U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2010–1310

Prepared in cooperation with the

Maryland Department of the Environment

Selected Low-Flow Frequency Statistics for 

Continuous-Record Streamgage Locations

in Maryland, 2010
Cover.  View of Mattawoman Creek looking upstream at the stream channel and MD-227 State Highway bridge from the center of the

stream channel. [Photograph taken on September 29, 2010 by David P. Brower, U.S. Geological Survey, at station 01658000, Mattawoman

Creek near Pomonkey, Maryland as part of a maintenence visit to the station.]
Selected Low-Flow Frequency Statistics 

for Continuous-Record Streamgage

Locations in Maryland, 2010

By Edward J. Doheny and William S.L. Banks

Open-File Report 2010–1310

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the

Maryland Department of the Environment
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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reproduce any copyrighted materials contained within this report.

Suggested citation:

Doheny, E.J., and Banks, W.S.L., 2010, Selected low-flow frequency statistics for continuous-record streamgage 

locations in Maryland, 2010: U.S. Geological Survey Open-File Report 2010–1310, 22 p.
iii

Contents

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

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

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

Physiography................................................................................................................................2

Climate...........................................................................................................................................3

Computation of Low-Flow Frequency Statistics.......................................................................................4

Data Limitations............................................................................................................................................21

Summary........................................................................................................................................................21

Acknowledgments.......................................................................................................................................21

References Cited..........................................................................................................................................22

Glossary.........................................................................................................................................................22

Figures

1–2. Maps showing—

1. Location of study area and physiographic provinces in Maryland.............................3

2. Locations of 114 continuous-record streamgages in Maryland for 

which low-flow frequency statistics were computed.................................................10

Tables

1. Continuous-record streamgage locations in Maryland for which 

low-flow frequency statistics were computed........................................................................5

2. Low-flow frequency statistics for continuous-record streamgage 

locations in Maryland ................................................................................................................12
iv

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

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

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.

Conversion Factors and Datums

BASINS Better Assessment Science Integrating Point and Nonpoint Sources 

GIS Geographic Information System

MDE Maryland Department of the Environment

SWSTAT Surface-Water Statistics 

USGS U.S. Geological Survey

Abbreviations


Selected Low-Flow Frequency Statistics for 

Continuous-Record Streamgage Locations 

in Maryland, 2010

By Edward J. Doheny and William S.L. Banks

Abstract

According to a 2008 report by the Governor’s Advisory 

Committee on the Management and Protection of the State’s 

Water Resources, Maryland’s population grew by 35 percent 

between 1970 and 2000, and is expected to increase by an 

additional 27 percent between 2000 and 2030. Because 

domestic water demand generally increases in proportion to 

population growth, Maryland will be facing increased pressure 

on water resources over the next 20 years. Water-resources 

decisions should be based on sound, comprehensive, longterm data and low-flow frequency statistics from all available 

streamgage locations with unregulated streamflow and adequate record lengths. To provide the Maryland Department of 

the Environment with tools for making future water-resources 

decisions, the U.S. Geological Survey initiated a study in 

October 2009 to compute low-flow frequency statistics for 

selected streamgage locations in Maryland with 10 or more 

years of continuous streamflow records. 

This report presents low-flow frequency statistics for 

114 continuous-record streamgage locations in Maryland. The 

computed statistics presented for each streamgage location 

include the mean 7-, 14-, and 30-consecutive day minimum 

daily low-flow discharges for recurrence intervals of 2, 10, and 

20 years, and are based on approved streamflow records that 

include a minimum of 10 complete climatic years of record 

as of June 2010. Descriptive information for each of these 

streamgage locations, including the station number, station 

name, latitude, longitude, county, physiographic province, and 

drainage area, also is presented. 

The statistics are planned for incorporation into 

StreamStats, which is a U.S. Geological Survey web application for obtaining stream information, and is being used by 

water-resource managers and decision makers in Maryland to 

address water-supply planning and management, water-use 

appropriation and permitting, wastewater and industrial discharge permitting, and setting minimum required streamflows 

to protect freshwater biota and ecosystems.

Introduction

Hydrologic data and statistics that define the magnitude 

and variability of streamflow during periods of low flow are 

critical to effective management of water resources (Carpenter 

and Hayes, 1996). Engineers, scientists, natural resource 

managers, and many others use low-flow frequency statistics 

for (1) establishment of minimum flow-by requirements for 

streams and rivers, (2) quantifying base flows1 in streams and 

rivers, (3) wastewater discharge permitting, (4) water-supply 

planning and management, (5) protection of stream biota, and 

(6) evaluation of time of travel and dilution of toxic spills 

(Ries, 2006; Carpenter and Hayes, 1996).

Low-flow frequency statistics are computed for locations 

where U.S. Geological Survey (USGS) streamgages have 

collected continuous records of daily streamflow that are 

computed each year as part of the long-term station record 

(Ries, 2006). Because the frequency statistics for different 

streamgage locations are representative of different record 

lengths and different periods of time, they should be considered estimates when used for predicting long-term and 

future low-flow conditions (Ries, 2006). Statistics also change 

over time as longer streamflow records become available for 

streamgage locations, and as extreme hydrologic conditions 

influence the computed statistics (Ries, 2006). As a result, 

low-flow frequency statistics should be updated periodically 

to reflect the longer record lengths that are available for the 

streamgage locations (Ries, 2006).

____________________ 1

 Words in bold are defined in the glossary section at the end of the report. 
2 Selected Low-Flow Frequency Statistics for Continuous-Record Streamgage Locations in Maryland, 2010

Low-flow frequency statistics were last published for 

streamgage locations in Maryland on a statewide basis by 

Carpenter and Hayes (1996). The 1996 investigation made 

use of streamflow records through March 1987 from 94 

continuous-record streamgage locations. Extreme drought 

conditions that occurred across Maryland in 1999 and 2002 

are now included in the long-term record for many streamgage 

locations that were part of the 1996 investigation. Ries (2006) 

published selected streamflow statistics for 47 streamgage 

locations in northeastern Maryland, based on streamflow 

records through September 2004. This 2006 study produced 

updated low-flow frequency statistics for 7 streamgage 

locations that were previously used in the investigation by 

Carpenter and Hayes (1996).

According to a 2008 report by the Governor’s Advisory 

Committee on the Management and Protection of the State’s 

Water Resources, Maryland’s population grew by 35 percent 

between 1970 and 2000, and is expected to increase by an 

additional 27 percent between 2000 and 2030 (Wolman, 

2008). Because domestic water demand generally increases 

in proportion to population growth, Maryland will be facing 

increased pressure on water resources over the next 20 years. 

Water-resources decisions should be based on sound, comprehensive, long-term data and low-flow frequency statistics from 

all available streamgage locations with unregulated streamflow 

and adequate record lengths (Wolman, 2008). To provide the 

Maryland Department of the Environment (MDE) with tools 

for making future water-resources decisions, the USGS initiated a study in October 2009 to compute low-flow frequency 

statistics for selected streamgage locations in Maryland with 

10 or more years of continuous streamflow records. 

The purpose of this report is to present low-flow frequency statistics for 114 continuous-record streamgage 

locations in Maryland, based on approved streamflow records 

that include a minimum of 10 complete climatic years of 

record as of June 2010. The statistics presented in this report 

include the mean 7-, 14-, and 30-consecutive day low-flow 

discharges for recurrence intervals of 2, 10, and 20 years. 

These statistics are planned for incorporation into StreamStats, 

a USGS web application for obtaining stream information, 

which is being used by water-resource managers and decision 

makers in Maryland for water-supply planning and management, water-use appropriation and permitting, wastewater and 

industrial discharge permitting, and setting minimum required 

streamflows to protect freshwater biota and ecosystems (Ries 

and others, 2004; Ries and others, 2008).

Description of Study Area

Maryland lies between 37°53′ and 39°43′ north latitude, 

and 75°04′ and 79°29′ west longitude (fig. 1). Maryland has a 

total area of about 12,407 mi2 (square miles), of which about 

9,775 mi2 is land area. About 2,633 mi2 are covered by water, 

which includes the Chesapeake Bay and other inland water 

(Netstate.com, 2010). Brief descriptions of Maryland’s physiography and climate follow.

Physiography

Maryland has five major physiographic provinces 

(Fenneman, 1938). These provinces include the Coastal Plain, 

Piedmont, Blue Ridge, Valley and Ridge, and Appalachian 

Plateaus (fig. 1). The following description of Maryland’s 

physiographic provinces includes excerpts that were most 

recently presented in studies conducted by Carpenter and 

Hayes (1996) and Dillow (1996). 

