Hans Burchard

Leibniz Institute for Baltic Sea Research Warnemünde

hans.burchard@io-warnemuende.de

Coastal Ocean Dynamics

Seventh course: Estuarine Dynamics

The principle of estuarine circulation

MacCready and Geyer (2010)

Knudsen formula of 1900

s=0Volume conservation:

Salt conservation: 0

Analytical solution for estuarine circulationBalance between pressure gradient and friction:

.

With

we obtain the analytical solution:

.

Example solution

Tidal straining

after flood

after ebb

MacCready and Geyer (2010) after Simpson et al. (1990)

MacCready & Geyer (2010) after Jay & Musiak (1994)

Estuarine circulation due to tidal straining

75% level

75% level

Result:Tidal straining makes about 2/3 of estuarine circulation.

With full-scale 1Dmodel (GOTM, www.gotm.net):Gravitational circulation and tidal straining profilescan be decomposed.

Burchard and Hetland (JPO 2010)

Estuarine circ.Straining

Gravitational

Simple model simulations of estuarine circulation

under tidally energetic conditions

MacCready & Geyer (2010)

Lateral circulation in tidal estuaries

Flood currents are faster in the deep channel such that salinity becomes higher in the channel centre than at the sides. This lateral density gradient then causes lateral circulation. Ebb is

vice versa.

Nunes & Simpson (1985)

Floating material collected at tidal front during flood

(Conwy River, Wales, UK)

MacCready & Geyer (2010)

Estuarine circulation due to lateral circulation

During flood high (positive) surface momentum is vertically transported to the near bed region. During ebb, relatively high

(negative, but less negative than in channel centre) is transported from the sides to the central near-bed region. This

both supports estuarine circulation.

Enhancement of estuarine circulation in channelised tidal flow

(2D slice modelling with GETM)

Burchard et al. (JPO 2011)

www.getm

.eu

Circulation in transverse estuary

Transverse structure of estuarine circulation

Burchard et al. (JPO 2011)

Tidal straining circulation Gravitational circulation

Advective circulation Barotropic circulation

Estuarinecirculationdrives SPMfluxes

Estuarine circulation drives SPM fluxes

Observations in the Elbe estuary:

Kappenberg et al. (1995)

Generation of estuarine turbidity maxima (ETMs)

Sediment accumulation

Consequences of estuarine circulationon sediment transport

ETM

ETM = estuarine turbidity maximum

Jay and Musiak (1994)

Modelling (2DV) ETM formation

Burchard and Baumert (1998)

The lower Elbe River

Observations of ETM in lower Elbe River

Salinity (g/kg)

Run-off Neu-Darchau = 707 m3/s

Courtesy Jens Kappenberg

Modelling (3D) ETM formation

Burchard et al. (2004)

ebb tide

flood tide

low water

high water

Ems as hyperturbid estuary

Talke et al. (2009)

Is there a positive feedback loop in estuarie?

Winterwerp, 2013

What happened to the Ems estuary?

Pers. Comm. Henk Schuttelaars, 2013

Winterwerp, 2013

Elbe