The runoff reduction method

11
UCOWRJournal of Contemporary Water Research & Education
Universities Council on Water Resources
Journal of Contemporary Water Research & Education
Issue 146, Pages 11-21, December 2010
The Runoff Reduction Method
Joseph Battiata, Kelly Collins, David Hirschman, and Greg Hoffmann
Center for Watershed Protection, Mechanicsville, VA
11
Abstract: The Runoff Reduction Method (RRM) provides an innovative approach to crediting the total
performance of stormwater best management practices (BMPs). Total BMP performance refers to
the pollutant removal and runoff volume reduction capabilities. The RRM tracks the implementation of
stormwater BMPs, including Low Impact Development (LID) strategies such as permeable pavement,
rainwater harvesting, downspout disconnection, soil amendments, etc., and credits the appropriate runoff
volume reduction, pollutant concentration reduction, or both towards compliance with stormwater quality
and quantity requirements. By providing a mechanism to credit the volume reduction associated with these
LID strategies the RRM also documents an allowable reduction of the overall size and footprint of structural
detention practices, thereby providing an economic incentive for the development community to implement
LID providing a better overall solution for minimizing the impact of development on the hydrologic cycle.
Keywords: Runoff reduction, site design, regulations
T
he Runoff Reduction Method (RRM) was
developed in early 2008 by the Center for
Watershed Protection and the Chesapeake
Stormwater Network as a compliance tool for
the proposed Virginia stormwater regulations.
The RRM includes incentives for minimizing the
increase in runoff associated with developed lands,
while also providing a measure of the capability of
both conventional and innovative stormwater Best
Management Practices (BMPs) (e.g., permeable
pavement, green roofs, rainwater harvesting,
bioretention, downspout disconnection) to reduce
the increased volume of runoff associated with
developed pervious and impervious land cover.
The RRM also accounts for the capability of certain
BMPs to remove pollutants from stormwater
runoff. The result is a comprehensive compliance
tool that promotes better site design as the first
step in compliance with both stormwater quality
and quantity requirements, and strives to properly
account for overall BMP effectiveness.
Most stormwater quality regulatory programs
require a reduction in the post-developed pollutant
load defined as an annual pollutant load measured
in pounds per acre per year (lb/ac/yr). The annual
pollutant load is typically the product of the annual
runoff volume and the concentration of pollutant
expected to be present in the developed condition
runoff. The RRM includes incentives for better
site design through the use of volumetric runoff
coefficients that reflect the hydrologic response
characteristics of both impervious and pervious
cover conditions including soil type, forested
land, managed turf, etc. Developing a design that
reflects a low volumetric runoff coefficient (i.e.
less impervious cover, less overall site disturbance,
less managed turf, and more forested or open space
areas) will result in a water quality benefit through
a reduced volume of runoff in the pollutant load
calculation.
The RRM further accounts for volume reduc-
tion through the use of various BMPs that have
a demonstrated capability to reduce the overall
volume of runoff based on the post-development
condition. Runoff can be reduced via canopy
interception, soil infiltration, evaporation, transpi-
ration, rainfall harvesting, engineered infiltration,
or extended filtration. The use of these practices in
conjunction with the site design incentives noted
above will reduce the volume of runoff used to com-
pute the annual pollutant load generated by the site.
Additional BMPs that serve to remove the
pollutants from stormwater through settling,
filtering, adsorption, biological update, or other

mechanisms can be combined with the volume
reduction strategy to further reduce the pollutant
load. The RRM strategy therefore includes BMPs
that achieve runoff reduction, pollutant removal, or
both.
In addition to water quality, the RRM provides a
metric for computing the volume reduction benefit
when calculating compliance with water quantity
requirements. These requirements typically include
the control of relatively large storms: 1 to 2-year
frequency design storms for channel protection,
and the 10-year frequency storm for localized flood
protection. The volume reduction that is achieved
through the use of RRM practices and strategies,
along with any uniformly distributed retention
storage can be utilized to satisfy the quantity
requirements through a curve number adjustment,
or if desired, the hydraulic routing of individual
facilities.
