U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010–5259

Prepared in cooperation with the Federal Emergency Management Agency

Flash Floods of August 10, 2009, in the Villages of 

Gowanda and Silver Creek, New York
Cover. Cattaraugus Creek at New York State Thruway, August 10, 2009 (photo courtesy of The Buffalo News, Buffalo, N.Y.)
Flash Floods of August 10, 2009, in the Villages 

of Gowanda and Silver Creek, New York 

By Carolyn O. Szabo, William F. Coon, and Thomas A. Niziol

Prepared in cooperation with the Federal Emergency Management Agency

Scientific Investigations Report 2010–5259

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: 2010

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Suggested citation:

Szabo, C.O., Coon, W.F., and Niziol, T.A., 2010, Flash floods of August 10, 2009, in the Villages of Gowanda and Silver 

Creek, New York: U.S. Geological Survey Scientific Investigations Report 2010-5259, 23 p.
iii

Contents

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

Introduction.....................................................................................................................................................2

Antecedent Hydrologic Conditions.............................................................................................................3

Storm Characteristics ...................................................................................................................................3

Description of the Floods..............................................................................................................................5

Collection of High-Water-Mark Data..........................................................................................................5

Floodwater-Surface Profiles...............................................................................................................6

Areal Extent of Flooding.......................................................................................................................7

Magnitudes of Peak Streamflows.............................................................................................................11

Annual Exceedance Probabilities of Peak Streamflows.......................................................................11

Summary........................................................................................................................................................16

Acknowledgments.......................................................................................................................................17

References Cited..........................................................................................................................................17

Appendix 1. High-water marks in the Villages of Gowanda and Silver Creek, N.Y., 

for the flash floods of August 10, 2009. .......................................................................................20

Figures

1. Map showing locations of study sites and selected U.S. Geological 

Survey streamgages and associated drainage basins in western New York...........2

2. Map showing storm-total radar-derived precipitation in western 

New York from 9:09 p.m. on August 9, 2009, through 12:09 a.m. Eastern 

Daylight Time on August 10, 2009......................................................................................4

3. Photographs of damage from the floods of August 10, 2009 ........................................6

4. Graph showing streamflow and gage-height for Cattaraugus Creek at 

Gowanda, New York, U.S. Geological Survey station 04213500, 

August 9-12, 2009 .................................................................................................................7

5. Examples of representative high-water marks from the floods of 

August 10, 2009: (A) debris line, (B) wash line, (C and D) mud lines, 

and (E) grass on tree ...........................................................................................................8

6. Graph showing water-surface elevations for the August 10, 2009, flood 

and the FEMA 0.2-percent annual exceedance probability flood for 

Grannis Brook at Gowanda, N.Y........................................................................................9

7. Graph showing water-surface elevations for the August 10, 2009, flood 

and the FEMA 0.2-percent annual exceedance probability flood for 

Thatcher Brook at Gowanda, N.Y......................................................................................9

8. Graph showing water-surface elevations for the August 10, 2009, flood 

and the FEMA 0.2-percent annual exceedance probability flood for 

Walnut Creek at Silver Creek, N.Y...................................................................................10

9. Graph showing ater-surface elevations for the August 10, 2009, flood 

and the FEMA 0.2-percent annual exceedance probability flood for 

Silver Creek at Silver Creek, N.Y......................................................................................10

10. Map showing areal extent and water-surface elevations of flooding 

in Gowanda, N.Y., August 10, 2009 ..................................................................................12

11. Map showing areal extent and water-surface elevations of flooding in 

Silver Creek, N.Y., August 10, 2009 ..................................................................................13
iv

Tables

1. Historic peak flows, and peak flows and associated annual 

exceedance probabilities for the floods of August 10, 2009, at 

selected U.S. Geological Survey streamgages in western New York. .....................14

2. Peak flows computed for the floods of August 10, 2009, at sites in 

Gowanda and Silver Creek, New York ...........................................................................15

3. Peak flows for indicated annual exceedance probabilities for 

selected streams in Gowanda and Silver Creek, New York .......................................16

Conversion Factors, Datums, and Abbreviations

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

) 2.590 square kilometer (km2) 

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)

cubic foot per second per square mile 

[(ft3

/s)/mi2] 0.01093 cubic meter per second per square kilometer [(m3/s)/km2]

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

(NGVD29) or the North American Vertical Datum of 1988 (NAVD88), as noted.

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD83).

Elevation, as used in this report, refers to distance above the vertical datum.

Abbreviations

EDT Eastern Daylight Time

EST Eastern Standard Time

FEMA Federal Emergency Management Agency

HEC-RAS Hydrologic Engineering Center River Analysis System

LiDAR Light Detection And Ranging

NAD83 North American Datum of 1983

NAVD88 North American Vertical Datum of 1988

NGVD29 National Geodetic Vertical Datum of 1929

NOAA National Oceanic and Atmospheric Administration

NWS National Weather Service

SPCS State Plane Coordinate System

USDA U.S. Department of Agriculture

USGS U.S. Geological Survey
 Flash Floods of August 10, 2009, in the Villages of 

 Gowanda and Silver Creek, New York 

By Carolyn O. Szabo1, William F. Coon1, and Thomas A. Niziol2

1

 U.S. Geological Survey, New York Water Science Center, Ithaca, N.Y.

2

 National Oceanic and Atmospheric Administration, National Weather 

 Service, Buffalo, N.Y.

Abstract

Late during the night of August 9, 2009, two storm 

systems intersected over western New York and produced 

torrential rain that caused severe flash flooding during the 

early morning hours of August 10 in parts of Cattaraugus, 

Chautauqua, and Erie Counties. Nearly 6 inches of rain 

fell in 1.5 hours as recorded by a National Weather Service 

weather observer in Perrysburg, which lies between Gowanda 

and Silver Creek—the communities that suffered the most 

damage. This storm intensity had an annual exceedance 

probability of less than 0.2 percent (recurrence interval greater 

than 500 years). Although flooding along Cattaraugus Creek 

occurred elsewhere, Cattaraugus Creek was responsible for 

very little flooding in Gowanda. Rather the small tributaries, 

Thatcher Brook and Grannis Brook, caused the flooding in 

Gowanda, as did Silver Creek and Walnut Creek in the 

Village of Silver Creek. 

Damages from the flooding were widespread. Numerous 

road culverts were washed out, and more than one‐quarter 

of the roads in Cattaraugus County were damaged. Many 

people were evacuated or rescued in Gowanda and Silver 

Creek, and two deaths occurred during the flood in Gowanda. 

The water supplies of both communities were compromised 

by damages to village reservoirs and water-transmission 

infrastructures. Water and mud damage to residential and 

commercial properties was extensive. The tri-county area was 

declared a Federal disaster area and more than $45 million 

in Federal disaster assistance was distributed to more than 

1,500 individuals and an estimated 1,100 public projects. The 

combined total estimate of damages from the flash floods was 

greater than $90 million.

Over 240 high-water marks were surveyed by the U.S. 

Geological Survey; a subset of these marks was used to create 

flood-water-surface profiles for four streams and to delineate 

the areal extent of flooding in Gowanda and Silver Creek. 

Flood elevations exceeded previously defined 0.2-percent 

annual exceedance probability (500-year recurrence interval) 

elevations by 2 to 4 feet in Gowanda and as much as 

6 to 8 feet in Silver Creek. Most of the high-water marks 

were used in indirect hydraulic computations to estimate peak 

flows for four streams. The peak flows in Grannis Brook and 

Thatcher Brook were computed, using the slope-area method, 

to be 1,400 and 7,600 cubic feet per second, respectively, and 

peak flow in Silver Creek was computed, using the widthcontraction method, to be 19,500 cubic feet per second. The 

annual exceedance probabilities for flows in these and other 

basins with small drainage areas that fell almost entirely 

within the area of heaviest precipitation were less than 

0.2 percent (or recurrence intervals greater than 500 years). 

The peak flow in Cattaraugus Creek at Gowanda was 

computed, using the slope-area method, to be 33,200 cubic 

feet per second with an annual exceedance probability of 

2.2 percent (recurrence interval of 45 years). 

