Hurricane Harvey Storm Sedimentation in the San Bernard National Wildlife Refuge, Texas: Fluvial Versus Storm Surge Deposition

Abstract

Few studies have documented the characteristics of fluvial flooding-induced storm deposits associated with a modern hurricane. Hurricane Harvey (2017) caused extensive flooding in coastal Texas due to a combination of storm surge and heavy precipitation. This study investigates the depositional process associated with Hurricane Harvey by means of loss-on-ignition (LOI) and X-ray fluorescence (XRF) analyses of 9 short cores and 17 surface samples collected from the San Bernard National Wildlife Refuge (SBNWR), Texas. Hurricane Harvey caused the largest flood within SBNWR over the last 28 years, and freshwater flooding from the San Bernard River was the predominant cause of this inundation. A distinct washover sand layer is lacking at all coring sites, but the intrusion of seawater can still be detected by a peak in the chlorine/bromine (Cl/Br) ratio of most sediment cores. Our study shows that Cl/Br ratios are higher in coastal environments than in terrestrial environments, thereby confirming that this elemental ratio can be used as a salinity indicator and, as a corollary, evidence of marine intrusion into lower-salinity environments. The ensuing phase of freshwater flooding and fluvial sedimentation is represented by a distinct flood deposit in only three cores, but is absent or indistinct in most cores. The elusiveness of the Harvey fluvial flood deposit can be explained by the relatively low discharge and suspended sediment load of the San Bernard River, the uneven distribution of this event deposit, and its indistinctiveness with the underlying deposits laid down by previous flood events.