In cooperation with the Department of Homeland Security, 

Federal Emergency Management Agency, Region III

Analysis of Flood-Magnitude and FloodFrequency Data for Streamflow-Gaging 

Stations in the Delaware and North Branch 

Susquehanna River Basins in Pennsylvania 

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2007-1235

Analysis of Flood-Magnitude and FloodFrequency Data for Streamflow-Gaging 

Stations in the Delaware and North Branch 

Susquehanna River Basins in Pennsylvania

By Mark A. Roland and Marla H. Stuckey

In cooperation with the Department of Homeland Security, 

Federal Emergency Management Agency, Region III

Open File Report 2007–1235

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Suggested citation:

Roland, M.A., and Stuckey, M.H., 2007, Analysis of flood-magnitude and flood-frequency data for streamflow-gaging 

station in the Delaware and North Branch Susquehanna River Basins in Pennsylvania: U.S. Geological Survey Open-File 

Report 2007-1235, 22 p. 
 iii

Contents

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

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

Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

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

Methodology Used in Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Analysis of Flood Magnitudes and Flood Frequencies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Annual Maximum Peak Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Partial-Duration Peak Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Possible Effects of Regulation and Urbanization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

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

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Selected References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Appendix 1. Station summary data for streamflow-gaging stations in the Delaware and North 

Branch Susquehanna River Basins, Pennsylvania. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Appendix 2. Flood frequencies determined by Flood Insurance Studies (FIS) and from annual 

maximum streamflow-gaging-station data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Appendix 3. Log-Pearson Type III flood frequencies determined from annual maximum and 

partial-duration streamflow-gaging-station data.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figures

1. Map showing streamflow-gaging stations used in the analysis of flood-magnitude 

and flood-frequency data in the Delaware and North Branch Susquehanna River 

Basins, Pennsylvania . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

2. Graph showing relation between the 100-year recurrence interval flood-peak 

discharges from Flood Insurance Studies and from U.S. Geological Survey streamflowgaging-station data, Delaware and North Branch Susquehanna River Basins, Pennsylvania. . . . .6

3. Graph showing hydrograph of June 28, 2006, flood for streamflow-gaging stations 

01473900 Wissahickon Creek at Fort Washington and 01471980 Manatawny Creek near 

Pottstown, Pennsylvania. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Tables 

1. Mean percentage difference between flood-peak discharge estimates determined 

from annual maximum series station data and Flood Insurance Studies, Delaware 

and North Branch Susquehanna River Basins, Pennsylvania . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

2. Stations with significant positive trends in annual maximum peak flows over period 

of record, Delaware and North Branch Susquehanna River Basins, Pennsylvania. . . . . . . . . . . . . . . .7

3. Mean percentage difference between flood-frequency magnitudes determined 

from partial-duration and annual maximum series peak flow data, Delaware and 

North Branch Susquehanna River Basins, Pennsylvania. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
iv 

Conversion Factors

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2

) 

Flow rate

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

cubic foot per second 

mile [(ft3

/s)/mi2]

per square 

 0.01093

cubic meter per second per 

square kilometer [(m3

/s)/km2]

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

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

Altitude, as used in this report, refers to distance above the vertical datum.
Analysis of Flood-Magnitude and Flood-Frequency Data 

for Streamflow-Gaging Stations in the Delaware and 

North Branch Susquehanna River Basins in Pennsylvania

By Mark A. Roland and Marla H. Stuckey

Abstract 

 The Delaware and North Branch Susquehanna River 

Basins in Pennsylvania experienced severe flooding as a result 

of intense rainfall during June 2006. The height of the flood 

waters on the rivers and tributaries approached or exceeded the 

peak of record at many locations. Updated flood-magnitude and 

flood-frequency data for streamflow-gaging stations on tributaries in the Delaware and North Branch Susquehanna River 

Basins were analyzed using data through the 2006 water year to 

determine if there were any major differences in the flood-discharge data. Flood frequencies for return intervals of 2, 5, 10, 

50, 100, and 500 years (Q2, Q5, Q10, Q50, Q100, and Q500) 

were determined from annual maximum series (AMS) data 

from continuous-record gaging stations (stations) and were 

compared to flood discharges obtained from previously published Flood Insurance Studies (FIS) and to flood frequencies 

using partial-duration series (PDS) data.

A Wilcoxon signed-rank test was performed to determine 

any statistically significant differences between flood frequencies computed from updated AMS station data and those 

obtained from FIS. Percentage differences between flood frequencies computed from updated AMS station data and those 

obtained from FIS also were determined for the 10, 50, 100, and 

500 return intervals. A Mann-Kendall trend test was performed 

to determine statistically significant trends in the updated AMS 

peak-flow data for the period of record at the 41 stations. In 

addition to AMS station data, PDS data were used to determine 

flood-frequency discharges. The AMS and PDS flood-frequency data were compared to determine any differences 

between the two data sets. An analysis also was performed on 

AMS-derived flood frequencies for four stations to evaluate the 

possible effects of flood-control reservoirs on peak flows. Additionally, flood frequencies for three stations were evaluated to 

determine possible effects of urbanization on peak flows.

The results of the Wilcoxon signed-rank test showed a significant difference at the 95-percent confidence level between 

the Q100 computed from AMS station data and the Q100 determined from previously published FIS for 97 sites. The floodfrequency discharges computed from AMS station data were 

consistently larger than the flood discharges from the FIS; mean 

percentage difference between the two data sets ranged from 14 

percent for the Q100 to 20 percent for the Q50. The results of 

the Mann-Kendall test showed that 8 stations exhibited a positive trend (i.e., increasing annual maximum peaks over time) 

over their respective periods of record at the 95-percent confidence level, and an additional 7 stations indicated a positive 

trend, for a total of 15 stations, at a confidence level of greater 

than or equal to 90 percent. The Q2, Q5, Q10, Q50, and Q100 

determined from AMS and PDS data for each station were compared by percentage. The flood magnitudes for the 2-year return 

period were 16 percent higher when partial-duration peaks were 

incorporated into the analyses, as opposed to using only the 

annual maximum peaks. The discharges then tended to converge around the 5-year return period, with a mean collective 

difference of only 1 percent. At the 10-, 50-, and 100-year return 

periods, the flood magnitudes based on annual maximum peaks 

were, on average, 6 percent higher compared to corresponding 

flood magnitudes based on partial-duration peaks. 

Possible effects on flood peaks from flood-control reservoirs and urban development within the basin also were examined. Annual maximum peak-flow data from four stations were 

divided into pre- and post-regulation periods. Comparisons 

were made between the Q100 determined from AMS station 

data for the periods of record pre- and post regulation. Two stations showed a nearly 60- and 20-percent reduction in the 

100-year discharges; the other two stations showed negligible 

differences in discharges. Three stations within urban basins 

were compared to 38 stations without significant urbanization. 

The Q100 was determined for each station and subsequently 

divided by its respective drainage area, producing a yield (cubic 

feet per second per square mile) for each station. The mean 

yield for the three urban sites was 365 (ft3/s)/mi2

 compared to 

174 (ft3/s)/mi2

 for the non-urban sites. 

Introduction

As a result of intense rainfall from June 23 through June 

29, 2006, the Delaware and North Branch Susquehanna River 

Basins in Pennsylvania experienced severe flooding. The height 

of the flood waters on the rivers and tributaries approached or 
2 Analysis of Flood-Magnitude and Flood-Frequency Data for Streamflow-Gaging Stations in Pennsylvania

exceeded the peak of record at many locations, prompting a 

Presidential disaster declaration on June 30, 2006. This was the 

third major flood along the Delaware River in 22 months. In 

response to this flooding, the Department of Homeland Security, Federal Emergency Management Agency (FEMA) Region 

III, and the U.S. Geological Survey (USGS) Pennsylvania 

Water Science Center began a study to analyze flood-magnitude and flood-frequency data for streamflow-gaging stations 

(stations) on tributaries within the Delaware and North Branch 

Susquehanna River Basins in Pennsylvania. 

This study updates and compares flood frequencies determined from annual maximum series (AMS) data from continuous-record stations to flood discharges obtained from previously published Flood Insurance Studies (FIS) to determine 

whether there were any major differences in the flood-discharge 

data. The study also computes flood frequencies using partialduration series (PDS) data to determine how the use of this PDS 

data may affect the flood frequencies compared to those determined using the AMS data. The potential effects of regulation 

and urbanization also were included in the study. 