Introduction

Severe thunderstorms during the night of August 9, 2009, 

caused extensive flooding during the early hours of August 10 

across parts of Cattaraugus, Chautauqua, and Erie Counties 

in western New York (fig. 1). Although many road culverts 

were washed out and more than one‐quarter of the roads in 

Cattaraugus County were damaged (National Oceanic and 

Atmospheric Administration, 2010a), the major damages and 

costs occurred in the residential and commercial sections of 

villages, such as Gowanda and Silver Creek. The flooding 

was caused by runoff from torrential rainfall that exceeded 

the capacity of small streams that flowed through these 

communities. Many people were evacuated or rescued in both 

communities, including patients in the Tri-County Memorial 

Hospital in Gowanda and residents of a creek-side trailer park 

in Silver Creek, which was destroyed. The water supplies of 

both communities were compromised by damages to village 

reservoirs and water-transmission infrastructures. Water 

depth in the flooded areas was about 1 to 3 ft, enough to fill 

basements and inundate the first floor of hundreds of homes 

and businesses. Damages resulted not only from water but also 

from mud that was carried by the sediment-laden floodwaters. 
2 Flash Floods of August 10, 2009, in the Villages of Gowanda and Silver Creek, New York

Lake 

 Erie

0 10 20 5 MILES

0 10 20 5 KILOMETERS

Chautauqua

 Lake

#

#

#

#

#

#

##

#

#

#

#

#

#

#

Buffalo Attica

Warsaw

Gowanda

Fredonia

Silver Creek

Salamanca

Falconer

Machias

Cattaraugus Creek

Buffalo

Ischua Creek

Cayuga Creek

Oatka Creek

Allegheny

River

Creek

Tonawanda Creek

Grannis Brook

Thatcher Brook

Walnut Creek

Silver Creek

Canadaway

Creek

Cazenovia Creek

Chadakoin

River

Ball Creek

03013800

04230380

04216418

04215500

04214500

04213508

04213500

04213490

04213376

03014500

03011020

03010734

0421350503

0421340305

042150000

79° 78°

43°

42°

Base from USGS digital data, Zone 18, Universal Transverse Mercator

ALLEGANY

CATTARAUGUS

CHAUTAUQUA

ERIE

GENESEE

NIAGARA

LIVINGSTON

New York

Pennsylvania

EXPLANATION

WYOMING

NEW Erie County YORK

Cattaraugus County

Chautauqua County

Location Map

03014500# U.S. Geological Survey streamgage 

and number

Drainage basin boundary

County boundary

Figure 1. Locations of study sites and selected U.S. Geological Survey streamgages and associated drainage basins in western New 

York. (Streamgage names are listed in table 1.)
Storm Characteristics 3

Two deaths occurred during the flood in Gowanda. One 

resident suffered a heart attack while emergency responders 

were delayed by flooded streets. A second resident drowned 

when he was swept into the rising floodwaters of Thatcher 

Brook (Fairbanks and others, 2009). The tri-county area 

was declared a Federal disaster area on September 1, 2009 

(Federal Emergency Management Agency, 2009a). More than 

$45 million in Federal disaster assistance was distributed 

to fund the recovery efforts of more than 1,500 individuals 

and an estimated 1,100 public projects (Federal Emergency 

Management Agency, 2009b). The total cost of damages 

estimated by emergency managers in the affected counties and 

municipalities exceeded $90 million (National Oceanic and 

Atmospheric Administration, 2010a).

In 2009 the U.S. Geological Survey (USGS), in 

cooperation with the Federal Emergency Management Agency 

(FEMA), conducted a study to document the meteorological 

and hydrologic conditions that resulted in the damaging flash 

floods on August 10, 2009, in western New York. This report 

presents high-water elevations and maps of the areal extent 

of flooding that occurred in Gowanda and Silver Creek. Peak 

flows, estimated by indirect measurement methods for Grannis 

Brook, Thatcher Brook, and Cattaraugus Creek at or near 

the Village of Gowanda, and for Silver Creek (downstream 

from the confluence with Walnut Creek) at the Village of 

Silver Creek, also are presented. The magnitudes and annual 

exceedance probabilities (recurrence intervals) of these peak 

flows are compared with similar data obtained from nearby 

USGS continuous-record and peak-flow-only streamgages, as 

well as to data contained in the most recent flood-insurance 

studies for these communities. 

Antecedent Hydrologic Conditions

Rainfall was scattered and varied in intensity during the 

first 3 days of August 2009. Rain fell across western New York 

on August 4 and ranged from 0.16 in. in Jamestown, 30 mi 

southwest of the study area, to 2.69 in. in Colden, northeast of 

the study area; over an inch of rain was recorded by a National 

Weather Service (NWS) cooperative weather observer in 

Perrysburg, which is about 3.5 mi west of Gowanda (National 

Oceanic and Atmospheric Administration, 2010b; fig. 2). No 

substantial precipitation fell during the next 3 days, but rain 

fell on August 8, and over 1 inch of rain fell across the area 

during the afternoon on August 9, prior to the flood-causing 

storm. The weather observer in Perrysburg recorded 1.29 in. 

of rain (National Oceanic and Atmospheric Administration, 

2010b) on August 9 between 7:00 a.m. and 10:30 p.m. Eastern 

Daylight Time (EDT), at which time the observer emptied 

the rain gauge. Saturated soil conditions existed prior to the 

intense storm that caused the flooding. Flows in streams 

that were monitored by the USGS in western New York 

were generally above average flow levels for August, and 

at 10:00 p.m. EDT on August 9, just before the major storm 

event, flows were receding from runoff that had occurred 

earlier in the day.

Storm Characteristics

A detailed analysis of the storm that caused the flooding 

on August 10, 2009, was performed by the National Weather 

Service office in Buffalo (National Weather Service, 2009). 

At 8:00 p.m. EDT on August 9, a line of severe thunderstorms 

located over Lake Ontario was moving south toward western 

New York (including the city of Buffalo). As the line of 

storms moved through Buffalo, damaging winds, frequent 

lightning, and heavy rainfall occurred. Although flows 

increased in streams, no flooding was reported because the 

storm was moving rapidly southward. Around 9:30 p.m. 

EDT, a second line of severe storms developed over Lake 

Erie and moved eastward over Cattaraugus and Chautauqua 

Counties. In addition to frequent lightning, this line of storms 

also produced very heavy rainfall. By 10:00 p.m. EDT the 

first line of storms intersected the second line and evolved 

from a wind-damaging weather system into a flash‐flood 

system. The combined storms stalled for a little more than 

an hour roughly along the southern boundary of Erie County 

(over an area that included Silver Creek and Gowanda) before 

weakening and continuing southward to the Pennsylvania 

border. During the period from 10:30 p.m. on August 9, 

through midnight EDT on August 10, the weather observer 

in Perrysburg reported 5.98 in. of rainfall. Radar-derived 

estimates of rainfall that occurred over the 3-hr period from 

9:09 p.m. on August 9 through 12:09 a.m. EDT on August 

10, 2009, (fig. 2) showed that rainfall exceeded 4 in. along 

a line just south of the Erie-Cattaraugus County line. On the 

basis of the weather observer’s “ground-truth” report, the 

radar-derived precipitation likely underestimated the actual 

precipitation quantities. The combination of torrential rains 

and the high-relief topography of the area resulted in extensive 

flash flooding. 

