nchrp 25-41 guidance for achieving volume reduction...
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NCHRP 25-41 GUIDANCE FOR ACHIEVING VOLUME REDUCTION OF HIGHWAY RUNOFF IN URBAN AREAS August 10, 2016
Today’s Presenters
• Moderator Michael Fitch, Virginia Transportation Research Council
• Guidance for Achieving Volume Reduction of Highway Runoff in Urban Areas Eric Strecker, Geosyntec Consultants Aaron Poresky, Geosyntec Consultants
NCHRP is...
A state-driven national program
• The state DOTs, through AASHTO’s Standing Committee on Research... – Are core sponsors of NCHRP
– Suggest research topics and select final projects
– Help select investigators and guide their work through oversight panels
NCHRP delivers...
Practical, ready-to-use results • Applied research aimed at state
DOT practitioners • Often become AASHTO
standards, specifications, guides, manuals
• Can be directly applied across the spectrum of highway concerns: planning, design, construction, operation, maintenance, safety
A range of approaches and products • Traditional NCHRP reports • Syntheses of highway practice • IDEA Program • Domestic Scan Program • Quick-Response Research for
AASHTO • Other products to foster
implementation: – Research Results Digests – Legal Research Digests – Web-Only Documents and CD-ROMs
NCHRP Webinar Series • Part of TRB’s larger webinar
program • Opportunity to interact with
investigators and apply research findings.
Today’s Presenters
• Eric Strecker and Aaron Poresky, Geosyntec Consultants
NCHRP 25-41
GUIDANCE FOR ACHIEVING VOLUME REDUCTION
OF HIGHWAY RUNOFF IN URBAN AREAS
Various regulatory trends and current motivators towards reduction of surface runoff volume (i.e., volume reduction)
Agencies’ desire to get “out in front” of trends to help inform policy, guide program development and limit unintended impacts
Need for practical guidance that could be adopted or adapted as part of local guidance
IMPETUS FOR PROJECT
NCHRP 25-41 PROJECT GOALS
Provide national-scale guidance on identifying constraints and assessing the feasibil ity of controll ing runoff volumes in the urban highway environment
Identify and/or develop a menu of potentially suitable volume reduction approaches (VRAs)
Provide a framework for selecting and conceptually designing VRAs for specific site and project conditions
Develop simple tools to predict and compare volume reduction performance of VRAs
Guidance Manual (NCHRP Report 802)
Technical Appendices VRA Fact Sheets Infiltration Testing Groundwater Quality and
Water Balance Geotechnical Issues Permeable Pavements
Volume Performance Tool (Spreadsheet) and User ’s Manual
PROJECT OUTCOMES
Project Officer:
Chris Hedges, NCHRP
Project Panel:
Mike Fitch, Chair, Virginia DOT
Brian Beucler, FHWA
David Ahdout, New Jersey DOT
Kristin Schuster, Michigan DOT
Mark Maurer, Washington State DOT
Meredith Upchurch, District of Columbia DOT
Paul Wirfs, Oregon DOT
Scott Taylor, RBF Consulting
Research Team
Geosyntec Consultants, Eric Strecker and Aaron Poresky
The Low Impact Development Center, Neil Weinstein
Venner Consulting, Marie Venner
NCHRP PANEL AND RESEARCH TEAM
High efficiency of pollutant removal compared to many treatment BMPs
Combined benefits of pollution and hydrologic control, plus groundwater recharge where applicable
Effective as an element in a treatment train
VRA = Volume Reduction Approach
WHY VOLUME REDUCTION?
