Wave‐formed sand ripples at Duck, North Carolina

Abstract

Abstract. A recently developed acoustic multiple transducer array was utilized to measure small-scale bed forms in the nearshore and inner shelf regions at Duck, North Carolina. Two populations of wave-formed ripples were observed: short wave ripples (SWR) with heights ranging from 3 mm to 2 cm and lengths ranging from 4 to 25 cm and long wave ripples (LWR) with heights ranging from 3 mm to 6 cm and lengths ranging from 35 to 200 cm. The SWR were only present sometimes, and their presence or absence was determined by a critical value of the near-bed mobility number. The SWR were highly dynamic, sometimes flattening during wave groups and reforming over several incident wave periods. The LWR, in contrast, were almost always present. They were longer and lower relief than predicted by models or generally observed previously. Both SWR and LWR were often observed to migrate shoreward but were rarely observed to migra. te seaward. The dimensions of the SWR, when they were present, were predictable by the

On the Influence of Currents and Grain Size on Wave Orbital Motion Scaling Dependence of Sand Ripple Geometry

“…This result suggests a more nuanced interaction between sediment size and hydrodynamic forcing, in which finer sediments may be more susceptible to forming multiple ripple modes even under shallow-water conditions. The findings are consistent with field observations reported by Hanes et al (2001) and Baas et al (2021), who documented the co-existence of large and small ripples on the seafloor, which refers to the simultaneous presence of ripple patterns with distinct wavelengths within the same observational window, including cases where shorterwavelength ripples are superimposed on longer-wavelength bedforms. In their study, smaller ripples were often observed to be superimposed on larger ones, resulting in a hierarchical ripple pattern.…”

On the Influence of Currents and Grain Size on Wave Orbital Motion Scaling Dependence of Sand Ripple Geometry

“…This result suggests a more nuanced interaction between sediment size and hydrodynamic forcing, in which finer sediments may be more susceptible to forming multiple ripple modes even under shallow-water conditions. The findings are consistent with field observations reported by Hanes et al (2001) and Baas et al (2021), who documented the co-existence of large and small ripples on the seafloor, which refers to the simultaneous presence of ripple patterns with distinct wavelengths within the same observational window, including cases where shorterwavelength ripples are superimposed on longer-wavelength bedforms. In their study, smaller ripples were often observed to be superimposed on larger ones, resulting in a hierarchical ripple pattern.…”

Geometry and dynamics of wave ripples in the nearshore zone of a coarse sandy beach

“…Similar to previous field investigations in sandy nearshores [ Vincent and Osborne , 1993; Thornton et al , 1998; Hanes et al , 2001], our observations of the bed morphology fall into two main classes: “small” wave ripple forms (SWR) with wave lengths less than 0.5 m and “large” wave ripple forms (LWR) with wave lengths larger than 0.5 m (including plane bed). The overwhelming majority of the ripples observed were SWR; LWR and plane bed conditions were only observed on a few occasions, under quite energetic surf zone conditions during which the SRP struggled to return a reliable image of the sea bed.…”

Intrawave observations of sediment entrainment processes above sand ripples under irregular waves

“…Figure 4 shows the temporal variation in these 2D bed profiles during the bursts, which were low‐pass filtered with a Gaussian filtering window to remove high frequency spatial fluctuations. Figure 4a, F08, for the fine‐medium‐grained bed shows the remnants of a rippled bed which was washed out to form a long wavelength bed form, similar to those observed by Hanes et al [2001]. This washed out bed approximates, for the purposes here, to an upper‐stage plane bed above which no rippled bed sediment dynamics were expected to occur.…”

On the Influence of Currents and Grain Size on Wave Orbital Motion Scaling Dependence of Sand Ripple Geometry

“…This result suggests a more nuanced interaction between sediment size and hydrodynamic forcing, in which finer sediments may be more susceptible to forming multiple ripple modes even under shallow-water conditions. The findings are consistent with field observations reported by Hanes et al (2001) and Baas et al (2021), who documented the co-existence of large and small ripples on the seafloor, which refers to the simultaneous presence of ripple patterns with distinct wavelengths within the same observational window, including cases where shorterwavelength ripples are superimposed on longer-wavelength bedforms. In their study, smaller ripples were often observed to be superimposed on larger ones, resulting in a hierarchical ripple pattern.…”

Geometry and dynamics of wave ripples in the nearshore zone of a coarse sandy beach

“…Similar to previous field investigations in sandy nearshores [ Vincent and Osborne , 1993; Thornton et al , 1998; Hanes et al , 2001], our observations of the bed morphology fall into two main classes: “small” wave ripple forms (SWR) with wave lengths less than 0.5 m and “large” wave ripple forms (LWR) with wave lengths larger than 0.5 m (including plane bed). The overwhelming majority of the ripples observed were SWR; LWR and plane bed conditions were only observed on a few occasions, under quite energetic surf zone conditions during which the SRP struggled to return a reliable image of the sea bed.…”

Intrawave observations of sediment entrainment processes above sand ripples under irregular waves

“…Figure 4 shows the temporal variation in these 2D bed profiles during the bursts, which were low‐pass filtered with a Gaussian filtering window to remove high frequency spatial fluctuations. Figure 4a, F08, for the fine‐medium‐grained bed shows the remnants of a rippled bed which was washed out to form a long wavelength bed form, similar to those observed by Hanes et al [2001]. This washed out bed approximates, for the purposes here, to an upper‐stage plane bed above which no rippled bed sediment dynamics were expected to occur.…”

On the Influence of Currents and Grain Size on Wave Orbital Motion Scaling Dependence of Sand Ripple Geometry

“…This result suggests a more nuanced interaction between sediment size and hydrodynamic forcing, in which finer sediments may be more susceptible to forming multiple ripple modes even under shallow-water conditions. The findings are consistent with field observations reported by Hanes et al (2001) and Baas et al (2021), who documented the co-existence of large and small ripples on the seafloor, which refers to the simultaneous presence of ripple patterns with distinct wavelengths within the same observational window, including cases where shorterwavelength ripples are superimposed on longer-wavelength bedforms. In their study, smaller ripples were often observed to be superimposed on larger ones, resulting in a hierarchical ripple pattern.…”

Geometry and dynamics of wave ripples in the nearshore zone of a coarse sandy beach

“…Similar to previous field investigations in sandy nearshores [ Vincent and Osborne , 1993; Thornton et al , 1998; Hanes et al , 2001], our observations of the bed morphology fall into two main classes: “small” wave ripple forms (SWR) with wave lengths less than 0.5 m and “large” wave ripple forms (LWR) with wave lengths larger than 0.5 m (including plane bed). The overwhelming majority of the ripples observed were SWR; LWR and plane bed conditions were only observed on a few occasions, under quite energetic surf zone conditions during which the SRP struggled to return a reliable image of the sea bed.…”

Intrawave observations of sediment entrainment processes above sand ripples under irregular waves

“…Figure 4 shows the temporal variation in these 2D bed profiles during the bursts, which were low‐pass filtered with a Gaussian filtering window to remove high frequency spatial fluctuations. Figure 4a, F08, for the fine‐medium‐grained bed shows the remnants of a rippled bed which was washed out to form a long wavelength bed form, similar to those observed by Hanes et al [2001]. This washed out bed approximates, for the purposes here, to an upper‐stage plane bed above which no rippled bed sediment dynamics were expected to occur.…”