Coastal Plain—The Coastal Plain Province in Maryland 

consists of two distinct divisions that are separated by the 

Chesapeake Bay: (1) the Eastern Coastal Plain on the east 

side of the Chesapeake Bay, and (2) the Western Coastal Plain 

located east of the Fall Line and west of the Chesapeake 

Bay. The Eastern Coastal Plain, commonly called the Eastern 

Shore, is characterized by relatively flat topography and low 

relief, with elevations rising from sea level to slightly less than 

100 ft (feet) above sea level. The Eastern Shore is drained by 

small, sluggish streams with very low gradients. The Western 

Coastal Plain rises to about 200 ft above sea level and has 

streams with slightly higher gradients that are less sluggish 

than those of the Eastern Shore. The Western Coastal Plain is 

a rolling upland with topography that more closely resembles 

the Piedmont Province than it does the Eastern Shore. Most 

streams and rivers in both parts of the Coastal Plain are 

affected by tides for considerable distances above their outlets. 

The Coastal Plain Province in Maryland includes almost 5,000 

mi2 of land area, which is nearly half of the total land area of 

the State.

Piedmont—The Piedmont Province in Maryland covers 

approximately 2,500 mi2 and is characterized by gently rolling 

topography, with hills and ridges rising to about 800 ft above 

sea level. The province is drained by many streams and rivers 

with moderate to fairly steep gradients in relatively deep, 

narrow valleys. Streams and rivers in the eastern part of the 

Piedmont drain into the Chesapeake Bay, whereas those in the 

western part of the province drain into the Potomac River.

Blue Ridge—The Blue Ridge Province in Maryland 

covers approximately 600 mi2 and is characterized by rugged 

topography, with high relief and fairly steep stream gradients. Elevations rise to more than 1,600 ft above sea level. 

The region is drained primarily by Catoctin Creek and its 

tributaries.

Valley and Ridge—The Valley and Ridge Province in 

Maryland covers almost 800 mi2 and consists of two distinct 

divisions: (1) the Great Valley, and (2) the Allegheny Ridges. 

The Great Valley consists of gently rolling, broad lowlands 

with elevations averaging about 500 to 600 ft above sea 

level. The valley is drained primarily by Antietam Creek and 

Conococheague Creek. Streams and rivers are gently sloped 

with relatively high sinuosity. Limestone underlies the valley, 

and caves, sinkholes, and springs are common. Streams in this 

region tend to have more uniform flows than streams in other 

areas of Maryland. The Allegheny Ridges are composed of a 

series of uniform, northeastward-trending hills and ridge lines 

that are located west of the Conococheague Creek watershed. 
Introduction 3

Elevations range from about 400 ft above sea level in the 

valleys to about 1,500 ft above sea level on the ridges. This 

region is drained by fairly steep, swift streams. 

Appalachian Plateaus—The Appalachian Plateaus 

Province in Maryland covers about 800 mi2 and is characterized as a broad, dissected upland with pronounced relief and 

rugged topography. Elevations in the Maryland section of the 

province range from about 1,500 to 3,000 ft above sea level, 

with a maximum elevation of 3,360 ft. Streams and rivers 

draining the Appalachian Plateaus generally have steep gradients, as well as rapids and waterfalls. 

Climate

Maryland’s climate can be described as generally moderate, with seasons that are well defined (Carpenter and Hayes, 

1996). Summers range in temperature from mild to hot, and in 

winter from moderate in the east and south, to very cold in the 

western part of the State (Maryland State Archives, 2010). The 

mean annual temperature for Maryland is about 55°F (degrees 

Fahrenheit). July is the warmest month with high temperatures 

averaging in the mid to upper 80s across the State. January is 

the coldest month with low temperatures averaging in the low 

to mid 20s (Maryland State Archives, 2010).

Mean annual precipitation for Maryland is about 41 in. 

(inches) (Maryland State Archives, 2010), and historically has 

ranged from about 36 to 52 in/yr (inches per year) in different 

regions of the State (Carpenter and Hayes, 1996). Precipitation 

is distributed fairly evenly throughout the year, but can vary 

from month to month depending on the magnitude of spring 

and summer thunderstorms that occur across the region. 

Average seasonal snowfall is about 20.6 in., and ranges from 

about 10 in. on the lower Eastern Shore to about 110 in. in the 

Appalachian Plateaus region (Maryland State Archives, 2010). 

Lowest streamflows typically occur between the months of 

July and September.

Figure 1. Location of study area and physiographic provinces in Maryland.
4 Selected Low-Flow Frequency Statistics for Continuous-Record Streamgage Locations in Maryland, 2010

Computation of Low-Flow Frequency 

Statistics

Low-flow frequency statistics for 114 continuous-record 

streamgage locations in Maryland are presented in this report. 

Streamgage locations used in the study included both active 

and discontinued stations with a minimum of 10 complete 

climatic years of record. Ten years of record was selected as 

the criteria for inclusion of stations because it is widely considered to be the minimum sufficient record length to warrant 

statistical analysis (Interagency Advisory Committee on Water 

Data, 1982). Descriptive information for each streamgage 

location, including the station number, station name, latitude, 

longitude, county or city, physiographic province, and drainage area, is shown in table 1. The streamgage locations that 

were included in the study are shown in figure 2.

Computer programs used to compute the statistics for this 

study included version 4.0 of the Better Assessment Science 

Integrating Point and Nonpoint Sources software (BASINS) 

(U.S. Environmental Protection Agency, 2007) and SurfaceWater Statistics (SWSTAT), which is a program developed 

by the USGS. BASINS is a geographic information system 

(GIS)-based program that was used for database management. 

SWSTAT was used for calculating the low-flow frequency 

statistics. The SWSTAT program incorporates standard USGS 

methods for computing low-flow frequency statistics that were 

originally described by Riggs (1972).

The statistics computed for each streamgage location 

included the mean 7-, 14-, and 30-consecutive day low-flow 

discharges for recurrence intervals of 2, 10, and 20 years. The 

statistics were computed from the annual series of minimum 

7-, 14-, and 30-consecutive day, daily mean discharges for 

each streamgage location.

For each streamgage location, the 7-, 14-, and 30-consecutive day period with the lowest daily mean discharge was 

identified for each climatic year of record. Five streamgage 

locations had periods of record that were truncated for the 

analysis so that only the periods where low flows were unaffected by regulation or diversions were included (table 1). 

Mann-Kendall nonparametric tests for monotonic trends 

were performed using the annual 7-day minimum daily 

mean streamflow for each streamgage location to determine 

if increases or decreases in the annual series may be occurring over time at the 95-percent confidence interval (Helsel 

and Hirsch, 1992). Twenty-five streamgage locations were 

identified where further investigation would be required to 

determine the significance of any trends in the annual 7-day 

minimum daily mean streamflow over time. These streamgage 

locations are shown in table 2, along with the computed lowflow frequency statistics. 

Low-flow frequency statistics were computed by fitting 

the logarithms of the annual 7-, 14-, and 30-day minimum 

daily mean discharges for each streamgage location to a 

log-Pearson, Type III frequency distribution to determine 

discharges corresponding to recurrence intervals of 2, 10, and 

20 years for the 7-, 14-, and 30-day minimum streamflows 

(Riggs, 1972; Ries, 2006). The discharge equal to or less than 

that given for a specific recurrence interval can be expected 

to occur, on average, once during that interval (Ries, 2006). 

For instance, a streamgage location with a computed 7-day, 

10-year low flow of 25 ft3/s (cubic feet per second) indicates 

that an average discharge of less than or equal to 25 ft3/s over 

the lowest 7 consecutive days in the year should be expected 

at that streamgage location, on average, once every 10 years. 

On a percentage basis, these streamflow conditions have a 

10-percent [(1 year/10 years) x 100] chance of occurring in 

any given climatic year. Similarly, a streamgage location with 

a computed 30-day, 20-year low flow of 10 ft3/s indicates that 

a discharge of less than or equal to 10 ft3/s, which is the average over the lowest 30 consecutive days in the year, should be 

expected at that streamgage location, on average, once every 

20 years. These streamflow conditions would have a 5-percent 

[(1 year/20 years) x 100] chance of occurring in any given 

climatic year. The low-flow frequency statistics for the 114 

streamgage locations in Maryland are presented in table 2.

The 14-day and 30-day statistics presented for station 

01583000, Slade Run near Glyndon, MD, are those that were 

previously published in Carpenter and Hayes (1996). Although 

the period of record for this streamgage location did not 

change since the last low-flow investigation was conducted 

for Maryland, SWSTAT did not produce comparable results 

for the 14-day and 30-day statistics. The previously published 

statistics are still considered valid for Slade Run because 

they are based on the same period of record that is currently 

available and because the land use in the watershed has not 

changed considerably over time (Carpenter and Hayes, 1996; 

McCandless and Everett, 2002).

The 10-year statistics for station 01585400, Brien Run at 

Stemmers Run, MD, were based on a manual verification and 

update of statistics that were previously published in Carpenter 

(1983), because SWSTAT produced questionable results for 

the 10-year statistics that could not be easily explained through 

analysis of the dataset or input to the program. The published 

statistics originally presented by Carpenter (1983) were based 

on 21 years of climatic record. The 7-, 14-, and 30-consecutive day periods with the lowest daily mean discharge were 

identified for an additional 8 years of climatic record that were 

available for analysis. The 10-year statistics were then manually updated and verified to account for the additional 8 years 

of climatic record and used in place of the SWSTAT output. 

Low-flow statistics that were produced by SWSTAT for 

other streamgage locations with periods of record that did 

not change since the last low-flow investigation for Maryland 

were checked against previously published values from 

Carpenter and Hayes (1996). The low-flow statistics for these 

streamgage locations were found to be comparable to the previously published values. 

The 7-day low-flow statistics for station 01493000, 

Unicorn Branch near Millington, MD, and station 01585200, 

West Branch Herring Run at Idlewylde, MD are not presented 

because the computed skews of the logarithms of the annual 

7-day minimum daily mean streamflows were -3.61 and -3.65, 

respectively. The SWSTAT program does not compute reliable 

low-flow frequencies when skew values exceed an absolute 

value of 3.3.
Computation of Low-Flow Frequency Statistics 5

Table 1. Continuous-record streamgage locations in Maryland for which low-flow frequency statistics were computed.

—Continued

[MD, Maryland; PA, Pennsylvania; WV, West Virginia; °, degrees; ′, minutes; ′′, seconds; mi2, square miles]

Station

number

Station 

name

Latitude

(° ‘ ”)

Longitude

(° ‘ “) County/City Physiographic province

Drainage

area

(mi2)

Remarks

0148471320 Birch Branch at Showell, MD 38 24 33.6 75 12 44.6 Worcester Coastal Plain 6.38

01485000 Pocomoke River near Willards, 

MD

38 23 20.0 75 19 28.0 Worcester Coastal Plain 60.5

01485500 Nassawango Creek near Snow 

Hill, MD

38 13 44.1 75 28 17.2 Worcester Coastal Plain 44.9

01486000 Manokin Branch near Princess 

Anne, MD

38 12 50.0 75 40 17.0 Somerset Coastal Plain 4.80

01489000 Faulkner Branch at 

Federalsburg, MD

38 42 44.0 75 47 34.0 Caroline Coastal Plain 7.10

01490000 Chicamacomico River near 

Salem, MD

38 30 42.0 75 52 47.7 Dorchester Coastal Plain 15.0

01491000 Choptank River near 

Greensboro, MD

38 59 49.9 75 47 08.9 Caroline Coastal Plain 113

01491500 Tuckahoe Creek near 

Ruthsburg, MD

38 58 00.5 75 56 35.0 Queen 

Anne's

Coastal Plain 85.2

01492000 Beaverdam Branch at Matthews, 

MD

38 48 41.0 75 58 15.0 Talbot Coastal Plain 5.85

01492500 Sallie Harris Creek near 

Carmichael, MD

38 57 53.6 76 06 31.8 Queen 

Anne's

Coastal Plain 8.09

01493000 Unicorn Branch near 

Millington, MD

39 14 58.9 75 51 40.7 Queen 

Anne's

Coastal Plain 19.7

01493500 Morgan Creek near 

Kennedyville, MD

39 16 48.1 76 00 52.4 Kent Coastal Plain 12.7

01495000 Big Elk Creek at Elk Mills, MD 39 39 25.4 75 49 20.5 Cecil Piedmont 52.6

01496000 Northeast Creek at Leslie, MD 39 37 38.0 75 56 40.0 Cecil Coastal Plain 24.3

01496200 Principio Creek near Principio 

Furnace, MD

39 37 34.0 76 02 27.0 Cecil Piedmont 9.03

01578500 Octoraro Creek near Rising Sun, 

MD

39 41 24.0 76 07 43.0 Cecil Piedmont 193 Truncated record 

(Use 1933–1949)

01580000 Deer Creek at Rocks, MD 39 37 47.9 76 24 11.9 Harford Piedmont 94.4

01580520 Deer Creek near Darlington, 

MD

39 37 02.8 76 11 30.7 Harford Piedmont 164

01581500 Bynum Run at Bel Air, MD 39 32 29.3 76 19 48.4 Harford Piedmont 8.52

01581700 Winters Run near Benson, MD 39 31 11.8 76 22 22.7 Harford Piedmont 34.8

01581810 Gunpowder Falls at 

Hoffmanville, MD

39 41 23.3 76 46 53.3 Baltimore Piedmont 27.0

01581830 Grave Run near Beckleysville, 

MD

39 39 17.3 76 46 51.3 Baltimore Piedmont 7.68

01581870 Georges Run near 

Beckleysville, MD

39 37 33.2 76 46 21.1 Baltimore Piedmont 15.8

01581960 Beetree Run at Bentley Springs, 

MD

39 40 23.1 76 40 30.7 Baltimore Piedmont 9.72

01582000 Little Falls at Blue Mount, MD 39 36 14.7 76 37 13.7 Baltimore Piedmont 52.9

01583000 Slade Run near Glyndon, MD 39 29 43.4 76 47 41.4 Baltimore Piedmont 2.09
6 Selected Low-Flow Frequency Statistics for Continuous-Record Streamgage Locations in Maryland, 2010

Table 1. Continuous-record streamgage locations in Maryland for which low-flow frequency statistics were computed.

—Continued

[MD, Maryland; PA, Pennsylvania; WV, West Virginia; °, degrees; ′, minutes; ′′, seconds; mi2, square miles]

Station

number

Station 

name

Latitude

(° ‘ ”)

Longitude

(° ‘ “) County/City Physiographic province

Drainage

area

(mi2)

Remarks

01583100 Piney Run at Dover, MD 39 31 14.2 76 46 00.8 Baltimore Piedmont 12.3

01583500 Western Run at Western Run, 

MD

39 30 38.8 76 40 35.4 Baltimore Piedmont 59.8

01583570 Pond Branch at Oregon Ridge, 

MD

39 28 49.1 76 41 15.0 Baltimore Piedmont 0.12

01583580 Baisman Run at Broadmoor, 

MD

39 28 46.1 76 40 40.9 Baltimore Piedmont 1.47

01583600 Beaverdam Run at 

Cockeysville, MD

39 29 08.1 76 38 44.6 Baltimore Piedmont 20.9

01584050 Long Green Creek at Glen Arm, 

MD

39 27 16.9 76 28 44.0 Baltimore Piedmont 9.40

01584500 Little Gunpowder Falls at 

Laurel Brook, MD

39 30 19.3 76 25 54.4 Baltimore Piedmont 36.1

01585090 Whitemarsh Run near Fullerton, 

MD

39 22 46.5 76 29 44.9 Baltimore Coastal Plain 2.73

01585095 North Fork Whitemarsh Run 

near White Marsh, MD

39 23 09.2 76 28 07.9 Baltimore Coastal Plain 1.34

01585100 Whitemarsh Run at 

Whitemarsh, MD

39 22 13.9 76 26 45.3 Baltimore Coastal Plain 7.61

01585104 Honeygo Run near White 

Marsh, MD

39 22 58.8 76 25 58.7 Baltimore Coastal Plain 2.50

01585200 West Branch Herring Run at 

Idlewylde, MD

39 22 25.1 76 35 03.6 Baltimore Piedmont 2.13

01585225 Moores Run Tributary near 

Todd Avenue at Baltimore, 

MD

39 20 12.1 76 32 26.2 Baltimore 

City

Coastal Plain 0.21

01585230 Moores Run at Radecke Avenue 

at Baltimore, MD

39 19 48.3 76 32 05.6 Baltimore 

City

Coastal Plain 3.52

01585300 Stemmers Run at Rossville, MD 39 20 28.0 76 29 17.0 Baltimore Coastal Plain 4.46

01585400 Brien Run at Stemmers Run, 

MD

39 20 01.0 76 28 23.0 Baltimore Coastal Plain 1.97

01586210 Beaver Run near Finksburg, MD 39 29 22.0 76 54 10.6 Carroll Piedmont 14.0

01586610 Morgan Run near Louisville, 

MD

39 27 06.8 76 57 19.1 Carroll Piedmont 28.0

01587000 North Branch Patapsco River 

near Marriottsville, MD 

39 21 56.0 76 53 06.0 Howard Piedmont 165 Truncated record 

(Use 1930–1951)

01587500 South Branch Patapsco River at 

Henryton, MD

39 21 05.0 76 54 50.0 Howard Piedmont 64.4

01588000 Piney Run near Sykesville, MD 39 22 55.0 76 58 00.0 Carroll Piedmont 11.4

01589100 East Branch Herbert Run at 

Arbutus, MD

39 14 24.0 76 41 31.9 Baltimore Coastal Plain 2.47

01589180 Gwynns Falls at Glyndon, MD 39 28 18.1 76 49 00.8 Baltimore Piedmont 0.32

01589197 Gwynns Falls near Delight, MD 39 26 34.6 76 47 00.3 Baltimore Piedmont 4.23

01589200 Gwynns Falls near Owings 

Mills, MD

39 26 16.0 76 46 57.0 Baltimore Piedmont 4.90
Computation of Low-Flow Frequency Statistics 7

Table 1. Continuous-record streamgage locations in Maryland for which low-flow frequency statistics were computed.

