Prepared in cooperation with the U.S. Environmental Protection Agency, 

Office of Research and Development

Hydrologic Characteristics of Low-Impact Stormwater 

Control Measures at Two Sites in Northeastern Ohio, 2008–13 

4" PVC SUBDRAIN 4" PVC DRAIN

6" PVC DRAIN

6" PVC INLET 6" PVC DRAIN.

FOR OVERFLOW OUTFLOW TO

BIO-RETENTION BASIN

A

B

WEATHER STATION

SWALE

BIORETENTION

BASIN

BUILDING

RAIN

GARDEN

STORM OUTLET PIPE

FROM DOWNSPOUTS

OUTLET

STRUCTURE

FLUME 3

FLUME 1

FLUME 2

Scientific Investigations Report 2015–5030

U.S. Department of the Interior

U.S. Geological Survey
Cover. Schematic site plan for stormwater best-management practices at the Washington Street site, 

Geauga County, Ohio (top), and photos of three flumes (bottom, left to right). Flume 1 measures surface 

flow over the parking lot, flume 2 measures any overflow from the rain garden, flume 3 measures the flow 

from the drain line. 
Hydrologic Characteristics of Low-Impact 

Stormwater Control Measures at Two Sites 

in Northeastern Ohio, 2008–13

By Robert A. Darner, William D. Shuster, and Denise H. Dumouchelle

Prepared in cooperation with the U.S. Environmental Protection Agency, 

Office of Research and Development

Scientific Investigations Report 2015–5030

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Darner, R.A., Shuster, W.D., and Dumouchelle, D.H., 2015, Hydrologic characteristics of low-impact stormwater 

control measures at two sites in northeastern Ohio, 2008–13: U.S. Geological Survey Scientific Investigations Report 

2015–5030, 27 p., http://dx.doi.org/10.3133/sir20155030.

ISSN 2328-0328 (online)
iii

Contents

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

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

Description of the Study Areas ..........................................................................................................2

Hydrologic Characteristics at the Sterncrest Drive Site.........................................................................2

Site Description and Methods............................................................................................................2

Data Analysis and Interpretation .......................................................................................................5

Hydrologic Characteristics at the Washington Street Site...................................................................10

Site Description and Methods..........................................................................................................10

Data Analysis and Interpretation .....................................................................................................10

Summary and Conclusions.........................................................................................................................21

References Cited..........................................................................................................................................21

Appendix 1. Statistical Output................................................................................................................23

Section A. Statistical difference of means of percent removal using

 the Tukey-Kramer test at the Washington Street site, 

Geauga County, Ohio, 2010–13 ............................................................................................23

Section B. Output for the linear model percent removal and total rain 

at the Washington Street site, Geauga County, Ohio, 2010–13......................................24

Section C. Output for the linear model percent removal and LOG_PN 

at the Washington Street site, Geauga County, Ohio, 2010–13......................................26

Figures

1. Map showing location of study area.........................................................................................3

2. Schematic site plan for the stormwater-control measure along the Sterncrest

Drive site, Cuyahoga County, Ohio.............................................................................................4

3. Graph showing cumulative overflow indicator and cumulative rain from 

April 1 to October 31 of each year at the Sterncrest Drive SR1 site, 

Cuyahoga County, Ohio................................................................................................................9

4. Schematic site plan for stormwater best-management practices at the

Washington Street site, Geauga County, Ohio.......................................................................11

5. Photographs showing three flumes at the Washington Street site, 

Geauga County, Ohio..................................................................................................................12

6. Boxplot showing percent removal and bar graph showing the depth of rain

starting April 1 and ending October 31, by year, at the Washington Street site,

Geauga County, Ohio..................................................................................................................13

7. Boxplots showing climatological and flow characteristics, Washington Street

site, Geauga County, Ohio, 2010–13 .........................................................................................14

8. Scatter plots and fit linear least-squares lines for 2010–13, Washington Street

site, Geauga County, Ohio .........................................................................................................16

9. Boxplot showing the percent removal residuals, by year, at the 

Washington Street site, Geauga County, Ohio.......................................................................17

10. Boxplots showing baseline moisture in soil-moisture sensors, 

Washington Street site, Geauga County, Ohio, 2010–13 ......................................................18
iv

Figures—continued

11. Boxplots showing precipitation-runoff centroid lag times for the Washington

Street site, Geauga County, Ohio, 2010–13.............................................................................19

12. Graph showing total flow through flumes 2 and 3 for April–October 2010–13 

at the Washington Street site, Geauga County, Ohio ...........................................................20

Tables

1. Rain garden overflow time, duration, and precipitation-event depths, 

Sterncrest Drive SR1 site, Cuyahoga County, Ohio, 2008–13.................................................6

2. Rain garden overflow time, duration, and precipitation-event depths, 

Sterncrest Drive SR2 site, Cuyahoga County, Ohio, 2008–12.................................................8

3. Percentage of 0.75 inch or greater rain events that caused an overflow at SR1

with respect to event duration, Sterncrest Drive site, Cuyahoga County, Ohio.................9

4. Spearman correlations of percent removal to measure antecedent conditions

and rain intensity for events with total rainfall greater than or equal to 

0.2 inches at the Washington Street site, Geauga County, Ohio ........................................15
v

Conversion Factors

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

) 2.590 square kilometer (km2) 

Flow rate

inch per hour (in/h) 2.54 centimeter per hour (m/h)

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

Datum

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

Abbreviations

BMPs best-management practices

CRWP Chagrin River Watershed Partners

CSO combined sewer overflow

CSS combined sewer systems

EPA U.S. Environmental Protection Agency

EPA-ORD U.S. Environmental Protection Agency-Office of Research and Development

ET evapotranspiration

GI green infrastructure

LID low impact development

MLR multiple linear regression

RR runoff ratio

SCM stormwater-control measure

TDR time-domain reflectometer

USGS U.S. Geological Survey

Hydrologic Characteristics of Low-Impact Stormwater 

Control Measures at Two Sites in Northeastern Ohio, 

2008–13

By Robert A. Darner,1 William D. Shuster,2 and Denise H. Dumouchelle1

1

 U.S. Geological Survey, Ohio Water Science Center.

2

 U.S. Environmental Protection Agency, Office of Research and 

Development.

Abstract

This report updates and examines hydrologic data 

gathered to characterize the performance of two stormwatercontrol measure (SCM) sites in the Chagrin River watershed, 

Ohio. At the Sterncrest Drive site, roadside bioswales and 

rain gardens were used to alleviate drainage problems in this 

residential neighborhood area. At the Washington Street site, 

a treatment train (including a pervious-paver system, rain garden, and bioswales) was used to reduce and delay stormwater 

runoff at a small business development. Selected metrics were 

used to demonstrate SCM system performance with regard to 

stormwater-management objectives at each site. Rain-garden 

overflow-frequency data collected at the Sterncrest Drive site 

during 2008–13 were used to characterize system sensitivity to rainfall characteristics. Approximately 70 percent of 

storms exceeding 0.75 inches during 3 hours or more resulted 

in overflows. Drainage-design features that may restrict flow 

through the system were identified. Overall, the data and local 

observations confirmed the continued success of the SCM at 

the Sterncrest Drive site in preventing roadway closure due to 

flooding. The additional years of data collected at the Washington Street site indicated that a previous analysis of increased 

runoff removal, based on only the first 2 years (2009–10) of 

data, provided premature conclusions. With 5 years of data 

(2009–13) and adjusting for changes in rainfall characteristics, it 

appears that the percentage of runoff removed by the system is 

decreasing; however, the lag time (time from onset of rainfall to 

runoff) has remained nearly constant. The annual mean percent 

removal for 2010–13 ranged from 55 to 37 percent with an 

overall mean of 45 percent, and this does meet the project 

objective of reducing runoff from the business complex. One 

possible explanation for the combination of increased volume 

of runoff and no change in the timing of runoff is the preferential flow paths developed in the SCM, increasing the capacity 

for internal drainage. Data indicated that the SCM system at 

the Washington Street site had reduced functionality over time. 

Introduction

Stormwater runoff in urban areas is one of the major 

water-resource management issues in the United States. 

Impervious surfaces, such as roadways, sidewalks, driveways, 

and roofs prevent infiltration of rainfall, increasing the volume 

of runoff from rain events relative to rural areas where more 

permeable vegetated landscapes have greater infiltration rates. 

Urban stormwater runoff typically is collected and transferred 

to a centralized treatment facility with the runoff moving 

through either separate or combined sewer systems (CSS). In 

the case of municipal separate storm sewer systems, runoff is 

routed to a receiving water body like a nearby river or pond. 

The runoff from the impervious surfaces is often delivered to 

the receiving water body faster and in greater volume than the 

surface-water system would naturally receive, which can cause 

flooding, disturbance to aquatic ecosystems, and increased 

peak flows in downstream municipalities (Booth and Jackson, 1997). For a CSS, wastewater and stormwater volumes 

are combined in the same pipe. During some storms, system 

capacity can be exceeded, and a combined sewer overflow 

(CSO) occurs, releasing the wastewater-stormwater mixture to 

the environment.

Low-impact development (LID) and green infrastructure (GI) are best-management practices (BMPs) for managing stormwater volume as near to the source as possible. 

