Stormwater Management Plan for the Town
of Blacksburg’s College Springs Watershed
BSE-4125 Comprehensive Design Project
May 12, 2009
Purpose: The purpose of this report is to present the final design for a localized
stormwater management plan for College Springs Park in Blacksburg, Virginia. This
includes a problem statement, literature review, design specifications, and economic
analysis.
Team Name:
College Spring
Group Members:
Andrew Jeffery
Ben Snyder*
Brandon Copeland
Advisor:
Dr. Wolfe: ________________________
Dr. Yagow: _______________________
College Springs Design Team
Executive Summary: Stormwater Management Plan for the Town of Blacksburg’s College Springs Watershed
A design has been requested by Matt Stolte, an engineer of the Town of Blacksburg, to
develop a stormwater management plan using best management practices (BMPs) to install as
retrofits to College Springs Park. The headwaters to Stroubles Creek lie in College Springs Park,
which has been identified as an impaired water body due to a lack of benthic macroinvertebrates.
The College Springs sub-watershed is a 180 acre (72.84 ha) drainage area located in a historic
section of Blacksburg with homes dating back to the 1950’s, many of which lack proper
stormwater management features.
The goal of the design was to develop a localized stormwater management plan with the
intent of reducing sediment and nutrient loadings entering the upper branch of Stroubles Creek.
Information has been gathered to determine the feasibility and effectiveness of various BMPs for
three different locations in the park. BMPs have been selected using a decision matrix evaluation
at three locations within the park. A literature review was performed on the following
management practices: bioretention facilities, pocket/constructed wetlands, water quality swales,
riparian buffer zone, dry extended detention basins, and daylighting.
On-site grab samples were taken to determine nutrient and sediment concentrations in the
stream baseflow. Samples were taken from the wooded spring area, the input from the spring
beneath the adjacent football field, and the outlet of the park. Average concentrations for total
nitrogen, total phosphorus, and total suspended solids (TSS) where 0.69 ppm (mg/L), 0.37 ppm
(mg/L), and below detection limits, respectively. Samples were taken on February 27, 2009,
during a high intensity, short duration storm over a period of 2 hours at the outlet of the park.
The highest concentrations measured during the storm event were 7.3 ppm (mg/L), 5.6 ppm
(mg/L), and 552 ppm (mg/L) for total nitrogen, total phosphorus, and total suspended solids,
respectively. Baseflow and storm event samples indicated high nutrient and sediment loadings
when compared to the EPA National Nutrient Parameters for Ecoregion IX
Geographic information systems (GIS) and TR-55 software were used to model hydrologic
characteristics of the sub-watershed and determine peak discharges for the 2-yr and 10-yr design
storms. GIS was used to identify specific land uses, delineate areas assigned to these land uses,
and obtain reach lengths within the sub-watershed. These values were used as inputs for TR-55,
which returned peak discharges of 42.2 cfs (1.2 m3/s) and 112.7 cfs (3.19 m3/s) for the 2-yr and
10-yr storms, respectively.
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College Springs Design Team
A water quality swale was chosen for the drainage area outside the Berryfield apartment
complex, which is an input to the College Springs Park. The swale will be 151.64 ft (46.22 m)
long, with a bottom width of 2.5 ft (0.76 m), a top width of 15 ft (4.57 m), and side slopes of 3:1.
The swale was designed to treat a drainage area of 1.48 acres (0.60 ha), and a water quality
volume of 2,094 ft3 (82.23 m3). Four check dams evenly spaced throughout the swale provide
adequate storage capacity for the water quality volume. This will allow for infiltration into an
underlying soil matrix to provide water quality treatment. Expected removal efficiencies for
phosphorus, nitrogen, and TSS are 35%, 30% and 84%, respectively. The total cost of the swale
will be $5,382.
Daylighting was chosen as the stormwater management practice in the piped channel under
the park. Daylighting will re-establish a natural stream corridor, allowing for biological uptake
and controlled flooding throughout the park. The daylit stream corridor was developed using a
reference reach from the same stream network just below the park. Based on the reference reach,
the new stream section was given a length of 181 ft (55.2 m), a cross sectional area of 1.57 ft2
(0.0010 m2 ), with in-stream slopes of 3:1, and outcropping side slopes of 4:1. The total cost of
the daylighting section was $36,381, which may be offset with donated materials and
volunteered labor.
Wetland enhancement was proposed for the spring area of the park. This is a process where
the wetland around the spring is rehabilitated using native vegetation. Warm season grasses,
terrestrial and aquatic plants were the types of vegetation used in the wetland enhancement plan.
Specific plants included water lotus, Indian grass, and annual lespedeza. These plants will reduce
sediment loads by stabilizing the banks around the spring and lower nutrient loads through the
process of biological uptake. The cost of the plants was $286 with a maintenance cost of $50 a
year.
The management practices chosen for the stormwater management plan will effectively work
together to reduce sediment and nutrient inputs to the Upper Stroubles Creek watershed.
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College Springs Design Team
Table of Contents: Stormwater Management Plan for the Town of Blacksburg’s College Springs Watershed
I. Executive Summary...................................................................................................................... i
II. Table of Contents ...................................................................................................................... ii
1.0 Background Information ........................................................................................................... 1
2.0 Problem Statement ................................................................................................................... 1
3.0 Connection to Contemporary Issues ......................................................................................... 1
4.0 Scope of Work .......................................................................................................................... 2
5.0 Design Criteria .......................................................................................................................... 2
6.0 Literature Review...................................................................................................................... 3
6.1Design Alternatives ........................................................................................................ 3
6.1.1 Bioretention Facilities .................................................................................... 3
6.1.1.a. Water Quality Control………………………………...………...….4
6.1.2 Riparian Buffer Zone ................................................................................................ 6
6.1.3 Grassed/Water Quality Swale ........................................................................ 8
6.1.4 Daylighting ................................................................................................... 9
6.1.5 Detention Basins .......................................................................................... 10
6.1.6 Constructed/Pocket Wetlands ...................................................................... 11
6.2 Safety Regulations and Concerns ............................................................................... 13
6.3 Construction and Maintenance Costs.......................................................................... 15
7.0 Design Process ........................................................................................................................ 16
7.1 Water Quality Sampling & Testing ............................................................................ 16
7.1.1. Baseflow Results and Analysis .................................................................. 16
7.1.2 Storm Event Results and Analysis .............................................................. 16
7.2 Hydrologic Modeling .................................................................................................. 17
8.0 Design Selection ..................................................................................................................... 19
8.1 Decision Matrix .......................................................................................................... 20
8.2 Final Selection ............................................................................................................ 20
9.0 Project Design ......................................................................................................................... 22
9.1 Vegetation Enhancement ............................................................................................ 22
9.1.1 Design Specifications.................................................................................. 22
9.1.2 Maintenance Plan ........................................................................................ 22
9.1.3 Costs............................................................................................................ 23
9.2 Daylighting ................................................................................................................. 23
9.2.1 Design Specifications.................................................................................. 23
9.2.2 Maintenance Plan ........................................................................................ 24
9.2.3 Pollution Reductions ................................................................................... 25
9.2.4 Costs............................................................................................................ 25
9.3 Water Quality Swale ................................................................................................... 25
9.3.1 Design Specifications.................................................................................. 25
9.3.1.a. Hydrology.………………………………………………………26
9.3.1.b. Swale Geometry…………………………………………………27
9.3.1.c. Underlying Soil Matrix....................................................….……27
9.3.1.d. Check Dams................................................……………………..27
9.3.1.e. Inflow and Outflow……………………………………………...28
9.3.1.f. Vegetation………………………………………………………..28
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9.3.2 Maintenance Plan ........................................................................................ 28
9.3.3 Performance Reductions ............................................................................. 29
9.3.4 Costs............................................................................................................ 30
9.4 Community Outreach ................................................................................................. 31
10.0 Work Plan ............................................................................................................................. 31
11.0 Project Timeline .................................................................................................................... 33
12.0 Summary & Conclusion ........................................................................................................ 34
13.0 References ............................................................................................................................. 35
14.0 Appendices ............................................................................................................................ 38
14.1 Figures........................................................................................................... 38
14.2 Tables ............................................................................................................ 48
14.3 Equations……………………………………………………...…………….56
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College Springs Design Team
Title: Stormwater Management Plan for the Town of Blacksburg’s College Springs Watershed
1.0 Background Information
The spring within College Springs Park is one of the main headwaters for Stroubles Creek.
Before the 1950’s, College Springs was the main source of water for the Town of Blacksburg
and Virginia Tech. Adjacent to the park is 180 acres (72.8 hectares) of historic urban watershed
that drains into the 1.25 acres (0.51 hectares) park. The watershed surrounding the park includes
modern apartment complexes and urban development that lack proper stormwater management
practices, contributing to the impairment of Stroubles Creek. Matt Stolte, an engineer for the
Town of Blacksburg, has recognized the need for improvement in the stormwater management of
the College Springs watershed and has requested a design project partnership with the BSE
department at Virginia Tech.
2.0 Problem Statement
Upper Stroubles Creek has been listed as an impaired water body for benthic macroinvertebrates by the Virginia Department of Environmental Quality (VDEQ). Sediment,
nutrients, and organic matter have been listed as significant stressors, with sediment being the
primary focus of the TMDL Implementation Plan. Urbanization has increased runoff volume
and strength, intensifying erosion and sediment control issues. A lack of stormwater best
management practices (BMPs) throughout the College Springs sub-watershed has contributed to
the impairment of Stroubles Creek. For this reason, an innovative stormwater management
system in the Town’s College Springs Park and adjacent urban areas will help to improve the
health of Stroubles Creek.
3.0 Connection to Contemporary Issues
Increased urbanization has led to elevated environmental impacts in watersheds across the
world. The high percentage of impervious surfaces in developed watersheds has led to increased
runoff volume and strength, creating pollution and channel erosion issues. Recently LID
features and stormwater BMPs have been shown to be effective in the battle to increase water
quality and stream stability. These practices are not limited to newly developed areas but can be
retrofitted to older residential areas in the improvement of water body health. The various BMPs
and LID implementations are essential to the sustainable development of community watersheds.
Current LID practices rely on localized stormwater management systems to reduce the
environmental impacts of urban neighborhoods. An essential component of these management
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College Springs Design Team
plans is community outreach and education. Water stewardship programs initiated by
community members have been shown to be effective in controlling runoff at its source through
homeowner BMPs and participation in local governments.
