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

obropta@envsci.rutgers.edu

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

Let’s Check It with HydroCAD

• HydroCAD

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

Let’s Check It with HydroCAD

• HydroCAD

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: