Nearshore Profiles Research Articles

Estimation of littoral drift for non monsoon using beach and nearshore profiles

ABSTRACT Beach profile measurements spatially and temporally or information on periodical dredging helps in assessing the littoral drift in an area. Beach profiling is one of the traditional methods to understand the beach as well as nearshore morphology in a short term. Exact quantification is always a challenging task near coasts as a part of coastal zone management activities due to the lack of enough information pertaining to sediments and its movement. In this study, the long and crossshore movements of sediments were analysed by using beach and nearshore profiles at three typical locations along South Karnataka coast in non-monsoon season. The rates of changes in areas and volumes were estimated along Gokarna, Honnavar and Malpe locations. All the locations are connected with inlets or estuaries or ports. The analysis of nearshore profiles indicated marginal changes in areas at Gokarna and Honnavar. The change is relatively more at Malpe site. The rate of volume changes of sediment over a study period increases towards south from Gokarna to Malpe and varies from 0.14 M m3 to 0.17 M m3. The potential longshore drift along the coast was also estimated whose correlation is strong with the shoreline orientations of the locations considered.

Factors controlling longshore variations of beach changes induced by Tropical Storm Eta (2020) along Pinellas County beaches, west-central Florida

Tropical Storm Eta impacted the coast of west-central Florida from 11 November to 12 November 2020 and generated high waves over elevated water levels for over 20 hours. A total of 148 beach and nearshore profiles, spaced about 300 m (984 ft) apart, were surveyed one to two weeks before and one to eight days after the storm to examine the beach changes along four barrier islands, including Sand Key, Treasure Island, Long Key, and Mullet Key. The high storm waves superimposed on elevated water level reached the toe of dunes or seawalls and caused dune erosion and overwash at various places. Throughout most of the coast, the dune, dry beach, and nearshore area was eroded and most of the sediment was deposited on the seaward slope of the nearshore bar, resulting in a roughly conserved sand volume above closure depth. The longshore variation of beach-profile volume loss demonstrates an overall southward decreasing trend, mainly due to a southward decreasing nearshore wave height as controlled by offshore bathymetry and shoreline configurations. The Storm Erosion Index (SEI) developed by Miller and Livermont (2008) captured the longshore variation of beach-profile volume loss reasonably well. The longshore variation of breaking wave height is the dominant factor controlling the longshore changes of SEI and beach erosion. Temporal variation of water level also played a significant role, while beach berm elevation was a minor factor. Although wider beaches tended to experience more volume loss from TS Eta due to the availability of sediment, they were effective in protecting the back beach and dune area from erosion. On the other hand, smaller profile-volume loss from narrow beach did not necessarily relate to less dune/ structure damage. The opposite is often true. Accurate evaluation of a storm’s severity in terms of erosion potential would benefit beach management especially under the circumstance of increasing storm activities due to climate change.

From local-to global-scale control factors of wave attenuation in mangrove environments and the role of indirect mangrove wave attenuation

Wave dissipation by drag forces is considered the dominant wave transformation process in fringe mangroves even though other process may be present. Furthermore, mangrove loss generates vertical erosion and changes in the nearshore profile that can affect wave breaking, whereas changes in vegetation density owing to species composition or disturbances may affect drag dissipation. The aim of this study is to identify local and global geographical control factors of wave attenuation in mangrove environments and to assess the effect of nearshore profile modifications by mangrove loss on wave breaking dissipation. Bottom wave attenuation from breaking and shoaling, the total wave energy attenuation rate, and wave reflection were estimated using modeling, pressure sensors, and reflection coefficients, respectively, at sites with contrasting wave power, bathymetric slope changes, vegetation density, and logging disturbance. Wave breaking changes by mangrove loss were estimated using wave evolution modeling under three successive slope increments by 0.7% in two background mangrove nearshore profiles. The wave energy attenuation rate at the study sites was affected by incident wave height (28–76%), epiphytic oyster presence, vegetation density, tidal inundation (41–55%), and wave reflection from cliffs. The last two variables explained the wave attenuation rate variability at a cliffed study site (61–70%), whereas the last three variables explained the wave attenuation rate variability on a global scale (92%). Wave attenuation rates by vegetation and bottom friction were underestimated (2–59% from global scale data) when wave shoaling was not considered. The wave energy increased or moved further inland in unvegetated scenarios in comparison with vegetated shores. In addition to drag forces, mangroves can promote wave attenuation by inducing friction, wave breaking, and wave reflection from prop-roots epiphytic organisms, shallow nearshore profiles, and cliffed edges, respectively.

