21/08/2014. Introduction MSc course Fluvial Systems GEO Fluvial systems. Four scales. Four scales (1) Dr. Maarten G.

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21/08/2014 A B Faculty of Geosciences River and delta morphodynamics Introduction MSc

Kleinhans C D 2 Fluvial systems geomorphology sedimentology / geology engineering in one

culture until you master the language of another (Chaim Potok, Wanderings) 4 Four scales

scales (1) Flow, sediment transport and channel morphodynamics (morphodynamic loop)

1 21/08/2014 A B Faculty of Geosciences River and delta morphodynamics Introduction MSc course Fluvial Systems GEO Dr. Maarten G. Kleinhans C D 2 Fluvial systems geomorphology sedimentology / geology engineering in one course challenge is to communicate 3 You cannot truly cross the borders of your own culture until you master the language of another (Chaim Potok, Wanderings) 4 Four scales Flow, sediment transport and channel morphodynamics (morphodynamic loop) repetition of earlier courses! River patterns Bifurcations and avulsion From source to sink and in between 5 Four scales (1) Flow, sediment transport and channel morphodynamics (morphodynamic loop) steady uniform flow and backwater effect equilibrium sediment transport exner equation required initial / boundary conditions effects of changing boundary conditions and time scale basics of numerical modelling 6 1

2 21/08/2014 The morphodynamic system flow sediment transport morphology also needed: source of flow and sediment initial valley shape vegetation? where it all ends: downstream Four scales (2) River patterns floodplain formation morphodynamic instability bar patterns river patterns underlying physics (sketch) necessary and sufficient boundary conditions effect of changing boundary conditions preservation, sedimentology 7 8 Four scales (3) Bifurcations and avulsion physics of bifurcation stability causes of avulsion accommodation space Four scales (4) From source to sink and in between simple cases: mass conservation sediment budgets and transfer through valleys and multiple basins reconstructing allogenic forcing accommodation space fluvial architecture 9 What is the use of all this? river engineering river management nature restoration geological resources sediments water, oil application to reconstruction predict effects of global change sustainable use of sinking/drowning deltas 11 approach scales logic basic techniques How do this course? didactics explicit clarification of terms play: do yourself discuss and provide constructive criticisms reflection on different disciplinary approaches! (it s one world ) 12 2

3 21/08/2014 Cross-talk: main terminology Morphodynamics: upstream boundary conditions downstream boundary conditions yet another term in the sediment mass balance wash load bed + suspended bed material load Quaternary Geology: climate base level, tides, waves tectonics / subsidence suspended load bed load Course activities Lectures tutorials contribute! discussion, questions, calculations, literature Read many papers Computer practicals to get you started, finish reports at home provides tools for creative programming assignment Delta project turn one delta inside out: explain/understand evolution Assessment The Matrix: matlab code: (1/3 grade) 5% for small exercises 18% for creative exercise also presented in 5 min in ppt The Delta Force: team project (1/3 grade) turn delta inside out presented in powerpoint + abstract individual contributions indicated The Final Frontier: exam (1/3 grade) tests insight Literature and resources Papers Library, course website Slides Course website, make your own notes Matlab instructions matlab help Us, the lecturers matlab code geological and morphological data STUDY the study guide! This lecture: main questions and points main questions help you think answer! your own summary = structure Before lectures: prepare! answer questions about prescribed literature How to read literature? title, abstract figures + captions what are you looking for? write your own papers like this too hints:

4 21/08/2014 Matlab programming build up from simple exercises build tools for data analyses (MSc thesis) building a simple model helps to understand existing complicated models evaluation: works? (does it run) understandable? (comments) does what it has to do? (RTFM) 19 Your creative Matlab project your own creative idea: anything fluvial flow, particles, avalanches, avulsions.. see things as if for the first time and ask the stupid questions analyse and plot (available) data sediment transport / bedforms experimental meandering core data of Rhine-Meuse delta model 1D morphological model (as in Parker E-book) meandering line or 2D cellular braiding Connect other model code/output 20 How conduct an investigation? curiosity question hypothesis method results evaluate hypothesis tell the world new questions 21/26 How to make a ppt presentation? structure question, hypothesis, methods, results, discussion, conclusion kill your darlings main message? elevator pitch figures not (much) words yet keep core of creative idea! simple language practice 22 Delta project Present delta project Choice from some well-documented deltas unravel causes and evolution: mechanisms avulsion / mouth bar formation subsidence, peat boundary conditions wash load base level rise how representative for other deltas in record wave/tide/fluvial dominated 23 As in scientific conference: On the basis of sound research (not armwaving, not guessing) 2 page referenced abstract with figures (densely written because scientists are busy) Brief presentation 24 4

however complicated a system, it must adhere to the laws of physics e.g.