LA Times (June 25, 2015) DWP to unveil plan to capture storm runoff http://www.latimes.com/local/california/la-me-stormwater-plan-20150625-story.html
EXAMPLE VOLUME REDUCTION APPROACHES
Vegetated conveyances
Dispersion (natural, engineered)
Media filter drains
Permeable pavement shoulders
Bioretention without underdrains
Bioretention with underdrains
Inf i l trat ion trenches
Inf i l trat ion basins
Underground inf i l trat ion systems
Volume reduction primarily based on infiltration, supported by evapotranspiration in some VRAs
Available space, set back from roadway and structures
Permeable to moderately permeable soils
Adequate subsurface capacity for additional infiltration
Groundwater table well below infrastructure
Groundwater recharge desirable
Shallower slopes
Absence of soil or GW contamination
Absence of geotechnical hazards
Setbacks from utilities and wells
At or near original grade
Isolated from major sediment sources
Incorporated into conveyance or flow control features
FAVORABLE CONDITIONS/OPPORTUNITIES
Limited space and lack of permeable soils in many projects
Site-specif ic condit ions appropriately inf luence many planning and design decisions
Uncertainty of success unti l implementation
Increasingly, volume reduction is a f irst and mandatory consideration
Limited ful l scale experience with VRAs, part icularly whole l i fecycle costs and maintenance
KEY CHALLENGES
On-site Retention BMPs
Example: Infiltration trench
On-site Biotreatment BMPs
Example: stormwater planter
Subregional/Regional Retention BMPs
Example: groundwater recharge basin
Subregional/Regional Biotreatment BMPs
Example: constructed wetland
Typical BMP selection hierarchy in California and other MS4 permits beginning circa 2009
ORANGE COUNT Y EXAMPLE
C O N TA M I N AT E D S O I L S / P L U M E S , D E P T H T O G W + A / B + N AT U R A L P L U M E S + C O N TA M I N AT E D S I T E S + I N D U S T R I A L L A N D U S E + S T E E P S LO P E S
EVAPOTRANSPIRATION- SPATIAL WATER BALANCE CONSIDERATIONS
Bioretention Areas
Natural Conditions Developed Conditions with VRAs
Imperviousness = 0%
1” Rainfall = 1” Over Pervious Surface Shallow localized ponding
Unsaturated infiltration dominates “Sponge” area ≈ watershed area
Imperviousness = 50%; BMP = 5%
1” Rainfall ≈ 10” Over SCM Concentrated ponding in SCM
Unsaturated and saturated infiltration “Sponge” area = SCM area
GENERAL WATER BALANCE IMPACTS
ET fraction estimated as 83-97% in Southern California Chaparral.1
1 Ng and Miller (1980) Soil Moisture Relations in the Southern California Chaparral. Ecology, Vol. 61, No. 1. (Feb., 1980), pp. 98-107
REGIONAL VARIABILITY IN WATER BUDGET Location: Annual Fluxes: Source: Northwest (Cascade Mountains); The two study watersheds adjoin each other in the upper McKenzie River watershed on the west side of the Oregon Cascades
Runoff and Baseflow = 70%; ET = 30%; Water Storage Change = 0%
Jefferson et. al., 2008
East of the Rocky Mountains Runoff and Baseflow = 27%; ET = 73%; Water Storage Change = 0%
Mill, 1994
Texas Runoff = 12.5 %; ET = 86 %; Recharge = 1.5%
Ward, 1993
South Eastern US: five-state study area (Georgia, South Carolina, North Carolina, Virginia, and Maryland)
Runoff and baseflow = 37%; ET and Recharge = 63%
Rose, 2009
Susquehanna River Basin Runoff and Baseflow = 49%; ET = 51%; Water Storage Change = 0%
Najjar, 1999
The Baptism River watershed in northern Minnesota. The watershed is heavily timbered with both deciduous and coniferous trees.
Runoff and Baseflow = 55% Mohseni & Stefan, 2001
The Little Washita River watershed in Oklahoma. One third of the watershed is cultivated and the rest is either pasture or wooded pasture.
Runoff and Baseflow = 7% ET and Recharge = 93%
Mohseni & Stefan, 2001
North Eastern US Runoff and Baseflow = 55% ET and Recharge = 45%
Church et al. 1995
Southern California Chaparral (average of two years of monitoring)
South facing: Runoff and Baseflow = 3%; ET = 97% North facing: Runoff and baseflow = 9%, ET = 83% and storage change = 8%.
Ng & Miller, 1980
POTENTIAL HABITAT CHANGES
Dry Ephemeral Stream
Perennial Stream
Infiltration Increased over Natural Levels
EFFECTIVENESS OF VRAS
Storage Volume: How much of the first storm can the VRA capture and manage?
Treatment /Loss Rate: How much of the next storm (and the next and the next…) can the VRA capture and manage?
Emerson, 2008 (Dissertation, Villanova)
Strecker and Poresky, 2009 (Water Report)
Storage volume and loss rate are both important
EFFECTIVENESS OF VRAS
Highway Geometric Design Standards
Vegetation and Landscaping Standards
Drainage and Flood Control
Construction practices conducive to successful VRA installation and long-term operation
OTHER HIGHWAY DESIGN REQUIREMENTS
Hydrology and VRA Design
Infiltration rates
Geotechnical
Hydrogeology
Utilities/ sanitary sewer
Groundwater protection
Pavement design
Vegetation selection and management
Geometric design and
vehicle safety
POTENTIAL INVESTIGATIONS AND DESIGN CONSIDERATIONS/COORDINATION
Effective site characterization
Early identif ication of suitable opportunit ies
Realist ic assessment of constraints and l imitat ions Limits of site
Regulatory limits
Limits of knowledge (e.g., future soil properties following construction)
Selection of VRAs compatible with opportunit ies and constraints Geometric compatibility
Infiltration feasibility
Need for adaptability/resiliency
Tools/framework for evaluating alternatives
KEYS TO ACHIEVING VOLUME REDUCTION
• Is it physically possible to implement a certain VRA based on the site conditions?
Can you do it?
• Would the use of a certain VRA have the potential to result in undesirable physical consequences on the project or the site environs?
Should you do it? If so, how much
should you do?
• Does the cost required to construct the VRA and/or mitigate potential risks posed by the VRA outweigh the volume control benefits it would achieve?
If you do it, do it carefully.
FEASIBILITY AND DESIRABILITY FRAMEWORK
Chapter 1 – Introduction
Chapter 2 – Stepwise Approach for Incorporating Volume Reduction: How to Use This Manual
Chapter 3 - Volume Reduction in the Urban Highway Environment
Chapter 4 – Volume Reduction Approaches
Chapter 5 – Selecting and Applying Volume Reduction Approaches
GUIDANCE MANUAL CONTENTS AND ORGANIZATION
Appendix A – VRA Fact Sheets
Appendix B – Users Guide for the Volume Performance Tool
Appendix C – Infi ltration Rates and Factors of Safety
Appendix D – Water Balance and Groundwater Quality
Appendix E – Geotechnical Considerations
Appendix F – Permeable Pavement Considerations
GUIDANCE MANUAL CONTENTS AND ORGANIZATION
Intended Users
DOT managers Permit writers
Consultants and planners
DOT project staff and design
engineers
Potential Uses
Understanding the technical basis of volume reduction requirements and setting
volume reduction goals
Providing a framework for discussion with regulators about technical feasibility and
desirability
Scoping the analyses necessary for incorporating VRAs into the project design
process
Understanding potential design implications of volume reduction goals
Refining project-specific estimates of achievable volume reduction
Conducting site assessment and feasibility analyses
Prioritizing, selecting, and applying VRAs
Plan
ning a
nd P
rogr
am
Mana
geme
nt Pr
oject
Desig
n and
Im
pleme
ntatio
n
STEPWISE APPROACH FOR INCORPORATING VOLUME REDUCTION
