The River Scheldt currently has a macrotidal estuary with a tidal reach of 160km. It covers a complete salinity gradient with a polyhaline, mesohaline and oligohaline zone and a fresh water part with long and short retention time of chloride. The estuary and its tidal tributaries Durme and Rupel have been heavily influenced by anthropogenic pressures such as land reclamation, harbour expansion, dredging activities, embankments and urbanisation. A good understanding of the impact of human interventions on the ecological functioning of the estuarine ecosystem is required. Based on this knowledge appropriate compensation or mitigation measures can be taken in response or anticipation to future negative effects of anthropogenic changes and relative sea level rise. In this study, all available data on tidal regime (1850-2000), bathymetric charts (1930, 1950, 1960, 1970, 1980, 1990, 2000) historical maps from the beginning of the 19th century onwards and aerial photographs from 1944 onwards were compiled and analysed for the Zeeschelde (Belgian part of the Scheldt estuary) and the tidal tributary river sections.The report deals with three main issues:(1) Ecological changes during the past century are analysed using a hierarchical ecotope approach.The evolution of the acreage of the distinguished physiotopes (physically characterised units) andecotopes such as shallow waters, tidal mudflats and marshes are analysed for each salinity zone or river section;(2) Changes in hydrodynamic and morphological parameters are analysed over the past century;(3) An overview of anthropogenic interventions and natural changes with potential effects onhabitat acreage and quality in the Zeeschelde and its tidal tributaries in the past two centuries. Thenature of the interventions is very diverse: reclamations, diking, land use change, infrastructureworks, dredging activities, canalisations, discharge manipulations and changes in river dynamics.Changes in tidal regimeBecause tidal regime is a key factor in an estuarine ecosystem, we analysed the characteristics ofthe ten year mean high water (MHW), mean low water (MLW), tidal asymmetry and the tidalamplitude. Temporal and spatial patterns of these parameters are examined within differentsalinity zones in the Scheldt, the Durme and the Rupel.MHW shows a gradual increase in the whole Scheldt estuary. The highest rise is located in the freshwater part with short retention time. Maximum MHW shifted 32km upstream from Antwerp to Sint-Amands within one century.MLW and tidal asymmetry show a more irregular pattern and are more sensitive to anthropogenicactivities such as dredging and deepening in the navigation channel. MLW dropped in the pastcentury in the harbour zone of the Scheldt between the Dutch-Belgian border and the confluence ofthe Rupel and along the Rupel. In the fresh water zone with long retention time, MLW and tidalasymmetry changed little till 1970 (1st deepening of the Scheldt). After this period MLW strongly dropped as in most other river sections. MLW and tidal asymmetry in the fresh water zone with short retention time increased between 1900 and 1970 and were presumably affected by river discharge reductions and canalisations. After the 70’s MLW and tidal asymmetry decreased again. In the Durme MLW dropped at the confluence, more upstream it rised because of sedimentation in the riverbed. Discharge deviation, damming and channel straighthening played an important role here as well. At the same time tidal asymmetry increased in the whole Durme.MHW and MLW changes resulted in a high increase of tidal amplitude in the Scheldt and Rupel. In the River Scheldt the highest tidal amplitude was recorded at Lillo (62km to North Sea) around 1890, while in the last ten years the maximum occurs in Temse (98km to Sea); a shift of 36km upstream in a bit more than a century. In the Rupel the amplitude increased overall in time but less so in the upstream part. The Durme has an irregu |
