16 ft, gage datum, or 

greater than the stage associated with the estimated 0.2-percent 

annual-exceedance-probability flood (500-year recurrence 

interval flood) and the maximum recorded peak flow. 

Study Area Description

The West Branch Delaware River is in the Catskill 

Mountain region of southeastern New York. Although the river 

starts in Schoharie County, most of the basin is in Delaware 

County, through which the river flows in a southwestwardly 

direction. At the USGS streamgage upstream from the Village 

of Delhi (01421900), the drainage area is 134 square miles. 

About 74 percent of the basin at this point is forested (U.S. 

Geological Survey, 2012a); most of the remaining basin is in 

agricultural and rural-developed land uses. The basin terrain 

is generally steep. The average basin slope is 0.17, and the 

main-channel slope is 0.004 (U.S. Geological Survey, 2012a). 

The mean annual precipitation is 43.2 inches (in.) (National 

Oceanic and Atmospheric Administration, 2012); the mean 

annual runoff is 24.5 in. (U.S. Geological Survey, 2012b). The 

study reach is approximately 5 mi long, has an average top-ofbank channel width of about 100 to150 ft, and has an average 

channel slope of 0.0017. Three major tributaries connect with 

the West Branch Delaware River in the vicinity of Delhi. Elk 

Creek and Falls Creek meet the river about 1 mi upstream 

from the village, whereas Steele Brook joins the river within 

the village limits. Two bridges cross the main channel within 

the village limits at Bridge Street and N.Y. Route 28 (Kingston Street). A third bridge at Sherwood Road is located at the 

downstream end of the study reach and just upstream from 

the confluence of the West Branch Delaware River with Little 

Delaware River. 

Previous Studies

FEMA flood insurance studies for both the Village and 

Town of Delhi were conducted by Leonard Jackson Associates in 1985 (Federal Emergency Management Agency, 1985a 

and b). These FISs were updated and included in a countywide 

study that was completed by URS Corporation, in association 

with Dewberry and Davis, LLC, in 2009 (Federal Emergency 

Management Agency, 2009a and b). The 2009 FIS covers West 

Branch Delaware River from about 5.5 mi upstream from the 

Village of Delhi to the confluence of the West Branch with 

East Branch Delaware River almost 60 mi downstream. The 

hydrologic and hydraulic analyses were performed by URS 

Corporation. The flood-inundation areas for all detailed study 

reaches were produced by Dewberry and Davis, LLC, and 

were delineated using high-resolution topographic data that 

were generated from LiDAR (Light Detection and Ranging) 

data (Federal Emergency Management Agency, 2009a). The 

LiDAR data were collected during 2007 and were used to more 

precisely delineate flood plains in the detailed study areas than 

was previously possible.

Approach

The USGS has standardized procedures for creating 

flood-inundation maps for flood-prone communities (U.S. 

Geological Survey, 2012c) so that the process followed and 

products produced are similar regardless of which USGS 

office is responsible for the work. Tasks specific to development of the flood maps for Delhi, N.Y., included (1) attainment of the hydraulic model that was used for the most recent 

FEMA flood insurance study (Federal Emergency Management Agency, 2009a and 2009b); (2) computation of watersurface profiles and production of estimated flood-inundation 

maps for various stream stages using the U.S. Army Corps 

of Engineer’s River Analysis System (HEC–RAS) computer 

program and mapping utility, RAS Mapper (U.S. Army Corps 

of Engineers, 2010); (3) collection of highwater elevations 

during the flood of August 28, 2011, to verify the estimated 

flood-inundation maps; and (4) preparation of the maps for 

display on the USGS Flood Inundation Mapping Science Web 

site (U.S. Geological Survey, 2011c).

Computation of Water-Surface Profiles

The water-surface profiles used to produce the 10 floodinundation maps in this study were computed using HEC–

RAS, version 4.1.0 (U.S. Army Corps of Engineers, 2010). 

HEC–RAS is a one-dimensional step-backwater model for 

simulation of water-surface profiles with steady-state (gradually varied) or unsteady-state flow computation options. 