In the areas of the two communities that are the focus 

of this report, radar-derived estimates of precipitation 

give daily (not just storm) totals of 7.06 in. for Gowanda 

and 6.28 in. for Silver Creek (Northeast Regional Climate 

Center, written instructions for retrieval of site-specific 

radar-derived precipitation, 2008). The maximum daily 

total precipitation that was reported by a NWS cooperative 

weather observer, again the observer from Perrysburg, was 

7.27 in. The Northeast Regional Climate Center assigned a 

recurrence interval for this daily total of 200 to 500 years. The 

120‐minutes duration, 500‐year return‐period precipitation 

quantity for this area is 4.18 in.; therefore, a rainfall of 5.98 in. 

in 90 min would have a recurrence interval far greater than 

500 years or a percent chance of occurring during a given year 

of less than 0.2 percent (K. Eggleston, Northeast Regional 

Climate Center, written commun., 2009). 
4 Flash Floods of August 10, 2009, in the Villages of Gowanda and Silver Creek, New York

Erie

Chautauqua Cattaraugus Allegany

Wyoming

Niagara

Genesee

Orleans

CANADA

Lake Erie

Silver Creek

Buffalo

Gowanda

Colden

Jamestown

Perrysburg

NEW YORK

PENNSYLVANIA

Storm-total radar derived

precipitation

Inches

5

4

3

2.5

2

1.5

1

0.6

0.3

0

EXPLANATION

Precipitation station

Municipality

County boundary

Pennsylvania

New 

York

Ohio

Location Map

CANADA

Lake

Erie

Lake Ontario

Lake

Huron

0 5 10 20 Miles

0 5 10 20 Kilometers

80° 79°30' 79° 78°30'

43°

42°30'

42°

Base from U.S. Geological Survey, Seamless Data Distribution System,

accessed in 2010 at http://seamless.usgs.gov 

State Plane Coordinate System projection, NAD83, SPCS Zone 3103

National Weather Service

 (source of radar)

Figure 2. Storm-total radar-derived precipitation in western New York from 9:09 p.m. on August 9, 2009, through 12:09 a.m. Eastern 

Daylight Time on August 10, 2009. (From the National Weather Service at http://www.wbuf.noaa.gov/svrwx/web_090810_Flashflood/

indexflood.html.)
Collection of High-Water-Mark Data 5

Description of the Floods

Flooding occurred in a relatively small area of western 

New York, primarily limited to Cattaraugus, Chautauqua, 

and Erie Counties. These counties were declared disaster 

areas by both the State and Federal governments. Flooding 

was primarily due to the under-capacity of small channels 

to convey the runoff that was generated by the intense 

precipitation; therefore, the most serious flooding and damages 

occurred in small stream basins. Outside of developed areas, 

the major flood damages resulted from the overtopping of 

roadways and, in many cases, the erosion of road surfaces 

and complete removal of culverts (fig. 3). In residential 

and commercial areas, such as Gowanda and Silver Creek, 

extensive flooding and damage from water and mud occurred 

(fig. 3). In both of these communities, flooding occurred 

outside previously defined flood-prone areas and caught many 

residents by surprise. In addition, the rate at which floodwaters 

rose was unusually fast and hampered rescue efforts by local 

emergency responders. Walnut Creek, which joins Silver 

Creek within the Village of Silver Creek, reportedly rose 

3 to 4 ft in 30 min (T. Roche, Silver Creek Police Chief, oral 

commun., 2009). 

In addition to the tremendous amount of runoff that 

was conveyed in small channels, the flooding in Gowanda 

was affected by the topographic characteristics of the area. 

Thatcher Brook and Grannis Brook approach Gowanda 

through high-relief areas where steep valley sides generally 

confine high flows. As these streams enter the village and 

the Cattaraugus Creek floodplain, the gradient decreases 

substantially, and the confining valley walls disappear. Sheetflow flooding across the residential and commercial areas of 

the village occurs whenever water levels exceed the tops of 

streambanks. Flooding on August 10, 2009, on the north side 

of Gowanda was exacerbated by a debris-clogged culvert on 

Grannis Brook. Residents of Gowanda were evacuated to a 

nearby school. Patients at the Tri-County Memorial Hospital 

in Gowanda were relocated, campers at Zoar Valley, upstream 

from Gowanda along Cattaraugus Creek, were rescued by 

helicopter, and a trailer park in Silver Creek was destroyed 

(Fairbanks and others, 2009; Thompson, 2009). Reservoirs 

that supplied water to both communities were overtopped 

during the floods, and the receding waters left mud, trees, and 

other debris behind. The water quality of these reservoirs was 

compromised, and the repairs to the reservoirs and watersupply infrastructures were estimated to take many months 

to return the reservoirs to their pre-flood functionality 

(Flynn, 2009). 

Cattaraugus Creek at Gowanda (station 04213500) 

rose 5 ft in 1 hr between 11:35 p.m. and 12:35 a.m. EDT 

(10:35 to 11:35 p.m. Eastern Standard Time (EST) on 

August 9) and had an initial peak of 12.88 ft at 1:35 a.m. EDT 

(12:35 a.m. EST) on August 10 (fig. 4). The creek receded 

slightly, then rose to its maximum recorded gage height of 

13.47 ft at 7:35 a.m. EDT (6:35 a.m. EST) on August 10. 

The tributaries entering Cattaraugus Creek—Thatcher Brook 

and Grannis Brook—peaked around 2:00 to 3:00 a.m. EDT 

on August 10 (Emergency responders, oral commun., 2009). 

Therefore, tributary inflows were decreasing as Cattaraugus 

Creek reached its highest stage 5 hours later, and peak flows 

in Cattaraugus Creek at Gowanda reflected contributions 

from headwater areas of the basin rather than from 

nearby tributaries. 

Cattaraugus Creek itself was not a source of major 

flooding in Gowanda compared to the tributaries Thatcher 

Brook and Grannis Brook, which caused extensive flooding 

to the south and north of Cattaraugus Creek, respectively. 

Although flooding along Cattaraugus Creek occurred 

elsewhere (for example, see report cover photograph), the 

flows in the creek within the village limits of Gowanda were 

mostly contained by high banks. The only noted exceptions 

occurred upstream from the bridge on U.S. Highway 62 

(Main Street) at the American Legion (on Legion Drive) on 

the north bank and at a residence directly across the creek 

(South Water Street) on the south bank. Both properties likely 

experienced some flooding from Grannis Brook and Thatcher 

Brook, respectively, but this flooding would have preceded 

flooding from Cattaraugus Creek by several hours. Flooding 

of these two properties occurred because they are at lower 

elevations than other properties along this reach.

Collection of High-Water-Mark Data

Two hundred forty-three high-water elevations in 

the flooded communities were surveyed by the USGS by 

differential leveling methods according to guidelines described 

by Kennedy (1988). A variety of surveying instruments, 

including an automatic optical level, a digital level, and a total 

station, were used to measure elevations to an accuracy of at 

least 0.01 ft. High-water marks are an indication of the water 

level at the peak stage of a river during a flood event and can 

be used to delineate a flooded area, compute peak streamflows, 

or calibrate peak-flow models used in flood-insurance studies. 

High-water marks are usually determined from mud, seed, 

or debris lines (or a combination thereof) left behind as the 

floodwaters receded or from wash lines where fine-grained 

soils have been eroded or loose vegetative material has been 

removed. High-water marks generally can be found on trees 

because seeds and small debris can get caught in the bark, 

but mud lines are common marks found in developed areas. 

The accuracy of the high-water marks is subjectively rated by 

the USGS personnel locating the mark, as outlined in Lumia 

and others (1986). High-water marks can be rated “excellent” 

(within 0.02 ft of the “true” high-water mark), “good” (within 

0.05 ft), “fair” (within 0.10 ft), or “poor” (greater than 0.10 ft). 

Typical high-water marks included debris lines (fig. 5A), 

wash lines on a sloping shale bank (fig. 5B), mud lines 

(fig. 5C and D), and seed lines or grass on trees (fig. 5E). 
6 Flash Floods of August 10, 2009, in the Villages of Gowanda and Silver Creek, New York

The fill above and the edge of the road on the downstream side of 

a concrete culvert were eroded.

A culvert and road were completely washed away.

Mud and debris covered residential lawns.

Figure 3. Photographs of damage from the floods of August 10, 2009.

Mud-covered belongings from flooded basements were discarded 

and lined the streets of Gowanda.

During the field activities related to the flooding, 

which were conducted on August 12-13, August 18-21, 

September 8-9, and October 19-21, 2009, 155 and 88 

high-water marks were located and surveyed within the 

village limits of Gowanda and Silver Creek, respectively. 

Many of these marks were used exclusively for estimation 

of peak flows in the streams that flowed through these 

communities. A subset of the marks (app. 1) was compiled 

to create water-surface profiles of the floods along the streams 

and maps of inundation in each of the flooded communities. 

