Ebb-tidal Delta Research Articles

Wave Climate Definition on Modeling Morphological Changes in Figueira da Foz Coastal System (W Portugal)

ABSTRACT Ferreira, C.; Silva, P.A.; Fernandez-Fernandez, S.; Baptista, P.; Abreu, T.; Romao, S.; Fontan-Bouzas, A.; Bertin, X., and Garrido, C. 2018. Wave Climate Definition on Modeling Morphological Changes in Figueira da Foz Coastal System (W Portugal). 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.1256–1260. Coconut Creek (Florida), ISSN 0749-0208. Field surveys at Figueira da Foz coastal system, a jettied river-mouth located to the W of Portugal, show a high impact of storm events on the morphological evolution of the ebb-tidal delta, with formation of a submerged sandbar and the quick infill of dredged areas. Non-stormy wave conditions produce minor morphological changes. The morphodynamic modeling of this system is being done to support coastal management. The methodology uses Delft3D modeling system that was previously calibrated for this coastal regio...

Dynamic preservation of Texel Inlet, the Netherlands: understanding the interaction of an ebb-tidal delta with its adjacent coast

AbstractTidal inlets and the associated ebb-tidal deltas can significantly impact the coastal sediment budget due to their ability to store or release large quantities of sand. Nearly 300 million m3(mcm) of sediments were eroded from Texel Inlet's ebb-tidal delta and the adjacent coasts following the closure of the Zuiderzee in 1932. This erosion continues even today as a net loss of 77 mcm was observed between 1986 and 2015. To compensate, over 30 mcm of sand has been placed on the adjacent coastlines since 1990, making maintenance of these beaches the most intensive of the entire Dutch coastal system.Highly frequent and detailed observations of both the hydrodynamics and morphodynamics of Texel Inlet have resulted in a unique dataset of this largest inlet of the Wadden Sea, providing an opportunity to investigate inlet sediment dynamics under the influence of anthropogenic pressure. By linking detailed measurements of bathymetric change to direct observations of processes we were able to unravel the various components that have contributed to the supply of sediment to the basin, and develop a four-stage conceptual model describing the multi-decadal adaptation of the ebb-tidal delta.Prior to closure of the Zuiderzee a dynamic equilibrium state (stage 1) existed with a stable ebb-tidal delta. The largest morphological changes occurred in roughly the first 40 years since the closure, and were dominated by the rotation and scouring of large tidal channels and landward retreat of the Noorderhaaks ebb shoal (stage 2; adaptation). Between 1975 and 2001 the general layout of main channels and shoals was stable, but large sediment losses continued to occur (stage 3; equilibrium erosional state). Since 2001, the erosion rates have significantly reduced to 2 mcm a−1(stage 4; stabilisation).Twenty-five years of data on ‘Dynamic Preservation’ prove that sand nourishments are well capable of keeping the coastlines adjacent to the Texel Inlet in place. Moreover, the abundant supply of sediment may also have compensated for the sediment losses on the larger scale of the southern part of the ebb-tidal delta, resulting in a recent stabilisation of its volume. This response illustrates the potential benefits of Dynamic Preservation not only for coastline resilience but also on the larger scale of the inlet system. Such knowledge is essential for future preservation, management and maintenance of inlet systems in the scope of climate change and accelerated sea-level rise.

Observations of morphological change at an ebb-tidal delta

Video observations of depth-limited wave-breaking patterns at an ebb-tidal delta on the energetic west coast of New Zealand at Raglan were used to identify geomorphic features over a 5-year period. The terminal lobe, mouth bar, channel margin linear bars, and swash bars were identified and tracked over the duration. Morphodynamic response was related to environmental conditions by correlating observed movements with concurrent wave and tidal conditions. Movements occurred throughout the record with a slight tendency to occur more during the transition between seasonal forcing trends. Winter deltas were generally broader and extended further seaward than the summer deltas which were more cuspate. The formation of a double-barred ebb-shoal was observed, with the cross-shore position of the outer bar influenced by wave conditions while the inner bar was influenced by ebb-jet strength. Furthermore, swash bars were observed to constrict the seaward extent of the main channel during large wave events, which was subsequently eroded by tidal currents. These observations are consistent with the present consensus that ebb-shoal features are dependent upon competition between ebb-jet strength and opposing waves. Interannual morphological changes were not significantly correlated to any particular environmental forcing, suggesting that either some process or combination of processes not considered were influential, or that the system might be showing signs of emergent behaviour.