The HEC–RAS model that was used for the 2009 FIS was 

used essentially “as-is” for production of flood maps so as 

to ensure agreement between published FIS flood maps and 

those produced by the current study. The HEC-RAS model 

was obtained from Dewberry and Davis, LLC (Dewberry and 

Davis, LLC, written commun., April 2011). Minor revisions 

made to the model are described in the following sections.

Topographic Data

Channel cross sections and bridge geometry data were 

obtained from the HEC–RAS model that was used for the 

2009 FIS. Data for seven cross sections—one at the current 

streamgage location and six at the upstream end of the study 

reach—were added to the model. Within the study reach, no 

structures have been modified or new structures added since 

the completion of the FIS (Federal Emergency Management 

Agency, 2009a and b). 

LiDAR data with horizontal resolution of 3.3 ft (1 meter) 

and vertical accuracy of 1.2 ft (0.61 ft or 18.5 centimeters root 

mean squared error) were used to extract elevation data for 

the new cross sections. The LiDAR data were collected for 

the New York City Department of Environmental Protection 

as part of the New York State Digital Orthoimagery Program 

through the New York State Office of Cyber Security and Critical Infrastructure Coordination (2009). The LiDAR data were 
Approach 5

collected during April to June 2009, and were postprocessed 

by the Sanborn Map Company, Colorado Springs, Colorado. 

The data, which were acquired from New York State Department of Environmental Conservation, were clipped to the area 

required to produce the flood-inundation maps for the West 

Branch Delaware River near Delhi. Elevations of the LiDAR 

data are referenced to the North American Vertical Datum of 

1988 (NAVD 88). 

HEC–GeoRAS (U.S. Army Corps of Engineers, 2009), a 

set of procedures, tools, and utilities for processing geospatial 

data in ArcGIS by using a graphical user interface, was used to 

extract digital elevation data from the LiDAR dataset for the 

seven new cross sections. These geometric data were subsequently imported into HEC–RAS. Because the LiDAR data 

could not provide the same level of detail for the submerged 

parts of the cross sections as is possible with surveyed data, 

the streambed elevations of the imported data were adjusted 

on the basis of bed elevations of the FIS cross sections 

proximal to the new cross sections and on the bed slope of 

the channel.

Hydrologic and Steady-State Flow Data

The study reach includes one streamgage (01421900; 

fig. 1; table 1) that has been in operation at the current site 

since December 1996. Stage is measured every 15 minutes, is 

transmitted hourly by a satellite radio in the streamgage, and 

is made available on the Internet through the USGS National 

Water Information System (U.S. Geological Survey, 2011a). 

Stage data from this streamgage are referenced to a local 

datum but can be converted to water-surface elevations referenced to the NAVD 88 by adding 1,350.82 ft. 

The HEC–RAS analysis for this study was done using 

the steady-state flow computation option. Steady-state flow 

data consist of the flow regime, boundary conditions (normal 

depth), and peak flows that produced water-surface elevations 

at the streamgage cross section, which matched target watersurface elevations. These target elevations coincided with even 

foot increments of stage, referenced to the local gage datum. 

The FIS model simulated the addition of flows downstream 

from Steele Brook about mid-way through the village. To 

ensure that the profiles developed as part of the current study 

would agree with those from the FIS, the increases in flows 

downstream from Steele Brook for these new profiles were 

extrapolated or interpolated from the FIS flows.

Model Calibration and Performance

The 2009 HEC–RAS model was used with no other 

changes than the addition of the seven cross sections as 

described previously. The roughness coefficients used for the 

six upstream cross sections were comparable to those used 

for other cross sections in the model. The roughness coefficients for the cross section at the streamgage were adjusted 

to minimize the differences between simulated water-surface 

elevations and those estimated from profile plots for the 

10-, 2-, 1-, and 0.2-percent annual-exceedance-probability 

floods that were presented in the FIS. The greatest discrepancy in water-surface elevations for these four simulations 

was 0.16 ft. For the 10 water-surface profiles that were created for this study, steady-flow discharges in the model were 

adjusted to produce the desired water-surface elevations at 

the streamgage.