4.0 Scope of Work
Objectives
1. Determine sediment and nutrient loads of College Springs inlets
2. Reduce sediment loads by a minimum of 54%
3. Determine runoff characteristics (peak discharge, total runoff volume, water quality
volume)
4. Identify sources of contaminants
5. Design appropriate stormwater management practices
6. Develop community brochure designed to educate residents of College Spring Watershed
of stormwater impacts
Deliverables
1. Design of BMPs and LID systems
2. Decision Matrix for alternative design systems
3. Projected stream quality improvements due to management practices
4. Cost-Benefit analysis of appropriated management techniques
5. TR-55 Hydrologic Model for College Springs watershed
6. Community brochure to be distributed to residents of College Springs sub-watershed
5.0 Design Criteria & Constraints
The purpose of this section is to identify criteria that can be used to assess BMP performance
in reducing nutrients, sediment, and peak discharge. The criteria were chosen based on water
quality and quantity control capabilities, economic feasibility, and aesthetic appeal. The water
quality criteria include the ability to reduce sediment loads by 54% (VDEQ, 1999). Water
quantity control criteria include ability to reduce peak discharge and runoff volume to that of
pre-development levels (VDCR, 1996). Economic criteria include construction and maintenance
costs needed to ensure long-term performance. These numbers will be based on previous
stormwater projects funded by the Town of Blacksburg. It is important that the chosen design be
aesthetically appealing and accepted by the community it serves. The criteria for aesthetic
appeal will be based on feedback of visual presentation from Blacksburg’s Stormwater Task
Force.
The constraints surrounding the design alternatives vary for each BMP alternative but will be
broadened for the purpose of this report. The surface area required is restricted due to the
dimensions of the four possible BMP sites. Water quality analysis is limited by the amount of
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funding provided. The chosen design must be compatible with existing hydrologic infrastructure
as far as the various input and output structures.
6.0 Literature Review
6.1 Design Alternatives
A localized stormwater management plan relies on a holistic approach to assessing various
sources of contamination within a watershed and designing appropriate BMPs to treat runoff at
its source. Dispersion of BMPs throughout the watershed alleviates the need for a large
treatment area at the outlet. Integrated management practices such as bioretention facilities and
other low-impact development systems are necessary components of localized stormwater
management plans. The following design alternatives are used as stormwater management
practices to mitigate runoff from urbanized areas on site. A literature review was performed on
these various management practices to assess their effectiveness and practicality for College
Springs Park.
6.1.1 Bioretention Facilities
Bioretention facilities are shallow basin BMPs with a vegetated covering designed to treat
stormwater runoff through biological processes in the soil media, uptake by plants, and
infiltration into the underlying soil strata. These facilities are often implemented in urban areas
because of their effectiveness in removing pollutants common to urban environments and their
aesthetic appeal (MDER, 2001). These facilities are designed to function similarly to an upland
forest floor, utilizing such processes as interception, evapotranspiration, assimilation, settling,
and microbial decomposition among others. A typical facility consists of a porous medium
supporting a vegetative layer with a surface layer of mulch on top. During large storm events,
ponding at the surface of the facility allows for pre-treatment of stormwater runoff before
filtration through the soil media. The extent to which specific processes take place is customized
in the design process based on the pollutant load of entering runoff. Although bioretention
facilities are typically designed for water quality treatment, they can provide partial to complete
water quantity control depending on land cover and use (VDCR, 1999). Their ability to provide
water treatment while decreasing channel erosion makes these facilities an attractive alternative
for an urban environment.
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6.1.1.a. Water Quality Control
Bioretention facilities utilize uptake of nutrients, filtration and settling, and microbial
interaction to improve water quality of entering runoff. Nutrient uptake and microbial
interaction are achieved in the vegetative and organic layers while filtering occurs in the soil
media and underlying soil strata. Ponding typically occurs above the vegetative layer allowing
for nutrient uptake and settling of sediment. In areas of low soil permeability, increased ponding
and flooding can allow for runoff to overflow and bypass the facility. These areas require an
underlying drain, reducing periods of flooding, but also decreasing groundwater recharge
(MDER, 2001). Soils with higher hydraulic conductivities are ideal for infiltration purposes, but
lack the amount of microbial and chemical interaction present in fine-grained soils. A proper
soil matrix ratio of rough to fine grained soils is necessary to maintain proper infiltration without
compromising pollutant reduction via microbial interaction.
Heavy metals along with oils and greases are common pollutants in urban environments due
to improper vehicle maintenance and pollutant build up on impervious surfaces. Pilot-scale
laboratory studies of bioretention facilities have indicated removal rates of greater than 92% for
copper, zinc, and lead. The 0.98 in (2.5 cm) thick mulch layer was identified by Hunt et al.
(2008) as a major contributor to metal attenuation, with levels 6 and 17 times larger than that of
the soil matrix for copper and zinc respectively. Removal rates of greater than 96% have also
been found for oils and greases (Hunt et al., 2008).
Although studies have indicated high removal capabilities for heavy metals, oil, and grease,
these pollutants are primarily removed through physical infiltration and are not entirely
indicative of the biological processes present in the facility. Biological processes such as
microbial interaction are essential in the reduction of nutrients. A combination of field and
laboratory studies of various media characteristics by Hunt et al. (2008) showed little to poor
removal rates for nitrate and ammonium, with no correlation between silt/clay contents and
removal abilities. The soil mixture containing intermediate levels of silt/clay proved best at total
phosphorus (TP) mass removal, although percent TP removal efficiency varied. Based on their
results, Hunt et al. (2008) recommended an underlying soil matrix consisting of vegetative and
coarse grained sand filtering layers. This would decrease ponding and allow for storage in the
upper layers in an attempt to increase exposure to microbial processes.
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Nutrient reduction ability will be an important factor when determining between design
alternatives. Hsieh and Davis (2005) have shown bioretention facilities to have effective
phosphorus removal rates, around 60-80%, with much lower numbers for nitrate removal, 020%, and in certain instances nitrate production. Table 1 shows their results for percent removal
versus depth for various pollutants. A current topic of research is possible soil amendments used
to enhance phosphorus or nitrate removal. A fly-ash soil amendment was shown to greatly
enhance the phosphorus removal of a sandy loam soil matrix (Wei et al., 2008).
Few studies examining the ability of bioretention facilities to remove pathogenic bacteria
have taken place. Field studies on an urban bioretention facility in Charlotte, NC indicated
removal rates of 69% and 71% for fecal coliform and E. coli, respectively (Hunt et al., 2008).
These are two primary indicator species for pathogenic bacteria. Similar studies conducted by
Dietz and Clausen (2005) found a 65% reduction in fecal coliform for roadside and urban sand
filters. They concluded that dry conditions and exposure to sunlight were two primary factors in
bacteria reduction. Bioretention facilities with appropriate clay/silt ratios to support microbial
interaction and ponding abilities for lengthened UV exposure offer potential for increased
bacteria removal rates.
Increased runoff volume and strength is a leading cause of channel erosion and sediment
input to water bodies. This is a direct effect of the increase in impervious surfaces in a
watershed. As a result, water quantity control is a primary factor to consider during the design of
an appropriate BMP. Peak runoff discharge and total runoff volume are two hydrologic
characteristics contributing to channel erosion and sediment loading. The TMDL for Upper
Stroubles Creek identifies sediment as the primary stressor leading to the impairment of the
stream and calls for a 54% reduction in sediment from urban sources (VDEQ, 2006).
Bioretention facilities are typically designed for water quality treatment, although they can
provide partial to complete water quantity control depending on land cover and use. The term
Integrated Management Practice (IMP) is used to describe bioretention facilities because of their
development for a wide range of applications, including the ability to mimic pre-existing
hydrologic conditions of a site (VDCR, 1999). These facilities are able to mitigate peak flows
because of high infiltration rates and the ability to store water in soil pores. A field study on an
urban bioretention cell in Charlotte, NC indicated mean peak inflow to outflow reductions of
greater than 96.5% for small to medium size storm events. During large storm events water can
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overflow facilities, reducing the potential for peak discharge reduction (Hunt et al, 2008). A two
year study of two bioretention facilities on the University of Maryland campus showed no
outflow from the facilities for 18% of the storm events, and a 44-63% reduction of peak flow
when outflow was present. The study stated that significant reductions can be expected for onethird to half of rainfall events (Davis, 2008).
6.1.2 Riparian Buffer
The Natural Resources Conservation Service (2001) defines a riparian buffer as, “an area of
predominantly trees and/or shrubs located adjacent to and up-gradient from watercourses or
water bodies.” A riparian buffer zone is established to reduce excess amounts of sediment,
organic matter, nutrients, and chemicals in shallow groundwater flow. A buffer zone will also
provide shade to reduce water temperature, provide habitat for native species, and protect the
surrounding soil from erosion (NRCS, 2001).
NRCS (2001) defines some specific qualifications for riparian buffers in Virginia. The
buffer must consist of at least two zones, zone one and zone two. Zone one must be a minimum
of 15 ft (4.57 m) beginning at the water line or the top of the bank. Zone two must be a
minimum of 20 ft (6.1 m) beginning at the end of zone one. The two zones combined must be a
total of 30.48 m (100 ft) or 30 percent of the floodplain, whichever is smaller, to a minimum of
35 ft (10.67 m). If there are highly erosive areas adjacent to the stream corridor, a third zone,
zone three, is required. This zone will be a grass filter that will follow the guidelines as defined
in the Virginia Conservation Practice Standard Filter Strip (Code 393). All trees and shrubs
planted in zones one and two will be established in accordance with Virginia Conservation
Practice Standard Tree/Shrub Establishment (Code 612). All trees and shrubs should be native
to promote natural diversity of species. While establishing the buffer, all VA spec sheets must
be filled out. Once the buffer is established, maintenance is required regularly to assure that the
filter is working. Such measures would include replacement of dead vegetation, mowing of
grass, and control of unwanted weed species such as A. Lanthis (NRCS, 2001).
Moore and Palmer (2005) explored the effect of urbanization on macroinvertebrate
populations in headwater streams and the mitigation of these negative effects using riparian
forest buffers. According to this article, the two main factors that affect invertebrate populations
are the amount of impervious surfaces and the quality of riparian forest. The study involved 29
headwater streams in the region just north of Washington D.C. with land uses that range from
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agricultural to urban with different qualities of riparian buffers. The headwater stream
catchments used in this study were chosen to be small, ranging from 667.18-2,273.4 acres (270
ha-920 ha). The small areas lessen the variety of the land uses and riparian buffers, making them
more homogenous. GIS was used to determine the percentage of land use and of impervious
surfaces. Invertebrate samples were taken from March 15 to April 15 of 2001 and 2002. Three
riffles and two areas in each riffle were sampled in each stream. The samples were analyzed for
richness of invertebrate populations by comparison to other literature.
The results of the study by Moore and Palmer (2005) showed that urban landuse had lower
diversity when compared to the agricultural land. There was a negative linear relationship
between the amount of impervious surface cover and macroinvertebrate diversity and richness,
meaning, as impervious surfaces increased, macroinvertebrates decreased. The study also found
a weak but significant linear relationship between the quality of riparian buffer and the richness
and diversity of the invertebrate populations in the urban areas. This suggests that biodiversity
of the invertebrate populations can be improved in urban areas by restoring and protecting
riparian forest buffers. Therefore, populations of invertebrates, which represent the water quality
of a stream, can be successfully mitigated by restoring riparian buffers.
