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Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Non-profit 501(c)3, non-advocacy organization founded
i...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Welcome and Introductions
Historical Perspective
Today’...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Goal of Today’s Workshop:
Understand the differences (a...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Detailed design instructions for BMPs;
Detailed analysi...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Be engaged
Ask critical questions
Share your expertise
...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Why is it different?
and,
Why do we care?
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
• Flat Terrain
• High water table
• Poorly drained soil...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Shoreline buffer and critical areas cannot be
used for ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Highway ditches serve as the primary stormwater
receivi...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Where is all that water going?
To the nearest waterway ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
The Economic Benefits of Cleaning Up the
Chesapeake
Che...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Ecosystem Service Valuation:
Water Flow Regulation;
Air...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
•• Extreme storms eventsExtreme storms events
•• Popula...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
“the effects of watershed alteration on coastal
resourc...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
10% 40%25%
Good
Fair
Poor
Watershed Impervious Cover
St...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Threshold values:
Coastal plain streams: 3.5 – 14%
Tida...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Sustainable Development in the Coastal Plain:
Land use ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
VA Erosion & Sediment Control Program
GC-7
MS-19:
Prope...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
. . . . Increases in runoff volume, . . .
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
. . . . velocity, and peak flow rate of
stormwater runo...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
b.The adequacy of all channels and pipes
shall be verif...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
(2) (a) Natural Channels:
2-yr erosion;
2-yr overtoppin...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
If existing pipes or channels are not adequate, the
app...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
If existing pipes or channels are not adequate, the
app...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
If existing pipes or channels are not adequate, the
app...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Assumed C soils; Pre-developed land cover = Woods, good...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
1988 Chesapeake Bay Preservation
Act
(§ 62.1‐44.15:67)
...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater BMP Sizing
and
Performance Credits
Performan...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
1998 Amendments to the VA SWM Regulations
Water Quality...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Simple Method: Average Annual Load
𝐿𝑜𝑎𝑑 = 𝑃 × 𝑃𝑗 × 𝑅 𝑣 ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Treatment Volume & BMP Sizing
𝑊𝑄𝑣 = Water Quality Volum...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
* Innovative or alternate BMPs not included in this tab...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Water Quantity Compliance:
 Properties and receiving w...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Water Quantity Compliance:
 Minimum Standard 19 of the...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Water Quantity Compliance:
2-yr post back to pre vs 1-y...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Assumed C soils; Pre-developed land cover = Woods, good...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
What types of BMPs or BMP strategies have
proven to be ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
2005 NOIRA: Update Virginia’s Stormwater
Management Reg...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
EPA Performance Standards
• Protect and restore the phy...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
2007 NOIRA: Replace & clarify the 2005 NOIRA:
1) Amendm...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Inspector General Report on efforts to restore the
Ches...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
2009 NOIRA:
0.28 lb/ac/yr
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Encourage Low Impact Development
Inclusion of land cove...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
evapotranspiration:
40-50%
interflow: 20-30%
surface ru...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
evapotranspiration:
~25%
interflow: 0-30%
surface runof...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Research shows:
 Extended Filtration mimics the hydrol...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Runoff Reduction is not just infiltration!
 Infiltrati...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Compliance Spreadsheet
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Codifies & incentivizes minimization and
avoidance
Goes...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Environmental Site Inventory & Assessment
• Forest cons...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
A 1990 study for the city of Virginia Beach
compared th...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
An Assessment of the Better Site Design Principles
for ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
The Economic Benefits of Watershed Protection
(CWP, 200...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
1. Site Data Input:
• Site Land cover
• Site level Trea...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Volumetric Runoff Coefficients
• Land Cover (acres) by ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
15 Acres
25 ½ acre lots
Drainage Area Land Cover (Acres...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Finger printing on large
lot construction:
Save trees, ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
• Reduced runoff
coefficients for
undisturbed pervious
...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Cover HSG A HSG B HSG C HSG D
Forest/Open 0.02 0.03 0.0...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Codifies & incentivizes minimization and
avoidance
Goes...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
• Impacts from grading and compaction of
soils
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
• Impacts from turf management activities
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Forest & Open Space:
• Undisturbed portions of resident...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Simple Method – Average Annual Load:
𝐿𝑜𝑎𝑑 = 𝑃 × 𝑃𝑗 × 𝑅 ...
New Rules (Part IIB)
• C = 0.26 mg/l
From:
Runoff Reduction Method
Technical Memorandum,
April 2008
𝐿 = 𝑃 × 𝑃𝑖 × 𝑅𝑣 𝑐𝑜𝑚𝑝𝑜𝑠...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
1. Weighted average soil cover derived from STATSGO sta...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
TvBMP = Design Treatment Volume from contributing
drain...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Washington Reagan Airport
0
1
2
3
4
5
6
0% 10% 20% 30% ...
Using the 90th percentile rainfall depth translates to
an annual average reduction
• Represents average over all storms an...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
0
0.25
0.5
0.75
1
Load(lb/ac/yr)
Required Level
of Trea...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Pollutant Removal
Practices
Minimization/ESDRunoff Redu...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Codifies & incentivizes minimization and
avoidance
Goes...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Total BMP Performance:
Runoff Reduction Reported Perfor...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Runoff Reduction (RR) and Pollutant Removal (PR):
• All...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Bioretention, Infiltration, Dry
Swales, Soil Amendments...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Site
Design
Runoff
Reduction
Pollutant
Removal
1. Rooft...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
BMP
1,000,000 liters of
stormwater
(multiple storm
even...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
100 mg/L of
pollutant
(average)
500,000 liters of
storm...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
The VRRM Technical Memo documented the
performance of B...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Codifies & incentivizes minimization and
avoidance
Goes...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Level 1 standard features included in all designs:
• Fu...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Level 2 design enhancements for increased RR, PR or
bot...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Comparative BMP
Level 1
& Level 2
Performance
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Consider guidance to standardize Process Diagrams to
tr...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Allow for compliance on high density sites;
Provide fle...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Level 1 Design (RR 40 TP: 25 ) Level 2 Design (RR: 80 T...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Project Graphic Courtesy of Geosyntec
19.8 acre single ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Turf = 12.09
Imp = 7.71
Area Total = 19.8 acres
Site Rv...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Credit Area (acres) to
Wet Pond Level 2:
Imp = 7.71 ac
...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Runoff Reduction = 0
TP Reduction = 17.06 lb/yr
Area Ch...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
1, 2, and 10-year
storm rainfall depths
CN = 83
1, 2, a...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Channel Protection:
Concentrated stormwater flow shall ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Goals:
• Establish “balance” exerted by pre- and post-
...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Simple “balance” offsets increase in volume and
peak fl...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Energy Balance
Post (Vol1-yr * Peak Q1-yr) ≤ Pre (Vol1-...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Use VRRM Spreadsheet to calculate the volume
reduction ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Roadway
Project Drainage
Area
Residential
Lots
Project ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
NEW PERVIOUS PAVEMENT
MANAGED TURF
BIORETENTION CELLS
R...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Same as traditional scenario, but with:
• Wet Pond area...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
NEW PERVIOUS PAVEMENT
MANAGED TURF
BIORETENTION CELLS
R...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
2
4
34
33
32
3
1
6
7
5
Disconnection
Disconnection
Disc...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Aggregated Credit Area to
Simple Disconnection = 5 ac
R...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Credit Area (Direct Runoff) to
Bioretention Level 2:
1....
