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GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING
JUNE 20, 2018
Association of State Floodplain Managers
Annual Conference
Session F8
Presentation by:
Rocky J. Keehn,
Common Sense Water Resources Engineering, LLC
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
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Why we need Green Infrastructure
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No People…No Problems –Rocky J. Keehn
The Challenge of GI Resiliency Design there are many perspectives of a “great” design
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Omaha – Green Roof
Kearney, NE – Rain Garden From my Stormwater Tours
North Liberty, IA – Porous Pavers
ENGINEERS
LANDSCAPE ARCHITECTS
POLTICIANS
PUBLIC WORKS
ACADEMICS
SCIENTISTS
REGULATORY
Landscape Architect Perspective
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Plants
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“I hope most of these survive and if not will plant something else”
Engineer’s Perspective
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OK…Green Engineer’s Perspective
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“My name is going on the plans so how do I this not get sued”
What I learned in College at UNL, in the early 80’s, Definition of Hydrology
ESTIMATION OF SOME ASPECT of the
quantity of water available is of prime
importance in all water resources
engineering. The analysis is basic to the
planning, design, and operation of water
resource systems
My first Hydrology Book, circa 1980 UNL Engineering,
book publish date 1975
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
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Hjelmfelt/Cassidy
What I learned in College at UNL, in the early 80’s, Definition of Hydrology
ESTIMATION OF SOME ASPECT of the
quantity of water available is of prime
importance in all water resources
engineering. The analysis is basic to the
planning, design, and operation of water
resource systems
My first Hydrology Book, circa 1980 UNL Engineering,
book publish date 1975
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
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Hjelmfelt/Cassidy
Primary Focus = simple equations?
What I learned in College at UNL, in the early 80’s, Definition of Hydrology
ESTIMATION OF SOME ASPECT of the
quantity of water available is of prime
importance in all water resources
engineering. The analysis is basic to the
planning, design, and operation of water
resource systems
My first Hydrology Book, circa 1980 UNL Engineering,
book publish date 1975
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn 9
Hjelmfelt/Cassidy
Common Sense
Proof it will work, modeling
What I learned in College at UNL, in the early 80’s, Definition of Hydrology
ESTIMATION OF SOME ASPECT of the
quantity of water available is of prime
importance in all water resources
engineering. The analysis is basic to the
planning, design, and operation of water
resource systems
My first Hydrology Book, circa 1980 UNL Engineering,
book publish date 1975
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
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Hjelmfelt/Cassidy
Common Sense
Maintenance and Resiliency
Modeling for Proof and Function
My Design Event Philosophy,in Layman Terms
Think of design events as…• FREQUENT EVENT – Volume Control for most (90%) of all rainfall events (old way pick a
pretty arbitrary value)• STABILITY EVENT - Channel and flow system stability (i.e. 2-yr)
• NUISANCE EVENT – Limited complaints, maximum water people will tolerate (i.e 10-yr)
• FLOOD EVENT– Major Damage or if flooding occurs major ramifications (i.e. 100-yr)
• “ACT OF GOD” EVENT– The nearly unimaginable event or unpredicable.
Or better yet….RESILIENCY of your system…or can it (or you!) bounce back quickly from a wide variety of
rainfall impacts or is easy to “fix” after a storm event.
GREEN INFRASTRUCTURE: have to deal with all these events!
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All GI’s can be modeled as “Detention” Ponds
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Losses
UncontrolledOutflow
Losses
UncontrolledOutflowD
epth
In
crea
se
Dep
th
Incr
ease
Green Roof System Porous Pavement System
Case Study – Spring Lake Park, South Omaha Nebraska
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ZOO
DOWNTOWN
AIRPORT
BOYS TOWN
SPRING LAKE PARK
Project is part of the City of Omaha’s Combined Sewer Overflow Program.
MISSOURI AVENUE SEWER SEPARATION/SPRING LAKE PARK
PROJECT
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
Grey to Green Project
36”
42”
48”
54”
416 acre watershed - 50%
residential/50% park.