6.1.3 Grassed/ Water Quality Swales
A grassed swale is defined as a “broad and shallow earthen channel vegetated with erosion
resistant, flood-tolerant grasses.” This is similar to a water quality swale, which is the same
thing but underlain by engineered soil mixture. The purpose of a grassed/water quality swale is
to convey water at non-erosive velocities and improve water quality through infiltration,
sedimentation, and filtration. These can have added water storage and lower peak discharge
during rain events by the addition of check dams. Check dams are blockages to the flow in a
swale which cause small temporary pooling. This allows for settling of sediment and infiltration
of water. Water quality is improved in a swale through the use of vegetation. The vegetation
slows down the water flow and physically blocks the sediment causing it to settle. Figure 1,
shows a water quality swale equipped with check dams (VDCR, 1999).
Grassed and water quality swales apply to small drainage areas due to the fact that they
cannot handle large flows. These swales must treat 10-yr storm events at non-erosive velocities.
The size of the drainage area and amount of impervious surfaces determines that size of the
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swale. In general, a grass swale is used for small urban areas of 16-21% impervious surface and
a water quality swale is used for 16-37% impervious surfaces (VDCR, 1999).
Important conditions for the location of swales include soil properties, topography, and depth
of the water table. The soil used to construct a grassed swale must have a minimum infiltration
rate of 0.27 inches/hour (0.69 cm/hour) to successfully drain water. This is the typical
infiltration rate of silt loam soil, making it a good soil for construction. A water quality swale
can, however, be used in soil with less than optimum infiltration rate due to the use of engineered
soils. The topography of the swale location should be relatively flat so that the desired slope can
be constructed. Also, the swale should be located at least 2 ft (0.61 m) above the water table to
help promote infiltration and lower the chances of permanent pooling (VDCR, 1999).
Specific design criteria according to VDCR (1999) for a grassed/water quality swale include:
-trapezoid cross-section with side slope a maximum of 3H:1V
-bottom width 2-6 feet (0.61-1.83 m)
-flow depth at the height of grass, height of 4 inches (10.16 cm) maximum
-water quality flow max of 1.5 ft/s (0.46 m/s), 2 year storm maximum 4 ft/s
(1.22 m/s), 10 year storm maximum 7 ft/s (2.13 m/s)
-slope typically between 1-3% with a maximum of 5%
-ponding depth behind check dam should not exceed 18 inches (45.7 cm)
-recommended grasses are tall fescue, reed canary grass, redtop, and rough-stalked blue grass
Maintenance requirements involve the upkeep of grass and the removal of sediment and
debris. The ground should be kept as a dense, vigorous grass cover. Grass should be
periodically mowed, but never cut lower than 3 - 6 in (7.62- 15.24 cm) is the best height.
Remove the sediment and debris behind the check dam on a biannual basis. If excessive
sediment builds up, removal and revegetation is required. If pores of the soil become clogged,
then tilling or aeration is required (VDCR, 1999).
A study in Brisbane, AU was conducted on the ability of a grassed swale to remove total
suspended solids (TSS), total phosphorous (TP), and total nitrogen (TN). The study involved a
controlled grass swale system along a highway (Figure 4). Inputs of sediment were added at
varying times and concentrations to mimic natural conditions. The results of the study were total
removal rates of 69% for TSS, 46% for TP, and 56% for TN. The study also included results
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from other studies on grassed swale removal rates, shown in Table 2 (Deletic and Fletcher,
2006).
The TRAVA model, that models the behavior in flow over grassed surfaces, was used in the
Brisbane study to make predictions about the performance of the grassed swale. The model
predicted concentrations within +/- 17% of the measured TSS and within +/- 11% of the total
mass of sediment removed. This confirmed the use of the TRAVA method for predicting the
performance of a grassed swale.
6.1.4 Daylighting
Daylighting is a practice started in the 1970’s which re-establishes and exposes a buried,
existing stream (Pinkham, 2000). Streams that are commonly daylighted are those encased by
concrete pipes and streams buried below streets, buildings, or other structures. Daylighting
streams can have considerable benefits. A case study in Zurich, Switzerland (Figures 2a and 2b)
(Pinkham, 2000), has shown water quality can be improved by exposing the water to air,
sunlight, vegetation, and soil, allowing for more biological activity to occur and incurring more
biological uptake of harmful pollutants. In order to provide for further biological uptake,
daylighting allows for additional best management practices to be implemented, such as riparian
buffer zones. Previous flooding problems can be alleviated by removing piping networks that are
under capacity. With increased urbanization, additional impervious surfaces create higher
volumes of runoff and daylighting allows for improved hydraulic capacity and flood control.
Lower velocities are experienced downstream with the improvement of flood control, along with
stream beds having natural aspects opposed to smooth, concrete beds. Daylighting is more cost
effective than replacing an old deteriorated pipe and is more easily managed, monitored, and
repaired. Exposure of a stream to its natural surroundings also gives a community a sense of
reconnection to a local waterway. Daylighting has also been used to allow for fish passage from
one section of a stream to another. Upon recreating the stream channel after a daylighting project
has been undertaken, a meander within the day lit section of the stream will allow for additional
sediment removal (Pinkham, 2000).
Despite all of the benefits there are a few challenges when considering daylighting a stream.
The largest challenge is total expense, which comes from excavation, channel re-alignment, and
transportation of soil and old piping. Finding the exact location of an old piping network may
prove to be difficult based on available mapping. Public safety is also an issue with regards to the
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possibility of children drowning, introduction of new vermin such as raccoons and muskrats, or
possibly increased environmental regulation concerns for local homeowners along the stream
(Pinkham, 2000).
6.1.5 Detention Basins
Traditional stormwater management techniques have generally involved basic detention
basins. Detention basins are designed for urbanized areas, in order to decrease peak flow rates.
Peak flow rates are control by detaining or collection of the stormwater. The pooled water in a
detention basin will allow for groundwater recharge along with lower discharge rates at the
outflow structure. Stormwater is detained only for a few hours to a few days based on the
intensity of a storm, leaving the basin dry during non-storm events. Detention basins aim to
remove sediment from stormwater through gravitational settling. Additionally detention basins
remove soluble phosphorus and total phosphorus, but at lower level of efficiency in comparison
to sediment removal. The removal efficiencies of detention basins are as follows, sediment
65%, total phosphorus 40-50%, and soluble phosphorus 35% (VDCR, 2008).
Detention basins require a maximum drainage area of 50-75 acres (20.2-30.35 hectares)
(VDCR, 2008). However provisions can be made to adjust sizing requirements for a detention
basin using baseflow measurements. Larger detention basins do not necessarily correlate with
increase removal efficiencies of pollutants. Detention basins are to be used in low visibility sites
to keep the public away from possible stagnation. Sites appropriate for detention basin use
include low and medium density residential and commercial sites. When designing a detention
basin 20 ft (6.1 m) vegetation buffers are required to be placed around the edges. Also soils with
low permeability should be used and karst conditions may require a liner or use of clay soils
(VDCR, 2008).
Recent information gathered has shown different styles of detention ponds have shown to
have increased removal efficiencies of all pollutants. One of these newly studied detention ponds
is an extended detention pond which uses a shallow marsh at the lower stage of the basin. Also
other structures have shown improvements with shallow marshes throughout the entire basin
along with any type of vegetation that can withstand high quantities of water along with
extended time periods without much water. The introduction of vegetation allows for more
biological uptake and effectively increases the removal rates of pollutants.
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6.1.6 Constructed/ Pocket Wetlands
In order to understand pocket wetlands it is important to define constructed wetlands and the
processes they use to improve water quality and decrease channel erosion. Constructed wetlands
are shallow basin BMPs that support the growth of aquatic vegetation and are designed to
improve stormwater quality runoff. They were initially used as treatment systems for pointsource wastewater with recent applications to urban and agricultural runoff. There are many
BMP variations within the constructed wetland paradigm, including shallow wetland, extended
detention wetland, the pond/wetland system, and the pocket wetland. Each variation differs in
the depth of water, surface area, and inclusion of pre-treatment BMPs (VDCR, 1999).
Constructed wetlands promote such processes as settling, plant uptake, filtration, and
biological decomposition to improve water quality. The pollutant removal efficiencies of
constructed wetlands are highly variable and often difficult to predict due to site specific factors
such as soil, climate, and hydrologic conditions. Studies by Carleton et al (2008) show that
pollutant removal rates of constructed wetlands are dependent on inflow and detention time,
which are functions of runoff volume and wetland size. Tilley and Brown (1996) studied the
effect of retention time on the pollutant removal rate for a constructed wetland in Tampa Bay,
Florida. They found a reduction of 94% in sediment and 90% in total phosphorus with a
retention time of 14 days, and a reduction of 67% in sediment and 57% in total phosphorus with
a retention time of only 5 days. Table 3 shows the range of reported removal rates according to
the Center for Watershed Protection (2007).
According to the Virginia Stormwater Management Handbook (2008) constructed wetlands
are not recommended for flood and channel erosion control. This is because of anticipated water
level fluctuations associated with water quantity control facilities. These fluctuations can cause
added stress to edge vegetation, thereby increasing susceptibility to channel erosion. According
to Birch et al (2004) constructed wetlands can reduce 5 to 10 percent of incoming runoff volume
via evapotranspiration and seepage losses. These are relatively minor reductions when compared
to other management practices.
Constructed wetlands often require upland, pre-treatment BMPs to decrease the pollutant
load entering the wetland, reducing maintenance requirements and increasing the life of the
wetland. The need for pre-treatment BMPs could be a deciding factor when choosing between
design alternatives. A typical pre-treatment BMP consists of a deep pond with macrophyte
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vegetation, designed to capture coarse grained sediment. Some wetlands utilize sediment traps,
or continuous deflective separation systems (CDSS), at the inflow of the wetland to capture large
sediment and pollutant particles. Although initially cheaper, CDSs typically require more
frequent maintenance than other pre-treatment BMPs (VDCR, 1999).
