资源环境科技发展态势分析平台

The modern Mississippi River Delta is plumbed by the Mississippi and Atchafalaya rivers, setting water and sediment dispersal pathways for Earth’s fifth‐largest river system. The Atchafalaya River’s (AR) partial annexation of discharge from the Mississippi River (MR), particularly between 1926 and 1950, prompted warnings of a rapid river avulsion and the construction of the Old River Control Structure to regulate flow. Natural and anthropogenic causes of this discharge annexation are difficult to disentangle. Here, we develop and validate a hydrodynamic model of flow partitioning through the historic channel network. We then isolate how several key changes to the system affected discharge partitioning and stage at the AR‐MR diversion. Simulations show that erosion of the upper AR can account for 73% of the water discharge increase. Dredging in the lower AR between 1932 and 1950 can account for 35% of the water discharge increase, and was also an important control on shear stress distribution. The lower MR was slightly erosional during this period, and therefore hindered the AR discharge increase. Significant lacustrine delta deposition in AR had little effect on partitioning. These findings highlight the importance of AR enlargement processes on avulsion dynamics at this site. Given the essential nature of this river junction to the society, transportation, and commerce of the United States, improved attribution of discharge increases may lead to future management strategies that are broadly impactful.

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