The field of stormwater management has
recently seen many new terms being adopted to
describe various related and overlapping design
approaches and philosophies such as low impact
development, environmental site design, green
infrastructure, etc. Runoff reduction describes a
process or function of BMPs that can be described
as bringing many of these strategies into a single
method. As such, it is a collection of methods that
has been derived to provide a simple and readily
implementable compliance tool that incentivizes
the use of minimization and avoidance of impacts
to achieve the stormwater quality and quantity
goals. The RRM approach also moves beyond
managing stormwater solely for peak rate and
water quality treatment by attempting to replicate
a more natural (or pre-development) hydrologic
condition. More specifically, it represents a more
comprehensive approach that addresses runoff
volume, duration, velocity, frequency, groundwater
recharge, and protection of stream channels. When
used in conjunction with site pollutant load limits,
the approach can help meet the pollutant reduction
goals (i.e. nutrient strategies, TMDLs) of the larger
watershed.
Overview of the Runoff Reduction
Method
The RRM relies on a three-step compliance
procedure, as described below:
Step 1: Reduce Stormwater Runoff by Design
Step one focuses on implementing better site
planning and design techniques during the early
phases of site layout. The goal is to minimize
impervious cover and mass grading, and maximize
retention of forest cover, natural areas and
undisturbed soils (especially those most conducive
to landscape-scale infiltration – Hydrologic
Soil Groups A and B). The RRM assigns runoff
coefficients for forest, disturbed soils, managed
pervious areas, and impervious cover to calculate a
site-specific target treatment volume.
Step 2: Reduce Volume of Post-
Construction Stormwater Runoff
In this step, the designer uses combinations
of small-scale, distributed, and conventional
practices that are effective at reducing runoff
from the site. In each case, the designer estimates
the area to be treated by each runoff reduction
practice to incrementally reduce the required
treatment volume for the site. The designer is
encouraged to use these practices in series
within individual drainage areas (such as rooftop
disconnection leading to a grass swale leading to
a bioretention area) in order to achieve a higher
level of runoff reduction.
Step 3: Capture and Treat Remaining
Stormwater Runoff
In this step, the designer applies pollutant
reduction values to the runoff reduction practices
used in Step 2. If the target pollutant limits are
not reached, the designer can select additional,
conventional BMPs – such as filtering practices,
wet ponds, and stormwater wetlands – to meet
the remaining pollutant reduction requirements.
The three-step process is iterative for most
sites. When compliance cannot be achieved on
the first try, designers can return to prior steps
to explore alternative combinations of site
planning, site design, runoff reduction practices,
and pollutant removal practices to achieve
compliance. A possible Step 4 would involve
paying an offset fee (or fee-in-lieu payment) to
compensate for any pollutant load that cannot
feasibly be met on particular sites. A related, but
simpler option would be to allow a developer to
Battiata, Collins, Hirschman, and Hoffmann12
Journal of Contemporary Water Research & EducationUCOWR

conduct an off-site mitigation project in lieu of
full on-site compliance. Table 1 includes a list of
site design and stormwater practices that can be
used for each step.
Runoff Coefficients and Treatment
Volume
The negative impacts of increased impervious
cover on receiving water bodies have been well
documented (Center for Watershed Protection 2003;
Walsh et al. 2004; Shuster et al. 2005; Bilkovic
et al. 2006). Due to widespread acceptance of
this relationship, impervious cover has frequently
been used in watershed and site design efforts as
a chief indicator of stormwater impacts. More
recent research, however, indicates that other land
covers, such as disturbed soils and managed turf,
also impact stormwater quality (Law et al. 2008).
Numerous studies have documented the impact
of grading and construction on the compaction
of soils, as measured by increase in bulk density,
declines in soil permeability, and increases in the
runoff coefficient (Ocean County Soil Conser
vation District et al. 2001; Pitt et al. 2002; Schueler
and Holland 2000). These areas of compacted
pervious cover (lawn or turf) have a much greater
hydrologicresponsetorainfallthanforest,meadow,
or pasture. The hydrologic effects of compaction
are significant enough that some jurisdictions
require a downgrading of the hydrologic soil type
and corresponding runoff curve number (RCN)
based solely on soil disturbance. For example, a
type A Hydrologic Soil Group (HSG) soil (highly
permeable, and therefore generating little runoff)
that is impacted by clearing and grading operations
will be automatically considered a type B soil (less
permeable, and therefore generating more runoff)
in the developed condition runoff calculations
(Anne Arundel County, MD 2006).