climate, setting such as North Sea basin forcings as explanations type locations as helpful tools in reconstruction 26 Mechanistic explanation (Machamer, Darden, Craver,

key to researchable question: unpeel your question!

as it is now) 27/26 28 Scales and explanatory elements explanation: scale: 1. river channel, river reach 2. river pattern, channel belt 3. fluvial plain, river displacement 4.

5 abduction 21/08/2014 Twisting the lion s tail 25 Physics and stamp collecting however complicated a system, it must adhere to the laws of physics e.g. mass conservation Physics lead to fantastic patterns mechanisms as explanations typical cases/classes as helpful tools Boundary / initial conditions also cause patterns e.g. climate, setting such as North Sea basin forcings as explanations type locations as helpful tools in reconstruction 26 Mechanistic explanation (Machamer, Darden, Craver, Philosophy of Science 2000) reduce a phenomenon to the workings of the underlying mechanisms examples: role of egg in pancakes why can we preserve food by salting or cooling? key to researchable question: unpeel your question! Logic laws / generalisations major premises mechanisms causes / minor premises / initial and boundary conditions (the world as it was) effects / consequent outcome (the world as it is now) 27/26 28 Scales and explanatory elements explanation: scale: 1. river channel, river reach 2. river pattern, channel belt 3. fluvial plain, river displacement 4. valley, delta mechanisms generalisations causes flow, sediment transport bar formation, floodplain formation constitutive (empirical) relations channel pattern diagrams bifurcation stability avulsion cycles subsidence, peat formation Wave/tide/fluvial dominated delta shapes required boundary conditions necessary conditions incl. hinterland boundary conditions, climate, base level Climate, tectonics 29 Now what? Collect + study indicated literature quick repetition flow, sed tr and morph learn matlab new material, new combinations of approaches first matlab project, then delta project professional scientific discourse scientific presentations exam: insight, combination, case? 30 5

8/21/2014 Faculty of Geosciences River and delta morphodynamics Flow, sediment transport and morphological change MSc course Fluvial Systems GEO4-4436 Dr. Maarten G.

6 8/21/2014 Faculty of Geosciences River and delta morphodynamics Flow, sediment transport and morphological change MSc course Fluvial Systems GEO Dr. Maarten G. Kleinhans This lecture: main questions and points quick review of basic concepts and equations for flow sediment transport morphology What are physical concepts behind the equations? Sediment transport is nonlinear function of flow force so what? 2 Position of this lecture in the course Flow, sediment transport and channel morphodynamics River patterns Bifurcations and avulsion From source to sink and in between Cross-talk: main terminology Morphodynamics: upstream boundary conditions downstream boundary conditions yet another term in the sediment mass balance wash load Quaternary Geology: climate base level tectonics / subsidence suspended load 3 bed + suspended bed material load bed load 4 The morphodynamic system flow sediment transport morphology Fluid mechanics Hydraulic roughness Bedforms Some essential review of knowledge: Remember 3 rd years course? Sediment transport Hydraulic geometry Bars, bends, islands Overbank sedimentation Channel patterns vegetation 5 1. Flow: essential fluid mechanics Steady uniform flow (normal flow) steady 1. Flow strength parameters 2. Turbulent flow uniform Steady nonuniform flow 3. Sub- and supercritical flow 4. Backwater effect u 0 x u 0 t u 0 x 6 1

8/21/2014 Big Questions about Flow How do we describe flow strength? Why would flow be nonuniform? What determines flow resistance? How account for complications of turbulence?

many different symbols in use! 7 8 Subcritical Supercritical slow downstream control Fr<1 fast no downstr. control Fr>1 Fr u gh c gh Rivers?

