U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010–5111

Prepared in cooperation with the

Maryland Department of the Environment

Incorporation of Water-Use Summaries 

into the StreamStats Web Application 

for Maryland 
Cover.  View of the StreamStats user interface for Maryland.
Incorporation of Water-Use Summaries 

into the StreamStats Web Application 

for Maryland

By Kernell G. Ries III, Marilee A. Horn, Mark R. Nardi, and Steven Tessler

Scientific Investigations Report 2010–5111

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:

Ries, K.G., III, Horn, M.A., Nardi, M.R., and Tessler, S., 2010, Incorporation of water-use summaries into the StreamStats web application for Maryland: U.S. Geological Survey Scientific Investigations Report 2010–5111, 18 p.

ISBN 978-1-4113-2932-4
iii

Contents

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

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

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

Description of Study Area ...................................................................................................................3

StreamStats Implementation for Maryland...............................................................................................4

Site-Specific Water-Use Data System (SWUDS) and Available Water-Use Data..............................8

Development of a Linkage Between StreamStats and the Site-Specific Water-Use 

Data System (SWUDS) ....................................................................................................................8

Obtaining Streamflow Statistics and Water-Use Summaries from the Maryland 

StreamStats Web Application......................................................................................................10

Maryland StreamStats User Interface............................................................................................11

Obtaining Streamflow Statistics for Data-Collection Stations....................................................11

Estimating Streamflow Statistics by Use of Regression Equations and 

Obtaining Water-Use Summaries for Ungaged Sites......................................................11

Estimating Streamflow Statistics for Ungaged Sites Based on the Flows 

at Nearby Streamgages .......................................................................................................13

Estimating Streamflow Statistics for Ungaged Sites in the Bynum Anomaly...........................13

Limitations for Estimates of Streamflow and Water Use for Ungaged Sites .....................................13

Summary and Conclusions.........................................................................................................................16

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

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

Figures

1. Map showing location of areas affected by Base Realignment and 

Closure (BRAC) activities in Maryland, including Aberdeen Proving 

Ground and Fort Meade...............................................................................................................2

2. View of the StreamStats user interface for Maryland with aqua lines 

showing the hydrologic accounting units in which the application is 

implemented and colored areas corresponding to the low-flow 

hydrologic regions of Carpenter and Hayes (1996).................................................................4

3. An example of modeling conveyance-based water-use data in the 

Site-Specific Water-Use Data System (SWUDS) showing 22 sites 

and 23 numbered conveyances .................................................................................................9

4. Data and databases used in construction of the Maryland SiteSpecific Water-Use Data System (SWUDS) conveyance database....................................9

5. The StreamStats link frame that appears on each Web page............................................10

6. Map showing example watershed delineation (black and yellow line) 

for an ungaged site in Maryland StreamStats, showing upstream datacollection stations (triangles), water withdrawals (small orange dots), 

and water discharge locations (small blue dots)..................................................................12

7. Example water-use summary report for the ungaged site shown in figure 6 ..................12

Tables

1. Peak-flow regression equations for the Piedmont and Western Coastal 

Plain in Maryland..........................................................................................................................5

2. Low-flow regression equations for subregions A through D in the Eastern 

Piedmont in Maryland..................................................................................................................7

3. Previously published streamflow statistics for streamgages and 

low-flow partial-record stations, and average values in the Bynum 

Anomaly area of Piedmont subregion C .................................................................................14
v

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)

Volume

gallon (gal) 3.785 liter (L)

gallon (gal) 0.003785 cubic meter (m3)

gallon (gal) 3.785 cubic decimeter (dm3)

million gallons (Mgal) 3,785 cubic meter (m3)

cubic foot (ft3) 28.32 cubic decimeter (dm3)

cubic foot (ft3) 0.02832 cubic meter (m3)

Flow rate

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

cubic foot per second per square 

mile [(ft3/sec)/mi2]

0.01093 cubic meter per second per square kilometer 

[(m3/sec)/km2]

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/sec)

APG Aberdeen Proving Ground

BRAC Federal Base Realignment and Closure process

DEM Digital Elevation Model

DoD U.S. Department of Defense

ESRI Environmental Systems Research Institute, Inc.

Fort Meade Fort George G. Meade

GIS Geographic Information System

HUC Hydrologic Unit Code accounting unit

ID Identification number or name

LFPR Low-flow partial-record

MCD U.S. Census Bureau Minor Civil Division

MDE Maryland Department of the Environment

NLCD National Land Cover Database of 2001

NSA U.S. National Security Agency

SWUDS U.S. Geological Survey Site-Specific Water-Use Database System

USGS U.S. Geological Survey

WMA Maryland Department of the Environment, Water Management Administration

Abbreviations and Acronyms

Incorporation of Water-Use Summaries into 

the StreamStats Web Application for 

Maryland

By Kernell G. Ries III, Marilee A. Horn, Mark R. Nardi, and Steven Tessler

Abstract

Approximately 25,000 new households and thousands 

of new jobs will be established in an area that extends from 

southwest to northeast of Baltimore, Maryland, as a result of 

the Federal Base Realignment and Closure (BRAC) process, 

with consequent new demands on the water resources of the 

area. The U.S. Geological Survey, in cooperation with the 

Maryland Department of the Environment, has extended the 

area of implementation and added functionality to an existing 

map-based Web application named StreamStats to provide an 

improved tool for planning and managing the water resources 

in the BRAC-affected areas. StreamStats previously was 

implemented for only a small area surrounding Baltimore, 

Maryland, and it was extended to cover all BRAC-affected 

areas.

StreamStats could provide previously published streamflow statistics, such as the 1-percent probability flood and the 

7-day, 10-year low flow, for U.S. Geological Survey data-collection stations and estimates of streamflow statistics for any 

user-selected point on a stream within the implemented area. 

The application was modified for this study to also provide 

summaries of water withdrawals and discharges upstream 

from any user-selected point on a stream. This new functionality was made possible by creating a Web service that accepts 

a drainage-basin delineation from StreamStats, overlays it 

on a spatial layer of water withdrawal and discharge points, 

extracts the water-use data for the identified points, and sends 

it back to StreamStats, where it is summarized for the user. 

The underlying water-use data were extracted from the U.S. 

Geological Survey’s Site-Specific Water-Use Database System 

(SWUDS) and placed into a Microsoft Access database that 

was created for this study for easy linkage to the Web service 

and StreamStats. This linkage of StreamStats with water-use 

information from SWUDS should enable Maryland regulators 

and planners to make more informed decisions on the use of 

water resources in the BRAC area, and the technology should 

be transferrable to other geographic areas.

Introduction

On May 13, 2005, the U.S. Department of Defense 

(DoD) issued a list of suggested military base realignments 

and closures that would aid in military transformation and 

reduce costs. Subsequently, the U.S. Congress appointed 

a Base Realignment and Closure (BRAC) Commission to 

provide an independent, non-partisan review of DoD’s recommendations and ensure the integrity of the BRAC process. The 

goals of the BRAC recommendations were to support force 

transformation, address new threats and strategies, consolidate 

business functions, and provide significant cost savings. The 

Commission released its final report to the President of the 

United States on September 8, 2005. The President approved 

the recommendations on September 15, 2005, and forwarded 

them to Congress. The recommendations became law on 

November 9, 2005. The military realignments as a result of the 

BRAC process are expected to have a substantial impact on 

the State of Maryland, where the Aberdeen Proving Ground 

(APG) in Harford County, and Fort George G. Meade (Fort 

Meade) in Anne Arundel County are expected to grow larger 

in order to accommodate transferred Army personnel and 

consolidated operations. 

