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Green Roofs Proposal for the City of Roanoke
By: Cassandra Archambault, Jonathan Honchar, Robert
Novakovic, Kelsea Pieters, & Benjamin White
This proposal, designed by the Environmental Group for Dr. Brown’s State & Local Government Class in
the Spring of 2011, addresses the flooding issue in the City of Roanoke. A very cost-effective approach to
dealing with this problem is to reduce the amount of rainwater runoff from 5 buildings within the city, each
of which are owned and operated by the city. These buildings are to have “green roofs” installed on them in
order to reduce the annual runoff amounts. At the same time, the energy efficiency of these buildings will
improve during the summer months when air-conditioning units are used to cool the buildings. This report
studies the cost of installation of these green roofs, the amount of rainwater runoff that will be reduced, and
the energy the City of Roanoke will save by having a reduced workload on air-conditioning units. This data
is also presented in a cost-benefit analysis, determining the city’s return on investment for each individual
building on which a green roof is installed in terms of the amount of annual energy savings.
State & Local Government
Dr. Health Brown
Presented on: April 20, 2011
Cover page photo courtesy of: http://2.bp.blogspot.com/_ufgubHhdk-U/S7qLrZOMkZI/AAAAAAAAAWw/EMOvGHFG-jY/s1600/overlooking+Roanoke+Virginia2.jpg
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Benjamin White
A. Problem Statement
Stormwater runoff management is an imperative issue that city managers must take highly into
consideration. Such management is necessary to ensure that a city is safeguarded from excessive
water build-up that can lead to flooding. Downtown Roanoke is no exception to this fact and is
arguably more inclined to deal with stormwater as the city is partly encompassed by the Roanoke
River’s flood plain. Traditional stormwater management systems, currently utilized by Roanoke
City, transport polluted runoff water through a series of pipelines under the city that ultimately
leads into a dumping basin. Municipal Separate Storm Sewer Systems (MS4s) are the typical
transportation systems that carry untreated stormwater away from a city (EPA). Polluted runoff
increases the extent of environmental degradation in and around the Roanoke River. Necessity
for an alternative means of drainage is at an unparalleled high. Based off of low impact
development (LID) techniques, green infrastructure is an ideal method of stormwater
management that could be implemented into several downtown Roanoke City buildings. Green
infrastructure is a cost-effective and sustainable technology that has the aptitude to effectively
manage surplus stormwater if applied to these buildings.
Benjamin White
B. Science and Technical Background
Green Infrastructure techniques are based around LID standards. Basically, green infrastructure
works by incorporating natural weather systems into the infrastructure it is installed on by
“capturing, cleansing and reducing stormwater runoff using plants, soils and microbes” (City of
Roanoke, 2010). Plant life is utilized for its natural absorption capabilities which help in
displacing large volumes of rainwater (EPA). Each green infrastructure retains characteristics
that are site-specific to carry out its goal of stormwater filtration, depending on an area’s unique
climatology. Maintaining stormwater in the green roof system recycles the water within the
infrastructure itself which ultimately keeps the runoff from ever reaching the city’s underground
pipelines. By regulating stormwater at its source, green infrastructure reduces the volume of
water that would typically run through the city’s MS4 system.
Green Roofing is the specific green infrastructure application proposed for integration into
several buildings in downtown Roanoke City. Green roofs are “designed to mimic natural
hydrologic functions and decrease the amount of impervious area and stormwater runoff from
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individual sites” (EPA Green Infrastructure). Green roofs are made up of several layers, each
with its own distinctive function, that contribute to the retention and recycling of stormwater.
The first two layers are known as the plant layer and the growing medium. The growing medium
separates the vegetation’s roots and houses them in order to retain water and to keep the plant’s
roots from penetrating the actual building (Green Roof, n.d.). Filter fabric is the next layer,
which is installed to ensure that no fine particles of soil enter the drainage layer (Green Roof,
n.d.). The filtration of stormwater runoff adds to the reduction of polluted water that does enter
the city’s stormwater drainage system. Drainage of the plant medium is a dire necessity. A
drainage layer is typically composed of a “lightweight granular medium or a synthetic layer,”
which keeps the plant layer from retaining excessive water (Green Roof, n.d.). The integrity of a
roof determines whether or not a green roof will be installed. Green roofs can weigh anywhere
between 10 and 30 pounds per square foot, which adds up quickly (Green Roof, n.d.). Together,
these layers are all laid on top of one another to ensure the vitally of the plant layer, which is the
main component in stormwater retention.