These decentralized source-control approaches to stormwater 

management shunt water away from water-treatment plants 

and involve both structural elements, such as detention basins 

or rain gardens, and non-structural elements, such as landmanagement education. The LID approach (Dietz, 2007) is 

a retrofit-oriented management response to excessive urban 

runoff volume, and is flexible with respect to design so that 

it can be applied at small scales of development, for example 

small shopping plazas, residential homes, small businesses, 

and neighborhoods. GI refers to the concept of linking site 

design and small-scale stormwater-management objectives 

across larger spatial scales (for example, municipalities, cities, 

or regions) by creating connected, contiguous corridors for 

stormwater detention (Ahern, 2007). BMPs, which may use 
2 Hydrologic Characteristics of Low-Impact Stormwater Control Measures at Two Sites in Northeastern Ohio, 2008–13

LID designs singly or in combination as a treatment train, 

include rain gardens, bioswales, pervious-paver systems, rain 

barrels or cisterns, tree box filters, and curbless roads with 

swales. LID practices reduce localized runoff, whether through 

detention, infiltration, or evapotranspiration of stormwater.

Limited data exist on how LID systems perform in 

practice, and monitoring data are needed to improve the 

understanding of LID as a stormwater-control measure (SCM). 

These data may be provided, in part, by targeted research into 

specific characteristics of SCMs with respect to water-quality 

benefits and actual reduction in stormwater runoff. Monitoring 

programs should be conducted for sufficiently long periods 

of time (for example, 3 to 5 years of typical environmental 

conditions). The purpose of a monitoring program is to measure the response of LID and GI practices to a broad range of 

precipitation and climate conditions, and also to understand 

changes in performance over time. With funding through the 

U.S. Environmental Protection Agency (EPA) National Community Decentralized Demonstration Project, the Chagrin 

River Watershed Partners (CRWP) selected four demonstration sites in the Chagrin River watershed to exemplify the 

process for the design, construction, operation, and monitoring 

of retrofit LID practices such as SCMs. After the projects had 

been designed, the EPA-Office of Research and Development 

(EPA-ORD) collaborated with the U.S. Geological Survey 

(USGS), Ohio Water Science Center to install and maintain 

hydrologic monitoring equipment at each of several CRWP 

projects. These demonstration sites used a range of different 

BMPs that varied by location as follows:

• A bioswale retrofit to a roadside drainage ditch, 

Sterncrest Road, Orange Village, Ohio. 

• A rain garden and pervious-paver system that drain 

to a bioretention swale and detention basin to handle 

stormwater from an expanding small business, 

Washington Street, Village of South Russell, Ohio. 

These projects were selected for long-term monitoring, which involves characterizing the landscape, delineating the drainage area (watershed) at each site, monitoring 

rainfall inputs, measuring runoff volume through each BMP, 

and determining water output from the practices as flow into 

receiving waters. Monitoring of precipitation inputs and runoff 

volumes was only conducted during the warm season. Darner 

and Dumouchelle (2011) presented precipitation and runoff 

data from the sites for 2008–10; in this report, performance 

characteristics of the BMPs were reexamined using the previously collected data supplemented with an additional 3 years 

of data collected from 2011 to 2013. Some of the material 

from Darner and Dumouchelle (2011) is repeated in this report 

for the reader’s convenience. A full discussion of the terms 

LID, GI, BMP, and SCM can be found in Fletcher and others 

(2014). For clarity, the treatment practices installed and monitored will be referred to as SCMs in this document.

Description of the Study Areas

Located east of the Cleveland metroplex, in northeastern 

Ohio, the Chagrin River watershed drains 265 square miles 

(mi2) of gently rolling hills. The two study sites are near the 

Chagrin River, where it crosses from Geauga into Cuyahoga 

County. The Sterncrest Drive site is in Cuyahoga County, 

near the western boundary of the watershed. The Washington 

Street site is in western Geauga County, in the upper reaches 

of the watershed (fig. 1). The area has a humid, temperate 

climate with average annual precipitation of 47 inches (in.) 

(Midwestern Regional Climate Center, 2010). Land use is 

highly variable and includes urban, suburban, rural-residential, 

forested, and agricultural uses (Jagucki and Darner, 2001). 

Glacial sediments range from a few feet to around 100 feet (ft) 

in thickness and overlie sandstone and shale bedrock. Most 

soils in the watershed are formed in the clay-rich glacial till 

and are generally classified as silt loams with generally low 

to very low (0.6 to <0.2 inches per hour [in/h]) permeability 

and high runoff potential. Artificial drainage is suggested for 

development in this watershed (Musgrave and Holloran, 1980; 

Williams and McCleary, 1982). The water table at both sites is 

near the land surface, within 1 to 3 ft, particularly in the winter 

and spring or during unusually wet periods, so the soil has 

little capacity to store infiltrated water. These soil conditions 

can lead to flooding; hence, there is a need for adding detention capacity to each of these neighborhood areas by way of 

retrofitted, short-term detention strategies.

Hydrologic Characteristics at the 

Sterncrest Drive Site

The SCM at the Sterncrest Drive site consists of a 

bioswale retrofit to a roadside drainage ditch with rain gardens. Additional site description and construction details are 

presented in Darner and Dumouchelle (2011). Precipitation 

and runoff data were collected at this site from March or April 

through October 2008–13. 

Site Description and Methods

Near the intersection of Sterncrest Drive and Lander 

Road, there has been a history of yard and road flooding. 

In 2007, in an effort to alleviate flooding, about 1,400 linear 

feet of existing roadside ditches were excavated to a depth of 

about 5 ft. Perforated drain pipe was installed on the north side 

(8-in. diameter) and south side (15-in. diameter). Bioswales 

were then created by backfilling the excavation with permeable sediments (sand-compost mixture) and planting grass. 

The bioswales receive stormwater runoff from the adjacent 

roadway and overland runoff from the residential area. 
Hydrologic Characteristics at the Sterncrest Drive Site 3

Project

OHIO

Chagrin River

McFarland Creek

81°28' 81°24'

41°26'

41°24'

2 KILOMETERS

0 2 MILES

0 1

1

Cuyahoga River

Chagrin River

Euclid Creek

Cuyahoga River

L A K E E R I E

Grand River

81°40' 81°20' Grand River 81°0'

41°40'

41°20'

Base from U.S. Geological Survey

Digital Data, UTM Zone 17 N

North American Datum of 1983. 0 10 20 KILOMETERS

0 10 20 MILES

Chagrin River 

 drainage area

Site locations

Road

Streams

County boundry

EXPLANATION

Chagrin River 

drainage area

GEAUGA

CUYAHOGA

LAKE

PORTAGE

SUMMIT

TRUMBULL ASHTABULA

Cleveland

Metroplex

STERNCREST DRIVE

CUYAHOGA

GEAUGA

WASHINGTON 

STREET

LANDER RD

Figure 1. Location of study area.
4 Hydrologic Characteristics of Low-Impact Stormwater Control Measures at Two Sites in Northeastern Ohio, 2008–13

A series of rain gardens were installed within the bioswales to 

increase infiltration and evapotranspiration. A non-perforated 

storm drain pipe crosses under the road from the north drain 

pipe to the south drain pipe at each of the paired rain gardens 

(fig. 2). The rain gardens, which are 4.5 ft wider than the 

bioswale, were planted with perennial plants and then mulched 

(Darner and Dumouchelle, 2011). Overflow grates elevated 

about 6 in. above the mulch prevent excessive ponding in the 

rain gardens. Water from the buried drains in the bioswale 

and from the rain-garden-overflow grate discharge to the local 

stormwater drain.

An unheated tipping-bucket rain gage and an air-temperature sensor were installed behind Orange Village Hall, 

approximately 1,400 ft west-northwest of the Sterncrest Drive 

site. The rain gage registered precipitation in 0.01-in. increments that were summed by a data logger on a 10-minute 

interval. Precipitation depths and peak intensities for 10-, 30-, 

60-, 120-, and 1,440-minute intervals were determined. Recurrence intervals of precipitation at the site were estimated by 

using precipitation-frequency tables compiled by the National 

Oceanic and Atmospheric Administration (Bonnin and others, 

2004).

The overflow grates on two rain gardens—one north 

(SR1) and one south (SR2) of Sterncrest Drive (fig. 2)—were 

instrumented with sensors that measured specific conductance and temperature. These sensors were used to determine 

the occurrence and duration of overflows; however, without 

additional instrumentation, the volume of the overflows could 

not be computed. The sensors were connected to a data logger 

adjacent to the rain garden. The data logger queried the sensor 

every minute and recorded the measurement if there was a 

change since the last measurement. Data also were recorded 

every 6 hours to ensure that the data logger was operational 

during periods when sensor readings were unchanging.

The maximum water levels in the SR1 and SR2 rain gardens were recorded with a crest-stage gage—a simple instrument that records only the highest water elevation, or stage, 

reached between routine maintenance visits when the gage is 

reset. The crest-stage reading was compared to the elevation of 

the overflow grate to verify that overflow did, or did not, occur 

as indicated by the sensor measurements. In no case was an 

overflow indicated by a crest-stage gage without an overflow 

also being indicated by a sensor reading. It cannot be said with 

certainty whether the reverse was true because more than one 

overflow may have occurred between inspections of the creststage gage.