Engineering goal, use green
infrastructure in the park
areas to reduce peak flows
so existing downstream
combined sewer would not
have to be upsized when
convert to a storm pipe.PIPES GI
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Saved$5 Million
Green Infrastructure Summary – Lots of “GREEN” going on!
• 6 - Extended Dry Detention Basin• 5 – Dry Detention Facilities• 3 – Infiltration Basins• 2 – Retention Wet Ponds• 2 – Constructed channels (replace pipes)• 1 – Constructed Wetland (multiple cells)• 1 – Bioretention basin or “Rain Garden”
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Or Lots of Future Maintenance!
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
Impact of Green Infrastructure
100-year with no Green
Infrastructure 1065.0 feet
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100-year with Green
Infrastructure 1063.1 feet
Entire watershed and all Green Infrastructure modeled in HydroCAD
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Phase 1 GI
Phase 2 GI
Grey System Downstream
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
Resiliency 101 - Preventing blowouts of GI during larger events!
Rain
Garden
36” RCP inlet into
Rain Garden
“Where
did that
BMP go?”
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Blowouts
First Flush Diversions
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn 19
Manholes Curb cuts
Blowouts
Overflow Structures as part of the GI
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Blowouts
Planned overflows
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First Flush Diversion, Modeling
1. Drainage Area
2. First Flush Diversion Manhole
3. Drop Manhole to Reduce Velocity
4. BMP or GI
5. Main Storm Sewer Line
6. Main Storm Sewer Line
1
2
3 4 6
5
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Flow rate splits out of Green Infrastructure
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Inflow into the first flush flow divert structure
All rainfall less then targeted water quality event, usually 90% of all rainfall events, flows into the GI/BMP
Volume in excess of the water quality event, bypass the BMP and flows to the main conveyance system.
Volume from the water quality event is detained, pollutants removed and then flows back into the main conveyance system
Volume in excess of the water quality event, depending on the amount, will flow either back into the main conveyance system or flow overland downstream.
HydroCAD Model – First Flush Structure
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn 24
Top of Casting reached in Manhole, non-pressure assumption, flows go into BMP/GI
Invert is at highwater in
manhole for 1” rainfall in this
case
HydroCAD Model – GI
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn 25
Not the control Structure
First Flush Model Results – 100 year
Watershed Runoff
Diversion Manhole Structure
BMP
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn 26
Event Outflow
100-yr 67 cfs
Event Flow to BMP
Flow Bypassed
100-yr 33 cfs 34 cfs
Event Inflow Outflow Highwater in BMP
100-yr 33 cfs 33 cfs 1086.23 ft
Blowouts, Weirs and Velocity
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
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Storm Q to main conveyance (6” Orifice)
BMP Highwater
Flow over Weir
Depth over Weir
Velocity over Weir
1” Rain 1.4 cfs 1084.04 ft 0 cfs 0.00 ft 0.0 ft/sec
10-year 2.0 cfs 1086.14 ft 11 cfs 0.14 ft 1.0 ft/sec
100-year 2.0 cfs 1086.28 ft 31 cfs 0.28 ft 1.3 ft/sec
Natural Grass Overflow
Challenge was we had to construct 600-800 feet pipe over steep bank full of trees
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Is there a Green Infrastructure Solution?
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
Current outlet
from drainage
area
Yes, Infiltration Basin…but
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MODELING June 20, 2018, R. Keehn
Needed a Pre-treatment BMP
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Pre-Treatment
Infiltration Basin
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
Pre-treatment Pond Outlets (No Diversion)
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June 20, 2018, R. Keehn
All flow less than 1” goes through
standpipe
Emergency Overflow when rain
exceeds 1”
Model, No 1st Flush Pretreatment
Elevation of berm based on 10-year not overtopping
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn 32
Modeling = It works!…I hope…
40- foot Overflow Weir
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn 33
Event Qin Qinfiltration Qoverflow Velocity Overflow
1” 1.0 cfs 0.1 cfs 0.0 cfs 0.0 ft/sec
10-yr 16.6 cfs 0.1 cfs 16.5 cfs 1.4 ft/sec
100-yr 22.5 cfs 0.1 cfs 22.5 cfs 1.5 ft/sec
Downstream overflows – Maintenance headache?
