Future River Analysis & Management Evaluation (frame): A New Approach To Forecasting Long-Term Morphological Evolution and Response In Rivers

Long-term forecasting of river channel evolution and morphological response to river management is needed to make informed decisions and develop resilient adaptation pathways in an uncertain future. However, long-term forecasting in rivers with a wide range of plausible future conditions is beyond the scope of currently available morphological models that are entirely physics-based and deterministic. To address this limitation, the US Army Engineer Research and Development Center (USACE-ERDC) is leading an international consortium of universities in the development of a new type of one-dimensional model. The FRAME (Future River Analysis & Management Evaluation) model is being designed for use by river managers and planners. Its outputs will provide decision makers with (i) foresight regarding the evolution of river forms and functions and (ii) forecasts of both the short-term morphological impacts and long-term river responses likely to be triggered by management actions.

FRAME employs annual flow duration curves to simulate hydrology, enabling investigation of morphological sensitivity to a range of climate projections. Representative, reach-averaged cross-sections with simplified geometries are used to increase computational efficiency. Sediment transport is calculated by grain size fraction with a simple hiding-exposure factor and active layer mixing to simulate fining or coarsening of bed material in response to erosion and deposition. However, unlike models that calculate sediment transport and channel change in response to time-stepping through hydrographs, FRAME performs its hydraulic and sediment transport calculations for discharge classes pertaining to each flow duration curve, with channel morphology adjusting in response to the imbalance in flow frequency-weighted, annual sediment loads between consecutive cross-sections. Although morphology is updated annually, sub-annual time-steps ensure model stability and orderly convergence towards sediment transport equilibrium.

In addition to simulating responses to future flow regimes, FRAME currently includes functionality to simulate bed erosion control, dikes, diversions, tributary inputs, bed material variation, and adjustment of sediment input. FRAME’s ongoing development has been aided by two testbed models: a 200-mile reach of the Mississippi River upstream of Vicksburg, MS (see related presentation by Biedenharn et al.); and Sabougla Creek, a tributary of the Yalobusha River, MS (see related poster by Cox et al.). Near-term priorities for transforming FRAME into a fully-operational, decision-support tool include adding capabilities for lateral channel adjustment (and bank stabilization), meandering and planform evolution, and implementing a beta testing program involving a working group of potential end-users. Complementary research on ‘RUles-Based morphological Response In river Channels’ (RUBRIC) interfaces with FRAME’s development, which (i) relates morphological responses to imbalances in sediment transport (see related presentation by Thorne et al.) and (ii) explores how forecasts can be translated into graphical indicators that are intuitive for management use (see related presentation by Downs et al.).

On release, FRAME’s ability to rapidly forecast river channel evolution over multiple decades with easy-to-test management options will support strategic decision-making that minimizes hazards to river users and communities while maximizing the functionality of the river and the ecosystem benefits it provides.