Floodwater-Surface Profiles

 High-water marks that were surveyed along Grannis 

Brook (fig. 6) and Thatcher Brook (fig. 7) in Gowanda, 

and Walnut Creek (fig. 8) and Silver Creek (fig. 9) in the 

Village of Silver Creek, were used to create profiles of the 

water-surface elevations of the flood as it passed through the 

two communities. The high-water mark locations were picked 

from a plan drawing of the inundated areas and referenced 

to street intersections or other landmarks. The profiles were 
Collection of High-Water-Mark Data 7

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

0

2

4

6

8

10

12

14

16

8/9/2009 8/10/2009 8/11/2009 8/12/2009

S

T

REA

MFL

O

W, IN

CUBI

C FEET PE

R SE

COND

GAGE HEIGH

T, IN FEET ABOVE GA

GE D

ATUM

Gage height

Streamflow

Figure 4. Streamflow and gage-height for Cattaraugus Creek at Gowanda, New York, U.S. Geological Survey station 04213500, 

August 9-12, 2009.

compared with those from the FEMA 0.2-percent annual 

exceedance probability (500-year recurrence interval) profiles 

(Federal Emergency Management Agency, 1983; 2009c). The 

profiles for Grannis Brook and Thatcher Brook were plotted 

to the North American Vertical Datum of 1988 (NAVD 88), 

whereas those for Walnut Creek and Silver Creek were plotted 

to the National Geodetic Vertical Datum of 1929 (NGVD 29), 

which are the respective datums used in the most recent 

FEMA flood-insurance reports. The plots showed that flood 

levels on August 10 along Grannis Brook were close to, or 

slightly higher than, the FEMA flood levels, whereas those 

along Thatcher Brook were 2 to 4 ft higher at some points. The 

flood levels along Walnut and Silver Creeks were noticeably 

higher than the FEMA flood levels, at some locations as much 

as 6 to 8 ft higher.

Areal Extent of Flooding

Floodwater-surface elevations, notes from USGS field 

personnel, and observations from community leaders and 
8 Flash Floods of August 10, 2009, in the Villages of Gowanda and Silver Creek, New York

A

E

C D

B

Figure 5. Examples of representative high-water marks from the 

floods of August 10, 2009: (A) debris line, (B) wash line, (C and D)

mud lines, and (E) grass on tree.
Collection of High-Water-Mark Data 9

720

740

760

780

800

0 500 1,000 1,500 2,000 2,500 3,000

ELE

V

A

TION, IN F

E

E

T (

N

A

VD 88)

DISTANCE UPSTREAM FROM MOUTH, IN FEET

August 10, 2009, flood elevation

FEMA 0.2 -percent annual exceedance probability flood elevation

Streambed elevation

Buffalo Street bridge

Cemetery Hill Road

Figure 6. Water-surface elevations for the August 10, 2009, flood and the FEMA 0.2-percent annual exceedance probability flood for 

Grannis Brook at Gowanda, N.Y.

710

730

750

770

790

810

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

ELE

V

A

TION, IN F

E

E

T (

N

A

VD 88)

DISTANCE UPSTREAM FROM MOUTH, IN FEET

August 10, 2009, flood elevation

FEMA 0.2 -percent annual exceedance probability flood elevation

Streambed elevation

West Main Street bridge

Jamestown Street bridge

Hill Street bridge

Dam

Figure 7. Water-surface elevations for the August 10, 2009, flood and the FEMA 0.2-percent annual exceedance probability flood for 

Thatcher Brook at Gowanda, N.Y.
10 Flash Floods of August 10, 2009, in the Villages of Gowanda and Silver Creek, New York

550

570

590

610

0 1,000 2,000 3,000 4,000 5,000 6,000

ELEVATION, IN FEET (NGVD29)

DISTANCE UPSTREAM FROM MOUTH, IN FEET

August 10, 2009, flood elevation

FEMA 0.2 -percent annual exceedance probability flood elevation

Streambed elevation

Central 

Avenue 

bridge

Main Street 

bridge

Figure 8. Water-surface elevations for the August 10, 2009, flood and the FEMA 0.2-percent annual exceedance probability flood for 

Walnut Creek at Silver Creek, N.Y.

550

570

590

610

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000

ELEVATION, IN FEET (NGVD29)

DISTANCE UPSTREAM FROM MOUTH, IN FEET

August 10, 2009, flood elevation

FEMA 0.2 -percent annual exceedance probability flood elevation

Streambed elevation

Central Avenue bridge

Figure 9. Water-surface elevations for the August 10, 2009, flood and the FEMA 0.2-percent annual exceedance probability flood for 

Silver Creek at Silver Creek, N.Y.
Annual Exceedance Probabilities of Peak Streamflows 11

emergency responders were used, along with a geographic 

information system, to create maps that showed the areal 

extent of flooding in Gowanda (fig. 10) and Silver Creek 

(fig. 11). Calculation of depth of inundation within these 

delineated areas was not possible because the 30‐meter 

digital elevation data that were available were imprecise, and 

high-accuracy land-surface elevation data (such as LiDAR) 

were unavailable. As was done with the presentation of the 

water-surface-profile plots, the high-water elevations that are 

presented in these figures are referenced to different datums. 

Those for the Gowanda area are referenced to NAVD 88, 

whereas those for the Silver Creek area are referenced to 

NGVD 29. Again, this was done so that the August 10, 2009, 

data would be directly comparable to the data presented in the 

most recent FEMA flood-insurance report for each community.

Grannis Brook flooding was exacerbated by the culvert 

at Cemetery Hill Road, which because of its small size could 

not convey the flood flows and was partly blocked by debris. 

Water outside of the channel at this point flowed down East 

Main Street and Perry Street, through the adjacent residential 

areas (fig. 10). Floodwaters, up to 3 ft deep, continued through 

the commercial area along Buffalo Street (U.S. Highway 62) 

before flowing into Cattaraugus Creek. At the south end of 

the village, floodwaters in Thatcher Brook had exceeded 

that channel’s capacity to such a degree that water levels 

just south of the village limit overtopped the western bank 

on which U.S. Highway 62 is located (fig. 10). Water flowed 

down U.S. Highway 62 (Jamestown Street) through a railroad 

underpass, then through a residential area that, for lesser 

magnitude floods, would have been protected from flooding by 

the railroad embankment between this neighborhood and the 

brook. Downstream from the end of the railroad embankment 

(upstream from Hill Street), the floodwaters on either side of 

the embankment combined and flowed as sheet flow, in some 

cases more than 3 ft deep, throughout the village from this 

point to Cattaraugus Creek.

Floodwaters in Silver Creek upstream from the village 

limit covered the vegetated floodplains on the insides of 

meander bends but were confined by the valley walls and 

caused no destruction of property. Once inside the village 

limits, however, floodwaters inundated the floodplain areas 

on which a trailer park and businesses had been built, caused 

extensive damage, and threatened the lives of residents 

and emergency responders. A similar situation occurred 

on Walnut Creek, but most of the damaged properties 

between Main Street (U.S. Highway 20) and Central Avenue 

(State Highway 5; fig. 11) were private residences. Water 

depths in these areas typically ranged from 3 to 5 ft but 

increased to as much as 8 ft in the area below the confluence 

of the two creeks, where the railroad embankment that 

parallels the Lake Erie shoreline caused the floodwater to 

pond before eventually draining through one of two 

outlets—Silver Creek or the Jackson Street railroad 

underpass (about 800 ft to the west; fig. 11). 

Magnitudes of Peak Streamflows

In addition to the flood sites on Grannis Brook, Thatcher 

Brook, and Silver Creek, peak streamflows presented in this 

report were determined at 12 USGS continuous-record or 

peak-flow-only streamgages in western New York (table 1). 

Stage-to-streamflow relations that had been previously defined 

by streamflow measurements at 11 of these sites were used to 

assign peak flows to the recorded peak gage heights. Indirect 

measurements of peak flows were made at four sites, including 

one continuous-record site where confirmation of the stageto-streamflow relation was desired and three ungaged sites 

on streams that were hardest hit by the August 10 floods but 

for which stage-to-streamflow relations had not been defined. 

Estimates of the peak flows in Grannis Brook, Thatcher Brook, 

and Cattaraugus Creek (all in Gowanda) were computed 

by the slope-area method following procedures described 

by Dalrymple and Benson (1967). Computations were 

performed by the USGS Slope-Area Computation program 

(Fulford, 1994). The estimated peak flows in Grannis Brook, 

Thatcher Brook, and Cattaraugus Creek were 1,400 ft3/s, 

7,600 ft3/s, and 33,200 ft3/s, respectively (table 2).

