A presentation about reducing nutrients from stormwater runoff through low-impact development/green infrastructure techniques. Presented by Rich Claytor, engineer with Horsley Witten Group, during the Buzzards Bay Coalition's 2013 Decision Makers Workshop series. Learn more at www.savebuzzardsbay.org/DecisionMakers

1. Managing the Watershed-
Reducing Nutrients in
Stormwater Runoff
Buzzards Bay Coalition
Decision-Makers Workshop Series
UMass Cranberry Station, E. Wareham, MA
March 20, 2013
Horsley Witten Group, Inc.

2. Today’s Agenda
• The basics of
stormwater and
watershed
management
• The evolution of stormwater management
towards Low Impact Development(LID)/
Green Infrastructure (GI)
• 2 Examples of watershed planning efforts
geared towards nutrient reduction
Horsley Witten Group, Inc.

3. Stormwater/Watershed basics
Watershed Hydrology What is a
watershed?
A: a building for water
storage
B: the land area that drains
to a given water body
C: a shack from which
fishing occurs
D: a moment in time when
you cross into a new area
E: a new way of organizing
http://planetearth.nerc.ac.uk/features/story.aspx?id=668
environmental agencies
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4. Watershed Boundaries
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5. Cape Cod Watersheds
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6. Stormwater/Watershed basics
Urbanization results in
increased surface runoff
BEFORE AFTER
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7. Components of Impervious Cover in the Urban Landscape
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8. Stormwater/Watershed basics
At ~10% impervious we
begin to see:
•Water quality issues
•Impacts to biological
communities
•Increased flooding
•Stream erosion
•Loss of recreational uses
•Shellfish bed closures
•Reduced baseflow and
recharge
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9. Stormwater/Watershed basics
8-10%
< 5% % impervious 20%
> 65% 30%
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10. Stormwater Evolution LID/GI
Community Planning Large Conventional
BMPs
LID/GI BMPs
LID Site Design
Receiving
Waters
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11. Stormwater Evolution LID/GI
Traditional controls LID/GI controls
• Goal: Get the water out • Goal: Reduce the amount of
of here as fast as possible surface runoff by reducing
impervious cover and
• Collect and storage in preserving natural areas
big, “hole in ground” off-
site • Rely on small, distributed on-
site practices
• Pipe discharge to a
stream or wetland • Infiltrate or reuse as much as
possible; filter before
• Limited water quality discharge
treatment and infiltration
• Source controls to minimize
• Stormwater is a waste pollution
product
• Stormwater is a resource
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12. Stormwater basics
Runoff Hydrograph
Post-development
Pre-development
Post-development (with
traditional controls)
Post-development
Runoff (cfs)
(with LID/GI)
Adapted from David Nyman, ENSR
Time (hrs)
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13. Low Impact Development (LID)
Traditional LID/GI
Site Design
BMPs
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14. LID/GI Practice Library: Bioretention
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15. LID/GI Practice Library: Bioretention
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16. LID/GI Practice Library: Rain gardens
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17. LID/GI Practice Library: Porous
Pavement/pavers
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20. LID/GI Practice Library: Infiltration
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21. LID/GI Practice Library: Green/blue
roofs
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22. LID/GI Practice Library: Swales
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23. LID/GI Practice Library: Sand Filters
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24. LID/GI Practice Library: Gravel wetlands
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25. LID/GI Practice Library:
Hydrodynamic separators
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26. LID Practice Library: Others
• Downspout
disconnection
• Pervious area
restoration/soil
amendments
• Urban reforestation
• Municipal pollution
source control (street
sweeping, catch basin
cleaning, leaf litter
pick-up, etc.)
Horsley Witten Group, Inc.

27. Pollutant Removal Capability
Source: 2010 Rhode
Island Stormwater
Design and Installation
Standards Manual
WVTS = wet
vegetative
treatment system =
constructed
wetland
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28. Pollutant Removal (continued)
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29. LID/GI Runoff Reduction Potential
Practice: Runoff Reduction
Ponds and Wetlands none to low
Infiltration highest
Bioretention moderate to high
Swales moderate to high
Porous Pavements high
Green Roofs moderate
Hydro-Separators none
Horsley Witten Group, Inc.

