vi. river engineering and geomorphology for transportation design
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VI. River Engineering And Geomorphology For Transportation Design. VI. River Engineering And Geomorphology For Transportation Design. Lecture Overview A Sedimentation and Scour B Dynamic Nature of Streams in the Arid West C Sediment Transport Models Next Lecture - PowerPoint PPT PresentationTRANSCRIPT
VI. 1
VI. River Engineering And Geomorphology For Transportation
Design
VI. 2
VI. River Engineering And Geomorphology For Transportation
Design
Lecture OverviewA Sedimentation and Scour
B Dynamic Nature of Streams in the Arid West
C Sediment Transport Models
Next Lecture Section VII – Effects of Transportation
Structures on Stream Systems
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VI. River Engineering And Geomorphology For Transportation
Design
A.1. Sedimentation And Scour: Basic Sediment Transport
Theorya) Sediment Continuity
b) Sediment Transport Capacity
c) Sediment Load
d) Sediment Transport Functions
e) Sediment Yield
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VI. River Engineering And Geomorphology For Transportation
Design
A.1. Basic Sediment Transport Theorya) Sediment Continuity Equation
Storage change = erosion or depositionStreams naturally balance sediment load Imbalances cause adjustments to occurFixing one problem may cause another
Sediment in – Sediment out = Storage Change
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VI. River Engineering And Geomorphology For Transportation
Design
A.1. Basic Sediment Transport Theoryc) Sediment Transport Capacity
The amount of sediment a stream can move
Basic Principles: Streams carry as much sediment as they can Streams deprived of sediment will find some Streams with excess will lose some There are several types of sediment transport
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VI. River Engineering And Geomorphology For Transportation
Design
A.1. Basic Sediment Transport Theoryc) Sediment Load
Types of Sediment load Bed-material load Wash load Total load
Types of Sediment Movement Sliding, rolling, saltation, suspension, solution
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A.1. Basic Sediment Transport Theoryc) Sediment Load: Classification
Sediment Load Classification Schemes. (After SCS, 1983, Figure 4-2.)
WashLoad
SuspendedBed-Material
Load
BedLoad
Suspended
Load
BedLoad
WashLoad
Bed-MaterialLoad
TOTAL
LOAD
VI. River Engineering And Geomorphology For Transportation
Design
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VI. River Engineering And Geomorphology For Transportation
Design
A.1. Basic Sediment Transport Theoryd) Sediment Transport Equations
Key References: ADWR, 1985 – Design Manual for Engineering
Analysis of Fluvial Systems ASCE Publications Sediment Transport Textbooks
Variables: shown on next slide
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Vegetation CoverSlopeDrainage AreaElevationGeologyValley SlopeSediment yieldHuman Impacts – UrbanizationGrazing Practices
Watershed Characteristics
Vegetation TypeRoot DepthRoot DensityBranch/Foliage DensityTrunk Pliability Growth RateGermination CycleGrazing Practices
Channel Vegetation
Engineering (short-term)Geologic (long-term)
Time Scale
Precipitation Type (snow?)Precipitation IntensityPrecipitation DurationSeasonal DistributionTemperature/Evaporation
Climate
Mean DiameterSize DistributionArmoring PotentialCohesionStratigraphy
Streambed and Bank Sediment
Magnitude (peak)Duration (flashy?)Ratio of Peak to Base FlowRatio of Rare to Frequent FloodsChannel CapacityLossesReservoirs/Flood Storage
