Stormwater Systems ARCH-433

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?

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

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

Terms Stormwater systems Roof drain (RD) Overflow system (OFL) Leader Flow control roof drain Downspout nozzle (DSN) Imperviousness Stormwater Harvesting Area Drain

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

Difference Between Sanitary and Stormwater Systems Absence of volatile gases No traps required No venting required Point of disposal varies

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

Stormwater Systems Roof drain systems Flat roofs Pitched roofs Site systems Q flow = Area (acres) x C R x I R = Ft 3 /Sec

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

Flat Roofs Advantages? Disadvantages?

Strategies - Roof Design

Strategies – Roof Design

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

What about Parking Structures Floor Drains Poor Design Consideration Designed by an Architect Designed by an Engineer Concrete rot Repairs

Roof Drains in a Flat Roof

Rainfall Rate (Table 8-15)

Pipe Capacity (Table 8-16)

Overflow Drain Systems OFL RD 2” DSN Beware of shortcuts!

Overflow Drain Systems Required by virtually every code Prevents overloading of the structure

Drain Installation

Overflows Can also use scupper drains Advantages Disadvantages

Strategies - Flow Control Roof Drain System

Siphonic Drain Systems Air Baffle

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

LEED SS Credit 6.1 Credit 6.1 Option 1 – Existing Imperviousness is ≤ 50% (undeveloped sites) Protect stream channels from excessive velocity

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

LEED SS Credit 6.1 Credit 6.1 Option 2 – Existing Imperviousness is ≥ 50% Bioswales Cisterns, holding ponds Green roofs Rainwater harvesting

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)

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

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

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

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, 3 rd Edition, 2005

Rainwater Harvesting Capacity Source: National Oceanic and Atmospheric Administration, Department of Commerce

Calculating Water Storage

What is Wrong with this Picture?

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

Green Roofs