Rain garden (SR1 and 

SR2 are instrumented)

House

Driveway 15-inch pipe flow direction 

8-inch pipe flow direction 

Stormwater pipe flow direction 

EXPLANATION

SR1

SR2

Sterncrest Road

Lander Road

Pond

Figure 2. Schematic site plan for the stormwater-control measure along the Sterncrest Drive site, Cuyahoga County, Ohio.
Hydrologic Characteristics at the Sterncrest Drive Site 5

Data Analysis and Interpretation

The frequency with which an SCM overflows is one 

measure of how well the feature functions in response to various rain events and over time. At the Sterncrest Drive site, 

overflow occurs when the water level in the rain garden rises 

above the overflow grate, and the overflow volume is shunted 

directly to the local stormwater system. The design storm for 

the site was reported to be 0.75 in. of precipitation, but the 

duration for this rainfall depth was not stated (Brian Mader, 

Stephen Hovancsek and Associates, Inc., written commun., 

2014); therefore, the analysis of data from this site focuses 

on the frequency of overflows as a function of precipitation 

amount, with particular emphasis on rain events in excess of 

0.75 in. 

There were 83 overflows at the SR1 site from 2008 to 

2013: 18 occurred when precipitation in the previous 96 hours 

did not exceed the 0.75-in. design storm, and 6 of those had 

precipitation of at least 0.73 in. (table 1). In the 6-year study 

period, only four overflows at SR1 were associated with a rain 

event that exceeded the 1-, 2- or 10-year recurrence interval 

(table 1). During 2008–10, there were 14 overflows at the SR1 

site. Additionally, there were 40 overflows in 2011, 11 overflows in 2012, and 18 overflows in 2013.

Only 17 overflows occurred at the SR2 site (table 2) from 

2008 to 2012. Six of the overflows occurred with rain totals of 

less than 0.75 in. in the previous 96 hours; however, three of 

these six overflows occurred on the same day as another event 

(2 and 3; 7 and 8), and the combined rain totals were in excess 

of 0.75 in. In addition, event 16 occurred on the same day as 

event 60 at SR1 (table 1), which produced 0.88 in. of precipitation. None of the overflow events at SR2 occurred with rain 

events that exceeded the 1-, 2- or 10-year recurrence interval.

Darner and Dumouchelle (2011) noted that differences 

in the diameter of drain pipes under each bioswale could be 

a contributing factor in the greater number of overflows at 

SR1 as compared to SR2. The north side of the road (SR1) is 

underlain by an 8-in. drain pipe, which discharges to the 15-in. 

pipe on the south side (SR2) of the road, which discharges to 

the storm sewer (fig. 2). A possible explanation for the difference in the number of overflows at SR1 and SR2 is the smaller 

conveyance of the 8-in. pipe versus the 15-in. pipe and possible backwater in pipes on the south side of the road retarding 

pipe flow from north to south.

Changes in overflow frequency over time could result 

from changes in drainage area or rainfall pattern. The drainage 

area of the SCM could be affected by homeowner landscaping activities that increase the drainage area, or increase the 

area of impervious surfaces leading to greater runoff. However, conversations with the local residents indicated that they 

had made no substantial changes to their properties yet they 

observed more standing water in their yards. In spite of those 

observations, Sterncrest Drive had not been closed due to 

flooding, which had occurred frequently before the installation 

of the bioswale (Matt Scharver, Chagrin River Watershed Partners, written commun., 2012). As the anecdotal information 

indicated no substantial changes in drainage area or imperviousness, rainfall patterns were investigated to help explain the 

increase in overflows over time.

Total rainfall measured during April 1–October 31, 2011, 

was much greater than in other years, which apparently drove 

the increase in overflow frequency (fig. 3) for that year. The 

relation between higher-frequency storms with greater overall 

seasonal depth and overflow status is illustrated in figure 3. If 

the data from 2011 are excluded (due to the unusual amount of 

rain), then the number of overflows (even with similar precipitation totals) is increasing year to year (fig. 3).

As noted above, the duration associated with the 0.75 in. 

design storm was not specified. Table 3 lists the percentage 

of rainfall events that equaled or exceeded a total of 0.75 in. 

for selected durations and resulted in overflows at SR1. Not 

surprisingly, overflows occur more frequently when 0.75 in. 

or greater of precipitation occurs over a short duration as 

compared to longer durations. The percentage of overflows 

associated with equaling or exceeding the 0.75 in. design 

depth appears to plateau at around 70 percent for durations 

greater than or equal to 3 hours. In other words, about 

70 percent of rainfall events that produced at least 0.75 in. 

of rain over 3 hours or more resulted in an overflow at SR1. 

At SR1, a rainfall of 1.24 in. over 3 hours has a 1-year average recurrence interval (Bonnin and others, 2004); thus, it 

could be expected that a smaller rainfall—such as 0.75 in. in 

3 hours—is likely to occur more frequently (averaging more 

than once per year). Therefore, the Sterncrest Drive SCM can 

be expected to overflow multiple times a year, a frequency that 

may be too often for the goals of other SCMs designs. However, this system has met the local objectives of street-level 

flood control in a residential neighborhood (Matt Scharver, 

Chagrin River Watershed Partners, written commun., 2012).

As the system continues to age, the number of overflows could increase due, in part, to clogging of bioswale 

surface soils and of the perforations in the pipes with sediment suspended in inflows, which could decrease infiltration 

rates. Also, clogging of the subsurface sediments may result 

in less system-detention capacity. Evidence of clogging could 

be observed in an uneven pattern in percolation, i.e., ponding 

in some areas of the bioswale. With either surficial or subsurface clogging, an increase in overflow frequency may then be 

observed for progressively smaller storms. 
6 Hydrologic Characteristics of Low-Impact Stormwater Control Measures at Two Sites in Northeastern Ohio, 2008–13

Table 1. Rain garden overflow time, duration, and precipitation-event depths, Sterncrest Drive SR1 site, Cuyahoga County, Ohio, 

2008–13.—Continued

[The durations of the precipitation depths are based on the start time of the overflow. Red highlight, greater than or equal to the 10-year precipitation event; 

green highlight, greater than or equal to the 2-year precipitation event; yellow highlight, greater than or equal to the 1-year precipitation event (based on precipitation magnitude and frequency computations by Bonnin and others, 2004)]

Event

Overflow 

characteristics

Precipitation depth (inches)

Maximum for indicated duration 

in prior 24 hours Total for time prior to start of overflow (hours)

Begin date Duration 

(minutes) 10-minute 1-hour 3-hour 12-hour 24 48 72 96

1 5/3/2008 149 0.21 0.44 0.49 0.98 1.00 2.00 2.00 2.04

2 7/8/2008 25 0.81 1.15 1.15 1.15 1.15 1.15 1.15 1.15

3 10/3/2008 116 0.04 0.12 0.25 0.26 0.26 0.72 2.49 3.21

4 7/1/2009 219 0.13 0.25 0.30 0.32 0.37 1.18 1.18 1.22

5 7/17/2009 5 0.64 1.06 1.06 1.07 1.07 1.07 1.07 1.07

6 8/1/2009 157 0.12 0.22 0.35 0.59 0.59 0.59 0.74 0.74

7 8/10/2009 66 0.42 0.74 0.74 0.74 0.74 1.03 1.15 1.15

8 8/29/2009 48 0.30 0.88 0.94 1.46 1.89 1.96 1.99 1.99

9 4/25/2010 69 0.23 0.51 0.51 0.53 1.02 1.02 1.02 1.02

10 5/17/2010 49 0.01 0.05 0.09 0.11 0.11 0.11 0.11 1.13

11 5/31/2010 209 0.39 0.78 0.78 0.89 0.89 0.89 0.89 0.89

12 6/6/2010 161 0.48 0.48 0.74 0.77 0.77 0.92 0.92 0.94

13 6/28/2010 124 0.24 0.44 0.44 0.64 1.08 1.08 1.08 1.08

14 9/16/2010 7 0.46 0.57 0.57 0.86 0.86 0.86 0.86 0.87

15 4/4/2011 800 0.14 0.18 0.37 0.65 0.65 0.65 0.65 0.98

16 4/8/2011 523 0.05 0.23 0.43 0.46 0.46 0.49 0.49 1.97

17 4/16/2011 257 0.05 0.18 0.32 0.55 0.55 0.55 0.55 0.56

18 4/19/2011 1,661 0.03 0.11 0.21 0.32 0.43 0.45 1.03 1.25

19 4/22/2011 1,235 0.05 0.16 0.26 0.40 0.40 0.40 0.99 1.41

20 4/24/2011 231 0.02 0.06 0.13 0.18 0.18 1.20 1.32 1.32

21 4/25/2011 1,164 0.02 0.06 0.13 0.18 0.32 0.39 1.51 1.53

22 5/3/2011 1,246 0.05 0.13 0.15 0.16 0.23 0.36 0.36 0.50

23 5/6/2011 267 0.16 0.31 0.31 0.40 0.40 0.40 0.43 1.18

24 5/14/2011 263 0.11 0.22 0.33 0.53 0.56 0.70 1.22 1.23

25 5/15/2011 321 0.04 0.11 0.15 0.28 0.30 0.91 1.05 1.57

26 5/18/2011 858 0.11 0.11 0.11 0.16 0.27 0.29 0.63 1.22

27 5/23/2011 436 0.20 0.32 0.32 0.44 0.44 0.58 0.58 0.58

28 5/25/2011 2,028 0.41 0.79 0.79 0.79 0.79 1.39 1.83 1.97

29 5/29/2011 234 0.18 0.26 0.26 0.26 0.48 0.48 0.49 2.31

30 6/7/2011 135 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10

31 7/19/2011 391 0.40 0.77 1.10 1.10 1.10 1.10 1.10 1.10

32 7/28/2011 453 0.41 0.50 0.65 1.13 1.13 1.13 1.13 1.13

33 8/1/2011 306 0.35 0.72 0.72 0.72 0.72 0.72 0.73 1.53

34 8/9/2011 29 0.28 0.35 0.54 0.54 0.64 1.04 1.04 1.22

35 8/14/2011 1,569 0.33 0.66 0.66 0.66 0.66 0.66 0.66 0.67

36 8/14/2011 82 0.33 0.78 0.79 1.21 1.21 1.21 1.21 1.21

37 8/15/2011 241 0.33 0.78 0.79 1.35 1.78 1.78 1.78 1.78

38 8/25/2011 167 0.11 0.28 0.34 0.34 0.45 0.45 0.45 0.67
Hydrologic Characteristics at the Sterncrest Drive Site 7

