Dynamics and sedimentary assessment of a rock-bounded estuary: a case study—Tina Mayor (NW Spain, Iberian Peninsula)

Abstract

Based on a comprehensive study of the Tina Mayor estuary, a conceptual morphosedimentary model is proposed for one of the best-preserved limestone sectors of the Iberian Peninsula. This mesotidal and rock-bounded estuary consists of a significant proportion of quartzitic gravel fractions, which is distinctive compared to the other nearby estuaries of Northwest Spain on the Iberian Peninsula. Fluvial discharges allow for high coarse fraction inputs to be distributed to all the geomorphological estuarine zones, particularly the mouth, the bay and the inner areas. Moreover, the narrowing of the rocky boundary affects the outermost sector of the mouth of the estuary, developing two coarse grain spits; the inner being much more extensive, while tidal flats occupy a greater reclaimed area than the natural ones. The dominant sedimentary flow regime was established based on tidal and current records during a tidal cycle. The flood currents crossing the bay change trajectory at the mouth boundary as a result of rocky narrowing from the western mouth to the eastern inner side in a reverse response to the Coriolis effect. Estuarine morphosedimentary units are mapped, including the large and minor bedforms in each estuarine zone. These have been characterised according to the average values of the granulometric parameters (coarsest 1-percentile grain size or centile, mean size, sorting, skewness and kurtosis), as well as the carbonate (bioclast) percentage, including the trend maps of the mean size, sorting and biogenic carbonate content. Furthermore, taking into account the mean tidal amplitude and mixing waters (QF/QT), a suitable classification can be established for any type of estuary, including the characteristics of the confinement of the estuary mouth.