Longshore currents drive changes of coastal morphology and also embody a potential threat for swimmer safety. This explains the interest of coastal managers and scientists in costefficient techniques to quantify alongshore flow patterns. Traditional in-situ methods like Electro Magnetic (EMF) flow meters are expensive, time-consuming, dangerous to deploy during rough wave conditions and lack synoptic coverage. Recently a new technique was developed which quantifies flow velocities from intra-wave video observations of the nearshore (Chickadel et al., 2003). This Optical Current Meter (OCM) was successfully tested against extensive field experiments at a swell-dominated, intermediate to reflective beach at Duck, NC (USA). In this thesis, we investigate the applicability of the OCM at a dissipative beach at Egmond and Noordwijk (the Netherlands), characterized by shorter waves and a mild beach slope. The Optical Current Meter (OCM) was developed at Oregon State University as part of the Argus video program (Holman et al., 1993). It is based on the analysis of short time series of image intensities, sampled from an alongshore array of pixels. This yields alongshore time stack images, which typically reveal the bright horizontal bands of passing breaking waves and the oblique traces of foam patches drifting with the prevailing alongshore current. The velocity of the foam patches gives a measure of the alongshore surface current velocity. To quantify the surface foam drift, intensity time stacks are first Fourier transformed to a frequency-wavenumber spectrum, and finally to a velocity distribution. A model of the velocity distribution is fit to the observed distribution to estimate the foam drift velocity. Field test comparisons against an in-situ bidirectional EM flow meter, involving one month of video data sampled during the 1997 SandyDuck experiment, showed an rms error of 0.10 m/s. To verify the generic applicability of the OCM, the model was applied to quantify alongshore flow velocities at two field sites along the Dutch coast. The first test, performed at Egmond, involved a comparison of video-derived flow velocities and ground-truth flow meter measurements, both collected at 500 m north of the video station. At this distance, alongshore pixel resolutions are in the order of 2 m. This resolution turned out to be insufficient to resolve foam patches, which explains poor OCM performance at Egmond. The second test involved the validation of OCM against a two-week dataset of hourlymeasured alongshore flow velocities, sampled directly in front of the Noordwijk video station. With an rms off-set of about 30 cm, the technique shows improved performance. For positive (i.e. southward-directed) velocities, video-derived velocities consistently overestimate the corresponding EMF-measured values. This can be explained from the observation that the OCM estimates surface velocities, whereas the EMF measures a velocity in the water column, at about 25 cm above the sea bed. To illustrate the potential of the OCM, the model was used to quantify flow-velocities along five cross-shore arrays spacing 10 m cross-shore. The result shows a realistic distribution of flow velocities across the surf zone, with maximum velocities up to 0.65 m/s at about 40 m off the shoreline. The OCM has proved to provide usable results at the Holland coast within a range of 200 m at both sides of a camera station. Improvements in camera resolution will also improve the usability of the OCM