Effective Stormwater Management Through the Use of Low-Impact Development (LID) Techniques

Effective Stormwater Management Through the Use of Low-Impact Development (LID) Techniques

Justin Gregory, PEJones Edmunds & Associates

October 3, 2012

OVERVIEW

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Low Impact Developmen

t

Current stormwater problems

New Facilities

RetrofitSwales

Regulations

Current Stormwater Situation

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Impairments

TMDLs and BMAPs

Energy Independence and Security Act

Current Stormwater Situation

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Traditional solutions not working well enough.

How do we meet our stormwater management goals?

Low Impact Development

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LID / Green Stormwater Infrastructure

Distributed

Treatment train

Replicate natural hydrologic response

NASA Propellants North Admin & Maintenance Facility

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LEED Platinum

Designed to reach net-zero energy

Rainwater harvesting key aspect of design

NASA Propellants North Admin & Maintenance Facility

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7,500-gallon rainwater harvesting.

• Toilets.• Irrigation.• Treated water for drinking and hand washing.

Supplies:

Other LID components

Sunset Boulevard Bioretention

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Community facing large nutrient load reduction goals

Erosion problem

LID Retrofit Opportunity

Existing Conditions

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Direct discharge to Indian River Lagoon

Erosion problems at discharge to Lagoon

Limited space within the ROW

High infiltration rates

Solution

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Offline bioretention

Median Swale/Inverted Median

Solution

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Curb cuts

• Overflow - Extreme Events.

Inverted median advantages

• 30% more volume than swales.

Normal Flow.

Overflow during extreme events

Performance

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8” Rainfall 7-9 Oct 2011.

• Visual Monitoring.• No observed runoff.• Recovered overnight.

Costs

• TN < 30% conventional treatment.• No land purchase needed.

Sarasota County Swale Study

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Enhance County-wide pollutant loading model

Measure effects of conveyance swales

Account for possible load reductions

Sarasota County Swale Study

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Promote distributed infiltration

Disconnect impervious area

Common in Sarasota County

Versus

Phillippi Creek Basin

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2 curb & gutter sites

3 swale sites

Besides drainage type all else was equal

7 months/40 samples

Phillippi Creek Basin

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TSS

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78% lower

Statistically significant

Literature 61-86%

Nitrogen

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TN - 68% lower.

TKN – 72% lower.

Nox – 22% lower.

Highest removal particulate nitrogen.

Phosphorus

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TP - 25% lower.

Ortho-Phosphorus – 17% lower.

Not statistically different.

Runoff

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Rainfall vs. Percent Runoff

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 0.5 1 1.5 2 2.5

Rainfall, in.

Perc

ent R

unof

f

Runoff Coefficient 58% lower

3x as much rain without runoff

5x lower annual runoff volume

Observed Load Differences

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TN – 93%

TP – 81%

TSS – 95%

BOD – 93%

LID Constraints

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Technical.

Inertia.

Regulatory.

LID Manuals

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Local Design Standards.

Account for local hydrology.

Provide reasonable assurance.

Meet WMD Permitting Requirements.

Promote LID.

Local Hydrology

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Varies across the state.

Significantly effects LID performance.

How do we account for this?

-6

-5

-4

-3

-2

-1

0Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Aver

age

Dept

h to

Wat

er (

feet

)

Average Depth to Water at USGS Well 270959082203003

Sarasota

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

01 2 3 4 5 6 7 8 9 10 11 12

Dept

h Be

low

SHW

T (F

eet)

Months

Jacksonville

Local Design Curves

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Consider local climate.

Consider local hydrology.

Simplify permitting.

Allow for BMAP credits.

Key Components

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Alter practices for local conditions.

Work with end user of the manual.

Performance based design curves.

Average annual effectiveness.

Conclusion

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LID provides additional tools to meet our stormwater requirements .

Replicate natural runoff response.

Conclusion

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Distributed stormwater treatment.

• Infiltration• Settling• Filtration• Sorption• Biogeochemical processes

Design should consider all removal mechanisms