Table 1. Rain garden overflow time, duration, and precipitation-event depths, Sterncrest Drive SR1 site, Cuyahoga County, Ohio, 

2008–13.—Continued

[The durations of the precipitation depths are based on the start time of the overflow. Red highlight, greater than or equal to the 10-year precipitation event; 

green highlight, greater than or equal to the 2-year precipitation event; yellow highlight, greater than or equal to the 1-year precipitation event (based on precipitation magnitude and frequency computations by Bonnin and others, 2004)]

Event

Overflow 

characteristics

Precipitation depth (inches)

Maximum for indicated duration Total for time prior to start of overflow (hours) in prior 24 hours

Duration Begin date (minutes) 10-minute 1-hour 3-hour 12-hour 24 48 72 96

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

9/4/2011

9/10/2011

9/12/2011

9/15/2011

9/20/2011

9/21/2011

9/23/2011

9/26/2011

9/30/2011

10/3/2011

10/13/2011

10/14/2011

10/19/2011

10/20/2011

10/26/2011

10/27/2011

4/30/2012

5/8/2012

6/17/2012

7/5/2012

8/10/2012

9/2/2012

9/4/2012

9/8/2012

10/6/2012

10/27/2012

10/28/2012

4/10/2013

4/24/2013 

4/29/2013

5/31/2013

6/2/2013

6/10/2013

6/13/2013

7/8/2013

7/10/2013

7/10/2013

7/20/2013

187

1,016

173

162

185

226

163

333

1,518

831

216

369

1,000

1,384

439

768

313

263

77

12

6

16

139

103

59

260

6,445

2,840

714

155

36

140

266

54

47

451

421

37

0.24

0.33

0.49

0.07

0.20

0.08

0.08

0.38

0.04

0.03

0.16

0.16

0.05

0.16

0.04

0.04

0.07

0.16

0.05

0.21

0.37

0.42

0.32

0.20

0.05

0.08

0.01

0.16

0.06

0.05

0.25

0.13

0.17

0.29

0.36

0.18

0.68

0.20

0.56

0.38

0.49

0.19

0.37

0.28

0.17

0.39

0.16

0.16

0.44

0.49

0.22

0.34

0.15

0.11

0.07

0.30

0.12

0.27

0.47

0.88

0.56

0.41

0.22

0.18

0.02

0.27

0.20

0.12

0.56

0.28

0.23

0.34

0.51

0.20

0.92

0.47

0.56

0.38

0.49

0.34

0.44

0.28

0.27

0.39

0.23

0.25

0.44

0.91

0.23

0.36

0.27

0.22

0.07

0.37

0.12

0.27

0.50

0.88

0.56

0.83

0.32

0.26

0.04

0.27

0.29

0.15

0.62

0.39

0.28

0.34

0.51

0.23

1.20

0.51

0.57

0.46

0.49

0.68

0.83

0.37

0.39

0.39

0.25

0.25

0.45

1.08

0.36

0.37

0.27

0.28

0.14

0.65

0.14

0.27

0.91

0.88

0.58

0.84

0.63

0.45

0.06

0.50

0.51

0.22

0.62

0.51

0.71

0.34

0.52

0.37

1.78

0.73

0.63

0.46

0.49

0.69

0.88

0.37

0.39

0.78

0.45

0.25

0.48

1.09

0.61

0.49

0.48

0.38

0.14

0.71

0.14

0.27

1.11

0.88

1.13

0.85

0.88

0.46

0.12

0.50

0.51

0.39

0.62

0.52

0.71

0.34

0.87

0.37

2.45

0.73

0.63

0.62

0.86

0.69

0.88

1.28

0.89

0.78

0.45

1.64

0.77

1.41

0.61

1.95

0.48

0.65

0.14

0.71

0.14

0.89

1.69

0.88

1.13

0.86

0.88

0.46

0.73

0.77

0.51

0.41

0.62

1.56

0.71

0.36

1.00

1.19

3.26

0.73

0.63

0.84

2.34

1.42

0.88

1.40

0.97

0.80

0.45

2.35

0.77

1.41

0.65

1.99

0.61

0.65

0.20

0.71

0.14

0.89

1.69

0.88

2.36

0.86

0.88

0.52

0.73

0.77

0.51

0.41

0.62

1.56

0.71

1.35

1.01

1.55

3.62

0.73

0.88

0.97

2.35

1.45

0.88

1.40

1.99

1.22

2.29

2.35

0.77

1.41

0.94

2.00

0.61

0.78

0.20

0.74

0.14

0.91

1.69

0.88

2.36

2.19

1.27

1.70

0.73

0.77

0.52

0.52

1.27

1.56

0.74

1.35

1.16

1.68

3.76

0.73
8 Hydrologic Characteristics of Low-Impact Stormwater Control Measures at Two Sites in Northeastern Ohio, 2008–13

Table 1. Rain garden overflow time, duration, and precipitation-event depths, Sterncrest Drive SR1 site, Cuyahoga County, Ohio, 

2008–13.—Continued

[The durations of the precipitation depths are based on the start time of the overflow. Red highlight, greater than or equal to the 10-year precipitation event; 

green highlight, greater than or equal to the 2-year precipitation event; yellow highlight, greater than or equal to the 1-year precipitation event (based on precipitation magnitude and frequency computations by Bonnin and others, 2004)]

Event

Overflow 

characteristics

Precipitation depth (inches)

Maximum for indicated duration Total for time prior to start of overflow (hours) in prior 24 hours

Duration Begin date (minutes) 10-minute 1-hour 3-hour 12-hour 24 48 72 96

77

78

79

80

81

82

83

7/20/2013

7/23/2013

8/2/2013

9/12/2013

9/21/2013

9/21/2013

10/7/2013

128

52

46

4

49

83

94

0.20

0.38

0.17

0.41

0.11

0.11

0.04

0.62

0.63

0.42

0.65

0.30

0.30

0.17

0.73

0.63

0.51

0.65

0.47

0.47

0.44

1.27

0.63

0.51

0.68

0.78

0.98

0.72

1.27

0.64

0.51

0.73

0.78

0.98

0.72

1.27

0.65

0.62

0.74

0.78

0.98

0.86

1.27

0.65

0.62

0.74

0.78

0.98

1.07

1.27

2.07

0.62

0.74

0.78

0.98

1.08

Table 2. Rain garden overflow time, duration, and precipitation-event depths, Sterncrest Drive SR2 site, Cuyahoga County, Ohio, 

2008–12.

[The durations of the precipitation depths are based on the start time of the overflow]

Event

Overflow 

characteristics

Precipitation depth (inches)

Maximum for indicated duration 

in prior 24 hours

Total for time prior to start of overflow 

(hours)

Begin date Duration 

(minutes)

10-minute 1-hour 3-hour 12-hour 24 48 72 96

1 8/10/2009 15 0.42 1.11 1.11 1.11 1.11 1.39 1.52 1.52

2 4/25/2010 3 0.05 0.17 0.20 0.29 0.29 0.29 0.29 0.29

3 4/25/2010 52 0.05 0.17 0.37 0.51 0.51 0.51 0.51 0.51

4 4/26/2010 8 0.23 0.52 0.55 0.72 0.88 1.23 1.23 1.23

5 5/14/2010 15 0.68 0.70 0.88 0.88 0.94 0.94 1.58 1.58

6 6/6/2010 12 0.48 0.48 0.74 0.77 0.77 0.92 0.92 0.94

7 4/16/2011 2 0.03 0.09 0.15 0.15 0.15 0.15 0.15 0.16

8 4/16/2011 2 0.17 0.23 0.41 0.76 0.79 0.79 0.79 0.79

9 4/21/2011 7 0.02 0.06 0.07 0.11 0.13 0.98 1.14 1.14

10 4/25/2011 8 0.02 0.06 0.13 0.21 0.25 0.48 1.39 1.39

11 6/7/2011 4 0.45 1.26 1.26 1.26 1.26 1.26 1.26 1.26

12 8/6/2011 3 0.12 0.18 0.18 0.18 0.18 0.18 0.19 0.88

13 8/9/2011 34 0.13 0.25 0.25 0.25 0.35 0.75 0.75 0.93

14 9/26/2011 71 0.49 0.87 0.87 0.88 1.27 1.27 1.29 1.71

15 4/21/2012 2 0.03 0.11 0.24 0.33 0.33 0.33 0.33 0.33

16 9/2/2012 15 0.42 0.43 0.43 0.43 0.43 0.43 0.43 0.43

17 9/18/2012 4 0.07 0.16 0.20 0.48 0.50 0.50 0.50 0.51
Hydrologic Characteristics at the Sterncrest Drive Site 9

Cumulative overflow indicator

Cumulative rain

EXPLANATION

50

0

10

20

30

40

Number of overflow occurences at SR1

1/1/2008 1/1/2009 1/1/2010 1/1/2011 1/1/2012 1/1/2013

Date

0

10

20

30

40

50

Rain totals, April 1 to October 31,

 in inches

17

5 7

40

11

3

Figure 3. Cumulative overflow indicator and cumulative rain from April 1 to October 31 of 

each year at the Sterncrest Drive SR1 site, Cuyahoga County, Ohio.