30. Roger Williams Park, Providence, RI
• Largest & Most
Important Open
Space in Providence
• 435 Acres
• 100+ Acres of Ponds
• 1 Million visitors per
year
• Horace Cleveland
(Olmstead School),
1874
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31. Roger Williams Park Ponds
Watershed Areas
South Watershed
North Watershed
Watershed Areas
North—977 acres
South—649 acres
Total—1,626 acres
50% Impervious
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32. Roger Williams Park
Pond System
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33. The Ponds Are Part of the Park’s
Historic Design and Character
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35. The Roger Williams Park Ponds
are in trouble today
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36. Rooted Aquatics
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37. Shallow Ponds,
generally less than
six feet deep
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38. Lots of Resident Geese
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39. Sedimentation
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40. Invasive Species
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41. Upper Watershed
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42. Upper Watershed
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43. Upper Watershed
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44. Preliminary Estimates of Annual Phosphorus Loads
Coming into the Roger Williams Park Ponds (lbs/year)
Total: 906 lbs/year
* Some Uncertainty Here ~70% Reduction required by TMDL
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45. Watershed Management Plan
Implementation Recommendations
• Structural Best Management Practices;
• Non-structural measures (pavement
removal/shoreline vegetation);
• Geese population management
• In-pond treatment (water column,
sediment);
• Education and Outreach;
• Water quality monitoring; and
• Upper Watershed recommendations
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46. Proposed
Structural and
Non-Structural
Sites
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47. Rapid Retrofit Reconnaissance
(RRR)
• Covered both Upper and Lower
Watersheds
• Assessed potential retrofits, shoreline
restoration/slope stabilization sites,
neighborhoods, hotspots, maintenance
needs, and overall watershed boundaries
• GIS maps, various existing design plans,
manhole poppers, measuring tapes, etc.
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48. Name this activity?
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50. Site 3B – Carousel Parking Lot
Bioretention (concept plan)
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51. Site 3B – Bioretention
Design Plan
Overflow/outlet
Bioretention
Planting Bed
Forebay
Diversion inlet/channel
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52. Site 3B – Bioretention Installation
and Training Workshop (day 1)
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53. Site 3B – Bioretention Installation
and Training Workshop (day 2)
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54. Site 3B – Nearly Complete
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55. Slope Stabilization and Buffer
Planting Horsley Witten Group, Inc.

56. Geese
Management
(not necessarily a
popular activity)
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57. Inflow Pipe from Upper Watershed
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58. In-pipe or In-lake Management?
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59. Educational Banners/Signage
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60. Rhode Island Salt Ponds
Watershed Restoration Plan
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61. Scope of Project
• Watershed Assessment
– Stormwater management inventory
– Existing wastewater management
programs/policies
– Alternative wastewater technologies,
disposal & funding options
• Watershed Management Plan
– Stormwater/Wastewater Management Options
– Outreach and education plan
– Specific Implementation plan
– Monitoring plan
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68. Nitrogen Thresholds and Water Quality
Classification
Classification Nitrogen (mg/L)
Excellent Quality <0.30
Good Quality 0.3 - 0.39
Moderate Impairment 0.39 - 0.50
Significant Impairment 0.50 - 0.70
Severely Degraded >0.70
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70. Total Loading and target TN Reduction:
Ninigret Pond: 71,237 #/year: Reduction needed = 0 #/yr
Green Hill Pond: 57,805 #/year: Reduction needed = 39,978 #/yr
Horsley Witten Group, Inc.

71. Stormwater Management Design
Objectives
• Runoff Reduction
• Groundwater Recharge
• Water Quality Mitigation
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78. Wastewater Treatment Alternatives
• Decentralized Treatment - Onsite
Individual Dwellings
• Centralized Treatment/Small
Scale/Cluster (multi-home) Treatment
• Porous de-nitrification media
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85. Other Pollutant Sources:
• Waterfowl (Canadian Geese and Mute
Swans);
• Other wildlife;
• Pets;
• Fertilizer from lawns/gardens;
• Some agricultural loading; and
• Atmospheric deposition.
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