7 8/21/2014 Big Questions about Flow How do we describe flow strength? Why would flow be nonuniform? What determines flow resistance? How account for complications of turbulence? Flow strength parameters u = flow velocity (averaged over depth h) Q = flow discharge:q = uhw = ua τ = flow shear stress: τ = ρghs S = gradient, ρ = fluid density (00kg/m 3 ) ω = stream power: ω = τu many different symbols in use! 7 8 Subcritical Supercritical slow downstream control Fr<1 fast no downstr. control Fr>1 Fr u gh c gh Rivers? 9 9/32 Bodewes & Leuven (2012), based on dataset Kleinhans Backwater effect subcritical flow: downstream roughness affects upstream flow (e.g. dams, vegetation) upstream distance over which water depth is affected: adaptation length Turbulence Self-generated resistance of flow (at boundaries) S,i h BW 63% BW : 63% adaptation h 3S 11 Reynolds number uh ud Re, Re laminar < 500 turbulent >

8 8/21/2014 Effect of turbulence vertical flow velocity gradient: logaritmic profile du dz u* z Flow velocity over depth 0 1 with shear velocity u* ( ms ) du u* Integration of gives : u dz z u* for uz 0 c ln z0 z u* ln z c u z u* ln z z 0 13 constant of von Kármán u How to deal with turbulence? Turbulence is very complicated and far from solved use semi-empirical equations 8gRS f Wh R W 2h 8 f empirical u grs Darcy-Weisbach law Friction I friction scales with R and roughness length k s 8 R 5.74log log f k s k 1D,1D, 2.5D up to 3D s 65 Semi-empirical formula R k s Note: [m/s]/([m/s 2 ][m][m/m]) 0.5 dimensional homogeneity Friction II Use the log-profile to get the friction law Roughness hydraulic roughness + obstruction = flow resistance u * uz ln u * 33R u * 12.14R u ln ln ek k u* u 18log z z 0 s given u u at z grs and ln 12R ks z s x R e log log x e RS and C 18log and k 33z s 12R ks 0 17 form friction + skin friction = total friction Bedforms Vegetation Engineering structures grains 18 3

Percent Finer 8/21/2014 Vegetation well-submerged vegetation submerged veg with through-flow Steady uniform flow shear: τ =

0.5 = [m 0.5 /s] Thus not dimensionally correct 19 20 2. Sediment transport Water flow results in sediment transport! 1. Sediments 2.

cum. freq.: 0 90 80 70 60 50 40 30 20 0 Sample Grain Size Distribution (with Extrapolation) D 90 = 0.700 mm D 50 = 0.

01 0.1 1 Grain Size mm Ways to measure: sieving, settling tube, lasers Best method depends on application D x is size such

height Mean and Standard deviation Skewness/Kurtosis 22 Sediment transport Flow energy, τ = τ +τ The beginning of motion

9 Percent Finer 8/21/2014 Vegetation well-submerged vegetation submerged veg with through-flow Steady uniform flow shear: τ = ρgrs and C RS u 2 u g C Turbulence is accounted for by: 12R C 18log k s through-flowed vegetation Note: [C]=[m/s]/([m][m/m]) 0.5 = [m 0.5 /s] Thus not dimensionally correct Sediment transport Water flow results in sediment transport! 1. Sediments 2. Bedload sediment transport 3. Suspended sediment transport 4. Washload 21 Sediments For example plot grain size against rel. cum. freq.: Sample Grain Size Distribution (with Extrapolation) D 90 = mm D 50 = mm Grain Size mm Ways to measure: sieving, settling tube, lasers Best method depends on application D x is size such that x percent of the sample is finer than D x Characteristics of sediment: Examples: D 50 = median size D 90 ~ roughness height Mean and Standard deviation Skewness/Kurtosis 22 Sediment transport Flow energy, τ = τ +τ The beginning of motion Shields (1936) curve dissipated by bedforms sediment transport We use: k s grain related roughness (skin friction) C grain related Chezy τ grain related shear stress θ grain related shields number 23 ' u * note : s ' gd 50 u * D Re* 24 4

8/21/2014 Bedload transport q b = c δ (c=celerity, δ=layer thickness) c depends on u* ~ τ 1/2 δ is related to τ So: q b = f(τ 3/2 ) Include treshold for motion: q b = f(τ -τ c ) 3/2 Bedload transport

calibrated for limited sets of conditions 26 Bedload transport Plot sediment transport against shields: Up to power 16 Suspended sediment transport Bagnold (1966) Van Rijn (1984) depends on sediment

10 8/21/2014 Bedload transport q b = c δ (c=celerity, δ=layer thickness) c depends on u* ~ τ 1/2 δ is related to τ So: q b = f(τ 3/2 ) Include treshold for motion: q b = f(τ -τ c ) 3/2 Bedload transport Many (semi) empirical forms: MPM Ribberink Parker Van Rijn general form Make dimensionless: φ b = f(θ -θ c ) 3/2 φ = dimensionless transport rate θ = dimensionless shear stress (skin friction) 25 calibrated for limited sets of conditions 26 Bedload transport Plot sediment transport against shields: Up to power 16 Suspended sediment transport Bagnold (1966) Van Rijn (1984) depends on sediment characteristics and flow shear stress to the power of 1.5 sediment transport is more nonlinear near beginning of motion total load predictor: Engelund and Hansen (1967) Washload transport (Almost) no exchange between bed and suspended sediment Limited by the amount of upstream supply Nonlinear q b = f(u 3 ) Why? Remember τ = Nonlinearity of sediment transport 29 29/4 Now: Why do rivers exist at all? 30 5

8/21/2014 Big Questions about Bedforms How

30 m Dunes Ripples on top of dunes 33 Best

ripples current dunes upper stage plane bed

11 8/21/2014 Big Questions about Bedforms How do we know which bedform is stable? When are bedforms in equillibrium? Are they in nature? Bedforms Sediment transport bedforms organised sediment transport and bedform friction 1. Bedform types 2. Bedform stability 3. Bedform dynamics Kleinhans (2002) Bedforms Dunes in Parana river phenomenon at boundary between two materials with different physical properties in transport 30 m Dunes Ripples on top of dunes 33 Best (2005) Parsons 34 34/41 Bedforms and bed states subcritical flow (Fr<0.8) lower stage plane bed (no motion) current ripples current dunes upper stage plane bed (sheet flow) Fr u gh Fr 1 1 Dunes and Antidunes supercritical flow (Fr>1) upper flow regime plane bed standing waves antidunes: migrate against the flow /41 6

duneheight (m) wavelength (m) 8/21/2014 Bedform stability (Van den Berg & van Gelder, 1993) Emperical Diagram 2 u ' 2 C' s 1D k ' 3D k ' D s 2 D* D50 12h C' 18log k ' s s 90 90 s 50 ( sand) ( gravel)

12 duneheight (m) wavelength (m) 8/21/2014 Bedform stability (Van den Berg & van Gelder, 1993) Emperical Diagram 2 u ' 2 C' s 1D k ' 3D k ' D s 2 D* D50 12h C' 18log k ' s s s 50 ( sand) ( gravel) 1 3 g Temp upper flow plane bed Bedform stability Lines are not hard tresholds, but gradual transitions Physically based diagram Bedforms depend on flow and sediment transport rate+mode Note: bedforms are often in disequilibrium because Fr>1!! Rivers during bankfull conditions Dune tracking Migration of dunes = sediment transport Can be measured by dune tracking: 1 q b 2 c Deviation from a triangle! Calibration in practice: q b c with Dunamics Dune length increases during and after flood: Dune height shows hysteresis during a flood: Discharge (m^3/s) flood 1982 flood 1988 flood 1995 flood Wilbers Discharge (m^3/s) flood 1982 flood 1988 flood 1995 flood Prediction of duneheight Different Equilibrium predictors: f (h,τ,d), e.g. D h h T 1 e 25 T / / cr 7.3h with T / cr van Rijn (1984) Julien & Klaassen (1995) Relaxation with adaptation time scale D h h 0.5 TvR t 1 / Teqtime e t t1, t t1 Note: Bedforms are often NOT in equilibrium! 7

8/21/2014 Bedforms? equilibrium form determined by particle size (Bonnefille number) mobility (Shields number) flow regime (Froude number) Morphodynamics uniform steady sediment transport no change!

model morphodynamics? How do rivers respond to changing boundary conditions? What are models (not) good at?

