Decarbonising Buildings: Making a net-zero built environment a reality
Asce nc jennings
1. Stream Restoration
Innovations and Opportunities
Greg Jennings, PhD, PE
Professor, Biological & Agricultural Engineering
North Carolina State University
jennings@ncsu.edu
2. Stream: A system of
fluvial forms & habitats
• Channel (bed & banks)
• Floodplain
• Water
• Sediment
• Plants & animals
Photo Credit: Eve Brantley, Auburn University
3. Streams are Ecosystems
• Communities of organisms and their physical,
chemical, and biological environments
4. What makes a stream healthy?
1. Bed stability & diversity
2. Sediment transport balance
3. In-stream habitat & flow diversity
4. Bank stability (native plant roots)
5. Riparian buffer (streamside forest)
6. Active floodplain
7. Healthy watershed
8. Why Restoration?
• Water quality impairments
• Habitat loss
• Ecosystem degradation
• Land loss
• Safety concerns
• Infrastructure damage
• Flooding
• Aesthetics
9. Standards for ecologically successful river restoration
Palmer et al., Journal of Applied Ecology, 2005, 42, 208–217
1. design of an ecological river restoration project should be
based on a specified guiding image of a more dynamic,
healthy river
2. river’s ecological condition must be measurably improved
3. river system must be more self-sustaining and resilient to
external perturbations so that only minimal follow-up
maintenance is needed
4. during the construction phase, no lasting harm should be
inflicted on the ecosystem
5. pre- and post-assessment must be completed and data
made publicly available
10. Outcomes of Ecosystem Restoration
• Habitats & water quality
• Natural flow regimes
• Recreation & aesthetics
• Public enthusiasm
14. Alluvial Channels
1. Movable boundary systems
2. Complex design approach: assess sediment continuity
and channel performance for a range of flows
3. Dependent variables: Width, Depth, Slope, Planform
4. Independent variables: Sediment inflow, Water inflow,
Bank composition
5. Empirical & Analytical approaches should be used
concurrently
15. Steady State Equilibrium
dimension, pattern and profile of the river and its
velocity have adjusted to transmit the discharge
and sediment load from its catchment under the
present climate and land use conditions without
any systematic erosion or deposition; namely
regime conditions (Hey)
16. Alluvial Channels – Analogy Approach
1. Reference reach: Must have similar bed/bank materials,
sediment inflow, slope, valley type, and hydrograph
2. Upstream/downstream of design reach is best
3. Nearby similar watershed acceptable
4. Use as a starting point or check (BE CAREFUL)
25. Natural Stream Channel Stability
(from Leopold)
• River has a stable dimension, pattern and profile
• Maintains channel features (riffles, pools, steps)
• Does not aggrade (fills) or degrade (erodes)
26. Dimension
(cross-section)
• Area
• Width
• Depth
• Width/Depth Ratio
• Entrenchment Ratio
• Bank Height Ratio
27. Bankfull Stage: “incipient flooding”
“corresponds to the discharge at which channel maintenance is the most
effective, that is, the discharge at which moving sediment, forming or
removing bars, forming or changing bends and meanders, and generally doing
work results in the average morphologic characteristics” (Dunne & Leopold,
1978)
Stream Corridor Restoration: Principles, Processes, and Practices. 1998. Federal Interagency Stream Restoration Working Group.
33. Sinuosity = stream length / valley length
K = 1850 / 980 = 1.9
Valley Length
34. Meander Length Ratio = meander length / width = 78/15 = 5.2
Meander Width Ratio = belt width / width = 57/15 = 3.8
Radius of Curvature Ratio = radius / width = 23/15 = 1.5
Belt
Width
Meander
Length
35. Profile (bedform)
Water Surface
Riffle Slope
Run Slope
Glide Slope
Thalweg Pool Slope
Pool Spacing, Lp-p
Riffle Slope Ratio, Srif / Sav
Pool Slope Ratio, Spool / Sav
Pool-to-Pool Spacing Ratio, Lp-p / Wbkf
37. Priority 1:
lift channel
Incised
Stream
Priority 2 & 3:
lower floodplain
Stream Corridor Restoration: Principles, Processes, and Practices.
1998. Federal Interagency Stream Restoration Working Group.
38. Priority 1: Raise channel to existing valley
and construct new meandering channel
ER = 15; W/d = 12
Rain will come during and
immediately following construction!
2006 Town Creek Tributary 2007
57. 3. Hydrologic & Hydraulic Analysis
Qbkf: Bankfull discharge (cfs) appropriate for watershed size,
sediment transport & valley conditions
Vav = Qbkf / Abkf: Bankfull average velocity (ft/s) appropriate for
valley, soils, bed material
τav: Bankfull average applied shear stress (lb/ft2) & local max
stresses appropriate for sediment transport conditions & bed/
bank restistance
ωav: Bankfull average stream power (lb/ft/s) appropriate for
sediment transport conditions
Riffle substrate size distribution appropriate for hydraulic
conditions & habitats
Streambank protection to resist erosion (short-term & long-term)
