Abstract
Freshwater pulses (during which river discharge is much higher than
average) occur in many estuaries, and strongly impact estuarine
functioning. To gain insight into the estuarine salinity response to
freshwater pulses, an idealized model is presented. With respect to
earlier models on the spatio-temporal behavior of salinity in estuaries,
it includes additional processes that provide a more detailed vertical
structure of salinity. Simulation of an observed salinity response to a
freshwater pulse in the Guadalquivir Estuary (Spain) shows that this is
important to adequately simulate the salinity structure. The model is
used to determine the dependency of the estuarine salinity response to
freshwater pulses for different background discharge, tides and
different intensities and durations of the pulses. Results indicate that
the change in salt intrusion length due to a freshwater pulse is
proportional to the ratio between peak and background river discharge
and depends linearly on the duration of the pulse if there is no
equilibration during the pulse. The adjustment time, which is the time
it takes for the estuary to reach equilibrium after an increase in river
discharge, scales with the ratio of the change in salt intrusion length
and the peak river discharge. The recovery time, i.e. the time it takes
for the estuary to reach equilibrium after a decrease in river
discharge, does not depend on the amount of decrease in salt intrusion
length caused by the pulse. The strength of the tides is of minor
importance to the salt dynamics during and after the pulse.