Purpose and Scope 

This report presents the results of (1) a comparison of 

updated AMS-derived flood-frequency discharges and flood 

discharges from previously published FIS, (2) a comparison of 

flood-frequency discharges computed using updated AMS and 

PDS peak-flow data, and (3) an analysis of the potential effects 

of regulation and urbanization on updated AMS-derived flood 

frequencies in the Delaware and North Branch Susquehanna 

River Basins. A flood-frequency analysis with recurrence intervals of 2, 5, 10, 50, 100, and 500 years (Q2, Q5, Q10, Q50, 

Q100, and Q500, respectively) was performed for 41 stations in 

the Delaware and North Branch Susquehanna River Basins in 

Pennsylvania (fig. 1) (appendix 1). Thirty-six of the 41 stations 

had 30 or more years of continuous record; the other 5 stations 

had 25 or more years of record. 

A Wilcoxon signed-rank test was performed to determine 

any statistically significant differences between flood frequencies computed from updated AMS station data and flood frequencies obtained from FIS. Percentage differences between 

flood frequencies computed from updated AMS station data 

and those flood frequencies obtained from FIS also were calculated for the 10-, 50-, 100-, and 500-year return intervals. A 

Mann-Kendall trend test was performed to determine any statistically significant trends in the updated AMS peak-flow data for 

the period of record at the 41 stations. In addition to AMS station data, PDS data were used to determine flood-frequency discharges. The AMS and PDS flood-frequency data were compared to determine any differences between the two data sets. 

An analysis was performed on AMS-derived flood frequencies 

for four stations to evaluate the possible effects of flood-control 

reservoirs on peak flows. Additionally, flood frequencies for 

three stations were evaluated to determine possible effects of 

urbanization on peak flows.

Previous Studies 

Bulletin 17B of the Interagency Advisory Committee on 

Water Data (Water Resources Council, Hydrology Committee, 

1981) outlines procedures for performing flood-frequency analysis of annual maximum peaks. Flood Insurance Study Reports 

have been developed for many communities in the Commonwealth and are available from the Federal Emergency Management Agency (2006).

Methodology Used in Analysis

A USGS computer program, PeakFQ, utilizing the LP3 

frequency distribution, was used to determine flood-frequency 

discharges (Kathleen Flynn, U.S. Geological Survey, written 

commun., 2005) at 41 streamflow-gaging stations within the 

Delaware and North Branch Susquehanna River Basins in 

Pennsylvania. This program performs statistical flood-frequency analyses of AMS data following procedures recommended in Bulletin 17B (Water Resources Council, Hydrology 

Committee, 1981). The flood-frequency analysis is sensitive to 

the number of annual maximum peaks used in the analysis, and 

the resulting flood-frequency discharge can be skewed either 

high or low by dominant wet or dry periods, respectively. Stations having a minimum of 30 years of record through the 2006 

water year1

 were used to limit the effect of possible bias associated with shorter periods of record. The exceptions were five 

stations having a minimum of 25 years record; four of these stations are subject to flood-control regulation and the period of 

record after regulation was used to reflect current conditions, 

the remaining station had a non-continuous period of record 

(with a collective total of 25 years). These stations along with 

their respective periods of record are identified in appendix 1. 

The peak-flow data from water year 2006 was provisional at the 

time of the analysis and is subject to change; however, it was 

used in the analysis to include the June 2006 flooding in the 

Delaware and North Branch Susquehanna River Basins.

To compare flood frequencies derived from AMS station 

data to those compiled from FIS, an initial list of 117 sites from 

FIS within a 10-mi radius of any of the 41 streamflow-gaging 

stations was compiled by FEMA Region III (Dana Moses, Federal Emergency Management Agency Region III, written commun., 2006). Four streamflow-gaging stations did not have any 

associated FIS data and were removed from the analysis. Floodfrequency discharges were computed for the remaining 37 sta1

 A water year is the 12-month period from October 1 through September 30. The water year is designated by the calendar year in which it ends and which 

includes 9 of the 12 months. Thus, the year ending September 30, 2006, is called the “2006 water year.”
Methodology Used in Analysis 3

tions using recommended procedures (Water Resources Council, Hydrology Committee, 1981). The flood frequencies were 

then transferred from the 37 streamflow-gaging stations to the 

117 sites from the FIS using drainage-area ratios. Twenty of 

these sites were removed from the analysis because they were 

outside the recommended range of 0.5 to 1.5 times the drainage 

area of the station for drainage-area ratio transfers (Stuckey and 

Reed, 2000). A total of 97 sites from 37 station-based FIS were 

used in the analysis. From these 97 sites, FEMA Region III 

identified 59 sites where flood frequencies were determined 

using station data, labeled as Log-Pearson Type III (LP3) or 

Bulletin 17B. The remaining 38 sites either utilized other methods to compute flood frequencies or the method used was 

unknown.

Flood frequencies and data were compared and analyzed 

using the Wilcoxon signed-rank test, percentage differences, 

and the Mann-Kendall test. The Wilcoxon signed-rank test is a 

nonparametric test that was used to determine whether the flood 

frequencies computed from AMS station data and those from 

the FIS were significantly different (Helsel and Hirsch, 1992). 

Percentage differences between flood frequencies determined 

from AMS station data and the FIS were determined for Q10, 

Q50, Q100, and Q500. However, there were instances when 

only the FIS Q100 was available for comparison to the corresponding AMS-derived flood frequency. The Mann-Kendall 

test is a nonparametric test used to detect trends within data sets 

(Helsel and Hirsch, 1992). It was performed on the annual maximum peaks for each of the 41 stations to determine if a positive 

Delaware River Basin

North Branch

Susquehanna River Basin

U.S. GEOLOGICAL SURVEY

 STREAMFLOW-GAGING

 STATION

EXPLANATION

Base from U.S. Geological Survey, 1:2,000,000 and 1:100,000 Digital Data

PENNSYLVANIA

Allentown

Reading

Philadelphia

Scranton

Bloomsburg

77°

75°

42°

40°

0 25 50 KILOMETERS

0 25 50 MILES

Figure 1. Streamflow-gaging stations used in the analysis of flood-magnitude and flood-frequency data in the 

Delaware and North Branch Susquehanna River Basins, Pennsylvania. 
4 Analysis of Flood-Magnitude and Flood-Frequency Data for Streamflow-Gaging Stations in Pennsylvania

trend existed, increasing annual peak flows over the period of 

record. The Wilcoxon signed-rank and Mann-Kendall tests 

were performed using a 95-percent confidence interval to provide a reasonable balance between maximizing the probability 

of finding significant differences between the data sets and minimizing the probability of failing to find any significant differences that exist.

In addition to AMS station data, PDS data were used to 

determine flood magnitudes and frequencies. PDS data include 

all peaks above a base discharge. The base discharge at each station is selected such that, on average, three independent peak 

discharges, including the annual maximum, exceed the base 

discharge each water year (Langbein and Iseri, 1960). 

The partial-duration peak discharges for 41 stations in the 

Delaware and North Branch Susquehanna River Basins were 

compiled and examined. Five stations were removed from the 

analyses because of an insufficient number of partial-duration 

peaks. 

Flood frequencies using PDS data were determined using 

the PeakFQ software and modifying the results. Because the 

PeakFQ program was designed to process AMS data, it has certain inherent characteristics that make it more difficult for PDS 

analysis. One such processing characteristic is that the number 

of peaks per station can not exceed 180. While this limitation 

was not an issue with the AMS data sets, there were some 

instances when the number of partial-duration peaks for an individual station exceeded this value. Although other methods may 

exist regarding the processing of PDS data by PeakFQ, the 

method implemented in this study consisted of PDS data-set 

reduction based on peak-flow distribution. Beginning with the 

lowest peaks within a PDS data set, duplicated values were 

removed until the data set was reduced to 180. The distribution 

of flows within a partial-duration peak data set tends to be 

skewed toward the lower end, where relatively smaller flows 

are more numerous, are closer in value, and are more likely to 

be duplicated. A sensitivity analysis was not performed to analyze the potential implications of a reduced PDS data set on the 

PeakFQ results.

