Justin Lennon, PE 3 Rivers Wet W eather Stream Sem inar June 22, 20 18
Justin Lennon, PE — WSP Water & Environm ent — Baltim ore, MD — National Technical Leader — Stream & Ecosystem Restoration — River and Bridge H ydraulics — Sustainability & Clim ate Change — 1 6-Years of experience — Over 20 m iles of stream restoration design —Maryland, Delaw are, New York, Virginia, Pennsylvania, North Carolina, Florida, Washington, and Haw aii — Over $1 2 m illion of restoration designs under construction in 20 1 8
Understanding streams — What is a stable channel? — Sustainability — Sedim ent balance — Floodplain connectivity 3 Source: Rosgen, D. (1 996) Applied River Morphology, Wildland Hydrology.
Stream Classification — Most w idely used system for defining stream condition and function — Defines a range of stable and unstable stream types — Bankfull based classification system — Bankfull discharge ~ channel form ing flow — Differentiates stream types based upon geom orphic characteristics — Bankfull w idth, depth, entrenchm ent, sinuosity, and slope Source: Rosgen, D. (1 996) Applied River Morphology, Wildland Hydrology.
Stream impairm ent and evolution — What happens w hen a channel destabilizes? — Schum m evolution m odel (1984) — Loss of bed level control — Incision / entrenchm ent — Widening — Bank erosion & m ass w asting — General w idening versus m eandering — Quazi-equilibrium Source: Rosgen, D. (2006) Watershed Assessm ent of River Stability and Sedim ent Supply (WARSSS), Wildland Hydrology .
Rosgen Stream Evolution Models Source: Rosgen, D. (20 0 6) Watershed Assessm ent of River Stability and Sedim ent Supply (WARSSS), Wildland Hydrology .
W hy are our stream s im paired? — Changing hydrology — Developm ent im pacts on stream flow s — Loss of balance between sedim ent m obility and Channel form — Man-m ade alteration — Straightening — Floodplain fill — Levees — Legacy sedim ent — Colonial era m ill dam s Western Run, Baltim ore, MD Im age Source: Google Earth
Pre-Industrial Mill Dams — Research pioneered by Merritts and Walter (F&M College) — ~1 ,70 0 m ill dam s by 1 840 — Allegheny, Beaver, Butler, Westm oreland, Fayette, Greene, and Washington Counties Density of w ater-pow ered m ill in eastern U.S. by 1 840 . Source: Walter, R. and Merritts, D. (20 08) “Natural Stream s and the Legacy of Water-Pow ered Mills”, Science
Mill Dam influence on River Valleys Left: Typical m ill dam w ith sedim entation patterns. Low er: Lancaster County m ill dam location m ap (1 840 ). Source: Walter, R. and Merritts, D. (20 0 8) “Natural Stream s and the Legacy of Water-Powered Mills”, Science
What happened to the m ill dam s? Upper: Profile of Little Conestoga Creek and West Branch w ith Mill Dam locations. Lower: Conceptual m odel of legacy sedim ent stratified stream . Source: Walter, R. and Merritts, D. (20 0 8) “Natural Stream s and the Legacy of Water- Pow ered Mills”, Science
Legacy Sediment Stream Valleys
W hat are our options? — Stabilization — broadly defined as any activity targeted at protection / hardening of stream banks / bed — Restoration — stream construction activity targeted at achieving one or m ore levels of functional uplift
Functional uplift — Stream function pyram id — Developed by RiverMechanics and USFWS — Basis for defining functional uplift Source: Harm an, W., Starr, R. et al ( 20 1 2) “A Function-based Fram ew ork for Stream Assessm ent and Restoration Projects”, US EPA
Hydrologic Uplift — Processes that transport Param eter w ater from the w atershed to the Channel-form ing discharges channel Rainfall/Runoff relationship — Base of the pyram id as it strongly effects higher Flood frequency level functions — Without surface flow Flow duration there w ould be no aquatic ecosystem
Hydraulic Uplift — Transport of w ater in the Parameter Metric channel, on the Floodplain Bank height ratio floodplain and through connectivity Entrenchm ent ratio the ground Stream velocity — Supported by hydrologic Flow dynam ics Shear stress function Groundw ater / GW level — Closely related to surface w ater Hyporheic geom orphologic interchange interaction functions
Geom orphic Uplift Param eter Metric — The transport of sedim ent to create and Sedim ent Mobility of Com petency bedload and riffle m aintain diverse bed arm or form s Sedim ent Transport supply — Dynam ic equilibrium Transport Capacity versus capacity — Direct support of upper Bank Migration / BANCS Lateral Stability Surveys level functions — Habitat diversity Riparian Buffer w idth and Vegetation com position — Creation and transport of w ater quality Bed Form Diversity Percentage of contam inants riffles and pools Bed Material Riffle arm or Stability stability