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Area Check - OK
Runoff Reduction Achieved = 23,065 ft3
...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
1, 2, and 10-year
storm rainfall depths
1, 2, and 10-ye...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Original design:
• No Volume Reduction;
• Treat 100% of...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Use VRRM Spreadsheet to calculate the volume
reduction ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Project Graphic Courtesy of Geosyntec
NEW PERVIOUS PAVE...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
2
4
34
33
32
3
1
6
7
5
Disconnection
Disconnection
Disc...
Challenge:
Provide quantity “credit” for distributed retention
practices
Avoid Complex routing/modeling of multiple practi...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Simplifying Assumptions:
• Assume retention is uniforml...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
5 Methods Considered:
1. Hydrograph Truncation
2. Hydro...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
0%
20%
40%
60%
80%
100%
0% 20% 40% 60% 80% 100%
Volume ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Runoff Depth Equations (TR-55):
Where:
Q = runoff depth...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Step 3: 1.28” runoff
Step 1: 2.8” rainfallStep 4: Adjus...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
1, 2, and 10-year
storm rainfall depths
1, 2, and 10-ye...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
One-Year Storm Hydrology Summary: 19.8 acres
Pre-
Devel...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
No RR shown; 34% reduction in volume!
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Slight increase in allowable release w/RR
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
St. Paul’s Boulevard, City of Norfolk, VA
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
< 1 ac of land disturbance: 10% load reduction
≥ 1 ac o...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
• Virginia Stormwater Management Handbook Appendix
6C: ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Maximize on-site micro-practices such as:
• Filter Stri...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
• Promote de-nitrification (create adjacent
anaerobic a...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Maximum bacteria removal:
— long residence time and lig...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
1. Preferred BMPs
2. Accepted BMPs
3. Discouraged BMPs
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
1. Widespread feasibility in the coastal plain
2. High ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Preferred Accepted Discouraged
Constructed Wetland Wet ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Coastal plain research places wet ponds in 2
general gr...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
James River Basin BMP type (n=3112)
43%
17%
14%
12%
7%
...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Review of coastal plain wet ponds (as installed &
maint...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Key design drivers:
• Eutrophication: function of nutri...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
• Expected nutrient removal rates are slightly reduced ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Runoff Reduction = 0
TP Reduction = 17.06 lb/yr
Area Ch...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
* Includes: multi-cell design, sediment forebays, pool ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Application of a maximum impervious area per
disconnect...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Key Design Consideration: Nomenclature!
Conserved Open ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Key Design Considerations:
• Establish or maintain good...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Key Design Consideration:
Engineered Level Spreader (EL...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
‒Vegetated Filter Strips
‒Rainwater Harvesting
‒Green R...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
“Water Spreading”
Trees of the poplar,
cottonwood, and ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater BMP Enhancements
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Photo Credit: Jeremy Balousek, P.E., Dane County, WI La...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
S. Day, S. Dickenson; Virginia Tech Departments of Fore...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Susan Downing Day
&
Sarah B. Dickenson
Virginia Tech
De...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Type of pavement materials
Pervious Concrete Porous Asp...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Level 1
Level 2 (infiltration)
Level 2 (infiltration su...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Design Option: ‘Upturned Elbow’
Anaerobic Zone for deni...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Pavement Structural Design
• Thickness of permeable
pav...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Key Design Consideration: External Drainage Areas
In al...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Key Design Consideration: Maintenance
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Annual runoff reduction volume credit only
awarded for ...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Street Sweepers
Vactor Trucks
Public Works
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Seasonal uses must be supplemented with runoff
reductio...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Location
Roof Area
Indoor
Demand
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Secondary
Drawdown
Cooling
Towers
Seasonal
Irrigation
S...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Additional Daily
Use:
• Vehicle wash
• Street Sweepers
...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Without a Smart Control With a Smart Control
Cumulative...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Overflow (and dry)
Volume & Days
(all storms)
Typical (...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
7,000 Gallon Cistern Water Levels and Precipitation dur...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Annual Runoff
Reduction Credit
(based on cistern
size)
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
Tank Design 2: Storage Associated with Treatment, Chann...
Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
“Stormwater Management in the Coastal Plain & Beyond" Workshop held on December, 15, 2014 - Part I section
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“Stormwater Management in the Coastal Plain & Beyond" Workshop held on December, 15, 2014 - Part I section

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“Stormwater Management in the Coastal Plain & Beyond" Workshop held on December, 15, 2014 - Part I section

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“Stormwater Management in the Coastal Plain & Beyond" Workshop held on December, 15, 2014 - Part I section

  1. 1. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  2. 2. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Non-profit 501(c)3, non-advocacy organization founded in 1992 Work with watershed groups, local, state and federal governments Provide tools to communities to protect lakes, rivers, streams, and estuaries 20 staff in Ellicott City, MD; Field Offices in Charlottesville, Richmond, & Leesburg, VA; & Ithaca, NY; and Philadelphia, PA www.cwp.org
  3. 3. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Welcome and Introductions Historical Perspective Today’s Perspective break Connecting the VRRM Dots: Quality lunch Connecting the VRRM Dots: Quantity break Meet the BMPs (Coastal Plain Adaptations) Design Examples & Discussion
  4. 4. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Goal of Today’s Workshop: Understand the differences (and similarities) between the old (Part IIC) & the new (Part IIB) criteria; Become familiar with the new menu of BMPs and their respective performance credits; Identify issues and/or specific topics for future training opportunities
  5. 5. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Detailed design instructions for BMPs; Detailed analysis of life-cycle cost of BMPs; Computational Hydrology & Hydraulics; Easy solution for stormwater design on challenging sites: • Tidal influenced drainage system; • High water table; • Flat terrain.
  6. 6. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Be engaged Ask critical questions Share your expertise Respect your colleagues:
  7. 7. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Why is it different? and, Why do we care?
  8. 8. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 • Flat Terrain • High water table • Poorly drained soils • Very well drained soils • Highly altered drainage
  9. 9. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Shoreline buffer and critical areas cannot be used for stormwater practices Dugout ponds intersect with shallow water table and connect to receiving estuaries Unique development patterns (waterfront, marinas, golf courses)
  10. 10. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Highway ditches serve as the primary stormwater receiving and conveyance system; Heavy seasonal rainfall (hurricanes & Nor’easters) Historical drainage intended to serve agriculture Sea level rise
  11. 11. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  12. 12. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Where is all that water going? To the nearest waterway — and it is traveling fast.
