Green vs. Gray Infrastructure Cost Rosa A. Fernández R.R. Dupont Civil and Environmental Engineering Utah State University
Transcript
Green vs. Gray Infrastructure CostRosa A. FernándezR.R. DupontCivil and Environmental EngineeringUtah State University
Outline
• Introduction▫ Gray infrastructure▫ Green infrastructure▫ Types of green infrastructure▫ Cost Analysis
• Cost estimation tool• Case studies• Summary and Conclusion • Questions
INTRODUCTION
Gray Infrastructure
General
Stormwater Management
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Presentation Notes
General definition: Generally considered to be human-built habitat that provides a functional benefit exclusively to humans. Sartre Specific to swm: all the components of the sewer system. (Curb, gutter, pipes) Important to note that the are ways of reducing urban runoff impact with gray infrastructure. Advantages: in wet weaher conditions it is a flood control system because it transport quickly the water from urban areas Disadvantages:erosion, transport of pollutants to water bodies, inhibits aquifer recharge. Stormwater As Nuisance. High Capital Cost. Does Not Add Beauty
Gray InfrastructureAdvantages Disadvantages
Quick transport of waterflood control
ErosionPollutes waterwaysInhibits rechargeHigh capital costDoes not add beauty
Source: USGSS Water Science School
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Advantages: in wet weaher conditions it is a flood control system because it transport quickly the water from urban areas Disadvantages:erosion, transport of pollutants to water bodies, inhibits aquifer recharge. Stormwater As Nuisance. High Capital Cost. Does Not Add Beauty
Green Infrastructure
• “A network of decentralized storm-water management practices that can capture and infiltrate rain where it falls, reducing stormwaterrunoff and improving the health of surrounding waterways.”
CNT’s Definition:
• “[…] An approach to wet weather management that is cost effective, sustainable and environmentally friendly […].”
EPA’s Definition:
Green Infrastructure
Advantages Disadvantages
• Reduces runoff volume
• Improves water quality
• Recharges aquifers.
• Landscape and cultural benefits
• Stormwater as resource
• Can reduce capital costs
• Adds beauty
• Can increase property values
• risk of contaminating groundwater
• May require irrigation during dry
season
Types of GI• Vegetated swales• Bioretention• Gravel Wetland• Porous Asphalt
Source: dottarchitecture.com
Types of Green Infrastructure
•Vegetated swales
Source: dottarchitecture.com
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Presentation Notes
: are broad, shallow channels designed to convey and infiltrate stormwater runoff. The swales are vegetated along the bottom and sides of the channel, with side vegetation at a height greater than the maximum design stormwater volume. The design of swales seeks to reduce stormwater volume through infiltration, improve water quality through infiltration and vegetative filtering, and reduce runoff velocity by increasing flow path lengths and channel roughness.
• Bioretention
Source: Bluegrasslawn.com
Types of Green Infrastructure
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These systems consist of landscaped depressions which collect runoff that subsequently ponds, filters through a soil mix, and infiltrates into the ground, or discharges to the surface.
• Gravel Wetland
Types of Green Infrastructure
Source: stormwater.wef.org
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Presentation Notes
is a horizontalflow filtration system and should not be confused with stormwater wetlands that function more like ponds. Instead, the subsurface gravel wetland includes a dense root mat, crushed stone, and an anaerobic microbe rich environment for improving water quality. Like other filtration systems, it demonstrates a tremendous capacity to reduce peak flow and improve water quality. By design, the subsurface gravel wetland by itself is not intended for infiltration of stormwater. Subsurface gravel wetlands can be used in many regions, with the exception of those that are too arid to support a wetland system. These systems have demonstrated exceptional water quality treatment, in particular for nutrients, for a range of land uses including commuter parking, high density commercial use, and major transportation corridors.
• Porous Asphalt
Types of Green Infrastructure
Source: asphaltpavement.org
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Presentation Notes
Porous asphalt (PA) is a very effective approach to stormwater management in terms of both quality and quantity. Unlike retention ponds, PA systems do not require large amounts of additional space. The marginal cost between standard and porous asphalt is typically less than the associated drainage infrastructure (curb, catch basins, piping, and ponds) for standard impervious pavements. With PA, rainfall filters through the system and infiltrates back into the ground, which significantly reduces runoff volume, lowers peak flows, decreases temperatures, and improves water quality. PA also speeds snow and ice melt and virtually eliminates black ice development, reducing salt requirements for winter maintenance.
Cost analysis
•Key points•Types of cost
Green Values Calculator
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Presentation Notes
The CNT’s Green Values Calculator is a Web-based interactive program that can assess the economics of green and conventional storm-water management technologies under different development patterns and over different time periods ~CNT, 2009!. Over 70 sources of data ~RSMeans standard engineering source books, publications by city engineering and public works departments, fact sheets, and published articles, reports, and studies! contributed to the Calculator’s construction costs, maintenance costs, and component life spans. Life-cycle estimates include the construction cost plus periodic maintenance and, where appropriate, replacement within a designated life cycle but does not include land costs.
CASE STUDIES
CASE STUDY #1New high density urban development
Residential Development1709 East Murray Holladay Road, Millcreek, UT
Description Area (acres) % of total area
Buildings 0.48 17%
Paved Parking 1.17 41%
Other impervious 0.21 7%
Landscaped areas 0.98 35%
Total 2.84 100%
Impervious: 1.86 acres = 65%Parking lot
Building
Legend
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Original Design: 4 Boxes, 313 ft of pipe, 2 snouts, underground chambers
Design Specifications
• Storm: 24-hr 10 years: 1.89 inches of rainfall• For impervious area = Building + Parking Lot + other impervious = 1.86
• a suburban residential subdivision on 20 acres,• A urban townhouse project on a 3-acre site, • a renovated urban commercial project on a 3.5-acre site
• Objective: comparing the economic savings and the volume of storm water diverted from conventional sewers by green infrastructure practices over a 30-year life cycle.