Pocket wetlands are a type of constructed wetland designed for smaller drainage areas,
typically around 1 to 10 acres (0.405 to 4.05 hectares). Pocket wetlands are often excavated to
the groundwater table to reduce periods of drought associated with stormwater dependent
systems. Figure 5, shows a schematic of a recommended pocket wetlands system according to
Minnesota’s Metropolitan Council on Environmental Services (2001). The figure shows a pretreatment swale separated from the pocket wetland to provide initial velocity and sediment
reduction. A buffer zone surrounding the facility is also recommended to limit common
difficulties including large debris and invasive species such as cattails. The high marsh wedges
are placed at 50 ft (15.24 m) intervals, perpendicular to the flow of water to limit dry weather
flow paths (MNMC, 2001). The application of constructed wetlands is restricted based on
numerous site specific details such as soil types, depth to bedrock, groundwater level, and
available land area. Medium to fine texture soils, NRCS soil types B, C, and D, are preferred to
allow adequate surface ponding, establish macrophyte vegetation, capture pollutants, and enable
groundwater recharge. Sufficient land area is required to provide for gradual water level
fluctuations by limiting the vertical depth of ponding water. Also, in areas of low soil
permeability an impermeable liner may be necessary to provide soil saturation and decrease the
possibility of groundwater contamination (MNMC, 2001).
6.2 Safety, Regulatory, and Environmental Considerations
According to Section 305(b) and 314 of the Clean Water Act (CWA), each state is required
to submit biennial reports to the EPA listing impaired water bodies and suggested improvements
(EPA, 2008). Monitoring and assessment done by the Virginia Department of Environmental
Quality (VDEQ) was used to place the upper branch of Stroubles Creek on Virginia’s 303(d) list
of impaired water bodies due to its benthic impairment. The TMDL report identified sediment as
the primary stressor impacting the habitat of benthic organisms with additional significant
contributions from nutrients and organic matter (VDEQ, 2006).
Section 18-613 of the Town of Blacksburg’s Stormwater Ordinance specifies performancebased and technology-based criteria for developing water quality management practices. Both
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criteria require comparison of post-development runoff pollutant loads to pollutant levels of predevelopment conditions based on average land cover or existing site conditions (Spencer, 2008).
A stormwater BMP is then designed based on pollutant removal efficiencies as specified in Table
4. Sizing and other design criteria are to be consistent with those specified in the Virginia
Stormwater Management Handbook.
According to Virginia Stormwater Management Regulations the ‘first flush’ (Water Quality
Volume) or ½’’ to 1’’ of runoff is required to be captured and treated (VDCR, 2005). As a
result, most BMP designs weigh heavily on the Water Quality Volume for sizing criteria. BMP
design criteria based on pollutant removal mechanisms such as settling, filtering, and biological
processes can be found in the Virginia Stormwater Management Handbook. According to the
handbook, significant settling of urban pollutants occurs in the first 6 to 12 hours of detention
time, with a required detention time of 30 hours for extended water quality design. Stormwater
BMPs designed with settling processes are typically capable of providing storage volume for
peak rates based on the water quality volume. Because stormwater filtration BMPs must allow
for adequate infiltration of runoff they are limited to small drainage areas and flow rates. The
sizing criterion of these BMPs is also the water quality volume. Filtration BMPs often require
construction of a diversion structure to minimize the ability of large flows to wash out previously
deposited pollutants. BMPs utilizing biological processes typically involve shallow, permanent
pool depths and plentiful vegetation. The sizing criterion is the size of these permanent pool
depths based on a multiple of the water quality volume (VDCR, 1999).
The town of Blacksburg’s Department of Engineering and GIS has issued a memorandum
outlining the minimum geotechnical requirements for most BMP practices. Due to the common
presence of karst conditions, sufficient investigations are necessary during the planning
processes of BMP applications. BMP applicants must submit the outcome of their investigations
based on local geology, soil maps, and a possible field verification of karst conditions (Hixon,
2008). The memorandum also specifies appropriate soil properties for individual BMPs and
directions for soil sampling.
Stream channel erosion has been recognized as a major contributor of sediment by the Upper
Stroubles Creek TMDL study, which calls for a reduction of 77% of sediment from this source
(VDEQ, 1996). Statewide ordinances address this issue by regulating the 2-yr storm event peak
runoff rate to comply with that of pre-development conditions. Although BMPs are designed to
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reduce the peak runoff to pre-development levels, the frequencies at which these levels occur are
greatly increased by the addition of impervious surfaces to a watershed, thereby increasing
channel erosion. The challenge in designing appropriate BMPs to reduce channel erosion is in
recognizing design criteria that properly identify pre-development sediment load transport
characteristics of the stream. Minimum Standard 19 of the Virginia Erosion and Sediment
Control Regulations requires stream channels to convey the peak runoff of the 2-yr storm event
at a non-erosive velocity, with constructed channels able to convey the peak runoff of the 10-yr
storm event at a non-erosive velocity (VDCR, 2008).
6.3 Construction and Maintenance Costs
The following numbers were based on Hanover County, Virginia’s BMP Summary Report.
These costs are averaged from construction endeavors within Hanover County and other county
governments.
Bioretention Facilities:
$186,284 /acre ($460,301 /hectare)
o Maintenance: 5-7% of construction costs
Constructed Wetlands:
$57,100 for a 1-acre-foot of facility ($245 /m3)
o $289,000 for a 10-acre-foot facility ($1238 /m3)
o $1,470,000 for a 100-acre-foot facility ($6296 /m3)
o Maintenance: 3-5% of construction costs
Buffer Strips/ Riparian Zones:
o If using seed: $0.30/ft2 ($3.26 /m2)
o If using sod: $0.70 ft2 ($7.61 /m2)
o $350/acre/year ($865/hectare/year)
Detention Ponds:
$45,700 for a 1-acre-foot of facility ($196 /m3)
o $232,000 for a 10-acre-foot facility ($994 /m3)
o $1,170,000 for a 100-acre-foot facility ($5003 /m3)
o Maintenance Costs: 3-5% of construction costs
Vegetated Swales/ Water Quality Swales:
o $0.50 /ft2 ($5.38 /m2)
o Maintenance Costs: $1.90/ linear meter/ year for a 0.5m deep channel
7.0 Design Process
7.1 Water Quality Sampling and Testing
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7.1.1 Baseflow Results and Analysis
On November 11, 2008 six water samples were collected from various locations within the
College Springs Park in Blacksburg, Virginia. Two samples were taken from each designated
location. The locations were chosen based on the two annually flowing inputs and the channel
flow downstream of these inputs. The results are shown in Table 5.
As shown in Table 1, five of the six samples measured below the detection limit for total
suspended solids. The first sample from the football field showed a relatively high TSS value of
6 mg/L. Total phosphorus levels were lowest for the spring samples and highest for both the
football field inlet and channel flows. Ammonia results were relatively constant for all samples,
with values between 0.17 and 0.19 mg/L. Average values for nitrate, total nitrogen, and nitrite
were lowest for the spring samples and highest for the football field and channel flow inlets.
Table 6 shows reference conditions for various pollutant levels based on the lower 25th
percentile of data for the EPA’s ecoregion IX. Virginia currently lacks water quality criteria for
nutrients and is in cooperation with the EPA on developing appropriate standards. For this
reason the water samples from College Springs were compared to the reference conditions of the
EPA’s National Nutrient Criteria. It is important to note that these are only recommendations
and that the responsibility for developing appropriate water quality standards are on the state
level. When compared with reference conditions of Ecoregion IX, nitrogen levels from College
Springs are significantly higher. The same is true for total phosphorus, with certain levels in
College Springs being greater by factors of 8 or higher.
Table 8 shows Virginia’s nutrient criteria for lakes and reservoirs as developed by the VDEQ
and approved by the EPA. The highest value for total phosphorus was 40 micrograms per liter.
The samples from College Springs ranged from 130 to 300 micrograms per liter, with an average
of 0.25 micrograms per liter. Table 4 indicates a concentration of 8 micrograms per liter for
ortho-phosphorus criteria in a natural lake in Virginia. Average values of ortho-phosphorus
levels were 6 micrograms per liter from the spring, 120 micrograms per liter from the channel
flow, and 105 micrograms per liter from the football field.
According to Table 6, total suspended sediment is very low in the spring and channel flow
and highest from the football field. The spring has low levels of sediment because of the large
volume of standing water, allowing for sediment to settle easily. The fact that the football field
inlet is able to mix with the spring water before becoming channel flow also gives more time for
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sediment to settle from this inlet, which could be a reason for low levels of TSS in the channel
flow. It is important to note that these are only baseflow measurements, and the storm event
samples collected on February 11 could contain high levels of TSS. BMPs designed in the
spring area should not necessarily be catered towards sediment reduction because of the settling
ability already present.
High levels of total phosphorus and nitrogen when compared to reference conditions for
EPA’s ecoregion IX indicate a nutrient loading problem in the College Springs Park. If an
effective stormwater management plan is to be implemented, BMP criteria must rely heavily on
nutrient reduction. Management practices from the football field, high levels of phosphorus in
decaking agents for roads, and homeowner practices could all be sources of these high nutrient
levels.
7.1.2 Storm Event Results and Analysis
A series of storm event samples were collected at College Springs Park over a two hour
period. Grab samples were taken once every five minutes for the first hour and every ten
minutes for the second hour, totaling eighteen samples. The samples were taken at the outlet of
College Springs Park where the stream is piped under the road, allowing for all inputs to be
collected. Samples were analyzed by the BSE Water Quality Lab Manager according to Table 9.
The samples were tested for total nitrogen, ammonia, nitrate, total suspended solids, total
phosphorus, along with orthophosphate. As shown in Figure 6, peak flow occurs during the third
sample at fifteen minutes, with a TSS concentration of 552 mg/L. As shown in Figure 7, nutrient
concentrations were also highest during this time. However Nitrate showed its highest
concentration at the ten minute sample time. The water quality standard, as specified in Virginia
Water Quality Standards Handbook, for total nitrogen levels in drinking water is 10 mg/L. All of
the samples collected contained concentrations above drinking water standards. Standards and
criteria for ammonia were not found and therefore didn’t allow us to analyze these concentration
levels. Nitrate recommended levels were 10 mg/L and all of the samples tested were below the
recommended standard. Standards and criteria for total suspended solids were construction
based because of no available in-stream TSS standards. The construction based standard which
may be high for a stream standard was 30 mg/L, which all of the samples collected during the
first flush showed extremely high levels. At peak flow, TSS had concentrations of 552 mg/L,
which is 18 times above the recommended levels. Total phosphorus standards and criteria were
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found to be 0.100 mg/L. Every sample collected, even after the first flush was shown to exceed
the standards and criteria. During the peak flow, total phosphorus exceeded standards and criteria
by 56 times. The standard for orthophosphate was set at 8 µg/L, and as with total phosphorus
every sample collected exceeded the recommended standard. At its highest during the peak
flow, orthophosphate was 225 times the recommended standard.
Storm event water quality analysis has shown that TSS, total phosphorus, and orthophosphate
are all problematic pollutants within our watershed. This would lead us to believe our BMP
designs should be have high removal rates of these three pollutants. The total nitrogen, being
below drinking water standards, was not a problem during this storm event. This, however, does
not exclude it from the nutrient problem. Base flow measurements show that nitrogen is a
problem, which implies that the nutrient was diluted to lower levels due to the increase in flow.