Sea-Level Rise and Coastal Submergence along the South–East Coast of Nigeria

Coastal submergence and shoreline retreat constitute a serious threat to shoreline management in the Niger Delta. Short-term and long-term changes on the shoreline adjoining Qua-Iboe River estuary, south-east coast of Nigeria are analysed to assess the impact of sea-level rise and climate change on the shoreline. A comparison of the 2002 and 2013 editions of the maps of the shoreline indicates a landward retreat of the shoreline and a submergence of village of Itak Abasi in the Atlantic Ocean over an estimated area of 180000 m2 along the coastline. Analysis of shoreline changes over neap-spring tidal phase confirmed that the submerged area of the updrift shoreline was threatened by severe and chronic erosion in which the rate has reduced to 178 m3 per day. The downdrift experienced high rate of accretion at 1490 m3 per day with sediment gained from the updrift shoreline and the ebb tidal delta as well as input from fluvial discharge into the estuary. Near-shore wave climate was characterized by the wave breaker heights which fluctuated between 30 cm and 70 cm at a period which ranged between 5 to 8 seconds, the occurrence of edge waves during mid-flood tidal stage along the mid foreshore, predominantly eastward directed long-shore currents and storm surge events at the updrift shoreline are considered as the hydrodynamic processes which caused the shoreline retreat and submergence. The intensity and magnitude of the impact of the processes on the shoreline are attributed to sea-level rise and climate change. Sustainable shoreline management strategies including measures for mitigations and adaptations to climate change are recommended.

Beach Evolution Adjacent to a Seasonally Varying Tidal Inlet in Central Vietnam

ABSTRACT Do, T.K.A.; de Vries, S., and Stive, M.J.F., 2018. Beach evolution adjacent to a seasonally varying tidal inlet in central Vietnam. Cua Dai Inlet is a typical, seasonally varying tidal inlet in central Vietnam. Since 1995 the northern adjacent coast, known as Cua Dai Beach, has experienced serious erosion. The decadal scale behavior of this inlet appears to reflect a nonperiodic cyclic process. Inlet channel shifting from north to south has welded the abandoned ebb-tidal delta with Cua Dai Beach, leading to accretion but subsequently triggering erosion. Although erosion of Cua Dai Beach was exacerbated by decrease of sediment supply from the estuary and ebb-tidal delta and by coastal developments, the channel shifting to the south, and the ebb shoal development were important primary controlling mechanisms. This study aims to quantify the main erosional processes in and near the Cua Dai coastal inlet and adjacent beaches since 1995. First, satellite data were used to detect shoreline change trend...

The ‘Voordelta’, the contiguous ebb-tidal deltas in the SW Netherlands: large-scale morphological changes and sediment budget 1965–2013; impacts of large-scale engineering

AbstractThe estuaries in the SW Netherlands, a series of distributaries of the rivers Rhine, Meuse and Scheldt known as the Dutch Delta, have been engineered to a large extent as part of the Delta Project. The Voordelta, a coalescing system of the ebb-tidal deltas of these estuaries, extendsc.10 km offshore and coversc.90 km of the coast. The complete or partial damming of the estuaries had an enormous impact on the ebb-tidal deltas. The strong reduction of the cross-shore directed tidal flow triggered a series of morphological changes that continue until today. This paper aims to give a concise overview of half a century of morphological changes and a sediment budget, both for the individual ebb-tidal deltas and the Voordelta as a whole, based on the analysis of a unique series of frequent bathymetric surveys. The well-monitored changes in the Voordelta, showing the differences in responses of the ebb-tidal deltas, provide clear insight into the underlying processes. Despite anthropogenic dominance, knowledge based on natural inlets can still explain the observed developments. Complete damming of the three northern estuaries Brielse Maas, Haringvliet and Grevelingen resulted in a regime shift, from mixed-energy to wave-dominated, and sediments are transported in landward and downdrift direction. This results in large morphodynamic changes – sediments are redistributed from the delta front landward – but small net volume changes – a 0.1–0.2 × 106m3a−1increase in volume over the period 1965–2010 – since the dams block sediment transport into the estuaries. Sediment volume losses of 106m3a−1are observed on the ebb-tidal delta of the partially closed Eastern Scheldt and still open Western Scheldt estuary. As a result of a reduction of the estuarine tide in the mouth of the Eastern Scheldt, the north–south-running North Sea tidal wave has gained impact on its ebb-tidal delta, which causes morphological adjustments and erosion of the Banjaard shoal area. Moreover, the Eastern Scheldt ebb-tidal delta delivers sediment to its neighbours. The stable ebb-tidal delta configuration in the Western Scheldt, despite major dredging activities, illustrates that these large inlet systems are robust and resilient to significant anthropogenic change, as long as the balance between the dominant hydrodynamic processes (tides and waves) does not alter significantly.

