Quantifying sediment accumulation and accretion using ²¹⁰Pb and ¹³⁷Cs

Approved for public release; distribution is unlimited. ERDC/TN-DOER-D20 May 2018 Quantifying Sediment Accumulation and Accretion using 210Pb and 137Cs by Brandon M. Boyd PURPOSE: This Dredging Operations and Environmental Research (DOER) Program Technical Note (TN) describes the use of the radionuclides 210Pb and 137Cs to measure rates of sediment accumulation and accretion and provides recommendations for best practices in field collection and laboratory analysis for U.S. Army Corps of Engineers (USACE) projects. BACKGROUND: The ability to quantify the flux of sediment to an area and the corresponding change in bed or surface elevation is useful in both sediment dynamic and hydrodynamic studies. Rates of accretion and accumulation can be used to determine past rates of contaminant and nutrient burial, constrain sediment budgets, identify areas experiencing long-term sedimentation, evaluate site-wide variability in sedimentation, and validate sediment transport models. Numerous radionuclides can be employed as tracers or can provide age control in a broad range of geophysical studies. This TN focuses on the quantification of sediment accumulation and accretion rates using lead-210 (210Pb; half-life = 22.2 years) and cesium-137 (137Cs; half-life = 30.7 years) methods. These methods have been successfully applied in a variety of terrestrial, coastal, and marine environments (Baskaran and Naidu 1995; Baskaran et al. 2015; Boyd et al. 2017). Estuarine sediment budgets, reservoir infilling, and engineering methods to increase wetland sedimentation are common focuses of USACE projects which can utilize radionuclide-based rates of sediment accumulation and accretion. The DOER Program supports ongoing research to evaluate the accretion dynamics of thin-layer placement and restored marshes. Sediment Accumulation and Accretion Rates. Sediment accumulation (mass/area/time) occurs when sediments are transported by a fluid (air or water) and subsequently deposited due to a redu