On the morphological long-term development of dumped material in a low-energetic environment close to the German Baltic coast

Abstract

The development of the bed bathymetry of an experimental dumping area was followed over three and a half years by means of multibeam echosounder techniques. Two types of material were discharged in the bight of Mecklenburg in the Baltic Sea in approximately 20 m of water depth. One set of the discharges was 2900 m³ of glacial till and the other set was a 2400 m³ mixture of glacial till, sand and minor amounts of cohesive matter. Only approximately 2500 m³ (86 %) of the glacial till and 1500 m³ (63 %) of the mixed soil materials were deposited on the seabed. This means that already during the dumping process a considerable part of the sediment material drifted away. The glacial till formed crater-like rings of 30 m diameter with peaks up to 1.4 m above seabed, whereas the spatial structure of the mixed soil material was somewhat more diffuse, but with similar magnitudes in the peaks and troughs.The morphological changes were small and their quantification required a high measuring precision in the order of few cm in the vertical. The dominant processes of surface deformation was flattening of peaks and filling of troughs. The speed of this process decreased with horizontal 2 scale: structures of less than 4 m horizontal extension had a trend to disappear within less than five years, whereas structures of larger than 8 m extension showed little change and are estimated to remain detectable for many decades. In contrast to the reworking of the matter inside the dumping structures, no net transport of material out the dumping area could be detected.Extrapolating the observed morphological changes into the future it is estimated that without significant decrease in internal shear strength of the disposed till the structures will persist for at least 70 years. This can be attributed to the high internal stability of the dumped glacial till and the low hydrodynamic forces present at the seabed in this region.

Morphological characteristics of the Basque continental shelf (Bay of Biscay, northern Spain); their implications for Integrated Coastal Zone Management

“…The majority of the dredged material disposal sites have not been characterised, up until the present time; as such, their extent and distribution have been essentially unknown. The distinctive`ring-likeś tructures of these sediments reflect the transfer of vertical, into horizontal, momentum when the disposal hits the seabed (Stockmann et al, 2009). It could be inferred that the applied shear stress was insufficiently high to enhance erosional processes of the coarser material.…”

“…Even if marine sand extraction is very limited in Spain, such material disposal sites reduce the availability of such sediment resources for beach nourishment. Dumping areas should be monitored during future surveys, with repetition sampling intervals of several years, as the observed processes occur slowly (Stockmann et al, 2009). …”

Morphological Characteristics and Control Factors of Bedforms in Southern Gyeonggi Bay, Yellow Sea

“…그러나 이 연구들은 단 빔음향측심기 또는 천부탄성파 자료를 통한 2차적인 연구로 제한되었으며, 실질적인 층면구조를 파악하기 위한 기술적 한계를 가지고 있다. 그러나 최근 십여 년 동안 고정밀 위치정보 시스템과 함께 고정밀 다 중빔음향측심기술이 해저지형 연구에 많이 적용되었 다 (Knappen and Hulscher, 2002;Wienberg et al, 2004;Wienberg and Hebbln, 2005;Thornton et al, 2006;Kubicki et al, 2007;Li and King, 2007;Stockmann et al, 2009 (Flemming, 1988). (Fig.…”

Assessment of the Influence of Dredge Spoil Dumping on the Seafloor Geological Integrity

“…Indeed, Lepland et al (2009) observed restricted spread of dumped mixture of mud, sand and gravel, and loadinginduced compaction of underlying natural organic-rich mud at a dumping site in Oslofjord, Norway. Stockmann et al (2009) and Tauber (2009) observed minimal change in the volume of experimentally dumped mounds of glacial till and mixed till, silt and sand, but modest smoothing of the surface roughness by reworking of fine-grained material to local depressions and the development of sandy lags on local elevations during 3 years in the Mecklenburg Bight, southern Baltic Sea.…”