Jamie MacMahan

Learn More
[1] Energetic very low frequency (VLF; frequencies <0.004 Hz) surf zone eddies (SZEs) were observed on a beach composed of shore-connected shoals with quasi-periodic ( 125 m) incised rip channels at Sand City, Monterey Bay, California. Incident waves consisted of predominantly shore-normal narrow-banded swell waves. SZEs were located outside the gravity(More)
[1] The retention of floating matter within the surf zone on a rip-channeled beach is examined with a combination of detailed field observations obtained during the Rip Current Experiment and a three-dimensional (3-D) wave and flow model. The acoustic Doppler current profiler–observed hourly vertical cross-shore velocity structure variability over a period(More)
[1] Numerical computations are used to explain the presence of very low frequency motions (VLFs), with frequencies less than 0.004 Hz, in the rip current velocity signals observed during the Rip-current field Experiment (RIPEX) field experiment. Observations show that the VLF motions are most intense within the surfzone and then quickly taper off in the(More)
[1] Novel observations of surface grain-size distributions are used in combination with intra-wave modeling to examine the processes responsible for the sorting of sediment grains on a relatively steep beach (slope = 1:7.5). The field observations of the mean grain size collected with a digital camera system at consecutive low and high tides for a 2 week(More)
[1] Observations of velocity fluctuations with periods between about 4 and 30 min, thus longer than infragravity waves and referred to as very low frequency (VLF) surf zone motions, are described and compared with numerical simulations. The VLF motions discussed here exclude instabilities (generated by the wave‐driven alongshore current velocity shear) that(More)
Rip currents are shore-normal, narrow, seaward-flowing currents that originate within surf zone, extend seaward of the breaking region (rip head), and can obtain relatively high velocities. Within the last decade, there have been a significant number of laboratory and field observations within rip current systems. An overview of rip current kinematics based(More)
Comprehensive field measurements in the throat of a rip current have been obtained for the first time as a rip current and its morphology migrated (∼ 4m/day) through a coherent cross-and alongshore array of co-located pressure and velocity sensors. The rip current is associated with a small bathymetric surfzone non-uniformity (1 in 300 alongshore(More)