Table 3. Percentage of 0.75 inch or greater rain events that caused an overflow at SR1 with respect to event duration, Sterncrest 

Drive site, Cuyahoga County, Ohio.

[Rain-recurrence interval information from Bonnin and others, 2004]

Rain duration

Number of rain 

events greater than 

or equal to 0.75 inch

Percentage that 

cause on overflow

1-year recurrence 

interval for rain, in 

inches

Number of 1-year 

recurrence interval 

rain events that 

occurred 

April–October 

2008–13

Number of times the 

1-year recurrence 

interval rain event 

caused an overflow

10-minute 1 100 0.50 5 4

30-minute 14 93 0.81 9 8

60-minute 18 83 0.99 7 7

2-hour 28 79 1.16 4 4

3-hour 37 70 1.24 5 5

6-hour 47 70 1.49 5 5

12-hour 70 63 1.75 5 3

24-hour 81 68 2.04 4 3

48-hour 90 71 2.36 3 2

3-day 89 71 2.70 4 3

4-day 93 72 3.27 9 6
10 Hydrologic Characteristics of Low-Impact Stormwater Control Measures at Two Sites in Northeastern Ohio, 2008–13

Hydrologic Characteristics at the 

Washington Street Site

The SCM at the Washington Street site consists of several 

elements that act in series to reduce runoff to receiving waters. 

Additional information on the site description, construction 

details, and methods are presented in Darner and Dumouchelle 

(2011). Precipitation and runoff data were collected at this site 

from April through September or October 2008–13.

Site Description and Methods

In 2008, the Washington Street site was undergoing construction of a commercial building and associated parking lot. 

The construction followed Leadership in Energy and Environmental Design (U.S. Green Building Council, 2014) principles 

to minimize stormwater runoff and conserve natural resources, 

all while maintaining an aesthetically pleasing appearance. 

The SCM features at the site include a rain garden, paver 

parking lot that is permeable (hereafter called pervious pavers) 

with surface and subsurface drains, a detention basin, and a 

vegetated swale (fig. 4). About one-half of the runoff from the 

roof of the building is directed to the rain garden; the remaining roof runoff drains to the swale (Darner and Dumouchelle, 

2011). 

Discharge from the pervious-paver subsurface drains 

(flume 3), overland flow from the parking lot (flume 1), and 

overflow from the rain garden (flume 2) (fig. 4) were determined by means of prefabricated H-flumes (fig. 5). Water 

levels in the flumes were measured in attached external 

stilling wells by means of pressure transducers connected to 

data loggers that initiated and stored the water-level readings. 

Water levels were measured every minute and, at a minimum, 

recorded every 10 minutes. When the stage exceeded 0.05 ft 

above no flow, any change in water level of more than 0.01 ft 

also was recorded. The corresponding specific conductance 

and water temperature were stored with each coincident waterlevel reading.

A weather station that included a heated tipping-bucket 

rain gage and an air-temperature sensor was maintained at the 

site (fig. 4). The rain gage registered precipitation in 0.01-in. 

increments, summed by the data logger over intervals of 

10 minutes. Precipitation depths and peak intensities for 

10-, 30-, 60-, 120-, and 1,440-minute intervals were determined 

for each precipitation event and compared to recurrence intervals determined from the tables in Bonnin and others (2004).

During construction of the parking lot, two clusters of 

three time-domain reflectometer (TDR) sensors were permanently installed in the permeable base under the pavers. 

The TDR determines soil-moisture content by measuring 

the permittivity, or dielectric constant, of the soil resulting 

from changes in soil moisture. Sensors in each cluster were 

installed at different depths (Darner and Dumouchelle, 2011, 

table 5) below the ground surface to facilitate analysis of the 

depth-dependent wetting characteristics of the permeable base 

material above the subsurface drains. The TDRs were controlled by a data logger that computed and recorded moisture 

content every 10 minutes.

Rain-event and runoff-event characteristics were compared using centroid lag time. Centroid lag time is defined 

as the time, in minutes, between the centroid of precipitation 

and the centroid of the flume flow (runoff). Centroid lag time 

is a measure of how quickly water moves off or through the 

impervious surfaces and other drainage routes to the discharge points. See Darner and Dumouchelle (2011) for a more 

detailed explanation.

Data Analysis and Interpretation

Data from this site were analyzed for April–October 2009 

and 2010 and were presented in Darner and Dumouchelle 

(2011). Additional data were collected from April 1, 2011 

through September or October 2011. During the entire period, 

no measurable runoff was recorded in flume 1 (which measures surface runoff from the pervious pavers) indicating all 

precipitation that fell on the parking lot was either infiltrated 

or lost to evaporation. The runoff data from flume 2 were 

included with the data from flume 3 to represent the total 

runoff from the site.

Rainfall metrics were used to capture the temporal 

dynamics of storm events and how these might have affected 

runoff processes. These metrics include the event rainfall 

depth, which was the amount of rain that fell during individual 

runoff events; and Rainws, which is defined as the depth of rain 

that fell over the warm-season of a given year (starting April 1 

and ending October 31). In Darner and Dumouchelle (2011), 

the reduction in runoff was evaluated using a runoff ratio 

(RR) and the delay in runoff was evaluated using centroid 

lag time; detailed descriptions of the derivation and basis for 

these metrics are described in the earlier report (Darner and 

Dumouchelle, 2011). 

The RR at this site was defined as the total volume of 

runoff divided by the total volume of rain that fell on the roof 

and parking lot, and is the complement of percent removal, 

although the RR is not expressed as a percentage. The RR 

characterizes each runoff event with a number between 0 and 

1. The closer the RR is to 0 or the percent removal to 100, the 

greater the amount of runoff removed through evapotranspiration (ET) or infiltration. In this report, the percent removal 

is used to quantify the proportion of runoff that the SCM 

detained or otherwise prevented from flowing to receiving 

waters as direct runoff. The percent removal is defined as 

the volume of water removed from the runoff through ET, 

infiltration, or other losses within the treatment system and is 

described by

percent removal = ∗ V V in − out Vin 100 ( ) / (1)

where

Vin is the volume of water from rain, and

Vout is the volume of water leaving the SCM.
4" PVC SUBDRAIN

4" PVC DRAIN

6" PVC DRAIN

6" PVC INLET 6" PVC DRAIN.

FOR OVERFLOW

OUTFLOW TO

BIO-RETENTION BASIN

A

B

WEATHER STATION

SWALE

BIORETENTIONBASIN

BUILDING

RAIN

GARDEN

STORM OUTLET PIPE

FROM DOWNSPOUTS

EXISTING PARKING

OUTLET

STRUCTURE

Porous pave

Rain garden overflow pipe  and flow direction

Downspout

Time domain reflectometry cluster

Land-surface  interval 1 f

Flume

Features are proportional butprecise dimensions are unknown

Paver parking drain  and flow direction

Downspout p and flow d

B

Site boundar

EXPLANATION

FLUME 3

FLUME 1

FLUME 2

Figure 4. Schematic site plan for stormwater best-management practices at the Washington Street site, Geauga County, Ohio.
12 Hydrologic Characteristics of Low-Impact Stormwater Control Measures at Two Sites in Northeastern Ohio, 2008–13

B. Flume 2

A. Flume 1

C. Flume 3

Figure 5. Three flumes at the Washington Street site, Geauga County, Ohio. A, Flume 1 

measures surface flow over the parking lot. B, Flume 2 measures any overflow from the 

rain garden. C, Flume 3 measures the flow from the drain line. 
Hydrologic Characteristics at the Washington Street Site 13

Standard statistical techniques were used to perform 

exploratory data analysis, analysis of variance, and correlation 

on datasets that include volume, soil moisture, precipitation 

totals and duration, and lag times. An alpha level of 0.05 was 

used in all tests of statistical significance. 

Rain events with totals less than 0.2 in. were excluded 

from the analysis. There were few rain events with depths less 

than 0.2 in. (6 percent in 2010, 10 percent in 2011, 7 percent 

in 2012, and 7 percent in 2013). The instrumentation used 

to measure stage in the flumes was not sensitive enough to 

measure the runoff from rainfall events less than 0.2 in. All 

rain events less than or equal to 0.20 were dropped from the 

analysis because their impact on discharge cannot be accurately measured. However, it is important to note even small 

rain events may have acted to increase soil moisture content 

and subsequently reducing infiltration capacity. This would 

potentially lead to shorter centroid lag times due to reduced 

infiltration capacity in the system, which may be manifested as 

a decrease in the percent reduction for the next rain event.

The Washington Street SCM is intended to reduce and 

(or) delay the runoff from the building and parking lot. Figure 

6 is a boxplot of percent removal and bar graph of Rainws by 

year. The mean amount of rain for the northeast region of Ohio 

for the months of April–October is 24.19 in. (National Oceanic 

and Atmospheric Administration, 2002). Rainws for 2011 was 

43.74 in., an increase of nearly 45 percent over average. The 

amount of Rainws in 2011 was greater than in any of the other 

years such that the 2011 value of Rainws was 93 percent of 

the average annual precipitation for this area of Ohio (Midwestern Regional Climate Center, 2010). The median percent removal in 2009 was slightly less than 25 percent with 

two outliers indicating episodically high detention of runoff 

volume (fig. 6). While the Rainws in 2010 was similar to 2009, 

the median percent removal increased to nearly 60 percent. In 

2011, the amount of Rainws was nearly twice that of 2009 and 

2010. An analysis of variance shows that the mean percent 

removal in 2011 was different than in 2010 (results in appendix 1), and the notched intervals for 2009, 2010, and 2011 

do not overlap indicating that the medians are significantly 

different at the 95-percent confidence level. The annual mean 

percent removal for 2010–13 ranged from 55 to 37 percent, 

with an overall mean of 45 percent. Darner and Dumouchelle 

(2011) stated that differences in runoff volume and lag times 

(discussed later) observed in 2009 as compared to 2010 might 

have been due to changes related to the establishment of the 

plants in the rain garden (overcoming the shock of transplantation, increasing root and foliage mass, and generally adapting 

to new environmental conditions), development of preferential 

flow paths, and (or) differing weather conditions. 

20

25

30

35

40

Rain total, in inches

45

2009 2010 2011 2012 2013

100

Percent removal

80

60

40

20

0 24.50 Rain total, April–October

31 Number of values 

EXPLANATION 

Largest value—greater than or equal 

to 1.5 times the IQR above the box

75th percentile

Median

25th percentile

Outlier

Interquartile 

range (IQR)

Mean

Largest value—less than or equal 

to 1.5 times the IQR below the box

Notch height 

(95-percent 

confidence interval 

for median)

Year

28 31 44 27 26

23.95 24.50 43.74 29.71 29.69

Figure 6. Percent removal and bar graph showing the depth of rain starting April 1 and ending October 31, by year, at the Washington 

Street site, Geauga County, Ohio.
14 Hydrologic Characteristics of Low-Impact Stormwater Control Measures at Two Sites in Northeastern Ohio, 2008–13

Rainfall dynamics, described by rain event totals, durations, and intensities affect the runoff characteristics at the site 

but with only 2 years of data in the original study (Darner and 

Dumouchelle, 2011) no such analysis could be performed. 

With additional data from 2011–13, it was possible to examine correlations between percent removal and Rainws to help 

assess whether changes in percent removal likely were due 

to changes in the SCM itself, or instead due to differences in 

rainfall pattern. Figure 7 shows boxplots for the rain-event 

total rainfall, rain-event duration, and percent removal for 

2010–13. The range in totals (fig. 7A) and duration of the 

individual rain events (fig. 7B) were similar from year to year. 

The rain events in 2011, while neither larger nor longer than 

the other years, were more frequent, which reduced the time 

between events for water to move through the SCM; thus, 

while there is a trend in decreasing percent removal, there was 

an increase from 2011 to 2012 (fig. 7C).

0

20

40

60

80

100

Percent removal

31 44 27 26

0

0.5

1.0

1.5

2.0

2.5

Rain event total, in inches

31 44 27 26

2010 2011 2012 2013

0

20

40

60

80

Rain event duration, in hours

31 44 27 26

2010 2011 2012 2013

Year

2010 2011 2012 2013

Year Year

A B

C

31 Number of values 

EXPLANATION 

Largest value—greater than or equal 

to 1.5 times the IQR above the box

75th percentile

Median

25th percentile

Outlier

Interquartile 

range (IQR)

Mean

Largest value—less than or equal 

to 1.5 times the IQR below the box

Notch height 

(95-percent 

confidence interval 

for median)

Figure 7. Climatological and flow characteristics, Washington Street site, Geauga County, Ohio, 2010–13. A, Rain-event total 

rainfall. B, Rain-event duration. C, Percent removal.
Hydrologic Characteristics at the Washington Street Site 15

Correlations (as indicated by Spearman’s rank correlation coefficient) between percent removal and event rain 

total; event duration; rainfall in the previous 24, 48, 96, and 

240 hours; and maximum event rainfall for 10-, 20-, 30-, and 

60-minute intervals are summarized in table 4. Also included 

is a term to account for the large-scale differences in total 

annual rainfall from year to year. The term is calculated as per

LOG PN Event Rain Rainws _ l = ∗ og10( ) (2)

LOG_PN is a cross-product term that weighs event total rain 

depth as a function of the seasonal total rain depth and will 

normalize each rain event by the total rain for the year. 

During 2010–13, the rain total and LOG_PN are significantly correlated to percent removal, indicating that percent 

removal is not independent of rainfall characteristics. The 

amount of rain in different time periods preceding the overflow was generally not significantly correlated to percent 

removal, and the maximum rain totals during overflows were 

only significantly correlated in 2011 (for 60-minute maximum 

totals) and 2012 (for 20-, 30-, and 60-minute maximum totals). 

In 2009, only rain duration was significantly correlated with 

percent removal, and in all other years there were at least three 

rain characteristics that were significantly correlated to percent 

removal (table 4). The difference in correlations plus the lower 

percent reduction and the presence of outliers (fig. 6) indicates 

that 2009 was an establishment year; therefore, the data from 

2009 are presented for completeness, but have been excluded 

from further analyses.

The effect of the rain total on percent removal also 

can be seen in plots of the data (fig. 8). In every year, as the 

event totals increase, the percent removal decreases. While 

it appears in figure 8A that the slope in 2010 is different, it 

is statistically the same as the other years at the 95-percent 

confidence interval (data not shown). It is interesting to note 

that the slopes are similar between the years indicating that the 

relation between rain-event size and percent-removal decline 

is consistent over time. The decline in percent removal from 

year to year can be observed on these plots by the decrease in 

the y-intercepts from 2010 to 2013.

To assess whether factors other than rain totals were 

associated with observed changes in percent removal over the 

4 years, a linear regression was done to remove the variance 

in percent removal associated with rainfall totals (results in

appendix 1, section B) and LOG_PN (results in appendix 1, 

section C). The regression with rain total, while significant, 

only explains about 25 percent of the variance in percent 

removal. The regression of LOG_PN only explains about 35 

percent of the variance in percent removal but when other rain 

characteristics were added as part of a multiple linear regression (MLR), the results did not improve (results of MLR not 

shown). The residuals (observed minus predicted values) from 

the linear regression of percent removal as the dependent 

variable and LOG_PN as the independent variable represent 

percent removal with the effects of LOG_PN removed, and 

boxplots of the residuals by year (fig. 9) show a declining percent removal over time. Analysis of variance of the residuals 

indicated that there was indeed a significant decline in percent 

removal from 2010 to 2013 and from 2012 to 2013 (results in 

appendix 1, section C). 

Table 4. Spearman correlations of percent removal to measure antecedent conditions and rain intensity for events with total rainfall 

greater than or equal to 0.2 inches at the Washington Street site, Geauga County, Ohio.

[Green text indicates statistical significance at alpha < 0.05; Rainws, depth of rain from April 1 to October 31 in any given year] 

2009 2010 2011 2012 2013 2010–13

Duration (hours) −0.40 −0.30 −0.19 −0.07 −0.47 −0.32

Total rain (inches) −0.32 −0.48 −0.47 −0.56 −0.53 −0.38

1

P24 0.13 0.03 −0.02 −0.14 0.16 0.10

1

P48 0.18 −0.04 0.09 0.21 0.15 0.08

1

P96 0.03 −0.10 0.01 0.04 0.04 0.05

1

P240 −0.03 −0.43 0.11 0.14 −0.41 −0.06

2

X10 −0.17 −0.15 −0.14 −0.35 −0.12 −0.05

2

X20 −0.16 −0.18 −0.22 −0.42 −0.12 −0.08

2

X30 −0.22 −0.24 −0.29 −0.49 −0.10 −0.10

2

X60 −0.19 −0.26 −0.36 −0.56 −0.04 −0.15

LOG_PN3 −0.32 −0.48 −0.47 −0.56 −0.53 −0.34

1

P# is the amount of rain in #-hour period preceding the event, in inches.

2

X# is the maximum #-minute rain total for the event, in inches.

3

Log10 (Event Rain/Rainws).
16 Hydrologic Characteristics of Low-Impact Stormwater Control Measures at Two Sites in Northeastern Ohio, 2008–13

2010

2011

2012

2013

EXPLANATION

Total rain, in inches

0 0.5 1.0 1.5 2.0 2.5

0

100

80

60

40

20

Percent of inflow removed

A

0

100

80

60

40

20

Percent of inflow removed

B

0.5 1.0 1.5 2.0

Log10 of the product of event rain total and season rain total

Figure 8. Scatter plots and fit linear least-squares lines for 2010–13, Washington Street site, 

Geauga County, Ohio. A, Percent removal and rain event total. B, Percent removal and log10 of 

the product of event rain total and season rain total.
Hydrologic Characteristics at the Washington Street Site 17

40

20

–40

–20

0

31 39 25 24

2010 2011 2012 2013

Residuals from regression

regression equation Percent Removal=–31.3 x log10(Event Rain x (total rain April to October)) + 85.6

Year

31 Number of values 

EXPLANATION 

Largest value—greater than or equal 

to 1.5 times the IQR above the box

75th percentile

Median

25th percentile

Outlier

Interquartile 

range (IQR)

Mean

Largest value—less than or equal 

to 1.5 times the IQR below the box

Notch height 

(95-percent 

confidence interval 

for median)

Figure 9. Percent removal residuals, by year, at the Washington Street site, Geauga County, Ohio.

Declines in percent removal over time could result 

from increased runoff due to clogging of the gravel substrate 

that underlies the pervious-paver system. Although it is not 

possible to determine if any clogging has occurred without 

removing the pavers, the data from the soil-moisture sensors 

may indicate that fine-grained sediments could be collecting in parts of the pervious-paver system. Increases in soil 

moisture recorded by the sensors in the gravel under the pavers may indicate that sediments are collecting in pore spaces 

and impeding infiltration of water through the gravel layer, 

because fine-grain sediments retain water better than coarsegrain gravels. Figure 10 shows the baseline (soil-moisture 

value the hour before rain started) data from the soil-moisture 

sensors. The baseline moisture in cluster A does not change 

much over the years. In cluster B, there is a rise in the baseline 

moisture in the shallowest sensors indicating that fines collect 

above a depth of 2.7 ft in the system near cluster B. Cluster B 

is located (fig. 4) in the lower (downgradient) portion of the 

parking lot where fines that are carried in sheet flow over the 

pavers would tend to settle and collect. 

The Washington Street SCM not only increases the 

immediate removal of runoff through infiltration into pervious 

pavers and soils that underlay the rain garden, but also delays 

the onset of runoff. The delay in runoff can be examined by 

comparing the temporal dynamics of runoff and its duration. 

Antecedent moisture conditions affect the time between the 

onset of rainfall and discharge from the SCM; therefore, the 

centroid of the rain event and centroid of the resulting runoff 

were used to normalize the effect of antecedent conditions, 

rain intensity, and duration. The centroid lag time is the 

time, in minutes, between the centroid of precipitation and 

the centroid of flume flow (runoff). The centroid lag time is 

an indicator of how long it takes for rain to pass through the 

SCM. With the exception of 2011, the median centroid lag was 

generally between 280 and 320 minutes, and there is no apparent trend to the centroid lag times (fig. 11A). Lag time typically will change as a function of the duration of the rainfall 

event. All other things being equal, as the duration of a rain 

event increases, so does the centroid lag time. Any observed 

trends in lag times may merely reflect trends in the duration 

of rainfall events. Consequently, to adjust for the rain duration 

effect, centroid lag times were normalized by rain durations 

(fig. 11B). Normalizing the lag times by the duration of the 

rain events indicates that differences in rain patterns over the 

years affected the centroid lag times; the median normalized 

lag time is similar for all 4 years (0.55, 0.52, 0.54, and 0.47 for 

2010–13, respectively). The duration of rain events in 2011 is 

the determining factor in why the lag times were significantly 

longer than the other years. 
18 Hydrologic Characteristics of Low-Impact Stormwater Control Measures at Two Sites in Northeastern Ohio, 2008–13

6

5

4

3

2

1

0

8

6

4

2

0

6

5

4

3

2

1

0

10

8

6

4

2

0

5

4

3

2

1

10.0

7.5

5.0

2.5

0

26 51 38 28 23 51 38 28

25 33 38 28 25 51 38 28

24 27 38 29 26 51 38 28

Year

Soil moisture, in percent

Cluster A Cluster B

31 Number of values 

EXPLANATION 

Largest value—greater than or equal 

to 1.5 times the IQR above the box

75th percentile

Median

25th percentile

Outlier

Interquartile 

range (IQR)

Mean

Largest value—less than or equal 

to 1.5 times the IQR below the box

Notch height 

(95-percent 

confidence 

interval for 

median)

2010 2011 2012 2013 2010 2011 2012 2013

A. 1.3 ft D. 1.5 ft

B. 1.5 ft E. 1.7 ft

C. 2.8 ft F. 2.7 ft

Figure 10. Baseline moisture in soil-moisture sensors, Washington Street site, Geauga County, Ohio, 2010–13.
Hydrologic Characteristics at the Washington Street Site 19

0

5

10

15

20

25

Centoid-lag time / rain event duration

31 44 18 26

Year

2010 2011 2012 2013

0

250

500

750

1,000

1,250

Centoid-lag time, in miuntes

31 44 18 26

A

B

31 Number of values 

EXPLANATION 

Largest value—greater than or equal 

to 1.5 times the IQR above the box

75th percentile

Median

25th percentile

Outlier

Interquartile 

range (IQR)

Mean

Largest value—less than or equal 

to 1.5 times the IQR below the box

Notch height 

(95-percent 

confidence interval 

for median)

Figure 11. Precipitation-runoff centroid lag times for the Washington Street site, Geauga County, Ohio, 

2010–13. A, In minutes. B, Rain event duration.
20 Hydrologic Characteristics of Low-Impact Stormwater Control Measures at Two Sites in Northeastern Ohio, 2008–13

As has been discussed, the data show that the percent 

removal has been declining over time at the Washington Street 

SCM. The behavior of the rain garden and the pervious-paver 

system of the SCM can be investigated by examining the data 

from flumes 2 and 3 (fig. 4). The volume of water that overflowed the rain garden (flume 2) was similar for 2010, 2012, 

and 2013 but was more than 2.5 times greater in 2011 (fig. 12). 

The larger volume of water in flume 2 in 2011 is not extraordinary, given the greater rainfall in 2011 and the smaller demand 

for water by the plants (i.e., less transpiration). Likewise, 

volumes through flume 3 were highest in 2011; however, the 

volume of water that drained from the pervious-paver system 

(flume 3) increased from 2010, to 2012 and 2013. Thus, the 

flume data indicate that the decline in the percent removal of 

the SCM is a function of the pervious-paver system; however, 

the exact cause is not known. Although the runoff increased 

(percent removal decreased) over time, the lag time remained 

fairly constant over time and therefore more water (runoff) 

moved through the system in roughly the same time, indicating that preferential flow paths have likely developed within 

the SCM.

2010 2011 2012 2013

Year

0

100

200

300

400

10,000

15,000

20,000

25,000

30,000

35,000

40,000

Total volume, in cubic feet

Flume2

Flume3

EXPLANATION

Figure 12. Total flow through flumes 2 and 3 for April–October 2010–13 at the Washington Street 

site, Geauga County, Ohio.
References Cited 21

Summary and Conclusions

The movement of water through retrofit low-impact 

development (LID) system installations was monitored at two 

sites in suburban areas of the greater Chagrin River watershed. 

Selected metrics were used to document LID system performance with regard to stormwater-volume management objectives at each site. Rain-garden overflow frequency data from 

the Sterncrest Drive site were used to characterize system performance relative to rainfall patterns, and to highlight certain 

design features that may restrict flow in the stormwater-control 

measures (SCM). Overflows at the site generally increased 

during the study; however, some of this increase was due to 

increases in the total precipitation in some years, specifically 

2011. The small drainage pipes (8-in.) on the north side of 

Sterncrest Drive likely played a role in the greater number of 

overflows at SR1 as compared to SR2. Although the storm 

duration associated with the 0.75 inch (in.) design storm was 

not specified, approximately 70 percent of the storms equaling or exceeding 0.75 in. over 3 hours or more resulted in 

an overflow at SR1. Clogging of the surface or subsurface 

sediments of the SCM could account for some of the increases 

in overflows; however, the pipes were not excavated to verify 

clogging. Overall, monitoring data and local observations 

demonstrate the continued success of the SCM in preventing 

roadway closure due to flooding through the warm season of 

2013. If clogging is the primary factor for increasing overflow, 

then the system may be inadequate to meet local objectives of 

reduced street flooding in future years. Additional monitoring 

would help to quantify the SCM functionality over time. 

The additional years of data collected at the Washington 

Street site illustrate the importance of longer-term monitoring 

in order to understand system dynamics and avoid premature 

conclusions. In the initial analysis of 2 years of data (2009–10) 

from the SCM at the Washington Street site, an increase in 

the percent removal (decrease in runoff) and a decrease in 

lag times (faster runoff) was observed; however, based on the 

additional data from 2011–13, it seems likely that the first year 

(2009) was an establishment year for the system. The analysis 

of the additional years of data also show that, while variations 

in rainfall may have an impact in any single year, it appears 

that system performance with respect to runoff removal is 

decreasing; however, the lag time between the centroid of 

precipitation and runoff remained fairly constant. The combination of decreased removal of runoff and no change in the 

timing of runoff production may be due to the development of 

preferential flow paths (short circuits) within the system. The 

SCM at the Washington Street site was designed to reduce and 

(or) delay runoff and it is still meeting those goals despite a 

decrease in the reduction of runoff over time. Similar to the 

SCM at the Sterncrest Drive site, additional monitoring at this 

site would help to establish the SCM functionality over time, 

specifically the pervious-paver component. 

References Cited

Ahern, J., 2007, Green infrastructure for cities—The spatial 

dimension, in Cities of the future towards sustainable water 

and landscape management, Novotny V., and Brown, P., eds.: 

London, IWA Publishing, p. 267–283.

Bonnin, G.M.; Martin, Deborah; Lin, Bingzhang; Parzybok, 

Tye; Yekta, Michael; and Riley, David, 2004, Precipitationfrequency atlas of the United States: Silver Spring, Md., 

National Oceanic and Atmospheric Administration, National 

Weather Service, NOAA Atlas 14, v. 2, ver. 3, accessed 

September 19, 2014, at http://www.nws.noaa.gov/oh/hdsc/

currentpf.htm.

Booth, D.B., and Jackson, C.R., 1997, Urbanization of 

aquatics—Degradation thresholds, stormwater detention, 

and limits of mitigation: Journal of the American Water 

Resources Association, v. 33, p. 1077–1090.