The level of nutrients and the level of sediment show a strong relationship between the figures.
This implies that if the sediment load was reduced then there would be a reduction in the nutrient
loads. Reducing sediment load is much easier than reducing nutrients which makes lowering
sediment a good alternative to addressing the nutrient problem.
7.2 Hydrologic Modeling
The model used to analyze the College Spring watershed was TR-55. TR-55 is a curve
number based program in which land uses, structures, and flow concentrations are entered and
peak discharges are returned for design storms. For our analysis, we chose design storms of 2
and 10 years.
The process of running TR-55 involved both GIS and field observations. The land uses were
determined using a land use layer on GIS that was provided by the Town of Blacksburg. This
provided information about what type of development was currently on the land. A summary of
the land uses is shown in Table 10. These land uses were matched to the respected curve number
and description in TR-55. It was assumed that the soil was in hydraulic soil group B due to the
universal moisture content and soil type.
The next step in TR-55 analysis was determining flow path and concentration. This was
done initially using observation from the digital elevation map in GIS. The contours were
observed for large depressions where water could accumulate. These areas were used to create
general diagram of where the water was expected to concentrate. The general diagram was then
confirmed and edited using field observations. Physical observations of the watershed were
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taken to see where the water was flowing during storm events. The result was the diagram
shown below in Figure 8.
The blue lines represent concentrated flow. Sub-watersheds were
delineated at every intersection to create four main areas. These sub-sheds were intersected with
the Blacksburg land use map in GIS and entered into TR-55 as sub-sheds A through D. Flow
lengths were then measured in GIS by taking the average distance from the outside of each subshed to the concentrated flow. The first 100 feet were considered sheet flow leaving the rest as
grassed shallow concentrated flow. The blue lines were measured as concentrated flow. All of
these values were entered into TR-55 which returned a time of concentration.
The next step was to identify which sub-shed drained into which concentrated flow, or reach.
Each area and reach were connected in order from the farthest point in the watershed to the
outlet. Structures were then identified through field observations and inserted into the flow path
at their respected sites.
Once all the above information was entered, TR-55 was run for a 2-yr and 10-yr storm. The
resulting peak flow rates were 42.5 cfs (1.2 m3/s) and 112.5 cfs (3.19 m3/s) respectively. These
values were used to determine the sizing of the BMPs that were being implemented in College
Spring Park.
8.0 Design Selection
8.1 Decision Matrix
The decision matrix was evaluated for each section within College Springs Park and the
surrounding areas that were deemed appropriate for management practices. Appropriate areas
were chosen based on existing drainage areas, proximity to the stream corridor, and visual
assessments during storm events. Four areas were selected including the spring, the park, the
drainage outlet of the Berryfield apartment complex, and the ditch next to Clay Street. The
ratings were on a scale from 1 to 5, with 5 being the best. These numbers were chosen based on
information gathered during the literature reviews. The ratings for each practice remained the
same for each area. The criteria were weighted differently for each area to take into account the
different characteristics of each area.
For the area within the park the dry detention basin, water quality swale, and bioretention
facility were not applicable because the stream corridor flows through this area. This is not
consistent with the criteria as stated in the Virginia Stormwater Management Handbook.
Community acceptance was the most heavily weighted criteria because of the location within the
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portion of the park maintained for recreational use along with its adjacency next to the parking
lot and road. Daylighting received the highest rating for community acceptance because of its
ability to reestablish a stream corridor with natural vegetation and flowing water. Although this
practice may restrict recreation within the park, it will provide an aesthetically pleasing area with
the potential to increase wildlife habitat. Sediment reduction was the second most heavily
weighted criteria because of reductions called for by the Upper Stroubles TMDL, as well as high
levels of TSS found during water quality analysis. Matt Stolte, Blacksburg Town Engineer, had
initially recommended daylighting as an appropriate management practice for community
awareness purposes. For this reason, along with the ratings given in the decision matrix as
shown in Table 11, daylighting is chosen as the most effective management practice for the area
within College Springs Park.
For the area along the side of the road opposite of the park the surface area required was the
most heavily weighted criteria. The existing drainage ditch is at the base of a slope and is
narrow in relation to the other areas. Nutrient and sediment reductions were also heavily
weighted because of the high levels of phosphorus and nitrogen determined from water quality
analysis. Community acceptance was weighted at 15 percent because of the area’s location next
to Clay St. The water quality swale was given a high rating on surface area required because of
its trapezoidal shape, consistent with that of the existing ditch. It was also given a high rating for
community acceptance because of the maintained landscape associated with water quality
swales. The water quality swale received a total rating of 3.8 as shown in Table 12, higher than
both the pocket wetland and bioretention facility. This practice was chosen as most effective for
the area along the side of the road.
Because the drainage area surrounding the Berryfield apartment complex is located on
private property, maintenance and construction costs were the most heavily weighted criteria.
As shown in Table 13, the water quality swale received the highest ratings for this section
because of the relatively cheap construction costs and little maintenance requirements.
Community acceptance was given a high weighting because of the location of the drainage area
within the complex, which is seen by the residents on a daily basis. Sediment reduction was
given a relatively lower weighting because of current practices within the drainage area. This
includes large rock pieces, approximately 6-10 inches in diameter, acting as sediment traps to
slow runoff and provide settling time. There is very little vegetation throughout the drainage
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area, providing little biological uptake and nutrient reduction. The water quality swale received
the highest rating of 3.85, well above the bioretention facility, pocket wetland, and dry detention
basin. A water quality swale was chosen as the most effective management practice for the
drainage area surrounding the Berryfield apartment complex.
For the spring area the only two applicable practices are a pocket wetland and wetland
enhancement. Nutrient reduction was weighted heaviest because of the high levels of
phosphorus and nitrogen found in the baseflow water quality analysis. Sediment reduction was
given a low weight because of the low TSS found in water quality analysis and the sediment
reduction abilities associated with the spring area. Large amounts of vegetation and large
storage time provide adequate sediment removal ability. Construction and maintenance costs
were heavily weighted because of large amounts of vegetation and a low water table that would
increase construction costs, as shown in Table14.
8.2. Final Design Selection
The four BMPs that scored the highest in the decision matrices were a water quality swale in
the Berryfield drainage area, daylighting for the park area, wetland enhancement for the spring
area, and a water quality swale for the runoff channel on the side of the road. After further
investigation of the runoff channel, we determined, through GIS and field observations, that the
drainage area was too small for an effective BMP and could be eliminated from consideration.
The other three BMPs were kept and chosen as the practices to be implemented in College
Springs Park.
9.0 Project Design
9.1 Vegetation Enhancement
9.1.1 Design Specifications
Wetland enhancement is a best management practice that modifies or rehabilitates a wetland
for a specific purpose. These purposes can range from creating wildlife for waterfowl to
establishing vegetation for reduced runoff and nutrient loading. The most common practice for
rehabilitating a wetland is vegetation enhancement. This is where native plant species are
established within wetland limits. A list of allowable native plant species can be found in the
Plant Establishment Guide for Virginia. It is recommended that plant materials should be
collected or grown within a 200-mile (322 km) radius of the wetland. A table acceptable plant
species for College Springs Park spring area is shown below in Table 15.
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Wetland enhancement benefits the surrounding watershed by reducing erosion, lowering
nutrient loads, and promoting native wildlife. Warm weather grasses that are planted along the
banks of the wetland help to stabilize the soil and hold it in place during a storm event. This
lessens the amount of sediment that enters the water and then, eventually, a stream. These
grasses will also promote physical sedimentation of sediments when water flows through them.
Vegetation that is planted in and around the wetland helps to reduce the nutrient loading in the
water through the process of biological uptake. Plants will use the nutrients in the water for
growth and therefore fix the plant mass. The vegetation will also provide habitat for native
species of fauna that may not have had habitat previously. This promotes biodiversity which is a
primary characteristic of a healthy ecosystem.
9.1.2 Maintenance Plan
A maintenance plan for a wetland enhancement project must be developed to ensure proper
functioning during the life of the wetland. A plan such as this should involve regular inspection
and servicing of the vegetation that makes up the enhancement project. Potential actions that can
be taken for maintenance include: replacement of dead plants, controlled burning of underbrush,
elimination of unwanted species, and fertilizing if there is a nutrient deficiency. A landscaping
company will be hired twice a year to do a full inspection of the grounds. The services they will
provide will be replacement of vegetation as well as an inspection and extermination of invasive
species.
9.1.3 Costs
The cost of purchasing the plants is $286. Maintenance cost will be $50 a year for a biannual
landscape inspection and clean up. The costs could be higher depending on how many plants
need to be replaced.
9.2 Daylighting
9.2.1 Design Specifications
The daylighting design within College Springs Park was developed using the reference
approach. The reference approach uses the measurements of a number of channel parameters to
derive dimensionless ratios. These ratios allow for extrapolation of values derived from one sized
watershed for use in another. The conditions used must be comparable. In the case of College
Springs Park the reference reach measured was the reach three-hundred feet below the park
itself. The reach directly below the park had a cross sectional area of 1.57 ft2 (0.0010 m2), a
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wetted perimeter of 13.78 ft (0.35 m), which gave a hydraulic radius of 0.1139 in (0.00289 m).
Also the float method was used to determine in stream velocities, as shown in Table 16. We had
considered creating a meander within the stream; however at such low velocities a meander
would not provide any significant decrease in velocity. In the park, discharge was measured at
the end of the concrete piped channel using bucket measurement, as shown in Table 17. The
discharge in the park was measured as being 0.005 m3/s, whereas the discharge in the reference
reach was measured as 0.021 m3/s, four times that of the upstream measurements. We consider
this error to be due to the crude measurements done while using the bucket measurements. As
measurements were taken there were difficulties in collecting the entire amount of flow coming
out of the concrete pipe. Some water leaked out below our funnel device along with other water
that was splashed out of the bucket due to the angle it had to be placed on. Because of this issue
the measurements used were based on the reference reach. However the reference reach had a
rectangular channel cross section and this needed to be altered allowing for a 2:1 side slope in
the daylighting section. From this a cross sectional view of the daylighting was developed as
shown in Figure 9, along with an isometric view as shown in Figure 10. The side slopes in
stream are 2:1 with outcropping side slopes of 4:1. The outcropping side slopes were placed at
4:1 to allow for a gradual grade into the stream area and to allow for mowing if recommended by
the town. Also the 4:1 slope allows for overflow of the stream during storm events. The depth of
the channel was set to 3 inches (0.076 m), replicating that of the downstream reference reach.
9.2.2 Maintenance Plan
As the case for most BMPs or stormwater management practices, daylighting will need a
maintenance plan for the first few years of existence to achieve its full potential. A series of
plantings should be used along the banks of the daylit section. Using a mixture of water tolerant
grasses and medium sized vegetation optimal stream bank stabilization will be maintained.