Discharges in the original HEC–RAS model were 

increased downstream from the confluence with Steele Brook 

at the site of the discontinued USGS streamgage (01422000). 

These increases presumably were intended to account for and 

maintain tributary inflows at flood-frequency magnitudes that 

were comparable to those being simulated in the main channel. Therefore, proportional increases in discharges (table 2) 

for the 10 simulations performed for the current study were 

selected with the assumption that the percentage of increase in 

discharge for any given simulation was the same as that for the 

2009 FIS.

Table 2. Simulated water-surface profiles, with corresponding 

estimated discharges, used in the HEC–RAS model for the West 

Branch Delaware River, Delhi, New York.

[NAVD 88, North American Vertical Datum of 1988; ft, feet; ft3/s, cubic feet 

per second. Water-surface profiles include ten 1-foot increments of stage, referenced to the U.S. Geological Survey streamgage upstream from Delhi, and 

four annual exceedence probability floods (AEPF) from the most recent flood 

insurance study (Federal Emergency Management Agency, 2009a). Bold

values are from the original HEC–RAS model developed for the most recent 

flood insurance study (Federal Emergency Management Agency, 2009a)]

Water-surface 

profile

Target 

water-surface 

elevation, 

in feet, 

NAVD 88

Estimated 

discharge at 

upstream end 

of study reach 

(ft3/s)

Estimated 

discharge 

downstream from 

confluence with 

Steele Brook 

(ft3/s)

Stage 7 ft 1,357.82 1,915 3,008

Stage 8 ft 1,358.82 2,625 4,123

Stage 9 ft 1,359.82 3,490 5,482

Stage 10 ft 1,360.82 4,460 7,006

Stage 11 ft 1,361.82 5,600 8,797

10-percent AEPF 11,362.3 6,399 9,986

Stage 12 ft 1,362.82 6,940 10,901

Stage 13 ft 1,363.82 8,575 13,470

2-percent AEPF 11,364.1 8,828 13,892

1-percent AEPF 11,364.6 9,883 15,559

Stage 14 ft 1,364.82 10,160 15,960

Stage 15 ft 1,365.82 12,210 19,180

0.2-percent AEPF 11,365.9 12,372 19,483

Stage 16 ft 1,366.82 14,350 22,541

1

Elevation was estimated from water-surface profile plot, Plate 154P, 

in Federal Emergency Management Agency (2009b).
6 Flood-Inundation Maps for the West Branch Delaware River, Delhi, New York, 2012

Development of Water-Surface Profiles

Water-surface profiles were developed for a total 

of 10 stages at 1-ft intervals referenced to the USGS 

streamgage West Branch Delaware River upstream from 

Delhi (01421900). The profiles range in stage from 7 ft, or 

near bankfull, to 16 ft, gage datum (1,357.82 to 1,366.82 ft, 

NAVD 88). The maximum stage exceeds the stages that 

correspond to both the estimated 0.2-percent annual-exceedance-probability flood from the 2009 FIS (12,370 cubic feet 

per second (ft3/s)) and the maximum recorded peak flow 

(13,000 ft3/s on January 19, 1996). Water-surface elevations at 

each cross section in the HEC–RAS model were computed for 

each simulated profile.

Development of Inundation Maps

Flood-inundation maps were created in a geographic 

information system (GIS) for the 10 water-surface profiles 

by combining the profiles and digital elevation model (DEM) 

data. The DEM data were derived from the same LiDAR data 

that were obtained from New York State Department of Environmental Conservation and used for elevation data for the 

cross sections added to the HEC–RAS model. 