After the necessary data sets were reduced to 180 values, 

the partial-duration peaks were processed by PeakFQ to determine flood magnitudes and frequencies. The Bulletin 17B procedures treat the occurrence of flooding at a site as a sequence 

of annual random events or trials (Kathleen Flynn, U.S. Geological Survey, written commun., 2005). Because each PDS year 

had more than one peak, the results needed to be normalized on 

the basis of the average number of peaks per year (r-value) for 

each station. For instance, if a station has observed flow for 61 

years during which 166 partial-duration peaks were recorded, 

its resulting r-value would be 166/61 = 2.72. The application of 

this value to the PeakFQ results consisted of dividing the return 

periods (for example; 2, 5, and 10) by the r-value; resulting in 

adjusted return periods (for example; 0.74, 1.84, and 3.68, 

respectively) being estimated for designated discharges. After 

the adjusted return periods were obtained, the desired return 

periods and associated discharges were calculated by interpolation. The following example shows the steps involved with the 

normalizing process for one station:

Example:

1. Station: 01451500, Lehigh River at Walnutport, Pa.

2. Period of record: 1946–2006 (61 years)

3. Number of partial-duration peaks: 166

4. r-value = number of partial-duration peaks/number of 

years of record

r-value = 166/61

r-value = 2.72

5. Calculate the desired return periods and associated 

discharges by interpolation for comparison to the AMS 

PeakFQ results for the 2-, 5-, 10-, 50-, and 100-year return 

periods.

Example of PeakFQ results with adjusted return periods for 

streamflow-gaging station 01451500 with 61 years of record and 

166 partial-duration peaks. 

Annual 

exceedence 

probability

Return 

period

Adjusted return 

period 

(Return Period / 

r-value)

Discharge 

(cubic feet per 

second)

0.995

.99

.95

.9

.8

.5

.2

.1

.04

.02

.01

.005

.002

1.005

1.010

1.053

1.111

1.250

2

5

10

25

50

100

200

500

0.37

.37

.39

.41

.46

.74

1.84

3.68

9.19

18.4

36.8

73.5

184

250

272

360

431

553

987

2,040

3,180

5,360

7,710

10,900

15,200

23,300

 Example of interpolated return periods 

and discharges for streamflow-gaging 

station 01451500 with 61 years of record and 

166 partial-duration peaks. 

Desired Return Discharge (cubic 

Period feet per second)

2 2,140

5 3,700

10 5,560

50 12,500

100 17,200
Analysis of Flood Magnitudes and Flood Frequencies 5

Four stations (three in the North Branch Susquehanna 

River Basin and one in the Delaware River Basin) were effected 

by flood-control reservoirs. Annual maximum peak-flow data 

from these four stations were divided into pre- and post-regulation periods to analyze the effects of flood-control reservoirs on 

flood peaks. A minimum of 10 percent of the watershed subjected to regulation was used as a threshold to divide the period 

of record.

Land-use data at the 41 stations in the North Branch Susquehanna and Delaware River Basins were compiled and examined. Only three of the stations had urban land use greater than 

50 percent. To explore the effects of urban development on 

peak discharges, the 3 stations with urban land use greater than 

50 percent were compared to the 38 stations with lower percentages of urbanization. 

Analysis of Flood Magnitudes and Flood 

Frequencies

Annual Maximum Peak Discharges

The results of the Wilcoxon signed-rank test (p-value = 

0.00) on data from 97 sites showed a significant difference at 

the 95-percent confidence level between the transferred Q100 

computed from AMS station data and the Q100 determined 

from previously published FIS. The Wilcoxon signed-rank test 

also was done on the 59 sites identified by FEMA Region III as 

using station data to determine Q100, and again, the results 

(p-value = 0.00) showed a significant difference between the 

two data sets. 

For the 97 sites used in the comparison, the flood-frequency discharges computed from AMS station data were consistently larger than the flood discharges from the FIS. The 

mean percentage difference between the two data sets ranged 

from 14 percent for the Q100 to 20 percent for the Q50 (table 1). 

Twenty of the 97 sites did not have Q10, Q50, and Q500 flood 

discharges available in the FIS. The complete comparison 

between the data sets is shown in appendix 2. The relation 

between the Q100 from the FIS and the transferred Q100 determined from AMS station data is shown in figure 2. As the discharge magnitudes increase, the transferred Q100 determined 

from AMS station data consistently is greater than the Q100 

from the FIS (fig. 2).

Of the 97 sites, 59 sites were identified by FEMA Region 

III as having flood frequencies determined using station data. 

Mean values were computed for the Q10, Q50, Q100, and Q500 

and were compared to corresponding mean values determined 

from AMS station data. The mean percentage difference 

between the two data sets ranged from 16 percent for the Q100 

to 21 percent for the Q10 (table 1). Fourteen of the 59 sites did 

not have Q10, Q50, and Q500 data available in the FIS. A possible explanation for the higher flood-frequency discharges 

associated with the AMS station data could be the inclusion of 

recent peak-flow data; flood-insurance studies completed prior 

to the recent flood events would not have incorporated these 

data into their flood-frequency estimates. 

Table 1. Mean percentage difference between flood-peak discharge estimates determined 

1 2 from annual maximum series station data and Flood Insurance Studies , Delaware and North 

Branch Susquehanna River Basins, Pennsylvania. 

Summary 

Statistic

Recurrence Interval

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

3 All methods

Mean 17 20 14 19

Count 77 77 97 77

4 Gaging-station methods

Mean 21 20 16 18

Count 45 45 59 45

1

Flood-frequency magnitudes computed from gaging-station data based on Log-Pearson Type III distribution 

of annual maximum peaks and transferred to sites using drainage-area ratios. 

2Flood-frequency magnitudes from Flood Insurance Studies compiled by Dana Moses (Federal Emergency 

Management Agency, written commun., 2005).

3

All methods refers to any method for determining flood-frequency magnitudes from the compiled Flood Insurance Studies.

4

Gaging-station methods refers to methods for determining flood-frequency magnitudes from the compiled 

Flood Insurance Studies as Log Pearson Type III or Bulletin 17B, which are based on gaging-station data.
6 Analysis of Flood-Magnitude and Flood-Frequency Data for Streamflow-Gaging Stations in Pennsylvania

The results of the Mann-Kendall test showed that eight stations exhibited a positive trend (increasing annual maximum 

peaks over time over their respective periods of record at the 95-

percent confidence level) (table 2). It is worth noting that the 

analyses for an additional seven stations indicated a positive 

trend, for a total of 15 stations, at a confidence level of greater 

than or equal to 90 percent. This positive trend could be attributed to a number of different factors, including increased intensity short-term rainfall, increased impervious surface, or urbanization, within the basin. 

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

Q100

050,000100,000150,000200,000250,000300,000350,000400,000

COMPUTED FROM ANNUAL MAXIMUM SERIES STATION DATA,

IN CUBIC FEET PER SECOND

Q100 DETERMINED FROM FLOOD INSURANCE STUDIES, IN CUBIC FEET PER SECOND

EQUAL LINE

Figure 2. Relation between the 100-year recurrence interval flood-peak discharges from Flood Insurance Studies and from U.S. 

Geological Survey streamflow-gaging-station data, Delaware and North Branch Susquehanna River Basins, Pennsylvania. 
Analysis of Flood Magnitudes and Flood Frequencies 7

Partial-Duration Peak Discharges

The partial-duration peak discharges for 41 stations in the 

Delaware and North Branch Susquehanna River Basins were 

compiled and examined. Five stations were removed from the 

analyses because of an insufficient number of partial-duration 

peaks. Hydrologic data from stations with regulated flow were 

divided into pre- and post-regulation periods. Because a focus 

of this study was primarily on current conditions, two stations 

were analyzed only on the basis of their post-regulated discharge period: 01531500 Susquehanna River at Towanda, Pa. 

(1980-2006), and 01536500 Susquehanna River at WilkesBarre, Pa. (1980-2006).

The Q2, Q5, Q10, Q50, and Q100 determined from AMS 

and PDS data for each station, along with their respective percentage differences, are shown in appendix 3. The mean values 

of the collective percentage differences for the various flood 

frequencies are shown in table 3. The flood magnitudes for the 

2-year return period are 16 percent higher when partial-duration 

peaks are incorporated into the analyses, as opposed to using 

only the annual maximum peaks. The discharges tend to converge around the 5-year return period; the mean collective difference was only -1 percent for the 5-year return period. At the 

10-year return period, the discharges associated with the PDS 

data are slightly lower (-5 percent) than when the AMS data are 

used. This trend continues for the 50- and 100-year return periods, where the differences between the PDS and AMS data are 

-7 and -6 percent, respectively. 

Table 2. Stations with significant positive trends in annual maximum 

and North Branch Susquehanna River Basins, Pennsylvania. 

peak flows over period of record, Delaware 

U.S. Geological Survey 

station identification 

number

Station name Period 

of record

Level of 

significance 

(p-value)

95-percent confidence 

01438300

01439500

01440300

01447720

01451500

01452000

01471980

01473900

90-percent confidence 

01442500

01447680

01452500

01516500

01531500

01532000

01540500

level

Vandermark Creek at Milford, Pa.

