The Impact of Navigation Chevrons in St. Louis Harbor

Three chevrons (U-shaped river training structures) were constructed in early 2008 in the St. Louis Harbor to improve the navigation channel and enhance environmental diversity. Post-construction surveys have shown the chevrons have created improved depth for fleeting along the Missouri shore and a deeper navigation channel along the Illinois shore. However, local professors of geology and planetary science have garnered much publicity by stating that the chevrons are "a loaded gun pointed at the levees protecting the Illinois floodplain" and raise flood levels significantly. Navigation works have not been found to have an effect on flood levels. The St. Louis District (SLD) will demonstrate that the chevrons have no impact on water levels in three ways: physical measurements of channel cross sections, comparison of stages at upstream and downstream locations for pre- and post chevron conditions, and by two- dimensional hydrodynamic modeling. Cross sectional area has increased by several thousand square feet following chevron construction. Gage stage comparisons show no significant difference in upstream stages for pre- and post- chevron construction. Although the 2D hydrodynamic modeling is not yet completed, it is expected that the simulation will also show that there is no significant impact on water levels.