The Maryland Department of Planning (2006) estimates 

that approximately 25,000 new households will be established 

in Maryland as a result of BRAC. Of these, approximately 56 

percent of them will be established due to new jobs at APG in 

Harford County, and approximately 42 percent of them will 

be established due to new jobs at Fort Meade in Anne Arundel 

County. The remaining 2 percent of new households will be 

established as a result of new jobs at Joint Base Andrews 

Naval Air Facility in Prince George’s County. This influx 

of new residents will lead to greater demands for housing, 

schools, and infrastructure for water, wastewater, power, telecommunications, and transportation, particularly in Harford 

and Cecil Counties.

The increased demand for water and wastewater capacity 

resulting from the influx of new residents to BRAC-affected 

areas will likely lead to applications for new permits for 
2 Incorporation of Water-Use Summaries into the StreamStats Web Application for Maryland

water withdrawals and wastewater-discharge permits. The 

Water Management Administration (WMA) of the Maryland 

Department of the Environment (MDE) is responsible for 

evaluating permit applications and issuing these permits 

(Maryland Department of the Environment, 2009). Making 

good permitting decisions will require the WMA to understand 

the natural availability of the affected water resources in relation to current and requested water withdrawals and return 

flows.

The U.S. Geological Survey (USGS), in cooperation 

with MDE, began a program of study in January 2008 of the 

potential impacts of BRAC on water resources in Maryland. 

The program consisted of four coordinated investigations: 

water-use activities, modeling of groundwater flow, low-flow 

statistical analysis for streams, and hydrologic monitoring. 

This report summarizes the investigation to estimate low-flow 

statistics for streams that potentially could be affected by new 

water withdrawals.

Areas in Maryland that will be affected by BRAC are 

in the Coastal Plain and Piedmont Physiographic Provinces, 

which are separated by the Fall Line (fig. 1). Fort Meade is 

in the Coastal Plain Physiographic Province near the Fall 

Line. Most of the anticipated water-resource impacts from 

expansion of this facility are expected to occur within the 

recharge areas of several important aquifers in the Coastal 

Plain Physiographic Province, although some impacts are 

also likely to occur in Piedmont Physiographic Province areas 

adjacent to the base. APG is located within the Coastal Plain 

Physiographic Province, but most of the increased water use 

from BRAC-related development is expected to occur in the 

surrounding counties, which are situated largely within the 

Piedmont Physiographic Province.

Figure 1. Location of areas affected by Base Realignment and Closure (BRAC) activities in Maryland, including Aberdeen 

Proving Ground and Fort Meade.
Introduction 3

The investigation to estimate low-flow statistics for 

streams that potentially could be affected by new water 

withdrawals as a result of the BRAC process was separated 

into two major tasks. One task was to modify an existing 

Web-based decision-support system named StreamStats to 

aid the WMA in evaluating permit applications for new water 

withdrawals and pollutant discharges in the BRAC area. The 

other task was to obtain streamflow measurements at a group 

of low-flow partial-record (LFPR) stations and relate those 

measurements to concurrent flows at nearby streamgages so 

that estimates of selected streamflow statistics at the LFPR 

stations could be determined from these relations. This report 

summarizes the first task. A separate report is planned that will 

summarize the second task.

Purpose and Scope

The purpose of this report is to describe the StreamStats 

Web application for Maryland and modifications made to the 

program that provide summaries of water use for user-selected 

locations along streams in BRAC-affected areas. This report 

includes brief descriptions of the study area, the StreamStats 

Web application, the database from which water-use data are 

extracted for display in StreamStats, and the method used 

to link StreamStats and the water-use database. In addition, 

instructions on how to use StreamStats to obtain the wateruse summaries are provided. Instructions for use of other 

StreamStats functionality are provided through links from the 

StreamStats home page at http://streamstats.usgs.gov.

Description of Study Area

The study area extends from northeast to southwest of 

Baltimore, Maryland (fig. 1), and includes areas in Maryland 

that are in hydrologic units 02050306 (Lower Susquehanna 

River Basin), 02060002 (Chester and Sassafras River Basins), 

02060003 (Gunpowder and Patapsco River Basins), 02060004 

(Severn River Basin), and 02060006 (Patuxent River Basin) 

(fig. 1). The counties in Maryland that primarily will be 

affected by BRAC are, from northeast to southwest, Cecil, 

Harford, Baltimore, Howard, Anne Arundel, Montgomery, and 

Prince George’s. The City of Baltimore is located approximately centrally within the study area, and also is expected to 

be affected by BRAC. These areas are located in the Piedmont 

and Coastal Plain Physiographic Provinces (Fenneman, 1938). 

The Fall Line, which roughly parallels U.S. Interstate 95 in 

the study area, separates the two physiographic provinces. 

The Piedmont Physiographic Province, northwest of the 

Fall Line, has a gently rolling landscape and streams with 

relatively high gradients, which drain to the Chesapeake Bay 

(Carpenter and Hayes, 1996). The Coastal Plain Physiographic 

Province, southeast of the Fall Line, is an area of low relief 

adjacent to the Chesapeake Bay. Streams in the Coastal Plain 

Physiographic Province have relatively flat gradients, and 

often are affected by tides for substantial distances above their 

mouths. The Fall Line extends north and south along much 

of the Eastern United States, and is named as such because 

numerous waterfalls occur along the line, where rivers transition from the higher Piedmont Physiographic Province onto 

the lower Coastal Plain Physiographic Province.

APG has been the Army’s primary chemical-warfare 

research and development center since World War I (Spencer 

and others, 2001). It is in Harford County, primarily on land 

along the northwestern shore of Chesapeake Bay. BRACrelated development in Harford County is expected to occur 

primarily in an inverted “T” shape, running northeast to southwest along the Interstate 95 corridor, with a perpendicular 

axis to the northwest along Maryland Route 24 into Bel Air, 

although some development also is expected in more sparsely 

developed areas in Harford and Cecil Counties (Michelle 

Dobson, Harford County, oral commun., July 2008). From a 

water-supply perspective, Harford County is concerned that 

thousands of additional people could be tapping into the fractured-rock aquifers of the Piedmont in areas west and north of 

Bel Air. Production of water from the fractured rocks already 

is marginal in some locations (Bolton and others, 2009), and 

the impact of many additional wells could cause significant 

declines in areas where municipal water supplies are not yet 

available. 

Fort Meade is an Army installation in Anne Arundel 

County, Maryland, that primarily supports intelligence, 

knowledge capital, information management organizations, 

and installation operations for facilities and infrastructure 

in support of DoD activities (Anne Arundel County, 2010). 

The campus of the U.S. National Security Agency (NSA) is 

near the western boundary of Fort Meade. BRAC will likely 

add about 5,695 direct new jobs at Fort Meade, while other 

components of growth expected at Fort Meade, including 

at the NSA, will likely bring the total of new jobs to about 

22,000 (Anne Arundel County, 2010). Development around 

the facility is expected to expand in almost a radial fashion, 

depending on accessibility to roads and highways 

(Anne Arundel County, 2010). Significant amounts of development also are anticipated to take place on the grounds of the 

fort itself. Numerous row houses have already been constructed on the site of the former base golf course, and more 

are planned. From a water-resource perspective, Maryland 

State agencies are concerned that the Fort Meade water-supply 

system, which relies primarily on groundwater withdrawn 

from the Patuxent and Patapsco aquifers, could further stress 

these aquifers. The Patuxent aquifer is used for municipal 

supply in areas just to the north and east of Fort Meade, and in 

2005, at the start of BRAC, it showed a potentiometric surface 

drawdown equivalent to more than 40 ft (feet) in areas north 

of the fort (Soeder and others, 2007). Withdrawals of groundwater from the Lower Patapsco aquifer, above the Patuxent 

aquifer, also are a concern. Fort Meade is within the recharge 

area of the Lower Patapsco aquifer, and pumpage, if excessive, could interfere with aquifer recharge.
4 Incorporation of Water-Use Summaries into the StreamStats Web Application for Maryland

StreamStats Implementation for 

Maryland

StreamStats is a Web-based Geographic Information 

System (GIS) application (fig. 2) that provides users with 

access to an assortment of analytical tools that are useful 

for water-resources planning and management, engineering 

design, and other applications. StreamStats was developed 

by the USGS, in cooperation with Environmental Systems 

Research Institute, Inc. (ESRI), using the ArcHydro Data 

Model and Tools (Environmental Systems Research Institute, 

Inc., 2010a) as its foundation. StreamStats functionality can 

be accessed through a map-based user interface that appears in 

the user’s Web browser (fig. 2), or individual functions can be 

requested remotely as Web services by other Web or desktop 

computer applications.

