Scenario Testing of The Frame Tool On A 200 Mile Reach of The Lower Mississippi River

Understanding the likely future long-term evolution of the Lower Mississippi River (LMR) is a challenging mission for the USACE but one that remains a challenge for conventional river engineering models. A new type of model is currently in development, 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 modeling with geomorphic rules for characterizing the nature of morphological response.

A testbed model for a 200-mile reach of the LMR extending from the Arkansas River to just downstream of Vicksburg MS was the platform for expanding the FRAME tool’s capabilities for long-term forecasting of river evolution under a range of possible future scenarios. A number of experimental runs using the LMR testbed reach were conducted to explore the ability of the testbed model to capture general morphologic trends. Experimental test runs using the LMR testbed reach included the following scenarios: 1) Flow and sediment diversions; 2) Impacts of varying bed material gradations; 3) Varying flow sequences using the FRAME tool flow multiplier to simulate potential climate change; 4) Geomorphic rules for dike filling, and 5) Effects of base level lowering. All of the FRAME testbed scenarios were run for 200 years and the cross sectional area trends compared to the Base condition to evaluate the relative impacts of the various scenarios. These experimental test runs confirmed that the FRAME tool is functioning with respect to the predicting broad scale morphologic trends along the LMR.