Effect of continental and nearshore slopes on tsunami height

In the present study, an attempt is made to understand the effect of continental and nearshore slopes on the transmission, propagation and run-up of tsunami. A numerical model study is carried out using shallow water equations that are solved using Crank-Nicolson finite difference approximation method on a staggered grid. A rectangular solitary wave is considered to propagate over typical continental slopes and nearshore profiles available along the Indian coast. The amplification or attenuation of tsunami characteristics over these cross-sections was studied. It was observed that the tsunami run-up is altered with varying continental slope, water depth on continental shelf and nearshore slope. The study suggests that tsunami height on the continental shelf increases for shallow continental shelf depths. The percentage increase in tsunami height with decrease in continental shelf depth from 200 m to 50 m is found to be 31%. Higher tsunami run-up was observed for deeper continental shelf and steeper continental slope, whereas lower tsunami run-up for deeper continental shelf and flatter continental slope. It was observed that for a steep continental slope (1:0.1), a reduction in nearshore slope (steep to flat) increases tsunami run-up up to a slope of 1:632 and then decreases.

Hindcast of Long-term Shoreline Change due to Coastal Interventions at Namhangjin, Korea

ABSTRACT Chang, Y.S.; Huisman, B.; Boer, W., and Yoo, J., 2018. Hindcast of Long-term Shoreline Change due to Coastal Interventions at Namhangjin, Korea. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 201–205. Coconut Creek (Florida), ISSN 0749-0208. Namhangjin beach is protected by multiple submerged breakwaters (SBWs) which were built to protect the ~4 km long sandy beach. A coastline model (UNIBEST) was used to investigate the long term effect of the SBW structures on the beach. The model computes long-term shoreline changes due to coastal structures as a result of the strong longshore sediment transport gradients at the structures. Bathymetry data of the shoreface and nearshore profiles were obtained from a field survey, while wave conditions from offshore WAM hindcast (Wave Modeling Group) were transformed towards the nearshore with the Delft3D+SWAN mode...

Retrieval of nearshore bathymetry from Landsat 8 images: A tool for coastal monitoring in shallow waters

Nearshore bathymetry is likely to be the coastal variable that most limits the investigation of coastal processes and the accuracy of numerical models in coastal areas, as acquiring medium spatial resolution data in the nearshore is highly demanding and costly. As such, the ability to derive bathymetry using remote sensing techniques is a topic of increasing interest in coastal monitoring and research. This contribution focuses on the application of the linear transform algorithm to obtain satellite-derived bathymetry (SDB) maps of the nearshore, at medium resolution (30m), from freely available and easily accessible Landsat 8 imagery. The algorithm was tuned with available bathymetric Light Detection and Ranging (LiDAR) data for a 60-km-long nearshore stretch of a highly complex coastal system that includes barrier islands, exposed sandy beaches, and tidal inlets (Ria Formosa, Portugal). A comparison of the retrieved depths is presented, enabling the configuration of nearshore profiles and extracted isobaths to be explored and compared with traditional topographic/bathymetric techniques (e.g., high- and medium-resolution LiDAR data and survey-grade echo-sounding combined with high-precision positioning systems). The results demonstrate that the linear algorithm is efficient for retrieving bathymetry from multi-spectral satellite data for shallow water depths (0 to 12m), showing a mean bias of −0.2m, a median difference of −0.1m, and a root mean square error of 0.89m. Accuracy is shown to be depth dependent, an inherent limitation of passive optical detection systems. Accuracy further decreases in areas where turbidity is likely to be higher, such as locations adjacent to tidal inlets. The SDB maps provide reliable estimations of the shoreline position and of nearshore isobaths for different cases along the complex coastline analysed. The use of freely available satellite imagery proved to be a quick and reliable method for acquiring updated medium-resolution, high-frequency (days and weeks), low-cost bathymetric information for large areas and depths of up to 12m in clear waters without wave breaking, allowing almost constant monitoring of the submerged beach and the shoreface.

Bedform geometry on a barred sandy shore

An instrumented sled was used to repeatedly measure nearshore profiles and bedform height ( η), length ( λ) and asymmetry ( α) on a double-barred beach at Mangawhai (Northland, New Zealand). The 6-week experiment measured cross-shore profiles at 30-m intervals to 12-m water depth and 500 m alongshore. Bedform response to changing wave conditions, that included both fairweather swell and storm waves, was sampled. Bedform geometry is closely tied to large-scale morphology with alternating bands of flat bed and lunate megaripples (LMR, η ≤ 0.3 m, λ ≤ 2.9 m) on the longshore bars. A transition in bedform morphology occurs on the seaward face of the outer bar, with symmetrical vortex ripples ( η ≤ 0.04 m, λ ≤ 0.7 m) replaced by LMR. Within the transition zone, η increases relative to λ, so that η/ λ increases onshore with a shift to increasingly 3-dimensional forms. Bedforms reconfigured to the fairweather swell 2 weeks after a storm at the start of the experiment. This was shown by a substantial reduction in longshore and cross-shore variability in average bedform size and steepness. Wave measurements made on the ripple field seaward of the longshore bars at − 5.2 and − 6.9 m mean sea level (MSL) indicate that sand mobilisation was episodic under fairweather swell (skin-friction Shields parameter ( θ w′) ≤ 0.35). By comparison, θ w′ ∼ 2 under storm waves indicates that the entire nearshore bed was active, at least to − 6.9 m MSL. This is consistent with the presence of LMR on storm deposits to − 6 m MSL. Lunate megaripples dominate bed roughness when parameterised by η 2/ λ. They persist seaward of the longshore bars for weeks after storms because substantial sand transport is required to reconfigure the bed to fairweather conditions. The natural variability in bedform geometry will need to be accounted for if realistic morphodynamic models are to be realised.

Morphologic properties derived from a simple cross‐shore sediment transport model

This paper builds on the now classical discussions by Bowen [1980] and Bailard [1981] on the applicability and implications of Bagnold's [1963] sediment transport model to nearshore profile modeling. We focus on the morphologic implications of both the strengths and weaknesses of Bagnold's model, isolating the transport terms that are well predicted (i.e., mean flow terms) from those that are not well predicted (i.e., transport due to correlations between flow and sediment load). We factor Bagnold's model into a dimensional transport magnitude and a nondimensional term. The nondimensional term describes the relative importance of transport due to undertow, gravity, and correlations between flow and sediment load. The transport magnitude largely determines the response time of nearshore profiles. For typical nearshore environments this response time was estimated to vary as a function of incident rms wave height (Hrms) from ∼500 years (Hrms ∼ 0.5 m) to 2 years (Hrms ∼ 3 m). The relative importance of competing transport mechanisms is shown to depend strongly on the relative wave height (defined as the ratio of the rms wave height to the local depth). Simplified nearshore transport parameterizations that are a function of this variable were derived and were interrogated for the existence and form of equilibrium profiles. Several differences from previously computed equilibrium profiles were noted. First, because the relative wave height saturates in natural surf zones, equilibrium profiles converge to a relatively flat profile near the shoreline. Second, under some situations a seaward sloping equilibrium profile may not exist. Third, the long response times combined with unknown stability of an equilibrium profile make it difficult to assess the physical connection between theoretical equilibrium profiles and profiles observed in nature.

Extracting decadal morphological behaviour from high-resolution, long-term bathymetric surveys along the Holland coast using eigenfunction analysis

The understanding and prediction of coastal behaviour over a time span of decades and alongshore stretches of tens of kilometres is important in coastal management. The controlling variables for coastal behaviour on these scales are yet unknown. It is hypothesised that regions exhibiting different large-scale coastal behaviour (LSCB-regions) are controlled by different hydrodynamic forcings, or by different sedimentological or morphological constraints, or by some combination of these factors.The objective of this study is to elaborate a method that effectively quantifies large-scale morphological changes from a large bathymetric data set (large temporal and spatial extent combined with a high resolution), such to define LSCB-regions. The method of analysis consists of a combination of the empirical eigenfunction technique and a moving window approach.The method has been applied on a data set of over 14,000 nearshore profiles. The data set consists of yearly soundings of the nearshore profile along a coastal stretch of 115 km length (the Holland coast). The alongshore profile spacing is generally 250 m. All profiles surveyed in the period 1963–1990 are included in the analysis.Application of the method on the Dutch data set reveals that LSCB-regions indeed can be identified. The sizes of the LSCB-regions are 5 km, 15 km, 20 km, 32 km, and 42 km. Differences in behaviour of the ‘secondary’ morphology (i.e. morphology other than the mean profile shape, e.g. nearshore bars) are most pronounced. The change in behaviour between LSCB-regions generally occurs over distances as short as about 2 km. The boundaries between the regions are therefore surprisingly sharp.In general, no clear long-term trends in the development of the shape of the sub-aqueous profile have been observed along the Holland coast. Along certain stretches, trends in cross-shore shifting of the sub-aqueous profile occurred. The average shape of the sub-aqueous profile seems to have no relation with the trend in cross-shore shifting of the shoreline (the +1 m-contour). The (sub)decadal shoreline fluctuations, however, are possibly related to the largescale dynamics of multiple bar systems.

Random breaking waves: Field verification of a wave-by-wave algorithm for engineering application

A simple numerical algorithm is utilized to test the wave-by-wave approach to modeling random wave transformation caused by shoaling, breaking and reforming across nearshore profiles of arbitrary shape. Histograms of wave height and associated statistics predicted by the model show favorable comparison to measurements from the nine tests of the DUCK'85 field experiment, with a root mean square error less than 10% for most wave statistics. Although suitable for use in many engineering applications, the model does overpredict the number of waves that reform as they pass over a trough formation, which is one facet that warrants improvement. Using the model predictions as a point of reference, the qualitative effects of (1) an offshore wind, (2) wave reflection and (3) surf beat are identified and discussed.

Simulating the movement of bed and suspended loads in the coastal environment

A dynamic computer simulation model is implemented to simulate wave-induced transport of bed and suspended material, and the associated development of nearshore profiles. The model uses the Airy, Stokes', cnoidal and solitary wave theories to compute the height, length, celerity, steepness, breaker indices, and horizontal, veritical, mass drift and orbital velocities of random waves propagating along a flat slope. With shoreward wave propagation both bed and suspended loads are computed at discrete grid points. The FORTRAN '77 simulation program is executed for 3000 iterations, with each iteration corresponding to one twelfth of a tidal cycle. The simulated results demonstrate that sediment movement is controlled by the magnitude of the drift, orbital and horizontal wave velocity components, with wave breaking having a direct influence on the deposition of transported bed load. The shallow water regions of cnoidal and solitary waves are characterized by the presence of high concentrations of suspended material. Over the runlength of the simulation, transport of bed and suspended material cause the initialized profile state to change through a sequence of ill-defined transient states to a final morphological state. Examination of the sequence of profile states indicate weak resemblances of barred and nonbarred profile configurations.

Sediment budget for Paradip port, India

A sediment budget calculation for Paradip port, situated on the east coast of India, is presented, taking into account longshore sand transport and nearshore erosion and deposition. Longshore sand transport rates have been computed using a CERC formula for which the average breaking wave characteristics, obtained from wave refraction diagrams were used. Quantities of nearshore erosion and deposition were obtained from the analysis of near-shore profiles. The study reveals that a quantity of nearly 0·8 million m 3 of sand is deposited in the approach channel, while as much as 1·3 million m 3 of sand is removed from the northern side of the port annually. It is also clear that the dumping of sand dredged from the port and its approaches beyond the 11 m depth contour on the northern side of the port, does not help to prevent erosion to the north of the port.

Controls on Formation and Form of Barred Nearshore Profiles

Linear regression is used to examine effects of maximum fetch length and nearshore slope in controlling characteristics of barred nearshore profiles. Data came from twelve sites in the Great Lakes and two in the Gulf of St. Lawrence. Fetch length is a good predictor of height of the outer bar, depth to the crest, and offshore distance; bar number correlates significantly with decreased nearshore slope. Incident waves are the dominant control on nearshore bar formation and maintenance during storms. THE purpose of this article is to examine the extent to which the variation in several morphological parameters of barred profiles can be explained by fetch length and nearshore slope. The approach is empirical, with data from sites in the Great Lakes and the Gulf of St. Lawrence, and the strength of the explanation is tested by linear regression. Barred profiles exist year-round at the two locations. This condition allows definition of a characteristic profile for each site and avoids complication induced by the seasonal change from a barred to a nonbarred profile that occurs on some oceanic coasts. Data for the analysis came from twelve sites in the lower Great Lakes and two in the Gulf of St. Lawrence (Fig. 1). Thirteen of the sites have one or more nearshore bars year-round, but the other site has a nonbarred profile throughout the year. My research was the source of data for ten sites; data for three other sites were taken from published studies (Hands 1976; Owens 1977; Gillie 1980), and John Coakley of the Canada Centre for Inland Waters provided data for one site. Typical profiles for each site appear in Figure 2, and selected characteristics of each site and profile are contained in Table I. The sites were chosen to encompass a wide range of fetch lengths, nearshore slopes, and nearshore-profile characteristics. However, short, steep storm waves dominate at all sites, swell waves having limited importance. During a period of years, the wind climate at all the Great Lakes sites should be very similar, and conditions at the two gulf sites are probably comparable. The actual wave climate at each site varies with orientation and fetch, but the magnitude of the dominant storm waves is controlled largely by fetch length and is generally independent of orientation. The Great Lakes sites are virtually tideless, although water level fluctuates seasonally by 0.3 to 0.4 m. Both sites in the gulf are microtidal, with a mean tidal range of less than 1 m. * Grants from the Natural Sciences and Engineering Research Council of Canada since 1977 supported the fieldwork on which this article is based. * Department of Geography, University of Guelph, Guelph, Ontario, Canada N1G 2W1. This content downloaded from 207.46.13.101 on Sat, 08 Oct 2016 05:42:06 UTC All use subject to http://about.jstor.org/terms 186 THE GEOGRAPHICAL REVIEW

Simulating the Effects of Random Waves on Concave-Shaped Nearshore Profiles

A dynamic model for the stochastic simulation of wave action on concave-shaped nearshore profiles is presented. The Airy, Stokes and Cnoidal wave theories, together with the appropriate shoaling equations are used in the simulation. Wave heights are adjusted for breaking conditions, and bed load and suspended load are computed with the best available equations. On each iteration, which is approximately seventy minutes of real time, deep water wave heights and periods are parameterized in the model with autocorrelated Rayleigh distributed variates. The tidal range, which changes every twelve iterations, is a normally distributed random variate. Using different initial slopes but identical wave and sediment input values, a FORTRAN IV program is executed for two simulation runs, with each run lasting for 1512 iterations. The results demonstrate that on a short-term basis the configuration of the profile developed for the first run of the simulation is not repeatable for the second simulation run. However, on each simulation run, the cumulative effects of low deepwater steepness values influence the development of a nonbarred configuration, while sustained high steepness values can be correlated with erosion and bar formation. Both barred and nonbarred configurations attain some form of temporary and repeatable equilibrium when sediment transport is not initiated, and when consecutive input values of wave heights and periods remain almost constant. Temporal variations in wave steepness not only give an indication of breaker type, but also reflect changes in the various components of wave velocity, and the magnitude and direction of sediment transport. It is shown that with plunging breakers the bulk of the transported load is deposited just seaward of the breakpoint position, while spilling breakers and higher steepness values generally cause an onshore movement and deposition of material.

