Research Topic Updated on Oct. 9, 2014

Transcription

1 Research Topic Updated on Oct. 9, 204

2 Mixed Cohesive/Non-cohesive Sediments Sedimentation in Estuary: Flocculation Deposition Erosion Transport Consolidation *: It has been recognized that when the fraction of fine-grained sediments is larger than about 0%, a mixture consisting of cohesive and non-cohesive sediments may exhibit cohesive properties. 2

3 Mixed Cohesive/Non-cohesive Sediments -D fractional sediment transport equation Q Q t U x tk tk Ebk Dbk qtlk tk (k=, 2,, N) Q tk E bk D bk β tk U q tlk total-load transport rate of size class k erosion rate deposition rate correction factor flow velocity side inflow of sediment per unit channel length Deposition Rate: D B C bk k sf, k k B a k w sf,k C k channel width deposition probability or adaptation coef. settling velocity section-averaged sediment concentration 3

4 Coefficient α k For non-cohesive sediment, k is the adaptation k coefficient, calculated by /6 a a a exp.5 h h h u sf, k * (Armanini and di Silvio, 988) For cohesive sediment, k is the deposition probability coefficient, which is related to the bed shear stress as / 0 b bd,min bd,max bd,min b bd,min bd,min b bd,max b bd,max 4

5 Settling Velocity w sf,k For cohesive sediment, sf,k is calculated by Wu and Wang s (2004) formula, through which the effect of flocculation is considered K K K K sf d s sa t sf median settling velocity of flocs sd d50 median settling velocity of dispersed particles K d / d K s d Ksa k r.0 50 kc k C 2 n n d r 0 C Cp C C p d 50 medium diameter d r reference diameter, about mm n d coefficient, approximated to.8 C concentration, in kg/m 3 C p sediment concentration at the maximum settling n, r, k, k 2 coefficient, ranging from to 2 n r k coefficient, equal to kc p / k2c p K t kt b / p ktb / p n t n t 2 0 p p k t, n t, n t2 p empirical coefficient threshold bed shear stress at maximum K t 5

6 Erosion Rate E p E * bk bk bk p bk E * bk fraction of the k th size class in the surface layer of bed material potential erosion rate of the k th size class For non-cohesive sediment For cohesive sediment E B Q * k sf, k * bk tk AUtk * b Ebk BM ce n ce critical bed shear stress for surface erosion M erodibility coef., related to bed material properties n coefficient, equal to 2.5 6

7 Critical Bed Shear Stress The incipient motion of non-cohesive sediment is affected by the cohesion if non-cohesive and cohesive sediments coexist in the bed material. ck, n ce p p / p p ck ck, n ce ck, n c c min c max c min p c cmin cmin c cmax c p p p p p p cmax ck,n critical bed shear stress of the size class in the situation where only non-cohesive sediment exists ce critical bed shear stress for cohesive sediment p c fraction of cohesive sediment p cmin minimum fraction of cohesive sediment, below which the critical bed shear stress for non-cohesive sediment is the same as that when no cohesive sediment exists p cmax maximum fraction of cohesive sediment, above which the critical bed shear stress of non-cohesive sediment is equal to that of cohesive sediment k ce0 d0 d ce ce0 d d 0 k, n (Nicholson and O Connor, 986) initial critical bed shear stress initial critical dry bed density dry bed density empirical coefficients n 7

8 Bed Deformation The fractional bed mass deformation rate is determined by M t Then the total rate of change in bed mass is bk M t b which can be converted to the change in bed cross-sectional area: Ab Mb p m t p t Bed Material Sorting s D E s bk bk N k M t ( M p ) M M M p t t t t m bk bk * m b bk m bk bed material porosity 8

9 Consolidation Dry bed density in the first year (Hayter, 983): d d ae pt Dry bed density after year (Lane and Koelzer,953): d d log t d d a,p t Bed Change due to Consolidation: t 0 j dj j dj J J n n n n dj zb, c j j j n j j dj t dry bed density at one-year consolidation time empirical coefficients consolidation time, in hour empirical coefficient consolidation time, in year thickness of the j th layer of bed material dry bed density of the j th layer of bed material 9

10 Mainstream: from a dam at De Pere to Green Bay ( km) Tributary: Lower Fox River East River (joins the Fox River approximately 2 km upstream from the river mouth) Size Classes: Fine ~ mm Medium ~ mm Coarse ~ mm 0

11 -D Simulation in Lower Fox River Flow Discharge at the Dam Sediment Concentration at the Dam Sediment Concentration at the River Mouth (Lin and Wu, 203)

12 Gironde Estuary, France 2

13 Gironde Estuary, France 2-D simulation using FASTER2D (Wu and Wang, 2004) Mesh: Δt=30 min Period: May 9-22, 974 3

14 Tidal Flow in Gironde Estuary, France Flood Tide ws Ebb Tide 4

15 Water Elevation (m) Water Elevation (m) Water Elevation (m) Tidal Level in Gironde Estuary 2 Simulated Measured (a). PK Time (hour) (b). Lamena (c). PK Time (hour) Time (hour) 5

16 Velocity (m/s) Velocity (m/s) Velocity (m/s) Velocity in Gironde Estuary Measured, m below Surface Measured, m above Bed Simulated (a). PK Time (hour) (b). Lamena (c). PK Time (hour) Time (hour) 6

17 Salinity (kg/m 3 ) Salinity (kg/m 3 ) Salinity (kg/m 3 ) Salinity in Gironde Estuary Simulated Measured, m below Surface Measured, m above Bed (a). PK (b). Lamena Time (hour) Time (hour) (c). PK Time (hour) 7

18 US (kg/m 2 s) US (kg/m 2 s) US (kg/m 2 s) Sediment Discharge in Gironde (a). PK Time (hour) 3 (b). PK (c). PK Time (hour) Time (hour) 8

19 San Francisco Bay 9

20 San Francisco Bay Mesh 3-D Simulation using CRESTS3D (Wu and Lin, 20) 20

21 Flow near Golden Gate Bridge 7000 m/s m/s 6000 (a) (b) 5000 Golden Gate Bridge Golden Gate Bridge (m) (m) 2

22 Flow near Port Chicago m/s (a) m/s (b) Port Chicago Port Chicago (m) (m) 22

23 Water Level 23

24 Currents 24

25 Publications Related W. Wu and S. S.Y. Wang (2004). Depth-averaged 2-D calculation of tidal flow, salinity and cohesive sediment transport in estuaries, Int. J. Sediment Research, 9(3), W. Wu and Q. Lin (20). An implicit 3-D finite-volume coastal hydrodynamic model. Proc., 7th Int. Symposium on River, Coastal and Estuarine Morphodynamics, September 6-8, Beijing, China. Q. Lin and W. Wu (203). A one-dimensional model of mixed cohesive and non-cohesive sediment transport in open channels. Journal of Hydraulic Research, IAHR, 5(5), , DOI: 0.080/