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 operateKnow the differences between stormwater and sanitary systemsStrategies available for reducing potable water useLEED credit points associated with a reduction in potable water use

What You Need To Be Able To Do

Predict stormwater drainage problemsBe able to sketch a stormwater riser diagramCorrectly size a stormwater systemCalculate the amount of stormwater available for non-potable usesMake management decisions on the use and implementation of stormwater systems

Terms

Stormwater systemsRoof drain (RD)Overflow system (OFL)LeaderFlow control roof drainDownspout nozzle (DSN)

ImperviousnessStormwater HarvestingArea Drain

Purpose of Stormwater Systems

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

Difference Between Sanitary and Stormwater Systems

Absence of volatile gasesNo traps requiredNo venting requiredPoint of disposal varies

Stormwater Discharge Points

GradeMunicipal storm sewer system Street

Stream, river, lake, ocean or other suitable pointYes BUT, is this really what we want!New Code Requirements

Stormwater Systems

Roof drain systems Flat roofs Pitched roofs

Site systems Qflow = Area (acres) x CR x IR = Ft3/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 DrainsPoor 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”

DSNBeware 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 SystemsAir 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%

BioswalesCisterns, holding pondsGreen roofsRainwater harvesting

LEED SS Credit 6.2Credit 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, 3rd Edition, 2005

Rainwater Harvesting Capacity

Source: National Oceanic and Atmospheric Administration, Department of Commerce

MonthMaximum Minimum 50%

January 1.59 0 0.54February 1.63 0.06 0.52March 6.65 0.06 1.7April 7.21 0.26 2.54May 10.09 0.91 3.89June 7.67 0.63 2.98July 12.5 0.37 3August 8.57 0.07 2.73September 8.28 0.29 2.35October 5.4 0.01 1.33November 3.81 0.01 1.12December 3.42 0.04 0.69

23.39

Lincoln

Ave. Annual Total

Calculating Water Storage

Month

Water Demand (Gals)

Irrigation Demand (Gals)

Total Demand (Gals)

Average Rainfall (inches)

Catchment Area

(Sq. Ft.)

Collection Coefficient

Collection Efficiency

Rainfall Collected

(Gals)

End of Month

Surplus (Gals)

Stored Amount (Gals)

Storage Capacity (Gals) 7,500Starting Storage (Gals) 0January 8,710 0 8,710 0.54 12,600 0.62 0.85 3,586 -5,124 -5,124February 8,710 0 8,710 0.52 12,600 0.62 0.85 3,453 -5,257 -10,381March 8,710 0 8,710 1.7 12,600 0.62 0.85 11,288 2,578 -7,803April 8,710 0 8,710 2.54 12,600 0.62 0.85 16,866 8,156 353May 8,710 0 8,710 3.89 12,600 0.62 0.85 25,830 17,120 7,500June 8,710 0 8,710 2.98 12,600 0.62 0.85 19,788 11,078 7,500July 8,710 0 8,710 3 12,600 0.62 0.85 19,921 11,211 7,500August 8,710 0 8,710 2.73 12,600 0.62 0.85 18,128 9,418 7,500September 8,710 0 8,710 2.35 12,600 0.62 0.85 15,604 6,894 7,500October 8,710 0 8,710 1.33 12,600 0.62 0.85 8,831 121 7,500November 8,710 0 8,710 1.12 12,600 0.62 0.85 7,437 -1,273 6,227December 8,710 0 8,710 0.69 12,600 0.62 0.85 4,582 -4,128 2,099

Total rainfall collected (Ave.) 155,31490% of average rainfall (SSc6.2) 139,783Difference 15,531Flush amount required 104,520

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