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Concrete Weir for
Flow Distribution
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
Event Velocity Overflow
1” 0.0 ft/sec
10-yr 1.4 ft/sec
100-yr 1.5 ft/sec
Downstream overflows – Maintenance headache?
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Looking Downstreamflows to a wide swale
Water just runs out of energyASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING
June 20, 2018, R. Keehn
Looking upstreamflows to a wide swale
Modeling helps check future issues
Water went over the maintenance road and caused bank erosion during rainfall
events less than 10-year event. The road was designed to become an
emergency overflow when it exceeded a 10-year event!
Checked the model and as-builts and found overflow structure was too high.
Lowered structure and have had no problems since. When designing for multiple events, project needs to be
constructed correctly to work.
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Debris/trash issues and sediment buildup?
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MODELING June 20, 2018, R. Keehn
What is the value of a model for this situation?
Use model to check impact of debris build-up
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Assume less efficient if outlet partially blocked
Higher starting water surface. Also may be used to predict when
sediment needs to be removed
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
Green Infrastructure Channel
Pond/Channel replaced 600
feet storm sewer pipe and
from LID perspective
increases travel time of runoff
Needed to be designed for
base flows from seepage,
smaller BMP storms,
2-year, 10-year and 100-
year
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No Blowouts…upstream detention
Channel
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn 40
Detention Pond
Resiliency and Vegetation
100-year define floodplain vegetation
HECRAS
Low flow over bounder drops
Low flow defines channel
HydroCADHydroCAD
Tailwater
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
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Modeling will estimate velocities in the channel to assure long-term stability
Results…looks pretty green!
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MODELING June 20, 2018, R. Keehn
Modeling showed a need for an Emergency Overflows – make it resilient!
Feb. 2017March 2016
FLEXAMAT
Detention Pond Overflow
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn 43
Fully Vegetated and ready for the “Big Storm”
June 2018
Vegetation and Drawdown Time
Drawdown time about 16
hours for 2-year event
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
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Complex of three wetlands in series for storage, habitat diversity and water quality improvement
Modeling what if’s…adds flexibility and checks changes
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Two Stop Log
Structures to adjust
Wetland and Lake
levels
Two Gates…one to control
flow from detention pond to
channel and one to drain
the lake
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
Is riprap a good idea or does it increase maintenance costs?
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FLEXAMAT
FLEXAMAT
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
Lake outlet very complex and fun to model!
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn 47
Downstream protection during a “dam” situation
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn 48
Worst Case,40 feet of head upstream. Think about the velocity at the outlet with this much head on a 48” culvert.
Modeling the entire Green Infrastructure Treatment Train..
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SAFL Baffle in
residential
neighborhood
First Flush
Diversion
Manhole
Extended
Dry
Detention
Basin
Dry
Detention
Facility
Meandering
Channel with
Boulder Drops
Constructed
Wetland
Flat
Sloped
Channel
Spring
Lake
Combined
Pipe now
Storm Pipe
Missouri
River
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
Modeling the entire Conveyance Train
Dry Detention
Pond and gated
outlet pipe
Meandering
Channel with
Boulder Drops
Constructed
Wetland and
outlet pipe under
trail to Lake
Energy Dissipation
Structure to “Natural”
Channel
Spring Lake and
pipe under “F”
Street
Low flow culvert
and “Texas
Crossing” to
wetland
Roof/impervious
surface near
houses
Though the
yards
Down the
Street
Storm pipes
through the
park
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
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GI level – What the Model tells us for this and other GI sites
Rate and volume of first flush flows and bypass flows – key
design component
Depth and time water is at various elevations during events –
helps with plant types
Velocity at outlets for a wide variety of flows – size erosion
control
Depth and occurrence of overflows – may be more than one
Erosion control of overflows
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn 51
Conclusion
planning, design, and operation
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn
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Hjelmfelt/Cassidy
THINK:MAINTENANCE? RESILANCY?,
MODEL
RESILIENT PROJECT
Questions?
•THANK YOU
ASFPM, GREEN INFRASTRUCTURE RESILIENCY AND COMPUTER MODELING June 20, 2018, R. Keehn 53
Rocky J. [email protected]