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  development, ­
  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  exposed ­
  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  intertidal ­
  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  reduction ­
  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