Bush Kill at Shoemakers, Pa.

Mill Creek at Mountainhome, Pa.

Tobyhanna Creek near Blakeslee, Pa.

Little Lehigh Creek near Allentown, Pa.

Jordan Creek at Allentown, Pa.

Manatawny Creek near Pottstown, Pa.

Wissahickon Creek at Fort Washington, Pa.

level

Brodhead Creek at Minisink Hills, Pa.

Tunkhannock Creek near Long Pond, Pa.

Monocacy Creek at Bethlehem, Pa.

Corey Creek near Mainesburg, Pa.

Susquehanna River at Towanda, Pa.

Towanda Creek near Monroeton, Pa.

Susquehanna River at Danville, Pa.

1962-2006

1909-2006

1961-2006

1962-2006

1946-2006

1945-2006

1975-2006

1962-2006

1970-2006

1966-2006

1945-2006

1955-2006

1980-2006

1914-2006

1980-2006

0.03

.01

.01

.03

.00

.04

.01

.00

.10

.08

.07

.08

.10

.06

.06

Table 3. Mean percentage difference between flood-frequency magnitudes determined from partial-duration 

and annual maximum series peak flow data, Delaware and North Branch Susquehanna River Basins, Pennsylvania.

Number of Recurrence interval

stations used in 

analysis

36

2-year

16

5-year

-1

10-year

-5

50-year

-7

100-year

-6
8 Analysis of Flood-Magnitude and Flood-Frequency Data for Streamflow-Gaging Stations in Pennsylvania

The relation of the results appears to be attributed to the 

larger number of lower magnitude peaks that are included in the 

partial-duration peak-flow data sets. Typically, recurrence 

intervals based on PDS and AMS data sets tend to converge 

after about 10 years. In ordinary hydrologic analysis, a 5 percent 

difference may be considered tolerable (Chow, 1964). Taking 

into consideration the 5-percent tolerance, the results of this 

analysis generally appear to support the conclusion that 

although differences may exist between the PDS and AMS 

flood-peak discharges for the lower return periods, the effect is 

not as significant at the higher return periods.

Possible Effects of Regulation and Urbanization

In an attempt to analyze the effects of flood-control reservoirs upstream of stations on the flood peaks, annual maximum 

peak-flow data from three stations on the Susquehanna River 

(01531500, 01536500, and 01540500) and one station on 

Tulpehocken Creek (01471000), a tributary to the Schuylkill 

River, were divided into pre- and post-regulation periods. A 

minimum of 10 percent of the watershed subjected to regulation 

was used as a threshold to divide the periods of record for the 

stations. Reservoir operating procedures were not taken into 

consideration. Comparisons were made between the Q100 

determined from AMS station data for the pre- and post-regulation periods of record. The results for station 01471000 Tulpehocken Creek near Reading and station 01531500 Susquehanna 

River at Towanda showed a nearly 60- and 20-percent reduction 

in the 100-year discharges, respectively. The results for station 

01536500 Susquehanna River at Wilkes-Barre and station 

01540500 Susquehanna River at Danville showed negligible 

differences in discharges.

This variability in results of the pre- and post-regulation 

comparison may be attributed to the length of respective periods 

of record and the percentage of basin previously influenced by 

regulation. For instance, the three Susquehanna River stations 

all had significantly longer periods of record associated with 

pre-regulation than with post-regulation. A shorter period of 

record is more likely to be influenced by either a dominant wet 

or dry period, which could bias the associated discharges. Secondly, with regard to percentage of basin previously influenced 

by flow regulation, a station is not categorized as a flow-regulated site until the percentage regulation is equal to or greater 

than 10 percent of the drainage area. Flows from each of the 

three Susquehanna River stations had previously been influenced by the effect of flow regulation (to varying degrees) prior 

to reaching the threshold of 10 percent. As a result, a station that 

had been subjected to increasing percentages of flow regulation 

over time may have experienced a resulting attenuation in flow 

discharge. This appears to be the case with stations 01536500 

and 01540500, which had experienced higher degrees of flow 

regulation compared to station 01531500. This attenuation 

could have affected the pre-regulated Q100 to the degree that 

once the station was classified as regulated, the post-regulated 

Q100 discharge may not be noticeably different. 

The drainage basins of each of the 41 stations included in 

this study have a percentage urban of less than 50 percent 

except for the basins of three stations in the Philadelphia 

area: 01465798 Poquessing Creek at Grant Ave. at Philadelphia, 01467048 Pennypack Creek at Lower Rhawn St. Bridge, 

Philadelphia, and 01473900 Wissahickon Creek at Fort Washington, which have percentages urban of 76, 74, and 54, respectively. The analyses of urban flood characteristics associated 

with these sites consisted of a comparison of the urban to nonurban Q100 yield and a hydrograph comparison for the June 

2006 peak-flow event.

To explore the potential effects of urban development on 

peak discharges, the 3 stations with higher percentages of 

urbanization were compared to the 38 stations without significant urbanization. The Q100 was determined for each station 

and subsequently divided by its respective drainage area, producing a yield (cubic feet per second per square mile) for each 

station. The Q100 yields for the urban sites ranged from 290 to 

460 (ft3

/s)/mi2, compared to a range of 28 to 426 (ft3/s)/mi2 for 

the non-urban sites. Mean yields were then calculated for the 

urban and non-urban sites. The mean yield for the three urban 

sites was 365 (ft3/s)/mi2 compared to 174 (ft3

/s)/mi2 for the 

non-urban sites, a difference of almost 110 percent. 

The hydrologic response of a watershed affected by urban 

development may differ from that of a drainage basin relatively 

unaffected by anthropogenic influences. This hydrologic 

response is likely to be most noticeable under peak-flow conditions through higher peaks with larger flood volumes. To examine this, hydrographs were developed for an urban station 

(01473900) and a non-urban station (01471980) for the June 28, 

2006, peak-flow event (fig. 3). The stations selected were comparable in drainage area and geographic location, and the June 

2006 flood ranked in the top five flood events of record at both. 

Urban development for these two basins comprises approximately 50 percent for the urban station and 2 percent for the 

non-urban station of their respective drainage areas. As evidenced from figure 3, the hydrographs differ in the sense that 

flow in the urban setting (station 01473900 Wissahickon Creek 

at Fort Washington) reached a higher peak than the non-urban 

station (01471980 Manatawny Creek near Pottstown). 

The analyses presented may not be solely a function of 

urbanization. Other factors, such as period of record, geology, 

rainfall intensity, or base-flow characteristics, also may have 

contributed to the observed effects. Further analyses with additional stations would be needed to more adequately define the 

effects of urbanization.
Summary 9

Summary

The Delaware and North Branch Susquehanna River 

Basins in Pennsylvania experienced severe flooding as a result 

of intense rainfall occurring June 23, 2006, through June 29, 

2006. The height of the flood waters on the rivers and tributaries 

approached or exceeded the peak of record at many locations. 

Updated flood-magnitude and flood-frequency data for streamflow-gaging stations (stations) were analyzed using data 

through the 2006 water year on tributaries within the Delaware 

and North Branch Susquehanna River Basins in Pennsylvania. 

Flood frequencies determined from annual maximum series 

(AMS) data from continuous-record stations were compared to 

flood discharges obtained from previously published Flood 

Insurance Studies (FIS) to determine whether there were any 

major differences in the flood-discharge data. The flood frequencies were compared using the Wilcoxon signed-rank test 

and percentage differences. The Mann-Kendall test was used to 

analyze trends in the AMS station data. Flood frequencies were 

computed using partial-duration series (PDS) data to determine 

how the use of PDS data may affect the flood frequencies compared to those determined using AMS data. The potential 

effects of regulation and urbanization also were included in the 

study. 

The results of the Wilcoxon signed-rank test on data from 

97 sites showed a significant difference between the Q100 computed from the AMS station data through the 2006 water year 

and the Q100 determined from previously published FIS. 

Flood-frequency magnitudes computed from updated station 

data were consistently larger than the flood-frequency discharges previously published in the FIS. The mean percentage 

difference between the two data sets ranged from 14 percent for 

the Q100 to 20 percent for the Q50. 

The results of the Mann-Kendall test showed that eight stations exhibited a positive trend (an increase in annual maximum 

peaks) over the period of record at the 95-percent confidence 

level. An additional 7 stations indicated a positive trend, for a 

total of 15 stations, at a confidence level of greater than or equal 

to 90 percent. This positive trend could be attributed to a number of different factors, including increased intensity short-term 

rainfall, increased impervious surface, or urbanization, within 

the basin.