The primary functionality of StreamStats is to enable 

users to (1) determine the drainage-basin boundary for a 

selected site on a stream; (2) compute the drainage area and 

other physical and climatic characteristics of the drainage 

basin; and (3) estimate various streamflow statistics for the 

selected site, assuming natural flow conditions at the site. 

In addition to this functionality, StreamStats can provide 

published streamflow statistics and other information for 

USGS streamgages, and it has numerous other tools that 

are described in a Fact Sheet by Ries and others (2008), 

and in the StreamStats user instructions. The StreamStats 

home page (http://streamstats.usgs.gov) provides a more 

detailed description of the application, links to the Maryland 

application and those for other states, as well as links to the 

user instructions and other documentation. For this study, 

StreamStats was modified to provide summaries of water use 

for user-selected sites. This functionality is further described 

on the following pages.

Figure 2. View of the StreamStats user interface for Maryland with aqua lines showing the hydrologic 

accounting units in which the application is implemented and colored areas corresponding to the low-flow 

hydrologic regions of Carpenter and Hayes (1996). (Hatched areas indicate where regression equations are not 

available for estimating low-flow statistics.)
StreamStats Implementation for Maryland 5

The StreamStats application for Maryland was first 

implemented in 2007, and worked only in the Gunpowder and 

Patapsco River Basins. Coverage now extends to Maryland 

areas of the five 8-digit Hydrologic Unit Code accounting 

units (HUCs) in the BRAC study area, including the ChesterSassafras (02060002), the Lower Susquehanna (02050306), 

the Gunpowder-Patapsco (02060003), the Severn (02060004), 

and the Patuxent (02060006) HUCs (Seaber and others, 1987) 

(figs. 1 and 2). Additional information about HUCs is available online at http://water.usgs.gov/GIS/huc.html.

StreamStats provides two tools for estimating streamflow 

statistics for ungaged sites. One tool provides the estimates 

by solving regression equations. The other tool transfers the 

flow per unit area for a nearby streamgage on the same stream 

to the location of the ungaged site. Regression equations are 

developed by statistically relating the streamflow statistics to 

the basin characteristics for a group of data-collection stations 

within a region. Estimates of streamflow statistics for ungaged 

sites can then be obtained by measuring the basin characteristics for the ungaged site and inserting them into the regression 

equations. StreamStats automates this process.

StreamStats for Maryland can compute estimates of peak 

streamflows for ungaged sites at the 2-, 5-, 10-, 25-, 50-, 100-, 

and 500-year recurrence intervals (peak streamflows having a 

50, 20, 10, 2, 1, and 0.2 percent probability of occurring in any 

given year, respectively) using regression equations developed 

by Dillow (1996). The application also is able to compute 7-, 

14-, and 30-day mean low flows that occur, on average, once 

in 2, 10, and 20 years using regression equations developed by 

Carpenter and Hayes (1996).

Dillow (1996) divided Maryland into five hydrologic 

regions, based primarily on physiography, and developed 

separate peak-flow equations for each hydrologic region. 

The regression equations for the Western Coastal Plain 

and the Piedmont hydrologic regions were implemented 

in StreamStats for the BRAC study. The Western Coastal 

Plain hydrologic region is the part of the Coastal Plain 

Physiographic Province that is bounded on the northwest 

by the Fall Line and on the east by the western shore of the 

Chesapeake Bay. The Piedmont hydrologic region corresponds 

with the Piedmont Physiographic Province. The equations are 

listed in table 1. The basin characteristics used as explanatory 

variables in both sets of regional equations included drainage 

area and percentage of forest cover. These characteristics 

were determined manually rather than by use of a GIS. Dillow 

(1996) suggested determining drainage area for ungaged 

Table 1. Peak-flow regression equations for the Piedmont and Western Coastal Plain in Maryland.

[Qx is the instantaneous peak flow that occurs, on average, once in x years, in cubic feet per second; A is drainage area, in square miles; F is percentage of 

forested land; ranges of applicability apply to all equations within a region. Equations are from Dillow (1996).]

Peak-flow 

recurrence 

interval 

(years)

Equation

Standard 

error of 

estimate 

(percent)

Standard 

error of 

prediction 

(percent)

Equivalent 

years of 

record

Ranges of applicability

Variable Minimum Maximum

Piedmont region

2 Q2 = 451A0.635(F+10)-0.266 38 39 3 A 0.26 165

5 Q5 = 839A0.6065(F+10)-0.248 34 36 7 F 0 96

10 Q10 = 1,210A0.589(F+10)-0.242 33 35 10

25 Q25 = 1,820A0.574(F+10)-0.239 34 37 15

50 Q50 = 2,390A0.565(F+10)-0.240 36 40 17

100 Q100 = 3,060A0.557(F+10)-0.241 39 43 19

500 Q500 = 5,190A0.543(F+10)-0.245 48 52 20

Western Coastal Plain region

2 Q2 = 1,410A0.761(F+10)-0.782 50 55 2 A 0.3 55

5 Q5 = 1,780A0.769(F+10)-0.687 46 51 4 F 19 83

10 Q10 = 1,910A0.771(F+10)-0.613 45 51 7

25 Q25 = 2,000A0.772(F+10)-0.519 46 54 10

50 Q50 = 2,060A0.771(F+10)-0.452 49 58 12

100 Q100 = 2,140A0.770(F+10)-0.391 52 63 13

500 Q500 = 2,380A0.765(F+10)-0.263 64 77 14
6 Incorporation of Water-Use Summaries into the StreamStats Web Application for Maryland

sites by drawing the basin boundary on a topographic map 

and using a planimeter to determine the area. Dillow also 

suggested using a planimeter to determine the total area of 

forest within the basin, as indicated by green-shaded areas on 

1:24,000-scale USGS topographic maps, dividing the forested 

area by the drainage area, and then multiplying by 100 to 

obtain the percentage of forested area for ungaged sites. 

Using the method suggested by Dillow (1996) to determine the percentage of forest cover would have required 

the development of a seamless digital dataset of forested 

areas by extracting the green areas from scanned images for 

each 1:24,000-scale USGS topographic map for the study 

area, which was beyond the scope of this study. Instead, the 

National Land Cover Database of 2001 (NLCD–http://www.

mrlc.gov/mrlc2k_nlcd.asp) was used to compute percentages 

of forested land area for StreamStats. 

Comparisons were made between the percentages of forest cover computed by StreamStats and the published values 

for 25 stations that were used by Dillow (1996) to develop 

the peak-flow regression equations. Of the stations, 21 were 

in the Piedmont hydrologic region and 4 were in the Western 

Coastal Plain hydrologic region. The comparisons of values of 

percentage of forest cover for the Piedmont yielded an average difference between the published values and the values 

computed by StreamStats of +0.8 percent, with differences 

for individual stations ranging from -42.7 to +72.6 percent. 