Spatiotemporal variability of sedimentology and morphology in the East Frisian barrier island system

The highly dynamic East Frisian barrier island system (southern North Sea) is characterized by a complex morphology of tidal inlets, ebb-tidal deltas and foreshore beaches that reacts to storms and fair-weather conditions with characteristic patterns of sediment grain-size distributions. The morphological and sedimentological response to varying hydrodynamic conditions yet occurs in short time spans that are not covered by common monitoring strategies with measuring intervals typically of years. This study applies process-based numerical modelling with multiple sediment fractions to interpolate morphological states in time between bathymetrical surveys conducted in the summer months of 2004 and 2006. Morphodynamic simulations driven by real-time boundary conditions of tides, wind and waves are carried out for a representative period of 2 years. The spatiotemporal variability of the nearshore sedimentology and morphology is assessed by graded ranges of bed dynamics (i.e. bed elevation range) and the definition of sediment grain-size variability (i.e. mean diameter range). The effect of storm events and timescales of the sedimentological adaptation after storms to typical fair-weather conditions are exemplified at an ebb-tidal delta lobe where the morphological and sedimentological variability is found to be largest in the study area. The proposed method may serve to identify areas of high sedimentological and morphological activity for system understanding or in the framework of coastal monitoring strategies.

Sediments Grain Size Sensitiveness of the Thakuran River Basin of the Sunderbans

Geomorphologically defined areas like mid-channel bars or flood-tidal delta, river mouth bar or ebb-tidal delta, point bar, swash platform, wash-over flat and river banks (levee) have been identified in the Thakuran River of the estuarine Sunderbans. These areas are delineated based on studies of the granulometric properties. A coarsening of graphic mean size (MZ), betterment of sorting (o1), and negative to positive skewness (SK1) have been noticed from the seaward to landward direction. Variations of these textural parameters are related to decreasing energy levels along the same direction. A bipartite granulometric model of sedimentation having sand-to-mud from the seaward to the landward direction of the tidal creek has been discerned. This is in contrast to a tripartite granulometric model typical of estuaries.

Morphological evolution of the Nerang River Entrance ebb-tidal delta

ABSTRACT Sedigh, M.; Tomlinson, R.; Cartright, N., and Etemad-Shahidi, A., 2016. Morphological evolution of the Nerang River Entrance ebb-tidal delta. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 238–242. Coconut Creek (Florida), ISSN 0749-0208. The Nerang River entrance is a tidal inlet that connects the Pacific Ocean to the extensive Gold Coast estuarine system known as the Broadwater. Due to relatively fast northward migration of the inlet from 1920 to 1985 and the importance of having a safe navigable channel, the inlet was stabilized with two training walls in 1986. A sand bypassing system was implemented upstream with an average sand bypassing rate equal to the estimated net northward lonshore sediment transport in the area to prevent the formation of a bar across the entrance. However, historical analysis of survey data has shown an ongo...

Cyclic behavior of sandy shoals on the ebb-tidal deltas of the Wadden Sea

Ebb-tidal deltas are bulges of sand that are located seaward of tidal inlets. Many of these deltas feature shoals that cyclically form and migrate towards the coast. The average period between successive shoals that attach to the coast varies among different inlets. In this study, a quantitative assessment of the cyclic behavior of shoals on the ebb-tidal deltas of the Wadden Sea is presented. Analysis of bathymetric data and Landsat satellite images revealed that at the majority of inlets along the Wadden Sea migrating shoals occur. The average period between succeeding shoals correlates to the tidal prism and has values ranging between 4 and 130 years. A larger tidal prism favors larger periods between successive shoal attachments. However, such a relationship was not found for wide inlets with multiple channels. There is a positive relationship between the frequency with which the shoals attach to the coast and their migration velocity, and a negative relationship between the migration velocity of the shoal and the tidal prism. Finally, the data were too sparse to assess whether the longshore sediment transport has a significant effect on the period between successive shoals that attach to the coasts downdrift of the observed tidal inlets.

