Regenerative Stormwater Conveyances: Giving Old, Perched Outfalls New Life APWA NC Stormwater Management Division Conference 16 September 2014 Ward Marotti Senior Scientist Project Manager David Kiker Technical Manager
Regenerative Stormwater Conveyances: Giving Old, Perched Outfalls New Life Problems Implementation Solutions Modeling RSCs Path Forward Research
Problem
Traditional Design
Conveyance
Discharge
Unintended Consequences
Unintended Consequences
Unintended Consequences
Unintended Consequences
Unintended Consequences
Unintended Consequences
Unintended Consequences
Unintended Consequences
Unintended Consequences
Unintended Consequences Hypoxia
Unintended Consequences
Traditional Design
Traditional Design William Kenneth Dickson 1929
Solutions
Modern Design
Modern Design
Modern Design
Modern Design
Traditional Retrofits Quantity/velocity OR Quality not both Expensive
Traditional Retrofits
Retrofit: RSC Regenerative Stormwater Conveyance
Retrofits Regenerative Stormwater Conveyance Figure Obtained From: Jane Hawkey, University of Maryland Center for Environmental Science
RSC Two Birds, One Stone Quantity/velocity AND Quality From Piolo Pascual ABS Project
Retrofit: RSC Regenerative Stormwater Conveyance Substrate
Alley et. Al 2002 Retrofit: RSC Regenerative Stormwater Conveyance Riffles and Pools
Retrofit: RSC Regenerative Stormwater Conveyance Substrate
Retrofit: RSC Regenerative Stormwater Conveyance Substrate Infiltration Detention Filtering Nutrient uptake (anaerobic decomposition) Nutrient adsorption
Retrofit: RSC Regenerative Stormwater Conveyance Riffles and Pools
Retrofit: RSC Regenerative Stormwater Conveyance Riffles and Pools Energy Dissipaters Sedimentation Reduce sheer stress Lateral and vertical bank/bed erosion
Retrofit: RSC Regenerative Stormwater Conveyance Riffles and Pools Grade Control Storage infiltration Widen flow path infiltration
Retrofit: RSC Regenerative Stormwater Conveyance Vegetation Native Storage infiltration Widen flow path infiltration
Retrofit: RSC Regenerative Stormwater Conveyance Vegetation Native Nutrient uptake Aesthetics Bank/substrate Stabilization (root mass) Energy Dissipation
Retrofit: RSC Regenerative Stormwater Conveyance
Retrofit: RSC Regenerative Stormwater Conveyance Effectiveness RSC 70% TP 70% TN 90% TSS Bioretention 45% TP 35% TN 85% TSS
Retrofit: RSC Regenerative Stormwater Conveyance
Retrofit: RSC Regenerative Stormwater Conveyance Effectiveness Quantity Storage Delayed Release Velocity/sheer stress reduction
Retrofit: RSC Regenerative Stormwater Conveyance Effectiveness Traditional = 2-3 x RSC /unit treatment
Retrofit: RSC Regenerative Stormwater Conveyance Effectiveness
Retrofit: RSC Regenerative Stormwater Conveyance Research
Retrofit: RSC Regenerative Stormwater Conveyance Research Quantity Storage Delayed Release Velocity/sheer stress
Retrofit: RSC Regenerative Stormwater Conveyance Research Cizek, 2014 Quantity Storage Delayed Release Velocity/sheer stress
Retrofit: RSC Regenerative Stormwater Conveyance Implementation
Retrofit: RSC Regenerative Stormwater Conveyance Linda Lake
Retrofit: RSC Regenerative Stormwater Conveyance Linda Lake
Baffles & IWS Zones Internal Water Storage (IWS) Zone Internal Water Storage (IWS) Zone From Anne Arundel County Design Guidelines Impervious Baffles Mimic bio-retention and IWS zones Improve WQ performance
Retrofit: RSC Regenerative Stormwater Conveyance Modeling
Why Model? Iterative Design Process Evaluate Overland Flow Design a stable system Size boulders and riffle material Manning s spreadsheet analysis HEC-RAS analysis Quantify Infiltration: Pilot study for pollutant removal capabilities Infiltration rate calculated Darcy s spreadsheet analysis
Design Process Rules of Thumbs Iterative Process Align in Thalweg Riffle/Pools Sequence Calculate Slopes Overall Slope <5% Cascades <10% Recent Findings Riffle Pool Cascade
Parabolic Boulder Section 8 min. top width 10(H): 1(V) side slopes Max riffle length of 8 feet; Min length of 4 feet Pool length > 2 x riffle length Homeport Farms, MD Courtesy of Anne Arundel County
Sequencing Alternating Riffles and Pools Cascade w/s Three Pools From West VA Stormwater Management & Design Guidance Manual
Design Process Iteratively Design Riffle Trial riffle width and D 50 Calculate Manning s n value Calculate V 100 Check permissible V with D 50 Target sub-critical flow (not supercritical) Adjust size/slope/lengths/riffle material
WK Dickson In-House Model RSC Infiltration Model HEC-HMS outflow hydrographs Stage-Storage relationships for pools Surface area of pools Assumed hydraulic conductivity Cell-by-cell infiltration estimated Routed inflow hydrograph Darcy s Eqn for groundwater flow
Retrofit: RSC Regenerative Stormwater Conveyance Little Jackson Creek/Up Ditch
Retrofit: RSC Regenerative Stormwater Conveyance Little Jackson Creek/RR Ditch
Unintended Consequences
Path Forward
Path Forward
Path Forward
Biofiltration Conveyance Step Pools
Ward Marotti Senior Scientist Project Manager 919-368-8043 wmarotti@wkdickson.com David Kiker Technical Manager 919-782-0495 djkiker@wkdickson.com