The small average difference in the values indicates that, on 

average, there is little bias in the StreamStats values for the 

Piedmont hydrologic region. The differences in values may 

be attributable to the differences in the source material and 

methods used to obtain the values, but they also may be due 

to actual changes in land use during the interval between 

development of the USGS topographic maps and development 

of the NLCD. 

The peak-flow regression equations for the Piedmont 

hydrologic region are not highly sensitive to the entered values 

of the percentage of forested land area. Although the differences in the values for individual stations were large, estimates 

of the 100-year flood flows determined from the equations 

were consistently within 10 percent of the published values. 

As a result, the peak-flow regression equations were implemented in StreamStats for the Piedmont hydrologic region, but 

actual standard errors of prediction for the estimates are likely 

larger than those provided in table 1 and in the StreamStats 

output. 

The comparisons of values of percentage of forest cover 

for the four streamgages in the Western Coastal Plain hydrologic region yielded an average difference of -55.8 percent, 

with differences for individual stations ranging from -29.2 

to -80.0 percent. The peak-flow regression equations for the 

Western Coastal Plain hydrologic region were much more sensitive to the entered values of the percentage of forested land 

area than the equations for the Piedmont hydrologic region, 

and the average difference of -55.8 percent indicates substantial bias in the measurements for this region. As a result, 

the peak-flow regression equations were not implemented in 

StreamStats for the Western Coastal Plain hydrologic region.

Like Dillow (1996), Carpenter and Hayes (1996) divided 

Maryland into hydrologic regions, based primarily on physiography, and developed separate low-flow equations for each 

hydrologic region. Carpenter and Hayes (1996) developed 

regression equations for four separate subregions within the 

Piedmont Physiographic Province, which they named Eastern 

Piedmont Subregions A through D. The equations are listed 

in table 2. Drainage area was the only explanatory variable 

used in these regression equations. Carpenter and Hayes 

(1996) were not able to determine regression equations for a 

small area within Eastern Piedmont Subregion C, which they 

named the Bynum Anomaly. The section titled “Estimating 

Streamflow Statistics for Ungaged Sites in the Bynum 

Anomaly” explains how estimates of streamflow statistics can 

be obtained for this area.

Carpenter and Hayes (1996) also were not able to define 

regression equations for an area that they designated as the 

Southern hydrologic region, which is roughly equivalent in 

spatial extent to the Western Coastal Plain of Dillow (1996). 

They determined that the density of streamgages in the southern region was insufficient to develop regression equations for 

the region. As an alternative, they suggested estimating lowflow statistics for ungaged sites in this region on the basis of 

a distance-weighted average of the flows per unit area for the 

low-flow statistics for streamgages in the region. Distances are 

measured from the centroid of the basin for the ungaged site to 

the centroids of the basins for the streamgages. An automated 

procedure is not available in StreamStats for determining the 

low-flow estimates based on the method that Carpenter and 

Hayes (1996) suggested for the Southern hydrologic region. 

The hydrologic regions that apply to the regression equations from both the Dillow (1996) and Carpenter and Hayes 

(1996) reports can be displayed as separate layers on the map 

in the Maryland StreamStats application. Boundaries used 

in StreamStats for the low-flow regions do not correspond 

exactly with the boundaries defined on plate 1 of Carpenter 

and Hayes (1996). The original boundaries were drawn by 

hand on a small-scale State map. When these boundaries were 

digitized and overlain in a GIS on a map of the 8-digit HUCs 

and streams in the study area, it was noted that the boundaries from their report often came close to but crossed back and 

forth across the HUC boundaries in some cases and the major 

streams in other cases. As a result, when StreamStats was first 

implemented using the boundaries from Carpenter and Hayes 

(1996), drainage areas determined from StreamStats often had 

very large percentages of their areas in one region and very 

small percentages in another region, where the entire drainage 

area probably should have been within one region. As a result, 

the low-flow hydrologic-region boundaries were edited to 

agree exactly with HUC boundaries and with major streams 

in areas where it was concluded that was the original intent of 

Carpenter and Hayes (1996).
StreamStats Implementation for Maryland 7

Table 2. Low-flow regression equations for subregions A through D in the Eastern Piedmont in Maryland.

[xQy is annual minimum x-day mean flow that occurs, on average, once in y years, in cubic feet per second; A is drainage area, in square miles; ranges of 

applicability apply to all equations within a region. Equations are from Carpenter and Hayes (1996).]

Peak-flow 

recurrence 

interval

Equation

Standard error of 

prediction 

(percent)

Ranges of applicability

Variable Minimum Maximum

Subregion A

7Q2 7Q2 = 0.201A1.000 16 A 2.45 101

7Q10 7Q10 = 0.0579A1.076 31

7Q20 7Q20 = 0.0357A1.103 44

14Q2 14Q2 = 0.235A0.983 16

14Q10 14Q10 = 0.0684A1.057 30

14Q20 14Q20 = 0.0446A1.077 42

30Q2 30Q2 = 0.273A0.991 17

30Q10 30Q10 = 0.0885A1.051 24

30Q20 30Q20 = 0.0655A1.056 33

Subregion B

7Q2 7Q2 = 0.329A0.955 26 A 2.01 165

7Q10 7Q10 = 0.136A0.956 44

7Q20 7Q20 = 0.0966A0.962 55

14Q2 14Q2 = 0.337A0.962 24

14Q10 14Q10 = 0.149A0.964 41

14Q20 14Q20 = 0.113A0.962 48

30Q2 30Q2 = 0.353A0.973 22

30Q10 30Q10 = 0.178A0.964 38

30Q20 30Q20 = 0.145A0.955 43

Subregion C, except Bynum Anomaly

7Q2 7Q2 = 0.371A1.048 12 A 2.09 133

7Q10 7Q10 = 0.164A1.092 20

7Q20 7Q20 = 0.117A1.128 25

14Q2 14Q2 = 0.405A1.037 10

14Q10 14Q10 = 0.190A1.069 19

14Q20 14Q20 = 0.142A1.092 24

30Q2 30Q2 = 0.441A1.031 8.9

30Q10 30Q10 = 0.220A1.060 18

30Q20 30Q20 = 0.170A1.081 12

Subregion D

7Q2 7Q2 = 0.186A1.160 17 A 3.05 287

7Q10 7Q10 = 0.0720A1.233 20

7Q20 7Q20 = 0.0526A1.143 23

14Q2 14Q20 = 0.216A1.143 18

14Q10 14Q10 = 0.0836A1.215 19

14Q20 14Q20 = 0.0597A1.243 22

30Q2 30Q2 = 0.282A1.106 23

30Q10 30Q10 = 0.109A1.180 21

30Q20 30Q20 = 0.0807A1.202 22
8 Incorporation of Water-Use Summaries into the StreamStats Web Application for Maryland

Site-Specific Water-Use Data System 

(SWUDS) and Available Water-Use 

Data

The USGS has developed the national Site-Specific 

Water-Use Data System (SWUDS) to store site- and ownerspecific water-use information, site-based measurements, and 

estimates of water-use values associated with a site or owner. 

SWUDS is a part of the internal National Water Information 

System (NWIS) used by the USGS to store, process, and 

serve all types of water data. The database runs within the 

Ingres database management system on a computer with a 

Unix operating system. SWUDS supports a link-node data 

structure where sites of water withdrawals, returns, and uses 

are represented as nodes and conveyances are represented as 

the links between the sites. This structure allows for tracking 

the movement of water from site to site (nodes) through the 

conveyances (links) (fig. 3). The conveyance capacity and 

conveyance type (pipe, canal, ditch, or stream) can be stored 

along with the type of water conveyed (groundwater, surface 

water, or treated water). All water-quantity data (annual or 

monthly) are associated with a conveyance.