In addition to the hydrologic response, managed
turf can contribute to elevated nutrient loads due
to excessive management in the early years of
establishing a dense turf cover after construction
activities, as well as long term maintenance by
homeowners. Typical turf management activities
include mowing, active recreational use, and
fertilizer and pesticide applications (Robbins and
Birkenholtz 2003). The combination of greater than
predicted runoff volumes due to soil compaction
and higher concentrations of pollutants resulting
from management activities yields a significantly
higher pollutant load. It should be noted that
properly managed native grasses, turf, or meadow
on an undisturbed soil profile are fundamentally
different than managed turf and should be
considered a beneficial strategy in terms of both
runoff volume and quality.
Table 1. Practices included in the runoff reduction method.
Step 1: Site Planning and Design
Practices
Step 2: Runoff Reduction (RR)
Practices
Step 3: Pollutant Removal (RR)
Practices
Forest Conservation Sheetflow to Conservation Area or
Filter Strip
Filtering Practice
Site Reforestation
Rooftop Disconnection:
• Simple
• To Soil Amendments
• To Rain Garden or Dry Well
• To Rain Tank or Cistern
Constructed Wetland
Wet Swale
Wet Pond
Soil Restoration (combined
with or separate from rooftop
disconnection)
Green Roof Grass Channels
Grass Channels Permeable Pavement
Permeable Pavement Bioretention
Bioretention Dry Swale (Water Quality Swale)
Dry Swale (Water Quality Swale) Infiltration
Infiltration Extended Detention (ED) Pond
Extended Detention (ED) Pond
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The runoff coefficients provided in Table 2 were
derived from research by Pitt et al. (2005), Lichter
and Lindsey (1994), Schueler (2001a), Schueler
(2001b), Legg et al (1996), Pitt et al. (1999),
Schueler (1987), and Cappiella et al. (2005). As
shown in this table, the effect of grading, site
disturbance, and soil compaction greatly increases
the runoff coefficient compared to forested areas.
The RRM uses runoff coefficients to calculate
a site-specific target treatment volume (Tv). A
site’s Tv is calculated by multiplying the “water
quality” rainfall depth by the runoff coefficients
that correspond to the site cover conditions (forest,
disturbed soils, and impervious cover), as shown
in Table 3. The “water quality” rainfall depth is
often defined as the rainfall depth associated with
90 percent of runoff-producing storm events on
an average annual basis. Use of this depth as a
design requirement for stormwater BMPS targets
90 percent of all storm events for treatment, as
well the first portion of all larger storm events.
The 90 percent storm event approach to defining
the treatment volume is widely accepted and is
consistent with several state stormwater manuals
(Maryland Department of the Environment 2000;
Atlanta Regional Commission 2001; NYDEC
2001; Vermont Department of Environmental
Conservation 2002; Ontario Ministry of the
Environment 2003; Minnesota Pollution Control
Agency 2005).
Using a site specific Tv has several distinct
advantages when it comes to evaluating runoff
reduction practices and sizing BMPs. In effect, Tv
provides an objective measure to gage the aggregate
performance of runoff reduction practices and
conventional BMPs using a common currency:
runoff volume. Calculating the Tv explicitly
acknowledges the difference between forest and
turf cover, and disturbed and undisturbed soils,
which creates incentives to conserve forests and
reduce mass grading. Further, since runoff is a
direct function of impervious cover and disturbed
soils, the Tv computation provides designers with
an incentive to minimize both at a development site.
Additionally, using the 90th
percentile rainfall
depth for the Tv computation ensures that storm
water practices are adequately sized to capture
runoff from a wide range of storm events. This
includes the small and more frequent runoff
producing events, as well as the equivalent
runoff volume under the rising limb of the
runoff hydrograph from larger storms. Managing
this volume through the RRM, which totals
approximately 90 percent of the annual runoff
volume, is important since the first flush effect in
terms of total load has been found to be modest for
many pollutants (Pitt et al. 2005).
Documenting BMP Performance
After implementing environmental site design
and site planning techniques to minimize the site’s
treatment volume, the next steps of the RRM
involve the selection of BMPs to reduce the Tv,
and consequently, the pollutant load from the
site. Center for Watershed Protection and CSN
conducted an extensive literature search to identify
the capabilities of various BMPs to reduce overall
runoff volume (runoff reduction) and pollutant
concentrations (pollutant removal). Historically,
BMP performance has been evaluated according to
only the pollutant removal efficiency of a practice.