However over the first few years, dead vegetation made need to be replaced and non-native
species removed to allow for new growth. Maintenance cost may be curbed by initially using
vegetation types that do not require pruning or replanting. The public must be made aware of the
fact that a daylighting project will not look aesthetically pleasing until all vegetation has rooted
which may take several months to a few years. It is suggested that monthly or quarterly pictures
of the new stream channel be taken, allowing for the public to notice the increasing natural
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aspects and aesthetic appeal of the stream. Monitoring devices or techniques should be
developed in stream and downstream to monitor sediment and pollutant reductions over time.
9.2.3 Pollution Reductions
Little is known about removal rates achieved due to daylighting. However, it is known that
daylighting can decrease levels of TSS through biological uptake and the creation of meanders
within the stream. Also, daylighting has shown decreases in nutrients such as nitrogen and
phosphorus due to biological uptake. Both TSS and nutrient reductions will be further increased
with added vegetation within the stream as well as the vegetation along the stream banks.
Furthermore, an addition of a riparian buffer zone around the newly created stream will lead to
further reductions.
9.2.4 Costs
Six different case studies, shown in Pinkham, 2000, described cost based on the length of
daylighting. The concrete piped channel currently running through College Springs park has a
length of 181ft (55.17 m), which is similar to the case studies. Several case studies were chosen
that were similar to College Springs Park lengths, determining an average cost. As shown below
in Table 18, the average cost of daylight section of stream was $201/ft ($659.02/m), which
would total $36,381 for the entire length of piped under College Springs park. A maintenance
plan for daylighting is factored into the above total cost. However the cost may be offset by
donated materials and equipment along with volunteered labor.
9.3 Water Quality Swale
9.3.1 Design Specifications
A water quality swale is defined as a broad, shallow earthen channel vegetated with erosion
resistant grasses and underlain by an engineered soil mixture. Check dams are placed throughout
the swale to encourage ponding of stormwater runoff. A water quality swale will be located in
the drainage area outside the Berryfield apartment complex, where a riprap channel currently
exists. The swale will treat stormwater from an area containing 1.48 acres (0.60 ha) of
impervious surfaces. The swale will provide water quantity control via ponding of incoming
runoff, and water quality control through infiltration into an underlying soil matrix. An
underdrain system will be located beneath the soil matrix to decrease excessive ponding time. A
grass buffer strip at the inlet, along with vegetated slopes to the top of the check dams, will
provide pretreatment of incoming runoff. A profile and cross-sectional view of a typical water
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quality swale as indicated by the Virginia Stormwater Management Handbook are shown in
Figure 1 (VDCR, 1999).
9.3.1.a Hydrology
The hydrology of the contributing drainage was determined using TR-55. The results can be
seen in section 7.2 of this report. Peak discharge from the 10 year storm event was used to
calculate the cross-sectional area necessary for the swale using equation 1. With a peak
discharge of 42.5 cfs (1.20 m3/s), and a maximum allowable velocity of 7 ft/s (2.13 m/s), the
cross-sectional area was calculated to be 17.55 ft2 (1.63 m2).
9.3.1.b Swale Geometry
The swale will have a trapezoidal cross-section to maintain sheet flow and decrease erosion
potential of incoming runoff. The side slopes of the swale will be 3 horizontal to 1 vertical. This
was chosen to allow for easy access during maintenance operations and to prevent erosion. A
flow depth of 4 in (10.16 cm) was chosen for the water quality volume, given an average grass
height of approximately 4 in (10.16 cm).
The bottom width will be 2.5 ft (0.76 m) to maintain sheet flow. This bottom width, along
with side slopes of 3:1, resulted in a top width of 15 ft (4.53 m) and the necessary cross-sectional
area of 17.55 ft2 (1.63 m2). The water quality volume of the drainage area was determined to be
2904 ft3 (82.23 m3). In order to provide adequate storage capacity for the water quality volume,
the swale will need to be 151.64 ft (46.22 m) in length.
The swale will be at a slope of 2 percent to allow for positive drainage while preventing
erosion. Also, the slope of the site was determined to be approximately 3 percent, which will
make grading easier. The slope, along with cross-sectional dimensions of the swale, were
calculated and adjusted to meet the maximum allowable velocities for the 2 yr and 10 yr storm
events using equation 2.
9.3.1.c Underlying Soil Matrix
The engineered soil matrix will underlay the bottom width of the swale, allowing for proper
infiltration and filtration of runoff. Even though the soil on site is a fairly permeable sandy loam,
the soil matrix will be implemented to reduce pooling time of water, preventing safety and
nuisance conditions. The soil matrix will consist of 50 percent sand, 20 percent leaf mulch, and
30 percent top soil as specified in the Virginia Stormwater Management Handbook (VDCR,
1999). The soil bed will be 2.5 ft (0.76 m) deep.
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College Springs Design Team
Two perforated underdrains will be placed underneath the soil matrix. These will allow for
proper drainage of the soil matrix. The drains will be 6 in (15.24 cm) diameter, smooth-walled,
PVC pipe. One foot of pea gravel as defined in the stormwater handbook will be placed
underneath the soil matrix (VDCR, 1999). The underdrains will be located 6 in (15.24 cm) into
the gravel at 2 ft (0.61 m) from either side.
9.3.1.d Check Dams
Four check dams will be even spaced throughout the swale to allow for ponding and proper
infiltration of stormwater runoff. The dams will be spaced at intervals of 30.33 ft (9.24 m), with
the first dam being constructed 30.33 ft (9.24 m) from the outlet. The check dams will
constructed at a height of 18 in (4.92 m). They will be anchored into the swale walls a minimum
of 2 ft (0.61 m) on each side. Toe protection consisting of VDOT No. 1 open-graded coarse
aggregate riprap will be placed at the down slope side of the check dam to provide erosion
protection from overflowing water. This will be 0.46 m (1.5 ft) long by 0.30 m (1 ft) deep. A
notch will be placed 1.13 ft (0.34 m) high on each check dam. This was designed to allow the
peak discharge from the 2 year storm event to overflow without coming into contact with the
abutments.
The check dams will be constructed of riprap currently being used for erosion control
purposes in the site. This will save in material costs for the practice. The riprap dams will
consist of VDOT No. 1 open-graded coarse aggregate placed into the ground a minimum of 6 in
(15.24 cm) with a Class A1 riprap shell. The check dams will be underlain by filter fabric
specified by geotextile fabric (VDCR, 1999).
9.3.1.e Inflow and Outflow
The inflow will consist of a grassed buffer strip with a width equal to the top width of the
swale and a length of 10 ft (3.05 m). This will prevent erosion and scouring of incoming runoff.
The outflow point will drain into a culvert which passes underneath Berryfield and enters the
College Springs Park. This outlet will be buffered by 6 ft (1.83 m) long VDOT No. 1 opengraded coarse aggregate riprap to prevent scouring.
9.3.1.f Vegetation
Vegetation for the swale will consist of water tolerant, high stem density grasses with a deep
root system. A Kentucky-31 blue grass was chosen for the swale because of similar species
surrounding the Berryfield apartment complex.
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College Springs Design Team
9.3.2 Maintenance Plan
Vegetation: Upkeep of the swale’s vegetative cover is necessary to reduce velocity of runoff,
increase biological uptake, and allow for proper infiltration. A dense grass covering should be
maintained on the bottom and side slopes of the swale. During the first three months of seeding,
grass covering should be checked on a monthly basis to ensure proper covering. Once a proper
vegetative cover is established, reseeding and stabilization should occur on a biannual basis if
necessary. Periodic mowing, which occurs at the discretion of the Berryfield owners, should cut
the grass to a minimum height of 3 in (7.62 cm) with a preferred height of 6 in (15.24 cm).
Upkeep of trees and shrubs along the slopes of the swale will ensure velocity reduction and
aesthetic appeal of the water quality swale. Overgrown shrubs and trees will also be pruned at
the discretion of the Berryfield owners. It is important to note that shrubs and trees that may
naturally seed within the sides and bottom of the swale beneath the check dams should be
removed. Additional herbaceous vegetation would alter Manning’s roughness coefficient, which
was used to calculate effective swale storage capacity and geometry.
Check Dams: Proper construction of check dams, including the 0.61 m (2 feet) long
abutment into each side slope is essential to adequate functioning of the dams. Periodic removal
of sediment that may accumulate behind the check dams should occur on a biannual basis along
with vegetation inspection. The area beneath the sediment accumulation may require reseeding.
If leaching within the riprap occurs, appropriate reconstruction efforts should be taken.
Grass Buffer Inlet: A vigorous vegetative cover should be maintained on the grass buffer
strip at the inlet of the swale. This should be inspected along with other vegetative coverings
within the swale. Sediment accumulation along the buffer should be removed accordingly.
Debris and litter accumulation may be a significant problem given the location within a
mostly student inhabited apartment complex. Litter accumulation has the potential to alter swale
hydraulics, potentially causing areas of concentrated flow and increased erosion (VDCR, 1999).
Removal may be necessary on a monthly or even bimonthly basis to ensure proper swale
functioning.
9.3.3 Performance Expectations
The water quality swale performance will be assessed on ability to provide water quality and
quantity control. Water quantity control can be measured by the storage capacity of the swale
and its associated reductions in peak discharge from various storm events. Although the 2-yr 24
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College Springs Design Team
hour storm is designed to pass over the check dam notches, storage capacity below the notches
will provide partial water quantity control, especially when compared to the riprap channel that
currently exists. This being said, all storm events smaller than the 2-yr, 24 hour storm will be
properly detained within the water quality swale, providing enhanced water quantity control.
Water quality control assessment is determined by the swale’s ability to decrease
phosphorus, nitrogen, bacteria, and total suspended solid concentrations. According to the
Virginia Stormwater Management Handbook, a target phosphorus removal efficiency of 35%
can be expected for water quality swales with percent impervious areas similar to the drainage
area of Berryfield (VDCR, 1999). Varying degrees of total suspended solids (TSS) removal
efficiencies found from the literature review were assessed, with an average value of 84%
determined (Lawrence et al, 1996). The little information found on nitrogen removal efficiencies
showed an average value of 30% (Lawrence et al). Bacteria removal efficiencies varied
dramatically, with some studies showing up to 62% removal and some reporting -74% removal
or addition of bacteria (Barrett, 2005). Due to variations in data, no bacteria removal efficiency
was chosen, although many studies show little removal, and in certain instances addition.
Overall the water quality swale provides enhanced water quantity control due to the check
dams and swale geometry, along with adequate water quality control. Sediment removals are
high among water quality swales in similar urban settings, correlating with management
objectives indicated in the Upper Stroubles TMDL. Partial water quality control is provided
through sufficient nitrogen and phosphorus removal rates. Variable bacteria removal rates
indicate a potential addition of bacteria in runoff leaving the underdrain system. Because
bacteria concentrations were not tested during the stormwater quality analysis, future monitoring
may be necessary to ensure limited concentrations.