Prior to this study, only water-withdrawal data were 

stored in SWUDS for Maryland. These data were stored as 

total withdrawals by permit. Water withdrawals by specific 

well or intake, conveyance, and discharge were needed for a 

better understanding of how upstream water-use activities can 

affect streamflow at specific locations. As a result, data from 

State, private, and Federal databases (fig. 4) were compiled, 

analyzed, and related to allow for better tracking of water. 

Data from four State programs were integrated and added to 

SWUDS for this study. The Maryland programs and associated databases include:

1. Water-allocation permitting and reporting program data 

from the Regulatory Analysis Management System 

(RAMS) water-use database;

2. Well-construction permitting program data from the 

Well Construction Permit database;

3. Drinking-water program data from the Public Drinking 

Water Information System (PDWIS) database; and

4. Wastewater program data from the National Pollutant 

Discharge Elimination System (NPDES) database of 

the U.S. Environmental Protection Agency. 

Other non-state databases included business information 

from Dun & Bradstreet, Inc. and data in an older version of 

SWUDS for Maryland. These data were compiled into an 

updated version of SWUDS for Maryland. 

Data describing major users who withdraw groundwater 

or surface water or have return flow to surface water were 

integrated from all six data sources, analyzed for completeness and accuracy, and entered into SWUDS. The database 

includes information and time series for all active permitted 

groundwater and surface-water withdrawals of greater than 

10,000 gal/d (gallons per day). Wells in the Well Construction 

Permit database were matched to the Water Appropriation 

Permit database by their Water Appropriation Identification 

Number (WAPID), which appears in both databases. RAMS 

provided aquifer information and the general locations for surface-water intakes and identified the resources from which the 

water was withdrawn. The Well Construction Permit database 

provided precise location information for the aquifers. The 

PDWIS database provided precise location information for all 

surface water withdrawn for drinking water. Community water 

systems (CWSs) in RAMS were matched based on Water 

Appropriation Permit information, usually by owner name, 

with the PDWIS database information to extract the higher 

credibility location information for active wells from the 

PDWIS database. 

Development of a Linkage Between 

StreamStats and the Site-Specific 

Water-Use Data System (SWUDS)

After data compilation into SWUDS was complete, data 

for 2005 on the quantity of water withdrawn from wells or 

surface-water intakes and returned through discharge pipes 

to surface water, as well as ancillary data, were retrieved 

from SWUDS and placed into the SWUDS Data Warehouse 

(SWUDS-DW), a new relational database that was created 

by the USGS. The SWUDS-DW was built using Microsoft 

Access so that it shares the same computer operating system 

as StreamStats, and thus facilitates the linking of the water-use 

data with StreamStats. In addition, the SWUDS-DW provides 

a more user-friendly environment for working with the wateruse data than SWUDS. A Visual Basic for Applications (VBA) 

program was developed to transfer data from SWUDS to 

the SWUDS-DW, which maintains a link-node topology and 

thus is consistent with the original SWUDS concept of water 

conveyances. SWUDS data were moved to the SWUDS-DW 

in two basic tables; attributed sites, and their associated wateruse values. Site coordinates maintained in SWUDS were 

plotted to points using the ArcGIS software (Environmental 

Research Systems, Inc., 2010b) and assigned a unique identifier equal to the unique site_id field in the attributed sites 

table of the SWUDS-DW. Water-use-quantity values were 

reported monthly, in million gallons per day (Mgal/d). The 

monthly values were stored in the water-use values table of 

the SWUDS-DW. The two tables were linked by means of a 

common site_id field. 

Data from the SWUDS-DW were imported into an 

ArcHydro geo-database using the ArcMap GIS software 

(Environmental Research Systems, Inc., 2010b) and the 

ArcHydro Data Model and Tools (Maidment, 2002). Wateruse points were added using ArcCatalog tools and segregated 

into WaterWithdrawal and WaterDischarge types based on 
Development of a Linkage Between StreamStats and the Site-Specific Water-Use Data System (SWUDS) 9

Figure 3. An example of modeling conveyance-based water-use data in the Site-Specific Water-Use Data 

System (SWUDS) showing 22 sites and 23 numbered conveyances.

Figure 4. Data and databases used in construction of the Maryland Site-Specific Water-Use Data System 

(SWUDS) conveyance database.
10 Incorporation of Water-Use Summaries into the StreamStats Web Application for Maryland

their SWUDS site-type codes. Water-withdrawal and waterdischarge data relationship classes were defined in ArcCatalog. 

These relationship classes were one to many (one site with 

potentially many withdrawal or discharge records) and were 

related by site_id. Monthly quantity records were loaded 

into the geo-database as time-series data using available 

ArcCatalog tools.

A Web service was developed using Visual Basic .NET 

(Microsoft Corp., 2009) to process the water-use data within 

the ArcGIS Server software environment. The Web service 

requires a single polygon representing a watershed as an 

input argument. This watershed polygon is sent to the Web 

service by StreamStats through the process described in the 

“Estimating Streamflow Statistics by Use of Regression 

Equations and Obtaining Water-Use Summaries for Ungaged 

Sites” section. The Web service overlays the watershed polygon on the water-use points layer and selects the points that 

fall within the polygon. The program then captures all of the 

water-use records related to each water-use point within the 

watershed. Next, it creates two XML tables, which it delivers 

back to StreamStats, where they are inserted into an output 

Web page that is generated when a user requests estimates of 

streamflow statistics from regression equations for an ungaged 

site. The first table provides totals of withdrawals and returns 

for each month and annual averages, as well as net values 

computed by subtracting total withdrawals from total returns. 

The second table is viewable only by users who have been 

given login privileges, and contains a list of all water-use 

points in the watershed that includes site_ids, owner names, 

and other information. This process of linking StreamStats 

with data from SWUDS should be easily transferable for use 

in other states.

Obtaining Streamflow Statistics 

and Water-Use Summaries from 

the Maryland StreamStats Web 

Application

The Maryland StreamStats Web application can be 

accessed from the national StreamStats home page at http://

streamstats.usgs.gov. The home page provides a brief description of the application. A gray box to the left of the page 

(fig. 5) provides links to other pages that document and 

provide access to the application. This gray box is duplicated 

on all other StreamStats Web pages for easy navigation. It is 

highly recommended that users read the linked documentation 

before attempting to use the application.

The State Applications link from the home page is used 

to access the individual state applications. It presents a map 

of the United States with individual states shown in different 

colors depending on their implementation status. Users can 

access the introductory page for Maryland either by selecting 

the state name from the scroll list at the top of the page, or by 

selecting Maryland on the national map.

The Maryland introductory page (1) identifies the areas 

in Maryland where StreamStats is currently implemented, (2) 

identifies the streamflow statistics for which there are regression equations available for estimating those statistics for 

ungaged sites, (3) identifies and provides links to the reports 

that describe the development of the equations, (4) provides a 

link to the state application, (5) describes limitations for use 

of the application, and (6) identifies MDE as the agency that 

worked in cooperation with the USGS to implement Maryland 

StreamStats. Users who plan to estimate streamflow statistics 

for ungaged sites should review the linked reports to understand how the regression equations were developed, and how 

they should be applied.