27

0H 6H 12H 18H

28

0H 6H 12H 18H

29

0H 6H 12H 18H

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

DISCHARGE, IN CUBIC FEET PER SECOND

JUNE 2006

01471980—MANATAWNY CREEK 

NEAR POTTSTOWN, PA

01473900—WISSAHICKON CREEK AT 

FORT WASHINGTON, PA

Figure 3. Hydrograph of June 28, 2006, flood for streamflow-gaging stations 01473900 Wissahickon Creek at Fort 

Washington and 01471980 Manatawny Creek near Pottstown, Pennsylvania. 
10 Analysis of Flood-Magnitude and Flood-Frequency Data for Streamflow-Gaging Stations in Pennsylvania

The mean flood-frequency magnitude determined using 

PDS station data for the 2-year return period was approximately 

16 percent higher than when using only the AMS station data. 

The flood-frequency discharges tend to converge around the 5-

year return period; the mean collective difference for the 5-year 

return period was only -1 percent. At the 10-year return period, 

the discharges associated with annual maximums are slightly 

higher (approximately 5 percent) than the partial-duration peak 

discharges. This trend continues for the 50- and 100-year return 

periods where the mean collective differences between the PDS 

and AMS data are -7 and -6 percent, respectively. The relation 

of the results appears to be attributed to the larger number of 

lower magnitude peaks that are included in the PDS data sets.

To examine potential effects of flow-regulated sites, comparisons were made at four stations between the Q100 determined for the pre-regulation period and the Q100 determined 

for the post-regulation period using updated AMS station data. 

The results for two stations showed a nearly 60- and 20-percent 

reduction in the 100-year discharges. The results for the other 

two stations showed negligible differences in discharges. This 

variability in results may be attributed to the length of respective periods of record and percentage of basin previously influenced by regulation.

Three stations with urbanization were compared to 38 stations without significant urbanization in order to explore the 

potential effects of urbanization on peak discharges. The AMSderived Q100 was determined for each station and subsequently 

divided by its respective drainage area, producing a yield (cubic 

feet per second per square mile) for each station. The mean 

Q100 yield for the three urban sites was 365 cubic feet per second per square mile compared to 174 cubic feet per second per 

square mile for the non-urban sites, a difference of almost 110 

percent. The results of the analyses may not be solely a function 

of urbanization. Other factors, such as period of record, geology, rainfall intensity, or base-flow characteristics, also may 

have contributed to the observed effects.

Acknowledgments

Special thanks are extended to David Soong of the USGS 

Illinois Water Science Center for his expertise and assistance in 

the evaluation of PDS data. Thanks also are due the USGS 

Pennsylvania Water Science Center data section for their compilation and meticulous review of station data that ultimately 

was used to determine flood frequencies. Critical reviews and 

suggestions were provided by Kirk White and David Soong, 

both with the USGS, and Kim Dunn with Dewberry, Inc. 

Selected References

Chow, V.T., 1964, ed., Handbook of applied hydrology: New 

York, McGraw-Hill, p. 8-20 – 8-23.

Federal Emergency Management Agency, 2006, Flood insurance studies: Washington, D.C., accessed July 16, 2007, at 

http://www.fema.gov/hazard/map/fis.shtm. 

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in 

water resources: New York, Elsevier Science Publishing 

Co., Inc., 522 p.

Langbein, W.B., and Iseri, K.T., 1960, General introduction and 

hydrologic definitions—Manual of hydrology—Part 1. General surface-water techniques: U.S. Geological Survey 

Water-Supply Paper 1541-A, 29 p.

Soong, D.T., Ishii, A.L., Sharpe, J.B., and Avery, C.F., 2004, 

Estimating flood-peak discharge magnitudes and frequencies 

for rural streams in Illinois: U.S. Geological Survey WaterResources Investigations Report 04-5103, 147 p.

Stuckey, M.H., and Reed, L.A., 2000, Techniques for estimating magnitude and frequency of peak flows for Pennsylvania 

streams: U.S. Geological Survey Water-Resources Investigations Report 00-4189, 43 p.

Water Resources Council, Hydrology Committee, 1981, Guidelines for determining flood flow frequencies: Washington, 

D.C., Bulletin 17B, variously paged.
Appendixes
12 Analysis of Flood-Magnitude and Flood-Frequency Data for Streamflow-Gaging Stations in Pennsylvania

Appendix 1. Station 

Pennsylvania.

[mi2, square miles]

summary data for streamflow-gaging stations in the Delaware and North Branch Susquehanna River Basins, 

U.S. Geological 

Survey station 

identification 

number

Station name

Drainage 

area

(mi2

)

Period of record Percent 

1 urban

01428750

01438300

01439500

01440300

01440400

01442500

01447500

01447680

01447720

01449360

01450500

01451500

01451800

01452000

01452500

01465500

01465798

01467048

01468500

01469500

01470500

01470779

01471000

01471980

01472157

01473900

01477000

01480300

01480500

01480617

01480675

01481000

01516500

01531500

01532000

01533400

01534000

West Branch Lackawaxen River near Aldenville, PA

2 Vandermark Creek at Milford, Pa.

Bush Kill at Shoemakers, Pa.

Mill Creek at Mountainhome, Pa.2

Brodhead Creek near Analomink, Pa.

Brodhead Creek at Minisink Hills, Pa.

Lehigh River at Stoddartsville, Pa.

Tunkhannock Creek near Long Pond, Pa.

Tobyhanna Creek near Blakeslee, Pa.

Pohopoco Creek at Kresgeville, Pa.

Aquashicola Creek at Palmerton, Pa.

Little Lehigh Creek near Allentown, Pa.

Jordan Creek near Schnecksville, Pa.

Jordan Creek at Allentown, Pa.

Monocacy Creek at Bethlehem, Pa.

Neshaminy Creek near Langhorne, Pa.

Poquessing Creek at Grant Ave. at Philadelphia, Pa.

PennyPack Cr at Lower Rhawn St Bdg, Phila., Pa.

Schuylkill River at Landingville, Pa.

Little Schuylkill River at Tamaqua, Pa.

Schuylkill River at Berne, Pa.

Tulpehocken Creek near Bernville, Pa.

Tulpehocken Creek near Reading, Pa.

Manatawny Creek near Pottstown, Pa.

French Creek near Phoenixville, Pa.

Wissahickon Creek at Fort Washington, Pa.

Chester Creek near Chester, Pa.

West Branch Brandywine Creek near Honey Brook, Pa.

West Branch Brandywine Creek at Coatesville, Pa.

West Branch Brandywine Creek at Modena, Pa.

Marsh Creek near Glenmoore, Pa.

Brandywine Creek at Chadds Ford, Pa.

Corey Creek near Mainesburg, Pa.

Susquehanna River at Towanda, Pa.

Towanda Creek near Monroeton, Pa.

Susquehanna River at Meshoppen, Pa.

Tunkhannock Creek near Tunkhannock, Pa.

40.6

5.4

117

5.8

65.9

259

91.7

20

118

49.9

76.7

80.8

53

75.8

44.5

210

21.4

49.8

133

42.9

355

66.5

211

85.5

59.1

40.8

61.1

18.7

45.8

55

8.6

287

12.2

7,797

215

8,720

383

1975 - 2006

1962 - 2006

1909 - 2006

1961 - 2006

1958 - 2006

1951 - 2006

1942 - 2006

1966 - 2006

1962 - 2006

1967 - 2006

1940 - 2006

1946 - 2006

1967 - 2006

1945 - 2006

1945 - 2006

1933 - 2006

1966 - 2006

1966 - 2006

1948 - 20063

1920 - 2006

1942 - 2006

1972 - 2006

1951 - 19784

, 1979 - 20065

1975 - 2006

1969 - 2006

1962 - 20063

1932 - 2006

1960 - 2006

1944 - 20063

1970 - 2006

1967 - 2006

1912 - 20063

1955 - 2006

1913 - 19794, 1980 - 20065

1914 - 2006

1977 - 2006

1914 - 2006

0.28

4.06

3.65

12.80

3.70

8.29

7.47

.74

9.90

7.30

2.03

13.02

1.79

4.96

12.76

26.78

76.27

74.41

8.61

3.96

5.74

4.51

3.94

2.22

1.76

53.55

38.06

2.61

4.33

10.54

1.49

11.72

.06

2.17

.57

2.02

3.06
Appendix 1 13

Appendix 1. Station summary data 

Pennsylvania.—Continued

for streamflow-gaging stations in the Delaware and North Branch Susquehanna River Basins, 

[mi2, square miles]

U.S. Geological 

Survey station 

identification 

number

Station name

Drainage 

area

(mi2

)

Period of record Percent 

1 urban

01536500

01538000

01539000

01540500

Susquehanna River at Wilkes-Barre, Pa.