9.3.4 Costs
The predicted total cost of the water quality swale is based on construction and maintenance
costs obtained from various case studies, along with the California Stormwater BMP Handbook.
The California BMP handbook recommends a total construction cost of $0.50 per ft2 ($5.38 per
m2). Similar estimates state $752 per m3, or $45 per linear meter for a 4.5 m top width (Barrett
et al, 1998). Costs using these estimates were found and combined to obtain an average total
construction cost of $5,382. These costs are subject to change based on the existing drainage
channel which currently exists within the site. This would require less cut than most sites. The
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College Springs Design Team
coarse aggregate stones that exist within the current channel will also be washed and utilized for
check dam and outlet protection, with potential cost-reduction implications.
Maintenance cost estimates of $1.90 per linear meter and $74 per m3 were averaged to obtain
an annual maintenance cost of $183. This will most likely be funded by the Berryfield apartment
complex, which currently pays for mowing and litter removal within the existing drainage
channel.
9.4 Community Outreach
Community outreach and education is an integral part in providing source control of
pollutants for a stormwater management plan. The majority of College Springs sub-watershed
consists of single-family residential lots, an optimal location for community outreach efforts.
Our community outreach plan is to design a brochure to be distributed throughout the subwatershed with the goals of educating residents about Upper Stroubles Creek Watershed and
how they can mitigate their stormwater impacts.
We have worked with the Town Gown Community Relations Committee of Blacksburg
along with the community outreach program SEEDS to develop an effective community
outreach brochure. The brochure was developed and revised with input from both programs.
The brochure contains:

A brief history of water use in Blacksburg

Information about Upper Stroubles Creek Watershed

Management practices that residents can implement

References for more information regarding these practices
Figures 14 and 15 show both sides of the brochure. The brochure will
hopefully reflect the cultural heritage surrounding College Springs as a major water source
for Blacksburg in the 19th century, and inform residents that its there in the first place. That
section is followed by information regarding Upper Stroubles Creek watershed and its
designation as an impaired waterbody. Finally, for those residents concerned with their
stormwater impacts, is a list of management practices that citizens and homeowners can
implement.
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College Springs Design Team
The brochure has been sent to Dr. Michael Rozenswig of SEEDS, who is involved in
community outreach efforts in Blacksburg. If accepted and implemented by the Town of
Blacksburg, the brochure may serve as an example for other sub-watersheds within the town.
10.0 Work Plan
The purpose of this plan is to create an outline of dates needed to meet specific objectives
and the tasks necessary to accomplish these.
Geographic information systems (GIS) knowledge is needed to appropriately model the
hydrologic characteristics of the watershed. Information derived from GIS will include land uses,
watershed delineation, flow lengths, reach data, and sub-watershed areas. This will allow for the
completion of TR-55 modeling and development of a hydrograph. Progress has been made
determining various inputs within TR-55, but further GIS help is needed to gather appropriate
data. (Feb. 16)
In order to define important runoff characteristics of design storm events, such as runoff
volume and peak runoff rate, measurements must be taken. A challenge in creating an
appropriate hydrograph to quantify these characteristics is measuring stream flow during a storm
event of known magnitude. Therefore the analysis will be done using the NRCS Curve Number
method to design an appropriate hydrologic model. Even if the opportunity to measure stream
flow during an event arises, the NRCS Curve Number method in conjunction with TR-55
software will be used to develop hydrographs for appropriate design storm events. (Feb. 16)
Six water quality samples have been collected at three different locations throughout College
Springs Park. These locations included both perennial spring locations, College Springs along
with the flow coming through the pipe under Clay Street from the football field. The third grab
sample was taken at the outlet of the pipe flowing directly under the park. Water quality tests
were performed in the Water Quality Lab, with results shown in Table 5. The initial water
quality analysis is shown in Appendix E as a draft. Further information regarding nutrient
criteria recommendations is needed to properly analyze our results. (Feb. 20-23)
Although the major portion of our literature review has been completed, information still
needs to be gathered regarding sub-watershed modeling techniques such as RUSLE2. This
model utilizes and empirical formula to determine sediment losses within a given watershed.
GIS is used to determine various components of the Universal Soil Loss Equation. (Feb. 23)
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College Springs Design Team
Storm event samples were collected on February 11, 2009 during a storm event. This will
allow us to determine pollutant concentrations entering College Springs Park during a storm
event. Dr. Wolfe has allocated appropriate funds and we are awaiting the results of the water
quality analysis. (Feb. 27)
Our initial decision matrix has been run for three spots within the College Springs park. This
a preliminary step in the processes of selecting a BMP, which needs oversight from our advisor.
Once it is overlooked, we can select our BMPs and determine sizing and pollutant removal
criteria from our runoff hydrograph and water quality analysis. (Feb. 27-30)
The community outreach aspect of our plan has been edited to include collaboration with
Blacksburg’s Environmental Management Program. We are hoping to discuss possible
watershed education tools with the director, Susan Garisson, and the leader of the watershed
management group Lee Hixon. On a similar note, the football field inlet into College Springs
has shown very high levels of all measured pollutants. For this reason we will determine the
current management practices and what conservation measures can be taken. (Feb. 27 – Mar 4)
In early April we will make a presentation of the project to present to Blacksburg’s
stormwater task force for professional input. We will outline the projected improvements and
cost-benefit analysis of our design to the task force. (April 21)
11.0 Project Timeline
Feb 16
Feb 17
Feb 20
Feb 20
Feb 22
Feb 22
Feb 23
Feb 25
Feb 26
Mar 1
Mar 2
Mar 8
Mar 15
Mar 17
Mar 30
Mar 31
April 12
April 20
GIS help from Dr. Hession
Discuss BMP matrix decisions with Dr. Wolfe
Complete TR-55 calculations
Discuss watershed education with Susan Garisson of Blacksburgs’
Environmental Management Program
Research RUSLE2 modeling
Determine management practices of middle school football field
Project Notebook (5)
Select BMPs
Begin designing BMPs
Run RUSLE2 modeling
Revised Work Plan
On-site BMP surveying
Finalize design of selected BMPs
Cost/ benefit analysis
Project notebook (6)
Present PowerPoint presentation of design to Blacksburg Stormwater Taskforce
Implement community outreach program
Submit draft of final report to Dr. Wolfe
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College Springs Design Team
April 21
May 1
May 4
May 13
Start designing PowerPoint presentation
Create and present project poster
Project notebook (7)
Final report due
12.0 Summary & Conclusions
Analysis has been performed on the College Springs watershed to address the high sediment
loading to Stroubles Creek. This has involved storm event flow analysis using TR-55, mapping
using GIS, and sampling of both baseflow and stormflow. The analysis concluded that the
College Spring Park was contributing significantly to the high sediment and nutrient load
occurring in Upper Stroubles Creek. Information was gathered involving BMPs that could
properly reduce the amount of sediment leaving the watershed. The final product was a selection
of three practices that can be implemented in the park: a water quality swale, wetland
enhancement, and daylighting. These practices have been proven to reduce the sediment loads in
their specific areas. Complete maintenance and cost plans have been provided so that if these
BMPs are implemented they will be managed properly and an estimation of the total cost will be
known.
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College Springs Design Team
13.0 References
Barrett, M.E, 2005. Performance comparison of structural stormwater best management
practices. Water Environmental Research. 77(1): 78-86.
Barrett, M.E., Walsh, P.M., Malina, J.F., and R.J. Charbeneau. 1998. Performance of vegetative
controls for treating highway runoff. Journal of Environmental Engineering. 124(11):
1121-1128.
Birch, G.F., C. Matthai, M.S. Fazeli, and J. Suh. 2004. Wetlands 24(2): 459-466.
Blacksburg. 2008. Code for the Town of Blacksburg.: Chapter 10 – Erosion and Sediment
Control.
California Stormwater Quality Association. 2003. Stormwater Best Management Practices
Handbook. Volumes 2 & 3, 3rd edition.
Carleton, J.N., T.J. Grizzard, A.N. Godrej, and H.E. Post. 2001. Factors affecting the
performance of stormwater treatment wetlands. US Environmental Protection Agency 35(6):
1552-1562.
Center for Watershed Protection. 2007. Urban Subwatershed Restoration Manual No. 3: Urban
Stormwater Retrofit Practices. Version 1.0.
Davis, A.P., 2008. Field Performance of Bioretention: Hydrology Impacts. Journal of
Hydrologic Engineering 13(2): 90-95.
Deletic, A. and T.D. Fletcher. 2006. Performance of Grass Filters Used for Stormwater
Treatment – A Field and Modeling Study. Journal of Hydrology. 317: 261-275.
Dietz, M.E., J.C. Clausen. 2005. A Field Evaluation of Rain Garden Flow and Pollutant
Treatment. Water, Air, & Soil Pollution 167(1-4): 123-138.
EPA. 2007. Community Culture and the Environment: A Guide to Understanding a Sense of
Place. Washington, DC
EPA. 2008. Priority area 3: Clean water act Section 303(d) and 305(b) integrated reports.
Available at: http://www.epa.gov/burdenreduction/pr/pr-3.htm. Accessed 11 Nov. 2008.
EPA/821/R-02/023. September 2002. “Escherichia coli in Water by Membrane Filtration using
Modified membrane-Thermotolerant Escherichia coli Agar”.
Heasom, W., R.G. Traver, and A. Welker. 2006. Hydrologic modeling of a bioinfiltration best
management practice. 2006. Journal of the American Water Resources Association 42(5):
1329 – 1347.
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College Springs Design Team
Hixon, F. Lee. 2008. Geotechnical Investigation Requirements for BMPs. Blacksburg, VA
Hogan D.M., M.R. Walbridge. 2007. Best management practices for nutrient and sediment
retention in urban stormwater runoff. Journal of Environmental Quality. 36:386-395.
Hsieh, C.H., and A.P. Davis. 2005. Evaluation and Optimization of Bioretention Media for
Treatment of Urban Storm Water Runoff. Journal of Environmental Engineering
131(11): 1521-1531.
Hunt, W.F., J.T. Smith, S.J. Jadlocki, J.M. Hathaway, and P.R. Eubanks. 2008. Pollutant
Removal and Peak Flow Mitigation by a Bioretention Cell in Urban Charlotte, N.C. Journal
of Environmental Engineering 134(5): 403-408.
Junker, B., and M. Buchecker. 2007. Aesthetic preferences versus ecological objectives in river
restorations. Landscape and Urban Planning 85(2008): 141-154.
Lawrence, A.I., Marsalek, J., Ellis, J.B., and B. Urbonas. 1996. Stormwater Detention & BMPs.
