372
C. Hoselmann . H. Streif
6
Summary and Conclusions
The mass-balance study funded by the Deutsche Forschungsgemeinschaft deals
with a quantification of Holocene sediment accumulation in the coastal zone between the estuaries of the Ems and Weser Rivers (Lower Saxony). This region is
highly suitable for this kind of research because it is built up of various coastal
sedimentary environments comprising barrier islands with sheltered and open
tidal flats, bay flats (Dollart, Jadebusen), and estuaries (Ems and Weser) probably involving different accumulation processes. The Holocene accumulation
wedge in this region was formed within the past 7500 years under the influence
of a sea-level rise of 25 m. Because of the great variety in sedimentary environments investigated, the study can serve as a model for general mass-transport
and sediment accumulation connected with transgressions over coastal lowlands. Making use of a great many published radiocarbon dates, the mass-balance study also offers the opportunity to work out the interaction between
changing rates of sea-level rise and corresponding accumulation rates of coastal
deposits. It is also hoped that quantitative studies of this kind will be useful for
predicting the future development of coastal lowland areas under the influence
of changing rates of sea-level rise.
As far as available, digital data from various coastal authorities in Lower Saxony were used to reconstruct the surface of the Holocene sediment wedge and to
determine the volume of a series of units. Hydrographic soundings were used to
calculate the volumes of water bodies below NN. In the tidal-flat area similar
data were used to reconstruct the surface morphology and determine the volumes of water below NN and sediment above NN. Topographic surveying data
were used as a basis for determining the volume of morphological depressions
in the marshland that lie below NN and are filled neither by water nor sediment.
The volume of coastal deposits above NN was calculated using data from the
same source. Any gaps in the above data sets were filled by systematic digitizing
of elevation points and contour lines on 1:5000 and 1:25000 topographic maps.
The digital data sets compiled in this manner contained at least 10 elevation
points per km 2 in the coastal marshlands, tidal flats, and subaquatic zone. A
much denser coverage was used in the case of the sand dunes on the East Frisian
Islands, where over 250 elevation points per km 2 were digitized.
The sediment volume below NN was calculated on the basis of boreholes,
which were sunk in the coastal area and which penetrated the entire sequence of
Holocene deposits. As a test of accuracy, (Figs. 5 and 8) volume calculations were
carried out with various computer programs (ISM, MacGRIDZO, and Surfer)
and gridding algorithms (minimum tension gridding, weighted least squares,
and kriging). Additional tests dealt with the different evaluation methods based
on manual construction of structure contour maps, planimetry and digitizing of
these isolines, and calculation of volumes directly from borehole data. Further
studies dealt with the influence of certain parameters (line spacing, number of
evaluated depth values) on calculations of a single grid node. The results of these
C. Hoselmann . H. Streif
6
Summary and Conclusions
The mass-balance study funded by the Deutsche Forschungsgemeinschaft deals
with a quantification of Holocene sediment accumulation in the coastal zone between the estuaries of the Ems and Weser Rivers (Lower Saxony). This region is
highly suitable for this kind of research because it is built up of various coastal
sedimentary environments comprising barrier islands with sheltered and open
tidal flats, bay flats (Dollart, Jadebusen), and estuaries (Ems and Weser) probably involving different accumulation processes. The Holocene accumulation
wedge in this region was formed within the past 7500 years under the influence
of a sea-level rise of 25 m. Because of the great variety in sedimentary environments investigated, the study can serve as a model for general mass-transport
and sediment accumulation connected with transgressions over coastal lowlands. Making use of a great many published radiocarbon dates, the mass-balance study also offers the opportunity to work out the interaction between
changing rates of sea-level rise and corresponding accumulation rates of coastal
deposits. It is also hoped that quantitative studies of this kind will be useful for
predicting the future development of coastal lowland areas under the influence
of changing rates of sea-level rise.
As far as available, digital data from various coastal authorities in Lower Saxony were used to reconstruct the surface of the Holocene sediment wedge and to
determine the volume of a series of units. Hydrographic soundings were used to
calculate the volumes of water bodies below NN. In the tidal-flat area similar
data were used to reconstruct the surface morphology and determine the volumes of water below NN and sediment above NN. Topographic surveying data
were used as a basis for determining the volume of morphological depressions
in the marshland that lie below NN and are filled neither by water nor sediment.
The volume of coastal deposits above NN was calculated using data from the
same source. Any gaps in the above data sets were filled by systematic digitizing
of elevation points and contour lines on 1:5000 and 1:25000 topographic maps.
The digital data sets compiled in this manner contained at least 10 elevation
points per km 2 in the coastal marshlands, tidal flats, and subaquatic zone. A
much denser coverage was used in the case of the sand dunes on the East Frisian
Islands, where over 250 elevation points per km 2 were digitized.
The sediment volume below NN was calculated on the basis of boreholes,
which were sunk in the coastal area and which penetrated the entire sequence of
Holocene deposits. As a test of accuracy, (Figs. 5 and 8) volume calculations were
carried out with various computer programs (ISM, MacGRIDZO, and Surfer)
and gridding algorithms (minimum tension gridding, weighted least squares,
and kriging). Additional tests dealt with the different evaluation methods based
on manual construction of structure contour maps, planimetry and digitizing of
these isolines, and calculation of volumes directly from borehole data. Further
studies dealt with the influence of certain parameters (line spacing, number of
evaluated depth values) on calculations of a single grid node. The results of these