Wapwallopen Creek near Wapwallopen, 

Fishing Creek near Bloomsburg, Pa.

Susquehanna River at Danville, Pa.

Pa.

9,960

43.8

274

11220

1899 - 19794, 1980 - 20065

1920 - 2006

1936 - 2006

1900 - 19794, 1980 - 20065

2.62

11.14

.30

3.11

1

Percent urban area is defined by low-intensity residential, high-intensity residential, commercial/industrial/transportation, 

residential without trees in the basin, determined by the National Land Cover Dataset, enhanced. 

2Partial-record crest-stage gage. Only the maximum discharge for each water year is published.

3

Period of record not continuous.

4

Pre-flow regulated period (less than 10 percent of drainage area subjected to flow regulation).

5Post-flow regulated period (greater than or equal to 10 percent of drainage area subjected to flow regulation).

residential with trees, and 
Appendix 2. Flood frequencies determined by Flood Insurance [mi2, square miles; ft3/s, cubic feet per second; –, no data] Studies (FIS) and from annual maximum streamflow-gaging-station data. Description Drainage area (mi2) FIS community FIS date Method1 FIS flood frequencies (ft3/s) Nearby station Transferred 

station flood frequencies (ft3/s) 

10-yr 50-yr 100-yr 500-yr 10-yr 50-yr 100-yr 500-y

Bush Kill Creek 117.0 Middle Smithfield Twp – 1 – – 14,400 – 01439500 4,430 8,240 10,500 18,00Bush Kill Creek 88.6 Middle Smithfield Twp – 1 – – 11,000 – 01439500 3,620 6,730 8,600 14,70Mill Creek 5.3 Barrett Twp – 1 – – 2,770 – 01440300 879 1,570 1,930 2,94

Broadhead Creek 68.9 Price Twp – 1 – – 16,400 – 01440400 7,300 12,700 15,600 23,50

Broadhead Creek 66.8 Price Twp – 1 – – 15,700 – 01440400 7,140 12,500 15,200 23,00

Broadhead Creek 61.2 Price Twp – 1 – – 14,600 – 01440400 6,700 11,700 14,300 21,60

Broadhead Creek 57.8 Price Twp – 1 – – 13,800 – 01440400 6,430 11,200 13,700 20,70

Broadhead Creek 46.9 Price Twp – 1 – – 11,300 – 01440400 5,520 9,640 11,800 17,80

Broadhead Creek 287.0 Smithfield Twp 3/2/88 1 21,200 42,900 54,100 105,000 01442500 23,900 46,800 60,700 107,00

Brodhead Creek 259.0 Smithfield Twp 3/1/88 1 19,500 39,500 49,800 96,300 01442500 22,100 43,400 56,300 99,30

Broad Head Creek 255.0 Borough of Strouds- burg 1/1/76 1 14,500 28,000 36,500 69,000 01442500 21,900 42,900 55,700 98,10

Lehigh River 91.7 Buck Twp 12/1/88 1 7,310 16,600 22,700 44,200 01447500 7,230 15,900 21,500 41,20

Upper Tunkhannock Creek 24.2 Tobyhanna Twp 12/1/88 2 – – 3,400 – 01447680 831 1,270 1,480 2,04Upper Tunkhannock Creek 19.6 Tobyhanna Twp 12/2/88 2 – – 2,760 – 01447680 713 1,090 1,270 1,75

Upper Tunkhannock Creek 15.0 Tobyhanna Twp 12/3/88 2 – – 2,130 – 01447680 587 896 1,050 1,44Tobyhanna Creek 118.0 Tobyhanna Twp 12/1/88 1 – – 18,000 – 01447720 7,960 14,200 17,500 26,90

Tobyhanna Creek 86.0 Tobyhanna Twp 12/2/88 1 – – 11,800 – 01447720 6,320 11,300 13,900 21,40

Pohopoco Creek 52.0 Polk Twp 9/1/87 2 – – 7,200 – 01449360 2,010 2,820 3,180 4,03

Aquashicola Creek 77.8 Borough of Palmer- ton 3/1/78 1 4,550 7,930 9,790 15,300 01450500 5,370 9,550 11,800 18,70

Aquashicola Creek 71.0 Lower Towamensing 

Twp

11/1/89 1 – – 9,700 – 01450500 5,020 8,930 11,100 17,50

Aquashicola Creek 69.2 Borough of Palmerton 3/1/78 1 4,130 7,250 8,960 14,100 01450500 4,930 8,770 10,900 17,10

Little Lehigh Cr 97.6 Lehigh Co 12/2/81 2 5,510 12,900 17,600 34,000 01451500 6,570 15,300 20,900 39,60

Little Lehigh Cr 80.8 Lehigh Co 11/1/01 1 4,800 11,400 15,600 30,400 01451500 5,730 13,300 18,200 34,50
Appendix 2. Flood frequencies determined by Flood Insurance [mi2, square miles; ft3/s, cubic feet per second; –, no data]

Studies (FIS) and from annual maximum streamflow-gaging-station data.—Continued

Description

Drainage 

area 

(mi2)

FIS 

community

FIS 

date Method1

FIS flood frequencies 

(ft3/s) Nearby 

station

Transferred 

station flood frequencies

(ft3/s)

10-yr 50-yr 100-yr 500-yr 10-yr 50-yr 100-yr 500-y

Little Lehigh Cr 66.2 Lehigh Co 12/3/81 2 4,150 9,990 13,700 27,000 01451500 4,960 11,500 15,700 29,90

Little Lehigh Cr 53.9 Lehigh Co 12/4/81 2 3,580 8,710 12,000 23,900 01451500 4,270 9,940 13,500 25,70

Jordan Creek 58.0 Lehigh Co – 1 5,270 9,320 11,500 18,200 01451800 5,460 8,910 10,600 15,20Jordan Creek 53.0 Lehigh Co – 1 4,880 8,470 10,400 16,100 01451800 5,110 8,340 9,940 14,20Jordan Creek 81.0 Lehigh Co – 1 6,960 13,000 16,400 27,000 01452000 7,570 13,700 17,000 26,70

Jordan Creek 75.8 Lehigh Co 12/7/81 1 6,630 12,400 15,700 26,000 01452000 7,210 13,000 16,200 25,50

Jordan Creek 70.4 Lehigh Co – 1 6,220 11,500 14,400 23,600 01452000 6,830 12,300 15,300 24,10

Monocacy Creek 50.0 Northampton Co 1/1/78 1 1,350 2,800 3,750 7,000 01452500 2,110 4,910 6,790 13,60

Monocacy Creek 37.1 Northampton Co 1/2/78 1 1,150 2,400 3,200 5,900 01452500 1,700 3,950 5,460 11,00

Monocacy Creek 35.7 Northampton Co 1/3/78 1 1,050 2,170 2,920 5,570 01452500 1,650 3,840 5,310 10,70

Neshaminy Creek 233.0 Bucks Co 3/2/77 1 20,700 34,100 41,100 61,000 01465500 24,100 39,700 48,000 71,60

Neshaminy Creek 221.3 Bucks Co 3/3/77 1 21,400 33,400 38,700 56,600 01465500 23,200 38,300 46,200 69,00

Neshaminy Creek 210.0 Bucks Co 3/1/77 1 20,300 31,800 36,900 53,900 01465500 22,300 36,800 44,500 66,40

Neshaminy Creek 187.8 Bucks Co 3/4/77 1 18,100 28,300 32,900 48,000 01465500 20,600 34,000 41,000 61,20

Neshaminy Creek 166.9 Bucks Co 3/5/77 1 16,800 26,200 30,400 44,400 01465500 18,900 31,200 37,600 56,20

Poquessing Cr 21.4 City of Philadelphia 2/1/92 1 5,630 8,940 10,600 15,500 01465798 5,690 8,490 9,850 13,50Pennypack Cr 47.1 City of Philadelphia 12/3/78 2 5,600 10,200 14,000 28,000 01467048 7,090 11,500 13,800 20,50

Pennypack Cr 42.8 City of Philadelphia 12/1/78 2 4,800 9,600 13,000 26,000 01467048 6,610 10,700 12,900 19,10

Pennypack Cr 37.9 City of Philadelphia 12/2/78 2 4,500 9,000 12,000 23,600 01467048 6,050 9,840 11,800 17,50