Jonathan Honchar
C. Methods
Mathematical analysis through equations and GIS-mapping software was used to calculate the
green roof area of the five city-owned buildings in Roanoke. This green roof data was then
analyzed to determine the actual cost of implementing green roofs on these five existing
structures and the potential benefits the city would reap from them. These benefits include the
reduction of rainwater runoff from the buildings and the potential energy savings of the
building’s cooling system during the summer months (May to October).
1. Calculation of Green Roof Area
Robert Novakovic, using the GIS mapping software ArcMap, calculated the green roof area of
the five buildings in question in the City of Roanoke. Mr. Novakovic calculated this area using
ArcMap’s geoprocessing function and highlighting the roof area of these five different buildings
using GIS map data obtained from Erica Taylor, who works for the city. By clipping these select
rooftops from the entire city, Mr. Novakovic was able to provide the actual square-footage of
roof space for these five buildings. It is vital to have an accurate estimation of the building’s
roof square footage in order to determine the actual rainwater runoff the building generates and
the actual cost of a green roof installation.
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2. Calculation of Rainwater Runoff from Roofs
Once square footage of the roofs was obtained, the actual rainwater runoff was calculated. This
calculation was performed using the following formula: (square footage of the roof)*(annual
rainfall in feet)*(7.48) = gallons of runoff from a building annually. The 7.48 number is the
coefficient that accounts for how many gallons of water are collected by one-foot of rain in a
one-square foot area, therefore applicable to that equation. Furthermore, it allows one to see how
much runoff a single building generates in gallons annually.
3. Calculation of Cost of Green Roof Installation
The installation costs of installing green roofs on the five buildings were calculated by
multiplying the roof’s square footage by the $17, the average cost of a green roof per square foot
according to the EPA. The total costs are given for all five buildings and are also given on an
individual basis.
4. Calculation of Rainwater Runoff Reduction
The rainwater runoff reduction was calculated by multiplying the annual rainwater runoff of the
buildings prior to installation of the green roofs by 67-percent (for a 2.5 inch green roof), the
average reduction rate according to the EPA. This number was then subtracted from the original
rainwater runoff to determine the amount of runoff in gallons after the green roofs were installed.
These reduction rates in gallons of runoff are presented annually based on the annual
precipitation rate the City of Roanoke receives in a given year and are given both for all five
buildings and on an individual basis.
5. Calculation of Energy Reduction & Return on Investment
The energy reduction of the buildings was calculated by multiplying the building’s annual
energy use for months when the building is being cooled via air conditioning units (May through
October) by 25-percent. According to the EPA, a green roof reduces summer energy cooling up
to 25-percent by absorbing the amount of direct sun the buildings roof receives. Kenneth
Cronin, the sustainability coordinator for the City of Roanoke, provided the daily energy use
during that period of six months (0.5 years) in usage per month for the four out of the five
buildings being studied; however, he was unable to provide the data for the US Bankruptcy
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Courthouse since that data had to come from the Federal Government. The original use (in
kilowatts per hour) was multiplied by 25-percent to determine reduction (kWh) amount. Mr.
Cronin also provided the monthly electricity costs the city pays AEP to provide electricity to
those buildings. These reduction costs were calculated the same way as the energy-used
reduction. The reduced costs of the building with a green roof were then subtracted from the
original costs to determine the annual savings. These savings are provided both as an overall
total and on an individual basis per building. Also included in this section is the time for return
on investment of the green roof installation for the city based solely on energy reduction. This
data is in a yearly time frame and shows how long it would take the city to obtain return on
investment for each building.
Jonathan Honchar
D. Results
The results portion is organized by the (1) rainwater runoff reduction, (2) the energy use
reduction, and (3) the return on investment for the city of each individual building and the totals
for all five buildings. The five buildings that were studied to determine the amount of rainwater
runoff are: Municipal Building, Police/Sheriff’s Department, Roanoke City Courthouse, US
Bankruptcy Courthouse, and the City of Roanoke Jail. The energy use that these buildings could
reduce with a green roof was studied for all of those buildings listed above except the US
Bankruptcy Courthouse because energy information could not be provided for that building.
This data allows comparisons to be made between the different buildings and also allows the
total runoff and energy use reduction to be seen all together. These comparisons will allow for
extensive discussion of the data and recommendations for the future.
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Figure 1. Map of buildings in the City of Roanoke that were studied and have the potential for a
green roof are highlighted in green. The square footage of available roof space that could have
a green roof was determined by this map.
