Quantifying overwash flux in barrier systems: An example from Martha's Vineyard, Massachusetts, USA

Abstract

Coastal barriers are particularly susceptible to the predicted effects of accelerated of sea-level rise and the potential for increased impacts of intense storms. Over centennial scales, barriers are maintained via overtopping during storms, causing deposition of washover fans on their landward sides. This study examines three washover fans on the south shore of Martha's Vineyard using a suite of data including vibracores, ground penetrating radar, high resolution dGPS, and LiDAR data. From these data, the volumes of the deposits were determined and range from 2.1-2.4 x 10 4 M .Two overwashes occurred during Hurricane Bob in 1991. The water levels produced by this storm have a return interval of ~28 years, resulting in an onshore sediment flux of 2.4-3.4 m 3 /m/yr. The third washover was deposited by a nor'easter in January 1997, which has a water level return interval of ~6 years, resulting in a flux of 8.5 m 3 /m/yr. These fluxes are smaller than the flux of sediment needed to maintain a geometrically stable barrier estimated from shoreline retreat rates, suggesting that the barrier is not in long-term equilibrium, a result supported by the thinning of the barrier over this time interval.

Interactions between barrier islands and backbarrier marshes affect island system response to sea level rise: Insights from a coupled model

“…In a recent study of several overwash fans on Martha's Vineyard, MA, by Carruthers et al [], overwash fluxes were found to be up to several times higher (2–8 m 3 /m/yr) than the maximum values used in simulations here. Given this finding, along with the potential for increased storm intensity and therefore increased overwash flux in the future, it is worth considering the effect of higher overwash fluxes on the barrier island‐marsh couplings.…”

Anthropogenic controls on overwash deposition: Evidence and consequences

“…Carruthers et al . [] compile 30 estimates of overwash fan geometric properties from a number of studies and report landward overwash extents of 13–359 m and volumes of 8–190 m 3 /m, respectively. Additionally, the average volume of 62 m 3 /m calculated for our natural environment is well in line with that estimated for overwash associated with the Hurricane of 1938 on Long Island, NY, of ~54–80 m 3 /m [ Redfield and Miller , ], an environment broadly similar to that studied here.…”

“…In recent decades, significant progress has been made in understanding the geological development of barrier islands and the important role of overwash in their evolution. Field‐based studies have captured measurements of overwash geometry, volume, and spatial configuration [e.g., Morton and Sallenger , ; Donnelly and Sallenger , ; Carruthers et al ., ; Williams , ; Shaw et al ., ; Lazarus and Armstrong , ]. Deposition of overwash sediment can occur as a result of wave runup exceeding the dune crest (classified as runup overwash) or as a result of the mean water level (tides plus storm surge) exceeding the dune crest (classified as inundation overwash) [ Sallenger , ].…”

Decadal behaviour of a washover fan, Skallingen Denmark

“…Recovery typically occurs during less energetic periods and is vitally important for long-term barrier preservation. However, barrier recovery is a slow process and relies on lengthy periods of accretion between storms and overwash, even more so since backbarrier accretion during an overwash event is typically much smaller than the sediment volume which is lost from the beach and shoreface at the same time (Matias et al, 2008;Carruthers et al, 2013). For example, Hawkes and Horton (2012) found that washover deposition during Hurricane Ike constituted only some 22-27% of the volume eroded from the beach and shoreface, while Houser and Hamilton (2009) estimated barrier accretion in northwest Florida one year after Hurricanes Ivan, Dennis and Katrina.…”