Indirect effects from tributary and upstream droughts account for most system-wide losses in the Mississippi River System

Abstract

Each year, inland waterways in the United States transport over $168 billion worth of cargo at around 675 ton-miles per gallon of fuel, making them the most cost-effective and environmentally friendly freight transportation mode. As the movement of cargo along waterways depends heavily on channel depth, droughts pose a serious risk to waterway freight transportation. While recent studies have improved the methodology used for modeling inland waterways, few models have been applied to a complete river system, making the cascading indirect effects of regional droughts largely unquantified. Therefore, a network-based Discrete Event Simulation (DES) model of the Mississippi River System is developed, finding that indirect effects are roughly 1.5 times larger than direct effects for tonnage loss (indirect: ~17.3 million tons; direct: ~11.3 million tons). A Tennessee River Region drought’s indirect tonnage loss exceeds its direct tonnage loss by around 6.2 times (indirect: ~1.7 million tons; direct: ~0.3 million tons). Droughts occurring within tributary regions and upstream regions produce the greatest system-wide tonnage losses, with the Ohio River Region drought producing the largest increase in tonnage losses of 186.7% above the baseline scenario (~13.5 million additional tons loss). The Upper Mississippi River Region drought produces the greatest direct effect, with a drop of local capacity utilization by 11.9 percentage points (82.3% to 70.4%), while the Ohio River Region drought produces the greatest indirect effect, with an increase in tonnage loss outside the region of 8.09 million tons. These results demonstrate the necessity of modeling droughts on a system-wide level to accurately convey the propagating effects through the system.