Estimated flood-inundation boundaries for each simulated 

profile were developed with RAS Mapper (U.S. Army Corps 

of Engineers, 2010), a mapping utility that overlays geometric 

data and water-surface profiles from HEC–RAS onto a digital 

terrain layer. As with the LiDAR data from which the flood 

maps were derived, the resulting flood maps have a vertical 

accuracy of about 1.2 ft. The mapped areas of inundation are 

overlaid on high-resolution, geo-referenced, aerial photographs of the study area. The most up-to-date orthoimagery 

available (Bing Maps Services, 2011) was downloaded from 

an Esri basemap Web site (Esri, 2011) for this purpose. Shapefile polygons and depth grids of the inundated areas for each 

profile were modified, as required, in the ArcMap application 

of ArcGIS, version 10 (Esri, 2011), to ensure a hydraulically 

reasonable transition of the flood boundaries between modeled cross sections. Any inundated areas that were detached 

from the main channel and, therefore, erroneously delineated 

as parts of the flood extent were removed from the mapped 

inundated areas. Bridge surfaces that were shown to be 

overtopped by flood waters, when in fact the water level was 

below the bridge deck, were corrected to depict non-inundated 

conditions. The shapefile polygons of the inundated areas are 

shaded to depict variations in water depth. Actual estimates of 

water depth can be obtained from the depth-grid data that are 

included with the presentation of the flood maps on the interactive online map-library Web site described in the following 

section, “Flood-Inundation Maps on the Internet.” 

High-water marks along the main channel following the 

flood of August 28, 2011, that was caused by Hurricane Irene 

were located with a hand-held global positioning system. The 

peak discharge of this flood was 8,860 ft3/s at a recorded stage 

of 12.53 ft, gage datum (1,363.35 ft, NAVD 88). The highwater marks, which identified the edge of the inundated area 

along the northwestern bank of the West Branch Delaware 

River, were superimposed on an inundation map that was 

created for this flood following the same procedures described 

above (fig. 2). The field-surveyed flood boundary closely 

matched the areal extent of the GIS-generated flood-inundation map produced by HEC–RAS and RAS Mapper.

The 10 flood maps at 1-ft increments of stage that were 

produced for West Branch Delaware River near Delhi are not 

included in this report. Rather they are available on the Internet, as described in the following section. Examination of the 

10 flood maps permits assessment of changes in the extents of 

flooding as the water level of the West Branch Delaware River 

increases. A critical stage value can be associated with specific areas of the village that are susceptible to flooding. For 

example, knowledge of the stages at which certain roadway 

or bridge flooding will occur (table 3) would be beneficial to 

emergency responders. Areas that are prone to flooding, but 

only during extreme events, can also be identified. Residents 

in these areas might be more at risk from the dangers of flooding simply because they lack the periodic exposure to floods 

that residents in other areas regularly experience.

Table 3. Occurrence of roadway flooding at selected stages of 

the West Branch Delaware River, Delhi, New York.

[Stage is referenced to the water level measured at the U.S. Geological Survey 

streamgage, West Branch Delaware River upstream from Delhi (01421900)]

Stage,

in feet Flood extent

10 Bridge Street flooding on right bank begins.

11 Bridge Street on right bank is inundated.

12 Sherwood Road flooding on left bank begins.

13 Bridge Street bridge is inundated.

Sherwood Road on left bank is inundated.

14 Kingston Street (Route 28) bridge is inundated.

Kingston Street flooding on right bank begins.

15

Kingston Street on right bank is inundated.

Main Street (Route 10) is flooded between 

Court Street and Division Street.

16

Sherwood Road bridge is inundated.

Main Street (Route 10) is flooded northeast 

of Bridge Street.
Approach 7

Figure 2. Flood-inundation map for West Branch Delaware River, Delhi, New York, with high-water marks from the 

Hurricane Irene flood of August 28, 2011. (Stage of 12.53 feet, gage datum, and 1,363.35 feet, North American Vertical 

Datum 1988, referenced to the U.S. Geological Survey streamgage 01421900)

01421900

01422000

74°55' 74°54'

42°17'

42°16'

New York State Plane Eastern Zone, units feet. North American Datum of 1983.