Flood Characteristics
WidthDepthHydraulic RadiusFriction FactorVelocityTopwidthTurbulenceTemperatureTransmission Losses
Flow
Channel WidthChannel DepthBank HeightBank SlopeBank MaterialsBank StratificationStream PatternBed FormsMeander AmplitudeMeander WavelengthSinuosityFloodplain WidthDepth of Floodplain FlowStream TerracesChannel SlopeAggradationDegradationLocal ScourBed SedimentBar SedimentPool & Riffle SequenceArmoringBedrock Outcrop & ControlHuman ModificationsBank ProtectionGrade ControlRoadway CrossingsUtility Crossings
Dominant DischargeMean Annual DischargeFlow Duration StatisticsVariation with SeasonDiversions and StorageFlow Source
Hydrology
River CharacteristicsVariable SubgroupVariable
Some Variables Affecting River Behavior and River Characteristics That Can Change With Time
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VI. River Engineering And Geomorphology For Transportation
Design
A.1. Basic Sediment Transport Theoryd) Sediment Transport: Typical Equation
Zeller-Fullerton (Einstein/Meyer-Peter Muller) Qs = W n1.77 V4.32 G0.45 Y-0.3 D 50
-0.61
Einstein’s suspended bed-material integration Meyer-Peter, Muller bedload equation Total bed-material discharge
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VI. River Engineering And Geomorphology For Transportation
Design A.1. Basic Sediment Transport Theory
d) Sediment Transport: Function Considerations Type of Load Variability
Spatial variation Within channel, along stream Geographic regions
Temporal Flow rates during hydrograph Seasonal
Initiation of Sediment Movement Source Data for Empirical Equations
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VI. River Engineering And Geomorphology For Transportation
Design
A.1. Basic Sediment Transport Theoryd) Sediment Transport: Yield
Definitions Erosion: soil loss Delivery: sediment yield
Factors Influencing Sediment YieldClimate, geology, vegetation, land use, topography, soils, runoff, channel conditions
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Sediment Yield Over Time
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VI. River Engineering And Geomorphology For Transportation
Design
A.1. Basic Sediment Transport Theorye) Sediment Yield: Methodologies
PSIAC Planning Level Average Annual Yield (Delivery) Total Load
MUSLE/USLE/RUSLE Soil Loss Event Based Model (MUSLE/RUSLE) Suspended Load
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VI. River Engineering And Geomorphology For Transportation
DesignA.1. Basic Sediment Transport Theory
e) Sediment Yield: MethodologiesReservoir Data
BUREC Equation (Design of Small Dams) Total Load Average Annual Sediment Delivery
Many Regional Methodologies Total Load Average Annual Sediment Delivery
04/21/23
VI. River Engineering And Geomorphology For Transportation
Design
A.1. Basic Sediment Transport Theorye) Sediment Yield: Implementation Rules
Real World: Yield Varies WidelyRules of Thumb
Average annual is poor predictor in Arizona For larger watersheds, use transport methods Sediment delivery is generally underestimated 10% sediment concentration
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VI. River Engineering And Geomorphology For Transportation
Design
A.2. Scour and Erosiona) Types of Scour
b) Scour Prediction
c) Scour Equation
d) Scour Mitigation
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VI. River Engineering And Geomorphology For Transportation
Design
A.2. Scour and Erosiona) Types of Scour
Short-Term Scour Scour is “lowering of a channel bed.” City of
Tucson Manual, p. 6.07 “Short-term changes in channel bed elevation.”