Journal of Hydraulic Research. 34(6): 799-814.
MDER. 2000. The Bioretention Manual. Prince George’s County, MD: Department of
Environmental Resources.
MNMC. 2001. Minnesota Urban Small Sites BMP Manual: Constructed Wetlands. Metropolitan
Council on Environmental Services.
Moore, A., and M. Palmer. 2005. Invertebrate Biodiversity in Agricultural and Urban Headwater
Streams: Implications for Conservation and Management. Ecological Applications, 15(4):
1169-1177.
Natural Resources Conservation Service. 2001. Virginia Conservation Practice Standard:
Riparian Forest Buffer. Technical Guide Section IV 391-VA-1
Pinkham R. 2000. Daylighting new life for buried streams. Old Snowmass, CO: Rocky Mountain
Institute.
Schueler, T.R. 1992. Design of Stormwater Wetland Systems: Guidelines for Creating Diverse and
Effective Stormwater Wetland Systems in the Mid-Atlantic Region. Washington, D.C.:
Metropolitan Washington Council of Governments.
Spencer, L.S., Schirmer, A.P. 2008. Chapter 18 Sewers and Stormwater Management: Article VI:
Stormwater Management. Blacksburg, VA. Council of the Town of Blacksburg. (Spencer)
Tilley, D.R., and M.T. Brown. 1996. Wetland networks for stormwater management in subtropical
urban watersheds. Ecological Engineering at EcoSummit. 96: 131-158.
Virginia Department of Conservation and Recreation. 1999. Virginia Stormwater Management
Handbook. Volumes 1 & 2: 1st Edition. Division of Soil and Water Conservation.
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College Springs Design Team
Virginia Department of Conservation and Recreation. 2005. Virginia Stormwater Management
Program Permit Regulations. Division of Soil and Water Conservation.
Virginia Department of Environmental Quality. 24 May 2006. TMDL Implementation Plan for
Stroubles Creek Benthic Impairment. Blacksburg, VA.
Virginia Department of Conservation and Recreation. 2008. Virginia Erosion and Sediment Control
Handbook. Division of Soil and Water Conservation.
Ward D.A., Trimble W.S. 2004,pp. 358-360. Environmental Hydrology. 2nd ed. Washington,
D.C.:Lewis Publishers.
Wei, Z., G.L. Brown, D.E. Storm, and H. Zhang. 2008. Fly-Ash-Amended Sand as Filter Media
in Bioretention Cells to Improve Phosphorus Removal. Water Environment Research 80(6):
507-516.
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College Springs Design Team
14.0 Appendices
14.1 Figures
Figure 1. Profile and cross-sectional views of a water quality swale with check dams (VDCR,
1999).
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College Springs Design Team
Figure 2a. The city of Zurich, Switzerland (Before daylighting) (Pinkham, 2000).
Figure 2b. The city of Zurich, Switzerland (After Daylighting) (Pinkham, 2000).
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College Springs Design Team
Figure 3. College Springs Park’s perennial inputs
Figure 4. Diagram of grassed swale plot in Brisbane, AU. (Deletic, 2006).
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College Springs Design Team
Figure 5. Arial view of a pocket wetland facility according to Minnesota’s Metropolitan Council
on Environmental Services. Objects to be noted are the sediment forebay (swale) at the input of
the facility, the surrounding buffer zone, and the perpendicular allocation of hi-marsh areas in
relation to water flow (MNMC, 2001).
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College Springs Design Team
Figure 6. TSS in mg/L as shown over a collection time of 2 hours.
Figure 7. Nutrient concentrations in mg/L over 2 hours.
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College Springs Design Team
Figure 8. Sub-watershed and concentrated flow for College Springs Park.
Figure 9. Cross section of daylighting (units in meters)
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College Springs Design Team
Figure 10. Isometric view of daylighting
Figure 12. Cross-sectional sketch of the water quality swale.
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College Springs Design Team
Figure 13. Isometric view of the water quality swale.
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College Springs Design Team
Figure 14. Printable version of the community outreach brochure with the cover on the furthest
right side and the back on the left
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College Springs Design Team
Figure 15. Inner pages of the community outreach brochure.
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College Springs Design Team
14.2 Tables
Table 1. Pollutant removal capacity versus depth of 18 bioretention laboratory columns and 6
existing facilities (Hsieh and Davis, 2005).
Table 2. Summary of removal rates for grassed swale from a selection of studies done in urban
and rural locations (Deletic, 2006).
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College Springs Design Team
Table 3. Removal rates of various pollutants for constructed wetlands (CWP, 2007).
Table 4. Specified phosphorus removal efficiencies based on the water quality BMP selected
(VDCR, 1999).
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College Springs Design Team
Table 5. Water quality results from College Springs sub-watershed located in Blacksburg,
Virginia.
Location
Channel
Flow 1
Channel
Flow 2
Spring 1
Spring 2
Football
Field 1
Football
Field 2
TSS
Ortho-P
(mg/L) (mg/L)
Total-P
(mg/L)
Ammonia
(mg/L)
Nitrate (mg/L)
Total Nitrogen
(mg/L)
Nitrite
(mg/L)
<1
0.12
0.30
0.18
14.7
16.0
0.004
<1
<1
<1
0.12
0.006
0.006
0.26
0.13
0.23
0.19
0.18
0.19
15.5
8.2
8.4
16.0
12.0
14.0
0.004
0.005
0.001
6
0.11
0.26
0.19
16.3
17.0
0.003
<1
0.10
0.30
0.17
16.6
17.0
0.004
Table 6. A summary of level III ecoregion values for TN, TP, chlorophyll, and Turbidity based
on the lower 25th percentile of the reference streams (EPA, 2008).
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College Springs Design Team
Table 7. Virginia criteria to protect fishery recreation and aquatic life as of April, 2006 (VDEQ,
2006)
Table 8. Site-specific criteria for two natural lakes in Virginia (VDEQ)
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College Springs Design Team
Table 9. Storm event water quality sampling data
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College Springs Design Team
Table 10. Total acreages of landuses within each subshed
Landuse
Agriculture / Vacant
Civic
Parks / Trails / Open
Space
Right of Ways
Single-Family Residential
Low Density Residential
Multi-Family Complex
Vacant
Condominiums
Cemeteries
Subshed_A
6.44
2.11
Acres
Subshed_B Subshed_C
0
6.44
2.44
20.7
6.76
7.49
27.71
0
0
26.37
0
0
0.35
7.49
10.58
5.47
4.59
18.34
0
0
6.23
7.49
7.87
0
0.88
10.86
4.12
0
Subshed_D
0
4.25
1.12
7.49
7.22
0
8.17
11.22
6.44
0.11
Table 11. Park area decision matrix
Nutrient Reduction
Sediment Reduction
Maintenance Costs
Construction Costs
Surface Area Req'd
Community
Acceptance
Total
*5 is the highest rating
Weight Riparian
(%)
Zone
10
4
20
5
10
5
10
3
15
2
35
100
2
3.2
Pocket
Wetland
3
3
3
2
3
Daylighting
2
3
3
2
3
3
2.9
5
3.5
Table 12. Spring Area decision matrix
Nutrient Reduction
Sediment Reduction
Maintenance Costs
Construction Costs
Surface Area Req'd
Community
Acceptance
Total
*5 is the highest rating
Weight Pocket
Wetland
(%)
Wetland Enhancement
30
3
3
5
3
2
25
3
5
30
2
4
5
3
4
5
100
3
2.7
4
3.85
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College Springs Design Team
Table 13. Side of road decision matrix
Nutrient Reduction
Sediment Reduction
Maintenance Costs
Construction Costs
Surface Area Req'd
Community
Acceptance
Total
*5 is the highest rating
Weight Pocket
(%)
Wetland
20
3
20
3
10
3
10
2
25
3
15
100
3
2.9
Bioretention
Facility
2
5
2
2
4
5
3.55
Water
quality
Swale
3
4
4
4
4
4
3.8
Table 14. Berryfield decision matrix
Nutrient Reduction
Sediment Reduction
Maintenance Costs
Construction Costs
Surface Area Req'd
Community
Acceptance
Total
Weight Pocket
(%)
Wetland
15
3
10
3
20
3
30
2
10
3
15
100
3
2.7
Dry
Detention
Basin
2
3
4
2
1
Bioretention
Facility
2
5
2
2
4
Water
quality
Swale
3
4
4
4
4
2
2.4
5
2.95
4
3.85
*5 is the highest rating
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College Springs Design Team
Table 15. Vegetation specifications and costs
Species
Amount
Establishment
Dates
 Indian Grass 5-7 lbs/acre 5/1 – 7/1
 Eastern
@ 0.4 acres
Gamma
=
Grass
2.8 lbs
 Switch
Grass
 Black-Eyed 1-8 oz/acre 2/1 – 5/15
Susan
@ 0.4 acres
 Maximillian =
Sunflower 3.2 oz
 Annual
Lespedeza
 Partridge
Pea
 Water Lotus 40 seeds
2/1 – 5/15
 Water Lilly
Prices
Total Price



11.49/lb
12.99/lb
6.5/lb



$32.17
$36.37
$18.20




24/lb
9.95/lb
1.70/lb
19.95/lb




$4.80
$1.99
$2.00
$3.99

6.95/ 10
seeds
20 / 5 seeds


$27.80
$80.00

Table 16. Velocity and discharge measurements for reference reach
Time
(sec)
Run
1
2
3
Average
Distance
(m)
79
77
82
79.3
Velocity
(m/s)
15
15
15
15
0.19
0.19
0.18
0.19
Area
Discharge
(m2)
(m3/s)
0.109
0.021
0.109
0.021
0.109
0.020
0.109
0.021
Page | 56
College Springs Design Team
Table 17. Discharge measurements for park area
Time
(sec)
Run
1
2
3
4
5
6
7
Average
2.32
1.47
1.02
1.04
1.12
1.12
1.16
1.32
Volume (L) Discharge (m3/s)
6.1
0.003
7.2
0.005
6.6
0.006
6.9
0.007
6.7
0.006
6.8
0.006
6.7
0.006
6.7
0.005
Table 18. Daylighting case studies of cost per foot, interpreted from (Pinkham,2000).
Length of
daylighting
(ft)
200
250
200
Cost ($)
50,000
144,000
14,500
$/ft
250
576
73
Rowley, MA
85
1,200
14
Roscoe, NY
Barrington, IL
160
250
9,000
60,000
Average cost/ft
56
240
$201
Study Location
Berkeley, CA
Berkeley, CA
DeKalb Co, GA
Notes
* volunteer labor
* donated materials & volunteer
labor
* donated materials & volunteer
labor & earthmoving costs
Page | 57
College Springs Design Team
14.3 Equations
Page | 58