1. Rainwater Runoff
Installing green roofs on five buildings owned by the city of Roanoke would prevent an
estimated 2.1 million gallons of rainwater from entering the city’s storm drains annually. This is
a 67% reduction in the amount of runoff that these buildings would prevent from flowing off of
otherwise impervious rooftops. Since the city jail has the largest roof space with about 36,500
ft2, it would prevent 654,200 gallons of runoff from following onto the city’s streets and other
impermeable surfaces. The second largest reduction would come from the Roanoke City
Courthouse with 476,900 gallons of runoff being prevent, followed by the Police/Sheriff’s
Department with 417,200, then the US Bankruptcy Courthouse at 304,700 and finally the
Municipal Building at 245,500 gallons annually. The before and after runoff amounts can be
seen in figure 2 below.
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The greatest amount of error in this data is the actual calculations of the square footage of the
roofs. These calculations were made by highlighting the rooftop areas on the map, and ArcMap
made the final calculations. However, it is thought that these calculations are accurate and yield
a respectable number to the reductions that City of Roanoke would experience by installing
green roofs on the buildings listed above.
Figure 2. The rainwater runoff of the five buildings before and after a green roof installation.
2. Reduced Energy Use
The total annual energy savings by the City of Roanoke would be about $99,000 for the four
buildings that were studied. By installing a green roof, the building can save up to 25-percent of
its annual energy use during the months when the building is being cooled via air-conditioning.
These numbers account for that 25-percent reduction that is the greatest potential for buildings
with green roofs.
The city jail would have the greatest savings annually with about $30,000, followed by the
Municipal Building at $27,000, then the Police/Sheriff’s Department with $22,000 and finally
the Roanoke City Courthouse with about $20,000 saved annually. The before and after energy
amounts of the four buildings can be seen in figure 3 below.
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Again, with this section, the greatest chance for error lies in determining the actual savings of
each building since these savings are based on past energy use. There are many different factors
that could sway a buildings energy use annually or even on a monthly basis. Therefore, only the
months of May through October, when the air-conditioning unit would be operating, were
factored into the calculation.
Figure 3. The energy savings of each individual building before and after green roof
installation.
3.Costs & Return on Investment
The actual cost of installing a green roof on a preexisting structure ranges between $15 to $20 for
a 2.5 inch green roof, which reduces rainwater runoff up to 67% and energy up to 25%.
Therefore, it was determined that a green roof in the City of Roanoke would cost the city about
$17 per square foot. The total cost of the green roofs was determined by multiplying each
building’s available green roof square footage by $17. Accordingly, the buildings with the
largest green roof space would be the most expensive. Figure 4 shows the total cost of installing
a green roof on each of the five building. If all five buildings were to have green roofs installed,
it would cost the city an estimated $2.1 million.
Green Roof Proposal for the City of Roanoke
Figure 4. The costs of installing a green roof on each of the five buildings in the City of
Roanoke.
In order for the city to install green roofs on the buildings, they would want to see direct
monetary savings over time specifically through energy reduction. Even though the city would
have reduced runoff, which would save them money, it would be difficult to calculate an actual
price tag for those savings. However, energy savings can easily be determined and would allow
for the city to see a return on their investment of a green roof. Figure 5 below shows the actual
returns on investment for the city by energy savings in years. However, energy will only be
saved during the summer months and, these returns do not factor maintenance costs of a green
roof into the formula. Only four buildings have these calculations since energy data was not
provided for the US Bankruptcy Courthouse.
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Green Roof Proposal for the City of Roanoke
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Figure 5. Return on investment for the City of Roanoke based on energy savings of the four
buildings with green roofs.
The greatest amount of error for the green roof installation costs and return on investment for the
city is discussed in the previous sections (D.1. and D.2.), since that data was used to determine
return on investment.
Cassandra Archambault
E. Discussion
Evidently, installing green roofs is an effective strategy for Roanoke City to (1) decrease the
city’s impact on stormwater and (2) conserve energy and funds, and an important note to touch
on is (3) significant funds and particularity of green roofs in Roanoke City. Green Roofs have
found, from our study, an effective measure of improvement for such an impervious setting
existent in Roanoke City. Discussion section has built off results and recommendations to offer
a common foothold for implications of this study.