—Continued

[MD, Maryland; PA, Pennsylvania; WV, West Virginia; °, degrees; ′, minutes; ′′, seconds; mi2, square miles]

Station

number

Station 

name

Latitude

(° ‘ ”)

Longitude

(° ‘ “) County/City Physiographic province

Drainage

area

(mi2)

Remarks

01589238 Gwynns Falls Tributary at 

McDonogh, MD

39 24 01.6 76 46 13.6 Baltimore Piedmont 0.03

01589300 Gwynns Falls at Villa Nova, 

MD

39 20 45.2 76 43 59.5 Baltimore Piedmont 32.5

01589330 Dead Run at Franklintown, MD 39 18 40.4 76 42 59.9 Baltimore Piedmont 5.52

01589352 Gwynns Falls at Washington 

Boulevard at Baltimore, MD

39 16 17.4 76 38 54.8 Baltimore 

City

Coastal Plain 65.9

01589440 Jones Falls at Sorrento, MD 39 23 30.2 76 39 39.4 Baltimore Piedmont 25.2

01589795 South Fork Jabez Branch at 

Millersville, MD

39 04 05.7 76 39 05.5 Anne 

Arundel

Coastal Plain 1.0

01590000 North River near Annapolis, 

MD

38 59 09.0 76 37 21.0 Anne 

Arundel

Coastal Plain 8.5

01591000 Patuxent River near Unity, MD 39 14 17.7 77 03 20.6 Montgomery Piedmont 34.8

01591400 Cattail Creek near Glenwood, 

MD

39 15 21.5 77 03 03.8 Howard Piedmont 22.9

01591700 Hawlings River near Sandy 

Spring, MD

39 10 28.8 77 01 17.7 Montgomery Piedmont 27.0

01593500 Little Patuxent River at 

Guilford, MD

39 10 03.9 76 51 04.5 Howard Piedmont 38.0

01594000 Little Patuxent River at Savage, 

MD 

39 08 03.9 76 48 58.2 Howard Coastal Plain 98.4

01594500 Western Branch near Largo, MD 38 52 24.0 76 47 54.0 Prince 

George's

Coastal Plain 30.2

01594526 Western Branch at Upper 

Marlboro, MD

38 48 51.2 76 44 55.4 Prince 

George's

Coastal Plain 89.7

01594600 Cocktown Creek near 

Huntingtown, MD

38 38 27.0 76 38 07.0 Calvert Coastal Plain 3.85

01594710 Killpeck Creek at Huntersville, 

MD

38 28 37.0 76 44 08.0 St. Mary's Coastal Plain 3.26

01594800 St. Leonard Creek near St. 

Leonard, MD

38 26 56.1 76 29 42.5 Calvert Coastal Plain 6.73

01594950 McMillan Fork near Fort 

Pendleton, MD

39 16 36.1 79 23 25.1 Garrett Appalachian 

Plateaus

2.30

01595000 North Branch Potomac River at 

Steyer, MD

39 18 06.8 79 18 24.8 Garrett Appalachian 

Plateaus

73.1

01596500 Savage River near Barton, MD 39 34 12.2 79 06 07.0 Garrett Appalachian 

Plateaus

49.1

01597000 Crabtree Creek near Swanton, 

MD

39 30 00.0 79 09 35.0 Garrett Appalachian 

Plateaus

16.7

01599000 Georges Creek at Franklin, MD 39 29 38.1 79 02 40.9 Allegany Appalachian 

Plateaus

72.4

01601500 Wills Creek near Cumberland, 

MD

39 40 10.6 78 47 16.9 Allegany Valley and 

Ridge

247

01609000 Town Creek near Oldtown, MD 39 33 11.6 78 33 18.0 Allegany Valley and 

Ridge

148
8 Selected Low-Flow Frequency Statistics for Continuous-Record Streamgage Locations in Maryland, 2010

Table 1. Continuous-record streamgage locations in Maryland for which low-flow frequency statistics were computed.

—Continued

[MD, Maryland; PA, Pennsylvania; WV, West Virginia; °, degrees; ′, minutes; ′′, seconds; mi2, square miles]

Station

number

Station 

name

Latitude

(° ‘ ”)

Longitude

(° ‘ “) County/City Physiographic province

Drainage

area

(mi2)

Remarks

01609500 Sawpit Run near Oldtown, MD 39 32 50.0 78 33 20.0 Allegany Valley and 

Ridge

5.08

01610000 Potomac River at Paw Paw, WV 39 32 20.1 78 27 23.0 Allegany Valley and 

Ridge

3,129

01610155 Sideling Hill Creek near 

Bellegrove, MD

39 38 58.3 78 20 38.9 Washington Valley and 

Ridge

102

01612500 Little Tonoloway Creek near 

Hancock, MD

39 42 45.0 78 13 55.0 Washington Valley and 

Ridge

16.9

01613000 Potomac River at Hancock, MD 39 41 51.2 78 10 40.4 Washington Valley and 

Ridge

4,064

01614500 Conococheague Creek at 

Fairview, MD

39 42 59.0 77 49 29.2 Washington Valley and 

Ridge

494

01617800 Marsh Run at Grimes, MD 39 30 52.4 77 46 38.0 Washington Valley and 

Ridge

18.9

01618000 Potomac River at 

Shepherdstown, WV

39 26 05.0 77 48 05.0 Jefferson Valley and 

Ridge

5,929

01619000 Antietam Creek near 

Waynesboro, PA

39 42 58.5 77 36 23.9 Washington Valley and 

Ridge

93.5

01637000 Little Catoctin Creek at 

Harmony, MD

39 28 55.0 77 32 20.0 Frederick Blue Ridge 8.83

01637500 Catoctin Creek near 

Middletown, MD

39 25 38.1 77 33 22.2 Frederick Blue Ridge 66.9

01638500 Potomac River at Point of 

Rocks, MD

39 16 24.9 77 32 35.2 Frederick Piedmont 9,651

01639000 Monocacy River at Bridgeport, 

MD

39 40 43.8 77 14 04.2 Frederick Piedmont 173

01639140 Piney Creek near Taneytown, 

MD

39 39 38.7 77 13 15.5 Carroll Piedmont 31.3

01639500 Big Pipe Creek at Bruceville, 

MD

39 36 44.5 77 14 14.8 Carroll Piedmont 102

01640500 Owens Creek at Lantz, MD 39 40 36.0 77 27 50.0 Frederick Blue Ridge 5.93

01640965 Hunting Creek near Foxville, 

MD

39 37 10.0 77 28 00.0 Frederick Blue Ridge 2.14

01641000 Hunting Creek at Jimtown, MD 39 35 40.0 77 23 50.0 Frederick Piedmont 18.4 Truncated record 

(Use 1950–1968)

01641500 Fishing Creek near Lewistown, 

MD

39 31 37.6 77 28 01.3 Frederick Blue Ridge 7.29

01642000 Monocacy River near Frederick, 

MD

39 27 09.0 77 22 16.0 Frederick Piedmont 665

01642500 Linganore Creek near Frederick, 

MD

39 24 55.0 77 20 00.0 Frederick Piedmont 82.3 Truncated record 

(Use 1935–1970)

01643000 Monocacy River at Jug Bridge 

near Frederick, MD

39 24 10.2 77 21 57.9 Frederick Piedmont 817

01643500 Bennett Creek at Park Mills, 

MD

39 17 38.9 77 24 25.5 Frederick Piedmont 62.8
Computation of Low-Flow Frequency Statistics 9

Table 1. Continuous-record streamgage locations in Maryland for which low-flow frequency statistics were computed.

