Designing channels for stream restoration...dynamism (e.g., flooding, erosion, and deposition) in streams that have been dammed, leveed, or channelized…. Restoring a channel to a

Designing channels for stream restorationA workshop hosted by Oklahoma State University

June 2, 2016

Arcadia Educational Center

Session 2: Channel design and threshold channels

Doug Shields, Jr. www.friendofrivers.com

Workshop overview

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• Review of recent research on stream restoration efficacy

• Design for three types of channels• Threshold

• Type I--Bed material immobile at design Q, negligible sediment supply

• Type II—transport capacity exceeds sediment supply but design Q will not erode channel boundary

• Alluvial• Bed material gradation and sediment supply gradation are similar

• Transport capacity = sediment supply

• Available information resources and tools

• Example problems 2

Channel design—two philosophies

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Different ways of looking at the same thing

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Actually, five design approaches for channels

• Regime method (British engineers, canals, sand beds, Cs < 30 mg/L)

• Hydraulic geometry (Leopold and others)

• Analogy or reference reach (NCD, Rosgen)

• Analytical method (Copeland, SAM, HEC-2)

• Extremal hypothesis (Yang and others)

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Also see NRCS (2007a)5

Comments on the five approaches (SUNY Buffalo)

• Regime Method: Dependent channel dimensions can be determined from regression relationships with independent variables

• Hydraulic Geometry Method: Dependent channel dimensions can be determined from regression relationships with independent variables

• Analogy Method: Channel dimensions from a reference reach can be transferred to another location

• Analytical Method: Depth and sediment transport can be calculated from physically-based equations

• Extremal Hypotheses: Alluvial channels will adjust channel dimensions so that some parameter is optimized


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Regime equations (Blench)

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Limitations on regime (Blench)

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Examples of hydraulic geometry

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Hydraulic geometry relation for width based on 32 sand-bed rivers with less or more than 50% tree cover on banks

wBF = aQBFb

a=5.19 (T1)a=3.31 (T2)b=0.5

Another example of hydraulic geometry


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Channel design guidance recognized by the engineering profession—”analytical method”

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Slate et al. (2007)

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“This committee proposes that stream restoration channel design standards be based on measurable criteria supported by current peer-reviewed scientific publications. Design goals should be clearly defined and based on general physical principles, rather than referenced to an empirically defined equilibrium state. More specifically, the questions “What is the supply of water and sediment?” and “What do you want to do with them?” provide a sound framework for restoration design (Wilcock 1997), leading to consideration of physical, ecological and management objectives on a consistent and quantitative basis through space and time. In the absence of more refined materials, the authors support the work previously published by members of the River Restoration Committee (Shields et al. 2003) and suggest using this work as a starting point for channel design standards.”


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Thoughts on training and credentials

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• Survey of existing training• Practitioner survey

• Lists of disciplines, subjects, skills needed

• Level of mastery required to perform various functions

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Similar content

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An analytical approach to channel design

• This science developed to produce channel geometries that were “stable.”

• “A stable channel is often defined as a channel where the planform, cross section, and longitudinal profile are sustainable over time. A natural channel can migrate en still be considered stable in that its overall shape and cross-sectional area do not change appreciably.”

• Two problems

• Stable channels are rare

• Stable channels are poor habitat

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Analytical method background• Grew out of engineering practice

for design of man made channels—canals, diversions, aqueducts, etc.

• “Stable channel design”

• Channels which were sized (mean W, D, S) to convey the sediment supplied to them but not erode their boundaries

• Largely based on physics-based analysis of forces acting on channel and sediment transport

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But stabilization is not restoration“Strategies for restoration projects often include promoting higher levels of physical dynamism (e.g., flooding, erosion, and deposition) in streams that have been dammed, leveed, or channelized…. Restoring a channel to a state of dynamic equilibrium may not be a socially acceptable outcome if the resulting situation poses threats to riparian resources or infrastructure. …a tension often exists between the dynamism needed for ecological objectives and erosion and flood control interests.”