The Interactive Map link provides access to the application. For security reasons, some information from StreamStats 

that is needed by the MDE and other State and Federal agencies cannot be made available to the general public. This information is primarily detailed withdrawal and discharge locations and site-specific withdrawal and discharge rates. When 

Figure 5. The StreamStats link frame 

that appears on each Web page.
Obtaining Streamflow Statistics and Water-Use Summaries from the Maryland StreamStats Web Application 11

the Interactive Map link is selected, a new Web browser window will appear on the user’s computer desktop that allows 

users to enter a login identification number or name (ID) and a 

password to gain access to the secure information. Users who 

do not need access to the secure information can click on the 

Continue button to gain access to the non-secure functionality. Also in this window is a link that allows users to request a 

login ID and password from MDE, which manages access to 

the secure information. After either clicking on the Continue

button (for regular users) or logging in (for approved users), a 

new Web page will appear that contains the StreamStats user 

interface for Maryland.

Maryland StreamStats User Interface

The Maryland StreamStats user interface (fig. 2) allows 

users to locate, select, and obtain information for gaged and 

ungaged sites of interest. The largest part of the interface consists of the Map Frame, which displays default and selected 

digital map layers. The Console, to the left of the map, allows 

control of the display of map layers and map navigation, and 

provides information about the map. The Toolbar above the 

map frame contains a series of buttons (tools) that are used to 

change the scale (zooming in and out) and the center (panning) 

of the map, and allow users to initiate the various StreamStats 

functions.

This report does not fully describe all of the available 

functions. The Help button, located at the top right of the 

Toolbar, gives access to brief directions for use of each of the 

buttons. Complete documentation can be accessed through the 

links provided on the main and other StreamStats Web pages.

Obtaining Streamflow Statistics for DataCollection Stations

StreamStats provides convenient access to descriptive 

information, basin characteristics, and streamflow statistics 

for USGS data-collection stations. Users can zoom in to the 

location of a data-collection station in the user interface, click 

on the Gaging Station Information button, and then click on 

the station symbol to obtain a report that contains available 

information for the station. 

Descriptive information provided in the StreamStats 

output for the data-collection stations includes: the USGS station identification number, station name, station type, period 

of record, latitude, longitude, hydrologic unit code, major 

drainage basin name, county, U.S. Census Bureau Minor 

Civil Division (MCD) name, directions to locate the station, 

and remarks indicating any effects of human impacts or other 

pertinent information about the stations. Only previously 

published basin characteristics and streamflow statistics are 

available from StreamStats. The output contains citations to 

the original source reports that explain the methods used to 

determine the information. The Definitions links from the 

StreamStats homepage define the Streamflow Statistics and 

Basin Characteristics provided in the output. Water-use summaries can be obtained for data-collection stations by following the instructions for ungaged sites that are provided in the 

following section and selecting the location of the data-collection station on the map in the StreamStats user interface. 

Estimating Streamflow Statistics by Use of 

Regression Equations and Obtaining Water-Use 

Summaries for Ungaged Sites

StreamStats can estimate streamflow statistics for 

ungaged sites either on the basis of regional regression 

equations or the known flows for nearby streamgages. Both 

methods are discussed in the following sections. Water-use 

summaries are provided only with estimates obtained on the 

basis of regional regression equations.

To obtain estimates of streamflow statistics from regression equations and a water-use summary for an ungaged site, 

users of Maryland StreamStats should (1) use the Zoom In

button or Zoom To tools to display the location of the site of 

interest on the map at a scale of at least 1:24:000, (2) click on 

the Point Delineation tool button and then on the site of interest on the map to obtain the drainage basin for the site (fig. 6), 

and finally (3) click on the Estimate Flows using Regression 

Equations tool button to obtain the estimates and the wateruse summary. When the process is completed, a Web browser 

window will appear that reports, from top to bottom, the date 

and time of the analysis, the location of the selected ungaged 

site, the basin characteristics used as explanatory variables in 

the regression equations, the estimated streamflow statistics 

and indicators of the errors associated with the estimates, and 

the water-use summary for the site (fig. 7). Site-specific wateruse information also is provided to users with login access. 

Currently (2010), withdrawal and return information are 

available only for 2005. As water-use information is entered 

into SWUDS for 2006 and beyond, StreamStats will be able to 

report this additional information.

StreamStats determines the drainage-basin boundary for 

a selected ungaged site by use of a Digital Elevation Model 

(DEM), which is a regularly spaced grid of elevation points, 

and a digital representation of the stream network. The DEM 

used for Maryland was a 10-meter grid from the National 

Elevation Dataset (Gesch and others, 2009). The stream 

network used was from the high-resolution (1:24,000-scale) 

National Hydrography Dataset (Simley and Carswell, 2009). 

The DEM used for delineation was processed to assure agreement with the stream network and with previously digitized 

drainage-basin delineations from the Watershed Boundary 

Dataset (National Resources Conservation Service, 2009). 

This processing minimizes errors that can occur when using a 

DEM for drainage-area delineations. The processed DEM is 

used only for delineations. Any basin characteristics that rely 

on elevation information, such as mean basin elevation, are 

computed from the original, unprocessed DEM.
12 Incorporation of Water-Use Summaries into the StreamStats Web Application for Maryland

Figure 6. Example watershed delineation (black and yellow line) for an ungaged site in Maryland StreamStats, 

showing upstream data-collection stations (triangles), water withdrawals (small orange dots), and water 

discharge locations (small blue dots). (The location of the ungaged site is shown as a large blue dot with red 

crosshairs along the southern edge of the delineated boundary.)

Figure 7. Example water-use summary report for the ungaged site shown in figure 6.
Limitations for Estimates of Streamflow and Water Use for Ungaged Sites 13

Estimating Streamflow Statistics for 

Ungaged Sites Based on the Flows at Nearby 

Streamgages

The process for obtaining estimates of flow statistics 

for an ungaged site based on the known flows for nearby 

streamgages is similar to the process for obtaining estimates 

from regression equations. Users still need to locate sites of 

interest and delineate the drainage boundaries. The Generate 

Flows Based on Similar Gages tool is then used to obtain the 

flow estimates. When this tool is used, StreamStats searches 

upstream and downstream along the stream network to locate 

nearby streamgages. Streamgages will be used as the basis 

for estimating streamflow statistics for the ungaged site if the 

drainage area for the ungaged site is within 0.5 and 1.5 times 

the drainage area for the streamgage. This range of drainagearea ratios can vary by state. The streamflow statistics and 

the drainage area for the station with the drainage-area ratio 

closest to one will be retrieved from a database and the flow 

per unit area will be computed for each statistic. These flows 

per unit area will then be multiplied by the drainage area for 

the ungaged site to obtain the estimates. If another station in 

the opposite direction along the stream network also has a 

drainage-area ratio within the specified limits, then it also will 

be used to estimate streamflow statistics for the ungaged site. 

If both an upstream and a downstream station were used for 

estimation, then final estimates will be determined by weighting the upstream and downstream estimates by a process 

explained in Ries and Dillow (2006). Water-use summaries are 

not provided in the outputs produced from this process.

Estimating Streamflow Statistics for Ungaged 

Sites in the Bynum Anomaly

Carpenter and Hayes (1996) suggested estimating lowflow statistics for ungaged sites in the Bynum Anomaly based 

on the average of the flows per unit area for data-collection 

stations within the area. Reports that contain descriptive 

information, and previously published basin characteristics 

and streamflow statistics for four stations in the Bynum 

Anomaly can be obtained from StreamStats by following the 

instructions provided in the “Streamflow Statistics for DataCollection Stations” section. For convenience, all previously 

published streamflow statistics, except for peak-flow statistics, 

are presented in table 3 along with the average values. The statistics in table 3 are in cubic feet per second per square mile, 

and were determined by dividing the previously published statistics by the drainage area for the station. Peak-flow statistics 

were not included for the stations in table 3 because regression equations are available to estimate peak-flow statistics 

for ungaged sites in the Bynum Anomaly. To obtain estimates 

of other streamflow statistics for an ungaged site within the 

Bynum Anomaly, first use StreamStats to delineate the drainage basin for the ungaged site and determine its drainage area. 