Step 1 Establish Volume Reduction Goals
Step 3 Identify Potentially Suitable VRAs
Step 4 Prioritize VRAs from Screened Menu
Step 2 Characterize Project Site and Watershed
Step 5 Select VRAs and Develop Conceptual Designs
Manual Reference Example Stepwise Process
Step 1 Establish Volume Reduction Goals
Step 3 Identify
Potentially Suitable VRAs
Step 5 Select VRAs and
Develop Conceptual
Designs
Step 2 Characterize
Project Site and Watershed
Understand regulatory context
Identify resource protection needs
Understand factors influencing volume
reduction
Conduct preliminary screening of applicability
Develop preliminary site
plans
Select VRAs
Develop conceptual
designs
Estimate performance and cost; compare to
goals
Identify highway and project type
and related factors
Obtain available information and coordinate with
applicable parties
Conduct site assessments
1.2 and 3.1 – Regulatory Setting 3.2 – Key Factors in Volume Reduction 3.3 – Urban Highway Types 3.4 – Site Assessment
3.4 – Site Assessment 4.0 – Volume Reduction Approaches Appendix: VRA Fact Sheets 5.2 – Initial Screening to Identify Potential VRAs
5.4 – Conceptual Design Development 4.4 – Additional Resources for VRA Design and Maintenance Information
3.2 – Key Factors in Volume Reduction 3.3 – Urban Highway Types 3.4 – Site Assessment
Refin
e goa
ls ba
sed o
n new
infor
matio
n
Step 4 Prioritize VRAs from Screened
Menu
Consider additional factors to differentiate between potentially
suitable VRAs
Weight and score factors to identify high
priority VRAs
5.3 – Prioritizing Approaches from Screened Menu of VRAs
Conduct preliminary screening of
feasibility and desirability
Overall stormwater management objectives: Manage pollutant loads Maintain recharge Control hydrologic impacts
Regulatory context: Absolute volume reduction
requirements vs. Volume reduction to MEP
vs. Opportunistic volume
reduction
STEP 1: ESTABLISH VOLUME REDUCTION GOALS
Topography and Drainage Patterns
Off-Site Drainage and Adjacent Land Uses
Soil and Geologic Condit ions
Groundwater Considerations
Geotechnical Considerations
Existing Uti l i t ies
Harvested Water Demand Assessment
Responsible Agencies and Other Stakeholders
Watershed-based and Other Joint Planning Opportunit ies
STEP 2: SITE ASSESSMENT ACTIVITIES
Planning Phase Assessment
Where within my project area are VRAs potentially feasible?
What VRAs are potentially suitable for my project?
Design Phase Assessment
What design parameters should I use to design volume reduction facilities?
Is the design safe? How does the design mitigate unacceptable levels of risk?
Is the design protective of potential unintended consequences for other media?
STEP 2: SITE ASSESSMENT ACTIVITIES
Larger area of interest
More focused area of interest
More efficient methods and
analyses
More rigorous
methods and analyses
Appendix C – Infi ltration Rates and Factors of Safety
Appendix D – Water Balance and Groundwater Quality
Appendix E – Geotechnical Considerations
SUPPORTING APPENDICES
STEP 3: IDENTIFY POTENTIAL VRAS
Site Design / Project Type Site Characteristics Watershed
Characteristics
Evaluate VRA Applicability [Section 5.2.2)
Which VRAs are potentially applicable for the project?
Evaluate Feasibility
and Desirability
(Section 5.2.3]
Which VRAs are potentially feasible and desirable for the project?