• Methodology: The life-cycle costs were calculated using the net present value of the construction cost and the estimated annual maintenance costs of the practice.
Case Study 2
GI practices:Downspouts disconnection.Replacement of 50% of lawn areaPorous Pavement
Green Roofs+25% tree coverVegetated Swales
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The Calculator showed that green infrastructure was, on average, about 24%more cost-effective than gray infrastructure over a 30-year period. The economic, engineering, and hydrological assumptions used by the CNT to generate these estimates are discussed in a report accessed through the Green Values Stormwater Calculator’s methodologyWeb page ~CNT, 2009!. Given its technical assumptions, running a variety of different scenarios through CNT’s Green Values Calculator shows that most of the six green infrastructure practices evaluated in this model—disconnection of downspouts to rain gardens, replacement of the half the lawn area with native landscaping, the use of porous pavement used for on-site paving, green roofs, additional tree cover for 25% of the lot, and the use of vegetated swales rather than pipes for storm-water conveyance—are more cost-effective than gray infrastructure at all scales and time periods, with the possible exception of green roofs. Moreover, not only are these green practices initially more economical than conventional infrastructure in terms of their construction costs, but the practices are also able to divert millions of gallons of storm water from conventional storm-water conveyance systems over their useful lives, thus also avoiding the indirect costs of providing additional detention capacity and, in the case of combined sewer systems, dealing with potential sewage overflow problems.
Results
• GI 24% more cost-effective than gray infrastructure over a 30-year period.
• More cost-effective than gray infrastructure at all scales and time periods, with the possible exception of green roofs.
• Not only are these green practices initially more economical than conventional infrastructure in terms of their construction costs, but the practices are also able to divert millions of gallons of storm water from conventional storm-water conveyance systems over their useful lives, thus also avoiding the indirect costs of providing additional detention capacity and, in the case of combined sewer systems, dealing with potential sewage overflow problems.
CASE STUDY #3University of New Hampshire
Stormwater Center (Houle et al., 2013)
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Presentation Notes
The UNHSC site was designed to function as a series of uniformly sized, isolated, and parallel treatment systems with capacity for stormwater to be conveyed to each treatment device without significant transmission impacts from the distribution systems upon processes such as sedimentation. The watershed is a 4.5-ha commuter parking lot.
The SCMs discussed in this paper include a vegetated swale, a wet pond, a dry pond, a sand filter, a subsurface gravel wetland, three bioretention systems (averaged), and a porous asphalt pavement. The treatment strategies are all uniformly sized to treat the same water quality flows and volumes, with equal capacity for conveying large flows.
Case Study #3
Maintenance cost
• Designs based on manuals from (NYSDEC), NHDES and Federal Highway Administration
• NYS manual: inspection checklists for operation, maintenance and management.
• Guideline were utilized on a monthly basis to track observations and maintenance activities for all SCMs
Results
• If maintenance activities are simple, periodic and routine maintenance costs are kept at a minimum.
• The type of maintenance affects the cost. Reactive, Periodic and predictive, proactive-adaptive
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This results are considered conservative because they document the most expensive period of maintenance that might be anticipated. This diminishes over time because of increased familiarity
Vegetated Swale Wet Pond
Detention PondSand Filter
Gravel Wetland Bioretention
Porous Asphalt
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Presentation Notes
As depicted in Figs. 1 and 2 and Table 2, maintenance burdens for vegetated filtration systems were generally less with respect to cost and personnel hours, compared to conventional SCMs such as ponds, with vegetated swales and sand filters as the exceptions. The sand filter system was found to require the most staff-hours, followed in declining sequence by the wet pond, dry pond, subsurface gravel wetland, bioretention, vegetated swale, and finally, the porous asphalt pavement. These results were surprising as many of the conventional systems such as wet and dry ponds were found to carry the largest maintenance burdens. Maintenance routines for these systems required more tasks and included more reactive activities such as algae removal and outlet cleaning which tend to be more complex and incur higher costs. Also interesting to note is that, although porous asphalt pavement is generally perceived as cost prohibitive because of high anticipated maintenance burdens, the porous asphalt system in this study was actually found to have the lowest maintenance burden overall in terms of personnel hours and the second lowest annual costs. Some systems, such as the wet pond and the subsurface gravel wetland [Figs. 1(b and e)], displayed cycling maintenance costs over the course of the study, while others, such as the vegetated swale, bioretention, and porous asphalt systems [Figs. 1(a, f and g)], reached a steady state after the first few years of operation.
Results
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Presentation Notes
While the vegetated swale is the least costly system in terms of maintenance, it is also the least effective in terms of annual pollutant load reductions. These data indicate that marginal costs and marginal pollutant load reductions for LID systems are less costly and require less effort to maintain but still achieve greater pollutant load reductions. Exceptions occur with respect to any LID or conventional SCM that does not have unit operations and processes that effectively target nutrients.
Summary
•Following recommended O&M guidelines•Properly designed GI systems can be more cost-effective than conventional infrastructure
•Type of maintanence affects costs•A lot of research opportunities in the O&M costs area.
References
• Houle, J., Roseen, R., Ballestero, T., Puls, T., & Sherrard, J. (2013). Comparison of Maintenance Cost, Labor Demands and System Performance for LID and Conventional Stormwater Management. Journal of Environmental Engineering, 932-938.
• Jaffe, M. (2010). Environmental Reviews & Case Studies. Environmental Practice, 357-365.
• University of New Hampshire Stormwater Center. (2012). BienialReport. UNHSC.