The computation of the peak flow in Silver Creek was 

complicated by erratic floodplain flow, a large contraction 

in flow area caused by a railroad bridge, and bypass flow 

though a railroad underpass. The peak flow in the main 

channel was computed using two methods: the openchannel width-contraction (or contracted opening) method 

(Matthai, 1967) and the critical-depth method (Barnes and 

Davidian, 1978) with the River Analysis System, HEC-RAS 

(Brunner, 2008). The results from the two computations 

agreed within 1 percent. The peak flow through the railroad 

underpass was computed using the flow-through-culvert 

method described by Bodhaine (1968) with the USGS Culvert 

Analysis Program (Fulford, 1998). The computed peak 

flows in the main and bypass channels of Silver Creek were 

19,000 ft3/s and 520 ft3/s, respectively (table 2).

Annual Exceedance Probabilities of 

Peak Streamflows

The annual exceedance probability is the chance that a 

flood of a given magnitude will be equaled or exceeded in any 

one year. The reciprocal of the annual exceedance probability 

is the recurrence interval, expressed in years. For example, a 

flood that has a 1 in 100 chance of being equaled or exceeded 

in any one year has an annual exceedance probability of 

1 percent and a recurrence interval of 100 years (Holmes and 

Dinicola, 2010). This flood is commonly referred to as the 

100-year flood. Similarly, a 500-year flood has a 0.2‐percent 

chance (or 1 in 500 chance) of being equaled or exceeded in a 
12 Flash Floods of August 10, 2009, in the Villages of Gowanda and Silver Creek, New York

^_

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^_

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Perry Street

West Main Street

Hill Street

Buffalo Street

A dl rich Street

East

Main Street

Jamestown

Street

Legion Drive

South Water Street

Hill Road

Cemetery

G1

760.92

G10

779.46

G11

775.98

G12

786.16

G13

785.57

G14

785.89

G15

781.36

G16

779.01

G17

775.92

G18

775.99

G19

772.86

G2

767.40

G20

763.30

G21

764.94

G22

768.75

G23

773.74 G24

780.65

G25

784.73

G26

796.24

G27

773.43

G28

758.97

G29

766.47

G3

767.43

G30

754.94

G31

754.79

G32

754.76

G33

752.81

G34

748.45

G35

749.85

G36

754.31

G37

756.62

G38

772.16

G39

772.25

G4

768.31

G40

757.41

G41

756.46

G42

754.47

G43

756.98

G44

755.89

G45

753.33

G46

754.05

G47

751.41

G48

751.32

G49

752.31

G5

768.34

G50

751.34

G51

749.33

G52

749.12

G53

748.16

G54

745.95

G55

745.76

G56

768.39

G57

753.98

G58

749.99

G59

751.09

G6

769.64

G7

770.23

G8

769.33 G9

769.60

78°56'30" 78°56'

42°28'

42°27'30"

42°27'

Orthophotography from USDA National Agriculture Imagery Program 2009 

http://www.fsa.usda.gov/FSA/apfoapp?area=home&subject=prog&topic=nai

Geographic Coordinate System projection, North American Datum of 1983

Dam

Grannis

Brook

Cattaraugus Creek

Thatcher Brook Cattaraugus Creek

#04213500

0 800 1,600 3,200 Feet

0 200 400 800 Meters

^_

 EXPLANATION

Inundated area

G56

768.39

#

04213500

and water-surface elevation (in feet, NAVD88)

Streamgage and station number

¬«39

¬«39

¤62

£¤62

¬«39

¬«39

£¤62

Figure 10. Areal extent and water-surface elevations of flooding in Gowanda, N.Y., August 10, 2009.
Annual Exceedance Probabilities of Peak Streamflows 13

¬«5

¬«5

79°10'30" 79°10' 79°9'30"

42°33'

42°32'30"

42°32'

S1

594.33

S2

594.33

S3

594.98 S5

596.83

S6

595.46

S7

594.56

S8

590.87

S9

590.58

S10

590.04

S11

586.60

S12

586.86 S13

590.88 S14

592.45

S17

602.11

S18

603.55

S19

604.68

S20

604.19

S21

604.58

S22

586.28

S23

586.20

S24

585.78

S27

586.06 S28

585.76

S29

585.66

S25

587.47

S26

586.92

S4

595.50

S15

596.00

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^_

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S16

602.40

Main Street

Central Avenue

Howard

Street

Jackson Street

New York Central Railroad

^_

 EXPLANATION

Inundated area

G56

768.39 and water-surface elevation (in feet, NGVD29)

0 850 1,700 3,400 Feet

0 220 440 880 Meters

Orthophotography from USDA National Agriculture Imagery Program 2009 

http://www.fsa.usda.gov/FSA/apfoapp?area=home&subject=prog&topic=nai

Universal Transverse Mercator projection, Zone 18, North American Datum of 1983

Silver Creek

Silver Creek

Walnut Creek

¤£20

¤£20

L ake Erie

Figure 11. Areal extent and water-surface elevations of flooding in Silver Creek, N.Y., August 10, 2009.
14 Flash Floods of August 10, 2009, in the Villages of Gowanda and Silver Creek, New York Table 1. Historic peak flows, and peak flows and associated annual exceedance probabilities for the floods of August 10, 2009, at selected U.S. Geological Survey streamgages in western New York. [Station locations are shown in figure 1. mi2, square miles; ft3/s, cubic feet per second; ft3/s/mi2, cubic feet per second per square mile; E, estimated; >, greater than; <, less than; --, no data] Maximum prior to flood of August 10, 2009 Flood of August 10, 2009 Station number Station name Drainage area (mi2

)

Period of

annual peak

flow record

(water years)

Date

of

peak

Peak

flow

(ft3/s)

Peak

flow

(ft3/s)

Peak

yield

(ft3/s/mi2

)

Annual

exceedance

probability1

(percent) 

Recurrence

interval1

(years)

03010734 Ischua Creek tributary near Machias 5.12 1978–81, 

83–2008

Sept. 14, 1979 570 329 64.2 25 4

03011020 Allegheny River at Salamanca 1,608 1904–2008 June 23, 1972 73,000 17,900 11.1 80 1.2503013800 Ball Creek at Stow 9.58 1974–2008 Sept. 14, 1979 2,000 E 300 31.3 > 100 < 103014500 Chadakoin River at Falconer 194 1935–2008 Sept. 14, 1979 2,250 1,340 6.91 50 204213376 Canadaway Creek at Fredonia 32.9 1979, 86–2008 Aug. 7, 1979 12,000 E 1,500 45.6 67 1.50421340305 Silver Creek at mouth at Silver Creek 51.8 None -- -- 19,500 376 2 < 0.2 2 > 50004213490 South Branch Cattaraugus Creek near Otto 25.1 1963–99 Sept. 14, 1979 4,350 E 7,400 295 < 0.2 > 50004213500 Cattaraugus Creek at Gowanda 436 1940–2008 Mar. 7, 1956 34,600 33,200 76.1 2.2 450421350503 Grannis Brook at Gowanda 32.48 None -- -- 1,400 564 2,4 < 0.2 2,4 > 50004213508 Thatcher Brook at Gowanda 36.49 1986 Aug. 1, 1986 3,100 7,600 1,170 2 < 0.2 2 > 50004214500 Buffalo Creek at Gardenville 142 1937, 39–2008 June, 1937 16,000 5,590 39.4 67 1.504215000 Cayuga Creek near Lancaster 96.4 1937, 39–68,

1972–2008

June, 1937 18,000 4,890 50.7 50 2

04215500 Cazenovia Creek at Ebenezer 135 1941–2008 Sept. 9, 2004 14,700 13,400 99.2 2.5 4004216418 Tonawanda Creek at Attica 76.9 1972, 78–2008 July 8, 1998 9,400 3,030 39.4 40 2.504230380 Oatka Creek at Warsaw 39.1 1964–2008 July 8, 1998 4,110 1,450 37.1 50 2

1 From Lumia and others (2006), unless otherwise specified.2 From table 3.3 Drainage area at peak-flow measurement site not at the mouth of the stream.4 From values estimated from a plot of peak discharges and drainage areas in Federal Emergency Management Agency (2009c), the Grannis Brook peak would have an annual exceedance probability of 2.8 

 percent (recurrence interval of 35 years); however this probability was deemed to be unreasonably high when the peak flow was compared to those estimated for other nearby small basins.
Annual Exceedance Probabilities of Peak Streamflows 15

given year. The estimates of annual exceedance probabilities, 

which are statistically derived and based on peak flows 

measured or recorded on a particular stream, can be improved 

as the peak-flow record is extended. On streams where flow 

records are unavailable, regression equations (based on 

long-term peak-flow records from streams with similar basin 

characteristics) can be used to estimate flows with particular 

annual exceedance probabilities. Regression equations to 

estimate peak flows on rural, unregulated streams in six 

hydrologic regions in New York were developed by Lumia 

and others (2006) and are included in the program StreamStats 

(U.S. Geological Survey, 2010). The basin characteristics, 

which were deemed significant in estimating peak flows in 

the southwestern hydrologic region of New York that includes 

the study area, are drainage area, the main-channel slope, and 

mean annual precipitation.