Physio-chem ical Uplift — Water quality Param eter Metric — Designs targeted at Level 3 –geom orphology Water Quality Tem perature, DO, pH, Turbidity in order to provide Level 4 uplift Nutrients TN, TP Organic Carbon
Biological Uplift Param eter — Dependent on all Microbial Com m unities underlying functions — Im pairm ent at any level Macrophyte Com m unities w ill im pair Level 5 Benthic Macroinvertebrate — Biodiversity of aquatic Com m unities and riparian organism s Fish Com m unities Landscape Connectivity
Stream Restoration Design m ethods — Natural Channel Design — Valley Restoration / Legacy Sedim ent Design — Regenerative Storm w ater Conveyance (RSC) — Hybrid Design Approaches
Natural Channel Design — Pioneered by Dave Rosgen — Bankfull discharge based design technique — Reference reach / natural analog based design — Channel sizing based on bankfull scaling of reference reach — Reference reach identified as an undisturbed naturally sustainable system — Sedim ent transport evaluations based upon non- dim ensionalized curves
Natural Channel Design — Pros: — Widely accepted / perm ittable m ethodology — Track record of successful projects across the Country — Cons: — Difficulty in identifying appropriate reference reach — Methodology is too focused on a singular discharge — Methodology is too cook-book, m ay not be w ell understood by practitioners — May not properly address the source of im pairm ent — Degree of riparian root zone reconnection is m ore lim ited than other options
Valley Restoration / Legacy Sediment Design — Method pioneered based upon research and observation into the role of colonial era developm ent on valley landform s and attendant stream interaction — Mill dam s, legacy sedim ents and stream evolution — Design approach generally involves excavation and rem oval of legacy sedim ents from valley bottom — Channel sizing target is << bankfull — Channel sizing largely based upon threshold transport of historic gravels
Legacy Sediment Design — Pros: — Addressed the source of im pairm ent — Greatly decreases in-channel velocity and erosive stresses — Highest degree of phreatic zone connection — Highest degree of floodplain connection — Cons: — Very high per LF project cost — May have significant natural resource im pacts — May have bedload transport lim itations in high yield system s Im age source: w ww .landstudies.com
Regenerative Storm water Conveyance — Coastal plain outfalls or regenerative step pool storm conveyance — Developed in Anne Arundle County, MD — Channel and pool sizing driven to capture up to the 1 0 -year flow in pool areas for infiltration — Sandfilter or bio m edia sub-base along channel Source: Anne Arundel County (20 1 2) “Design Guidelines for Step Pool Storm Conveyance”.
Regenerative Stormwater Conveyance — Pros — Hydrologic function uplift — Water quality treatm ent — Can w ork w ith im paired landscape — Cons 25 — Lim ited applicability — Space lim itations m ay lim it treatm ent effectiveness — Specialized construction m aterials —Sandstone Im age source: Anne Arundel County (20 1 2) “Design Guidelines for Step Pool Storm Conveyance”.
Hybrid Design Approaches — Borrow concepts from other m ethodologies to adapt to context of any situation — Generally m ore heavily reliant on sedim ent transport role in the design of the channel — Frequently sub-bankfull design, but not exclusively so — Design typically considers a w ide range of flow conditions
Priority levels of Restoration — Developed by Dave Rosgen (1 997) — Sim ple descriptive classification system for restoration approaches — Priority levels 1 through 4 Im age Source: North Carolina Stream Restoration Institute; Stream Restoration –A Natural Channel Design Handbook
Priority 1 — Construct channel to reconnect to the upper terrace floodplain — Preserves natural resources 28 — Floodplain Im pacts — CLOMR? — Net fill
Peachwood Park Tributary — AFTER — BEFORE
Priority 2 & 3 — Balanced construction, raising of channel bed / grading of in-set floodplain benches — Potential for cut / fill 30 balance — Not likely though — Priority 2 vs 3 — Balance or im prove floodplain m anagem ent
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