—Continued

[MD, Maryland; PA, Pennsylvania; WV, West Virginia; °, degrees; ′, minutes; ′′, seconds; mi2, square miles]

Station

number

Station 

name

Latitude

(° ‘ ”)

Longitude

(° ‘ “) County/City Physiographic province

Drainage

area

(mi2)

Remarks

01645000 Seneca Creek at Dawsonville, 

MD

39 07 41.1 77 20 08.8 Montgomery Piedmont 101

01645200 Watts Branch at Rockville, MD 39 05 03.0 77 10 38.0 Montgomery Piedmont 3.70

01646550 Little Falls Branch near 

Bethesda, MD

38 57 27.0 77 06 31.0 Montgomery Piedmont 4.10

01649500 Northeast Branch Anacostia 

River at Riverdale, MD

38 57 36.9 76 55 33.5 Prince 

George's

Coastal Plain 72.8

01650500 Northwest Branch Anacostia 

River near Colesville, MD

39 03 56.4 77 01 45.6 Montgomery Piedmont 21.0

01651000 Northwest Branch Anacostia 

River near Hyattsville, MD

38 57 08.4 76 57 57.8 Prince 

George's

Coastal Plain 49.4 Truncated record 

(Use 1962–2008)

01653500 Henson Creek at Oxon Hill, MD 38 47 16.0 76 58 42.0 Prince 

George's

Coastal Plain 16.7

01653600 Piscataway Creek at Piscataway, 

MD

38 42 20.8 76 57 58.3 Prince 

George's

Coastal Plain 39.5

01658000 Mattawoman Creek near 

Pomonkey, MD

38 35 46.1 77 03 21.7 Charles Coastal Plain 54.8

01660920 Zekiah Swamp Run near 

Newtown, MD

38 29 26.1 76 55 37.5 Charles Coastal Plain 79.9

01661000 Chaptico Creek at Chaptico, 

MD

38 22 45.0 76 46 56.0 St. Mary's Coastal Plain 10.4

01661050 St. Clement Creek near 

Clements, MD

38 19 59.9 76 43 30.0 St. Mary's Coastal Plain 18.5

01661500 St. Marys River at Great Mills, 

MD

38 14 30.3 76 30 13.2 St. Mary's Coastal Plain 24.0

03075500 Youghiogheny River near 

Oakland, MD

39 25 17.7 79 25 25.1 Garrett Appalachian 

Plateaus

134

03076600 Bear Creek at Friendsville, MD 39 39 22.1 79 23 38.8 Garrett Appalachian 

Plateaus

48.9

03078000 Casselman River at Grantsville, 

MD

39 42 07.9 79 08 11.0 Garrett Appalachian 

Plateaus

62.5
10 Selected Low-Flow Frequency Statistics for Continuous-Record Streamgage Locations in Maryland, 2010

Figure 2. Locations of 114 continuous-record streamgages in Maryland for which low-flow frequency statistics were computed.
Computation of Low-Flow Frequency Statistics 11

Figure 2. Locations of 114 continuous-record streamgages in Maryland for which low-flow frequency statistics were computed.

—Continued
12 Selected Low-Flow Frequency Statistics for Continuous-Record Streamgage Locations in Maryland, 2010

Table 2. Low-flow frequency statistics for continuous-record streamgage locations in Maryland.—Continued

[ft3/s, cubic feet per second; -- not included]

Station number Period of record 

(climatic years) Probability

Recurrence 

interval 

(years)

Minimum daily mean streamflow 

over given number of days Remarks

7-Day 

(ft3/s)

14-Day 

(ft3/s)

30-Day 

(ft3/s)

0148471320 0.5 2 0.4 0.5 0.5

2000–2009 0.1 10 0.2 0.2 0.2

0.05 20 0.2 0.2 0.2

01485000 1950–2003 0.5 2 6.5 7.0 8.1

2007–2008 0.1 10 2.7 3.0 3.4

0.05 20 2.1 2.3 2.7

01485500 0.5 2 2.3 2.6 3.5

Trend analysis needed for 

7-day statistics 1950–2008 0.1 10 1.2 1.3 1.5

0.05 20 1.1 1.2 1.3

01486000 1951–1970 0.5 2 0.3 0.3 0.4

Trend analysis needed for 

7-day statistics 1975–2008 0.1 10 0.1 0.1 0.1

0.05 20 0.0 0.1 0.1

01489000 0.5 2 1.1 1.2 1.4

1951–1990 0.1 10 0.3 0.5 0.7

0.05 20 0.2 0.4 0.6

01490000 1952–1979 0.5 2 3.7 4.2 4.9

Trend analysis needed for 

7-day statistics 2001–2008 0.1 10 0.9 1.4 1.9

0.05 20 0.5 0.9 1.4

01491000 0.5 2 12.9 14.1 16.1

1948–2008 0.1 10 4.0 5.2 6.7

0.05 20 2.7 3.9 5.3

01491500 1951–1955 0.5 2 16.9 19.2 23.1

2001–2008 0.1 10 4.7 5.5 7.3

0.05 20 2.9 3.4 4.6

01492000 0.5 2 0.1 0.2 0.3

1951–1980 0.1 10 0.0 0.0 0.1

0.05 20 0.0 0.0 0.0

01492500 1952–1955 0.5 2 1.9 2.0 2.3

2001–2008 0.1 10 1.4 1.5 1.7

0.05 20 1.3 1.4 1.6

01493000 1948–2004 0.5 2 -- 7.6 8.3

2007–2008 0.1 10 -- 4.4 5.1

0.05 20 -- 3.7 4.4

01493500 1952–2004 0.5 2 3.4 3.6 4.0

2007–2008 0.1 10 1.6 1.7 2.0

0.05 20 1.2 1.3 1.5

01495000 0.5 2 19.3 21.0 23.1

1932–2008 0.1 10 8.7 9.4 11.1

0.05 20 6.5 7.0 8.7
Computation of Low-Flow Frequency Statistics 13

Table 2. Low-flow frequency statistics for continuous-record streamgage locations in Maryland.—Continued

[ft3/s, cubic feet per second; -- not included]

Station number Period of record 

(climatic years) Probability

Recurrence 

interval 

(years)

Minimum daily mean streamflow 

over given number of days Remarks

7-Day 

(ft3/s)

14-Day 

(ft3/s)

30-Day 

(ft3/s)

01496000 0.5 2 5.5 6.0 6.8

1949–1983 0.1 10 2.7 3.0 3.3

0.05 20 2.1 2.3 2.7

01496200 0.5 2 2.5 2.6 3.0

1968–1991 0.1 10 1.3 1.5 1.7

0.05 20 1.1 1.2 1.4

01578500 0.5 2 91.7 96.6 107.1

1933–1949 0.1 10 55.1 56.9 64.0

0.05 20 45.6 46.9 53.0

01580000 0.5 2 48.0 49.6 51.7

1927–2008 0.1 10 22.8 24.2 28.1

0.05 20 17.0 18.6 23.2

01580520 0.5 2 79.6 82.6 87.6

2000–2009 0.1 10 19.5 22.1 29.8

0.05 20 10.9 13.0 20.5

01581500 1945–1950 0.5 2 1.2 1.4 1.7

1956–1969 0.1 10 0.3 0.4 0.8

2000–2008 0.05 20 0.1 0.2 0.6

01581700 0.5 2 17.2 17.7 18.0

1968–2008 0.1 10 5.4 6.2 8.0

0.05 20 3.3 4.0 6.2

01581810 0.5 2 10.3 10.8 11.8

2000–2009 0.1 10 3.7 3.7 4.6

0.05 20 2.5 2.6 3.5

01581830 0.5 2 2.9 3.1 3.4

2000–2009 0.1 10 1.0 1.1 1.4

0.05 20 0.7 0.8 1.1

01581870 0.5 2 5.4 5.8 7.0

2000–2009 0.1 10 3.8 3.9 4.1

0.05 20 3.6 3.6 3.6

01581960 0.5 2 5.3 5.5 5.9

2000–2009 0.1 10 2.3 2.5 3.1

0.05 20 1.7 1.9 2.5

01582000 0.5 2 24.9 26.2 27.9

1945-–2008 0.1 10 12.5 13.4 15.6

0.05 20 10.0 10.8 13.1

01583000 0.5 2 0.7 0.8 0.9

1948–1980 0.1 10 0.3 0.3 0.4

0.05 20 0.2 0.2 0.2
14 Selected Low-Flow Frequency Statistics for Continuous-Record Streamgage Locations in Maryland, 2010

Table 2. Low-flow frequency statistics for continuous-record streamgage locations in Maryland.—Continued

[ft3/s, cubic feet per second; -- not included]

Station number Period of record 

(climatic years) Probability

Recurrence 

interval 

(years)

Minimum daily mean streamflow 

over given number of days Remarks

7-Day 

(ft3/s)

14-Day 

(ft3/s)

30-Day 

(ft3/s)