Annual exceedance probabilities for peak flows at the 

indirect-measurement sites were compiled from available 

sources (table 3). Those for Grannis Brook, Thatcher Brook, 

and Cattaraugus Creek at Gowanda were obtained from 

the FEMA flood-insurance report for Erie County (Federal 

Emergency Management Agency, 2009c), and those for Silver 

Creek were obtained from the flood-insurance report for the 

Village of Silver Creek (Federal Emergency Management 

Agency, 1983). For comparison, peak flows for given annual 

exceedance probabilities were computed using StreamStats 

(U.S. Geological Survey, 2010) and also are presented in 

table 3. 

The peak flow in Cattaraugus Creek at Gowanda had 

an annual exceedance probability of 2.2 percent (45-year 

recurrence interval; table 1). The peak flows in Thatcher Brook 

and Silver Creek had annual exceedance probabilities less 

than 0.2 percent (recurrence intervals greater than 500 years). 

The annual exceedance probability of the peak flow in 

Grannis Brook was uncertain. On the basis of the FEMA 

flood-insurance report (Federal Emergency Management 

Agency, 2009c), the peak flow had an annual exceedance 

probability of 2.8 percent (35-year recurrence interval), which 

was incongruent when compared with the annual exceedance 

probabilities of the flows at other sites with small drainage 

areas that fell almost entirely within the area of heaviest 

precipitation. From StreamStats estimates (U.S. Geological 

Survey, 2010), the annual exceedance probability for the 

Grannis Brook peak was 0.2 percent (500‐year recurrence 

interval; table 3), which agrees with the results for the other 

small-basin sites. Given the relative magnitude and flooding 

extent of the peak flow in Grannis Brook compared to those 

in Thatcher Brook and Silver Creek, an annual exceedance 

probability of 0.2 percent is reasonable and is presented in 

table 1 to quantify this peak flow.

Peak flows that occurred on August 10, 2009, and their 

annual exceedance probabilities were compiled for other 

USGS continuous-record and peak-flow-only streamgages 

in western New York (fig. 1; table 1). These data indicate 

that high flows occurred throughout western New York, but 

severe flooding was limited to the area that received the 

most intensive rainfall, as shown in figure 2. Only the site on 

South Branch Cattaraugus Creek near Otto (a discontinued 

peak-flow-only USGS streamgage) experienced a flood of a 

magnitude similar to the hard-hit areas of Gowanda and Silver 

Creek (less than 0.2 percent chance of exceedance). Cazenovia 

Creek at Ebenezer (near Buffalo) had a flow with a 2.5-percent 

Table 2. Peak flows computed for the floods of August 10, 2009, at sites in Gowanda and Silver Creek, New York.

[Site locations are shown in figure 1. mi2, square miles; ft3/s, cubic feet per second; --, no data]

Number of high-water marks

Community Stream Drainage

area1

 (mi2) Surveyed Included in final maps and tables2

Type of indirect

measurement of flow

Peak

flow

(ft3

/s)

Silver Creek Walnut Creek 26.3 12 12 (3) -Silver Creek 51.8 76 17 Width contraction 4

19,500

Gowanda Cattaraugus Creek 436 49 16 Slope area 33,200

Grannis Brook 2.48 47 21 Slope area 1,400

Thatcher Brook 6.49 59 22 Slope area 7,600

1

 Drainage area at discharge measurement site.

2

 See appendix 1 for list of high-water marks.

3

 The Silver Creek indirect measurement was made downstream from the confluence of Silver and Walnut Creeks and, therefore, is a measure of the combined 

 flows in both streams.

4

 Includes 520 ft3/s bypass flow through Jackson Street railroad underpass.
16 Flash Floods of August 10, 2009, in the Villages of Gowanda and Silver Creek, New York

Table 3. Peak flows for indicated annual exceedance probabilities for selected streams in Gowanda and Silver Creek, New York.

[Site locations are shown in figure 1. mi2, square miles; ft3/s, cubic feet per second; ‐‐, no data]

Peak flows (ft3/s) for indicated annual exceedance probabilities

Stream and location

Drainage

area (mi2

) 10-percent 4-percent 2-percent 1-percent 0.2-percent

Silver Creek at mouth

at Silver Creek1

51.8 4,450 -- 6,100 7,000 9,000

Cattaraugus Creek

at Gowanda2

436 26,800 -- 36,800 41,500 52,000

Grannis Brook at mouth

at Gowanda2

3

 2.68 1,040 -- 1,600 1,740 2,050

Thatcher Brook at mouth

at Gowanda2

3

 7.38 1,650 -- 2,400 2,700 3,100

Peak flows (ft3

/s) for indicated annual exceedance

probabilities computed using StreamStats4

10-percent 4-percent 2-percent 1-percent 0.2-percent

Silver Creek at mouth at 

Silver Creek

5,200 6,880 8,320 9,790 13,600

Cattaraugus Creek at 

Gowanda5

24,400 29,900 34,200 38,700 50,000

Grannis Brook at mouth at 

Gowanda

518 690 840 992 1,390

Thatcher Brook at mouth 

at Gowanda

1,360 1,820 2,230 2,640 3,730

1

 Federal Emergency Management Agency (1983).

2

 Values estimated from figure 5, a plot of peak discharges and drainage areas, in Federal Emergency Management Agency (2009c). 

3

 Drainage area at the mouth of the stream (Wagner and Dixson, 1985).

4

 U.S. Geological Survey (2010).

5

 Values are same as those presented by Lumia and others (2006).

annual exceedance probability (40-year recurrence interval). 

Other sites distant from the intensive precipitation area had 

flows with annual exceedance probabilities equal to or greater 

than 25 percent (recurrence intervals equal to or less than 

4 years).

Summary

A severe thunderstorm struck western New York, south 

of Buffalo, during the night of August 9, 2009, and caused 

flash flooding during the early morning of August 10 in parts 

of Cattaraugus, Chautauqua, and Erie Counties. Nearly 6 

inches of rain fell in 1.5 hours as recorded by a National 

Weather Service observer in Perrysburg, which lies between 

Gowanda and Silver Creek, the communities that suffered 

the most damage. The rainfall intensity of this storm had less 

than a 0.2‐percent chance of occurring during a given year 

(that is, it exceeded the 500-year storm event) and reportedly 

caused water levels in Walnut Creek in the Village of Silver 

Creek to rise 3 to 4 feet in 30 minutes. Numerous road 

culverts were washed out, and more than one‐quarter of the 

roads in Cattaraugus County were damaged. Many people 

were evacuated or rescued in both communities, including 

patients in the Tri-County Memorial Hospital in Gowanda 

and residents of a creek-side trailer park in Silver Creek, 

which was destroyed. The water supplies of both communities 

were compromised by damages to village reservoirs and 

water-transmission infrastructures. Water and mud damage 

to residential and commercial properties was extensive. Two 

deaths occurred during the flood in Gowanda. One resident 

suffered a heart attack while emergency responders were 

delayed by floodwaters. A second resident drowned when he 
References Cited 17

fell into Thatcher Brook after the floodwaters had undercut 

the land on which he was standing. The tri-county area was 

declared a Federal disaster area, and more than $45 million 

in Federal assistance was distributed to more than 1,500 

individuals and an estimated 1,100 public projects. The total 

cost of damages estimated by emergency managers in the 

affected counties and municipalities exceeded $90 million.

Peak flows in small basins, such as Grannis Brook, 

Thatcher Brook, and Silver Creek, occurred between 

2:00 and 3:00 a.m. EDT on August 10, 2009, and were the 

cause of the severe flooding and associated damages in the 

Villages of Gowanda and Silver Creek. The peak flow in 

Cattaraugus Creek at Gowanda, which was not a cause of 

major flooding in this community, occurred about 5 hours 

after the small tributaries had peaked. 