1. Rain water runoff decreased
Providing a solution to stormwater runoff and flooding in the City of Roanoke is an important
step to decreasing storm drain reliance, and possible pollution. Roanoke City would be
decreasing impervious area a significant amount, therefore decreasing amount of rainfall runoff
that fills the streams and storm drains each year, especially significant if and when flooding
occurs in the floodplain location of Roanoke City. The total drainage area within City Boundary
is 18,880 acres incorporating 14 receiving waters for any water which goes down the storm drain
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(MS4 Program Plan). An intense rainfall would send water to all of these, and eventually to the
Roanoke River, filling the waterway and thus reaching into the floodplain. This is a real scenario
Roanoke City has the potential to face again. Decreasing the amount of impervious area through
installation of green roofs would increase the city’s absorption capacity, therefore decreasing
gallons sent over roads and to storm drains. The city has a total of 12.85 miles of impervious
area, and the municipal buildings count for .93 miles (MS4 Project Plan). The municipal sector
could set the foundational precedent for green roofing much of the rest of the city. Green roofing
these buildings would save approximately 2.1 million gallons of rainwater per year from entering
the storm drain system.
2. Energy Consumption Efficiency
The efficiency of several green roofs on municipal buildings of the City of Roanoke is in the
calculations, as built off the fact that the green roofs offer vegetative insulation between indoor
and outdoor temperatures. Energy expenditure per building, especially during the summer
months is evidently high, thus changing just one building could make an extreme difference.
Take the City Jail, for example, $30,000 energy savings would be reaped by the city. The City
Jail, though is barely an exception, the other municipal buildings proposed to receive green roofs
have also potential savings near $30,000. Each building would save large amounts of electricity
and money to pay for it. Four buildings acquiring green roofs would save a total of energy
equivalent to about $99,000.
3. Prestige and Symbolic Benefits
Adding a green roof to this up and coming city of art, music and gentrification, increases the
influx of funds and interest. Note that during economic hardships, any city is competing for
educated individuals to come, and to stay in their city. Having a green roof increases particularity
of Roanoke City, something the city is already striving for with a future green roof in Center of
the Square (Justin and Christopher relayed this information, might, though, be common
knowledge). Installation of a green roof is a cost to jump. The city has the opportunity to merge
two facts into one, which for this project would build citizen knowledge and support. The costs
of installation, and ironically the amount of gallons of rainwater runoff prevented yearly, is $2.1
million.
Green Roof Proposal for the City of Roanoke
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Kelsea Pieters
F. Recommendations
The effect a green roof can have on a building and its surrounding area is environmentally and
economically advantageous. Furthermore, green roofs can be beneficial aesthetically as well.
Possibly the most valuable function of a green roof is its assistance in stormwater control. The
soil and vegetation of the roof intercept runoff by absorbing rainfall, thus naturally managing the
amount of possible stormwater. The vegetation on a green roof can also absorb contaminants
from rainwater that would otherwise flow into various natural water sources. Economically,
installation of a green roof can also reduce use of air conditioning because of its natural
insulation assets as opposed to an exposed surface of an impervious roof. In the City Of
Roanoke specifically, where flooding is somewhat of an imperative issue, green roofs could
mitigate stormwater and the threat of flooding significantly. Since this city does have a history
with extreme flooding, most recently the damaging flood of 1985 that reached the second story
of most buildings, the advantages of green roofs should unquestionably be considered for this
purpose. In addition, the buildings analyzed evidently spend a considerable amount of money
annually on energy costs, expenditures such as the cooling systems that could be reduced
extensively by the installation of a green roof.
In regards to the five buildings evaluated, it was calculated that the installation of a green roof
would reduce the amount of runoff annually and save a substantial amount of money in energy
costs. The effect a green roof would have on the municipal building, for example, would prevent
245,512 gallons of runoff water and save $27,165 in energy costs annually. Though instillation
may be somewhat expensive, the initial cost could be warranted after a number of years and the
lasting effects of having a green roof would be extremely advantageous for buildings and the
downtown area of Roanoke in many ways.
Kelsea Pieters
G. Summary
Green roofs are a natural and fiscally responsible solution to some issues downtown Roanoke has
faced. Since the city has a noteworthy history of flooding, the placement of green roofs on
several buildings can significantly reduce the risk. They can also reduce extraneous expenditures
in cooling costs through natural insulation properties. Through calculations, it was discovered
that the installation of a green roof on five buildings downtown reduces the risk of runoff due to
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rainfall and costs due to energy use considerably. Though it was also calculated that installation
of a green roof on each building is somewhat costly, these rates will be justified ultimately
through years of savings in energy costs.