01583100 1983–1986 0.5 2 5.6 5.8 6.0

Trend analysis needed for 

7-day statistics 1997–2008 0.1 10 2.4 2.6 3.3

0.05 20 1.8 1.9 2.7

01583500 0.5 2 23.9 25.1 26.8

1945–2008 0.1 10 10.7 11.4 13.4

0.05 20 8.1 8.8 10.8

01583570 1983–1985 0.5 2 0.0 0.0 0.1

1999–2008 0.1 10 0.0 0.0 0.0

0.05 20 0.0 0.0 0.0

01583580 1965–1968 0.5 2 0.4 0.4 0.4

Trend analysis needed for 

7-day statistics 2000–2008 0.1 10 0.0 0.0 0.1

0.05 20 0.0 0.0 0.1

01583600 0.5 2 9.4 10.0 11.4

1983–2008 0.1 10 5.6 6.1 7.3

0.05 20 4.9 5.4 6.6

01584050 0.5 2 3.3 3.4 3.8

1976–2009 0.1 10 1.6 1.7 1.9

0.05 20 1.3 1.4 1.6

01584500 1927–1969 0.5 2 16.1 16.8 17.7

Trend analysis needed for 

7-day statistics 1999–2008 0.1 10 6.5 7.0 8.3

0.05 20 4.5 5.0 6.3

01585090 0.5 2 0.2 0.3 0.4

1995–2008 0.1 10 0.0 0.0 0.2

0.05 20 0.0 0.0 0.1

01585095 0.5 2 0.1 0.1 0.2

1993–2008 0.1 10 0.0 0.0 0.1

0.05 20 0.0 0.0 0.0

01585100 1959–1988 0.5 2 1.0 1.2 1.7

1992–2008 0.1 10 0.4 0.6 0.9

0.05 20 0.4 0.5 0.8

01585104 0.5 2 0.1 0.2 0.3

2000–2009 0.1 10 0.0 0.0 0.2

0.05 20 0.0 0.0 0.2

01585200 1958–1964 0.5 2 -- 0.4 0.6

Trend analysis needed for 

7-day statistics 1966–1986 0.1 10 -- 0.2 0.3

1997–2008 0.05 20 -- 0.2 0.2

01585225 0.5 2 0.0 0.0 0.0

1997–2008 0.1 10 0.0 0.0 0.0

0.05 20 0.0 0.0 0.0
Computation of Low-Flow Frequency Statistics 15

Table 2. Low-flow frequency statistics for continuous-record streamgage locations in Maryland.—Continued

[ft3/s, cubic feet per second; -- not included]

Station number Period of record 

(climatic years) Probability

Recurrence 

interval 

(years)

Minimum daily mean streamflow 

over given number of days Remarks

7-Day 

(ft3/s)

14-Day 

(ft3/s)

30-Day 

(ft3/s)

01585230 0.5 2 0.3 0.4 0.7

1997–2008 0.1 10 0.2 0.2 0.4

0.05 20 0.2 0.2 0.3

01585300 1959–1971 0.5 2 0.3 0.4 0.7

1974–1988 0.1 10 0.1 0.2 0.3

0.05 20 0.1 0.1 0.2

01585400 0.5 2 0.4 0.5 0.5

1959–1986 0.1 10 0.2 0.2 0.3

0.05 20 0.0 0.0 0.2

01586210 0.5 2 4.5 4.7 5.0

1983–2008 0.1 10 1.6 1.8 2.5

0.05 20 1.0 1.3 2.1

01586610 0.5 2 8.1 8.6 9.1

1983–2008 0.1 10 3.0 3.2 4.2

0.05 20 2.1 2.3 3.3

01587000 0.5 2 50.4 54.5 62.6

Trend analysis needed for 

7-day statistics 1930–1951 0.1 10 27.4 29.6 34.2

0.05 20 22.5 24.2 27.9

01587500 0.5 2 19.8 20.0 20.9

1949–1979 0.1 10 5.3 6.7 8.9

0.05 20 3.0 4.4 6.7

01588000 0.5 2 3.5 3.8 4.4

1932–1957 0.1 10 1.8 2.0 2.3

0.05 20 1.5 1.6 1.9

01589100 1958–1988 0.5 2 0.6 0.7 0.9

Trend analysis needed for 

7-day statistics 1999–2008 0.1 10 0.3 0.4 0.5

0.05 20 0.3 0.3 0.4

01589180 0.5 2 0.0 0.0 0.0

1999–2008 0.1 10 0.0 0.0 0.0

0.05 20 0.0 0.0 0.0

01589197 0.5 2 1.2 1.3 1.3

1999–2008 0.1 10 0.5 0.5 0.7

0.05 20 0.3 0.4 0.6

01589200 0.5 2 1.7 1.7 2.0

1959–1974 0.1 10 0.9 1.0 1.2

0.05 20 0.7 0.8 1.1

01589238 0.5 2 0.0 0.0 0.0

2000–2009 0.1 10 0.0 0.0 0.0

0.05 20 0.0 0.0 0.0
16 Selected Low-Flow Frequency Statistics for Continuous-Record Streamgage Locations in Maryland, 2010

Table 2. Low-flow frequency statistics for continuous-record streamgage locations in Maryland.—Continued

[ft3/s, cubic feet per second; -- not included]

Station number Period of record 

(climatic years) Probability

Recurrence 

interval 

(years)

Minimum daily mean streamflow 

over given number of days Remarks

7-Day 

(ft3/s)

14-Day 

(ft3/s)

30-Day 

(ft3/s)

01589300 1957–1987 0.5 2 8.0 8.9 10.6

1997–2008 0.1 10 3.7 4.2 5.7

0.05 20 2.9 3.3 4.7

01589330 1960–1986 0.5 2 0.6 0.7 1.0

1999–2008 0.1 10 0.3 0.3 0.5

0.05 20 0.2 0.3 0.4

01589352 0.5 2 15.9 17.8 23.5

1999–2008 0.1 10 10.4 11.4 15.2

0.05 20 9.5 10.3 13.9

01589440 1966–1987 0.5 2 8.1 8.6 9.5

Trend analysis needed for 

7-day statistics 1997–2008 0.1 10 3.4 3.6 4.5

0.05 20 2.6 2.7 3.6

01589795 0.5 2 0.2 0.2 0.2

Trend analysis needed for 

7-day statistics 1998–2008 0.1 10 0.1 0.1 0.1

0.05 20 0.1 0.1 0.1

01590000 0.5 2 3.7 3.9 4.5

Trend analysis needed for 

7-day statistics 1932–1973 0.1 10 2.0 2.2 2.6

0.05 20 1.7 1.8 2.2

01591000 0.5 2 8.3 8.8 9.4

1945–2008 0.1 10 2.1 2.6 3.6

0.05 20 1.2 1.6 2.6

01591400 0.5 2 5.8 6.1 6.4

1979–2008 0.1 10 1.2 1.5 2.2

0.05 20 0.7 0.9 1.6

01591700 0.5 2 4.4 4.8 5.5

1979–2008 0.1 10 1.0 1.1 1.6

0.05 20 0.5 0.6 1.1

01593500 0.5 2 8.2 8.8 10.1

1932–2008 0.1 10 3.1 3.6 5.1

0.05 20 2.2 2.7 4.2

01594000 1940–1957 0.5 2 20.9 22.5 26.0

1976–1979 0.1 10 7.5 8.7 12.1

1986–2008 0.05 20 5.4 6.5 9.8

01594500 0.5 2 2.6 2.9 3.4

1950–1974 0.1 10 0.4 0.6 1.0

0.05 20 0.2 0.3 0.7

01594526 1986–1988 0.5 2 7.1 8.1 11.7

1992–2008 0.1 10 2.1 2.4 3.9

0.05 20 1.4 1.7 2.9
Computation of Low-Flow Frequency Statistics 17

Table 2. Low-flow frequency statistics for continuous-record streamgage locations in Maryland.—Continued

[ft3/s, cubic feet per second; -- not included]

Station number Period of record 

(climatic years) Probability

Recurrence 

interval 

(years)

Minimum daily mean streamflow 

over given number of days Remarks

7-Day 

(ft3/s)

14-Day 

(ft3/s)

30-Day 

(ft3/s)

01594600 0.5 2 0.3 0.4 0.5

1957–1975 0.1 10 0.0 0.0 0.1

0.05 20 0.0 0.0 0.1

01594710 0.5 2 0.7 0.8 1.0

1986–1996 0.1 10 0.3 0.3 0.4

0.05 20 0.2 0.3 0.3

01594800 0.5 2 1.1 1.4 1.9

Trend analysis needed for 

7-day statistics 1957–1967 0.1 10 0.2 0.4 0.4

0.05 20 0.0 0.1 0.2

01594950 0.5 2 0.1 0.1 0.1

1987–2008 0.1 10 0.0 0.0 0.0

0.05 20 0.0 0.0 0.0

01595000 0.5 2 14.9 17.6 21.9

Trend analysis needed for 

7-day statistics 1957–2008 0.1 10 6.5 7.8 9.9

0.05 20 5.0 6.1 7.9

01596500 0.5 2 2.4 2.8 3.7

1949–2008 0.1 10 1.0 1.1 1.7

0.05 20 0.8 0.9 1.4

01597000 0.5 2 1.7 1.8 2.0

1949–1980 0.1 10 1.1 1.1 1.3

0.05 20 1.0 1.0 1.2

01599000 0.5 2 6.2 6.7 7.7

Trend analysis needed for 

7-day statistics 1930–2008 0.1 10 3.3 3.5 4.0

0.05 20 2.7 2.9 3.4

01601500 0.5 2 23.4 25.1 29.0

Trend analysis needed for 

7-day statistics 1930–2008 0.1 10 13.9 14.7 16.6

0.05 20 12.2 12.8 14.5

01609000 1929–1934 0.5 2 6.4 7.6 9.8

1968–1980 0.1 10 1.9 2.2 3.1

2002–03, 2007–08 0.05 20 1.3 1.5 2.1

01609500 0.5 2 0.0 0.0 0.0

1948–1957 0.1 10 0.0 0.0 0.0

0.05 20 0.0 0.0 0.0

01610000 0.5 2 382.2 409.5 459.0

Trend analysis needed for 

7-day statistics 1939–2009 0.1 10 240.9 253.6 280.2

0.05 20 215.4 226.4 252.1

01610155 1968–1976 0.5 2 0.2 0.4 1.0

1999–2008 0.1 10 0.0 0.0 0.1

0.05 20 0.0 0.0 0.0
18 Selected Low-Flow Frequency Statistics for Continuous-Record Streamgage Locations in Maryland, 2010

