TY - JOUR
T1 - The influence of channel deepening on estuarine turbidity levels and dynamics, as exemplified by the Ems estuary
AU - de Jonge, V.N.
AU - Schuttelaars, H.M.
AU - van Beusekom, J.E.E.
AU - Talke, S.A.
AU - de Swart, H.E.
PY - 2014
Y1 - 2014
N2 - Active deepening of tidal channels usually results in the alteration of the vertical and the horizontal tide.
This may lead to concurrent significant increases in mean suspended matter concentrations (SPM) in
coastal plain estuaries, the turbidity maximum (ETM) included. This is exemplified by an extensive
analysis of the Ems estuary, a prototypical heavily stressed estuary in the Dutch-German border area.
Measurements show that the SPM concentrations in the lower reaches of the estuary have increased an
average of 2- to 3-fold between 1954 and 2005, with a 10-fold increase observed in the upper estuary
(tidal river). Longitudinal profiles of surface SPM demonstrate that the ETM has moved upstream by up to
25 km and has broadened into a zone 30 km in length which extends into the freshwater tidal river. On
an annual scale, variations in freshwater discharge significantly influence the formation and breakdown
of the ETM: during low river discharge the ETM approaches equilibrium over 2e3 months, whilst
elevated river discharges relocate the ETM downstream over several weeks.
An exploratory, semi-analytical model is calibrated to simulate the equilibrium SPM distribution in the
upper estuary during five time periods from 1965 to 2005, using archival bathymetric and tidal data.
Results suggest that the deepening of tidal channels and a reduction in hydraulic drag have most likely
resulted in a landward shift of the SPM trapping location. The measured increase in SPM concentrations
and the development of fluid mud around the 1990s likely contributed to reduced mixing and bottom
drag, creating a feedback loop that further altered tidal and SPM dynamics. It is argued that the removal
of some non-erodible (consolidated) layers in the lower reaches of the estuary has created new internal
sediment sources that may be responsible for feeding the observed high SPM concentrations, rather than
increased sediment input from the boundaries. All findings are based on and supported by measured
short-term seasonal fluctuations, as well as long-term developments of yearly averaged concentrations
in the longitudinal SPM distribution.
AB - Active deepening of tidal channels usually results in the alteration of the vertical and the horizontal tide.
This may lead to concurrent significant increases in mean suspended matter concentrations (SPM) in
coastal plain estuaries, the turbidity maximum (ETM) included. This is exemplified by an extensive
analysis of the Ems estuary, a prototypical heavily stressed estuary in the Dutch-German border area.
Measurements show that the SPM concentrations in the lower reaches of the estuary have increased an
average of 2- to 3-fold between 1954 and 2005, with a 10-fold increase observed in the upper estuary
(tidal river). Longitudinal profiles of surface SPM demonstrate that the ETM has moved upstream by up to
25 km and has broadened into a zone 30 km in length which extends into the freshwater tidal river. On
an annual scale, variations in freshwater discharge significantly influence the formation and breakdown
of the ETM: during low river discharge the ETM approaches equilibrium over 2e3 months, whilst
elevated river discharges relocate the ETM downstream over several weeks.
An exploratory, semi-analytical model is calibrated to simulate the equilibrium SPM distribution in the
upper estuary during five time periods from 1965 to 2005, using archival bathymetric and tidal data.
Results suggest that the deepening of tidal channels and a reduction in hydraulic drag have most likely
resulted in a landward shift of the SPM trapping location. The measured increase in SPM concentrations
and the development of fluid mud around the 1990s likely contributed to reduced mixing and bottom
drag, creating a feedback loop that further altered tidal and SPM dynamics. It is argued that the removal
of some non-erodible (consolidated) layers in the lower reaches of the estuary has created new internal
sediment sources that may be responsible for feeding the observed high SPM concentrations, rather than
increased sediment input from the boundaries. All findings are based on and supported by measured
short-term seasonal fluctuations, as well as long-term developments of yearly averaged concentrations
in the longitudinal SPM distribution.
U2 - 10.1016/j.ecss.2013.12.030
DO - 10.1016/j.ecss.2013.12.030
M3 - Article
SN - 0272-7714
VL - 139
SP - 46
EP - 59
JO - Estuarine, Coastal and Shelf Science
JF - Estuarine, Coastal and Shelf Science
ER -