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TRANSCRIPT
Paraprofessional Training Session 1
Part 3: Disconnection
November 26, 2012 Rutgers University, Cook Campus
Christopher C. Obropta, Ph.D., P.E.
Extension Specialist in Water Resources
Associate Professor in Environmental Sciences
www.water.rutgers.edu
The Hydrologic Cycle
Important Consideration
Connected Impervious Surfaces
vs.
Disconnected Impervious Surfaces
Connected vs. Disconnected
Connected or Disconnected?
The Solution…
PLACE A STORMWATER BEST MANAGEMENT PRACTICE (BMP)
BETWEEN IMPERVIOUS AREAS AND THE STORM SEWER SYSTEM
Rooftop runoff is now “disconnected” from flowing directly into the storm sewer system
Disconnection Math
208.7 ft
208.7 ft
1 foot
1 foot 1 sq. ft. or 1 ft2
1 foot
1 foot
1 foot
1 cu. ft. or 1 ft3
43,560 sq. ft. or 1 acre
1 foot 208.7 ft
208.7 ft
1 acre-ft
1 acre = 43,560 sq. ft.
7.5 gallons = 1 cu. ft. 1 cu. yd. = 27 cu. ft.
1 sq. yard = 9 sq. ft. 3 feet
3 feet
Runoff
Direction
1 acre directly
connected
impervious cover
2 acres
pervious cover
Total drainage area = 3 acres
For 1.25 inch storm, 3,794 cubic feet of runoff = 28,600 gallons
Stormwater
Inlet
3,755 cu.ft. 39 cu.ft.
1 acre directly
connected
impervious cover
2 acres
pervious cover
Total drainage area = 3 acres
For 1.25 inch storm, 574 cubic feet of runoff = 4,330 gallons
Runoff Direction
Stormwater
Inlet
3,755 cu.ft. 574 cu.ft.
Let’s Do the Math
• 3794 cubic feet of water runs off the parking lot onto 2 acres of pervious surface
• 3794 ft3 / (43560 ft2/acres x 2 acres) = 0.0435 ft = 0.52 inches
• This means that the pervious surface receives 1.25 inches + 0.52 inches = 1.77 inches of rain
Volume of Runoff
Design
Storm
Connected
(gallons)
Disconnected
(gallons)
Percent
Difference
1.25 inches
(water quality
storm)
28,600 4,330 85%
Impervious area is now “disconnected” from flowing directly into the storm sewer system
Table 3-3: New Jersey 24-Hour Rainfall Frequency Data Rainfall amounts in Inches
County
Rainfall Frequency Data
1-
Year
2-
Year
5-
Year
10-
Year
25-
Year
50-
Year
100-
Year
Atlantic 2.8 3.3 4.3 5.2 6.5 7.6 8.9
Burlington 2.8 3.4 4.3 5.2 6.4 7.6 8.8
Camden 2.8 3.3 4.3 5.1 6.3 7.3 8.5
Cape May 2.8 3.3 4.2 5.1 6.4 7.5 8.8
Cumberland 2.8 3.3 4.2 5.1 6.4 7.5 8.8
Gloucester 2.8 3.3 4.2 5.0 6.2 7.3 8.5
Hudson 2.7 3.3 4.2 5.0 6.2 7.2 8.3
Hunterdon 2.9 3.4 4.3 5.0 6.1 7.0 8.0
Mercer 2.8 3.3 4.2 5.0 6.2 7.2 8.3
Volume of Runoff
Design
Storm
Connected
(gallons)
Disconnected
(gallons)
Percent
Difference
1.25 inches
(water quality
storm)
28,600 4,330 85%
5.0 inches
(10-year
storm)
219,915 185,365 16%
Subaru of America, Inc.
Demonstration Rain Garden
Example
• Small parking lot 10,000 sq. ft.
Example • Let’s calculate the runoff volume for the
water quality storm
..042,1..000,10/12
25.1ftcuftsq
ftin
in
Bioretention size =
200’ long x 10.5’ wide x 0.5’ deep
Questions?
What’s Coming Up?
Project Identifier Geographic Coordinates
MB5_We i N40°58.956’ W074°02.610’
Site Description and BMP Implementation Opportunities: This site is occupied
by Brookside Elementary School and contains directly connected sidewalks, roof,
and parking lot. The site offers an opportunity for a 400 square-foot rain garden
installation at the main entrance. Students and teachers would benefit from both an
in-class lesson and hands-on learning experience related to non-point source
pollution and stormwater management.
Site Photos: