S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment...
-
Upload
gwenda-sanders -
Category
Documents
-
view
218 -
download
0
Transcript of S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment...
![Page 1: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/1.jpg)
S.A. Talke , H.E. de Swart, H.M. Schuttelaars
Feedback between residual circulations and sediment distribution in highly turbid
estuaries: an analytical model
Netherlands
![Page 2: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/2.jpg)
•Observation: Some estuaries have extremely high suspended sediment concentrations and fluid mud layers at their Estuarine Turbidity Maximum
•We present a simple model to explain how turbidity currents affect the longitudinal distribution of suspended sediment
Overview
![Page 3: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/3.jpg)
Observationsof Ems Estuary
Ems Estuary
Amsterdam
Utrecht
~350 km
Germany
Netherlands
0 km 45 km
100 km(Tidal Weir)
Longitudinal Survey
![Page 4: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/4.jpg)
Variations in sediment concentration huge(!) along longitudinal axisvariation from < 100 mg/L (marine) to > 10 g/L (brackish)
Thus, longitudinal distribution of sediment concentration affects density gradients
Sediment Concentrations
Low Flow Conditions
Q ~ 20 m3/s
![Page 5: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/5.jpg)
Distance from N. Sea (km)
Large salinity and turbidity gradients in longitudinal direction
Gradients oppose each other downstream of ETM
Gradients in same direction upstream of ETM
UpstreamDownstream
Q=35 m3/s
What controls shape,extent and position of ETM?
Longitudinal Distribution of Turbidity and Salinity
![Page 6: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/6.jpg)
Development of a simple model(1) Assumptions
Non-cohesive, fine grained sediments
Constant settling velocity
Constant Eddy viscosity and diffusivity
Salinity well mixed
Constant Width
Constant Depth
<Tidally Averaged>
![Page 7: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/7.jpg)
Development of a simple model(2) Gravitational Circulation
Z
X
Sea River
Essentially, gravitational circulation reproduced with a convergence zone
z
uA
zx
pz0 g
z
p
H
QubdzCso (1) (2) (4)(3)
Longitudinal Salinity Profile
![Page 8: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/8.jpg)
Development of a simple model(3) Add sediment dynamics
z
uA
zx
pz0 g
z
p
H
Qubdz
Z
X
Sea River
(1) (2) (4)(3)
•Vertically integrated flux of sediment vanishes during equilibrium conditions
H
dzx
CKuC 0(6)
MorphodynamicEquilibrium
(5) 0)(
z
CKCw
z zs
Solution now closed to arbitrary constant, c*
c* is total integrated
bottom sediment
Cso
Data Points
CTD Profile
Exponential Profile
![Page 9: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/9.jpg)
Model Sensitivity StudyParameters
Z
X
Model shows that distribution of sediment sensitive to these parameters
Ws = 1 mm/s
Av = 0.001 m2/s
Q= 15 m3/sq= 0.03 m2/sH = 7 m
C* = 2 g/L
K = 100 m2/s
![Page 10: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/10.jpg)
As reference concentration is increased, Longitudinal spread of ETM increasesLocation of ETM stays the same!
At ETM, dc/dx is zero. Thus, location set bythe balance between freshwater flow and salinity
Morphodynamic Equilibrium
![Page 11: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/11.jpg)
Morphodynamic Equilibrium
Example forHigh sedimentConcentration
c*= 200 g/ls* = 12 psu
Gravitational Circulation
Turbidity Circulation
Combined Circulation
Velocity structure:Reduced residual circulation downstream: Maximum turbidity currents and salinity currents occur at the same (downstream) location Turbidity currents zero at maximumpersistent near-bottom upstream flow of > 2 mm/s
> 200 m per day!
![Page 12: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/12.jpg)
Three Basic Conditions predicted by model:Low Flow Sediment concentration largest at upstream boundaryIntermediate FlowETM forms with asymmetric profileHigh Flow Sediment is flushed out of estuary
Affect of varying freshwater flow, q
Morphodynamic Equilibrium
![Page 13: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/13.jpg)
Morphodynamic Equilibrium
As the eddy viscosity is increased, the ETM moves downstream
Affect of varyingeddy viscosity and diffusivity
![Page 14: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/14.jpg)
Morphodynamic Equilibrium
As depth is increased, the ETM moves upstream asymmetry of ETM shape enhanced
Affect of varying depth
![Page 15: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/15.jpg)
High Sediment concentration Less vertical mixing (50%)
ETM moves upstream Higher Concentration causes larger upstream spread
Increased depth ETM moves upstream
Conceptual Model for theeffect of deepening a river(low flow conditions) H= 5m
(1980, Ems)
H=7 m(2005, Ems)
Dredging Scenario
![Page 16: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/16.jpg)
Discussion
• Recall longitudinal transect of sediment concentration
Consistent with model for low flow conditions!– Sediment piles up at
Tidal weir
![Page 17: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/17.jpg)
Discussion
• No feedback between salinity field and turbidity currents
• Tidally varying processes not included– Literature and measurements show this to be
important
![Page 18: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/18.jpg)
Sediment Concentration at a cross section
Strong variation in sediment concentration w.r.t. tidal phase
![Page 19: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/19.jpg)
Cross Sectional Measurements
Salinity over a tide
Salinity 3ppt less atbottom thanmiddle of water column!
During flood, salty clean water is moved over fresh, muddy waterIn upper layer, ‘normal’ salinity stratification (interaction in lateral direction?)
Complex, tidally varying mixing and residual circulation
Conventionalstratification
![Page 20: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/20.jpg)
Conclusions
• Longitudinal gradients of both sediment concentration and salinity drive tidally-averaged circulation
• Large Sediment concentrations result in an increased upstream extent of turbid zone
• The upstream migration of ETM in Ems is likely both due to increased water depth and reduced mixing due to high sediment concentrations
![Page 21: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/21.jpg)
![Page 22: S.A. Talke, H.E. de Swart, H.M. Schuttelaars Feedback between residual circulations and sediment distribution in highly turbid estuaries: an analytical.](https://reader035.fdocuments.us/reader035/viewer/2022081516/56649f415503460f94c607f0/html5/thumbnails/22.jpg)