Long-Term ScourLateral Erosion
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VI. River Engineering And Geomorphology For Transportation
Design
A.2. Scour and Erosiona) Types of Scour
Components of scour General Bend Thalweg Bed form Local [Long-term]
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Scour Components
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Scour Components
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1
2
3
4
San Juan RiverNear Bluff, UT
Example of Scour During a Flood
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Natural Local Scour
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Field Evidence of Scour Depth
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Local Scour (PHOTO)
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VI. River Engineering And Geomorphology For Transportation
DesignA.2. Scour and Erosion
a) Types of Scour (CONTINUED)
Long-Term Scour (Degradation) Time Scale Causes
Geologic forces Hydrologic regime change Sediment supply Slope adjustments Change in erodibility PROCESS-BASED
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VI. River Engineering And Geomorphology For Transportation
DesignA.2. Scour and Erosion
b) Scour Prediction: Factors That Influence ScourHydraulics
Velocity, Depth, Slope Bend angle
Obstructions Piers, walls, natural – shape, width, encroachment
Other factors Flow rate Material characteristics
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VI. River Engineering And Geomorphology For Transportation
Design
A.2. Scour and Erosionc) Scour Equations: Estimating Long-Term
ScourArroyo Evolution Model (AMAFCA Manual)Equilibrium Slope (ADWR and COT Manuals)State Standard 5-96Field and Historical Data
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Field Evidence Of Scour
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Field Evidence OfLong-Term Scour
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Field Evidence Of Long-Term Scour
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Field Evidence Of Long-Term Scour
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Field Evidence Of Long-Term Scour
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VI. River Engineering And Geomorphology For Transportation
Design
A.2. Scour and Erosion d) Scour Mitigation Measures
Resistant MaterialsNon-Transportable MaterialsChange HydraulicsMonitor and MaintenanceReferences:
Highways in Riverine Environment HEC-18/HEC-20
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VI. River Engineering And Geomorphology For Transportation
Design
A.3. Recurrence Intervals Small flows Large floods
Sediment transportScourLateral erosion
Peak vs. Volume
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VI. River Engineering And Geomorphology For Transportation
DesignB. Dynamic Nature of Streams in the Arid West
1. Humid vs. Arid Environments
2. Alluvial Streams
3. Ephemeral vs. Perennial Streams
4. Lateral Erosion, Avulsion and Meandering
5. Aggradation/Degradation
6. Flash Floods
7. Flood Ratios, Flood Volume
8. Alluvial Fans
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Humid Region Streams Perennial Low Flood Ratio Long Durations Small Floods Dominate Meandering Slow Erosion Fast Recovery Free Flowing Low Sediment Load Resistant to Change
Arid Region Streams Ephemeral High Flood Ratio Short Durations Large Floods Dominate Braided, Straight Fast Erosion Slow Recovery Dams and Diversions High Sediment Load Sensitive to Change
B.1. Humid vs. Arid Environments
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VI. River Engineering And Geomorphology For Transportation
Design
B.2. Alluvial Streams Formed by Materials it Carries Boundaries Subject to Transport Balance Between Transport/Deposition Change the Boundaries, Change the Stream
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Perennial Equilibrium Non-flood
recovery Defined banks Well vegetated Environmental
protection
Ephemeral Non-equilibrium Work only in floods Poorly defined
banks Poorly vegetated Less environmental
protection
B.3. Ephemeral vs. Perennial
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VI. River Engineering And Geomorphology For Transportation
Design
B.4. Lateral Erosion Bank Erosion Widening Meandering Avulsion
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Mechanisms Of Bank Erosion
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Bank Erosion
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Bank Erosion
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Bank Erosion
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Widening Of Braided Streams
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Meandering
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ChannelAvulsion
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VI. River Engineering And Geomorphology For Transportation
Design
B.5. Aggradation/Degradation Aggradation – Bed Elevation Increases
Some braided streamsAlluvial fansObstructions
Degradation – Bed Elevation DecreasesUrban riversEncroachment In-stream mining
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Field Techniques: Terraces/Headcuts
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Channel Pattern Changes
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VI. River Engineering And Geomorphology For Transportation
Design
B.6. Flash Floods Time to Peak Recession Time Transportation Issues:
Response TimeObservation of Floods Interruption TimeRisk
