Forecasting sediment transport and morphological response in the Mississippi River

The Mississippi delta is being degraded at an unsustainable rate with serious potential to undermine the benefits the delta provides to wildlife, people and the U.S. economy unless action is taken to address the long-term decline in sediment load delivered by the Lower Mississippi River. Understanding the likely future evolution of the river in response to its changing sediment budget is imperative but remains a vision beyond the capabilities of conventional river engineering models that focus on short-term investigations of hydraulics, flooding, habitats and channel morphological response, typically within reaches of interest and over project-design time-scales.A new type of model is currently in development for the lower Mississippi River, tasked with revealing uncertainty-bounded trends in sediment transport and channel morphology over annual, decadal and centennial time-scales. The FRAME (Future River Analysis & Management Evaluation) tool is being designed with river managers and planners in mind where results will offer exploratory insights into plausible river futures and their potential impacts. A unique attribute of the tool is its hybrid interfacing of traditional one-dimensional hydraulic and sediment transport modelling with a rules-based expert system for characterising the nature of morphological response. The tool employs probabilistic annual flow duration curves to define ensembles of hypothetical average years, wetter than average years and drier than average years that in sequence enable the design of long-term hydrological storylines. A testbed model for a 200-mile reach of the Mississippi River upstream of Vicksburg currently provides a platform for FRAME’s development, testing and, critically, for realising the multiple benefits that such a tool would deliver. While the lower Mississippi River provides a prominent case where long-term forecasting of sediment transport and morphological response would be invaluable, such a tool would be transferable to other river settings and management programs seeking to mitigate against undesirable future outcomes.