Table 2. Low-flow frequency statistics for continuous-record streamgage locations in Maryland.—Continued

[ft3/s, cubic feet per second; -- not included]

Station number Period of record 

(climatic years) Probability

Recurrence 

interval 

(years)

Minimum daily mean streamflow 

over given number of days Remarks

7-Day 

(ft3/s)

14-Day 

(ft3/s)

30-Day 

(ft3/s)

01612500 0.5 2 0.1 0.1 0.2

1948–1962 0.1 10 0.0 0.0 0.0

0.05 20 0.0 0.0 0.0

01613000 0.5 2 445.7 477.1 533.2

Trend analysis needed for 

7-day statistics 1933–2009 0.1 10 287.9 306.3 337.5

0.05 20 258.4 276.2 307.0

01614500 0.5 2 92.0 96.1 105.4

Trend analysis needed for 

7-day statistics 1929–2008 0.1 10 55.2 57.9 65.6

0.05 20 47.7 50.5 58.6

01617800 0.5 2 3.0 3.2 3.4

1965–2008 0.1 10 0.6 0.7 1.0

0.05 20 0.3 0.4 0.6

01618000 1929–1993 0.5 2 707.9 762.9 868.9

2001–2003 0.1 10 423.7 453.8 516.1

0.05 20 370.0 397.3 455.2

01619000 1949–1950 0.5 2 37.4 38.8 41.7

1966–1980 0.1 10 23.7 24.4 26.2

2006–2008 0.05 20 20.2 20.9 22.4

01637000 0.5 2 1.1 1.2 1.4

Trend analysis needed for 

7-day statistics 1948–1957 0.1 10 0.5 0.6 0.8

0.05 20 0.4 0.5 0.6

01637500 0.5 2 3.2 3.9 5.4

1948–2008 0.1 10 0.9 1.2 1.7

0.05 20 0.6 0.8 1.2

01638500 0.5 2 1,387.1 1,473.7 1,623.0

1895–2009 0.1 10 903.4 957.5 1,066.5

0.05 20 808.9 859.8 972.1

01639000 0.5 2 4.7 5.8 8.2

1943–2008 0.1 10 0.9 1.4 2.9

0.05 20 0.4 0.8 2.2

01639140 0.5 2 0.9 0.9 1.5

1991–2000 0.1 10 0.1 0.2 0.3

0.05 20 0.0 0.1 0.2

01639500 0.5 2 23.8 25.8 26.6

1948–2008 0.1 10 7.2 7.9 10.4

0.05 20 4.1 4.6 7.4

01640500 0.5 2 0.6 0.7 0.8

1932–1983 0.1 10 0.2 0.2 0.3

0.05 20 0.1 0.1 0.2
Computation of Low-Flow Frequency Statistics 19

Table 2. Low-flow frequency statistics for continuous-record streamgage locations in Maryland.—Continued

[ft3/s, cubic feet per second; -- not included]

Station number Period of record 

(climatic years) Probability

Recurrence 

interval 

(years)

Minimum daily mean streamflow 

over given number of days Remarks

7-Day 

(ft3/s)

14-Day 

(ft3/s)

30-Day 

(ft3/s)

01640965 0.5 2 0.1 0.1 0.1

1982–1993 0.1 10 0.0 0.0 0.1

0.05 20 0.0 0.0 0.0

01641000 0.5 2 1.9 2.1 2.5

Trend analysis needed for 

7-day statistics 1950–1968 0.1 10 1.1 1.2 1.5

0.05 20 1.0 1.0 1.3

01641500 0.5 2 1.5 1.6 1.8

1948–1983 0.1 10 0.9 1.0 1.1

0.05 20 0.8 0.8 1.0

01642000 0.5 2 84.9 95.5 124.2

1897–1929 0.1 10 35.8 41.8 60.4

0.05 20 27.0 32.2 47.9

01642500 0.5 2 15.3 16.5 18.4

1935–1970 0.1 10 6.9 7.5 9.0

0.05 20 5.2 5.6 7.1

01643000 0.5 2 103.9 112.2 127.5

Trend analysis needed for 

7-day statistics 1930–2008 0.1 10 49.2 52.8 64.1

0.05 20 38.9 42.1 53.7

01643500 1949–1957 0.5 2 10.8 11.8 13.0

1967–2008 0.1 10 3.8 4.3 5.9

0.05 20 2.6 3.1 4.8

01645000 0.5 2 25.8 27.7 30.4

Trend analysis needed for 

7-day statistics 1931–2008 0.1 10 9.5 10.5 13.6

0.05 20 6.7 7.5 10.6

01645200 0.5 2 0.6 0.7 0.9

1958–1986 0.1 10 0.2 0.3 0.4

0.05 20 0.2 0.2 0.3

01646550 1945–1958 0.5 2 0.3 0.3 0.5

Trend analysis needed for 

7-day statistics 1962–1977 0.1 10 0.1 0.1 0.2

0.05 20 0.0 0.1 0.2

01649500 0.5 2 11.7 13.3 17.2

1939–2008 0.1 10 5.5 6.5 8.7

0.05 20 4.2 5.3 7.1

01650500 1924–1982 0.5 2 3.9 4.9 5.6

Trend analysis needed for 

7-day statistics 1998–2008 0.1 10 0.7 0.7 1.3

0.05 20 0.2 0.3 0.8

01651000 0.5 2 5.9 7.2 10.2

1962–2008 0.1 10 2.1 2.8 4.3

0.05 20 1.5 2.1 3.4
20 Selected Low-Flow Frequency Statistics for Continuous-Record Streamgage Locations in Maryland, 2010

Table 2. Low-flow frequency statistics for continuous-record streamgage locations in Maryland.—Continued

[ft3/s, cubic feet per second; -- not included]

Station number Period of record 

(climatic years) Probability

Recurrence 

interval 

(years)

Minimum daily mean streamflow 

over given number of days Remarks

7-Day 

(ft3/s)

14-Day 

(ft3/s)

30-Day 

(ft3/s)

01653500 0.5 2 1.1 1.5 2.3

1949–1977 0.1 10 0.1 0.3 0.5

0.05 20 0.0 0.1 0.3

01653600 1966–2004 0.5 2 0.1 0.5 1.5

2007–2008 0.1 10 0.0 0.0 0.0

0.05 20 0.0 0.0 0.0

01658000 1950–1971 0.5 2 0.0 0.0 0.0

2001–2008 0.1 10 0.0 0.0 0.0

0.05 20 0.0 0.0 0.0

01660920 1984–2004 0.5 2 0.1 0.4 1.7

2007–2008 0.1 10 0.0 0.0 0.0

0.05 20 0.0 0.0 0.0

01661000 0.5 2 0.4 0.7 1.1

1948–1971 0.1 10 0.0 0.0 0.1

0.05 20 0.0 0.0 0.0

01661050 1969–2004 0.5 2 0.5 0.7 1.4

2007–2008 0.1 10 0.0 0.0 0.0

0.05 20 0.0 0.0 0.0

01661500 1947–2004 0.5 2 2.5 2.9 3.6

2007–2008 0.1 10 0.9 1.0 1.4

0.05 20 0.6 0.7 1.1

03075500 0.5 2 16.1 18.6 24.9

1942–2008 0.1 10 6.3 7.1 9.9

0.05 20 4.7 5.4 7.7

03076600 0.5 2 6.2 6.9 8.3

1965–2008 0.1 10 3.0 3.5 4.1

0.05 20 2.5 2.9 3.4

03078000 0.5 2 5.0 6.0 8.4

1948–2008 0.1 10 1.7 2.0 2.8

0.05 20 1.2 1.4 2.0
Summary 21

Data Limitations

The streamgage locations included in this analysis were 

selected because they were minimally affected by regulation 

and diversions. Streamgage locations with flows that are 

significantly or completely regulated were eliminated from use 

in this investigation, or the period of record used for analysis 

was truncated to include only the periods with minimal or no 

regulation. Some streamgage locations used in this analysis 

may include data with occasional periods of minor diversions 

for irrigation, occasional low-flow regulation, or slight diurnal 

fluctuations caused by upstream mills, dams, or coal mining.

