Stormwater Systems

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Stormwater Systems

• ARCH-433

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Attendance

• This water closet, installed in Pullman,
  Washington, flushes in a counterclockwise
  rotation. In what direction would the water
  rotate if it is installed in Sydney, Australia?

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What You Need To Know

• Understand how and why stormwater systems operate
• Know the differences between stormwater and
  sanitary systems
• Strategies available for reducing potable water
  use
• LEED credit points associated with a reduction in
  potable water use

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What You Need To Be Able To Do

• Predict stormwater drainage problems
• Be able to sketch a stormwater riser diagram
• Correctly size a stormwater system
• Calculate the amount of stormwater available for
  non-potable uses
• Make management decisions on the use and
  implementation of stormwater systems

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Terms

• Stormwater systems
• Roof drain (RD)
• Overflow system (OFL)
• Leader
• Flow control roof drain
• Downspout nozzle (DSN)

• Imperviousness
• Stormwater Harvesting
• Area Drain

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Purpose of Stormwater Systems

• Collect stormwater from the roof and move it to a
  point of disposal away from the foundation
• Collect stormwater from the site and move it to
  an approved point of disposal

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Difference Between Sanitary and Stormwater Systems

• Absence of volatile gases
• No traps required
• No venting required
• Point of disposal varies

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Stormwater Discharge Points

• Grade
• Municipal storm sewer system
• Street
• Stream, river, lake, ocean or other suitable
  point
• Yes BUT, is this really what we want!
• New Code Requirements

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Stormwater Systems

• Roof drain systems
• Flat roofs
• Pitched roofs
• Site systems
• Qflow Area (acres) x CR x IR Ft3/Sec

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Roof Drain Systems

• Pitched Roofs
• Gutters and leaders
• Flat Roofs
• Roof drains
• Overflow drains
• Flow control systems

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Flat Roofs

• Advantages?
• Disadvantages?

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Strategies - Roof Design
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Strategies Roof Design
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Sizing Stormwater Systems

• Variables for commercial roof drain systems
• Area of the roof
• Rainfall rate
• Number of roof drains
• Slope of piping

• Variables for residential gutter systems
• Area of the roof
• Rainfall rate
• Number of gutters
• Slope of gutter

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What about Parking Structures

• Floor Drains
• Poor Design Consideration
• Designed by an Architect
• Designed by an Engineer
• Concrete rot
• Repairs

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Roof Drains in a Flat Roof
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Rainfall Rate (Table 8-15)
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Pipe Capacity (Table 8-16)
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Overflow Drain Systems
OFL
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RD
Beware of shortcuts!
DSN
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Overflow Drain Systems

• Required by virtually every code
• Prevents overloading of the structure

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Drain Installation
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Overflows

• Can also use scupper drains
• Advantages
• Disadvantages

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Strategies - Flow Control Roof Drain System
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Siphonic Drain Systems
Air Baffle
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LEED SS Credit 6.1

• Credit 6.1
• Option 1 Existing Imperviousness is 50
  (undeveloped sites)
• Implement a stormwater management plan that
  prevents the post development discharge rate and
  quantity from exceeding the pre-development
  levels or
• Implement a stormwater management plan that
  protects receiving stream channels

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LEED SS Credit 6.1

• Credit 6.1
• Option 1 Existing Imperviousness is 50
  (undeveloped sites)

Protect stream channels from excessive velocity
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LEED SS Credit 6.1

• Credit 6.1
• Option 2 Existing Imperviousness is 50
• Implement a stormwater management plan that
  results in a 25 decrease in volume of stormwater
  runoff from the two-year, 24 hour storm

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LEED SS Credit 6.1

• Credit 6.1
• Option 2 Existing Imperviousness is 50
• Bioswales
• Cisterns, holding ponds
• Green roofs
• Rainwater harvesting

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LEED SS Credit 6.2

• Credit 6.2
• Implement a stormwater management plan that
  reduces impervious cover, promotes infiltration
  and captures and treats stormwater runoff from
  90 of the average annual rainfall using
  acceptable best management practices (BMP)
• Remove 80 of the average annual post Total
  Suspended Solids (TSS)

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LEED WE Credit 2

• Credit 2
• Reduce the use of municipally provided potable
  water for building sewage conveyance by at least
  50
• or
• Treat 100 of wastewater on site to tertiary
  standards

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Water Reduction Strategies

• Use of Stormwater/Grey water to
• Flush water closets and urinals
• Water landscape
• Avoid non-native plants
• Reduce the amount of water flowing across site

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Carpenter

• How much stormwater (clear water) do we need?
• ? gals per day to flush low flow water closets
• How many work days per year?

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How Much Rainwater is Available?

• Based upon .62 gallons/inch/sq. ft.
• Efficiency varies between 75 and 90
• V collected Rainfall x Area x Efficiency x .62
  gals/inch/sq. ft.

Source Texas Manual on Rainwater Harvesting, 3rd
Edition, 2005
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Rainwater Harvesting Capacity
Source National Oceanic and Atmospheric
Administration, Department of Commerce
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Calculating Water Storage
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What is Wrong with this Picture?
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Strategies

• Two 7,500 gal tanks installed to capture
  rainwater
• Rainwater is filtered with a recirculation system
  and used to flush water closets
• Capture system reduces stormwater discharge

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Green Roofs