Further, removal efficiencies do not always address
runoff volume reductions in BMPs (Strecker et al.
2004; Jones et al. 2008). Therefore, the lack of
volume reduction data can lead to the assumption
that the total load reduction was the result of the
pollutant concentration (EMC) reduction, leading
to an over-estimation of the pollutant removal
capabilities, while ignoring the additional benefits
of volume reduction.
More recent BMP performance research has
focused on runoff reduction as well as overall
pollutant removal. In order to isolate the pollutant
removal mechanisms of a BMP apart from runoff
reduction, both EMC-based pollutant removal
efficiencies and volume reduction efficiencies
Table 2. Site cover runoff coefficients (Rv).
Soil Condition Runoff Coefficient
Forest Cover (Rvf) 0.02-0.05*
Disturbed Soils/Management 0.15-0.25*
Impervious Cover (Rvt) 0.95
*Range dependent on original Hydrologic Soil
Group (HSG)
Forest A: 0.02 B: 0.03 C: 0.04 D: 0.05
Disturbed Soils A: 0.15 B: 0.20 C: 0.22 D: 0.25

were researched. For several practices, there were
a limited number of studies available that reported
runoff reduction or EMC-based nutrient removal
efficiencies. As a result, some of the values
listed in Table 4: Runoff Reduction, and Table 5:
EMC-Based Pollutant Removal will be subject to
change as more studies and data become available.
The values represent the authors’ best judgment
based on currently available information. Further
documentation on the derivation of these values
can be found in Hirschman et al. (2008).
Runoff Reduction Practices
As described earlier in this paper, various BMPs
are capable of reducing the overall volume of
runoff based on the post-development condition.
Runoff can be reduced via canopy interception,
soil infiltration, evaporation, transpiration, rainfall
harvesting, engineered infiltration, or extended
filtration. Extended filtration includes bioretention
or dry swales with underdrains that delay the
delivery of stormwater from small sites to the
stream system by six hours or more.
While runoff reduction data were limited for
manypractices,runoffreductionrateswereassigned
to the various BMPs based on the research findings,
as shown in Table 4. A range of values represents
the median and 75th percentile runoff reduction
rates based on the literature search. Several BMPs
reflected moderate to high capabilities for reducing
annual runoff volume. Others – including filtering,
wet swales, wet ponds, and stormwater wetlands
– were found to have a negligible effect on runoff
volumes, and were not assigned runoff reduction
rates. The runoff reduction performance of any
given BMP can often depend upon the specific
BMP characteristics (i.e., geometry, sizing, etc.),
therefore specific design criteria are important to
define for each BMP type.
Pollutant Removal Practices
In order to isolate the pollutant removal
mechanisms of a BMP and offer a better approach
to assessing BMP pollutant removal performance
(as distinct from runoff reduction), EMC-based
pollutant removal rates for nitrogen and phosphorus
were researched. EMC-based pollutant removal
is accomplished via processes such as settling,
filtering, adsorption, and biological uptake. This
is separate from changes in the overall volume of
runoff entering and leaving the BMP.
Based on the research findings, EMC-based
pollutant removal rates were assigned to various
BMPs, as shown in Table 5. The range of values
represents the median and 75th percentile runoff
reduction rates based on the literature search.
It should be noted that the data used to estimate
pollutant removal were derived from practices in
good condition; most studies focused on BMPs that
were monitored within three years of construction.
As with runoff reduction, since pollutant removal
rates are dependent on site characteristics and BMP
geometry, these EMC-based pollutant removal
numbers are associated with specific design
criteria.
Accountability for Better BMP Design
A range of performance values are provided
for certain BMPs in Tables 4 and 5. These values
are associated with specific design criteria and
are identified as Level 1 and Level 2 designs. A
standard, or Level 1 design can be expected to
achieve the median value of Runoff Reduction
and Pollutant Removal derived from the research,
while an enhanced, or Level 2 design achieves the
75th percentile values.
Based on the evaluation of BMP performance
in the literature, design factors – such as sizing,
pretreatment, flow path geometry, vegetative
condition, and treatment processes – that enhance
nutrient pollutant removal and runoff reduction
Table 3. Determining the stormwater treatment volume.