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Wilcock approach

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Courtesy Peter Wilcock, Utah State Univ


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Wilcock approach

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Courtesy Peter Wilcock, Utah State Univ


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The problem (in general)• Given Q, Qs, ds

• Find W, D, S for a channel reach

• Constraint: the resulting channel will not aggrade or erode its bed or banks

• Three equations

• Flow resistance (Manning)

• Momentum (shear stress)

• Sediment transport

• The last two equations introduce an addition unknown variable, t

• Since there are three equations and four unknowns, the result is a “family” of solutions

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Finding the “givens”• Sv, Wmax, Q, Qs, ds, tc*

• Sv is the valley slope—and thus is the maximum channel slope

• Wmax is the maximum channel top width allowed by site constraints

• Q is the discharge that fills the designed channel• Threshold—what do you want it to be?

• Alluvial--“channel forming discharge”

• Qs is the bed-material load supplied to the design reach from upstream when Q = Qs

• ds, tc*

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Bed sediment size

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• Should be the sediment size in the constructed channel bed• Take borings?• Consider sediment inflows• Natural armoring• Constructed armor or linings

• Not the bank sediment size• Not the current (existing) channel

sediment size• Not the sediment load size• Usually one or more “characteristic”

sizes (d50, d84, d75)• Design is very sensitive to ds


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Sediment supply• For design, we need Qs,

sediment rate (dimensions of mass/time) when water discharge = Qcf

• To check our design for stability, we need a sediment rating curve Qs = f(Q)

• Rarely measured• Usually must be computed• Computations typically

require special training and skills Sh

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What value to use for tc*• Rep > 500 0.03–0.06

• 4000 < Rep <100000 0.01–0.09 Buffington and Montgomery (1997), coarse-bedded steep streams

• Buffington and Montgomery (1997) attribute the variability to differences in bed stability (or bed mobility) as well as differences in computations and field methods.

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Bunte et al. Water Resources Research 49.11 (2013): 7427-7447.


Lots of correction factors, etc. to compensate for the differences

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The ultimate wild card

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Analytical design for three types of channels

• Threshold ( t < tc)

• This tc is critical shear stress to mobilize bed sediment particles

• Qs in ~ 0 (Type I)

• Qs in > 0 but ttransport< t < tc (Type II)

• Alluvial ( t >>> tc)

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All three types must obey the same laws of physics.


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Workshop overview

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• Review of recent research on stream restoration efficacy

• Design for three types of channels• Threshold

• Type I--Bed material immobile at design Q, negligible sediment supply

• Type II—transport capacity exceeds sediment supply but design Q will not erode channel boundary

• Alluvial• Bed material gradation and sediment

supply gradation are similar• Transport capacity = sediment supply

• Available information resources and tools• Example problems


NRCS (2007b)27

Threshold channels

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• Channel boundary material has no significant movement during design flow

• Bed is composed of o Erosion resistant bedrock or cohesive materialo Coarse material too large to be transported by

flowo Grass, riprap, pavement….

• Examples includeo Bed material formed by glacier outflows or dam breakso Channels downstream from reservoirs with greatly reduced peak dischargeso Channels incised into erosion resistant stratao Channels designed and constructed with immobile boundaries

• Can a sand bed channel be a threshold channel?


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Examples of threshold channels

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Threshold channel design• Q = WDV (continuity)

• V = (1.486/n)D2/3S1/2 (Manning flow resistance)

• For sediment transport relation, we use a Shields type relation (no relation to me!):

qs = a(t* - tc*)b

(note qs is transport rate of bed material per unit width = Qs/W )

• Since Qs = 0, then t* = tc*, or

0.047 = DS/(1.65ds)

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Threshold channel design• Four equations, five unknowns (W, D, S, V, t)

• Q = WDV

• t = gDS

• V = (1.486/n)D2/3S1/2

• S =[Qn/(1.486WD5/3)]2

• tc* = DS/(1.65ds)

• D = 0.07755ds/S

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For simplicity, assume rectangular channel with Qs = 0, R ~ D and constant Manning n


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Threshold channel designLet tc*= 0.047 x 0.9

Combine

• S =[Qn/(1.486WD5/3)]2

• D = 0.07755ds/S

To get S = f(W)

• S = 0.0184(Qn) -6/7ds10/7W7/6

“Given”

• Q = 400 cfs

• ds = 45 mm (convert to ft)

