Long-term evolution of estuaries and tidal-basins
Conclusions
• Tidal inlets only persist when there is river inflow.
• Estuaries can develop a stable configuration wherein sediment input equals sediment output.
• Tidal basins are unstable landforms that fill and close over time. They initially aggrade with sand and later with mud, which is trapped by vegetation.
Faculty of Geosciences
Research group River and delta morphodynamics
Long-term evolution of estuaries and tidal basins:
lessons from the Holocene evolution of the Dutch coast
Tjalling de Haas 1,P , Harm Jan Pierik 1 , & Maarten G. Kleinhans 1
1) Utrecht University, Faculty of Geosciences, Department of Physical Geography, Utrecht, The Netherlands. P) Presenting author, t.dehaas@uu.nl
Objectives
We review the Holocene evolution of the Dutch coast, focussing on the long-term evolution of estuaries and tidal basins (Fig. 1), to answer the following questions:
• How do rivers influence the long-term evolution of estuaries and tidal basins?
• Are estuaries and tidal basins stable, persisting, landforms over long time-scales?
Holocene coastal evolution
Why are tidal basins unstable?
Estuaries and tidal basins in the subsurface
Tjalling de Haas
Fig. 3) Longshore time diagram of coastal plain development, extended from Pierik et al. (In prep.).
Fig. 1: Paleogeographical maps of the Holocene evolution of the Dutch coast (Vos, 2015).
Fig. 4) Tidal basin evolution. (I) Ini- tial stage: infilling with sand by tidal asymmetry and formation of shoals until dynamic equilibrium occurs. (II) Mature stage: infilling of mud by lag effects and vegetation dynamics re- sult in growth of supratidal area and reduction of intertidal shoal area, restoring the tidal wave asymmetry.
This feedback eventually results in closure of the basin. Extended from
Van den Berg et al. ( 1996). References: (1) Pierik, H., Cohen, K., Vos, P., van der Spek, A., Stouthamer, E., In prep. Late Holocene coastal plain evolution of the Netherlands: human-induced transgression and its interaction with initial conditions.
Geomorphology. (2) Van den Berg, J. H., Jeuken, C. J., Van der Spek, A. J., 1996. Hydraulic processes acting the morphology and evolution of the Westerschelde estuary. In: Estuarine Shores: Evolution, Environments and Human Alterations. John Wiley & Sons. (3) Vos, P., 2015. Origin of the dutch coastal landscape. Ph.D. thesis, Utrecht University.
Fig. 2) (a) Oer-IJ estuary. (b) Hun- ze estuary. (c) Rijswijk-Zoeter- meer tidal sytem.
(d) Remnants of tidal channels and creeks in Walcheren. (e) Remnants of tid- al channels of the Bergen inlet sys- tem. Elevation in m O.D., north is up in all panels.
Source: AHN.
1. Transgression 2. Stabilization 3. Closure
4. Ingression
Tidal inlets:
- remain open in the presence of a river!
- close in the absence of a river!
tidal wave
asymmetry formation
of shoals
lag
effects growth of
supratidal areas
colonization by
vegetation stabilization/growth
supratidal areas dominant
mechanism morphological
mechanism stage
I
II
11000 BP 7500 BP 6000 BP
5000 BP 3500 BP 2500 BP
1900 BP 1200 BP 500 BP
150 BP
! (
HOLOCENE LANDSCAPE Coastal dunes
High dunes
Low dunes / beach ridges Beach-plaine / dune valleys Land dunes
Sand-drift areas Flooded areas
Intertidal areas:
sand- and mudflats Fluvial flood plain and marine salt-marsh areas Salt-marsh levees / ridges:
relatively high parts in the salt-marsch areas
Peat areas Peat
Permanently submerged
Inner water: freshwater; river channels and lakes
Outer water: brackish / marine;
Sea, tidal channels, lagoons
ANTHROPOGENIC AREAS
Embanked / reclaimed Former lakes (dry land) Urban areas
PLEISTOCENE LANDSCAPE
Fluvial areas / brook valleys
Pleastocene sand areas:
below 16 m NAP Pleistocene sand areas:
between16 - 0 m NAP Pleistocene sand areas:
above 0 m NAP River dunes
Ice-pushed moraines / drumlins
SYMBOLS
Outline present-day Netherlands
Cities
Present
0 50 100 km
Vecht Texel high
Rhine-Meuse
11000 BP 7500 BP 6000 BP
5000 BP 3500 BP 2500 BP
1900 BP 1200 BP 500 BP
150 BP
! (
HOLOCENE LANDSCAPE Coastal dunes
High dunes
Low dunes / beach ridges Beach-plaine / dune valleys Land dunes
Sand-drift areas Flooded areas
Intertidal areas:
sand- and mudflats Fluvial flood plain and marine salt-marsh areas Salt-marsh levees / ridges:
relatively high parts in the salt-marsch areas
Peat areas Peat
Permanently submerged
Inner water: freshwater; river channels and lakes
Outer water: brackish / marine;
Sea, tidal channels, lagoons
ANTHROPOGENIC AREAS
Embanked / reclaimed Former lakes (dry land) Urban areas
PLEISTOCENE LANDSCAPE
Fluvial areas / brook valleys
Pleastocene sand areas:
below 16 m NAP Pleistocene sand areas:
between16 - 0 m NAP Pleistocene sand areas:
above 0 m NAP River dunes
Ice-pushed moraines / drumlins
SYMBOLS
Outline present-day Netherlands
Cities
Present
0 50 100 km
Vecht Texel high
Rhine-Meuse
11000 BP 7500 BP 6000 BP
5000 BP 3500 BP 2500 BP
1900 BP 1200 BP 500 BP
150 BP
! (