Post-Little Ice Age Development of a High Arctic Paraglacial Beach Complex

We reconstruct the behaviour of a High Arctic gravel-dominated beach complex that has developed in central Spitsbergen, Svalbard, since the end of the Little Ice Age (LIA). The studied coastal environment in northern Billefjorden (Petuniabukta) is characterised by limited wave action and ephemeral sediment delivery from non-glaciated, mainly snow-fed fans and talus slopes. Aerial photographic evidence and morpho-sedimentological observations of a beach-ridge plain and spit complex in northern Billefjorden reveal a dynamic coastal system. During the post-LIA period, a prominent coastal barrier at the mouth of the Ebbaelva migrated seawards several tens of metres and prograded northwards to form new spit systems, each > 150 m in length. The post-LIA coastal evolution occurred in two main phases. In the first half of the 20th century, increased paraglacial sediment released by retreating land-based glaciers led to the development of a subaqueous spit platform and the progradation of an ebb-tide delta into the mouth of the Ebbaelva, diverting its mouth to the northwest. In the second half of the 20th century, the barrier prograded onto this platform, promoting the development of three massive spits. Sedimentological data suggest that changes in beach-ridge composition that occurred during the 20th century are linked to episodic sediment delivery from an adjacent permafrost and snow-fed alluvial fan and delta system. Our work provides a basis for a new model of paraglacial barrier development that recognises the fundamental role of climate and sediment supply as two intimately connected processes that control coastal development in the High Arctic over decadal to centennial timescales. Copyright © 2015 John Wiley & Sons, Ltd.

Hydrodynamic and sediment transport modeling of New River Inlet (NC) under the interaction of tides and waves

AbstractThe interactions between waves, tidal currents, and bathymetry near New River Inlet, NC, USA are investigated to understand the effects on the resulting hydrodynamics and sediment transport. A quasi‐3‐D nearshore community model, NearCoM‐TVD, is used in this integrated observational and modeling study. The model is validated with observations of waves and currents at 30 locations, including in a recently dredged navigation channel and a shallower channel, and on the ebb tidal delta, for a range of flow and offshore wave conditions during May 2012. In the channels, model skills for flow velocity and wave height are high. Near the ebb tidal delta, the model reproduces the observed rapid onshore (offshore) decay of wave heights (current velocities). Model results reveal that this sharp transition coincides with the location of the breaker zone over the ebb tidal delta, which is modulated by semidiurnal tides and by wave intensity. The modulation of wave heights is primarily owing to depth changes rather than direct wave‐current interaction. The modeled tidally averaged residual flow patterns show that waves play an important role in generating vortices and landward‐directed currents near the inlet entrance. Numerical experiments suggest that these flow patterns are associated with the channel‐shoal bathymetry near the inlet, similar to the generation of rip currents. Consistent with other inlet studies, model results suggest that tidal currents drive sediment fluxes in the channels, but that sediment fluxes on the ebb tidal delta are driven primarily by waves.

Sand bypass and updrift beach evolution after jetty construction at an ebb-tidal delta

The evolution of an ebb-tidal delta (Guadiana, South Portugal) and its updrift beach after jetty construction (in 1972–1974) is analysed based on 24 ortho-rectified aerial photographs (1940–2012) and 13 bathymetric maps (1969–2014). The objectives are to evaluate the re-establishment of the sand bypassing process and if the disruption of the historical delta may affect the updrift beach evolution. Post-jetty progradation of the updrift beach resulted from two large accretion events. The second (largest) event (110 m progradation in 1985–1994) was due to beach attachment of a shoal produced by the erosion of a broad shallow area relict of the historical delta. The reworking of sand from this relict area also enables the individualisation of a lateral updrift bar simultaneously with the new ebb shoal proper formation. Both morphological features were close to (volume) equilibrium in 1995, indicating that most of the sand was transported towards the downdrift side of the inlet at that time. This study shows that erosion of the historical delta may enhance significantly the updrift shoreline progradation and may promote the re-establishment of sand bypassing after jetty construction.