Next, multiply the drainage area for the ungaged site by the 

average values of flow per unit area in the right-hand column 

of table 3 to determine the corresponding flow estimate for the 

ungaged site. The Basin Characteristics tool or the Estimate 

Flows using Regression Equations tool may be used to obtain 

the drainage area and other basin characteristics for the 

ungaged site. The Estimate Flows using Regression Equations

tool will provide the peak-flow estimates and the water-use 

summary for the ungaged site.

Carpenter and Hayes (1996) originally suggested three 

stations for use in estimating streamflow statistics in the 

Bynum Anomaly, the streamgage at Bynum Run at Bel Air, 

MD (01581500) and the low-flow partial-record stations 

James Run at Bush, MD (01581650) and Bynum Run at 

Bush, MD (01581600). Since Carpenter and Hayes’ report 

was published, another streamgage was established within the 

Bynum Anomaly, Bynum Run near Bel Air, MD (01581000). 

Statistics for all four stations are provided in table 3. These 

statistics are subject to change whenever new streamflow 

statistics are published for the stations.

Limitations for Estimates of Streamflow 

and Water Use for Ungaged Sites

Estimates of streamflow statistics that are obtained from 

regression equations are based on the assumption of natural 

flow conditions at the ungaged site. If human activities such 

as dam regulation, water withdrawals, or return flows substantially affect the timing, magnitude, or duration of flows at 

a selected site and estimates of actual flows are desired, then 

the regression-equation estimates provided by StreamStats 

should be adjusted by the user to account for these activities. 

StreamStats for Maryland has been modified to provide summaries of withdrawals and return flows, but it does not account 

for the effects of dam regulation of flow. The water-use summaries also do not consider the fate of the water once it is 

withdrawn from a particular location. Part or all of the water 

may be exported from the basin or lost to consumptive uses. 

Alternately, much of the withdrawn water may be returned to 

the basin through individual septic systems or through municipal water-treatment-plant discharges. 

StreamStats can be used to obtain regression-equation 

estimates of streamflow statistics for USGS data-collection 

stations. Users should understand that there are errors associated with estimates determined from available data for the 

stations as well as estimates determined from regression 

equations, and some disagreement between the two sets of 

estimates is expected. If the flows at the stations are affected 

by human activities, then users should not assume that the 

differences between the data-based estimates and the regression-equation estimates are equivalent to the effects of human 

activities on streamflow at the stations.

When StreamStats is used to obtain regression-equation 

estimates for sites with basin characteristics outside the ranges 

of those for the sites used to develop the regression equations, 
14 Incorporation of Water-Use Summaries into the StreamStats Web Application for Maryland

Table 3. Previously published streamflow statistics for streamgages and low-flow partial-record stations, and average values in the 

Bynum Anomaly area of Piedmont subregion C.—Continued

[Values are in cubic feet per second per square mile, except daily flow years are in years.]

Statistic 

name

Streamgages Low-flow partial-record stations

Average 

value

01581000

(Bynum Run near 

Bel Air, MD)

01581500

(Bynum Run at 

Bel Air, MD)

01581650

(James Run at 

Bush, MD)

01581600

(Bynum Run at 

Bush, MD)

Value Reference Value Reference Value Reference Value Reference

Low-flow statistics

1-day 1.01-year low flow 0.293 3

1-day 2-year low flow 0.141 3

1-day 5-year low flow 0.047 3

1-day 10-year low flow 0.023 3

1-day 20-year low flow 0.012 3

1-day 50-year low flow 0.000 3

1-day 100-year low flow 0.000 3

7-day 1.01-year low flow 0.411 3

7-day 2-year low flow 0.141 3 0.099 4 0.236 4 0.158

7-day 5-year low flow 0.059 3

7-day 10-year low flow 0.023 3

7-day 20-year low flow 0.012 3 0.009 4 0.027 4 0.016

7-day 50-year low flow 0.012 3

7-day 100-year low flow 0.000 3 0.009 4 0.053 4

14-day 1.01-year low flow 0.516 3

14-day 2-year low flow 0.164 3 0.108 4 0.262 4 0.178

14-day 5-year low flow 0.070 3

14-day 10-year low flow 0.035 3 0.018 4 0.076 4 0.043

14-day 20-year low flow 0.023 3 0.009 4 0.049 4 0.027

14-day 50-year low flow 0.012 3

14-day 100-year low flow 0.012 3

30-day 1.01-year low flow 0.904 3

30-day 2-year low flow 0.200 3 0.144 4 0.324 4 0.223

30-day 5-year low flow 0.117 3 0.117

30-day 10-year low flow 0.094 3 0.045 4 0.142 4 0.094

30-day 20-year low flow 0.070 3 0.036 4 0.107 4 0.071

30-day 50-year low flow 0.059 3

30-day 100-year low flow 0.047 3

Flow-duration statistics

1-percent duration 24.4 1 14.9 3 19.6

2-percent duration 9.00 3 9.00

5-percent duration 4.96 1 4.41 3 4.69

10-percent duration 2.67 1 2.39 3 2.53

15-percent duration 1.68 3 1.68
Limitations for Estimates of Streamflow and Water Use for Ungaged Sites 15

Table 3. Previously published streamflow statistics for streamgages and low-flow partial-record stations, and average values in the 

Bynum Anomaly area of Piedmont subregion C.—Continued

[Values are in cubic feet per second per square mile, except daily flow years are in years.]

Statistic 

name

Streamgages Low-flow partial-record stations

Average 

value

01581000

(Bynum Run near 

Bel Air, MD)

01581500

(Bynum Run at 

Bel Air, MD)

01581650

(James Run at 

Bush, MD)

01581600

(Bynum Run at 

Bush, MD)

Value Reference Value Reference Value Reference Value Reference

20-percent duration 1.60 1 1.31 3 1.46

25-percent duration 1.33 1 1.06 3 1.20

30-percent duration 1.16 1 0.948 3 1.05

40-percent duration 0.853 1 0.742 3 0.798

50-percent duration 0.613 1 0.606 3 0.609

60-percent duration 0.467 1 0.481 3 0.474

70-percent duration 0.347 1 0.372 3 0.359

75-percent duration 0.293 1 0.327 3 0.310

80-percent duration 0.240 1 0.283 3 0.261

85-percent duration 0.237 3 0.237

90-percent duration 0.147 1 0.190 3 0.168

95-percent duration 0.080 1 0.133 3 0.106

98-percent duration 0.077 3 0.077

99-percent duration 0.053 1 0.060 3 0.057

Annual-flow statistics

Daily flow years 60 3

Mean annual flow 1.31 3

Standard deviation of mean 

annual flow

0.366 3

General-flow statistics

Average daily streamflow 1.68 1 1.28 1 1.48

Maximum daily flow 85.1 1 272 1 179

Minimum daily flow 0.04 1 0.001 1 0.021

Standard deviation of daily 

flows

5 1 4.15 1 4.58

Base-flow statistics

Average base-flow index 

value

0.041 2 0.043 2 0.042

Number of years to compute 

base-flow index

0.667 2 3.05 2 1.86

Standard deviation of annual 

base-flow index values

0.009 2 0.007 2 0.008

References:

1

 Wolock, 2003a.

2

 Wolock, 2003b.

3

 Ries, 2006.