Over 240 high-water marks were surveyed by the U.S. 

Geological Survey; a subset of these marks was used to 

create floodwater-surface profiles for four streams and to 

delineate the areal extent of flooding in Gowanda and Silver 

Creek. Flood elevations exceeded previously defined Federal 

Emergency Management Agency (FEMA) 0.2-percent 

annual exceedance probability (500-year recurrence interval) 

elevations by 2 to 4 feet in Gowanda and as much as 6 to 8 ft 

in Silver Creek. Most of the high-water marks were used in 

indirect hydraulic computations to estimate peak flows for 

four streams. The peak flows in Grannis Brook and Thatcher 

Brook were computed, using the slope-area method, to be 

1,400 and 7,600 cubic feet per second, respectively, and 

peak flow in Silver Creek was computed, using the widthcontraction method, to be 19,500 cubic feet per second. The 

annual exceedance probabilities for flows in these and other 

basins with small drainage areas that fell almost entirely 

within the area of heaviest precipitation were less than 

0.2 percent (or recurrence intervals greater than 500 years). 

The peak flow in Cattaraugus Creek at Gowanda was 

computed, using the slope-area method, to be 33,200 cubic 

feet per second and had an annual exceedance probability of 

2.2 percent (recurrence interval of 45 years).

Acknowledgments

The authors thank the many residents of the flooded 

communities for their descriptions of the flood and their 

cooperation in helping field crews locate high-water marks. 

Timothy Roche, Chief of Police, Silver Creek, provided 

valuable information regarding the flood in Silver Creek, as 

well as photographs of flood damage in the village. Ralph 

Crawford, Silver Creek Highway Superintendent, and 

Michael Hutchinson, Gowanda Superintendent of Public 

Works, provided feedback on the delineation of the 

inundated areas in their respective communities.

References Cited

Barnes, H.H., and Davidian, J., 1978, Indirect methods, in

Herschy, R.W., ed., Hydrometry–principles and practices: 

New York, Wiley, p. 189-190.

Bodhaine, G.L., 1968, Measurement of peak discharge at 

culverts by indirect methods: U.S. Geological Survey 

Techniques of Water-Resources Investigations, book 3, 

chap. A3, 60 p.

Brunner, G.W., 2008, HEC-RAS, River analysis system 

user’s manual, version 4.0: U.S. Army Corps of Engineers, 

Hydrologic Engineering Center, report CPD‐68, 733 p.

Dalrymple, Tate, and Benson, M.A., 1967, Measurement of 

peak discharge by the slope-area method: U.S. Geological 

Survey Techniques of Water-Resources Investigations, 

book 3, chap. A2, 12 p.

Fairbanks, Phil, Michel, Lou, and Binkley, Collin, 2009, 

Creek goes on rampage: The Buffalo News Newspaper, 

August 11, 2009, p. 1-2.

Federal Emergency Management Agency, 1983, Flood 

insurance study, Village of Silver Creek, Chautauqua 

County, New York: Federal Emergency Management 

Agency, 18 p.

Federal Emergency Management Agency, 2009a, President 

declares major disaster for New York: Federal Emergency 

Management Agency, accessed July 29, 2010, at http://

www.fema.gov/news/newsrelease.fema?id=49434.

Federal Emergency Management Agency, 2009b, Combined 

disaster assistance to western New York will top $45 

million: Federal Emergency Management Agency, accessed 

July 29, 2010, at http://www.fema.gov/news/newsrelease.

fema?id=49960.

Federal Emergency Management Agency, 2009c, Flood 

insurance study, Erie County, New York (all jurisdictions), 

Volume 1 of 5: Federal Emergency Management Agency, 

accessed February 10, 2010, at New York – Mapping Status, 

http://www.rampp-team.com/ny.htm.

Flynn, Lisa, 2009, Gowanda water supply dwindling: WIVB.

com, accessed April 20, 2010, at http://www.wivb.com/dpp/

news/gowanda_water_supply_dwindling_090811.

Fulford, J.M., 1994, User’s guide to SAC, a computer program 

for computing discharge by slope-area method: U.S. 

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Flooding of December 29, 1984 through January 2, 1985, 

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Magnitude and frequency of floods in New York: U.S. 

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t=1273767408015l.
Appendix 1. High-water marks in the Villages of Gowanda and Silver Creek, N.Y., 

for the flash floods of August 10, 2009
20 Flash Floods of August 10, 2009, in the Villages of Gowanda and Silver Creek, New York Appendix 1. High-water marks in the Villages of Gowanda and Silver Creek, New York, for flash floods of August 10, 2009. [High-water marks shown in figures 10 and 11. Mark numbers in bold type are those high-water marks used to create water-surface profile figures 6-9. Latitude and longitude are in degrees, minutes, and seconds. ft, feet; NGVD29, National Geodetic Vertical Datum of 1929; NAVD88, North American Vertical Datum of 1988] Mark number Latitude Longitude Elevation, ft NGVD29 Elevation, ft NAVD88 Distance, ft above ground Quality Description Address Grannis Brook G1 42 27 49.0 78 56 02.9 761.37 760.92 0.4 Good Mud line on side of building G2 42 27 50.7 78 56 00.5 767.85 767.40 0.6 Fair Mud line on fence G3 42 27 51.2 78 55 58.7 767.88 767.43 0.8 Good Mud line on steps of front porch G4 42 27 53.3 78 55 58.6 768.76 768.31 1.2 Good Mud line on basement window G5 42 27 51.0 78 55 57.7 768.79 768.34 1.3 Excellent Mud line on inside garage wall G6 42 27 48.8 78 55 50.0 770.09 769.64 2.5 Good Mud line on side of barn G7 42 27 47.3 78 55 48.2 770.68 770.23 0.5 Fair Debris line on small bush G8 42 27 50.6 78 55 53.6 769.78 769.33 1.1 Excellent Mud line on Church window frame G9 42 27 50.5 78 55 51.4 770.05 769.60 1.3 Excellent Mud line on side of garage G10 42 27 53.3 78 55 49.6 779.91 779.46 1.4 Good Mud line on back door 46 Park Street G11 42 27 53.4 78 55 50.9 776.43 775.98 1.4 Good Mud line transposed from inside garage G12 42 27 54.5 78 55 49.8 786.61 786.16 2.6 Excellent Mud line on wooden shed G13 42 27 55.7 78 55 49.7 786.02 785.57 0.0 Fair Debris line on ground G14 42 27 55.8 78 55 51.7 786.34 785.89 3.0 Fair Seed line on tree G15 42 27 54.0 78 55 52.1 781.81 781.36 2.2 Good Mud line transposed from inside barn G16 42 27 57.7 78 55 55.7 779.46 779.01 1.6 Not noted Debris on telephone pole 61 Perry Street G17 42 27 57.3 78 55 56.1 776.37 775.92 0.9 Fair Debris line in lattice below porch 61 Perry Street G18 42 27 57.5 78 55 56.6 776.44 775.99 0.9 Good Mud line on inside of front door 55 Perry Street G19 42 27 58.3 78 56 00.6 773.31 772.86 0.0 Good Debris line on ground 27 Perry Street G49 42 28 04.3 78 56 15.6 752.76 752.31 1.0 Fair Grass in fence rail Union Street

G50 42 28 04.6 78 56 17.0 751.79 751.34 0.5 Fair Grass in tree Union StreetG56 42 28 04.6 78 56 03.3 768.84 768.39 0.8 Good Mud line on shed behind house 133 Buffalo StreetG57 42 28 01.5 78 56 10.3 754.43 753.98 1.4 Good Mud line on shed behind house 30 Union Street

Thatcher Brook

G20 42 27 43.6 78 56 09.1 763.75 763.30 2.5 Fair Seed line in bushes Front of Burger KingG21 42 27 40.5 78 56 12.5 765.39 764.94 2.2 Good Mud line on Church doorG22 42 27 36.7 78 56 14.0 769.20 768.75 0.0 Good Debris line in front yard 118 Jamestown Street
Appendix 1. High-water marks in the Villages of Gowanda and Silver Creek, N.Y., for the flash floods of August 10, 2009 21