Tv
= P ×[(RvI
×%I) + (RvT
×%T) + (RvF
× %F] × SA
12
Where
Tv
= Runoff treatment volume in acre feet
P= Depth of rainfall for “water quality” event
RvI
= runoff coefficient for impervious cover
RvT
= runoff coefficient for turf cover or disturbed
soils1
RvF
= runoff coefficient for forest cover1
%I = percent of site in impervious cover (fraction)
%T = percent of site in turf cover (fraction)
%F = percent of site in forest cover (fraction)
SA = total site area, in acres
1
Rv
values from Table 1.
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Table 4. Runoff reduction for various BMPs (based on
average rainfall in the Virginia Piedmont areas).
of BMPs were identified. These design factors
were then applied to Level 1 and Level 2 BMPs.
The specified design factors associated with these
levels must be met in order to achieve credited
runoff reduction and pollutant removal rates.
The scientific rationale and assumptions used to
assign sizing and design features to the standard
and enhanced BMP levels involved identifying
the “standard” or basic functional design features
that should be included in all designs (i.e., not
directly related to differential nutrient removal
or runoff reduction rates). A review of individual
BMP studies and corresponding modifications
of design point tables in the Stormwater Retrofit
Manual, Appendix B (Schueler et al. 2007) were
then utilized to reflect the more specific goals of
reducing runoff and nutrient removal for BMPs.
For example, the bioretention Level 2 design
provides for an increase in both runoff reduction
and pollutant removal credit as compared to
Level 1 through an increase in the storage volume
(provided as either surface or subsurface storage)
and the minimum soil media depth, and the ability
to infiltrate into the underlying soils or provide a
deep sump. In addition, expanded design criteria
Practice
Runoff Reduction
(percent) *
Green Roof 45-60
Rooftop Disconnection 25-50
Raintanks and Cisterns 40
Permeable Pavement 45-75
Grass Channel 10-20
Bioretention 40-80
Dry Swale 40-60
Wet Swale 0
Infiltration 50-90
ED Pond 0-15
Soil Amendments 50-75
Sheetflow to Open Space 50-75
Filtering Practice 0
Constructed Wetland 0
Wet Pond 0
*Range of values is for median (Level 1) and 75th
percentile (Level 2) designs.
related to pre-treatment techniques, the landscaping
plan, and the overall bioretention basin geometry
such as minimum flow path lengths for each inflow
point, also serves to support an increase in total
credited performance. Another example of a Level
1 and Level 2 distinction is the wet pond design
criteria. The Level 2 design provides for increased
pollutant removal through a 50 percent increase in
the treatment volume (which can be in the form
of the normal pool and an extended detention
volume above the normal pool). More importantly,
the Level 2 design also includes requirements for
shallow marsh areas and more stringent geometry
criteria such as minimum flow path lengths and
multiple treatment cells.
It is important to note that the assigned rates are
based on the assumption that BMP designs will
meet certain minimum “eligibility criteria” for the
designated level. That is, the BMPs will be located
and designed based on appropriate site conditions
andlimitationswithregardtosoils,slopes,available
head, drainage area size, and other factors. The
specific design factors and eligibility criteria for
various BMPs are detailed in the Runoff Reduction
Technical Memo (Hirschman et al, 2008).
Peak Flow Reduction
RRM utilizes an “annual” volume reduction
with which to calculate the “annual” pollutant
load coming out of the practice. In principle, when
runoff reduction practices are used to capture and
retain or infiltrate runoff, downstream stormwater
management practices should not have to detain,
retain or otherwise treat the volume that is
removed. In other words, the volume of runoff
reduction provided should be subtracted from
the volume calculated by stormwater runoff peak
flow computations. The challenge lies in how to
accurately credit the annual volume reduction
to the computation of the peak rate of runoff
from larger single event storms for purposes of
channel or flood protection. Peak flow reduction is
accomplished by providing watershed storage and
runoff attenuation.
Many of the volume-based BMPs used in
the RRM also provide some amount of storage
and runoff attenuation. While one could apply
hydraulic routing to a volume-based BMP, the

response characteristics of the practice may not
follow the traditional detention/retention design
parameters. Routing of BMPs can be a difficult
and complex task, given all the hydrologic and
hydraulic variables associated with volume and
peak rate reduction, such as evapo-transpiration,
storage within the soil media, infiltration, and
extended filtration.