Schuylkill River 160.0 West Brunswick 11/2/96 1 8,600 13,800 16,500 24,000 01468500 8,270 14,100 17,200 26,50

Twp

Schuylkill River 133.0 Schuykill Haven 11/1/96 1 6,790 11,000 13,200 19,400 01468500 7,230 12,300 15,100 23,10

Little Schuylkill 77.0 Tamaqua 12/1/89 1 – – 13,500 – 01469500 4,890 7,900 9,320 13,00

River

Schuylkill River 640.0 Berks Co 12/1/97 2 28,800 43,500 50,700 69,000 01470500 36,500 57,000 66,900 92,50

Schuylkill River 335.0 Berks Co 12/2/97 2 23,200 36,300 42,800 60,200 01470500 22,800 35,600 41,700 57,80

Tulpehocken Creek 56.4 Berks Co 8/1/88 1 – – 7,280 – 01470779 4,890 9,300 11,700 18,70

Tulpehocken Creek 49.8 Berks Co 8/2/88 1 – – 6,650 – 01470779 4,470 8,490 10,700 17,10

Tulpehocken Creek 70.4 Berks Co – 1 2,100 3,500 4,100 6,400 01470779 5,750 10,900 13,700 22,00

Tulpehocken Creek 219.0 Berks Co 12/2/97 1 3,210 5,600 6,750 10,500 01471000 4,650 6,520 7,360 9,46

Tulpehocken Creek 211.0 Berks Co 12/1/97 1 2,180 5,400 6,550 9,850 01471000 4,530 6,340 7,170 9,21

Tulpehocken Creek 175.0 Berks Co – 3 2,000 2,000 2,400 5,900 01471000 3,950 5,540 6,250 8,04

Manatawny Creek 61.9 Berks Co – 2 4,700 6,900 10,500 14,900 01471980 5,000 7,260 8,280 10,80
Appendix 2. Flood frequencies determined by Flood Insurance [mi2, square miles; ft3/s, cubic feet per second; –, no data] Studies (FIS) and from annual maximum streamflow-gaging-station data.—Continued Description Drainage area (mi2) FIS community FIS date Method1 FIS flood frequencies (ft3/s) Nearby station Transferred 

station flood frequencies (ft3/s) 

10-yr 50-yr 100-yr 500-yr 10-yr 50-yr 100-yr 500-y

Manatawny Creek 59.2 Berks Co – 3 4,300 6,300 9,500 13,100 01471980 4,840 7,030 8,020 10,50

Manatawny Creek 57.2 Berks Co – 3 4,000 5,900 8,700 11,700 01471980 4,720 6,850 7,820 10,20

French Creek 70.2 Chester Co – 3 9,740 13,200 14,800 18,600 01472157 7,270 13,800 17,500 29,00

French Creek 67.1 Chester Co – 3 9,440 12,700 14,300 18,000 01472157 7,030 13,300 16,900 28,00

French Creek 64.1 Chester Co – 3 9,100 12,200 13,800 17,300 01472157 6,800 12,900 16,400 27,10

French Creek 62.6 Chester Co – 3 8,960 12,000 13,500 17,000 01472157 6,680 12,700 16,100 26,60

French Creek 54.9 Chester Co – 3 7,760 10,500 12,000 15,400 01472157 6,080 11,500 14,600 24,20French Creek 43.7 Chester Co – 3 5,340 8,680 10,400 13,700 01472157 5,150 9,760 12,400 20,50

French Creek 44.8 Chester Co – 3 – – 10,200 – 01472157 5,240 9,940 12,600 20,90Wissahickon Creek 64.0 City of Philadelphia 6/1/79 1 6,600 11,900 15,000 25,200 01473900 9,290 15,900 19,600 31,10

Wissahickon Creek 53.6 City of Philadelphia 6/2/79 1 6,000 10,900 13,800 24,500 01473900 8,160 14,000 17,200 27,40

Wissahickon Creek 49.8 Montgomery Co 12/1/77 2 8,300 11,200 12,600 15,700 01473900 7,740 13,200 16,300 25,90

Wissahickon Creek 27.3 Montgomery Co 12/2/77 2 5,400 7,400 8,330 10,800 01473900 4,990 8,540 10,500 16,80

Wissahickon Creek 24.1 Montgomery Co 12/3/77 2 4,980 6,830 7,650 9,900 01473900 4,560 7,800 9,630 15,30

Chester Creek 61.1 Delaware Co 5/1/95 1 8,090 15,600 20,300 35,800 01477000 7,480 14,500 18,700 32,40

W Br Brandywine Creek 37.5 Chester Co – 3 3,920 6,890 8,870 13,900 01480300 5,020 9,020 11,200 17,50W Br Brandywine Creek 18.8 Chester Co – 3 2,520 4,530 5,970 9,660 01480300 3,040 5,450 6,760 10,60W Br Brandywine Creek 15.4 Chester Co – 3 2,240 4,140 5,540 9,190 01480300 2,630 4,720 5,850 9,14

W Br Brandywine Creek 52.0 Chester Co – 3 5,100 8,700 10,400 15,600 01480500 5,260 9,740 12,200 19,80

W Br Brandywine Creek 45.8 Chester Co – 3 4,500 7,700 9,300 14,000 01480500 4,800 8,880 11,200 18,00

W Br Brandywine Creek 64.4 Chester Co – 3 5,670 9,730 12,400 19,000 01480617 7,070 12,400 15,100 22,90

W Br Brandywine Creek 57.5 Chester Co – 3 – – 11,500 – 01480617 6,510 11,400 13,900 21,10

W Br Brandywine 

Creek

54.0 Chester Co – 3 5,200 8,900 10,600 15,800 01480617 6,220 10,900 13,300 20,10

Brandywine Creek 295.0 Delaware Co 5/2/95 1 13,100 18,600 22,200 34,000 01481000 14,700 23,600 28,200 40,90

Brandywine Creek 281.1 Delaware Co 5/1/95 1 12,500 18,000 21,300 32,500 01481000 14,100 22,800 27,200 39,40

Susquehanna River 8,196.0 Asylum Twp 2/1/80 2 144,000 197,000 217,000 275,000 01531500 158,000 208,000 230,000 282,00
Appendix 2. Flood frequencies determined by Flood Insurance [mi2, square miles; ft3/s, cubic feet per second; –, no data]

Studies (FIS) and from annual maximum streamflow-gaging-station data.—Continued

Description

Drainage 

area 

(mi2)

FIS 

community

FIS 

date Method1

FIS flood frequencies 

(ft3/s) Nearby 

station

Transferred 

station flood frequencies

(ft3/s)

10-yr 50-yr 100-yr 500-yr 10-yr 50-yr 100-yr 500-y

Susquehanna River 7,797.0 Wysox Twp 8/1/77 1 140,000 192,000 212,000 270,000 01531500 153,000 201,000 222,000 271,00

Susquehanna River at 7,797.0 Windham Twp 9/1/87 1 140,000 192,000 212,000 270,000 01531500 153,000 201,000 222,000 271,00

station 01531500

Towanda Creek 263.6 Monroe Borough 9/2/92 1 26,800 48,900 61,800 99,700 01532000 28,200 52,200 65,900 108,00

Towanda Creek 215.0 Monroe Borough 9/1/92 1 23,000 42,000 53,000 85,600 01532000 24,300 45,000 56,800 92,90

Susquehanna River 9,539.0 Eaton Twp 11/1/79 1 160,000 221,000 248,000 324,000 01533400 195,000 263,000 293,000 367,00

Susquehanna River 8,913.0 Meshoppen Twp 8/1/79 2 154,000 212,000 238,000 308,000 01533400 185,000 250,000 279,000 350,00

Tunkhannock Creek 413.0 Tunkhannock Bor- 8/1/79 1 26,300 37,600 42,500 53,900 01534000 26,200 37,500 42,300 53,80

ough

Tunkhannock Creek 383.0 Tunkhannock Twp 8/1/99 1 24,800 35,500 40,100 50,900 01534000 24,800 35,500 40,100 50,90

at station 01534000

Susquehanna River 10,215.0 Hunlock Twp 10/1/79 1 167,000 232,000 260,000 340,000 01536500 202,000 277,000 310,000 393,00

Susquehanna River 9,539.0 Ransom 10/1/79 1 160,000 221,000 248,000 324,000 01536500 192,000 263,000 295,000 374,00

Susquehanna River 9,925.0 City of Wilkes-Barre 3/1/92 2 165,000 227,000 225,000 335,000 01536500 198,000 271,000 304,000 385,00

Wapwallopen Creek 42.2 Hollenback Twp 3/1/80 1 2,350 3,770 4,490 6,470 01538000 2,550 4,190 5,020 7,30

Big Wapwallopen 30.8 Dorrance Twp 2/1/80 2 1,810 2,900 3,450 4,970 01538000 2,030 3,330 3,990 5,81

Creek

Fishing Creek 385.0 Montour Twp 2/1/79 1 24,300 45,700 58,500 102,000 01539000 24,200 40,200 48,500 71,30

Fishing Creek 292.0 Orange Twp 2/1/78 1 20,000 38,000 48,800 87,000 01539000 19,800 32,900 39,600 58,30

Susquehanna River 11,210.0 Montour Twp 2/1/79 1 182,000 259,000 292,000 377,000 01540500 204,000 282,000 318,000 406,00

Susquehanna River 10,963.0 Montour Twp 2/1/79 1 176,000 250,000 282,000 365,000 01540500 200,000 278,000 313,000 399,00

1Method refers to method listed in FIS to determine hydrology as compiled by Federal Emergency Management Agency Region 3; 1 is based on gaging-station data; 2 is based 

tion data; 3 is unknown. 

