Tasas de avance/retroceso de la línea de costa mediantemorfometría fotogramétrica en el sector Sanlúcar de Barrameda – Rota (provincia de Cádiz)

Zusammenfassung

This study deals with the application of photogrammetric techniques to establish the coastline evolution during the last decades between Sanlucar and Rota (South Atlantic Spanish coast), from 1956 to 2001. A detailed geomorphological map was also elaborated, accompanied by field work. In order to obtain the recent coastal trends, coastlines from seven different photogrammetric flights were compared, by measuring 28 transepts normal to the shoreline on stereoscopic photopairs. Since this is a mesotidal coast, the dune foot was considered to represent the coastline or, if absent, the cliff edge behind the beach. A high-resolution prism stereoscope was used for the measurements. However, these photographs introduce displacements and optical deformations in the images. For this reason a systematic calculation procedure was performed by which errors were taken into account when measuring distances in every photograph. Afterwards, a comparison was made among the obtained data, the calculated error and the dispersion rate, the last one represented by the standard deviation. The obtained results indicated the intensity of coastline change, included in a series of five classes: strong/moderate erosion, stability and moderate/strong accretion. The tendencies obtained by this method show contrasted behaviours along this coast, both in time and space. Temporal changes are controlled by the historical artificial regulation of the Guadalquivir river basin and by the storm frequency. Spatial variations are conditioned by the local geomorphological characteristics, which induce changes in the physical processes responsible for the littoral erosion/ sedimentation. These longitudinal variations give rise to a group of seven littoral cells distributed along the coast, each one with a different evolutive behaviour. This kind of information is very useful in the correct profit estimation of coastal settlements and uses, present and future. It also helps in establishing priorities when preparing coastal protection plans.