  13. 13. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 The Economic Benefits of Cleaning Up the Chesapeake Chesapeake Bay Foundation, 2014 Annual economic benefits derived from the land and waters of the Chesapeake Bay region ~ $107 billion Continued/Improved implementation of multiple targeted programs (Chesapeake Clean Water Blueprint) are expected to increase the value 21% (~ $130 billion);
  14. 14. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Ecosystem Service Valuation: Water Flow Regulation; Air Pollution Treatment; Food Production; Water Supply; Waste Treatment; Climate Stability; Aesthetic Value; and Recreation.
  15. 15. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 •• Extreme storms eventsExtreme storms events •• Population growth & rapidPopulation growth & rapid developmentdevelopment •• Wetland, contiguous forest,Wetland, contiguous forest, & upland habitat preservation& upland habitat preservation •• Wastewater disposalWastewater disposal •• Shellfish prohibitionsShellfish prohibitions •• Harmful algal bloomsHarmful algal blooms •• Pollution preventionPollution prevention –– NitrogenNitrogen –– BacteriaBacteria •• Maintain waterMaintain water--basedbased recreationrecreation Coastal ConcernsCoastal ConcernsCoastal Concerns Impact to Recreation and Economic Resources: Shellfish bed closures; Beach closures; Decreased fisheries; Algal blooms
  16. 16. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 “the effects of watershed alteration on coastal resources are poorly understood and inaccessible to watershed and coastal resource managers.” (DeVoe and Kleppel, 2006) Studies suggest a strong negative relationship between land development (multiple metrics) and the biological, physical and chemical conditions of coastal water resources
  17. 17. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 10% 40%25% Good Fair Poor Watershed Impervious Cover StreamQuality 60% 100% Urban Drainage Over 200 studies: • Hydrologic Indicators • Stream Habitat Indicators • Water Quality Indicators • Aquatic Diversity Indicators
  18. 18. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Threshold values: Coastal plain streams: 3.5 – 14% Tidal creeks: 10 – 30% Estuariane: 24 – 35% Coastal Plain Watershed Management; Watershed Protection Techniques Vol. 4; No. 1; 2010
  19. 19. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  20. 20. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Sustainable Development in the Coastal Plain: Land use plans should allocate lands to their most appropriate uses; Requires knowledge and consideration of physical constraints; important natural features and the functions they provide; potential hazard areas; and the capacity of the land to support a given use. Coastal Plain Watershed Management; Watershed Protection Techniques Vol. 4; No. 1; 2010
  21. 21. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  22. 22. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  23. 23. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 VA Erosion & Sediment Control Program GC-7 MS-19: Properties and waterways downstream of development shall be protected from sediment deposition, erosion and damage due to . . .
  24. 24. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 . . . . Increases in runoff volume, . . .
  25. 25. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 . . . . velocity, and peak flow rate of stormwater runoff . . . . . . in accordance with the following:
  26. 26. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 b.The adequacy of all channels and pipes shall be verified in the following manner: (1) 1% rule the applicant shall demonstrate that the total drainage area to the point of outfall analysis is 100 times greater than the contributing DA of the project
  27. 27. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 (2) (a) Natural Channels: 2-yr erosion; 2-yr overtopping the banks. (b) Manmade Channels: 2-yr erosion; 10-yr overtopping the banks. (c) Pipes and storm sewers: 10-yr capacity
  28. 28. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 If existing pipes or channels are not adequate, the applicant shall: (1) Improve the channel, or (2) Improve the pipe system, or
  29. 29. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 If existing pipes or channels are not adequate, the applicant shall (continued): (3) Develop a site design that does not cause an increase in the 2-yr peak rate of runoff;
  30. 30. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 If existing pipes or channels are not adequate, the applicant shall (continued): Or: (4) “Provide a combination of channel improvement, stormwater detention, or other measures satisfactory to the VESCP Authority . . . ”
  31. 31. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Assumed C soils; Pre-developed land cover = Woods, good condition
  32. 32. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 1988 Chesapeake Bay Preservation Act (§ 62.1‐44.15:67) & The Chesapeake Bay Preservation Area Designation and Management Regulations (9VAC25-830)
  33. 33. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Stormwater BMP Sizing and Performance Credits Performance: Low to Moderate to High measured from 0 to 100% (Nationwide Urban Runoff Program 1979 - ’83) Sizing: 1st Flush to 2” runoff depth
  34. 34. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 1998 Amendments to the VA SWM Regulations Water Quality Compliance:  Performance-Based Criteria; or • Development Situations 1 thru 4; • Compliance with Average Land Cover Condition: 16% IC • Equivalent Annual TP Load = 0.45 lb/ac/yr  Technology Based Criteria
  35. 35. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Simple Method: Average Annual Load 𝐿𝑜𝑎𝑑 = 𝑃 × 𝑃𝑗 × 𝑅 𝑣 × 𝐶 × 𝐴 × 2.72/12 P = average annual rainfall depth (inches) = 43 inches (VA) Pj = fraction of rainfall events that produce runoff = 0.9 Rv = volumetric runoff coefficient = 0.05 + (0.009 × I); I = impervious cover C = flow-weighted event mean concentration (EMC) of TP = (mg/L) = 0.26 mg/L A = contributing drainage area (acres) 2.72 = unit conversion factor: L to ft3, mg to lb, and acres to ft2 12 = unit conversion factor: rainfall inches to feet
  36. 36. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Treatment Volume & BMP Sizing 𝑊𝑄𝑣 = Water Quality Volume 𝐼𝐶 = Impervious Cover in the contributing drainage area to the stormwater practice 𝑊𝑄𝑣 = 0.5" × 𝐼𝐶
  37. 37. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 * Innovative or alternate BMPs not included in this table may be allowed at the discretion of the local program administrator or the Department.
  38. 38. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Water Quantity Compliance:  Properties and receiving waterways downstream of any land development project shall be protected from erosion and damage due to increases in volume, velocity and peak flow rate of stormwater runoff in accordance with . . .
  39. 39. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Water Quantity Compliance:  Minimum Standard 19 of the ESC Regulations; or  The plan approving authority may determine that some receiving stream systems require enhanced criteria to address increased frequency of bankfull flows and therefore require: 24-hour Extended Detention of the runoff from the 1-year 24-hour storm
  40. 40. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Water Quantity Compliance: 2-yr post back to pre vs 1-yr ED Moderate development (32% IC): • > 2 x increase in runoff volume • 4 to 8 x increased Frequency of bankfull flows; . . . . significant reduction in stream channel erosion below facilities designed for 24-hour ED of the 1-yr frequency runoff (Galli, MWCOG 1992)
  41. 41. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Assumed C soils; Pre-developed land cover = Woods, good condition
  42. 42. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  43. 43. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 What types of BMPs or BMP strategies have proven to be effective in coastal plain?
