Barge-driven resuspension facilitates sediment bypass in the Gulf Intracoastal Waterway (Louisiana, USA)

Ship traffic can increase sediment resuspension in shallow channels and coastal areas. Here we show that ship-driven resuspension is the major morphodynamic agent in the Gulf Intracoastal Waterway (GIWW), a 4-5 m deep and 60-150 m wide navigational channel located in the Mississippi Delta (Louisiana, USA). Single ship passage increases total suspended sediment (TSS) from the background value of-20 mg/l to peaks of 100-400 mg/l, which then decay exponentially with an e -folding time of about 1 h. Resuspension is mainly driven by barge traffic, and it is associated with the primary wave (Bernoulli drawdown) rather than the short waves in the Kelvin wake. Sediment resuspension is strongly correlated to the maximum velocity of the primary wave (up to 0.8 m/s), whose magnitude is mainly controlled by the barge draft and hence by the barge load. When averaged over time, ship traffic (-10 loaded barges per day) increases the mean TSS to about 50 mg/ l, i.e., double the background value. We suggest that this resuspension explains how the GIWW can transport sediment over-150 km - from the Atchafalaya River to Barataria Basin - despite relatively low advection velocity (0.1-0.2 m/s). More generally, we suggest that ship traffic in confined channels, as opposed to in channels bordering tidal flats, facilitates sediment bypass and should reduce in-channel sedimentation.