Early Identification of VRA Opportunity Locations
Develop Drainage, Grading, and Util ity Configurations to Accommodate VRA Opportunity Locations
Limit Footprint of Disturbance
Minimize Non-Essential Impervious Surface
Conserve and/or Amend Topsoil
SITE DESIGN APPROACHES
Looped Interchanges
Diamond Interchanges
Irregular ROW
Shoulder Outside of Clear Zone
Shoulder Inside of Clear Zone or Breakdown Lane
Median or Inside Breakdown Lane
VRA FACT SHEETS (APPENDIX A)
Geometric Siting Opportunity VRA
01
Veg
etat
ed
Conv
eyan
ce
VRA
02
Disp
ersio
n
VRA
03
Med
ia Fi
lter D
rain
VR
A 04
P
erm
eabl
e Sh
ould
ers
VRA
05 B
iore
tent
ion
w/o
unde
rdra
in
VRA
06 B
iore
tent
ion
with
und
erdr
ain
VRA
07
Infil
tratio
n Tr
ench
es
VRA
08
Infil
tratio
n Ba
sins
VRA
09
Infil
tratio
n Ga
llerie
s
Medians X X X X X X
Shoulders, including breakdown lane and area within Clear Zone (less than approx.15% or 6H:1V)
X X X X X X
Shoulders, outside of Clear Zone (less than approx.15% or 6H:1V)
X X X X X X X
Moderately Steeper Shoulders (steeper than approx.15% or 6H:1V but less than approximately 25% or 4:1)
X
ROW Locations with Limited Uses (i.e., wide spots, irregular geometries)
X X X X X X X X
Adjacent Natural Areas X
Looped Interchange Medians X X X X X X X X
Diamond Interchange Medians X X X X X X X X
Low Traffic Areas - Maintenance Yards, etc. X X X1 X X X X X
GEOMETRIC SITING OPPORTUNITIES
STEP 3 (CONTINUED): EVALUATE FEASIBILITY AND DESIRABILITY
Site Design / Project Type Site Characteristics Watershed
Characteristics
Evaluate VRA Applicability [Section 5.2.2)
Which VRAs are potentially applicable for the project?
Evaluate Feasibility
and Desirability
(Section 5.2.3]
Which VRAs are potentially feasible and desirable for the project?
INFILTRATION FEASIBILITY AND DESIRABILITY CATEGORIES
Category 3: Infiltration not Recommended/Allowed
Category 1: Full Infiltration
Category 2: Marginal/ Partial Infiltration
• Consider VRAs that provide full infiltration • Conduct more rigorous site-specific analysis as part of design
(and potentially construction) to confirm that full infiltration is feasible and desirable
• Include provisions to allow designs to be adapted to Category 2 if actual conditions different than planned.
• Select VRAs that provide opportunity for partial infiltration and supplemental discharge
• Design VRAs to be adaptable for range of actual conditions
• Do not use infiltration • Consider VRAs based on harvest and use (limited feasibility
for DOTs) and/or ET
VRA
Total Relative Volume
Reduction Potential
Relative Portion of Losses to
Deeper Percolation in
Typical Conditions
Relative Potential to
Infiltrate More than
Natural
Possible to Adapt for Marginal Conditions?
VRA 01 Vegetated Conveyance L/M L/M L/M Yes, inherent VRA 02 Dispersion M/H L/M L/M Yes, inherent VRA 03 Media Filter Drain M/H L/M L/M Yes, by design VRA 04 Permeable Pavement M/H M/H M/H Yes, by design VRA 05 Bioretention w/o underdrain H M/H M/H No VRA 06 Bioretention with underdrain M/H M/H L/M Yes, by design VRA 07 Infiltration Trenches H H M/H Not easily VRA 08 Infiltration Basins H H M/H Not easily VRA 09 Infiltration Galleries H H M/H Not easily
SUMMARY OF VOLUME REDUCTION MECHANISMS AND ADAPTABILITY
STEP 4: PRIORITIZE VRAS
Screened List of Potential VRAs
Prioritize Approaches from Screened Menu of VRAs [Section 5.3]
Relative O&M Impact to Agency Relative Cost Relative Reliability
and Safety
Screened and Prioritized VRAs
Relative Performance
Routine Maintenance Activities VRA
01
Veg
etated
Co
nvey
ance
VRA
02
Disp
ersio
n
VRA
03
Med
ia Fil
ter D
rain
VRA
04
Per
meab
le Sh
oulde
rs VR
A 05
B
iorete
ntion
w/o
unde
rdra
in VR
A 06
B
iorete
ntion
with
un
derd
rain
VRA
07
Infilt
ratio
n Tr
ench
es
VRA
08
Infilt
ratio
n Bas
ins
VRA
09
Infilt
ratio
n Ga
llerie
s
Mowing
Maintain Level Spreading Functions
