Transverse rivers draining the Spanish Pyrenees: large scale patterns of sediment erosion and deposition

Abstract

AbstractData collected from six transverse rivers draining the Spanish Pyrenees highlight how the rate of change in river gradients downstream controls long-term deposition and erosion patterns acroos the mountain belt. The rivers draining the Spanish Pyrenees provide evidence for an important relationship between gradient (S) and distance from the drainage divide (x), such that S is proportional to xΩ. This can be expressed quantitatively as a power function relation S ∞ L−R. In areas dominated by erosion Ω has a value > − 5, while in areas of deposition Ω has a value < −0.4. The contrast between areas of erosion and deposition is also reflected in downstream increases and decreases, respectively, in stream power and bed shear stress along the whole of the mountain front.It is proposed, based upon previous empirical studies of loose to semi-armoured channels, that the downstream variations of stream power and bed shear stress result in variations of bed-load transport rates, which in turn create the erosional and depositional patterns associated with variations of channel gradient.These results highlight the complex response of the fluvial system, emphasizing the need for regional approaches for examining long-term changes in rivers draining orogenic belts and the importance for incorporation of hydraulic data into geomorphological models to assist interpretations of the mass distribution of sediment.