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nhc Study overview Literature Stormwater Loading Field BMP Review - - PowerPoint PPT Presentation
nhc Study overview Literature Stormwater Loading Field BMP Review - - PowerPoint PPT Presentation
Infiltration BMP Design and Maintenance Optimization Preliminary Results Lake Tahoe Basin Science Conference May 23, 2012 nhc Study overview Literature Stormwater Loading Field BMP Review Simulations Survey 2 nhc Field data collection
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Field data collection
Study Sites
3 nhc
- Concentrated in the South Lake area
- Coordinated with TRPA and landowners
- 45 Sites
- 45% Single and Multi Residential
- 45% Commercial
- 10% other
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Field data collection 4 nhc Sub-surface Infiltration Systems Infiltration Basins Pervious Pavement Dry Wells Infiltration Trenches
6 2 15 2 45
Observations and Measurements:
BMP design, condition, performance Drainage size, surfaces, condition
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Field data analysis 5 nhc
1 5 3
Condition: Visual estimate of sediment accumulation
5 4 3 2 1 14 12 10 8 6 4 2 Average Condition Score Frequency
Mean 3.064 StDev 1.082 N 56
Normal
Infiltration BMP Media Condition
Condition Score
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Field data analysis
Drainage Surface and Infiltration Performance
6 nhc
640 480 320 160
- 160
20 15 10 5 1L Infiltration Time (seconds) Frequency
Impervious Roofs Surface
Histogram of Imp1LInfilTime, Roof1LInfilTime
Performance diagnostic - time for infiltration of 1L water.
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Field data analysis
Field Survey Insights
7 nhc
- Visual condition estimate is a
poor indicator of performance
- Non-design runoff results in
severe declines
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BMP stormwater loading simulations
Approach
- Load stormwater with typical
Tahoe Basin FSP mg/L
- Vary stormwater composition
and BMP designs
- Quantify infiltration
performance changes
8 nhc
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BMP stormwater loading simulations
Experimental Challenges
9 nhc
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BMP stormwater loading simulations
Clogging Mechanisms
10 nhc
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BMP stormwater loading simulations
Infiltration Performance Decline
11 nhc
10 20 30 40 50 60 70 80 90 100 25 50 75 100 125 150 175 200 225
Infiltration Rate (in/hr) FSP Load (grams)
Replicate measurements < 1SD of the mean
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BMP stormwater loading simulations
Scaling up to In-Situ BMPs
12 nhc
Assumptions:
- Stormwater with constant FSP concentrations
- Rain = 30 in/yr, RO coef = 1
- BMP = No depth, 12.8 in/hr soil
Surface Type FSP (mg/L) BMP/ Drainage
Roof 5 1:12 Parking Lot 100 1:12
Surface Type BMP/ Drainage FSP (mg/L) 3 year Infiltration Decline (%)
Roof 1:9 5 Parking Lot 1:9 100
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BMP stormwater loading simulations 13 nhc Roof @ 3 yrs = 25% decline Parking Lot @ 3 yrs 99.7% decline
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Conclusions
Findings that we should care about
- All surface types not equal
in clogging potential
- Results may indicate
severe performance declines within 3 years
- Severe declines also results
in loss of stormwater volume reduction benefits 14 nhc
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Conclusions
Next steps
- Continue loading simulations
- Lateral infiltration
- Stormwater composition
- BMP designs
- Field verification of
performance declines
- Draft BMP design and
maintenance recommendations 15 nhc
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