INCORPORATING STREAMBED ROUGHNESS AND CAVITY SHAPE

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Oliver Mills
5 years ago
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Tracie Jackson Roy Haggerty Sourabh Apte Ben O Connor ater

1 A MAN RSIDNC TIM RATIONSHIP FOR ATRA CAVITIS IN GRAV-BD RIVRS AND STRAMS: INCORPORATING STRAMBD ROGHNSS AND CAVITY SHAP Tracie Jackson Roy Haggerty Sourabh Apte Ben O Connor ater Resources ngineering Program Oregon State niversity Jackson et al. [2013 RR]

2 Surface Transient Storage STS is the short-term storage of solutes and suspended particulates in recirculating flow in the stream channel. Functional significance: Refugia for aquatic communities Improves water quality Source: O Connor et al. (2010)

3 Motivation Accurate estimates of mass-exchange parameters in TS zones needed to better understand and quantify solute transport and dispersion in riverine systems. Shear layer ith arge-scale Coherent Structures Primary Gyre d d c Secondary Gyres B Main Channel ateral Cavity

4 Motivation To date an accurate and reliable MRT relationship quantifying mass exchange in lateral cavities has not been identified: τ = d kd c Shear layer ith arge-scale Coherent Structures d d c Primary Gyre Secondary Gyres B Main Channel ateral Cavity

5 Motivation Variance in k may be reduced if include effect of bed roughness and cavity shape. τ = d kd c Shear layer ith arge-scale Coherent Structures d d c Primary Gyre Secondary Gyres B Main Channel ateral Cavity

6 Study Objective To present 2 MRT relationships for lateral cavities in natural rivers and streams that incorporate streambed roughness and shape. Relationships developed using dimensional analysis and verified through comparison to previous laboratory and field studies.

7 Dimensional Analysis MRT can depend on following parameters: Buckingham Pi Theorem: ) ( * 1 c d d g u f υ τ = = d u gd d d d f c c * 1 υ τ

8 Dimensional Analysis MRT can depend on following parameters: τ = f ( u g υ * d d 1 c ) Buckingham Pi Theorem: τ 1 = f d d Fr u c * Re d c Geometric Ratios Hydraulic Quantities Roughness Factor Shape Factor

9 τ1 = d υ 0.15 gd 0.56 d 3/ 2 3/ 2 c 2 d 0. 44

10 21 0. * / 2 3/ = u d d gd d c υ τ

11 Significance Tools hydrologists and water managers can use to predict conservative solute transport in natural systems with lateral cavities over a range of geometry (0.2 < / < 0.75) complex shapes roughness and flow conditions ( < Re < ). Few field-measureable parameters (i.e. d d c n R d 50 ) xamples: Solute Transport: predict solute MRT in lateral cavities within natural streams and rivers. Stream Restoration: estimate MRT of in-stream structures emplaced to enhance stream biodiversity.

12 Considerations & Future ork 3 key considerations when using relationships: 1) Derived for gravel-bed systems: May or may not hold for substrates other than gravel or heavily vegetated systems. 2) Channel roughness could be more significant than observed if roughness parameters are measured in cavity vicinity. More detailed data of roughness parameters near shear layer needed to fully test hypothesis. 3) Relationship derived and tested for conservative solutes. Additional term(s) needed (e.g. retention factor) to account for nonconservative solutes.

13 Conclusions MRT relationships for lateral cavities in natural gravel-bed streams and rivers can be computed from 6 nondimensional groups: Fr Re / d c /d Shape factor Roughness factor 2 empirical MRT relationships formulated. Relationships valid for conservative tracers within a range of geometry (0.2 < / < 0.75) and flow conditions ( < Re < ).

14 Questions? Questions? Ducks?

15 Roughness Parameters u = * τ 0 / ρ τ = 0 ρgrs f S f = n 2 2 / R 4 / 3 Shear velocity: u * 2 2 1/ 3 = gn R Chen and Cotton [1988] method (shallow flow < 1 m): n = 1/ 6 ( R / ) log( R / d 50 ) Henderson [1966] method (deeper flow > 1 m): n = 0.034(3.28d 1/ 6 50 )

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