Research Summaries

Back CAREER: Hydrodynamic and morphodynamic of beach breaching and closure

Fiscal Year 2021
Division Graduate School of Engineering & Applied Science
Department Oceanography
Investigator(s) Orescanin, Mara S.M.
Sponsor National Science Foundation (NSF)
Summary This study proposes to obtain in-situ measurements at the wave-dominated mouth of two ephemeral rivers during breaching and closure events to quantify both the hydrodynamic and morphological processes. Field observations will include long-term time series during the winter months and short-term, high-resolution aerial and hydrodynamic measurements during and after a breach/closure of the inlet during the five year study. The objectives are to determine the interplay between short term (hours) and long term (seasonal) morphological evolution at an ephemeral river by examining the relative forcing of waves, tides, and discharge and how this relates to morphological evolution. The hypotheses to be tested are: H1: There are three dynamically different stages of breach evolution: 1. Initial breaching, where river forcing dominates all locations within the breach and the cross-sectional area of the inlet changes rapidly with respect to the tidal time scale; 2. Steady state breaching, where river forcing is comparable to, but stronger than, ocean forcing from wave breaking, but that morphological evolution is slow relative to the tidal scale; 3. Breach closure, where river forcing is weak relative to ocean forcing from wave breaking, and development of a sediment sill decreases the cross-sectional area. H2: Location of the breach (river) plume extends into the inner shelf during initial breaching but the location is dependent on offshore wave characteristics during periods of steady state breaching. During breach closure, the plume is trapped within the surfzone, indicating wave dominance. H3: Long term morphological trends are balanced between years with breach channel migration and years with no migration, yielding nearly steady state sediment budgets on longer timescales. H4: Coastal ocean wave characteristics and nearshore bathymetry impact the location of the breach (river) plume, where wide surf zones (shallow slope) enhance longshore orientation and narrow surf zones (steep slope) have enhanced offshore presence.
Keywords
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