Simulating the Effects of Random Waves on Concave-Shaped Nearshore Profiles

Simulating the Effects of Random Waves on Concave-Shaped Nearshore Profiles

ON PREDICTING INFRAGRAVITY ENERGY IN THE SURF ZONE

Flow data were obtained in the surf zone across a barred profile during a storm. RMS cross-shore velocities due to waves in the infragravity band (wave periods greater than 20 s) had maxima in excess of 0.5 m/s over the bar crest. For comparison to measured spectra, synthetic spectra of cross-shore flow were computed using measured nearshore profiles. The synthetic spectra were calculated assuming a white runup spectrum of mode-4 edge waves of unit amplitude, although the results would be essentially the same for standing waves or any edge-wave mode above 2. The structure, in the infragravity band, of these synthetic spectra corresponded reasonably well with the structure of the measured spectra. Total variances of measured cross-shore flow within the infragravity band were nondimensionalized by dividing by total infragravity variances of synthetic spectra. These nondimensional variances were independent of distance offshore and increased with the square of the breaker height. Thus, cross-shore flow due to infragravity waves can be estimated with knowledge of the nearshore profile and incident wave conditions.

SURVEY TECHNIQUES USED TO MEASURE NEARSHORE PROFILES

The three most common survey techniques used to measure nearshore profiles are (1) conventional boat-sonic depth sounder; (2) hydrostatic pressure profiler; and (3) the self powered Coastal Research Amphibious Buggy (CRAB)- Theory of operation and methodology used for each technique are summarized and evaluated. Three separate field tests using survey data from each technique are evaluated for system repeatability. Data reduction, sea surface correction, and filtering methods for boat-depth sounder survey data are examined.

Bottom sediments of Lake Rotoma

Abstract Lake Rotoma is a deep (70–80 m), oligotrophic, warm monomictic lake of volcanic origin with insignificant stream inflow and no clearly defined outflow. For at least 60 years up to 1972 the lake level fluctuated markedly about an overall rising trend of some 6–10 m. Nearshore profiles are related to the prevailing wave climate superimposed upon the overall rising lake level, shelves being wider, less steep, and deeper about the more exposed eastern and southern shorelines. The outer portions of shelves extending well below modern storm wave base into waters as deep as 15–25 m are relict features from lower lake level stands. Sediments fine from sand‐gravel mixtures nearshore to silts in basinal areas. Their composition reflects a composite provenance involving the lavas and tephras about the lake, as well as intralake diatom frustules and organic matter. The distribution pattern of surficial bottom sediments is an interplay between grains of both biological and terrigenous origin, supplied present...

Morphodynamics of reflective and dissipative beach and inshore systems: Southeastern Australia