  44. 44. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  45. 45. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 2005 NOIRA: Update Virginia’s Stormwater Management Regulations: 1) allow for the delegation of the VSMP to localities; 2) develop a framework for the Commonwealth to run local programs as needed; 3) allow for changes as needed to improve the administration and implementation; and 4) allow for removal of the out-of-date BMPs (Table 1)
  46. 46. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 EPA Performance Standards • Protect and restore the physical, chemical and biological integrity of receiving waters; • Treat flow (volume) as a surrogate for other pollutants (reference the National Research Council: Urban Stormwater Management in the United States); • Replicate pre-development hydrology: Infiltrate, evapotranspirate, or reuse the runoff from the 90th percentile rainfall event
  47. 47. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 2007 NOIRA: Replace & clarify the 2005 NOIRA: 1) Amendments, deletions, or additions to Part I (Definitions, Purpose, and Applicability); 2) Amendments, deletions, or additions to Part II (Technical Criteria); 3) Amendments, deletions, or additions to Part III (Local Programs); and 4) Other technical amendments, deletions, or additions (as may be needed).
  48. 48. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Inspector General Report on efforts to restore the Chesapeake Bay (2007) • % increase in Impervious cover 5 times that of population; • Pollutant load from urban runoff represents the only increasing source; • Cost effective solutions dependent on initial site- specific assessment of topography, soil conditions, etc. • Ineffective use of regulatory programs;
  49. 49. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 2009 NOIRA: 0.28 lb/ac/yr
  50. 50. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  51. 51. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  52. 52. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Encourage Low Impact Development Inclusion of land cover type in pollutant and hydrologic loading factors (good science) New treatment options with performance credit breakouts (better science) RR + PR (EMC)  Mass Load Reduction Step-wise (iterative) simplified compliance process. Environmental Site Design
  53. 53. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 evapotranspiration: 40-50% interflow: 20-30% surface runoff: <1%
  54. 54. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 evapotranspiration: ~25% interflow: 0-30% surface runoff: ~30%
  55. 55. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Research shows:  Extended Filtration mimics the hydrologic characteristics (meaning stormflow reaching a stream) of an undeveloped watershed.  Data also indicates that extended filtration releases water over a much longer period of time than an undeveloped (agricultural) watershed; and likely a comparable period of time as a forested watershed. Hunt et al., NCSU 2010
  56. 56. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Runoff Reduction is not just infiltration!  Infiltration  Canopy Interception  Evaporation  Transpiration  Rainwater Harvesting  Extended Filtration  Soil Amendments
  57. 57. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  58. 58. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Compliance Spreadsheet
  59. 59. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Codifies & incentivizes minimization and avoidance Goes beyond impervious cover as a water quality indicator Utilizes latest BMP research for Total Performance (Total Mass Load Removal) Credits total BMP performance
  60. 60. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Environmental Site Inventory & Assessment • Forest conservation • Suitable soils • Steep slopes • Drainage • Wetlands • Zero-order streams • Buffers • Sensitive areas • Limits of disturbance • Computed nutrient loads & treatment volume
  61. 61. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  62. 62. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  63. 63. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  64. 64. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 A 1990 study for the city of Virginia Beach compared the costs and benefits of conventional and smart growth development patterns. The study found: smart growth pattern resulted in 45% more land preserved, 45% less in infrastructure costs to the city, and 50% reduction in impervious surface due to roads (Siemon, Larsen and Purdy, et al., 1990)
  65. 65. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 An Assessment of the Better Site Design Principles for Communities Implementing Virginia’s Chesapeake Bay Preservation Act (CWP, 2000) • 16 Model Development Principles • 4 development projects • Average 28% reduction in Total Infrastructure Costs (47%; 15%; 49%; NC)
  66. 66. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 The Economic Benefits of Watershed Protection (CWP, 2001) 1. Watershed Planning 2. Land Conservation 3. Aquatic Buffers 4. Better Site Design 5. Erosion & Sediment Control 6. Stormwater Treatment 7. Non-Stormwater Discharges 8. Watershed Stewardship
  67. 67. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 1. Site Data Input: • Site Land cover • Site level Treatment Volume (Tv) • Site level pollutant loads and Removal Requirement 2. Drainage Area Inputs: • DA Land Cover • TvBMP (used for BMP sizing) • Area treated check • DA pollutant removal 1. Site Data Input 2. Drainage Area Inputs 4. Channel/Flood Protection Check 3. Water Quality Check 5. Summary Print-out
  68. 68. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Volumetric Runoff Coefficients • Land Cover (acres) by HSG • Definitions Provided in Guidance Composite Site Rv Post-Dev Tv Pollutant Load (TP & TN) Total Load Reduction Reqd. Weighted (by HSG) Rv for Forest, Turf, & Imp
  69. 69. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 15 Acres 25 ½ acre lots Drainage Area Land Cover (Acres) Land Cover Total ½ acre lots Total ¼ acre lots Forest 0.87 4.31 Turf 8.32 5.26 Impervious 2.26 1.88 15 Acres 25 ¼ acre lots Drainage Area Water Quality Requirements Total ½ acre lots Total ¼ acre lots Post-Dev Treatment Vol 14,452 ft3 11,198 ft3 Post-Dev TP Load 9.08 lb/yr 7.04 lb/yr Pollutant Removal Reqd. 4.39 lb/yr 2.34 lb/yr
  70. 70. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  71. 71. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  72. 72. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Finger printing on large lot construction: Save trees, soil, etc. Finger-printing subdivision construction: narrow streets; shorter setbacks, etc.