The RRM points to a simpler method for
crediting specific runoff reduction values toward
peak flow reduction. The method utilizes the
Natural Resource Conservation Service runoff
equations 2-1 through 2-4 provided in Urban
Hydrology for Small Watersheds (USDA 1986)
to derive a curve number adjustment that reflects
the reduced runoff volume. A simplified derivation
of the computational procedure starts with the
combined Runoff Equations 2-1 and 2-2 in order
to express the runoff depth in terms of rainfall
and potential maximum retention, Equation 2-3.
In addition, the potential maximum retention,
S, is related to soil and cover conditions of the
watershed through the runoff curve number (CN)
as described by Equation 2-4.
Q =
(P-Ia
)2
(P-Ia
) + S Eq. 2-1, TR-55
Ia
= 0.2S Eq. 2-2, TR-55
Q =
(P-0.2S)2
(P + 0.8S) Eq. 2-3, TR-55
S =
1000 - 10
CN Eq. 2-4, TR-55
Q - R =
(P - 0.2S)2
(P + 0.8S) Modified Eq. 2-3
where: Q = runoff depth (cm),
P = rainfall depth (cm),
Ia
= Initial abstraction (cm),
S = potential maximum retention after
runoff begins (cm),
CN = Runoff Curve Number, and
R = Retention storage provided by runoff
reduction practices (cm).
The retention storage depth equivalent to the
runoff reduction values assigned by the RRM and
any additional retention storage provided on the
site (expressed in terms of retention storage R) are
subtracted from the total runoff depth associated
with the developed condition CN, which then will
provide for a new value of S (Modified Equation
2-3). A new CN is then back-calculated from the
new value of S using Equation 2-4 (Koch 2005).
While it is not easy to predict the absolute runoff
hydrograph modification provided by reducing
stormwater runoff volumes, it is clear that reducing
runoff volumes will have an impact on the runoff
hydrograph of a development site. Simple routing
exercises have indicated that this curve number
Practice
Total
Phosphorus
Pollutant
Removal
(percent)*
Total
Nitrogen
Pollutant
Removal
(percent)*
Green Roof 0 0
Disconnection 0 0
Rainwater harvesting
and Cisterns
0 0
Permeable Pavement 25 25
Grass Channel 15 20
Bioretention 25-50 40-60
Dry Swale 20-40 25-35
Wet Swale 20-40 25-35
Infiltration 25 15
ED Pond 15 10
Soil Amendments 0 0
Sheetflow to Open
Space
0 0
Filtering Practice 60-65 30-45
Constructed Wetland 50-75 25-55
Wet Pond 50-75 30-40
*Range of values is for median (Level 1) and 75th
percentile (Level 2) designs.
Table 5. EMC-based pollutant removal for various
BMPs.
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quantity control compliance for larger storms.
Flexibility is provided for designers to account
for the actual retention storage provided by
volume-based practices rather than the annual
reduction credit to calculate individual storm
curve number adjustments.
• Georgia — The Georgia Department of
Natural Resources modified the RRM for a
new Coastal Stormwater Management Manual
Supplement. The manual requires that the
stormwater runoff volume from the 1.2 inch
(3.05 cm) rainfall event (85th percentile event)
be retained, reused, or reduced to the maximum
extent practical, on a new development or
redevelopment site.
Additional efforts to incorporate the concept
of runoff reduction into updated stormwater
regulations and design manuals are underway
in the States of Delaware, Maryland, and the
District of Columbia (Cappiella et al. 2007;
DeBlander et al. 2008; Maryland Stormwater
Consortium 2008).The Pennsylvania Stormwater
Best Management Practices Manual (PA DEP
2006) already incorporates standards for volume
control achieved by structural and nonstructural
BMPs.
Conclusion
The concept of runoff reduction marks an
important philosophical milestone that will help
define the next generation of stormwater design.
The promise of runoff reduction is that the benefits
go beyond water quality improvement. The RRM
provides an effective and readily implemented
compliance tool that serves to incentivize site
design strategies that minimize and avoid impacts
to the natural or existing hydrologic response of the
site. These types of site design strategies have long
been promoted, but not necessarily implemented.