• n = 0.035

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0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.020

0 20 40 60 80

Slo

pe

Channel Width, ft

Slope v Width for Rectangular Channel

Use constraints and design objectives to select a single W or S


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Threshold channel design

Combine

• S =[Qn/(1.486WD5/3)]2

• D = 0.07755ds/S

To get S = f(W)

• S = 0.0184(Qn) -6/7ds10/7W7/6

• D = 0.07755 ds /S

• If Q = 400 cfs, ds = 45 mm (convert to ft), n = 0.035

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0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0 20 40 60 80

De

pth

, ft

Channel Width, ft

Depth v Width for Rectangular Channel


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Threshold design example• Example from NRCS NEH 654.08 pp. 40-41

• Type I threshold design

• Note that this is a trapezoidal channel

• Keys

• Assume n = f(ds) or is constant

• Use constant side slope

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Threshold design example 1Given Find

• Channel W, D, S

• Sinuosity

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Threshold design example 1Steps

Determine ds

• Determine prelim W

• Estimate tc

• Estimate flow resistance (Manning n)

• Calculate D and S

• Determine planform

• Assess stability

Methods

• As described above

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Determine ds

Determine prelim W

• Estimate tc





Methods

As described above

Use hydraulic geometry or regime formula (why is this a problem?). W = 2.03Q0.5 = 2.03(400)0.5

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22 to 74 ft


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Determine ds

Determine prelim W

Estimate tc





Methods

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As described above Use hydraulic geometry or regime formula Use Shields relation. Consult literature or

use experience with similar streams.


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Determine ds

Determine prelim W

Estimate tc

Estimate flow resistance (Manning n)




Methods

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As described above

Use hydraulic geometry or regime formula

Use Shields relation.

Grain and total resistance using Strickler or Limerinos plus Cowan


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Determine ds

Determine prelim W

Estimate tc


Calculate D and S



Methods

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As described above




Use iterative process—vary S, compute D, compute Q until desired Q is reached. Table or….

graph of discharge v slope


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../analytical channel design.xlsx


Determine ds

Determine prelim W

Estimate tc


Calculate D and S

Determine planform


Methods

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As described above




Use successive approximations or graph of discharge v slope

Compute sinuosity = Valley slope/channel slope


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../analytical channel design.xlsx


Determine ds

Determine prelim W

Estimate tc


Calculate D and S

Determine planform

Assess stability

Methods

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As described above




Use successive approximations or graph of discharge v slope

Compute sinuosity = Valley slope/channel slope

Consider stability at higher and lower flows and with different values of ds and tc* --Bank protection?

W = 41 ft, D = 1.9 ft, = 0.0047, P = 1.4842

HEC RAS 5.0 Stable Channel Design

• Width is B in HEC RAS literature

• Threshold

• Tractive force

• Regime

• Design is a suitable combination of W, D, S, ds

• Alluvial

• Copeland

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Threshold design with HEC RAS• Referred to as the “tractive force” method

• Reduces the six variable system (W, D, S, Q, Qs, ds) to a five-variable system (W, D, S, Q, ds) since it is assumed that Qs ~ 0.

• The user must supply Q and tc*

• The user must supply two of the four remaining variables and HEC RAS will compute the other two.

• For example, user supplies ds and W, program computes D and S

• Note extreme sensitivity to Shields no. and ds

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../HEC-RAS 5.0.1.lnk

Compare NEH and HEC RAS results

NEH 654.08

• Limerinos used for Manning n

• W = 41 ft

• D = 1.94 ft

• S = 0.0047

• P = 1.48

HEC RAS 5.0

• Manning n supplied by user or computed with Strickler

• W = 41 ft

• D = 1.88 ft

• S = 0.0048

• P = 1.45

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These dimensions are for planning or preliminary design. Variability and detail must be added, and stability checks across a range of discharges are needed.