  73. 73. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 • Reduced runoff coefficients for undisturbed pervious areas; • Increased runoff coefficients for impacted soils & managed turf;
  74. 74. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Cover HSG A HSG B HSG C HSG D Forest/Open 0.02 0.03 0.04 0.05 Managed Turf / Disturbed Soil 0.15 0.20 0.22 0.25 Impervious Cover 0.95 0.95 0.95 0.95 1 Center for Watershed Protection – Technical Memorandum: The Runoff Reduction Method; 4/18/08 Pitt et al (2005), Lichter and Lindsey (1994), Schueler (2001a, 2001b, 1987), Legg et al (1996), Pitt et al (1999), and Cappiella et al (2005)
  75. 75. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Codifies & incentivizes minimization and avoidance Goes beyond impervious cover as a water quality indicator Utilizes latest BMP research for Total Performance (Total Mass Load Removal) Credits total BMP performance
  76. 76. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 • Impacts from grading and compaction of soils
  77. 77. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 • Impacts from turf management activities
  78. 78. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Forest & Open Space: • Undisturbed portions of residential development; • Open space left in natural vegetated state that will not be managed as turf (regular mowing, fertilized, etc.); includes utility ROW’s with periodic bush- hogging; • Surface area of BMPs that have vegetative cover (not wet ponds, green roof, permeable pavement); Managed Turf Impervious Cover
  79. 79. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Simple Method – Average Annual Load: 𝐿𝑜𝑎𝑑 = 𝑃 × 𝑃𝑗 × 𝑅 𝑣 × 𝐶 × 𝐴 × 2.72/12 P = average annual rainfall depth (inches) = 43 inches (VA) Pj = fraction of rainfall events that produce runoff = 0.9 Rv = volumetric runoff coefficient = 0.05 + (0.009 × I); I = impervious cover C = flow-weighted event mean concentration (EMC) of TP = (mg/L) = 0.26 mg/L A = contributing drainage area (acres) 2.72 = unit conversion factor: L to ft3, mg to lb, and acres to ft2 12 = unit conversion factor: rainfall inches to feet 𝐿 = 𝑃 × 𝑃𝑖 × 𝑅𝑣 𝑐𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒 × 𝐶 × 𝐴 × 2.72 12 𝑅𝑣 𝑐𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒 = 𝑅𝑣𝐼 × %𝐼 + 𝑅𝑣 𝑇 × %𝑇 + 𝑅𝑣 𝐹 × %𝐹
  80. 80. New Rules (Part IIB) • C = 0.26 mg/l From: Runoff Reduction Method Technical Memorandum, April 2008 𝐿 = 𝑃 × 𝑃𝑖 × 𝑅𝑣 𝑐𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒 × 𝐶 × 𝐴 × 2.72 12 Center for Watershed Protection
  81. 81. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  82. 82. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 1. Weighted average soil cover derived from STATSGO state-wide soils database soil breakdown for VA outside of the Chesapeake Bay Watershed. 2. Schueler, T., Fraley-McNeal, L., and Capiella, K. “Is Impervious Cover Still Important? Review of Recent Research” Journal of Hydrologic Engineering, April 2009 1 2 𝐿 = 𝑃 × 𝑃𝑖 × 𝑅𝑣 𝑐𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒 × 𝐶 × 𝐴 × 2.72 12
  83. 83. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 TvBMP = Design Treatment Volume from contributing drainage area to stormwater practice (does not include remaining runoff from upstream practices) P = 90th Percentile rainfall depth = 1” Rvcomposite = Composite runoff coefficient A = Direct contributing drainage area to the stormwater practice 𝑇𝑣 𝐵𝑀𝑃 = 𝑃 × 𝑅𝑣 𝑐𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒 × 𝐴 12
  84. 84. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Washington Reagan Airport 0 1 2 3 4 5 6 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Precipitation Event Percentile PrecipitationDepth(inches) 90th Percentile rainfall depth 1” annual average: Washington Reagan Airport, Richmond Airport, Harrisonburg, Lynchburg, Bristol
  85. 85. Using the 90th percentile rainfall depth translates to an annual average reduction • Represents average over all storms and not individual single-event modeled storms • Oversizing practice does not necessarily provide for increase in “annual” RR or PR performance • Oversizing can help meet quantity control storage requirements when modeled on single event basis
  86. 86. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 0 0.25 0.5 0.75 1 Load(lb/ac/yr) Required Level of Treatment Allowable Load (lb/ac/yr) Part II C Requirements Part II B Requirements Required Treatment 0.45 0.41
  87. 87. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Pollutant Removal Practices Minimization/ESDRunoff Reduction Practices
  88. 88. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Codifies & incentivizes minimization and avoidance Goes beyond impervious cover as a water quality indicator Utilizes latest BMP research for Total Performance (Total Mass Load Removal) Credits total BMP performance
  89. 89. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Total BMP Performance: Runoff Reduction Reported Performance: 𝑹𝒖𝒏𝒐𝒇𝒇 𝑽𝒐𝒍 𝑰𝑵 𝒗𝒔 𝑹𝒖𝒏𝒐𝒇𝒇 𝑽𝒐𝒍 𝑶𝑼𝑻 + Pollutant Removal Reported Performance: 𝑬𝑴𝑪 𝑰𝑵 𝒗𝒔 𝑬𝑴𝑪 𝑶𝑼𝑻 = Total BMP Performance (reported as Load Reduction): 𝑽𝒐𝒍 𝑰𝑵 × 𝑬𝑴𝑪 𝑰𝑵 𝒗𝒔 𝑽𝒐𝒍 𝑶𝑼𝑻 𝑬𝑴𝑪 𝑶𝑼𝑻 Center for Watershed
  90. 90. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Runoff Reduction (RR) and Pollutant Removal (PR): • Allows for reductions beyond irreducible concentrations by reducing the volume; • Provides for maximum performance through a “Treatment Train” approach including non-structural practices
  91. 91. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Bioretention, Infiltration, Dry Swales, Soil Amendments, disconnection, and Related Practices Reduce Runoff Volumes by 50 to 90% Wet Ponds, ED Ponds and Constructed Wetlands and Filters Reduce Runoff Volumes by zero to 10%
  92. 92. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Site Design Runoff Reduction Pollutant Removal 1. Rooftop Disconnection   2. Filter Strip   3. Grass Channel   4. Soil Amendments *  5. Green Roof  6. Rain Tanks & Cisterns  7. Permeable Pavement   8. Infiltration   9. Bioretention   10. Dry Swales   12. Filtering Practices  13. Constructed Wetlands  14. Wet Ponds  15. ED Ponds  
  93. 93. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 BMP 1,000,000 liters of stormwater (multiple storm events) 100 mg/L pollutant (average) 1,000,000 liters of stormwater (multiple storm events) 50 mg/L of pollutant (average) No volume reduction, only EMC reduction 100 kg Total pollutant load 50 kg Total pollutant load SOURCE: VA DEQ, 2013 50% PR
  94. 94. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 100 mg/L of pollutant (average) 500,000 liters of stormwater (multiple storm events) 50 mg/L pollutants (average) Total Performance = 75% load reduction! 25 kg Total pollutant load BMP 100 kg Total pollutant load SOURCE: VA DEQ, 2013 (CORRECTED) 1,000,000 liters of stormwater (multiple storm events) 50% RR 50% PR +
  95. 95. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 The VRRM Technical Memo documented the performance of BMPs:  RR performance more consistent than PR performance;  Nutrient PR in stormwater BMPs is notoriously inconsistent;  RR rates are an annual average based on the individual study site water balance.  The recommended rates are conservative estimates  The RR rates in the regulations are dependent on meeting Level 1 or Level 2 criteria.