Field experiments involving direct measurement of surf and inshore current spectra, inshore circulation patterns, and depositional morphology have been replicated under different energy conditions and in several environmentally contrasting beach localities on the high-energy coast of New South Wales, Australia. The region exhibits compartmentalized beach systems and is dominated by a highly variable wind-wave climate superimposed on persistent high-energy swell ( T = 10–14 sec). Two general types of beach system occur: (1) predominantly reflective systems in which much of the incidentwave energy is reflected from the beach face; and (2) dissipative systems with wide surf zones and high turbulent energy dissipation. Reflective systems are characterized by steep, linear beach faces, well-developed berms and beach cusps, and surging breakers with high runup and minimum setup; rip cells and associated three-dimensional inshore topography are absent. Wave height and current spectra from reflective beaches consistently have their dominant peaks at incident wave and subharmonic frequencies, and cross-spectra indicate the existence of low-mode edge waves at those frequencies. Infra-gravity peaks are negligible. Under low-energy conditions subharmonic peaks are low relative to incident-wave peaks; however, increasing breaker height tends to be accompanied by increasing subharmonic dominance. Analyses of shore-normal currents near the bed show that under all conditions the strongest shoreward motions are induced by the incident waves; however, seaward motion near the beach face is subharmonic-dominated. Dissipative systems characterize the exposed open coast and are fronted by concaveupward nearshore (seaward of break) profiles and wide flat surf zones. Waves break 75–300 m seaward of the beach and dissipate much of their energy before reaching the beach, creating significant radiation-stress gradients and setup. Topography is much more complex and varied than in the case of reflective beaches; one or more bars, three-dimensional inshore topography and different scales of rip cells are normally present. The commonly occurring time-and-environment-dependent morphologic states can be classified into six general types. The greatest total dissipation is associated with Type 1 which prevails in the regions of most abundant inshore sediments or during and immediately after severe storms. Setup is highest and runup is lowest (relative to incident-wave height) with this type and the dominant energy near the beach is in the surf-beat part (80–120 sec) of the spectrum. As the bar migrates shoreward (Types 2 and 3) and beach face steepens and a deep trough develops within which the partially dissipated waves reform. Although the outer surf zone remains dissipative, synchronous and subharmonic resonance occurs near the beach face and, as with reflective beaches, low-mode edge waves form beach cusps. A conspicuous feature of Types 2 and 3 is the occurrence of pronounced resonant spectral peaks at 4 T ( ⋍ 40–50 sec ) within the trough and on the bar. Edge waves at this frequency may be responsible for the development of the crescentic bar forms (Type 3). Lower frequency surf beat peaks also remain present but are secondary. The peak at 4 T attenuates as Type 4 develops and is not present with Type 5 topography but the first subharmonic (2 T) becomes more pronounced, particularly with high tide. Type 6 morphology represents the fully accreted beach state and occurs only after prolonged periods of low swell. This type is a reflective beach with a steep linear beach face and a very high berm which remains continuous for long distances alongshore; rips are always absent. Wave and current spectra are also similar to those described for reflective beaches.

TRACKED VEHICLE FOR CONTINUOUS NEARSHORE PROFILES

The measurement of nearshore profiles has been the traditional method for evaluating on- and offshore transport of beach sand by waves. The measurement on that portion of the beach face which is dry at low tide presents no particular problems and can be effectively accomplished with conventional rod and level surveying techniques. Once the measurement location moves into the wet part of the foreshore, however, the problems rapidly increase. In general, it requires an extremely dedicated rod man to remain on position in breakers larger than a meter, although measurements in breakers up to 2 meters in height have been accomplished on a nonroutine basis. When waves exceed this height, or when the water depth exceeds the ability of a man to stand and hold the rod, this method must be abandoned. In deeper water, and well outside the surf zone, a boat and fathometer approach is normally employed with considerable loss in vertical and horizontal accuracy. In particular, the vertical resolution is decreased by the uncertainties in knowledge of the instantaneous sea level because of the combination of tides, waves and storm surge. If the tides are large and the waves small, it is possible to achieve an overlap between the boat survey and the shore survey. When the wave height exceeds the ability of the boat to operate, this method also must be abandoned. Although larger boats can operate in larger waves, they are generally also restricted to deeper water. The result of all of the restrictions described above is that profiles can be measured with reasonable accuracy only during periods of low waves. Unfortunately, the episodes of greatest interest are the rapid cutting back of the beach face and the accompanying offshore bar building which occur during times of high waves. The technology to measure the storm waves has been available for many years. The ability to correlate wave parameters with offshore transport rates requires the ability to make accurate profiles from the dry beach through and beyond the breaker line under storm wave conditions. This paper describes a vehicle that was developed to meet this need.