SIMPLIFIED MODELS OF RIVER AVULSION AND ALLUVIAL ARCHITECTURE: CONNECTING TO FIELD DATA

Modeling is a powerful tool for studying sedimentary processes like avulsion, that have long recurrence intervals and depend on landscape-scale feedbacks. Simplified modeling approaches, such as cellular models and process-analogue experiments, have been particularly useful for exploring alternative hypotheses and evaluating first-order controls on river avulsion and alluvial architecture.

But while simplified models have proliferated in recent years, generating many intriguing hypotheses to be evaluated (in terms of both “equations” and “rocks”), their impact is limited by their isolation from the field data which could validate (or invalidate) them.

Many basic questions remain, such as: What thresholds control avulsion initiation? How do floodplain processes influence avulsion dynamics (and consequent channel-belt stacking)? What determines where (and if) an avulsion channel stabilizes? Answering these questions will require targeted modeling efforts coupled to data from ancient systems.

Here we survey the current state of the art in simplified avulsion and alluvial architecture models, focusing on how results and insights from these models can be incorporated into field and subsurface studies (and vice versa). Interestingly, while simplified models can seem particularly frustrating in this regard, since their results can “look” very different from the field, many of the same correspondence issues also occur in modern-ancient field comparisons (i.e. compare what to what?). We emphasize features that can be used to choose (or design) fit-for-purpose models, and we outline how quantitative data useful for model selection , (input) parameter estimation, and validation can be obtained from modern systems and ancient deposits. Our approach provides a consistent basis for inter-comparison of different models and/or data based on comparable measurements of processes (morphodynamics) and products (morphometrics).

Matching model goals with targeted questions, and model parameters and predictions with quantitative field data, will help tighten communication between field- and model-oriented sedimentary geologists, which is essential to advancing our understanding of river avulsion and alluvial architecture.