Orthoimagery from ESRI base-map download of Bing Maps Aerial Imagery (January 11, 2012).

0 0.25 0.5 1 MILE

0 0.25 0.5 1 KILOMETER

EXPLANATION

Current U.S. Geological Survey streamgage and identifier

Discontinued U.S. Geological Survey streamgage and identifier

High-water marks from flood of August 28, 2011

Inundation area

01421900

01422000

N.Y. Route 10 (Main Street)

Kingston Street

Bridge Street

Sherwood Road

N.Y Route 28
8 Flood-Inundation Maps for the West Branch Delaware River, Delhi, New York, 2012

Flood-Inundation Maps on the Internet

The flood-inundation maps and current study documentation are available online at the U.S. Geological Survey 

Publications Warehouse (http://pubs.usgs.gov/sim/3216/). 

Also, a Flood Inundation Mapping Science Web site (U.S. 

Geological Survey, 2011c) has been established to provide 

a portal at http://water.usgs.gov/osw/flood_inundation/ to 

make USGS flood-inundation study information available to 

the public. That Web portal has a link (http://wim.usgs.gov/

FIMI/FloodInundationMapper.html) to interactive online map 

libraries that can be downloaded in several commonly used 

electronic file formats. Included on this latter Web site is a 

link to the USGS National Water Information System (U.S. 

Geological Survey, 2011a), which presents graphs of the current stage and streamflow at the USGS streamgage 01421900 

to which the inundation maps are referenced. A link also is 

provided to the NWS Advanced Hydrologic Prediction Service 

(AHPS) site (National Weather Service, 2011); however, 

because the NWS does not forecast stage at this site, the data 

presented on the USGS and NWS Web sites are identical. The 

estimated flood-inundation maps are displayed in sufficient 

detail to note the extent of flooding with respect to individual 

structures so that preparations for flooding and decisions for 

emergency response can be performed in a timely and efficient 

manner. Roadways and bridges were closely reviewed and 

are shown as shaded (inundated and likely impassable) or not 

shaded (dry and passable) to facilitate emergency planning and 

response. However, buildings that are shaded do not reflect 

inundation but denote that bare earth surfaces in the vicinity of 

the buildings are inundated. When the water depth (as indicated in the Web Mapping Application at http://wim.usgs.gov/

FIMI/FloodInundationMapper.html by holding the cursor over 

an inundated area) in the vicinity of the building of interest 

exceeds that building’s height, the structure can be considered 

fully submerged.

Disclaimer for Flood-Inundation Maps

Inundated areas shown on the flood maps should not be 

used for navigation, regulatory, permitting, or other legal purposes. The USGS provides these maps “as-is” for a quick reference, emergency planning tool but assumes no legal liability 

or responsibility resulting from the use of this information.

Uncertainty Associated with Inundation Maps

Although the flood-inundation maps represent the 

boundaries of inundated areas with a distinct line, some 

uncertainty is associated with these maps. The flood boundaries shown were estimated on the basis of stages at the USGS 

streamgage upstream from Delhi (01421900). Water-surface 

elevations along the stream reaches were estimated by steadystate hydraulic modeling, assuming unobstructed flow, and 

using streamflows and hydrologic conditions anticipated at the 

USGS streamgage. The hydraulic model reflects the land-cover 

characteristics and any bridge or other hydraulic structures 

existing as of March 2012. Unique meteorological factors (timing and distribution of precipitation) may cause actual streamflows along the modeled reach to vary from those assumed during a flood, which may lead to deviations in the water-surface 

elevations and inundation boundaries shown. Additional areas 

may be flooded as a result of unanticipated conditions, such as 

changes in the streambed elevation or roughness, backwater 

into major tributaries along a main stem river, or backwater 

from localized debris or ice jams. The accuracy of the floodwater extent portrayed on these maps will vary with the accuracy 

of the digital elevation model used to simulate the land surface. 

If this series of flood-inundation maps will be used in 

conjunction with National Weather Service (NWS) river 

forecasts, the user should be aware of additional uncertainties 

that may be inherent or factored into NWS forecast procedures. 