In this report, physiographic provinces were reported for 

each streamgage location based on the actual physical location 

of the streamgage, rather than the predominant physiographic 

province. Although some streamgages are physically located 

in the Western Coastal Plain, the upstream watershed may be 

hydrologically influenced predominantly by the Piedmont. 

Streamgage locations that fall into this category include: 

(1) station 01496000, Northeast Creek at Leslie, MD; (2) 

station 01585090, Whitemarsh Run near Fullerton, MD; (3) 

station 01589352, Gwynns Falls at Washington Boulevard at 

Baltimore, MD; (4) station 01594000, Little Patuxent River 

at Savage, MD; and (5) station 01651000, Northwest Branch 

Anacostia River near Hyattsville, MD. 

Streamgage locations in watersheds with percentages of 

suburban or urban land use that would affect streamflow were 

not excluded from the dataset solely on that basis. No attempt 

was made to adjust streamflow records for watershed development patterns or percentages, or to limit the periods of record 

for analyses based on development condition, or other changes 

in land use.

Low-flow frequency statistics that were computed for 

each streamgage location in this study were based on the 

period of continuous streamflow record that was approved as 

of June 2010. Provisional data were not included in the analysis. Streamgage locations with breaks in the continuous record 

were included in the analysis, provided that the total period of 

continuous record was at least 10 complete climatic years. No 

attempt was made to adjust any low-flow frequency statistics 

based on any historical data or periods outside the continuous 

record. 

No attempts were made to adjust streamflow records or 

statistical analyses based on trends in the annual 7-day minimum daily-mean streamflow over time. Further investigation 

would be required to determine the significance and sources 

of possible trends for 25 of the 114 streamgage locations that 

were included in this study. 

There is potential that low-flow frequency statistics could 

be estimated for additional streamgage locations that were not 

included in this study because of continuous-record lengths 

that are less than 10 years. Correlations developed between 

daily-mean discharges at short-record streamgage locations, 

and those for nearby long-term streamgage locations that were 

used in the analysis, could be used as a basis for augmenting 

or extending the record lengths of the short-term streamgage 

locations with synthesized data, which would allow for computation of low-flow frequency statistics that represent a longer period of time (Ries, 2006; Carpenter and Hayes, 1996).

Summary

Because of continued population growth and increasing 

domestic water demand, Maryland will be facing increased 

pressure on water resources over the next 20 years. Waterresources decisions should be based on sound, comprehensive, long-term data and low-flow frequency statistics from 

all available streamgage locations with unregulated streamflow and adequate record lengths. To provide the Maryland 

Department of the Environment with tools for making future 

water-resources decisions, the U.S. Geological Survey conducted a study to compute low-flow frequency statistics for 

selected streamgage locations in Maryland with 10 or more 

years of continuous streamflow records. 

This report presents low-flow frequency statistics for 

114 continuous-record streamgage locations in Maryland. 

Streamgage locations used in the study included both active 

and discontinued stations with approved streamflow records 

with a minimum of 10 complete climatic years of record 

as of June 2010. Descriptive information for each of these 

streamgage locations, including the station number, station 

name, latitude, longitude, county or city, physiographic province, and drainage area, is presented, along with the computed 

low-flow statistics for the mean 7-, 14-, and 30-consecutive 

day low-flow discharges with recurrence intervals of 2, 10, 

and 20 years. These statistics are planned for incorporation 

into StreamStats, a U.S. Geological Survey web application 

for obtaining stream information, which is being used by 

water-resource managers and decision makers in Maryland for 

water-supply planning and management, water-use appropriation and permitting, wastewater and industrial discharge permitting, and setting minimum required streamflows in streams 

and rivers for protection of freshwater biota and ecosystems.

Acknowledgments

Thanks are extended to John W. Grace of the Maryland 

Department of the Environment, Water Supply Program, for 

planning assistance and technical input. The authors would 

like to thank Brandon J. Fleming of the USGS for assistance 

and support with project management. Thanks are also 

extended to Jonathan J.A. Dillow and Kernell G. Ries III of 

the USGS, for their assistance, advice, and support with technical issues and data interpretation.
22 Selected Low-Flow Frequency Statistics for Continuous-Record Streamgage Locations in Maryland, 2010

References Cited

Carpenter, D.H., 1983, Characteristics of streamflow in 

Maryland: Maryland Geological Survey Report of 

Investigations No. 35, 237 p.

Carpenter, D.H., and Hayes, D.C., 1996, Low-flow characteristics of streams in Maryland and Delaware: U.S. 

Geological Survey Water-Resources Investigations Report 

94–4020, 113 p.

Dillow, J.J.A., 1996, Technique for estimating magnitude and 

frequency of peak flows in Maryland: U.S. Geological 

Survey Water-Resources Investigations Report 95–4154, 

55 p., available online at http://pubs.usgs.gov/wri/wri95-

4154/index.html.

Fenneman, N.M., 1938, Physiography of the Eastern United 

States: New York, McGraw Hill, 714 p.

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

water resources: New York, Elsevier, 522 p.

Interagency Advisory Committee on Water Data, 1982, 

Guidelines for determining flood flow frequency: Water 

Resources Council Bulletin 17B, 28 p.

Maryland State Archives, 2010, Maryland Manual 

On-Line—Maryland at a Glance—Weather—Climate, 

accessed April 23, 2010 at http://www.msa.md.gov/msa/

mdmanual/01glance/html/climate.html.

McCandless, T.L., and Everett, R.A., 2002, Maryland stream 

survey: Bankfull discharge and channel characteristics of 

streams in the Piedmont hydrologic region: U.S. Fish and 

Wildlife Service, Chesapeake Bay Field Office, Report 

CBFO–S02–01, 41 p.

Netstate.com, 2010, The Geography of Maryland, accessed 

November 19, 2010 at http://www.netstate.com/states/

geography/md_geography.htm.

Ries, K.G., III, 2006, Selected streamflow statistics for 

streamgaging stations in Northeastern Maryland, 2006: 

U.S. Geological Survey Open-File Report 2006–1335, 

16 p., available online at http://pubs.usgs.gov/of/2006/1335/.

Ries, K.G., III, Guthrie, J.D., Rea, A.H., Steeves, P.A., and 

Stewart, D.W., 2008, StreamStats: A water resources web 

application: U.S. Geological Survey Fact Sheet 2008–3067, 

6 p., available online at http://pubs.usgs.gov/fs/2008/3067/.

Ries, K.G., III, Steeves, P.A., Coles, J.D., Rea, A.H., and 

Stewart, D.W., 2004, StreamStats: A U.S. Geological 

Survey web application for stream information: U.S. 

Geological Survey Fact Sheet 2004–3115, 4 p., available 

online at http://pubs.usgs.gov/fs/2004/3115/.

Riggs, H.C., 1972, Low-flow investigations: U.S. Geological 

Survey Techniques of Water-Resources Investigations, 

book 4, chap. B3, 15 p.

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Fact Sheet, accessed May 19, 2010 at http://www.epa.gov/

waterscience/basins/fs-basins4.html.

Wolman, M.G., 2008, Water for Maryland’s future: what we 

must do today: Final report of the Advisory Committee 

on the Management and Protection of the State’s Water 

Resources, v. 1, 33 p., available online at http://www.mde.

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state.md.us/assets/document/WolmanReport_Vol1.pdf.

Glossary

Annual 7-day minimum daily mean streamflow The lowest 

daily mean streamflow for any 7-consecutive-day period in a 

year. For low-flow frequency analyses, a year is defined as the 

climatic year. 

Base flow The contribution of flow in a stream or river from 

groundwater or spring effluent.

Climatic year The climatic year is the 12-month period from 

April 1 through March 31. The climatic year is designated 

by the calendar year in which it begins. For example, the 

12-month period starting on April 1, 2008 and ending March 

31, 2009 is the 2008 climatic year.

Fall Line The line marking the point on each stream where 

the flow descends from the eastern section of the Piedmont 

Physiographic Province to the Western Coastal Plain in 

Maryland. The Fall Line is characterized by an abrupt 

decrease in channel slope in transition between the Piedmont 

and Coastal Plain Physiographic Provinces.

Records Unit value or daily mean discharge data that are 

collected continuously from streamgage locations, electronically stored, published, and archived according to U.S. 

Geological Survey protocols. 

Recurrence interval As applied to low-flow statistics, the 

recurrence interval is the average number of years within 

which the streamflow will be equal to or less than the given 

statistic on one occasion.
Prepared by USGS West Trenton Publishing Service Center.

Edited by Valerie M. Gaine.

Graphics and layout by Timothy W. Auer.

For additional information, contact:

Director, MD-DE-DC Water Science Center

U.S. Geological Survey

5522 Research Park Drive

Baltimore, MD 21228

or visit our Web site at:

http://md.water.usgs.gov
Doheny, E.J., and Banks, W.S.L.—Selected Low-Flow Frequency Statistics for Continuous-Record Streamgage Locations in Maryland, 2010—Open-File Report 2010–1310

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