Two-band (100 and 500 kHz) synchronous side-scan-sonar was developed for manrine investigations, but this experimental survey carried out in the navigable Guadalquivir river, southern Spain, demonstrated that is a powerful new tool for river-bottom studies aud suggests that will be most useful for other river surveys. Computer image processing of extracts of synchronous lOO and 500 kHz sonographs to produce independent images differentiated and deliuneated the different textures and conformations of the underwater sediments and helped us to identified and characterised riverbed morphologies. The surveys were carried out rapidly and precisely. Erosional and depositional morphologies on the river bed were easily visualised on the screen and in the raw images. The Fourier wedge filter attenuated particularly well the confusing noise in the 100 kHz band The Roberts' edgeenhancement filter and the Laplacean convolution filter enhanced topographical features and revealed geomorphological patterns.

Th autbors would like to thank Dr. De Andrés for his valuable suggestions and advice about geological interpretations and the Spanish Oceanographic Institute (IEO) for kindly providing the sonographic images. The authors a1so wish to thank Mr. D. W. Schofield for his critical review of the English version.

8 pages, 3 figures, 15 references. Presentación oral 8.

Peer reviewed