The NWS uses forecast models to estimate the quantity and 

timing of water flowing through selected stream reaches in the 

United States. These forecast models (1) estimate the amount 

of runoff generated by precipitation and snowmelt, (2) simulate the movement of floodwater as it proceeds downstream, 

and (3) predict the flow and stage (water-surface elevation) for 

the stream at a given location (AHPS forecast point) throughout the forecast period (every 6 hours and 3 to 5 days out in 

many locations). For more information on AHPS forecasts, 

please see: http://water.weather.gov/ahps/pcpn_and_river_

forecasting.pdf. 

Summary

A series of 10 digital flood-inundation maps were developed, in cooperation with the Village of Delhi, New York; the 

Delaware County Soil and Water Conservation District; and the 

Delaware County Planning Department, for the West Branch 

Delaware River near Delhi. The maps cover a reach about 

5 miles (mi) long from about 2 mi upstream from the village’s 

northeastern boundary near the confluence of West Branch 

Delaware River and Elk Creek to about 0.5 mi downstream 

from the village’s southwestern boundary at the confluence 

of West Branch Delaware River and Little Delaware River. 

An existing hydraulic model, developed using the U.S. Army 

Corps of Engineers’ HEC–RAS program and used to create flood-inundation maps for the most recent (2009) flood 

insurance studies for the Village and Town of Delhi, was used 

to compute water-surface profiles for the study reach. Ten 

water-surface profiles for flood stages at 1-foot (ft) intervals, 

referenced to the streamgage datum and ranging from 7 ft, or 

near bankfull, to 16 ft, gage datum (1,357.82 to 1,366.82 ft, 

NAVD 88), were created. The maximum stage exceeds the 

stages that correspond to both the estimated 0.2-percent annualexceedance-probability flood and the maximum recorded 

peak flow. The simulated water-surface profiles were then 

combined with a geographic information system (GIS) digital 

elevation model (derived from Light Detection and Ranging 

(LiDAR) data) and RAS Mapper, a mapping utility included in 
References Cited 9

HEC–RAS, to delineate estimated flood-inundation areas as 

shapefile polygons and depth grids for each profile. A map that 

was produced by this method to delineate the inundated area 

for the flood that occurred on August 28, 2011, agreed well 

with highwater marks that had been located in the field using a 

global positioning system. These maps were overlaid on highresolution, georeferenced, aerial photographs of the study area 

and were shaded to give a general indication of depth of water 

at any point. The maps were modified, as required, to remove 

any inundated areas that were detached from the main channel 

and were erroneously delineated as part of the flood extent and 

to correctly depict inundation of bridge surfaces. 

Current conditions at the USGS streamgage (01421900) 

can be obtained on the Internet through the USGS National 

Water Information System (http://waterdata.usgs.gov/nwis/) 

or the National Weather Service (NWS) Advanced Hydrologic 

Prediction Service (AHPS; http://water.weather.gov/ahps/). 

The NWS forecasts flood stages for many places that are collocated with USGS streamgages, but because of the relatively 

small drainage area of the West Branch Delaware River at 

Delhi and the short time between peak rainfall and peak 

streamflow at Delhi, the NWS does not forecast flood stages 

for this site. The flood maps, available at the USGS Flood 

Inundation Mapping Science Web site, in conjunction with 

the real-time stage data from the USGS streamgage, will help 

to guide the general public in taking individual safety precautions and will provide emergency management personnel with 

a tool to efficiently manage emergency flood operations and 

post-flood recovery efforts. 

References Cited

Bing Maps Services, 2011, Bing Maps Aerial Imagery: ArcGIS Online web mapping service, accessed November 22, 

2011, at http://www.esri.com/software/arcgis/arcgisonline/

bing-maps.html.

Esri, 2011, ArcGIS 10, accessed November 22, 2011, at http://

www.esri.com/software/arcgis/arcgis10/index.html.