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VI. River Engineering And Geomorphology For Transportation
Design
B.7. Flood Ratio and Volume Examples of Flood Ratios
Central ArizonaNorthern ArizonaEast Coast
Annual Flow Volume vs. Flood VolumeSalt RiverSkunk CreekSynthetic Hydrograph
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VI. River Engineering And Geomorphology For Transportation
DesignB.8 Alluvial Fans
Depositional Landform Uncertain Flow Paths Channelized and Unchannelized Flow Avulsive Channel Change
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Alluvial Fans
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Alluvial Fans
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Alluvial Fans
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ArizonaAlluvial Fans
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VI. River Engineering And Geomorphology For Transportation
Design
C.Sediment Transport Models1. Types of Models
2. Sediment TransportComputer Models
3. Evaluation of Results
4. Application of SedimentTransport Equations
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VI. River Engineering And Geomorphology For Transportation
Design
C.Sediment Transport Models1. Types of Models:
Computer ModelsMathematical ModelsPhysical ModelsQualitative Models
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VI. River Engineering And Geomorphology For Transportation
DesignC.Sediment Transport Models
2. Sediment Transport Computer Models: Examples
HEC-6, 6T Kovacs-Parker FLUVIAL-12 Darby-Thorne GSTARS Wiele STREAM2 Simon et. al. WIDTH Pizzuto RIPA Alonso-Co QUASED
Many others
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VI. River Engineering And Geomorphology For Transportation
DesignC.Sediment Transport Models
2. Sediment Transport Computer ModelsHEC-6
One dimensional Steady discharge Uniform scour or deposition Sediment continuity Initial conditions Time scale Sediment sources Sediment transport calculations Equilibrium Time step Bridges and culverts
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C.Sediment Transport Models2. Sediment Transport Computer Models
Hydraulic modeling Gradually varied Steady flow One-dimensional Slope is low Discharge is known Loss coefficients are known Geometry is accurate Single channel – tributary pattern
VI. River Engineering And Geomorphology For Transportation
Design
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VI. River Engineering And Geomorphology For Transportation
DesignC.Sediment Transport Models
2. Sediment Transport Computer ModelsContinuity principle:
Inflow – outflow = change in storageTransport function selectionContribution of bank material Upstream control of sediment processUniform sediment flux Ignores base level adjustmentsChannel vs. floodplain processes
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C. Sediment Transport Models
2. Sediment Transport Computer Models: HEC-6 Assumptions
HEC-6 Modeling Assumptions and Limitations
Assumption/Limitation Assumption Generally Valid in Arizona? One Dimensional No. But probably gradually varied Uniform Scour or Deposition No. Braided system with bars No Bank Erosion No. Banks unstable in design flood Steady Flow Condition Modeled No. Flash flood hydrograph Sediment Continuity Initial Conditions for Suspended Sediment Yes. Ephemeral stream Time Scale of Hydrograph No. Flash flood conditions Sediment Sources Yes. Bed is primary source of sediment Sediment Calculations Yes. Equilibrium Achieved in Time Step No. Short duration hydrograph Time Step Length Adequate Yes. Scour limited in time steps
No. Inadequate travel time through model No Bridges and Culverts No. Generally the point of investigation Low slope Yes. Single channel No. Braided, avulsive, sheet, distributary Accurate topographic mapping No. Accuracy within prediction range Know sediment size, hydraulic coefficients No. Varies temporally and spatially
Yes.
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VI. River Engineering And Geomorphology For Transportation
DesignC.Sediment Transport Models
2. Sediment Transport Computer Models: HEC-6 ResultsUniform bed elevation changeNo bank erosionNo scour in floodplainDOSChannel pattern adjustmentsAvulsive channel erosionTime scale: poor long-term modeling
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VI. River Engineering And Geomorphology For Transportation
Design
C.Sediment Transport Models
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VI. River Engineering And Geomorphology For Transportation
Design
C.Sediment Transport Models3. Evaluation of results
Sensitivity analysisCalibration and verification
Field data Historical data Comparative cross sections
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VI. River Engineering And Geomorphology For Transportation
DesignC.Sediment Transport Models
4. Application of Sediment Transport Principles:Lane’s Relation
Tool to evaluate / anticipate direction and nature of change from changes in sediment
Q S QS D50
Q = discharge
S = energy slope
QS = sediment discharge
D50 = median sediment diameter
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VI. River Engineering And Geomorphology For Transportation
DesignC.Sediment Transport Models
4. Application of Sediment Transport Equations:Zeller-Fullerton Equation
Tool to evaluate / anticipate direction and nature of change from changes in sediment
Qs = W n1.77 V4.32 G0.45 Y-0.3 D50-0.61
If V increase, Qs ____________
If V decrease, Qs ____________
If n decrease, Qs ____________
If Y increase, Qs _____________
If D50 decrease, Qs ___________