Freshwater related transport processes in the Elbe Estuary

Hartmut Hein, Stephan Mai, Ulrich Barjenbruch

Thursday 2 july 2015

12:00 - 12:15h at Europe 1 & 2 (level 0)

Themes: (T) Managing deltas, (ST) Saline and freshwater interaction

Parallel session: 11K. Managing deltas - Saline

One paradigm of estuarine ecology is that the ecology (e.g. phytoplankton) responds to changes in vertical stratification, which is controlled by the balance between buoyancy flux from freshwater inflow and the dissipation of kinetic energy by tidal (or wind) mixing. The Elbe River is one of the largest rivers in Europe (O(1000 km)) and tidal influences in the estuary reaches O(150 km) inward from the center of the German Bight to the weir in Geesthacht. The hydrological regime of the Elbe estuary is dominated by tides, mainly by the M2 tide and its overtides. Tidal dispersion modifies the discharge power spectrum upstream the brackish water zone, where mixing and straining processes establish density driven circulation patterns. Long-term measurements, originated from the Federal Waterways and Shipping Administration - spanning the years 1998 to 2013 - are analyzed. The measurement instruments of conductivity and currents are placed near surface as well as near bottom. They attain temporal resolutions of 5 minutes and a spatial resolution of 20 km. The measurements of discharge, conductivity and currents undergo strictly quality assurance including outlier testing, gab filling and breakpoint search. Based on current velocity and conductivity measurements salinity dynamics are analyzed. Processes like advection, straining and mixing are related to each other. By the means of numerical modellings the results are reproduced and the density related potential energy anomalies are estimated. By using different boundary condition the role of the M2 tide and its overtides on the density driven circulation and the related upstream transport is estimated. Beside tidal dominance in the Elbe estuary discharge variations on monthly to seasonal timescales modify the freshwater related transport processes.