![]() ![]() During this event, monitoring of hydrodynamics and morphological evolution was implemented, making it possible to better understand the impact of concomitant marine storm and fluvial flood during an extreme meteorological event on spit breaching of a small Mediterranean river mouth. This concomitance of river flood and marine storm is quite common in the western Mediterranean Sea, and was the case for the Gloria event, considered to be the most extreme event in recent decades. While the morphological response during floods or during marine storm events has been widely documented in the literature, little is known about the mechanisms acting during the co-occurrence of fluvial and marine hazards. River mouths are highly dynamic environments responding very rapidly to changes in wave energy or river floods. This relationship between area and volume unlocks information about past storm deposition captured in aerial photo archives, and enables estimation of washover volume where direct measurement of volume is unavailable or impossible. What if three‐dimensional washover volume could be estimated from the two‐dimensional shape and size of washover deposits visible in aerial photos? Here, we created washover deposits in a laboratory and compared them to washover in field settings to show that the area of a washover deposit is a good predictor of its volume. However, washover volume is expensive to measure over large spatial scales-so despite its importance to sediment budgets, washover volume often goes unquantified. An accurate sediment budget provides an indication of environmental functioning and sustainability. Knowing the total volume of washover delivered by a storm event helps coastal managers account for the amount of sediment that moves through a beach system over time, known as a sediment budget. ![]() ![]() That deposit, which might settle among dunes, on a marsh, or on the streets of a neighborhood, is called washover. When a coastal storm drives water up and over the crest of a beach, sediment gets picked up by the flow and deposited behind the beach. Something we were uniquely able to observe in the experiment is a marked morphological distinction between inundation-and wave-driven washover (Figure 4)-the two forcing regimes at the upper end of the Sallenger storm-impact scale (Sallenger, 2000). Overwash processes and washover formation are notoriously difficult to observe and record in situ (Engelstad et al., 2017 (Engelstad et al.,, 2018Leatherman & Zaremba, 1987 Matias & Masselink, 2017), and as long as three-dimensional surveys of post-storm impacts remain sparse, physical experiments can inform and corroborate numerical modeling of storm impacts on barrier systems (e.g., McCall et al., 2010 Miselis & Lorenzo-Trueba, 2017 Nienhuis et al., 2021 Passeri et al., 2020 Rogers et al., 2015 Smallegan & Irish, 2017) and motivate testable hypotheses regarding future barrier dynamics. That is, rather than requiring different scaling relationships across a range of built fractions, volume as a function of area describes a single scaling relationship for all built fractions. ![]()
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