Numerical analysis of stratification and destratification processes in a tidally energetic inlet with an ebb tidal delta

AbstractStratification and destratification processes in a tidally energetic, weakly stratified inlet in the Wadden Sea (south eastern North Sea) are investigated in this modeling study. Observations of current velocity and vertical density structure show strain‐induced periodic stratification for the southern shoal of the tidal channel. In contrast to this, in the nearby central region of the channel, increased stratification is already observed directly after full flood. To investigate the processes leading to this different behavior, a nested model system using GETM is set up and successfully validated against field data. The simulated density development along a cross section that includes both stations shows that cross‐channel stratification is strongly increasing during flood, such that available potential energy is released in the deeper part of the channel during flood. An analysis of the potential energy anomaly budget confirms that the early onset of vertical stratification during flood at the deeper station is mainly controlled by the stratifying cross‐channel straining of the density field. In contrast to this, in the shallow part of the channel, the relatively weak cross‐channel straining is balanced by along‐channel straining and vertical mixing. An idealized analytical model confirms the following hypothesis: The laterally convergent flood current advecting laterally stratified water masses from the shallow and wide ebb tidal delta to the deep and narrow tidal channel has the tendency to substantially increase cross‐channel density gradients in the tidal channel. This process leads to stratification during flood.

Sediment Sources and Transport Pathway Identification Based on Grain-Size Distributions on the SW Coast of Portugal

Espichel-Sines is an embayed coast in SW Portugal, consisting of two capes at both extremities, a tidal inlet and associated ebb tidal delta, a barrier spit, sandy beaches, sea cliffs, and a submarine canyon. Beach berm, backshore, near shore and inner shelf sediment samples were taken. Samples were analyzed for their grain-size compositions. This study ranks the hypothetical sediment sources influences on the sediment distributions in the study area using the multivariate Empirical Orthogonal Function (EOF) techniques. Transport pathways in this study were independently identified using the grain size trend analysis (GSTA) technique to verify the EOF findings. The results show that the cliff-erosion sediment is composed of pebbles and sand and is the most important sediment source for the entire embayment. The sediment at the inlet mouth is a mixture of pebbles, sand, silt, and clay, which is a minor sediment source that only has local influence. The overall grain-size distributions on the shelf are dominated by the sand except for the high mud content around the tidal delta front in the northern embayment. Sediment transport patterns on the inner shelf at the landward and north sides of the canyon head are landward and northward along the barrier spit, respectively. On the south side of the canyon head, the prevailing sediment transport is seaward. Sediment transport occurs in both directions along the shore.

HYDRODYNAMIC MODELING OF NEW RIVER INLET, NORTH CAROLINA USING NEARCOM-TVD

The goal of this study is to investigate the role of wave-current interaction in tidal inlet hydrodynamics. A quasi-3D nearshore community model, NearCoM-TVD, is used to simulate circulation and waves at New River Inlet, NC, USA. Model skill for waves and circulation is evaluated at about 30 locations throughout the inlet, including a recently dredged navigation channel, a shallower channel, a flood tidal delta, and ebb tidal deltas, for a range of flow conditions in May 2012. Model skills for flow velocity and wave height are high in the channels. The numerical model also captures the sharp transition between wave-dominated and tide-dominated flows near the ebb tidal deltas. Model results demonstrate that wave intensity plays an important role in circulation (vortex) generation near inlet entrances.

SCALES & SIGNATURES OF EPISODIC SAND BYPASSING AT A TIDE-DOMINATED INLET — FRIPP INLET, SOUTH CAROLINA

This paper provides a case example of meso-scale sand circulation and volumes in a tide-dominated inlet (Fripp Inlet, South Carolina, USA) and the adjacent barrier island. Episodic bypassing is the dominant process controlling shoreline change in this area (Gaudiano & Kana 2001). The scale of bypassing in this case has proven to be more than adequate to restore a highly eroding armored beach along Fripp Island. Upward of 2.7 million cubic meters (m³) shifted from the ebb-tidal delta of Fripp Inlet to a central oceanfront area of Fripp Island between 1989 and 2012. This volume, representing roughly 10 percent of the ebb-tidal delta volume, provided natural nourishment equivalent to nearly 600 cubic meters per meter of shoreline (m³/m) along the nearly 5-kilometer (km) long barrier island. The volume density varied greatly with some beach segments widening by more than 500 m. Prior to the bypassing events, there was no beach at high tide along most of the island. The paper discusses the possible trigger for recent bypassing events and documents changes in Fripp Inlet. Channel rotation into a seawall, southerly deflection of the ebb-delta centroid, and large inputs of sand from the adjacent barrier island appear to have produced conditions promoting large releases of sand to Fripp Island. While the influx of sand has restored much of the oceanfront, full restoration of a sandy beach along the inlet margin will require a channel avulsion or realignment such that the principal erosion-causing process—ebb jet in the main channel—no longer encroaches on the seawall. A channel realignment plan developed by the authors will require upward of 1.2 million m³ of dredging under present conditions but possibly less volume in the near future because of the formation of an incipient new channel.