13 8/21/2014 Bedforms? equilibrium form determined by particle size (Bonnefille number) mobility (Shields number) flow regime (Froude number) Morphodynamics uniform steady sediment transport no change! needs gradient in sediment transport to change morphology in nature often not in equilibrium relaxed adaptation Modelling: big Questions How are flow, sed transp and mass conservation combined to model morphodynamics? How do rivers respond to changing boundary conditions? What are models (not) good at? 45 Sediment continuity / mass conservation Storage = Flux in Flux out 1 storage p 1 p bed level change t qb - t x transport gradient (out-in) q b,in q x b,out = porosity = bed level q b = transport rate t = time x = location This is the Exner equation Used in modeling/to predict changes in morphology 46 Equilibrium? water depth h 0 grain flow thickness h g slope i When IN = OUT YES!! So when the slope remains exactly the same discharge and sediment feeder sediment bed Model the morphodynamic system flow sediment transport Introduction Hydraulic roughness and bedforms Sediment transport First 1D modelling, then 3D modelling 47 morphology Hydraulic geometry Bars, bends, islands Overbank sedimentation Channel patterns vegetation 48 8

14 8/21/2014 1D modelling 1. Equations needed 2. Input values needed 3. Model 4. Case study: terrace crossing Q,W S u(x), h(x) Input values k s Specification of flow: h 49 Q b,s S S(x), (x) Specification of sediment transport: D 50, D 90, bed porosity: λ 50 Q, H, z Information propagation Numerics step by step direction of influence water level in upstream direction sediment in downstream direction boundaries see Parker e-book chapter 20 AgDegBW 51 Morphological change General rate of change: Think about gradients! 1. Exner: /t~q b /x 2. So after sudden change, gradient (and thus q b /x) is large 3. Therefore morph change fast 4. But then gradient decreases and morph change less fast 5. (t) = equil +/- e -t 6. Exponential decrease or increase with representative T: parameter Case study Netherlands, river Rhine Holocene sea level rise reduced supply of upstream sediment Result: In the downstream part: sedimentation (layercake) In the upstream part: incision (formation terraces) In between: terrace crossing T ~63 % of change accomplished at T time

time scale of phenomenon 8/21/2014 Simple model result elucidates Compare with reality 55 56 Modelling philosophy (1) models not good at details in

et al. 1994) so, models rarely predict well without calibration how much of physics-based explanation in calibration?

billion years million years 00 years year minute noise turbulence forcing boundary condition earthquake formation of solar system plate tectonics,

meandering, coastal erosion coastal dunefields ripples, dunes meteorite impact 1 cm 1 m 1 km 00 km million km length scale of phenomenon noise 59

15 time scale of phenomenon 8/21/2014 Simple model result elucidates Compare with reality Modelling philosophy (1) models not good at details in reality must be specified in initial/boundary conditions given uncertainty in both initial conditions and laws: models cannot be verified (Oreskes et al. 1994) so, models rarely predict well without calibration how much of physics-based explanation in calibration? Spitsbergen, Svalbard, see Process, noise or boundary condition? billion years million years 00 years year minute noise turbulence forcing boundary condition earthquake formation of solar system plate tectonics, mantle convection delta formation glacials and interglacials river terrace forming ocean circulation El Nino and storm events: La Nina river meandering, coastal erosion coastal dunefields ripples, dunes meteorite impact 1 cm 1 m 1 km 00 km million km length scale of phenomenon noise 59 Modelling philosophy (2) models good at trends and behaviour! comprehend results of complicated set of equations manipulation: sensitivity to parameters run scenarios for certain changes mediate between theory (laws of physics) and nature 60

16 8/21/2014 Application build a simple model in matlab use (your own) model for delta project understand modellers in practice approach and value uncertainties initial and boundary conditions numerics 11

What? River response to base level rise. The morphodynamic system. Why? Channel-forming discharge. Flow. u = What s in a name. Flow Sediment transport

What? River response to base level rise. The morphodynamic system. Why? Channel-forming discharge. Flow. u = What s in a name. Flow Sediment transport River response to base level rise and other boundary conditions Dr. Maarten Kleinhans Summer course climate change and fluvial systems Course materials of Prof. Gary Parker Flow Sediment transport What?