Observations of fine scale stratigraphy using a digital imaging system

Although beaches appear to consist of uniform sands, upon closer inspection, a broad range of sizes can exist on a beach. Recent studies have shown that not only does grain size vary on the surface of beaches, it is also correlated with the morphology and the grain size surface patterns change as the morphology changes. XBeach is now being used, with a multi grain size module, to predict transport of different grain sizes, their sorting and separation and to determine the importance of grain size variation on the beach. However, only surface grain sizes have been measured and compared with model results. In March and April of 2014, a pilot experiment was performed at the Army Corps of Engineers Field Research Facility. During the experiment, 36 stratigraphic cores were collected along a cross-shore profile from the dune to the lowest extent of the swash. These cores are being sampled with a digital imaging system (DIS) to estimate grain size. The DIS can streamline the process of collecting grain size information. Errors associated with the technique and with coring (and compaction) will be discussed. Grain size stratigraphy in the beach and its variations with location and in time are being examined at this time. These data will be used, together with observations from a large trench (see related abstract by Wadman et al.), to interpret layering in the beach owing to storms, rising and falling tides and wave-by-wave transport mechanism. In addition, the data will be used to drive model predictions to assess the importance of grain size variation, differential grain transport and layering on the morphodynamics of beaches (see related abstract by Reniers et al.).