Recent evolution of the river mouth intertidal zone at the Río San Pedro tidal channel (Cádiz Bay, SW Spain): controlling factors of geomorphologic and depositional changes

Abstract

Sedimentary and photogrammetric analysis of a sector of Cádiz Bay (SW Spain), including the intertidal zone on the left bank of the Río San Pedro tidal channel, were performed to understand its environmental evolution and the main factors that controled it. The study of this especially vulnerable environment has allowed to establish its depositional and morphological responses to the dynamic processes caused by recent environmental or climate changes. In the bank of the Río San Pedro tidal channel, there is a well-developed saltmarsh, which alternates with sandy beaches the data indicate erosional processes. The saltmarsh retreat rate was estimated in 0.65m/yr from 1977 to 2008. In this time-period, the tidal channel experienced a lateral displacement toward the SE of 1.24m/yr, and the beach width decreased from 50 to 21m. Three evolutionary stages were established: a youth stage, represented by a relatively high water energy beach environments; a maturity stage: represented by saltmarsh with deposition of mud and halophyte vegetation; a reactivation stage: represented by erosive features in the saltmarsh, such as tidal pools, tidal channel, etc. The geological location of Cádiz, close to the Eurasian–African plate boundary, account for its relatively high seismic and tsunami activity, that caused significant depositional changes in the area. Others important factors controlling the sedimentation are: first the tides, followed by the waves and the proximity to a sand source, such as the sandy mantle of La Algaida.