Fluvial morphology and erosion in abrupt curves of the Ucayali River, Peru.

Abstract

The Ucayali River originates in the high Andean Mountains and drains in the folded and faulted Andean Foreland in the vicinity of the famous Inca sites of Machu Picchu and Cusco. The Ucayali River displays a progressive change in channel pattern. It has a complex anastomosing and meandering stream with abundant vegetated and non-vegetated islands. Further downstream, islands become far less abundant, and meanders dominate, forming sharp bends described by long point bars in the inner side and scour holes in the outer side. Changes of the river planform and of the cross-sectional shape of the Ucayali River and changes in the river morphology due to sedimentation and erosion cause deep scour holes along the outer bend of the river. Since no major tributaries enter the river, the change in channel pattern for the Ucayali results from downstream decreases in channel slope and sediment size. Based on a research on "detailed bed topography and scour in sharp river bends, and influence of bank protection works", related to the meandering conditions of Amazon rivers and taking into account recently detailed information available on the Ucayali River in a length of 1,000 km from the city of Pucallpa up to its confluence by the left bank with the Marañón River of around 50 catalogued sharp bends, an application to a real case is presented regarding proposed formulae for prediction of maximum scour depth in sharp bends without bank protection, together with the corresponding countermeasure by an estimation formula for prediction of maximum scour depth in sharp bends with flexible bank protection based on rockfill revetment.