Analysis and modelling framework for sediment production and yield in mountain basins under climate change.

Aims and objectives

The aim in this project is to quantitatively assess the variability in sediment yields in mountain basins across a range of timescales. Three fundamental topics will be addressed:

• A simple data-driven conceptual modelling framework for sediment production, transfer, yield and their interactions will be developed. A systematic modelling framework will allow us to develop testable hypotheses about sediment dynamics in mountain basins, to objectively evaluate the sensitivity of different components of the system, and to analyse possible scenarios in climatic driving forces. Within this framework we will be able to address questions of space and time scales in sediment delivery and the role of landscape connectivity.
• The modelling framework has to explicitly account for sediment residence and travel times in different morphological elements of the fluvial system. It is on the basis of residence times that the discrepancies between short and long-term sediment yields observed in many studies can be reconciled.
• The episodic nature of extreme rainfall events and the erosion they trigger have to be properly accounted for. Time series of sediment yield carry signatures of events at all frequencies. Triggering mechanisms have to be included as stochastic forcing because they may be able to explain long-memory effects and complex response which are not obvious from observations of sediment yield alone.

The objective in this proposal is to develop an analysis and modelling framework to study the impacts of climate change on sediment dynamics in mountain basins on the basis of data collected at the individual SedyMONT study sites. The analysis part will consist of the quantification of past, present and future climatic variables for the study areas and their trends. The modelling part will consist of the development of the numerical model, its adaptation to each individual study site, and model calibration/validation. The joint framework will include the interpretation of data and model results, analysis of uncertainty propagation from data, through model to results, and investigations of scale effects, thresholds and complex response.

Modelling framework

The aproach we take is a conceptual source-sink model to interpret the field-based datasets collected within the SedyMONT sites. The conceptual model will capture the key elements of basin storm response and sediment delivery processes. It will be based on the impulse-response concept for fluxes between different components of a system (river basin) in a transient state. The model will consist of two (or more) independent components simulated by a sequence of linear (or nonlinear) reservoirs in series. For example, the first component may represent hillslope storage and the second channel storage. Sediment is supplied to the hillslope component at a production rate e(t) and exits the channel component as sediment yield y(t) based on mass continuity (see figure below).