4

 Carpenter and Hayes, 1996.
16 Incorporation of Water-Use Summaries into the StreamStats Web Application for Maryland

the estimates are extrapolated. Errors associated with these 

estimates are unknown and may be very large. StreamStats 

provides a warning when extrapolation occurs. Errors associated with estimates obtained by use of the methods recommended in this report for ungaged sites within the Bynum 

Anomaly also are unknown.

When the Generate Flows Based on Similar Gages tool 

is used to obtain estimates for ungaged sites, StreamStats 

users can specify whether to include only stations with natural 

flow conditions in the analysis or to also include stations 

that are affected by flow regulations. This decision must be 

made carefully. If users choose to allow use of regulated stations, then they should consider how the effects of regulation 

could change between the streamgage and the ungaged site. 

If a regulated station is downstream from the ungaged site, 

for example, it is possible that the stream is not affected by 

regulation at the ungaged site, and therefore the streamflow 

statistics estimated on the basis of the flow per unit area at the 

station will not be representative of the flow conditions at the 

ungaged site. Conversely, if the regulated station is upstream 

from the ungaged site, streamflow from tributaries entering 

between the station and the ungaged site may dampen the 

effects of the regulation at the station and cause the estimated 

streamflow statistics to be unrepresentative of conditions at the 

ungaged site.

Summary and Conclusions

Approximately 25,000 new households and thousands 

of new jobs will be established in an area that extends from 

southwest to northeast of Baltimore, Maryland, as a result of 

the Federal Base Realignment and Closure (BRAC) process, 

with consequent new demands on the water resources of the 

area. The Maryland Department of the Environment (MDE), 

which is responsible for issuing permits for water withdrawals and wastewater discharges throughout Maryland, needs 

to understand the natural availability of the water resources 

in relation to current and requested water withdrawals and 

wastewater discharges as a basis for making good permitting 

decisions in BRAC-affected areas. The U.S. Geological 

Survey (USGS), in cooperation with the MDE, has extended 

the area of implementation and added functionality to an 

existing map-based Web application named StreamStats to 

provide an improved tool for planning and managing the water 

resources in the BRAC-affected areas. StreamStats previously 

was implemented for only a small area surrounding Baltimore, 

Maryland, and it has now been extended to cover all BRACaffected areas in Maryland.

StreamStats is a map-based Web application that allows 

users to obtain information on streamflow availability at 

USGS data-collection stations and at user-selected ungaged 

sites. Prior to completion of the study that is described in this 

report, StreamStats was available only in the GunpowderPatapsco hydrologic accounting unit in Maryland. Users 

could obtain descriptive information and previously published 

basin characteristics and streamflow statistics for datacollection stations. Users also could obtain drainage-basin 

delineations, computed basin characteristics, and estimated 

streamflow statistics for ungaged sites in the implemented 

area. StreamStats has now been implemented in the entire 

area that is expected to be affected by the BRAC process. 

This area includes the Chester-Sassafras, Lower Susquehanna, 

Gunpowder-Patapsco, Severn, and Patuxent hydrologic 

accounting units in Maryland. In addition, StreamStats was 

modified to provide summaries of water-use activities for userselected sites in the BRAC area. This was accomplished by 

creating a link between StreamStats and the USGS SWUDS 

water-use database.

StreamStats can provide estimates of peak-flow 

frequency statistics, such as the 1-percent probability 

(100-year recurrence interval) flood, and low-flow frequency 

statistics, such as the 7-day, 10-year low flow, for ungaged 

sites by solving previously published regression equations. 

These equations were developed from regression analyses 

using basin characteristics that were measured manually as 

the explanatory variables, whereas StreamStats determines 

the basin characteristics from digital datasets. In testing, it 

was determined that StreamStats was not able to accurately 

reproduce the manual measurements of percentage of forest 

cover that were used as an explanatory variable in the peakflow frequency equations. The peak-flow frequency equations 

for the Piedmont hydrologic region are much less sensitive 

to the measured values of percentage of forest cover than the 

equations for the Western Coastal Plain hydrologic region. 

As a result, the peak-flow frequency equations were made 

available to StreamStats users in the Piedmont hydrologic 

region but not in the Western Coastal Plain hydrologic region. 

The standard errors of prediction for estimates of peak flow 

provided by StreamStats are likely somewhat larger than the 

previously published standard errors of prediction, which 

ranged from 35 percent for the 10-percent probability 

(10-year recurrence interval) flood to 52 percent for the 0.2 

percent probability (500-year recurrence interval) flood.

Previously published low-flow frequency equations were 

implemented in StreamStats for subregions A through D of 

the Eastern Piedmont hydrologic region. Standard errors of 

prediction for the equations ranged from 8.9 percent for the 
References Cited 17

30-day, 2-year low flow in subregion C to 55 percent for the 

7-day, 20-year low flow in subregion B. Equations were not 

available for a small area within Eastern Piedmont subregion 

C named the Bynum Anomaly, or for the Southern hydrologic 

region, which roughly corresponds with the part of the Coastal 

Plain Physiographic Province that is along the western shore 

of the Chesapeake Bay. This report provides a semi-automated 

method for obtaining estimates of low-flow statistics in the 

Bynum Anomaly, but no method is available for estimating 

low-flow statistics in the Southern hydrologic region.

Information on water discharges and conveyances was 

added to the Site-Specific Water-Use Data System (SWUDS) 

for this study. Only water-withdrawal information was 

available beforehand. The additional information allowed 

tracking of water from the point of withdrawal to the point of 

discharge. Data from several state databases and a commercial 

database were used to fully document the water conveyances. 

Water withdrawal and discharge data were extracted from 

SWUDS and entered into the SWUDS Data Warehouse, a 

Microsoft Access database that was created for this study 

to facilitate linkage of the water-use data with StreamStats. 

A Web service was then created that would accept a basin 

delineation from StreamStats, overlay it on a Geographic 

Information System layer of withdrawals and discharges, and 

send a summary of the withdrawals and discharges back to the 

StreamStats user. This linkage of StreamStats with water-use 

information from SWUDS should enable Maryland regulators 

and planners to make more informed decisions on the use of 

water resources in the BRAC area, and is transferrable to other 

geographic areas.

Acknowledgments

The authors would like to thank the MDE for its support 

of this work. In particular, John Grace and Patrick Hammond 

provided perspective on the needs of the MDE for streamflow 

statistics and how the MDE uses that information. The MDE 

also provided feedback on design of the StreamStats wateruse summaries, and they provided other guidance throughout 

the project. In addition, the authors acknowledge hydrologist 

Michael Koterba, of the USGS, for providing some of the 

information used to describe the study area in this report. 

Finally, the authors appreciate the help of USGS employees 

Valerie Gaine, Gloria Wilson, Betzaida Reyes, and 

Timothy Auer, for providing editing, illustrations preparation, 

and final layout of this report.

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18 Incorporation of Water-Use Summaries into the StreamStats Web Application for Maryland

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Prepared by USGS West Trenton Publishing Service Center.

Edited by Valerie M. Gaine.

Graphics and layout by Timothy W. Auer.

For additional information, contact:

Kernell G. Ries III, Office of Surface Water

443-498-5617

or Director, MD-DE-DC Water Science Center

U.S. Geological Survey

5522 Research Park Drive

Baltimore, MD 21228

443-498-5500

or visit the MD-DE-DC Water Science Center Web site at:

http://md.water.usgs.gov 

or the StreamStats homepage at:

http://streamstats.usgs.gov
Ries, K.G., III and others—Incorporation of Water-Use Summaries into the StreamStats Web Application for Maryland—Scientific Investigations Report 2010–5111

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