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<p>Wave-generated longshore current is routinely monitored in coastal environments globally because of its role in diverse coastal management issues. Its flow direction as dictated by theory is dependent on the breaker-opening angle direction, at least in straight shoreline settings. Therefore, knowledge on the degree of non-coherence in directions of both variables on a non-straight shoreline configuration setting marked by an estuary mouth bar and reversing longshore currents at tidal frequencies becomes imperative. Results from an annual monitoring cycle of surf zones contiguous to Qua Iboe River estuary, S.E. coast of Nigeria, show four patterns of wave breaker-opening angle direction (<i>θ</i><sub>d</sub>) and longshore current direction (<i>V</i><sub>d</sub>). These are categorized as EE (<i>θ</i><sub>d</sub> and <i>V</i><sub>d</sub> are eastward-directed), WW (<i>θ</i><sub>d</sub> and <i>V</i><sub>d</sub> are westward-directed), EW (eastward <i>θ</i><sub>d</sub> and westward <i>V</i><sub>d</sub>), and WE (westward <i>θ</i><sub>d</sub> and eastward <i>V</i><sub>d</sub>). The frequency of non-coherent direction categories (EW and WE) in the estuary-proximal surf zones averaged 26% on the up-drift and 57% on the down-drift shoreline. All direction categories showed flood-stage asymmetry except for EE and WE in the down-drift surf zone which showed ebb-stage asymmetry. While the mechanism for some direction pattern categories is exploratory, wave refraction by the estuarine mouth bar, shoaling wave interaction with estuarine flow, and resultant shore-parallel pressure gradient flow are expressive in the presented data. Non-cognizance of spatiotemporal variation of these directional patterns will result in net sediment transport errors of the order of %-frequency of non-coherence, thus leading to poor performance of its many applications.</p>

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On Non-coherence in Directions of Wave Breaker-Opening Angle and Resulting Wave-Generated Longshore Current in Surf Zones of an Offset Shoreline, S.E. Nigeria

  • 期刊论文

  • 发表日期：

    2025年7月30日

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  • Effiom E. Antia

摘要

Wave-generated longshore current is routinely monitored in coastal environments globally because of its role in diverse coastal management issues. Its flow direction as dictated by theory is dependent on the breaker-opening angle direction, at least in straight shoreline settings. Therefore, knowledge on the degree of non-coherence in directions of both variables on a non-straight shoreline configuration setting marked by an estuary mouth bar and reversing longshore currents at tidal frequencies becomes imperative. Results from an annual monitoring cycle of surf zones contiguous to Qua Iboe River estuary, S.E. coast of Nigeria, show four patterns of wave breaker-opening angle direction (θd) and longshore current direction (Vd). These are categorized as EE (θd and Vd are eastward-directed), WW (θd and Vd are westward-directed), EW (eastward θd and westward Vd), and WE (westward θd and eastward Vd). The frequency of non-coherent direction categories (EW and WE) in the estuary-proximal surf zones averaged 26% on the up-drift and 57% on the down-drift shoreline. All direction categories showed flood-stage asymmetry except for EE and WE in the down-drift surf zone which showed ebb-stage asymmetry. While the mechanism for some direction pattern categories is exploratory, wave refraction by the estuarine mouth bar, shoaling wave interaction with estuarine flow, and resultant shore-parallel pressure gradient flow are expressive in the presented data. Non-cognizance of spatiotemporal variation of these directional patterns will result in net sediment transport errors of the order of %-frequency of non-coherence, thus leading to poor performance of its many applications.