  96. 96. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Codifies & incentivizes minimization and avoidance Goes beyond impervious cover as a water quality indicator Utilizes latest BMP research for Total Performance (Total Mass Load Removal) Credits total BMP performance
  97. 97. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Level 1 standard features included in all designs: • Function; • Safety; • Appearance; • Safe conveyance; • Performance longevity • Maintenance
  98. 98. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Level 2 design enhancements for increased RR, PR or both: • Increased Tv sizing (by a factor of 1.1, 1.25 or 1.5 times the Tv); • Enhanced design geometry; • Vegetative condition; • Multiple cells; • Multiple treatment pathways; and Other bells and whistles, e.g., increased pretreatment, increased media depth, etc.
  99. 99. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Comparative BMP Level 1 & Level 2 Performance
  100. 100. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Consider guidance to standardize Process Diagrams to track volume and load through complex treatment trains
  101. 101. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Allow for compliance on high density sites; Provide flexibility on small/tight sites by allowing multiple smaller BMPs to treat stormwater near the source; • as the drainage area incrementally increases (with each RR practice); • the RR practices incrementally reduce the runoff volume and TvBMP, • each successive BMP is not sized on the entire upstream drainage area; • Rather, the BMP is sized by the TvBMP from the directly contributing drainage area + any remaining runoff from upstream RR practices.
  102. 102. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Level 1 Design (RR 40 TP: 25 ) Level 2 Design (RR: 80 TP: 50) Sizing (Section 6.1): TvBMP = [(1)(Rv)(A) / 12] + any remaining volume from upstream BMP Sizing (Section 6.1): TvBMP = [(1.25)(Rv)(A) / 12] + any remaining volume from upstream BMP Design Summary Table BMP Design Specification No. 9: Bioretention
  103. 103. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Project Graphic Courtesy of Geosyntec 19.8 acre single Family Subdivision 2.2 acres of R.O.W. 34 lots (avg lot size = ½ acre)
  104. 104. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Turf = 12.09 Imp = 7.71 Area Total = 19.8 acres Site Rv = 0.50 Post Dev Tv = 0.83 ac-ft Post Dev TP Load = 22.77 lb/yr Load Reduction Required = 14.65 lb/yr Site Data Tab Site Avg BMP Eff. = 14.65/22.77 x 100 = 65%
  105. 105. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Credit Area (acres) to Wet Pond Level 2: Imp = 7.71 ac Turf = 12.09 ac TP Removed = 17.06 lb/yr 0 Runoff Reduction Area Check: OK Drainage Area Tab Remaining Runoff & TP load
  106. 106. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Runoff Reduction = 0 TP Reduction = 17.06 lb/yr Area Check: OK
  107. 107. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 1, 2, and 10-year storm rainfall depths CN = 83 1, 2, and 10-year volume (RV) measured in watershed inches = RV1 = 1.28 inches RV2 = 1.76 inches RV10 = 3.30 inches No RR No CN Adjustment! No volume reduction
  108. 108. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  109. 109. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  110. 110. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Channel Protection: Concentrated stormwater flow shall be released in to a stormwater conveyance system: Photo: Williamsburg Environmental Group Manmade Stormwater Conveyance System Restored Stormwater Conveyance System Natural Stormwater Conveyance System
  111. 111. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Goals: • Establish “balance” exerted by pre- and post- developed 1-yr peak stormwater discharge; • Incentivize Better Site Design (and volume reduction); • Keep it Simple (Qpeak*Vol)pre (Qpeak*Vol)post
  112. 112. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Simple “balance” offsets increase in volume and peak flow of developed condition hydrology Post-development runoff volume increases Allowable discharge decreases
  113. 113. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Energy Balance Post (Vol1-yr * Peak Q1-yr) ≤ Pre (Vol1-yr * Peak Q1-yr) re-written: IF = Improvement Factor: (0.8 for sites > 1 acre or 0.9 for sites ≤ 1 acre) 𝑞1𝑝𝑜𝑠𝑡 ≤ 𝑞1𝑝𝑟𝑒 𝑃𝑟𝑒 𝑉𝑜𝑙1 𝑃𝑜𝑠𝑡 𝑉𝑜𝑙1 𝐼𝐹
  114. 114. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Use VRRM Spreadsheet to calculate the volume reduction with a double credit: • Reduced Volpost1 for Energy Balance Equation; and • Reduced Curve Number (CN) for computing the q1post 𝑞1𝑝𝑜𝑠𝑡 ≤ 𝑞1𝑝𝑟𝑒 𝑃𝑟𝑒 𝑉𝑜𝑙1 𝑃𝑜𝑠𝑡 𝑉𝑜𝑙1 𝐼𝐹 Must consider the pre- and post- condition drainage areas!
  115. 115. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Roadway Project Drainage Area Residential Lots Project Graphic Courtesy of Geosyntec Typical subdivision development:
  116. 116. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 NEW PERVIOUS PAVEMENT MANAGED TURF BIORETENTION CELLS RESIDENTIAL LOTS Project Graphic Courtesy of Geosyntec NEW PERVIOUS PAVEMENT MANAGED TURF BIORETENTION CELLS RESIDENTIAL LOTS ROOFTOP DISCONNECTION
  117. 117. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Same as traditional scenario, but with: • Wet Pond area partially converted from ‘Impervious Cover’ to ‘Managed Turf’ • BMP areas converted from ‘Managed Turf’ to ‘Forest/Open Space’ Slight change in Tv, TP Load, and Reduction Requirement Center for Watershed 118
  118. 118. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 NEW PERVIOUS PAVEMENT MANAGED TURF BIORETENTION CELLS RESIDENTIAL LOTS Project Graphic Courtesy of Geosyntec NEW PERVIOUS PAVEMENT MANAGED TURF BIORETENTION CELLS RESIDENTIAL LOTS ROOFTOP DISCONNECTION
  119. 119. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 2 4 34 33 32 3 1 6 7 5 Disconnection Disconnection Disconnection Disconnection Disconnection Disconnection Disconnection Disconnection Disconnection Disconnection No. 1 Bio L2 No. 2 Bio L2 No. 18 Bio L2 ?