If site and stormwater designs can successfully
implement runoff reduction strategies, then they
will do a better job at replicating a more natural
(or pre-development) hydrologic response that
goes beyond peak rate control to also address
runoff volume, duration, velocity, frequency, and
groundwater recharge. Important future work
will involve continued integration of the runoff
reduction concept with stormwater requirements
adjustment approach represents a conservative
estimate of peak reduction.
Additional research to compare the results of
hydraulic routing of management practices with the
measured volume reduction in the field is needed to
better predict the ability of these practices to modify
the runoff hydrograph and reduce peak discharges.
Documenting an accurate volume reduction for
the larger storm events can provide a tremendous
incentive to further maximize the use of site design
techniques as a way to reduce the footprint and
long-term operation and maintenance of large
BMPs, while also providing better protection of
aquatic resources.
Transferability of the Runoff
Reduction Concept
While the RRM was originally developed
in tandem with the Virginia Department of
Conservation and Recreation (DCR) efforts to
update the stormwater regulations and handbook,
the concept is widely applicable to other state
and local stormwater planning procedures. The
focus on runoff volume as the common currency
for BMP evaluation is gaining wider acceptance
across the county (U.S. EPA 2008). Currently,
various state programs are in the process of using
or adopting methods similar to the RRM as part
of regulatory and non-regulatory programs. With
the incorporation of the RRM into these programs,
communities are poised for the widespread
implementation of runoff reduction practices on
development sites.
• Virginia — The Virginia Department of
Conservation and Recreation is integrating the
RRM into proposed stormwater management
regulations and an updated stormwater
management handbook. The method focuses
on compliance to meet site-based pollutant
load limits, aimed at limiting the total nutrient
load leaving a new development site. A site
design compliance spreadsheet was developed
to ensure runoff reduction and nutrient loading
requirements for the site are met.
The annual runoff reduction credit
(measured as a percentage of the 1-inch, or
2.54 cm, event) is then used to calculate the
corresponding curve number adjustment for

for channel protection and flood control, so that
stormwater criteria can be presented in a unified
approach.
Author Bios and Contact Information
Joseph Battiata is a Senior Water Resources Engineer
with the Center for Watershed Protection. He has over 25
years of experience in water resources and stormwater
management in the private and public sector. Notably,
Mr. Battiata developed and managed the implementation
of the Virginia Department of Transportation’s first
Municipal Separate Storm Sewer System (MS4)
and Construction General Permit Programs. He also
served as the Stormwater Program Manager and Chief
Engineer with the Virginia Department of Conservation
and Recreation (DCR). Joe started his career as a
consultant in the D.C. metro area after graduating from
The Catholic University of America with a B.S. in Civil
Engineering. He may be contacted at jgb@cwp.org or at
Center for Watershed Protection, 7368 Sunshine Court,
Mechanicsville VA 23111.
Kelly Collins is a Water Resources Engineer with the
CenterforWatershedProtection. Kellyisknowledgeable
in several areas of watershed and stormwater
management, including stormwater retrofit evaluation,
planning and design of stormwater management
practices, local stormwater and watershed management
program development, stormwater monitoring, and
watershed management planning. Kelly has a Master
of Science in Biological and Agricultural engineering
from North Carolina State University and a Bachelor of
Science in Biological andAgricultural engineering from
Pennsylvania State University. She may be reached at
kac@cwp.org.
David Hirschman serves as a Program Director for
the Center for Watershed Protection. In this capacity,
he works on a variety of stormwater, watershed, and
training programs. He has 27 years of experience in the
public, private, and non-profit sectors. Prior to working
for CWP, he served as Water Resources Manager for
Albemarle County, Virginia, where he was responsible
for the development and implementation of a stormwater
management program. He has a B.A. in Biology from
Duke University and a Master of Urban & Regional
Planning from Virginia Tech. He may be contacted at
djh@cwp.org.
Greg Hoffmann, a Wisconsin native, is a Professional
Engineer with a Master of Engineering from Michigan
Technological University. Greg began at the Center
for Watershed Protection in 2008, and specializes in
development of stormwater regulations and guidance
documents, stormwater retrofitting, watershed
assessment and planning, and training on various
stormwater and watershed topics. Prior to joining the
Center, Greg worked for a private consulting firm in Port
Huron, Michigan. Greg lives in Baltimore with his wife,
Elizabeth, and spends his spare time hiking, traveling,
and working in his garden. He may be reached at gph@
cwp.org.
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