Die Küste, 74 ICCE (2008), 31-44 
35 
Fig. 4: Thickness of the mobile sand cover along the German North Sea coast (Zeiler et ah, 2000). 
Source: Shelf Geology Explorer (BSH) 
2.2 Tidal Flats 
The tidal flats of the Wadden Sea form the interface between the open North Sea and the 
mainland. They extend from Denmark to the Netherlands over a distance of about 450 km 
and can reach a width of up to 25 km along the German coast. This marginal belt between 
the barrier islands, whose genesis differs from the North to the South (Kohlus, f 998), and 
the mainland is comprised of salt marshes, extensive intertidal flats, numerous tidal gullies 
and streams. The sediments mainly consist of fine sand with various proportions of slightly 
coarser material or mud (silt and clay) (Ahrendt, 2006). Depending on the geological devel 
opment, locally peat or clay-rich layers can be found in the subsurface (Streif, f 990). 
The overall thickness of the sediment body can reach nearly 40 m (Ahrendt, 2006). The 
surficial sediments show a typical zoning from predominantly sandy sediments in more ex 
posed areas to muddy deposits in sheltered or more elevated parts. Overall, a dominance of 
sandy flats with a mud content of less than 10 % is observed (Berner et al., 1986; Bayerl et ah, 
1998; Koster, 1998; Ricklefs and Asp Neto, 2005). The present distribution of muddy inter 
tidal sediments (more than 50 % silt and clay), however, is mainly limited to small areas. This 
is due to a lack of adequate depositional environments mainly as a consequence of intensive 
land reclamation activities along the marshland coasts since the early Middle Age (Flemming 
and Ziegler, 1995; Brockamp and Zuther, 2000). Land reclamation and the substantial reduc 
tion of catchment areas resulted in an enlargement of the East Frisian barrier islands and a 
decrease of mudflats and salt-marsh areas as well. Along with a rising MSL and the increase in