Federal Emergency Management Agency, 1985a, Flood 

Insurance Study, Town of Delhi, Delaware County, New 

York, July 18, 1985: Washington, D.C., Federal Emergency 

Management Agency, 26 p.

Federal Emergency Management Agency, 1985b, Flood 

Insurance Study, Village of Delhi, Delaware County, New 

York, July 18, 1985: Washington, D.C., Federal Emergency 

Management Agency, 21 p.

Federal Emergency Management Agency, 2009a, Flood insurance study, Delaware County, New York (all jurisdictions), 

Volume 1: Federal Emergency Management Agency, 140 p., 

accessed November 15, 2011, at http://www.ramppteam.

com/county_maps/new_york/delaware/delaware_ny_fis_

tables1.pdf.

Federal Emergency Management Agency, 2009b, Flood insurance study, Delaware County, New York (all jurisdictions), 

Volume 2: Federal Emergency Management Agency, 110 p., 

accessed November 15, 2011, at http://www.ramppteam.

com/county_maps/new_york/delaware/delaware_ny_fis_

tables2.pdf.

National Oceanic and Atmospheric Administration, 2012, 

National Climatic Data Center: National Oceanic and Atmospheric Administration, Satellite and Information Service, 

accessed February 1, 2012, at http://www.ncdc.noaa.gov/oa/

ncdc.html.

National Weather Service, 2011, Advanced Hydrologic Prediction Service, accessed December 16, 2011, at http://water.

weather.gov/ahps2/index.php?wfo=bgm.

New York State Office of Cyber Security and Critical Infrastructure Coordination, 2009, 2009 LiDAR metadata for the 

NYCDEP (New York City Department of Environmental 

Protection) project area: New York State Digital Orthoimagery Program, Albany, N.Y.

U.S. Army Corps of Engineers, Hydrologic Engineering Center, 2009, HEC–GeoRAS, GIS Tools for Support of HEC–

RAS using ArcGIS, User’s Manual, version 4.2: U.S. Army 

Corps of Engineers, [variously paged]. 

U.S. Army Corps of Engineers, Hydrologic Engineering 

Center, 2010, HEC–RAS River Analysis System, Hydraulic 

Reference Manual, version 4.1: U.S. Army Corps of Engineers, [variously paged].

U.S. Geological Survey, 2011a, USGS 01421900 West Branch 

Delaware River upstream from Delhi, N.Y.: U.S. Geological 

Survey, accessed December 16, 2011, at http://waterdata.

usgs.gov/ny/nwis/uv?site_no=01421900.

U.S. Geological Survey, 2011b, USGS Surface-water data for 

the Nation: U.S. Geological Survey, accessed December 16, 

2011, at http://waterdata.usgs.gov/nwis/sw.

U.S. Geological Survey, 2011c, Federal flood inundation mapper: U.S. Geological Survey, accessed December 16, 2011, 

at http://wim.usgs.gov/FIMI/FloodInundationMapper.html.

U.S. Geological Survey, 2012a, New York StreamStats: U.S. 

Geological Survey, accessed January 12, 2012, at http://

streamstatsags.cr.usgs.gov/ny_ss/default.aspx?stabbr=ny&d

t=1273767408015l.

U.S. Geological Survey, 2012b, Water-resources data for the 

United States, water year 2010: U.S. Geological Survey, 

accessed February 1, 2012, at http://wdr.water.usgs.gov/

wy2010/pdfs/01421900.2010.pdf.

U.S. Geological Survey, 2012c, USGS Flood Inundation Mapping Science: U.S. Geological Survey, accessed February 

3, 2012, at http://water.usgs.gov/osw/flood_inundation/

toolbox/.

For more information, contact:

Director

U.S. Geological Survey

New York Water Science Center

425 Jordan Road

Troy, NY 12180-8349

or visit our Web site at:

http://ny.water.usgs.gov/

Document prepared by the West Trenton Publishing Service Center
Coon and Breaker—Flood-Inunation Maps for the West Branch Delaware River, Delhi, New York, 2012—Scientific Investigations Map 3216