The impact of tidal pumping,

turbidity maxima, density

gradients on sediment

retention in estuaries

Dr Gerardo M. E. PerilloInstituto Argentino de Oceanografía

Departamento de Geología - UNS

Where sediment is trapped

• Estuarine deltas (head, tidal, tributarymouths)

• Inner wetlands (mangroves, marshes,tidal flats)

• Point and interchannel bars

• Other geomorphologic andhydrodynamic induced traps

• Artificial structures (harbours, jetties,etc.)

What traps sediment

• General and local geomorphology

• General and local sediment inputs

• Within-estuary tidal range gradients

• Tidal pumping

• Turbidity maxima

• Vertical and longitudinal density gradients

• Coastal dynamics

• Climate dynamics

• Events

• Biological interactions

However!!!!

• Sediment and water input from rivers

– What happens with dams and watershed

retention??

– How much sediment is retained in lower

catchment (below the last gaging station)

• Sediment input from the sea

– Barrier effects (i.e., tidal deltas, barriers)

Lack of input implies internal erosion and

sediment export

• Ratio ocean vs

continental E.

• Sediment input

• Coastal stability

• Climatic regions

0 2 64

Deltasfluviales

Barreras

Deltas ddemarea

Bocas demarea

Bancosalineados

Planicies de marea

Marismas

Micromarea l Mesomarea l Macromareal

Amplitud de marea (m)

-59 -58 -57 -56 -55

Longitud

-36

-35

La

titu

d

10

8

6

8 2030

35

20

25

20

30

40

50 55

20

15

10

8

6

10

10

8

15 20

25

15

6

25

U R U G U A Y

A R G E N T I N A

MontevideoBuenosAires

La Plata

Colonia del Sacramento

Pir

iápo

lis

P. d

el E

ste

P. Rasa

P. Piedras

P. T

igre

Canal M

arítimo

Banco

Ro u

en

Bar

ra d

el In

dio

BancoArquímedes

Banco Inglés

Canal Oriental

Bahía deSamborombón

Antico, 2002

Antico, 2002

0.E+00

1.E-04

2.E-04

3.E-04

4.E-04

5.E-04

6.E-04

7.E-04

8.E-04

0 50 100 150 200 250 300

x ( km )

Gx

( m

2 s-3 )

Gx media

Gx máxima

Gx máxima - Gx media

0 20 40 60 80Distance from head (km)

0

4

8

12

16

Gx/G

0

ENERGY DISSIPATION

Río de la Plata – Antico, 2002

Bahía Blanca Est.

Perillo & Piccolo, 1991

TIDAL ASYMMETRY

Fluvial effect on the tidal

range.

- Increase inland

- Changes in tidal asymmetry

- Potential sediment outflow

Kimmerer WJ. 2004.

http://repositories.cdlib.org/jmie/sfews/vol2/iss1/art1

San Francisco Bay

Headward influence increase

A.D. Heap et al. /

Sedimentary

Geology 168 (2004)

1–17

A.D. Heap et al. /

Sedimentary

Geology 168 (2004)

1–17

J.O. Blanton et al. / Estuarine, Coastal and Shelf Science 57 (2003) 993–1006

Wurpts, 2006

SALT WEDGE (A)

FJORD

PARTLY MIXED (B)

VERTICALLY HOMOGENEOUS

Residual Fluxes

Interaction with

• Estuarine Geomorphology

• Density gradients

• Wind

• Freshwater discharge

uL = uS + uE

Lagrangean Flux = Stokes Drift + Eulerian Flux

Stokes Drift (uS)

• Interaction between the partly

progressive tidal wave and the

topography

• Headward

• Associated to Tidal Pumping

uAu

AS=< >

< >

~~

Eulerian Flux (uE)• Response to the set up induced by the

tidal pumping

• By continuity generates seaward flow

<QE> = -<QS> uE = <Au>/<A>

• Valid for steady state

• Without river discharge

Lagrangean Flux (uL)

• Transport due to density gradient

uL= <Qvt>/<A>

• River runoff (uf)

uf= <Qf>/<A> <Qf>=R

uL = uf

In steady state, near the head

Residual Flux Calculation

Datos Ui,j,k ; Si,j,k ; Ci,j,k ; Ai,j,k

Donde i = total # of levels …. I ; j = total # of columns…. J; k = time k = 0, 1, …, n k = T

F uCdA=

F IJUCA J A u c I A u c Fvtk i i

i

j j

j

= + + +• • • •

*

Where

FL = FTP + FVS + FTS + F*

F A u s

F A u s

vs i i

i

ts j j

j

=

=

• •

• •

F Q C

F QC

L

TP

=< >< >

=< >~

CONCLUSIONS

• Hydraulic processes are key to

sediment retention/export in estuaries

• Geomorphology is as or more

important

• Some processes have been considered

only for the whole system or in

individual portions of some estuaries