 —Continued

Mark

number Latitude Longitude Elevation, ft NGVD29 Elevation, ft NAVD88 Distance, ft above ground Quality Description Address

Thatcher Brook—Continued

G23 42 27 33.9 78 56 16.0 774.19 773.74 2.8 Excellent Mud line on inside garage wall Corner Jamestown &

Torrance Streets

G24 42 27 29.6 78 56 21.1 781.10 780.65 1.4 Good Mud line on playground set Jamestown Street near 

South Chapel Street

G25 42 27 26.1 78 56 21.1 785.18 784.73 3.0 Good Mud line on carport leg 220 Jamestown Street

G26 42 27 17.2 78 56 27.1 796.69 796.24 2.2 Good Mud line on garage door frame 336 Jamestown Street

G27 42 27 34.0 78 56 23.7 773.88 773.43 1.2 Good Mud line on swimming pool filter 24 Orchard Place

G28 42 27 42.0 78 56 30.4 759.42 758.97 2.4 Excellent Mud line on shed 184 West Main Street

G29 42 27 39.0 78 56 17.1 766.92 766.47 3.6 Excellent Mud line on shed Behind Lutheran Church

G30 42 27 50.8 78 56 22.8 755.39 754.94 2.2 Not noted Mud line on house 18 St. Johns Street

G31 42 27 50.9 78 56 22.9 755.24 754.79 2.1 Not noted Mud line on house 20 St. Johns Street

G32 42 27 49.9 78 56 23.8 755.21 754.76 2.1 Not noted Mud line on garage 24 St. Johns Street

G33 42 27 54.7 78 56 31.5 753.26 752.81 2.0 Excellent Mud line on garage 106 Aldrich Street

G34 42 28 03.5 78 56 29.2 748.90 748.45 0.0 Fair Debris line on ground East road embankment of 

Aldrich Street

G35 42 28 00.5 78 56 28.8 750.30 749.85 1.5 Fair Debris line in chain-link fence School athletic field

G36 42 27 57.6 78 56 19.2 754.76 754.31 0.8 Not noted Debris line below front door House between 135 and 

149 North Water Street 

G37 42 27 53.9 78 56 15.2 757.07 756.62 0.5 Excellent Mud line on foundation St. Mary’s Episcopal 

Church

G38 42 27 34.2 78 56 10.1 772.61 772.16 0.0 Good Mud line on ground Chestnut Street

G39 42 27 34.0 78 56 04.1 772.70 772.25 0.0 Fair Mud line on ground Chestnut Street

G58 42 28 02.7 78 56 36.0 750.44 749.99 1.1 Good Mud line inside bus garage North Water Street

G59 42 27 54.3 78 56 38.6 751.54 751.09 1.5 Good Mud line on window Tri-County Memorial 

Hospital

Cattaraugus Creek

G40 42 27 41.8 78 55 59.6 757.86 757.41 0.0 Good Debris line 72 South Water Street

G41 42 27 43.5 78 56 01.5 756.91 756.46 0.0 Good Debris line

G42 42 27 48.7 78 56 07.2 754.92 754.47 0.0 Good Seed/debris line
22 Flash Floods of August 10, 2009, in the Villages of Gowanda and Silver Creek, New York —Continued Mark number Latitude Longitude Elevation, ft NGVD29 Elevation, ft NAVD88 Distance, ft above ground Quality Description Address Cattaraugus Creek—Continued G43 42 27 44.3 78 55 57.5 757.43 756.98 0.5 Good Mud line on door American Legion G44 42 27 46.3 78 56 01.6 756.34 755.89 0.0 Good Seed line G45 42 27 51.5 78 56 07.8 753.78 753.33 0.0 Good Wash line G46 42 27 56.4 78 56 10.0 754.50 754.05 1.0 Poor Mud line on tree In village park G47 42 28 01.5 78 56 12.5 751.86 751.41 0.0 Good Debris line on ground In village park G48 42 28 01.9 78 56 13.4 751.77 751.32 1.5 Good Seed line on tree In village park G51 42 28 05.2 78 56 19.3 749.78 749.33 0.0 Good Debris line Seneca Street G52 42 28 05.5 78 56 20.0 749.57 749.12 0.0 Good Debris line Seneca Street G53 42 28 06.9 78 56 24.2 748.61 748.16 0.0 Good Seed line G54 42 28 07.3 78 56 29.3 746.40 745.95 0.0 Fair Debris line East side of Aldrich Street G55 42 28 07.1 78 56 30.1 746.21 745.76 0.0 Good Seed line West side of Aldrich Street Walnut Creek S1 42 32 25.3 79 10 10.2 594.33 593.88 0.0 Good Fine debris line S2 42 32 25.3 79 10 10.4 594.33 593.88 0.0 Good Fine debris line S3 42 32 23.8 79 10 11.1 594.98 594.53 0.0 Good Fine debris line S4 42 32 23.8 79 10 11.5 595.50 595.05 0.0 Fair Fine debris line S5 42 32 22.1 79 10 12.8 596.83 596.38 1.0 Fair Silt line on tree S6 42 32 26.3 79 10 15.7 595.46 595.01 1.0 Fair Silt line S7 42 32 28.9 79 10 15.3 594.56 594.11 1.3 Fair Silt line on fence S8 42 32 33.6 79 10 13.9 590.87 590.42 3.0 Poor Silt line on house

S9 42 32 36.7 79 10 13.2 590.58 590.13 4.1 Fair Debris line on house

S10 42 32 40.6 79 10 11.3 590.04 589.59 5.4 Good Mud line on house

S11 42 32 45.6 79 10 12.8 586.60 586.15 4.5 Good Mud line on fence

S12 42 32 47.3 79 10 13.9 586.86 586.41 6.0 Fair Mud line on phone pole

Silver Creek

S13 42 32 45.0 79 09 59.6 590.88 590.43 1.5 Fair Mud line on metal shed

S14 42 32 44.2 79 09 56.1 592.45 592.00 6.0 Excellent Mud line Inside Department of

Public Works building
Appendix 1. High-water marks in the Villages of Gowanda and Silver Creek, N.Y., for the flash floods of August 10, 2009 23

 —Continued

Mark

number Latitude Longitude Elevation, ft NGVD29 Elevation, ft NAVD88 Distance, ft above ground Quality Description Address

Silver Creek—Continued

S15 42 32 39.3 79 09 52.7 596.00 595.55 0.0 Poor Debris line

S16 42 32 36.8 79 09 52.8 602.40 601.95 4.5 Fair Mud line Same coordinates as S17

S17 42 32 36.8 79 09 52.8 602.11 601.66 4.5 Good Mud line

S18 42 32 31.7 79 09 52.2 603.55 603.10 5.5 Good Mud line on house

S19 42 32 31.2 79 09 47.1 604.68 604.23 0.0 Poor Seed line

S20 42 32 31.3 79 09 46.6 604.19 603.74 1.8 Fair Seed line on tree

S21 42 32 31.2 79 09 47.1 604.58 604.13 0.0 Fair Seed line in grass Same coordinates as S19

S22 42 32 48.3 79 10 20.0 586.28 585.83 3.0 Good Mud line on tree 11 Jackson Street

S23 42 32 49.5 79 10 13.4 586.20 585.75 5.0 Good Seed line on tree

S24 42 32 53.4 79 10 07.9 585.78 585.33 0.0 Poor Mud line On railroad embankment

S25 42 32 45.6 79 10 05.6 587.47 587.02 3.0 Good Mud line on garage

S26 42 32 45.0 79 10 08.8 586.92 586.47 2.5 Good Mud line on shed Behind wastewater-treat‐

ment plant

S27 42 32 49.0 79 10 07.5 586.06 585.61 7.4 Good Seed line on tree

S28 42 32 49.8 79 10 09.9 585.76 585.31 6.5 Good Seed line on tree

S29 42 32 50.9 79 10 09.6 585.66 585.21 8.0 Good Seed line on tree
Prepared by the Pembroke, Lafayette and West Trenton 

Publishing Service Centers.

For more information concerning this report, contact:

Director

U.S. Geological Survey

New York Water Science Center

425 Jordon Rd

Troy, NY 12180

dc_ny@usgs.gov

or visit our Web site at:

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Szabo and others—Flash Floods of August 10, 2009, in the Villages of Gowanda and Silver Creek, New York—Scientific Investigations Report 2010–5259