MODELLING THE MORPHOLOGICAL RESPONSE OF AN EBB TIDAL DELTA TO STORM WAVE FORCING

The Nerang river outlet - located on the Australian east coast - was stabilised with two entrance jetties in 1986. The entrance, now known as the Gold Coast Seaway, has been the subject of growing concern about the ongoing growth of the ebb tidal delta. Historical analysis of surveying data confirmed the gradual growth of ebb tidal delta, although a sand bypassing system was implemented upstream when the entrance was stabilised. The dredging of the Seaway ebb delta is inevitable to keep the navigation channel open and safe. However, the dredging operation is both time and budget consuming and therefore having a more accurate model which can predict the pattern of morphological changes precisely seems essential. A coupled wave, flow and sediment transport model was developed using MIKE 21 Coupled Model to investigate the sediment transport pattern mainly in the area of the ebb-tidal delta and its linkage with littoral drift in the adjacent open coast. The hydrodynamics of the model were calibrated and verified against current measurements inside the Seaway and offshore wave data obtained from the Gold Coast Wave Rider Buoy. The pattern of the simulated morphological changes was qualitatively similar to that of the observations, and the model’s results show that the storm waves forcing govern the growth of the ebb-tidal delta, and also leads to severe bathymetry changes along the adjacent ocean beaches. The model was found to underestimated the volume of sediment transport in the domain and so further model sensitivity analysis is ongoing in an effort to reach to a quantitatively calibrated morphological model.

Mobility of meso-scale morphology on a microtidal ebb delta measured using remote sensing

Abstract Ebb tidal deltas usually consist of several large lobes of sediment separated by channels in which the bulk of the tidal exchange takes place. The purpose of this paper is to describe and quantify the migration pattern of bedform features associated with an ebb-tidal delta using a new remote video sensing method during a 23 day experiment at New River Inlet (North Carolina). To quantify the migration rates, a Lagged Least Squares Algorithm (LLSA) was developed that found the vector rate for which the suite of lagged images were most similar, computed on a tile-by-tile basis. Our observations revealed a complex set of bedform features that migrated in a circular pattern with movement in offshore regions being away from the inlet mouth and toward the shore while nearshore migration was back toward the inlet. 60% of the wavelength variability of these features is at scales that are smaller than the coherent channel and swash bar structures but much longer than megaripples, i.e., between 10 and 100 m. We have chosen to call these bedform features of meso-scale morphologies. The mean migration rate of these features was found to be 1.53 m/day ± 0.76 m/day. 72% of estimated rates were greater than 1.0 m/day, 31% were larger than 2.0 m/day, and the maximum rate was around 3.5 m/day, averaged over 23 days. Alongshore averages of cross-shore migration rates showed a node at 110 m from the shoreline that separates migration away from the inlet from migration toward the inlet (near the shore). The circular pattern of migration appeared to be consistent with expected residual flow of an ebb-tidal delta system.

Can recreational echosounder-chartplotter systems be used to perform accurate nearshore bathymetric surveys?

This work intends to determine if low-cost surveying techniques based on recreational echosounders can be used to perform nearshore bathymetry for analysing evolution of coastal sectors. For that purpose, two hydrographic surveying techniques were compared, i.e. (1) a real-time kinematic differential global positioning system (RTK-DGPS) synchronised with a single beam echosounder with real-time tidal elevation correction and (2) a low-cost recreational echosounder-chartplotter system using Global Navigation Satellite Systems (GNSS) with real-time European Geostationary Navigation Overlay Service (EGNOS) augmentation services and depth values post-processed using measured sea level. Two bathymetric data sets were obtained, one by each method, for the same area and survey lines at an ebb tidal delta (Tavira Inlet, Ria Formosa Portugal). Vertical differences were determined assuming no morphological variations between surveys. Results showed that depth elevation differences between bathymetric surfaces were of 0.10 ± 0.16 m, slightly higher but within the same order of the error attributable to the used interpolator (0.00 ± 0.11 m, triangular surface fitting). The differences between surveys performed with two different equipment sets and using different methodologies for correcting water elevations are very small both quantitative and qualitatively. Those differences can be diminished by improving the tidal level correction and uncertainties associated to different tidal slopes throughout the survey area. Pitch/roll corrections performed with low-cost GPS receivers would be also a valuable addition to the accuracy and precision of the method. It is then concluded that navigation with EGNOS augmentation services and sounding devices ten times cheaper than combined RTK-DGPS with single beam echosounders allow to measure and monitor accurately the nearshore bathymetry.