Landscaping and Weeding
Routine Woody Vegetation Management
Sediment Removal/ Management
Vacuum Sweeping
Trash and Debris Removal
Erosion Repair
Rodent Hole or Beaver Dam Repair
Fence or Access Repair
EXAMPLE COMPARISON TABLE: ROUTINE MAINTENANCE BY VRA
Key: Primary maintenance activity; Minor maintenance activity; may not apply in some cases or may be limited; Not usually applicable
Screened and Priortized VRAs (From Section 5.2 and 5.3)
Analyze Volume Reduction Performance
and Cost (5.4.3, 5.4.4, 5.4.5)
Compare Performance and Cost to Project Goals
Develop Initial Conceptual Designs (5.4.2)
Develop Volume Reduction Design
Goals Not Met
Goals Met
Adapt Conceptual Design and/or Goals,
as needed (5.4.6)
Other Guidance Manual content: Introduction to
Volume Performance Tool and potential uses
Options for increasing performance and/or reducing costs
STEP 5: DEVELOP AND EVALUATE CONCEPTUAL DESIGN
Consider sensitivity to key parameters
Checklists and Worksheets Site assessment Suitability screening Feasibility screening VRA prioritization
Conceptual Design Tools Volume Performance Tool Conceptual design schematics Whole lifecycle cost forms
PRACTICAL TOOLS FOR DOT USERS (AND OTHERS)
Based on long term VRA performance of 344 rain gauges Uses pre-calculated
nomographs from SWMM modeling to optimize tool performance Provides planning level long
term hydrologic VRA performance without the need for more detailed long-term modeling
Can simulate treatment train performance
VOLUME PERFORMANCE TOOL
Inputs Location-specific climate data Tributary data (area, % impervious, Soil
type) Specific VRA data (type and design
attributes specific to that VRA)
Resul ts Baseline Average Annual Runoff
Volume with no VRAs Reduction in Runoff Volume Captured, Treated, and Released Runoff Volume Bypassed
VOLUME PERFORMANCE TOOL
Olympia, WA Nomograph Providence, RI Nomograph
Two nomographs generated by the tool showing the same VRA and tributary area in different locations
Behind the scenes:
PROJECT LOCATION TAB
Navigation Bar
Project-specific Information
Climate Region Select
Precipitation Gage Select
344 climate divisions supported for the conterminous US; allows adjustment for climate variations within division
PROJECT DESIGN TAB
Tributary Area Input Parameters
VRA DESIGN
VRA design parameters
Embedded schematic to explain VRA design
parameters Option to add second VRA in treatment
train
Overall approach: Enter parameters to describe location, watershed and VRA obtain near real-time estimate of volume performance and capture efficiency
Average long term estimates: Volume Reduction Capture Efficiency Bypass
Reported as volume per year and relative percentages
VOLUME PERFORMANCE SUMMARY
SENSITIVITY ANALYSIS
Select VRA design parameters and define sensitivity
bounds
Tool generates “bow-tie plot” to compare sensitivity of key parameters
Many factors influence the feasibil ity, desirability, and effectiveness of volume reduction and selection of VRAs
A defined process can help organize activities and produce consistent/defensible decisions
Adaptability and resil iency in BMP selection is important where there is increasing pressure to achieve volume reduction in marginal environments
Volume performance tool allows evaluation of effectiveness and sensitivity
KEY OUTCOMES/FINDINGS
NCHRP 25-51: Limitations of the Infiltration Approach to Stormwater Management in the Highway Environment
Build upon previous research: Volume reduction (NCHRP 25-41) Whole lifecycle cost and performance (NCHRP 25-40) Ultra-urban BMPs (NCHRP 25-31)
Incorporate field-scale case studies/lessons learned
More in-depth research into limits, particularly in the highway prism
Identif ication and evaluation of more adaptable/resil ient design and construction approaches
More detailed investigation and design guidance
FUTURE WORK