SEDIMENT ACCRETION RATES OF CREVASSE-SPLAY DEPOSITS IN THE MISSISSIPPI DELTA DETERMINED BY OPTICALLY-STIMULATED LUMINESCENCE DATING: IMPLICATIONS FOR COASTAL RESTORATION

River diversion plans for coastal restoration in the Mississippi Delta have been suggested for decades, but implementation has been slow. By studying natural analogs of river diversions such as crevasse splays, it may be possible to improve the understanding about the viability of diverting freshwater and sediment from the Mississippi River into the adjacent wetlands. This study investigated sediment accretion rates of the Attakapas Splay near Napoleonville, Louisiana, using optically-stimulated luminescence (OSL) dating. Lithologic investigation shows that the thickness of the crevasse-splay deposit ranges from 3 to 9 m. Twelve samples from four cores were dated using a single aliquot regenerative dose (SAR) protocol. OSL was measured for 4-11 μm and 75-180 μm quartz grains. OSL dating results demonstrate that the Attakapas Splay was probably formed by multiple crevassing events from 700 to 1200 years ago. Sediment accretion rates were found to be >2.5 cm yr^-1 for individual crevassing episodes and >1 cm yr^-1 on average for the entire lifespan of the splay in proximal settings. The Attakapas Splay was formed by Bayou Lafourche, which likely discharged half of the Mississippi River at the time. Thus, the Bayou Lafourche sediment load may be comparable to that of the present day Mississippi River, which has experienced a reduction of its sediment load by ~50% due to anthropogenic intervention. This study shows that artificial crevassing has significant potential for vertical land growth and long-term wetland stability. Comparing our accretion rates to estimates of present-day rates of eustatic sea-level rise of ~0.3 cm yr^-1 globally and relative sea-level rise (RSL) as high as ~1 cm yr^-1 or more along portions of the Louisiana coast, we conclude that river diversions comparable to crevasse splays are capable of keeping pace with RSL rise and can potentially create new land.