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HEC RAS anomalous solutions

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If you have a very large ds, you can get a very large D…leading to a small B. 46

Threshold design with FHWA• Hydraulic toolbox

• Channel lining analysis

• Threshold type I check

• Allows a range of cross sectional shapes

• Provide ds, Manning n, Q, Width, Slope

• Computes D (flow depth) and assesses stability

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../HydraulicToolbox - Shortcut.lnk

Two stage threshold channel design

• Given

• Slope and valley slope

• Bed D84

• Shields number Qbankfull

• Q5

• Find

• Inset channel width

• Inset channel depth

• Floodplain channel width

• Floodplain channel depth

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Resop, et al. (2014) Journal of Soil and Water Conservation 69.4 (2014): 306-315.

Effect of uncertainty

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Two stage channel design

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Regular deterministic analysis• w1 = 9 m• w2 = 50 m• d1 = 0.5 m• d2 = 0.8 m


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Monte Carlo varying Qb, D84, n, Shields number


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To recap…...• Several approaches used for stream restoration channel design

• Analytical approach endorsed by NRCS and recommended by ASCE

• Analytical approach revolves around sediment transport

• Three main types of channel

• Threshold type I—bed does not move, little to no sediment transport

• Threshold type II—bed does not move, significant sediment transport

• Alluvial—bed moves and significant sediment transport Shie

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References• Brookes, A., and Shields Jr, F. D. (1996). River channel restoration: guiding principles for sustainable

projects. John Wiley & Sons, New York.

• Bunte, K., Abt, S. R., Swingle, K. W., Cenderelli, D. A. and Schneider, J. M. (2013). Critical Shields values in coarse‐bedded steep streams. Water Resources Research, 49(11), 7427-7447.

• Buffington, J. M., and Montgomery, D. R. (1997). A systematic analysis of eight decades of incipient motion studies, with special reference to gravel‐bedded rivers. Water Resources Research, 33(8), 1993-2029.

• Copeland, R. R., D. N. McComas, et al., Eds. (2001). Hydraulic Design of Stream Restoration Projects. U.S. Army Corps of Engineers: Engineer Research and Development Center, Vicksburg, MS.

• Federal Interagency Stream Restoration Working Group. (1998). Stream corridor restoration: principles, processes, and practices.

• National Resources Conservation Service (NRCS) (2007a). Basic Principles of Channel Design. Stream Restoration Design, Chapter 7, National Engineering Handbook Part 654.7. USDA NRCS, Washington, D. C.

• National Resources Conservation Service (NRCS) (2007b). Basic Principles of Channel Design. Stream Restoration Design, Chapter 8. National Engineering Handbook Part 654.8. USDA NRCS Washington, D. C.

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References (continued)• Niezgoda, S.L., Wilcock, P.R., Baker, D.W., Price, J.M., Castro, J.M., Curran, J.C., Wynn-Thompson, T.,

Schwartz, J.S. and Shields Jr, F.D. (2014). Defining a stream restoration body of knowledge as a basis for national certification. Journal of Hydraulic Engineering 140(2), pp.123-136.

• Resop, J. P., Hession, W. C. and Wynn-Thompson, T. (2014). Quantifying the parameter uncertainty in the cross-sectional dimensions for a stream restoration design of a gravel-bed stream. Journal of Soil and Water Conservation 69.4 (2014): 306-315.

• Shields, F. D., Copeland, R.R., Klingeman, P.C., Doyle, M.W. and Simon, A. (2003). Design for Stream Restoration. Journal of Hydraulic Engineering 129(8): 575-584.

• Shields, F. D., Jr., Copeland, R. R., Klingeman, P. C., Doyle, M. W. and Simon, A. (2008). Stream restoration. Chapter 9 in Sedimentation Engineering: Processes, Measurements, Modeling and Practice, Manual of Practice 110, American Society of Engineers, Reston, Virginia. 461-499 pp.

• Slate, L. O. Shields, F.D., Schwartz, J.S., Carpenter, D.D. and Freeman, G.E (2007). Engineering Design Standards and Liability for Stream Channel Restoration. Journal of Hydraulic Engineering133(10) ,1099-1102.

• Wilcock, P. R. (1997). Friction between science and practice: the case of river restoration. Eos, Transactions, Am. Geophysical Union 78(41): 454.

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Documents

Designing channels for stream restoration...dynamism (e.g., flooding, erosion, and deposition) in streams that have been dammed, leveed, or channelized…. Restoring a channel to a