From the movement of rivers, to the generation of catastrophic landslides and the evolution of entire landscapes, many processes that shape the surface of the earth are characterized by a high degree of variability; variability that is not linked to environmental factors, but to complex internal dynamics. Describing such complexity and variability requires stochastic models that describe processes probabilistically and large datasets to calibrate these models. What can we do when nature presents to us only one of the many possible evolutions of a highly complex system?

In this paper, we describe a framework to calibrate stochastic models of morphodynamic systems with a single time-series of data. By “morphodynamic system” we refer to a system that is characterized by changes in shapes or position of objects. Rivers that are moving back and forth across a floodplain are a great example for a morphodynamic system that is characterized by complex internal dynamics. Here, we demonstrate the framework using an experiment of braided rivers moving in a flume. Yes, this is the same experiment that we used in our last paper to study the average behavior of lateral channel movements (Link). Here, we are interested in the variability.

In simple terms, the framework consists of generating a large number of “synthetic” time-series from a stochastic model. These synthetic time-series will vary depending on the input parameters to the model. We calibrate these parameters by finding model outputs that are statistically equivalent to the data. One of the key aspects of the framework is the choice of statistical tests to compare the data to the model. We propose three statistical tests to compare the behavior of channel movements in model and datasets, but these statistical comparisons are modular and can be adapted or expanded to suit the studied morphodynamic system.

Hoffimann, J., Bufe, A., Caers J. (accepted). Morphodynamic Analysis and Statistical Synthesis of Geomorphic Data: Application to a Flume Experiment. Journal of Geophysical Research: Earth Surface. Journal link.

Natural lowland rivers tend to erode their banks and migrate across an alluvial surface. In our new paper, we use data from experiments to develop a model for lateral channel migration rates of braided streams. Surprisingly, we find that the direct influence of sediment discharge on migration rates is relatively weak, and that the main controls on migration rates are the water discharge and the channel bank height. Of course, the channel bank height itself is influenced by water and sediment discharges – this is where our results need to be combined with models for the long-profile evolution of streams, which leaves exciting new research avenues ahead.|

Bufe, A., Turowski, J.M., Burbank, D.W., Paola, C., Wickert, A.D., Tofelde, S. (accepted) Controls on the lateral channel migration rate of braided channel systems in coarse non-cohesive sediment. Earth Surface Processes and Landforms, Journal Link

River terraces hold information about perturbations in climate and tectonics, but different perturbations can have similar effects on the stratigraphic record. For example, both a decrease in sediment discharge or an increase in water discharge can cause river incision, which complicates the interpretation of incised terraces. In our new paper that is open for review and discussion in Earth Surface Dynamics, we present results from physical experiments of channels that were subject to perturbations of water and sediment discharges. We demonstrate that combining terrace geometries with information on (1) the timescales of terrace formation and/or (2) the sediment discharge from the river system, allows to distinguish between water and sediment discharges as the driver for river incision. You can have a closer look and discuss the paper here.

Tofelde, S., Savi, S., Wickert A.W., Bufe, A., Schildgen, T. Alluvial channel response to environmental perturbations: Fill-terrace formation and sediment-signal disruption. under review at Earth Surface Dynamics