VI. 1 VI. River Engineering And Geomorphology For Transportation Design

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VI. River Engineering And Geomorphology For Transportation

Design

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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

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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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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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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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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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Design

B.6. Flash Floods Time to Peak Recession Time Transportation Issues:

Response TimeObservation of Floods Interruption TimeRisk

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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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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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Design

C.Sediment Transport Models

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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 ___________