Darner, R.A., and Dumouchelle, D.H., 2011, Hydraulic characteristics of low-impact development practices in northeastern Ohio, 2008–2010: U.S. Geological Survey Scientific 

Investigations Report 2011–5165, 19 p.

Dietz, M.E., 2007, Low impact development practices—A 

review of current research and recommendations for future 

directions: Water, Air, and Soil Pollution, v. 186, no. 1–4, 

p. 351–363.

Fletcher, T.D.; Shuster, William; Hunt, W.F.; Ashley, Richard; 

Butler, David; Arthur, Scott; Trowsdale, Sam; Barraud, 

Sylvie; Semadeni-Davies, Annette; Bertrand-Krajewski, 

Jean-Luc; Mikkelsen, P.S.; Rivard, Gilles; Uhl, Mathias; 

Dagenais, Danielle; and Viklander, Maria, 2014, SUDS, 

LID, BMPs, WSUD and more—The evolution and application of terminology surrounding urban drainage: Urban 

Water Journal, DOI: 10.1080/1573062X.2014.916314, 

accessed August 12, 2014, at http://www.tandfonline.com/

doi/full/10.1080/1573062X.2014.916314.

Jagucki, M.L., and Darner, R.A., 2001, Ground-water 

quality in Geauga County, Ohio; review of previous studies, 

status in 1999, and comparison of 1986 and 1999 data: 

U.S. Geological Survey Water-Resources Investigations 

Report 01–4160, 61 p.

Midwestern Regional Climate Center, 2010, Station 331657 

Cleveland Hopkins, and station 331458 Chardon, accessed 

December 30, 2010, at http://mrcc.isws.illinois.edu.

Musgrave, D.K., and Holloran, D.M., 1980, Soil survey of 

Cuyahoga County, Ohio: U.S. Department of Agriculture, 

Soil Conservation Service, 157 p., 64 sheets.
22 Hydrologic Characteristics of Low-Impact Stormwater Control Measures at Two Sites in Northeastern Ohio, 2008–13

National Oceanic and Atmospheric Administration, 2002, 

Climatography of the United States, no. 85, Divisional 

normals and standard deviations of temperature, precipitation, and heating and cooling degree days 1971–2000 (and 

previous normals periods), accessed December 15, 2014, at

http://www.ncdc.noaa.gov/climatenormals/clim85/

CLIM85_PRCP02.pdf.

U.S. Green Building Council, 2014, LEED (Leadership in 

Energy & Environmental Design) USGBC Web page, 

accessed December 2014 at http://www.usgbc.org/leed.

Williams, N.L., and McCleary, F.E., 1982, Soil survey of 

Geauga County, Ohio: U.S. Department of Agriculture, Soil 

Conservation Service, 169 p., 56 sheets.
Appendix 1. Statistical Output 23

Appendix 1. Statistical Output

Section A. Statistical difference of means of percent removal using the Tukey-Kramer test 

at the Washington Street site, Geauga County, Ohio, 2010–13.

24

Appendix 1. Statistical Output

Section A. Statistical difference of means of percent removal using the Tukey-Kramer test at the 

Washington Street site, Geauga County, Ohio, 2010–13.

 Comparisons significant at the 0.05 level are indicated by ***.

 Difference

 YEAR Between Simultaneous 95%

 Comparison Means Confidence Limits

 2010 - 2012 6.039 −2.706 14.783

 2010 - 2011 12.420 4.630 20.209 ***

 2010 - 2013 15.134 6.300 23.968 ***

 2010 - 2009 28.173 19.513 36.834 ***

 2012 - 2010 −6.039 −14.783 2.706

 2012 - 2011 6.381 −1.740 14.502

 2012 - 2013 9.095 −0.033 18.223

 2012 - 2009 22.135 13.175 31.095 ***

 2011 - 2010 −12.420 −20.209 −4.630 ***

 2011 - 2012 −6.381 −14.502 1.740

 2011 - 2013 2.714 −5.503 10.931

 2011 - 2009 15.754 7.723 23.784 ***

 2013 - 2010 −15.134 −23.968 −6.300 ***

 2013 - 2012 −9.095 −18.223 0.033

 2013 - 2011 −2.714 −10.931 5.503

 2013 - 2009 13.040 3.992 22.087 ***

 2009 - 2010 −28.173 −36.834 −19.513 ***

 2009 - 2012 −22.135 −31.095 −13.175 ***

 2009 - 2011 −15.754 −23.784 −7.723 ***

 2009 - 2013 −13.040 −22.087 −3.992 ***
24 Hydrologic Characteristics of Low-Impact Stormwater Control Measures at Two Sites in Northeastern Ohio, 2008–13

Section B. Output for the linear model percent removal and total rain at the Washington Street site, 

Geauga County, Ohio, 2010–13.

25

Section B. Output for the linear model percent removal and total rain at the Washington Stre

Geauga County, Ohio, 2010–13.

 The REG Procedure

 Model: MODEL1

 Dependent Variable: PREMOVE PREMOVE

 Number of Observations Read 128

 Number of Observations Used 128

 Analysis of Variance

 Sum of Mean

 Source DF Squares Square F Value Pr > F

 Model 1 7476.65137 7476.65137 42.34 <.0001

 Error 126 22250 176.58651

 Corrected Total 127 29727

 Root MSE 13.28859 R-Square 0.2515

 Dependent Mean 44.88049 Adj R-Sq 0.2456

 Coeff Var 29.60883

 Parameter Estimates

 Parameter Standard

 Variable Label DF Estimate Error t Value Pr > |t|

 Intercept Intercept 1 56.97196 2.19834 25.92 <.0001

 RAINTOT RAINTOT 1 −16.32357 2.50865 −6.51 <.0001
Appendix 1. Statistical Output 25

 

 The GLM Procedure

 Tukey's Studentized Range (HSD) Test for R

 NOTE: This test controls the Type I experimentwise error rate.

 Alpha 0.05

 Error Degrees of Freedom 124

 Error Mean Square 147.1613

 Critical Value of Studentized Range 3.68291

 Comparisons significant at the 0.05 level are indicated by ***.

 Difference

 YEAR Between Simultaneous 95%

 Comparison Means Confidence Limits

 2010– - 2012 5.790 −2.526 14.106

 2010– - 2011 12.081 4.673 19.489 ***

 2010– - 2013 14.709 6.307 23.110 ***

 2012– - 2010 −5.790 −14.106 2.526

 2012– - 2011 6.290 −1.433 14.014

 2012– - 2013 8.918 0.238 17.599 ***

 2011– - 2010 −12.081 −19.489 −4.673 ***

 2011– - 2012 −6.290 −14.014 1.433

 2011– - 2013 2.628 −5.187 10.442

 2013– - 2010 −14.709 −23.110 −6.307 ***

 2013– - 2012 −8.918 −17.599 −0.238 ***

 2013– - 2011 −2.628 −10.442 5.187

> return to page 15
26 Hydrologic Characteristics of Low-Impact Stormwater Control Measures at Two Sites in Northeastern Ohio, 2008–13

Section C. Output for the linear model percent removal and LOG_PN at the Washington Street site, 

Geauga County, Ohio, 2010–13.

27

Section C. Output for the linear model percent removal and LOG_PN at the Washington Street 

Geauga County, Ohio, 2010–13.

 The REG Procedure

 Model: MODEL1

 Dependent Variable: PREMOVE PREMOVE

 Number of Observations Read 128

 Number of Observations Used 128

 Analysis of Variance

 Sum of Mean

 Source DF Squares Square F Value Pr > F

 Model 1 10443 10443 68.24 <.0001

 Error 126 19284 153.04396

 Corrected Total 127 29727

 Root MSE 12.37109 R-Square 0.3513

 Dependent Mean 44.88049 Adj R-Sq 0.3462

 Coeff Var 27.56453

 Parameter Estimates

 Parameter Standard

 Variable Label DF Estimate Error t Value Pr > |t|

 Intercept Intercept 1 85.60583 5.04995 16.95 <.0001

loged 1 −31.30854 3.79016 −8.26 <.0001

 
Appendix 1. Statistical Output 27

The GLM Procedure

 Tukey's Studentized Range (HSD) Test for R

 NOTE: This test controls the Type I experimentwise error rate.

 Alpha 0.05

 Error Degrees of Freedom 124

 Error Mean Square 140.212

 Critical Value of Studentized Range 3.68291

 Comparisons significant at the 0.05 level are indicated by ***.

 Difference

 YEAR Between Simultaneous 95%

 Comparison Means Confidence Limits

 2010– - 2012 2.500 −5.617 10.618

 2010– - 2011 4.233 −2.998 11.464

 2010– - 2013 11.197 2.996 19.397 ***

 2012– - 2010 −2.500 −10.618 5.617

 2012– - 2011 1.732 −5.806 9.271

 2012– - 2013 8.696 0.223 17.169 ***

 2011– - 2010 −4.233 −11.464 2.998

 2011– - 2012 −1.732 −9.271 5.806

 2011– - 2013 6.964 −0.664 14.592

 2013– - 2010 −11.197 −19.397 −2.996 ***

 2013– - 2012 −8.696 −17.169 −0.223 ***

 2013– - 2011 −6.964 −14.592 0.664

> return to page 15
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For more information concerning the research in this report 

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Darner and others—Hydrologic Characteristics of Low-Impact Stormwater Control Measures at Two Sites in Northeastern Ohio, 2008–13—Scientific Investigations Report 2015–5030

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20155030