  120. 120. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Aggregated Credit Area to Simple Disconnection = 5 ac Runoff Reduction = 4,311 ft3 Runoff Remaining = 12,932 ft3 Downstream Treatment: Bioretention L2 Load Reduction = 2.71 lb Load Remaining = 8.12 lb
  121. 121. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Credit Area (Direct Runoff) to Bioretention Level 2: 1.89 ac Impervious 5.0 ac Turf Volume from upstream RR practice: 12,932 ft3 Runoff Reduction = 18,754 ft3 Runoff Remaining = 4,689 ft3 Load Reduction = 2.71 lb Load Remaining = 8.12 lb Load from upstream RR practice: 8.12 lb
  122. 122. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Area Check - OK Runoff Reduction Achieved = 23,065 ft3 TP Load Reduction Achieved = 15.96 lb
  123. 123. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 1, 2, and 10-year storm rainfall depths 1, 2, and 10-year volume (RV) reduction = RV1 = 1.28” 0.96” CN1 83 77 RV2 = 1.76” 1.44” CN2 83 78 RV10 = 3.30” 2.98” CN10 83 80 Volume Reduction = 23,065 ft3
  124. 124. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Original design: • No Volume Reduction; • Treat 100% of the site (19.8 ac) with Wet Pond Level 2 • Compliance: exceed reqmt. by 2.4 lb/yr RR Design: • Treat 11.9 acres • Compliance: exceed reqmt. by 2.2 lb/yr • No wet pond Reqd (for water quality) • Reduce 23,065 ft3 volume (from site Tv = 34,816 ft3) • Reduce 1-yr CN from 83 to 77
  125. 125. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Use VRRM Spreadsheet to calculate the volume reduction with a double credit: • Reduced Volpost1 for Energy Balance Equation; and • Reduced Curve Number (CN) for computing the q1post 𝑞1𝑝𝑜𝑠𝑡 ≤ 𝑞1𝑝𝑟𝑒 𝑃𝑟𝑒 𝑉𝑜𝑙1 𝑃𝑜𝑠𝑡 𝑉𝑜𝑙1 𝐼𝐹 Must consider the pre- and post- condition drainage areas!
  126. 126. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Project Graphic Courtesy of Geosyntec NEW PERVIOUS PAVEMENT MANAGED TURF BIORETENTION CELLS RESIDENTIAL LOTS ROOFTOP DISCONNECTION
  127. 127. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 2 4 34 33 32 3 1 6 7 5 Disconnection Disconnection Disconnection Disconnection Disconnection Disconnection Disconnection Disconnection Disconnection Disconnection No. 1 Bio L2 No. 2 Bio L2 No. 18 Bio L2 ??
  128. 128. Challenge: Provide quantity “credit” for distributed retention practices Avoid Complex routing/modeling of multiple practices, yet simulate single event modeling Allow designers to target volume as primary metric (quantity and quality) Various methods explored by VA TAC
  129. 129. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Simplifying Assumptions: • Assume retention is uniformly distributed if considering multiple features or sub-areas; • Assume negligible discharge from under-drains (if any)
  130. 130. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 5 Methods Considered: 1. Hydrograph Truncation 2. Hydrograph Scalar Multiplication 3. Precipitation Adjustment 4. Runoff Adjustment 5. Curve Number Adjustment Excerpted from work by Paul R. Koch, Ph.D., P.E.
  131. 131. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Volume Stored, as Percent of Total Runoff PercentofRunoffPeakRemaining R_trunc R_as_P R_as_Q CN_adj Scalar Method of Analysis CN Adjustment Excerpted from work by Paul R. Koch, Ph.D., P.E.
  132. 132. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Runoff Depth Equations (TR-55): Where: Q = runoff depth (in) P = precipitation depth (in) S = potential maximum retention after runoff begins Ia = initial abstraction, volume filled before runoff begins. 𝑄 = 𝑃 − 𝐼 𝑎 2 𝑃 − 𝐼 𝑎 + 𝑆 𝐼 𝑎 = 0.2𝑆 𝑆 = 1000 𝐶𝑁 − 10 Eq. 2-1: Eq. 2-2: Eq. 2-4:
  133. 133. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Step 3: 1.28” runoff Step 1: 2.8” rainfallStep 4: Adjust For Retention (-0.32”) Step 5: Adjusted CN ~ 77 Step 2: Original CN = 83
  134. 134. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 1, 2, and 10-year storm rainfall depths 1, 2, and 10-year volume (RV) reduction = RV1 = 1.28” 0.96” CN1 83 77 RV2 = 1.76” 1.44” CN2 83 78 RV10 = 3.30” 2.98” CN10 83 80 Volume Reduction = 23,065 ft3
  135. 135. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 One-Year Storm Hydrology Summary: 19.8 acres Pre- Developed Post- Developed no RR Post- Developed with RR Runoff Curve Number 71 83 77 Runoff Volume (RV) 0.62 in 1.28 in 0.96 in Runoff Volume 1.02 ac-ft. 2.11 ac-ft. 1.58 ac-ft. Peak Discharge (q1) 9 cfs 39 cfs 27 cfs Post Developed EB Allowed Peak Discharge (cfs) 3.5 cfs 4.7 cfs Storage Volume Reqd. (ac-ft) 1.16 ac-ft.* 0.76 ac-ft.* 34% Reduction in required 1-yr EB Storage Volume
  136. 136. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 No RR shown; 34% reduction in volume!
  137. 137. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Slight increase in allowable release w/RR
  138. 138. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 St. Paul’s Boulevard, City of Norfolk, VA
  139. 139. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 < 1 ac of land disturbance: 10% load reduction ≥ 1 ac of disturbance: 20% load reduction Increase in impervious cover from existing: • New impervious acreage is managed as new development (0.41 lb/ac/yr); • Remainder of site is managed to a 10% or 20% reduction (as required). • Definition of site = area of land disturbance
  140. 140. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  141. 141. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  142. 142. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 • Virginia Stormwater Management Handbook Appendix 6C: Stormwater Design in the Coastal Plain • Chesapeake Stormwater Network Technical Bulletin No. 2 (v1.0): Stormwater Design in the Coastal Plain • HRPDC: Land & Water Quality Protection Phase II Discouraged BMPs • Center for Watershed Protection: Watershed Protection Techniques Vol.4, No. 1, 2010
  143. 143. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Maximize on-site micro-practices such as: • Filter Strips; • Buffers (reforestation), • Simple Disconnection; • Alternative Disconnection — cisterns, — dry wells, — rain gardens, & — compost amended filter path;
  144. 144. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 • Promote de-nitrification (create adjacent anaerobic and aerobic zones); • Avoid infiltration in areas with high water table; • Utilize native plants; • Create a rooftop to buffer in-line treatment train; and • Relax some design criteria to keep practice depths shallow!
