**1. Introduction**

The high alluvial risk existing in the Lluta basin due to the presence of large mountains subject to inclement weather, added to the growing urban pressure to use sectors of the lower basin that are increasingly exposed to this type of event, justify studies on the behavior of debris flows, and the possibility of mitigating their effects through the construction of protection and control works. For this purpose, the hydrogeomorphological chart for this basin has been prepared, being a management support tool, the main objective of this work.

The hydrographic basin of the river Lluta and its valley of the same name is located in the XV Region of Chile, comprised between parallels 18° and 18°30' South Latitude and meridians 70°20 and 69°22' West Longitude, in the Provinces of Arica and Parinacota, whose main river flows into the Pacific Ocean in the coastal sector called Chacalluta Valley.

This basin, in a natural regime, presents permanent surface runoff to the sea throughout the year with an average flow of 0.45m3 sec. at 1.44m3 sec., the Lluta river has carved out a quite narrow and deep valley, which is limited by quite steep and

high slopes. The high alluvial risk existing in this basin due to the presence of large mountains subject to inclement weather, added to the growing urban pressure to use sectors of the lower basin, justify studies on the behavior of debris flows, and the possibility of mitigating their effects through the construction of protection and control works. The impact of the increase in flow does not occur homogeneously throughout the basin, showing notorious spatial differences in terms of the level of danger that it causes. Totally different from what was described as the 2001 flood, which manifested itself in the lower Lluta basin, where the road infrastructure suffered great damage due to undermining and landslides, resulting in the reconstruction of road and railway bridges, implying a strong investment in fluvial protection works on the banks upstream of the bridges, that is, fluvial defense works were carried out in specific areas.