2Flood frequencies were computed for stations using annual maximum streamflow-gaging-station data and transferred to nearby FIS sites using drainage-area ratios. 
Appendix 3. Log-Pearson Type III flood frequencies determined from annual maximum (AMS) and partial-duration (PDS) streamflow-gaging-station d

 Station number Station name Drainage area (square miles) Period of Record 1 r-value Type of peak flow Flood-frequency 

(cubic feet per 

2-year 5-year 10-yea

01428750 01439500 01440400 01442500 01447500 01447680 0144772001449360

West Branch Lackawaxen River near Aldenville, Pa.

Bush Kill at Shoemakers, Pa.

Brodhead Creek near Analomink, Pa.

Brodhead Creek at Minisink Hills, Pa.Lehigh River at Stoddartsville, Pa.

Tunkhannock Creek near Long Pond, Pa.

Tobyhanna Creek near Blakeslee, Pa.

Pohopoco Creek at Kresgeville, Pa.

40.6

117

65.9

259

91.7

20

118

49.9

1975-20061909-20061958-20061951-20061942-20061966-20061962-20061967-2006

2.131.842.802.962.081.662.492.85

AMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% Difference

2,0502,330

14

1,9802,360

19

2,9103,220

11

8,900

11,000

24

2,4103,040

26

346360

4

3,1304,040

29

1,0801,200

11

3,6903,620

-2

3,2603,470

6

5,1904,730

-9

15,70015,900

1

4,8204,980

3

530522

-2

5,7505,770

0

1,6001,560

-3

5,314,82

-

4,434,36

-

7,076,35

-1

22,1021,10

-

7,236,79

-

6763

-

7,967,57

-

1,951,90

-
Appendix 3. Log-Pearson Type III flood frequencies determined from annual maximum (AMS) and partial-duration (PDS) streamflow-gaging-station d

 Station 

number

Station 

name

Drainage 

area 

(square 

miles)

Period of 

Record

1 r-value Type of peak flow

Flood-frequency 

(cubic feet per 

2-year 5-year 10-yea

014505000145150001451800014520000145250001465500014657980146704801468500

Aquashicola Creek at Palmerton, Pa.

Little Lehigh Creek near Allentown, Pa.

Jordan Creek near Schnecksville, Pa.

Jordan Creek at Allentown, Pa.

Monocacy Creek at Bethlehem, Pa.Neshaminy Creek near Langhorne, Pa.

Poquessing Creek at Grant Ave. at Philadelphia, Pa.

PennyPack Cr at Lower Rhawn St Bdg, Phila., Pa.Schuylkill River at Landingville, Pa.

76.7

80.8

53

75.8

44.5

210

21.4

49.8

133

1940-20061946-20061967-20061945-20061945-20061933-20061966-20061966-20061948-2006

2.692.723.932.372.842.474.394.394.19

AMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% Difference

2,2702,660

17

1,5502,140

38

2,3102,530

10

2,9303,520

20

596817

37

10,80011,400

6

3,1103,550

14

3,6904,340

18

3,3703,850

14

3,9103,790

-3

3,6103,700

2

3,8803,660

-6

5,2305,190

-1

1,2501,270

2

17,10016,000

-6

4,5804,680

2

5,7305,830

2

5,4705,320

-3

5,315,00

-

5,735,56

-

5,114,78

-

7,216,88

-

1,921,79

-

22,3020,70

-

5,695,66

-

7,387,20

-

7,236,75

-
Appendix 3. Log-Pearson Type III flood frequencies determined from annual maximum (AMS) and partial-duration (PDS) streamflow-gaging-station d

 Station number Station name Drainage area (square miles) Period of Record 1 r-value Type of peak flow Flood-frequency 

(cubic feet per 

2-year 5-year 10-yea

01469500 01470500 01470779 01471980 01472157 01473900 01477000 0148030001480500

Little Schuylkill River at Tamaqua, Pa.

Schuylkill River at Berne, Pa.

Tulpehocken Creek near Bernville, Pa.Manatawny Creek near Pottstown, Pa.

French Creek near Phoenixville, Pa.

Wissahickon Creek at Fort Washington, Pa.

Chester Creek near Chester, Pa.West Branch Brandywine Creek near Honey Brook, 

West Branch Brandywine Creek at Coatesville, Pa.

Pa.

42.9

355

66.5

85.559.1

40.8

61.1

18.7

45.8

1920-20061942-20061972-20061975-20061969-20061962-20061932-20061960-20061944-2006

2.023.002.064.474.743.562.403.834.00

AMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% Difference

1,4001,700

21

11,50012,500

9

1,9502,390

23

3,4303,690

8

2,4802,940

19

3,3203,700

11

2,9903,670

23

1,2301,570

28

1,9102,360

24

2,4102,500

4

18,50017,600

-5

3,8503,770

-2

5,1204,900

-4

4,5504,370

-4

5,1305,190

1

5,3305,340

0

2,2002,240

2

3,4503,410

-1

3,193,04

-

23,8022,80

-

5,524,87

-1

6,326,01

-

6,415,82

-

6,696,64

-

7,487,07

-

3,032,93

-

4,804,47

-
Appendix 3. Log-Pearson Type III flood frequencies determined from annual maximum (AMS) and partial-duration (PDS) streamflow-gaging-station d

 Station 

number

Station 

name

Drainage 

area 

(square 

miles)

Period of 

Record

1 r-value Type of peak flow

Flood-frequency 

(cubic feet per 

2-year 5-year 10-yea

0148061701480675015165000153150001532000015334000153400001536500

West Branch Brandywine Creek at Modena, 

Marsh Creek near Glenmoore, Pa.

Corey Creek near Mainesburg, Pa.

Susquehanna River at Towanda, Pa.

Towanda Creek near Monroeton, Pa.

Susquehanna River at Meshoppen, Pa.

Tunkhannock Creek near Tunkhannock, Pa.

Susquehanna River at Wilkes-Barre, Pa.

Pa. 55

8.6

12.2

7797

215

8720

383

9960

1970-20061967-20061955-20061980-20061914-20061977-20061914-20061980-2006

3.732.833.102.001.942.671.942.26

AMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% DifferenceAMS

AMS and PDS

% Difference

2,5903,110

20

247302

22

810941

16

98,100

109,000

11

9,890

10,600

7

113,000129,000

14

13,20012,600

-5

121,000139,000

15

4,6204,480

-3

426410

-4

1,4801,420

-4

131,000137,000

5

17,50016,800

-4

154,000157,000

2

20,10018,700

-7

167,000173,000

4

6,305,88

-

5751

-

2,091,94

-

153,00153,00

24,3022,00

-

182,00183,00

24,8023,30

-

198,00199,00
Appendix 3. Log-Pearson Type III flood frequencies determined from annual maximum (AMS) and partial-duration (PDS) streamflow-gaging-station d

Drainage Flood-frequency 

Station number Station name area (square miles) Period of Record 1 r-value Type of peak flow (cubic feet per 

2-year 5-year 10-yea

01538000 Wapwallopen Creek near Wapwallopen, Pa. 43.8 1920-2006 AMS 1,210 2,000 2,62

2.07 AMS and PDS 1,240 1,840 2,35

% Difference 2 -8 -1

01539000 Fishing Creek near Bloomsburg, Pa. 274 1936-2006 AMS 8,630 14,300 18,90

2.32 AMS and PDS 9,560 13,800 17,90

% Difference 11 -3 -

1The r-value is the total number of partial-duration peaks divided by the number of years of continuous record for any given station.