  145. 145. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Maximum bacteria removal: — long residence time and light exposure for coliform die off; — Reduce turf around open water to discourage geese and waterfowl; — Use shallow wetlands and benches to create natural micro-predators; — Minimize resuspension of bottom sediments
  146. 146. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 1. Preferred BMPs 2. Accepted BMPs 3. Discouraged BMPs
  147. 147. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 1. Widespread feasibility in the coastal plain 2. High runoff reduction capacity 3. Moderate to high removal of nitrogen and bacteria 4. Low mosquito breeding capability when installed and maintained properly Preferred means the practice does well on at least three factors; Discouraged does not mean prohibited; rather it suggests ruling out an alternative preferred practice first
  148. 148. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Preferred Accepted Discouraged Constructed Wetland Wet Ponds Large Scale Infiltration Shallow Bioretention & Dry Swales Small-scale Infiltration Dry ED ponds Wet Swale Green Roofs Grass Channels Rain Tanks/Cisterns Soil Compost Amendments Roof Disconnection & Filter Strips Sand Filter Permeable Pavers
  149. 149. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Coastal plain research places wet ponds in 2 general groups: 1. Standard ponds: do not meet criteria and have low to negative nutrient removal performance; 2. Enhanced ponds: performed much better resulting from design features: • geometry: L:W ratio; multiple cells; • macrophytes and other wetland characteristics (wetland cells, benches, etc.); • Extended detention time of incoming runoff;
  150. 150. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 James River Basin BMP type (n=3112) 43% 17% 14% 12% 7% 2% 2% 2% 1% 0% 0% 0% 0% 0% 0% 0% 10% 20% 30% 40% 50% Wet Pond Pond, Unidentified Detention Grass Channel Infiltration Other Pond, Water Quality Detention Proprietary Device Bioretention Constructed Wetland Underground Storage Filter Practice Permeable Pavement Dry Swale Level Spreader Wet Swale • Hirschman and Woodworth, 2009; and • Literature Synthesis of SC and NC studies; Drescher at al, 2007)
  151. 151. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Review of coastal plain wet ponds (as installed & maintained): • A large number fail to meet basic (minimum) design criteria (and enhanced guidelines); • Many exhibited functional problems relating to a lack of maintenance (sediment deposition, excessive plant growth, trees on embankment); • worst performing were small (pocket style) with a small contributing drainage area (squeezed onto site)
  152. 152. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Key design drivers: • Eutrophication: function of nutrient input and residence time (defined as pool vol/annual runoff input); and • Depth of the anoxic zone (which increases the nutrient release from the bottom sediments).
  153. 153. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 • Expected nutrient removal rates are slightly reduced in the coastal plain due to the influence of groundwater, • Certain design features are essential to achieving reduction (multiple cells, benches, flow path, etc.) • Certain design features can enhance performance (landscaping, bubblers & fountains, floating wetlands) can improve their function. • Wet ponds can produce and or export harmful algal blooms if they interact with brackish ground or surface waters
  154. 154. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  155. 155. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Runoff Reduction = 0 TP Reduction = 17.06 lb/yr Area Check: OK New Level 2 TP reduction Credit (65%) = 14.8 (coastal plain): Congratulations!!
  156. 156. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 * Includes: multi-cell design, sediment forebays, pool geometry (L:W = 2:1) ** Aquatic Bench Part IIC Retention Basin WQv Pool Volume (ac-ft.) TP Reduction Credit Retention Basin I* 0.475 ac-ft. (3x) = 1.425 40% Retention Basin II* (4x) = 1.90 50% Retention Basin III** (4x) = 1.90 65% Part IIB Retention Basin Tv Pool Volume (ac-ft.) TP Reduction Credit Retention Basin L1* 1.180 ac-ft. 1.180 50% (45%) Retention Basin L2** 1.77 75% (65%) * Includes: safety bench, aquatic bench, sediment forebays, L:W = 2:1 ** Multi-cell design, 10% surface area wetland; 50% of Tv can be in ED above normal pool, L:W = 3:1;
  157. 157. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  158. 158. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  159. 159. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  160. 160. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Application of a maximum impervious area per disconnection: • Alternate Disconnection; or • Vegetated Filter Strips
  161. 161. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  162. 162. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  163. 163. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  164. 164. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Key Design Consideration: Nomenclature! Conserved Open Space Width Width Length
  165. 165. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Key Design Considerations: • Establish or maintain good vegetative cover; • Establish and maintain sheet flow • Thick no-mow (low maintenance) vegetation. http://www.clemson.edu/extension
  166. 166. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Key Design Consideration: Engineered Level Spreader (ELS) combined with forebay, energy dissipator, rigid lip, & gravel diaphragm Photo: R. Winston; BAE Stormwater Engineering Group, NCSU
  167. 167. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  168. 168. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 ‒Vegetated Filter Strips ‒Rainwater Harvesting ‒Green Roofs ‒TREES!!!! SWM Benefits of Trees (D. Wible, CH2MHILL)
  169. 169. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 “Water Spreading” Trees of the poplar, cottonwood, and willow family have been shown to draw as much as 200 gallons of water per day (EPA, Introduction to Phytoremediation)
  170. 170. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  171. 171. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  172. 172. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Stormwater BMP Enhancements
  173. 173. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Photo Credit: Jeremy Balousek, P.E., Dane County, WI Land and Water Resources Department Photo Credit: Richard McLaughlin, Ph.D., North Carolina State University Soil Restoration
  174. 174. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  175. 175. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  176. 176. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 S. Day, S. Dickenson; Virginia Tech Departments of Forestry and Horticulture Managing Stormwater for Urban Sustainability Using Trees and Structural Soils
  177. 177. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Susan Downing Day & Sarah B. Dickenson Virginia Tech Departments of Forestry and Horticulture
  178. 178. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Type of pavement materials Pervious Concrete Porous Asphalt Permeable Interlocking Concrete Pavers Concrete Grid Pavers Pervious Composites Permeable Rubber Overlays
  179. 179. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Level 1 Level 2 (infiltration) Level 2 (infiltration sump)
  180. 180. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Design Option: ‘Upturned Elbow’ Anaerobic Zone for denitrification
  181. 181. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Pavement Structural Design • Thickness of permeable pavement and reservoir layer must be sized to support structural loads • Primary design elements: – Anticipated traffic loads; – Underlying soil properties; – Surface and bedding strength coefficients
  182. 182. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Key Design Consideration: External Drainage Areas In all cases, external drainage areas should be limited to impervious surfaces to reduce potential sediment loading
  183. 183. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Key Design Consideration: Maintenance
  184. 184. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014
  185. 185. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Annual runoff reduction volume credit only awarded for dedicated year-round water drawdown/demand Laundry washing Vehicle washingToilet flushing
  186. 186. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Street Sweepers Vactor Trucks Public Works
  187. 187. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Seasonal uses must be supplemented with runoff reduction drawdown practice Irrigation Cooling tower make-up water
  188. 188. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Location Roof Area Indoor Demand
  189. 189. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Secondary Drawdown Cooling Towers Seasonal Irrigation Seasonal with or w/o smart control
  190. 190. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Additional Daily Use: • Vehicle wash • Street Sweepers • Vactor Truck • Etc.with or Additional Sources of water Losses
  191. 191. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Without a Smart Control With a Smart Control Cumulative Daily Water Use and Equivalent Year Round Use
  192. 192. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Overflow (and dry) Volume & Days (all storms) Typical (rain) Year
  193. 193. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 7,000 Gallon Cistern Water Levels and Precipitation during a Normal Rainfall Year
  194. 194. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Annual Runoff Reduction Credit (based on cistern size)
  195. 195. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014 Tank Design 2: Storage Associated with Treatment, Channel Protection and Flood Volume Tank Design 1: Storage Associated with Treatment Volume (Tv) only
  196. 196. Stormwater in the Coastal Plain – Virginia Beach, December 3, 2014

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