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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
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