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Works Cited
Berghage, R. D., Beattie, D., Jarrett, A. R., Thuring, C., Razaei, F., & O'Connor, T. P. 2009.
Green Roofs for Stormwater Runoff Control. National Risk Management Research
Laboratory, Office of Research & Development. Cincinnati: US EPA.
City of Roanoke. 2010. Stormwater Management Design Manual. City of Roanoke, Department
of Planning, Building, & Development, Roanoke.
Green Infrastructure: Managing Wet Weather with Green Infrastructure . 2010, November 4.
Retrieved April 17, 2011, from U.S. Environmental Protection Agency:
http://cfpub.epa.gov/npdes/greeninfrastructure/technology.cfm.
Install a Green Roof. n.d. Retrieved April 17, 2011, from Philadelphia Water Development:
phillyriverinfo.org.
National Pollutant Discharge Elimination System (NPDES). 2011, March 10. Retrieved April
17, 2011, from U.S. Environmental Protection Agency:
http://cfpub.epa.gov/npdes/stormwater/munic.cfm.
Office of Environmental Management. 2010. Virginia Pollutant Discharge Elimination System
(VPDES). City of Roanoke Virginia, Department of Public Works, Roanoke.
Sonne, J. 2006. Evaluating Green Roof Energy Performance. American Society of Heating,
Refrigerating, and Air-Conditioning Engineers Journal , 48, 89-61.
Tanner, S., & Scholz-Barth, K. 2004, September. Green Roofs. Federal Technology Alert .
Trevey, J. Ed. 2010. Eco-Book: A green building practices resource guide Vol. 1. Lynchburg:
Eco-Book.
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Background on Authors, Journal of Contacts and Additional Notes/Information
Authors:
- Cassandra “Kassi” Archambault
o Class of 2012
o Major: Political Science
o Minor: Environmental Policy
o Responsible for Discussion section
- Jonathan “Jon” Honchar
o Class of 2011
o Major: Environmental Policy
o Responsible for Cover page, Methods, Results, Graphs, and Editing
- Robert “Bob” Novakovic
o Class of 2012
o Major: Environmental Science
o Responsible for GIS Data & Mapping
- Kelsea Pieters
o Class of 2013
o Major: Communications
o Responsible for Recommendations, Summary, and Editing
- Benjamin “Ben” White IV
o Class of 2011
o Major: Environmental Policy
o Responsible for Problem Statement and Science and Technical Background
Contact Journal
April 6, 2011
- Erica Taylor
o Spoke with Ms. Taylor about obtaining green building information
o Informed us to send her an email asking her specific what info we were seeking
- Danielle Bishop
o Spoke with Mrs. Bishop about calculating rainwater runoff for flat roof buildings
o Obtained information needed from link on City of Roanoke’s website
April 7, 2011
- Kenneth Cronin
o Mr. White & Mr. Honchar spoke with Mr. Cronin at VMI after a presentation for
the Virginia Environmental Conference in regards to energy use for city buildings
o Informed us to send him an email asking him specifically what he was looking
April 11, 2011
- Erica Taylor
o Spoke via email about requesting information about city buildings and flood areas
in the city
o Informed us to meet with her Wednesday morning to obtain maps and data
- Kenneth Cronin
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o Mr. White emailed Mr. Cronin about energy information for city buildings and
Mr. Cronin said he would retrieve that information for the project.
April 12, 2011
- Justin Harness & Christopher Blakeman
o Miss Archambault contacted these men via email to obtain rainwater runoff data
and waste water toxin levels for the city
April 13, 2011
- Erica Taylor
o Mr. Honchar & Miss Pieter’s visited Erica Taylor and was given the maps and
GIS data for the city.
o Also obtained maps showing underground creeks in city and flood plain.
April 14, 2011
- Dr. Kathy O’Neill
o Mr. Novakovic contacted Dr. O’Neill for assistance with the geoprocessing of
GIS data to determine roofs’ square footage.
- Kenneth Cronin
o Provided energy use and energy costs for four of the five buildings requested.
o He was unable to get us the US Bankruptcy Courthouse’s energy use until 4pm
Monday since that data had to be obtained from the Federal Government.
