1. Using Low Impact Design and Green Infrastructure
The Design Process
09/12/2018

2. Stormwater Management Methodologies
Old Way
Detain or Retain runoff using detention/retention basins for a chosen design storm
Remove as much runoff from the site as possible using piping and inlets
Maintenance-free BMPs (Best Management Practice) with Maintenance-free plantings

3. The New “Green” Way
Use smaller more focused BMPs to store and infiltrate the Water Quality storm (1.25” or 2-year storm)
Focus on using native plantings
Focus on implementation of stormwater management within the urban/complete street setting or footprint
Use LID (Low-Impact Design) wherever possible
Warnock Foundation

4. Design Process Assess Existing Stormwater Issues
Identify Site Opportunities
Evaluate Green Infrastructure Feasibility
Design Green Infrastructure Practice

5. Assess Existing Stormwater Issues
Assess Existing Impervious Area
Large amount impervious area in NJ – 12.1% (1,055 SQ miles)
1” rainfall event = 18.3 BILLION gallons of runoff
1” rainfall event in NJ impervious areas 18.3 billion gallons = Metlife Stadium 38 times
USGS Mapping

6. Use GIS Databases – NJDEP 2007 Land Use Layer
A large percentage of NJ urban areas are impervious
Urban Areas = 500% increase in runoff

7. Combined Sewer Constraints
U.S. Environmental Protection Agency (EPA) - U.S. Environmental Protection Agency, Washington, D.C. "Report to Congress: Impacts and Control of CSOs and SSOs." Document No. EPA 833-R

8. Identify Site Opportunities
City of Philadelphia

9. Remove Impervious Remove impervious area – “Depave”
Remove impervious and replace with infiltration promoting soils and vegetation
Re-establish with native plantings
Model D - Detroit

10. Reduce or Convert Impervious
Green Alleys/Driveways
Porous pavement
Wolf Paving

11. Disconnect Impervious
Media Group Lifestyle
Rain Barrel, Planter, Bioswale
Windsor, CT
Philadelphia Water Department

12. Evaluate Green Infrastructure Feasibility
NJ Green Infrastructure Manual

13. Site Assessment – Site Visit
Identify runoff flow
Existing topography analysis
Existing impervious area analysis
Identify ponding or flooding areas
Identify disconnect opportunities
Identify existing utilities and ROW
Existing soil information
Georgetown Climate Center

14. Design Practice Design Storms
NJDEP 1.2” of rain for 2 hour period – Water Quality Storm
Rutgers Cooperative recommends sizing to manage 2-year storm (3.2 in to 2.5 in of rain in 24 hours) using TR-55
Green Infrastructure designed to pass through the larger storm events

15. 2-Year Storm Advantages
Flooding Resiliency – Handle Larger Rain Events
Better for Combined Sewer Areas
Super storm Sandy New York City - Justin Lane, EPA

16. Calculate Drainage Area
Site observations and Topography
Cover Analysis (Curve Number Values)
Using GIS and USGS information
Conduct Survey – Most accurate
Remember to account for offsite drainage when sizing facilities
Anne Arundel County Maryland

17. Sizing Facility
Calculate runoff for 2-year storm (Good Rule of Thumb use 1.5” of rain
Use modeling software to create Green Infrastructure Hydrograph and calculate runoff
Size Facility to manage (*Tip* make sure to include the area of the facility its self)
Add infiltration rate from soil testing (Use ½ of rate measured in field)
Use Underdrain if necessary (field infiltration rate < 1” per hour)
0.07 cfs
Type III 24-hr
Rainfall=3.03" Runoff Area =1,0 0 sf Runoff Volume=256 cf Runoff Depth=3.07"
Tc=6.0 min
CN=98
Flow (cfs)
Time

18. Design Constraints Right-of-Way/Available space
Impervious Area (Building, parking, etc.)
Utility Conflicts
Existing Soil Conditions – “no infiltration”
Existing site ordinances

19. Maintenance Major Obstacle Who Maintains?
What happens if not maintained?
Maintenance Plan
NYC Water

20. FAQ’s GI and mosquitoes Is GI More Expensive?
Since mosquitoes can go through their life cycle in less than one week, green infrastructure practices are typically designed to drain within 72 hours or less, which will prevent completion of their life cycle.
Is GI More Expensive?
Many case studies show that green infrastructure is cheaper than conventional grey infrastructure, both in capital and maintenance costs. The USEPA estimates costs savings of 15%-80%. Savings can come in the form of reduced lifecycle costs, reduced need for expensive grey infrastructure (curbs, gutters, and ponds), and reduced land requirements. At the same time, green infrastructure offers additional economic benefits like flood-reduction, reduced liability for slips and falls, reduced need for road salt, fewer days of closed beaches, and lower water and energy bills. Philadelphia is saving an estimated $5.6 billion dollars over 25 years by investing in green infrastructure instead of only grey.

21. FAQ’s What about Maintenance? Permeable pavement in cold climates
Green stormwater infrastructure maintenance may include vacuuming of permeable pavement, clearing debris from inlets for rain gardens and bioswales, and weeding. Bioretention may require sediment removal from the soil medium and replanting. Activities like weeding and litter collection can be done with regular landscaping maintenance (of boulevard gardens, etc.). Community engagement programs have been successful in getting volunteers perform basic maintenance of rain gardens and bioswales. Maintenance costs are relatively low, when compared with the costs of dredging stormwater ponds (estimated to be at least $260,000 for a single pond).
Permeable pavement in cold climates
There is no evidence for increased damage from frost heave for permeable pavement compared with regular pavement, due to the lack of standing water and associated freeze-thaw cycles. Green infrastructure measures reduce icing hazards by infiltrating water and avoiding surface pooling. Many cities which experience harsh winters (Milwaukee, Philadelphia, New York) have had success with green infrastructure.
Clogging problems are mainly an issue of design. If a natural area with grass or exposed soil is allowed to drain stormwater across a pervious concrete pavement, fine material can be introduced into the system causing localized clogging. Vegetative matter can collect on the surface of the pervious concrete causing some clogging, but routine sweeping or vacuuming will restore porosity. Studies have been conducted that indicate pressure washing will restore the porosity of clogged pervious concrete to nearly new conditions.

22. FAQ’s GI and existing parking? GI and extreme weather events
Most rain gardens are installed in the sidewalk and are designed to have no impact on parking. When larger rain gardens are proposed, DEP and DOT work to minimize parking impacts.
GI and extreme weather events
Green infrastructure on a community-wide scale helps make cities more resilient. Capturing and infiltrating the first inch of rainfall helps delay peak flows during extreme events, allowing existing grey stormwater infrastructure to work more effectively. Climate change can increase volumes in mid-intensity events, not only extreme events, and green infrastructure can greatly reduce or eliminate runoff from these events. Studies have shown that green infrastructure reduces average losses from flood events, even in areas with low infiltration soils.
GI and street typology
Green Streets projects are not required to include any amenities for pedestrians and bicyclists. However, many of the features of Green Streets are considered to be tools used by communities interested in traffic calming.

23. Lessons Learned Not every site is suitable for infiltration practices
Consider subsurface utilities/Water elevation
Plantings require maintenance/enforcement
Ownership

24. Michael Grantner, P.E. – mgrantner@mccormicktaylor.com
Thank You!
Michael Grantner, P.E. –
Living Community Lab