- Just Harness & Christopher Blakeman
o Provided Miss Archambault with information about the MS4 Program Plan in
accordance with the Virginia Pollutant Discharge Elimination System
Additional Notes
Notes: MS4 Program Plan –gained from Justin and Christopher on the 14th by Miss Archambault
Our focus: rainfall, runoff, impervious surfaces
 Total Drainage Area within City Boundary = 18,880 acres (page 3)
 TMDL Wasteload Allocations to the City of Roanoke MS4
o Sediment for the Roanoke River and all tributaries within the boundaries of the
City of Roanoke = 953 tons/yr (page 4)
 A great map of waterways in the city of Roanoke page 5
 Main purpose of MS4 Program Plan (no intention linked with all the circles)
o As noted above Total Maximum Daily Load, Wasteload Allocations (TMDL WLA) have
o been established for the priority pollutants sediment and bacteria. In accordance with
o the provisions of Section I B of the current General Permit, the City has updated its MS4
o Program Plan as required to ensure MS4 Program Plan consistency with the
o assumptions of the TMDL WLA. All current BMPs, ordinances, policies, plans,
o procedures and contracts implemented as a component of the City’s MS4 Program Plan
o have been and will continue to be reviewed and evaluated as to their appropriateness
o and effectiveness at reducing the priority pollutants identified in the WLA. (page 6)
 Main purpose in outline format:
o The following outline provides the structure for this Program Plan evaluation:
o 1. Update status of the BMPs associated with the permit requirements for the Six
o Minimum Control Measures.
o a. Item 1 above is addressed in the MS4 Annual Report.
o 2. Provide a list of tools used to comply with the permit conditions and assess
Green Roof Proposal for the City of Roanoke
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o
o
o
o
o
o
o
o
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their strength, particularly in regard to their ability to mitigate the TMDL Priority
Pollutants, sediment and bacteria.
a. Where weaknesses are identified, develop a schedule of interim goals as
needed to implement appropriate changes/improvements.
3. Provide an estimate of annual stormwater discharge.
a. Include an estimate of sediment and bacteria discharge.
A description of the existing policies, and other tools and procedures used to
implement the City’s BMPs for preventing and/or controlling stormwater pollution is
included below. (page 6-7)
Municipality-Owned
As with the Multi-Family and Commercial/Industrial properties, AMEC used parcelspecific GIS assessment techniques to derive the total impervious area estimate for
City-Owned properties.
25,824,348 ft2
Unit Conversion Table
Impervious Area –(see page 8 for chart)
Property Type Designation Square Feet Acres Square Miles
Streets 129,246,149.60 2,967.08 4.64
Single Family Residential 55,194,240 1,267.09 1.98
Multi-Family Residential and
Commercial/Industrial
147,760,657 3,392.12 5.30
Municipality-Owned 25,824,348 592.85 0.93
Total 390,336,932 8,960.90 12.85
____________________________
IMPORTANT INFORMATION listed below (for the rest of the document) is the Estimates of
Stormwater Discharge in FY10. This is broken down to annual weather data—especially interesting is
precipitation, then there’s data on city’s impervious area (we should focus on municipal and total). Then,
there is a runoff volume factors. (page 9 of report) Page 10 is helpful only if we wish to utilize the runoff
calculation.
kassi
2010 Estimates of Stormwater Discharge in FY10
In addition to our runoff volume estimates, the City of Roanoke is subject to TMD
both sediment and bacteria.
Background Information:
Annual (7/1/09 – 6/30/10) weather data for Roanoke, VA
(Source: www.wunderground.com) Max: Avg: Min: Sum:
Temperature:
Max Temperature 97 °F 67 °F 24 °F
Mean Temperature 85 °F 58 °F 21 °F
Min Temperature 75 °F 48 °F 12 °F
Precipitation:
Precipitation 2.36 in 0.16 in 0.00 in 50.38 in
Green Roof Proposal for the City of Roanoke
Snow Depth 14.0 in 0.8 in 0.0 in City of Roanoke - Estimated Impervious Area
(derived from 2010 City-wide GIS analysis)
Square Feet Acres Square Miles
Roads 129,246,149.60 2,967.08 4.64
Municipal 25,824,348.00 592.85 0.93
Single Family Homes 55,194,240.00 1,267.09 1.98
Multi-Family Homes, Commercial 147,760,657.00 3,392.12 5.30
Total 390,336,932.00 8,960.90 12.85
Percent Impervious
(total impervious/total sq. miles) 29.95%
Runoff Volume Factors Value
Percent Impervious Land Cover 0.29
Reporting Year Precipitation Total 50.38 in
Total Area - City of Roanoke 42.90 mi2
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